Multiple alphaII-spectrin breakdown products distinguish calpain and caspase dominated necrotic and apoptotic cell death pathways.

Apoptosis and oncotic necrosis in neuronal and glial cells have been documented in many neurological diseases. Distinguishing between these two major types of cell death in different neurological diseases is needed in order to better reveal the injury mechanisms so as to open up opportunities for therapy development. Accumulating evidence suggests apoptosis and oncosis epitomize the extreme ends of a broad spectrum of morphological and biochemical events. Biochemical markers that can distinguish between the calpain and caspase dominated types of cell death would help in this process. In this study, three chemical agents, maitotoxin (MTX), staurosporine (STS) and thylenediaminetetraacetic acid (EDTA), were used to induce different types of cell death in PC12 neuronal-like cells. MTX-induced necrosis, as determined by the increased levels of calpain-specific cleaved fragments of spectrin by antibodies specific to the calpain-cleaved 150 kDa alphaII-spectrin breakdown product (SBDP150) and 145 kDa alphaII-spectrin breakdown product (SBDP145). In this paradigm, there were no detectable SBDP150i and SBDP120 fragments as determined by antibodies specific to the caspase-cleaved specific fragments similar to those seen in the EDTA-mediated apoptotic PC-12 cells. In contrast to the calpain specific MTX necrosis treatment and the caspase EDTA apoptotic treatment is the STS treatment which induced both proteases as shown by the increase in all the SBDP fragments. Furthermore, compared to SBDP150, SBDP145 appears to be a more specific and sensitive biomarker for calpain activation. Taken together, our results suggested calpains and caspases which dominate the two major types of cell death could be independently discriminated by specifically examining the multiple alphaII-spectrin cleavage breakdown products.