Explore the vast range of titles available.

Dynamin-related protein 1 (Drp1) is essential for mitochondrial and peroxisomal fission. Recent studies propose that Drp1 does not sever but rather constricts mitochondrial membranes allowing dynamin 2 (Dnm2) to execute final scission. Here, we report that unlike Drp1, Dnm2 is dispensable for peroxisomal and mitochondrial fission, as these events occurred in Dnm2 knockout cells. Fission events were also observed in mouse embryonic fibroblasts lacking Dnm1, 2 and 3. Using reconstitution experiments on preformed membrane tubes, we show that Drp1 alone both constricts and severs membrane tubes. Scission required the membrane binding, self-assembling and GTPase activities of Drp1 and occurred on tubes up to 250 nm in radius. In contrast, Dnm2 exhibited severely restricted fission capacity with occasional severing of tubes below 50 nm in radius. We conclude that Drp1 has both membrane constricting and severing abilities and is the dominant dynamin performing mitochondrial and peroxisomal fission. Drp1 and Dnm2 have been implicated in mitochondrial fission events, although their specific activities in constriction and scission have been unclear. Here, the authors demonstrate that Drp1 is sufficient to constrict and sever mitochondrial and peroxisomal membranes in the absence of Dnm proteins.

Mitochondria form tubular networks that undergo coordinated cycles of fission and fusion. Emerging evidence suggests that a direct yet unresolved interaction of the mechanoenzymatic GTPase dynamin-related protein 1 (Drp1) with mitochondrial outer membrane–localized cardiolipin (CL), externalized under stress conditions including mitophagy, catalyzes essential mitochondrial hyperfragmentation. Here, using a comprehensive set of structural, biophysical, and cell biological tools, we have uncovered a CL-binding motif (CBM) conserved between the Drp1 variable domain (VD) and the unrelated ADP/ATP carrier (AAC/ANT) that intercalates into the membrane core to effect specific CL interactions. CBM mutations that weaken VD–CL interactions manifestly impair Drp1-dependent fission under stress conditions and induce “donut” mitochondria formation. Importantly, VD membrane insertion and GTP-dependent conformational rearrangements mediate only transient CL nonbilayer topological forays and high local membrane constriction, indicating that Drp1–CL interactions alone are insufficient for fission. Our studies establish the structural and mechanistic bases of Drp1–CL interactions in stressinduced mitochondrial fission.

Mitochondria are highly dynamic organelles undergoing cycles of fusion and fission to modulate their morphology, distribution, and function, which are referred as ‘mitochondrial dynamics’. Dynamin-related protein 1 (Drp1) is known as the major pro-fission protein whose activity is tightly regulated to clear the damaged mitochondria via mitophagy, ensuring a strict control over the intricate process of cellular and organ dynamics in heart. Various posttranslational modifications (PTMs) of Drp1 have been identified including phosphorylation, SUMOylation, palmitoylation, ubiquitination, S-nitrosylation, and O-GlcNAcylation, which implicate a role in the regulation of mitochondrial dynamics. An intact mitochondrial homeostasis is critical for heart to fuel contractile function and cardiomyocyte metabolism, while defects in mitochondrial dynamics constitute an essential part of the pathophysiology underlying various cardiovascular diseases (CVDs). In this review, we summarize current knowledge on the critical role of Drp1 in the pathogenesis of CVDs including endothelial dysfunction, smooth muscle remodeling, cardiac hypertrophy, pulmonary arterial hypertension, myocardial ischemia–reperfusion, and myocardial infarction. We also highlight how the targeting of Drp1 could potentially contribute to CVDs treatments.

Mitochondria form dynamic networks in the cell that are balanced by the flux of iterative fusion and fission events of the organelles. It is now appreciated that mitochondrial fission also represents an end-point event in a signalling axis that allows cells to sense and respond to external cues. The fission process is orchestrated by membrane-associated adaptors, influenced by organellar and cytoskeletal interactions and ultimately executed by the dynamin-like GTPase DRP1. Here we invoke the framework of the ‘mitochondrial divisome’, which is conceptually and operationally similar to the bacterial cell-division machinery. We review the functional and regulatory aspects of the mitochondrial divisome and, within this framework, parse the core from the accessory machinery. In so doing, we transition from a phenomenological to a mechanistic understanding of the fission process. The functional and regulatory aspects of the ‘mitochondrial divisome’ are separated into core and accessory machinery, thus providing a mechanistic understanding of the process of mitochondrial fission.

Energy stress, such as ischemia, induces mitochondrial damage and death in the heart. Degradation of damaged mitochondria by mitophagy is essential for the maintenance of healthy mitochondria and survival. Here, we show that mitophagy during myocardial ischemia was mediated predominantly through autophagy characterized by Rab9-associated autophagosomes, rather than the well-characterized form of autophagy that is dependent on the autophagy-related 7 (Atg) conjugation system and LC3. This form of mitophagy played an essential role in protecting the heart against ischemia and was mediated by a protein complex consisting of unc-51 like kinase 1 (Ulk1), Rab9, receptor-interacting serine/thronine protein kinase 1 (Rip1), and dynamin-related protein 1 (Drp1). This complex allowed the recruitment of trans-Golgi membranes associated with Rab9 to damaged mitochondria through S179 phosphorylation of Rab9 by Ulk1 and S616 phosphorylation of Drp1 by Rip1. Knockin of Rab9 (S179A) abolished mitophagy and exacerbated the injury in response to myocardial ischemia, without affecting conventional autophagy. Mitophagy mediated through the Ulk1/Rab9/Rip1/Drp1 pathway protected the heart against ischemia by maintaining healthy mitochondria.

Key Points Dynamin, the founding member of a family of dynamin-like proteins (DLPs) implicated in membrane remodelling, has a critical role in endocytic membrane fission events. The use of complementary approaches, including live-cell imaging, cell-free studies, X-ray crystallography and genetic studies in mice, has greatly advanced our understanding of the mechanisms by which dynamin acts. The mechanisms by which dynamin drives membrane fission have been the subject of intense debate. Recent crystallographic and cryo-electron microscopy studies of dynamin and DLPs support a model in which dynamin polymerization serves to bring two GTPase domains together, which allows GTP hydrolysis and the conformational changes in dynamin that are necessary for helix constriction and membrane fission. The role of dynamin is best defined during clathrin-dependent endocytosis and is essential only for a late step when membrane fission occurs. Gene-knockout studies in mice and the cells derived from them have provided numerous insights into dynamin function and the specific roles of the three dynamin isoforms. Dynamin 2 is ubiquitously expressed and has a housekeeping role in membrane dynamics. By contrast, dynamin 1 and dynamin 3 are specific to the nervous system and, although neither is essential for supporting a specific form of endocytosis at synapses, they may be important for allowing clathrin-mediated endocytosis to function over a very broad range of neuronal activities. Roles of abnormal dynamin function in genetic disease have begun to emerge. Whereas mutations in dynamin 2 show links to tissue-specific diseases, mutations in dynamin 1 specifically affect the nervous system. The dynamin GTPase mediates membrane remodelling during endocytosis. Through complementary approaches, including structural and genetic studies, the mechanisms by which dynamin regulates membrane fission events, and the unique physiological roles of its three isoforms, are becoming clear. Dynamin, the founding member of a family of dynamin-like proteins (DLPs) implicated in membrane remodelling, has a critical role in endocytic membrane fission events. The use of complementary approaches, including live-cell imaging, cell-free studies, X-ray crystallography and genetic studies in mice, has greatly advanced our understanding of the mechanisms by which dynamin acts, its essential roles in cell physiology and the specific function of different dynamin isoforms. In addition, several connections between dynamin and human disease have also emerged, highlighting specific contributions of this GTPase to the physiology of different tissues.

Mitochondrial fission and fusion are important for mitochondrial function, and dynamin 1‐like protein (DNM1L) is a key regulator of mitochondrial fission. We investigated the effect of mitochondrial fission on mitochondrial function and inflammation in fibroblast‐like synoviocytes (FLSs) during rheumatoid arthritis (RA). DNM1L expression was determined in synovial tissues (STs) from RA and non‐RA patients. FLSs were isolated from STs and treated with a DNM1L inhibitor (mdivi‐1, mitochondrial division inhibitor 1) or transfected with DNM1L‐specific siRNA. Mitochondrial morphology, DNM1L expression, cell viability, mitochondrial membrane potential, reactive oxygen species (ROS), apoptosis, inflammatory cytokine expression and autophagy were examined. The impact of mdivi‐1 treatment on development and severity of collagen‐induced arthritis (CIA) was determined in mice. Up‐regulated DNM1L expression was associated with reduced mitochondrial length in STs from patients with RA and increased RA severity. Inhibition of DNM1L in FLSs triggered mitochondrial depolarization, mitochondrial elongation, decreased cell viability, production of ROS, IL‐8 and COX‐2, and increased apoptosis. DNM1L deficiency inhibited IL‐1β–mediated AKT/IKK activation, NF‐κBp65 nuclear translocation and LC3B‐related autophagy, but enhanced NFKBIA expression. Treatment of CIA mice with mdivi‐1 decreased disease severity by modulating inflammatory cytokine and ROS production. Our major results are that up‐regulated DNM1L and mitochondrial fission promoted survival, LC3B‐related autophagy and ROS production in FLSs, factors that lead to inflammation by regulating AKT/IKK/NFKBIA/NF‐κB signalling. Thus, inhibition of DNM1L may be a new strategy for treatment of RA.

Well-balanced mitochondrial fission and fusion processes are essential for nervous system development. Loss of function of the main mitochondrial fission mediator, dynamin-related protein 1 (Drp1), is lethal early during embryonic development or around birth, but the role of mitochondrial fission in adult neurons remains unclear. Here we show that inducible Drp1 ablation in neurons of the adult mouse forebrain results in progressive, neuronal subtype-specific alterations of mitochondrial morphology in the hippocampus that are marginally responsive to antioxidant treatment. Furthermore, DRP1 loss affects synaptic transmission and memory function. Although these changes culminate in hippocampal atrophy, they are not sufficient to cause neuronal cell death within 10 weeks of genetic Drp1 ablation. Collectively, our in vivo observations clarify the role of mitochondrial fission in neurons, demonstrating that Drp1 ablation in adult forebrain neurons compromises critical neuronal functions without causing overt neurodegeneration.

Mitochondria and peroxisomes proliferate by division. During division, a part of their membrane is pinched off by constriction of the ring-shaped mitochondrial division (MD) and peroxisome-dividing (POD) machinery. This constriction is mediated by a dynamin-like GTPase Dnm1 that requires a large amount of GTP as an energy source. Here, via proteomics of the isolated division machinery, we show that the 17-kDa nucleoside diphosphate kinase-like protein, dynamin-based ring motive-force organizer 1 (DYNAMO1), locally generates GTP in MD and POD machineries. DYNAMO1 is widely conserved among eukaryotes and colocalizes with Dnm1 on the division machineries. DYNAMO1 converts ATP to GTP, and disruption of its activity impairs mitochondrial and peroxisomal fissions. DYNAMO1 forms a ring-shaped complex with Dnm1 and increases the magnitude of the constricting force. Our results identify DYNAMO1 as an essential component of MD and POD machineries, suggesting that local GTP generation in Dnm1-based machinery regulates motive force for membrane severance. Mitochondria and peroxisomes require a dynamin-like GTPase to remodel membranes during division. Here the authors identify DYNAMO1, a nucleoside diphosphate kinase-like protein that generates a local source of GTP to promote constriction of the division machinery and produce daughter organelles.

During clathrin mediated endocytosis (CME), the concerted action of dynamin and its interacting partners drives membrane scission. Essential interactions occur between the proline/arginine-rich domain of dynamin (dynPRD) and the Src-homology domain 3 (SH3) of various proteins including amphiphysins. Here we show that multiple SH3 domains must bind simultaneously to dynPRD through three adjacent motifs for dynamin’s efficient recruitment and function. First, we show that mutant dynamins modified in a single motif, including the central amphiphysin SH3 (amphSH3) binding motif, partially rescue CME in dynamin triple knock-out cells. However, mutating two motifs largely prevents that ability. Furthermore, we designed divalent dynPRD-derived peptides. These ligands bind multimers of amphSH3 with >100-fold higher affinity than monovalent ones in vitro. Accordingly, dialyzing living cells with these divalent peptides through a patch-clamp pipette blocks CME much more effectively than with monovalent ones. We conclude that dynamin drives vesicle scission via multivalent interactions in cells. During clathrin mediated endocytosis (CME), membrane scission is achieved by the concerted action of dynamin and its interacting partners such as amphiphysins. Here authors show that efficient recruitment and function of dynamin requires simultaneous binding of multiple amphiphysin SH3 domains.