CaMKII induces permeability transition through Drp1 phosphorylation during chronic β-AR stimulation

MCU inhibition protects against intestinal ischemia‒reperfusion by inhibiting Drp1-dependent mitochondrial fission

Intestinal ischemia‒reperfusion (IIR) injury is a common complication of surgery, but clear molecular insights and valuable therapeutic targets are lacking. Mitochondrial calcium overload is an early sign of various diseases and is considered a vital factor in ischemia‒reperfusion injury. The mitochondrial calcium uniporter (MCU), which is located on the inner mitochondrial membrane, is the primary mediator of calcium ion entry into the mitochondria. However, the specific mechanism of MCU in IIR injury remains to be clarified. In this study, we generated an IIR model using C57BL/6 mice and Caco-2 cells and found increases in the calcium levels and MCU expression following IIR injury. The specific inhibition of MCU markedly attenuated IIR injury. Moreover, MCU knockdown alleviates mitochondrial dysfunction by reducing oxidative stress and apoptosis. Mechanistically, MCU knockdown substantially reduced the translocation of Drp1 and thus its binding to Fis1 receptors, resulting in decreased mitochondrial fission. Taken together, our findings demonstrated that MCU is a novel upstream regulator of Drp1 in ischemia‒reperfusion and represents a predictive and therapeutic target for IIR.

Decreasing mitochondrial fission ameliorates HIF-1α-dependent pathological retinal angiogenesis

Angiogenesis plays a critical role in many pathological processes, including irreversible blindness in eye diseases such as retinopathy of prematurity. Endothelial mitochondria are dynamic organelles that undergo constant fusion and fission and are critical signalling hubs that modulate angiogenesis by coordinating reactive oxygen species (ROS) production and calcium signalling and metabolism. In this study, we investigated the role of mitochondrial dynamics in pathological retinal angiogenesis. We showed that treatment with vascular endothelial growth factor (VEGF; 20 ng/ml) induced mitochondrial fission in HUVECs by promoting the phosphorylation of dynamin-related protein 1 (DRP1). DRP1 knockdown or pretreatment with the DRP1 inhibitor Mdivi-1 (5 μM) blocked VEGF-induced cell migration, proliferation, and tube formation in HUVECs. We demonstrated that VEGF treatment increased mitochondrial ROS production in HUVECs, which was necessary for HIF-1α-dependent glycolysis, as well as proliferation, migration, and tube formation, and the inhibition of mitochondrial fission prevented VEGF-induced mitochondrial ROS production. In an oxygen-induced retinopathy (OIR) mouse model, we found that active DRP1 was highly expressed in endothelial cells in neovascular tufts. The administration of Mdivi-1 (10 mg·kg-1·d-1, i.p.) for three days from postnatal day (P) 13 until P15 significantly alleviated pathological angiogenesis in the retina. Our results suggest that targeting mitochondrial fission may be a therapeutic strategy for proliferative retinopathies and other diseases that are dependent on pathological angiogenesis.

ROS-mediated cytoplasmic localization of CARM1 induces mitochondrial fission through DRP1 methylation

The dynamic regulation of mitochondria through fission and fusion is essential for maintaining cellular homeostasis. In this study, we discovered a role of coactivator-associated arginine methyltransferase 1 (CARM1) in mitochondrial dynamics. CARM1 methylates specific residues (R403 and R634) on dynamin-related protein 1 (DRP1). Methylated DRP1 interacts with mitochondrial fission factor (Mff) and forms self-assembly on the outer mitochondrial membrane, thereby triggering fission, reducing oxygen consumption, and increasing reactive oxygen species (ROS) production. This sets in motion a feedback loop that facilitates the translocation of CARM1 from the nucleus to the cytoplasm, enhancing DRP1 methylation and ROS production through mitochondrial fragmentation. Consequently, ROS reinforces the CARM1-DRP1-ROS axis, resulting in cellular senescence. Depletion of CARM1 or DRP1 impedes cellular senescence by reducing ROS accumulation. The uncovering of the above-described mechanism fills a missing piece in the vicious cycle of ROS-induced senescence and contributes to a better understanding of the aging process.

miR-483-5p-Containing exosomes treatment ameliorated deep vein thrombosis‑induced inflammatory response

Peripheral vascular condition, known as deep vein thrombosis (DVT), is a common ailment that may lead to deadly pulmonary embolism. Inflammation is closely connected to venous thrombosis, which results in blood stasis, leading to ischemia and hypoxia, as indicated by research. The objective of this research was to investigate the mechanism by which exosomes derived from adipose stem cells (ADSCs) prevent deep vein thrombosis. Our data showed that Exo-483 effectively reduced the thrombus weight in DVT rats by intravenous injection. Exo-483 decreased the expression of tissue factor (TF) protein, the influx of inflammatory cells into the thrombosed vein wall, and the levels of cytokines in the serum. Furthermore, Exo-483 suppressed the expression of Mitogen-activated protein kinase 1 (MAPK1) and decreased the expression of NLRP3 inflammasomes. In an oxygen-glucose deprivation (OGD) cell model, the tube-forming and migratory abilities of primary human umbilical vein endothelial cells (HUVEC) and EA.hy926 cells were suppressed by Exo-483 pretreatment.Exo-483 is also linked to regulating Dynamin-related protein 1 (DRP1) production downstream of MAPK1.By decreasing the mitochondrial localization and phosphorylation at the S616 site of DRP1, it diminishes the expression of NLRP3 inflammasomes. Moreover, according to Bioinformatics analysis, miR-483-5p was anticipated to target MAPK1. The research conducted by our team revealed that the miR-483-5p exosome derived from ADSCs exhibited anti-inflammatory properties through the modulation of downstream DRP1-NLRP3 expression by targeting MAPK1.The findings of this research propose that miR-483-5p may be regarded as an innovative treatment target for DVT.

Systemic phospho-defective and phospho-mimetic Drp1 mice exhibit normal growth and development with altered anxiety-like behavior

Mitochondrial division controls the size, distribution, and turnover of this essential organelle. A dynamin-related GTPase, Drp1, drives membrane division as a force-generating mechano-chemical enzyme. Drp1 is regulated by multiple mechanisms, including phosphorylation at two primary sites: serine 579 and serine 600. While previous studies in cell culture systems have shown that Drp1 S579 phosphorylation promotes mitochondrial division, its physiological functions remained unclear. Here, we generated phospho-mimetic Drp1 S579D and phospho-defective Drp1 S579R mice using the CRISPR-Cas system. Both mouse models exhibited normal growth, development, and breeding. We found that Drp1 is highly phosphorylated at S579 in brain neurons. Notably, the Drp1 S579D mice showed decreased anxiety-like behaviors, whereas the Drp1 S579R mice displayed increased anxiety-like behaviors. These findings suggest a critical role for Drp1 S579 phosphorylation in brain function. The Drp1 S579D and S579R mice thus offer valuable in vivo models for specific analysis of Drp1 S579 phosphorylation.

The main molecular mechanisms of ferroptosis and its role in chronic kidney disease

The term ferroptosis, coined in 2012, has been widely applied in various disease research fields. Ferroptosis is a newly regulated form of cell death distinct from apoptosis, necrosis, and autophagy, the mechanisms of which have been extensively studied. Chronic kidney disease, characterized by renal dysfunction, is a common disease severely affecting human health, with its occurrence and development influenced by multiple factors and leading to dysfunction in multiple systems. It often lacks obvious clinical symptoms in the early stages, and thus, diagnosis is typically made in the later stages, complicating treatment. While research on ferroptosis and acute kidney injury has made continuous progress, studies on the association between ferroptosis and chronic kidney disease remain limited. This review aims to summarize chronic kidney disease, investigate the mechanism and regulation of ferroptosis, and attempt to elucidate the role of ferroptosis in the occurrence and development of chronic kidney disease.

CaMKII activity and metabolic imbalance-related neurological diseases: Focus on vascular dysfunction, synaptic plasticity, amyloid beta accumulation, and lipid metabolism

Metabolic syndrome (MetS) is characterized by insulin resistance, hyperglycemia, excessive fat accumulation and dyslipidemia, and is known to be accompanied by neuropathological symptoms such as memory loss, anxiety, and depression. As the number of MetS patients is rapidly increasing globally, studies on the mechanisms of metabolic imbalance-related neuropathology are emerging as an important issue. Ca2+/calmodulin-dependent kinase II (CaMKII) is the main Ca2+ sensor and contributes to diverse intracellular signaling in peripheral organs and the central nervous system (CNS). CaMKII exerts diverse functions in cells, related to mechanisms such as RNA splicing, reactive oxygen species (ROS) generation, cytoskeleton, and protein-protein interactions. In the CNS, CaMKII regulates vascular function, neuronal circuits, neurotransmission, synaptic plasticity, amyloid beta toxicity, lipid metabolism, and mitochondrial function. Here, we review recent evidence for the role of CaMKII in neuropathologic issues associated with metabolic disorders.

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.

Toosendanin Induces Lung Squamous Cell Carcinoma Cell Apoptosis and Inhibits Tumor Progression via the BNIP3/AMPK Signaling Pathway

Lung squamous cell carcinoma (LUSC) is the second most common type of non-small cell lung cancer. Toosendanin can target critical cancer cell survival and proliferation. However, the function of toosendanin in LUSC is limited. Cancer cell proliferative capacity is detected using cell morphology, colony formation, and flow cytometry. The invasiveness of the cells is detected by a Transwell assay, western blotting, and RT-qPCR. Nude mice are injected with H226 (1×106) and received an intraperitoneal injection of toosendanin every 2 days for 21 days. RNA sequence transcriptome analysis is performed on toosendanin-treated cells to identify target genes and signaling pathways. With increasing concentrations of toosendanin, the rate of cell proliferation decreases and apoptotic cells increases. The number of migrated cells significantly reduces and epithelial-mesenchymal transition is reversed. Injection of toosendanin in nude mice leads to a reduction in tumor volume, weight, and the number of metastatic tumors. Furthermore, KEGG shows that genes related to the AMPK pathway are highly enriched. BNIP3 is the most differentially expressed gene, and its expression along with phosphorylated-AMPK significantly increases in toosendanin-treated cells. Toosendanin exerts anticancer effects, induces apoptosis in LUSC cells, and inhibits tumor progression via the BNIP3/AMPK signaling pathway.

Multifaceted role of dynamin-related protein 1 in cardiovascular disease: From mitochondrial fission to therapeutic interventions

Mitochondria are central to cellular energy production and metabolic regulation, particularly in cardiomyocytes. These organelles constantly undergo cycles of fusion and fission, orchestrated by key proteins like Dynamin-related Protein 1 (Drp-1). This review focuses on the intricate roles of Drp-1 in regulating mitochondrial dynamics, its implications in cardiovascular health, and particularly in myocardial infarction. Drp-1 is not merely a mediator of mitochondrial fission; it also plays pivotal roles in autophagy, mitophagy, apoptosis, and necrosis in cardiac cells. This multifaceted functionality is often modulated through various post-translational alterations, and Drp-1's interaction with intracellular calcium (Ca2 + ) adds another layer of complexity. We also explore the pathological consequences of Drp-1 dysregulation, including increased reactive oxygen species (ROS) production and endothelial dysfunction. Furthermore, this review delves into the potential therapeutic interventions targeting Drp-1 to modulate mitochondrial dynamics and improve cardiovascular outcomes. We highlight recent findings on the interaction between Drp-1 and sirtuin-3 and suggest that understanding this interaction may open new avenues for therapeutically modulating endothelial cells, fibroblasts, and cardiomyocytes. As the cardiovascular system increasingly becomes the focal point of aging and chronic disease research, understanding the nuances of Drp-1's functionality can lead to innovative therapeutic approaches.

Cdk8/CDK19 promotes mitochondrial fission through Drp1 phosphorylation and can phenotypically suppress pink1 deficiency in Drosophila

Cdk8 in Drosophila is the orthologue of vertebrate CDK8 and CDK19. These proteins have been shown to modulate transcriptional control by RNA polymerase II. We found that neuronal loss of Cdk8 severely reduces fly lifespan and causes bang sensitivity. Remarkably, these defects can be rescued by expression of human CDK19, found in the cytoplasm of neurons, suggesting a non-nuclear function of CDK19/Cdk8. Here we show that Cdk8 plays a critical role in the cytoplasm, with its loss causing elongated mitochondria in both muscles and neurons. We find that endogenous GFP-tagged Cdk8 can be found in both the cytoplasm and nucleus. We show that Cdk8 promotes the phosphorylation of Drp1 at S616, a protein required for mitochondrial fission. Interestingly, Pink1, a mitochondrial kinase implicated in Parkinson's disease, also phosphorylates Drp1 at the same residue. Indeed, overexpression of Cdk8 significantly suppresses the phenotypes observed in flies with low levels of Pink1, including elevated levels of ROS, mitochondrial dysmorphology, and behavioral defects. In summary, we propose that Pink1 and Cdk8 perform similar functions to promote Drp1-mediated fission.

The CaMK Family Differentially Promotes Necroptosis and Mouse Cardiac Graft Injury and Rejection

Organ transplantation is associated with various forms of programmed cell death which can accelerate transplant injury and rejection. Targeting cell death in donor organs may represent a novel strategy for preventing allograft injury. We have previously demonstrated that necroptosis plays a key role in promoting transplant injury. Recently, we have found that mitochondria function is linked to necroptosis. However, it remains unknown how necroptosis signaling pathways regulate mitochondrial function during necroptosis. In this study, we investigated the receptor-interacting protein kinase 3 (RIPK3) mediated mitochondrial dysfunction and necroptosis. We demonstrate that the calmodulin-dependent protein kinase (CaMK) family members CaMK1, 2, and 4 form a complex with RIPK3 in mouse cardiac endothelial cells, to promote trans-phosphorylation during necroptosis. CaMK1 and 4 directly activated the dynamin-related protein-1 (Drp1), while CaMK2 indirectly activated Drp1 via the phosphoglycerate mutase 5 (PGAM5). The inhibition of CaMKs restored mitochondrial function and effectively prevented endothelial cell death. CaMKs inhibition inhibited activation of CaMKs and Drp1, and cell death and heart tissue injury (n = 6/group, p < 0.01) in a murine model of cardiac transplantation. Importantly, the inhibition of CaMKs greatly prolonged heart graft survival (n = 8/group, p < 0.01). In conclusion, CaMK family members orchestrate cell death in two different pathways and may be potential therapeutic targets in preventing cell death and transplant injury.

GTPBP8 modulates mitochondrial fission through a Drp1-dependent process

Mitochondrial fission is a tightly regulated process involving multiple proteins and cell signaling. Despite extensive studies on mitochondrial fission factors, our understanding of the regulatory mechanisms remains limited. This study shows the critical role of a mitochondrial GTPase, GTPBP8, in orchestrating mitochondrial fission in mammalian cells. Depletion of GTPBP8 resulted in drastic elongation and interconnectedness of mitochondria. Conversely, overexpression of GTPBP8 shifted mitochondrial morphology from tubular to fragmented. Notably, the induced mitochondrial fragmentation from GTPBP8 overexpression was inhibited in cells either depleted of the mitochondrial fission protein Drp1 (also known as DNM1L) or carrying mutated forms of Drp1. Importantly, downregulation of GTPBP8 caused an increase in oxidative stress, modulating cell signaling involved in the increased phosphorylation of Drp1 at Ser637. This phosphorylation hindered the recruitment of Drp1 to mitochondria, leading to mitochondrial fission defects. By contrast, GTPBP8 overexpression triggered enhanced recruitment and assembly of Drp1 at mitochondria. In summary, our study illuminates the cellular function of GTPBP8 as a pivotal modulator of the mitochondrial division apparatus, inherently reliant on its influence on Drp1.

Hyperglycemia triggers RyR2-dependent alterations of mitochondrial calcium homeostasis in response to cardiac ischemia-reperfusion: Key role of DRP1 activation

Hyperglycemia increases the heart sensitivity to ischemia-reperfusion (IR), but the underlying cellular mechanisms remain unclear. Mitochondrial dynamics (the processes that govern mitochondrial morphology and their interactions with other organelles, such as the reticulum), has emerged as a key factor in the heart vulnerability to IR. However, it is unknown whether mitochondrial dynamics contributes to hyperglycemia deleterious effect during IR. We hypothesized that (i) the higher heart vulnerability to IR in hyperglycemic conditions could be explained by hyperglycemia effect on the complex interplay between mitochondrial dynamics, Ca2+ homeostasis, and reactive oxygen species (ROS) production; and (ii) the activation of DRP1, a key regulator of mitochondrial dynamics, could play a central role. Using transmission electron microscopy and proteomic analysis, we showed that the interactions between sarcoplasmic reticulum and mitochondria and mitochondrial fission were increased during IR in isolated rat hearts perfused with a hyperglycemic buffer compared with hearts perfused with a normoglycemic buffer. In isolated mitochondria and cardiomyocytes, hyperglycemia increased mitochondrial ROS production and Ca2+ uptake. This was associated with higher RyR2 instability. These results could contribute to explain the early mPTP activation in mitochondria from isolated hearts perfused with a hyperglycemic buffer and in hearts from streptozotocin-treated rats (to increase the blood glucose). DRP1 inhibition by Mdivi-1 during the hyperglycemic phase and before IR induction, normalized Ca2+ homeostasis, ROS production, mPTP activation, and reduced the heart sensitivity to IR in streptozotocin-treated rats. In conclusion, hyperglycemia-dependent DRP1 activation results in higher reticulum-mitochondria calcium exchange that contribute to the higher heart vulnerability to IR.

USP28 Serves as a Key Suppressor of Mitochondrial Morphofunctional Defects and Cardiac Dysfunction in the Diabetic Heart

BACKGROUND

The majority of people with diabetes are susceptible to cardiac dysfunction and heart failure, and conventional drug therapy cannot correct diabetic cardiomyopathy progression. Herein, we assessed the potential role and therapeutic value of USP28 (ubiquitin-specific protease 28) on the metabolic vulnerability of diabetic cardiomyopathy.

METHODS

The type 2 diabetes mouse model was established using db/db leptin receptor-deficient mice and high-fat diet/streptozotocin-induced mice. Cardiac-specific knockout of USP28 in the db/db background mice was generated by crossbreeding db/m and Myh6-Cre+/USP28fl/fl mice. Recombinant adeno-associated virus serotype 9 carrying USP28 under cardiac troponin T promoter was injected into db/db mice. High glucose plus palmitic acid-incubated neonatal rat ventricular myocytes and human induced pluripotent stem cell-derived cardiomyocytes were used to imitate diabetic cardiomyopathy in vitro. The molecular mechanism was explored through RNA sequencing, immunoprecipitation and mass spectrometry analysis, protein pull-down, chromatin immunoprecipitation sequencing, and chromatin immunoprecipitation assay.

RESULTS

Microarray profiling of the UPS (ubiquitin-proteasome system) on the basis of db/db mouse hearts and diabetic patients' hearts demonstrated that the diabetic ventricle presented a significant reduction in USP28 expression. Diabetic Myh6-Cre+/USP28fl/fl mice exhibited more severe progressive cardiac dysfunction, lipid accumulation, and mitochondrial disarrangement, compared with their controls. On the other hand, USP28 overexpression improved systolic and diastolic dysfunction and ameliorated cardiac hypertrophy and fibrosis in the diabetic heart. Adeno-associated virus serotype 9-USP28 diabetic mice also exhibited less lipid storage, reduced reactive oxygen species formation, and mitochondrial impairment in heart tissues than adeno-associated virus serotype 9-null diabetic mice. As a result, USP28 overexpression attenuated cardiac remodeling and dysfunction, lipid accumulation, and mitochondrial impairment in high-fat diet/streptozotocin-induced type 2 diabetes mice. These results were also confirmed in neonatal rat ventricular myocytes and human induced pluripotent stem cell-derived cardiomyocytes. RNA sequencing, immunoprecipitation and mass spectrometry analysis, chromatin immunoprecipitation assays, chromatin immunoprecipitation sequencing, and protein pull-down assay mechanistically revealed that USP28 directly interacted with PPARα (peroxisome proliferator-activated receptor α), deubiquitinating and stabilizing PPARα (Lys152) to promote Mfn2 (mitofusin 2) transcription, thereby impeding mitochondrial morphofunctional defects. However, such cardioprotective benefits of USP28 were largely abrogated in db/db mice with PPARα deletion and conditional loss-of-function of Mfn2.

CONCLUSIONS

Our findings provide a USP28-modulated mitochondria homeostasis mechanism that involves the PPARα-Mfn2 axis in diabetic hearts, suggesting that USP28 activation or adeno-associated virus therapy targeting USP28 represents a potential therapeutic strategy for diabetic cardiomyopathy.

Effects of phosphorylation on Drp1 activation by its receptors, actin, and cardiolipin

Drp1 is a dynamin family GTPase required for mitochondrial and peroxisomal division. Oligomerization increases Drp1 GTPase activity through interactions between neighboring GTPase domains. In cells, Drp1 is regulated by several factors including Drp1 receptors, actin filaments, cardiolipin, and phosphorylation at two sites: S579 and S600. Commonly, phosphorylation of S579 is considered activating, while S600 phosphorylation is considered inhibiting. However, direct effects of phosphorylation on Drp1 GTPase activity have not been investigated in detail. Here, we compare effects of S579 and S600 phosphorylation on purified Drp1, using phosphomimetic mutants and in vitro phosphorylation. Both phosphomimetic mutants are shifted toward smaller oligomers. Both phosphomimetic mutations maintain basal GTPase activity, but eliminate GTPase stimulation by actin and decrease GTPase stimulation by cardiolipin, Mff, and MiD49. Phosphorylation of S579 by Erk2 produces similar effects. When mixed with wildtype Drp1, both S579D and S600D phosphomimetic mutants reduce the actin-stimulated GTPase activity of Drp1-WT. Conversely, a Drp1 mutant (K38A) lacking GTPase activity stimulates Drp1-WT GTPase activity under both basal and actin-stimulated conditions. These results suggest that the effect of S579 phosphorylation is not to activate Drp1 directly. In addition, our results suggest that nearest neighbor interactions within the Drp1 oligomer affect catalytic activity.

Dapagliflozin Suppresses Isoprenaline-Induced Cardiac Hypertrophy Through Inhibition of Mitochondrial Fission

ABSTRACT

Dapagliflozin (DAPA) is a novel oral hypoglycemic agent, and there is increasing evidence that DAPA has a protective effect against cardiovascular disease. The study aimed to investigate how DAPA inhibits cardiac hypertrophy and explore its potential mechanisms. By continuously infusing isoprenaline (ISO) for 2 weeks using a subcutaneous osmotic pump, a cardiac hypertrophic model was established in male C57BL/6 mice. On day 14 after surgery, echocardiography showed that left ventricle mass (LV mass), interventricular septum, left ventricle posterior wall diastole, and left ventricular posterior wall systole were significantly increased, and ejection fraction was decreased compared with control mice. Masson and Wheat Germ Agglutinin staining indicated enhanced myocardial fibrosis and cell morphology compared with control mice. Importantly, these effects were inhibited by DAPA treatment in ISO-induced mice. In H9c2 cells and neonatal rat cardiomyocytes, we found that mitochondrial fragmentation and mitochondrial oxidative stress were significantly augmented in the ISO-induced group. However, DAPA rescued the cardiac hypertrophy in ISO-induced H9c2 cells and neonatal rat cardiomyocytes. Mechanistically, we found that DAPA restored the PIM1 activity in ISO-induced H9c2 cells and subsequent increase in dynamin-associated protein 1 (Drp1) phosphorylation at S616 and decrease in Drp1 phosphorylation at S637 in ISO-induced cells. We found that DAPA mitigated ISO-induced cardiac hypertrophy by suppressing Drp1-mediated mitochondrial fission in a PIM1-dependent fashion.

Mitochondrial Responses to Sublethal Doxorubicin in H9c2 Cardiomyocytes: The Role of Phosphorylated CaMKII

Background

Doxorubicin (Dox) is effective against different types of cancers, but it poses cardiotoxic side effects, frequently resulting in irreversible heart failure. However, the complexities surrounding this cardiotoxicity, especially at sublethal dosages, remain to be fully elucidated. We investigated early cellular disruptions in response to sublethal Dox, with a specific emphasis on the role of phosphorylated calcium/calmodulin-dependent protein kinase II (CaMKII) in initiating mitochondrial dysfunction.

Methods

This study utilized the H9c2 cardiomyocyte model to identify a sublethal concentration of Dox and investigate its impact on mitochondrial health using markers such as mitochondrial membrane potential (MMP), mitophagy initiation, and mitochondrial calcium dynamics. We examined the roles of and interactions between CaMKII, dynamin-related protein 1 (Drp1), and the mitochondrial calcium uniporter (MCU) in Dox-induced mitochondrial disruption using specific inhibitors, such as KN-93, Mdivi-1, and Ru360, respectively.

Results

Exposure to a sublethal dose of Dox reduced the MMP red-to-green fluorescence ratio in H9c2 cells by 40.6% compared with vehicle, and increased the proportion of cells undergoing mitophagy from negligible levels compared with vehicle to 62.2%. Mitochondrial calcium levels also increased by 8.7-fold compared with the vehicle group. Notably, the activation of CaMKII, particularly its phosphorylated form, was pivotal in driving these mitochondrial changes, as inhibition using KN-93 restored MMP and decreased mitophagy. However, inhibition of Drp1 and MCU functions had a limited impact on the observed mitochondrial disruptions.

Conclusion

Sublethal administration of Dox is closely linked to CaMKII activation through phosphorylation, emphasizing its pivotal role in early mitochondrial disruption. These findings present a promising direction for developing therapeutic strategies that may alleviate the cardiotoxic effects of Dox, potentially increasing its clinical efficacy.

Kinase signalling adaptation supports dysfunctional mitochondria in disease

Mitochondria form a critical control nexus which are essential for maintaining correct tissue homeostasis. An increasing number of studies have identified dysregulation of mitochondria as a driver in cancer. However, which pathways support and promote this adapted mitochondrial function? A key hallmark of cancer is perturbation of kinase signalling pathways. These pathways include mitogen activated protein kinases (MAPK), lipid secondary messenger networks, cyclic-AMP-activated (cAMP)/AMP-activated kinases (AMPK), and Ca2+/calmodulin-dependent protein kinase (CaMK) networks. These signalling pathways have multiple substrates which support initiation and persistence of cancer. Many of these are involved in the regulation of mitochondrial morphology, mitochondrial apoptosis, mitochondrial calcium homeostasis, mitochondrial associated membranes (MAMs), and retrograde ROS signalling. This review will aim to both explore how kinase signalling integrates with these critical mitochondrial pathways and highlight how these systems can be usurped to support the development of disease. In addition, we will identify areas which require further investigation to fully understand the complexities of these regulatory interactions. Overall, this review will emphasize how studying the interaction between kinase signalling and mitochondria improves our understanding of mitochondrial homeostasis and can yield novel therapeutic targets to treat disease.

Berberine alleviates myocardial diastolic dysfunction by modulating Drp1-mediated mitochondrial fission and Ca2+ homeostasis in a murine model of HFpEF

Heart failure with preserved ejection fraction (HFpEF) displays normal or near-normal left ventricular ejection fraction, diastolic dysfunction, cardiac hypertrophy, and poor exercise capacity. Berberine, an isoquinoline alkaloid, possesses cardiovascular benefits. Adult male mice were assigned to chow or high-fat diet with L-NAME ("two-hit" model) for 15 weeks. Diastolic function was assessed using echocardiography and noninvasive Doppler technique. Myocardial morphology, mitochondrial ultrastructure, and cardiomyocyte mechanical properties were evaluated. Proteomics analysis, autophagic flux, and intracellular Ca2+ were also assessed in chow and HFpEF mice. The results show exercise intolerance and cardiac diastolic dysfunction in "two-hit"-induced HFpEF model, in which unfavorable geometric changes such as increased cell size, interstitial fibrosis, and mitochondrial swelling occurred in the myocardium. Diastolic dysfunction was indicated by the elevated E value, mitral E/A ratio, and E/e' ratio, decreased e' value and maximal velocity of re-lengthening (-dL/dt), and prolonged re-lengthening in HFpEF mice. The effects of these processes were alleviated by berberine. Moreover, berberine ameliorated autophagic flux, alleviated Drp1 mitochondrial localization, mitochondrial Ca2+ overload and fragmentation, and promoted intracellular Ca2+ reuptake into sarcoplasmic reticulum by regulating phospholamban and SERCA2a. Finally, berberine alleviated diastolic dysfunction in "two-hit" diet-induced HFpEF model possibly because of the promotion of autophagic flux, inhibition of mitochondrial fragmentation, and cytosolic Ca2+ overload.

The role of mitochondrial dynamics in disease

Mitochondria are multifaceted and dynamic organelles regulating various important cellular processes from signal transduction to determining cell fate. As dynamic properties of mitochondria, fusion and fission accompanied with mitophagy, undergo constant changes in number and morphology to sustain mitochondrial homeostasis in response to cell context changes. Thus, the dysregulation of mitochondrial dynamics and mitophagy is unsurprisingly related with various diseases, but the unclear underlying mechanism hinders their clinical application. In this review, we summarize the recent developments in the molecular mechanism of mitochondrial dynamics and mitophagy, particularly the different roles of key components in mitochondrial dynamics in different context. We also summarize the roles of mitochondrial dynamics and target treatment in diseases related to the cardiovascular system, nervous system, respiratory system, and tumor cell metabolism demanding high-energy. In these diseases, it is common that excessive mitochondrial fission is dominant and accompanied by impaired fusion and mitophagy. But there have been many conflicting findings about them recently, which are specifically highlighted in this view. We look forward that these findings will help broaden our understanding of the roles of the mitochondrial dynamics in diseases and will be beneficial to the discovery of novel selective therapeutic targets.

Targeting mitochondrial shape: at the heart of cardioprotection

There remains an unmet need to identify novel therapeutic strategies capable of protecting the myocardium against the detrimental effects of acute ischemia-reperfusion injury (IRI), to reduce myocardial infarct (MI) size and prevent the onset of heart failure (HF) following acute myocardial infarction (AMI). In this regard, perturbations in mitochondrial morphology with an imbalance in mitochondrial fusion and fission can disrupt mitochondrial metabolism, calcium homeostasis, and reactive oxygen species production, factors which are all known to be critical determinants of cardiomyocyte death following acute myocardial IRI. As such, therapeutic approaches directed at preserving the morphology and functionality of mitochondria may provide an important strategy for cardioprotection. In this article, we provide an overview of the alterations in mitochondrial morphology which occur in response to acute myocardial IRI, and highlight the emerging therapeutic strategies for targeting mitochondrial shape to preserve mitochondrial function which have the future therapeutic potential to improve health outcomes in patients presenting with AMI.

The romantic history of signaling pathway discovery in cell death: an updated review

Cell death is a fundamental physiological process in all living organisms. Processes such as embryonic development, organ formation, tissue growth, organismal immunity, and drug response are accompanied by cell death. In recent years with the development of electron microscopy as well as biological techniques, especially the discovery of novel death modes such as ferroptosis, cuprotosis, alkaliptosis, oxeiptosis, and disulfidptosis, researchers have been promoted to have a deeper understanding of cell death modes. In this systematic review, we examined the current understanding of modes of cell death, including the recently discovered novel death modes. Our analysis highlights the common and unique pathways of these death modes, as well as their impact on surrounding cells and the organism as a whole. Our aim was to provide a comprehensive overview of the current state of research on cell death, with a focus on identifying gaps in our knowledge and opportunities for future investigation. We also presented a new insight for macroscopic intracellular survival patterns, namely that intracellular molecular homeostasis is central to the balance of different cell death modes, and this viewpoint can be well justified by the signaling crosstalk of different death modes. These concepts can facilitate the future research about cell death in clinical diagnosis, drug development, and therapeutic modalities.

TCH-165 attenuates cardiac ischaemia/reperfusion injury by balancing mitochondrial dynamics via increasing proteasome activity

The proteasome is the main complex responsible for maintaining intracellular protein homeostasis, impairment of which is associated with cardiac ischaemia/reperfusion (I/R) injury. The small molecule TCH-165 has been found to activate the 20S proteasome to remove disordered proteins in multiple myeloma and glioblastoma. However, the preventive effect of TCH-165 against I/R-mediated cardiac impairment in mice remains largely unknown. Here, a cardiac I/R model was established in mice. Heart function was assessed with echocardiography. Cardiac infarction, myocyte death, and superoxide level were evaluated by 2,3,5-triphenyltetrazolium chloride (TTC)-Evans blue staining, terminal deoxynucleotidyl transferase-mediated dUTP nick and labelling (TUNEL) assay and immunostaining, respectively. Our results showed that TCH-165 treatment markedly ameliorated I/R-mediated cardiac dysfunction and decreased the infarct size, apoptosis, and superoxide levels. Mechanistically, TCH-165 increased immunoproteasome subunit expression/activity, increasing pro-fission protein dynamin-1-like protein (DNM1L, also known as DRP1) degradation and the expression of the pro-fusion proteins mitofusin 1/2 (Mfn1/2) and thereby leading to mitochondrial fission/fusion balance. In vitro experiments confirmed that inhibition of proteasome activity by epoxomicin abolished the protective effect of TCH-165 against hypoxia/reoxygenation (H/R)-induced increases in cardiomyocyte apoptosis, superoxide production and mitochondrial fission. In summary, TCH-165 is a newly discovered inducer of immunoproteasome activity that exerts a preventive effect against cardiac I/R damage by targeting Drp1 degradation, indicating that it may be as a potential therapeutic candidate for ischaemic heart disease.

TRPV4-mediated mitochondrial dysfunction induces pyroptosis and cartilage degradation in osteoarthritis via the Drp1-HK2 axis

Osteoarthritis (OA) is an age-related chronic degenerative disease with complex pathophysiological mechanisms. Accumulating evidence indicates that nod-like receptor pyrin domain 3 (NLRP3) inflammasome-mediated pyroptosis of chondrocytes plays a crucial role in the OA progression. Transient Receptor Potential Vanilloid 4 (TRPV4), described as a calcium-permeable cation channel, isassociated with proinflammatory factors and pyroptosis. In this study, we studied the potential functions of TRPV4 in chondrocyte pyroptosis and cartilage degradation. We found that lipopolysaccharides(LPS)-induced mitochondrial reactive oxygen species (mtROS) accumulation aggravated chondrocyte pyroptosis and cartilage degeneration. TRPV4 induces dynamin-related protein 1 (Drp1) mitochondrial translocation through the Ca2+-calmodulin-dependent protein kinase II (CaMKII) signaling pathway, which subsequently caused the mitochondrial dysfunction (e.g., mPTP over opening; Δψm depolarization; ATP production decreased; mtROS accumulation), pyroptosis and extracellular matrix (ECM) degradation through hexokinase 2 (HK2) dissociation from mitochondrial membrane. Moreover, TRPV4 inhibition reversed Drp1-involved chondrocyte pyroptosis and cartilage degeneration in the anterior cruciate ligament transection (ACLT) mouse model. Our findings revealed the internal mechanisms underlying TRPV4 regulation in chondrocytes and its intrinsic therapeutic efficacy for OA.

Current Advances of Mitochondrial Dysfunction and Cardiovascular Disease and Promising Therapeutic Strategies

Mitochondria are cellular power stations and essential organelles for maintaining cellular homeostasis. Dysfunctional mitochondria have emerged as a key factor in the occurrence and development of cardiovascular disease. This review focuses on advances in the relationship between mitochondrial dysfunction and cardiovascular diseases such as atherosclerosis, heart failure, myocardial ischemia reperfusion injury, and pulmonary arterial hypertension. The clinical value and challenges of mitochondria-targeted strategies, including mitochondria-targeted antioxidants, mitochondrial quality control modulators, mitochondrial function protectors, mitochondrial biogenesis promoters, and recently developed mitochondrial transplants, are also discussed.

Mitochondria in health, disease, and aging

Mitochondria are well known as organelles responsible for the maintenance of cellular bioenergetics through the production of ATP. Although oxidative phosphorylation may be their most important function, mitochondria are also integral for the synthesis of metabolic precursors, calcium regulation, the production of reactive oxygen species, immune signaling, and apoptosis. Considering the breadth of their responsibilities, mitochondria are fundamental for cellular metabolism and homeostasis. Appreciating this significance, translational medicine has begun to investigate how mitochondrial dysfunction can represent a harbinger of disease. In this review, we provide a detailed overview of mitochondrial metabolism, cellular bioenergetics, mitochondrial dynamics, autophagy, mitochondrial damage-associated molecular patterns, mitochondria-mediated cell death pathways, and how mitochondrial dysfunction at any of these levels is associated with disease pathogenesis. Mitochondria-dependent pathways may thereby represent an attractive therapeutic target for ameliorating human disease.

Mitochondrial dynamics in health and disease: mechanisms and potential targets

Mitochondria are organelles that are able to adjust and respond to different stressors and metabolic needs within a cell, showcasing their plasticity and dynamic nature. These abilities allow them to effectively coordinate various cellular functions. Mitochondrial dynamics refers to the changing process of fission, fusion, mitophagy and transport, which is crucial for optimal function in signal transduction and metabolism. An imbalance in mitochondrial dynamics can disrupt mitochondrial function, leading to abnormal cellular fate, and a range of diseases, including neurodegenerative disorders, metabolic diseases, cardiovascular diseases and cancers. Herein, we review the mechanism of mitochondrial dynamics, and its impacts on cellular function. We also delve into the changes that occur in mitochondrial dynamics during health and disease, and offer novel perspectives on how to target the modulation of mitochondrial dynamics.

Effects of phosphorylation on Drp1 activation by its receptors, actin, and cardiolipin

Drp1 is a dynamin family GTPase that is required for mitochondrial and peroxisomal division, in which it oligomerizes into a ring and constricts the underlying membrane in a GTP hydrolysis-dependent manner. Oligomerization increases Drp1 GTPase activity through interactions between neighboring GTPase domains. In cells, Drp1 is regulated by several factors including Drp1 receptors, actin filaments, cardiolipin, and phosphorylation at two sites: S579 and S600. Phosphorylation of S579 is widely regarded as activating, while S600 phosphorylation is commonly considered inhibiting. However, the direct effects of phosphorylation on Drp1 GTPase activity have not been investigated in detail. In this study, we compare the effects of S579 and S600 phosphorylation on purified Drp1, using phospho-mimetic mutants and in vitro phosphorylation. The oligomerization state of both phospho-mimetic mutants is shifted toward smaller oligomers. Both phospho-mimetic mutations maintain basal GTPase activity, but eliminate GTPase stimulation by actin and decrease GTPase stimulation by cardiolipin, Mff, and MiD49. Phosphorylation of S579 by Erk2 produces similar effects. When mixed with wild-type Drp1, both S579D and S600D phospho-mimetic mutants reduce the actin-stimulated GTPase activity of Drp1-WT. Conversely, a Drp1 mutant that lacks GTPase activity, the K38A mutant, stimulates Drp1-WT GTPase activity under both basal and actin-stimulated conditions, similar to previous results for dynamin-1. These results suggest that the effect of S579 phosphorylation is not to activate Drp1 directly, and likely requires additional factors for stimulation of mitochondrial fission in cells. In addition, our results suggest that nearest neighbor interactions within the Drp1 oligomer affect catalytic activity.

Targeting dynamin-related protein-1 as a potential therapeutic approach for mitochondrial dysfunction in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that manifests its pathology through synaptic damage, mitochondrial abnormalities, microRNA deregulation, hormonal imbalance, increased astrocytes & microglia, accumulation of amyloid β (Aβ) and phosphorylated Tau in the brains of AD patients. Despite extensive research, the effective treatment of AD is still unknown. Tau hyperphosphorylation and mitochondrial abnormalities are involved in the loss of synapses, defective axonal transport and cognitive decline in patients with AD. Mitochondrial dysfunction is evidenced by enhanced mitochondrial fragmentation, impaired mitochondrial dynamics, mitochondrial biogenesis and defective mitophagy in AD. Hence, targeting mitochondrial proteins might be a promising therapeutic strategy in treating AD. Recently, dynamin-related protein 1 (Drp1), a mitochondrial fission protein, has gained attention due to its interactions with Aβ and hyperphosphorylated Tau, altering mitochondrial morphology, dynamics, and bioenergetics. These interactions affect ATP production in mitochondria. A reduction in Drp1 GTPase activity protects against neurodegeneration in AD models. This article provides a comprehensive overview of Drp1's involvement in oxidative damage, apoptosis, mitophagy, and axonal transport of mitochondria. We also highlighted the interaction of Drp1 with Aβ and Tau, which may contribute to AD progression. In conclusion, targeting Drp1 could be a potential therapeutic approach for preventing AD pathology.

MFN2-mediated mitochondrial fusion facilitates acute hypobaric hypoxia-induced cardiac dysfunction by increasing glucose catabolism and ROS production

BACKGROUND

Rapid ascent to high-altitude environment which is characterized by acute hypobaric hypoxia (HH) may increase the risk of cardiac dysfunction. However, the potential regulatory mechanisms and prevention strategies for acute HH-induced cardiac dysfunction have not been fully clarified. Mitofusin 2 (MFN2) is highly expressed in the heart and is involved in the regulation of mitochondrial fusion and cell metabolism. To date, however, the significance of MFN2 in the heart under acute HH has not been investigated.

METHODS AND RESULTS

Our study revealed that MFN2 upregulation in hearts of mice during acute HH led to cardiac dysfunction. In vitro experiments showed that the decrease in oxygen concentration induced upregulation of MFN2, impairing cardiomyocyte contractility and increasing the risk of QT prolongation. Additionally, acute HH-induced MFN2 upregulation promoted glucose catabolism and led to excessive mitochondrial reactive oxygen species (ROS) production in cardiomyocytes, ultimately resulting in decreased mitochondrial function. Furthermore, co-immunoprecipitation (co-IP) and mass spectrometry analyses indicated that MFN2 interacted with the NADH-ubiquinone oxidoreductase 23 kDa subunit (NDUFS8). Specifically, acute HH-induced MFN2 upregulation increased NDUFS8-dependent complex I activity.

CONCLUSIONS

Taken together, our studies provide the first direct evidence that MFN2 upregulation exacerbates acute HH-induced cardiac dysfunction by increasing glucose catabolism and ROS production.

GENERAL SIGNIFICANCE

Our studies indicate that MFN2 may be a promising therapeutic target for cardiac dysfunction under acute HH.

Pseudolaric acid B triggers cell apoptosis by activating AMPK/JNK/DRP1/mitochondrial fission pathway in hepatocellular carcinoma

Pseudolaric acid B (PAB), a natural product isolated from the root bark of Pseudolarix kaempferi, has been reported to exert inhibitory effects in various cancers. However, the underlying mechanisms remain largely unclear. In the present study, we investigated the mechanism through which PAB exert its anticancer effects in hepatocellular carcinoma (HCC). PAB inhibited the viability of and induced apoptosis in Hepa1-6 cells in a dose-dependent manner. It disrupted mitochondrial membrane potential (MMP) and impaired ATP production. Furthermore, PAB induced phosphorylation of DRP1 at Ser616 and mitochondrial fission. Blocking DRP1 phosphorylation by Mdivi-1 inhibited mitochondrial fission and PAB-induced apoptosis. Moreover, c-Jun N-terminal kinase (JNK) was activated by PAB, and blocking JNK activity using SP600125 inhibited PAB-induced mitochondrial fission and cell apoptosis. Furthermore, PAB activated AMP-activated protein kinase (AMPK), and inhibiting AMPK by compound C attenuated PAB-stimulated JNK activation and blocked DRP1-dependent mitochondrial fission and apoptosis. Our in vivo data confirmed that PAB inhibited tumor growth and induced apoptosis in an HCC syngeneic mouse model by inducing the AMPK/JNK/DRP1/mitochondrial fission signaling pathway. Furthermore, a combination of PAB and sorafenib showed a synergistic effect in inhibiting tumor growth in vivo. Taken together, our findings highlight a potential therapeutic strategy for HCC.

FTY720-P, a Biased S1PR Ligand, Increases Mitochondrial Function through STAT3 Activation in Cardiac Cells

FTY720 is an FDA-approved sphingosine derivative drug for the treatment of multiple sclerosis. This compound blocks lymphocyte egress from lymphoid organs and autoimmunity through sphingosine 1-phosphate (S1P) receptor blockage. Drug repurposing of FTY720 has revealed improvements in glucose metabolism and metabolic diseases. Studies also demonstrate that preconditioning with this compound preserves the ATP levels during cardiac ischemia in rats. The molecular mechanisms by which FTY720 promotes metabolism are not well understood. Here, we demonstrate that nanomolar concentrations of the phosphorylated form of FTY720 (FTY720-P), the active ligand of S1P receptor (S1PR), activates mitochondrial respiration and the mitochondrial ATP production rate in AC16 human cardiomyocyte cells. Additionally, FTY720-P increases the number of mitochondrial nucleoids, promotes mitochondrial morphology alterations, and induces activation of STAT3, a transcription factor that promotes mitochondrial function. Notably, the effect of FTY720-P on mitochondrial function was suppressed in the presence of a STAT3 inhibitor. In summary, our results suggest that FTY720 promotes the activation of mitochondrial function, in part, through a STAT3 action.

Ca2+/Calmodulin-Dependent Protein Kinase II Disrupts the Voltage Dependency of the Voltage-Dependent Anion Channel on the Lipid Bilayer Membrane

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a key enzyme that plays a significant role in intracellular signaling and the modulation of mitochondrial membrane properties. It is known that the voltage-dependent anion channel (VDAC) is one of the most abundant outer mitochondrial membrane (OMM) proteins acting as a significant passageway and regulatory site for various enzymes, proteins, ions, and metabolites. Considering this, we hypothesize that VDAC could be one of the targets for CaMKII enzymatic activity. Our in vitro experiments indicate that VDAC can be phosphorylated by the CaMKII enzyme. Moreover, the bilayer electrophysiology experimental data indicate that CaMKII significantly reduces VDAC's single-channel conductivity; its open probability remains high at all the applied potentials between +60 and -60 mV, and the voltage dependency was lost, which suggests that CaMKII disrupted the VDAC's single-channel activities. Hence, we can infer that VDAC interacts with CaMKII and thus acts as a vital target for its activity. Furthermore, our findings suggest that CaMKII could play a significant role during the transport of ions and metabolites across the outer mitochondrial membrane (OMM) through VDAC and thus regulate apoptotic events.

The Interplay Between Autophagy and Regulated Necrosis

Significance: Autophagy is critical to cellular homeostasis. Emergence of the concept of regulated necrosis, such as necroptosis, ferroptosis, pyroptosis, and mitochondrial membrane-permeability transition (MPT)-derived necrosis, has revolutionized the research into necrosis. Both altered autophagy and regulated necrosis contribute to major human diseases. Recent studies reveal an intricate interplay between autophagy and regulated necrosis. Understanding the interplay at the molecular level will provide new insights into the pathophysiology of related diseases. Recent Advances: Among the three forms of autophagy, macroautophagy is better studied for its crosstalk with regulated necrosis. Macroautophagy seemingly can either antagonize or promote regulated necrosis, depending upon the form of regulated necrosis, the type of cells or stimuli, and other cellular contexts. This review will critically analyze recent advances in the molecular mechanisms governing the intricate dialogues between macroautophagy and main forms of regulated necrosis. Critical Issues: The dual roles of autophagy, either pro-survival or pro-death characteristics, intricate the mechanistic relationship between autophagy and regulated necrosis at molecular level in various pathological conditions. Meanwhile, key components of regulated necrosis are also involved in the regulation of autophagy, which further complicates the interrelationship. Future Directions: Resolving the controversies over causation between altered autophagy and a specific form of regulated necrosis requires approaches that are more definitive, where rigorous evaluation of autophagic flux and the development of more reliable and specific methods to quantify each form of necrosis will be essential. The relationship between chaperone-mediated autophagy or microautophagy and regulated necrosis remains largely unstudied. Antioxid. Redox Signal. 38, 550-580.

Pharmacological Targeting of Mitochondria in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) in the United States and many other countries. DKD occurs through a variety of pathogenic processes that are in part driven by hyperglycemia and glomerular hypertension, leading to gradual loss of kidney function and eventually progressing to ESRD. In type 2 diabetes, chronic hyperglycemia and glomerular hyperfiltration leads to glomerular and proximal tubular dysfunction. Simultaneously, mitochondrial dysfunction occurs in the early stages of hyperglycemia and has been identified as a key event in the development of DKD. Clinical management for DKD relies primarily on blood pressure and glycemic control through the use of numerous therapeutics that slow disease progression. Because mitochondrial function is key for renal health over time, therapeutics that improve mitochondrial function could be of value in different renal diseases. Increasing evidence supports the idea that targeting aspects of mitochondrial dysfunction, such as mitochondrial biogenesis and dynamics, restores mitochondrial function and improves renal function in DKD. We will review mitochondrial function in DKD and the effects of current and experimental therapeutics on mitochondrial biogenesis and homeostasis in DKD over time. SIGNIFICANCE STATEMENT: Diabetic kidney disease (DKD) affects 20% to 40% of patients with diabetes and has limited treatment options. Mitochondrial dysfunction has been identified as a key event in the progression of DKD, and pharmacologically restoring mitochondrial function in the early stages of DKD may be a potential therapeutic strategy in preventing disease progression.

Novel insights into the involvement of mitochondrial fission/fusion in heart failure: From molecular mechanisms to targeted therapies

Mitochondria are dynamic organelles that alter their morphology through fission (fragmentation) and fusion (elongation). These morphological changes correlate highly with mitochondrial functional adaptations to stressors, such as hypoxia, pressure overload, and inflammation, and are important in the setting of heart failure. Pathological mitochondrial remodeling, characterized by increased fission and reduced fusion, is associated with impaired mitochondrial respiration, increased mitochondrial oxidative stress, abnormal cytoplasmic calcium handling, and increased cardiomyocyte apoptosis. Considering the impact of the mitochondrial morphology on mitochondrial behavior and cardiomyocyte performance, altered mitochondrial dynamics could be expected to induce or exacerbate the pathogenesis and progression of heart failure. However, whether alterations in mitochondrial fission and fusion accelerate or retard the progression of heart failure has been the subject of intense debate. In this review, we first describe the physiological processes and regulatory mechanisms of mitochondrial fission and fusion. Then, we extensively discuss the pathological contributions of mitochondrial fission and fusion to heart failure. Lastly, we examine potential therapeutic approaches targeting mitochondrial fission/fusion to treat patients with heart failure.

Mitochondrial dynamics in macrophages: divide to conquer or unite to survive?

Mitochondria have long been appreciated as the metabolic hub of cells. Emerging evidence also posits these organelles as hubs for innate immune signalling and activation, particularly in macrophages. Macrophages are front-line cellular defenders against endogenous and exogenous threats in mammals. These cells use an array of receptors and downstream signalling molecules to respond to a diverse range of stimuli, with mitochondrial biology implicated in many of these responses. Mitochondria have the capacity to both divide through mitochondrial fission and coalesce through mitochondrial fusion. Mitochondrial dynamics, the balance between fission and fusion, regulate many cellular functions, including innate immune pathways in macrophages. In these cells, mitochondrial fission has primarily been associated with pro-inflammatory responses and metabolic adaptation, so can be considered as a combative strategy utilised by immune cells. In contrast, mitochondrial fusion has a more protective role in limiting cell death under conditions of nutrient starvation. Hence, fusion can be viewed as a cellular survival strategy. Here we broadly review the role of mitochondria in macrophage functions, with a focus on how regulated mitochondrial dynamics control different functional responses in these cells.

Non-conventional mitochondrial permeability transition: Its regulation by mitochondrial dynamics

Mitochondrial permeability transition (MPT) is a phenomenon that the inner mitochondrial membrane (IMM) loses its selective permeability, leading to mitochondrial dysfunction and cell injury. Electrophysiological evidence indicates the presence of a mega-channel commonly called permeability transition pore (PTP) whose opening is responsible for MPT. However, the molecular identity of the PTP is still under intensive investigations and debates, although cyclophilin D that is inhibited by cyclosporine A (CsA) is the established regulatory component of the PTP. PTP can also open transiently and functions as a rapid mitochondrial Ca2+ releasing mechanism. Mitochondrial fission and fusion, the main components of mitochondrial dynamics, control the number and size of mitochondria, and have been shown to play a role in regulating MPT directly or indirectly. Studies by us and others have indicated the potential existence of a form of transient MPT that is insensitive to CsA. This "non-conventional" MPT is regulated by mitochondrial dynamics and may serve a protective role possibly by decreasing the susceptibility for a frequent or sustained PTP opening; hence, it may have a therapeutic value in many disease conditions involving MPT.

Klf4 deficiency exacerbates myocardial ischemia/reperfusion injury in mice via enhancing ROCK1/DRP1 pathway-dependent mitochondrial fission

RATIONAL

Excessive mitochondrial fission is considered key process involved in myocardial ischemia/reperfusion (I/R) injury. However, the upstream mechanism remains largely unclear. Decreased level of Kruppel Like Factor 4 (KLF4) has been implicated in the pathogenesis of mitochondrial dysfunction and heart's adaption to stress. However, the role of Klf4 in I/R process is not fully elucidated. This study aims to investigate how Klf4 regulates mitochondrial dynamics and further clarify its underlying mechanism during cardiac I/R injury.

METHODS

Loss-of-function and gain-of-function strategies were applied to investigate the role of Klf4 in cardiac I/R injury via genetic ablation or intra-myocardial adenovirus injection. Mitochondrial dynamics was analyzed by confocal microscopy in vitro and transmission electron microscopy in vivo. Chromatin immunoprecipitation and luciferase reporter assay were performed to explore the underlying mechanisms.

RESULTS

KLF4 was downregulated in I/R heart. Cardiac-specific Klf4 knockout significantly exacerbated cardiac dysfunction in I/R mice. Mechanistically, Klf4 deficiency aggravated mitochondrial apoptosis, reduced ATP generation and boosted ROS overproduction via enhancing DRP1-dependent mitochondrial fission. ROCK1 was identified as a kinase regulating DRP1 activity at Ser616. Klf4 deficiency upregulated the expression of ROCK1 at transcriptional level, thus increasing S616-DRP1-mediated mitochondrial fission during I/R. Finally, reconstitution of Klf4 inhibited mitochondrial fission, restored mitochondrial function and alleviated I/R injury.

CONCLUSION

Our study provides the first evidence that Klf4 deficiency exacerbates myocardial I/R injury through regulating ROCK1 expression at transcriptional level to induce DRP1-mediated mitochondrial fission. Targeting mitochondrial dynamics by restoring Klf4 might be potentially cardio-protective strategies attenuating I/R injury.

The role of Mitochondrial Fission Proteins in Mitochondrial Dynamics in Kidney Disease

Mitochondria have many forms and can change their shape through fusion and fission of the outer and inner membranes, called "mitochondrial dynamics". Mitochondrial outer membrane proteins, such as mitochondrial fission protein 1 (FIS1), mitochondrial fission factor (MFF), mitochondrial 98 dynamics proteins of 49 kDa (MiD49), and mitochondrial dynamics proteins of 51 kDa (MiD51), can aggregate at the outer mitochondrial membrane and thus attract Dynamin-related protein 1 (DRP1) from the cytoplasm to the outer mitochondrial membrane, where DRP1 can perform a scissor-like function to cut a complete mitochondrion into two separate mitochondria. Other organelles can promote mitochondrial fission alongside mitochondria. FIS1 plays an important role in mitochondrial-lysosomal contacts, differentiating itself from other mitochondrial-fission-associated proteins. The contact between the two can also induce asymmetric mitochondrial fission. The kidney is a mitochondria-rich organ, requiring large amounts of mitochondria to produce energy for blood circulation and waste elimination. Pathological increases in mitochondrial fission can lead to kidney damage that can be ameliorated by suppressing their excessive fission. This article reviews the current knowledge on the key role of mitochondrial-fission-associated proteins in the pathogenesis of kidney injury and the role of their various post-translational modifications in activation or degradation of fission-associated proteins and targeted drug therapy.

The role of mitochondrial fission in cardiovascular health and disease

Mitochondria are organelles involved in the regulation of various important cellular processes, ranging from ATP generation to immune activation. A healthy mitochondrial network is essential for cardiovascular function and adaptation to pathological stressors. Mitochondria undergo fission or fusion in response to various environmental cues, and these dynamic changes are vital for mitochondrial function and health. In particular, mitochondrial fission is closely coordinated with the cell cycle and is linked to changes in mitochondrial respiration and membrane permeability. Another key function of fission is the segregation of damaged mitochondrial components for degradation by mitochondrial autophagy (mitophagy). Mitochondrial fission is induced by the large GTPase dynamin-related protein 1 (DRP1) and is subject to sophisticated regulation. Activation requires various post-translational modifications of DRP1, actin polymerization and the involvement of other organelles such as the endoplasmic reticulum, Golgi apparatus and lysosomes. A decrease in mitochondrial fusion can also shift the balance towards mitochondrial fission. Although mitochondrial fission is necessary for cellular homeostasis, this process is often aberrantly activated in cardiovascular disease. Indeed, strong evidence exists that abnormal mitochondrial fission directly contributes to disease development. In this Review, we compare the physiological and pathophysiological roles of mitochondrial fission and discuss the therapeutic potential of preventing excessive mitochondrial fission in the heart and vasculature.

Cystathionine γ lyase S-sulfhydrates Drp1 to ameliorate heart dysfunction

Hydrogen sulfide (H₂S), produced by cystathionine γ lyase (CSE), is an important endogenous gasotransmitter to maintain heart function. However, the molecular mechanism for how H₂S influences the mitochondrial morphology during heart failure remains poorly understood. Here, we found that CSE/H₂S pathway mediated cardiac function and mitochondrial morphology through regulating dynamin related protein 1 (Drp1) activity and translocation. Mechanistically, elevation of H₂S levels by CSE overexpression declined protein level, phosphorylation (Ser 616), oligomerization and GTPase activity of Drp1 by S-sulfhydration in mouse hearts. Interestingly, Drp1 S-sulfhydration directly competed with S-nitrosylation by nitric oxide at the specific cysteine 607. The non-S-sulfhydration of Drp1 mutation (C607A) attenuated the regulatory effect of H₂S on Drp1 activation, mitochondrial fission and heart function. Moreover, the non-canonical role of Drp1 mediated isoprenaline-induced mitochondrial dysfunction and cardiomyocyte death through interaction with voltage-dependent anion channel 1. These results uncover that a novel mechanism that H₂S S-sulfhydrated Drp1 at cysteine 607 to prevent heart failure through modulating its activity and mitochondrial translocation. Our findings also provide initial evidence demonstrating that Drp1 may be a critical regulator as well as an effective strategy for heart dysfunction.

Dynamin-Related Protein 1 Is Involved in Mitochondrial Damage, Defective Mitophagy, and NLRP3 Inflammasome Activation Induced by MSU Crystals

Excessive generation of reactive oxygen species (ROS) has great impacts on MSU crystal-induced inflammation. Drp1-dependent mitochondrial fission is closely associated with mitochondrial ROS levels. However, whether Drp1 signaling contributes to MSU crystal-induced inflammation remains unclear. Mice bone marrow-derived macrophages (BMDMs) were primed with LPS and then stimulated with MSU suspensions for 12 h. The protein levels associated with mitochondrial dynamics, oxidative stress, and mitophagy were detected by Western blot. BMDMs were loaded with MitoTracker Green probe to detect mitochondrial morphology. To measure mitochondrial reactive oxygen species (ROS) and total ROS levels, cells were loaded, respectively, with MitoSOX and DHE probes. The effects of Mito-TEMPO, an antioxidant that targets the mitochondria or DRP1 inhibitor (Mdivi-1) on MSU crystal-induced peritonitis and arthritis mouse models, were evaluated. Our study revealed that MSU crystal stimulation resulted in elevation of mitochondrial fragmentation of BMDMs. Treatment with Mito-TEMPO or Drp1 knockdown significantly ameliorated the mitochondrial damage induced by MSU crystals. BMDMs exposure to MSU crystals increased the expression of auto/mitophagy marker proteins and promoted the fusion of mitophagosomes with lysosomes, leading to accumulation of mitolysosomes. Drp1 knockdown alleviated defective mitophagy and activation of the NLRP3 inflammasome in MSU crystal-treated BMDMs. This study indicates that there is crosstalk between mitochondrial ROS and Drp1 signaling in MSU crystal-induced inflammation. Drp1 signaling is involved in MSU crystal-induced mitochondrial damage, impaired mitophagy and NLRP3 inflammasome activation.

Silica nanoparticles perturbed mitochondrial dynamics and induced myocardial apoptosis via PKA-DRP1-mitochondrial fission signaling

Silica nanoparticles (SiNPs) are among the most abundantly produced nanosized particles in the global market, and their potential toxicity has aroused a great concern. Increasing epidemiological investigations and experimental evidence revealed the threaten of SiNPs exposure to cardiovascular system. The myocardial toxicity caused by SiNPs was gradually demonstrated, nevertheless, the underlying mechanisms remain unclear. In view of mitochondria serving as the centrality in the prominent of cardiovascular disease, we investigated the role of mitochondria and related mechanisms in SiNPs-induced adverse effects on cardiomyocytes. As a result, SiNPs were found in cytoplasm, accompanied with morphological alterations in mitochondria, such as cristae fracture or disappearance, vacuolation. The induction of mitochondrial dysfunction by SiNPs was confirmed, as indicated by the excessive reactive oxygen species (ROS) formation, and blockage of cellular respiratory and ATP production. Concomitantly, SiNPs activated mitochondria-mediated apoptotic signaling in view of the up-regulated BAX, increased Caspase-9 cleavage and declined Bcl-2, ultimately resulting in myocardial apoptosis. It was noteworthy that SiNPs disturbed mitochondrial dynamics toward fission phenotype, which was supported by the dysregulated fission/fusion regulators. Especially, DRP1 and its phosphorylated level at s616 (p-DRP1^s616) were up-regulated, whilst its phosphorylated level at s637 (p-DRP1^s637) and PKA phosphorylation were down-regulated in SiNPs-treated cardiomyocytes in a dose-dependent manner. More importantly, the mechanistic investigations revealed PKA-DRP1-mediated mitochondrial fission was responsible for SiNPs-induced cardiomyocyte apoptosis through the mitochondria-mediated apoptotic way. This study firstly demonstrated the disturbance of mitochondrial dynamics played a crucial role in cardiomyocyte apoptosis caused by SiNPs, attributing to PKA-DRP1-mitochondrial fission signaling.

Cdk5 Promotes Mitochondrial Fission via Drp1 Phosphorylation at S616 in Chronic Ethanol Exposure-Induced Cognitive Impairment

Excessive alcohol consumption can lead to alterations in brain structure and function, even causing irreversible learning and memory disorders. The hippocampus is one of the most sensitive areas to alcohol neurotoxicity in the brain. Accumulating evidence indicates that mitochondrial dysfunction contributes to alcohol neurotoxicity. However, little is known about the underlying molecular mechanisms. In this study, we found that chronic exposure to ethanol caused abnormal mitochondrial fission/fusion and morphology by activating the mitochondrial fission protein dynamin-related protein 1 (Drp1) and upregulating Drp1 receptors, such as fission protein 1 (Fis1), mitochondrial dynamics protein of 49 kDa (Mid49), and mitochondrial fission factor (Mff), combined with decreasing optic atrophy 1 (Opa1) and mitochondrial fusion protein mitofusin 1 (Mfn1) levels. In addition, mitochondrial division inhibitor 1 (mdivi-1) abrogated ethanol-induced mitochondrial dysfunction and improved hippocampal synapses and cognitive function in ethanol-exposed mice. Chronic ethanol exposure also resulted in cyclin-dependent kinase 5 (Cdk5) overactivation, as shown by the increase in the levels of Cdk5 and its activator P25 in the hippocampus. Furthermore, a Cdk5/P25 inhibitor (roscovitine) or Cdk5 knockdown using small interfering RNA (LVi-Cdk5) exerted neuroprotection by inhibiting abnormal mitochondrial fission through Drp1 phosphorylation at Ser616 and mitochondrial translocation after chronic ethanol exposure. Taken together, the present study demonstrated that inhibition of aberrant Cdk5 activation attenuates hippocampal neuron injury and cognitive deficits induced by chronic exposure to ethanol through Drp1-mediated mitochondrial fission and mitochondrial dysfunction. Interfering with this pathway might serve as a potential therapeutic approach to prevent ethanol-induced neurotoxicity in the brain.

Adrenergic Receptor Regulation of Mitochondrial Function in Cardiomyocytes

ABSTRACT

Adrenergic receptors (ARs) are G protein-coupled receptors that are stimulated by catecholamines to induce a wide array of physiological effects across tissue types. Both α1- and β-ARs are found on cardiomyocytes and regulate cardiac contractility and hypertrophy through diverse molecular pathways. Acute activation of cardiomyocyte β-ARs increases heart rate and contractility as an adaptive stress response. However, chronic β-AR stimulation contributes to the pathobiology of heart failure. By contrast, mounting evidence suggests that α1-ARs serve protective functions that may mitigate the deleterious effects of chronic β-AR activation. Here, we will review recent studies demonstrating that α1- and β-ARs differentially regulate mitochondrial biogenesis and dynamics, mitochondrial calcium handling, and oxidative phosphorylation in cardiomyocytes. We will identify potential mechanisms of these actions and focus on the implications of these findings for the modulation of contractile function in the uninjured and failing heart. Collectively, we hope to elucidate important physiological processes through which these well-studied and clinically relevant receptors stimulate and fuel cardiac contraction to contribute to myocardial health and disease.

Fibroblast growth factor 21, a stress regulator, inhibits Drp1 activation to alleviate skeletal muscle ischemia/reperfusion injury

Abnormal Drp1 activation and subsequent excessive mitochondrial fission play a critical role in ischemia-reperfusion injury (I/RI). Although fibroblast growth factor 21 (FGF21) protects organs against I/RI and regulates metabolism, which indicates that FGF21 is involved in mitochondria homeostasis, the detailed mechanism remains unclear. Herein, we investigated whether FGF21 had an effect on Drp1 activation during skeletal muscle I/RI. Drp1 phosphorylation and its translocation to mitochondria, as regulated by FGF21, was examined in mouse and C2C12 cell I/RI models. Mice overexpressing FGF21 displayed alleviation of serum index, histological lesions and apoptosis levels. Moreover, FGF21 markedly decreased cyclin-dependent kinase 1 (CDK1) and Drp1 phosphorylation at Ser616, accompanied by reduced accumulation in mitochondria. In parallel in vitro studies, cells with FGF21 knockdown displayed enhanced Drp1 activation, and the reverse effect was found when FGF21 was added. More importantly, FGF21 attenuated mitochondrial fission with linear mitochondria rather than fragmented mitochondria. Furthermore, a CDK1 inhibitor reduced Drp1 activation and mitochondrial fission due to FGF21 knockdown. This study shows that FGF21 inhibits Drp1 activation to protect mitochondria from fission, thereby rescuing cells from I/RI-induced apoptosis. Our findings may provide a new therapeutic approach to ameliorate skeletal muscle I/RI.

New Mechanisms and Targets of Subarachnoid Hemorrhage: A Focus on Mitochondria

Spontaneous subarachnoid hemorrhage (SAH) accounts for 5-10% of all strokes and is a subtype of hemorrhagic stroke that places a heavy burden on health care. Despite great progress in surgical clipping and endovascular treatment for ruptured aneurysms, cerebral vasospasm (CVS) and delayed cerebral ischemia (DCI) threaten the long-term outcomes of patients with SAH. Moreover, there are limited drugs available to reduce the risk of DCI and adverse outcomes in SAH patients. New insight suggests that early brain injury (EBI), which occurs within 72 h after the onset of SAH, may lay the foundation for further DCI development and poor outcomes. The mechanisms of EBI mainly include excitotoxicity, oxidative stress, neuroinflammation, blood-brain barrier (BBB) destruction, and cellular death. Mitochondria are a double-membrane organelle, and they play an important role in energy production, cell growth, differentiation, apoptosis, and survival. Mitochondrial dysfunction, which can lead to mitochondrial membrane potential (Δψm) collapse, overproduction of reactive oxygen species (ROS), release of apoptogenic proteins, disorders of mitochondrial dynamics, and activation of mitochondria-related inflammation, is considered a novel mechanism of EBI related to DCI as well as post-SAH outcomes. In addition, mitophagy is activated after SAH. In this review, we discuss the latest perspectives on the role of mitochondria in EBI and DCI after SAH. We emphasize the potential of mitochondria as therapeutic targets and summarize the promising therapeutic strategies targeting mitochondria for SAH.