Unique precursors for the mesenchymal cells involved in injury response and fibrosis.

We investigated an alternative pathway for emergence of the mesenchymal cells involved in epithelial sheet wound healing and a source of myofibroblasts that cause fibrosis. Using a mock cataract surgery model, we discovered a unique subpopulation of polyploid mesenchymal progenitors nestled in small niches among lens epithelial cells that expressed the surface antigen G8 and mRNA for the myogenic transcription factor MyoD. These cells rapidly responded to wounding of the lens epithelium with population expansion, acquisition of a mesenchymal phenotype, and migration to the wound edges where they regulate the wound response of the epithelium. These mesenchymal cells also were a principal source of myofibroblasts that emerged following lens injury and were responsible for fibrotic disease of the lens that occurs following cataract surgery. These studies provide insight into the mechanisms of wound-healing and fibrosis.