The hypertrophic effect of transforming growth factor-beta is reduced in the absence of cyclin-dependent kinase-inhibitors p21 and p27

The Role of Tubule-Interstitial Crosstalk in Renal Injury and Recovery

Renal epithelial cells show remarkable regenerative capacity to recover from acute injury, which involves specific phenotypic changes, but also significant profibrotic tubule-interstitial crosstalk. Tubule-derived profibrotic stimuli and subsequent myofibroblast activation and extracellular matrix deposition have been linked closely with decline of renal function and nephron loss. However, recent data have questioned the view of purely detrimental effects of myofibroblast activation in the injured kidney and even suggested its beneficial role for epithelial regeneration. This article reviews the current understanding of the underlying mechanisms of tubular cell turnover, new suggested pathways of proregenerative tubular-interstitial crosstalk, and relevant insights of proliferation-enhancing effects of myofibroblasts on epithelial cells in nonrenal tissues.

LncRNA NEAT1 Promotes High Glucose-Induced Mesangial Cell Hypertrophy by Targeting miR-222-3p/CDKN1B Axis

Glomerular hypertrophy is an early morphological alteration in diabetic nephropathy. Cyclin-Dependent Kinases have been shown to be required for high glucose (HG)-induced hypertrophy; however, the upstream regulators of CDKN1B in glomerular hypertrophy remain unclear. Herein we describe a novel pathway in which Long noncoding RNA (lncRNA) NEAT1 regulates the progression of mesangial cell hypertrophy via a competing endogenous RNA (ceRNA) mechanism. Real-time PCR was performed to detect the relative NEAT1 and miR-222-3p expressions and further confirmed the relationship between NEAT1 and miR-222-3p. Cell cycle was evaluated by flow cytometry. The related mechanisms were explored by Western blot, RNA immunoprecipitation and chromatin immunoprecipitation assay. We show that NEAT1 forms double stranded RNA (dsRNA) with miR-222-3p, thus limiting miR-222-3p's binding with CDKN1B. This release of CDKN1B mRNA leads to elevated CDKN1B protein expression, resulting in hypertrophy. In addition, we demonstrated that STAT3 which is activated by HG induces the transcription of NEAT1 by binding to its promoter. Our findings underscore an unexpected role of lncRNAs on gene regulation and introduce a new mode of proliferation regulation in mesangial cells.

Diabetic condition induces hypertrophy and vacuolization in glomerular parietal epithelial cells

Diabetic nephropathy (DN) is accompanied by characteristic changes in the glomerulus, but little is known about the effect of diabetes on parietal epithelial cells (PECs). In this study, a descriptive analysis of PECs was undertaken in diabetic db/db mice and in diabetic patients. PEC hypertrophy was significantly more prominent in diabetic mice than in nondiabetic mice, and this was evident even at the early stage. Additionally, the number of vacuoles in PECs was markedly increased in diabetic mice, suggesting the presence of cellular injury in PECs in DN. Although rare, binuclear cells were observed in mice with early diabetes. In cultured PECs, a high glucose condition, compared with normal glucose condition, induced cellular hypertrophy and apoptosis. Flow cytometry showed that some PECs in the G0 phase reentered the cell cycle but got arrested in the S phase. Finally, in human diabetic subjects, hypertrophy and vacuolization were observed in the PECs. Our data showed that PECs undergo substantial changes in DN and may participate in rearrangement for differentiation into podocytes.

The Role of Cell Cycle Regulators in Cell Survival-Dual Functions of Cyclin-Dependent Kinase 20 and p21Cip1/Waf1

The mammalian cell cycle is important in controlling normal cell proliferation and the development of various diseases. Cell cycle checkpoints are well regulated by both activators and inhibitors to avoid cell growth disorder and cancerogenesis. Cyclin dependent kinase 20 (CDK20) and p21^Cip1/Waf1 are widely recognized as key regulators of cell cycle checkpoints controlling cell proliferation/growth and involving in developing multiple cancers. Emerging evidence demonstrates that these two cell cycle regulators also play an essential role in promoting cell survival independent of the cell cycle, particularly in those cells with a limited capability of proliferation, such as cardiomyocytes. These findings bring new insights into understanding cytoprotection in these tissues. Here, we summarize the new progress of the studies on these two molecules in regulating cell cycle/growth, and their new roles in cell survival by inhibiting various cell death mechanisms. We also outline their potential implications in cancerogenesis and protection in heart diseases. This information renews the knowledge in molecular natures and cellular functions of these regulators, leading to a better understanding of the pathogenesis of the associated diseases and the discovery of new therapeutic strategies.

Depletion of cyclic-GMP levels and inhibition of cGMP-dependent protein kinase activate p21Cip1 /p27Kip1 pathways and lead to renal fibrosis and dysfunction

Cell-cycle regulatory proteins (p21^Cip1 /p27^Kip1 ) inhibit cyclin and cyclin-dependent kinase (CDK) complex that promotes fibrosis and hypertrophy. The present study examined the role of CDK blockers, p21^Cip1 /p27^Kip1 in the progression of renal fibrosis and dysfunction using Npr1 (encoding guanylyl cyclase/natriuretic peptide receptor-A, GC-A/NPRA) gene-knockout (0-copy; Npr1^-/- ), 2-copy (Npr1^+/+ ), and 4-copy (Npr1^++/++ ) mice treated with GC inhibitor, A71915 and cGMP-dependent protein kinase (cGK) inhibitor, (Rp-8-Br-cGMPS). A significant decrease in renal cGMP levels and cGK activity was observed in 0-copy mice and A71915- and Rp-treated 2-copy and 4-copy mice compared with controls. An increased phosphorylation of Erk1/2, p38, p21^Cip1 , and p27^Kip1 occurred in 0-copy and A71915-treated 2-copy and 4-copy mice, while Rp treatment caused minimal changes than controls. Pro-inflammatory (TNF-α, IL-6) and pro-fibrotic (TGF-β1) cytokines were significantly increased in plasma and kidneys of 0-copy and A71915-treated 2-copy mice, but to lesser extent in 4-copy mice. Progressive renal pathologies, including fibrosis, mesangial matrix expansion, and tubular hypertrophy were observed in 0-copy and A71915-treated 2-copy and 4-copy mice, but minimally occurred in Rp-treated mice compared with controls. These results indicate that Npr1 has pivotal roles in inhibiting renal fibrosis and hypertrophy and exerts protective effects involving cGMP/cGK axis by repressing CDK blockers p21^Cip1 and p27^Kip1 .

Cellular Effects of Butyrate on Vascular Smooth Muscle Cells are Mediated through Disparate Actions on Dual Targets, Histone Deacetylase (HDAC) Activity and PI3K/Akt Signaling Network

Vascular remodeling is a characteristic feature of cardiovascular diseases. Altered cellular processes of vascular smooth muscle cells (VSMCs) is a crucial component in vascular remodeling. Histone deacetylase inhibitor (HDACI), butyrate, arrests VSMC proliferation and promotes cell growth. The objective of the study is to determine the mechanism of butyrate-induced VSMC growth. Using proliferating VSMCs exposed to 5 mM butyrate, immunoblotting studies are performed to determine whether PI3K/Akt pathway that regulates different cellular effects is a target of butyrate-induced VSMC growth. Butyrate inhibits phosphorylation-dependent activation of PI3K, PDK1, and Akt, eliciting differential effects on downstream targets of Akt. Along with previously reported Ser9 phosphorylation-mediated GSK3 inactivation leading to stability, increased expression and accumulation of cyclin D1, and epigenetic histone modifications, inactivation of Akt by butyrate results in: transcriptional activation of FOXO1 and FOXO3 promoting G1 arrest through p21Cip1/Waf1 and p15INK4B upregulation; inactivation of mTOR inhibiting activation of its targets p70S6K and 4E-BP1 impeding protein synthesis; inhibition of caspase 3 cleavage and downregulation of PARP preventing apoptosis. Our findings imply butyrate abrogates Akt activation, causing differential effects on Akt targets promoting convergence of cross-talk between their complimentary actions leading to VSMC growth by arresting proliferation and inhibiting apoptosis through its effect on dual targets, HDAC activity and PI3K/Akt pathway network.

New Altered Non-Fibrillar Collagens in Human Dilated Cardiomyopathy: Role in the Remodeling Process

Background

In dilated cardiomyopathy (DCM), cardiac failure is accompanied by profound alterations of extracellular matrix associated with the progression of cardiac dilation and left ventricular (LV) dysfunction. Recently, we reported alterations of non-fibrillar collagen expression in ischemic cardiomyopathy linked to fibrosis and cardiac remodeling. We suspect that expression changes in genes coding for non-fibrillar collagens may have a potential role in DCM development.

Objectives

This study sought to analyze changes in the expression profile of non-fibrillar collagen genes in patients with DCM and to examine relationships between cardiac remodeling parameters and the expression levels of these genes.

Methods and Results

Twenty-three human left ventricle tissue samples were obtained from DCM patients (n = 13) undergoing heart transplantation and control donors (n = 10) for RNA sequencing analysis. We found increased mRNA levels of six non-fibrillar collagen genes, such as COL4A5, COL9A1, COL21A1, and COL23A1 (P < 0.05 for all), not previously described in DCM. Protein levels of COL8A1 and COL16A1 (P < 0.05 for both), were correspondingly increased. We also identified TGF-β1 significantly upregulated and related to both COL8A1 and COL16A1. Interestingly, we found a significant relationship between LV mass index and the gene expression level of COL8A1 (r = 0.653, P < 0.05).

Conclusions

In our research, we identified new non-fibrillar collagens with altered expression in DCM, being COL8A1 overexpression directly related to LV mass index, suggesting that they may be involved in the progression of cardiac dilation and remodeling.

Histone Lysine Methylation in TGF-β1 Mediated p21 Gene Expression in Rat Mesangial Cells

Transforming growth factor beta1- (TGF-β1-) induced p21-dependent mesangial cell (MC) hypertrophy plays a key role in the pathogenesis of chronic renal diseases including diabetic nephropathy (DN). Increasing evidence demonstrated the role of posttranscriptional modifications (PTMs) in the event; however, the precise regulatory mechanism of histone lysine methylation remains largely unknown. Here, we examined the roles of both histone H3 lysine 4 and lysine 9 methylations (H3K4me/H3K9me) in TGF-β1 induced p21 gene expression in rat mesangial cells (RMCs). Our results indicated that TGF-β1 upregulated the expression of p21 gene in RMCs, which was positively correlated with the increased chromatin marks associated with active genes (H3K4me1/H3K4me2/H3K4me3) and negatively correlated with the decreased levels of repressive marks (H3K9me2/H3K9me3) at p21 gene promoter. TGF-β1 also elevated the recruitment of the H3K4 methyltransferase (HMT) SET7/9 to the p21 gene promoter. SET7/9 gene silencing with small interfering RNAs (siRNAs) significantly abolished the TGF-β1 induced p21 gene expression. Taken together, these results reveal the key role of histone H3Kme in TGF-β1 mediated p21 gene expression in RMC, partly through HMT SET7/9 occupancy, suggesting H3Kme and SET7/9 may be potential renoprotective agents in managing chronic renal diseases.

ZO-2 silencing induces renal hypertrophy through a cell cycle mechanism and the activation of YAP and the mTOR pathway

Renal compensatory hypertrophy (RCH) restores normal kidney function after disease or loss of kidney tissue and is characterized by an increase in organ size due to cell enlargement and not to cell proliferation. In MDCK renal epithelial cells, silencing of the tight junction protein zona occludens 2 (ZO-2 KD) induces cell hypertrophy by two mechanisms: prolonging the time that cells spend at the G1 phase of the cell cycle due to an increase in cyclin D1 level, and augmenting the rate of protein synthesis. The latter is triggered by the nuclear accumulation and increased transcriptional activity of Yes-associated protein (YAP), the main target of the Hippo pathway, which results in decreased expression of phosphatase and tensin homologue. This in turn increased the level of phosphatidylinositol (3,4,5)-triphosphate, which transactivates the Akt/mammalian target of rapamycin pathway, leading to activation of the kinase S6K1 and increased synthesis of proteins and cell size. In agreement, in a rat model of uninephrectomy, RCH is accompanied by decreased expression of ZO-2 and nuclear expression of YAP. Our results reveal a novel role of ZO-2 as a modulator of cell size.

Phosphorylation of ribosomal protein S6 mediates compensatory renal hypertrophy

The molecular mechanism underlying renal hypertrophy and progressive nephron damage remains poorly understood. Here we generated congenic ribosomal protein S6 (rpS6) knockin mice expressing non-phosphorylatable rpS6 and found that uninephrectomy-induced renal hypertrophy was significantly blunted in these knockin mice. Uninephrectomy-induced increases in cyclin D1 and decreases in cyclin E in the remaining kidney were attenuated in the knockin mice compared to their wild-type littermates. Uninephrectomy induced rpS6 phosphorylation in the wild type mice; however, no rpS6 phosphorylation was detected in uninephrectomized or sham-operated knockin mice. Nonetheless, uninephrectomy stimulated comparable 4E-BP1 phosphorylation in both knockin and wild type mice, indicating that mTORC1 was still activated in the knockin mice. Moreover, the mTORC1 inhibitor rapamycin prevented both rpS6 and 4E-BP1 phosphorylation, significantly blunted uninephrectomy-induced renal hypertrophy in wild type mice, but did not prevent residual renal hypertrophy despite inhibiting 4E-BP1 phosphorylation in uninephrectomized knockin mice. Thus, both genetic and pharmacological approaches unequivocally demonstrate that phosphorylated rpS6 is a downstream effector of the mTORC1-S6K1 signaling pathway mediating renal hypertrophy. Hence, rpS6 phosphorylation facilitates the increase in cyclin D1 and decrease in cyclin E1 that underlie the hypertrophic nature of uninephrectomy-induced kidney growth.

TBX3, a downstream target of TGF-β1, inhibits mesangial cell apoptosis

Chronic kidney disease (CKD) is an increasingly common condition characterized by progressive loss of functional nephrons leading to renal failure. TGF-β1-induced mesangial cell (MC) phenotype alterations have been linked to the genesis of CKD. Here we show that TGF-β1 regulates TBX3 gene expression in MC. This gene encodes for two main isoforms, TBX3.1 and TBX3+2α. TBX3.1 has been implicated in cell immortalization, proliferation and apoptosis by inhibiting p14(ARF)-Mdm2-p53 pathway, while TBX3+2α role has not been defined. We demonstrated that TBX3 overexpression abrogated MC apoptosis induced by serum deprivation. Moreover, we observed an enhancement in TBX3 protein expression both in glomerular and tubular regions in the model of 5/6 nephrectomy, temporally related to increased expression of TGF-β1, type IV collagen and fibronectin. Our results indicate that TBX3 acts as an anti-apoptotic factor in MC in vitro and may be involved in the mechanism by which TGF-β1 induces glomerulosclerosis and tubular fibrosis during the progression of nephropathies.

The selected traditional chinese medicinal formulas for treating diabetic nephropathy: perspective of modern science

With the increasing patients and limited therapeutic options, diabetic nephropathy (DN) is a long-term complication of diabetic mellitus. The precise mechanism of DN is not yet fully understood and the effective blockade of the progression of nephropathy remains a therapeutic challenge. Application of traditional Chinese medicine (TCM) for diabetes and its related complications has received increasing attention due to its wide availability, low side effects, and proven therapeutic mechanisms and benefits. In the current review, we mainly focus on the recent laboratory studies of the TCM formulas including Wu-Ling-San (Poria Five Powder; Wǔ Líng Sǎn), Danggui-Buxue-Tang (Tangkuei and Astragalus Decoction; Dāng Guī Bǔ Xuè Tang), and Danggui-Shaoyao-San (Tangkuei and Paeonia Formula; Dāng Guī Sháo Yào Sǎn), conducted by the Committee on Chinese Medicine and Pharmacy at the Department of Health of Taiwan Government, in the amelioration of DN. These selected TCM formulas have anti-diabetic properties, with antihyperglycemic activity accompanied by amelioration of advanced glycation end product–mediated renal damage in streptozotocin-induced diabetic rats. However, the renoprotective effects of the selected TCM formulas did not correlate with suppressing renal renin–angiotensin system hyperactivity in diabetic rats. These TCM formulas also have the capacity to ameliorate the defective antioxidative defense system, leading to modulation of the oxidative stress, thereby resulting in downregulation of nuclear factor-kB as well as transforming growth factor-β1 and, consequently, attenuation of extracellular matrix components such as fibronectin or type IV collagen expression in diabetic renal cortex tissue. More detailed mechanistic researches and long-term clinical evaluations, as well as evaluation of safety of the selected TCM formulas are needed for their future applications in DN therapy.

p21(WAF1/CIP1) Expression is Differentially Regulated by Metformin and Rapamycin

The mammalian target of rapamycin (mTOR) pathway plays an important role in the development of diabetic nephropathy and other age-related diseases. One of the features of DN is the elevated expression of p21^WAF1/CIP1. However, the importance of the mTOR signalling pathway in p21 regulation is poorly understood. Here we investigated the effect of metformin and rapamycin on mTOR-related phenotypes in cell lines of epithelial origin. This study reports that metformin inhibits high glucose-induced p21 expression. High glucose opposed metformin in regulating cell size, proliferation, and protein synthesis. These effects were associated with reduced AMPK activation, affecting downstream mTOR signalling. However, the inhibition of the mTOR pathway by rapamycin did not have a negative effect on p21 expression, suggesting that metformin regulates p21 upstream of mTOR. These findings provide support for the hypothesis that AMPK activation may regulate p21 expression, which may have implications for diabetic nephropathy and other age-related pathologies.

Berberine attenuates high glucose-induced proliferation and extracellular matrix accumulation in mesangial cells: involvement of suppression of cell cycle progression and NF-κB/AP-1 pathways

Berberine has been shown to have renoprotective effects on diabetes through attenuating TGF-β1 and fibronectin (FN) expression. However, how berberine regulates TGF-β1 and FN is not fully clear. Here we investigated whether berberine inhibited TGF-β1 and FN expression in high glucose-cultured mesangial cells. Berberine significantly inhibited mesangial cell proliferation and hypertrophy by increasing the cell population in G1-phase and reducing that in S-phase. In addition, berberine reversed high glucose-induced down-regulation of cyclin-dependent kinase inhibitor p21(Waf1)/(Cip1) and p27(Kip1). Berberine inhibited p65 translocation to the nucleus and c-jun phosphorylation induced by high glucose. Furthermore, berberine attenuated high glucose-induced expression of TGF-β1 and FN. Using a luciferase reporter assay, we found that high glucose-induced transcription activity of NF-κB and AP-1 was blocked by berberine. Electrophoretic mobility shift assay showed that high glucose increased that NF-κB and AP-1 DNA binding activity. These data indicate that berberine inhibited mesangial cell proliferation and hypertrophy by modulating cell cycle progress. In addition, berberine suppressed high glucose-induced TGF-β1 and FN expression by blocking NF-κB/AP-1 pathways.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

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.

Therapeutic potential of Nrf2 activators in streptozotocin-induced diabetic nephropathy

OBJECTIVE

To determine whether dietary compounds targeting NFE2-related factor 2 (Nrf2) activation can be used to attenuate renal damage and preserve renal function during the course of streptozotocin (STZ)-induced diabetic nephropathy.

RESEARCH DESIGN AND METHODS

Diabetes was induced in Nrf2(+/+) and Nrf2(-/-) mice by STZ injection. Sulforaphane (SF) or cinnamic aldehyde (CA) was administered 2 weeks after STZ injection and metabolic indices and renal structure and function were assessed (18 weeks). Markers of diabetes including blood glucose, insulin, polydipsia, polyuria, and weight loss were measured. Pathological alterations and oxidative damage in glomeruli were also determined. Changes in protein expression of the Nrf2 pathway, as well as transforming growth factor-β1 (TGF-β1), fibronectin (FN), collagen IV, and p21/WAF1Cip1 (p21) were analyzed. The molecular mechanisms of Nrf2-mediated protection were investigated in an in vitro model using human renal mesangial cells (HRMCs).

RESULTS

SF or CA significantly attenuated common metabolic disorder symptoms associated with diabetes in Nrf2(+/+) but not in Nrf2(-/-) mice, indicating SF and CA function through specific activation of the Nrf2 pathway. Furthermore, SF or CA improved renal performance and minimized pathological alterations in the glomerulus of STZ-Nrf2(+/+) mice. Nrf2 activation reduced oxidative damage and suppressed the expression of TGF-β1, extracellular matrix proteins and p21 both in vivo and in HRMCs. In addition, Nrf2 activation reverted p21-mediated growth inhibition and hypertrophy of HRMCs under hyperglycemic conditions.

CONCLUSIONS

We provide experimental evidence indicating that dietary compounds targeting Nrf2 activation can be used therapeutically to improve metabolic disorder and relieve renal damage induced by diabetes.

Type VIII collagen modulates TGF-β1-induced proliferation of mesangial cells

Mesangial cells in diabetic mice and human kidneys with diabetic nephropathy exhibit increased type VIII collagen, a nonfibrillar protein that exists as a heterodimer composed of α1(VIII) and α2(VIII), encoded by Col8a1 and Col8a2, respectively. Because TGF-β1 promotes the development of diabetic glomerulosclerosis, we studied whether type VIII collagen modulates the effects of TGF-β1 in mesangial cells. We obtained primary cultures of mesangial cells from wild-type, doubly heterozygous (Col8a1(+/-)/Col8a2(+/-)), and double-knockout (Col8a1(-/-)/Col8a2(-/-)) mice. TGF-β1 bound normally to double-knockout mesangial cells. In wild-type mesangial cells, TGF-β1 inhibited proliferation, but in double-knockout cells, it stimulated proliferation, promoted cell cycle progression, and reduced apoptosis; we could reverse this effect by reconstituting α1(VIII). Furthermore, in wild-type cells, TGF-β1 mainly stimulated the Smad pathways, whereas in double-knockout cells, it activated the MAPK and PI3K/Akt pathways and induced expression of fibroblast growth factor 21 (FGF21). Inhibiting FGF21 expression by either interfering with activation of the MAPK and PI3K/Akt pathways or by FGF21 siRNA attenuated the TGF-β1-induced proliferation of double-knockout mesangial cells. In vivo, diabetic double-knockout mice had significantly higher expression of renal FGF21 mRNA and protein compared with diabetic wild-type mice. Immunohistochemistry revealed strong expression of FGF21 in both glomerular (mesangial) and tubular cells of diabetic mice. Taken together, these data suggest that type VIII collagen significantly modulates the effect of TGF-β1 on mesangial cells and may therefore play a role in the pathogenesis of diabetic nephropathy.

Parathyroid hormone-related protein induces hypertrophy in podocytes via TGF-beta(1) and p27(Kip1): implications for diabetic nephropathy

BACKGROUND

Hypertrophy of podocytes is characteristic in diabetic nephropathy (DN). Previously, we observed the upregulation of parathyroid hormone-related protein (PTHrP) and its receptor PTH1R, in experimental DN, associated with renal hypertrophy. Herein, we test the hypothesis that PTHrP participates in the mechanism of high glucose (HG)-induced podocyte hypertrophy.

METHODS

On mouse podocytes, hypertrophy was assessed by protein content/cell and [H(3)]leucine incorporation. Podocytes were stimulated with HG (25 mM), PTHrP(1-36) (100 nM), angiotensin II (AngII) (100 nM) or TGF-beta(1) (5 ng/mL) in the presence or absence of PTHrP-neutralizing antibodies (alpha-PTHrP), the PTH1R antagonist JB4250 (10 microM), PTHrP silencer RNA (siRNA) or TGF-beta(1) siRNA. Protein expression was analysed by western blot and immunohistochemistry.

RESULTS

HG-induced hypertrophy was abolished in the presence of either alpha-PTHrP or PTHrP siRNA. This effect was associated with an inhibition of the upregulation of TGF-beta(1) and p27(Kip1). JB4250 also inhibited HG-induced p27(Kip1) upregulation. Interestingly, whilst HG and AngII were unable to stimulate the expression of p27(Kip1) on PTHrP siRNA-transfected podocytes, TGF-beta(1) was still able to upregulate p27(Kip1) in these cells. Moreover, HG and PTHrP-induced hypertrophy as well as p27(Kip1) upregulation were abolished on TGF-beta(1) siRNA-transfected podocytes. Furthermore, the glomeruli of transgenic PTHrP-overexpressing mice showed a constitutive overexpression of TGF-beta(1) and p27(Kip1) to a degree similar to that of diabetic animals.

CONCLUSIONS

PTHrP seems to participate in the hypertrophic signalling triggered by HG. In this condition, AngII induces the upregulation of PTHrP, which might induce the expression of TGF-beta(1) and p27(Kip1). These findings provide new insights into the protective effects of AngII antagonists in DN, opening new paths for intervention.

Thiazolidinediones alter growth and epithelial cell integrity, independent of PPAR-γ and MAPK activation, in mouse M1 cortical collecting duct cells

Peroxisome proliferator-activated receptor (PPAR)-γ is highly expressed in the collecting duct (CD), yet little is known about the effects of PPAR-γ ligands, thiazolidinediones (TZDs), on CD cell structure and function. M1 mouse cortical CD cells were treated with 5 μM troglitazone (TRO) and rosiglitazone (ROSI). First, growth was measured by [(3)H]thymidine and [(3)H]leucine incorporation, as well as analysis of cyclin D1 and the CDK inhibitor p27 by Western blot. [(3)H]thymidine incorporation was reduced by 56 and 24% by TRO and ROSI at 6 h, and [(3)H]leucine by 21 and 10%. A similar growth inhibition was also observed after 24 h for thymidine, but leucine was reduced by 48 and 24%, respectively. Likewise, cyclin D1 was diminished 60% by TRO, and p27 was elevated 1.6- and 1.7-fold in response to TRO and ROSI. Next, epithelial cell integrity was assessed by measuring different markers by Western blot analysis. While fibronectin and α-smooth muscle actin levels were unchanged, by 24 h E-cadherin was decreased by 50%, and β-catenin levels were reduced 2- and 1.5-fold in response to TRO and ROSI, respectively. GW9662, a PPAR-γ antagonist, did not reverse any of the TZD responses in M1 cells. Of interest, phosho-p38 levels were also elevated 2-fold in response to TRO and 2.3-fold to ROSI, but MAPK inhibition by PD98059 or SB203580 caused an additive inhibition of cell growth and did not alter E-cadherin or β-catenin in response to TZDs. Finally, apoptotic death was assessed by Western blot, but cleaved caspase-3 levels were unchanged from 15 min to 24 h in response to TZDs, and TRO did not affect cell viability or reactive oxygen species generation. Our data suggest that TZDs cause a disruption of M1 cell integrity that is preceded by an inhibition of cell growth. This response is independent of p38 or PPAR-γ activation.

S6 kinase 1 knockout inhibits uninephrectomy- or diabetes-induced renal hypertrophy

Removal of one kidney stimulates synthesis of RNA and protein, with minimal DNA replication, in all nephron segments of the remaining kidney, resulting in cell growth (increase in cell size) with minimal cell proliferation (increase in cell number). In addition to the compensatory renal hypertrophy caused by nephron loss, pathophysiological renal hypertrophy can occur as a consequence of early uncontrolled diabetes. However, the molecular mechanism underlying renal hypertrophy in these conditions remains unclear. In the present study, we report that deletion of S6 kinase 1 (S6K1) inhibited renal hypertrophy seen following either contralateral nephrectomy or induction of diabetes. In wild-type mice, hypertrophic stimuli increased phosphorylation of 40S ribosomal protein S6 (rpS6), a known target of S6K1. Immunoblotting analysis revealed that S6K1(-/-) mice exhibited moderately elevated basal levels of rpS6, which did not increase further in response to the hypertrophic stimuli. Northern blotting indicated a moderate upregulation of S6K2 expression in the kidneys of S6K1(-/-) mice. Phosphorylation of the eukaryotic translation initiation factor 4E-binding protein 1, another downstream target of the mammalian target of rapamycin (mTOR), was stimulated to equivalent levels in S6K1(-/-) and S6K1(+/+) littermates during renal hypertrophy, indicating that mTOR was still activated in the S6K1(-/-) mice. The highly selective mTOR inhibitor, rapamycin, inhibited increased phosphorylation of rpS6 and blocked 60-70% of the hypertrophy seen in wild-type mice but failed to prevent the approximately 10% hypertrophy seen in S6K1(-/-) mice in response to uninephrectomy (UNX) although it did inhibit the basal rpS6 phosphorylation. Thus the present study provides the first genetic evidence that S6K1 plays a major role in the development of compensatory renal hypertrophy as well as diabetic renal hypertrophy and indicates that UNX- and diabetes-mediated mTOR activation can selectively activate S6K1 without activating S6K2.

Role of PPARgamma in renoprotection in Type 2 diabetes: molecular mechanisms and therapeutic potential

DN (diabetic nephropathy) is a chronic disease characterized by proteinuria, glomerular hypertrophy, decreased glomerular filtration and renal fibrosis with loss of renal function. DN is the leading cause of ESRD (end-stage renal disease), accounting for millions of deaths worldwide. TZDs (thiazolidinediones) are synthetic ligands of PPARgamma (peroxisome-proliferator-activated receptor gamma), which is involved in many important physiological processes, including adipose differentiation, lipid and glucose metabolism, energy homoeostasis, cell proliferation, inflammation, reproduction and renoprotection. A large body of research over the past decade has revealed that, in addition to their insulin-sensitizing effects, TZDs play an important role in delaying and preventing the progression of chronic kidney disease in Type 2 diabetes. Although PPARgamma activation by TZDs is in general considered beneficial for the amelioration of diabetic renal complications in Type 2 diabetes, the underlying mechanism(s) remains only partially characterized. In this review, we summarize and discuss recent findings regarding the renoprotective effects of PPARgamma in Type 2 diabetes and the potential underlying mechanisms.

Hexosamine induction of oxidative stress, hypertrophy and laminin expression in renal mesangial cells: effect of the anti-oxidant alpha-lipoic acid

We have previously shown that one of the potential mediators of the deleterious effects of high glucose on extracellular matrix protein (ECM) expression in renal mesangial cells is its metabolic flux through the hexosamine biosynthesis pathway (HBP). Here, we investigate further whether the hexosamines induce oxidative stress, cell-cycle arrest and ECM expression using SV-40-transformed rat mesangial (MES) cells and whether the anti-oxidant alpha-lipoic acid will reverse some of these effects. Culturing renal MES cells with high glucose (HG, 25 mM) or glucosamine (GlcN, 1.5 mM) for 48 h stimulates laminin gamma1 subunit expression significantly approximately 1.5 +/- 0.2- and 1.9 +/- 0.3-fold, respectively, when compared to low glucose (LG, 5 mM). Similarly, HG and GlcN increase the level of G0/G1 cell-cycle progression factor cyclin D1 significantly approximately 1.7 +/- 0.2- and 1.4 +/- 0.04-fold, respectively, versus LG (p < 0.01 for both). Azaserine, an inhibitor of glutamine:fruc-6-PO(4) amidotransferase (GFAT) in the HBP, blocks the HG-induced expression of laminin gamma1 and cyclin D1, but not GlcN's effect because it exerts its metabolic function distal to GFAT. HG and GlcN also elevate reactive oxygen species (ROS) generation, pro-apoptotic caspase-3 activity, and lead to mesangial cell death as revealed by TUNEL and Live/Dead assays. FACS analysis of cell-cycle progression shows that the cells are arrested at G1 phase; however, they undergo cell growth and hypertrophy as the RNA/DNA ratio is significantly (p < 0.05) increased in HG or GlcN-treated cells relative to LG. The anti-oxidant alpha-lipoic acid (150 microM) reverses ROS generation and mesangial cell death induced by HG and GlcN. Alpha-lipoic acid also reduces HG and GlcN-induced laminin gamma1 and cyclin D1 expression in MES cells. In addition, induction of diabetes in rats by streptozotocin (STZ) increases both laminin gamma1 and cyclin D1 expression in the renal cortex and treatment of the diabetic rats with alpha-lipoic acid (400 mg kg(-1) body weight) reduces the level of both proteins significantly (p < 0.05) when compared to untreated diabetic rats. These results support the hypothesis that the hexosamine pathway mediates mesangial cell oxidative stress, ECM expression and apoptosis. Anti-oxidant alpha-lipoic acid reverses the effects of high glucose, hexosamine and diabetes on oxidative stress and ECM expression in mesangial cells and rat kidney.

Alteration of glomerulogenesis- and podocyte structure-related gene expression in early diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease. Several pathways, including the renin-angiotensin system, have been postulated as potential mechanisms of diabetic nephropathy. In addition, glomerulogenesis-related molecules are involved in the pathogenesis of diabetic nephropathy, especially at the early stage. They can be divided into three groups by function, that is, fibrosis-related, podocyte differentiation-related and angiogenesis-related molecules. Most of the molecules are expressed in the podocyte and upregulated, even during the normoalbuminuric stage. Expression of several podocyte structure-related molecules are also altered at the normoalbuminuric stage. They can contribute to the structural alteration of the podocyte in diabetic nephropathy. Thus, normalization of the expression of glomerulogenesis-related molecules could be a new target for preventing the initiation and progression of diabetic nephropathy.

Kidney growth, hypertrophy and the unifying mechanism of diabetic complications

Michael Brownlee has proposed a 'Unifying Mechanism' of hyperglycemia-induced damage in diabetes mellitus. At the crux of this hypothesis is the generation of reactive oxygen species (ROS), and their impact on glycolytic pathways. Diabetes is the leading cause of chronic kidney failure. In the early phase of diabetes, prior to establishment of proteinuria or fibrosis, comes kidney growth and hyperfiltration. This early growth phase consists of an early period of hyperplasia followed by hypertrophy. Hypertrophy also contributes to cellular oxidative stress, and may precede the ROS perturbation of glycolytic pathways described in the Brownlee proposal. This increase in growth promotes hyperfiltration, and along with the hypertrophic phenotype appears required for hyperglycemia-induced cell damage and the progression of downstream diabetic complications. Here we will evaluate this growth phenomenon in the context of diabetes mellitus.

Transforming growth factor-beta 1 stimulates angiotensinogen gene expression in kidney proximal tubular cells

The present study investigated whether transforming growth factor-beta 1 (TGF-beta1) exerts an autocrine positive effect on angiotensinogen (ANG) gene expression in rat kidney proximal tubular cells, and delineates its underlying mechanism(s) of action. Rat immortalized renal proximal tubular cells (IRPTCs) and freshly isolated mouse renal proximal tubules were incubated in the absence or presence of active human TGF-beta1. IRPTCs were also stably transfected with rat TGF-beta1 or p53 tumor suppressor protein (p53) cDNA in sense (S) and antisense (AS) orientations. ANG mRNA and p53 protein expression were assessed by reverse transcription-polymerase chain reaction and Western blotting, respectively. Reactive oxygen species (ROS) generation was quantified by lucigenin assay. Active TGF-beta1 evoked ROS generation and stimulated ANG mRNA and p53 protein expression, whereas a superoxide scavenger and inhibitors of nicotinamide adenine dinucleotide oxidase and p38 mitogen-activated protein kinase (p38 MAPK) abolished the TGF-beta1 effect. Stable transfer of p53 cDNA (S) enhanced and p53 cDNA (AS) abolished the stimulatory effect of TGF-beta1 on ANG mRNA expression in IRPTCs. Our results demonstrate that TGF-beta1 stimulates ANG gene expression and its action is mediated, at least in part, via ROS generation, p38 MAPK activation, and p53 expression, suggesting that angiotensin II and TGF-beta1 may form a positive feedback loop to enhance their respective gene expression, leading to renal injury.

Renal injury due to renin-angiotensin-aldosterone system activation of the transforming growth factor-beta pathway

Glomerulosclerosis, interstitial fibrosis, and tubular atrophy occur with end-stage kidney failure, irrespective of the primary etiology. The transforming growth factor-beta (TGF-beta) is a key factor in these alterations either directly, by stimulating synthesis of extracellular matrix components and reducing collagenase production, or indirectly through other profibrogenic factors such as connective tissue growth factor (CTGF). TGF-beta is important for the proliferation of intrarenal fibroblasts and the epithelial-mesenchymal transition through which tubular cells become fibroblasts. Although several factors induce TGF-beta expression in the kidney, one very interesting aspect is the link between the renin-angiotensin-aldosterone (Aldo) system (RAAS) and TGF-beta. Angiotensin II (ANG II) stimulates TGF-beta expression in the kidney by various mechanisms and upregulates receptors for TGF-beta. ANG II can directly phosphorylate Smads without inducing TGF-beta. Recent data provide compelling evidence that other components of the RAAS including ANG III, renin, and Aldo also activate the TGF-beta system. As direct modulation of the TGF-beta system is not yet feasible in humans, angiotensin-converting enzyme (ACE) inhibitors and angiotensin type 1 (AT1)-receptor blockers are currently the most potential drugs to interfere with this ANG II-mediated TGF-beta expression. This review highlights some current aspects of the interaction between the RAAS and the TGF-beta axis.

Effects of tight blood pressure control on glomerular hypertrophy in a model of genetic hypertension and experimental diabetes mellitus

The aim of this study was to evaluate the effect of prevention of hypertension on glomerular hypertrophy, renal cell replication and accumulation of glomerular fibronectin in a model of genetic hypertension and experimental diabetes. Four-week-old streptozotocin induced spontaneously hypertensive rats (SHR) were randomized for no treatment, or for treatment with captopril, losartan or triple therapy (hydrochlorothiazide, reserpine and hydralazine) for 20 days. Increase in systolic blood pressure was equally prevented by captopril (118+/-15 mmHg), losartan (111+/-9) and triple therapy (112+/-14, p<0.0001). Glomerular size was higher (p<0.005) in diabetic SHR (27,300+/-2130 microm(2)) compared with non-diabetic SHR (23,800+/-307). The antihypertensive therapy with captopril (23,900+/-175), losartan (23,800+/-120), and triple therapy (23,400+/-210) prevented the glomerular enlargement in diabetic SHR. Glomerular expression of fibronectin was increased in diabetic SHR (7.61+/-1.22 densitometric unit) as compared to the controls (2.27+/-2.15, p<0.0001), and was decreased (p<0.0001 vs diabetic SHR) with captopril (2.49+/-1.42), losartan (1.57+/-1.1) and triple therapy (2.04+/-1.42). The number of replicating glomerular cell significantly decreased in diabetic SHR and it was restored by all three antihypertensive regimes. The glomerular expression of p27(Kip1) was increased in diabetic SHR but it was not modified by antihypertensive treatment. Strict blood pressure control, in diabetic SHR independently of the class of antihypertensive agent, restores glomerular hypertrophy and renal cellular replication, and prevents the increment in glomerular fibronectin.

Reversal of renal fibrosis, inflammation, and glomerular hypertrophy by kallikrein gene delivery

Evidence suggests that the progression of renal fibrosis is a reversible process. Because inflammation plays a crucial role in the development of renal injury, we examined the effect of kallikrein and activation of the kinin B2 receptor on the reversal of salt-induced inflammation and renal fibrosis in Dahl salt-sensitive (DSS) rats. Four weeks after high salt loading, when renal injury was apparent, adenovirus harboring the human tissue kallikrein gene was injected into DSS rats. To determine the role of the B2 receptor in mediating the actions of kallikrein, icatibant, a kinin B2 receptor antagonist, was infused with kallikrein gene delivery. Two weeks after adenovirus injection, salt-induced glomerular sclerosis, tubular protein cast formation, and monocyte/ macrophage accumulation in the kidney were notably reversed by kallikrein. Decreased intercellular adhesion molecule-1 expression paralleled this observation. Kallikrein gene delivery also dramatically reduced collagens I, III, and IV and reticulin deposition, accompanied by a decline in myofibroblast accumulation and transforming growth factor-beta(1) expression. Moreover, kallikrein reversed salt-induced glomerular hypertrophy and inhibited the increase in levels of the cell cycle-inhibitory proteins p21 and p27. These protective actions of kallikrein were abolished by icatibant, indicating a B2 receptor-mediated event. In addition, kallikrein protected against salt-induced renal injury by diminishing urinary protein and blood urea nitrogen levels. Furthermore, kallikrein gene delivery restored nitric oxide production and suppressed NADH oxidase activity and superoxide generation. These results indicate that tissue kallikrein, through the kinin B2 receptor, reverses salt-induced inflammation, renal fibrosis, and glomerular hypertrophy via suppression of oxidative stress.

Thiazolidinediones ameliorate diabetic nephropathy via cell cycle-dependent mechanisms

Thiazolidinediones are ligands for peroxisome proliferator-activated receptor (PPAR)-gamma, widely used as insulin sensitizer in type 2 diabetic patients and implicated in apoptosis, cell proliferation, and cell cycle regulation. Here, the effect of thiazolidinediones on G1-phase cell cycle arrest, the hallmark in diabetic nephropathy, was investigated. Eight-week-old male Otsuka Long-Evans Tokushima fatty rats were treated with pioglitazone (1 mg x kg body wt(-1) x day(-1)) until 50 weeks of age and compared with insulin treatment. Although similar HbA(1c) levels were observed in both groups, pioglitazone significantly inhibited glomerular hypertrophy and mesangial matrix expansion and reduced urinary albumin excretion compared with the insulin-treated group. In addition, pioglitazone significantly reduced the number of glomerular p27(Kip1)-positive cells. Because prominent expression of PPAR-gamma was observed in podocytes in glomeruli and cultured cells, conditionally immortalized mouse podocyte cells were cultured under 5.5 and 25 mmol/l D-glucose supplemented with pioglitazone. Pioglitazone inhibited cell hypertrophy revealed by [(3)H]thymidine and [(3)H]proline incorporation, and pioglitazone reversed high glucose-induced G1-phase cell cycle arrest, i.e., an increase in G0/G1 phase and decrease in S and G2 phases. Pioglitazone suppressed high glucose-induced phosphorylation of p44/42 mitogen-activated protein kinase and reduced Bcl-2 and p27(Kip1) protein levels. Besides glucose-lowering action, pioglitazone ameliorates diabetic nephropathy via cell cycle-dependent mechanisms.

Primary kidney growth and its consequences at the onset of diabetes mellitus

Diabetes mellitus is a primary contributor to progressive kidney dysfunction leading to end-stage renal disease (ESRD). In the early phase of diabetes, prior to the onset of further complications, both kidney size and glomerular filtration rate (GFR) increase. Glomerular hyperfiltration is considered a risk factor for downstream complications and progression to ESRD. Abnormalities in vascular control have been purported to account for the glomerular hyperfiltration in early diabetes. In this review we discuss a tubulo-centric concept in which tubular growth and subsequent hyper-reabsorption contribute to the onset of glomerular hyperfiltration that demarks the early stage of diabetes. Kidney growth, in this concept, is no longer relegated to a compensatory response to hyperfiltration, but rather plays a primary and active role in its genesis and progression. As such, components of kidney growth, such as the polyamines, may provide a means of early detection of diabetic kidney dysfunction and more effective therapeutic intervention.

Role of EGF Receptor Activation in Angiotensin II–Induced Renal Epithelial Cell Hypertrophy

For determination of the molecular mechanisms underlying the induction of epithelial cell hypertrophy by angiotensin II (Ang II), a well-characterized porcine renal proximal tubular cell line LLCPKcl4, which does not express endogenous Ang II receptor subtypes, was transfected with cDNA encoding Ang II subtype 1 receptor (AT1R/Cl4). Ang II transactivated the EGF receptor (EGFR) in these AT1R/Cl4 cells, which was blocked by the selective AT1R antagonist losartan but not by the selective AT2R antagonist PD123319. Ang II did not transactivate EGFR in empty vector-transfected LLCPKcl4 cells (Vector/Cl4). Ang II elicited release of soluble heparin-binding EGF-like growth factor (HB-EGF) from AT1R/Cl4 cells, and Ang II-induced EGFR activation was prevented by pretreatment with the specific HB-EGF inhibitor CRM197 or the metalloproteinase inhibitors batimastat or phenanthroline, none of which had any effect on EGFR activation by exogenously administered EGF. Ang II stimulated protein synthesis and cell hypertrophy in AT1R/Cl4 cells without increasing cell number, and signaling studies revealed that Ang II stimulated phosphorylation of the 40S ribosomal protein S6 and the eukaryotic translation initiation factor 4E-binding protein 1, the two downstream target proteins of the mammalian target of rapamycin, which is a central regulator of protein synthesis and cell size. Ang II-induced mammalian target of rapamycin activation, [3H]leucine incorporation, and cellular hypertrophy were inhibited by pretreatment with either batimastat or CRM197 or by pretreatment with rapamycin or the EGFR tyrosine kinase inhibitor AG1478. Ang II also stimulated Smad 2/3 phosphorylation, which was blocked by a selective TGF-beta receptor I kinase inhibitor but not by CRM197. With blockade of TGF-beta receptor, Ang II-mediated hypertrophy was converted into cell proliferation, which was blocked by CRM197. In summary, this is the first demonstration that HB-EGF shedding-dependent EGFR transactivation, along with activation of TGF-beta signaling pathways, mediates Ang II-induced renal tubular epithelial cell hypertrophy.

Cell Cycle and Glomerular Disease: A Minireview

Globally, glomerular diseases are a leading cause of chronic and end-stage renal disease. In the mature glomerulus, under normal conditions, glomerular cells have a low turnover rate. However, in disease, a variety of pathophysiological stimuli can lead to disturbances in glomerular cell biology, including toxins, immune-mediated stresses, metabolic derangements, drugs, infections, hemodynamic changes, growth factors, and cytokines. Not only does the form of injury govern the histologic and clinical manifestations of disease, but also the nature of the response to injury. This response to injury is largely cell-type specific, and the glomerulus represents a rare microcosm of the larger organism in which one can study the cellular responses of three very distinct cell types: mesangial cells, visceral epithelial cells or podocytes, and endothelial cells. These cells can undergo several cell fates in response to injury, including proliferation, de-differentiation, hypertrophy, senescence, apoptosis, or necrosis. The regulation of these responses occurs at the level of the cell cycle, coordinated by positive regulators, cyclins and cyclin-dependent kinases, and negative regulators, cyclin-dependent kinase inhibitors. There is now a large body of literature confirming the importance of cell cycle regulatory proteins in the glomerular cellular response to injury. The recent advances in cell cycle biology in diseases of the mesangial cell and the podocyte are the focus of this minireview.

Distinct functions for Ras GTPases in the control of proliferation and apoptosis in mouse and human mesangial cells

In previous work, we have demonstrated that Ras GTPases regulate proliferation in a range of human renal cells. The present work compares human and mouse mesangial cell (HMC and MMC) responses to specific knockdown of Ras genes with antisense oligonucleotides (AS-oligos), and examines the role of the p21 (cip1) and p27 (kip1) cyclin-dependent kinase inhibitors in these responses in mouse cells. HMC and MMC were lipofectin transfected with ras-targeted AS-oligo at 200-400 nM for 18 h followed by growth of cells in 20% serum for 18-72 h. Cell proliferation was assessed with an MTS assay and bromodeoxyuridine (BrdU) uptake. Apoptosis was quantified using nuclear stain with Hoechst 33342 dye. In MMC, Ha-ras AS-oligo caused an increase in apoptosis from <2% to 10-15% of cells after 18 h in serum (P<0.01). Control, Ki-ras and N-ras AS-oligos had minimal effects on apoptosis. BrdU uptake studies showed that BrdU+ve MMC were increased by 20-40% (P<0.05) after Ha-ras AS-oligo at 24 h; other ras AS-oligos were inactive. HMC number was reduced by 40-80% (P<0.01) at 48-72 h by both Ha-ras and Ki-ras AS-oligos. These actions were associated with reductions in BrdU+ve cells. In HMC, the ras AS-oligos did not induce apoptosis. p21(-,-) MMC showed exaggerated apoptotic responses to Ha-Ras AS-oligo. In mouse cells, Ha-Ras expression appears necessary to prevent apoptotic cell death; Ras expression does not appear necessary for cells to progress through the cell cycle. In human cells, Ras does not appear necessary to prevent apoptosis but Ha-Ras and Ki-Ras appear to be required for cell cycle progression.

Gas6 induces Akt/mTOR-mediated mesangial hypertrophy in diabetic nephropathy

BACKGROUND

We have already reported Gas6 is involved in glomerular hypertrophy observed in diabetic nephropathy. However, the molecular mechanisms involved in glomerular hypertrophy are still unknown, especially in vivo.

METHODS

In vivo, diabetes was induced in rats and mice by streptozotocin (STZ) and the activation of the Akt/mTOR pathway in glomeruli was examined. In vitro, mesangial hypertrophy was assessed by [(3)H]leucine incorporation and measuring cell areas.

RESULTS

Akt, p70 S6 kinase, and 4E-BP-1 were induced and phosphorylated in rat glomerular lysates after 12 weeks of STZ injection when mesangial and glomerular hypertrophy was observed. We then examined the role of Gas6 by treating STZ-rats with warfarin, and found that warfarin treatment inhibited the phosphorylation of these molecules as well as the hypertrophy. We next examined whether high glucose stimulation can induce the expression of Gas6/Axl in mesangial cells. Stimulation of the cells with 25 mmol/L of glucose increased the expression of Gas6/Axl and mesangial cell size compared with that with 5.6 mmol/L of glucose. This hypertrophic effect was abolished in mesangial cells derived from Gas6 knockout mice. We also found that LY294002 and rapamycin blocked Gas6-induced activation of the Akt/mTOR pathway and mesangial hypertrophy. Furthermore, less phosphorylated Akt-positive or 4E-BP-1-positive areas were found in STZ-treated Gas6 knockout mice than in STZ-treated wild-type mice.

CONCLUSION

Our study indicates that the Akt/mTOR pathway is a key signaling cascade in Gas6-mediated mesangial and glomerular hypertrophy and revealed a crucial role of Gas6/Axl and the Akt/mTOR pathway in the development of diabetic nephropathy.

p27Kip1 knockout mice are protected from diabetic nephropathy: Evidence for p27Kip1 haplotype insufficiency11See editorial by Qi and Breyer, p. 1896

BACKGROUND

High glucose up-regulates the mesangial cell expression of p27(Kip1), an inhibitor of cyclin-dependent kinases/cyclin complexes. Previous in vitro studies using cultured mesangial cells from p27(Kip1-/-) mice demonstrated that these cells do not undergo high glucose-mediated cellular hypertrophy. Since glomerular hypertrophy is an early feature of diabetic nephropathy and may precede the development of glomerulosclerosis, interference with p27(Kip1) expression may attenuate diabetic nephropathy. However, it is unclear whether deletion of p27(Kip1) protects the kidneys of diabetic nephropathy in vivo.

METHODS

Type 1 diabetes mellitus was induced in p27(Kip1+/+), p27(Kip1+/-), and p27(Kip1-/-) mice by injection of streptozotocin (STZ). Mice were studied for 6 weeks. Animals injected with citrate buffer only served as controls. At the end of the experiments, urine was collected, albuminuria was determined with an enzyme-linked immunosorbent assay (ELISA), and blood glucose concentrations were measured. Kidneys were perfusion-fixed for quantitative morphologic analysis with glutaraldehyde and for immunohistochemical studies with formaldehyde. Glomerular cell number and volume were analyzed. Glomerulosclerosis, tubulointerstitial, and vascular damage indices were semiquantitatively assessed according to standard methodology. Quantitative glomerular parameters (cell numbers and volumes of endothelial, mesangial, and epithelial cells) were measured on semithin sections. Expression of transforming growth factor-beta1 (TGF-beta1), laminin, and collagen type IV were determined by immunohistochemical staining.

RESULTS

In contrast to animals only injected with citrate buffer, mice that received STZ developed hyperglycemia. There was no significant difference in the degree of hyperglycemia among p27(Kip1+/+), p27(Kip1+/-), and p27(Kip1-/-) mice. Diabetic p27(Kip1+/+), but not control p27(Kip1+/+) animals, developed albuminuria. Albuminuria was significantly reduced in diabetic p27(Kip1+/-) and more profoundly in p27(Kip1-/-) animals. Diabetic p27(Kip1+/+) mice revealed a significant increase in mean glomerular volume at 6 weeks. The volumes of mesangial and endothelial cells and podocytes all increased, whereas cell numbers were reduced, consistent with cell hypertrophy. Glomerular, endothelial, mesangial and podocyte hypertrophy were reduced in diabetic p27(Kip1+/-) and p27(Kip1-/-) animals. Diabetic p27(Kip1) (+/+) animals had significantly increased glomerulosclerosis, tubulointerstium, and vascular damage indices compared to nondiabetic p27(Kip1+/+) controls. Diabetic p27(Kip1-/-) mice exhibited significantly less structural damage than diabetic wild-type animals. Diabetic p27(Kip1+/-) animals revealed intermediate glomerulosclerosis, tubulointerstium, and vascular damage values. Immunohistological stainings demonstrated increases in TGF-beta1, collagen type IV, and laminin expression in kidneys of diabetic p27(Kip1+/+) animals compared to nondiabetic p27(Kip1+/+) controls. Staining intensity for type IV collagen and laminin, but not for TGF-beta1, was significantly lower in diabetic p27(Kip1-/-) mice.

CONCLUSION

Deletion of p27(Kip1) attenuates the functional and morphologic features of diabetic nephropathy. Although deletion of p27(Kip1) abolished some parameters of diabetic glomerular hypertrophy, the significant reduction of TGF-beta1 expression in the tubulointerstitium indicates that other protective mechanisms could be operative. The p27(Kip1) gene is haplo-insufficient because diabetic p27(Kip1)+/- mice exhibited an intermediate degree of functional and structural renal injury. Our data shows that p27(Kip1) plays an important role in diabetic nephropathy.

Galectin-9 Inhibits Glomerular Hypertrophy indb/dbDiabetic MiceviaCell-Cycle–Dependent Mechanisms

Galectins are beta-galactoside-binding lectins that are involved in various biologic processes, such as apoptosis, cell proliferation, and cell-cycle regulation. Galectin-9 (Gal-9) was identified previously and demonstrated to have apoptotic potential to thymocytes in mice and activated CD8(+) T cells in nephrotoxic serum nephritis model. In this study, the effect of Gal-9 on G1-phase cell-cycle arrest, one of the hallmark pathologic changes in early diabetic nephropathy, was investigated. Eight-week-old male db/db mice received injections of recombinant Gal-9 or vehicle for 8 wk. The injection of Gal-9 into db/db mice significantly inhibited glomerular hypertrophy and mesangial matrix expansion and reduced urinary albumin excretion. Gal-9 reduced glomerular expression of TGF-beta1 and the number of p27(Kip1)- and p21(Cip1)-positive cells in glomeruli. Double staining with nephrin and type IV collagen revealed that podocytes were mainly positive for p27(Kip1). For further confirming the cell-cycle regulation by Gal-9, conditionally immortalized mouse podocyte cells were cultured under 5.5 and 25 mM d-glucose supplemented with Gal-9. Cell-cycle distribution analyses revealed that Gal-9 maintained further progression of cell cycle from the G1 phase. Gal-9 reversed the high-glucose-mediated upregulation of p27(Kip1) and p21(Cip1) and inhibited cell-cycle-dependent hypertrophy, i.e., reduced [(3)H]proline incorporation. The data suggest that Gal-9 plays a central role in inducing their successful progression from G1 to G2 phase by suppressing glomerular expression of TGF-beta1 and inhibition of cyclin-dependent kinase inhibitors. Gal-9 may give an impetus to develop new therapeutic tools targeted toward diabetic nephropathy.

Prostacyclin signaling in the kidney: implications for health and disease

The balance between vasodilator and vasoconstrictor pathways is key to the maintenance of homeostasis and the outcome of disease. In the kidney, prostaglandins (PGs) uphold this balance and regulate renal function: hemodynamics, renin secretion, growth responses, tubular transport processes, and cell fate. With the advent of cyclooxygenase (COX)-2-selective inhibitors, targeted deletions in mice (COX knockouts, PG receptor knockouts), and the discovery of intracrine signaling options for PGs (peroxisome proliferator-activated receptors and perinuclear PGE2receptors: EP1,3,4), many advances have been made in the study of arachidonic acid metabolites. Although prostacyclin (PGI2) is a major product of the COX pathway, there is very little emphasis on its importance to the kidney. This review will discuss PGI2biology and its relevance to different aspects of renal disease (growth, fibrosis, apoptosis), highlighting the most significant research from the past decade of PGI2literature, what we have learned from other organ systems, while stressing the significance of cross talk between various PGI2signaling pathways and its implications for renal health and disease.

Mechanical stretch induces podocyte hypertrophy in vitro

BACKGROUND

Increased intraglomerular pressure is a final pathway toward glomerulosclerosis in systemic hypertension, diabetes, and focal segmental glomerulosclerosis (FSGS). Increased intraglomerular pressure causes stress-tension, or stretch, on resident glomerular cells. However, the effects of stretch on podocyte growth, and the mechanisms that underlie this, have not been elucidated.

METHODS

To test the hypothesis that stretch alters podocyte growth, cultured mouse podocytes were exposed to cyclic mechanical stretch created by vacuum; control cells were grown under similar conditions, but not exposed to stretch. Proliferation (cell cycle phases) and hypertrophy (forward light scatter) were measured in stretched and control podocytes by flow cytometry. The role of the cyclin-dependent kinase (CDK) inhibitors, p21 and p27, was examined by stretching podocytes isolated from p21 and p27 knockout (-/-) mice, and the role of specific signaling pathways was assessed by Western blot analysis and blocking studies.

RESULTS

Our results showed that stretch reduced cell cycle progression in wild-type and single p27-/- podocytes and induced hypertrophy in these cells in all phases of the cell cycle at 24, 48, and 72 hours. In contrast, stretch did not induce hypertrophy in single p21-/- and double p21/p27-/- podocytes. Stretch-induced hypertrophy required cell cycle entry, and was prevented by specifically blocking extracellular signal-regulated kinase 1/2 (Erk1/2) or Akt. Although stretch increased p38 activation, inhibition of this pathway had no effect on hypertrophy.

CONCLUSION

Mechanical stretch induces hypertrophy in podocytes in vitro in all phases of the cell cycle. This effect is cell cycle dependent, and requires p21, Erk1/2, and Akt. Stretch may play a role in podocyte injury when intraglomerular pressure is increased.

Kallikrein gene transfer reduces renal fibrosis, hypertrophy, and proliferation in DOCA-salt hypertensive rats

In DOCA-salt hypertension, renal kallikrein levels are increased and may play a protective role in renal injury. We investigated the effect of enhanced kallikrein levels on kidney remodeling of DOCA-salt hypertensive rats by systemic delivery of adenovirus containing human tissue kallikrein gene. Recombinant human kallikrein was detected in the urine and serum of rats after gene delivery. Kallikrein gene transfer significantly decreased DOCA- and salt-induced proteinuria, glomerular sclerosis, tubular dilatation, and luminal protein casts. Sirius red staining showed that kallikrein gene transfer reduced renal fibrosis, which was confirmed by decreased collagen I and fibronectin levels. Furthermore, kallikrein gene delivery diminished myofibroblast accumulation in the interstitium of the cortex and medulla, as well as transforming growth factor (TGF)-beta1 immunostaining in glomeruli. Western blot analysis and ELISA verified the decrease in immunoreactive TGF-beta1 levels. Kallikrein gene transfer also significantly reduced kidney weight, glomerular size, proliferating tubular epithelial cells, and macrophages/monocytes. Reduction of proliferation and hypertrophy was associated with reduced levels of the cyclin-dependent kinase inhibitor p27(Kip1), and the phosphorylation of c-Jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). The protective effects of kallikrein were accompanied by increased urinary nitrate/nitrite and cGMP levels, and suppression of superoxide formation. These results indicate that kallikrein protects against mineralocorticoid-induced renal fibrosis glomerular hypertrophy, and renal cell proliferation via inhibition of oxidative stress, JNK/ERK activation, and p27(Kip1) and TGF-beta1 expression.

AGEs activate mesangial TGF-beta-Smad signaling via an angiotensin II type I receptor interaction

BACKGROUND

The renin-angiotensin system (RAS) and the accumulation of advanced glycation end products (AGEs) have been implicated in the pathogenesis of diabetic nephropathy. Whether there is a functional interaction between the RAS and AGEs in diabetic nephropathy is not known. In this study, we investigated whether AGEs could activate autocrine angiotensin II (Ang II) signaling and subsequently induce transforming growth factor-beta (TGF-beta)-Smad signaling in cultured rat mesangial cells.

METHODS

The intracellular formation of reactive oxygen species (ROS) was detected using the fluorescent probe CM-H2DCFDA. Ang II was measured by radioimmunoassay. TGF-beta released into media was quantitatively analyzed in an enzyme-linked immunosorbent assay (ELISA). Smad2, p27(Kip1) (p27), fibronectin, and receptor for AGEs (RAGE) protein expression were determined by Western blot analysis. TGF-beta-inducible promoter activity was analyzed by a luciferase assay. DNA synthesis was evaluated by 5-bomo-2'-deoxyuridine (BrdU) incorporation and de novo protein synthesis was determined by [3H]leucine incorporation.

RESULTS

AGEs increased intracellular ROS generation in mesangial cells, and this effect was significantly inhibited by an antiserum against RAGE. AGEs also were found to stimulate Ang II production in a time- and dose-dependent manner, which was completely prevented by an antioxidant, N-acetylcysteine (NAC). AGE-induced TGF-beta overproduction was completely blocked by candesartan, an Ang II type 1 receptor (AT1R) antagonist. Both candesartan and neutralizing antibody against TGF-beta completely prevented AGEs-induced Smad2 phosphorylation and TGF-beta-inducible promoter activity. Furthermore, AGEs were found to inhibit DNA synthesis and to stimulate de novo protein synthesis and fibronectin production in association with up-regulation of p27. All of these phenomena were completely prevented by candesartan or a polyclonal antibody against TGF-beta.

CONCLUSION

The present study suggests that AGE-RAGE-mediated ROS generation activates TGF-beta-Smad signaling and subsequently induces mesangial cell hypertrophy and fibronectin synthesis by autocrine production of Ang II. This pathway may provide an important link between metabolic and haemodynamic factors in promoting the development and progression of diabetic nephropathy.

Human endothelial nitric oxide synthase gene delivery protects against cardiac remodeling and reduces oxidative stress after myocardial infarction

Nitric oxide (NO) has been shown to play a key role in the regulation of cardiac hypertrophy and fibrosis in response to myocardial ischemia in part by antagonizing the action of angiotensin II (Ang II). In this study, we investigated the potential protective role of human endothelial nitric oxide synthase (eNOS) in left ventricular (LV) remodeling after myocardial infarction (MI) by a somatic gene transfer approach. Male Wistar rats underwent coronary artery ligation to induce MI. One week after surgery, adenovirus encoding the human eNOS or luciferase gene under the control of the CMV promoter/enhancer was injected into rats via the tail vein, and animals were sacrificed at 1 and 5 weeks after gene transfer. Successful gene transfer was evaluated based on increased levels of NO and cGMP in the heart, measured at one week after eNOS gene delivery. Six weeks after MI, the LV end-diastolic pressure, heart weight, LV axis length and cardiomyocyte size were markedly increased compared to the Sham group, while eNOS gene delivery significantly reduced these parameters. Rats receiving control virus developed considerably more fibrotic lesions identified by Sirius Red staining and collagen I immunostaining compared to Sham rats, and eNOS gene delivery significantly reduced collagen accumulation. eNOS gene transfer also reduced TUNEL-positive apoptotic cells. The cardioprotective effect of NO was accompanied by reduced NADH and NADPH oxidase activities and superoxide formation, TGF-beta1 and p27 levels, JNK activation, NF-kappa B nuclear translocation, and caspase-3 activity. This study shows that NO may play an important role in attenuating cardiac remodeling and apoptosis after myocardial infarction via suppression of oxidative stress-mediated signaling pathways.

Role of Mammalian Target of Rapamycin Signaling in Compensatory Renal Hypertrophy

Loss of functioning nephrons stimulates the growth of residual kidney tissue to augment work capacity and maintain normal renal function. This growth largely occurs by hypertrophy rather than from hyperplasia of the remaining nephrons. The signaling mechanisms that increase RNA and protein synthesis during compensatory renal hypertrophy are unknown. This study found that the remaining kidney hypertrophied 42% by 16 d after unilateral nephrectomy (UNX) in DBA/2 mice. Immunoblotting analysis revealed increased phosphorylation of the 40S ribosomal protein S6 (rpS6) and the eukaryotic translation initiation factor (eIF) 4E-binding protein 1 (4E-BP1), the two downstream effectors of the mammalian target of rapamycin (mTOR). The highly specific mTOR inhibitor rapamycin blocked UNX-increased phosphorylation of both rpS6 and 4E-BP1. UNX increased the content of not only 40S and 60S ribosomal subunits but also 80S monosomes and polysomes in the remaining kidney. Administration of rapamycin decreased UNX-induced polysome formation and shifted the polysome profile in the direction of monosomes and ribosomal subunits. Pretreatment of the mice with rapamycin inhibited UNX-induced hypertrophy. These studies demonstrate that activation of the mTOR signaling pathway in the remaining kidney after UNX plays an essential role in modulating RNA and protein synthesis during development of compensatory renal hypertrophy.

ZAK re-programs atrial natriuretic factor expression and induces hypertrophic growth in H9c2 cardiomyoblast cells

Various intracellular or intercellular stimuli have been associated with the development of cardiac cell hypertrophy. However, the mechanisms underlying this association are not completely understood. In a previous study we determined that ZAK mRNA expression is abundant in heart. ZAK is a mitogen-activated protein kinase kinase kinase (MAP3K) that activates the stress-activated protein kinase/c-jun N-terminal kinase pathway and activates NF-kappaB. We, therefore, investigated the potential involvement of ZAK (which in cultured H9c2 cardiomyoblast cell is a positive mediator of cell hypertrophy). Our results showed that the expression of a wild-type form of ZAK induces the characteristic hypertrophic growth features, including increased cell size, elevated atrial natriuretic factor expression, and increased actin fiber organization.

The rapamycin derivative RAD inhibits mesangial cell migration through the CDK-inhibitor p27KIP1

The link between mesangial cell (MC) proliferation and migration during glomerular repair in the experimental mesangial proliferative glomerulonephritis suggests that cell cycle regulation and cell migration require similar pathways, such as cell cycle proteins. The immunosuppressant RAD inhibits mesangial cell (MC) proliferation via G1/S arrest. Moreover, RAD dramatically impairs glomerular healing in the anti-Thy1 model. We tested the hypothesis that RAD alters MC migration in vitro and that this effect was mediated by the CDK-inhibitors p21(CIP1) and p27(KIP1). Using a modified Boyden chamber in vitro migration assay, our results showed that RAD dose dependently (1-50 nM) inhibited fibronectin-induced chemotaxis in wild-type (wt) MC. RAD treatment prevented the decrease in p27(KIP1) induced by mitogenic growth factors, but had no effect on p21(CIP1) by Western blot analysis. The antimigratory effect of RAD in wt MC was substantially dependent on p27(KIP1), but not p21(CIP1), since the inhibitory effects of 1-10 nM RAD on MC migration were similar in p21(CIP1) deficient and wild-type MC. The effect of RAD on MC migration was also examined in the anti-Thy1 model by BrdU-labeling of proliferating MC on day 3 that typically repopulate the glomerulus from the hilus. A control biopsy on day 3 was taken to define the starting point prior to the initiation of RAD (3 mg/kg or placebo). MC migration was determined on day 7 by measuring the distances of BrdU-labeled MC (OX-7+/BrdU+cells) from the glomerular hilus using computerized morphometry. RAD significantly reduced the migratory response of BrdU-labeled MC compared to controls. We conclude that the immunosuppressant RAD effectively inhibits MC migration in vivo and in vitro thereby limiting the normal glomerular repair process after severe injury. Moreover, RAD-induced inhibition of MC migration in vitro is partially mediated by the CDK-inhibitor p27(KIP1), but not p21(CIP1).

Angiotensin II and Cell Cycle Regulation

Angiotensin II has emerged as an important growth factor for vascular, cardiac, and renal cells. Depending on the specific cell type and presence of other growth factors, angiotensin II induces proliferation (replication of DNA with subsequent successful division of cells), hypertrophy (increase in cell size, cell protein, and mRNA content without DNA replication), apoptosis (programmed cell death), or differentiation. Such angiotensin II-mediated modulation of growth process may underlie various pathophysiological processes such as atherosclerosis, vascular and cardiac remodeling, and progression of chronic renal disease. Clearly, angiotensin II-induced proliferation requires complete cell progression through the various steps of the cell cycle. In contrast, cells undergoing angiotensin II-mediated hypertrophy are arrested in the G1-phase. Upregulation of cell cycle-dependent kinase inhibitors (eg, p27Kip1) plays an important role in this process. Although accumulating evidence suggests that apoptosis is cell cycle-dependent, only few data are currently available concerning the interaction of angiotensin II with the cell cycle machinery in apoptosis. We review the various angiotensin II-mediated growth processes and their relationship to events governing cell cycle regulation.

Lipoxins inhibit Akt/PKB activation and cell cycle progression in human mesangial cells

Lipoxins (LX) are endogenously produced eicosanoids with a spectrum of bioactions that suggest anti-inflammatory, pro-resolution roles for these agents. Mesangial cell (MC) proliferation plays a pivotal role in the pathophysiology of glomerular inflammation and is coupled to sclerosis and tubulointerstitial fibrosis. We have previously reported that LXA4 acts through a specific G-protein-coupled-receptor (GPCR) to modulate MC proliferation in response to the proinflammatory mediators LTD4 and platelet-derived growth factor (PDGF). Further investigations revealed that these effects were mediated by modulation of receptor tyrosine kinase activity. Here we have explored the underlying mechanisms and report inhibition of growth factor (PDGF; epithelial growth factor) activation of Akt/PKB by LXA4. LXA4 (10 nmol/L) modulates PDGF-induced (10 ng/ml, 24 hours) decrements in the levels of cyclin kinase inhibitors p21Cip1 and p27Kip1. PDGF-induced increases in CDK2-cyclin E complex formation are also inhibited by LXA4. The potential of LXA4 as an anti-inflammatory therapeutic is compromised by its degradation; this has been circumvented by synthesis of stable analogs. We report that 15-(R/S)-methyl-LXA4 and 16-phenoxy-LXA4 mimic the native compound with respect to modulation of cell proliferation and PDGF-induced changes in cell cycle proteins. In vivo, MC proliferation in response to PDGF is associated with TGFbeta1 production and the subsequent development of renal fibrosis. Here we demonstrate that prolonged (24 to 48 hours) exposure to PDGF is associated with autocrine TGFbeta1 production, which is significantly reduced by LXA4. In aggregate these data demonstrate that LX inhibit PDGF stimulated proliferation via modulation of the PI-3-kinase pathway preventing mitogen-elicited G1-S phase progression and suggest the therapeutic potential of LX as anti-fibrotic agents.