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Endocrinology Vol. 143, No. 10 4065-4073
Copyright © 2002 by The Endocrine Society

ARTICLE

Bone Marrow Adipocytes: A Neglected Target Tissue for Growth Hormone

Evelien F. Gevers, Nigel Loveridge and Iain C. A. F. Robinson

Division of Molecular Neuroendocrinology (E.F.G., I.C.A.F.R.), National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom; and Bone Research Group (Medical Research Council) (N.L.), University of Cambridge, Department of Medicine, Addenbrooke’s Hospital, Cambridge CB2 2QQ, United Kingdom

Address all correspondence and requests for reprints to: Dr. Evelien F. Gevers, Division of Molecular Neuroendocrinology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom. E-mail: egevers{at}nimr.mrc.ac.uk.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Bone marrow (BM) contains numerous adipocytes. These share a common precursor with osteoblasts and chondrocytes, but their function is unknown. It is unclear what regulates the differentiation of these three different cell types, though their subsequent metabolic activity is under hormonal regulation. GH and estrogen stimulate bone growth and mineralization, by direct effects on chondrocytes and osteoblasts. GH also stimulates lipolysis in subcutaneous and visceral adipocytes. However, adipocytes in BM have largely been ignored as potential targets for GH or estrogen action. We have addressed this by measuring BM adipocyte number, perimeter and area as well as bone area and osteoblast activity in GH-deficient dwarf (dw/dw), normal, or ovariectomized (Ovx) rats, with or without GH, IGF-1, PTH, or estrogen treatment or high fat feeding.

Marrow adipocyte numbers were increased 5-fold (P < 0.001) in dw/dw rats, and cell size was also increased by 20%. These values returned toward normal in dw/dw rats given GH but not when given IGF-1. Cancellous bone area and osteoblast number were significantly (P < 0.005) lower in dw/dw rats, though alkaline phosphatase (ALP) activity in individual osteoblasts was unchanged. GH treatment increased % osteoblast covered bone surface without affecting individual cell ALP activity. Ovariectomy in normal or dw/dw rats had no affect on marrow adipocyte number nor size, although estrogen treatment in ovariectomized (Ovx) normal rats did increase adipocyte number. Ovx decreased tibial cancellous bone area in normal rats (64%; P < 0.05) and decreased osteoblast ALP-activity (P < 0.01) but did not affect the percentage of osteoblast-covered bone surface. Estrogen replacement reversed these changes. While treatment with PTH by continuous sc infusion decreased cancellous bone (P < 0.05) and high fat feeding increased the size of BM adipocytes (P < 0.01), they did not affect BM adipocyte number. These results suggest that GH has a specific action on BM adipocytes that is not simply due to altered bone or fat metabolism.

We conclude that the marrow adipocyte lineage is an important and specific target for GH action. The inverse relationship between adipocyte number and osteoblast covered bone surface, together with the well-known effects of GH on epiphysial chondrocytes leads us to propose that GH plays two important roles on cells of all three lineages. During differentiation, it regulates the numbers of each cell type that are maintained from the common precursor lineage. Subsequently it has cell-specific effects on the metabolic activities of the differentiated cells. In the case of marrow adipocytes, GH-dependent lipolysis could provide an important hormonally regulated local high energy source in bone.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
IN BOTH HUMANS AND RATS, a decrease in bone volume is often accompanied by an increase in bone marrow (BM) fat, for example, in old age, immobility and corticosteroid induced osteoporosis (1, 2, 3, 4). However, the relevance of these changes, and indeed the role of adipocytes in BM, is far from clear. Osteoblasts and adipocytes share a common mesenchymal precursor (5), so a shift in differentiation, survival, or elimination rates from one lineage to another could lead to an altered ratio of fat to bone cells. The physiological and molecular mechanisms involved in regulating these separate lineages are currently unknown, though several factors [bone morphogenetic proteins (6), ILs (7, 8), glucocorticoids (9), transcription factors (10, 11)] have been implicated. Most studies have focused on the osteoblast lineage; the regulation and function of the adipocyte lineage in this tissue has received much less attention.

We were interested in the possibility that GH may be directly involved in the regulation of marrow adipocytes because there is much circumstantial evidence supporting such an effect on adipocytes in other depots. Both body fat and BM fat increase with age (2) as GH secretion decreases (12), and GH-deficient humans show increased relative adiposity and reduced lean body mass, reversed by GH treatment (13). Although many GH effects may be mediated via IGF-1, adipocytes express GH receptors, which mediate direct effects on lipolysis (14, 15). GH may also affect adipocyte number directly because it affects preadipocyte/adipocyte differentiation in vitro (16, 17).

GH also stimulates longitudinal growth and bone formation (18, 19, 20), and GH deficiency is associated with a decreased bone mass (21) that can be increased with GH treatment (22, 23). Because it has been suggested that marrow fat might act as a spacefiller, increasing fat volume as the bone content decreases (24), an increase in marrow fat in GH deficiency could simply be secondary to bone loss.

Similar arguments could be made in favor of estrogen, which also affects both bone and peripheral fat metabolism. Estrogen stimulates bone metabolism directly via receptors on osteoblasts, and stimulates both osteoclastogenesis and osteoblastogenesis (25). It is well known that estrogen affects the accumulation and distribution of peripheral fat during sexual maturation and menopause (26, 27), but there is also some evidence that ovarietomy-induced bone loss is accompanied by an increased fat mass in BM (28, 29), suggesting that BM fat may also be a target for estrogen.

We have now studied BM adipocytes in dwarf rats (dw/dw) with isolated GH deficiency (30), and in rats rendered estrogen deficient by ovariectomy, with or without appropriate replacement therapy with GH, IGF-1, or estrogen. The number and size of BM adipocytes, the alkaline phosphatase (ALP) activity in individual osteoblasts, the bone area covered by ALP-positive osteoblasts, the cancellous bone area, cortical bone thickness, and cellular proliferation rates were measured by histological techniques and computed tomography scans. To assess whether the effects of GH we observed, were secondary to its effects on bone or fat metabolism, further experiments were performed in which rats were treated with PTH or were fed a high fat diet.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animal experiments
GH-deficient dwarf (dw/dw) rats were used. These have profound isolated GH deficiency, low circulating IGF-1 levels, and a reduced rate of bone growth (30, 31). For the first two experiments, dw/dw rats and controls on a Lewis background were obtained from Harlan (Maastricht, The Netherlands). For all the other experiments, dw/dw and control rats were from our NIMR colony, which was established on an AS background (30). No significant differences were observed in GH responses or marrow fat mass between these substrains, and controls were always from the appropriate background. All rats were housed in temperature- and light-controlled rooms (23–25 C, 14 h light) with food and water available ad libitum. Experiments were approved by the local ethical committee.

To study the effects of GH and/or estrogen deficiency, groups of normal and GH-deficient female dw/dw rats were ovariectomized (Ovx) or sham-operated at the age of 8–9 wk, under halothane/O2/N2O anesthesia. One group of normal Ovx rats and one group of dw/dw Ovx rats were given estrogen implants (Innovative Research of America, Sarasota, FL) delivering 25 µg estradiol (E2)/d sc for 21 d. After 3 wk the rats were killed by decapitation. One tibia was fixed in 70% ethanol and one tibia was dipped into 5% polyvinylalcohol and frozen (32). One femur was fixed for 36 h in Burchardt’s fixative after which cortical thickness was measured by quantitative peripheral computed tomography (Stratec XCT 960A; Stratec, Birkenfield, Germany) as previously described (33).

In the next experiment, 8 young (6 wk) female dw/dw rats were equipped with indwelling jugular vein catheters under halothane/O2/N2O anesthesia. Two days after surgery, the catheters were connected to a computer-controlled infusion system and rats were treated with three hourly iv pulses of recombinant human GH (hGH, 144 µg/d Genotropin, Pharmacia-Upjohn, Stockholm, Sweden) or vehicle for 7 d, as previously described (34). After 1 wk, rats were weighed and injected with bromodeoxyuridine [BrdU, Sigma (St. Louis, MO); 25 mg/kg, ip] and killed 1 h later. Tibiae were isolated and prepared as described above.

To study the effects of GH in older animals, 4-month-old female dw/dw and normal rats (n = 5–7) were sham-operated or implanted sc with osmotic minipumps (Alzet 2002, CA) delivering hGH (200 µg/d). After 2 wk, the rats were killed, a terminal blood sample was taken and the proximal half of the tibia was isolated and fixed in 4% paraformaldehyde/PBS for 5 d.

Another group of 8- to 9-wk-old female dw/dw rats (n=5–6) were sham-operated or implanted with sc osmotic minipumps delivering recombinant human IGF-1 (Genentech, Inc., San Francisco, CA) in a dose of 60 µg/d for 2 wk. At the end of the experiment, blood and tibiae samples were taken and prepared as described above. In addition, renal and ovarian fat pad weights were determined.

In the next experiment, 7-wk-old female rats (n=7 per group) were fed either normal or increased fat diets for 11 wk. The normal chow diet consisted of 3.4% fat, 18.8% protein, 3.7% fiber, 60.3% carbohydrate, and 3.8% ash (15.6 MJ/kg), whereas the high fat diet, made by mixing normal rat chow with 60% fat containing chow (Special Diet Services, Witham, UK), consisted of 41.1% fat, 19.6% protein, 29.0% carbohydrate, and 2.3% ash (24.0 MJ/kg). Rats were weighed weekly. At the end of the experiment, ovarian and renal fat pads were weighed and tibiae were taken as described above.

Finally, normal 9- to 10-wk-old female rats were treated for 2 wk with 80 µg/kg human PTH (1–34) (Bachem, Merseyside, UK), dissolved in water with 0.05% BSA, via sc implanted osmotic minipumps, as described before. Control rats were sham-operated. At the end of the experiment, ovarian and renal fat pads were weighed and tibiae were taken as described above.

Tissue preparation
Cryostat sections (10 µm), always taken in a frontal plane from the middle of the tibia, were used for ALP activity and BrdU measurements. Other sections were stained, unfixed, for adipocytes with Sudan Black (1.4% in 70% ethanol) for 7 min, rinsed in 70% ethanol and mounted in Glycergel (Sigma).

In the first experiments, tibiae were fixed in 70% ethanol, embedded in methylmethacrylate and sectioned (7 µm). To visualize adipocytes, sections were then stained overnight in crystal violet. In later experiments, tibiae were fixed in 4% paraformaldehyde/PBS for 5 d and decalcified in 20% EDTA (BDH, Poole, UK) (pH = 8.0) for 3 wk. They were then embedded in paraffin, and sections (6 µm) were stained with Masson’s trichrome. Therefore, ALP-activity (see below) could not be determined in these experiments.

ALP-activity and BrdU incorporation
ALP-activity in osteoblasts was determined on frozen sections and measured by microdensitometry as previously described (32, 35). ALP-activity is shown as mean integrated absorbance x 100 (MIA x 100) ± SEM. Imaging software [GENBONE (36)] was used to assess the perimeter of bone within the secondary spongiosa which had ALP activity on its surface, reflecting osteoblast number (37).

BrdU incorporation in BM cells was detected using immunohistochemistry as previously described (32). BrdU-positive cells were counted in an area of 0.1296 mm2. Two such areas in four sections from each bone were analyzed and the results presented as the mean number of BrdU-positive cells ± SEM per mm2.

Image analysis
Adipocyte measurements.
Adipocyte number and size was determined in sections stained with crystal violet and Masson’s trichrome, using NIH Image 1.62. In the first two experiments two fields from the secondary spongiosa were analyzed. In the other experiments, sections of the complete proximal half of the tibia were reconstructed by computer montage and analyzed (Fig. 1AGo). In this method, intracellular fat deposits have been removed during tissue processing and the adipocytes are readily visualized as white round holes (Fig. 1BGo). After import into NIH Image, the image was inverted, thresholded and transformed into binary images so that the adipocytes appear as round black dots. Adipocyte perimeter, number and total adipocyte area could then be analyzed semiautomatically. Cells were counted as adipocytes if their size was between 60 and 1500 µm2 and the ratio of the major and the minor axis was smaller than 2.



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  		Figure 1. Quantitative analysis of bone marrow adipocytes. A, Computer image of a tibial section (magnification, x6). B, Magnification of one area (x45). The white holes represent the adipocytes.

 
Bone parameters.
Bone area and marrow area were measured in the same images, by outlining the cancellous and cortical bone surfaces, and the total image area so that the marrow area, the percentage of cancellous bone area and % BM fat could then be calculated. The number of adipocytes was corrected for the size of the BM area and expressed as density (number of adipocytes/mm2 BM). The variability of these semiautomated methods was assessed by analyzing three different sections of one tibia from each treatment group of one experiment. Coefficients of variation were 11.2% (absolute adipocyte number), 6.6% (adipocyte size), 3.7% (BM area), 4.1% (bone area), 19.3% (% BM fat), and 12.9% (adipocyte number/mm2 BM).

Statistics
Results are presented as mean ± SEM. In the first two experiments, two-tailed Student’s t tests were used to determine differences between groups. In the other experiments ANOVAs were used, if necessary followed by Tukey-Kramer tests. A statistical significant difference was accepted below P = 0.05.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
GH-deficient rats
Figure 2Go shows cryostat sections of tibiae of an 11-wk-old normal and dw/dw female rat, stained with Sudan Black, which stains fat black. Cancellous bone area was clearly reduced and marrow fat area markedly increased in the dw/dw female compared with the normal female. At the higher magnification, the increased number and size of adipocytes can easily be seen.



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  		Figure 2. BM adipocytes in normal and GH-deficient rats. Photomicrographs of longitudinal sections from the tibias of normal (A and C) or GH-deficient (B and D) rats stained with Sudan black. Note the increase in the number of adipocytes in the BM of the GH-deficient rats. Magnification, x2.5 (A and B) and x20 (C and D).

 
Image analysis confirmed that GH deficiency (experiment 1) markedly increased the percentage of marrow fat area (Fig. 3AGo). The increase in percentage of marrow fat area was mainly due to a marked increase in adipocyte number (P < 0.005) with a marginal increase in adipocyte perimeter (P < 0.01) (Fig. 3Go, B and C). Cancellous bone area in the secondary spongiosa was decreased in dw/dw rats compared with normal rats (90%, P < 0.05, Fig. 3DGo), as was the femoral cortical thickness (0.61 ± 0.01 mm vs. 0.74 ± 0.01 mm, P < 0.001). Percentage osteoblast-covered bone surface was significantly decreased in dw/dw rats (P < 0.01, Fig. 3EGo) but ALP activity in individual osteoblasts was similar in normal and dw/dw rats (Fig. 3FGo).



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  		Figure 3. GH deficiency increases BM fat and increases osteoblast surface. Fields in the secondary spongiosa of tibial sections of 11- to 12-wk-old normal and GH-deficient dwarf (dw/dw) rats were compared using NIH Image. A, Percentage of BM fat; B, adipocyte number (no)/mm2 BM; C, adipocyte size; D, percentage of cancellous bone area/field; E, percentage of osteoblast surface in cancellous bone; F, ALP activity in individual osteoblasts, measured using in situ biochemistry and microdensitometry. Data are the mean ± SEM from three rats (A–C) or 6 rats (D–F). **, P < 0.01; ***, P < 0.005.

 
Estrogen-deficient rats
Ovx had no effect on the percentage of marrow fat area (Fig. 4AGo). Estrogen replacement showed a tendency to increase marrow fat in the secondary spongiosa of normal but not dw/dw rats but this was not significant (P = 0.116). Ovx had no effect on marrow adipocyte number or size in either normal or dw/dw rats (Table 1Go). Estrogen replacement significantly increased the number of adipocytes in normal rats (Fig. 4Go, B and C) but this did not occur in dw/dw rats (Table 1Go).



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  		Figure 4. Ovariectomy decreases cancellous bone but does not affect BM adipocytes or osteoblast surface. Groups of 8- to 9-wk-old normal rats were sham-operated, or Ovx, and treated with 25 µg/d E2 (Ovx +E2) for 3 wk. Fields in the secondary spongiosa of tibial sections were analyzed using NIH Image. A, Percentage of BM fat; B, adipocyte number (no)/mm2 BM; C, adipocyte size; D, percentage of cancellous bone area/field; E, percentage of osteoblast surface in cancellous bone; F, ALP-activity in individual osteoblasts. Data are the mean ± SEM from three rats (A–C) or six rats (D–F). *, P < 0.05 vs. sham-operated rats; **, P < 0.05; ***, P < 0.001 vs. sham-operated normals; ###, P < 0.001 vs. Ovx rats.

 

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  		Table 1. Marrow fat and bone parameters in Ovx dw/dw rats

 
As expected, Ovx in normal rats reduced the cancellous bone area in the secondary spongiosa (64%, P < 0.05) and this was prevented by estrogen (Fig. 4DGo). Cortical thickness was unaffected by ovariectomy or estrogen treatment (normal 0.74 ± 0.01, Ovx 0.75 ± 0.01, Ovx + E2 0.75 ± 0.01 mm). In contrast to GH deficiency, Ovx also decreased ALP activity of individual osteoblasts and estrogen administration prevented this (Fig. 4FGo). The osteoblast surface, however, was unaffected by Ovx (Fig. 4EGo). Similar effects, of smaller magnitude, were observed in Ovx dw/dw rats (data not shown). When data from Figs. 3Go and 4Go were pooled, there was a highly significant negative correlation between adipocyte number (y) and osteoblast surface (x) (r2 0.675; x= -15.8*y + 2354, n=3 per group, P < 0.0001).

Effect of GH treatment
In 6 wk dw/dw rats, pulsatile GH treatment for 7 d stimulated growth ({Delta} wt 4.6 ± 0.7 vs. 1.7 ± 0.5 g/d in saline-treated dw/dw rats, P < 0.05). At the time the rats were killed, the percentage marrow fat in the GH-treated group (0.62 ± 0.12%) was significantly (P < 0.05) lower than that in the saline-treated animals (1.07 ± 0.11%). This was due to a decreased adipocyte number (saline 37.9 ± 2.4, GH 25.5 ± 4.9/mm2 BM, P = 0.065) rather than size (saline 68.9 ± 2.6, GH 62.7 ± 3.1 µm, NS). GH administration significantly increased the % osteoblast surface in the secondary spongiosa (50.7 ± 0.5% vs. 35.6 ± 7% ALP-covered bone surface, P < 0.01) but had no effect on the ALP activity of individual osteoblasts (GH 48.9 ± 3.2, saline 50.6 ± 5.4 MIA x 100), confirming the previous experiment. GH increased the cell proliferation within the marrow space, as assessed by an increased BrdU labeling (1994 ± 76 vs. 1664 ± 64 cells per mm2, P < 0.01). It was notable that in the saline-treated young dw/dw rats in this experiment the percentage marrow fat was much lower than in the corresponding control group of older dw/dw animals in experiment 1 (8.6 ± 1.0%, measured at 11–12 wk).

A further experiment was performed in older dw/dw rats (4 months of age), given a continuous sc infusion of GH. These rats gained only 0.82 ± 0.14 g/d on GH vs. 0.24 ± 0.12 g/d on saline (P < 0.05). Percentage marrow fat was much higher in these older dw/dw rats (7.8 ± 0.5%) than in age-matched normal animals (3.1 ± 0.3%, P < 0.001), and continuous GH treatment reduced the percentage marrow fat to normal levels (Fig. 5AGo). Again, the number of adipocytes was much higher in dw/dw rats than in normals and was reduced by GH treatment. Adipocyte size was not statistically different between untreated dw/dw rats and normals, though GH treatment reduced size slightly (Fig. 5Go, B and C). Representative images of BM of a normal rat, a dw/dw rat, and a GH-treated dw/dw rat are shown in Fig. 5Go, D–F.



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  		Figure 5. hGH treatment reduces adipocyte number in GH-deficient dw/dw rats. Four-month-old dw/dw rats received hGH (200 µg/d) or saline (sal) sc for 2 wk and were compared with normal rats. Image analysis of entire tibial sections was performed using NIH-Image. A, Percentage of BM fat; B, adipocyte number (no)/mm2 BM; C, adipocyte size. Data are the mean ± SEM from five to seven rats. ***, P < 0.001 vs. normals; ##, P < 0.01; ###, P < 0.001 vs. dw/dw + saline. D–F show representative images of tibial BM of a (D) normal rat, (E) dw/dw rat, and (F) GH-treated dw/dw rat.

 
Effect of IGF-1 treatment
dw/dw rats showed a significantly increased weight gain during the first week of treatment with IGF-1 (8.3 ± 0.7 vs. 4.2 ± 0.6 g/wk, P < 0.01) though the difference lost statistical significance over the total treatment period (11.5 ± 1.8 g vs. 6.3 ± 1.7 g/2 wk, P = 0.076). IGF-1 did not affect % marrow fat or adipocyte number (Fig. 6Go, A and B). However, adipocyte size was significantly decreased (Fig. 6CGo). Renal and ovarian fat pad weights were unaltered, as were leptin levels.



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  		Figure 6. IGF-1 reduces BM adipocyte size but not number in GH-deficient dw/dw rats. Eight- to 9-wk-old dw/dw rats received rh IGF-1 (60 µg/d) for 2 wk via sc implanted osmotic minipumps and were compared with untreated dw/dw rats. Image analysis of entire tibial sections was performed using NIH-Image. A, Percentage of BM fat; B, adipocyte number (no)/mm2 BM; C, adipocyte size. Data are the mean ± SEM from five to six rats. **, P < 0.01 vs. control dw/dw.

 
Effect of high fat feeding
Fat feeding increased body weight slowly and rats on the high fat diet were 15% heavier than the controls at the end of the experiment (257.5 ± 6.9 vs. 228.6 ± 7.8 g, P < 0.01). Renal and ovarian fat pads were doubled in weight compared with the controls (renal: 4.6 ± 0.5 vs. 2.0 ± 0.2 g, ovarian: 3.3 ± 0.2 vs. 1.6 ± 0.2 g, P < 0.01). Percentage BM fat was higher in the rats on the high fat diet (6.3 ± 0.4% vs. 3.9 ± 0.4%, P < 0.01) and this was primarily due to a larger adipocyte cell size and not to an increase in cell number/mm2 BM (Fig. 7Go, A–C). Percentage cancellous bone was not affected by fat feeding (data not shown).



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  		Figure 7. High-fat feeding increases BM adipocyte size but not number in rats. Seven-wk-old rats were fed a high fat diet (40% fat) for 11 wk or a normal chow diet (3.4% fat). Image analysis of entire tibial sections was performed using NIH-Image. A, Percentage of BM fat; B, adipocyte number (no)/mm2 BM; C, adipocyte size. Data are the mean ± SEM from seven rats. **, P < 0.01 vs. chow-fed rats.

 
Effect of PTH treatment
Continuous PTH treatment did not affect weight gain or weights of renal and ovarian fat pads. As expected for continuous PTH treatment, percentage cancellous bone was lower in PTH-treated rats compared with untreated rats (35.0 ± 1.0 vs. 39.5 ± 4.0%, P < 0.05). Percentage marrow fat (2.9 ± 0.1% vs. 2.6 ± 0.2%), adipocyte number/mm2 BM (111 ± 9 vs. 99 ± 6), and adipocyte size (271 ± 10 µm2 vs. 269 ± 6 µm2, human PTH vs. saline) were all unchanged.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Peripheral fat depots are well-known targets of GH action. In humans, GH deficiency results in adiposity and GH treatment reduces fat mass (38) probably acting directly via GH receptors expressed in adipocytes, to activate Stat5 and increase lipolysis (14, 39, 40). However, BM fat depots have largely been ignored as a target for GH. In this study we show for the first time that dw/dw rats with isolated GH deficiency have a markedly increased number of adipocytes in the BM compared with normal rats, and that these adipocytes are also larger, implying increased fat storage in BM. GH treatment counteracted these changes, reducing adipocyte number and size and restoring the amount of BM fat to normal.

The change in adipocyte size could be due to a direct effect of GH to increase lipolysis because GH receptors have been demonstrated on adipocytes in human BM (41). It could also be indirect, via IGF-1 generation because IGF-1 treatment also decreased adipocyte size. The effects on adipocyte number were only seen with GH, and not with IGF-1, and thus could be due to a direct effect of GH on the proliferation or differentiation of preadipocytes to adipocytes, and/or their elimination rate. However, our in vivo experiments cannot establish that GH acts directly on marrow adipocytes. It is possible that GH affects other target cells in BM, which then indirectly affects the adipocyte population.

Adipocytes, chondrocytes, and osteoblasts share a common mesenchymal stem cell (5), and there is both circumstantial and direct evidence suggesting that these lineages may be coregulated. In osteoporotic bone loss, the amount of fat in BM increases (4). Conversely, increases in bone formation and chondrocyte proliferation induced by GH are accompanied by simultaneous decreases in peripheral fat (38). Most studies on GH and bone formation have focused on mature osteoblasts since they express GH receptors and can proliferate and differentiate in vitro in response to GH (42, 43). However, GH receptors are also present on BM stromal progenitor cells (41) and GH can increase the proliferation of stromal osteoblast-like precursors in vitro (44). GH could therefore act on the progenitors of adipocytes and osteoblasts, to affect their proliferation and differentiation.

In younger rats, GH deficiency reduced, and GH treatment restored, the amount of cancellous bone and the proportion of the cancellous surface occupied by ALP-positive cells, reflecting active osteoblasts, but did not affect ALP activity within individual cells. Furthermore, there was a highly significant inverse correlation between ALP-positive surface and adipocyte numbers, suggesting a link between changes in cancellous bone area and marrow fat and corresponding changes in numbers of osteoblasts and adipocytes. A further link is the well-established effect of GH on chondrocyte proliferation, which, though not specifically addressed in this study, was readily apparent in the tibial growth plates of GH-treated dw/dw rats (32).

We suggest that GH acts as an important regulator of all three lineages in two distinct phases (Fig. 8Go). Firstly, GH affects the lineage fate of the common mesenchymal precursors of these cells, stimulating osteoblastogenesis and chondrogenesis, while inhibiting adipogenesis. Once these cells are differentiated, GH has a second phase of action to regulate their metabolic, mitotic, and apoptotic activities in a cell-specific fashion. In the absence of GH, the precursors differentiate, as a default, into adipocytes.



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  		Figure 8. Hypothesis on the effects of GH on BM adipocytes. Firstly, GH acts on the common progenitor of the adipocyte, osteoblast, and chondrocyte lineage and thereby regulates the number of cells going toward each lineage. This results in a decreased number of BM adipocytes, concurrent with an increase in the other lineages. Secondly, GH acts on mature adipocytes (by analogy with GH’s action on mature osteoblasts and chondrocytes), to stimulate lipolysis to provide energy for other cellular activities in the bone and BM.

 
The involvement of GH in differentiation of stem cells in this lineage is not new, having been well established for both chondrocyte and hematopoeietic progenitors, as well as for peripheral adipocytes (16, 18, 45). The dramatic GH-dependent changes we observed in marrow adipocyte number places these cells also into this category. These may not even complete the list of GH targets in this lineage because we also noted an apparent increase in BM megakaryocytes after GH treatment (our unpublished observations). Since our studies were completed, it was recently shown that the age-associated decline in medullary and extramedullary hematopoiesis was restored by GH treatment and that this was accompanied by a simultaneous decrease in BM adipocyte number, in agreement with our results (46). GH could affect proliferation, survival, or elimination of BM target cells, and has been shown to stimulate the clonal expansion of chondrocytes (47). We found that GH did increase the number of marrow cells incorporating BrdU, but we did not identify the cell types responding in this way, so further studies will be needed with cell-specific markers.

It is still hotly debated whether the effects of GH on the chondrocytes involved in linear bone growth are direct or mediated by the generation of paracrine or endocrine IGF-1 (48, 49, 50). Because IGF-1 treatment did not affect the number of marrow adipocytes, we believe that this effect of GH is direct and not secondary to increased tissue or serum IGF-1 levels caused by GH treatment. However, marrow adipocyte size was affected by IGF-1, suggesting that IGF-1 may mediate some of the effects of GH on adipocyte fat storage. hGH can also stimulate prolactin (PRL) receptors in the rat, and PRL receptors are present in osteoblasts and adipocytes (51, 52). However, our dw/dw rats are not PRL deficient (53), and PRL stimulates rather than inhibits adipocyte differentiation of BM stromal cells (54).

We wished to test whether the effects of GH on BM fat would also occur with other endocrine manipulations of bone metabolism that altered osteoblast activity. One obvious hormonal candidate to test was estrogen because it has important functions in both bone and fat metabolism (25, 26) and both osteoblasts and adipocytes have estrogen receptors (25, 55). Although ovariectomy decreased cancellous bone area, it did not alter the number or size of adipocytes in these rats. Estrogen replacement in Ovx rats caused a 50% increase in cancellous bone volume, but this was accompanied by an increase, not a decrease, in adipocyte number. Furthermore, whereas GH affected the bone surface occupied by osteoblasts but not individual osteoblast ALP activity, estrogen only affected individual osteoblast activity. This also suggests that estrogen does not affect lineage choice of the progenitor cells.

We also tested the effects of altering bone metabolism by PTH (1–34) treatment because PTH affects bone turnover by a different mechanism than estrogen (56). In contrast to intermittent PTH exposure, continuous PTH treatment leads to a decreased bone mass, mainly due to a decreased cortical bone mass and slightly due to a decreased epiphyseal cancellous bone mass (57). We confirmed a decrease in cancellous bone volume in rats treated with PTH (1–34), but neither BM adipocyte number nor adipocyte size was affected by PTH (1–34) treatment. These results suggest that alterations in BM adipocyte numbers by GH are not simply secondary to hormone-induced alterations in bone volume or stimulation of bone metabolism per se.

The effects of GH in dw/dw rats depends on the pattern of administration with pulsatile GH most effective for longitudinal growth, while continuous exposure is more effective in reducing fat mass (34, 58). Both pulsatile and continuous GH were effective in reducing marrow fat mass, and the greatest effect was observed in dw/dw rats with continuous GH exposure. However, we interpret this observation with caution because these rats were older and had much higher amounts of marrow fat before treatment. Aging is known to be accompanied by an increased marrow fat compartment in both humans and rats (46, 59), and we found a higher BM adipocyte number in older rats of both normal and dw/dw strains. Because GH also reduced BM adiposity when given to older normal rats (46), an increased marrow adiposity with age may partly be due to the reduced GH secretion that occurs with aging.

It is unlikely that the increased BM adipocyte number found in GH-deficient dw/dw rats is simply due to general obesity because these animals are not obese when fed a normal chow diet (58). However, to assess how sensitive BM adipose mass is to peripheral adiposity, we compared groups of rats given normal or high fat diets. We showed that BM fat mass indeed increased, parallel to peripheral fat pad weights, when normal rats were fed a high fat diet. However, in contrast to GH deficiency, the increase was entirely due to a larger adipocyte size, reflecting increased fat storage, and not to an increased adipocyte number.

What could be the role of GH in regulating BM adipocytes? It seems likely that they play a more active role than simply filling the space between the bone. One obvious possibility is that they provide a lightweight high energy source for local metabolism in the bone or BM, especially because osteoclasts are known to use fatty acid oxidation as their major energy supply (60). If this is the case, changes in adipocyte size might reflect responses to changes in energy demand from other metabolically active cells.

Another possibility is that the marrow adipocytes provide a source of paracrine factors, perhaps regulating osteoblastogenesis, osteoclastogenesis, or hematopoiesis. The peripheral adipocyte is now recognized as a source of several regulatory factors, some of which could also play important local roles at high concentrations in BM (61, 62). The obvious example is leptin, which is known to be produced by BM adipocytes (63) and can favor differentiation of human mesenchymal stem cells into osteoblasts rather than adipocytes (64). Whether leptin production from marrow adipocytes is regulated directly by GH, or indirectly by changes in fat mass, remains to be determined.

A final question is the functional relevance of our findings. The large differences in marrow fat in rodents are present without any manipulation, change markedly when the GH axis is normalized, and increase with age (46), suggesting that these are physiological, not pharmacological, changes. Despite the enormous interest in imaging the effects of GH on bone density in human subjects, much less attention has been paid to the possible functional role of changes in BM fat. However, we showed that administration of GH to a patient with severe osteopenia resulted in an increase in biochemical markers of bone formation, osteoid and osteoblast surface and also clearly decreased adipocyte number and size (65), indicating that the effect of GH we observed in rodents can also occur in humans. We suggest that the adipocyte population in human bone is an important primary target for GH and merits closer attention.


   Acknowledgments
 
We would like to thank Pharmacia-Upjohn for providing hGH, Genentech, Inc. for providing recombinant human IGF-1, and Organon BV, The Netherlands, for performing cortical thickness measurements. We also thank Mrs. Wendy Hatton for assistance with histological techniques.


   Footnotes
 
This work was funded by the Medical Research Council (MRC) (I.C.A.F.R., E.F.G.) and by MRC program Grant No. 9321536 (to N.L.).

Abbreviations: ALP, Alkaline phosphatase; BM, bone marrow; BrdU, bromodeoxyuridine; E2, estradiol; GH-deficient dwarf; hGH, human GH; Ovx, ovariectomized; PRL, prolactin.

Received April 22, 2002.

Accepted for publication July 1, 2002.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Meunier P, Aaron J, Edouard C, Vignon G 1971 Osteoporosis and the replacement of cell populations of the marrow by adipose tissue. A quantitative study of 84 iliac bone biopsies. Clin Orthop 80:147–54[Medline]
  2. Burkhardt R, Kettner G, Bohm W, Schmidmeier M, Schlag R, Frisch B, Mallmann B, Eisenmenger W, Gilg T 1987 Changes in trabecular bone, hematopoiesis and bone marrow vessels in aplastic anemia, primary osteoporosis, and old age: a comparative histomorphometric study. Bone 8:157–164[Medline]
  3. Kajkenova O, Lecka-Czernik B, Gubrij I, Hauser SP, Takahashi K, Parfitt AM, Jilka RL, Manolagas SC, Lipschitz DA 1997 Increased adipogenesis and myelopoiesis in the bone marrow of SAMP6, a murine model of defective osteoblastogenesis and low turnover osteopenia. J Bone Miner Res 12:1772–1779[CrossRef][Medline]
  4. Nuttall ME, Gimble JM 2000 Is there a therapeutic opportunity to either prevent or treat osteopenic disorders by inhibiting marrow adipogenesis? Bone 27:177–184[Medline]
  5. Pittenger MF, Mackay AM, Beck SC, Jaiswal RK, Douglas R, Mosca JD, Moorman MA, Simonetti DW, Craig S, Marshak DR 1999 Multilineage potential of adult human mesenchymal stem cells. Science 284:143–147[Abstract/Free Full Text]
  6. Chen D, Ji X, Harris MA, Feng JQ, Karsenty G, Celeste AJ, Rosen V, Mundy GR, Harris SE 1998 Differential roles for bone morphogenetic protein (BMP) receptor type IB and IA in differentiation and specification of mesenchymal precursor cells to osteoblast and adipocyte lineages. J Cell Biol 142:295–305[Abstract/Free Full Text]
  7. Kodama Y, Takeuchi Y, Suzawa M, Fukumoto S, Murayama H, Yamato H, Fujita T, Kurokawa T, Matsumoto T 1998 Reduced expression of interleukin-11 in bone marrow stromal cells of senescence-accelerated mice (SAMP6): relationship to osteopenia with enhanced adipogenesis. J Bone Miner Res 13:1370–1377[CrossRef][Medline]
  8. Taguchi Y, Yamamoto M, Yamate T, Lin SC, Mocharla H, DeTogni P, Nakayama N, Boyce BF, Abe E, Manolagas SC 1998 Interleukin-6-type cytokines stimulate mesenchymal progenitor differentiation toward the osteoblastic lineage. Proc Assoc Am Physicians 110:559–574[Medline]
  9. Jaiswal N, Haynesworth SE, Caplan AI, Bruder SP 1997 Osteogenic differentiation of purified, culture-expanded human mesenchymal stem cells in vitro. J Cell Biochem 64:295–312[CrossRef][Medline]
  10. Sabatakos G, Sims NA, Chen J, Aoki K, Kelz MB, Amling M, Bouali Y, Mukhopadhyay K, Ford K, Nestler EJ, Baron R 2000 Overexpression of DeltaFosB transcription factor(s) increases bone formation and inhibits adipogenesis. Nat Med 6:985–990[CrossRef][Medline]
  11. Jaiswal RK, Jaiswal N, Bruder SP, Mbalaviele G, Marshak DR, Pittenger MF 2000 Adult human mesenchymal stem cell differentiation to the osteogenic or adipogenic lineage is regulated by mitogen-activated protein kinase. J Biol Chem 275:9645–9652[Abstract/Free Full Text]
  12. Corpas E, Harman SM, Blackman MR 1993 Human growth hormone and human aging. Endocr Rev 14:20–39[Abstract]
  13. Snel YE, Brummer RJ, Doerga ME, Zelissen PM, Bakker CJ, Hendriks MJ, Koppeschaar HP 1995 Adipose tissue assessed by magnetic resonance imaging in growth hormone-deficient adults: the effect of growth hormone replacement and a comparison with control subjects. Am J Clin Nutr 61:1290–1294[Abstract/Free Full Text]
  14. Vikman K, Carlsson B, Billig H, Eden S 1991 Expression and regulation of growth hormone (GH) receptor messenger ribonucleic acid (mRNA) in rat adipose tissue, adipocytes, and adipocyte precursor cells: GH regulation of GH receptor mRNA. Endocrinology 129:1155–1161[Abstract]
  15. Yang S, Bjorntorp P, Liu X, Eden S 1996 Growth hormone treatment of hypophysectomized rats increases catecholamine-induced lipolysis and the number of ß-adrenergic receptors in adipocytes: no differences in the effects of growth hormone on different fat depots. Obes Res 4:471–478[Medline]
  16. Green H, Morikawa M, Nixon T 1985 A dual effector theory of growth-hormone action. Differentiation 29:195–198[CrossRef][Medline]
  17. Hansen LH, Madsen B, Teisner B, Nielsen JH, Billestrup N 1998 Characterization of the inhibitory effect of growth hormone on primary preadipocyte differentiation. Mol Endocrinol 12:1140–1149[Abstract/Free Full Text]
  18. Isaksson OGP, Lindahl A, Nilsson A, Isgaard J 1987 Review paper: Mechanism of the stimulatory effect of growth hormone on longitudinal bone growth. Endocr Rev 8:426–438[Medline]
  19. Ohlsson C, Bengtsson BA, Isaksson OG, Andreassen TT, Slootweg MC 1998 Growth hormone and bone. Endocr Rev 19:55–79[Abstract/Free Full Text]
  20. Andreassen TT, Oxlund, H 2001 The effects of growth hormone on cortical and cancellous bone. J Musculoskel Neuron Interact 2:49–58[CrossRef]
  21. de Boer H, Blok GJ, Van der Veen EA 1995 Clinical aspects of growth hormone deficiency in adults. Endocr Rev 16:63–86[CrossRef][Medline]
  22. Vandeweghe M, Taelman P, Kaufman JM 1993 Short and long-term effects of growth hormone treatment on bone turnover and bone mineral content in adult growth hormone-deficient males. Clin Endocrinol (Oxf) 39:409–415[Medline]
  23. Johansson AG, Engstrom BE, Ljunghall S, Karlsson FA, Burman P 1999 Gender differences in the effects of long term growth hormone (GH) treatment on bone in adults with GH deficiency. J Clin Endocrinol Metab 84:2002–2007[Abstract/Free Full Text]
  24. Gimble JM 1990 The function of adipocytes in the bone marrow stroma. New Biol 2:304–312[Medline]
  25. Compston JE 2001 Sex steroids and bone. Physiol Rev 81:419–447[Abstract/Free Full Text]
  26. Tchernof A, Poehlman ET, Despres JP 2000 Body fat distribution, the menopause transition, and hormone replacement therapy. Diabetes Metab 26:12–20[Medline]
  27. O’Sullivan AJ, Martin A, Brown MA 2001 Efficient fat storage in premenopausal women and in early pregnancy: a role for estrogen. J Clin Endocrinol Metab 86:4951–4956[Abstract/Free Full Text]
  28. Martin RB, Zissimos SL 1991 Relationships between marrow fat and bone turnover in ovariectomized and intact rats. Bone 12:123–131[Medline]
  29. Benayahu D, Shur I, Ben-Eliyahu S 2000 Hormonal changes affect the bone and bone marrow cells in a rat model. J Cell Biochem 79:407–415[CrossRef][Medline]
  30. Charlton HM, Clark RG, Robinson ICAF, Porter-Goff AE, Cox BS, Bugnon C, Bloch BS 1988 Growth hormone-deficient dwarfism in the rat: a new mutation. J Endocrinol 119:51–58[Abstract]
  31. Spiteri-Grech J, Bartlett JM, Nieschlag E 1991 Regulation of testicular insulin-like growth factor-I in pubertal growth hormone-deficient male rats. J Endocrinol 131:279–285[Abstract]
  32. Gevers EF, Milne J, Robinson ICAF, Loveridge N 1996 Single cell enzyme activity and proliferation in the growth plate: effects of growth hormone. J Bone Miner Res 11:1103–1111[Medline]
  33. Ederveen AG, Spanjers CP, Quaijtaal JH, Kloosterboer HJ 2001 Effect of 16 months of treatment with tibolone on bone mass, turnover, and biomechanical quality in mature ovariectomized rats. J Bone Miner Res 16:1674–1681[CrossRef][Medline]
  34. Gevers EF, Wit JM, Robinson ICAF 1996 Growth, growth hormone (GH)-binding protein and GH receptors are differentially regulated in the rat by peak and trough components of the GH secretory pattern. Endocrinology 137:1013–1018[Abstract]
  35. Loveridge N, Dean V, Goltzman D, Hendy GN 1991 Bioactivity of parathyroid hormone and parathyroid hormone-like peptide: agonist and antagonist activities of amino-terminal fragments as assessed by the cytochemical bioassay and in situ biochemistry. Endocrinology 128:1938–1946[Abstract]
  36. Bell KL, Loveridge N, Lindsay PC, Lunt M, Garrahan N, Compston JE, Reeve J 1997 Cortical remodeling following suppression of endogenous estrogen with analogs of gonadotrophin releasing hormone. J Bone Miner Res 12:1231–1240[CrossRef][Medline]
  37. Bradbeer JN, Zanelli JM, Lindsay PC, Pearson J, Reeve J 1992 Relationship between the location of osteoblastic alkaline phosphatase activity and bone formation in human iliac crest bone. J Bone Miner Res 7:905–912[Medline]
  38. Bengtsson BA, Johannsson G, Shalet SM, Simpson H, Sonken PH 2000 Treatment of growth hormone deficiency in adults. J Clin Endocrinol Metab 85:933–942[Free Full Text]
  39. Ridderstrale M, Groop L 2001 Differential phosphorylation of Janus kinase 2, Stat5A and Stat5B in response to growth hormone in primary rat adipocytes. Mol Cell Endocrinol 183:49–54[CrossRef][Medline]
  40. Davidson MB 1987 Effect of growth hormone on carbohydrate and lipid metabolism. Endocr Rev 8:115–131[Medline]
  41. Lincoln DT, Sinowatz F, Gabius S, Gabius HJ, Temmim L, Baker H, Mathew TC, Waters MJ 1997 Subpopulations of stromal cells from long-term human bone marrow cultures: ontogeny of progenitor cells and expression of growth hormone receptors. Anat Histol Embryol 26:11–28[Medline]
  42. Barnard R, Ng KW, Martin TJ, Waters MJ 1991 Growth hormone (GH) receptors in clonal osteoblast-like cells mediate a mitogenic response to GH. Endocrinology 128:1459–1464[Abstract]
  43. Kassem M, Blum W, Ristelli J, Mosekilde L, Eriksen EF 1993 Growth hormone stimulates proliferation and differentiation of normal human osteoblast-like cells in vitro. Calcif Tissue Int 52:222–226[CrossRef][Medline]
  44. Kassem M, Mosekilde L, Eriksen EF 1994 Growth hormone stimulates proliferation of normal human bone marrow stromal osteoblast precursor cells in vitro. Growth Regul 4:131–135[Medline]
  45. Merchav S 1998 The haematopoietic effects of growth hormone and insulin-like growth factor-I. J Pediatr Endocrinol Metab 11:677–685[Medline]
  46. French RA, Broussard SR, Meier WA, Minshall C, Arkins S, Zachary JF, Dantzer R, Kelley KW 2002 Age-associated loss of bone marrow hematopoietic cells is reversed by GH and accompanies thymic reconstitution. Endocrinology 143:690–699[Abstract/Free Full Text]
  47. Lindahl A, Isgaard J, Carlsson L, Isaksson O 1987 Differential effects of growth hormone and insulin-like growth factor I on colony formation of epiphyseal chondrocytes in suspension culture in rats of different ages. Endocrinology 121:1061–1069[Abstract]
  48. Backeljauw PF, Underwood LE 1996 Prolonged treatment with recombinant insulin-like growth factor-I in children with growth hormone insensitivity syndrome—a clinical research center study. GHIS Collaborative Group. J Clin Endocrinol Metab 81:3312–3317[Abstract]
  49. Sjogren K, Liu JL, Blad K, Skrtic S, Vidal O, Wallenius V, LeRoith D, Tornell J, Isaksson OG, Jansson JO, Ohlsson C 1999 Liver-derived insulin-like growth factor I (IGF-I) is the principal source of IGF-I in blood but is not required for postnatal body growth in mice. Proc Natl Acad Sci USA 96:7088–7092[Abstract/Free Full Text]
  50. D’Ercole AJ, Calikoglu AS 2001 Editorial review: the case of local versus endocrine IGF-I actions: the jury is still out. Growth Horm IGF Res 11:261–265[CrossRef][Medline]
  51. Clement-Lacroix P, Ormandy C, Lepescheux L, Ammann P, Damotte D, Goffin V, Bouchard B, Amling M, Gaillard-Kelly M, Binart N, Baron R, Kelly PA 1999 Osteoblasts are a new target for prolactin: analysis of bone formation in prolactin receptor knockout mice. Endocrinology 140:96–105[Abstract/Free Full Text]
  52. Ling C, Billig H 2001 Prl receptor-mediated effects in female mouse adipocytes: prl induces suppressors of cytokine signaling expression and suppresses insulin-induced leptin production in adipocytes in vitro. Endocrinology 142:4880–4890[Abstract/Free Full Text]
  53. Bartlett J, Charlton H, Robinson I, Nieschlag E 1990 Pubertal development and testicular function in the male growth hormone-deficient rat. J Endocrinol 126:193–201[Abstract]
  54. McAveney KM, Gimble JM, Yu-Lee L 1996 Prolactin receptor expression during adipocyte differentiation of bone marrow stroma. Endocrinology 137:5723–5726[Abstract]
  55. Pedersen SB, Borglum JD, Moller-Pedersen T, Richelsen B 1992 Effects of in vivo estrogen treatment on adipose tissue metabolism and nuclear estrogen receptor binding in isolated rat adipocytes. Mol Cell Endocrinol 85:13–19[CrossRef][Medline]
  56. Dobnig H, Turner RT 1995 Evidence that intermittent treatment with parathyroid hormone increases bone formation in adult rats by activation of bone lining cells. Endocrinology 136:3632–3638[Abstract]
  57. Uzawa T, Hori M, Ejiri S, Ozawa H 1995 Comparison of the effects of intermittent and continuous administration of human parathyroid hormone(1–34) on rat bone. Bone 16:477–484[Medline]
  58. Clark RG, Mortensen DL, Carlsson LM, Carlsson B, Carmignac D, Robinson IC 1996 The obese growth hormone (GH)-deficient dwarf rat: body fat responses to patterned delivery of GH and insulin-like growth factor-I. Endocrinology 137:1904–1912[Abstract]
  59. Rozman C, Feliu E, Berga L, Reverter JC, Climent C, Ferran MJ 1989 Age-related variations of fat tissue fraction in normal human bone marrow depend both on size and number of adipocytes: a stereological study. Exp Hematol 17:34–37[Medline]
  60. Dodds RA, Gowen M, Bradbeer JN 1994 Microcytophotometric analysis of human osteoclast metabolism: lack of activity in certain oxidative pathways indicates inability to sustain biosynthesis during resorption. J Histochem Cytochem 42:599–606[Abstract]
  61. Trayhurn P, Beattie JH 2001 Physiological role of adipose tissue: white adipose tissue as an endocrine and secretory organ. Proc Nutr Soc 60:329–339[Medline]
  62. Manolagas SC, Jilka RL 1995 Bone marrow, cytokines, and bone remodeling. Emerging insights into the pathophysiology of osteoporosis. N Engl J Med 332:305–311[Free Full Text]
  63. Laharrague P, Larrouy D, Fontanilles AM, Truel N, Campfield A, Tenenbaum R, Galitzky J, Corberand JX, Penicaud L, Casteilla L 1998 High expression of leptin by human bone marrow adipocytes in primary culture. FASEB J 12:747–752[Abstract/Free Full Text]
  64. Thomas T, Gori F, Khosla S, Jensen MD, Burguera B, Riggs BL 1999 Leptin acts on human marrow stromal cells to enhance differentiation to osteoblasts and to inhibit differentiation to adipocytes. Endocrinology 140:1630–1638[Abstract/Free Full Text]
  65. Kroger H, Soppi E, Loveridge N 1997 Growth hormone, osteoblasts, and marrow adipocytes: a case report. Calcif Tissue Int 61:33–35[CrossRef][Medline]



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