Abstract 14717: Endocrine Mechanisms against Ischemic Cardiomyocyte Calcification

Abstract

Myocardial infarction causes cardiomyocyte calcification or deposition of hydroxyapatite crystals, structures disrupting cardiomyocytes and intensifying myocardial injury. While cardiomyocyte calcification is well recognized, the underlying mechanisms remain elusive and few treatment strategies have been established. Here, we test the hypotheses that annexins (ANXs), intracellular Ca++ carriers associated with the plasma membrane, contribute to ischemic cardiomyocyte calcification and the endocrine protein trefoil factor 3 (TFF3) is upregulated and released from the liver in ischemic myocardial injury, protecting ischemic cardiomyocytes from annexin-dependent calcification. Myocardial ischemia/reperfusion injury in 129s1/sv Imj mice caused translocation of ANXs A2, A3, A4, A5, and A7 from the cardiomyocyte membrane to α actin filaments in association with hydroxyapatite deposition to α actin filaments prior to cardiomyocyte death from 1 to 10 days. siRNA-mediated silencing of the ANX A2, A3, A4, A5, and A7 genes reduced the fraction of calcified cardiomyocytes at day 5 from 6.3+/-1.8% (control siRNA) to 2.1+/-0.6% in reference to the infarct area (p<0.01), suggesting a pro-calcification role for these ANXs. Myocardial injury caused upregulation and release of TFF3 from the liver. TFF3-/- mice exhibited intensified ischemic cardiomyocyte calcification (17.8+/-5.2%) compared to wildtype mice (5.6+/-2.3%, p<0.001), suggesting an anti-calcification role for TFF3. TFF3 was able to bind to ANXs A2, A3, A4, A5, and A7, demonstrated by TFF3 crosslinking assay and mass spectroscopy. ANX A2, A3, A4, A5, or A7 was able to co-immunoprecipitate with TFF3 in ischemic cardiomyocytes. Computational molecular interaction analyses by using the Autodocking software system showed TFF3 interaction with the ANX C-terminus, a structure binding to actin filaments. Myocardial administration of recombinant TFF3 reduced ANX-dependent cardiomyocyte calcification. These observations suggest that ANXs cause ischemic cardiomyocyte calcification by binding to α actin filaments and TFF3 is upregulated and released from the liver in myocardial ischemia, mitigating cardiomyocyte calcification by blocking ANX binding to actin filaments.