CTGF Inhibits BMP-7 Signaling in Diabetic Nephropathy

Abstract

In diabetic nephropathy, connective tissue growth factor (CTGF) is upregulated and bone morphogenetic protein 7 (BMP-7) is downregulated. CTGF is known to inhibit BMP-4, but similar cross-talk between BMP-7 and CTGF has not been studied. In this study, it was hypothesized that CTGF acts as an inhibitor of BMP-7 signaling activity in diabetic nephropathy. Compared with diabetic wild-type CTGF ϩ/ϩ mice, diabetic CTGF ϩ/Ϫ mice had approximately 50% lower CTGF mRNA and protein, less severe albuminuria, no thickening of the glomerular basement membrane, and preserved matrix metalloproteinase (MMP) activity. Although the amount of BMP-7 mRNA was similar in the kidneys of diabetic CTGF ϩ/ϩ and CTGF ϩ/Ϫ mice, phosphorylation of the BMP signal transduction protein Smad1/5 and expression of the BMP target gene Id1 were lower in diabetic CTGF ϩ/ϩ mice.Moreover, renal Id1 mRNA expression correlated with albuminuria (R ϭ Ϫ0.86) and MMP activity (R ϭ 0.76). In normoglycemic mice, intraperitoneal injection of CTGF led to a decrease of pSmad1/5 in the renal cortex. In cultured renal glomerular and tubulointerstitial cells, CTGF diminished BMP-7 signaling activity, evidenced by lower levels of pSmad1/5, Id1 mRNA, and BMP-responsive elementluciferase activity. Co-immunoprecipitation, solid-phase binding assay, and surface plasmon resonance analysis showed that CTGF binds BMP-7 with high affinity (Kd approximately 14 nM). In conclusion, upregulation of CTGF inhibits BMP-7 signal transduction in the diabetic kidney and contributes to altered gene transcription, reduced MMP activity, glomerular basement membrane thickening, and albuminuria, all of which are hallmarks of diabetic nephropathy.

BMP Signaling and Podocyte Markers are Decreased in Human Diabetic Nephropathy in Association with CTGF Overexpression

“…Also, albuminuria was less pronounced in diabetic CTGF 1/2 compared with diabetic wild-type mice (Nguyen et al 2008a). To this we add that pSmad1/5/8 was mainly localized in podocytes.…”

“…Exogenous recombinant human CTGF reduced pSmad1/5/8 level in the renal cortex, indicating that CTGF level significantly affects renal BMP signaling activity (Nguyen et al 2008a). Moreover, inhibition of CTGF attenuated experimental diabetic nephropathy in at least three independent and fundamentally distinct studies involving neutralizing anti-CTGF antibodies, CTGF antisense oligonucleotides, and genetic deletion of one CTGF allele (CTGF 1/2 ) (Flyvbjerg et al 2004;Guha et al 2007;Nguyen et al 2008a;Yokoi et al 2008). In a previous study, we observed a decrease of pSmad1/5/8 abundance in diabetic CTGF 1/1 as compared with CTGF 1/2 mice in Western blots of total renal cortex (Nguyen et al 2008a).…”

Renal Allograft Fibrosis: Biology and Therapeutic Targets

“…However, CTGF can also activate TGF-b1 and inhibit the antifibrotic effects of BMP-7 (282,283). In both experimental and human renal allografts, CTGF is overexpressed in fibrotic kidneys and may represent a biomarker of renal fibrosis (284).…”

Novel CT domain-encoding splice forms of CTGF/CCN2 are expressed in B-lineage acute lymphoblastic leukaemia

“…This mosaic structure has resulted in CTGF and other CCN proteins being implicated both directly and indirectly in a vast array of biological processes and has made it difficult to predict the function of CTGF in any given biological context (Holbourn, Acharya et al 2008;Chen and Lau 2009). However, there is a growing body of evidence that CTGF acts to connect cells to the microenvironment by providing adhesive signals (Gao and Brigstock 2006;Hoshijima, Hattori et al 2006) as well as modulating the availability and function of soluble growth factors A c c e p t e d M a n u s c r i p t 4 (Abreu, Ketpura et al 2002;Hashimoto, Inoki et al 2002;Nguyen, Roestenberg et al 2008). Thus, the tissue context within which CTGF is expressed is likely to play a key role in determining its biological function in any given microenvironment.…”