Calpain-1 C2L domain peptide protects mouse hippocampus-derived neuronal HT22 cells against glutamate-induced oxytosis

Calpains are Ca2+-dependent cysteine proteases; their aberrant activation is associated with several neurodegenerative diseases. The mu-calpain catalytic subunit, calpain-1, is located in the cytoplasm as well as in the mitochondria. Mitochondrial calpain-1 cleaves apoptosis-inducing factor (AIF), leading to apoptotic cell death. We have previously reported that short peptides of calpain-1 C2-like domain conjugated with cell penetrating peptide HIV-Tat (Tat-mu CL) selectively inhibit mitochondrial calpain-1 and effectively prevent neurodegenerative diseases of the eye. In this study, we determined whether mitochondrial calpain-1 mediates oxytosis (oxidative glutamate toxicity) in hippocampal HT22 cells using Tat-mu CL and newly generated polyhistidine-conjugated mu CL peptide and compared their efficacies in preventing oxytosis. TUNEL assay and single strand DNA staining revealed that both mu CL peptides inhibited glutamate-induced oxytosis. Additionally, both the peptides suppressed the mitochondrial AIF translocation into the nucleus. All polyhistidine-mu CL peptides (containing 4-16 histidine residues) showed higher cell permeability than Tat-mu CL. Notably, tetrahistidine (H4)-mu CL exerted the highest cytoprotective activity. Thus, H4-mu CL may be a potential peptide drug for calpain-1-mediated neurodegenerative diseases such as Alzheimer's disease.