The objective of this proposal is to investigate the molecular mechanisms of organophosphorus compound induced delayed neurotoxicity (OPIDN). OPIDN is a central-peripheral distal axonopathy. Early ultrastructural alterations in OPIDN are characterized by the presence in the distal axon of aggregated cytoskeletal proteins; microtubules, and neurofilaments. The investigators have demonstrated that central to the pathogenesis of OPIDN is an anomalous increase in Ca2+/calmodulin-dependent kinase- mediated phosphorylation of the cytoskeletal proteins, i.e. neurofilament triplet proteins, and tublin, microtubule associated protein-2 (MAP-2), and tau protein. Although in OPIDN there is an enhanced activity and autophosphorylation of Ca2+/calmodulin dependent kinase II (CAM kinase II), this enzyme, however, does not seem to account for all of the increase in Ca2+/calmodulin-dependent phosphorylation of cytoskeletal proteins. In addition, other kinases are likely to be involved. Consistent with enhanced phosphorylation of cytoskeletal proteins are the PIs recent findings of the increase in CaM kinase II mRNA expression and slow axonal transport of radiolabeled neurofilament proteins in OPIDN. In this proposal, the investigators propose to investigate the hypothesis that sustained and prolonged hyperphosphorylation of cytoskeletal proteins results in an exaggeration of normal phosphorylation and induced conformational changes leading to their aggregation and impairment of vital axonal processes such as axonal transport with subsequent degeneration of the axon. There are four elements in this approach: 1) identification and characterization of the kinases that may be involved in the conversion of normal cytoskeletal proteins into the """"""""hyperphosphorylated"""""""" state and assessment of the possibility that aberrantly activated kinases act in concert to generate abnormally phosphorylated cytoskeletal proteins; 2) delineation of the time-course and extent of phosphorylation of amino acid residues that are hyperphosphorylated in cytoskeletal proteins; 3) determination of functional, structural, and biochemical consequences of the transformation of cytoskeletal proteins; and 4) investigation of the time-course and mechanisms of transcriptional alterations in cytoskeletal proteins, associated kinases, and immediate early genes. Taken together, they plan to identify the differences between normal and pathological cytoskeletal proteins and assess how hyperphosphorylation of these proteins disrupts their assembly and compromises their stability, leading to functional alterations and axonal degeneration.
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