Relationships between mesangial cell proliferation and types I and IV collagen mRNA levels in vitro

Changes in the composition of the mesangial extracellular matrix (ECM) and cell turnover are present in glomerular disease. To determine if ECM changes play a role in perpetuating mesangial cell dysfunction, we examined a line of mouse mesangial cells cultured on films or gels of several ECM components and also on methyl cellulose, an inert substrate that prevents attachment. Cells on films of fibronectin or type IV or I collagen had persistently high growth rates and high levels of alpha 1-I and alpha 1-IV collagen mRNAs. In contrast, on gels of type IV or I collagen or matrigel, the growth rate was low. The alpha 1-IV collagen mRNA levels were low on type IV collagen gel or matrigel, whereas the alpha 1-I collagen mRNA levels remained high. In contrast, the alpha 1-I collagen mRNA levels were low on type I collagen gel, and the alpha 1-IV collagen mRNA levels were high. Cells on methyl cellulose formed floating aggregates, did not proliferate, and had a 5- to 10-fold decrease in both alpha 1-I and alpha 1-IV collagen mRNA levels. These phenotypic changes were largely reversible. Finally, when matrigel was layered over cells on fibronectin films, alpha 1-IV collagen mRNA levels decreased, but alpha 1-I collagen mRNA levels and proliferation remained high. Thus proliferation and alpha 1-I and alpha 1-IV collagen mRNA levels in mesangial cells were independently regulated and depended on attachment and the nature of the adjacent matrix.

Molecular analysis of spontaneous glomerulosclerosis in Os/+ mice, a model with reduced nephron mass

Oligosyndactyly mice (ROP Os/+) are a radiation-induced mutant strain with reduced glomerular number and increased glomerular size. We found that they develop glomerulosclerosis. At 3 mo, ROP Os/+ mice had diffuse mesangial expansion by light microscopy, whereas their +/+ littermates did not. Electron microscopic morphometry revealed a twofold increase in mesangial areas but no changes in the thickness of glomerular basal laminae. Mean glomerular volume was increased 1.8-fold. Cell number and thymidine labeling index were increased 1.3- and 2.4-fold, respectively. The amount of glomerular type IV collagen and tenascin but not laminin was increased by immunofluorescence microscopy. mRNA levels in microdissected glomeruli were measured by competetive reverse transcription-polymerase chain reaction and corrected for cell number. alpha 1-Chain type IV collagen and tenascin mRNAs were increased 3.2-fold and 1.8-fold, whereas laminin B1 mRNA levels were not. The levels of 72-kDa collagenase mRNA were increased 1.6-fold. Transforming growth factor-beta 1 mRNA levels were elevated 1.8-fold, but platelet-derived growth factor-B mRNA levels remained normal. This is the first analysis of glomerular molecular and cellular changes in a model of congenital nephron reduction.

Collagen and collagenase mRNAs in normal and sclerotic glomeruli: predictors of progression and response to therapy

Progressive glomerulosclerosis is associated with decreasing kidney function, eventuating in end-stage renal failure. There are multiple components of the extracellular matrix, and the exact composition in various renal diseases is not known. Thus, we examined some of the major components of the extracellular matrix (ECM) in murine and human glomerular diseases. We studied matrix synthesis and degradation at the level of gene expression and ECM composition in the intact glomerulus. To determine whether the composition of sclerosis was similar among diseases, we examined a normal mouse strain and compared it with strains which spontaneously developed glomerulosclerosis. The baseline levels of matrix components varied between different mouse strains, and this level correlated with their propensity to develop glomerulosclerosis. In addition, when glomerulosclerosis was induced, the baseline ECM mRNA level predicted the subsequent outcome. We studied mice transgenic for bovine growth hormone, since they develop progressive glomerulosclerosis. Treatment with heparin substantially decreased the lesions without changes in type IV collagen mRNAs. However, there was an up-regulation of both the mRNA and enzyme activity for the 92 kD matrix metalloproteinase. In contrast, when these mice were treated with either angiotensin converting enzyme inhibitors or angiotensin II (Ang II) receptor antagonists, the glomerulosclerosis was accentuated histologically and the ECM synthetic and degradative mRNAs were elevated. These data suggest that the mRNA levels reflect response to therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration of AGEs in vivo induces genes implicated in diabetic glomerulosclerosis

Administration of advanced glycosylation end products (AGEs), prepared on mouse albumin, to normal young adult mice, resulted in an increase in mean glomerular volume and up-regulation of laminin B1 and alpha 1 type IV collagen mRNAs measured by competitive PCR in single microdissected glomeruli. Both glomerular hypertrophy and overexpression of genes coding for extracellular matrix were abrogated when aminoguanidine, an inhibitor of AGE cross-linking, was added to the AGEs injections, suggesting that the glomerular response to AGEs was specific. The effects of AGEs administration in vivo are comparable to those occurring in the early stage of diabetic nephropathy, suggesting a participation of AGEs in these events.

Effects of streptozotocin treatment in growth hormone (GH) and GH antagonist transgenic mice

To investigate GH's role in diabetic end organ damage, experimental diabetes was induced with streptozotocin (STZ) in bovine GH (bGH) or bGH antagonist transgenic mice and in their nontransgenic (NTG) litter mates. Body growth, blood glucose, serum insulin-like growth factor-I levels, liver GH receptor (GHR) binding, and kidney histology of these animals were evaluated. After administration of multiple low doses of STZ, 90% of the mice developed hyperglycemia. The diabetic animals, especially those expressing GH and GH antagonist transgenes, demonstrated retarded body growth and reduced insulin-like growth factor-I levels when compared with their nondiabetic litter mates. Kidney histology revealed severe glomerulosclerosis in diabetic and nondiabetic bGH transgenic mice. Diabetic NTG mice exhibited moderate kidney lesions. Diabetic bGH antagonist transgenic mice possessed normal glomeruli indistinguishable from those seen in nondiabetic NTG mice. GHR-binding assays revealed that liver GHR-binding sites were significantly reduced in diabetic NTG mice and transgenic dwarf mice when compared with their nondiabetic controls. Conversely, liver GHR-binding ability was significantly increased in bGH transgenic mice as compared with their NTG littermates and remained high during diabetes. It is concluded that transgenic mice that express a GH antagonist are protected from diabetes and or GH-induced nephropathy.

Overexpression of transforming growth factor-beta 1 mRNA is associated with up-regulation of glomerular tenascin and laminin gene expression in nonobese diabetic mice

Nonobese diabetic (NOD) mice spontaneously develop immune-mediated insulin-dependent diabetes mellitus and nephropathy, providing an opportunity to study the early molecular events in a model of diabetic glomerulosclerosis. The expression of several genes coding for growth factors and extracellular matrix was examined in microdissected glomeruli, by the use of reverse transcription-competitive polymerase chain reaction, in diabetic NOD mice (mean duration of diabetes, 28.5 +/- 7 days) and age-matched nondiabetic NOD mice with normal glucose tolerance. The levels of mRNA coding for transforming growth factor-beta 1, tenascin, and laminin B1 increased 1.9-, 2.0-, and 1.7-fold, respectively, whereas platelet-derived growth factor (PDGF)-B, alpha 1(IV) collagen, 72-kd collagenase, alpha-smooth muscle actin, and beta-actin mRNA remained stable in the diabetic mice. The kidney advanced glycosylation end-products levels increased 2.1-fold in the diabetic mice, and the diabetic glomeruli showed an accumulation of tenascin and laminin but not of type IV collagen by immunofluorescence microscopy. There was no increase in cell number per glomerulus after the onset of diabetes, a finding consistent with stable PDGF-B and alpha-smooth muscle actin mRNA levels. These findings provide evidence that increased glomerular transforming growth factor-beta 1, but not PDGF-B, mRNA is associated with the up-regulation of tenascin and laminin expression after advanced glycosylation endproduct accumulation, early after the onset of diabetes.

Screening and management of microalbuminuria in patients with diabetes mellitus: recommendations to the Scientific Advisory Board of the National Kidney Foundation from an ad hoc committee of the Council on Diabetes Mellitus of the National Kidney Foundation

All individuals with diabetes mellitus should be screened yearly with a spot urine albumin:creatinine ratio to identify those who are at increased risk for the development of complications of diabetes mellitus, including nephropathy, retinopathy, and cardiovascular disease. Once these high-risk individuals are appropriately identified, it is recommended that therapy with an angiotensin-converting enzyme (ACE) inhibitor be initiated. In addition, cardiovascular risk factors should be investigated, and when appropriate, therapeutic interventions should be initiated according to existing recommendations.

Assessment of 72-kilodalton gelatinase and TIMP-1 gene expression in normal and sclerotic murine glomeruli

Mice transgenic for bovine growth hormone (bGH) develop progressive diffuse glomerulosclerosis. Because murine mesangial cells in vitro were found to express the genes for 72-kd gelatinase and the metalloproteinase inhibitor TIMP-1, the expression of these genes in vivo in isolated whole glomeruli from bGH mice and normal control littermates was examined. Intact glomeruli were isolated by microdissection and subjected to reverse transcription. TIMP-1 cDNA was not detected by standard polymerase chain reaction (PCR) in glomeruli from bGH or control mice. In contrast, cDNA for 72-kd gelatinase was detected by standard PCR in both bGH and control mice, and the level was subsequently measured by quantitative competitive PCR. The gelatinase cDNA level was 14.7 +/- 2.8 x 10(-4) attomoles/glomerulus in 2- to 3-month-old control mice and was unchanged in 6-month-old controls. The bGH mice had 3.5-fold and 4.5-fold higher cDNA levels at 2 to 3 months and 6 months of age, respectively. Finally, zymography of glomerular extracts revealed increased levels of 72-kd and 96- to 100-kd gelatinase activity in bGH glomeruli in comparison to that in controls. In summary, whereas the genes for both TIMP-1 and 72-kd gelatinase are expressed in vitro in cultured mesangial cells, only the gelatinase gene appeared to be expressed in vivo in intact glomeruli. In addition, there was an up-regulation in the glomerular expression of the 72-kd gelatinase in bGH mice, a murine model of glomerulosclerosis.

The molecular basis of increased glomerulosclerosis after blockade of the renin angiotensin system in growth hormone transgenic mice

BACKGROUND

Angiotensin converting enzyme inhibitor (ACEi) therapy delays the onset of renal failure in diabetic nephropathy and inhibits or delays the onset of proteinuria in several animal models.

MATERIALS AND METHODS

We examined this question using a transgenic model of chronic glomerulosclerosis caused by an excess production of growth hormone (GH) in which there is progressive glomerular scarring leading to uremia. In addition, since GH mice do not have systemic hypertension or an elevated glomerular filtration rate, we could address the question of whether ACEi or angiotensin II receptor antagonists (AII RA) had an effect on the development of glomerulosclerosis under these conditions. Since excess matrix accumulates in glomerulosclerosis because of alterations in the balance between its synthesis and degradation, we examined the effect of ACEi and AII RA on these parameters.

RESULTS

Systemic blood pressure was unaffected by ACEi treatment, but the glomerular filtration rate decreased 85%. ACEi-treated mice had increased mesangial deposition of type I collagen and decreased 105 kD complex collagenase activity. In addition, ACEi-treated GH mice had increased glomerular alpha 1 type I collagen, alpha 1 type IV collagen, and alpha-smooth muscle cell actin mRNAs. No changes were noted in beta actin, or 72 kD metalloproteinase mRNAs. The result of these changes was a net increase in sclerosis. Surprisingly, GH mice treated with ACEi or AngII RA developed marked renal arteriolar lesions.

CONCLUSIONS

In some forms of glomerulosclerosis, the lesions develop independently of angiotensin II. Pharmacological inhibition of angiotensin II, in this circumstance, may aggravate the lesions through disregulation of the levels and the balance between glomerular matrix synthesis and degradation.

Advanced glycation end products up-regulate gene expression found in diabetic glomerular disease

Several lines of evidence suggest that the excessive accumulation of extracellular matrix in the glomeruli of diabetic kidneys may be due to reactive intermediates forming between glucose and matrix proteins called advanced glycation end products (AGEs). Normal mice received AGE-modified mouse serum albumin i.p. for 4 weeks, and glomerular extracellular matrix, growth factor mRNA levels, and morphology were examined. We found that AGE induced an increase in glomerular extracellular matrix alpha 1(IV) collagen, laminin B1, and transforming growth factor beta 1 mRNA levels, as measured by competitive PCR, as well as glomerular hypertrophy. The AGE response was specific because the coadministration of an AGE inhibitor, aminoguanidine, reduced all these changes. We conclude that AGEs affected expression of genes implicated in diabetic kidney disease and may play a major role in nephropathy.

Mesangial cells from diabetic NOD mice constitutively secrete increased amounts of insulin-like growth factor-I

Experimental evidence has suggested that insulin-like growth factor-I (IGF-I) may contribute to diabetic complications. Previously, we and others have shown that normal glomerular mesangial cells have receptors for, synthesize, and exhibit a mitogenic response to IGF-I. We investigated the IGF-I response in cells derived from a genetic model of diabetes, the nonobese diabetic (NOD) mouse. Mesangial cell lines were derived from diabetic (D-NOD) and nondiabetic adult mice. D-NOD cells released more IGF-I into the supernatant and had a decreased binding of IGF-I to surface receptors. Analysis according to Scatchard revealed a decreased number of receptor sites on D-NOD cells, although the structure of the IGF-I receptor visualized by cross-linking was identical for both cell types. Preincubation of D-NOD cells with an antibody to IGF-I resulted in an increase in the number of receptor sites. This suggested that autocrine IGF-I was responsible for the decrease in D-NOD receptor number and that diabetes had resulted in a stable phenotypic change.

Insulin uptake and processing by cultured mouse glomerular endothelial cells

Endothelial cells isolated from a variety of vascular beds bind and transport insulin but exhibit relatively low insulin degrading activity. Because endothelial cells exhibit heterogeneity and since kidney is a major site of insulin degradation, we studied the processing of insulin by glomerular endothelial cells (GEC). When exposed to 2 x 10(-10) M 125I-labeled insulin, GEC associated with the hormone in a specific manner. This interaction was inhibited by insulin but not by a number of unrelated peptide hormones. Over a 90-min period, GEC degraded 42 +/- 3% of the 125I-insulin, as measured by solubility in trichloroacetic acid (TCA). Degradation was inhibited 90% by an excess of insulin or adrenocorticotropic hormone (10(-6) M) and 57% by glucagon, whereas growth hormone and calcitonin were without effect. Separation of plasma membrane bound from internalized insulin was achieved by decreasing extracellular pH. In the steady state, 43% of cell-associated insulin was membrane bound and 57% internalized. The fate of the internalized 125I-insulin was examined by incubating acid-washed cells at 37 degrees C for 60 min. Over this time 18% of the radioactivity was released as TCA insoluble- and 72% as TCA-soluble radioactivity. Release was increased by insulin (10(-6) M) but not by unrelated peptide hormones. In the presence of chloroquine, 125I-insulin release increased by one third while degradation fell. High-performance liquid chromatography revealed that GEC released both intact insulin and large intermediates and that chloroquine inhibited intermediate formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Human glomeruli express TIMP-1 mRNA and TIMP-2 protein and mRNA

Alterations in the balance between synthesis and degradation of extracellular matrix may result in glomerulosclerosis. The interaction between metalloproteinases and their inhibitors presumably modulates the rate of glomerular matrix degradation. We examined the gene expression of tissue inhibitor of metalloproteinases (TIMP)-1 and TIMP-2 in human glomeruli and TIMP-2 protein in tissue sections. Kidney tissue was obtained from adults undergoing nephrectomy for renal tumor (n = 9) or biopsy for nephrosis and renal failure (n = 1). Glomeruli were microdissected and subjected to reverse transcription. TIMP cDNAs were quantitated by competitive polymerase chain reaction assays. Five nephrectomy specimens had normal glomeruli and four had diffuse glomerulosclerosis. TIMP-1 and TIMP-2 cDNA levels, detected in glomeruli from all patients, were increased fourfold and threefold, respectively, in patients with glomerulosclerosis. The elevated TIMP cDNA levels could not be attributed to an increased number of glomerular cells. TIMP-2 protein was detected within normal and sclerotic glomeruli. In conclusion, both TIMP genes were expressed in normal glomeruli, and their level of expression was increased in glomerulosclerosis associated with renal carcinoma, suggesting that expression of these inhibitors may correlate with the development of sclerosis.

Glomerulosclerosis and body growth are mediated by different portions of bovine growth hormone. Studies in transgenic mice

BACKGROUND

Mice transgenic for bovine growth hormone (bGH) gene have increased body weight and severe glomerulosclerosis leading to death in uremia.

EXPERIMENTAL DESIGN

The aim of this study was to determine if body growth and glomerulosclerosis were mediated by different bGH regions. Amino acid substitutions in the bGH alpha-helix III were generated, and lines of transgenic mice that expressed these products were developed. Female transgenic mice carrying the native bGH gene (bGH mice), a mutated bGH gene that encodes a destabilized alpha-helix III (bGH-L121P, E126G; bGH-m11 mice), or a mutated bGH gene that encodes a perfect amphiphilic alpha-helix III (bGH-E117L, G119R, A122D; bGH-m8 mice) were examined at 2-3 months and 6-9 months of age. Body, kidney, and heart weights were measured. Urinary glucose, albumin, creatinine, and serum glucose were measured in all mice. Serum levels of insulin-like growth factor I (IGF-I) were measured in the 2-3 month group. Whole blood hemoglobin A1 was measured in some mice of the 6-9 month group. Kidney sections were examined by light and immunofluorescence microscopy. Glomerular volume was measured and related to body weight by allometry.

RESULTS

The bGH-m11 mice developed glomerulosclerosis indistinguishable from that seen in bGH transgenic mice, even though they had normal body size. Glomerular growth exceeded body growth by allometry in both bGH and bGH-m11 strains. bGH-m8 mice had glomeruli of appropriate size and normal histologic appearance; however, they were dwarfs. IGF-I was increased in bGH mice; they also had an increased albumin/creatinine ratio at 6-9 months. None of the mice were hyperglycemic.

CONCLUSIONS

These data indicated that development of glomerulosclerosis and body growth promotion were mediated by different regions of the growth hormone molecule. The glomerular response to bGH was unique and consisted of increased size and glomerulosclerosis.

Studies by competitive PCR of glomerulosclerosis in growth hormone transgenic mice

We have shown that the glomerulosclerotic lesions of mice transgenic for bovine growth hormone (bGH mice) consisted of a change in the phenotype of glomerular collagens and an elevation of the mRNAs for these collagens in whole kidney. The purpose of this study was to determine whether these phenotypic and quantitative changes were present in the glomeruli. We used the increased sensitivity afforded by reverse transcription followed by the polymerase chain reaction (RT-PCR) to detect type I collagen mRNA and a quantitative PCR assay to quantitate type IV collagen mRNA in microdissected glomeruli. There was a six- to eightfold increase in alpha 1IV collagen mRNA in the glomeruli of bGh mice. alpha 1(I) collagen mRNA was present in glomeruli of bGH mice, which is consistent with our previous findings that the sclerotic mesangium contained type I collagen peptides by immunofluorescence microscopy. Normal glomeruli did not contain detectable amounts of alpha 1I collagen mRNA. In summary, we found a phenotypic change in glomeruli of mice transgenic for bGH consisting of increased type IV collagen mRNA levels and the appearance of type I collagen mRNA. Thus, the development of glomerulosclerosis appeared to be at least partially regulated at a pretranslational level.

Glomerulosclerosis in mice transgenic for native or mutated bovine growth hormone gene

Mice transgenic for bovine growth hormone (bGH) develop an increase in body weight and glomerular lesions characterized by a disproportionate increment in glomerular volume and progressive mesangial sclerosis. The relationship between glomerular size and body growth in bGH mice was further investigated by examining mice transgenic for a mutated GH gene (bGH-m11) which failed to enhance body growth. The glomeruli in bGH-m11 mice exhibited an increase in size and glomerulosclerosis comparable to those found in bGH mice. The levels of alpha 1 type IV collagen mRNA, as measured by the competitive polymerase chain reaction in isolated microdissected glomeruli, were markedly elevated in mice transgenic for both bGH and bGH-m11 genes. These data suggest that body growth on one hand, and glomerular hypertrophy and sclerosis on the other hand, are mediated by different portions of GH or different second messenger signaling systems.

The contribution of increased collagen synthesis to human glomerulosclerosis: a quantitative analysis of alpha 2IV collagen mRNA expression by competitive polymerase chain reaction

We previously reported that one of the main components of the sclerotic material in human glomerular diseases was type IV collagen. In this study we examined the contribution of increased synthesis to this process at the gene expression level. Sufficient material has not been available to study type IV collagen synthesis by normal or sclerotic glomeruli in humans. We took advantage of the availability of nephrectomy specimens from patients with renal carcinoma, and of the observation that approximately 50% of these patients develop varying degrees of glomerulosclerosis. We microdissected glomeruli from 10 patients and analyzed them using in situ reverse transcription coupled with polymerase chain reaction (PCR) analyses (in situ RT-PCR). alpha 2IV collagen mRNA, after reverse transcription into cDNA, was detected in all patients and appeared to be increased in those with glomerulosclerosis (n = 5). A competitive PCR assay was developed to quantitate this change. There was an average 3.7-fold increase in glomerular type IV collagen cDNA in patients with significant sclerosis. This change was not due to an increased number of glomerular cells. Thus, glomerulosclerosis in humans is associated with an elevation of glomerular type IV collagen gene expression, suggesting that increased synthesis of type IV collagen may represent one component of this process.

Age-related changes in alpha 1- and alpha 2-chain type IV collagen mRNAs in adult mouse glomeruli: competitive PCR

Studies of age-related changes in glomerular extracellular matrix (ECM) synthesis in normal mice have been hampered by the difficulty of isolating sufficient numbers of intact glomeruli and by the inability to quantify different mRNA species. The purpose of this study was to identify and quantitate the individual mRNAs coding for alpha 1- and alpha 2-chains of type IV collagen in isolated, single glomeruli of normal mice at different ages. These data on normal ECM synthesis were necessary for the understanding of glomerulosclerosis, a condition characterized by excess deposition of collagen. Pools of freshly microdissected adult mouse glomeruli were reverse transcribed in situ, and alpha 1-IV and alpha 2-IV collagen mRNAs were individually amplified by means of specific primers and the polymerase chain reaction (PCR), according to a previously published method. A competitive PCR assay, based on utilization of mutated cDNAs, allowed the reproducible, quantitative, and separate determination of the absolute amounts of both alpha 1-IV and alpha 2-IV mRNAs measured, as their respective cDNAs, in one-tenth of one glomerulus. The levels of alpha 1-IV and alpha 2-IV collagen mRNA were 208 +/- 36.0 x 10(-4) and 161.2 +/- 18.6 x 10(-4) amol/glomerulus in 5-wk-old mice. There were no significant age-related differences at 8, 12, and 24 wk. The mean levels over this period were 60.2 +/- 4.9 x 10(-4) for alpha 1-IV collagen mRNA and 63.9 +/- 5.8 x 10(-4) amol/glomerulus for alpha 2-IV collagen mRNA. Two of three 24-wk-old mice had mild glomerulosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Large glomerular size in Pima Indians: lack of change with diabetic nephropathy

The mean glomerular volume, glomerular fraction of cortical volume, and percentage of obsolescent glomeruli were calculated in kidney specimens from autopsies on 34 Pima Indians, of whom 15 had non-insulin dependent diabetes mellitus and kidney disease of diabetes mellitus. These values were compared with those of black, white, and non-Pima native American individuals without diabetes mellitus. Glomerular volume in the Pima Indians was similar in the diabetic and nondiabetic subjects and significantly greater than in the white subjects. Black and non-Pima native American individuals had glomerular volumes intermediate between white individuals and Pima Indians. The mean glomerular volume was not affected by the number of obsolescent glomeruli in diabetic Pima Indians. The glomerular volume fraction was greater in the Pimas than in the other groups. These data showed that glomerular volume in the Pima Indians was significantly greater than that in white subjects. There was no difference between diabetic and nondiabetics Pimas, and glomerular size was not correlated with the presence or degree of glomerulosclerosis in this population.

Receptor-specific increase in extracellular matrix production in mouse mesangial cells by advanced glycosylation end products is mediated via platelet-derived growth factor

Renal disease is one of the most common and severe complications of diabetes mellitus. The hallmark of the disease, glomerulosclerosis, is characterized by an accumulation of extracellular matrix in the mesangial areas, leading to progressive obliteration of the vascular spaces. The role of the metabolic derangements of diabetes mellitus in the development of these lesions is incompletely understood. One of the consequences of hyperglycemia is the formation of advanced glycosylation end products (AGEs), which result from a series of rearrangements secondary to nonenzymatic reaction of glucose with proteins. Specific receptors for proteins modified by AGEs, present in several cell types, were recently described in human and rat mesangial cells. Furthermore, exposure of mesangial cells to AGEs was followed by an increase in fibronectin production. In the present study we show evidence that mouse mesangial cells exhibit an increase in collagen type IV mRNA and peptide synthesis after exposure to AGEs. Antibodies to AGE receptors prevent this increase, indicating that the response is AGE-receptor-mediated. In addition, anti-platelet-derived growth factor abrogates the AGE response, suggesting that platelet-derived growth factor acts as an intermediate factor. Transcription assay reveals that the elevated mRNA levels are due to an increase in the transcription rate, rather than to an increase in the stability of the message. Finally, the mRNAs coding for laminin and heparan sulfate proteoglycan are also increased after exposure to AGE, whereas glyceraldehyde 3-phosphate dehydrogenase mRNA levels remain constant. The increase in extracellular matrix mRNAs seen in the current study suggests that AGE formation in vivo may be one of the metabolic events leading to the development of diabetic glomerulosclerosis.

Glomerulosclerosis at both early and late stages is associated with increased cell turnover in mice transgenic for growth hormone

The evolution of glomerulosclerosis consists of a progressive increase in mesangial matrix with gradual glomerular obliteration. The sclerotic process is thought to be irreversible and include a progressive loss of glomerular cells. To investigate this process, we selected mice transgenic for bovine growth hormone because they develop progressive glomerulosclerosis and renal failure. The sequence of histologic events in the growth hormone mice consists initially of an increase in the number of centrolobular glomerular cells, followed by an accumulation of extracellular matrix. This is accompanied by an increase in glomerular size which is disproportionate to the overall increment in kidney or body weight. The [3H]thymidine labeling index of the cells of the glomerular tuft was assessed before the development of recognizable sclerosis and at a time when the sclerosis was far advanced. The labeling index was more than five-fold increased over controls at the early time point. Contrary to what was expected, the labeling index remained at the same high levels in densely sclerotic glomeruli at the late time point. In conclusion, increased cell turnover is a significant component of the sclerotic process both at the onset and in the late stages of this model.

Glomerulosclerosis in mice transgenic for growth hormone. Increased mesangial extracellular matrix is correlated with kidney mRNA levels

Mice transgenic for growth hormone (GH) develop progressive glomerulosclerosis. The compositions of kidney extracellular matrix (ECM) and ECM mRNA were examined. The glomerulosclerotic areas in GH mice contained types I and IV collagen, laminin, and basement membrane heparan sulfate proteoglycan (HSPG), which increased with age. The type IV collagen, laminin B2, and HSPG mRNA levels in GH mice, measured by a solution hybridization RNase protection assay, were increased over normal littermates. These findings suggest that the accumulation of ECM components in the glomeruli of GH mice is regulated at the transcriptional level and that glomerulosclerosis is, in part, due to the excess production of ECM rather than simply a reduction in its turnover. The glomerular lesions in GH mice resemble diabetic nephropathy and may allow further dissection of the molecular basis of certain forms of glomerulosclerosis.

Mouse glomerular endothelial cells have an insulin receptor

An insulin receptor was found on the surface of cloned mouse glomerular endothelial cells in vitro. Total specific binding was 2.5 +/- 0.3%/10(6) cells at 90 min and 22 degrees C. Analysis according to Scatchard resulted in a curvilinear plot, with a kd for the high and low affinity sites estimated at 1.41 x 10(-10) and 8.2 x 10(-8) respectively. Insulin binding decreased following 12 hour exposure to 50 ng/ml of insulin suggesting that down regulation of the receptor had occurred, an effect which was reversible. Covalent crosslinking of the receptor to 125I insulin revealed one band at Mr 125,000 by SDS-PAGE which disappeared following preincubation with excess unlabeled insulin. Insulin was also able to stimulate phosphorylation of the beta subunit. The characteristics of this insulin receptor appear very similar to that of endothelial cell types from other microvascular beds.

Glomerular lesions in mice transgenic for growth hormone and insulinlike growth factor-I. I. Relationship between increased glomerular size and mesangial sclerosis

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.

Glomerular lesions in nonobese diabetic mouse: before and after the onset of hyperglycemia

The natural history of renal lesions in nonobese diabetic mice was assessed. This strain develops a spontaneous overt insulin-dependent diabetes that has a female predominance and an autoimmune pathogenesis. We compared mice that had a normal glucose tolerance test with mice that had a diabetes of 2 to 15 weeks' duration. The glomerular surface area was increased in all diabetic mice regardless of the duration of hyperglycemia. There was an increase in the albumin/creatinine ratio in the urine of diabetic mice. Finally, nonobese diabetic mice all showed mesangial sclerosis that was more pronounced in the diabetic mice. This suggests that this strain is susceptible to glomerulosclerosis and that the occurrence of hyperglycemia results in an increase of glomerular size, mesangial sclerosis, and proteinuria, soon after glycosuria is first demonstrated.

Relationship of glomerular hypertrophy and sclerosis: studies in SV40 transgenic 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.

The contribution of glomerular mesangial cells to progressive glomerulosclerosis

These data from in vitro studies, partially confirmed on intact glomeruli, suggest that glomerular cells are not only responsive to a number of growth-regulatory peptides but they are also important sources of several of these agents. The studies on transgenic mice confirm the potential role of the insulin-like peptides. This model also provides clear evidence that genetically directed modifications of cell behavior are important in the pathogenesis of glomerulosclerosis. The ability of glomerular cells to undergo proliferation and participate in hypertrophy of the glomerulus may be a critical determinant in the development of progressive glomerulosclerosis. That this ability is controlled by genetic differences between species and individuals seems well-established in both animal studies and clinical experience.

Binding of insulin-like growth factor-I by glomerular endothelial and epithelial cells: further evidence for IGF-I action in the renal glomerulus

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.