Regulation of collagen synthesis by inhibitory Smad7 in cardiac myofibroblasts

Abstract

Transforming growth factor-beta(1) (TGF-beta(1)) signal and downstream Smads play an important role in tissue fibrosis and matrix remodeling in various etiologies of heart failure. Inhibitory Smad7 (I-Smad7) is an inducible regulatory Smad protein that antagonizes TGF-beta(1) signal mediated via direct abrogation of R-Smad phosphorylation. The effect of ectopic I-Smad7 on net collagen production was investigated using hydroxyproline assay. Adenovirus-mediated I-Smad7 gene (at 100 multiplicity of infection) transfer was associated with significant decrease of collagen synthesis in the presence and absence of TGF-beta(1) in primary rat cardiac myofibroblasts. In I-Smad7-infected cells, we also observed the ablation of TGF-beta(1)-induced R-Smad2 phosphorylation vs. LacZ controls. Overdriven I-Smad7 was associated with significantly increased expression of immunoreactive 65-kDa matrix metalloproteinase-2 (MMP-2) protein in culture medium of myofibroblast compared with LacZ-infected cells. Expression of the 72-kDa MMP-2 variant, e.g., the inactive form, was not altered by exogenous I-Smad7 transfection/overexpression. Furthermore, I-Smad7 overexpression was associated with a significant increase and decrease in expression of p27 and phospho-Rb protein, respectively, as well as reduced [(3)H]thymidine incorporation vs. Ad-LacZ-infected controls. We suggest that negative modulation of R-Smad phosphorylation by ectopic I-Smad7 may contribute to the downregulation of collagen in cardiac myofibroblasts and may suppress the proliferation of these cells. Thus treatments targeting the collagen deposition by overexpression of I-Smad7 may provide a new therapeutic strategy for cardiac fibrosis.

TGFβ1regulates Scleraxis expression in primary cardiac myofibroblasts by a Smad-independent mechanism

“…Activation of resident cardiac fibroblasts into hypersynthetic/secretory myofibroblasts is now generally regarded as the seminal event in the upregulation and enhanced deposition of fibrillar collagens and ECM, which in acute phases assists in cardiac wound healing but in chronic phases ultimately culminates in cardiac dysfunction due to global stiffening of the noninfarcted myocardium remote to the infarct scar (8,34,40,42,43,45). Traditional TGF␤ 1 /Smad signaling has been described as a key regulator of the fibrotic response in the post-MI heart (44).…”

“…Of these factors, transforming growth factor ␤ 1 (TGF␤ 1 ) has been extensively described as a key regulator of the fibrotic response following tissue injury (5,13,15,36,37,43). TGF␤ 1 signals through a pair of membranebound serine/threonine kinase receptors that form heterodimers upon ligand binding (28,47).…”

Role for high-glucose-induced protein O-GlcNAcylation in stimulating cardiac fibroblast collagen synthesis

“…Multiple pathways can be activated by TGF-␤1. However, the SMAD 2/3 protein complex is recognized as a key mediator of TGF-␤1 profibrotic effects as the complex can translocate into the nucleus where it binds to gene promoter regions (37). SMAD 7 can inhibit the translocation of SMAD 2/3 by competing for the TGF-␤1 receptor binding site of SMAD 2/3 and also enhancing receptor degradation (24).…”

Transcriptional changes in bone marrow stromal cells of patients with heart failure

“…17 In vivo and in vitro studies revealed that overexpression of Smad7 inhibited collagen deposition induced by angiotensin II and TGFβ1 in cardiac fibroblasts and myofibroblasts. 18,19 In contrast, increased expression of β5 integrin subunit was associated with elevated collagen production in dermal fibroblasts. 20,21 Therefore, increased expression of ITGB5 and SMAD7, which was associated with BMI <30 in our study, may contribute to pro-and antifibrotic properties of BMSCs, respectively.…”