The Role of MCTP2 in Health and Disease

Abstract

MCTP2 (multiple C2 domain transmembrane containing protein 2) encodes a protein with poorly understood roles in lipid metabolism and lipid droplet biogenesis. Genetic studies previously identified variations in MCTP2 in conjunction with left ventricular outflow tract obstructive forms of congenital heart disease (CHD). This dissertation research aimed to delineate the biomedical significance of Mctp2 by investigating its expression and consequences of its genetic deletion in mouse models. Temporal and spatial expression of Mctp2 was investigated by RT-PCR and in-situ hybridization. A novel isoform, designated as isoform 2 in mice, results from alternative pre-mRNA splicing. Similar levels of Mctp2 isoforms 1 and 2 are present in embryonic tissues, whereas isoform 1 is preferentially expressed in adult tissues with high lipid metabolism. During mouse embryonic development, in-situ hybridization suggests expression of Mctp2 at the gut tube, liver bud and near the pharyngeal arches from E8.5 – E10.5. Given association of MCTP2 with CHD, the biological significance of Mctp2 was addressed using gene trap (GT) and conditional mouse models. Survival of Mctp2 GT mice was dependent on the genetic background strain, suggesting a role for strain-specific modifiers. Conditional knockout of Mctp2 in cardiac progenitor cells displayed no effect on survival. The role of Mctp2 in cardiac development remains to be delineated. The role of Mctp2 in cardiac function was addressed in both mouse models. Initial findings suggest Mctp2 allele dosage effects on the development of heart failure. GT mice lacking one, or both, copies of Mctp2 display cardiac systolic dysfunction, with upregulation of heart failure markers at 50 weeks of age in heterozygotes and increases in cardiac fibrosis in homozygotes. Systemic conditional deletion of Mctp2 did not show heart failure phenotypes using the strain protective from lethality. However, cardiac specific deletion of Mctp2 using the Nkx2.5-Cre driver, a line that is sensitized for cardiac dysfunction, led to decreased ejection fraction and fractional shortening in mice with conditional deletion of both copies of Mctp2 as well as Mctp2 dosage dependent penetrance of cardiac dilation. These studies of knockout mice suggest a role for Mctp2 in maintenance of cardiac function and possible genetic interaction with Nkx2.5.