Bacteria in hypertrophic scars promote scar formation through HSBP1-mediated autophagy.

Abstract

Bacterial colonisation in hypertrophic scars (HSs) has been reported, yet the precise mechanism of their contribution to scar formation remains elusive. To address this, we examined HS and normal skin (NS) tissues through Gram staining and immunofluorescence. We co-cultured fibroblasts with heat-inactivated Staphylococcus aureus (S. aureus) and evaluated their levels of apoptosis and proliferation by flow cytometry and Cell Counting Kit-8 assay, respectively. Additionally, we performed proteomic analysis and western blotting to identify upregulated proteins. To assess autophagy levels, we examined light chain 3 (LC3) expression through western blotting and immunofluorescence, and transmission electron microscopy (TEM) was performed to detect autophagy-associated vesicles. Our results demonstrated a notable increase in bacterial load, primarily S. aureus, in HS tissues. Furthermore, S. aureus promoted fibroblast proliferation and enhanced the expression of profibrotic markers such as transforming growth factor β1 (TGF-β1), vascular endothelial growth factor (VEGF), collagen I, collagen III and α smooth muscle actin (α-SMA). Proteomic analysis highlighted heat shock factor-binding protein 1 (HSBP1) as a key upregulated protein mediating the profibrotic effects induced by S. aureus. Knockdown of HSBP1 reversed these effects. Intriguingly, HSBP1 also upregulated LC3 and Beclin-1 expression and increased the number of autophagosomes in fibroblasts. Finally, when fibroblasts stimulated by S. aureus were treated with HSBP1 siRNA, autophagy levels decreased significantly. Collectively, our findings suggest that S. aureus, via HSBP1, stimulates fibroblast proliferation and promotes their transition into myofibroblasts, triggering autophagy and fibrosis. These results underscore the potential of HSBP1 as a therapeutic target for the management of HSs.