Molecular mechanisms of diabetic renal hypertrophy
Authors: Gunter Wolf, Fuad N. Ziyadeh
Journal: Kidney International (1999)

Molecular mechanisms of diabetic renal hypertrophy. Altered growth of renal cells is one of the early abnormalities detected after the onset of diabetes. Cell culture studies whereby renal cells are exposed to high glucose concentrations have provided a considerable amount of insight into mechanisms of growth. In the glomerular compartment, there is a very early and self-limited proliferation of mesangial cells with subsequent hypertrophy, whereas proximal tubular cells primarily undergo hypertrophy. There is overwhelming evidence from in vivo and cell culture studies that induction of the transforming growth factor-βbgr; (TGF-βbgr;) system mediates the actions of high ambient glucose and that this system is pivotal for the hypertrophy of mesangial and tubular cells. Other factors such as hemodynamic forces, protein glycation products, and several mediators (for example, angiotensin II, endothelin-1, thromboxane, and platelet-derived growth factor) may further amplify the synthesis of TGF-βbgr; and/or the expression of its receptors in the diabetic state. Cellular hypertrophy can be characterized by cell cycle arrest in the G1 phase. The molecular mechanism arresting mesangial cells in the G1 phase of the cell cycle is the induction of cyclin-dependent kinase (CdK) inhibitors such as p27Kip1 and p21, which bind to and inactivate cyclin-CdK complexes responsible for G1-phase exit. High-glucose–induced activation of protein kinase C and stimulated TGF-βbgr; expression appear to be essential for stimulated expression of p27Kip1. In addition, a decreased turnover of protein caused by the inhibition of proteases contributes to hypertrophy. The development of irreversible renal changes in diabetes mellitus such as glomerulosclerosis and tubulointerstitial fibrosis is always preceded by the early hypertrophic processes in the glomerular and the tubular compartments. It may still be debated whether diabetic renal hypertrophy will inevitably lead to irreversible fibrotic changes in the absence of other factors such as altered intraglomerular hemodynamics and genetic predisposition. Nevertheless, understanding cellular growth on a molecular level may help design a novel therapeutic approach to prevent or treat diabetic nephropathy effectively. Molecular mechanisms of diabetic renal hypertrophy. Altered growth of renal cells is one of the early abnormalities detected after the onset of diabetes. Cell culture studies whereby renal cells are exposed to high glucose concentrations have provided a considerable amount of insight into mechanisms of growth. In the glomerular compartment, there is a very early and self-limited proliferation of mesangial cells with subsequent hypertrophy, whereas proximal tubular cells primarily undergo hypertrophy. There is overwhelming evidence from in vivo and cell culture studies that induction of the transforming growth factor-βbgr; (TGF-βbgr;) system mediates the actions of high ambient glucose and that this system is pivotal for the hypertrophy of mesangial and tubular cells. Other factors such as hemodynamic forces, protein glycation products, and several mediators (for example, angiotensin II, endothelin-1, thromboxane, and platelet-derived growth factor) may further amplify the synthesis of TGF-βbgr; and/or the expression of its receptors in the diabetic state. Cellular hypertrophy can be characterized by cell cycle arrest in the G1 phase. The molecular mechanism arresting mesangial cells in the G1 phase of the cell cycle is the induction of cyclin-dependent kinase (CdK) inhibitors such as p27Kip1 and p21, which bind to and inactivate cyclin-CdK complexes responsible for G1-phase exit. High-glucose–induced activation of protein kinase C and stimulated TGF-βbgr; expression appear to be essential for stimulated expression of p27Kip1. In addition, a decreased turnover of protein caused by the inhibition of proteases contributes to hypertrophy. The development of irreversible renal changes in diabetes mellitus such as glomerulosclerosis and tubulointerstitial fibrosis is always preceded by the early hypertrophic processes in the glomerular and the tubular compartments. It may still be debated whether diabetic renal hypertrophy will inevitably lead to irreversible fibrotic changes in the absence of other factors such as altered intraglomerular hemodynamics and genetic predisposition. Nevertheless, understanding cellular growth on a molecular level may help design a novel therapeutic approach to prevent or treat diabetic nephropathy effectively. Although the Papyrus Ebers, which dates to approximately 1500 B.C., contains what is thought to be the first reference to diabetes mellitus1.Major R.H. Classic Descriptions of Disease. Charles C. Thomas, Springfield1932: 185-213Google Scholar, Richard Bright (1789–1858) often receives credit for the clinical-pathological correlation that albuminuria reflects serious affliction of the kidney in diabetes mellitus2.Bright P. Dr. Richard Bright (1789–1858). The Bodley Head, London1983: 131-142Google Scholar. The French physician Pierre-François-Olivier Rayer (1793–1867), known for his outstanding three-volume textbook on renal disease, was presumably the first to describe diabetic glomerular hypertrophy3.Ritz E. Zeier M. Lundin P. French and German nephrologists in the mid-19th century: The impact of Richard Bright on the continent.Am J Nephrol. 1989; 9: 167-172Crossref PubMed Google Scholar,4.Wolf G. Changing concepts of compensatory renal growth: From humoral pathology to molecular biology.Am J Nephrol. 1992; 12: 369-373Crossref PubMed Scopus (7) Google Scholar. He wrote, “In diabetes, one finds hypertrophy of the renal cortex … without any abnormality except hypertrophy … the vessels are enlarged and the Malpighian corpuscles are much more prominent”4.Wolf G. Changing concepts of compensatory renal growth: From humoral pathology to molecular biology.Am J Nephrol. 1992; 12: 369-373Crossref PubMed Scopus (7) Google Scholar. Elliott P. Joslin (1869–1962), one of the first clinicians to specialize in the treatment of diabetic patients, wrote foresightedly in 1917, “The renal complications of diabetes have been unimportant in the past, but with the prolongation of life which modern treatment is bringing about they will deserve attention”5.Joslin E.P. Treatment of Diabetes Mellitus. Lea & Filbinger, Philadelphia1917: 419Google Scholar. This almost prophetic statement, made just five years before the introduction of insulin into clinical practice, has unfortunately been proven correct because more than one third of patients entering maintenance dialysis today suffer from diabetic nephropathy. Diabetic nephropathy encompasses discrete structural alterations, including renal hypertrophy, thickening of basement membranes, and progressive glomerular accumulation of extracellular matrix components6.Ziyadeh F.N. 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Early abnormalities.Diabetologia. 1975; 11: 225-229Crossref PubMed Google Scholar, 11.Osterby R. Morphometric studies of the peripheral glomerular basement membrane in early juvenile diabetes. I. Development of initial basement membrane thickening.Diabetologia. 1972; 8: 84-92Crossref PubMed Scopus (78) Google Scholar. Tubuloepithelial hypertrophy and tubular basement membrane thickening also occur very early in the course of diabetic renal involvement and are most likely the precursors of the later irreversible changes in the tubulointerstitial architecture leading to tubular atrophy and interstitial fibrosis6.Ziyadeh F.N. The extracellular matrix in diabetic nephropathy.Am J Kidney Dis. 1993; 22: 736-744Abstract Full Text PDF PubMed Google Scholar,9.Seyer-Hansen K. Renal hypertrophy in streptozotocin-diabetic rats.Clin Sci Mol Med. 1976; 51: 551-555PubMed Google Scholar. Although originally described in type 1 diabetes, it is currently increasingly recognized that there are no substantial differences between types 1 and 2 diabetes with respect to these morphological changes, including renal growth12.Ritz E. Stefanski A. Diabetic nephropathy in type II diabetes.Am J Kidney Dis. 1996; 27: 167-194Abstract Full Text PDF PubMed Google Scholar, 13.Schmitz A. Gundersen H.J. Osterby R. Glomerular morphology by light microscopy in non-insulin-dependent diabetes mellitus.Diabetes. 1988; 37: 38-43Crossref PubMed Google Scholar, 14.Rodby R.A. Type II diabetic nephropathy: Its clinical course and therapeutic implications.Semin Nephrol. 1997; 17: 132-147PubMed Google Scholar, 15.Wirta O.R. Pasternack A.I. Glomerular filtration rate and kidney size in type 2 (non-insulin-dependent) diabetes mellitus.Clin Nephrol. 1995; 44: 1-7PubMed Google Scholar, 16.Pagtalunan M.E. Miller P.L. Jumping-Eagle S. Nelson R.G. Myeres B.D. Rennke H.G. Coplon N.S. Sun L. Meyer T.W. Podocyte loss and progressive glomerular injury in type II diabetes.J Clin Invest. 1997; 99: 342-348Crossref PubMed Google Scholar. This review focuses on some recent advancements in understanding the molecular mechanisms of diabetic renal hypertrophy and the potential link to irreversible renal failure and will summarize the growing evidence of the involvement of relevant growth factors in this link. Glomerular hypertrophy in diabetes mellitus is associated with an increase in the glomerular filtration rate, mainly caused by increased plasma flow and glomerular capillary hydrostatic pressure17.Ibrahim H.N. Hostetter T.H. Diabetic nephropathy.J Am Soc Nephrol. 1997; 8: 487-493PubMed Google Scholar, 18.Hostetter T.H. Troy J.L. Brenner B.M. Glomerular hemodynamics in experimental diabetes mellitus.Kidney Int. 1981; 19: 410-415Abstract Full Text PDF PubMed Google Scholar, 19.O'bryan G.T. Hostetter T.H. 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Couser W.G. Johnson R.J. Glomerular cell proliferation and PDGF expression precede glomerulosclerosis in the remnant kidney model.Kidney Int. 1992; 41: 297-309Abstract Full Text PDF PubMed Google Scholar. Parallel observations have been made for the tubulointerstitial compartment in which the initial adaptive tubular hypertrophy is often followed by atrophy of epithelial cells and interstitial fibrosis26.Wolf G. Neilson E.G. Molecular mechanisms of tubulointerstitial hypertrophy and hyperplasia.Kidney Int. 1991; 39: 401-420Abstract Full Text PDF PubMed Google Scholar,27.Eddy A.A. Molecular insights into renal interstitial fibrosis.J Am Soc Nephrol. 1996; 7: 2495-2508Crossref PubMed Google Scholar. Part of this association between growth and fibrogenesis may be due to the fact that similar networks of cytokines and growth factors that induce cellular hypertrophy can also stimulate extracellular matrix synthesis and deposition28.Fogo A. Ichikawa I. 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It is also very likely that hyperglycemia and Ang II exert additive hypertrophic and prosclerotic effects. Because cells undergoing hypertrophy can theoretically have a significant increase in mitochondrial oxygen consumption, the resultant stimulation in oxygen radical formation can lead to lipid peroxidation and can accentuate the renal injury34.Schrier R.W. Harris D.C. Chan L. Shapiro J.I. Caramelo C. Tubular hypermetabolism as a factor in the progression of chronic renal failure.Am J Kidney Dis. 1988; 12: 243-249Abstract Full Text PDF PubMed Google Scholar,35.Culpepper R.M. Schoolwerth A.C. Remnant kidney oxygen consumption: Hypermetabolism or hyperbole?.J Am Soc Nephrol. 1992; 3: 151-156PubMed Google Scholar. Furthermore, cells in their growth phase may release vasoactive factors, which could impair capillary blood flow to subordinate vascular beds; this may contribute to ischemic/fibrotic changes31.Wolf G. Molecular mechanisms of angiotensin II in the kidney: Emerging role in the progression of renal disease beyond haemodynamics.Nephrol Dial Transplant. 1998; 13: 1131-1142Crossref PubMed Scopus (86) Google Scholar. Associations between renal growth and the subsequent development of irreversible loss of renal function have long been suspected in the course of diabetic nephropathy10.Osterby R. Gundersen H.J.G. Glomerular size and structure in diabetes mellitus. I. Early abnormalities.Diabetologia. 1975; 11: 225-229Crossref PubMed Google Scholar, 11.Osterby R. Morphometric studies of the peripheral glomerular basement membrane in early juvenile diabetes. I. Development of initial basement membrane thickening.Diabetologia. 1972; 8: 84-92Crossref PubMed Scopus (78) Google Scholar, 36.Mauer S.M. Steffes M.W. Ellis E.N. Sutherland D.E.R. Brown D.M. Goetz F.C. Structural-functional relationships in diabetic nephropathy.J Clin Invest. 1984; 74: 1143-1155Crossref PubMed Google Scholar. In a seminal study in the field, Mauer et al investigated structural-functional relationships in a cross-section of patients with type 1 diabetes36.Mauer S.M. Steffes M.W. Ellis E.N. Sutherland D.E.R. Brown D.M. Goetz F.C. Structural-functional relationships in diabetic nephropathy.J Clin Invest. 1984; 74: 1143-1155Crossref PubMed Google Scholar. They found a close correlation between mesangial expansion, which is partly generated by abnormal growth of mesangial cells in addition to increased extracellular matrix components, and clinical manifestations of diabetic nephropathy such as albuminuria, hypertension, and a decreased glomerular filtration rate36.Mauer S.M. Steffes M.W. Ellis E.N. Sutherland D.E.R. Brown D.M. Goetz F.C. Structural-functional relationships in diabetic nephropathy.J Clin Invest. 1984; 74: 1143-1155Crossref PubMed Google Scholar. 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Renal hypertrophy, growth factors, and nephropathy in diabetes mellitus.Semin Nephrol. 1990; 10: 242-253PubMed Google Scholar, tubular hypertrophy is quantitatively responsible for the largest component of renal enlargement in diabetes mellitus40.Schwieger J. Fine L.G. Renal hypertrophy, growth factors, and nephropathy in diabetes mellitus.Semin Nephrol. 1990; 10: 242-253PubMed Google Scholar,41.Wolf G. Cellular mechanisms of tubule hypertrophy and hyperplasia in renal injury.Miner Electrolyte Metab. 1995; 21: 303-316PubMed Google Scholar. Thus, it is evident that both glomerular and tubulointerstitial growth processes precede the development of diabetic renal disease36.Mauer S.M. Steffes M.W. Ellis E.N. Sutherland D.E.R. Brown D.M. Goetz F.C. Structural-functional relationships in diabetic nephropathy.J Clin Invest. 1984; 74: 1143-1155Crossref PubMed Google Scholar,37.Lane P.H. Steffes M.W. Fioretto P. Mauer S.M. Renal interstitial expansion in insulin-dependent diabetes mellitus.Kidney Int. 1993; 43: 661-667Abstract Full Text PDF PubMed Google Scholar. Studies of animals made diabetic with streptozotocin have provided evidence that cellular growth associated with diabetic nephropathy is a dynamic process9.Seyer-Hansen K. Renal hypertrophy in streptozotocin-diabetic rats.Clin Sci Mol Med. 1976; 51: 551-555PubMed Google Scholar, 42.Romen W. Takahashi A. Autoradiographic studies on the proliferation of glomerular and tubular cells of the rat kidney in early diabetes.Virchows Arch B. 1982; 40: 339-345Crossref Scopus (0) Google Scholar, 43.Rasch R. Norgaard J.O. Renal enlargement: Comparative autoradiographic studies of 3H-thymidine uptake in diabetic and uninephrectomized rats.Diabetologia. 1983; 25: 280-287Crossref PubMed Scopus (96) Google Scholar, 44.Young B.A. Johnson R.J. Alpers C.A. Eng E. Gordon K. Floege J. Couser W.G. Cellular events in the evolution of experimental diabetic nephropathy.Kidney Int. 1995; 47: 935-944Abstract Full Text PDF PubMed Google Scholar. Renal cells can, in general, undergo either proliferation or hypertrophy, two totally different growth responses41.Wolf G. Cellular mechanisms of tubule hypertrophy and hyperplasia in renal injury.Miner Electrolyte Metab. 1995; 21: 303-316PubMed Google Scholar. A distinct renal cell exposed to a stimulus such as the diabetic milieu may exhibit one or the other growth response at different times. In addition, the various cell types along the nephron may behave differently in diabetes mellitus (proliferation vs. hypertrophy), depending on their intrinsic genetic program, the concentration of growth factors in the local microenvironment, and the presence of growth factor receptors on their cell surfaces40.Schwieger J. Fine L.G. Renal hypertrophy, growth factors, and nephropathy in diabetes mellitus.Semin Nephrol. 1990; 10: 242-253PubMed Google Scholar,41.Wolf G. Cellular mechanisms of tubule hypertrophy and hyperplasia in renal injury.Miner Electrolyte Metab. 1995; 21: 303-316PubMed Google Scholar. Early studies showed that diabetic rats exhibit a 15% increment of whole kidney weight within 72 hours of induction with streptozotocin9.Seyer-Hansen K. Renal hypertrophy in streptozotocin-diabetic rats.Clin Sci Mol Med. 1976; 51: 551-555PubMed Google Scholar,10.Osterby R. Gundersen H.J.G. Glomerular size and structure in diabetes mellitus. I. Early abnormalities.Diabetologia. 1975; 11: 225-229Crossref PubMed Google Scholar. More detailed studies by Romen and Takahashi applying autoradiography after [3H]-thymidine infusion and electron microscopic morphometry indicated that glomerular enlargement is accompanied by glomerular cell proliferation in the early phase of streptozotocin-induced diabetes in rats42.Romen W. Takahashi A. Autoradiographic studies on the proliferation of glomerular and tubular cells of the rat kidney in early diabetes.Virchows Arch B. 1982; 40: 339-345Crossref Scopus (0) Google Scholar. In contrast, other investigators found no differences in the incorporation of thymidine into glomerular nuclei when comparing diabetic to control rats43.Rasch R. Norgaard J.O. Renal enlargement: Comparative autoradiographic studies of 3H-thymidine uptake in diabetic and uninephrectomized rats.Diabetologia. 1983; 25: 280-287Crossref PubMed Scopus (96) Google Scholar. This apparent contradiction may be resolved by the observation that proliferation occurs early and transiently, during a narrow window after induction of diabetes44.Young B.A. Johnson R.J. Alpers C.A. Eng E. Gordon K. Floege J. Couser W.G. Cellular events in the evolution of experimental diabetic nephropathy.Kidney Int. 1995; 47: 935-944Abstract Full Text PDF PubMed Google Scholar. Young et al have meticulously quantitated glomerular proliferation at various time points in experimentally induced diabetic kidney disease using a panel of antibodies44.Young B.A. Johnson R.J. Alpers C.A. Eng E. Gordon K. Floege J. Couser W.G. Cellular events in the evolution of experimental diabetic nephropathy.Kidney Int. 1995; 47: 935-944Abstract Full Text PDF PubMed Google Scholar. By staining for the proliferating cell nuclear antigen (PCNA), they found a prominent but self-limited mesangial cell proliferation that peaked at day 3 after induction of diabetes with streptozotocin and returned to baseline after 30 days. This proliferation of mesangial cells was associated with de novo expression of α-smooth muscle actin, an activation marker of the proliferative mesangial cell phenotype44.Young B.A. Johnson R.J. Alpers C.A. Eng E. Gordon K. Floege J. Couser W.G. Cellular events in the evolution of experimental diabetic nephropathy.Kidney Int. 1995; 47: 935-944Abstract Full Text PDF PubMed Google Scholar. In addition, an infiltration of proliferating macrophages/monocytes reached peak values at day 30 after diabetes induction and contributed only a minor extent to the early (day 3) overall glomerular proliferation44.Young B.A. Johnson R.J. Alpers C.A. Eng E. Gordon K. Floege J. Couser W.G. Cellular events in the evolution of experimental diabetic nephropathy.Kidney Int. 1995; 47: 935-944Abstract Full Text PDF PubMed Google Scholar. Insulin treatment of diabetic rats prevented the early proliferation of mesangial cells, α-actin expression, and the macrophage/monocyte infiltration. A significant increase in mesangial cell proliferation was reported by Mahadevan et al in rats 21 days after streptozotocin-induced diabetes compared with controls45.Mahadevan P. Larkins R.G. Fraser J.R. Dunlop M.E. Effect of prostaglandin E2 and hyaluronan on mesangial cell proliferation: A potential contribution to glomerular hypercellularity in diabetes.Diabetes. 1996; 45: 44-50Crossref PubMed Google Scholar. To discern the relative role of local metabolic changes from systemic or hemodynamic alterations (for example, stretch, which may modulate mesangial cell growth in vivo), we developed a cell culture approach to assess mesangial