Background/Purpose: Systemic sclerosis (SSc) is a multi-system autoimmune connective tissue disorder that leads to fibrosis of the skin and internal organs, resulting in significant patient morbidity and mortality. The fibroblast is considered a key target cell type for possible therapies aimed at modifying excessive deposition of extracellular matrix in affected organs. Several studies have assessed the role of protein tyrosine kinases (PTKs) in the pathophysiology of SSc fibroblasts and fibrosis. However the role of protein tyrosine phosphatases (PTPs), a family of enzymes that naturally balance the action of PTKs in signal transduction, in fibrosis remains mostly unexplored.

Methods: We analyzed the mRNA expression profile of all the PTPs (109 genes) in primary dermal fibroblasts from 9 patients with diffuse SSc compared to 9 healthy subjects. Whole transcriptome analysis by Next Generation Sequencing (NGS) was performed on normal human dermal fibroblasts (NHDF) subjected to silencing of the PTP4A1 gene. In NHDF we investigated the effects of PTP4A1 silencing on TGFbeta1 stimulated COL1A2 and ACTA2 gene expression and on SMAD3 and alphaSMA protein level by qPCR and immunoblotting, respectively. Luciferase assays were performed using a SMAD reporter in HEK 293T cell and in vivo experiments were carried out in mice using a bleomycin-induced fibrosis model.

Results:  PTP4A1 gene displayed increased expression in SSc dermal fibroblast lines studied (Mann-Whitney test, p<0.05). NGS of normal dermal fibroblasts showed that silencing of PTP4A1 correlated with reduced expression of human pro-fibrotic genes and in particular of SMAD3, which pointed to a possible role of PTP4A1 in the TGFbeta-dependent pro-fibrotic pathway. NGS data for SMAD3 and other pro-fibrotic genes were confirmed at the protein level by immunoblotting. Co-transfection of HEK 293T with a human PTP4A1-encoding pCDNA4 vector together with a luciferase SMAD reporter showed that PTP4A1 enhances activation of SMAD signaling after TGFbeta1 stimulation (Mann-Whitney test, p<0.05). In vivo experiments showed that knockout of PTP4A1 significantly attenuates bleomycin-induced fibrosis model in mice.

Conclusion: These results suggest that PTP4A1, a PTP overexpressed in SSc dermal fibroblasts, plays a role in the pathogenesis of SSc by promoting pro-fibrotic TGFbeta/SMAD3 signaling.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/role-of-ptp4a1-tyrosine-phosphatase-in-systemic-sclerosis/