FNDC-1-mediated mitophagy and ATFS-1 coordinate to protect against hypoxia-reoxygenation

Programmed mitophagy at the oocyte-to-zygote transition promotes species immortality

The quality of mitochondria inherited from the oocyte determines embryonic viability, metabolic health throughout progeny lifetime, and future generation endurance. High levels of endogenous reactive oxygen species and exogenous toxicants are threats to mitochondrial DNA (mtDNA) in fully developed oocytes. Deleterious mtDNA is commonly detected in developed oocytes, but is absent in embryos, suggesting the existence of a cryptic purifying selection mechanism. Here we discover that in C. elegans, the onset of oocyte-to-zygote transition (OZT) developmentally triggers a rapid mitophagy event. We show that mitophagy at OZT (MOZT) requires mitochondrial fragmentation, the macroautophagy pathway, and the mitophagy receptor FUNDC1, but not the prevalent mitophagy factors PINK1 and BNIP3. Impaired MOZT leads to increased deleterious mtDNA inheritance and decreases embryonic survival. Inherited mtDNA damage accumulates across generations, leading to the extinction of descendent populations. Thus, MOZT represents a strategy that preserves mitochondrial health during the mother-to-offspring transmission and promotes species continuity.

Mitophagy at the oocyte-to-zygote transition promotes species immortality

The quality of inherited mitochondria determines embryonic viability 1 , metabolic health during adulthood and future generation endurance. The oocyte is the source of all zygotic mitochondria 2 , and mitochondrial health is under strict developmental regulation during early oogenesis 3-5 . Yet, fully developed oocytes exhibit the presence of deleterious mitochondrial DNA (mtDNA) 6,7 and mitochondrial dysfunction from high levels of endogenous reactive oxygen species 8 and exogenous toxicants 9 . How fully developed oocytes prevent transmission of damaged mitochondria to the zygotes is unknown. Here we discover that the onset of oocyte-to-zygote transition (OZT) developmentally triggers a robust and rapid mitophagy event that we term mitophagy at OZT (MOZT). We show that MOZT requires mitochondrial fragmentation, activation of the macroautophagy system and the mitophagy receptor FUNDC1, but not the prevalent mitophagy factors PINK1 and BNIP3. Oocytes upregulate expression of FUNDC1 in response to diverse mitochondrial insults, including mtDNA mutations and damage, uncoupling stress, and mitochondrial dysfunction, thereby promoting selection against damaged mitochondria. Loss of MOZT leads to increased inheritance of deleterious mtDNA and impaired bioenergetic health in the progeny, resulting in diminished embryonic viability and the extinction of descendent populations. Our findings reveal FUNDC1-mediated MOZT as a mechanism that preserves mitochondrial health during the mother-to-offspring transmission and promotes species continuity. These results may explain how mature oocytes from many species harboring mutant mtDNA give rise to healthy embryos with reduced deleterious mtDNA.

Tau phosphorylation suppresses oxidative stress-induced mitophagy via FKBP8 receptor modulation

Neurodegenerative diseases are often characterized by mitochondrial dysfunction. In Alzheimer's disease, abnormal tau phosphorylation disrupts mitophagy, a quality control process through which damaged organelles are selectively removed from the mitochondrial network. The precise mechanism through which this occurs remains unclear. Previously, we showed that tau which has been mutated at Thr-231 to glutamic acid to mimic an Alzheimer's-relevant phospho-epitope expressed early in disease selectively inhibits oxidative stress-induced mitophagy in Caenorhabditis elegans. Here, we use immortalized mouse hippocampal neuronal cell lines to extend that result into mammalian cells. Specifically, we show that phosphomimetic tau at Ser-396/404 (EC) or Thr-231/Ser-235 (EM) partly inhibits mitophagy induction by paraquat, a potent inducer of mitochondrial oxidative stress. Moreover, a combination of immunologic and biochemical approaches demonstrates that the levels of the mitophagy receptor FKBP8, significantly decrease in response to paraquat in cells expressing EC or EM tau mutants, but not in cells expressing wildtype tau. In contrast, paraquat treatment results in a decrease in the levels of the mitophagy receptors FUNDC1 and BNIP3 in the presence of both wildtype tau and the tau mutants. Interestingly, FKBP8 is normally trafficked to the endoplasmic reticulum during oxidative stress induced mitophagy, and our results support a model where this trafficking is impacted by disease-relevant tau, perhaps through a direct interaction. We provide new insights into the molecular mechanisms underlying tau pathology in Alzheimer's disease and highlight FKBP8 receptor as a potential target for mitigating mitochondrial dysfunction in neurodegenerative diseases.

Tumor necrosis factor-stimulated gene-6 inhibits endoplasmic reticulum stress in the ischemic mouse kidney

Kidney tissue injury in renal artery stenosis (RAS) involves inflammation, endoplasmic reticulum stress (ERS), and mitochondria damage. Tumor necrosis factor-stimulated gene-6 (TSG-6), an endogenous reparative molecule, may decrease ERS and improve renal function. To assess its impact on the stenotic murine kidney, we injected TSG-6 or vehicle for two weeks in mice with RAS. At completion, we assessed stenotic kidney function and oxygenation, inflammation, and expression of ERS-related genes. TSG-6 treatment reduced renal hypoxia, urinary protein and plasma creatinine levels, renal fibrosis, and apoptosis. TSG-6 also exhibited an anti-inflammatory effect, reflected in the downregulated expression of the Toll-like receptor 4 (TLR4)/nuclear factor κB (NF-κB) pathway in murine kidneys in vivo and HK-2 cells in vitro. Moreover, ERS-related molecules were downregulated after TSG-6 treatment, while most indicators of mitochondrial unfolded protein response remained unaltered. Therefore, TSG-6 alleviates inflammation, ERS, apoptosis, and fibrosis in the post-stenotic mouse kidney. These observations position TSG-6 as a potential therapeutic tool in RAS.

Mitochondrial Quality Control in Alzheimer's Disease: Insights from Caenorhabditis elegans Models

Alzheimer's disease (AD) is a complex neurodegenerative disorder that is classically defined by the extracellular deposition of senile plaques rich in amyloid-beta (Aβ) protein and the intracellular accumulation of neurofibrillary tangles (NFTs) that are rich in aberrantly modified tau protein. In addition to aggregative and proteostatic abnormalities, neurons affected by AD also frequently possess dysfunctional mitochondria and disrupted mitochondrial maintenance, such as the inability to eliminate damaged mitochondria via mitophagy. Decades have been spent interrogating the etiopathogenesis of AD, and contributions from model organism research have aided in developing a more fundamental understanding of molecular dysfunction caused by Aβ and toxic tau aggregates. The soil nematode C. elegans is a genetic model organism that has been widely used for interrogating neurodegenerative mechanisms including AD. In this review, we discuss the advantages and limitations of the many C. elegans AD models, with a special focus and discussion on how mitochondrial quality control pathways (namely mitophagy) may contribute to AD development. We also summarize evidence on how targeting mitophagy has been therapeutically beneficial in AD. Lastly, we delineate possible mechanisms that can work alone or in concert to ultimately lead to mitophagy impairment in neurons and may contribute to AD etiopathology.

Mechanisms of mitochondrial resilience in teleostean radial glia under hypoxic stress

Radial glial cells (RGCs) are remarkable cells, essential for normal development of the vertebrate central nervous system. In teleost fishes, RGCs play a pivotal role in neurogenesis and regeneration of injured neurons and glia. RGCs also exhibit resilience to environmental stressors like hypoxia via metabolic adaptations. In this study, we assessed the physiology of RGCs following varying degrees of hypoxia, with an emphasis on reactive oxygen species (ROS) generation, mitochondrial membrane potential (MMP), mitophagy, and energy metabolism. Our findings demonstrated that hypoxia significantly elevated ROS production and induced MMP depolarization in RGCs. The mitochondrial disturbances were closely associated with increased mitophagy, based on the co-localization of mitochondria and lysosomes. Key mitophagy-related genes were also up-regulated, including those of the BNIP3/NIX mediated pathway as well as the FUNDC1 mediated pathway. Such responses suggest robust cellular mechanisms are initiated to counteract mitochondrial damage due to increasing hypoxia. A significant metabolic shift from oxidative phosphorylation to glycolysis was also observed in RGCs, which may underlie an adaptive response to sustain cellular function and viability following a reduction in oxygen availability. Furthermore, hypoxia inhibited the synthesis of mitochondrial complexes subunits in RGCs, potentially related to elevated HIF-2α expression with 3 % O2. Taken together, RGCs appear to exhibit complex adaptive responses to hypoxic stress, characterized by metabolic reprogramming and the activation of mitophagy pathways to mitigate mitochondrial dysfunction.

Tau phosphorylation suppresses oxidative stress-induced mitophagy via FKBP8 receptor modulation

Neurodegenerative diseases are often characterized by mitochondrial dysfunction. In Alzheimer's disease, abnormal tau phosphorylation disrupts mitophagy, a quality control process through which damaged organelles are selectively removed from the mitochondrial network. The precise mechanism through which this occurs remains unclear. Previously, we showed that tau which has been mutated at Thr-231 to glutamic acid to mimic an Alzheimer's-relevant phospho-epitope expressed early in disease selectively inhibits oxidative stress-induced mitophagy in C. elegans. Here, we use immortalized mouse hippocampal neuronal cell lines to extend that result into mammalian cells. Specifically, we show that phosphomimetic tau at Ser-396/404 (EC) or Thr-231/Ser-235 (EM) partly inhibits mitophagy induction by paraquat, a potent inducer of mitochondrial oxidative stress. Moreover, a combination of immunologic and biochemical approaches demonstrates that the levels of the mitophagy receptor FKBP8, significantly decrease in response to paraquat in cells expressing EC or EM tau mutants, but not in cells expressing wildtype tau. In contrast, paraquat treatment results in a decrease in the levels of the mitophagy receptors FUNDC1 and BNIP3 in the presence of both wildtype tau and the tau mutants. Interestingly, FKBP8 is normally trafficked to the endoplasmic reticulum during oxidative stress induced mitophagy, and our results support a model where this trafficking is impacted by disease-relevant tau, perhaps through a direct interaction. We provide new insights into the molecular mechanisms underlying tau pathology in Alzheimer's disease and highlight FKBP8 receptor as a potential target for mitigating mitochondrial dysfunction in neurodegenerative diseases.

C. elegans as a model to study mitochondrial biology and disease

Mitochondria perform a myriad of essential functions that ensure organismal homeostasis, including maintaining bioenergetic capacity, sensing and signalling the presence of pathogenic threats, and determining cell fate. Their function is highly dependent on mitochondrial quality control and the appropriate regulation of mitochondrial size, shape, and distribution during an entire lifetime, as well as their inheritance across generations. The roundworm Caenorhabditis elegans has emerged as an ideal model organism through which to study mitochondria. The remarkable conservation of mitochondrial biology has allowed C. elegans researchers to investigate complex processes that are challenging to study in higher organisms. In this review, we explore the key recent contributions of C. elegans to mitochondrial biology through the lens of mitochondrial dynamics, organellar removal, and mitochondrial inheritance, as well as their involvement in immune responses, various types of stress, and transgenerational signalling.

Mitochondrial stress: a key role of neuroinflammation in stroke

Stroke is a clinical syndrome characterized by an acute, focal neurological deficit, primarily caused by the occlusion or rupture of cerebral blood vessels. In stroke, neuroinflammation emerges as a pivotal event contributing to neuronal cell death. The occurrence and progression of neuroinflammation entail intricate processes, prominently featuring mitochondrial dysfunction and adaptive responses. Mitochondria, a double membrane-bound organelle are recognized as the "energy workshop" of the body. Brain is particularly vulnerable to mitochondrial disturbances due to its high energy demands from mitochondria-related energy production. The interplay between mitochondria and neuroinflammation plays a significant role in the pathogenesis of stroke. The biological and pathological consequences resulting from mitochondrial stress have substantial implications for cerebral function. Mitochondrial stress serves as an adaptive mechanism aimed at mitigating the stress induced by the import of misfolded proteins, which occurs in response to stroke. This adaptive response involves a reduction in misfolded protein accumulation and overall protein synthesis. The influence of mitochondrial stress on the pathological state of stroke is underscored by its capacity to interact with neuroinflammation. The impact of mitochondrial stress on neuroinflammation varies according to its severity. Moderate mitochondrial stress can bolster cellular adaptive defenses, enabling cells to better withstand detrimental stressors. In contrast, sustained and excessive mitochondrial stress detrimentally affects cellular and tissue integrity. The relationship between neuroinflammation and mitochondrial stress depends on the degree of mitochondrial stress present. Understanding its role in stroke pathogenesis is instrumental in excavating the novel treatment of stroke. This review aims to provide the evaluation of the cross-talk between mitochondrial stress and neuroinflammation within the context of stroke. We aim to reveal how mitochondrial stress affects neuroinflammation environment in stroke.

Neutrophil extracellular traps drive intestinal microvascular endothelial ferroptosis by impairing Fundc1-dependent mitophagy

Microvascular endothelial damage caused by intestinal ischemia‒reperfusion (II/R) is a primary catalyst for microcirculation dysfunction and enterogenous infection. Previous studies have mainly focused on how neutrophil extracellular traps (NETs) and ferroptosis cause intestinal epithelial injury, and little attention has been given to how NETs, mainly from circulatory neutrophils, affect intestinal endothelial cells during II/R. This study aimed to unravel the mechanisms through which NETs cause intestinal microvascular dysfunction. We first detected heightened local NET infiltration around the intestinal microvasculature, accompanied by increased endothelial cell ferroptosis, resulting in microcirculation dysfunction in both human and animal II/R models. However, the administration of the ferroptosis inhibitor ferrostatin-1 or the inhibition of NETs via neutrophil-specific peptidylarginine deiminase 4 (Pad4) deficiency led to positive outcomes, with reduced intestinal endothelial ferroptosis and microvascular function recovery. Moreover, RNA-seq analysis revealed a significant enrichment of mitophagy- and ferroptosis-related signaling pathways in HUVECs incubated with NETs. Mechanistically, elevated NET formation induced Fundc1 phosphorylation at Tyr18 in intestinal endothelial cells, which led to mitophagy inhibition, mitochondrial quality control imbalance, and excessive mitochondrial ROS generation and lipid peroxidation, resulting in endothelial ferroptosis and microvascular dysfunction. Nevertheless, using the mitophagy activator urolithin A or AAV-Fundc1 transfection could reverse this process and ameliorate microvascular damage. We first demonstrate that increased NETosis could result in intestinal microcirculatory dysfunction and conclude that suppressed NET formation can mitigate intestinal endothelial ferroptosis by improving Fundc1-dependent mitophagy. Targeting NETs could be a promising approach for treating II/R-induced intestinal microcirculatory dysfunction.

ATF5 regulates tubulointerstitial injury in diabetic kidney disease via mitochondrial unfolded protein response

BACKGROUND

Mitochondrial quality control (MQC) plays a critical role in the progression of tubulointerstitial injury in diabetic kidney disease (DKD). The mitochondrial unfolded protein response (UPRmt), which is an important MQC process, is activated to maintain mitochondrial protein homeostasis in response to mitochondrial stress. Activating transcription factor 5 (ATF5) is critical in the mammalian UPRmt via mitochondria-nuclear translocation. However, the role of ATF5 and UPRmt in tubular injury under DKD conditions is unknown.

METHODS

ATF5 and UPRmt-related proteins including heat shock protein 60 (HSP60) and Lon peptidase 1 (LONP1), in DKD patients and db/db mice were examined by immunohistochemistry (IHC) and western blot analysis. Eight-week-old db/db mice were injected with ATF5-shRNA lentiviruses via the tail vein, and a negative lentivirus was used as a control. The mice were euthanized at 12 weeks, and dihydroethidium (DHE) and TdT-mediated dUTP nick end labeling (TUNEL) assays were performed to evaluate reactive oxygen species (ROS) production and apoptosis in kidney sections, respectively. In vitro, ATF5-siRNA, ATF5 overexpression plasmids or HSP60-siRNA were transfected into HK-2 cells to evaluate the effect of ATF5 and HSP60 on tubular injury under ambient hyperglycemic conditions. Mitochondrial superoxide (MitoSOX) staining was used to gauge mitochondrial oxidative stress levels, and the early stage of cell apoptosis was examined by Annexin V-FITC kits.

RESULTS

Increased ATF5, HSP60 and LONP1 expression was observed in the kidney tissue of DKD patients and db/db mice and was tightly correlated with tubular damage. The inhibition of HSP60 and LONP1, improvements in serum creatinine, tubulointerstitial fibrosis and apoptosis were observed in db/db mice treated with lentiviruses carrying ATF5 shRNA. In vitro, the expression of ATF5 was increased in HK-2 cells exposed to high glucose (HG) in a time-dependent manner, which was accompanied by the overexpression of HSP60, fibronectin (FN) and cleaved-caspase3 (C-CAS3). ATF5-siRNA transfection inhibited the expression of HSP60 and LONP1, which was accompanied by reduced oxidative stress and apoptosis in HK-2 cells exposed to sustained exogenous high glucose. ATF5 overexpression exacerbated these impairments. HSP60-siRNA transfection blocked the effect of ATF5 on HK-2 cells exposed to continuous HG treatment. Interestingly, ATF5 inhibition exacerbated mitochondrial ROS levels and apoptosis in HK-2 cells in the early period of HG intervention (6 h).

CONCLUSIONS

ATF5 could exert a protective effect in a very early stage but promoted tubulointerstitial injury by regulating HSP60 and the UPRmt pathway under DKD conditions, providing a potential target for the prevention of DKD progression.

Selenium alleviates cadmium-induced mitophagy through FUNDC1-mediated mitochondrial quality control pathway in the lungs of sheep

Cadmium (Cd) is a poisonous metal element that causes mitochondrial dysfunction. Selenium (Se) can reduce the damage of Cd to various organs of animals, but the protective mechanism of Se in Cd-induced lung injury has not been fully elucidated. For purpose of further illustrating the specific mechanism of Se alleviated Cd-triggered pulmonary toxicity, 48 sheep were divided into 4 groups, of which the sheep in the treatment group were taken 1 mg/kg body weight (BW) of Cd, 0.34 mg/kg BW of Se, and 0.34 mg Se + 1 mg/kg BW of Cd by intragastric administration for 50 d, respectively. The results indicated that Cd caused inflammatory cell infiltration and alveolar wall thickening, which facilitated mitochondrial vacuolation and formation of mitophagosomes in lung tissues. Simultaneously, Cd treatment impaired the antioxidant capacity of sheep lung tissue. Additionally, Cd treatment down-regulated the expression levels of mitochondrial biogenesis and mitochondrial fusion, but up-regulated the levels of mitochondrial fission and mitophagy mediated by FUNDC1. Moreover, the immunofluorescence co-localization puncta of LC3B/COX IV, LC3B/FUNDC1 were increased after Cd treatment. Nevertheless, co-treatment with Se improved effectively the above variation caused by Cd exposure. In summary, Se could mitigate Cd-generated mitophagy through FUNDC1-mediated mitochondrial quality control pathway in the lungs of sheep.

Mitochondrial unfolded protein response in ischemia-reperfusion injury

Mitochondrial unfolded protein response (UPRmt) is a mitochondrial stress response that activates the transcriptional program of mitochondrial chaperone proteins and proteases to keep protein homeostasis in mitochondria. Ischemia-reperfusion injury results in multiple severe clinical issues linked to high morbidity and mortality in various disorders. The pathophysiology and pathogenesis of ischemia-reperfusion injury are complex and multifactorial. Emerging evidence showed the roles of UPRmt signaling in ischemia-reperfusion injury. Herein, we discuss the regulatory mechanisms underlying UPRmt signaling in C. elegans and mammals. Furthermore, we review the recent studies into the roles and mechanisms of UPRmt signaling in ischemia-reperfusion injury of the heart, brain, kidney, and liver. Further research of UPRmt signaling will potentially develop novel therapeutic strategies against ischemia-reperfusion injury.

Selective disruption of Drp1-independent mitophagy and mitolysosome trafficking by an Alzheimer's disease relevant tau modification in a novel Caenorhabditis elegans model

Accumulation of inappropriately phosphorylated tau into neurofibrillary tangles is a defining feature of Alzheimer's disease, with Tau pT231 being an early harbinger of tau pathology. Previously, we demonstrated that expressing a single genomic copy of human phosphomimetic mutant tau (T231E) in Caenorhabditis elegans drove age-dependent neurodegeneration. A critical finding was that T231E, unlike wild-type tau, completely and selectively suppressed oxidative stress-induced mitophagy. Here, we used dynamic imaging approaches to analyze T231E-associated changes in mitochondria and mitolysosome morphology, abundance, trafficking, and stress-induced mitophagy as a function of mitochondrial fission mediator dynamin-related protein 1, which has been demonstrated to interact with hyper phosphorylated tau and contribute to Alzheimer's disease pathogenesis, as well as Pink1, a well-recognized mediator of mitochondrial quality control that works together with Parkin to support stress-induced mitophagy. T231E impacted both mitophagy and mitolysosome neurite trafficking with exquisite selectivity, sparing macroautophagy as well as lysosome and autolysosome trafficking. Both oxidative-stress-induced mitophagy and the ability of T231E to suppress it were independent of drp-1, but at least partially dependent on pink-1. Organelle trafficking was more complicated, with drp-1 and pink-1 mutants exerting independent effects, but generally supported the idea that the mitophagy phenotype is of greater physiologic impact in T231E. Collectively, our results refine the mechanistic pathway through which T231E causes neurodegeneration, demonstrating pathologic selectivity for mutations that mimic tauopathy-associated post-translational modifications, physiologic selectivity for organelles that contain damaged mitochondria, and molecular selectivity for dynamin-related protein 1-independent, Pink1-dependent, perhaps adaptive, and mitophagy.

Role of Mitophagy in neurodegenerative Diseases and potential tagarts for Therapy

Mitochondria dysfunction has been defined as one of the hallmarks of aging-related diseases as is characterized by the destroyed integrity, abnormal distribution and size, insufficient ATP supply, increased ROS production, and subsequently damage and oxidize the proteins, lipids and nucleic acid. Mitophagy, an efficient way of removing damaged or defective mitochondria by autophagy, plays a pivotal role in maintaining the mitochondrial quantity and quality control enabling the degradation of unwanted mitochondria, and thus rescues cellular homeostasis in response to stress. Accumulating evidence demonstrates that impaired mitophagy has been associated with many neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) in a variety of patients and disease models with neural death, oxidative stress and disturbed metabolism, either as the cause or consequence. These findings suggest that modulation of mitophagy may be considered as a valid therapeutic strategy in neurodegenerative diseases. In this review, we summarize recent findings on the mechanisms of mitophagy and its role in neurodegenerative diseases, with a particular focus on mitochondrial proteins acting as receptors that mediate mitophagy in these diseases.

The multifaceted regulation of mitophagy by endogenous metabolites

Owing to the dominant functions of mitochondria in multiple cellular metabolisms and distinct types of regulated cell death, maintaining a functional mitochondrial network is fundamental for the cellular homeostasis and body fitness in response to physiological adaptations and stressed conditions. The process of mitophagy, in which the dysfunctional or superfluous mitochondria are selectively engulfed by autophagosome and subsequently degraded in lysosome, has been well formulated as one of the major mechanisms for mitochondrial quality control. To date, the PINK1-PRKN-dependent and receptors (including proteins and lipids)-dependent pathways have been characterized to determine the mitophagy in mammalian cells. The mitophagy is highly responsive to the dynamics of endogenous metabolites, including iron-, calcium-, glycolysis-TCA-, NAD+-, amino acids-, fatty acids-, and cAMP-associated metabolites. Herein, we summarize the recent advances toward the molecular details of mitophagy regulation in mammalian cells. We also highlight the key regulations of mammalian mitophagy by endogenous metabolites, shed new light on the bidirectional interplay between mitophagy and cellular metabolisms, with attempting to provide a perspective insight into the nutritional intervention of metabolic disorders with mitophagy deficit.Abbreviations: acetyl-CoA: acetyl-coenzyme A; ACO1: aconitase 1; ADCYs: adenylate cyclases; AMPK: AMP-activated protein kinase; ATM: ATM serine/threonine kinase; BCL2L1: BCL2 like 1; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; Ca2+: calcium ion; CALCOCO2: calcium binding and coiled-coil domain 2; CANX: calnexin; CO: carbon monoxide; CYCS: cytochrome c, somatic; DFP: deferiprone; DNM1L: dynamin 1 like; ER: endoplasmic reticulum; FKBP8: FKBP prolyl isomerase 8; FOXO3: forkhead box O3; FTMT: ferritin mitochondrial; FUNDC1: FUN14 domain containing 1; GABA: γ-aminobutyric acid; GSH: glutathione; HIF1A: hypoxia inducible factor 1 subunit alpha; IMMT: inner membrane mitochondrial protein; IRP1: iron regulatory protein 1; ISC: iron-sulfur cluster; ITPR2: inositol 1,4,5-trisphosphate type 2 receptor; KMO: kynurenine 3-monooxygenase; LIR: LC3 interacting region; MAM: mitochondria-associated membrane; MAP1LC3: microtubule associated protein 1 light chain 3; MFNs: mitofusins; mitophagy: mitochondrial autophagy; mPTP: mitochondrial permeability transition pore; MTOR: mechanistic target of rapamycin kinase; NAD+: nicotinamide adenine dinucleotide; NAM: nicotinamide; NMN: nicotinamide mononucleotide; NO: nitric oxide; NPA: Niemann-Pick type A; NR: nicotinamide riboside; NR4A1: nuclear receptor subfamily 4 group A member 1; NRF1: nuclear respiratory factor 1; OPA1: OPA1 mitochondrial dynamin like GTPase; OPTN: optineurin; PARL: presenilin associated rhomboid like; PARPs: poly(ADP-ribose) polymerases; PC: phosphatidylcholine; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; PPARG: peroxisome proliferator activated receptor gamma; PPARGC1A: PPARG coactivator 1 alpha; PRKA: protein kinase AMP-activated; PRKDC: protein kinase, DNA-activated, catalytic subunit; PRKN: parkin RBR E3 ubiquitin protein ligase; RHOT: ras homolog family member T; ROS: reactive oxygen species; SIRTs: sirtuins; STK11: serine/threonine kinase 11; TCA: tricarboxylic acid; TP53: tumor protein p53; ULK1: unc-51 like autophagy activating kinase 1; VDAC1: voltage dependent anion channel 1.

FUN14 Domain Containing 1 (FUNDC1): A Promising Mitophagy Receptor Regulating Mitochondrial Homeostasis in Cardiovascular Diseases

Mitochondria, the intracellular organelles for cellular aerobic respiration and energy production, play an important role in the regulation of cell metabolism and cell fate. Mitophagy, a selective form of autophagy, maintains dynamic homeostasis of cells through targeting long-lived or defective mitochondria for timely clearance and recycling. Dysfunction in mitophagy is involved in the molecular mechanism responsible for the onset and development of human diseases. FUN14 domain containing 1 (FUNDC1) is a mitochondrial receptor located in the outer mitochondria membrane (OMM) to govern mitophagy process. Emerging evidence has demonstrated that levels and phosphorylation states of FUNDC1 are closely related to the occurrence, progression and prognosis of cardiovascular diseases, indicating a novel role for this mitophagy receptor in the regulation of mitochondrial homeostasis in cardiovascular system. Here we review mitophagy mediated by FUNDC1 in mitochondria and its role in various forms of cardiovascular diseases.

FUNDC1: A Promising Mitophagy Regulator at the Mitochondria-Associated Membrane for Cardiovascular Diseases

Mitochondrial autophagy (or mitophagy) regulates the mitochondrial network and function to contribute to multiple cellular processes. The protective effect of homeostatic mitophagy in cardiovascular diseases (CVDs) has attracted increasing attention. FUN14 domain containing 1 (FUNDC1), an identified mitophagy receptor, plays an essential role in CVDs. Different expression levels of FUNDC1 and its phosphorylated state at different sites alleviate or exacerbate hypoxia and ischemia/reperfusion injury, cardiac hypertrophy, or metabolic damage through promotion or inhibition of mitophagy. In addition, FUNDC1 can be enriched at contact sites between mitochondria and the endoplasmic reticulum (ER), determining the formation of mitochondria-associated membranes (MAMs) that regulate cellular calcium (Ca²⁺) homeostasis and mitochondrial dynamics to prevent heart dysfunction. Moreover, FUNDC1 has also been involved in inflammatory cardiac diseases such as septic cardiomyopathy. In this review, we collect and summarize the evidence on the roles of FUNDC1 exclusively in various CVDs, describing its interactions with different cellular organelles, its involvement in multiple cellular processes, and its associated signaling pathways. FUNDC1 may become a promising therapeutic target for the prevention and management of various CVDs.

Mitophagy coordinates the mitochondrial unfolded protein response to attenuate inflammation-mediated myocardial injury

Mitochondrial dysfunction is a fundamental challenge in septic cardiomyopathy. Mitophagy and the mitochondrial unfolded protein response (UPR^mt) are the predominant stress-responsive and protective mechanisms involved in repairing damaged mitochondria. Although mitochondrial homeostasis requires the coordinated actions of mitophagy and UPR^mt, their molecular basis and interactive actions are poorly understood in sepsis-induced myocardial injury. Our investigations showed that lipopolysaccharide (LPS)-induced sepsis contributed to cardiac dysfunction and mitochondrial damage. Although both mitophagy and UPR^mt were slightly activated by LPS in cardiomyocytes, their endogenous activation failed to prevent sepsis-mediated myocardial injury. However, administration of urolithin A, an inducer of mitophagy, obviously reduced sepsis-mediated cardiac depression by normalizing mitochondrial function. Interestingly, this beneficial action was undetectable in cardiomyocyte-specific FUNDC1 knockout (FUNDC1^CKO) mice. Notably, supplementation with a mitophagy inducer had no impact on UPR^mt, whereas genetic ablation of FUNDC1 significantly upregulated the expression of genes related to UPR^mt in LPS-treated hearts. In contrast, enhancement of endogenous UPR^mt through oligomycin administration reduced sepsis-mediated mitochondrial injury and myocardial dysfunction; this cardioprotective effect was imperceptible in FUNDC1^CKO mice. Lastly, once UPR^mt was inhibited, mitophagy-mediated protection of mitochondria and cardiomyocytes was partly blunted. Taken together, it is plausible that endogenous UPR^mt and mitophagy are slightly activated by myocardial stress and they work together to sustain mitochondrial performance and cardiac function. Endogenous UPR^mt, a downstream signal of mitophagy, played a compensatory role in maintaining mitochondrial homeostasis in the case of mitophagy inhibition. Although UPR^mt activation had no negative impact on mitophagy, UPR^mt inhibition compromised the partial cardioprotective actions of mitophagy. This study shows how mitophagy modulates UPR^mt to attenuate inflammation-related myocardial injury and suggests the potential application of mitophagy and UPR^mt targeting in the treatment of myocardial stress.

•

Mitochondrial dysfunction is a fundamental challenge in septic cardiomyopathy.

•

LPS-induced sepsis contributes to cardiac dysfunction and mitochondrial damage.

•

Endogenous UPR^mt and mitophagy could be slightly activated by myocardial stress.

•

Mitophagy modulates UPR^mt to attenuate inflammation-related myocardial injury.

•

Mitophagy and UPR^mt targeting can be applied in treatment of myocardial stress.

The Role of Mitochondrial Quality Control in Cardiac Ischemia/Reperfusion Injury

A healthy mitochondrial network produces a large amount of ATP and biosynthetic intermediates to provide sufficient energy for myocardium and maintain normal cell metabolism. Mitochondria form a dynamic and interconnected network involved in various cellular metabolic signaling pathways. As mitochondria are damaged, controlling mitochondrial quantity and quality is activated by changing their morphology and tube network structure, mitophagy, and biogenesis to replenish a healthy mitochondrial network to preserve cell function. There is no doubt that mitochondrial dysfunction has become a key factor in many diseases. Ischemia/reperfusion (IR) injury is a pathological manifestation of various heart diseases. Cardiac ischemia causes temporary tissue and organelle damage. Although reperfusion is essential to compensate for nutrient deficiency, blood flow restoration inconsequently further kills the previously ischemic cardiomyocytes. To date, dysfunctional mitochondria and disturbed mitochondrial quality control have been identified as critical IR injury mechanisms. Many researchers have detected abnormal mitochondrial morphology and mitophagy, as well as aberrant levels and activity of mitochondrial biogenesis factors in the IR injury model. Although mitochondrial damage is well-known in myocardial IR injury, the causal relationship between abnormal mitochondrial quality control and IR injury has not been established. This review briefly describes the molecular mechanisms of mitochondrial quality control, summarizes our current understanding of the complex role of mitochondrial quality control in IR injury, and finally speculates on the possibility of targeted control of mitochondria and the methods available to mitigate IR injury.