We and several other investigators have previously reported that neurotransmitter receptors, such as serotonergic and adrenergic, and specific effectors of these receptor-mediated signal transduction systems are altered in the postmortem brain of suicide victims. Recent investigations in our laboratory have revealed that the functional characteristics and the expression of transcription factor CREB, a common substrate for many neurotransmitter receptor systems implicated in the pathophysiology of suicide, and the expressions of its target gene BDNF and receptor for BDNF, i.e., TrkB, are significantly altered in the postmortem brain of suicide victims, suggesting that these molecules may be playing an important role in the pathophysiology of suicidal behavior. However, the significance and consequences of these alterations at the functional level in suicide brain are not clear. ERK-1/2 and PI3-kinase cascades are the two most important signaling systems in the CNS that are activated by TrkB and mediate the physiological functions of BDNF. The major objective of the proposed research is to elucidate the cellular and the molecular mechanisms associated with suicide by examining whether abnormalities in BDNF and TrkB are associated with abnormalities further downstream in the ERK-1/2 and the PI3-kinase pathways, both at the level of kinases and at the functional level in the substrate molecules responsible for physiological actions in the brain. More specifically, in postmortem brain of suicide victims and well-matched nonpsychiatric control subjects, we will study the activation and the expression of upstream kinases Raf-1, MEK-1, ERK-1, ERK-2, PI3-kinase, Akt-1, Akt-3, and of downstream substrates, transcription factors Elk-1 and FKHRL1, and regulatory proteins Bcl-2 and Bad, both at the molecular and the cellular level. These studies will be performed in prefrontal cortical and hippocampal brain areas utilizing quantitative RT-PCR, Western blot, immunoprecipitation, enzymatic assays, in-situ hybridization, and gold-immunolabeling techniques. Furthermore, to examine whether observed changes are restricted to depression, we will compare the findings in the proposed measures between suicide victims with a firm diagnosis of major depression and those diagnosed with other psychiatric disorders. We will also study whether there is coordinated regulation of the proposed measures (upstream kinases, downstream substrates, and regulatory proteins) of the two signaling pathways within the same brain by examining the correlational structure overall and individually within the group and by statistical path analysis. The proposed research is based on the central hypothesis that there may be abnormalities in the components of ERK-1/2 and PI-3 kinase signaling pathways in postmortem brain of suicide victims, which may be associated with abnormalities in activation and/or expression of the substrate molecules responsible for BDNF-elicited neuronal functions, and that these abnormalities may play an important role in the pathophysiology of suicidal behavior. Elucidation of the alterations in ERK-1/2 and PI3-kinase pathways in postmortem brain of suicide victims will yield important information on the neurobiology of suicide and will indicate possible novel sites for therapeutic interventions, which may eventually lead to better treatment and possibly prevention of suicidal behavior.
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