Abstract 1603: Hypoxia Inducible Factor-1 Up Regulates Adiponectin mRNA and Protein Levels In Diabetic Mouse Hearts and Attenuates Post-Ischemic Injury
Background: Adiponectin (Acrp30) is an adipocyte cytokine that is significantly reduced in patients with Type II diabetes mellitus (DM) and cardiovascular disease. The mechanisms leading to diminished Acrp30 remain unknown. Recently, Acrp30 was found to be synthesized by cardiomyocytes. Hypoxia Inducible Factor-1 (HIF-1) modulates expression of genes essential for cell survival in ischemic environments. The oxygen-sensing enzyme prolyl 4-hydroxylase 2 (P4HA2) targets HIF-1α for destruction in normoxic environments. We employed small interfering RNA (siRNA) to silence murine P4HA2, producing activation of HIF-1 under normoxic conditions. We hypothesized that Acrp30 is a HIF-1 regulated gene and that induction of cardiomyocyte Acrp30 expression via HIF-1 activation in diabetic hearts attenuates myocardial damage following ischemia reperfusion (I/R) injury.
Methods and Results: Cardiac Acrp30 mRNA levels quantified by real time quantitative PCR in leptin receptor−/− mice (Leprdb, formerly db/db), a model of Type II DM, were 75% less than that observed in corresponding C57BL/6J wild type mice (n=3/group, P <0.05). Wild type mice injected intra-peritoneally (IP) with P4HA2 siRNA exhibited 22-fold induction in cardiac adiponectin mRNA 24 hours following injection (n=3/group, P <0.001). Acrp30 mRNA remained significantly elevated at 2 days (5-fold), declining to 2-fold increase over control hearts by day 5. Acrp30 protein levels, assessed via Western blot analysis, progressively increased in P4HA2 silenced hearts. P4HA2 siRNA injected 24 hours prior to study increased cardiac Acrp30 mRNA in Leprdb mice (>5-fold) when compared to Leprdb mice injected with a non-targeting control siRNA (n=3/group, P <0.01). P4HA2 silencing in Leprdb mice significantly diminished infarct size in hearts exposed to global ischemia (30 min) followed by reperfusion (60 min) when compared to saline infused Leprdb mice (14.4 ± 0.1% vs. 22.85 ± 0.65% respectively; P <0.01, expressed as % of risk area; mean ± SE, n=3/group).
Conclusion: Acrp30 is a novel target for HIF-1. In vivo cardiac Acrp30 induction by targeted siRNA-mediated P4HA2 silencing is associated with attenuated cardiac I/R injury in diabetic hearts.