Age-related dystrophic calcification in the human cardiovascular system is extremely common, perhaps more prevalent than ischemic heart disease in the oldest age groups, and can contribute significantly to cardiac dysfunction. Despite the high prevalence and clinical significance, few experimental model systems exist and little mechanistic data are available. We propose to exploit a known genetic susceptibility in mice to further delineate the molecular understanding of cardiovascular degeneration and calcification in aging. The long-range goal of this application is to identify the specific genes underlying spontaneous dystrophic cardiac calcification (DCC) in strain DBA/2 (D2) mice. DCC is an age-related strain-specific lesion mainly of cardiac muscle occurring in D2 mice and related strains. Susceptibility to DCC is conferred by at least two autosomal recessive genes; the residence of one appears to have been narrowed to one chromosomal region. Dyscalc, from which we have recently nominated a candidate gene. Our objectives in this pilot project application are to: (1) perform a genome exclusion mapping study using sequence tagged site markers to identify the locations of all DCC loci; and (2) conduct the initial evaluation of a novel mechanistic hypothesis for DCC based upon a candidate gene, Myocyte Enhancer Factor 2A (MEF2A), a key transcription factor in muscle. MEF2A maps to the Dyscalc region and controls the expression of the intermediate filament protein desmin; desmin null knockout mice manifest a close phenocopy of DCC. We hypothesize that the D2 MEF2A gene alters the expression of certain critical genes such as desmin that result in DCC, perhaps through apoptosis. We propose to perform a histological based apoptosis assay and immunohistochemical analysis of desmin and vimentin on hearts from DCC sensitive strain D2 and resistant C57BL/6 (B6) mice to test this hypothesis. In addition, we plan to conduct initial structural analysis of the MEF2A gene in D2 and B6 mice. Completion of these aims will constitute significant progress toward identifying the specific genes underlying DCC and evaluating the potential role of MEF2A, providing valuable preliminary data for subsequent studies. The genes conferring susceptibility to DCC in mice should provide a novel molecular approach to age-related calcification occurring in the human cardiovascular system.
