Activation of cyclin D1-Cdk4 and Cdk4-directed phosphorylation of RB protein in diabetic mesangial hypertrophy

Regulatory Mechanisms That Guide the Fetal to Postnatal Transition of Cardiomyocytes

Heart disease remains a global leading cause of death and disability, necessitating a comprehensive understanding of the heart's development, repair, and dysfunction. This review surveys recent discoveries that explore the developmental transition of proliferative fetal cardiomyocytes into hypertrophic postnatal cardiomyocytes, a process yet to be well-defined. This transition is key to the heart's growth and has promising therapeutic potential, particularly for congenital or acquired heart damage, such as myocardial infarctions. Although significant progress has been made, much work is needed to unravel the complex interplay of signaling pathways that regulate cardiomyocyte proliferation and hypertrophy. This review provides a detailed perspective for future research directions aimed at the potential therapeutic harnessing of the perinatal heart transitions.

PFKFB3 mediates tubular cell death in cisplatin nephrotoxicity by activating CDK4

Nephrotoxicity is a major side effect of cisplatin, a widely used cancer therapy drug. However, the mechanism of cisplatin nephrotoxicity remains unclear and no effective kidney protective strategies are available. Here, we report the induction of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) in both in vitro cell culture and in vivo mouse models of cisplatin nephrotoxicity. Notably, PFKFB3 was mainly induced in the nucleus of kidney tubular cells, suggesting a novel function other than its canonical role in glycolysis. Both pharmacological inhibition and genetic silencing of PFKFB3 led to the suppression of cisplatin-induced apoptosis in cultured renal proximal tubular cells (RPTCs). Moreover, cisplatin-induced kidney injury or nephrotoxicity was ameliorated in renal proximal tubule-specific PFKFB3 knockout mice. Mechanistically, we demonstrated the interaction of PFKFB3 with cyclin-dependent kinase 4 (CDK4) during cisplatin treatment, resulting in CDK4 activation and consequent phosphorylation and inactivation of retinoblastoma tumor suppressor (Rb). Inhibition of CDK4 reduced cisplatin-induced apoptosis in RPTCs and kidney injury in mice. Collectively, this study unveils a novel pathological role of PFKFB3 in cisplatin nephrotoxicity through the activation of the CDK4/Rb pathway, suggesting a new kidney protective strategy for cancer patients by blocking PFKFB3.

Iso-suillin-induced DNA damage leading to cell cycle arrest and apoptosis arised from p53 phosphorylation in A549 cells

Extensive investigations have revealed that iso-suillin, a secondary metabolite isolated from Suillus flavus, could induce cell cycle arrest and apoptosis in human chronic myeloid leukemia K562 cells, human hepatocellular carcinoma SMMC-7721 cell line, and human small cell lung cancer H446 cell line in vitro. In the present study, human lung cancer A549 cells were used to reveal the mechanism of iso-suillin's effects on lung adenocarcinoma, which were detected both in vitro and in vivo. Results showed that iso-suillin potently inhibited A549 cell proliferation through an early G₁ arrest. Iso-suillin also induced A549 cell apoptosis in vitro. Phosphorylation of p53 at serines 15 and 20 may be one of the pivotal factors for cell cycle arrest and apoptosis after treatment of iso-suillin in A549 cells. Moreover, in an A549 xenograft model, tumor growth and progression could be inhibited by iso-suillin. Body weight change and some vital organs toxicity was also roughly examined, no significant toxic effects of iso-suillin were shown (at a dose of 5 mg/kg for each administration). The in vitro and in vivo anti-tumor effects implied that iso-suillin may act as a tumor growth inhibitor, and its induction of p53 phosphorylation is pivotal for cell cycle arrest and apoptosis in A549 cells.

The multifaceted role of cell cycle regulators in the coordination of growth and metabolism

Adapting to changes in nutrient availability and environmental conditions is a fundamental property of cells. This adaptation requires a multi‐directional coordination between metabolism, growth, and the cell cycle regulators (consisting of the family of cyclin‐dependent kinases (CDKs), their regulatory subunits known as cyclins, CDK inhibitors, the retinoblastoma family members, and the E2F transcription factors). Deciphering the mechanisms accountable for this coordination is crucial for understanding various patho‐physiological processes. While it is well established that metabolism and growth affect cell division, this review will focus on recent observations that demonstrate how cell cycle regulators coordinate metabolism, cell cycle progression, and growth. We will discuss how the cell cycle regulators directly regulate metabolic enzymes and pathways and summarize their involvement in the endolysosomal pathway and in the functions and dynamics of mitochondria.

Prognostic significance and biological function of Lamina-associated polypeptide 2 in non-small-cell lung cancer

Purpose: Lamina-associated polypeptide 2 (LAP2; encoded by TMPO), is a nuclear protein that may affect chromatin regulation and gene expression through dynamically binding to nuclear lamin. TMPO (LAP2) plays dual roles of either suppressing or promoting proliferation of cells, depending on the status of the cell. It has been reported that TMPO is up-regulated in various cancer types. However, its function in lung cancer has not been studied yet.

Materials and methods: A series of clinical microarray datasets for lung cancer were investigated to demonstrate the expression of TMPO. The transcription of TMPO gene in human lung cancer was analyzed using Oncomine platform (www.oncomine.org) according to the standardized procedures described previously. Four separate datasets (Hou Lung, Okayama Lung, Beer Lung, and Garber Lung) were analyzed.

Results: Here, we show that TMPO is over-expressed in lung cancer tissues, and that a high level of TMPO indicates a poor prognosis in lung cancer patients. Knockdown of TMPO in lung cancer cells inhibits cell proliferation and induces apoptosis. Also, down-regulation of TMPO leads to an impaired metastatic ability of tumor cells. A nude mice tumor model show that knockdown of TMPO suppresses tumor formation in vivo.

Conclusion: Collectively, this study suggests TMPO as an oncogene and a novel prognostic gene in lung cancer.

MicroRNA-610 suppresses the proliferation of human glioblastoma cells by repressing CCND2 and AKT3

Previous studies have shown that microRNA (miR)-610 is crucial in a variety of biological processes in various types of human cancer cells. However, the role of this microRNA in glioblastoma (GBM) is presently unclear. In this study, the role of miR-610 in cell proliferation was investigated in GBM. It was demonstrated that miR-610 expression is markedly downregulated in GBM cells and GBM tissues compared with normal human astrocytes (NHAs) and normal brain tissue, respectively. Ectopic expression of miR-610 reduced the proliferation and anchorage-independent growth of GBM cells, whereas inhibition of miR-610 promoted this effect. Bioinformatics analysis further revealed cyclin D2 (CCND2) and AKT3, putative tumor promoters, as potential targets of miR-610. Data from reporter assays showed that miR-610 directly binds to the 3′-untranslated region of CCND2 and AKT3 mRNA, and represses their expression at the transcriptional and translational levels. In conclusion, the data provide compelling evidence that miR-610 functions as an anti-onco-miRNA, which is important in inhibiting cell proliferation in GBM, and its anti-oncogenic effects are mediated chiefly through direct suppression of CCND2 and AKT3 expression.

Reduction in maternal circulating ouabain impairs offspring growth and kidney development

Ouabain, a steroid present in the circulation and in various tissues, was shown to affect the growth and viability of various cells in culture. To test for the possible influence of this steroid on growth and viability in vivo, we investigated the involvement of maternal circulating ouabain in the regulation of fetal growth and organ development. We show that intraperitoneal administration of anti-ouabain antibodies to pregnant mice resulted in a >80% decline in the circulating ouabain level. This reduction caused a significant decrease in offspring body weight, accompanied by enlargement of the offspring heart and inhibition of kidney and liver growth. Kidney growth inhibition was manifested by a decrease in the size and number of nephrons. After the reduction in maternal circulating ouabain, kidney expression of cyclin D1 was reduced and the expression of the α1 isoform of the Na(+), K(+)-ATPase was increased. In addition, the elevation of proliferation signals including ERK1/2, p-90RSK, Akt, PCNA, and Ki-67, and a reduction in apoptotic factors such as Bax, caspase-3, and TUNEL were detected. During human pregnancy, the circulating maternal ouabain level increased and the highest concentration of the steroid was found in the placenta. Furthermore, circulating ouabain levels in women with small-for-gestational age neonates were significantly lower than the levels in women with normal-for-gestational age newborns. These results support the notion that ouabain is a growth factor and suggest that a reduction in the concentration of this hormone during pregnancy may increase the risk of impaired growth and kidney development.

The heart: mostly postmitotic or mostly premitotic? Myocyte cell cycle, senescence, and quiescence

The concept of myocyte division and myocyte-mediated regeneration has re-emerged in the past 5 years through development of sophisticated transgenic mice and carbon-dating of cells. Although recently, a couple of studies have been conducted as an attempt to intervene in myocyte division, the efficiency in adult animals remains discouragingly low. Re-enforcing myocyte division is a vision that has been desired for decades, leading to years of experience in myocyte resistance to proproliferative stimuli. Previous attempts have indeed provided a platform for basic knowledge on molecular players and signalling in myocytes. However, natural biological processes such as hypertrophy and binucleation provide layers of complexity in interpretation of previous and current findings. A major hurdle in mediating myocyte division is a lack of insight in the myocyte cell cycle. To date, no knowledge is gained on myoycte cell cycle progression and/or duration. This review will include an overview of previous and current literature on myocyte cell cycle and division. Furthermore, the limitations of current approaches and basic questions that might be essential in understanding myocardial resistance to division will be discussed.

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.

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 multiple connections between pRB and cell metabolism

The pRB tumor suppressor is traditionally seen as an important regulator of the cell cycle. pRB represses the transcriptional activation of a diverse set of genes by the E2F transcription factors and prevents inappropriate S-phase entry. Advances in our understanding of pRB have documented roles that extend beyond the cell cycle and this review summarizes recent studies that link pRB to the control of cell metabolism. pRB has been shown to regulate glucose tolerance, mitogenesis, glutathione synthesis, and the expression of genes involved in central carbon metabolism. Several studies have demonstrated that pRB directly targets a set of genes that are crucial for nucleotide metabolism, and this seems likely to represent one of the ways by which pRB influences the G1/S-phase transition and S-phase progression.

Aldose reductase regulates vascular smooth muscle cell proliferation by modulating G1/S phase transition of cell cycle

Abnormal proliferation of vascular smooth muscle cells (VSMC) is a key feature of development of cardiovascular complications, atherosclerosis, and restenosis. Patients with diabetes have higher risk for restenosis after coronary angioplasty than nondiabetic patients due to hyperglycemia-induced release of cytokines such as TNF-alpha. However, the molecular mechanisms regulating VSMC proliferation remain unclear. Herein, we report that inhibition of the polyol pathway enzyme aldose reductase (AR) prevents high glucose (HG)- and/or TNF-alpha-induced VSMC proliferation by accumulating cells at the G1 phase of the cell cycle. Treatment of VSMC with AR inhibitor sorbinil prevented HG- as well as TNF-alpha-induced phosphorylation of retinoblastoma protein and activation of E2F-1. Inhibition of AR also prevented HG- and TNF-alpha-induced phosphorylation of cyclin-dependent kinase (cdk)-2 and expression of G1/S transition regulatory proteins such as cyclin D1, cyclin E, cdk-4, c-myc, and proliferative cell nuclear antigen. More importantly, inhibition of AR prevented the increased expression of E2F-1 and proliferative cell nuclear antigen in diabetic rat aorta. Treatment of VSMC with the most abundant and toxic lipid aldehyde 4-hydroxy-trans-2-nonenal (HNE) or its glutathione conjugate [glutathionyl (GS)-HNE] or AR-catalyzed product of GS-HNE, GS-1,4-dihydroxynonane, resulted in increased E2F-1 expression. Inhibition of AR prevented HNE- or GS-HNE-induced but not GS-1,4-dihydroxynonane-induced up-regulation of E2F-1. Collectively, these results show that AR could regulate HG- and TNF-alpha-induced VSMC proliferation by altering the activation of G1/S-phase proteins such as E2F-1, cdks, and cyclins. Thus, inhibition of AR may be a useful therapeutic approach in preventing vascular complications.

Regulation of mRNA translation in renal physiology and disease

Translation, a process of generating a peptide from the codons present in messenger RNA, can be a site of independent regulation of protein synthesis; it has not been well studied in the kidney. Translation occurs in three stages (initiation, elongation, and termination), each with its own set of regulatory factors. Mechanisms controlling translation include small inhibitory RNAs such as microRNAs, binding proteins, and signaling reactions. Role of translation in renal injury in diabetes, endoplasmic reticulum stress, acute kidney injury, and, in physiological adaptation to loss of nephrons is reviewed here. Contribution of mRNA translation to physiology and disease is not well understood. Because it is involved in such diverse areas as development and cancer, it should prove a fertile field for investigation in renal science.

IGF-1 increases laminin, cyclin D1, and p21Cip1 expression in glomerular mesangial cells: an investigation of the intracellular signaling pathway and cell-cycle progression

Insulin-like growth factor (IGF)-1 is accumulated in the diabetic kidney and is considered to be involved in the development of glomerular sclerosis. Here, we investigate IGF-1 regulation of laminin, an extracellular matrix (ECM) component, and cyclin D1 and p21Cip1, cell-cycle progression factor, expressions in glomerular mesangial cells. We show that IGF-1 increases the level of laminin gamma1 and beta1 subunits approximately 1.5- and 2.5-fold, respectively, in a time-dependent manner. IGF-1 also stimulates protein kinase Akt/PKB phosphorylation at Thr 308, which correlates with its activity, up to 24 h. The Akt activation is coupled with Ser 9 phosphorylation of its downstream target, glycogen synthase kinase-3beta (GSK-3beta), which inhibits its kinase activity. Laminin beta1 is reduced significantly (P < 0.03) by inhibitors of Akt and p38MAPK whereas laminin gamma1 is not affected. Surprisingly, IGF-1 activates the expression of both cyclin D1 and cell-cycle arrest factor, p21Cip1 parallely. Pharmacological inhibition of calcineurin by cyclosporin A blocks IGF-1-induced cyclin D1 and p21Cip1expression significantly (P < 0.05). IGF-1 enhances cellular metabolic activity and viability of rat mesangial cells; however, they are arrested at the G1 phase of cell cycle as revealed by the FACS analysis. These results indicate that IGF-1 mediates mesangial cell-cycle progression, hypertrophy, and ECM protein synthesis. The Akt/GSK-3beta, p38MAPK, and calcineurin pathways may play an important role in IGF-1 signaling, cell-cycle regulation, and matrix gene expression in mesangial cells leading to the development of diabetic glomerulopathy.

Acute renal failure during sepsis: potential role of cell cycle regulation

OBJECTIVES

This study aimed to evaluate cell cycle regulation in acute kidney injury after intraperitoneal sepsis in rats.

METHODS

Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in rats. At 0, 6, 12, 24, 48, and 72 h after CLP, serum creatinine was evaluated. DNA content of isolated kidney cells was analyzed using flow cytometer. Furthermore, the expression of p21, p53, cyclin D1, cyclin E, CDK2, CDK4 and P-pRb was also measured by western blot.

RESULTS

After sepsis-induced by CLP, kidney injury of rat was associated with G1 cell cycle arrest, however, recovery of renal function related to cell cycle progression 48h after CLP. Results also showed that the upregulation of p53 and p21 was correlated with G1 cell arrest in 48h after CLP. Nevertheless, upregulation of cyclin D1/CDK4 and cyclin E/CDK2 induced pRb phosphorylation, which resulted in the G1/S transition 48 h after CLP.

CONCLUSION

The data suggest that G1 cell cycle arrest may play a role in the initiation of kidney injury, whereas, through regulating cell cycle, p53, p21, CDKs, cyclins and P-pRb may be involved in the injury or recovery of renal function after intraperitoneal sepsis.

Soluble and insoluble nickel compounds exert a differential inhibitory effect on cell growth through IKKalpha-dependent cyclin D1 down-regulation

It is well-known that insoluble nickel compounds possess much more potent carcinogenic activities as compared with soluble nickel compounds. Although it is assumed that the different entry and clearance rate are responsible for the difference, the mechanisms underlying the different carcinogenic activities are still not well understood yet. In the present study, we found that exposure to soluble, but not insoluble nickel compounds, caused a significant inhibition of cell growth and G1/G0 cell cycle arrest, which was concomitant with a marked down-regulation of cylin D1, an essential nuclear protein for controlling G1/S transition, while both soluble and insoluble nickel compounds showed similar effects on NFkappaB activation, HIF-1alpha protein accumulation and TNF-alpha transcription and CAP43 protein expression at same doses range. The down-regulation of cyclin D1 is due to protein degradation rather than inhibition of transcription, because the nickel compounds treatment did not change cyclin D1 mRNA level, while MG132, the proteasome inhibitor, can rescue the degradation of cyclin D1 caused by soluble nickel compound. Moreover, the soluble nickel-induced cyclin D1 degradation is dependent on its Thr286 residue and requires IKKalpha, but not HIF-1alpha, which are both reported to be involved in cyclin D1 down-regulation. Taken together, we demonstrate that soluble, but not insoluble nickel compound, is able to cause cyclin D1 degradation and a cell growth arrest in an IKKalpha-dependent manner. Given the role of cyclin D1 and cell proliferation in carcinogenesis, we anticipate that the different effects of soluble and insoluble nickel compounds on cyclin D1 degradation and cell growth arrest may at least partially account for their different carcinogenic activities.

PPAR-alpha agonist fenofibrate induces renal CYP enzymes and reduces blood pressure and glomerular hypertrophy in Zucker diabetic fatty rats

We have previously shown that fenofibrate, a peroxisome proliferator-activated receptor-alpha activator, increases renal cytochrome P450 (CYP)-derived eicosanoids and improves endothelial function in pre-diabetic obese rats. The present study was designed to explore the efficacy of fenofibrate on blood pressure and renal injury in the advanced stage of type-2 diabetes. 26-week-old male Zucker diabetic fatty rats (ZDF) were fed fenofibrate (100 mg/kg/day) for 6 weeks. Chronic treatment with fenofibrate normalized systolic blood pressure and reduced glomerular size by 19% in diabetic rats. Western blot and fluorescent immunostaining revealed that the over-expression of collagen type IV and alpha-smooth muscle actin was significantly attenuated in the kidney of fenofibrate-treated ZDF (F-ZDF) rats. In addition, fenofibrate administration dramatically decreased the cyclin D1 protein level in the kidney of diabetic rats. In contrast, renal CYP2C23 and CYP4A proteins were significantly increased in F-ZDF rats. These fenofibrate effects were observed in the absence of significant changes in glucose, insulin or lipid levels. Taken together, our results demonstrate that fenofibrate may lower blood pressure and attenuate glomerular hypertrophy and collagen accumulation through the downregulation of cyclin D1 and upregulation of CYP monooxygenases in the late stage of type-2 diabetes.

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.

Enhanced cell cycle entry and mitogen-activated protein kinase-signaling and downregulation of matrix metalloproteinase-1 and -3 in human diabetic arterial vasculature

Diabetic patients have a strong predilection for atherosclerosis and postangioplasty restenosis. Accelerated cell proliferation and excessive extracellular matrix deposition are believed to contribute to the development of atherosclerotic plaques and neointima. We investigated the effect of diabetes on cell cycle, proliferation signaling, and the activation of matrix metalloproteinases (MMPs). Segments of internal mammary arteries from 26 type 2 diabetic and 26 non-diabetic patients undergoing coronary artery bypass grafting surgery were compared. Increased levels of cyclin D1 mRNA (by 135+/-14%) and protein expression (by 93.8+/-7.0%), retinoblastoma protein phosphorylation (by 45.9+/-4.8%), and beta-catenin nuclear localization (by 176+/-16%) indicated the enhanced cell cycle entry in the diabetic arteries. Diabetes increased phosphorylation of extracellular signal-regulated kinase-1/2 and p-38-mitogen-activated protein kinase (MAPK) by 76.0+/-6.8 and 62.3+/-4.3%. Increased collagen deposition was evidenced in the diabetic arteries. mRNA levels of MMP-1 and MMP-3 were decreased in the diabetic tissue to 55 and 82%, respectively, compared to the non-diabetic group; protein levels were also decreased accompanied with decreased enzymatic activities by 21 and 50%, respectively. In conclusion, enhanced cell cycle entry, increased MAPK signaling, and downregulated MMP-1 and MMP-3 were characteristic of diabetic arterial vasculature, and could contribute to the progressive atherosclerosis and postangioplasty restenosis in diabetic patients.

A role for AMP-activated protein kinase in diabetes-induced renal hypertrophy

We tested the hypothesis that AMP-activated protein kinase (AMPK), an energy sensor, regulates diabetes-induced renal hypertrophy. In kidney glomerular epithelial cells, high glucose (30 mM), but not equimolar mannitol, stimulated de novo protein synthesis and induced hypertrophy in association with increased phosphorylation of eukaryotic initiation factor 4E binding protein 1 and decreased phosphorylation of eukaryotic elongation factor 2, regulatory events in mRNA translation. These high-glucose-induced changes in protein synthesis were phosphatidylinositol 3-kinase, Akt, and mammalian target of rapamycin (mTOR) dependent and transforming growth factor-beta independent. High glucose reduced AMPK alpha-subunit theronine (Thr) 172 phosphorylation, which required Akt activation. Changes in AMP and ATP content could not fully account for high-glucose-induced reductions in AMPK phosphorylation. Metformin and 5-aminoimidazole-4-carboxamide-1beta-riboside (AICAR) increased AMPK phosphorylation, inhibited high-glucose stimulation of protein synthesis, and prevented high-glucose-induced changes in phosphorylation of 4E binding protein 1 and eukaryotic elongation factor 2. Expression of kinase-inactive AMPK further increased high-glucose-induced protein synthesis. Renal hypertrophy in rats with Type 1 diabetes was associated with reduction in AMPK phosphorylation and increased mTOR activity. In diabetic rats, metformin and AICAR increased renal AMPK phosphorylation, reversed mTOR activation, and inhibited renal hypertrophy, without affecting hyperglycemia. AMPK is a newly identified regulator of renal hypertrophy in diabetes.

mRNA translation: unexplored territory in renal science

Ambient protein levels are under coordinated control of transcription, mRNA translation, and degradation. Whereas transcription and degradation mechanisms have been studied in depth in renal science, the role of mRNA translation, the process by which peptide synthesis occurs according to the genetic code that is present in the mRNA, has not received much attention. mRNA translation occurs in three phases: Initiation, elongation, and termination. Each phase is controlled by unique eukaryotic factors. In the initiation phase, mRNA and ribosomal subunits are brought together. During the elongation phase, amino acids are added to the nascent peptide chain in accordance with codon sequences in the mRNA. During the termination phase, the fully synthesized peptide is released from the ribosome for posttranslational processing. Signaling pathways figure prominently in regulation of mRNA translation, particularly the phosphatidylinositol 3 kinase-Akt-mammalian target of rapamycin pathway, the AMP-activated protein kinase-tuberous sclerosis complex protein 1/tuberous sclerosis complex protein 2-Rheb pathway, and the extracellular signal-regulated kinase 1/2 type mitogen-activated protein kinase signaling pathway; there is significant cross-talk among these pathways. Regulation by mRNA translation is suggested when changes in mRNA and protein levels do not correlate and in the setting of rapid protein synthesis. Ongoing work suggests an important role for mRNA translation in compensatory renal growth, hypertrophy and extracellular matrix synthesis in diabetic nephropathy, growth factor synthesis by kidney cells, and glomerulonephritis. Considering that mRNA translation plays an important role in cell growth, development, malignancy, apoptosis, and response to stress, its study should provide novel insights in renal physiology and pathology.

Preplaced cell division: a critical mechanism of autoprotection againstS-1,2-dichlorovinyl-l-cysteine-induced acute renal failure and death in mice

Previous studies have shown that renal injury initiated by a lethal dose of S-1,2-dichlorovinyl-l-cysteine (DCVC) progresses due to inhibition of cell division and hence renal repair, leading to acute renal failure (ARF) and death in mice. Renal injury initiated by low to moderate doses of DCVC is repaired by timely and adequate stimulation of renal cell division, tubular repair, restoration of renal structure and function leading to survival of mice. Recent studies have established that mice primed with a low dose of DCVC (15 mg/kg ip) 72 h before administration of a normally lethal dose (75 mg/kg ip) are protected from ARF and death (nephro-autoprotection). We showed that renal cell division and tissue repair stimulated by the low dose are sustained even after the lethal dose administration resulting in survival from ARF and death. If renal cell division induced by the low dose is indeed the critical mechanism of this autoprotection, then its ablation by the antimitotic agent colchicine (1.5 mg CLC/kg ip) should abolish autoprotection. The present interventional experiments were designed to test the hypothesis that DCVC autoprotection is due to stimulated cell division and tissue repair by the priming low dose. CLC intervention at 42 and 66 h after the priming dose resulted in marked progressive elevation of plasma blood urea nitrogen and creatinine resulting in ARF and death of mice. Light microscopic examination of hematoxylin and eosin-stained kidney sections revealed progression of renal necrosis concordant with progressively failing renal function. With CLC intervention, S-phase stimulation (as assessed by BrdU pulse labeling), G1-to-S phase clearance, and cell division were diminished essentially abolishing the promitogenic effect of the priming low dose of DCVC. Phospho-retinoblastoma protein (P-pRB), a crucial protein for S-phase stimulation, and other cellular signaling mechanisms regulating P-pRB were investigated. We report that decreased P-pRB via activation of protein phosphatase-1 by CLC is the critical mechanism of this inhibited S-phase stimulation and ablation of autoprotection with CLC intervention. These findings lend additional support to the notion that stimulated cell division and renal tissue repair by the priming dose of DCVC are the critical mechanisms that allow sustained compensatory tissue repair and survival of mice in nephro-autoprotection.

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.

Transforming growth factor-β1 regulation of laminin γ1 and fibronectin expression and survival of mouse mesangial cells

The transforming growth factor-beta (TGF-beta) 1 is a mediator of extracellular matrix (ECM) gene expression in mesangial cells and the development of diabetic glomerulopathy. Here, we investigate the effects of TGF-beta1 on laminin gamma1 and fibronectin polypeptide expression and cell survival in mouse mesangial cells (MES-13). TGF-beta1 (10 ng/ml) stimulates laminin-gamma1 and fibronectin expression approximately two-fold in a time-dependent manner (0-48 h). TGF-beta1 treatment also retards laminin-gamma1 mobility on SDS-gels, and tunicamycin, an inhibitor of the N-linked glycosylation, blocks the mobility shift. TGF-beta1 increases the binding of laminin gamma1 to WGA-agarose and the binding is abolished by tunicamycin suggesting that laminin gamma1 is modified by N-linked glycosylation. TGF-beta1 also elevates fibronectin glycosylation but its mobility is not altered. The degradation of laminin gamma1 and fibronectin proteins is reduced by their glycosylation. In addition, TGF-beta1 enhances mesangial cell viability and metabolic activities initially (0-24 h); however, eventually leads to cell death (24-48 h). TGF-beta1 elevates pro-apoptotic caspase-3 activity and decrease cell cycle progression factor cyclin D1 expression, which parallels cell death. These results indicate that TGF-beta1 plays an important role in ECM expression, protein glycosylation and demise of mesangial cells in the diabetic glomerular mesangium.

Molecular mechanisms of enhanced renal cell division in protection againstS-1,2-dichlorovinyl-l-cysteine-induced acute renal failure and death

Sustained activation of ERK 1/2 by a low dose (15 mg/kg ip) of S-1,2-dichlorovinyl-l-cysteine (DCVC) 72 h before administration of a lethal dose of DCVC (75 mg/kg ip) enhances renal cell division and protects mice against acute renal failure (ARF) and death (autoprotection). The objective of this study was to determine correlation among extent of S-phase DNA synthesis, activation of transcription factors, expression of G1/S cyclins, cyclin-dependent kinases (CDKs), and CDK inhibitors downstream of ERK 1/2 following DCVC-induced ARF in autoprotection. Administration of the lethal dose alone caused a general downregulation or an unsustainable increase, in transcriptional and posttranscriptional events thereby preventing G1-S transition of renal cell cycle. Phosphorylation of IκBα was inhibited resulting in limited nuclear translocation of NF-κB. However, cyclin D1 expression was high probably due to transcriptional cooperation of AP-1. Cyclin D1/cyclin-dependent kinase 4 (cdk4)-cdk6 system-mediated phosphorylation of retinoblastoma protein was downregulated due to overexpression of p16 at 24 h after exposure to the lethal dose alone. Inhibition of S-phase stimulation was confirmed by proliferating cell nuclear antigen assay (PCNA). This inhibitory response was prevented if the lethal dose was administered 72 h after the low priming dose of DCVC due to promitogenic effect of the low dose. NF-κB-DNA binding is not limited if mice were pretreated with the priming dose. Cyclin D1/cdk4-cdk6 expression stimulated by the priming dose of DCVC was unaltered even after the lethal dose in the autoprotected group, explaining higher phosphorylated-pRB and S-phase stimulation found in this group. These results were corroborated with PCNA immunohistochemistry. These findings suggest that the priming dose relieves the block on compensatory tissue repair by upregulation of promitogenic mechanisms, normally blocked by the high dose when administered without the prior priming dose.

Validation of internal control genes for gene expression analysis in diabetic glomerulosclerosis

BACKGROUND

Gene expression analysis is an invaluable tool in the study of diabetic glomerulosclerosis. The necessary denominator for the quantitative expression of a specific gene is the expression level of a second gene that is presumed to remain unchanged. Thus, it is critical that the stability of this housekeeping gene in diabetic glomeruli or in cultured glomerular cells is not altered by the disease or a high glucose environment, respectively. Although gene expression quantification, achieved by Northern blot analysis or real-time reverse transcription-polymerase chain reaction (RT-PCR) has been extensively applied in diabetic renal tissue in vivo and in vitro, there are no studies validating the use of any specific endogenous control gene in these measurements.

METHODS

We performed real-time RT-PCR using RNA from microdissected diabetic glomeruli and from mesangial cells cultured in high glucose concentration to investigate gene expression stability of beta-actin, glyceraldehyde-3-phosphate dehydrogenase (GADPH), phospholipase A2, beta2-microglobulin, acidic ribosomal protein 36B4, and cyclophilin A.

RESULTS

Using an analysis method which is independent of gene abundance and compares the pair-wise variation of a given housekeeping gene with all other control genes, beta-actin and phospholipase A2, were found to be the most stable genes in diabetic glomeruli and in primary mesangial cells exposed to 20 mmol/L glucose.

CONCLUSION

It is proposed that the expression level of these genes is the best reference to evaluate relative changes in gene activity in diabetic/high glucose exposed glomerular tissues.

Bimodal Effect of Advanced Glycation End Products on Mesangial Cell Proliferation Is Mediated by Neutral Ceramidase Regulation and Endogenous Sphingolipids

Advanced glycation end-products (AGE) are generated by chronic hyperglycaemia and may cause diabetic microvascular complications such as diabetic nephropathy. Many factors influence the development of diabetic nephropathy; however, dysregulation of mesangial cell (MC) proliferation appears to play an early and crucial role. In this study, we investigated the effects of AGE on rat MC proliferation and the involvement of sphingolipids in the AGE response. Results show a bimodal effect of AGE on MC proliferation. Thus, low AGE concentrations (<1 microm) induced a significant increase (+26%) of MC proliferation, whereas higher concentrations (10 microm) markedly reduced it (-24%). In parallel, AGE exerted biphasic effects on neutral ceramidase expression and activity. Low AGE concentrations increased neutral ceramidase activity and expression, whereas high AGE concentrations showed opposite effects. Surprisingly, neutral ceramidase modulation did not result in changes of ceramide levels. However, the AGE (10 microm)-inhibitory effect on MC proliferation was associated with accumulation of sphingosine and was specifically prevented by blocking glucosylceramide synthesis, suggesting that the high AGE concentration effects are mediated by sphingosine and/or glycolipids. On the other hand, treatment of cells with low AGE concentrations led to an increase of sphingosine kinase activity and sphingosine-1-phosphate production that drove the increase of MC proliferation. Interestingly, in glomeruli isolated from streptozotocin-diabetic rats, a time-dependent modulation of ceramidase activity was observed as compared with controls. These results suggest that AGE regulate MC growth by modulating neutral ceramidase and endogenous sphingolipids.

RAGE‐ and TGF‐ β receptor‐mediated signals converge on STAT5 and p21wafto control cell‐cycle progression of mesangial cells: a possible role in the development and progression of diabetic nephropathy

The molecular events associated with acute and chronic exposure of mesangial cells (MC) to hyperglycemia were evaluated. We found that, unlike high glucose (HG) and Amadori adducts, advanced glycation end products (AGE) and transforming growth factor-beta (TGF-beta) induced p21waf expression and accumulation of MC in G0/G1. TGF-beta1 blockade inhibited AGE-mediated collagen production but only partially affected AGE-induced p21waf expression and cell-cycle events, indicating that AGE by binding to AGE receptor (RAGE) per se could control MC growth. Moreover, AGE and TGF-beta treatment led to the activation of the signal transduction and activators of transcription (STAT)5 and the formation of a STAT5/p21SIE2 complex. The role of STAT5 in AGE- and TGF-beta-mediated p21waf expression and growth arrest, but not collagen production, was confirmed by the expression of the dominant negative STAT5 (DeltaSTAT5) or the constitutively activated STAT5 (1*6-STAT5) constructs. Finally, in p21waf-/- fibroblasts both AGE and TGF-beta failed to inhibit cell-cycle progression. A potential in vivo role of these mechanisms was sustained by the increasing immunoreactivity for the activated STAT5 and p21(waf) in kidney biopsies from early to advanced stage of diabetic nephropathy. Our data indicate that AGE- and TGF-beta-mediated signals, by converging on STAT5 activation and p21waf expression, may regulate MC growth.

The role of cell cycle proteins in Glomerular disease

Although initially identified and characterized as regulators of the cell cycle and hence proliferation, an extended role for cell cycle proteins has been appreciated more recently in a number of physiologic and pathologic processes, including development, differentiation, hypertrophy, and apoptosis. Their precise contribution to the cellular response to injury appears to be dependent on both the cell type and the nature of the initiating injury. The glomerulus offers a remarkable situation in which to study the cell cycle proteins, as each of the 3 major resident cell types (the mesangial cell, podocyte, and glomerular endothelial cell) has a specific pattern of cell cycle protein expression when quiescent and responds uniquely after injury. Defining their roles may lead to potential therapeutic strategies in glomerular disease.