Aging is a major risk for developing cardiac and skeletal muscle dysfunction, yet the underlying mechanism remains elusive. Here we demonstrated that the mitochondria-associated endoplasmic reticulum membranes (MAMs) in the rat heart and skeletal muscle were disrupted during aging. Using quantitative morphological analysis, we showed that the mitochondria-endoplasmic reticulum contacts (MERCs) were reduced by half over the lifespan with an early onset of accelerated thickening in the clefts. The ultrastructural changes were further validated by proteomic profiling of the MAM fractions. A combination of subcellular fractionation and quantitative mass spectrometry identified 1306 MAM-enriched proteins in both heart and skeletal muscle, with a catalog of proteins dysregulated with aging. Functional mapping of the MAM proteome suggested several aging signatures to be closely associated with the ER-mitochondria crosstalk, including local metabolic rewiring, calcium homeostasis imbalance, and impaired organelle dynamics and autophagy. Moreover, we identified a subset of highly interconnected proteins in an ER-mitochondria organization network, which were consistently down-regulated with aging. These decreased proteins, including VDAC1, SAMM50, MTX1 and MIC60, were considered as potential contributors to the age-related MAM dysfunction. This study highlights the perturbation in MAM integrity during the striated muscle aging process, and provides a framework for understanding aging biology from the perspective of organelle interactions.

BACKGROUND: Pathological cardiac remodeling after myocardial infarction (MI) is a leading cause of heart failure and sudden death. The detailed mechanisms underlying the transition to heart failure after MI are not fully understood. Disruptions in the endoplasmic reticulum (ER)–mitochondria connectivity, along with mitochondrial dysfunction, are substantial contributors to this remodeling process. In this study, we aimed to explore the impact of mitochondrial tumor suppressor 1A (Mtus1A) on cardiac remodeling subsequent to MI and elucidate its regulatory role in ER-mitochondria interactions. METHODS: Single-nucleus RNA sequencing analysis was performed to delineate the expression patterns of mitochondrial tumor suppressor 1 (Mtus1) in human cardiomyocytes under ischemic stress. MI models were induced in mice by left coronary artery ligation and replicated in vitro using primary neonatal rat ventricular myocytes exposed to oxygen glucose deprivation. Cardiac-specific deletion of Mtus1 was achieved by crossing floxed Mtus1 mice with the Myh6-MerCreMer mice. The impact of Mtus1A, a mitochondrial isoform of Mtus1, on cardiac function and the molecular mechanisms were investigated in both in vivo and in vitro settings. Mitochondria-associated ER membranes (MAMs) coupling levels were evaluated by transmission electron microscopy and live-cell imaging. Protein interactions involving Mtus1A were explored through immunoprecipitation–mass spectrometry, coimmunoprecipitation, and proximity ligation assay. The roles of Mtus1A and Fbxo7 (F-box protein 7) were validated in a murine MI model using adeno-associated virus serotype 9 (AAV9). RESULTS: Bioinformatics analysis revealed a significant downregulation of Mtus1 expression in human cardiomyocytes under ischemic conditions, indicating its potential role in stress response. The predominant isoform in murine cardiomyocytes, Mtus1A, showed reduced expression in the left ventricle of mice after MI, which is consistent with the decreased levels of its orthologs in heart tissues from patients with MI. Cardiac-specific Mtus1-knockout mice exhibited worsened cardiac dysfunction after MI. Further studies demonstrated that Mtus1A partially localizes to MAMs, where it modulates MAMs coupling and preserves mitochondrial function. Mechanistically, Mtus1A functions as a scaffold protein that maintains the formation of inositol 1,4,5-trisphosphate receptor 1 (IP ₃ R1)–glucose-regulated protein 75 (Grp75)–voltage-dependent anion channel 1 (VDAC1) complex through its amino acid sequence 189-219. In addition, Mtus1A protein is stabilized by K6-linked ubiquitination through the E3 ubiquitin ligase Fbxo7. Mtus1A overexpression in mice mitigated MI-induced cardiac dysfunction and remodeling by maintaining MAMs integrity. CONCLUSIONS: Our study demonstrates that Mtus1A is crucial for modulating MI-induced cardiac remodeling by preserving ER-mitochondria communication and ameliorating mitochondrial function in cardiomyocytes. Mtus1A may serve as a potential therapeutic target for treating heart failure after MI.

Background: Early prediction and classification of prognosis is essential for patients in the coronary care unit (CCU). We applied a machine learning (ML) model using the eXtreme Gradient Boosting (XGBoost) algorithm to prognosticate CCU patients and compared XGBoost with traditional classification models.Methods: CCU patients' data were extracted from the MIMIC-III v1.4 clinical database, and divided into four groups based on the time to death: <30 days, 30 days−1 year, 1–5 years, and ≥5 years. Four classification models, including XGBoost, naïve Bayes (NB), logistic regression (LR), and support vector machine (SVM) were constructed using the Python software. These four models were tested and compared for accuracy, F1 score, Matthews correlation coefficient (MCC), and area under the curve (AUC) of the receiver operating characteristic curves. Subsequently, Local Interpretable Model-Agnostic Explanations method was performed to improve XGBoost model interpretability. We also constructed sub-models of each model based on the different categories of death time and compared the differences by decision curve analysis. The optimal model was further analyzed using a clinical impact curve. At last, feature ablation curves of the XGBoost model were conducted to obtain the simplified model.Results: Overall, 5360 CCU patients were included. Compared to NB, LR, and SVM, the XGBoost model showed better accuracy (0.663, 0.605, 0.632, and 0.622), micro-AUCs (0.873, 0.811, 0.841, and 0.818), and MCC (0.337, 0.317, 0.250, and 0.182). In subgroup analysis, the XGBoost model had a better predictive performance in acute myocardial infarction subgroup. The decision curve and clinical impact curve analyses verified the clinical utility of the XGBoost model for different categories of patients. Finally, we obtained a simplified model with thirty features.Conclusions: For CCU physicians, the ML technique by XGBoost is a potential predictive tool in patients with different conditions, and it may contribute to improvements in prognosis.

Background: Bioresorbable stents are designed to provide temporary mechanical support to the coronary arteries and then slowly degrade in vivo to avoid chronic inflammation. Zinc (Zn) is a promising material for bioresorbable stents; However, it can cause inflammation and neointimal formation after being implanted into blood vessels. Methods: To improve biocompatibility of Zn, we first coated it with polydopamine (PDA), followed by immobilization of endothelial vascular growth factor (VEGF) onto the PDA coatings. Adhesion, proliferation, and phenotype maintenance of endothelial cells (ECs) on the coated Zn were evaluated in vitro. Then, a wire aortic implantation model in rats mimicking endovascular stent implantation in humans was used to assess vascular responses to the coated Zn wires in vivo. Thrombosis in aortas post Zn wire implantation, degradation of Zn wires in vivo, neointimal formation surrounding Zn wires, and macrophage infiltration and extracellular matrix (ECM) remodeling in the neointimas were examined. Results: In vitro data showed that the PDA-coated Zn encouraged EC adhesion, spreading, proliferation, and phenotype maintenance on its surfaces. VEGF functionalization on PDA coatings further enhanced the biocompatibility of Zn to ECs. Implantation of PDA-coated Zn wires into rat aortas didn’t cause thrombosis and showed a faster blood flow than pure Zn or the Zn wires coated with VEGF alone. In addition, the PDA coating didn’t affect the degradation of Zn wires in vivo. Besides, the PDA-coated Zn wires reduced neointimal formation, increased EC coverage, decreased macrophage infiltration, and declined aggrecan accumulation in ECM. VEGF immobilization onto PDA coatings didn’t cause thrombosis and affect Zn degradation in vivo as well, and further increased the endothelization percentage as compared to PDA coating alone, thus resulting in thinner neointimas. Conclusion: These results indicate that PDA coatings with VEGF immobilization would be a promising approach to functionalize Zn surfaces to increase biocompatibility, reduce inflammation, and inhibit neointimal formation after Zn implantation in vivo. Graphical