Search

The accumulation of advanced glycation end products (AGE) is a key factor in diabetic nephropathy (DN). Pyridoxamine inhibits AGE formation and protects against type I DN. Herein we tested: (1) whether C57BL6 db/db mice as a model of established type II DN resembled patients treated with drugs which inhibit angiotensin II action; (2) whether pyridoxamine was effective as a single therapy; and (3) whether pyridoxamine would add to the benefit of angiotensin-converting enzyme inhibition (ACEi) by enalapril. In first set of experiments mice were treated with ACEi (benazepril) and an angiotensin II receptor blocker (valsartan) combination for 16 weeks after the onset of diabetes. In second group, mice with established DN were treated with pyridoxamine for 8 weeks. In a third set, mice with established DN were treated with pyridoxamine and enalapril combination for 16 weeks. Benazepril and valsartan combination partially prevented the development and progression of DN. Pyridoxamine treatment, as single therapy, decreased the progression of albuminuria and glomerular lesions. The combination of pyridoxamine with enalapril reduced both mortality and the progression of DN. In conclusion, (1) C57 BL6 db/db mice are a model of progressive type II DN; (2) The combination of pyridoxamine with enalapril decreased progression of type 2 DN and overall mortality. Thus, pyridoxamine could be a valuable adjunct to the current treatment of established type II DN.

The glomeruli of postmenopausal C57BL6 mice, and age-matched males, show progressive hypertrophy and glomerulosclerosis. We asked whether this was a multistage process, was due to alterations in glomerular progenitors, and was reversible in female mice. Using cross bone marrow transplants (BMT) between young and old females, we found that BMT delivered a phenotype that was donor age-specific. The fact that lesions in young recipients were more severe if the donors were in late rather than early menopause suggested that new progenitor phenotypes had appeared. Postmenopausal recipients of BMT from young donors had reduced glomerular hypertrophy and sclerosis, implying that the aging lesions in females were reversible and that progenitors, rather than the local environment, determined the glomerular profile. The altered phenotype included increased extracellular matrix synthesis and decreased matrix metalloproteinase-2 levels as well as cell hypertrophy. The mechanism of the cellular hypertrophy was due to uncoupling of hypertrophy from proliferation, resulting from elevated p27 levels. Thus, glomerular hypertrophy and sclerosis in aging females is a multistage process, is reversible, and may be determined by the phenotype of bone marrow-derived progenitor cells.

Age-associated renal changes may be an important cause of renal failure. We recently found that aged female B6 mice developed progressive glomerular lesions. This was associated with macrophage infiltration, a frequent finding in glomerulosclerosis. We used these mice as a model for studying the mechanisms of glomerular aging. We compared the gene expression profile of intact glomeruli from late postmenopausal (28-month-old) mice to that of intact glomeruli from premenopausal (5-month-old) mice. We found that inflammation-related genes, especially those expressed by activated macrophages, were up-regulated in the glomeruli of 28-month-old mice, a result correlating with the histological observation of glomerular macrophage infiltration. The mechanism for macrophage recruitment could have been stable phenotypic changes in mesangial cells because we found that mesangial cells isolated from 28-month-old mice expressed higher levels of RANTES and VCAM-1 than cells from 5-month-old mice. The elevated serum tumor necrosis factor (TNF)-alpha levels present in aged mice may contribute to increased RANTES and VCAM-1 expression in mesangial cells. Furthermore, cells from 28-month-old mice were more sensitive to TNF-alpha-induced RANTES and VCAM-1 up-regulation. The effect of TNF-alpha on RANTES expression was mediated by TNF receptor 1. Interestingly, mesangial cells isolated from 28-month-old mice had increased nuclear factor-kappaB transcriptional activity. Inhibition of nuclear factor-kappaB activity decreased baseline as well as TNF-alpha-induced RANTES and VCAM-1 expression in mesangial cells isolated from 28-month-old mice. Thus, phenotypic changes in mesangial cells may predispose them to inflammatory stimuli, such as TNF-alpha, which would contribute to glomerular macrophage infiltration and inflammatory lesions in aging.

Estrogen deficiency may contribute to the development and progression of glomerulosclerosis in postmenopausal women. The responsiveness to estrogens could be controlled by genetic traits related to those that determine the susceptibility to glomerular scarring. This study was undertaken to determine whether the intensity of the sclerotic response was modified by the estrogen status in sclerosis-prone ROP Os/+ mice. Ovariectomized ROP Os/+ mice developed more severe renal dysfunction and glomerulosclerosis than intact, ie, estrogen sufficient age-matched female mice. Ovariectomized ROP Os/+ exhibited increased accumulation of extracellular matrix, predominantly of laminin, and a marked distortion of the glomerular architecture. We found an increase in macrophage infiltration in the mesangium of ovariectomized ROP Os/+. Estrogen deficiency decreased glomerular estrogen receptor expression in ROP Os/+ mice, which we had previously found to be low in the parental ROP strain. Thus, although physiological estrogen levels in young ROP Os/+ mice could not prevent the development of glomerulosclerosis, estrogen deficiency accelerated the progression of glomerular scarring in this mouse strain. This suggests that estrogen replacement will slow but not prevent the progression of glomerulosclerosis. It underscores the importance of the genetic composition of individuals that determines the susceptibility to diseases as well as the response to treatment.

The frequency of chronic renal failure increases with age, especially in women after menopause. Glomerulosclerosis is a common cause of chronic renal failure in aging. We reported that pre-menopausal female C57BL6 (B6) mice are resistant to glomerulosclerosis, irrespective of the type of injury. However, we now show that B6 mice develop progressive glomerulosclerosis after menopause. Glomerular lesions, first recognized in 18-month-old mice, consisted of hypertrophy, vascular pole sclerosis, and mesangial cell proliferation. Diffuse but moderate mesangial sclerosis and more marked hypertrophy were present at 22 months. At 28 to 30 months the glomerulosclerosis was diffuse and increased levels of type I and type IV collagen and transforming growth factor-beta 1 mRNA were present. Urine albumin excretion was significantly increased in 30-month-old mice. Mesangial cells isolated from 28-month-old mice retained their sclerotic phenotype in vitro. Comparison of the effects of uninephrectomy (Nx) in 20-month-old and 2.5-month-old mice revealed a 1.7-fold increase in urine albumin excretion, accelerated glomerulosclerosis, and renal function insufficiency in 20-month-old Nx mice, but not in 2.5-month-old Nx mice. Glycemic levels, glucose, insulin tolerance, and blood pressure were normal at all ages. Thus, B6 mice model the increased frequency of chronic renal failure in postmenopausal women and provide a model for studying the mechanism(s) of glomerulosclerosis in aging women.

The development and progression of glomerulosclerosis (GS) is determined by the genetic background. The incidence of end-stage renal disease is increased in postmenopausal women, suggesting that estrogen deficiency may play a role in the accumulation of extracellular matrix by mesangial cells (MCs), which are primarily responsible for the synthesis and degradation of this matrix. Using mouse models that are prone or resistant to the development of GS, we compared the expression of estrogen receptor (ER)-alpha and ER-beta subtypes in GS-prone and GS-resistant glomeruli and isolated MCs, and examined the effects of estrogens on ER, collagen, and matrix metalloproteinase (MMP) expression in MCs. Glomeruli and MCs from GS-prone mice had decreased expression of ER-alpha and ER-beta subtypes and ER transcriptional activity was also decreased in their MCs. Importantly, although 17 beta-estradiol treatment resulted in decreased collagen accumulation and increased MMP-9 expression and activity in MCs from GS-resistant mice, there was, paradoxically, no effect on collagen accumulation and decreased MMP-9 expression and activity in MCs from GS-prone mice. Thus, GS susceptibility is associated with diminished ER expression in MCs. The renal protective effects of estrogens, including decreased collagen accumulation and increased MMP-9 expression, seem to be blunted in GS-prone MCs.

Cyclosporin A (CsA) nephropathy is associated with altered expression of apoptosis regulatory genes such as Fas-ligand and Bcl-2 family members in the glomerular, tubulointerstitial, and vascular compartments. Both hepatocyte growth factor (HGF) and insulin-like growth factor (IGF-I) protect against apoptosis, and HGF specifically up-regulates Bcl-xL, a protein that regulates apoptosis. We investigated whether Bcl-xL and Fas/Fas-ligand were regulated by CsA in cultured podocytes and whether CsA-induced apoptosis was prevented by HGF or IGF-I. A murine podocyte cell line was treated with CsA in the presence or absence of HGF or IGF-I. Apoptosis was quantitated by ELISA and by flow cytometry; Bcl-xL, Fas, and Fas-ligand were measured by Western blotting. Inhibitors of MAP kinase/ERK kinase (MEK)-1 and of phosphatidylinositol 3'-kinase (PI3'-K) were used to determine the signaling pathways involved in Bcl-xL regulation. Apoptosis was induced by CsA in a dose- and time-dependent fashion. CsA also decreased Bcl-xL levels. HGF, but not IGF-I, prevented apoptosis and restored Bcl-xL levels. The regulation of Bcl-xL by HGF was mediated by the PI3'-K but not by the MEK-1 pathway. In summary, we showed that CsA induces apoptosis in podocytes. Apoptosis was prevented by pretreatment with HGF but not IGF-I. Decreased apoptosis appeared to be mediated by regulation of Bcl-xL via the PI3'-K pathway. Our data suggest that the effect of CsA on podocytes may contribute to the glomerular damage and that HGF could provide protection.

Background: The growth hormone (GH)/insulin-like growth factor (IGF) system is thought to participate in the glomerulosclerosis process. Because IGF-binding proteins (IGFBPs) modulate IGF actions and hence GH secretion, this study assessed whether mice transgenic for human IGFBP-1 have altered susceptibility to glomerulosclerosis., Methods: A line of transgenic mice that express human IGFBP-1 mRNA in the liver under the control of the alpha1-antitrypsin promoter has been obtained, and morphological changes in the kidney tissue were assessed. Glomerulosclerosis was identified using light microscopy, light microscopic morphometry, and electron microscopy. Extracellular matrix components were analyzed by immunohistochemistry., Results: There was a marked increase in mesangial extracellular matrix area in homozygous transgenic mice at three months of age as compared with heterozygous transgenic mice and nontransgenic littermates. These changes were not associated with alterations in glomerular volume or cellularity. The expansion of extracellular matrix area was related to a marked increase in laminin and type IV collagen and to the appearance of type I collagen., Conclusions: These observations indicate that the enhanced expression of IGFBP-1 may result in the development of glomerulosclerosis without glomerular hypertrophy. The changes are potentially related to a decrease in IGF-I availability and/or to an IGF-I-independent role of IGFBP-1.

Background: We have previously found that nephron number was not fixed, that is, there was a direct correlation between low birth weight and decreased nephron number in infants. In sclerosis-prone rats, we found that gentamicin exposure in utero induced a reduction in glomerular number and aggravated glomerulosclerosis in adults. In mice, we found that an inborn 50% reduction in nephron number, caused by the Os mutation, was associated with glomerulosclerosis in sclerosis-prone (ROP+/+) mice, but not in sclerosis-resistant (C57BL/6J) mice. Because the genetic background determined the response to decreased nephron number, we asked whether the susceptibility changes in glomerular number and glomerulosclerosis were linked., Methods: Gentamicin was administered before and after the onset of fetal nephrogenesis. (1) Prior to the onset of nephrogenesis, two groups of pregnant mice were treated from embryonic day (E) E8 to E12. In group A, early glomerular development was studied by placing ureteric ridges removed on E12 in vitro for four days, following which the ureteric bud branches and glomeruli were counted using lectin staining. In group B, nephron number was determined in spontaneously delivered 14-day-old (14PN) pups by counting glomeruli. (2) After the onset of nephrogenesis, to determine the direct effects of gentamicin on nephron induction, ureteric ridges were placed in organ culture at E12 of normal gestation, in the presence or absence of gentamicin. The number of glomeruli and ureteric bud branches were counted after six days in culture., Results: A decrease in glomerular number and ureteric bud branches was observed in sclerosis-prone (ROP+/+) mice, irrespective of whether gentamicin was administered prior to or after the onset of nephrogenesis. Glomerular number and ureteric bud branching were not decreased by gentamicin in sclerosis-resistant (C57BL/6) mice., Conclusions: These data provide evidence that there is a positive correlation between the susceptibility to glomerulosclerosis in adulthood and a reduction in nephron number in utero. Thus, exposure to nephrotoxins in utero compounds the risk of renal failure as an adult in sclerosis-prone individuals.

Nephron reduction is an important factor in the development of glomerulosclerosis. In a study of the oligosyndactyly (Os) mutation that causes a congenital 50% reduction in nephron number, we previously found that ROP Os/+ mice developed glomerulosclerosis whereas C57B1/6J Os/+ mice did not. We concluded that the predisposition to glomerulosclerosis depended largely on the genetic background, the ROP being sclerosis-prone whereas the C57 strain was sclerosis-resistant. In the current experiments we asked whether the intensity of the sclerotic response to nephron reduction in the ROP strain was related to the time at which it occurred, ie, a pre- or post-natal event. We also determined whether the absence of lesions in C57 Os/+ mice was caused by a higher threshold for the induction of a sclerotic response in C57 mice. We further examined the relationship between glomerular hypertrophy and sclerosis. C57 +/+, C57 Os/+, ROP +/+, and ROP Os/+ mice were uninephrectomized (NX) at age 10 weeks and followed for 8 weeks. We found no sclerotic changes in NX C57 +/+ and C57 Os/+ mice, despite a 75% reduction in nephron number in the latter. In contrast, both NX ROP +/+ and NX ROP Os/+ mice had glomerulosclerosis, which was more severe in the NX ROP Os/+ mice. Examination of extracellular matrix synthesis and degradation at the mRNA level revealed that synthesis exceeded degradation in ROP Os/+ mice. The lesions in NX ROP +/+ were less severe than in sham-operated ROP/Os mice, suggesting that the timing of nephron reduction affected the amplitude of the sclerotic response in this strain. Following NX, an increase in glomerular volume was found in C57 +/+, ROP +/+, and ROP Os/+ mice. However, NX did not lead to a further increase in glomerular volume in C57 Os/+ mice. We make three conclusions: 1) sclerosis was more severe in the ROP strain when nephron reduction occurred in utero; 2) the absence of glomerulosclerosis in C57 mice was not related to a higher threshold for a sclerosis response in this strain; and 3) whereas glomerular size continued to increase as nephron number decreased in ROP mice, it reached a plateau in C57 mice.

Background: We reported that ROP, but not C57, mice were prone to glomerulosclerosis (GS) after nephron reduction (J Clin Invest 97:1242, 1996)., Methods: In this study, we induced diabetes in ROP and C57 mice to determine if the glomerulosclerotic response was stimulus specific. We used the oligosyndactyly mutation (Os), to produce a congenital 50% reduction in nephron number. Stable hyperglycemia was induced by streptozotocin and mice were maintained for 12 weeks without insulin treatment., Results: Glomerular hypertrophy occurred in diabetic ROP +/+ and C57 +/+ mice, but glomeruli of diabetic ROP +/+ mice had 1.92-fold higher laminin B1 and 1.5-fold higher tenascin mRNA levels than diabetic C57 +/+ mice. Diabetic ROP Os/+ mice had severe glomerulosclerosis with arteriolar and tubulointerstitial lesions while there was only moderate mesangial sclerosis in diabetic C57 Os/+ mice. Glomerular size was increased in all non-diabetic Os/+ mice. It was further increased in diabetic ROP Os/+ mice, but not in diabetic C57 Os/+ mice. Glomerular mRNA levels were higher in diabetic ROP OS/+ than in diabetic C57 OS/+ mice [alpha 1 (i.v.) collagen 3.2-fold, laminin B1 2.1-fold, and tenascin 1.6-fold]., Conclusion: Overall, our data further support the hypothesis that the susceptibility to glomerulosclerosis is inherited, and suggest that hyperglycemia serves principally as a triggering event in the development of diabetic nephropathy. Since the acceleration of diabetic nephropathy by nephron reduction was also largely strain dependent, it appears that the propensity to glomerulosclerosis is a general renal response and is not stimulus specific.

Streptozotocin-treated C57B1/SJL mice developed glomerular hypertrophy and light microscopic lesions mimicking human diabetic glomerulosclerosis. In contrast, there were no glomerular hypertrophy and lesions in diabetic mice transgenic (TG) for a mutated growth hormone (bGH-G119K) that competes with native endogenous GH and results in dwarfism. We examined the molecular events underlying these findings. The non-transgenic (non-TG) diabetic mouse glomeruli had an increase in mRNA coding for alpha 1IV collagen, laminin B1, TGF-beta 1, 72 kDa collagenase, and TIMP-3. In contrast, glomerular type IV collagen and laminin B1 mRNA levels were normal in diabetic TG dwarf mice. However, the 72 kDa gelatinase, TIMP-3, and TGF-beta 1 mRNAs were elevated in the diabetic dwarfs. Type IV collagen and laminin accumulated in the glomeruli of diabetic non-TG, but not of diabetic dwarf mice, by immunofluorescence microscopy, confirming the mRNA data. GH binding protein mRNA levels were comparable in glomeruli from dwarf and non-TG mice, both diabetic and non-diabetic. We did not detect GH receptor mRNA in glomeruli. These data suggest that diabetic glomerulosclerosis is associated with an increase in type IV collagen and laminin synthesis, and that these changes do not occur in mice transgenic for bGH119K, a functional antagonist of GH. The increase of 72 kDa gelatinase, TIMP-3 and TGF-beta 1 mRNAs, independent of GH, suggested that these changes induced by hyperglycemia were not sufficient for the induction of glomerulosclerosis.

The glomeruli of mice transgenic for bovine growth hormone (GH mice) were disproportionately enlarged as a function of either kidney or body weight. Glomerular size correlated with mesangial sclerosis and the urine albumin/creatinine ratio. The glomerular lesions consisted of mesangial proliferation (4 to 5 weeks) followed by progressive mesangial sclerosis (19 weeks), resulting in complete glomerulosclerosis at 30 to 37 weeks. Albuminuria paralleled the glomerulosclerosis. In contrast, mice transgenic for insulinlike growth factor-I (IGF-I mice) did not develop glomerulosclerosis, even though glomerular size significantly increased. Glomerular hypertrophy, however, did not reach that in GH mice. These data suggest that high levels of circulating GH lead to a disproportionate increase in glomerular cellularity and volume, as well as glomerulosclerosis. This does not appear to be the result of high levels of circulating IGF-I stimulated by GH, as the serum IGF-I level in GH mice was lower than that in IGF-I mice.

We previously described the development of glomerulosclerosis in mice transgenic for large T-antigen, a gene whose in vitro expression markedly increases proliferation of cultured cells. In the current study we sought to determine the effect of unilateral nephrectomy on these sclerosis-prone animals which have a genetically defined potential for increased renal growth. In comparison with sham nephrectomy animals, nephrectomized transgenic female mice had significantly larger kidneys, larger glomeruli (5886 mu2 npx vs. 3796 mu2 sham), more cells per glomerulus and more severe glomerulosclerosis. Nephrectomized transgenic male animals had variable increases in kidney size, no significant increase in glomerular size (4750 mu2 npx vs. 4502 mu2 sham) or cellularity, and no worsening of glomerulosclerosis. In non-transgenic female animals nephrectomy induced an increase in kidney size but not in glomerular size (2640 mu2 npx vs. 2625 mu2 sham) and failed to induce glomerular lesions. A close correlation (r = 0.91) was found between glomerular size and severity of glomerulosclerosis in these animals. This finding supports the hypothesis that a pathophysiologic link exists between glomerular enlargement and glomerulosclerosis. We also found that increases in total kidney size and glomerular size did not consistently parallel each other, that is, renal hypertrophy may occur without an increase in glomerular size. This finding suggests that total kidney growth and glomerular growth may be independently regulated or may have different thresholds for activation following unilateral nephrectomy.

To obtain a better understanding of the sequential development of sclerosis in immune glomerular disease, the authors induced experimental membranous nephropathy in unilaterally nephrectomized rats and evaluated the lesions that developed over a 35-week period. Serial renal biopsies were examined by light and immunofluorescence microscopy for IgG, C3, neoantigens of the membrane attack complex (MAC), and interstitial (Type III) and basement membrane (Type IV) collagen. Urinary protein excretion increased from 208 +/- 19 mg/day to 308 +/- 36 mg/day during the period of observation. Progressive mesangial sclerosis, crescent formation, and interstitial fibrosis developed in association with deposition of Type IV but not Type III collagen in the glomeruli. Capillary wall deposits of IgG, C3, and MAC gradually decreased, whereas coarse granular deposits of C3 and MAC were visible in sclerotic areas beginning at 8 weeks. The appearance of complement components in early sclerotic lesions raises the possibility that they are of pathogenetic importance. The absence of interstitial collagen in sclerotic glomeruli suggests that the components of the lesion are produced solely by glomerular cells.

An increase in glomerular size occurs in normal maturation after subtotal renal ablation and disease states such as diabetes mellitus. The role that growth hormone (GH), growth hormone releasing factor (GHRF), and insulinlike growth factor-1 (IGF-1) play in these processes has been investigated using transgenic mice chronically expressing these hormones. The glomeruli were enlarged in all 3 strains of mice. Mesangial proliferation followed by progressive glomerulosclerosis was observed in the GH and GHRF animals only. In the IGF-1 mice the large glomeruli remained morphologically normal except for the enlargement. These data suggest that the glomerulosclerosis was due, in part, to disordered mesangial cell growth in response to circulating GH. The mesangial lesions in mice with chronically high plasma GH levels mimicked those in human diabetes mellitus. These models provide a means to study the hormonal regulation of glomerular growth and the role that specific hormones might play in the pathogenesis of glomerulosclerosis.

Considerable evidence indicates that genetic determinants play a major role in the pathogenesis of a variety of human and experimentally-induced renal diseases. There are, however, no firm data to indicate which genes or types of genes can induce or promote renal disease. The recently acquired ability to make specific alterations in the genetic background of an animal affords a unique opportunity to assess the effect(s) of a given gene on the structure and function of an organ of interest. Such modifications have been carried out in the creation of transgenic mice. We examined mice transgenic for the transforming gene encoding large T-antigen which is present in the early region of simian virus 40 (SV40). Renal lesions were present in most animals. While there was some heterogeneity in the type and severity of the renal lesions observed, a majority of the older mice displayed glomerulosclerosis and/or proliferative tubular lesions which in some were associated with multiple, large tubular cysts. The appearance of these lesions in mice transgenic for a transforming gene suggests that renal expression of a gene which controls cell proliferation may be associated with the development of glomerulosclerosis and renal cysts. These findings indicate a possible role for other transforming genes, or oncogenes, in the pathogenesis of glomerulosclerosis and cystic renal disease in humans and other animal models.

The culture of glomerular cells has represented an important tool in the understanding of individual glomerular cell functions. However, the complexity of the glomerulus has made it difficult to obtain pure cell populations. It has also been difficult to culture glomerular endothelial cells, even as mixed cell populations. At present there are no established glomerular cell lines from any source. We have established permanent cell lines of cloned glomerular epithelial, mesangial, and endothelial cells from a line of mice transgenic for the early region of simian virus 40 (SV40). These mice appear normal at birth but by three to four months of age have sclerosis affecting a variable percentage of their glomeruli. The cells maintain features characteristic of their normal counterparts despite their transformed phenotype. These cell lines could be useful tools in understanding the pathogenesis of glomerulosclerosis in this transgenic mouse model and in studying those features of normal glomerular cell biology which are not altered by a transformed phenotype.

The renal glomerulus is both a site of action and synthesis of IGF-I. We previously demonstrated the presence of IGF-I receptor and synthesis in glomerular mesangial cells. In this study we investigated the presence of specific IGF-I receptors on mouse glomerular endothelial and epithelial cells in culture. [125I]IGF-I specifically bound to the cell surface of both cell types. Maximum specific binding, 0.141 B/F for endothelial cells and 0.301 B/F for epithelial cells, was obtained at 22 degrees C after 150 min incubation. The estimated Kd values were 2.25 x 10(-9) for endothelial cells and 1.5 x 10(-9) for epithelial cells. Cross-linking studies showed a single band of radioactivity with an estimated mol wt of 145K, consistent with the alpha-subunit of the IGF-I receptor. Radiolabelled IGF-I was not degraded by either cell types. These findings suggest a possible paracrine action of IGF-I in the renal glomerulus.

Mesangial cell hyperplasia is a feature common to several human glomerular diseases. The cause of this increased cell number is unknown. The authors assessed human mesangial cells in vitro and found that they possessed an insulinlike growth factor-1 (IGF-1) receptor consisting of alpha and beta units (Mr, 130 k and 90 k respectively). Fifty percent inhibition of IGF-1 specific binding to the receptor required 1 X 10(-9) M IGF-1, greater than 1 X 10(-6) M insulin and 1 X 10(-7) M multiplication stimulating activity (MSA). Analysis of binding by the method of Scatchard revealed one type of IGF-1 receptor with a Kd of 1.35 X 10(-9) M, and a number per cell of 1.04 X 10(5). Binding studies on whole glomeruli had similar specificity and there were 7.17 X 10(7) receptors per glomerulus (Kd, 1.12 X 10(-9) M). Examination of the effect of IGF-1 on the cell cycle revealed that exposure of cells to both IGF-1 and platelet-derived growth factor (PDGF) led to a significant increase in 3H-thymidine incorporation into cell layers. Antibody to PDGF abolished only that response due to PDGF. Similarly, the labeling index of cells pretreated with PDGF, washed, and then exposed to IGF-1 was increased, whereas if the order of ligand exposure was reversed, there was no such additive effect. Finally, PDGF increased RNA and protein synthesis, and this response was not enhanced by IGF-1. In summary, human mesangial cells and whole glomeruli possess IGF-1-specific receptors and IGF-1 was found to act as a progression factor in the cell cycle.