Introduction

Ischemic heart disease is a leading contributor to global mortality, representing the most prevalent cause of death within the broad spectrum of cardiovascular diseases, which constitute a substantial health burden worldwide [1]. Unlike the repair processes in other tissues, adult cardiomyocytes possess negligible regenerative capacity. Consequently, the healing of damaged myocardial tissue is predominantly mediated by immune cells and fibroblasts, leading to scar formation [2,3]. Among them, macrophages, which originate from both circulating pools and resident populations, are considered the most crucial players in post-injury cardiac repair. They not only exhibit the function of regulating inflammation, but also interact with cardiomyocytes, endothelial cells, and fibroblasts, fundamentally driving post-MI cardiac remodeling [4]. However, factors such as hypoxia, oxidative stress, and metabolic disturbances in the infarcted area severely impair mitochondrial function in macrophages, hindering their transition to the reparative phenotype and thereby delaying and weakening the heart's self-healing capacity [5]. Although recent strategies targeting mitochondrial antioxidation and metabolic modulation have partially restored cellular function [6,7], their therapeutic efficacy is limited in cells with pre-existing mitochondrial dysfunction and damaged mitochondrial DNA (mtDNA) [8]. Therefore, developing interventions that systemically enhance the metabolic adaptability and reparative functions of macrophage mitochondria will represent a key direction in myocardial repair and regenerative therapy.

Mitochondrial transplantation therapy (MTT) is an innovative and promising strategy that delivers the healthy mitochondria either derived from normal cells or reassembled through synthetic biology into the cells and tissues to replace their defective mitochondria and restore their function [9]. Pioneering clinical studies have demonstrated that autologous mitochondrial transplantation improved outcomes in pediatric patients with myocardial ischemia-reperfusion injury, while a recent trial has expanded the therapeutic scope to inflammatory myopathies [10,11]. However, the clinical translation of MTT has been severely constrained by interrelated bottlenecks. First, isolated mitochondria are extraordinarily fragile, losing functional viability within approximately 1 h in vitro [12]. Beyond this narrow window, mitochondrial membrane potential dissipates, respiratory chain function deteriorates, and therapeutic efficacy is substantially compromised [13,14]. Second, the infarcted microenvironment, characterized by pathological oxidative stress and calcium overload, rapidly compromises transplanted organelle function and induces permeability transition [15]. Third, the efficiency of naked mitochondrial internalization by recipient cells remains extremely low, leading to substantial wastage and undesired degradation [16]. Although various biomaterials, including hydrogels, microvesicles, and polymeric microcapsules, have been developed to encapsulate and protect donor mitochondria, their protective effects are merely confined to physical shielding and rely on modifications of conventional cell delivery strategies [[17], [18], [19], [20]]. It remains challenging to develop a simple, feasible, and rapidly scalable protective strategy that can effectively preserve mitochondrial structural integrity and improve mitochondrial delivery efficiency.

MDPs, a unique class of peptides encoded by short open reading frames in mtDNA, function as an intrinsic cellular defense mechanism against mitochondrial dysfunction, primarily by enhancing mitochondrial function through the regulation of energy metabolism and antioxidant responses [21]. As a recently identified MDP, Mitochondrial Open Reading Frame of the 12S rRNA Type-C (MOTS-c) promotes systemic metabolic homeostasis mainly by modulating glucose and lipid metabolism and decreasing ROS production, thereby exerting a mitochondrial protective function (Fig. 1A) [22,23]. Inspired by these unique characteristics, we hypothesized that MOTS-c could serve as a potential protective candidate for mitochondrial transplantation; however its application is constrained by its high solubility and low bioavailability [24]. Herein, we further conjugated MOTS-c with Q11 peptide to fabricate a co-assembled hydrogel platform (MQgel) for the delivery and protection of donor mitochondria. The Q11 peptide, a low-molecular-weight peptide with 11 amino acids, was selected for its ability to rapidly self-assemble into elastic hydrogels with tunable mechanical properties and inherent self-healing capability [25]. The isolation of functional mitochondria and their activity protection by MQgel (referred to as MQgel@Mito) were systematically characterized (Fig. 1B). Furthermore, this study explored the internalization of donor mitochondria and the regulatory effects of MQgel@Mito on macrophage phenotypic transformation. Moreover, metabolic profiling analysis was conducted to reveal the mechanism of MQgel@Mito-induced inflammatory phenotype transition of macrophages. Besides, we evaluated the influence of MQgel@Mito on the mitochondrial homeostasis and cellular apoptosis of macrophages under oxidative stress. Additionally, the therapeutic effects of MQgel@Mito on cardiac function in rats with MI were evaluated (Fig. 1C).

Fig. 1: Scheme illustrating the protective effect of MQgel on donor mitochondria and the therapeutic effect of MQgel@Mitoagainst MI. (A) MOTS-c is a typical MDP and exerts mitochondrial protective functions. (B) The fabrication of MQgel@Mito and the protective effect on isolated donor mitochondria. (C) The therapeutic effect and mechanism of MQgel@Mito on promoting cardiac repair via macrophage metabolic reprogramming.