Capns1 Specific Deletion in Macrophage Attenuates Skin Inflammation and Fibrosis in Systemic Sclerosis by Suppressing SHP2

Background: In systemic sclerosis (SSc), Capns1 is largely up-regulated in dermal tissue to control calpain activities, thus providing pro-inflammatory and pro-fibrotic effect. However, the mechanisms under this process still remain unknown. We aimed at investigating how Capns1 participates in SSc inflammation and fibrosis progression. Methods: This study includes clinical skin biopsy samples from 7 SSc patients and 5 healthy controls to detect the expression pattern of Capns1 and its downstreaming regulator SHP2. In vitro , bone marrow-derived macrophage (BMDM) and Raw264.7 cell line are utilized to clarify the relation between Capns1 and SHP2-mediated inflammatory response. We further explore the macrophage-fibroblast interaction and its signaling pathway targets after SHP2 knockout. In vivo , we breed myeloid-specific Capns1 deletion mice to evaluate its effect, and the therapeutic function of SHP2 inhibition is investigated by systemic administration of its pharmacological inhibitor with different intervention regimens. Results: Clinical skin samples show that Capns1 and SHP2 are both amplified in SSc dermis and co-express in CD68 ⁺ macrophages. In vivo , myeloid-specific Capns1 deletion mice show significant lower levels of SHP2 expression in dermal tissue, attenuating dermal thickness and subcutaneous fat loss. In vitro , when incubating fibroblasts with macrophage supernatant, the Capns1 deletion group indicates less amount of fibrotic protein production[1] . Additionally, SHP2 knockdown can downregulate NF-κB activation and inflammatory cytokines secretion in Raw264.7, such as interleukin-1β (IL-1β). Conversely, pharmacological SHP2 inhibitor provides significant mitigation in a intervention time-dependent manner. Conclusions: Collectively, our results indicate that Capns1-SHP2 axis is over-activated to regulate macrophage inflammatory response in SSc, which activates nearby fibroblasts to further drive skin fibrosis. Macrophage Capns1 deficiency and pharmacological SHP2 inhibition can significantly provide the anti-fibrotic protection against disease progression.