Background

We investigated the myocardial perfusion differences and changes in immune cell response in heart-transplant patients with nonspecific graft dysfunction (NGD) compared to cardiac allograft vasculopathy (CAV) patients and normal heart-transplant patients.

Methods and Results

We prospectively studied 17 heart-transplant patients (59.8±14.1 years, 78% male) from January to June 2016. Regadenoson stress cardiac MRI was performed in the patients and peripheral blood obtained contemporaneously to isolate peripheral blood mononuclear cells (PBMCs). Stress myocardial perfusion showed significantly decreased myocardial perfusion using maximum upslope method in NGD and CAV patients compared to normal heart-transplant patients. Myocardial scar by late gadolinium enhancement also was significantly increased in nonspecific graft dysfunction patients compared to normal. Evaluation of PBMCs by flow cytometry showed a trend towards increased activated HLA-DR + T cells in NGD patients compared to normal. Clinical outcomes for cardiac hospitalization, allograft loss/retransplant, death were assessed at 8 years.

Conclusions

NGD shows decreased stress myocardial perfusion by cardiac MRI and a trend towards increased activated T cells in PBMCs, suggestive of an immune-mediated cause for allograft dysfunction.

Background

Donor-derived cell-free DNA (dd-cfDNA) testing is an emerging screening modality for noninvasive detection of acute rejection (AR). This study compared the testing accuracy for AR of two commercially available dd-cfDNA and gene-expression profiling (GEP) testing in heart transplant (HTx) recipients.

Methods

This is a retrospective, observational study of HTx only patients who underwent standard and expanded single nucleotide polymorphism (SNP) dd-cfDNA between October 2020 to January 2022. Comparison with GEP was also performed. Assays were compared for correlation, accurate classification, and prediction for AR.

Results

A total of 428 samples from 112 unique HTx patients were used for the study. A positive standard SNP correlated with the expanded SNP assay (p < .001). Both standard and expanded SNP tests showed low sensitivity (39%, p = 1.0) but high specificity (82% and 84%, p = 1.0) for AR. GEP did not improve sensitivity and showed worse specificity (p < .001) compared to standard dd-cfDNA.

Conclusion

We found no significant difference between standard and expanded SNP assays in detecting AR. We show improved specificity without change in sensitivity using dd-cfDNA in place of GEP testing. Prospective controlled studies to address how to best implement dd-cfDNA testing into clinical practice are needed.

Background

Mitochondrial dysfunction results in an imbalance between energy supply and demand in a failing heart. An innovative therapy that targets the intracellular bioenergetics directly through mitochondria transfer may be necessary.

Objectives

The purpose of this study was to establish a preclinical proof-of-concept that extracellular vesicle (EV)-mediated transfer of autologous mitochondria and their related energy source enhance cardiac function through restoration of myocardial bioenergetics.

Methods

Human-induced pluripotent stem cell-derived cardiomyocytes (iCMs) were employed. iCM-conditioned medium was ultracentrifuged to collect mitochondria-rich EVs (M-EVs). Therapeutic effects of M-EVs were investigated using in vivo murine myocardial infarction (MI) model.

Results

Electron microscopy revealed healthy-shaped mitochondria inside M-EVs. Confocal microscopy showed that M-EV-derived mitochondria were transferred into the recipient iCMs and fused with their endogenous mitochondrial networks. Treatment with 1.0 × 10⁸/ml M-EVs significantly restored the intracellular adenosine triphosphate production and improved contractile profiles of hypoxia-injured iCMs as early as 3 h after treatment. In contrast, isolated mitochondria that contained 300× more mitochondrial proteins than 1.0 × 10⁸/ml M-EVs showed no effect after 24 h. M-EVs contained mitochondrial biogenesis-related messenger ribonucleic acids, including proliferator-activated receptor γ coactivator-1α, which on transfer activated mitochondrial biogenesis in the recipient iCMs at 24 h after treatment. Finally, intramyocardial injection of 1.0 × 10⁸ M-EVs demonstrated significantly improved post-MI cardiac function through restoration of bioenergetics and mitochondrial biogenesis.

Conclusions

M-EVs facilitated immediate transfer of their mitochondrial and nonmitochondrial cargos, contributing to improved intracellular energetics in vitro. Intramyocardial injection of M-EVs enhanced post-MI cardiac function in vivo. This therapy can be developed as a novel, precision therapeutic for mitochondria-related diseases including heart failure.

Endogenous capability of the post-mitotic human heart holds great promise to restore the injured myocardium. Recent evidence indicates that the extracellular vesicles (EVs) regulate cardiac homeostasis and regeneration. Here, we investigated the molecular mechanism of EVs for self-repair. We isolated EVs from human iPSC-derived cardiomyocytes (iCMs), which were exposed to hypoxic (hEVs) and normoxic conditions (nEVs), and examined their roles in in vitro and in vivo models of cardiac injury. hEV treatment significantly improved the viability of hypoxic iCMs in vitro and cardiac function of severely injured murine myocardium in vivo. Microarray analysis of the EVs revealed significantly enriched expression of the miR-106a-363 cluster (miR cluster) in hEVs vs. nEVs. This miR cluster preserved survival and contractility of hypoxia-injured iCMs and maintained murine left-ventricular (LV) chamber size, improved LV ejection fraction, and reduced myocardial fibrosis of the injured myocardium. RNA-Seq analysis identified Jag1-Notch3-Hes1 as a target intracellular pathway of the miR cluster. Moreover, the study found that the cell cycle activator and cytokinesis genes were significantly up-regulated in the iCMs treated with miR cluster and Notch3 siRNA. Together, these results suggested that the miR cluster in the EVs stimulated cardiomyocyte cell cycle re-entry by repressing Notch3 to induce cell proliferation and augment myocardial self-repair. The miR cluster may represent an effective therapeutic approach for ischemic cardiomyopathy.

Genetic variation in the FAM13A (Family with Sequence Similarity 13 Member A) locus has been associated with several glycemic and metabolic traits in genome-wide association studies (GWAS). Here, we demonstrate that in humans, FAM13A alleles are associated with increased FAM13A expression in subcutaneous adipose tissue (SAT) and an insulin resistance-related phenotype (e.g. higher waist-to-hip ratio and fasting insulin levels, but lower body fat). In human adipocyte models, knockdown of FAM13A in preadipocytes accelerates adipocyte differentiation. In mice, Fam13a knockout (KO) have a lower visceral to subcutaneous fat (VAT/SAT) ratio after high-fat diet challenge, in comparison to their wild-type counterparts. Subcutaneous adipocytes in KO mice show a size distribution shift toward an increased number of smaller adipocytes, along with an improved adipogenic potential. Our results indicate that GWAS-associated variants within the FAM13A locus alter adipose FAM13A expression, which in turn, regulates adipocyte differentiation and contribute to changes in body fat distribution.