Identification and differential expression of the microphthalmia-associated transcription factor in heart and isolated cardiomyocytes from Guinea pigs: Possible role in hypertrophy and viability

Introduction: The microphthalmia-associated transcription factor (MITF) regulates the expression of specific genes and its cardiac expression and function is not known. Objectives: To identify the expression of MITF in hearts and isolated cardiomyocytes from Guinea pigs, to describe morphological changes associated with mRNA interference of MITF and to evaluate their relative changes in expression in isolated cardiomyocytes under ischemic preconditioning. Materials and methods: The cardiac specific isoform, MITF-H, and relative expression level analysis, was determined by semi-quantitative real time PCR, sequencing and Western blotting. Reduction of mRNA-MITF-H was induced by transduction of specific-MITF-shRNAi interference. The cardiac morphological changes, diameter and number of cardiac fibers were evaluated by direct observation and light microscopy. Results: A cDNA fragment of 281 bp was amplified from heart and isolated ventricular cardiac myocytes. Sequence analysis confirmed the identity of the isoform MITF-H, exon 1. The MITF silencing was associated with an increase in cardiac index (heart weight/body weight vs. 5.46 x 10(-3) vs 4.6 x 10(-3)) and higher diameter of cardiac fibers (50.2 +/- 16 mu m vs 38,7 +/- 14,7 mu m p<0.05, n=150). In isolated cardiac myocytes under ischemic preconditioning we observed a higher relative expression compared with that measured in myocytes exposed to normoxia and simulated ischemia (eighty and one hundred times, p<0.05, n = 5). Conclusion. The results suggest that MITF-H isoform may be involved in Guinea pig cardiac hypertrophy, response to stress by ischemia and cardiomyocytes survival.