scholarly journals Loss of the Mitochondrial Fission GTPase Drp1 Contributes to Neurodegeneration in a Drosophila Model of Hereditary Spastic Paraplegia

2020 ◽  
Vol 10 (9) ◽  
pp. 646
Author(s):  
Philippa C. Fowler ◽  
Dwayne J. Byrne ◽  
Craig Blackstone ◽  
Niamh C. O'Sullivan
Keyword(s):  
Hereditary Spastic Paraplegia ◽  
Neurodegenerative Disorder ◽  
Mitochondrial Fission ◽  
Dominant Negative ◽  
In Vivo Model ◽  
Mitochondrial Morphology ◽  
Autophagic Flux ◽  
Spastic Paraplegia ◽  
Drosophila Model

Mitochondrial morphology, distribution and function are maintained by the opposing forces of mitochondrial fission and fusion, the perturbation of which gives rise to several neurodegenerative disorders. The large guanosine triphosphate (GTP)ase dynamin-related protein 1 (Drp1) is a critical regulator of mitochondrial fission by mediating membrane scission, often at points of mitochondrial constriction at endoplasmic reticulum (ER)-mitochondrial contacts. Hereditary spastic paraplegia (HSP) subtype SPG61 is a rare neurodegenerative disorder caused by mutations in the ER-shaping protein Arl6IP1. We have previously reported defects in both the ER and mitochondrial networks in a Drosophila model of SPG61. In this study, we report that knockdown of Arl6IP1 lowers Drp1 protein levels, resulting in reduced ER–mitochondrial contacts and impaired mitochondrial load at the distal ends of long motor neurons. Increasing mitochondrial fission, by overexpression of wild-type Drp1 but not a dominant negative Drp1, increases ER–mitochondrial contacts, restores mitochondrial load within axons and partially rescues locomotor deficits. Arl6IP1 knockdown Drosophila also demonstrate impaired autophagic flux and an accumulation of ubiquitinated proteins, which occur independent of Drp1-mediated mitochondrial fission defects. Together, these findings provide evidence that impaired mitochondrial fission contributes to neurodegeneration in this in vivo model of HSP.

scholarly journals Spastin, atlastin, and ER relocalization are involved in axon but not dendrite regeneration

2016 ◽  
Vol 27 (21) ◽  
pp. 3245-3256 ◽  
Author(s):  
Kavitha Rao ◽  
Michelle C. Stone ◽  
Alexis T. Weiner ◽  
Kyle W. Gheres ◽  
Chaoming Zhou ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Hereditary Spastic Paraplegia ◽  
Genetic Background ◽  
Axon Regeneration ◽  
Dominant Negative ◽  
Partial Reduction ◽  
Spastic Paraplegia ◽  
Axon Injury ◽  
Drosophila Model

Mutations in >50 genes, including spastin and atlastin, lead to hereditary spastic paraplegia (HSP). We previously demonstrated that reduction of spastin leads to a deficit in axon regeneration in a Drosophila model. Axon regeneration was similarly impaired in neurons when HSP proteins atlastin, seipin, and spichthyin were reduced. Impaired regeneration was dependent on genetic background and was observed when partial reduction of HSP proteins was combined with expression of dominant-negative microtubule regulators, suggesting that HSP proteins work with microtubules to promote regeneration. Microtubule rearrangements triggered by axon injury were, however, normal in all genotypes. We examined other markers to identify additional changes associated with regeneration. Whereas mitochondria, endosomes, and ribosomes did not exhibit dramatic repatterning during regeneration, the endoplasmic reticulum (ER) was frequently concentrated near the tip of the growing axon. In atlastin RNAi and spastin mutant animals, ER accumulation near single growing axon tips was impaired. ER tip concentration was observed only during axon regeneration and not during dendrite regeneration. In addition, dendrite regeneration was unaffected by reduction of spastin or atlastin. We propose that the HSP proteins spastin and atlastin promote axon regeneration by coordinating concentration of the ER and microtubules at the growing axon tip.

LncRNA PVT1 Mediated by ZFP36L2 Regulates Myocardial Ischemia/Reperfusion Injury and Attenuates Mitochondrial Fusion and Fission via Activating miR-21-5p/MARCH5 Axis

2020 ◽  
Author(s):  
Weifeng Huang ◽  
Qin Tan ◽  
Yong Guo ◽  
Yongmei Cao ◽  
Jiawei Shang ◽  
...  
Keyword(s):  
Zinc Finger Protein ◽  
Ischemia Reperfusion Injury ◽  
Ischemia Reperfusion ◽  
Mitochondrial Fission ◽  
Tumor Biology ◽  
Luciferase Reporter ◽  
Mitochondrial Morphology ◽  
Mrna Levels

Abstract BackgroundAmong several leading cardiovascular disorders, ischemia-reperfusion (I/R) injury causes severe manifestations including acute heart failure, inflammation, and systemic dysfunction. Recently, there has been increasing evidence suggesting that alterations in mitochondrial morphology play a role in the prognoses of cardiac disorders. Long non-coding RNAs (lncRNAs) form major regulatory networks to modify gene transcription and translation. While several roles of lncRNAs have been explored in cancer and tumor biology, their implications on mitochondrial morphology and functions remain to be elucidated. MethodsThe functional roles of ZFP36L2 and lncRNA PVT1 were determined by a series of cardiomyocyte hypoxia/ reoxygenation (H/R) in vitro and myocardial I/R injury in vivo experiments. Quantitative Reverse transcription-polymerase chain reaction (qRT-PCR) and western blot analysis were used to detect the mRNA levels of ZFP36L2 and mitochondrial fission and fusion markers in the myocardial tissues and cardiomyocyte. Cardiac function was determined by immunohistochemistry, H&E, Masson’s staining and echocardiogram. Ultrastructural analysis of mitochondrial fission was performed using transmission electron microscopy (TEM). The mechanistic model of PVT1 with ZFP36L2 and miR-21-5p with MARCH5 was detected by subcellular fraction, RNA pull down, FISH, and luciferase reporter assays.ResultsIn this study, we report a novel regulatory axis involving lncRNA PVT1, microRNA miR-21-5p, and E3 ubiquitin ligase MARCH5, which alters mitochondrial morphology during myocardial I/R injury. Using an in vivo I/R injury mouse model and in vitro cardiomyocyte H/R model, we observed that zinc finger protein ZFP36L2 directly associated with PVT1 and altered mitochondrial fission and fusion. PVT1 also interacted with miR-21-5p and suppressed its expression and activity. Furthermore, we identified MARCH5 as a modifier of miR-21-5p, and expression of MARCH5 and its effect on mitochondrial fission and fusion were directly proportional to PVT1 expression during H/R injury. ConclusionsOur findings demonstrated that manipulation of PVT1-miR-21-5p-MARCH5-mediated mitochondrial fission and fusion via ZFP36L2 may be a novel therapeutic approach to regulate myocardial I/R injury.

scholarly journals Mitochondrial pyruvate and fatty acid flux modulate MICU1-dependent control of MCU activity

2020 ◽  
Vol 13 (628) ◽  
pp. eaaz6206 ◽  
Author(s):  
Neeharika Nemani ◽  
Zhiwei Dong ◽  
Cassidy C. Daw ◽  
Travis R. Madaris ◽  
Karthik Ramachandran ◽  
...  
Keyword(s):  
Fatty Acid ◽  
Tca Cycle ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Mitochondrial Morphology ◽  
Autophagic Flux ◽  
Fatty Acid Transport ◽  
Mitochondrial Matrix ◽  
Genetic Ablation ◽  
Mitochondrial Fatty Acid

The tricarboxylic acid (TCA) cycle converts the end products of glycolysis and fatty acid β-oxidation into the reducing equivalents NADH and FADH2. Although mitochondrial matrix uptake of Ca2+ enhances ATP production, it remains unclear whether deprivation of mitochondrial TCA substrates alters mitochondrial Ca2+ flux. We investigated the effect of TCA cycle substrates on MCU-mediated mitochondrial matrix uptake of Ca2+, mitochondrial bioenergetics, and autophagic flux. Inhibition of glycolysis, mitochondrial pyruvate transport, or mitochondrial fatty acid transport triggered expression of the MCU gatekeeper MICU1 but not the MCU core subunit. Knockdown of mitochondrial pyruvate carrier (MPC) isoforms or expression of the dominant negative mutant MPC1R97W resulted in increased MICU1 protein abundance and inhibition of MCU-mediated mitochondrial matrix uptake of Ca2+. We also found that genetic ablation of MPC1 in hepatocytes and mouse embryonic fibroblasts resulted in reduced resting matrix Ca2+, likely because of increased MICU1 expression, but resulted in changes in mitochondrial morphology. TCA cycle substrate–dependent MICU1 expression was mediated by the transcription factor early growth response 1 (EGR1). Blocking mitochondrial pyruvate or fatty acid flux was linked to increased autophagy marker abundance. These studies reveal a mechanism that controls the MCU-mediated Ca2+ flux machinery and that depends on TCA cycle substrate availability. This mechanism generates a metabolic homeostatic circuit that protects cells from bioenergetic crisis and mitochondrial Ca2+ overload during periods of nutrient stress.

Upper Motor Neuron Disorders Hereditary Spastic Paraplegia and Primary Lateral Sclerosis

2017 ◽  
Author(s):  
Sabrina Paganoni ◽  
Nazem Atassi
Keyword(s):  
Motor Neuron ◽  
Hereditary Spastic Paraplegia ◽  
Disease Modeling ◽  
Primary Lateral Sclerosis ◽  
Spastic Paraplegia ◽  
Underlying Pathophysiology ◽  
Primary Lateral ◽  
Lateral Sclerosis

Upper motor neuron (UMN) syndromes are a group of rare, degenerative neurological disorders that are classified as either hereditary spastic paraplegia (HSP) or primary lateral sclerosis (PLS). Our understanding of their underlying pathophysiology is unfortunately very limited and has been a significant barrier to the development of disease-modifying treatments. Recent advances in genetics and in vitro and in vivo disease modeling have provided new insights into disease mechanisms and hold the promise to lead to the future development of mechanism-based therapies.

scholarly journals Stop-gain mutations in UBAP1 cause pure autosomal-dominant spastic paraplegia

Brain ◽  
2019 ◽  
Vol 142 (8) ◽  
pp. 2238-2252 ◽  
Author(s):  
Xiang Lin ◽  
Hui-Zhen Su ◽  
En-Lin Dong ◽  
Xiao-Hong Lin ◽  
Miao Zhao ◽  
...  
Keyword(s):  
Exome Sequencing ◽  
Cortical Neurons ◽  
Hereditary Spastic Paraplegia ◽  
Autosomal Dominant ◽  
Wild Type Mouse ◽  
Spastic Paraplegia ◽  
Endosomal Sorting ◽  
Hereditary Spastic Paraplegias ◽  
Cultured Cortical Neurons

Abstract Hereditary spastic paraplegias refer to a heterogeneous group of neurodegenerative disorders resulting from degeneration of the corticospinal tract. Clinical characterization of patients with hereditary spastic paraplegias represents progressive spasticity, exaggerated reflexes and muscular weakness. Here, to expand on the increasingly broad pools of previously unknown hereditary spastic paraplegia causative genes and subtypes, we performed whole exome sequencing for six affected and two unaffected individuals from two unrelated Chinese families with an autosomal dominant hereditary spastic paraplegia and lacking mutations in known hereditary spastic paraplegia implicated genes. The exome sequencing revealed two stop-gain mutations, c.247_248insGTGAATTC (p.I83Sfs*11) and c.526G>T (p.E176*), in the ubiquitin-associated protein 1 (UBAP1) gene, which co-segregated with the spastic paraplegia. We also identified two UBAP1 frameshift mutations, c.324_325delCA (p.H108Qfs*10) and c.425_426delAG (p.K143Sfs*15), in two unrelated families from an additional 38 Chinese pedigrees with autosomal dominant hereditary spastic paraplegias and lacking mutations in known causative genes. The primary disease presentation was a pure lower limb predominant spastic paraplegia. In vivo downregulation of Ubap1 in zebrafish causes abnormal organismal morphology, inhibited motor neuron outgrowth, decreased mobility, and shorter lifespan. UBAP1 is incorporated into endosomal sorting complexes required for transport complex I and binds ubiquitin to function in endosome sorting. Patient-derived truncated form(s) of UBAP1 cause aberrant endosome clustering, pronounced endosome enlargement, and cytoplasmic accumulation of ubiquitinated proteins in HeLa cells and wild-type mouse cortical neuron cultures. Biochemical and immunocytochemical experiments in cultured cortical neurons derived from transgenic Ubap1flox mice confirmed that disruption of UBAP1 leads to dysregulation of both early endosome processing and ubiquitinated protein sorting. Strikingly, deletion of Ubap1 promotes neurodegeneration, potentially mediated by apoptosis. Our study provides genetic and biochemical evidence that mutations in UBAP1 can cause pure autosomal dominant spastic paraplegia.

scholarly journals In Vivo Deletion of β-Cell Drp1 Impairs Insulin Secretion Without Affecting Islet Oxygen Consumption

Endocrinology ◽  
2018 ◽  
Vol 159 (9) ◽  
pp. 3245-3256 ◽  
Author(s):  
Thomas G Hennings ◽  
Deeksha G Chopra ◽  
Elizabeth R DeLeon ◽  
Halena R VanDeusen ◽  
Hiromi Sesaki ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Insulin Secretion ◽  
Tricarboxylic Acid Cycle ◽  
Mitochondrial Fission ◽  
Calcium Handling ◽  
Mitochondrial Morphology ◽  
Second Phase ◽  
Β Cell ◽  
Insulin Secretion In Vivo

Abstract Mitochondria are dynamic organelles that undergo frequent fission and fusion events. Mitochondrial fission is required for ATP production, the tricarboxylic acid cycle, and processes beyond metabolism in a cell-type specific manner. Ex vivo and cell line studies have demonstrated that Drp1, a central regulator of mitochondrial fission, is required for glucose-stimulated insulin secretion (GSIS) in pancreatic β cells. Herein, we set out to interrogate the role of Drp1 in β-cell insulin secretion in vivo. We generated β-cell–specific Drp1 knockout (KO) mice (Drp1β-KO) by crossing a conditional allele of Drp1 to Ins1cre mice, in which Cre recombinase replaces the coding region of the Ins1 gene. Drp1β-KO mice were glucose intolerant due to impaired GSIS but did not progress to fasting hyperglycemia as adults. Despite markedly abnormal mitochondrial morphology, Drp1β-KO islets exhibited normal oxygen consumption rates and an unchanged glucose threshold for intracellular calcium mobilization. Instead, the most profound consequences of β-cell Drp1 deletion were impaired second-phase insulin secretion and impaired glucose-stimulated amplification of insulin secretion. Our data establish Drp1 as an important regulator of insulin secretion in vivo and demonstrate a role for Drp1 in metabolic amplification and calcium handling without affecting oxygen consumption.

scholarly journals Mitochondrial Deficits With Neural and Social Damage in Early-Stage Alzheimer’s Disease Model Mice

2021 ◽  
Vol 13 ◽  
Author(s):  
Afzal Misrani ◽  
Sidra Tabassum ◽  
Qingwei Huo ◽  
Sumaiya Tabassum ◽  
Jinxiang Jiang ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Neurodegenerative Disorder ◽  
Early Stage ◽  
Mitochondrial Dynamics ◽  
Mitochondrial Fission ◽  
Neuronal Morphology ◽  
Therapeutic Interventions ◽  
Early Event ◽  
Mitochondrial Morphology

Alzheimer’s disease (AD) is the most common neurodegenerative disorder worldwide. Mitochondrial dysfunction is thought to be an early event in the onset and progression of AD; however, the precise underlying mechanisms remain unclear. In this study, we investigated mitochondrial proteins involved in organelle dynamics, morphology and energy production in the medial prefrontal cortex (mPFC) and hippocampus (HIPP) of young (1∼2 months), adult (4∼5 months) and aged (9∼10, 12∼18 months) APP/PS1 mice. We observed increased levels of mitochondrial fission protein, Drp1, and decreased levels of ATP synthase subunit, ATP5A, leading to abnormal mitochondrial morphology, increased oxidative stress, glial activation, apoptosis, and altered neuronal morphology as early as 4∼5 months of age in APP/PS1 mice. Electrophysiological recordings revealed abnormal miniature excitatory postsynaptic current in the mPFC together with a minor connectivity change between the mPFC and HIPP, correlating with social deficits. These results suggest that abnormal mitochondrial dynamics, which worsen with disease progression, could be a biomarker of early-stage AD. Therapeutic interventions that improve mitochondrial function thus represent a promising approach for slowing the progression or delaying the onset of AD.

scholarly journals Functional conservation of human Spastin in a Drosophila model of autosomal dominant-hereditary spastic paraplegia

2010 ◽  
Vol 19 (10) ◽  
pp. 1883-1896 ◽  
Author(s):  
Fang Du ◽  
Emily F. Ozdowski ◽  
Ingrid K. Kotowski ◽  
Douglas A. Marchuk ◽  
Nina Tang Sherwood
Keyword(s):  
Hereditary Spastic Paraplegia ◽  
Autosomal Dominant ◽  
Spastic Paraplegia ◽  
Functional Conservation ◽  
Drosophila Model

scholarly journals The Drosophila effector caspase Dcp-1 regulates mitochondrial dynamics and autophagic flux via SesB

2014 ◽  
Vol 205 (4) ◽  
pp. 477-492 ◽  
Author(s):  
Lindsay DeVorkin ◽  
Nancy Erro Go ◽  
Ying-Chen Claire Hou ◽  
Annie Moradian ◽  
Gregg B. Morin ◽  
...  
Keyword(s):  
Adenine Nucleotide ◽  
Mitochondrial Dynamics ◽  
Negative Regulator ◽  
Mitochondrial Morphology ◽  
Autophagic Flux ◽  
Loss Of Function ◽  
Effector Caspase ◽  
Apoptosis Pathways ◽  
Mitochondrial Elongation

Increasing evidence reveals that a subset of proteins participates in both the autophagy and apoptosis pathways, and this intersection is important in normal physiological contexts and in pathological settings. In this paper, we show that the Drosophila effector caspase, Drosophila caspase 1 (Dcp-1), localizes within mitochondria and regulates mitochondrial morphology and autophagic flux. Loss of Dcp-1 led to mitochondrial elongation, increased levels of the mitochondrial adenine nucleotide translocase stress-sensitive B (SesB), increased adenosine triphosphate (ATP), and a reduction in autophagic flux. Moreover, we find that SesB suppresses autophagic flux during midoogenesis, identifying a novel negative regulator of autophagy. Reduced SesB activity or depletion of ATP by oligomycin A could rescue the autophagic defect in Dcp-1 loss-of-function flies, demonstrating that Dcp-1 promotes autophagy by negatively regulating SesB and ATP levels. Furthermore, we find that pro–Dcp-1 interacts with SesB in a nonproteolytic manner to regulate its stability. These data reveal a new mitochondrial-associated molecular link between nonapoptotic caspase function and autophagy regulation in vivo.

scholarly journals SRP54 mutations induce Congenital Neutropenia via dominant-negative effects on XBP1 splicing

Blood ◽  
2020 ◽  
Author(s):  
Christoph Schürch ◽  
Thorsten Schaefer ◽  
Joëlle Seraina Müller ◽  
Pauline Hanns ◽  
Marlon Arnone ◽  
...  
Keyword(s):  
De Novo ◽  
Dominant Negative ◽  
Severe Neutropenia ◽  
In Vivo Model ◽  
Factor X ◽  
Negative Effects ◽  
Congenital Neutropenia ◽  
Developmental Defects ◽  
Xbp1 Mrna

Heterozygous de novo missense variants of SRP54 were recently identified in patients with congenital neutropenia (CN), displaying symptoms overlapping with Shwachman-Diamond-Syndrome (SDS).1 Here, we investigate srp54 KO zebrafish as the first in vivo model of SRP54 deficiency. srp54-/- zebrafish are embryonically lethal and display, next to severe neutropenia, multi-systemic developmental defects. In contrast, srp54+/- zebrafish are viable, fertile and only show mild neutropenia. Interestingly, injection of human SRP54 mRNAs carrying mutations observed in patients (T115A, T117Δ and G226E) aggravated neutropenia and induced pancreatic defects in srp54+/- fish, mimicking the corresponding human clinical phenotypes. These data suggest that the variable phenotypes observed in patients may be due to mutation-specific dominant negative effects on the functionality of the residual wildtype SRP54 protein. Consistently, overexpression of mutated SRP54 also induced neutropenia in wildtype fish and impaired granulocytic maturation of human promyelocytic HL-60 cells as well as of healthy cord-blood derived CD34+ HSPCs. Mechanistically, srp54 mutant fish and human cells show impaired unconventional splicing of the transcription factor X-box binding protein 1 (Xbp1). Vice-versa, xbp1 morphants recapitulate phenotypes observed in srp54 deficiency and, importantly, injection of spliced, but not unspliced xbp1 mRNA rescues neutropenia in srp54+/- zebrafish. Together, these data indicate that SRP54 is critical for the development of various tissues, with neutrophils reacting most sensitively to SRP54 loss. The heterogenic phenotypes observed in patients, ranging from mild CN to SDS-like disease, may be due to different dominant negative effects of mutated SRP54 proteins on downstream XBP1 splicing, which represents a potential therapeutic target.

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