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Identification of the Glomerular Podocyte as a Target for Growth Hormone Action

Departments of Pediatrics and Communicable Diseases (G.R.R., M.J.P., R.F.R., R.K.M.), Internal Medicine (L.B.H., F.C.B.), and Molecular and Integrative Physiology (F.C.B., R.K.M.), University of Michigan, Ann Arbor, Michigan 48109-0718; Department of Biological Sciences (M.D.), University of Toledo, Toledo, Ohio 43606; Academic and Children’s Renal Unit (P.M., M.A.S.), University of Bristol, Bristol BS1 3NY, United Kingdom; Edison Biotechnology Institute and Department of Biomedical Sciences (E.O.L., J.J.K.), College of Osteopathic Medicine, Ohio University, Athens, Ohio 45701; and Department of Internal Medicine (S.J.F.), University of Alabama, Birmingham, Alabama 35294

Address all correspondence and requests for reprints to: Ram K. Menon, M.D., University of Michigan Medical School, 1205 MPB Box 0718, 1500 East Medical Center Drive, Ann Arbor, Michigan 48109-0718. E-mail: rammenon{at}umich.edu.

GH excess in both the human and transgenic animal models is characterized by significant changes in blood pressure and renal function. The GH/GH receptor (GHR) axis is also implicated in the development of diabetic nephropathy. However, it is not clear whether GH’s actions on renal function are due to indirect actions mediated via changes in blood pressure and vascular tone or due to direct action of GH on the kidney. We hypothesized that functional GHRs are expressed on the glomerular podocyte enabling direct actions of GH on glomerular function. Real-time PCR, immunohistochemistry, and Western blot analysis of murine podocyte cells (MPC-5) and kidney glomeruli demonstrated expression of GHR mRNA and protein. Exposure of both murine and human podocytes to GH (50–500 ng/ml) resulted in an increase in abundance of phosphorylated signal transducer and activator of transcription-5, Janus kinase-2, and ERK1/2 proteins. Exposure of podocytes to GH also caused changes in the intracellular distribution of the Janus kinase-2 adapter protein Src homology 2-Bß, stimulation of focal adhesion kinase, increase in reactive oxygen species, and GH-dependent changes in the actin cytoskeleton. We conclude that glomerular podocytes express functional GHRs and that GH increases levels of reactive oxygen species and induces reorganization of the actin cytoskeleton in these cells. These results provide a novel mechanistic link between GH’s actions and glomerular dysfunction in disorders such as acromegaly and diabetic glomerulosclerosis.

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