Protection of thymosin beta-4 on corneal endothelial cells from UVB-induced apoptosis

Cornea absorbs most of daily ultraviolet (UV) light. An excess of UV damages results in not only keratopathy and cataract but also maculopathy. It has been reported that thymosin beta-4 (Tβ ₄ ) promotes wound healing, decreases inflammatory response and prevents apoptosis of corneal epithelial cells. However, it is not clear whether Tβ ₄ protects UVB-induced corneal injury, particularly in corneal endothelial cells because of its non-proliferation in nature. The purpose of this study is to compare the protective effects of Tβ ₄ on bovine corneal endothelial (BCE) cells from low- and high-dose UVB damage. In this study, 1 μg/ml of Tβ ₄ was added to BCE cells 2 h before low (12.5 mj/cm ² ) or high dosage (100 mj/cm ² ) UVB exposure. Using a fluorogenic substrate cleavage assay, we found that Tβ ₄ diminished the reactive oxygen species level in BCE cells elicited by UVB. However, the protection of viability by Tβ ₄ could only be detected under low-dose UVB exposure. Moreover, both caspase-9 activity and annexin V/propidium iodine staining demonstrated that Tβ ₄ only protected BCE cells from low-dose UVBinduced apoptosis but not high-dose UVB-induced necrosis. Together, Tβ ₄ protected corneal endothelial cells from UVB-induced oxidative stress and apoptosis after low-dose UVB exposure. The results support further investigation towards topical use or anterior chamber injection of this small hydrophilic peptide in treating and preventing UVB-induced corneal endothelial damage.