Epithelial Cells In Diabetic Nephropathy Research Articles

Lysine Acetylation in the Proteome of Renal Tubular Epithelial Cells in Diabetic Nephropathy.

Diabetic nephropathy is considered one of the most common microvascular complications of diabetes and the pathophysiology involves multiple factors. Progressive diabetic nephropathy is believed to be related to the structure and function of the tubular epithelial cells in the kidney. However, the role of lysine acetylation in lesions of the renal tubular epithelial cells arising from hyperglycemia is poorly understood. Consequently, in this study, we cultured mouse renal tubular epithelial cells in vitro under high glucose conditions and analyzed the acetylation levels of proteins by liquid chromatography-high-resolution mass spectrometry. We identified 48 upregulated proteins and downregulated 86 proteins. In addition, we identified 113 sites with higher acetylation levels and 374 sites with lower acetylation levels. Subcellular localization analysis showed that the majority of the acetylated proteins were located in the mitochondria (43.17%), nucleus (28.57%) and cytoplasm (16.19%). Enrichment analysis indicated that these acetylated proteins are primarily associated with oxidative phosphorylation, the citrate cycle (TCA cycle), metabolic pathways and carbon metabolism. In addition, we used the MCODE plug-in and the cytoHubba plug-in in Cytoscape software to analyze the PPI network and displayed the first four most compact MOCDEs and the top 10 hub genes from the differentially expressed proteins between global and acetylated proteomes. Finally, we extracted 37 conserved motifs from 4915 acetylated peptides. Collectively, this comprehensive analysis of the proteome reveals novel insights into the role of lysine acetylation in tubular epithelial cells and may make a valuable contribution towards the identification of the pathological mechanisms of diabetic nephropathy.

SMAD3 promotes autophagy dysregulation by triggering lysosome depletion in tubular epithelial cells in diabetic nephropathy

ABSTRACT Macroautophagy/autophagy dysregulation has been noted in diabetic nephropathy; however, the regulatory mechanisms controlling this process remain unclear. In this study, we showed that SMAD3 (SMAD family member 3), the key effector of TGFB (transforming growth factor beta)-SMAD signaling, induces lysosome depletion via the inhibition of TFEB-dependent lysosome biogenesis. The pharmacological inhibition or genetic deletion of SMAD3 restored lysosome biogenesis activity by alleviating the suppression of TFEB, thereby protecting lysosomes from depletion and improving autophagic flux in renal tubular epithelial cells in diabetic nephropathy. Mechanistically, we found that SMAD3 directly binds to the 3ʹ-UTR of TFEB and inhibits its transcription. Silencing TFEB suppressed lysosome biogenesis and resulted in a loss of the protective effects of SMAD3 inactivation on lysosome depletion under diabetic conditions. In conclusion, SMAD3 promotes lysosome depletion via the inhibition of TFEB-dependent lysosome biogenesis; this may be an important mechanism underlying autophagy dysregulation in the progression of diabetic nephropathy. Abbreviations: AGEs: advanced glycation end products; ATP6V1H: ATPase H+ transporting V1 subunit H; CTSB: cathepsin B; ChIP: chromatin immunoprecipitation; Co-BSA: control bovine serum albumin; DN: diabetic nephropathy; ELISA: enzyme-linked immunosorbent assay; FN1: fibronectin 1; HAVCR1/TIM1/KIM-1: hepatitis A virus cellular receptor 1; LAMP1: lysosomal associated membrane protein 1; LMP: lysosome membrane permeabilization; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; NC: negative control; SIS3: specific inhibitor of SMAD3; SMAD3: SMAD family member 3; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; TECs: tubular epithelial cells; TFEB: transcription factor EB; TGFB1: transforming growth factor beta 1; TGFBR1: transforming growth factor beta receptor 1; UTR: untranslated region; VPS11: VPS11 core subunit of CORVET and HOPS complexes.

Metformin Reduces the Senescence of Renal Tubular Epithelial Cells in Diabetic Nephropathy via the MBNL1/miR-130a-3p/STAT3 Pathway

Senescence of renal tubular epithelial cells plays an important role in diabetic nephropathy, but the mechanism is unknown. Metformin may alleviate diabetic nephropathy by reducing this senescence. This study is aimed at clarifying the effects and mechanism of metformin on the senescence of renal tubular epithelial cells in diabetic nephropathy. We found that metformin reduced the expression of senescence-associated gene P21 in high-glucose-induced (30 mmol/L) renal tubular epithelial cells and decreased the β-galactosidase positive staining rate (decreased 16%, p < 0.01). Metformin was able to reduce senescence by upregulating the expression of RNA-binding protein MBNL1 and miR-130a-3p and reducing STAT3 expression. MBNL1 prolonged the half-life of miR-130a-3p, and miR-130a-3p could negatively regulate STAT3 by binding to its mRNA 3′UTR. In db/db diabetic mice, we found an enhanced senescence level combined with low expression of MBNL1 and miR-130a-3p and high expression of STAT3 compared with db/m control mice during nephropathy development. Meanwhile, metformin (200 mg/kg/day) could increase the expression of MBNL1 and miR-130a-3p and decreased STAT3 expression, thus reducing this senescence in db/db mice. Our results suggest that metformin reduces the senescence of renal tubular epithelial cells in diabetic nephropathy via the MBNL1/miR-130a-3p/STAT3 pathway, which provided new ideas for the therapy of this disease.

Mitochondria transfer from mesenchymal stem cells structurally and functionally repairs renal proximal tubular epithelial cells in diabetic nephropathy in vivo

The underlying therapeutic mechanism of renal tubular epithelium repair of diabetic nephropathy (DN) by bone marrow-derived mesenchymal stem cells (BM-MSCs) has not been fully elucidated. Recently, mitochondria (Mt) transfer was reported as a novel action of BM-MSCs to rescue injured cells. We investigated Mt transfer from systemically administered BM-MSCs to renal proximal tubular epithelial cells (PTECs) in streptozotocin (STZ)-induced diabetic animals. BM-MSCs also transferred their Mt to impaired PTECs when co-cultured in vitro, which suppressed apoptosis of impaired PTECs. Additionally, BM-MSC-derived isolated Mt enhanced the expression of mitochondrial superoxide dismutase 2 and Bcl-2 expression and inhibited reactive oxygen species (ROS) production in vitro. Isolated Mt also inhibited nuclear translocation of PGC-1α and restored the expression of megalin and SGLT2 under high glucose condition (HG) in PTECs. Moreover, isolated Mt directly injected under the renal capsule of STZ rats improved the cellular morphology of STZ-PTECs, and the structure of the tubular basement membrane and brush border in vivo. This study is the first to show Mt transfer from systemically administered BM-MSCs to damaged PTECs in vivo, and the first to investigate mechanisms underlying the potential therapeutic effects of Mt transfer from BM-MSCs in DN.

Pentosan polysulfate ameliorates apoptosis and inflammation by suppressing activation of the p38 MAPK pathway in high glucose‑treated HK‑2 cells.

The apoptosis of tubular epithelial cells in diabetic nephropathy (DN) is commonly observed in human renal biopsies. Inflammation plays a key role in DN, and pentosan polysulfate (PPS) has been shown to largely attenuate the inflammation of nephropathy in aging diabetic mice. p38 mitogen-activated protein kinase (p38 MAPK) plays a crucial role in tissue inflammation and cell apoptosis, and it is activated by hyperglycemia. In the present study, high glucose (HG)-treated human renal proximal tubular epithelial cells (HK-2) were used to examine the protective effects of PPS against HG-stimulated apoptosis and inflammation. The results of the study revealed that PPS markedly suppressed the HG-induced reduction in cell viability. Incubation of HK-2 cells with HG activated the p38 MAPK pathway and, subsequently, as confirmed by western blot analysis and flow cytometry, increased cell apoptosis, which was blocked by PPS. In addition, PPS treatment significantly inhibited HG-stimulated p38 MAPK and nuclear factor-κB activation, and reduced the production of pro-inflammatory cytokines, such as tumor necrosis factor-α, interleukin (IL)-1β and IL-6. In conclusion, PPS ameliorates p38 MAPK-mediated renal cell apoptosis and inflammation. The anti-apoptotic actions and anti-inflammatory effects of PPS prompt further investigation of this compound as a promising therapeutic agent against DN.

The Expression of Electron Transfer Flavoprotein β Mediating Apoptosis of Renal Tubular Epithelial Cells in Diabetic Nephropathy

The Expression of Electron Transfer Flavoprotein β Mediating Apoptosis of Renal Tubular Epithelial Cells in Diabetic Nephropathy

Correlation Study of the Sharing Molecule of Endocytosis and Autophagy Rab7 and Matrix Metalloproteinase-2 (MMP-2) of Renal Tubular Epithelial Cells in Diabetic Nephropathy

Correlation Study of the Sharing Molecule of Endocytosis and Autophagy Rab7 and Matrix Metalloproteinase-2 (MMP-2) of Renal Tubular Epithelial Cells in Diabetic Nephropathy

The renoprotective role of autophagy activation in proximal tubular epithelial cells in diabetic nephropathy

With intensive investigations recently, autophagy is hoped to be a potential therapeutic target to prevent or alleviate diabetic nephropathy (DN). Our previous study revealed that lipotoxicity participated in epithelial-to-mesenchymal transition (EMT) of proximal tubular epithelial cells (PTECs) under diabetic conditions. Based on evidences that autophagy and lipid metabolism are closely related, we investigated autophagy under diabetic conditions and how it contributed in the lipotoxicity and EMT. In high-glucose-cultured PTECs, we found that Beclin1 and LC3-II were elevated, while p62 was decreased. These results indicate that autophagy activity was elevated under diabetic conditions. Autophagy deficiency induced by autophagy inhibitors, chloroquine diphosphate (CQ) and 3-Methyladenine (3-MA), and by Atg5 siRNA transfection exacerbated lipid accumulation and EMT. This supports that the elevated autophagy activity acts as a renoprotective response under diabetic conditions. Treatment of rapamycin, which is a mammalian target of rapamycin (mTOR) receptor-specific inhibitor and a known autophagy activator, attenuated high-glucose-induced lipid accumulation and EMT. The Atg5 silence counteracted the protective effect of rapamycin. The present study deepens our understanding of the role of autophagy in DN, suggesting a complex interplay of autophagy, metabolic pathways, lipotoxicity and EMT.

Impact of ER stress-regulated ATF4/p16 signaling on the premature senescence of renal tubular epithelial cells in diabetic nephropathy.

Premature senescence is an important event during diabetic nephropathy (DN) progression. Here, we investigated the role of endoplasmic reticulum (ER) stress-regulated activation of transcription factor 4 (ATF4)/p16 signaling in the premature senescence of renal tubular epithelial cells (RTECs) during DN development. In the renal tissues of Type 2 DN patients, we detected an increased number of senescent cells; elevated deposition of advanced glycation end products (AGEs); upregulated expression of ER stress marker, glucose-regulated protein 78; as well as overexpression of ATF4 and p16. Similarly, these phenomena were also observed in cultured mouse RTECs following AGE treatment. Interestingly, AGE-induced p16 expression and premature senescence were successfully attenuated by ER stress inhibitor and ATF4 gene silencing. Moreover, AGE-induced premature senescence was mimicked by ER stress inducers and ATF4 overexpression, while suppressed by p16 gene silencing. In addition, ER stress inducers can augment ATF4 expression. Therefore, our results demonstrate that the ER stress-regulated ATF4/p16 pathway is involved in the premature senescence of RTECs during DN progression.

Alterations in tubular epithelial cells in diabetic nephropathy

Renal hypertrophy, matrix protein accumulation and tubulointerstitial fibrosis are major pathological features of diabetic nephropathy (DN) that eventuate in renal failure. Hyperglycemia and high concentration of glucose increase matrix protein expression, but the pathogenic mechanisms are not fully understood. We have previously reported that inactivation of tuberin resulting in activation of the mammalian target of rapamycin (mTOR) pathway and increased matrix protein accumulation in cultured proximal tubular cells exposed to high glucose and in kidney cortex of rats with type 1 diabetes. In this report, we show that kidney sections of diabetic patients express higher levels of phospho-tuberin (inactive form of tuberin), and that is associated with an increase in mTOR activation as measured by phosphorylation level of p70S6K. Inactivation of tuberin and activation of mTOR lead to accumulated cell matrix proteins (fibronectin and collagen IV) mainly in tubular epithelial cells of the kidneys of diabetic patients. In addition, significant staining of vimentin as a marker of cells undergoing an epithelial-to-mesenchymal transition (EMT) was detected in kidney sections of diabetic patients. On the other hand, very weak or nondetectable staining of cell matrix proteins, p-tuberin and P-p70S6K as well as vimentin was found in normal kidney sections of healthy subjects. The morphological changes in kidney sections of diabetic patients showed tubular thickening, glomerular and tubular hypertrophy, compared to normal structure of tubuli and glomeruli in kidney from healthy control subjects. These data suggest that alterations in tubular cells' structure, including tubular thickening and hypertrophy, are major mediators of the fibrotic process in DN.

Jagged/Notch signalling is required for a subset of TGFβ1 responses in human kidney epithelial cells

The Jagged/Notch pathway has been implicated in TGFβ1 responses in epithelial cells in diabetic nephropathy and other fibrotic conditions in vivo. Here, we identify that Jagged/Notch signalling is required for a subset of TGFβ1-stimulated gene responses in human kidney epithelial cells in vitro. TGFβ1 treatment of HK-2 and RPTEC cells for 24 h increased Jagged1 (a Notch ligand) and Hes1 (a Notch target) mRNA. This response was inhibited by co-incubation with Compound E, an inhibitor of γ-secretase (GSI), an enzyme required for Notch receptor cleavage and transcription regulation. In both cell types, TGFβ1-responsive genes associated with epithelial–mesenchymal transition such as E-cadherin and vimentin were also affected by γ-secretase inhibition, but other TGFβ1 targets such as connective tissue growth factor (CTGF) and thrombospondin-1 (THBS1) were not. TGFβ1-induced changes in Jagged1 expression preceded EMT-associated gene changes, and co-incubation with GSI altered TGFβ1-induced changes in cell shape and cytoskeleton. Transfection of cells with the activated, cleaved form of Notch (NICD) triggered decreased expression of E-cadherin in the absence of TGFβ1, but did not affect α-smooth muscle actin expression, suggesting differential requirements for Notch signalling within the TGFβ1-responsive gene subset. Increased Jagged1 expression upon TGFβ1 exposure required Smad3 signalling, and was also regulated by PI3K and ERK. These data suggest that Jagged/Notch signalling is required for a subset of TGFβ1-responsive genes, and that complex signalling pathways are involved in the crosstalk between TGFβ1 and Notch cascades in kidney epithelia.

Upregulated IL-18 expression in type 2 diabetic subjects with nephropathy: TGF-β 1 enhanced IL-18 expression in human renal proximal tubular epithelial cells

Aim In order to clarify the importance of Interleukin (IL)-18 in the development of diabetic nephropathy (DN), we evaluated the expressions of IL-18 in diabetic kidney. Methods We performed immmunohistochemical analysis of IL-18 and IL-18 receptor (IL-18 R) in human kidney tissue derived from 12 subjects with type 2 diabetes and overt nephropathy, and compared with those in 7 subjects with minimal change nephrotic syndrome (MCNS). In addition, we examined the regulation of IL-18 expression using human renal proximal tubular epithelial cells (HRPTECs) in culture. Results IL-18 expression in tubular cells was observed in higher rate (83%) in patients with diabetes, whereas one positive specimen (14.3%) for IL-18 in patients with MCNS. In contrast, IL-18 R was expressed in glomerular mesangial cells and endothelial cells as well as tubular cells, similarly in almost of both groups. Exposure to transforming growth factor beta (TGF-β 1) led to two-fold increase in IL-18 gene expression in HRPTECs, and mitogen-activated protein kinases (MAPK) inhibitors abolished TGF-β 1-induced IL-18 mRNA expression. Western blot analysis showed the IL-18 protein in HRPTECs. Conclusion The present data indicate that IL-18 is overexpressed in human tubular epithelial cells in diabetic nephropathy, probably through the activation of MAPK pathways induced by TGF-β 1.

The Notch pathway in podocytes plays a role in the development of glomerular disease

Albuminuria associated with sclerosis of the glomerulus leads to a progressive decline in renal function affecting millions of people. Here we report that activation of the Notch pathway, which is critical in glomerular patterning, contributes to the development of glomerular disease. Expression of the intracellular domain of Notch1 (ICN1) was increased in glomerular epithelial cells in diabetic nephropathy and in focal segmental glomerulosclerosis. Conditional re-expression of ICN1 in vivo exclusively in podocytes caused proteinuria and glomerulosclerosis. In vitro and in vivo studies showed that ICN1 induced apoptosis of podocytes through the activation of p53. Genetic deletion of a Notch transcriptional partner (Rbpj) specifically in podocytes or pharmacological inhibition of the Notch pathway (with a gamma-secretase inhibitor) protected rats with proteinuric kidney diseases. Collectively, our observations suggest that Notch activation in mature podocytes is a new mechanism in the pathogenesis of glomerular disease and thus could represent a new therapeutic target.

Activation of Tubular Epithelial Cells in Diabetic Nephropathy and the Role of the Peroxisome Proliferator–Activated Receptor-γ Agonist

The effects of advanced glycation end products (AGE) in the form of glycated albumin (GA) on the proinflammatory phenotype of cultured renal proximal tubular epithelial cells (PTEC) and the therapeutic potential of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist were studied. Human PTEC were exposed to medium alone or supplemented with albumin or GA with or without previous addition of rosiglitazone (0.1 to 0.5 microM). Exposure to GA (up to 0.5 mg/ml) but not the equivalent dose of neat albumin significantly upregulated both mRNA and protein expression of IL-8 and soluble intercellular adhesion molecule-1 (sICAM-1) in a dose- and time-dependent manner. Using immunohistochemistry, ICAM-1 signals were detected in the tubular epithelia and peritubular capillaries in association with AGE deposition and leukocyte infiltration, whereas IL-8 staining was localized in the tubular epithelia of human diabetic kidney biopsies. Also in a dose-dependent manner, GA (0.5 mg/ml) but not albumin caused nuclear translocation of NF-kappaB and activation of mitogen-activated protein kinase (MAPK) p44/p42 and signal transducer and activator of transcription (STAT-1). Inhibition of these pathways with pyrrolidine dithiocarbamate, PD 98059, and fludarabine, respectively, attenuated GA-induced IL-8 secretion. Rosiglitazone dose-dependently attenuated GA-induced IL-8 and ICAM-1 signals in PTEC and completely abolished GA-induced STAT-1 signals but had no effect on NF-kappaB and MAPK activation. These findings suggest that AGE stimulate renal tubular expression of adhesion molecule and chemokine that together may account for the transmigration of inflammatory cells into the interstitial space during diabetic tubulopathy. Such proinflammatory phenotype may be partially modified by PPAR-gamma ligation through STAT-1 inhibition independent of NF-kappaB transcriptional activity and MAPK signaling.

Activation of tubular epithelial cells in diabetic nephropathy.

Previous studies have shown that renal function in type 2 diabetes correlates better with tubular changes than with glomerular pathology. Since advanced glycation end products (AGEs; AGE-albumin) and in particular carboxymethyllysine (CML) are known to play a central role in diabetic nephropathy, we studied the activation of nuclear factor kappaB (NF-kappaB) in tubular epithelial cells in vivo and in vitro by AGE-albumin and CML. Urine samples from healthy control subjects (n = 50) and type 2 diabetic patients (n = 100) were collected and tested for excretion of CML and the presence of proximal tubular epithelial cells (pTECs). CML excretion was significantly higher in diabetic patients than in healthy control subjects (P < 0.0001) and correlated with the degree of albuminuria (r = 0.7, P < 0.0001), while there was no correlation between CML excretion and HbA(1c) (r = 0.03, P = 0.76). Urine sediments from 20 of 100 patients contained pTECs, evidenced by cytokeratin 18 positivity, while healthy control subjects (n = 50) showed none (P < 0.0001). Activated NF-kappaB could be detected in the nuclear region of excreted pTECs in 8 of 20 patients with pTECs in the urine sediment (40%). Five of eight NF-kappaBp65 antigen-positive cells stained positive for interleukin-6 (IL-6) antigen (62%), while only one of the NF-kappaB-negative cells showed IL-6 positivity. pTECs in the urine sediment correlated positively with albuminuria (r = 0.57, P < 0.0001) and CML excretion (r = 0.55, P < 0.0001). Immunohistochemistry in diabetic rat kidneys and a human diabetic kidney confirmed strong expression of NF-kappaB in tubular cells. To further prove an AGE/CML-induced NF-kappaB activation in pTECs, NF-kappaB activation was studied in cultured human pTECs by electrophoretic mobility shift assays (EMSAs) and Western blot. Stimulation of NF-kappaB binding activity was dose dependent and was one-half maximal at 250 nmol/l AGE-albumin or CML and time dependent at a maximum of activation after 4 days. Functional relevance of the observed NF-kappaB activation was demonstrated in pTECs transfected with a NF-kappaB-driven luciferase reporter plasmid and was associated with an increased release of IL-6 into the supernatant. The AGE- and CML-dependent activation of NF-kappaBp65 and NF-kappaB-dependent IL-6 expression could be inhibited using the soluble form of the receptor for AGEs (RAGE) (soluble RAGE [sRAGE]), RAGE-specific antibody, or the antioxidant thioctic acid. In addition transcriptional activity and IL-6 release from transfected cells could be inhibited by overexpression of the NF-kappaB-specific inhibitor kappaBalpha. The findings that excreted pTECs demonstrate activated NF-kappaB and IL-6 antigen and that AGE-albumin and CML lead to a perpetuated activation of NF-kappaB in vitro infer that a perpetuated increase in proinflammtory gene products, such as IL-6, plays a role in damaging the renal tubule.

Regulation of basement membrane heparan sulfate proteoglycan, perlecan, gene expression in glomerular epithelial cells by high glucose medium.

Proteinuria in diabetic nephropathy has been correlated with reduction in heparan sulfate proteoglycan (HSPG) content of the glomerular basement membrane. We have previously shown that the underlying mechanism probably involves reduction in the synthesis by glomerular epithelial cells. In this study we explored whether high glucose medium regulates basement membrane HSPG gene expression. Northern analysis demonstrated that rat glomerular epithelial cells in vitro constitutively express mRNA for basement membrane HSPG, similar to that observed in rat kidney glomerulus. RNase protection assay showed that incubation of glomerular epithelial cells with 30 mM glucose for 24 h and 7 days resulted in reduction in HSPG mRNA abundance. The decrease in mRNA abundance correlated with reduction in the synthesis of 35SO4-labeled basement membrane HSPG as measured by immunoprecipitation. Reduction in synthesis of HSPG could not be entirely accounted for by decrease in mRNA abundance, suggesting both transcriptional and posttranscriptional mechanisms may be involved in reduction of glomerular basement membrane HSPG synthesis by glomerular epithelial cells in diabetic nephropathy.

Regulation of basement membrane heparan sulfate proteoglycan, perlecan, gene expression in glomerular epithelial cells by high glucose medium

Proteinuria in diabetic nephropathy has been correlated with reduction in heparan sulfate proteoglycan (HSPG) content of the glomerular basement membrane. We have previously shown that the underlying mechanism probably involves reduction in the synthesis by glomerular epithelial cells. In this study we explored whether high glucose medium regulates basement membrane HSPG gene expression. Northern analysis demonstrated that rat glomerular epithelial cells in vitro constitutively express mRNA for basement membrane HSPG, similar to that observed in rat kidney glomerulus. RNase protection assay showed that incubation of glomerular epithelial cells with 30 mM glucose for 24 h and 7 days resulted in reduction in HSPG mRNA abundance. The decrease in mRNA abundance correlated with reduction in the synthesis of 35 SO4-labeled basement membrane HSPG as measured by immunoprecipitation. Reduction in synthesis of HSPG could not be entirely accounted for by decrease in mRNA abundance, suggesting both transcriptional and posttranscriptional mechanisms may be involved in reduction of glomerular basement membrane HSPG synthesis by glomerular epithelial cells in diabetic nephropathy. © 1996 Wiley-Liss, Inc.

Synthesis of type III Collagen and type IV collagen by tubular epithelial cells in diabetic nephropathy

Overproduction of extracellular matrix (ECM) is considered to be primarily responsible for both glomerular and tubulointerstitial (TI) changes in diabetic nephropathy (DN). To clarify the possible role of the collagens in TI damage in DN, type III interstitial collagen and type IV basement membrane collagen were studied in 10 cases of DN and 10 control cases by immunohistochemistry and in situ hybridization techniques. In control cases, no immunostaining for type III collagen was found in the renal tubules, while strongly positive in the adjacent interstitium. On the other hand, type IV collagen was found weakly in the tubular basement membrane (TBM) in control cases. In DN, increased immunostaining for both type III and type IV collagens were found in the damaged tubulointenstitium (TI). To determine the sources of these collagens in TI damage, non-radioactive in situ hybridization was performed utilizing thymine-thymine (T-T) dimerized synthetic oligonucleotides complementary to either human pro alpha 1 (III) chain or pro alpha 1 (IV) chain mRNA as probe. In normal tubules, tubular epithelial cells were not uniformly but persistently positive for pro alpha 1 (IV) mRNA. Meanwhile, no specifically detectable positive hybridization signals for pro alpha 1 (III) mRNA was found in the normal tubular epithelial cells. Accelerated synthesis of both type III and type IV collagens by tubular epithelial cells was noted in TI damage in DN. From the results we concluded that excessive synthesis of both type III and type IV collagens by tubular epithelial cells might significantly contribute to the TI damage found in DN.