Repair in avascular tissues: fibrosis in the transparent structures of the eye and thrombospondin 1.

Wound repair is a process which is normally dependent on the vasculature of the damaged tissue. However, the transparent structures of the eye (e.g. central cornea, lens, vitreous) are avascular and yet are still subject to repair and fibrosis. Moreover, the resulting ophthalmic scars often remain avascular. Since this type of ocular scarring may result in blindness, it is the subject of intense research. An aspect of avascular ophthalmic fibrosis which has attracted attention is the question concerning early wound healing components that are usually derived from blood constituents. One such molecule is the glycoprotein thrombospondin 1. Thrombospondin 1 is thought to be a key regulator of cell behaviour in early wound repair and appears to be derived totally from platelet alpha-granules during repair of incisional skin wounds. It has been shown that the ocular cells involved in avascular repair processes, and which are thus responsible for healing in the absence of platelet-derived thrombospondin 1, are capable of synthesizing the protein themselves. It is suggested that cells involved in ophthalmic repair processes produce thrombospondin 1 in the absence of the platelet-derived molecule. Local synthesis of thrombospondin 1 may represent a therapeutic target in the management of ophthalmic fibrosis.