Excessive branched-chain amino acid accumulation restricts mesenchymal stem cell-based therapy efficacy in myocardial infarction.

Mesenchymal stem cells (MSCs) delivered into the post-ischemic heart milieu have a low survival and retention rate, thus restricting the cardioreparative efficacy of MSC-based therapy. Chronic ischemia results in metabolic reprogramming in the heart, but little is known about how these metabolic changes influence implanted MSCs. Here, we found that excessive branched-chain amino acid (BCAA) accumulation, a metabolic signature seen in the post-ischemic heart, was disadvantageous to the retention and cardioprotection of intramyocardially injected MSCs. Discovery-driven experiments revealed that BCAA at pathological levels sensitized MSCs to stress-induced cell death and premature senescence via accelerating the loss of histone 3 lysine 9 trimethylation (H3K9me3). A novel mTORC1/DUX4/KDM4E axis was identified as the cause of BCAA-induced H3K9me3 loss and adverse phenotype acquisition. Enhancing BCAA catabolic capability in MSCs via genetic/pharmacological approaches greatly improved their adaptation to the high BCAA milieu and strengthened their cardioprotective efficacy. We conclude that aberrant BCAA accumulation is detrimental to implanted MSCs via a previously unknown metabolite-signaling-epigenetic mechanism, emphasizing that the metabolic changes of the post-ischemic heart crucially influence the fate of implanted MSCs and their therapeutic benefits.