Phosphoinositide 3-kinase is required for high glucose-induced hypertrophy and p21WAF1 expression in LLC-PK1 cells

Reversal of the renal hyperglycemic memory in diabetic kidney disease by targeting sustained tubular p21 expression

A major obstacle in diabetes is the metabolic or hyperglycemic memory, which lacks specific therapies. Here we show that glucose-mediated changes in gene expression largely persist in diabetic kidney disease (DKD) despite reversing hyperglycemia. The senescence-associated cyclin-dependent kinase inhibitor p21 (Cdkn1a) was the top hit among genes persistently induced by hyperglycemia and was associated with induction of the p53-p21 pathway. Persistent p21 induction was confirmed in various animal models, human samples and in vitro models. Tubular and urinary p21-levels were associated with DKD severity and remained elevated despite improved blood glucose levels in humans. Mechanistically, sustained tubular p21 expression in DKD is linked to demethylation of its promoter and reduced DNMT1 expression. Two disease resolving agents, protease activated protein C (3K3A-aPC) and parmodulin-2, reversed sustained tubular p21 expression, tubular senescence, and DKD. Thus, p21-dependent tubular senescence is a pathway contributing to the hyperglycemic memory, which can be therapeutically targeted.

Persistent diabetic complications despite controlled blood glucose levels, known as hyperglycemic memory, remain a poorly understood phenomenon in diabetic kidney disease. Here the authors identify senescence-associated gene p21 as a regulator of hyperglycemic memory, the suppression of which improves hyperglycemic memory and renal function.

Baricitinib counteracts metaflammation, thus protecting against diet-induced metabolic abnormalities in mice

OBJECTIVE

Recent evidence suggests the substantial pathogenic role of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway in the development of low-grade chronic inflammatory response, known as "metaflammation," which contributes to obesity and type 2 diabetes. In this study, we investigated the effects of the JAK1/2 inhibitor baricitinib, recently approved for the treatment of rheumatoid arthritis, in a murine high-fat-high sugar diet model.

METHODS

Male C57BL/6 mice were fed with a control normal diet (ND) or a high-fat-high sugar diet (HD) for 22 weeks. A sub-group of HD fed mice was treated with baricitinib (10 mg/kg die, p.o.) for the last 16 weeks (HD + Bar).

RESULTS

HD feeding resulted in obesity, insulin-resistance, hypercholesterolemia and alterations in gut microbial composition. The metabolic abnormalities were dramatically reduced by chronic baricitinib administration. Treatment of HD mice with baricitinib did not change the diet-induced alterations in the gut, but restored insulin signaling in the liver and skeletal muscle, resulting in improvements of diet-induced myosteatosis, mesangial expansion and associated proteinuria. The skeletal muscle and renal protection were due to inhibition of the local JAK2-STAT2 pathway by baricitinib. We also demonstrated that restored tissue levels of JAK2-STAT2 activity were associated with a significant reduction in cytokine levels in the blood.

CONCLUSIONS

In summary, our data suggest that the JAK2-STAT2 pathway may represent a novel candidate for the treatment of diet-related metabolic derangements, with the potential for EMA- and FDA-approved JAK inhibitors to be repurposed for the treatment of type 2 diabetes and/or its complications.

Renoprotective Effects of Aldose Reductase Inhibitor Epalrestat against High Glucose-Induced Cellular Injury

Diabetic nephropathy (DN) is the leading cause of end stage renal disease worldwide. Increased glucose flux into the aldose reductase (AR) pathway during diabetes was reported to exert deleterious effects on the kidney. The objective of this study was to investigate the renoprotective effects of AR inhibition in high glucose milieu in vitro. Rat renal tubular (NRK-52E) cells were exposed to high glucose (30 mM) or normal glucose (5 mM) media for 24 to 48 hours with or without the AR inhibitor epalrestat (1 μM) and assessed for changes in Akt and ERK1/2 signaling, AR expression (using western blotting), and alterations in mitochondrial membrane potential (using JC-1 staining), cell viability (using MTT assay), and cell cycle. Exposure of NRK-52E cells to high glucose media caused acute activation of Akt and ERK pathways and depolarization of mitochondrial membrane at 24 hours. Prolonged high glucose exposure (for 48 hours) induced AR expression and G1 cell cycle arrest and decreased cell viability (84% compared to control) in NRK-52E cells. Coincubation of cells with epalrestat prevented the signaling changes and renal cell injury induced by high glucose. Thus, AR inhibition represents a potential therapeutic strategy to prevent DN.

Involvement of Histone Lysine Methylation in p21 Gene Expression in Rat Kidney In Vivo and Rat Mesangial Cells In Vitro under Diabetic Conditions

Diabetic nephropathy (DN), a common complication associated with type 1 and type 2 diabetes mellitus (DM), characterized by glomerular mesangial expansion, inflammation, accumulation of extracellular matrix (ECM) protein, and hypertrophy, is the major cause of end-stage renal disease (ESRD). Increasing evidence suggested that p21-dependent glomerular and mesangial cell (MC) hypertrophy play key roles in the pathogenesis of DN. Recently, posttranscriptional modifications (PTMs) have uncovered novel molecular mechanisms involved in DN. However, precise regulatory mechanism of histone lysine methylation (HKme) mediating p21 related hypertrophy associated with DN is not clear. We evaluated the roles of HKme and histone methyltransferase (HMT) SET7/9 in p21 gene expression in glomeruli of diabetic rats and in high glucose- (HG-) treated rat mesangial cells (RMCs). p21 gene expression was upregulated in diabetic rats glomeruli; chromatin immunoprecipitation (ChIP) assays showed decreased histone H3-lysine9-dimethylation (H3K9me2) accompanied with enhanced histone H3-lysine4-methylation (H3K4me1/3) and SET7/9 occupancies at the p21 promoter. HG-treated RMCs exhibited increased p21 mRNA, H3K4me level, SET7/9 recruitment, and inverse H3K9me, which were reversed by TGF-β1 antibody. These data uncovered key roles of H3Kme and SET7/9 responsible for p21 gene expression in vivo and in vitro under diabetic conditions and confirmed preventive effect of TGF-β1 antibody on DN.

Research progress in signalling pathway in diabetic nephropathy

Diabetic nephropathy, a lethal diabetic complication, is a leading cause of end-stage renal disease, which is pathologically characterized by thickened tubular basal and glomerular membranes, accumulated extracellular matrix, and progressive mesangial hypertrophy. Growing evidence indicates that diabetic nephropathy is induced by multiple conditions, such as glucose metabolism disorder, oxidative stress, numerous inflammatory factors and cytokines, and haemodynamic changes that lead to the occurrence and development of diabetic nephropathy based on genetic susceptibility. A variety of abnormalities in the signalling pathway may interact to produce these pathologic processes. Research has aimed to highlight the signalling pathway mechanisms that lead to diabetic nephropathy so that preventative strategies and effective therapies might be developed. In this review, important pathways that appear to be involved in driving these processes are discussed.

miR-200c regulates IL8 expression by targeting IKBKB: a potential mediator of inflammation in leiomyoma pathogenesis

We have previously reported that leiomyoma expressed lower levels of miR-200c and elevated IL8 as compared to paired myometrium. Here we addressed the regulatory functions of miR-200c on the expression of inflammatory mediators and cellular viability using leiomyomas and paired myometrium and their isolated primary smooth muscle cells. Our results indicated that gain-of function or knockdown of miR-200c in leiomyoma smooth muscle cells (LSMC) regulated IL8 mRNA and protein expression through direct targeting of IKBKB and alteration of NF-kB activity. Additionally, leiomyoma expressed higher levels of phosphorylated IKBKB with no significant difference in the level of IKBKB mRNA and protein as compared to matched myometrium. Gain-of function of miR-200c in LSMC resulted in decreased IkBα phosphorylation and p65 nuclear translocation, which led to decreased p65 transcriptional activity of IL8 promoter, and increased caspase 3/7 activity which was not reversible following IL8 restoration. Collectively, our results suggest that NF-κB signaling pathway is a target of miR-200c regulatory function, and low level of miR-200c expression in leiomyoma by transcriptional regulation of inflammatory mediators such as IL8, in part account for development of leiomyomas.

Role of podocyte B7-1 in diabetic nephropathy

Podocyte injury and resulting albuminuria are hallmarks of diabetic nephropathy, but targeted therapies to halt or prevent these complications are currently not available. Here, we show that the immune-related molecule B7-1/CD80 is a critical mediator of podocyte injury in type 2 diabetic nephropathy. We report the induction of podocyte B7-1 in kidney biopsy specimens from patients with type 2 diabetes. Genetic and epidemiologic studies revealed the association of two single nucleotide polymorphisms at the B7-1 gene with diabetic nephropathy. Furthermore, increased levels of the soluble isoform of the B7-1 ligand CD28 correlated with the progression to ESRD in individuals with type 2 diabetes. In vitro, high glucose conditions prompted the phosphatidylinositol 3 kinase-dependent upregulation of B7-1 in podocytes, and the ectopic expression of B7-1 in podocytes increased apoptosis and induced disruption of the cytoskeleton that were reversed by the B7-1 inhibitor CTLA4-Ig. Podocyte expression of B7-1 was also induced in vivo in two murine models of diabetic nephropathy, and treatment with CTLA4-Ig prevented increased urinary albumin excretion and improved kidney pathology in these animals. Taken together, these results identify B7-1 inhibition as a potential therapeutic strategy for the prevention or treatment of diabetic nephropathy.

FOG2 protein down-regulation by transforming growth factor-β1-induced microRNA-200b/c leads to Akt kinase activation and glomerular mesangial hypertrophy related to diabetic nephropathy

Glomerular hypertrophy is a hallmark of diabetic nephropathy. Akt kinase activated by transforming growth factor-β1 (TGF-β) plays an important role in glomerular mesangial hypertrophy. However, the mechanisms of Akt activation by TGF-β are not fully understood. Recently, miR-200 and its target FOG2 were reported to regulate the activity of phosphatidylinositol 3-kinase (the upstream activator of Akt) in insulin signaling. Here, we show that TGF-β activates Akt in glomerular mesangial cells by inducing miR-200b and miR-200c, both of which target FOG2, an inhibitor of phosphatidylinositol 3-kinase activation. FOG2 expression was reduced in the glomeruli of diabetic mice as well as TGF-β-treated mouse mesangial cells (MMC). FOG2 knockdown by siRNAs in MMC activated Akt and increased the protein content/cell ratio suggesting hypertrophy. A significant increase of miR-200b/c levels was detected in diabetic mouse glomeruli and TGF-β-treated MMC. Transfection of MMC with miR-200b/c mimics significantly decreased the expression of FOG2. Conversely, miR-200b/c inhibitors attenuated TGF-β-induced decrease in FOG2 expression. Furthermore, miR-200b/c mimics increased the protein content/cell ratio, whereas miR-200b/c inhibitors abrogated the TGF-β-induced increase in protein content/cell. In addition, down-regulation of FOG2 by miR-200b/c could activate not only Akt but also ERK, which was also through PI3K activation. These data suggest a new mechanism for TGF-β-induced Akt activation through FOG2 down-regulation by miR-200b/c, which can lead to glomerular mesangial hypertrophy in the progression of diabetic nephropathy.

The influence of high glucose on the Cip/Kip family expression profiles in HRECs

Neovascularization is the main characteristic of the proliferative stage of diabetic retinopathy. It has been proven that cell cycle regulation is involved in angiogenesis. The cell cycle regulators, Cip/Kip protein family, belong to the cyclin-dependent kinase inhibitors, are versatile proteins, and except for their function in cell cycle regulation, they also participate in transcription, apoptosis and migration. The expression profiles of the Cip/Kip family in human retina microvascular endothelial cells (HRECs) under normal or high glucose conditions has not been described before. This study was undertaken to determine the expression profiles of the Cip/Kip family proteins, e.g., proteins which are influenced by high glucose and in what manner. Western blot and immunofluorescence analyses were used to investigate the protein expression profiles. Only p21(cip1) and p27(kip1) were detected in HRECs, and they were located in the nucleus. P21(cip1) protein abundance was higher than p27(kip1) in HRECs. Incubation of HRECs in medium containing 30 mM D-glucose for 48 h resulted in downregulation of p21(cip1) protein expression, but had no influence on p27(kip1) protein levels or p21(cip1) mRNA abundance. These results were accompanied by cell cycle G1 phase exit and a lower cell survival rate. Our data show for the first time that high glucose changes the Cip/Kip family expression profiles in HRECs, which may be the foundation for the investigation of the role of the Cip/Kip family in the pathogenesis of diabetic retinopathy.

miR-93/106b and their host gene, MCM7, are differentially expressed in leiomyomas and functionally target F3 and IL-8

miR-93/106b and their host gene minichromosome maintenance complex component 7 (MCM7) reside at chr7q22, a region frequently rearranged in leiomyomas. We explored the expression of miR-93/106b in leiomyoma and paired myometrium (n = 63) from untreated and patients exposed to hormonal therapies (GnRH agonist, Depo-Provera, and oral contraceptives) from African-Americans and Caucasians and their regulatory functions in isolated paired (n = 15) leiomyoma and myometrial smooth muscle cells and the leiomyosarcoma cell line. At tissue level leiomyomas expressed significantly lower levels of miR-93 and elevated MCM7 as compared with myometrium with limited racial influence or hormonal exposure on their expression. Assessing the regulatory function of miR-93/106b through doxycycline-inducible lentiviral transduction in a microarray analysis, tissue factor (F3) and IL8 were identified as their possible targets. At the tissue level, leiomyomas expressed a significantly lower level of F3 and an elevated IL-8 level, which exhibited an inverse relationship with miR-93 but with limited racial or hormonal influences. The gain of function of miR-93/106b in leiomyoma smooth muscle cells, myometrial smooth muscle cells, and the leiomyosarcoma cell line dose dependently repressed F3 and IL8 through direct interactions with their respective 3'-untranslated region and indirectly through F3 repression inhibited IL8, CTGF, and PAI-1 expression, confirmed by using small interfering RNA silencing or factor Vlla (FVIIa) activation of F3, as well as reducing the rate of proliferation, while increasing caspase-3/7 activity. We concluded that differential expression of miR-93/106b and their direct and/or indirect regulatory functions on F3, IL8, CTGF, and PAI-1 expression, with key roles in inflammation and tissue turnover may be of significance in the outcome of leiomyoma growth and associated symptoms.

Epac1-mediated, high glucose-induced renal proximal tubular cells hypertrophy via the Akt/p21 pathway

The mechanisms involved in tubular hypertrophy in diabetic nephropathy are unclear. We investigated the role of exchange protein activated by cAMP 1(Epac1), which activates Rap-family G proteins in cellular hypertrophy. Epac1 is expressed in heart, renal tubules, and in the HK-2 cell line. In diabetic mice, increased Epac1 expression was observed, and under high glucose ambience (HGA), HK-2 cells also exhibited increased Epac1 expression. We isolated a 1614-bp DNA fragment upstream of the initiation codon of Epac1 gene, inclusive of glucose response elements (GREs). HK-2 or COS7 cells transfected with the Epac1 promoter revealed a dose-dependent increase in its activity under HGA. Mutations in GRE motifs resulted in decreased promoter activity. HK-2 cells exhibited a hypertrophic response and increased protein synthesis under HGA, which was reduced by Epac1-siRNA or -mutants, whereas the use of a protein kinase A inhibitor had minimal effect. Epac1 transfection led to cellular hypertrophy and increased protein synthesis, which was accentuated by HGA. HGA increased the proportion of cells in the G0/G1 cell-cycle phase, and the expression of pAkt and the cyclin-dependent kinase inhibitors p21 and p27 was increased while the activity of cyclin-dependent kinase 4 decreased. These effects were reversed following transfection of cells with Epac1-siRNA or -mutants. These data suggest that HGA increases GRE-dependent Epac1 transcription, leading to cell cycle arrest and instigation of cellular hypertrophy.

Nodal signaling via an autocrine pathway promotes proliferation of mouse spermatogonial stem/progenitor cells through Smad2/3 and Oct-4 activation

Spermatogenesis is the process that involves the division and differentiation of spermatogonial stem cells into spermatozoa. However, the autocrine molecules and signaling pathways controlling their fate remain unknown. This study was designed to identify novel growth factors and signaling pathways that regulate proliferation, differentiation, and survival of spermatogonial stem/progenitor cells. To this end, we have for the first time explored the expression, function, and signaling pathway of Nodal, a member of the transforming growth factor-beta superfamily, in mouse spermatogonial stem/progenitor cells. We demonstrate that both Nodal and its receptors are present in these cells and in a spermatogonial stem/progenitor cell line (C18-4 cells), whereas Nodal is undetected in Sertoli cells or differentiated germ cells, as assayed by reverse transcription-polymerase chain reaction, Western blots, and immunocytochemistry. Nodal promotes proliferation of spermatogonial stem/progenitor cells and C18-4 cells, whereas Nodal receptor inhibitor SB431542 blocks their propagation as shown by proliferation and bromodeoxyuridine incorporation assays. Nodal knockdown by RNA interference results in a marked increase of cell apoptosis and a reduction of cell division as indicated by terminal deoxynucleotidyl transferase dUTP nick-end labeling and proliferation assays. Conversely, overexpression of Nodal leads to an increase of cell proliferation. Nodal activates Smad2/3 phosphorylation, Oct-4 transcription, cyclin D1, and cyclin E expression, whereas SB431542 completely abolishes their increase. Together, Nodal was identified as the first autocrine signaling molecule that promotes proliferation of mouse spermatogonial stem/progenitor cells via Smad2/3 and Oct-4 activation. This study thus provides novel and important insights into molecular mechanisms regulating proliferation and survival of spermatogonial stem/progenitor cells.

PKC-beta1 mediates glucose-induced Akt activation and TGF-beta1 upregulation in mesangial cells

Accumulation of glomerular matrix is a hallmark of diabetic nephropathy. The serine/threonine kinase Akt mediates glucose-induced upregulation of collagen I in mesangial cells through transactivation of the EGF receptor (EGFR). In addition, in renal tubular cells, glucose-induced secretion of TGF-beta requires phosphoinositide-3-OH kinase, suggesting a possible role for Akt in the modulation of TGF-beta expression, but the mechanisms of Akt activation and its involvement in TGF-beta regulation are unknown. Here, in primary mesangial cells, high glucose induced AktS473 phosphorylation, which correlates with its activation, in a protein kinase C beta (PKC-beta)-dependent manner. Glucose led to PKC-beta1 membrane translocation and association with Akt, and PKC-beta1 immunoprecipitated from glucose-treated cells phosphorylated recombinant Akt on S473. PKC is known to mediate glucose-induced TGF-beta1 upregulation through the transcription factor AP-1; here, inhibitors of phosphoinositide-3-OH kinase, PKC-beta and Akt, and dominant-negative Akt all prevented glucose-induced activation of AP-1 and upregulation of TGF-beta1. Finally, pharmacologic and dominant negative inhibition of EGFR blocked glucose-induced activation of PKC-beta1, phosphorylation of AktS473, activation of AP-1, and upregulation of TGF-beta1. In vivo, the PKC-beta inhibitor ruboxistaurin prevented Akt activation in the renal cortex of diabetic rats. In conclusion, PKC-beta1 is an Akt S473 kinase in glucose-treated mesangial cells, and TGF-beta1 transcriptional upregulation requires EGFR/PKC-beta1/Akt signaling. New therapeutic approaches for diabetic nephropathy may result from targeting components of this pathway, particularly the initial EGFR transactivation.

Renal activity of Akt kinase in obese Zucker rats

Insulin resistance (IR) and consequent hyperinsulinemia are hallmarks of Type 2 diabetes (DM2). Akt kinase (Akt) is an important molecule in insulin signaling, implicated in regulation of glucose uptake, cell growth, cell survival, protein synthesis, and endothelial nitric oxide (NO) production. Impaired Akt activation in insulin-sensitive tissues contributes to IR. However, Akt activity in other tissues, particularly those affected by complications of DM2, has been less studied. We hypothesized that hyperinsulinemia could have an impact on activity of Akt and its effectors involved in regulation of renal morphology and function in DM2. To address this issue, renal cortical Akt was determined in obese Zucker rats (ZO), a model of DM2, and lean controls (ZL). We also studied expression and phosphorylation of the mammalian target of rapamycin (mTOR) and endothelial NO synthase (eNOS), molecules downstream of Akt in the insulin signaling cascade, and documented modulators of renal injury. Akt activity was measured by a kinase assay with GSK-3 as a substrate. Expression of phosphorylated (active) and total proteins was measured by immunoblotting and immunohistochemistry. Renal Akt activity was increased in ZO as compared to ZL rats, in parallel with progressive hyperinsulinemia. No differences in Akt were observed in the skeletal muscle. Corresponding to increases in Akt activity, ZO rats demonstrated enhanced phosphorylation of renal mTOR. Acute PI3K inhibition with wortmannin (100 mug/kg) attenuated renal Akt and mTOR activities in ZO, but not in ZL rats. In contrast to mTOR, eNOS phosphorylation was similar in ZO and ZL rats, despite higher total eNOS expression. In conclusion, ZO rats demonstrated increases in renal Akt and mTOR activity and expression. However, eNOS phosphorylation did not follow this pattern. These data suggest that DM2 is associated with selective IR in the kidney, allowing pro-growth signaling via mTOR, whereas potentially protective effects mediated by eNOS are blunted.

Protein kinase B/Akt activity is involved in renal TGF-beta1-driven epithelial-mesenchymal transition in vitro and in vivo

The molecular pathogenesis of diabetic nephropathy (DN), the leading cause of end-stage renal disease worldwide, is complex and not fully understood. Transforming growth factor-β (TGF-β1) plays a critical role in many fibrotic disorders, including DN. In this study, we report protein kinase B (PKB/Akt) activation as a downstream event contributing to the pathophysiology of DN. We investigated the potential of PKB/Akt to mediate the profibrotic bioactions of TGF-β1 in kidney. Treatment of normal rat kidney epithelial cells (NRK52E) with TGF-β1 resulted in activation of phosphatidylinositol 3-kinase (PI3K) and PKB/Akt as evidenced by increased Ser⁴⁷³ phosphorylation and GSK-3β phosphorylation. TGF-β1 also stimulated increased Smad3 phosphorylation in these cells, a response that was insensitive to inhibition of PI3K or PKB/Akt. NRK52E cells displayed a loss of zona occludins 1 and E-cadherin and a gain in vimentin and α-smooth muscle actin expression, consistent with the fibrotic actions of TGF-β1. These effects were blocked with inhibitors of PI3K and PKB/Akt. Furthermore, overexpression of PTEN, the lipid phosphatase regulator of PKB/Akt activation, inhibited TGF-β1-induced PKB/Akt activation. Interestingly, in the Goto-Kakizaki rat model of type 2 diabetes, we also detected increased phosphorylation of PKB/Akt and its downstream target, GSK-3β, in the tubules, relative to that in control Wistar rats. Elevated Smad3 phosphorylation was also detected in kidney extracts from Goto-Kakizaki rats with chronic diabetes. Together, these data suggest that TGF-β1-mediated PKB/Akt activation may be important in renal fibrosis during diabetic nephropathy.

Failure to phosphorylate AKT in podocytes from mice with early diabetic nephropathy promotes cell death

Loss of podocytes by apoptosis characterizes the early stages of diabetic nephropathy. To examine its mechanism we studied glomeruli and podocytes isolated from db/db mice with early diabetic nephropathy and albuminuria. Phosphorylation of AKT (protein kinase B, a key survival protein) was found to be lower in the glomeruli of 12 week old db/db compared to db/+ mice. In vitro, insulin phosphorylated AKT solely in podocytes from db/+ mice. Serum deprivation and exposure to tumor necrosis factor-alpha significantly compromised cell viability in podocytes from db/db but not from db/+ mice, and this was associated with a significant decrease in AKT phosphorylation. Inhibition of AKT was necessary to achieve the same degree of cell death in db/+ podocytes. Our study shows that podocyte inability to respond to insulin and susceptibility to cell death may partially account for the decreased podocyte number seen in early diabetic nephropathy.

Diabetes: caught in the Akt?

One complication of diabetes is a pronounced renal cellular hypertrophy, inevitably resulting in chronic fibrotic changes. Chuang and colleagues demonstrate that hypertrophy in vitro is dependent on an increased phosphoinositide 3-kinase (PI3K) activity and is correlated with increased levels of p21(WAF1/Cip1), a cell-cycle regulator that was previously associated with renal fibrosis and sclerosis from nondiabetic causes.

Sp1 and Smad3 are required for high glucose-induced p21WAF1 gene transcription in LLC-PK1 cells

The cyclin-dependent kinase inhibitor p21(WAF1) is required for diabetic glomerular hypertrophy. High glucose-induced hypertrophy in proximal tubule cells is dependent on transforming growth factor-beta (TGF-beta). Many of the TGF-beta-induced effects are dependent on Smad2/3. Thus, the molecular mechanisms of high glucose-induced p21(WAF1) and hypertrophy were studied in high glucose-cultured proximal tubule-like LLC-PK(1) cells. We found that high glucose (30 mM) induced hypertrophy at 72 h. High glucose also increased the expression of p21(WAF1) protein and p21(WAF1) mRNA transcription and abundance at 48 h. The DNA element in the 5' regulatory region of p21(WAF1) gene essential for high glucose-induced p21(WAF1) gene transcription was identified as Sp1 by a series of the 5' regulatory region of p21(WAF1) gene deletion mutants. Moreover, high glucose activated Smad2/3 while increasing the Sp1 DNA-binding activity. High glucose also increased the Sp1-dependent transcriptional activity of p21(WAF1) gene. High glucose-induced hypertrophy was attenuated by p21(WAF1) short interfering RNA and Smad3 dominant-negative plasmid transfection. We concluded that high glucose induced hypertrophy via Sp1-Smad2/3-dependent activation of p21(WAF1) gene transcription in LLC-PK(1) cells.