Phospho-mimetic cardiac troponin I Ser43/45 produces early changes in mitochondria.

Abstract

Our work tests whether chronic protein kinase C (PKC)-mediated phosphorylation of cardiac troponin I (cTnI) Ser43/45 diminishes cardiac function and initiates progressive heart failure via early increases in oxidative stress and mitochondria. The current work focuses on early gene expression responses in mice after cardiac-specific phospho-mimetic cTnI S43/45D (SD) replacement of endogenous cTnI. Dose-dependent changes in cTnISD replacement do not significantly change function, when measured by echocardiography at 1 month (mos) of age in male or female mice. However, by 2 mos of age, the highest cTnISD replacement line develop significant dysfunction and 100% mortality by 16 weeks of age, with males (M) dying earlier than females (F; F = 14.6 ± 0.4 wks, n = 32; M = 9.3 ± 0.3 wks, n = 68). Based on gene expression measured by quantitative PCR (QPCR) analysis, 1 mos old hearts from this high replacement cTnISD line of mice develop significant reductions in mitochondrially-encoded cytochrome oxidase and cytochrome b in males, which are followed by similar changes at 2 mos of age in females. Reductions in gene expression of critical mitochondrial proteins PGC-1α and SOD2 also develop by 1 mos of age in males. In contrast, there are no detected changes in gene expression of the endoplasmic reticulum (ER) and nuclear stress markers, ATF6 and Nrf2, respectively for males and/or females by 2 mos of age in the high replacement cTnISD mice. Ongoing work is determining whether similar changes develop in the protein expression of these genes in young adult mice. The present results are consistent with the idea that chronic modification of the sarcomere produces a stress signal leading to early mitochondrial and oxidative stress responses, which are predicted to lay the foundation for the progressive deterioration in cardiac function observed in this model.