Phosphatidylinositol 3-Kinase Is Involved in α2(I) Collagen Gene Expression in Normal and Scleroderma Fibroblasts

108

120

Apoptosis of endothelial cells (EC) is appreciated as a primary pathogenic event in systemic sclerosis. Yet, how apoptosis of EC leads to fibrosis remains to be determined. We report that apoptosis of EC triggers the release of novel fibrogenic mediators. Medium conditioned by apoptotic EC (SSC) was found to inhibit apoptosis of fibroblasts, whereas medium conditioned by EC in which apoptosis was blocked (with either pan-caspase inhibition or Bcl-xL overexpression) did not. PI3K was activated in fibroblasts exposed to SSC. This was associated with downstream repression of Bim-EL and long-term up-regulation of Bcl-xL protein levels. RNA interference for Bim-EL in fibroblasts blocked apoptosis. SSC also induced PI3K-dependent myofibroblast differentiation with expression of α-smooth muscle actin, formation of stress fibers, and production of collagen I. A C-terminal fragment of the domain V of perlecan was identified as one of the fibrogenic mediators present in SSC. A synthetic peptide containing an EGF motif present on the perlecan fragment and chondroitin 4-sulfate, a glycosaminoglycan anchored on the domain V of perlecan, induced PI3K-dependent resistance to apoptosis in fibroblasts and myofibroblast differentiation. Human fibroblasts derived from sclerodermic skin lesions were more sensitive to the antiapoptotic activities of the synthetic peptide and chondroitin 4-sulfate than fibroblasts derived from normal controls. Hence, we propose that a chronic increase in endothelial apoptosis and/or increased sensitivity of fibroblasts to mediators produced by apoptotic EC could form the basis of a fibrotic response characterized by sustained induction of an antiapoptotic phenotype in fibroblasts and persistent myofibroblast differentiation.

Section: Discussionsupporting

confidence: 93%

Novel Fibrogenic Pathways Are Activated in Response to Endothelial Apoptosis: Implications in the Pathophysiology of Systemic Sclerosis

Laplante

Raymond

Gagnon

et al. 2005

108

120

“…Based on these data, we performed the DNA affinity precipitation assay. Consistent with our previous report (37), as shown in Fig. 9D, the constitutive DNA-Smad3 binding was detected in SSc fibroblasts, and the marked DNA-Smad3 binding were detected in normal fibroblasts treated with TGF-␤1.…”

Section: Blockade Of ␣ V ␤ 3 Reverses the Ssc Phenotypesupporting

confidence: 80%

Increased Expression of Integrin αvβ3 Contributes to the Establishment of Autocrine TGF-β Signaling in Scleroderma Fibroblasts

Asano

Ihn

Yamane

et al. 2005

Self Cite

207

153

The constitutive secretion of latent TGF-β by many cell types in culture suggests that extracellular mechanisms to control the activity of this potent cytokine are important in the pathogenesis of the diseases in which this cytokine may be involved, including fibrotic disorders. In this study, we focused on the αvβ3 integrin, which is recently demonstrated to function as an active receptor for latent TGF-β1 through its interaction with latency-associated peptide-β1, and investigated the involvement of this integrin in the pathogenesis of scleroderma. Scleroderma fibroblasts exhibited increased αvβ3 expression compared with normal fibroblasts in vivo and in vitro. In scleroderma fibroblasts, ERK pathway was constitutively activated and such abnormality induced the up-regulation of αvβ3. Transient overexpression of αvβ3 in normal fibroblasts induced the increase in the promoter activity of human α2(I) collagen gene and the decrease in that of human MMP-1 gene. These effects of αvβ3 were almost completely abolished by the treatment with anti-TGF-β Ab or TGF-β1 antisense oligonucleotide. Furthermore, the addition of anti-αvβ3 Ab reversed the expression of type I procollagen protein and MMP-1 protein, the promoter activity of human α2(I) collagen gene, and the myofibroblastic phenotype in scleroderma fibroblasts. These results suggest that the up-regulated expression of αvβ3 contributes to the establishment of autocrine TGF-β loop in scleroderma fibroblasts, and this integrin is a potent target for the treatment of scleroderma.

“…Localized scleroderma (LSc) also manifests tissue fibrosis limited to the skin and s.c. tissue, occasionally involving the muscular tissues beneath the cutaneous lesions (1,2), but the presence of Raynaud's phenomenon, acrosclerosis, and involvement of internal organs differentiates SSc from LSc (3). Abnormal collagen metabolism (4)(5)(6)(7)(8) and autoimmunity (9,10) are considered to be fundamental common characteristics of SSc and LSc, and especially, excess collagen production by dermal fibroblasts is thought to be caused by intrinsic activation of TGF-b signaling in both diseases (5,11).…”

mentioning

confidence: 99%

The Downregulation of microRNA let-7a Contributes to the Excessive Expression of Type I Collagen in Systemic and Localized Scleroderma

Makino

Jinnin

Hirano

et al. 2013

Self Cite

147

111

Systemic and localized scleroderma (SSc and LSc) is characterized by excessive deposition of collagen and tissue fibrosis in the skin. Although they have fundamental common characteristics including autoimmunity, little is known about the exact mechanism that mediates the excessive collagen expression in these disorders. In the current study, we tried to evaluate the possibility that microRNAs (miRNAs) play some roles in the pathogenesis of fibrosis seen in these diseases. miRNA expression patterns were evaluated by miRNA array analysis, real-time PCR, and in situ hybridization. The function of miRNAs in dermal fibroblasts was assessed using miRNA inhibitors, precursors, or protectors. In the mouse model of bleomycin-induced dermal sclerosis, the overexpression of miRNAs was performed by i.p. miRNA injection. We demonstrated let-7a expression was downregulated in SSc and LSc skin both in vivo and in vitro, compared with normal or keloid skin. The inhibition or overexpression of let-7a in human or mouse skin fibroblasts affected the protein expression of type I collagen or luciferase activity of collagen 3′-untranslated region. Also, we found let-7a was detectable and quantitative in the serum and investigated serum let-7a levels in patients with SSc or LSc. let-7a concentration was significantly decreased in these patients, especially in LSc patients. Moreover, we revealed that the intermittent overexpression of let-7a in the skin by i.p. miRNA injection improved the skin fibrosis induced by bleomycin in mice. Investigation of more detailed mechanisms of miRNA-mediated regulation of collagen expression may lead to new therapeutic approaches against SSc and LSc.