miR-129-1-3p down-regulation promotes BAG cochaperone 3 (BAG3)-driven pro-fibrotic processes in primary fibroblasts from patients with recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare and severe skin fragility disease due to loss-of-function mutations in the <i>COL7A1</i> gene. RDEB patients suffer from relentless mucocutaneous blisters that evolve into chronic wounds with inflammation and progressive fibrosis, which heavily impacts the disease course. RDEB-associated fibrosis is the result of a complex dialogue among different cell types, signalling pathways and epigenetic players that are still poorly characterized. The expression levels of over 750 mature microRNAs were investigated in primary fibroblasts from patients with RDEB (RDEB-FBs) and healthy donors using TaqMan Low-Density Arrays. Among deregulated molecules, only the miR-129-1-3p was down-regulated in RDEB-FBs. Therefore, the role of miR-129-1-3p in regulating the fibrotic features of RDEB-FBs was explored by biochemical and functional assays in cells transfected with a miR-129-1-3p mimic or a small interfering RNA specific for BAG3 (BAG cochaperone 3), a newly identified miR-129-1-3p target. BAG3 expression levels were significantly increased in RDEB-FBs grown under basal conditions and reduced in response to their transfection with a miR-129-1-3p mimic. In RDEB-FBs, the over-expression of miR-129-1-3p or BAG3 silencing markedly impaired cell contractility, a typical feature of activated/pro-fibrotic fibroblasts, decreased phospho-AKT (Ser473) levels, and reduced the ability to synthetize and deposit collagen in the extracellular matrix. Treatment of patients' fibroblasts with the AKT inhibitor perifosine (KRX-0401) recapitulated the effects observed with the mimic molecule of miR-129-1-3p and BAG3 silencing. Our results highlight the role of the miR-129-1-3p/BAG3/AKT axis in RDEB pathogenesis, complementing and expanding the knowledge on non-coding RNAs involved in fibrosis-related processes. Taken together, these findings may contribute to enlarge the toolkit of molecules and pathways that can be exploited as therapeutic targets in skin fibrosis.