1385 Dual mechanism of Type VII collagen transfer by bone marrow mesenchymal stem cell extracellular vesicles to recessive dystrophic epidermolysis bullosa fibroblasts

Abstract

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe blistering disease resulting from a lack of type VII collagen production. Recent clinical trials have shown efficacy of bone marrow-derived stem cells (BM-MSCs) in the treatment of epidermolysis bullosa, including improved basement membrane restructuring and cutaneous wound healing. The mechanism as to how type VII collagen is transferred from donor stem cell to recipient RDEB cells has not been defined. Here, we report that BM-MSC-derived extracellular vesicles serve at least two roles: 1) to help transport the insoluble type VII collagen alpha chains within the extracellular space; and 2) to feed RDEB fibroblasts with messenger RNA that codes for type VII collagen, resulting in COL7A1 translation and synthesis of normal type VII collagen alpha chain proteins, eventually secreted by RDEB fibroblasts. Utilizing a chemoselective ligation detection method, we found RDEB cells that were treated simultaneously with BM-MSC EVs and an L-methionine analog, L-homopropargylglycine (HPG), synthesized collagen VII alpha chain protein that contained the alkyne group of HPG to react (i.e. undergo the Click-iT® reaction) with azide-modified Alexa 594, enabling detection and suggesting de novo synthesis of type VII collagen by RDEB fibroblasts. These dual mechanisms could result in a net positive “transfer” of type VII collagen to the extracellular environment of skin in RDEB patients, likely improving both basement membrane integrity and wound healing. Therapies that utilize EVs to enhance delivery of type VII collagen, both in terms of nucleic acids and protein, have potential to improve the functions of skin in RDEB patients.