Involvement of Multiple Variants of Soluble CD146 in Systemic Sclerosis: Identification of a Novel Profibrotic Factor

Abstract

Objective. Systemic sclerosis (SSc) is an autoimmune disorder characterized by excessive fibrosis, immune dysfunction, and vascular damage, in which the expression of many growth factors is deregulated. CD146 was recently described as a major actor in SSc. Since CD146 also exists as a circulating soluble form (sCD146) that acts as a growth factor in numerous angiogenic-and inflammation-related pathologies, we sought to identify the mechanisms underlying the generation of sCD146 and to characterize the regulation and functions of the different variants identified in SSc.Methods. We performed in vitro experiments, including RNA-Seq and antibody arrays, and in vivo experiments using animal models of bleomycin-induced SSc and hind limb ischemia.Results. Multiple forms of sCD146, generated by both shedding and alternative splicing of the primary transcript, were discovered. The shed form of sCD146 was generated from the cleavage of both long and short membrane isoforms of CD146 through ADAM-10 and TACE metalloproteinases, respectively. In addition, 2 novel sCD146 splice variants, I5-13-sCD146 and I10-sCD146, were identified. Of interest, I5-13-sCD146 was significantly increased in the sera of SSc patients (P < 0.001; n = 117), in particular in patients with pulmonary fibrosis (P < 0.01; n = 112), whereas I10-sCD146 was decreased (P < 0.05; n = 117). Further experiments revealed that shed sCD146 and I10-sCD146 displayed proangiogenic activity through the focal adhesion kinase and protein kinase Cε signaling pathways, respectively, whereas I5-13-sCD146 displayed profibrotic effects through the Wnt-1/β-catenin/WISP-1 pathway.Conclusion. Variants of sCD146, and in particular the novel I5-13-sCD146 splice variant, could constitute novel biomarkers and/or molecular targets for the diagnosis and treatment of SSc and other angiogenesis-or fibrosis-related disorders.

Novel biomarkers in systemic sclerosis

“…High levels of a form of the CD146 protein, normally found on endothelial cells -those that line blood vessel walls -may be a potential biomarker in identifying people with systemic sclerosis (SSc), a study suggests [19].Certain forms of the protein are implicated in lung scarring (pulmonary fibrosis) and in controlling skin thickness, having potential as therapeutic targets.…”

CD146 expression profile in human skin and pre-vascularized dermo-epidermal skin substitutes in vivo

“…However, CD146 expression needs to be spatiotemporally regulated, in order to increase during inflammation to stimulate angiogenesis, and then decrease again. Indeed, excessive overexpression of CD146 has been correlated with several chronic inflammatory diseases [ 35 , 36 ]. For example, in multiple sclerosis CD146 plays a crucial role in mediating lymphocyte transmigration across the blood–brain barrier and inducing neuronal inflammation [ 37 ].…”

“…For example, in multiple sclerosis CD146 plays a crucial role in mediating lymphocyte transmigration across the blood–brain barrier and inducing neuronal inflammation [ 37 ]. In systemic sclerosis patients show high levels of different isoforms of soluble CD146 (scCD146), which are responsible for profibrotic effects through dysregulation of the Wnt-1/ β-catenin pathway and proangiogenic activity via up-regulation of the PKCε pathway [ 36 ]. Moreover, aberrant up-regulation of CD146 has been associated with various cancers, where it is involved in the early step of cancer formation and progression through vascular metastasis [ 1 , 14 , 35 ].…”

Targeting of the NOX1/ADAM17 Enzymatic Complex Regulates Soluble MCAM-Dependent Pro-Tumorigenic Activity in Colorectal Cancer

“…Both generate sMCAM from the short or the long mMCAM isoform, respectively. This specificity is mainly due to the concomitant cellular localization of ADAM17 with the short mMCAM isoform at the apical side of the endothelial cell surface, and ADAM10 with the long mMCAM isoform at the basolateral side of the cell surface [38]. However, the mechanism regulating mM-CAM cleavage supported by ADAM17 under physiological and pathological conditions remains elusive at this point.…”