Background/Purpose: Chronic digital ulcers (DU) due to peripheral microangiopathy are a major complication in systemic sclerosis (SSc). Chronic wounds are often enriched in bacteria without overt clinical signs of infection and inflammation. Current treatment comprises vasodilation, local disinfection, mechanical wound cleaning and antibiotics. Data on the role of skin commensal bacteria on wound repair are conflicting with both beneficial and detrimental effects. A recent study provided evidence for previously unknown direct interactions between skin bacteria, dermal cells and extracellular matrix proteins even in normal skin. Therefore, we investigated whether skin commensal bacteria might be involved in wound healing responses in SSc.

Methods: Wound swabs of SSc patients with DU (n=36) were subjected to microbial analysis. The presence of skin commensals in human skin sections processed under sterile conditions was examined by Gram stain and IF. Dermal fibroblasts isolated from healthy controls (HC; n=4) and patients with diffuse cutaneous SSc (dcSSc; n=3) were stimulated with heat-killed S. epidermidis (HKSE) and S. aureus (HKSA). The concentration of IL-6, IL-8 and MCP-1 (monocyte chemoattractant protein-1) in cell culture supernatants was measured by ELISA. Expression of collagen type 1 (COL1A1) and alpha-smooth muscle actin (α-SMA) was evaluated by qPCR, ELISA and Western blotting. Expression of stress fibers and α-SMA was examined by phalloidin staining and IF. Cell proliferation was evaluated with a colorimetric assay. Contractility was analyzed by collagen gel contraction assay.

Results: Superficial and deep wound swabs (n=60) showed that 65% of wounds were primarily colonized with skin commensals including SA and SE. Gram-stain and IF of skin sections of HC and dcSSc (n=3 each) revealed Gram-positive bacteria in the deeper dermis and the epidermis. Upon HKSE/A stimulation, the secretion of IL-6 and IL-8 was increased in both HC and dcSSc fibroblasts, but MCP-1 was increased in dcSSc only. In HKSE/A-stimulated dermal fibroblasts, expression of α-SMA on mRNA and protein level was decreased in both HC (0.53/0.56-fold, p<0.05 each) and dcSSc (0.62/0.60-fold, p=0.06 each) whereas expression of COL1A1 was not changed. Moreover, simultaneous stimulation with HKSE and TGF-β revealed an inhibitory effect of HKSE on TGF-β-induced α-SMA expression on mRNA and protein level in both HC (0.69-fold, p=0.06) and dcSSc (0.49-fold, p=0.06). HKSE-stimulated fibroblasts also showed increased proliferation in dcSSc, but less in HC (1.85-fold vs. 1.27-fold, p=0.20). Accordingly, the expression of stress fibers was more abundant in dcSSc compared to HC. The contractility of dermal fibroblasts upon HKSE stimulation was decreased in both HC and dcSSc (relative gel area to untreated cells; 116% vs. 114%).

Conclusion: Skin commensals inhibit the activation of dermal fibroblasts, but provoke strong inflammatory responses and increase proliferation. Our data indicate that bacterial exposure of dermal fibroblasts might result in chronic activation of innate immune responses with detrimental effects on wound repair.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/skin-commensal-bacteria-might-affect-wound-repair-in-ssc-by-preventing-fibroblast-activation-and-by-provoking-chronic-inflammatory-reaction/