Heart surgery

University of Alabama at Birmingham: Changing gene expression after heart surgery prolongs cardiomyocyte regeneration | India Education | Latest Education News | World Education News


While lower vertebrates can repair their adult hearts after a heart attack, mammals, including humans, cannot. The ability to regenerate dead muscle tissue in the mammalian heart disappears just days after birth as heart muscle cells, called cardiomyocytes, leave the cell cycle.

After that, all heart growth comes from the enlargement of existing cells, not from the creation of new muscle cells. In an adult heart attack, heart failure occurs when lost cardiomyocytes are replaced with fibrous scar tissue, instead of new muscle cells. This sets off a vicious cycle of cardiac enlargement, loss of pumping function, and eventual death.

In 2020, researchers at the University of Alabama at Birmingham reported that surgery to remove the apex of the left ventricle from the hearts of pigs, one day after birth, somehow prolonged the replication capacity of pigs. heart muscle cells. In fact, after such surgery, pigs can fully recover from a heart attack four weeks after birth, with no scarring or decline in heart function.

To better understand the underlying gene expression changes in this extended regeneration window, UAB researchers now report nuclear RNA sequencing of heart muscle cells, using this porcine model. With this knowledge and much more research to come, clinicians could potentially learn how to regenerate adult cardiac cardiomyocytes after a heart attack.

This study, led by Jianyi “Jay” Zhang, MD, Ph.D., chair of UAB’s Department of Biomedical Engineering, is published as a circulation research letter.

The researchers compared heart tissue nuclei from five groups of pigs. Two groups were regenerative models that had left ventricular apical resections, or AR, on the first postnatal day, or P1. One of these two groups then underwent anterior descending coronary artery ligation four weeks after birth, or P28, to induce myocardial infarction, or MI; this group is called ARP1MIP28. The other group, called ARP1, had no ligature.

Two non-regenerative controls did not have the P1 apical resection, but one had the induced heart attack at P28. These two groups were called Control and MIP28.

Hearts were removed for single-nucleus RNA sequencing from P30 to P56 for ARP1MIP28 animals, and hearts from all other groups were explanted for sequencing on P1, P28, or P56.

The fifth group consisted of fetal hearts, or FHs, at embryonic day 80.

A total of 218,945 high-quality nuclei were captured and a network biology cluster analysis identified the eight major cardiac cell types. Complete gene core data were available for 94,844 cardiomyocytes. Cardiomyocytes have been divided into six groups, named cardiomyocytes 1 to cardiomyocytes 6.

Three clusters were almost entirely composed of cardiomyocytes from a single experimental group: cardiomyocyte 2 from control – P56, cardiomyocyte 3 from control – P1, and cardiomyocyte 6 from FH.

Cardiomyocyte groups 4 and 5 contained mainly ARP1MIP28–P35 cardiomyocytes. Cardiomyocyte group 1 included cardiomyocytes from all other animal groups and time points and a small number of ARP1MIP28–P35 cardiomyocytes, but few fetal or control cardiomyocytes–P56.

Cardiomyocyte clusters 4 and 5 that contained mostly ARP1MIP28–P35 cardiomyocytes showed increased cell cycle activity and proliferation, changes that helped remuscularize the left ventricle after an experimental heart attack, without scarring. The researchers also found 506 genes positively correlated with the highly proliferative cardiomyocytes ARP1MIP28–P30 and ARP1MIP28–P35; these genes participate in pathways that regulate cardiac development, cell proliferation, and cardiomyocyte proliferation.

“It will be interesting to examine these two distinct cell populations of the ARP1MIP28 lesion in future studies,” Zhang said. “The results are very impactful because they show, for the first time, that the left ventricle can remuscularize myocardial infarction beyond the seventh postnatal day, or P7, in large mammals. These observations provide a basis for future investigations of the molecular mechanisms and signaling molecules that regulate injury-induced preservation of cardiomyocyte cell cycle activity in neonatal large mammals, and ultimately to remuscularize cardiac muscle in patients with heart attacks, thus preventing heart failure.”