Insights into the mechanisms underlying calpain-related pathology

The molecular interactions underlying vitreoretinopathy are poorly understood. Mutations in calpain-5 (CAPN5) were identified as the cause of autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV). CAPN5 is a member of the calcium-activated cysteine protease family referred to as calpains, which modulate the function of their targets through limited proteolysis. Although increases in calpain activity are associated with many different diseases, ADNIV-causing mutations in CAPN5 are the first reported intrinsically hyperactive case of a calpain. Although ADNIV is relatively rare, it shares overlapping phenotypes with multiple, more common ocular diseases, including diabetic retinopathy. This provides an unprecedented starting point for investigating the substantial gap in our understanding of the molecular basis of vitreoretinopathy. In this thesis, the expression patterns of CAPN5 in the eye and brain are reported (Chapters 2 and 3). I discuss the identification and validation of a CAPN5 substrate and its role in ADNIV. This association is extended as an underlying mechanism in diabetic retinopathy. Utilizing this information, I identify the proteolysis site and alter it to create the first CAPN5-specific and ADNIV-causing-mutation specific inhibitors (Chapter 4). Insights gained from these studies may be used to design therapies for ADNIV, diabetic retinopathy, and other calpain-associated pathologies. Lastly, in an attempt to better understand how increased calpain activity contributes to a myriad of diseases, we created a mouse model in which we express a synthetic hyperactive calpain protein (Chapter 5).