CASPASE CLEAVAGE OF BRAIN FODRIN

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Many neuropathological markers have been linked to Alzheimer s disease (AD), among them is an increase in total brain fodrin (non-erythroid spectrin) and accumulation of abnormal depositions of this protein in degenerating neurons. Fodrin, a peripheral membrane protein, provides a critical link between the plasma membrane and the cytoskeleton in neurons. The fodrin deposits in AD correlate with a significant increase in 150kDa breakdown product (BDP). This fodrin BDP is believed to result from calpain cleavage of the alpha-subunit of fodrin, and widespread activation of calpain has been detected in AD brains. More recently, however, caspase cleavage of critical cellular proteins is believed to be responsible for the morphological and functional changes observed when cells undergo apoptosis. The cleavage of fodrin by caspases has been directly linked to the exposure of phosphatidylserine on the cell surface, and has also been implicated in triggering membrane blebbing. A putative caspase cleavage site has been identified in the alpha-subunit of fodrin, just downstream of the major calpain cleavage site. Moreover, antibodies developed against the calpain-mediated cleavage site in fodrin also recognize the caspase-derived BDP. These surprising results coupled with increasing evidence implicating apoptosis as the mechanism of neuronal loss in AD, suggest that more than one mechanism may be involved in the accumulation of fodrin BDP in AD. Additionally, because the fodrin BDPs accumulate as stable intracellular deposits and are cleaved by two distinct families of proteases they represent death products with novel antigenic epitopes that provide a signature of the contribution of calpain and caspases to neurodegenerative diseases. We propose to: 1) study the fodrin BDP profiles in neurons exposed to several distinct apoptotic insults and identify the caspase cleavage site(s) the alpha-subunit of fodrin; 2) determine whether the putative caspase cleavage sites in the beta- subunit of fodrin are cleaved during apoptosis; 3) determine if the erythroid forms of fodrin that are restricted to dendrites and some are also caspase substrates; and 4) develop cleavage fodrin site-directed antibodies against the caspase-mediated BDPs of fodrin identified in the above aims. The BDPs of fodrin clearly represent a unique signature of the neuropathological changes that occur in AD, and antibodies that specifically recognize caspase cleavage death products should provide insights into the contribution of apoptosis in neurodegenerative diseases.