Genes for Apolipoprotein B and Microsomal Triglyceride Transfer Protein Are Expressed in the Heart Evidence That the Heart Has the Capacity to Synthesize and Secrete Lipoproteins

Background—Expression of both the apolipoprotein B (apoB) gene and the microsomal triglyceride transfer protein (MTP) gene is required for the assembly and secretion of triglyceride-rich lipoproteins in the liver and intestine. Both genes have been assumed to be silent in the heart. Methods and Results—Northern blot and RNase protection analyses showed that the apoB and MTP genes were expressed in the hearts of mice and humans. In situ hybridization studies revealed that the apoB mRNA was produced in cardiac myocytes. Electron microscopy of human cardiac myocytes revealed lipid-staining particles of relatively small diameter (≈250 A) within the Golgi apparatus. Conclusions—These studies strongly suggest that the heart synthesizes and secretes apoB-containing lipoproteins.