SREBP-1 activation by glucose mediates TGF-β upregulation in mesangial cells

Am J Physiol Renal Physiol. 2012 Feb 1;302(3):F329-41. doi: 10.1152/ajprenal.00136.2011. Epub 2011 Oct 26.

Abstract

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. Recent studies showed that overexpression of the transcription factor sterol-responsive element-binding protein (SREBP)-1 induces pathology reminiscent of diabetic nephropathy, and SREBP-1 upregulation was observed in diabetic kidneys. We thus studied whether SREBP-1 is activated by high glucose (HG) and mediates its profibrogenic responses. In primary rat mesangial cells, HG activated SREBP-1 by 30 min, seen by the appearance of its cleaved nuclear form (nSREBP-1), EMSA, and by activation of an SREBP-1 response element (SRE)-driven green fluorescent protein construct. Activation was dose dependent and not induced by an osmotic control. Site 1 protease was required, since its inhibition by AEBSF prevented SREBP-1 activation. SCAP, the ER-associated chaperone for SREBP-1, was also necessary since its inhibitor fatostatin also blocked SREBP-1 activation. Signaling through the EGFR/phosphatidylinositol 3-kinase (PI3K) pathway, which we previously showed mediates HG-induced TGF-β1 upregulation, and through RhoA, were upstream of SREBP-1 activation (Wu D, Peng F, Zhang B, Ingram AJ, Gao B, Krepinsky JC. Diabetologia 50: 2008-2018, 2007; Wu D, Peng F, Zhang B, Ingram AJ, Kelly DJ, Gilbert RE, Gao B, Krepinsky JC. J Am Soc Nephrol 20: 554-566, 2009). Fatostatin and AEBSF prevented HG-induced TGF-β1 upregulation by Northern blot analysis, and HG-induced TGF-β1 promoter activation was inhibited by both fatostatin and dominant negative SREBP-1a. Chromatin immunoprecipitation analysis confirmed that HG led to SREBP-1 binding to the TGF-β1 promoter in a region containing a putative SREBP-1 binding site (SRE). Thus HG-induced SREBP-1 activation requires EGFR/PI3K/RhoA signaling and SCAP-mediated transport to the Golgi for its proteolytic cleavage. Activated SREBP-1 binds to the TGF-β promoter, resulting in TGF-β1 upregulation in response to HG. SREBP-1 thus provides a potential novel therapeutic target for the treatment of diabetic nephropathy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Diabetes Mellitus, Experimental / metabolism
  • Diabetic Nephropathies / metabolism*
  • ErbB Receptors / metabolism
  • Glucose / metabolism*
  • Glucose / pharmacology
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Membrane Proteins / metabolism
  • Mesangial Cells / cytology
  • Mesangial Cells / drug effects
  • Mesangial Cells / metabolism*
  • Mice
  • Mice, Inbred Strains
  • Phosphatidylinositol 3-Kinases / metabolism
  • Primary Cell Culture
  • Promoter Regions, Genetic / physiology
  • Proto-Oncogene Proteins c-akt / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Sterol Regulatory Element Binding Protein 1 / genetics
  • Sterol Regulatory Element Binding Protein 1 / metabolism*
  • Transcriptional Activation / drug effects
  • Transcriptional Activation / physiology
  • Transforming Growth Factor beta1 / genetics
  • Transforming Growth Factor beta1 / metabolism*
  • Up-Regulation / drug effects
  • Up-Regulation / physiology
  • rhoA GTP-Binding Protein / metabolism

Substances

  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • SREBP cleavage-activating protein
  • Srebf1 protein, mouse
  • Srebf1 protein, rat
  • Sterol Regulatory Element Binding Protein 1
  • Transforming Growth Factor beta1
  • Phosphatidylinositol 3-Kinases
  • ErbB Receptors
  • Proto-Oncogene Proteins c-akt
  • rhoA GTP-Binding Protein
  • Glucose