No abstract

Ischemic preconditioning increases the heart's tolerance to a subsequent longer ischemic period. The aim of this study was to investigate the effect of early and delayed preconditioning on gap junction communication, connexin abundance, and phosphorylation in cultured neonatal rat cardiac myocytes. Prolonged ischemia followed 5 minutes after preconditioning in the early protocol, whereas 20 hours separated preconditioning and prolonged ischemia in the delayed preconditioning protocol. Gap junctional intercellular communication (GJIC) was assessed by Lucifer yellow dye transfer. An initial reduction in communication in response to sublethal ischemia was observed. This may be one mechanism whereby neighboring cells are protected from damaging substances produced during the first phase of subsequent regional ischemia in early preconditioning protocols. With respect to delayed preconditioning, the transient decrease in GJIC disappeared prior to prolonged ischemia, indicating that other mechanisms are responsible for delayed protection. Both early and delayed preconditioning preserved intercellular coupling after prolonged ischemia and this correlated with presence of less connexin43 dephosphorylation assessed by immunoblot.

The hepatic glucose fasting response is gaining traction as a therapeutic pathway to enhance hepatic and wholehost metabolism. However, the mechanisms underlying these metabolic effects remain unclear. Here, we demonstrate the lipoxygenase, ALOXE3, is a novel effector of the therapeutic fasting response. We show that ALOXE3 is activated during fasting, glucose withdrawal, or trehalose/trehalose analogue treatment. Hepatocytespecific ALOXE3 expression reduced weight gain and hepatic steatosis in diet-induced and genetically obese (db/db) models. ALOXE3 expression moreover enhanced basal thermogenesis and abrogated insulin resistance in db/db diabetic mice. Targeted metabolomics demonstrated accumulation of the PPARg ligand, 12-KETE in hepatocytes overexpressing ALOXE3. Strikingly, PPARg inhibition reversed hepatic ALOXE3-mediated insulin sensitization, suppression of hepatocellular ATP production and oxygen consumption, and gene induction of PPARg coactivator-1a (PGC1a) expression. Moreover, hepatocyte-specific PPARg deletion reversed the therapeutic effect of hepatic ALOXE3 expression on diet-induced insulin intolerance. ALOXE3 is therefore a novel effector of the hepatocellular fasting response that leverages both PPARg-mediated and pleiotropic effects to augment hepatic and whole-host metabolism, and is thus a promising target to ameliorate metabolic disease.