Necrotic neuronal death is recently known to be mediated by the calpain-cathepsin cascade from simpler organisms to primates. The main event of this cascade is calpain-mediated lysosomal rupture and the resultant release of lysosomal cathepsins into the cytoplasm. However, the in-vivo substrate of calpain for inducing lysosomal destabilization still remains completely unknown. The recent proteomics data using the post-ischemic hippocampal CA1 tissues and glaucoma-suffered retina from the primates suggested that heat shock protein (Hsp) 70.1 might be the in-vivo substrate of activated mu-calpain at the lysosomal membrane of neurons. Hsp70.1 is known to stabilize lysosomal membrane by recycling damaged proteins and protect cells from oxidative stresses. Here, we studied the molecular interaction between activated mu-calpain and the lysosomal Hsp70.1 in the monkey hippocampal CA1 neurons after the ischemia-reperfusion insult. Immunofluorescence histochemistry showed a colocalization of the activated mu-calpain and upregulated Hsp70.1 at the lysosomal membrane of the post-ischemic CA1 neurons. In-vitro cleavage assay of hippocampal Hsp70.1 by Western blotting demonstrated that Hsp70.1 in the CA1 tissue is an in-vivo substrate of activated mu-calpain, and that carbonylated Hsp70.1 in the CA1 tissue by artificial oxidative stressors such as hydroxynonenal (HNE) or hydrogen peroxide is much more vulnerable to the calpain cleavage. These data altogether suggested that Hsp70.1 can become a target of the carbonylation by HNE, and Hsp70.1 is a modulator of calpain-mediated lysosomal rupture/permeabilization after the ischemia-reperfusion injury. (C) 2010 Elsevier Inc. All rights reserved.