Mitochondrial fission facilitates mitophagy in Saccharomyces cerevisiae

As a highly dynamic organelle, mitochondria undergo constitutive fusion and fission as well as biogenesis and degradation. Mitophagy, selective mitochondrial degradation through autophagy, is a conserved cellular process used for the elimination of excessive and damaged mitochondria in eukaryotes. Despite the significance of mitophagy in cellular physiology and pathophysiologies, the underlying mechanism of this process is far from clear. In this report, we studied the role of mitochondrial fission during mitophagy, and uncover a direct link between the fission complex and mitophagy machinery in Saccharomyces cerevisiae.     

Mitochondrial quality control in diabetic cardiomyopathy: from molecular mechanisms to therapeutic strategies

In diabetic cardiomyopathy (DCM), a major diabetic complication, the myocardium is structurally and functionally altered without evidence of coronary artery disease, hypertension or valvular disease. Although numerous anti-diabetic drugs have been applied clinically, specific medicines to prevent DCM progression are unavailable, so the prognosis of DCM remains poor. Mitochondrial ATP production maintains the energetic requirements of cardiomyocytes, whereas mitochondrial dysfunction can induce or aggravate DCM by promoting oxidative stress, dysregulated calcium homeostasis, metabolic reprogramming, abnormal intracellular signaling and mitochondrial apoptosis in cardiomyocytes. In response to mitochondrial dysfunction, the mitochondrial quality control (MQC) system (including mitochondrial fission, fusion, and mitophagy) is activated to repair damaged mitochondria. Physiological mitochondrial fission fragments the network to isolate damaged mitochondria. Mitophagy then allows dysfunctional mitochondria to be engulfed by autophagosomes and degraded in lysosomes. However, abnormal MQC results in excessive mitochondrial fission, impaired mitochondrial fusion and delayed mitophagy, causing fragmented mitochondria to accumulate in cardiomyocytes. In this review, we summarize the molecular mechanisms of MQC and discuss how pathological MQC contributes to DCM development. We then present promising therapeutic approaches to improve MQC and prevent DCM progression.     

Functions of outer mitochondrial membrane proteins: mediating the crosstalk between mitochondrial dynamics and mitophagy

Most cellular stress responses converge on the mitochondria. Consequently, the mitochondria must rapidly respond to maintain cellular homeostasis and physiological demands by fine-tuning a plethora of mitochondria-associated processes. The outer mitochondrial membrane (OMM) proteins are central to mediating mitochondrial dynamics, coupled with continuous fission and fusion. These OMM proteins also have vital roles in controlling mitochondrial quality and serving as mitophagic receptors for autophagosome enclosure during mitophagy. Mitochondrial fission segregates impaired mitochondria in smaller sizes from the mother mitochondria and may favor mitophagy for eliminating damaged mitochondria. Conversely, mitochondrial fusion mixes dysfunctional mitochondria with healthy ones to repair the damage by diluting the impaired components and consequently prevents mitochondrial clearance via mitophagy. Despite extensive research efforts into deciphering the interplay between fission–fusion and mitophagy, it is still not clear whether mitochondrial fission essentially precedes mitophagy. In this review, we summarize recent breakthroughs concerning OMM research, and dissect the functions of these proteins in mitophagy from their traditional roles in fission–fusion dynamics, in response to distinct context, at the intersection of the OMM platform. These insights into the OMM proteins in mechanistic researches would lead to new aspects of mitochondrial quality control and better understanding of mitochondrial homeostasis intimately tied to pathological impacts.Subject terms: Macroautophagy, Protein quality control     

Musical chairs during mitophagy

Mitophagy, or the autophagic degradation of mitochondria, is thought to be important in mitochondrial quality control, and hence in cellular physiology. Defects in mitophagy correlate with late onset pathologies and aging. Here, we discuss recent results that shed light on the interrelationship between mitophagy and mitochondrial dynamics, based on proteomic analyses of protein dynamics in wild-type and mutant cells. These studies show that different mitochondrial matrix proteins undergo mitophagy at different rates, and that the rate differences are affected by mitochondrial dynamics. These results are consistent with models in which phase separation within the mitochondrial matrix leads to unequal segregation of proteins during mitochondrial fission. Repeated fusion and fission cycles may thus lead to “distillation” of components that are destined for degradation.     

Musical chairs during mitophagy

Mitophagy, or the autophagic degradation of mitochondria, is thought to be important in mitochondrial quality control, and hence in cellular physiology. Defects in mitophagy correlate with late onset pathologies and aging. Here, we discuss recent results that shed light on the interrelationship between mitophagy and mitochondrial dynamics, based on proteomic analyses of protein dynamics in wild-type and mutant cells. These studies show that different mitochondrial matrix proteins undergo mitophagy at different rates, and that the rate differences are affected by mitochondrial dynamics. These results are consistent with models in which phase separation within the mitochondrial matrix leads to unequal segregation of proteins during mitochondrial fission. Repeated fusion and fission cycles may thus lead to “distillation” of components that are destined for degradation.     

Mitophagy receptor FUNDC1 regulates mitochondrial dynamics and mitophagy

Mitochondrial fragmentation due to imbalanced fission and fusion of mitochondria is a prerequisite for mitophagy, however, the exact “coupling” of mitochondrial dynamics and mitophagy remains unclear. We have previously identified that FUNDC1 recruits MAP1LC3B/LC3B (LC3) through its LC3-interacting region (LIR) motif to initiate mitophagy in mammalian cells. Here, we show that FUNDC1 interacts with both DNM1L/DRP1 and OPA1 to coordinate mitochondrial fission or fusion and mitophagy. OPA1 interacted with FUNDC1 via its Lys70 (K70) residue, and mutation of K70 to Ala (A), but not to Arg (R), abolished the interaction and promoted mitochondrial fission and mitophagy. Mitochondrial stress such as selenite or FCCP treatment caused the disassembly of the FUNDC1-OPA1 complex while enhancing DNM1L recruitment to the mitochondria. Furthermore, we observed that dephosphorylation of FUNDC1 under stress conditions promotes the dissociation of FUNDC1 from OPA1 and association with DNM1L. Our data suggest that FUNDC1 regulates both mitochondrial fission or fusion and mitophagy and mediates the “coupling” across the double membrane for mitochondrial dynamics and quality control.     

Deceleration of fusion-fission cycles improves mitochondrial quality control during aging

Mitochondrial dynamics and mitophagy play a key role in ensuring mitochondrial quality control. Impairment thereof was proposed to be causative to neurodegenerative diseases, diabetes, and cancer. Accumulation of mitochondrial dysfunction was further linked to aging. Here we applied a probabilistic modeling approach integrating our current knowledge on mitochondrial biology allowing us to simulate mitochondrial function and quality control during aging in silico. We demonstrate that cycles of fusion and fission and mitophagy indeed are essential for ensuring a high average quality of mitochondria, even under conditions in which random molecular damage is present. Prompted by earlier observations that mitochondrial fission itself can cause a partial drop in mitochondrial membrane potential, we tested the consequences of mitochondrial dynamics being harmful on its own. Next to directly impairing mitochondrial function, pre-existing molecular damage may be propagated and enhanced across the mitochondrial population by content mixing. In this situation, such an infection-like phenomenon impairs mitochondrial quality control progressively. However, when imposing an age-dependent deceleration of cycles of fusion and fission, we observe a delay in the loss of average quality of mitochondria. This provides a rational why fusion and fission rates are reduced during aging and why loss of a mitochondrial fission factor can extend life span in fungi. We propose the 'mitochondrial infectious damage adaptation' (MIDA) model according to which a deceleration of fusion-fission cycles reflects a systemic adaptation increasing life span.     

线粒体质量控制与米色脂肪之间的关系

近年来,肥胖患病率不断上升,肥胖已成为全球性公共卫生问题.肥胖能够增加高血压、冠心病等心血管疾病的发病风险,防治肥胖已经成为亟待解决的社会问题.米色脂肪是一种产热型脂肪细胞,可在受到寒冷、药物、运动等外界刺激下由白色脂肪细胞转化而来,但其形态和功能却与白色脂肪细胞不同,而与棕色脂肪细胞类似,即米色脂肪同样含有丰富的线粒...     

Regulation by mitophagy

Eukaryotes employ elaborate mitochondrial quality control to maintain the function of the power-generating organelle. Mitochondrial quality control is particularly important for the maintenance of neural and muscular tissues. Mitophagy is specialized version of the autophagy pathway. Mitophagy delivers damaged mitochondria to lysosomes for degradation. Recently, a series of elegant studies have demonstrated that two Parkinson's disease-associated genes PINK1 and parkin are involved in the maintenance of healthy mitochondria as mitophagy. Parkin in co-operation with PINK1 specifically recognizes damaged mitochondria with reduced mitochondrial membrane potential (Δψm), rapidly isolates them from the mitochondrial network and eliminates them through the ubiquitin–proteasome and autophagy pathways. Here we introduce and review recent studies that contribute to understanding the molecular mechanisms of mitophagy such as PINK1 and Parkin-mediated mitochondrial regulation. We also discuss how defects in the PINK1–Parkin pathway may cause neurodegeneration in Parkinson's disease.     

Frequency and Selectivity of Mitochondrial Fusion Are Key to Its Quality Maintenance Function

Turnover of mitochondria by autophagy constitutes an essential quality maintenance mechanism. Recent studies have demonstrated that efficient clearance of damaged mitochondrial components depends on mitochondrial dynamics, a process characterized by frequent fusion and fission events that enable the redistribution of mitochondrial components across a population of hundreds of individual mitochondria. The presented simulation identifies kinetic parameters of fusion and fission that may influence the maintenance of mitochondrial function. The program simulated repetitive cycles of fusion and fission events in which intact and damaged mitochondrial contents were redistributed between fusion mates. Redistribution impacted mitochondrial function, thereby influencing the fate of each mitochondrion, to be either destined for a subsequent fusion or eliminated by autophagy. Our findings indicate that, when paired with fission, fusion events may serve to accelerate the removal of damaged mitochondrial components by autophagy. The model predicts the existence of an optimal frequency of fusion and fission events that can maintain respiratory function at steady-state levels amid the existence of a continuous damaging process that inactivates mitochondrial components. A further elevation of the fusion frequency can increase the clearance efficiency of damaged content. However, this requires fusion to be a selective process in which depolarized mitochondria are excluded from the fusing population. The selectivity of fusion was found to be particularly beneficial in conditions of elevated rate of damage, because it permits the increase of fusion frequency without compromising the removal of damaged content by autophagy.     

PINK1 disables the anti-fission machinery to segregate damaged mitochondria for mitophagy

Mitochondrial fission is essential for the degradation of damaged mitochondria. It is currently unknown how the dynamin-related protein 1 (DRP1)–associated fission machinery is selectively targeted to segregate damaged mitochondria. We show that PTEN-induced putative kinase (PINK1) serves as a pro-fission signal, independently of Parkin. Normally, the scaffold protein AKAP1 recruits protein kinase A (PKA) to the outer mitochondrial membrane to phospho-inhibit DRP1. We reveal that after damage, PINK1 triggers PKA displacement from A-kinase anchoring protein 1. By ejecting PKA, PINK1 ensures the requisite fission of damaged mitochondria for organelle degradation. We propose that PINK1 functions as a master mitophagy regulator by activating Parkin and DRP1 in response to damage. We confirm that PINK1 mutations causing Parkinson disease interfere with the orchestration of selective fission and mitophagy by PINK1.     

线粒体自噬的研究进展

线粒体自噬(mitophagy)是指细胞通过自噬机制选择性清除多余或损伤线粒体的过程,对于线粒体质量控制以及细胞生存具有重要作用。在线粒体自噬的过程中,线粒体自噬受体FUNDCl、Nix、BNIP3,接头蛋白OPTN、NDP52以及去泛素化酶UPS30、UPS8等发挥了重要的调控作用。近年来,研究发现线粒体自噬与神经退行性疾病、脑损伤以及胶质瘤相关。因此,研究线粒体自噬的分子机制具有重要意义。本文就与哺乳动物相关的线粒体自噬分子机制及最新研究进展做一综述。     

Mitochondrial fission and mitophagy are independent mechanisms regulating ischemia/reperfusion injury in primary neurons

Mitochondrial dynamics and mitophagy are constitutive and complex systems that ensure a healthy mitochondrial network through the segregation and subsequent degradation of damaged mitochondria. Disruption of these systems can lead to mitochondrial dysfunction and has been established as a central mechanism of ischemia/reperfusion (I/R) injury. Emerging evidence suggests that mitochondrial dynamics and mitophagy are integrated systems; however, the role of this relationship in the context of I/R injury remains unclear. To investigate this concept, we utilized primary cortical neurons isolated from the novel dual-reporter mitochondrial quality control knockin mice (C57BL/6-Gt(ROSA)26Sortm1(CAG-mCherry/GFP)Ganl/J) with conditional knockout (KO) of Drp1 to investigate changes in mitochondrial dynamics and mitophagic flux during in vitro I/R injury. Mitochondrial dynamics was quantitatively measured in an unbiased manner using a machine learning mitochondrial morphology classification system, which consisted of four different classifications: network, unbranched, swollen, and punctate. Evaluation of mitochondrial morphology and mitophagic flux in primary neurons exposed to oxygen-glucose deprivation (OGD) and reoxygenation (OGD/R) revealed extensive mitochondrial fragmentation and swelling, together with a significant upregulation in mitophagic flux. Furthermore, the primary morphology of mitochondria undergoing mitophagy was classified as punctate. Colocalization using immunofluorescence as well as western blot analysis revealed that the PINK1/Parkin pathway of mitophagy was activated following OGD/R. Conditional KO of Drp1 prevented mitochondrial fragmentation and swelling following OGD/R but did not alter mitophagic flux. These data provide novel evidence that Drp1 plays a causal role in the progression of I/R injury, but mitophagy does not require Drp1-mediated mitochondrial fission.Subject terms: Mitophagy, Mechanisms of disease     

PINK1/parkin通路调控线粒体自噬机制的研究进展

线粒体自噬指细胞通过自噬机制选择性除去损伤或多余的线粒体。真核生物通过线粒体自噬调控线粒体质量,维持供能细胞器的功能。大量研究表明,帕金森病相关基因PINK1和parkin可通过线粒体自噬参与并维持线粒体功能。PINK1与parkin能协同特异性识别损伤的线粒体,PINK1作为线粒体质量调控的探测器被活化,此过程中泛素化酶和去泛素化酶对维持parkin活性及线粒体自噬的效率有重要作用。本文主要总结PINK1/parkin通路在线粒体自噬中的功能与作用。     

Mitochondrial quality control as a key determinant of cell survival

Mitochondria are the energy producing dynamic double-membraned organelles essential for cellular and organismal survival. A multitude of intra- and extra-cellular signals involved in the regulation of energy metabolism and cell fate determination converge on mitochondria to promote or prevent cell survival by modulating mitochondrial function and structure. Mitochondrial fitness is maintained by mitophagy, a pathway of selective degradation of dysfunctional organelles. Mitophagy impairment and altered clearance results in increased levels of dysfunctional and structurally aberrant mitochondria, changes in energy production, loss of responsiveness to intra- and extra-cellular signals and ultimately cell death. The decline of mitochondrial function and homeostasis with age is reported to be central to age-related pathologies. Here we discuss the molecular mechanisms controlling mitochondrial dynamics, mitophagy and cell death signalling and how their perturbation may contribute to ageing and age-related illness.     

Mitochondrial quality control in stroke: From the mechanisms to therapeutic potentials

Mitochondrial damage is a critical contributor to stroke‐induced injury, and mitochondrial quality control (MQC) is the cornerstone of restoring mitochondrial homeostasis and plays an indispensable role in alleviating pathological process of stroke. Mitochondria quality control promotes neuronal survival via various adaptive responses for preserving mitochondria structure, morphology, quantity and function. The processes of mitochondrial fission and fusion allow for damaged mitochondria to be segregated and facilitate the equilibration of mitochondrial components such as DNA, proteins and metabolites. The process of mitophagy is responsible for the degradation and recycling of damaged mitochondria. This review aims to offer a synopsis of the molecular mechanisms involved in MQC for recapitulating our current understanding of the complex role that MQC plays in the progression of stroke. Speculating on the prospect that targeted manipulation of MQC mechanisms may be exploited for the rationale design of novel therapeutic interventions in the ischaemic stroke and haemorrhagic stroke. In the review, we highlight the potential of MQC as therapeutic targets for stroke treatment and provide valuable insights for clinical strategies.     

SAMM50 acts with p62 in piecemeal basal- and OXPHOS-induced mitophagy of SAM and MICOS components

Mitophagy is the degradation of surplus or damaged mitochondria by autophagy. In addition to programmed and stress-induced mitophagy, basal mitophagy processes exert organelle quality control. Here, we show that the sorting and assembly machinery (SAM) complex protein SAMM50 interacts directly with ATG8 family proteins and p62/SQSTM1 to act as a receptor for a basal mitophagy of components of the SAM and mitochondrial contact site and cristae organizing system (MICOS) complexes. SAMM50 regulates mitochondrial architecture by controlling formation and assembly of the MICOS complex decisive for normal cristae morphology and exerts quality control of MICOS components. To this end, SAMM50 recruits ATG8 family proteins through a canonical LIR motif and interacts with p62/SQSTM1 to mediate basal mitophagy of SAM and MICOS components. Upon metabolic switch to oxidative phosphorylation, SAMM50 and p62 cooperate to mediate efficient mitophagy.     

Inhibition of mitoNEET induces Pink1-Parkin-mediated mitophagy

MitoNEET, a mitochondrial outer membrane protein containing the Asn-Glu-Glu-Thr (NEET) sequence, controls the formation of intermitochondrial junctions and confers autophagy resistance. Moreover, mitoNEET as a mitochondrial substrate undergoes ubiquitination by activated Parkin during the initiation of mitophagy. Therefore, mitoNEET is linked to the regulation of autophagy and mitophagy. Mitophagy is the selective removal of the damaged or unnecessary mitochondria, which is crucial to sustaining mitochondrial quality control. In numerous human diseases, the accumulation of damaged mitochondria by impaired mitophagy has been observed. However, the therapeutic strategy targeting of mitoNEET as a mitophagy-enhancing mediator requires further research. Herein, we confirmed that mitophagy is indeed activated by mitoNEET inhibition. CCCP (carbonyl cyanide m-chlorophenyl hydrazone), which leads to mitochondrial depolarization, induces mitochondrial dysfunction and superoxide production. This, in turn, contributes to the induction of mitophagy; mitoNEET protein levels were initially increased before an increase in LC3-Ⅱ protein following CCCP treatment. Pharmacological inhibition of mitoNEET using mitoNEET Ligand-1 (NL-1) promoted accumulation of Pink1 and Parkin, which are mitophagy-associated proteins, and activation of mitochondria–lysosome crosstalk, in comparison to CCCP alone. Inhibition of mitoNEET using NL-1, or mitoNEET shRNA transfected into RAW264.7 cells, abrogated CCCP-induced ROS and mitochondrial cell death; additionally, it activated the expression of PGC-1α and SOD2, regulators of oxidative metabolism. In particular, the increase in PGC-1α, which is a major regulator of mitochondrial biogenesis, promotes mitochondrial quality control. These results indicated that mitoNEET is a potential therapeutic target in numerous human diseases to enhance mitophagy and protect cells by maintaining a network of healthy mitochondria.     

Mitophagy in Ischaemia/Reperfusion Induced Cerebral Injury

Mitochondrial autophagy (Mitophagy), the specific autophagic elimination of mitochondria, has been related with several forms of degenerative disease and mitochondrial dysfunction. It is involved in multiple cellular processes. In addition to one of its established key roles in the maintenance of normal cellular phenotype and function, there is growing interest in the concept that targeted modulation of mitophagy may reduce cerebral ischaemia/reperfusion injury. Induction of mitophagy results in selective clearance of damaged mitochondria in cells. In response to stress such as ischaemia/reperfusion, prosurvival and prodeath pathways are concomitantly activated in neuronal cells.