Role of Brd4 in enhancing old donor heart preservation quality via 3D chromosomal restructuring

About This Grant

Project Summary/Abstract While heart transplantation is the gold standard to treat patients with end-stage heart failure, there is a shortage of donor hearts for recipients. However, many donor hearts on offer are not accepted for transplant. This can be for multiple reasons, but the risk of primary graft dysfunction (PGD) is a major factor in turning down donor hearts. Unfortunately, older donors are associated with a higher incidence of PGD19, and hearts from donors >55 years of age are often not considered for the transplant. In 2024, only 303 hearts from a total of 6608 donors > 50 years were used for transplantation. Therefore, there is a large potential donor pool that exists beyond the traditional age threshold for donor heart acceptance. Expanding our molecular understanding of aging biology in determining donor heart preservation quality is needed to fully utilize the potential donor heart pool. Brd4 is a member of the bromodomain and extraterminal domain (BET) family of epigenetic readers. It plays an important role in many cardiac diseases, such as cardiac hypertrophy and coronary atherosclerosis. Brd4 interacts with numerous factors that regulate transcription, histone modification, chromatin accessibility and architecture. We show that in-vivo inhibition of Brd4 by JQ1 or Brd4 knockdown in cardiomyocytes greatly improves ex-vivo old donor heart function after preservation-reperfusion, similar to that of young donor hearts. We also demonstrate that the BRD4-associated chromatin loop increased in the old human donor heart compared to young hearts, which is further elevated after cold preservation-reperfusion injury. Moreover, we found that the increased Brd4 genomic recruitment is associated with increased histone acetylation due to reduced NAD+ levels in old donor hearts. We hypothesize that Brd4 senses the histone acetylation increase in aging hearts and modulates genomic architectural restructuring that promotes cardiac injury. In Aim 1, we will determine the mechanism by which Brd4 modulates the epigenetic landscape of old donor hearts during preservation. We will define Brd4’s role in influencing the cardiac function of cold- preserved old donor hearts as well as the specific epigenetic architectural changes in young and old donor hearts during preservation. In Aim 2, we will determine if increased Brd4 recruitment to the genome of old donor hearts is mediated by increased histone acetylation due to changes in NAD+ availability. In Aim 3, we will determine if pharmacological BRD4 inhibition improves old human donor heart preservation quality. The proposed work will define Brd4's mechanism of modulating epigenetic and 3D chromatin conformation to promote the vulnerability of old donor hearts to preservation injury. This is expected to expand the donor pool and has broad implications for other solid organ transplants and ischemic pathologies like heart attack and stroke.