HEME OXYGENASE-1 IN HEPATIC ISCHEMIA/REPERFUSION INJURY

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DESCRIPTION (provided by applicant): lschemia/reperfusion (I/R) insult remains one of the major limitations of orthotopic liver transplantation (OLT). This proposal is built upon the insights gained from our studies on a novel approach of inducing heme oxygenase-1 (HO-1) expression in OLTs. We hypothesize that: (i) HO-I facilitates a systemic mileu, which via STAT6 pathway leads to emergence of a dominant "cytoprotectlve" type-2 T cell subset; (ii) HO-1 depresses apoptotic machinery and triggers type-2 anti-apoptotic cytoprotactive mechanisms; (iii) hyaluronic acid (HA) provides a "danger" signal to activate toll-like receptor 4 (TLR 4) complex on Kupffer cells; HO-1 - TLR 4 cross-talk prevents l/R insult by keeping Kupffer cetl activation in check. We propose following specific aims: (1). To evaluate local vs. systemic ceil requirements for HO-1-facilitated cytoprotection; By using HO-1 Tg mice, we will determine impact of local (endothelial/parenchymal) vs. systemic (lymphocyte) HO-1 expression. We will analyze which hepatic components vs. spleen T cell subsets are instrumental in HO-1 effects. The role of STAT6 in the emergence of a dominant HO-1-dependent cytoprotective type-2 T cell will be assessed. (2). To dissect apoptotic/anti-apoptotic pathways in the mechanism of HO-1-facilitated cytoprotection: We plan to determine the molecular basis of HO-1 mediated cytoprotection in OLT recipients and in primary mouse hepatocyte cultures upon the death signaling machinery (TNF/FasL), and apoptotic stimuli (ROS). This will include activation of caspases, cytochrome c release, and expression of anti-/pro-apoptotic genes. We will analyze whether HO-1-mediated depression of apoptotic machinery in hepatocytes and upregulation of endothelial anti-apoptotic molecules represents local hepatic or systemic T cell-dependent feature. (3). To explore cross-talk between HO-1 and TLR 4 complex - I/R injury a case for innate immunity? We will study how HA, shed from damaged sinusoidai endothelial cells, interacts with Kupffer cells, to what extent HA triggers expression/activation of Kupffer ceils in TLR 4 mutant/deficient vs. WT mice. The ability of sHA to affect hepatic I/R insult in TLR 4 mutant/TLR 4 KO mice will be probed. We will analyze by which mechanism depression of HO activity affects innate immunity balance, and triggers phenotypic/functional TLR4 activation.