Calpain and photoreceptor apoptosis.

Photoreceptor apoptosis is present in various retinopathies such as retinitis pigmentosa and glaucoma where caspases are generally considered to be the main executioners of apoptosis in various tissues. However, accumulating evidence suggests apoptosis could occur in a caspase-independent fashion. In this view, many studies have shown that calpain activation is associated with photoreceptor apoptosis in various animal and light-induced retinal degeneration models. Thus, calpain could be a potential target for treatment and may promote cell survival in cases where caspase inhibition has failed. Herein, we review current thinking on this topic and also present data showing protection of photoreceptors to apoptosis by systemic delivery of a calpain inhibitor in a light-induced model of retinal degeneration by modulation of the inner blood retina barrier (iBRB).