Myocardial ischemia occurs when blood flow to the heart is reduced, resulting in an imbalance between the oxygen supply and demand of the myocardium, which triggers ischemic damage (45). Revascularization is currently the most effective strategy to lower the mortality rate among ischemic patients; however, reperfusion at this stage can also cause additional myocardial damage, a phenomenon known as 'reperfusion injury' (46). During ischemia, myocardial cells are deprived of oxygen, nutrients and survival factors. Prolonged ischemia leads to progressive and irreversible changes in the structure and function of the myocardium, with the most significant damage being the injury or death of myocardial cells (47). While reperfusion is essential to rescue myocardial infarction, the sudden reoxygenation of previously ischemic myocardial cells causes excessive ROS production, intracellular Ca²⁺ accumulation, and ultimately, myocardial cell death (48). Research has shown that mCa²⁺ overload is a key mechanism of myocardial cell injury during I/R injury. During this process, pathological elevations of Ca²⁺ in the mitochondrial matrix led to the opening of mitochondrial permeability transition pores (mPTP), which results in the release of solutes and small proteins from the mitochondrial matrix, causing mitochondrial swelling and, eventually, cell death (49). Therefore, understanding how to regulate mCa²⁺ channels during I/R is crucial for preventing further myocardial cell loss.

Studies have shown that the MCU plays a significant role in the development of myocardial I/R injury (50,51). Recent research has highlighted the relationship between myocardial I/R and the MCU complex. By inhibiting the MCU complex, mCa²⁺ influx and subsequent Ca²⁺ overload can be reduced, which ultimately decreases mitochondrial fragmentation and apoptosis, alleviating cardiac microvascular I/R injury (50,52,53). Liang's team demonstrated that inhibiting the MCU in cardiac I/R exerts cardioprotective effects by reducing the abnormal opening of the mPTP in cardiac microvascular endothelial cells (53). One current hypothesis suggests that during ischemia and reperfusion, Ca²⁺ enters the mitochondria via the MCU, activating the PTP (54). Inhibiting MCU during I/R may be a potential strategy to reduce PTP opening (55). In addition, studies have found that MCUb expression increases following cardiac ischemic injury. Overexpression of MCUb has demonstrated protective effects against myocardial I/R injury, potentially related to reduced mCa²⁺ uptake and increased efflux (26). By contrast, Rasmussen et al (56) observed different outcomes. They developed a transgenic mouse model expressing a dominant-negative (DN) form of the MCU specifically in the myocardium. Unexpectedly, DN-MCU mice, which lacked MCU-mediated mCa²⁺ entry, exhibited higher oxygen consumption rates and reduced ROS generation compared to wild-type mice (56). Chapoy Villanueva et al (57) proposed that these differences may be due to the varying durations of MCU deficiency. Chronic disruption of MCU activity may trigger compensatory adaptations to maintain cellular metabolic processes in the absence of rapid mCa²⁺ influx. Their team confirmed that the responses to I/R injury differ between chronic and acute MCU deficiency mouse models. Furthermore, using both short-term and long-term EMRE-deficient adult mouse models, they showed that the protective effects against I/R injury were lost in long-term EMRE-deficient mice (57). MICU1, a crucial regulator of mCa²⁺ homeostasis, has also been studied in the context of I/R injury. Studies have shown that MICU1 knockout significantly exacerbates myocardial I/R injury, as evidenced by increased infarct size, impaired cardiac function and elevated myocardial cell apoptosis. The absence of MICU1 leads to pronounced mCa²⁺ overload, which disrupts mitochondrial morphology, inhibits mitochondrial function and reduces ATP production (58). However, the precise mechanisms underlying these effects require further investigation.

The pathological changes in vascular diseases primarily include three conditions: i) Loss of elasticity in the vascular wall due to lesions, resulting in aneurysmal changes and, in severe cases, rupture and bleeding. ii) Lesions causing lumen narrowing, which can lead to ischemia and even necrosis of the affected organ or limb. iii) Lesions inducing endothelial injury, which can trigger intravascular coagulation and thrombosis, potentially causing ischemia in organs or tissues. Emboli may also dislodge and obstruct distal vessels (59,60). Common vascular diseases include PAH, aneurysms, PAD and aortic coarctation (61-64). These conditions have complex and varied etiologies, with mCa²⁺ playing a role in their pathogenesis. As a unidirectional channel for mCa²⁺ influx, the MCU is also involved in the development of these vascular diseases.

PAH is a life-threatening obstructive arterial disease characterized by excessive pulmonary vascular proliferation, loss of vascular lumen, vascular remodeling and, ultimately, right ventricular failure, which can lead to death (65). The etiology of PAH is highly complex and a reduction in mCa²⁺ has been observed in PAH for some time (66). Research has shown that vascular constriction and cell proliferation in PAH are also caused by decreased MCU expression and increased MICU1 expression, leading to reduced MCU complex function, elevated cytosolic Ca²⁺, decreased mCa²⁺, mitochondrial fragmentation and the Warburg effect, thereby promoting pulmonary vascular overproliferation (67,68). Given this, the role of the MCU complex in PAH deserves closer attention. Wu et al (68) conducted research using Fura-2 acetoxymethyl ester and fluorescence resonance energy transfer probes to assess calcium localization, demonstrating elevated cytosolic Ca²⁺ and reduced mCa²⁺ in Pulmonary artery smooth muscle cells (PASMCs) from patients with PAH. Further investigation using mRNA expression profiling and super-resolution confocal microscopy confirmed that the reduced mCa²⁺ in PAH PASMCs could be attributed to decreased MCU expression. Immunoblotting also revealed significantly increased MICU1 levels in human PAH PASMCs and similar MCU downregulation was observed in the lungs of monocrotaline-induced PAH rats (68). The study concluded that reduced MCU expression leads to decreased mCa², which impairs PDH activity, affects glycolysis and ultimately results in smooth muscle cell apoptosis and proliferation (67). These findings highlight the critical regulatory role of the MCU complex in PAH-related mCa²⁺ dynamics.

The decline in MCU complex function in PAH is attributed to two key factors: Epigenetic mechanisms driven by increased expression of microRNA (miR)-138 and miR-25 (67), and increased calcium sensitization mediated by Rho-associated kinase (ROCK) in PAH PASMCs. ROCK increases myosin contractility by inactivating myosin light chain phosphatase, allowing sustained vasoconstriction independent of calcium influx. As a result, ROCK activation leads to calcium sensitization, contributing to the decline in MCU complex function. Increased activity of the G protein RhoA and its downstream target ROCK has been observed in idiopathic pulmonary arterial hypertension (PAH) and animal PAH models, primarily due to serotonylation (69) and superoxide-mediated activation (70), forming a calcium-sensitivity mechanism. Therefore, the interaction between the MCU complex, G protein RhoA and ROCK may represent a potential mechanism in PAH pathogenesis.

Calcium transport is also widely studied in other vascular diseases. For instance, in familial thoracic aortic aneurysm and dissection (FTAAD), a metabolomics and transcriptomics analysis using two different mouse models by Tomida et al (71) revealed that increasing the cytosolic Ca²⁺ concentration can help prevent FTAAD. Similarly, in pregnancy-induced hypertension, altered calcium transport gene expression, which leads to calcium loss in urine, has been associated with preeclampsia and calcium deficiency (72). This suggests that calcium transport may play a role in vascular disease pathogenesis through calcium imbalance. Therefore, the study of the MCU complex, as a mitochondrial calcium uniporter, in vascular diseases warrants further exploration.

Cardiac remodeling refers to changes in the size, shape and function of the heart resulting from molecular and genetic alterations in response to cardiac injury or hemodynamic stress. It is widely recognized as a key mechanism in the progression of HF (73). Research has shown that Ca²⁺ imbalance can damage mitochondria, leading to cardiomyocyte death, pathological hypertrophy and ultimately heart failure (74). Wang et al (74) used chronic administration of isoproterenol (ISO) to create MCU knockout or transgenic mice and confirmed increased levels of the MCU complex and MCU in the mitochondria of ischemic mouse hearts. Of note, ISO-induced myocardial fibrosis, cardiac hypertrophy and contractile dysfunction were exacerbated in global MCU knockout mice, whereas cardiac-specific MCU overexpression maintained intracellular Ca²⁺ homeostasis and contractility, inhibited cell hypertrophy and prevented ISO-induced cardiac dysfunction and hypertrophy (74). The study by Zhang et al (75) supports these findings, showing that MCU complex expression decreased in a propranolol-induced heart failure model, while maintaining MCU-dependent mitochondrial energy metabolism improved heart failure outcomes (75). Liu et al (76) further reinforced this perspective by demonstrating that MCU overexpression increased mCa²⁺ uptake rates in failing cardiomyocytes, reduced ROS production, corrected intracellular Ca²⁺ handling defects and improved contractile function. The authors also indicated that excessive sarcoplasmic reticulum (SR) Ca²⁺ leak leads to decreased SR Ca²⁺ load in cardiomyocytes and that MCU overexpression was sufficient to correct SR leak and cytosolic Ca²⁺ transients (76). While Garbincius and Elrod (77) praised the work by Liu et al (76), they raised concerns that the study was short-term, focusing only on the consequences of MCU overexpression within two weeks, without investigating potential long-term adverse effects. They questioned whether harmful consequences may emerge over a longer observation period, or if compensatory changes in unidirectional transporter channel regulation or mCa²⁺ efflux could offset negative effects. In addition, it remains elusive how mCa²⁺ homeostasis is affected in a guinea pig (ACi) model. The peak mCa²⁺ concentration was reduced during electrical stimulation in intact ACi cardiomyocytes, but interpreting this measurement may be complicated by factors such as reduced SR Ca²⁺ load and cytosolic Ca²⁺ transients (76,77). In a study of diabetic cardiomyopathy, MCU complex member protein levels were reduced and adenoviral MCU overexpression restored mCa²⁺ handling and improved cardiac function (78).

However, there are differing views on the role of the MCU complex in cardiac remodeling and heart failure. Tarazón et al (79) found increased MCU levels in heart transplant patients, which were associated with cardiac dysfunction caused by acute rejection. In their analysis of ventricular septal samples from patients with pressure-overload-induced cardiac hypertrophy, they observed significantly elevated MCU and MICU1 protein levels. As seen in the studies mentioned above, members of the MCU complex exhibit varied responses in cardiac remodeling and heart failure. One possible explanation is that the heart may be at different stages of disease. For instance, the samples in the study by Tarazón et al (79) represented moderate hypertrophy rather than end-stage hypertrophy or heart failure, and the increased MCU expression may reflect a compensatory phase of hypertrophy. In end-stage heart failure, elevated cytosolic Na⁺ concentrations promote Na⁺/Ca²⁺ exchange, leading to reduced mCa²⁺ levels (80,81). This reduction in mCa²⁺ efflux limits mitochondrial ATP production, further impairing contractility in the failing heart. MCU supplementation can promote mCa²⁺ uptake, compensating for mCa²⁺ deficiency due to increased efflux, thereby boosting mitochondrial ATP production and supporting cardiac bioenergetics (82). As such, targeting the expression or function of the MCU complex may offer a promising therapeutic approach for future studies on cardiac remodeling and heart failure.

Arrhythmias, characterized by irregular heart rhythms, are a leading cause of morbidity and mortality associated with CVD worldwide. These irregular heart rhythms present substantial treatment challenges (83). The mechanisms underlying arrhythmias are complex, with intracellular Ca²⁺ homeostasis recognized as a key factor in their development (84). Wang et al (85) developed a zebrafish MCU mutant model that survives into adulthood and observed weakened heart contractions in the mutants. Pathological examination revealed damaged myofibrils and swollen mitochondria in the hearts of these MCU mutants. Electrocardiograms showed conduction system defects and abnormal rhythms, including prolonged pauses resembling sinus arrest (86). This study highlights the critical role of the MCU complex in the development of arrhythmias.

MCU not only plays a significant role in the development of arrhythmias but also serves as a potential therapeutic target. Wiersma et al (87) identified mitochondrial changes in the atrial tissue of patients with atrial fibrillation (AF), potentially caused by mCa²⁺ transients due to increased Ca²⁺ influx mediated by the MCU. The use of the MCU inhibitor Ru360 or moderate downregulation of MCU prevented adverse mitochondrial changes induced by rapid pacing. Furthermore, treatment with Ru360 improved contractile dysfunction in a Drosophila melanogaster AF model, providing protection to cardiomyocytes (87). These findings suggest that targeting MCU to prevent mitochondrial dysfunction could represent a novel therapeutic approach for addressing AF remodeling. Joseph et al (88) demonstrated that cardiac-specific deletion of the MCU gene in high-fat diet (HFD)-induced long QT syndrome, inducible ventricular tachycardia and abnormal ventricular repolarization offered protection. Cardiac iron overload, which can lead to iron overload cardiomyopathy and arrhythmias, was shown by Sripetchwandee et al (89) to be fully prevented with the use of MCU blockers. Sander et al (90) found that the mCa²⁺ uniporter activator kaempferol restored rhythmic heart contractions in zebrafish and inhibited arrhythmias in ventricular myocytes of mice with polymorphic ventricular tachycardia. Further research revealed that only moderate increases in MCU levels provided protection against arrhythmias, though the specific mechanisms remain to be fully explored (91).

These studies significantly expand the current understanding of the MCU complex's involvement in arrhythmias, highlighting its key role in the progression of these conditions. Furthermore, the findings provide compelling evidence for the potential value of assessing and targeting MCU expression in the diagnosis and treatment of arrhythmias.

Myocarditis is characterized by localized or diffuse inflammation in the myocardium, with a wide range of etiologies, including both infectious and non-infectious factors. In a study of viral myocarditis, Hu et al (92) used flow cytometry to monitor transient changes in intracellular calcium, finding that Ca²⁺ levels in cardiomyocytes infected with CVB3 were 1.7 and 4 times higher than in the control group at 6 and 12 h post-infection, respectively, leading to intracellular calcium overload. Another study followed 102 patients with dengue hemorrhagic fever from Colombia for a year, performing immunohistochemical analysis on cardiac tissues from autopsies and conducting in vitro studies on myotubes infected with dengue virus. This study found that disruptions in Ca²⁺ storage in infected cells may directly contribute to myocarditis in pediatric patients (93). Furthermore, Huynh et al (94) discovered that after treating human cardiomyocytes with the S1 protein for 72 h, there was an increase in ROS, mCa²⁺ and intracellular Ca²⁺ levels, leading to reduced mitochondrial respiratory rates and mitochondrial dysfunction, which ultimately resulted in myocarditis and cardiac dysfunction. Collectively, these studies indicate that intracellular calcium overload, both in the cytosol and mitochondria, leads to mitochondrial dysfunction, contributing to the development of myocarditis and cardiac dysfunction.

In non-viral studies, Maass et al (95) measured cytoplasmic and mCa²⁺ levels in cardiomyocytes from the control group and burn patients with >40% total body surface area burns. They found that 24 h post-burn, cytoplasmic Ca²⁺ levels increased from 90±3 to 293±6 nM (P<0.05) and mCa²⁺ levels also rose significantly from 24±1 to 75±2 nM (P<0.05). Similar observations were made in in vitro models, where lipopolysaccharide-treated groups exhibited a 112% increase in cytoplasmic Ca²⁺ (185±15 nM, P<0.05) and an 87% increase in mCa²⁺ (P<0.05) compared to a control group (95). These results align with findings from Wan-Yi et al (96), who reported that ruthenium red prevented burn-induced myocardial Ca²⁺ accumulation and alleviated related myocardial and mitochondrial damage. Both Maass et al (94) and White et al (97) suggested that administering Ca²⁺ antagonists post-burn could prevent the rise in cytoplasmic Ca²⁺ and improve myocardial contractility. Another significant pathophysiological mechanism in anthracycline-induced cardiotoxicity is the disruption of cellular and mitochondrial calcium signaling (98).

Currently, the most well-established and widely studied pathway for mCa²⁺ uptake is through the MCU complex (99,100). The driving force for this process is the large electrochemical gradient across the IMM, with the mitochondrial membrane potential being ~-180 mV. This suggests that the MCU complex, as the channel responsible for mCa²⁺ uptake, may be involved in the pathogenesis of myocarditis. The rapid uptake of calcium into the mitochondrial matrix is driven by the mitochondrial membrane potential and facilitated by the mitochondrial calcium ion carrier channel (101). Although current research on the role of the MCU complex in both infectious and non-infectious myocarditis is limited, this area holds great potential for further exploration.

In addition to MCU itself, MICU1, as a regulatory factor of MCU, has an important role in cardiovascular function. Studies on MICU1 have shown that it not only acts as the 'gatekeeper' of MCU, but also regulates the mitochondrial cristae structure by interacting with the mitochondria contact site and cristae organizing system complex, thereby affecting calcium ion transport and mitochondrial function (103). However, Tomar et al (38), have proposed an alternative viewpoint, suggesting that MICU1 does not fully regulate calcium flux by blocking the MCU channel, but rather exerts its effect by enhancing the opening probability of MCU. This perspective offers new insights into understanding the role of MICU1 under different pathological conditions.

In a study on patients with HF, it has been observed that the protein ratio of MICU1 to MCU increased ~2-fold, whereas the protein levels of MCU or MCUb did not show significant changes in the non-HF control group (104). This change is in contrast with the upregulation of MCUb in the mouse I/R model (26). Although differences in rhythm frequency and energy demands between mouse and human hearts may lead to certain inconsistencies in results, it is noteworthy that changes in MCUb expression in mouse I/R injury typically require 2 to 3 days to become evident. Therefore, further investigation into the temporal expression pattern of MCUb in both human HF and mouse HF models will contribute to a better understanding of its role in CVD.

RuR and its derivative Ru360 inhibit the MCU by binding to the selective filter DIME group of the MCU (119). Ru360 has been shown to improve postoperative cognitive dysfunction and reduce cardiac injury following ischemia-reperfusion in mice (120). A recent study showed that, compared to the parent compounds Ru265 and Os245, their complexes exhibit stronger cellular uptake capabilities (121). Mitoxantrone has been reported to alleviate hepatic steatosis through MCU inhibition (108). A recent study by Arduino et al (118) characterized Mitoxantrone, an anthraquinone-derived cell inhibitor used in treating hematologic malignancies, as a specific MCU inhibitor that can increase tumor resistance. NecroX-5, a derivative of the reactive oxygen scavenger NecroX series compounds, has been found to reduce Ca²⁺ accumulation in cultured cardiomyocytes (122). In addition, Minocycline, an antibiotic, has been shown to inhibit Ca²⁺ uptake in isolated rat liver mitochondria (123). Although these inhibitors have not yet been tested in clinical trials for CVD, their widespread use in animal models highlights their potential for future clinical trials and therapeutic applications. The European Society of Cardiology recommends trimetazidine as an adjunct therapy for angina. Xiao et al (124) discovered through in vivo and in vitro experiments that its mechanism of action is related to the inhibition of the MCU.

Kon et al (117) first introduced the MCU inhibitor DS16570511, which exhibits cell-permeable and selective inhibitory properties. Compared to RuR, DS16570511 may more effectively inhibit human mitochondrial MCU rather than porcine or rat MCU. Of note, DS16570511 can increase cardiac contractility without affecting the heart rate in perfused hearts. The study also revealed that DS16570511 inhibits both endogenous mCa²⁺ uptake activity and Ca²⁺ uptake driven by exogenously expressed MCU or MICU1. This suggests that both MCU and MICU1 are potential binding targets for DS16570511, making it a promising lead compound for treating CVD, warranting further investigation (117).

In recent years, certain plant-based medicines have gained widespread attention. As an essential component of traditional medicine, Chinese herbal medicine has demonstrated significant potential in modern pharmacological research. Several studies have shown that active small molecules in Chinese herbs can regulate mitochondrial Ca²⁺ homeostasis by targeting the MCU complex, thereby exerting various biological effects such as anti-inflammatory, anti-apoptotic and antioxidant actions. This provides new insights for drug development targeting the MCU complex. This article will systematically review the research progress on the regulation of the MCU complex by active small molecules in Chinese herbal medicines and their potential applications in disease intervention, offering theoretical support and new research directions for the treatment of MCU-related diseases (Table II).