In the healthy myocardium, ATP is predominantly generated through mitochondrial oxidative phosphorylation (OXPHOS), which accounts for approximately 95% of total ATP production; the remaining ~ 5% is derived from glycolysis^[18,19]. The reducing equivalents that fuel OXPHOS are primarily supplied by the oxidation of fatty acids, lactate, glucose, ketone bodies, and amino acids. Among these substrates, fatty acid oxidation contributes the largest share (40%~60%), followed by glucose oxidation (20%~40%)^[20]. Critically, the healthy heart exhibits remarkable metabolic flexibility—dynamically shifting its substrate preference in response to changes in substrate availability, hormonal signals, and hemodynamic workload to meet its high energy demands^[20].

In contrast, the failing heart undergoes profound alterations in energy metabolism, characterized by impaired metabolic flexibility, reduced overall ATP production, and a shift in substrate utilization. Although the precise nature of these metabolic changes remains somewhat controversial across different HF phenotypes, a consistent finding is the uncoupling of glycolysis from glucose oxidation—an inefficiency that compromises cardiac work efficiency regardless of whether glycolytic flux is increased or decreased.

Notably, Mericskay et al. reported divergent metabolic adaptations in HF with preserved ejection fraction (HFpEF) vs. HF with reduced ejection fraction (HFrEF)^[21]. In HFpEF, they observed increased fatty acid oxidation coupled with reduced ketone body oxidation, contributing to diminished metabolic flexibility and cardiac efficiency. Conversely, in HFrEF, ketone body oxidation is upregulated—potentially as a compensatory mechanism to sustain energy production in the face of bioenergetic deficit^[21].

Zhang et al. reported elevated levels of miR-195 in the plasma, serum, and myocardial tissues of patients with advanced HF^[22]. Subsequent work demonstrated that, in failing myocardium induced by transverse aortic constriction (TAC) or myocardial infarction (MI), miR-195 directly suppresses the expression of sirtuin 3 (SIRT3), a mitochondrial NAD⁺-dependent deacetylase. This downregulation leads to hyperacetylation of key enzymes involved in mitochondrial energy metabolism—most notably the pyruvate dehydrogenase complex (PDH) and ATP synthase. The resulting reduction in enzymatic activity impairs glucose oxidation, diminishes ATP production, and compromises mitochondrial respiratory capacity, thereby accelerating HF progression^[22,23]. In a separate study, Ding et al. observed significant upregulation of miR-214 in cardiomyocytes in an angiotensin II (Ang II)-induced model of cardiac hypertrophy. Through integrated molecular and in vivo approaches, they confirmed that miR-214 exerts its detrimental effects via a mechanism closely resembling that of miR-195^[23].

Additionally, miR-152 is among the most significantly upregulated miRNAs in the human failing myocardium, and its expression is also markedly activated in animal models of cardiac pressure overload. Larocca et al. demonstrated that in HF mice induced by TAC, miR-152 disrupts myocardial iron homeostasis and impairs mitochondrial metabolism by directly targeting glutaredoxin 5 (Glrx5)—a critical regulator of iron-sulfur cluster biogenesis within mitochondria^[24]. Notably, targeted inhibition of miR-152 in preclinical models attenuated adverse cardiac remodeling, slowed the decline in systolic function, and reduced ventricular dilation and myocardial fibrosis—highlighting its potential as a therapeutic target in HF^[24].

Using integrated transcriptomic profiling and functional assays, Wu et al. demonstrated that miR-654-3p is significantly downregulated in MI tissue^[25]. This reduction is associated with impaired mitochondrial energy metabolism and diminished ATP production. Importantly, restoration of miR-654-3p expression reversed these metabolic deficits and enhanced cardiac energy supply, underscoring its protective role in post-infarction remodeling^[25]. Song et al. revealed that under ischemia/reperfusion (I/R) stress, miR-210 drives a metabolic shift in cardiomyocytes—from oxidative phosphorylation toward glycolysis^[26]. This adaptive reprogramming appears to optimize cellular energy production and survival under hypoxic or stressful conditions, positioning miR-210 as a critical regulator of metabolic flexibility in the stressed heart^[26].

The studies summarized above collectively demonstrate that miR-195, miR-214, and miR-152 are upregulated in HF and actively contribute to the deterioration of cardiac function by disrupting mitochondrial energy metabolism through distinct molecular mechanisms. In contrast, miR-654-3p and miR-210 appear to exert cardioprotective effects—either by restoring mitochondrial bioenergetics or by facilitating adaptive metabolic reprogramming under stress conditions. Although these miRNAs converge on the regulation of mitochondrial function, their individual targets and downstream pathways differ, underscoring the complexity and context-dependency of miRNA-mediated gene regulation in HF.

Moreover, the failing heart consistently exhibits dysregulation of multiple miRNAs, and experimental evidence shows that targeted modulation—either inhibition of detrimental miRNAs or restoration of beneficial ones—can ameliorate key features of HF across diverse preclinical models^[16,27]. These findings highlight the dual potential of miRNAs as both sensitive biomarkers for disease stratification and promising therapeutic targets for precision intervention in HF.

Under physiological conditions, cardiomyocytes generate low levels of reactive oxygen species (ROS), which serve as signaling molecules in the regulation of various transcription factors and redox-sensitive pathways. These basal ROS levels are effectively neutralized by endogenous antioxidant systems, maintaining cellular redox homeostasis. In the failing heart, however, mitochondrial ROS production markedly exceeds the capacity of antioxidant defenses, resulting in oxidative stress. Elevated superoxide levels have been consistently documented across multiple experimental models of HF^[28]. Excessive ROS accumulation not only damages lipids, proteins, and DNA but also disrupts calcium handling, thereby exacerbating cardiomyocyte injury. Mitochondrial electron transport chain complexes I, II, and III have been identified as the primary sites of pathological ROS generation in HF^[29-31]. Among the key antioxidant enzymes, superoxide dismutase (SOD) plays a critical role in mitigating mitochondrial oxidative stress. Deficiency or inactivation of SOD has been linked to worsened mitochondrial dysfunction and accelerated progression of cardiac failure.

miR-181c, although transcribed in the nucleus, has been shown to localize to mitochondria, where it directly targets the mRNA of mitochondrial-encoded cytochrome c oxidase subunit 1 (mt-COX1). Das et al. discovered that overexpression of miR-181c in H9C2 cells causes structural remodeling and functional disruption of mitochondrial Complex IV by suppressing mt-COX1^[32]. As the terminal part of Electron Transport Chain (ETC), Complex IV partial inhibition leads to electron congestion in upstream Complex, and directly reduces oxygen to superoxide, exacerbating oxidative stress^[32]. Another study observed significant upregulation of miR-762 in myocardial tissue from I/R mice. MiR-762 directly inhibits the expression of NADH dehydrogenase subunit 2 (ND2), a core assembly subunit of Complex I. This inhibition disrupts electron flow through Complex I, leading to impaired ATP synthesis, increased ROS production, and further deterioration of cardiac function—highlighting miR-762 as another pathogenic miRNA that amplifies mitochondrial oxidative damage in HF^[33].

Additionally, Lin et al. reported elevated expression of miR-665 in MI rats. MiR-665 was shown to directly suppress the glucagon-like peptide-1 receptor (GLP1R), leading to inactivation of the cAMP signaling pathway and abnormal expression of downstream proteins, especially SOD^[34]. The consequent reduction in SOD activity exacerbates oxidative stress, contributing to myocardial injury and dysfunction. Importantly, administration of a miR-665 inhibitor in the same HF model effectively restored GLP1R signaling, normalized SOD levels, and ameliorated cardiac remodeling and functional decline—highlighting miR-665 as a potential therapeutic target in HF^[34].

Song et al. demonstrated that miR-210 exerts cardioprotective effects, in part, by suppressing mitochondrial reactive oxygen species (mtROS) production in I/R myocardium^[26]. A key target of miR-210 is glycerol-3-phosphate dehydrogenase 2 (GPD2), a mitochondrial enzyme that plays a dual role in the glycerol phosphate shuttle and as a component of the electron transport chain. GPD2 has been identified as a significant source of mtROS under pathological conditions. By downregulating GPD2 expression, miR-210 reduces electron leakage from the respiratory chain, thereby attenuating oxidative stress and preserving mitochondrial integrity and function^[26].

Notably, beyond its well-established role in regulating mitochondrial energy metabolism, miR-210 also demonstrates a potent ability to modulate oxidative stress—highlighting its multifaceted influence on cardiac homeostasis. This dual functionality suggests that miR-210 may occupy an upstream regulatory node within the molecular network governing HF pathogenesis, enabling it to coordinately influence both bioenergetic and redox pathways. Given its capacity to enhance metabolic adaptability while simultaneously mitigating oxidative damage, we propose that miR-210 represents a particularly promising and high-priority candidate for the development of miRNA-based therapeutics in HF.

Mitochondrial biogenesis—the process by which cells generate new mitochondria to maintain organelle function and meet energy demands—is essential for sustaining cardiac bioenergetics. Impairment of this process compromises ATP production and disrupts the energetic homeostasis. A central regulator that upregulates mitochondrial biogenesis is peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). And the activity of PGC-1α is tightly modulated by post-translational modifications: it is activated via phosphorylation by AMP-activated protein kinase (AMPK) and deacetylation by sirtuin 1 (SIRT1)^[35]. Notably, studies by Whittington et al. and Li et al. indicated that both the expression and activity of PGC-1α are reduced in HF^[36,37]. Importantly, interventions that directly or indirectly enhance PGC-1α levels have consistently shown therapeutic benefits across diverse preclinical HF models. These findings firmly establish PGC-1α as a master regulator of mitochondrial biogenesis and a pivotal node in both the pathogenesis of HF and the development of potential metabolic therapies.

Study has demonstrated that miR-22 directly targets the 3’ untranslated region (3’UTR) of PGC-1α mRNA, leading to its post-transcriptional repression and reduced protein expression in I/R rats^[38]. Sun et al. observed myocardial injury in ovariectomy-induced estrogen-deficient mice and clarified that this outcome was partially due to miR-23a targeting PGC-1α via the same mechanism^[39]. In addition, Du et al. reported that miR-22 also suppresses SIRT1 expression, thereby further inhibiting PGC-1α activity through the SIRT1-PGC-1α signaling axis^[38]. Given that PGC-1α is a master regulator of mitochondrial biogenesis, the downregulation of this pathway by miR-22 and miR-23a results in impaired mitochondrial renewal, diminished oxidative capacity, and compromised bioenergetic support in cardiomyocytes—ultimately accelerating myocardial injury.

Caravia et al. reported that, under physiological conditions, miR-29 fine-tunes mitochondrial biogenesis by moderately repressing PGC-1α expression and plays a protective role^[40]. In this context, loss of miR-29 leads to unchecked PGC-1α overexpression, which may drive aberrant mitochondrial biogenesis. Paradoxically, this results in the accumulation of structurally and functionally impaired mitochondria, disrupts cellular energy balance, and ultimately exacerbates HFpEF^[40].

This apparent contradiction—where both miR-22/23a and miR-29 target PGC-1α yet exert opposing effects on HF progression—has drawn our particular attention. We hypothesize that miR-29, while suppressing biogenesis, simultaneously promotes mitochondrial quality control (e.g., through enhanced mitophagy or improved proteostasis), yielding a net protective effect. In contrast, miR-22 and miR-23a appear to suppress biogenesis without concomitant enhancement of quality mechanisms, leading to energetic insufficiency and cardiomyocyte dysfunction. These observations underscore that the functional outcome of modulating mitochondrial biogenesis depends not only on the quantity of mitochondria generated but also on their functional integrity. However, direct experimental validation for this hypothesis is currently lacking. Future research should address the unknown influence of miRNAs on mitochondrial quality to provide a more comprehensive understanding of the opposing effects on HF progression.

Moreover, while current research has predominantly centered on the PGC-1α axis as the primary regulator of biogenesis, the broader regulatory landscape likely involves additional miRNA-mediated pathways that remain underexplored. Future studies should aim to delineate these alternative mechanisms to fully elucidate how miRNAs orchestrate the delicate balance between mitochondrial quantity, quality, and function in the failing heart.

Mitochondria are highly dynamic organelles that continuously undergo fusion and fission to maintain their morphology, subcellular distribution, functional integrity, and homeostatic abundance. Mitochondrial fission is primarily regulated by dynamin-related protein 1 (Drp1). Upon activation, Drp1 translocates to the outer mitochondrial membrane (OMM), where it is recruited by adaptor proteins, and then initiates fission^[41]. During mitochondrial fusion, OMM fusion occurs first, mediated by proteins such as Mitofusin 1/2 (Mfn1/2), and followed by inner mitochondrial membrane (IMM) fusion, which is mainly mediated by Optic atrophy 1 (Opa1)^[41,42]. Additionally, Opa1 also plays a critical role in maintaining cristae architecture and facilitating the proper assembly and stability of respiratory chain supercomplexes. Dysregulated mitochondrial dynamics are a hallmark of the failing heart. In HF, levels of fusion-related proteins often decrease while fission-related protein levels typically increase, collectively leading to excessive mitochondrial fission and a fragmented morphology^[43,44].

As previously discussed, mitochondrial dynamics are profoundly disrupted in HF, typically manifesting as excessive fission and impaired fusion. Studies have confirmed that under I/R- or drug-induced cardiac dysfunction, expression levels of miR-140, miR-153-3p, and miR-122 in cardiomyocytes are significantly elevated^[45-47]. Among these, miR-140 and miR-153-3p contribute to mitochondrial dysfunction in HF by targeting Mfn1, while miR-122 upregulates Drp1 expression by directly inhibiting the transcription factor Hand2. And this leads to excessive mitochondrial fission, induces cardiomyocyte apoptosis, and ultimately amplifies the progression of the HF phenotype^[45-47].

Several studies have demonstrated that miR-30, miR-129-3p, and miR-499 exert cardioprotective effects respectively in HF models induced by H₂O₂, Ang-(1-9), and I/R by converging on Drp1, yet each operates through distinct molecular mechanisms. Li et al. reported that miR-30 attenuates Drp1 expression indirectly by targeting tumor protein p53 mRNA, thereby suppressing the p53-Drp1 signaling axis^[48]. In contrast, miR-129-3p targets protein kinase A inhibitor (PKIA), thereby lifting the inhibitory effect of PKIA on PKA. This activation of PKA signaling enhances phosphorylation of Drp1 at Ser637, which inhibits its function^[49]. Another study revealed that miR-499 directly targets the catalytic subunit of calcineurin to reduce its level and activity. This results in decreased dephosphorylation of Drp1 at Ser656, consequently suppressing Drp1 translocation from the cytoplasm to the OMM^[50].

In addition to miRNAs that modulate Drp1, Wang et al. further identified miR-652-3p as a regulator of mitochondrial fission^[51]. This miRNA effectively suppresses mitochondrial division by directly targeting and inhibiting mitochondrial protein 18 kDa (MTP18), a protein that promotes mitochondrial fission^[51].

Current research on miRNA-mediated regulation of mitochondrial dynamics has primarily focused on a limited set of targets, notably Drp1 and Mfn1. However, the processes of mitochondrial fusion and fission are highly complex, involving coordinated actions of numerous proteins. Whether miRNAs can target other components within these pathways to fine-tune mitochondrial dynamics remains an open question worthy of further investigation.

Moreover, alterations in mitochondrial dynamics influence not only organelle quantity but also qualitative aspects. Therefore, functional assessments of mitochondria following fusion or fission events are essential. Future studies should determine whether newly formed mitochondria can properly execute their physiological functions, particularly in energy production and cellular homeostasis, to fully explain the functional consequences of miRNA-mediated regulation.

Mitophagy represents a selective autophagic process essential for removing damaged mitochondria, thereby preserving mitochondrial fitness. As a critical component of mitochondrial quality control, appropriate mitophagy exerts a protective effect on cellular homeostasis. In cardiomyocytes, mitophagy is primarily mediated by the ubiquitin-dependent PINK1/Parkin pathway, which is considered the canonical mechanism^[52]. Additionally, receptor proteins like PTEN-induced putative kinase 1 (FUNDC1), BCL2-interacting protein 3 (BNIP3), and Nip3-like protein X (NIX) activate alternative, ubiquitin-independent pathways^[53]. In the context of HF, clinical evidence indicates impaired mitophagy. For instance, Billia et al. found decreased PINK1 protein expression and reduced mitophagy levels in advanced HF patients, whereas pharmacological augmentation of autophagy improved cardiac function^[54]. Similarly, myocardial tissue from HF patients exhibits significantly downregulated FUNDC1 expression. Experimental upregulation of the FUNDC1-mediated mitophagy has been proven protective for the failing heart^[55]. Collectively, these studies underscore that maintaining mitophagy balance is crucial for ensuring mitochondrial homeostasis, highlighting its potential as a therapeutic target for HF.

Gap junction protein alpha 1 (GJA1) is recognized as a key regulator of mitochondrial function, in part through its ability to activate FUNDC1-mediated mitophagy. Yan et al. discovered significantly elevated expression of miR-130a-3p in both myocardial tissue from I/R rats and blood from acute myocardial infarction (AMI) patients^[56]. Mechanistically, miR-130a-3p directly targets and suppresses GJA1 expression. This inhibition thereby obstructs mitophagy, preventing the effective clearance of damaged mitochondria, and ultimately exacerbating myocardial injury^[56].

Mitochondrial homeostasis depends on a balance between clearance and biogenesis, which could be disrupted by uncontrolled mitophagy. This results in a state of mitochondrial suboptimal state, potentially accelerating the progression of diseases^[57,58]. Mu et al. revealed the loss of miR-494-3p during H/R injury relieves its inhibitory effect on the target gene PGC-1α. The subsequent upregulation of PGC-1α activates the PINK/Parkin-mediated mitophagy, ultimately bringing about excessive mitophagy^[59]. Importantly, exogenous administration of miR-494-3p can reverse this process, inhibit excessive mitophagy, and exert a cardioprotective effect^[59]. Current understanding of how specific miRNAs govern mitophagy in HF remains incomplete, highlighting a critical gap in knowledge that warrants focused investigation. Furthermore, mitophagy represents a highly dynamic process. Pathological outcomes can arise not only from its impairment but equally from its overactivation, each contributing to mitochondrial insufficiency. This highlights the importance of developing strategies to modulate mitophagy within an optimal range, aiming to restore physiological balance rather than blanket inhibition or promotion.