TGF beta in fibroproliferative diseases in the eye

Transforming growth factor b (TGF beta) is believed to be the most important ligand in the pathogenesis of fibrotic diseases in the eye. Such ocular fibrotic diseases include scarring in the cornea and conjunctiva, fibrosis in the corneal endothelium, post-cataract surgery fibrosis of the lens capsule, excess scarring the tissue around the extraocular muscles in the strabismus surgery and proliferative vitreoretinopathy. In the proliferative stage of diabetic retinopathy, fibrogenic reaction causes tractional retinal detachment in association with contraction of the tissue. A myofibroblast, the major cellular component in the fibrotic lesions, is derived from both mesenchymal cells (in cornea and conjunctiva) and epithelial cell types (lens or retinal pigment epithelium or corneal endothelium) through epithelial-mesenchymal transition (EMT). The myofibroblasts cause excess accumulation of fibrogenic extracellular matrix with resultant tissue contraction and impaired functions. Although various cytokine signaling pathways are involved in the fibrogenic reaction in tissues, TGF beta/Smad signal is the critical one. Blocking Smad signal by chemical or natural inhibitors or anti-Smad gene introduction effectively suppress fibrogenic reaction; inhibition of both fibroblast-myofibroblast conversion or EMT. Such strategies can be clinically tested.