The cellular mechanisms regulating survival are complex and comprise parallel and potentially interactive pathways. In neurons, one pathway effective in serum-deprivation is known to commence with increased L calcium channel activity. This application focuses on establishing the intracellular signaling processes by which L channel activity is neuroprotective. Because our recent work has demonstrated that insulin-like growth factor-l (IGF-l) is protective through, in part, the rapid regulation of L channels via an IGF-l receptor-PT 3-kinase-Akt and src signal transduction cascade, we will also determine whether physiological levels of IGF-1 govern particular survival pathways via potentiating L channel-mediated influx. Although the mechanisms remain largely unknown, studies on L channel-induced neuroprotection are now underway. Several groups have shown that calcium influx promotes survival via calmodulin and that survival is associated with a rise in nuclear calcium levels. Because nuclear calcium and calmodulin-dependent kinases (CaMK) promote transcription, calcium-dependent transcription of anti-apoptotic genes has been suggested to mediate IGF-l-neuroprotection in ischemia. Our data indicate that CaMKIV is protective in serum withdrawal via L channel activity and that IGF-1 is protective in hypoglycemia, partially through an L channel-dependent mechanism. Conversely, preliminary data suggest that the transcription factor, C/EBPb, may be pro-apoptotic, antagonizing L channel-dependent survival. Here, we will establish the means by which L channel-mediated influx protects neurons from toxic insults, determining: (1) if L channel activity, IGF- 1 or IGF- i/L channel-modulation are neuroprotective in hypoxia, hyper- or hypoglycemia, (2) if ser/thr phosphorylation of neuronal a1C, the primary subunit of the neuronal L channel modulated by IGF-1, is essential for IGF-1-potentiation, and (3) if L channel-mediated influx, either by direct stimulation or via L channel-potentiation, activates specific nuclear signaling cascades, leading to survival. Together, the proposed experiments will significantly advance our understanding of the mechanisms that regulate neuronal survival in the central nervous system, with particular relevance to diabetic neuropathies and traumatic disorders such as stroke.
