Abstract
Transforming growth factor-beta2 (TGF-beta2) stimulates the expression of pro-fibrotic connective tissue growth factor (CTGF) during the course of renal disease. Because sphingosine kinase-1 (SK-1) activity is also upregulated by TGF-beta, we studied its effect on CTGF expression and on the development of renal fibrosis. When TGF-beta2 was added to an immortalized human podocyte cell line we found that it activated the promoter of SK-1, resulting in upregulation of its mRNA and protein expression. Further, depletion of SK-1 by small interfering RNA or its pharmacological inhibition led to accelerated CTGF expression in the podocytes. Over-expression of SK-1 reduced CTGF induction, an effect mediated by intracellular sphingosine-1-phosphate. In vivo, SK-1 expression was also increased in the podocytes of kidney sections of patients with diabetic nephropathy when compared to normal sections of kidney obtained from patients with renal cancer. Similarly, in a mouse model of streptozotocin-induced diabetic nephropathy, SK-1 and CTGF were upregulated in podocytes. In SK-1 deficient mice, exacerbation of disease was detected by increased albuminuria and CTGF expression when compared to wild-type mice. Thus, SK-1 activity has a protective role in the fibrotic process and its deletion or inhibition aggravates fibrotic disease.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Albuminuria / enzymology
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Albuminuria / etiology
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Animals
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Cell Line
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Connective Tissue Growth Factor / metabolism*
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Diabetes Mellitus, Experimental / complications*
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Diabetes Mellitus, Experimental / enzymology
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Diabetes Mellitus, Experimental / pathology
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Diabetic Nephropathies / enzymology*
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Diabetic Nephropathies / etiology
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Diabetic Nephropathies / pathology
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Down-Regulation
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Fibrosis
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Gene Expression Regulation, Enzymologic
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Humans
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Lysophospholipids / metabolism*
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Male
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Mice
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Mice, Inbred C57BL
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Mice, Knockout
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Mutation
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Phosphotransferases (Alcohol Group Acceptor) / antagonists & inhibitors
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Phosphotransferases (Alcohol Group Acceptor) / deficiency
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Phosphotransferases (Alcohol Group Acceptor) / genetics
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Phosphotransferases (Alcohol Group Acceptor) / metabolism*
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Podocytes / drug effects
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Podocytes / enzymology*
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Podocytes / pathology
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Promoter Regions, Genetic
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Protein Kinase Inhibitors / pharmacology
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RNA Interference
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RNA, Messenger / metabolism
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Smad4 Protein / genetics
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Smad4 Protein / metabolism
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Sphingosine / analogs & derivatives*
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Sphingosine / metabolism
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Time Factors
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Transforming Growth Factor beta1 / metabolism
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Transforming Growth Factor beta2 / metabolism*
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Up-Regulation
Substances
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CCN2 protein, human
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CCN2 protein, mouse
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Lysophospholipids
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Protein Kinase Inhibitors
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RNA, Messenger
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SMAD4 protein, human
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Smad4 Protein
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Transforming Growth Factor beta1
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Transforming Growth Factor beta2
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Connective Tissue Growth Factor
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sphingosine 1-phosphate
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Phosphotransferases (Alcohol Group Acceptor)
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sphingosine kinase
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Sphingosine