Alcohol abuse predisposes the host to bacterial infections. A prominent feature of alcohol abusers with severe bacterial infection is that they frequently present with granulocytopenia, which is an indicator of increased mortality. Representing the largest population of phagocytes in the systemic circulation, granulocytes constitute the first line of host defense against invading pathogens. In response to bacterial infection, the bone marrow increases granulocyte production in order to reinforce host defense against invading pathogens. During this process, primitive hematopoietic precursor cells are reprogrammed to polarize their lineage commitment toward granulopoiesis. Our recent studies have revealed that the number of bone marrow lin-cKit+Sca-1+ cells (LKS cells, a population of enriched hematopoietic stem cells) is rapidly increased during septicemia. This LKS cell response is primarily supported by the up-regulation of Sca-1 expression, which is critical for the enhancement of granulocyte production. Alcohol intoxication impairs this response. My preliminary studies for this application show that Sca-1 expression during septicemia is also enhanced in downstream granulocyte lineage committed cells that express low levels of granulocyte differentiation antigen- 1 (Gr1). The up-regulated expression of Sca-1 in this committed cell compartment is associated with enhanced proliferation of granulopoietic precursors and accelerated production of granulocytes. This process involves key cell signaling pathways that down-regulate STAT3 signaling and enhance p44/p42-cyclin D signaling. Alcohol intoxication disrupts these adjustments in cell signaling activity and impairs Sca-1 associated enhancement of granulocyte production by an unknown mechanism. Based on these preliminary studies, my hypothesis is that alcohol impairs Sca-1 signaling in the early stage of granulocyte development and blocks the granulopoietic response to septicemia.
Two specific aims are: (1) To test the prediction that alcohol impairs Sca-1 mediated enhancement of p44/42-cyclin D signaling in promoting Gr1lo cell proliferation during septicemia;(2) To test the prediction that alcohol disrupts Sca-1 mediated down- regulation of STAT3 signaling in the regulation of Gr1lo cell proliferation during septicemia. This study will provide novel information about the molecular mechanism underlying alcohol-induced impairment of the granulopoietic response to bacterial infection. It will also build a foundation for developing effective therapeutic strategies to treat myelosuppression in alcohol abusers with severe bacterial infection.
Understanding how alcohol affects Sca-1 expression in Gr1lo granulopoietic precursor cells during septicemia will provide novel information about the pathogenesis of granulocytopenia in alcohol abusers with severe infection. Alcohol may be inhibiting yet unknown endogenous mechanisms that expand the granulopoietic precursor cell compartment and enhance the granulopoietic activity of precursor cells during infection. Information from this study will elucidate potential therapeutic interventions for the effective treatment of blood-borne infections in these immunocompromised hosts.
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