Biomedical subjects

Sun Lin

Publications and source records attributed to Sun Lin.

9 recordsLinked to original sources

PubMed2005

Hyperglycemia: its imminent effects on mammalian nephrogenesis.

A sustained exposure of the mammalian embryo to very high glucose ambience is associated with a multitude of congenital birth defects, including those of the cardiovascular, CNS, skeletal and urogenital systems during the first 6-8 weeks of gestation in humans. These urogenital abnormalities may be associated with "caudal regression syndrome" or may occur alone in the form of partial or total renal agenesis. Similarly, an increase in the incidence of morphogenetic defects is observed in the offspring of streptozotocin-induced diabetic rats and mice, and also in non-obese diabetic mice. In certain cases, failure during the growth of the lower parts of embryos or newborn mice involving the genitourinary system has been observed in animals with severe diabetes. Investigators have utilized whole organ culture systems to delineate the mechanisms relevant to dysmorphogenesis of the embryonic metanephros. A marked dysmorphogenesis of the metanephros is observed upon treatment with a high concentration of D: -glucose. Associated with it are changes that include branching dysmorphogenesis of the ureteric bud iterations, reduced population of nascent nephrons, decreased expression of basement membrane proteoglycans, depletion of ATP stores, and fulminant apoptosis of the cells at the interface of mesenchyme and ureteric bud epithelium. The latter findings suggest that disruption of epithelial:mesenchymal interactions may be the major event responsible for the metanephric dysmorphogenesis induced by high glucose ambience.

Animals↗

PubMed2004

Matrix metalloproteinases in renal development.

Matrix metalloproteinases (MMPs) are enzymes with metal ion-dependent activity that degrade extracellular matrix (ECM) glycoproteins. MMPs play a vital role in various biological processes, such as embryogenesis, tissue remodeling, angiogenesis, and wound healing, and in certain disease processes, for example, metastasis of cancer cells. Following their activation, MMPs are believed to modulate both cell-cell and cell-matrix interactions, which in turn regulate cellular differentiation, migration, proliferation, and cell survival. Being involved in pericellular proteolysis, they maintain a gradient of ECM proteins by balancing ECM synthesis and degradation. Such a balance is critical for various mammalian developmental processes during embryonic life and also for the homeostasis of various organs and reparative processes in later life. During the past two decades the role of MMPs in the morphogenesis of various organs, including that of the metanephros, has been investigated extensively. Mammalian nephrogenesis comprises a series of intricate events characterized by a sustained remodeling and turnover of ECM, suggesting a potential role of MMPs in renal development. Conceivably, reciprocal inductive epithelial-mesenchymal interactions that take place at the very commencement of nephrogenesis are modulated by a number of ECM proteins. Their expression, especially at the epithelial-mesenchymal interface, are critical for metanephric development, and such a strategic expression is likely to be modified by a number of different macromolecules that exhibit spatiotemporal and stage-specific expression. Among them the most suitable candidate that could exert such a control would be MMPs. This review addresses the current status of our understanding of the functions and the role of MMPs in renal development.

Animals↗

PubMed2004

Update of extracellular matrix, its receptors, and cell adhesion molecules in mammalian nephrogenesis.

One of the hallmarks of mammalian nephrogenesis includes a mesenchymal-epithelial transition that is accomplished by intercalation of the ureteric bud, an epithelium-lined tubelike structure, into an undifferentiated mesenchyme, and the latter then undergoes an inductive transformation and differentiates into an epithelial phenotype. At the same time, the differentiating mesenchyme reciprocates by inducing branching morphogenesis of the ureteric bud, which forms a treelike structure with dichotomous iterations. These reciprocal inductive interactions lead to the development of a functioning nephron unit made up of a glomerulus and proximal and distal tubules. The inductive interactions and differentiation events are modulated by a number of transcription factors, protooncogenes, and growth factors and their receptors, which regulate the expression of target morphogenetic modulators including the ECM, integrin receptors, and cell adhesion molecules. These target macromolecules exhibit spatiotemporal and stage-specific developmental regulation in the metanephros. The ECM molecules expressed at the epithelial-mesenchymal interface are perhaps the most relevant and conducive to the paracrine-juxtacrine interactions in a scenario where the ligand is expressed in the mesenchyme while the receptor is located in the ureteric bud epithelium or vice versa. In addition, expression of the target ECM macromolecules is regulated by matrix metalloproteinases and their inhibitors to generate a concentration gradient at the interface to further propel epithelial-mesenchymal interactions so that nephrogenesis can proceed seamlessly. In this review, we discuss and update our current understanding of the role of the ECM and related macromolecules with respect to metanephric development.

Animals↗

PubMed2003

Imprinted mesodermal specific transcript (MEST) and H19 genes in renal development and diabetes.

BACKGROUND: Imprinted genes, mesodermal specific cDNA or transcript (MEST) and H19, are implicated in peri-implantation embryogenesis, and their expression was assessed in embryonic kidneys undergoing glucose-induced dysmorphogenesis. METHODS: MEST and H19 mRNA expression was assessed by Northern blot analysis in embryonic kidneys of mice harvested at day 15 to day 19 of gestation and of 1-week-old mice obtained from hyperglycemic mothers. A full-length mouse MEST cDNA was isolated, subcloned into an expression vector, a recombinant protein prepared and an antibody raised; the latter was used to assess protein expression by immunoprecipitation and immunofluorescence microscopy in day 13 metanephric explants subjected to high glucose ambience. Also, MEST mRNA expression was assessed in high d glucose-treated explants by competitive reverse transcription-polymerase chain reaction (RT-PCR) analyses and by in situ tissue autoradiography. RESULTS: A high expression of MEST and H19 with respective transcript size of approximately 2.7 and approximately 2.4 kb was observed in fetal kidneys, and their expression decreased during the successive stages of gestation and was undetectable in the postnatal period. At day 13, the MEST mRNA was expressed in the mesenchyme, while H19 was expressed in the ureteric bud branches and epithelial elements of the metanephros. Their expression decreased with progression of gestation. By competitive RT-PCR and Northern blot and in situ autoradiographic analyses, both MEST and H19 expressions decreased in day 13 explants treated with high glucose and in the kidneys of fetuses obtained from diabetic mothers. The MEST protein expression was observed in the metanephric epithelial elements and ureteric bud branches instead of in the mesenchyme, and its expression decreased in glucose-treated dysmorphogenetic explants, as assessed by immunofluorescence and immunoprecipitation methods. CONCLUSION: MEST and H19 imprinted genes are strategically located in the mammalian embryonic metanephros. They are developmentally regulated and their concomitant decreased expression in high glucose ambience or diabetic state did not follow the prevailing dogma of reciprocal inactivation/activation of imprinted genes, and such a decrease may be responsible for the perturbed epithelial:mesenchymal interactions leading to dysmorphogenesis of the mammalian metanephros.

Animals↗

PubMed2002

High glucose stimulates synthesis of fibronectin via a novel protein kinase C, Rap1b, and B-Raf signaling pathway.

The molecular mechanism(s) by which high glucose induces fibronectin expression via G-protein activation in the kidney are largely unknown. This investigation describes the effect of high glucose (HG) on a small GTP-binding protein, Rap1b, expression and activation, and the relevance of protein kinase C (PKC) and Raf pathways in fibronectin synthesis in cultured renal glomerular mesangial cells (MCs). In vivo experiments revealed a dose-dependent increase in Rap1b expression in glomeruli of diabetic rat kidneys. Similarly, in vitro exposure of MCs to HG led to an up-regulation of Rap1b with concomitant increase in fibronectin (FN) mRNA and protein expression. The up-regulation of Rap1b mRNA was mitigated by the PKC inhibitors, calphostin C, and bisindolymaleimide, while also reducing HG- induced FN expression in non-transfected MCs. Overexpression of Rap1b by transfection with pcDNA 3.1/Rap1b in MCs resulted in the stimulation of FN synthesis; however, the PKC inhibitors had no significant effect in reducing FN expression in Rap1b-transfected MCs. Transfection of Rap1b mutants S17N (Ser --> Asn) or T61R (Thr --> Arg) in MCs inhibited the HG-induced increased FN synthesis. B-Raf and Raf-1 expression was investigated to assess whether Rap1b effects are mediated via the Raf pathway. B-Raf, and not Raf-1, expression was increased in MCs transfected with Rap1b. HG also caused activation of Rap1b, which was largely unaffected by anti-platelet-derived growth factor (PDGF) antibodies. HG-induced activation of Rap1b was specific, since Rap2b activation and expression of Rap2a and Rap2b were unaffected by HG. These findings indicate that hyperglycemia and HG cause an activation and up-regulation of Rap1b in renal glomeruli and in cultured MCs, which then stimulates FN synthesis. This effect appears to be PKC-dependent and PDGF-independent, but involves B-Raf, suggesting a novel PKC-Rap1b-B-Raf pathway responsible for HG-induced increased mesangial matrix synthesis, a hallmark of diabetic nephropathy.

Animals↗

PubMed2002

3-Hydroxy-3-methylglutaryl CoA reductase inhibitors prevent high glucose-induced proliferation of mesangial cells via modulation of Rho GTPase/ p21 signaling pathway: Implications for diabetic nephropathy.

Inhibitors of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase, also known as statins, are lipid-lowering agents widely used in the prevention of coronary heart disease. Recent experimental and clinical data, however, indicate that the overall benefits of statin therapy may exceed its cholesterol-lowering properties. We postulate that statins may ameliorate the detrimental effects of high glucose (HG)-induced proliferation of mesangial cells (MCs), a feature of early stages of diabetic nephropathy, by preventing Rho isoprenylation. Rat MCs cultured in HG milieu were treated with and without simvastatin, an HMG-CoA reductase inhibitor. Simvastatin inhibited HG-induced MC proliferation as measured by [(3)H]thymidine incorporation. This inhibitory effect was reversed with geranylgeranyl pyrophosphate, an isoprenoid intermediate of the cholesterol biosynthetic pathway. At the cell-cycle level, the HG-induced proliferation of MCs was associated with a decrease in cyclin dependent kinase (CDK) inhibitor p21 protein expression accompanied by an increase in CDK4 and CDK2 kinase activities. Simvastatin reversed the down-regulation of p21 protein expression and decreased CDK4 and CDK2 kinase activities. Exposure of MCs to HG was associated with an increase in membrane-associated Ras and Rho GTPase protein expression. Cotreatment of MCs with simvastatin reversed HG-induced Ras and Rho membrane translocation. Immunofluorescence microscopy revealed that the overexpression of the dominant-negative RhoA led to a significant increase in p21 expression. Our data suggest that simvastatin represses the HG-induced Rho GTPase/p21 signaling in glomerular MCs. Thus, this study provides a molecular basis for the use of statins, independently of their cholesterol-lowering effect, in early stages of diabetic nephropathy.

Animals↗

PubMed2002

Relevance of renal-specific oxidoreductase in tubulogenesis during mammalian nephron development.

Renal-specific oxidoreductase (RSOR), an enzyme relevant to diabetic nephropathy, is exclusively expressed in renal tubules. Studies were initiated to determine whether, like other tubule-specific proteins, it selectively modulates tubulogenesis. Northern blot analyses revealed a approximately 1.5-kb transcript, and RSOR expression was detectable in mice embryonic kidneys at day 13, gradually increased by day 17, and extended into neo- and postnatal periods. RSOR mRNA and protein expression was confined to proximal tubules, commencing at gestational day 17 and increasing subsequently, but remained absent in glomeruli and medulla. Treatment with RSOR antisense oligodeoxynucleotide resulted in a dose-dependent dysmorphogenesis of metanephric explants harvested at gestational day 13. The explants were smaller and had expanded mesenchyme, and the population of tubules was markedly decreased. The glomeruli were unaffected, as assessed by mRNA expression of glomerular epithelial protein 1 and reactivity with wheat germ agglutinin. Antisense treatment led to a selective reduction of RSOR mRNA. Immunoprecipitation also indicated a selective translational blockade of RSOR. These findings suggest that RSOR is developmentally regulated, exhibits a distinct spatiotemporal distribution, and probably plays a role in tubulogenesis.

Aldehyde Reductase↗

PubMed2002

Identification of developmentally regulated mesodermal-specific transcript in mouse embryonic metanephros.

Mesodermal-specific cDNA or transcript (MEST) was identified by suppression subtractive hybridization-PCR of cDNA isolated from embryonic day 13 vs. newborn mice kidneys. At day 13 of mouse gestation, a high expression of MEST, with a single approximately 2.7-kb transcript that was exclusively localized to the metanephric mesenchyme was observed. The MEST mRNA expression gradually decreased during the later stages and then abruptly decreased in the newborn kidneys and subsequent postnatal life, after which a very mild expression persisted in the glomerular mesangium. Regression in mRNA expression during embryonic renal development appears to be related to methylation of the MEST gene. Treatment of metanephroi, harvested at day 13 of gestation with MEST-specific antisense oligodeoxynucleotide resulted in a dose-dependent decrease in the size of the explants and the nephron population. This was associated with a selective decrease in MEST mRNA expression and accelerated apoptosis of the mesenchyme. These findings suggest that MEST, a gene with a putative mesenchymal cell-derived protein, conceivably plays a role in mammalian metanephric development.

Animals↗

PubMed2002

Renal gene expression in embryonic and newborn diabetic mice.

Several novel genes that are upregulated in diabetic kidneys have been identified. Recently, transforming growth factor beta driven secreted proteins, i.e., connective tissue growth factor and gremlin (bone morphogenetic protein 2), have been identified, and their expression has been correlated with the tissue changes seen in diabetic nephropathy in the adult population. However, there are very few studies reported in the literature that describe the gene expression in the diabetic state during embryonic and neonatal life. It is well known that exposure to glucose or its epimer, i.e., mannose, induces marked dysmorphogenesis of the embryonic metanephros in an organ culture system. These changes are associated with ATP depletion and marked apoptosis, suggesting an oxidant stress in the induction of dysmorphogenesis of the embryonic metanephros. In view of the glucose-induced changes in the fetal metanephros, a diabetic state was induced by the administration of streptozotocin during pregnancy, and newborn mouse kidneys were processed for suppression subtractive hybridization-PCR. In addition, a diabetic state was induced in newborn diabetic mice, and after 1 week their kidneys were harvested and subjected to representational difference analysis of cDNA. Four novel genes with upregulated mRNA expression were identified. They included: (1) a translocase inner mitochondrial membrane 44 that is involved in the ATP-dependent import of preproteins from the cytosol into the mitochondrial matrix; (2) a kidney-specific aldo-keto reductase that utilizes NADPH and NADH as cofactors in the reduction of aromatic aldehydes and aldohexoses; (3) Rap1b, a Ras-related small GTP-binding protein that behaves as a GTPase and cycles between GTP-bound (active) and GDP-bound (inactive) states associated with conformational change, and (4) a fusion protein of ubiquitin polypeptide and ribosomal protein L40 (UbA(52) or ubiquitin/60) that is intimately involved in the ubiquitin-dependent proteasome pathway related to the accelerated degradation of proteins under various stress conditions, such as those seen in patients with cancer and diabetes mellitus.

Alcohol Oxidoreductases↗