Upregulated expression of proteolytic enzymes in the cultured retinal pigment epithelial cells of minipig transgenic for the human mutated huntingtin

Purpose Huntington′s disease (HD) belongs to the hereditary neurodegenerative disorder that is caused by an expansion of a polyglutamine (polyQ) domain in the protein of huntingtin (Htt). Since mutant Htt (mtHtt) and especially their small proteolytic fragments are very toxic to all HD cells (particularly those of neuroectodermal origin such as neurons or retinal pigment epithelial cells), it has been suggested that upregulated proteolysis of mtHtt plays a crucial role in the HD pathogenesis including damage of the retina. Therefore, the purpose of the present study was to investigate the possible participation of the proteolytic enzymes from the group of caspases, matrix metalloproteinases (MMP), calpains in HD pathology of retinal pigment epithelial cells. Methods In this study we used wild type (WT) and transgenic minipigs for N-terminal part of the human mtHtt (TgHD) (548aaHTT-145Q, F2 generation age 36 and 48 months, respectively). Proteases were examined in cultured retinal pigment epithelial cells immunocytochemically (ICC) or biochemically by western blotting (WB) using the following primary antibodies: anti-caspase-3, anti-caspase-8, anti-calpain-5, anti-MMP-9. Results Using biochemical and immunocytochemical analysis, we detected increased expressions of caspase-3, caspase-8, matrix metalloproteinase-9, calpain-5, and probably its multiple proteolytic cleavage products (generated from mtHtt) in cultured RPE cells of TgHD minipigs in comparison to WT animals. Conclusions Increased expression of proteolytic enzymes in TgHD RPE cells can contribute to the retinal damage during development of HD.