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 t he assembly and secretion of triglyceride-rich lipoproteins in the liv er and intestine. Both genes have been assumed to be silent in the hea rt. Methods and Results-Northern blot and RNase protection analyses sh owed 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 diamet er ( approximate to 250 Angstrom) within the Golgi apparatus. Conclusi ons-These studies strongly suggest that the heart synthesizes and secr etes apoB-containing lipoproteins.