Endocrinology Vol. 140, No. 10 4644-4650
Copyright © 1999 by The Endocrine Society
Chronic Exposure to High Glucose Concentrations Increases Proglucagon Messenger Ribonucleic Acid Levels and Glucagon Release from InR1G9 Cells1
Eric Dumonteil,
Beate Ritz-Laser,
Chistophe Magnan,
Iléana Grigorescu,
Alain Ktorza and
Jacques Philippe
Diabetes Unit (E.D., B.R.-L., I.G., J.P.), Centre Médical
Universtaire, 1211 Genève 4, Switzerland CH-1211; Laboratoire
de Physiopathologie de la Nutrition (C.M., A.K.), Groupe Endocrinologie
métabolique, Université Paris 7, Tour 23–33, F-75251 Paris
Cedex 05, France
Address all correspondence and requests for reprints to: Jacques Philippe, M.D., Diabetes Unit, Centre Médical Universitaire, 1211 Genève 4, Switzerland Ch-1211. E-mail:
jacquesphilippe{at}hcuge.ch
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Abstract
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cell function is impaired in diabetes. In diabetics, plasma levels
of glucagon are high despite persistently elevated glucose levels and
may even rise paradoxically in response to a glucose load; high plasma
glucagon levels are accompanied by increased proglucagon gene
expression. We have investigated the effects of high glucose
concentrations on InR1G9 cells, a glucagon-producing cell line. We show
here that chronically elevated glucose concentrations increase glucagon
release by 2.5- to 4-fold, glucagon cell content by 2.5- to 3-fold, and
proglucagon messenger RNA levels by 4- to 8-fold, whereas changes for
24 h have no effect on proglucagon messenger RNA levels.
Persistently elevated glucose affects proglucagon gene expression at
the level of transcription and insulin is capable of preventing this
effect. We conclude that chronically elevated glucose may be an
important factor in the cell dysfunction that occurs in diabetes
and thus that glucose may not only affect the ß cell but also the
cell.
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Introduction
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DIABETES results from an inadequate
response of the ß cells of the endocrine pancreas to match insulin
release to the prevailing glucose concentrations, resulting in
hyperglycemia. It is now well established that sustained hyperglycemia
leads to the so-called glucose toxicity. In support of the glucose
toxicity concept, chronic exposure of primary islets or insulinoma
cells to elevated glucose concentrations impairs glucose-responsive
insulin secretion and biosynthesis (1, 2).
The mechanisms by which chronic hyperglycemia reduces insulin
production have been recently analyzed; high glucose leads to a
paradoxical decrease in insulin messenger RNA (mRNA) levels through an
inhibition of insulin gene transcription (3, 4, 5, 6, 7, 8, 9).
The ß cell is not the only cell type of the islet that does not
function properly in diabetes. cell function has been reported be
abnormal in all forms of diabetes. The normal reciprocal relationship
between glucose and glucagon concentrations is thus lost. In contrast
to nondiabetics, in whom hyperglycemia suppresses and hypoglycemia
stimulates glucagon secretion, in diabetics, plasma levels of glucagon
are constantly high despite varying degrees of hyperglycemia; in fact,
glucagon levels may rise paradoxically during hyperglycemia produced by
a carbohydrate meal (10). In addition to these in vivo
observations, it has been shown that prolonged culture of isolated
mouse or rat islets at high extracellular glucose concentrations
results in paradoxically increased glucagon secretion (11, 12). The
loss of -cell response to changes in glucose concentrations appears
to be selective inasmuch as glucagon secretion in diabetes is normally
suppressed by increased FFA and is hyperresponsive to stimulation by
arginine (13).
While the existence of -cell dysfunction in diabetes is generally
accepted, the explanation for the apparent -cell insensitivity or
even paradoxical response to glucose remains unclear. It has been
suggested that -cell dysfunction is an abnormality separate from the
ß-cell disorder or alternatively that it is the passive consequence
of insulin deficiency (13). Accumulating evidence suggests that neither
view is strictly correct. Indeed, while insulin treatment leads to
reductions of plasma glucagon levels, it may not restore the normal
-cell ability to secrete glucagon appropriately in response to
changes in glucose concentration. The concept of glucose toxicity could
thus apply to the observed cell dysfunction.
We recently showed that, in vivo, insulinopenic diabetes is
characterized by both elevated plasma glucagon and proglucagon mRNA
levels; these levels rise despite marked hyperglycemia suggesting that
the cell becomes progressively insensitive to glucose (14).
We have investigated the possibility that chronically elevated glucose
levels might affect the function of glucagon-producing cells. We show
here that exposure of InR1G9 cells to high glucose leads to an increase
in glucagon release, glucagon cell content and proglucagon mRNA levels;
this increase does not occur within 24 h but, over a period of
days, is reversible, and prevented by insulin. The mechanism by which
high glucose increases proglucagon gene expression is through the
stimulation of transcription and the first 138 bp of the promoter are
necessary for this effect. We conclude that hyperglycemia may not only
affect the ß cells by decreasing insulin bioynthesis but also the
-cells by stimulating glucagon production.
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Materials and Methods
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Cell culture and transfection studies
InR1G9 cells are glucagon-producing cells and grow in monolayers
(15, 16). As most islet cell lines InR1G9 cells are usually cultured in
11 mM glucose; this glucose concentration may not be
optimal for cell function, as previously demonstrated for ß cells
(3). We cultured InR1G9 cells in RPMI 1640 at a glucose concentration
of either 5 or 11 mM, supplemented with 5% FCS and 5%
new-born calf serum, 100 U/ml of penicillin, and 100 µg/ml of
streptomycin. Cells were passaged once weekly after trypsinization and
fed every 48 h with medium except that new medium without serum
was added 24 h before glucagon measurements. For counting, cells
were plated at a density of 105 cells in 12-well plates;
cells were detached with trypsin-EDTA after 7 days and counted in a
hematocytometer chamber for four successive periods. The number of
nonviable cells was substracted from the total number of cells. Cell
viability was assessed by trypan blue exclusion. Cells were transfected
in suspension by the DEAE dextran method (17) with 3 µg of a CAT
reporter plasmid and 1 µg of the plasmid pSV2A pap to
monitor transfection efficiency. PSV2Apap contains the
human placental alkaline phosphatase gene driven by the simian virus 40
long terminal repeat (18). 5'-deleted mutants of the rat glucagon gene
upstream sequence were subcloned into poCAT as previously described
(17). Transfections were performed between weeks 13 and 20. Insulin was
added to the culture medium (in the absence of serum) at a
concentration of 10-8 M in specific
experiments. Of note, the insulin concentrations in the media
(from FCS and newborn calf serum) averaged 2.9 to 5.5 µU/ml.
Cell extract were prepared 48 h after transfection and analyzed
for CAT and alkaline phosphatase activity as described (18, 19).
Protein concentrations were determined with a Bio-Rad Laboratories, Inc. protein assay kit.
Northern blot analysis
Cells from a 10 cm diameter culture plate per experimental
condition (
107 cells) were lysed in guanidine
thiocyanate and RNA was extracted through a cesium chloride gradient as
previously described (16). Twenty micrograms of total RNA, representing
each experimental condition were analyzed by Northern blot (16) using
[32P]-labeled rat proglucagon and mouse ß-actin
complementary DNA probes; quantification of the signals was done by
scanning of the membranes using a Phosphor imager (Molecular Dynamics, Inc.).
RIAs
Glucagon was determined in both culture media and acid-ethanol
extracted cells by radioimmunoassays (Bio data, Rome, Italy). The
protease inhibitor aprotinin was added at 250 KIU/ml of fresh culture
media 24 h before measurement of immunoreactive glucagon. For
glucagon cell content determination, InR1G9 cells were washed with PBS
buffer and immunoreactive glucagon was measured after acid/ethanol
(1.5% HCL, 75% ethanol) extraction (20). The sensitivity of the assay
was 14.5 ng/liter for glucagon and the coefficient of variation within
and between assays was 6%.
Presentation of the results and data analysis
Results are presented as mean ± SEM.
Statistical analysis of differences between groups were carried out
using ANOVA and the paired, two-tailed Student’s t
tests.
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Results
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High glucose exposure increases glucagon release, glucagon cell
content and proglucagon mRNA levels
To investigate whether changes in glucose concentrations could
affect glucagon release, glucagon cell content and proglucagon mRNA
levels, we incubated InR1G9 cells in either 5 or 11 mM
glucose for 5 weeks; at the end of each period of 1 week, glucagon
release (for the last 24 h), glucagon cell content and proglucagon
mRNA levels were measured. As shown in Fig. 1
, glucagon released in the medium during
24 h was 2- to 3-fold higher at 11 mM compared with 5
mM; similar results were obtained for glucagon cell content
and proglucagon mRNA levels, although the difference in proglucagon
mRNA levels between 5 and 11 mM was higher, in the range of
4- to 8-fold, compared with both release and cell content.
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Figure 1. Effect of chronically high glucose concentrations
on glucagon release, glucagon cell content and proglucagon mRNA levels.
InR1G9 cells were cultured in RPMI-1640 medium containing either 5 or
11 mM glucose for 5 weeks. Glucagon release (A), glucagon
cell content (B) and proglucagon mRNA levels (C and D) were measured at
the end of each weekly period. Glucagon release and content are
expressed in ng/500'000 cells, whereas proglucagon mRNA levels were
quantified by Northern blot (C), corrected for the respective ß-actin
signals and are expressed as percentage of the value obtained at week 1
at 11 mM glucose (D). Values are derived from three
independent experiments; * and " indicate significant differences
(P < 0.01 and P < 0.05,
respectively)
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To study whether the changes observed in proglucagon mRNA levels
between 5 and 11 mM glucose were stable over a more
prolonged period and reversible, we incubated InR1G9 cells in 5 and 11
mM glucose for 12 weeks (Fig. 2). We also tested for the reversibility
of these changes by switching at weeks 10 and 11 subsets of the cells
incubated at 5 mM to 11 mM glucose. Proglucagon
mRNA levels were measured weekly as before. As shown in Fig. 2, a 3- to
4-fold higher level of proglucagon mRNA was still observed after 12
weeks of culture in 11 mM glucose. In addition, changing
glucose from 5 to 11 mM at weeks 10 and 11 resulted in a
return to high mRNA levels values at weeks 11 and 12; reversibility of
the increase was also verified by switching cells from 11
mM to 5 mM glucose. We conclude from these data
that chronically high glucose levels result in a reversible increase in
glucagon release, glucagon cell content and proglucagon mRNA levels
over prolonged periods in InR1G9 cells.
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Figure 2. Reversibility of the glucose effects on
proglucagon mRNA levels. InR1G9 cells were cultured in RPMI-1640 medium
containing either 5 or 11 mM glucose for 12 weeks. At weeks
10 and 11, aliquots of InR1G9 cells cultured at 5 mM
glucose were switched to 11 mM and cells cultured at 11
mM were switched to 5 mM. Proglucagon mRNA
levels were measured at the end of weeks 1, 10, 11, and 12 by Northern
blot as in Fig. 1 . A, A representative Northern blot; B, proglucagon
mRNA levels are corrected for the respective ß-actin signals and are
expressed as percentage of the values obtained at week 1 at 11
mM glucose. Values are derived from three independent
experiments; * indicate significant differences (P
< 0.01).
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To ascertain that cell number and viability were not affected by the
different glucose concentrations used, viable cells were determined by
trypan blue exclusion and cells were counted at the end of each week
for a 4-week period (Fig. 3). We did not
observe any difference in cell number whether the cells were cultured
at 5 or 11 mM glucose; furthermore, cell viability was
similar at both glucose concentrations, between 90 and 95%.
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Figure 3. Different glucose concentrations do not affect
cell number. InR1G9 cells were cultured in RPMI-1640 medium containing
either 5 or 11 mM glucose and plated at a density of
105 cells; they were counted after 7 days for four
successive periods. Values are derived from four different experiments.
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Chronic changes in glucose concentrations affect glucagon release,
glucagon cell content and proglucagon mRNA levels
To determine whether glucagon release, glucagon cell content
and proglucagon mRNA levels are affected by less prolonged changes in
glucose concentrations, we switched InR1G9 cells incubated in 5
mM glucose to either 2 or 11 mM and cells
incubated in 11 mM to either 2 or 5 mM for
24 h and measured glucagon release, glucagon cell content and
proglucagon mRNA levels. As shown in Fig. 4, changes from 5 to either 2 or 11
mM or from 11 to either 2 or 5 mM glucose did
not significantly affect either glucagon release, glucagon cell content
or proglucagon mRNA levels. Of note similar results were obtained from
isolated primary rat islets incubated under the same conditions
(Dumonteil, E., manuscript in preparation).
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Figure 4. Changes in glucose concentrations during 24 h
do not affect glucagon release, glucagon cell content, or proglucagon
mRNA levels. InR1G9 cells were cultured in RPMI-1640 medium containing
either 5 or 11 mM glucose; cells incubated with 5
mM glucose were then switched to medium containing either 2
or 11 mM, whereas cells incubated in 11 mM
glucose were switched to either 2 or 5 mM glucose for
24 h. At the end of the incubation period, glucagon was measured
both in the medium (A) or cells (B) and proglucagon mRNA levels by Northern blot (C). Values are derived from three
different experiments and are expressed as the percentage of the values
obtained at 11 mM glucose. * and " indicate significant
differences (P < 0.01 and P <
0.05, respectively)
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To investigate the time course of glucose effects on proglucagon mRNA
levels, we switched InR1G9 cells chronically incubated at 11
mM glucose to 5 mM and measured proglucagon
mRNA levels daily. Significant decreases in mRNA levels occurred
between day 4 and 5; stable values were then observed from day 6 (Fig. 5A). Similarly, cells chronically
incubated at 5 mM glucose were switched to 11
mM and proglucagon mRNA levels were assessed daily. As
shown in Fig. 5B, mRNA levels started to increase after 4 days to reach
95% of the values observed in cells chronically incubated in 11
mM glucose. These data indicate that in InR1G9 cells
glucose does not affect proglucagon mRNA levels within 24 h; it
takes indeed several days and up to a week to reach a new steady
state.
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Figure 5. Time-course of the changes in proglucagon mRNA
levels induced by glucose. InR1G9 cells were incubated in RPMI-1640
medium containing either 11 mM (A) or 5 mM
glucose (B). After 12 weeks, cells were then switched to 5
mM (A) or 11 mM glucose (B), respectively, and
proglucagon mRNA levels were measured every day for 7 days and
quantified by Northern blot as in Fig. 1. Values are derived from three
different experiments and are expressed as the percentage of the values
obtained at day 0 at 11 mM glucose. * and " indicate
significant differences (P < 0.01 and
P < 0.05, repectively).
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Insulin prevents the increase in proglucagon mRNA levels induced by
high glucose
We and others previously reported that insulin was capable to
decrease glucagon biosynthesis through a decrease in proglucagon gene
transcription (14, 16, 19, 21, 22). To study whether insulin might
affect the increase in proglucagon gene expression induced by
chronically elevated glucose concentrations, we switched InR1G9 cells
incubated in 5 mM glucose to 11 mM in the
presence or absence of 10-8 M insulin for 1
week; proglucagon mRNA levels were measured at the end of the
experimental period. Figure 6 shows that
insulin was able to prevent the increase in proglucagon mRNA levels
induced by high glucose.
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Figure 6. Insulin prevents the glucose-induced increase in
proglucagon mRNA levels. InR1G9 cells were cultured in RPMI-1640 medium
containing either 5 or 11 mM glucose. Cells incubated with
5 mM glucose were switched to 11 mM with (+i)
or without 10-8 M insulin for 7 days. At the
end of the incubation period, total RNA was analyzed by Northern blot.
Values are derived from three different experiments and are expressed
as the percentage of the values obtained at 11 mM glucose.
" indicate significant difference (P < 0.05).
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High glucose affects proglucagon gene expression at the
transcription level
To determine the mechanisms by which chronically high glucose
increases proglucagon mRNA levels, we transfected 292 base pairs (bp)
of the rat proglucagon gene 5'-flanking sequence linked to the CAT
reporter gene (-292 CAT) into InR1G9 cells chronically cultured in
either 5 or 11 mM glucose. Transcriptional activity of
-292 CAT was found to be 4-fold higher in cells incubated chronically
at 11 compared with 5 mM glucose (Fig. 7). In contrast, changes in glucose
concentrations from 5 to either 2 or 11 mM or from 11 to
either 2 or 5 mM 24 h after transfection did not
affect CAT activity.
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Figure 7. Chronically elevated glucose regulates proglucagon
gene expression through an increase in transcription. InR1G9 cells were
cultured in RPMI-1640 medium containing either 5 or 11 mM
glucose. Cells were transfected with 3 µg of -292 CAT containing 292
bp of the rat proglucagon gene promoter linked to the CAT reporter
gene. Cells incubated in 5 mM glucose were then switched to
either 2 or 11 mM glucose and cells incubated in 11
mM glucose were switched to either 2 or 5 mM
for 24 h. Cells were then harvested and CAT activity was measured.
Values are derived from three different experiments and are expressed
as the percentage of the values obtained at 11 mM glucose.
* indicate significant difference (P < 0.01 and
P < 0.05, respectively).
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To localize further the DNA sequences, which mediate the glucose effect
on proglucagon gene expression, we assessed transcriptional activity of
shorter fragments of the rat proglucagon gene (-213 CAT, -168 CAT,
and -138 CAT) into InR1G9 cells cultured in either 5 or 11
mM glucose. As shown on Fig. 8, the first 138 bp of the promoter are
still capable of mediating the glucose effect.
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Figure 8. The 138 first base pairs of the proglucagon gene
promoter are sufficient to mediate the effects of chronically elevated
glucose. InR1G9 cells were cultured in RPMI-1640 containing either 5 or
11 mM glucose for 10 weeks. Cells were transfected with 3
µg -292 CAT, -200 CAT, -168 CAT and -138 CAT containing 292 bp,
200 bp, 168 bp, and 138 bp, respectively, of the rat proglucagon gene
promoter linked to the CAT gene. CAT activities are derived from three
different experiments and are expressed as the percentage of the values
obtained at 11 mM glucose. * and " indicate significant
difference (P < 0.01 and P <
0.05, respectively).
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Our data thus indicate that chronically high glucose affects
proglucagon gene expression at the level of transcription and that the
effect is mediated within 138 bp of the proglucagon gene promoter.
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Discussion
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We present evidence in our studies that chronically elevated
glucose concentrations increase glucagon release, glucagon cell
content, and proglucagon gene expression in InR1G9 cells. The effects
of glucose are rather slow taking more than 1 day to be fully
manifest.
The changes induced by glucose are fully reversible inasmuch as
switching from 5 to 11 mM glucose or from 11 to 5
mM glucose for 6 to 7 days results in a 3- to 5-fold
increase or decrease, respectively, in glucagon release, glucagon cell
content and proglucagon mRNA levels. The mechanisms by which
chronically high glucose affects glucagon gene expression are to be
fully defined but glucose effects are mediated through an increase in
gene transcription and DNA sequences within 138 bp of the proglucagon
gene promoter are necessary for this increase. The lag time between the
change in glucose concentration and the observed consequences on
proglucagon gene expression suggests that new protein synthesis is
required to affect gene transcription; we hypothesize that high glucose
may either decrease the abundance or function of a transcription factor
that inhibits glucagon gene expression or inversely increase or induce
the synthesis of a positively acting factor. Precise definition of the
DNA sequences mediating the glucose effect should help resolving these
possibilities.
An important aspect of these studies is that insulin is
capable of preventing the effects of a prolonged
exposure to high glucose concentrations. Because InR1G9 cells were
incubated in media containing 10% serum, thus in the presence of 0.3
to 0.5 µU/ml insulin, it is possible that the chronic glucose effects
on glucagon release, glucagon cell content and proglucagon gene
expression might have been underestimated due to the potential
inhibitory effects of the low concentrations of insulin. Insulin has
been reported to inhibit proglucagon gene expression both in
vivo and in vitro (14, 16, 19, 21, 22, 23); insulin is able
to acutely decrease proglucagon gene transcription through the enhancer
element G3, which is localized between -290 to -260 bp
relative to the transcriptional start site (19, 20, 21); however, as the
glucose-induced changes on proglucagon gene transcription are
mediated by the proximal 138 bp of the promoter, the mechanisms by
which insulin prevents the glucose effects will thus need to be further
analyzed. Prevention of the glucose effect is likely to be indirect;
however, in view of the lag time between the changes in glucose
concentrations and increased gene transcription, one possibility would
be that insulin counteracts the effects of glucose on the synthesis of
a specific protein involved in the regulation of proglucagon gene
expression.
In type 2 diabetes, ß cell function deteriorates progressively over
time leading to more pronounced hyperglycemia (1, 2). The concept of
glucose toxicity implicates that a sustained elevation in glucose
levels exerts by itself deleterious effects on pancreatic ß cells.
Impaired ß cell function in the presence of high glucose has been
demonstrated in several experimental systems (1, 2, 3, 4, 5, 6, 7, 8, 9); proinsulin gene
expression as well as insulin biosynthesis and secretion are
impaired.
The effect of glucose on proinsulin mRNA levels has been proposed to
decrease the activity of positively acting transcription factors such
as IDX-1, IEF-1, and the RIPE3b-binding proteins
interacting with the gene promoter and possibly up-regulating
transcriptional repressors of insulin gene transcription, such as C/EBP
ß (6, 7, 8, 9).
cell function is also impaired in diabetes; there is both a loss of
glycemic control of glucagon secretion and hyperresponsiveness of
glucagon secretion to stimuli such as amino acids (13). The respective
roles of insulin and glucose in these abnormalies have been abundantly
debated; it appears likely, however, that they are both influential in
the control of cell function. Insulin has been clearly shown to
affect both glucagon release and proglucagon gene expression, whereas
glucose is the major regulator of glucagon secretion. In diabetes,
plasma glucagon and proglucagon mRNA levels are chronically elevated
despite hyperglycemia (14); insulin treatment is capable of correcting
the elevated glucagon levels to normal (13). Elevated glucose by itself
may impair cell function. Prolonged culture of isolated mouse and
rat islets at high glucose concentrations results indeed in
paradoxically increased glucagon secretion (11, 12); these data are
reminiscent of the paradoxical rise in glucagon levels during
hyperglycemia produced by a carbohydrate meals in human diabetics (10).
It has also been proposed that cells have a glucose-sensing system
that is reversibly attenuated by hyperglycemia (24) and that glucagon
responsiveness to hypoglycemia may be improved by insulin-independent
correction of hyperglycemia (25).
Our results extend these finding by suggesting that sustained
elevations of glucose levels may increase glucagon release and
proglucagon gene expression and thus participate in abnormal cell
function observed in diabetes. There is no reason to believe that
chronically elevated glucose affects only ß cells; cells display
indeed similar glucose-sensing mechanisms as ß cells, such as a
glucose transporter, GLUT-1, and the rate-limiting enzyme in glucose
metabolism, glucokinase (26, 27). Glucose is the major regulator of
both glucagon and insulin secretion, whereas acutely raised glucose
levels stimulate and inhibit insulin and glucagon release,
respectively, sustained elevations of glucose inhibit insulin release
and biosynthesis as well as proinsulin gene expression; the effects of
sustained elevations of glucose on glucagon release and proglucagon
gene expression would be expected to be the opposite. Our recently
published in vivo data as well as the present data suggest
indeed that chronically high glucose concentrations stimulate glucagon
release and proglucagon gene expression (14). It must be stressed,
however, that these results have been obtained from experiments done
with a cultured cell line producing glucagon; the response of these
cells to glucose may be different compared with those of primary
cells. There is, however, no satisfactory primary cell system at
present to validate our results, but more detailed knowledge of the
glucose sensing mechanisms of the cell should allow a better
understanding of the physiological and pathophysiological role of
glucose in cell function.
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Acknowledgments
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We thank C. Robert-Tissot for typing the manuscript and I.
Constant and N. Klages for expert technical assistance.
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Footnotes
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1 This work was supported by the Swiss National Science Foundation
(grant 3200–046816), by the Institute for Human Genetics and
Biochemistry and by the Berger Foundation. 
Received January 26, 1999.
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References
|
|---|
-
Järvinen HY 1992 Glucose toxicity.
Endocr Rev 13:415–431[Abstract/Free Full Text]
-
Leahy JL, Bonner-Weir S, Weir GC 1992 ß-cell
dysfunction induced by chronic hyperglycemia. Diabetes Care 15:442–451[Abstract]
-
Robertson RP, Zhang HJ, Pyzdrowski KL, Walseth TF 1992 Preservation of insulin mRNA levels and insulin secretion in HIT
cells by avoidance of chronic exposure to high glucose concentrations.
J Clin Invest 90:320–325
-
Olson LK, Redmon JB, Towle HC, Robertson RP 1993 Chronic exposure of HIT cells to high glucose concentrations
paradoxically decreases insulin gene transcription and alters binding
of insulin gene regulatory protein. J Clin Invest 92:514–519
-
Eizirik DL, Korbutt GS, Hellerström C 1992 Prolonged exposure of human pancreatic islet to high glucose
concentrations in vitro impairs the ß-cell
function. J Clin Invest 90:1263–1268
-
Sharma A, Olson LK, Robertson RP, Stein R 1995 The
reduction of insulin gene transcription in HIT-T15 ß cells
chronically exposed to high glucose concentration is associated with
the loss of RIPE3b1 and STF-1 transcription factor expression. Mol
Endocrinol 9:1127–1134[Abstract/Free Full Text]
-
Olson LK, Sharma A, Peshavaria M, Wright CVE, Towle HC,
Robertson RP, Stein R 1995 Reduction of insulin gene transcription
in HIT-T15 ß cells chronically exposed to a supraphysiologic glucose
concentration is associated with loss of STF-1 transcription factor
expression. Proc Natl Acad Sci USA 92:9127–9131[Abstract/Free Full Text]
-
Poitout V, Olson LK, Robertson RP 1996 Chronic
exposure of ßTC-6 cells to supraphysiologic concentrations of glucose
decreases binding of the RIPE3b1 insulin gene transcription activator.
J Clin Invest 97:1041–1046[Medline]
-
Seufert J, Weir GC, Habener JF 1998 Differential
expression of the insulin gene transcriptional repressor
CCAAT/enhancer-binding protein ß and transactivator islet duodenum
homeobox-1 in rat pancreatic ß cells during the development of
diabetes mellitus. J Clin Invest 101:2528–2539[Medline]
-
Buchanan KD, McCarroll AM 1972 Abnomalies of
glucagon metabolism in untreated diabetes mellitus. Lancet 2:1394–1395[Medline]
-
Segerström K, Anderson A, Lundquist G, Peterson B,
Hellerström C 1976 Regulation of the glucagon release from
mouse pancreatic islets maintained in tissue culture at widely
different glucose concentrations. Diabetes 2:45–48
-
Ziegler M, Hahn HJ, Ziegler B, Kohler E, Fiedler H 1975 Paradoxical glucagon response after stimulation with glucose and
arginine in isolated pancreatic and rat islets. Diabetologia 11:63–69[CrossRef][Medline]
-
Unger RH, Orci L 1983 Glucagon II. In:
Lefèbvre PJ (ed) Handb Exp Pharm 66/II. Springer-Verlag,
Berlin, Heidelberg, pp 431–450
-
Dumonteil E, Magnan C, Ritz-Laser B, Meda P, Dussoix P,
Gilbert M, Ktorza A, Philippe J 1998 Insulin, but not glucose
lowering corrects the hyperglucagonemia and increased proglucagon mRNA
levels observed in insulinopenic diabetes. Endocrinology 139:4540–4546[Abstract/Free Full Text]
-
Takaki R, Ono J, Nakamura M, Yokogawa Y, Kumae S,
Hiraoka T, Yamaguchi K, Uchida S 1986 Isolation of
glucagon-secreting cell lines by cloning insulinoma cells. In Vitro
Cell Dev Biol 22:120–126[Medline]
-
Philippe J 1989 Glucagon gene transcription is
negatively regulated by insulin in a hamster islet cell line. J
Clin Invest 84:672–677
-
Philippe J, Drucker DJ, Knepel W, Japeal L, Habener
JF 1988 -cell-specific expression of the glucagon gene is
conferred to the glucagon promoter element by the interactions of
DNA-binding proteins. Mol Cell Biol 8:4877–4888[Abstract/Free Full Text]
-
Henthorn P, Zervos P, Raducha M, Harris H, Kadesch
T 1988 Expression of a human placental alkaline phosphatase gene
in transfected cells: use as a reporter for studies of gene expression.
Proc Natl Acad Sci USA 85:6342–6346[Abstract/Free Full Text]
-
Philippe J 1991 Insulin regulation of the glucagon
gene is mediated by an insulin-responsive DNA element. Proc Natl Acad
Sci USA 88:7224–7227[Abstract/Free Full Text]
-
Bernard C, Thibault C, Berthault MF, Magnan C, Saulnier
C, Portha B, Pralong W, Penicaud L, Ktorza A 1998 Pancreatic B
cell regeneration after 48h glucose infusion in mildly diabetic rats is
not correlated with functional improvement. Diabetes 47:1058–1065[Abstract]
-
Philippe J, Morel C, Cordier-Bussat M 1995 Islet-specific proteins interact with the insulin-response element of
the glucagon gene. J Biol Chem 270:3039–3045[Abstract/Free Full Text]
-
Chen L, Komiya I, Inman L, McCorkle K, Alam T, Unger
RH 1989 Molecular and cellular responses of islets during
perturbations of glucose homeostasis determined by in situ
hybridization histochemistry. Proc Natl Acad USA 86:1367–1371[Abstract/Free Full Text]
-
Chen L, Komiya I, Inman L, O’Neil J, Appel M, Alam T,
Unger RH 1989 Effect of hypoglycemia and prolonged fasting on
insulin and glucagon gene expression. J Clin Invest 84:711–714
-
Gerich JE 1983 Glucose in the control of glucagon
secretion. In: Lefèbvre PJ (ed) Handb Exp Pharm 66/II.
Springer-Verlag, Berlin, Heidelberg, pp 3–18
-
Shi ZQ, Rastogi KS, Lekas M, Efendis S, Drucker DJ,
Vranic M 1996 Glucagon response to hypoglycemia is improved by
insulin-independent restoration of normoglycemia in diabetic rats.
Endocrinology 137:3193–3199[Abstract]
-
Heimberg H, De Vost A, Pipeleers D, Thorens B, Schuit
F 1995 Differences in glucose transporter gene expression between
rat pancreatic - and ß-cells are correlated to differences in
glucose transport but not in glucose utilization. J Biol Chem 270:8971–8975[Abstract/Free Full Text]
-
Heimberg H, De Vos A, Moens K, Quartier E, Bouwens L,
Pipeleers D, Van Schaftingen E, Madsen O, Schuit F 1996 The
glucose sensor protein glucokinase is expressed in glucagon-producing
-cells. Proc Natl Acad Sci USA 93:7036–7041[Abstract/Free Full Text]
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Abstract
Introduction
