Abstract 28: Detrimental Effect of Leptin on Intracerebral Hemorrhage via STAT3 signal pathway

Abstract

Background: Leptin, one of the most alleged adipokines, is a key regulator of energy balance and body weight. Leptin exerts its tissue protective effect in ischemic injuries via anti-apoptotic mechanisms. However, few studies have elaborated on the association between leptin and tissue damages in intracerebral hemorrhage (ICH). Methods: We induced ICH in ICR mice via the infusion of collagenase, and recombinant leptin or PBS was administered intraperitoneally. To determine the effects of leptin deficiency, ICH-induction was done in wild-type (WT) or leptin-deficient Lep ob /Lep ob ( ob/ob ) mice. Brain water content, reflecting peri-hematomal edema, and hemorrhage volume were measured at 72 hours. The number of inflammatory cells (OX6-positive cells) was measured at 48 hours, and western blotting was performed at 24 hours. To identify the role of STAT3, a phosphorylated-STAT3 (pSTAT3) inhibitor, NCS74859 , was administered after inducing ICH in hyperleptinemic mice. To localize the working site of pSTAT3, we performed double-staining with a pSTAT3 antibody and a marker of neuron, astrocyte, or macrophage. Results: We compared two doses of leptin and the brain water contents were increased dose-dependently (ρ=0.53, p<0.01). The water contents were 81.5±0.2% in leptin-injected group (8 mg/kg) and 80.1±0.3% in control group (p<0.01). The water content of ob/ob mice was decreased, compared to WT mice in hemorrhagic hemispheres (WT mice: 79.7±0.6%, ob/ob mice: 78.8±0.6%; p<0.05). Mean hemorrhage volumes were not different respectively between ob/ob and WT mice, and between leptin-injected and control groups. The leptin-injected group exhibited a higher number of OX6-positive cells (leptin-injected group: 129±13 cells/mm 3 ; control group: 88±10 cell/mm 3 ; p<0.05). Western blotting revealed that the exogenous-leptin had affected an increase in the levels of pSTAT3, and the relative optical-density was higher, by 1.8-fold, in leptin-injected group than in control group (p<0.05). After inhibiting pSTAT3 using NSC74859 , the brain water content of pSTAT3-inhibiting group was decreased, compared to non-inhibiting group (pSTAT3-inhibiting group: 79.8±0.8%, non-inhibiting group: 81.5±0.2%; p<0.05). Ox6-positive cells were co-localized by pSTAT3, but in neurons and astrocytes, pSTAT3 was not detected. Conclusion: Our study documented that peri-hematomal edema and inflammation were increased by leptin via STAT3 signal pathway. These results may indicate the potentially detrimental role of leptin on ICH.