MORN4 protects cardiomyocytes against ischemic injury via MFN2-mediated mitochondrial dynamics and mitophagy

Melatonin Ameliorates Heat Stress-Induced Oxidative Apoptosis in Mouse Spermatocytes via Autophagy and Ferroptosis Pathways

Testicular heat stress is a critical factor contributing to male infertility, with spermatocytes exhibiting heightened sensitivity to temperature elevation. This study systematically elucidates the protective mechanisms of melatonin against heat stress-induced spermatocyte injury. In a murine heat stress model, melatonin intervention significantly reduced testicular accumulation of malondialdehyde (MDA) induced by heat stress, enhanced the activities of catalase (CAT) and superoxide dismutase (SOD), and suppressed germ cell apoptosis by downregulating the pro-apoptotic protein Bax and upregulating GPX4 expression. Sycp3 immunohistochemistry demonstrated that melatonin significantly improved spermatocyte structural integrity. In the GC-2spd (ts) spermatocyte cell line model, melatonin treatment markedly reduced MDA levels and alleviated heat stress-induced oxidative apoptosis and proliferation inhibition by downregulating key apoptotic proteins (Bax, Caspase3, and cleaved-Caspase3). Mechanistic studies revealed that melatonin restores autophagic balance by modulating the expression of autophagy-related proteins LC3-I, LC3-II, and P62. Concurrently, melatonin downregulated ferroptosis markers P53 and COX2, inhibiting ferroptosis by blocking DNA damage response and inflammatory amplification pathways. Melatonin synergistically maintained cellular redox homeostasis by downregulating the NRF2/HO-1 pathway and upregulating GPX4 expression, significantly reducing Fe²⁺ accumulation and ameliorating iron metabolism dysregulation. This study unveils the molecular mechanisms by which melatonin mitigates testicular heat stress injury through a multi-target regulatory network, providing novel therapeutic strategies for clinical intervention in heat stress-associated infertility.

Mitochondrial dysfunction in AMI: mechanisms and therapeutic perspectives

Acute myocardial infarction (AMI) and the myocardial ischemia-reperfusion injury (MI/RI) that typically ensues represent a significant global health burden, accounting for a considerable number of deaths and disabilities. In the context of AMI, percutaneous coronary intervention (PCI) is the preferred treatment option for reducing acute ischemic damage to the heart. Despite the modernity of PCI therapy, pathological damage to cardiomyocytes due to MI/RI remains an important target for intervention that affects the long-term prognosis of patients. In recent years, mitochondrial dysfunction during AMI has been increasingly recognized as a critical factor in cardiomyocyte death. Damaged mitochondria play an active role in the formation of an inflammatory environment by triggering key signaling pathways, including those mediated by cyclic GMP-AMP synthase, NOD-like receptors and Toll-like receptors. This review emphasizes the dual role of mitochondria as both contributors to and regulators of inflammation. The aim is to explore the complex mechanisms of mitochondrial dysfunction in AMI and its profound impact on immune dysregulation. Specific interventions including mitochondrial-targeted antioxidants, membrane-stabilizing peptides, and mitochondrial transplantation therapies have demonstrated efficacy in preclinical AMI models.

GATAD1 is involved in sphingosylphosphorylcholine-attenuated myocardial ischemia-reperfusion injury by modulating myocardial fatty acid oxidation and glucose oxidation

Modulating the equilibrium between glucose metabolism and fatty acid metabolism represents highly promising novel strategies for therapy of myocardial ischemia/reperfusion (I/R) injury. Sphingosylphosphorylcholine (SPC), an intermediate metabolite of sphingolipids, has shown cardioprotective roles during myocardial infarction by regulating the activities of various transcript factors. Gene microarray revealed that SPC significantly upregulated the expression of GATA zinc finger domain protein 1 (GATAD1), which is a vital transcript factor affecting heart development and various heart diseases. However, it remains unclear whether SPC is involved in the regulation of cardiac fatty acid and glucose metabolism via GATAD1. In this study, we found that myocardium-specific Gatad1 knockout (Gatad1 CKO) significantly increased the myocardial infarct size, impaired cardiac function in I/R mice, and disrupted the protective effect of SPC on the hearts of I/R mice. Immunofluorescence experiment and Western blot evaluation of the nuclear-cytoplasmic fractionation sample showed that GATAD1 acted as a transcription factor and was regulated by SPC. Double fluorescence reporting experiment and quantitative polymerase chain reaction (qPCR) revealed that GATAD1 could inhibit the expression of genes involved in fatty acid oxidation (FAO), i.e., acetyl-coenzyme A acyltransferase 2 (Acaa2) and medium-chain acyl-CoA dehydrogenase (Acadm), and promoted the expression of genes involved in glucose oxidation, i.e., pyruvate dehydrogenase E1 α subunit (Pdha1). Small interfering RNA (SiRNA) or overexpression strategies confirmed the pro-apoptotic roles of Acaa2 and Acadm and anti-apoptotic role of Pdha1 in cardiac myocytes challenged with I/R treatment. In summary, our findings suggest that SPC can be used as a candidate to prevent I/R injury by reshaping fatty acid and glucose metabolism. Transcription factor GATAD1 plays a crucial role in regulating fatty acid oxidation and glucose oxidation homeostasis and is involved in SPC-mediated cardioprotection during I/R of the heart. Our study identifies GATAD1 as a new therapeutic target for clinical treatment of myocardial I/R injury.

MicroRNA-15b promotes cardiac ischemia injury by the inhibition of Mitofusin 2/PERK pathway

MicroRNA and mitofusin-2 (Mfn2) play an important role in the myocardial apoptosis induced by acute myocardial infarction (AMI). However, the target relationship and underlying mechanism associated with interorganelle interaction between endoplasmic reticulum (ER) and mitochondria under ischemic condition is not completely clear. MI-induced injury, Mfn2 expression, Mfn2-mediated mitochondrial function and ER stress, and target regulation by miRNA-15b (miR-15b) were evaluated by animal MI and cellular hypoxic models with advanced molecular techniques. The results confirmed that Mfn2 was down-regulated and miR-15b was up-regulated upon the target binding profile under ischemic/hypoxic condition. Our data showed that miR-15b caused cardiac apoptotic injury that was reversed by rAAV9-anti-miR-15b or AMO-15b. The damage effect of miR-15b on Mfn2 expression and mitochondrial function was observed and rescued by rAAV9-anti-miR-15b or AMO-15b. The targeted regulation of miR-15b on Mfn2 was verified by luciferase reporter and microRNA-masking. Importantly, miR-15b-mediated Mfn2 suppression activated PERK/CHOP pathway, by which leads to ER stress and mitochondrial dysfunction, and cardiac apoptosis eventually. In conclusion, our research, for the first time, revealed the missing molecular link in Mfn2 and apoptosis and elucidated that pro-apoptotic miR-15b plays crucial roles during the pathogenesis of AMI through down-regulation of Mfn2 and activation of PERK-mediated ER stress. These findings may provide an opportunity to develop new therapies for prophylaxis and treatment of ischemic heart disease.

Mitochondrial quality control in human health and disease

Mitochondria, the most crucial energy-generating organelles in eukaryotic cells, play a pivotal role in regulating energy metabolism. However, their significance extends beyond this, as they are also indispensable in vital life processes such as cell proliferation, differentiation, immune responses, and redox balance. In response to various physiological signals or external stimuli, a sophisticated mitochondrial quality control (MQC) mechanism has evolved, encompassing key processes like mitochondrial biogenesis, mitochondrial dynamics, and mitophagy, which have garnered increasing attention from researchers to unveil their specific molecular mechanisms. In this review, we present a comprehensive summary of the primary mechanisms and functions of key regulators involved in major components of MQC. Furthermore, the critical physiological functions regulated by MQC and its diverse roles in the progression of various systemic diseases have been described in detail. We also discuss agonists or antagonists targeting MQC, aiming to explore potential therapeutic and research prospects by enhancing MQC to stabilize mitochondrial function.

NRF2 activation by cysteine as a survival mechanism for triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) is a very aggressive and heterogeneous group of tumors. In order to develop effective therapeutic strategies, it is therefore essential to identify the subtype-specific molecular mechanisms underlying disease progression and resistance to chemotherapy. TNBC cells are highly dependent on exogenous cystine, provided by overexpression of the cystine/glutamate antiporter SLC7A11/xCT, to fuel glutathione synthesis and promote an oxidative stress response consistent with their high metabolic demands. Here we show that TNBC cells of the mesenchymal stem-like subtype (MSL) utilize forced cystine uptake to induce activation of the transcription factor NRF2 and promote a glutathione-independent mechanism to defend against oxidative stress. Mechanistically, we demonstrate that NRF2 activation is mediated by direct cysteinylation of the inhibitor KEAP1. Furthermore, we show that cystine-mediated NRF2 activation induces the expression of important genes involved in oxidative stress response, but also in epithelial-to-mesenchymal transition and stem-like phenotype. Remarkably, in survival analysis, four upregulated genes (OSGIN1, RGS17, SRXN1, AKR1B10) are negative prognostic markers for TNBC. Finally, expression of exogenous OSGIN1, similarly to expression of exogenous NRF2, can prevent cystine depletion-dependent death of MSL TNBC cells. The results suggest that the cystine/NRF2/OSGIN1 axis is a potential target for effective treatment of MSL TNBCs.

Mitophagy for cardioprotection

Mitochondrial function is maintained by several strictly coordinated mechanisms, collectively termed mitochondrial quality control mechanisms, including fusion and fission, degradation, and biogenesis. As the primary source of energy in cardiomyocytes, mitochondria are the central organelle for maintaining cardiac function. Since adult cardiomyocytes in humans rarely divide, the number of dysfunctional mitochondria cannot easily be diluted through cell division. Thus, efficient degradation of dysfunctional mitochondria is crucial to maintaining cellular function. Mitophagy, a mitochondria specific form of autophagy, is a major mechanism by which damaged or unnecessary mitochondria are targeted and eliminated. Mitophagy is active in cardiomyocytes at baseline and in response to stress, and plays an essential role in maintaining the quality of mitochondria in cardiomyocytes. Mitophagy is mediated through multiple mechanisms in the heart, and each of these mechanisms can partially compensate for the loss of another mechanism. However, insufficient levels of mitophagy eventually lead to mitochondrial dysfunction and the development of heart failure. In this review, we discuss the molecular mechanisms of mitophagy in the heart and the role of mitophagy in cardiac pathophysiology, with the focus on recent findings in the field.

PGAM5 is an MFN2 phosphatase that plays an essential role in the regulation of mitochondrial dynamics

Mitochondrial morphology is regulated by the post-translational modifications of the dynamin family GTPase proteins including mitofusin 1 (MFN1), MFN2, and dynamin-related protein 1 (DRP1). Mitochondrial phosphatase phosphoglycerate mutase 5 (PGAM5) is emerging as a regulator of these post-translational modifications; however, its precise role in the regulation of mitochondrial morphology is unknown. We show that PGAM5 interacts with MFN2 and DRP1 in a stress-sensitive manner. PGAM5 regulates MFN2 phosphorylation and consequently protects it from ubiquitination and degradation. Further, phosphorylation and dephosphorylation modification of MFN2 regulates its fusion ability. Phosphorylation enhances fission and degradation, whereas dephosphorylation enhances fusion. PGAM5 dephosphorylates MFN2 to promote mitochondrial network formation. Further, using a Drosophila genetic model, we demonstrate that the MFN2 homolog Marf and dPGAM5 are in the same biological pathway. Our results identify MFN2 dephosphorylation as a regulator of mitochondrial fusion and PGAM5 as an MFN2 phosphatase.