Overexpression of pink1 or parkin in indirect flight muscles promotes mitochondrial proteostasis and extends lifespan in Drosophila melanogaster

Targeting ATAD3A Phosphorylation Mediated by TBK1 Ameliorates Senescence-Associated Pathologies

Targeting cellular senescence, one of the hallmarks of aging and aging-related pathologies emerges as an effective strategy for anti-aging and cancer chemotherapy. Here, a switch from TBK1-OPTN axis to TBK1-ATAD3A axis to promote cellular senescence is shown. Mechanically, TBK1 protein is abnormally activated and localized to the mitochondria during senescence, which directly phosphorylates ATAD3A at Ser321. Phosphorylated ATAD3A is significantly elevated in cellular senescence as well as in physiological and pathological aging and is essential for suppressing Pink1-mediated mitophagy by facilitating Pink1 mitochondrial import. Inhibition of ATAD3A phosphorylation at Ser321 by either TBK1 deficiency or by a Ser321A mutation rescues the cellular senescence. A blocking peptide, TAT-PEP, specifically abrogating ATAD3A phosphorylation, results in elevated cell death by preventing doxorubicin-induced senescence, thus leading to enhanced tumor sensitivity to chemotherapy. TAT-PEP treatment also ameliorates various phenotypes associated with physiological aging. Collectively, these results reveal the TBK1-ATAD3A-Pink1 axis as a driving force in cellular senescence and suggest a potential mitochondrial target for anti-aging therapy.

Aberrant expression of thyroidal hormone receptor α exasperating mitochondrial dysfunction induced sarcopenia in aged mice

Disrupted mitochondrial dynamics and mitophagy contribute to functional deterioration of skeletal muscle (SM) during aging, but the regulatory mechanisms are poorly understood. Our previous study demonstrated that the expression of thyroid hormone receptor α (TRα) decreased significantly in aged mice, suggesting that the alteration of thyroidal elements, especially the decreased TRα, might attenuate local THs action thus to cause the degeneration of SM with aging, while the underlying mechanism remains to be further explored. In this study, decreased expression of myogenic regulators Myf5, MyoD1, mitophagy markers Pink1, LC3II/I, p62, as well as mitochondrial dynamic factors Mfn1 and Opa1, accompanied by increased reactive oxygen species (ROS), showed concomitant changes with reduced TRα expression in aged mice. Further TRα loss- and gain-of-function studies in C2C12 revealed that silencing of TRα not only down-regulated the expression of above-mentioned myogenic regulators, mitophagy markers and mitochondrial dynamic factors, but also led to a significant decrease in mitochondrial activity and maximum respiratory capacity, as well as more mitochondrial ROS and damaged mitochondria. Notedly, overexpression of TRα could up-regulate the expression of those myogenic regulators, mitophagy markers and mitochondrial dynamic factors, meanwhile also led to an increase in mitochondrial activity and number. These results confirmed that TRα could concertedly regulate mitochondrial dynamics, autophagy, and activity, and myogenic regulators rhythmically altered with TRα expression. Summarily, these results suggested that the decline of TRα might cause the degeneration of SM with aging by regulating mitochondrial dynamics, mitophagy and myogenesis.

Markers and mechanisms of death in Drosophila

Parameters correlated with age and mortality in Drosophila melanogaster include decreased negative geotaxis and centrophobism behaviors, decreased climbing and walking speed, and darkened pigments in oenocytes and eye. Cessation of egg laying predicts death within approximately 5 days. Endogenous green fluorescence in eye and body increases hours prior to death. Many flies exhibit erratic movement hours before death, often leading to falls. Loss of intestinal barrier integrity (IBI) is assayed by feeding blue dye ("Smurf" phenotype), and Smurf flies typically die within 0-48 h. Some studies report most flies exhibit Smurf, whereas multiple groups report most flies die without exhibiting Smurf. Transgenic reporters containing heat shock gene promoters and innate immune response gene promoters progressively increase expression with age, and partly predict remaining life span. Innate immune reporters increase with age in every fly, prior to any Smurf phenotype, in presence or absence of antibiotics. Many flies die on their side or supine (on their back) position. The data suggest three mechanisms for death of Drosophila. One is loss of IBI, as revealed by Smurf assay. The second is nervous system malfunction, leading to erratic behavior, locomotor malfunction, and falls. The aged fly is often unable to right itself after a fall to a side-ways or supine position, leading to inability to access the food and subsequent dehydration/starvation. Finally, some flies die upright without Smurf phenotype, suggesting a possible third mechanism. The frequency of these mechanisms varies between strains and culture conditions, which may affect efficacy of life span interventions.

Interactions of mitochondrial and skeletal muscle biology in mitochondrial myopathy

Mitochondrial dysfunction in skeletal muscle fibres occurs with both healthy aging and a range of neuromuscular diseases. The impact of mitochondrial dysfunction in skeletal muscle and the way muscle fibres adapt to this dysfunction is important to understand disease mechanisms and to develop therapeutic interventions. Furthermore, interactions between mitochondrial dysfunction and skeletal muscle biology, in mitochondrial myopathy, likely have important implications for normal muscle function and physiology. In this review, we will try to give an overview of what is known to date about these interactions including metabolic remodelling, mitochondrial morphology, mitochondrial turnover, cellular processes and muscle cell structure and function. Each of these topics is at a different stage of understanding, with some being well researched and understood, and others in their infancy. Furthermore, some of what we know comes from disease models. Whilst some findings are confirmed in humans, where this is not yet the case, we must be cautious in interpreting findings in the context of human muscle and disease. Here, our goal is to discuss what is known, highlight what is unknown and give a perspective on the future direction of research in this area.

Senolytic and senomorphic secondary metabolites as therapeutic agents in Drosophila melanogaster models of Parkinson's disease

Drosophila melanogaster is a valuable model organism for a wide range of biological exploration. The well-known advantages of D. melanogaster include its relatively simple biology, the ease with which it is genetically modified, the relatively low financial and time costs associated with their short gestation and life cycles, and the large number of offspring they produce per generation. D. melanogaster has facilitated the discovery of many significant insights into the pathology of Parkinson's disease (PD) and has served as an excellent preclinical model of PD-related therapeutic discovery. In this review, we provide an overview of the major D. melanogaster models of PD, each of which provide unique insights into PD-relevant pathology and therapeutic targets. These models are discussed in the context of their past, current, and future potential use for studying the utility of secondary metabolites as therapeutic agents in PD. Over the last decade, senolytics have garnered an exponential interest in their ability to mitigate a broad spectrum of diseases, including PD. Therefore, an emphasis is placed on the senolytic and senomorphic properties of secondary metabolites. It is expected that D. melanogaster will continue to be critical in the effort to understand and improve treatment of PD, including their involvement in translational studies focused on secondary metabolites.

Bypassing mitochondrial defects rescues Huntington's phenotypes in Drosophila

Huntington's disease (HD) is a fatal neurodegenerative disease with limited treatment options. Human and animal studies have suggested that metabolic and mitochondrial dysfunctions contribute to HD pathogenesis. Here, we use high-resolution respirometry to uncover defective mitochondrial oxidative phosphorylation and electron transfer capacity when a mutant huntingtin fragment is targeted to neurons or muscles in Drosophila and find that enhancing mitochondrial function can ameliorate these defects. In particular, we find that co-expression of parkin, an E3 ubiquitin ligase critical for mitochondrial dynamics and homeostasis, produces significant enhancement of mitochondrial respiration when expressed either in neurons or muscles, resulting in significant rescue of neurodegeneration, viability and longevity in HD model flies. Targeting mutant HTT to muscles results in larger mitochondria and higher mitochondrial mass, while co-expression of parkin increases mitochondrial fission and decreases mass. Furthermore, directly addressing HD-mediated defects in the fly's mitochondrial electron transport system, by rerouting electrons to either bypass mitochondrial complex I or complexes III-IV, significantly increases mitochondrial respiration and results in a striking rescue of all phenotypes arising from neuronal mutant huntingtin expression. These observations suggest that bypassing impaired mitochondrial respiratory complexes in HD may have therapeutic potential for the treatment of this devastating disorder.

The Small-Molecule Enhancers of Autophagy AUTEN-67 and -99 Delay Ageing in Drosophila Striated Muscle Cells

Autophagy (cellular self-degradation) plays a major role in maintaining the functional integrity (homeostasis) of essentially all eukaryotic cells. During the process, superfluous and damaged cellular constituents are delivered into the lysosomal compartment for enzymatic degradation. In humans, age-related defects in autophagy have been linked to the incidence of various age-associated degenerative pathologies (e.g., cancer, neurodegenerative diseases, diabetes, tissue atrophy and fibrosis, and immune deficiency) and accelerated ageing. Muscle mass decreases at detectable levels already in middle-aged patients, and this change can increase up to 30-50% at age 80. AUTEN-67 and -99, two small-molecule enhancers of autophagy with cytoprotective and anti-ageing effects have been previously identified and initially characterized. These compounds can increase the life span in wild-type and neurodegenerative model strains of the fruit fly Drosophila melanogaster. Adult flies were treated with these AUTEN molecules via feeding. Fluorescence and electron microscopy and Western blotting were used to assess the level of autophagy and cellular senescence. Flying tests were used to measure the locomotor ability of the treated animals at different ages. In the current study, the effects of AUTEN-67 and -99 were observed on striated muscle cells using the Drosophila indirect flight muscle (IFM) as a model. The two molecules were capable of inducing autophagy in IFM cells, thereby lowering the accumulation of protein aggregates and damaged mitochondria, both characterizing muscle ageing. Furthermore, the two molecules significantly improved the flying ability of treated animals. AUTEN-67 and -99 decrease the rate at which striated muscle cells age. These results may have a significant medical relevance that could be further examined in mammalian models.

Role of muscle FOXO gene in exercise against the skeletal muscle and cardiac age-related defects and mortality caused by high-salt intake in Drosophila

FOXO has long been associated with aging, exercise, and tissue homeostasis, but it remains unclear what the role is of the muscle FOXO gene in E against high-salt intake(HSI)-induced age-related defects of the skeletal muscle, heart, and mortality. In this research, overexpression and RNAi of the FOXO gene in the skeletal and heart muscle of Drosophila were constructed by building Mhc-GAL4/FOXO-UAS-overexpression and Mhc-GAL4/FOXO-UAS-RNAi system. The skeletal muscle and heart function, the balance of oxidation and antioxidant, and mitochondrial homeostasis were measured. The results showed that exercise reversed the age-related decline in climbing ability and downregulation of muscle FOXO expression induced by HSI. Muscle-specific FOXO-RNAi (FOXO-RNAi) and -overexpression (FOXO-OE) promoted or slowed the age-related decline in climbing ability, heart function, and skeletal muscle and heart structure damage, which was accompanied by the inhibition or activation of FOXO/PGC-1α/SDH and FOXO/SOD pathway activity, and oxidative stress (ROS) increased or decreased in both skeletal muscle and heart. The protective effect of exercise on the skeletal muscle and heart was blocked by FOXO-RNAi in aged HSI flies. FOXO-OE prolonged its lifespan, but it did not resist the HSI-induced lifespan shortening. Exercise did not improve HSI-induced lifespan shortening in FOXO-RNAi flies. Therefore, current results confirmed that the muscle FOXO gene played a vital role in exercise against age-related defects of the skeletal muscle and heart induced by HSI because it determined the activity of muscle FOXO/SOD and FOXO/PGC-1α/SDH pathways. The muscle FOXO gene also played an important role in exercise against HSI-induced mortality in aging flies.

The impact of high-fat feeding and parkin overexpression on skeletal muscle mass, mitochondrial respiration, and H2O2 emission

Obesity is a major risk factor for developing various health problems, including insulin resistance and type 2 diabetes. Although controversial, accumulation of mitochondrial dysfunction, and notably an increase in mitochondrial reactive oxygen species (ROS) production, was proposed as a key contributor leading to obesity-induced insulin resistance. Here, our goal was to investigate whether Parkin overexpression, a key regulator of the removal of dysfunctional mitochondria through mitophagy, could confer protection against obesity-induced mitochondrial dysfunction. To this end, intramuscular injections of adeno-associated viruses (AAVs) were performed to overexpress Parkin in limb muscle of 6-mo-old mice fed a control diet (CD) or a high-fat diet (HFD) for 12 wk. An AAV-expressing the green fluorescent protein (GFP) was used as control. HFD increased fat mass, altered glycemia, and resulted in insulin resistance. Parkin overexpression resulted in an increase in muscle mass in both CD and HFD mice. In CD mice, Parkin overexpression increased maximal mitochondrial respiration and lowered H₂O₂ emission. HFD increased mitochondrial respiration and, surprisingly, also lowered H₂O₂ emission. Parkin overexpression did not significantly impact mitochondrial function in HFD mice. Taken altogether, our results indicate that Parkin overexpression positively impacts muscle and mitochondrial health under basal conditions and challenges the notion that intrinsic mitochondrial dysfunction is involved in the development of insulin resistance caused by high-fat feeding.

Artemisinin Alleviates Cerebral Ischemia/Reperfusion-Induced Oxidative Damage via Regulating PHB2-Mediated Autophagy in the Human Neuroblastoma SH-SY5Y Cell Line

Oxidative stress plays a key role in cerebral ischemia/reperfusion injury. Artemisinin (ART) has antioxidative stress activity in addition to its powerful antimalarial effects. In this article, we investigated the effect of ART on OGD/R-induced oxidative stress injury and its underlying mechanisms. We used oxygen-glucose deprivation/reoxygenation (OGD/R) to establish an in vitro model of cerebral ischemia/reperfusion (I/R) injury. CCK-8 and lactate dehydrogenase (LDH) release were used to assess cellular damage. Measurement of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), and mitochondrial membrane potential (MMP) estimates oxidative stress-induced damage and protection from ART effect. OGD/R treatment aggravated oxidative stress damage, whereas ART reversed the effects of OGD/R. Autophagy is closely related to oxidative stress; in order to confirm whether the antioxidative stress effect of ART is related to PHB2-mediated autophagy, we examined the protein expression of prohibitin 2 (PHB2), TOMM20, p62, and the conversion of microtubule-associated protein light chain 3I (LC3I) to LC3II and found that the protein expression of PHB2, TOMM20, p62, and LC3II/LC3I was significantly correlated with OGD/R treatment. The colocalization of PHB2 and LC3, TOMM20, and LC3 was reduced after OGD/R treatment, and ART reversed this change. After silencing PHB2, the protective effect of ART against OGD/R-induced oxidative stress injury was reduced, the protein expressions of PHB2, TOMM20 and LC3II/LC3I and the colocalization of PHB2 and LC3, TOMM20, and LC3 were decreased. We used chloroquine to block the lysosomal pathway and found that ART increased the conversion of LC3I to LC3II, silencing PHB2 which inhibited the conversion of LC3I to LC3II, and impaired mitophagy. Our findings showed that ART attenuated OGD/R-induced oxidative stress damage through PHB2-mediated mitophagy. To the current knowledge, our study is the first to demonstrate that ART attenuates OGD/R-induced oxidative stress injury through PHB2-mediated autophagy in the human neuroblastoma SH-SY5Y cell line, which provided new insights into the treatment of OGD/R injury.

PINK1 overexpression prevents forskolin-induced tau hyperphosphorylation and oxidative stress in a rat model of Alzheimer's disease

PTEN-induced putative kinase 1 (PINK1)/parkin pathway mediates mitophagy, which is a specialized form of autophagy. Evidence shows that PINK1 can exert protective effects against stress-induced neuronal cell death. In the present study we investigated the effects of PINK1 overexpression on tau hyperphosphorylation, mitochondrial dysfunction and oxidative stress in a specific rat model of tau hyperphosphorylation. We showed that intracerebroventricular (ICV) microinjection of forskolin (FSK, 80 μmol) induced tau hyperphosphorylation in the rat brain and resulted in significant spatial working memory impairments in Y-maze test, accompanied by synaptic dysfunction (reduced expression of synaptic proteins synaptophysin and postsynaptic density protein 95), and neuronal loss in the hippocampus. Adeno-associated virus (AAV)-mediated overexpression of PINK1 prevented ICV-FSK-induced cognition defect and pathological alterations in the hippocampus, whereas PINK1-knockout significantly exacerbated ICV-FSK-induced deteriorated effects. Furthermore, we revealed that AAV-PINK1-mediated overexpression of PINK1 alleviated ICV-FSK-induced tau hyperphosphorylation by restoring the activity of PI3K/Akt/GSK3β signaling. PINK1 overexpression reversed the abnormal changes in mitochondrial dynamics, defective mitophagy, and decreased ATP levels in the hippocampus. Moreover, PINK1 overexpression activated Nrf2 signaling, thereby increasing the expression of antioxidant proteins and reducing oxidative damage. These results suggest that PINK1 deficiency exacerbates FSK-induced tau pathology, synaptic damage, mitochondrial dysfunction, and antioxidant system defects, which were reversed by PINK1 overexpression. Our data support a critical role of PINK1-mediated mitophagy in controlling mitochondrial quality, tau hyperphosphorylation, and oxidative stress in a rat model of Alzheimer's disease.

Reversible mitophagy drives metabolic suppression in diapausing beetles

Many insects enter a state of dormancy (diapause) during winter in which they lower their metabolism to save energy. Metabolic suppression is a hallmark of diapause, yet we know little about the mechanisms underpinning metabolic suppression in winter or how it is reversed in the spring. Here, we show that metabolic suppression in dormant Colorado potato beetles results from the breakdown of flight muscle mitochondria via mitophagy. Diapausing Colorado potato beetles suppress their metabolism by 90%, and this lowered metabolic rate coincides with a similar reduction in flight muscle mitochondrial function and density. During early diapause, beetles increase the expression of mitophagy-related transcripts (Parkin and ATG5) in their flight muscle coincident with an increase in mitophagy-related structures in the flight muscle. Knocking down Parkin expression with RNA interference in diapausing beetles prevented some mitochondrial breakdown and partially restored the whole animal metabolic rate, suggesting that metabolic suppression in diapausing beetles is driven by mitophagy. In other animals and in models of disease, such large-scale mitochondrial degradation is irreversible. However, we show that as diapause ends, beetles reverse mitophagy and increase the expression of PGC1α and NRF1 to replenish flight muscle mitochondrial pools. This mitochondrial biogenesis is activated in anticipation of diapause termination and in the absence of external stimuli. Our study provides a mechanistic link between mitochondrial degradation in insect tissues over the winter and whole-animal metabolic suppression.

Ubiquitin Ligases in Longevity and Aging Skeletal Muscle

The development and prevalence of diseases associated with aging presents a global health burden on society. One hallmark of aging is the loss of proteostasis which is caused in part by alterations to the ubiquitin-proteasome system (UPS) and lysosome-autophagy system leading to impaired function and maintenance of mass in tissues such as skeletal muscle. In the instance of skeletal muscle, the impairment of function occurs early in the aging process and is dependent on proteostatic mechanisms. The UPS plays a pivotal role in degradation of misfolded and aggregated proteins. For the purpose of this review, we will discuss the role of the UPS system in the context of age-related loss of muscle mass and function. We highlight the significant role that E3 ubiquitin ligases play in the turnover of key components (e.g., mitochondria and neuromuscular junction) essential to skeletal muscle function and the influence of aging. In addition, we will briefly discuss the contribution of the UPS system to lifespan. By understanding the UPS system as part of the proteostasis network in age-related diseases and disorders such as sarcopenia, new discoveries can be made and new interventions can be developed which will preserve muscle function and maintain quality of life with advancing age.

Parkin: A potential target to promote healthy aging

Parkin is an E3 ubiquitin ligase mostly known for its role in regulating the removal of defective mitochondria via mitophagy. However, increasing experimental evidence that Parkin regulates several other aspects of mitochondrial biology in addition to its role in mitophagy has emerged over the past two decades. Indeed, Parkin has been shown to regulate mitochondrial biogenesis and dynamics and mitochondrial-derived vesicle formation, suggesting that Parkin plays key roles in maintaining healthy mitochondria. While Parkin is commonly described as a cytosolic E3 ubiquitin ligase, Parkin was also detected in other cellular compartments, including the nucleus, where it regulates transcription factors and acts as a transcription factor itself. New evidence also suggests that Parkin overexpression can be leveraged to delay aging. In D. melanogaster, for example, Parkin overexpression extends lifespan. In mammals, Parkin overexpression delays hallmarks of aging in several tissues and cell types. Parkin overexpression also confers protection in various models of cellular senescence and neurological disorders closely associated with aging, such as Alzheimer's and Parkinson's diseases. Recently, Parkin overexpression has also been shown to suppress tumor growth. In this review, we discuss newly emerging biological roles of Parkin as a modulator of cellular homeostasis, survival, and healthy aging, and we explore potential mechanisms through which Parkin exerts its beneficial effects on cellular health. Abstract figure legend Parkin: A potential target to promote healthy aging Illustration of key aspects of Parkin biology, including Parkin function and cellular localization and key roles in the regulation of mitochondrial quality control. The organs and systems in which Parkin overexpression was shown to exert protective effects relevant to the promotion of healthy aging are highlighted in the black rectangle at the bottom of the Figure. This article is protected by copyright. All rights reserved.

Role of the mtDNA Mutations and Mitophagy in Inflammaging

Ageing is an unavoidable multi-factorial process, characterised by a gradual decrease in physiological functionality and increasing vulnerability of the organism to environmental factors and pathogens, ending, eventually, in death. One of the most elaborated ageing theories implies a direct connection between ROS-mediated mtDNA damage and mutations. In this review, we focus on the role of mitochondrial metabolism, mitochondria generated ROS, mitochondrial dynamics and mitophagy in normal ageing and pathological conditions, such as inflammation. Also, a chronic form of inflammation, which could change the long-term status of the immune system in an age-dependent way, is discussed. Finally, the role of inflammaging in the most common neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, is also discussed.

Drosophila ZIP13 overexpression or transferrin1 RNAi influences the muscle degeneration of Pink1 RNAi by elevating iron levels in mitochondria

Disruption of iron homeostasis in the brain of Parkinson's disease (PD) patients has been reported for many years, but the underlying mechanisms remain unclear. To investigate iron metabolism genes related to PTEN-induced kinase 1 (Pink1) and parkin (E3 ubiquitin ligase), two PD-associated proteins that function to coordinate mitochondrial turnover via induction of selective mitophagy, we conducted a genetic screen in Drosophila and found that altered expression of genes involved in iron metabolism, such as Drosophila ZIP13 (dZIP13) or transferrin1 (Tsf1), significantly influences the disease progression related to Pink1 but not parkin. Several phenotypes of Pink1 mutant and Pink1 RNAi but not parkin mutant were significantly rescued by overexpression (OE) of dZIP13 (dZIP13 OE) or silencing of Tsf1 (Tsf1 RNAi) in the flight muscles. The rescue effects of dZIP13 OE or Tsf1 RNAi were not exerted through mitochondrial disruption or mitophagy, instead, the iron levels in mitochondira were significantly increased, resulting in enhanced activity of enzymes participating in respiration and increased ATP synthesis. Consistently, the rescue effects of dZIP13 OE or Tsf1 RNAi on Pink1 RNAi can be inhibited by decreasing the iron levels in mitochondria through mitoferrin (dmfrn) RNAi. This study suggests that dZIP13, Tsf1 and dmfrn might act independently of parkin in a parallel pathway downstream of Pink1 by modulating respiration and indicates that manipulation of iron levels in mitochondria may provide a novel therapeutic strategy for PD associated with Pink1.

Mitophagy in aging and longevity

The clearance of damaged or unwanted mitochondria by autophagy (also known as mitophagy) is a mitochondrial quality control mechanism postulated to play an essential role in cellular homeostasis, metabolism, and development and confers protection against a wide range of diseases. Proper removal of damaged or unwanted mitochondria is essential for organismal health. Defects in mitophagy are associated with Parkinson's, Alzheimer's disease, cancer, and other degenerative disorders. Mitochondria regulate organismal fitness and longevity via multiple pathways, including cellular senescence, stem cell function, inflammation, mitochondrial unfolded protein response (mtUPR), and bioenergetics. Thus, mitophagy is postulated to be pivotal for maintaining organismal healthspan and lifespan and the protection against aged-related degeneration. In this review, we will summarize recent understanding of the mechanism of mitophagy and aspects of mitochondrial functions. We will focus on mitochondria-related cellular processes that are linked to aging and examine current genetic evidence that supports the hypothesis that mitophagy is a pro-longevity mechanism.

Gene Therapeutic Approaches for the Treatment of Mitochondrial Dysfunction in Parkinson's Disease

Background: Mitochondrial dysfunction has been identified as a pathophysiological hallmark of disease onset and progression in patients with Parkinsonian disorders. Besides the overall emergence of gene therapies in treating these patients, this highly relevant molecular concept has not yet been defined as a target for gene therapeutic approaches. Methods: This narrative review will discuss the experimental evidence suggesting mitochondrial dysfunction as a viable treatment target in patients with monogenic and idiopathic Parkinson’s disease. In addition, we will focus on general treatment strategies and crucial challenges which need to be overcome. Results: Our current understanding of mitochondrial biology in parkinsonian disorders opens up the avenue for viable treatment strategies in Parkinsonian disorders. Insights can be obtained from primary mitochondrial diseases. However, substantial knowledge gaps and unique challenges of mitochondria-targeted gene therapies need to be addressed to provide innovative treatments in the future. Conclusions: Mitochondria-targeted gene therapies are a potential strategy to improve an important primary disease mechanism in Parkinsonian disorders. However, further studies are needed to address the unique design challenges for mitochondria-targeted gene therapies.

iTRAQ-based quantitative proteomics suggests mitophagy involvement after Rice black-streaked dwarf virus acquisition in insect vector small brown planthopper Laodelphax striatellus Fallén

Plant viruses trigger numerous responses in their insect vectors. Using iTRAQ-based quantitative proteomics analysis, early responses of the insect vector, the small brown planthopper (Laodelphax striatellus Fallén, SBPH), after acquiring Rice black-streaked dwarf virus (RBSDV) at 3 days and 5 days post first access to diseased plants (padp) were revealed. A total of 582 differentially abundant proteins (DAPs) in SBPH with a fold change >1.500 or <0.667 (p-value < 0.05) were identified. The proteomic analysis in SBPH at 3 days padp revealed 106 highly abundant proteins and 193 of low abundance, while 5 days padp revealed 214 highly abundant proteins and 182 of low abundance. Among them, 51 highly abundant proteins and 42 of low abundance were shown consistently at both 3 days and 5 days padp. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis mapping and Gene Ontology (GO) term classification suggested impairment of mitochondria in SBPH after RBSDV acquisition, and the 77 out of 582 differentially abundant SBPH proteins analyzed by the STRING program revealed the interaction network of the mitochondrial DAPs, showing an overall down-regulation of mitochondrial proteins including the electron transport chain proteins and mitochondrial ribosome proteins. The high abundance of Parkin at 5 days padp suggests that activation of mitophagy induced degradation of mitochondria occurred. Further verification of autophagy/mitophagy-related genes by reverse-transcription quantitative RT-PCR (RT-qPCR) in SBPH after RBSDV acquisition showed up-regulation of the autophagy receptors Optineurin (OPTN), Sequestosome-1 (SQSTM1, also known as p62) and Tax1-binding protein 1 (TAX1BP1) which targets ubiquitinated damaged mitochondria during mitophagy. The phosphorylation of the three autophagy receptors may be up-regulated through an increase of transcription level TRAF-associated NFκB activator (TANK)-binding kinase 1 (TBK1). As a result, an overall reduction in the abundance of mitochondrial proteins was observed and the selective autophagic degradation was up-regulated through increased transcription level of OPTN, p62/SQSTM1, TAX1BP1 and TBK1. Therefore, acquisition of RBSDV associated with up-regulated autophagy and selective mitochondrial degradation in SBPH suggest prevention of mitochondrial-mediated apoptosis and extension of the vector life span. BIOLOGICAL SIGNIFICANCE: RBSDV causes severe yield loss in rice plants. RBSDV is transmitted efficiently only through SBPH. It is important to understand how RBSDV infects SBPH in a persistent, circulative and propagative manner. However, there has been no study on the interaction between RBSDV and SBPH at the early acquisition stage using a proteomics approach. In this study, we combined iTRAQ technique and LC-MS/MS to analyze the vector proteomics at both the initial and latent infection stages after RBSDV acquisition and verified the results by RT-qPCR. Our results revealed that significantly low DAPs were involved in various pathways, including biosynthesis of secondary metabolites, ribosomes, carbon metabolism, biosynthesis of amino acids and TCA cycle. Further clustering of the DAPs revealed significant changes in SBPH mitochondria, including decreased proteins in mitochondrial ribosomes and electron transport chain complex I, II and V. On the other hand, there was a high abundance of Parkin, suggesting the occurrence of mitochondria damage and subsequent Parkin-mediated mitophagy for clearance of impaired mitochondria. Moreover, the decreased level of PMPCB in terms of gene expression and protein abundance suggested decreased PINK1 turnover, promoting Parkin/PINK1-mediated mitophagy. Further analysis on autophagy/mitophagy-related gene transcription level indicated up-regulation of OPTN, p62/SQSTM1, TAX1BP1 and TBK1, promoting selective autophagy in SBPH after RBSDV acquisition. These findings provided new insights into the effects of RBSDV on SBPH after early acquisition by selective degradation of mitochondria, especially on reprogramming of energy metabolism and decreased mitochondria biogenesis, to prevent apoptosis and prolong the life span of SBPH post virus acquisition.

Mitophagy and Oxidative Stress: The Role of Aging

Mitochondrial dysfunction is a hallmark of aging. Dysfunctional mitochondria are recognized and degraded by a selective type of macroautophagy, named mitophagy. One of the main factors contributing to aging is oxidative stress, and one of the early responses to excessive reactive oxygen species (ROS) production is the induction of mitophagy to remove damaged mitochondria. However, mitochondrial damage caused at least in part by chronic oxidative stress can accumulate, and autophagic and mitophagic pathways can become overwhelmed. The imbalance of the delicate equilibrium among mitophagy, ROS production and mitochondrial damage can start, drive, or accelerate the aging process, either in physiological aging, or in pathological age-related conditions, such as Alzheimer’s and Parkinson’s diseases. It remains to be determined which is the prime mover of this imbalance, i.e., whether it is the mitochondrial damage caused by ROS that initiates the dysregulation of mitophagy, thus activating a vicious circle that leads to the reduced ability to remove damaged mitochondria, or an alteration in the regulation of mitophagy leading to the excessive production of ROS by damaged mitochondria.

The Interplay between Mitochondrial Morphology and Myomitokines in Aging Sarcopenia

Sarcopenia is a chronic disease characterized by the progressive loss of skeletal muscle mass, force, and function during aging. It is an emerging public problem associated with poor quality of life, disability, frailty, and high mortality. A decline in mitochondria quality control pathways constitutes a major mechanism driving aging sarcopenia, causing abnormal organelle accumulation over a lifetime. The resulting mitochondrial dysfunction in sarcopenic muscles feedbacks systemically by releasing the myomitokines fibroblast growth factor 21 (FGF21) and growth and differentiation factor 15 (GDF15), influencing the whole-body homeostasis and dictating healthy or unhealthy aging. This review describes the principal pathways controlling mitochondrial quality, many of which are potential therapeutic targets against muscle aging, and the connection between mitochondrial dysfunction and the myomitokines FGF21 and GDF15 in the pathogenesis of aging sarcopenia.

Proteostasis-associated aging: lessons from a Drosophila model

As cells age, they lose their ability to properly fold proteins, maintain protein folding, and eliminate misfolded proteins, which leads to the accumulation of abnormal protein aggregates and loss of protein homeostasis (proteostasis). Loss of proteostasis can accelerate aging and the onset of neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. Mechanisms exist to prevent the detrimental effects of abnormal proteins that incorporate chaperones, autophagy, and the ubiquitin-proteasome system. These mechanisms are evolutionarily conserved across various species. Therefore, the effect of impaired proteostasis on aging has been studied using model organisms that are appropriate for aging studies. In this review, we focus on the relationship between proteostasis and aging, and factors that affect proteostasis in Drosophila. The manipulation of proteostasis can alter lifespan, modulate neurotoxicity, and delay the onset of neurodegeneration, indicating that proteostasis may be a novel pharmacological target for the development of treatments for various age-associated diseases.

The connection between the dynamic remodeling of the mitochondrial network and the regulation of muscle mass

The dynamic coordination of processes controlling the quality of the mitochondrial network is crucial to maintain the function of mitochondria in skeletal muscle. Changes of mitochondrial proteolytic system, dynamics (fusion/fission), and mitophagy induce pathways that affect muscle mass and performance. When muscle mass is lost, the risk of disease onset and premature death is dramatically increased. For instance, poor quality of muscles correlates with the onset progression of several age-related disorders such as diabetes, obesity, cancer, and aging sarcopenia. To date, there are no drug therapies to reverse muscle loss, and exercise remains the best approach to improve mitochondrial health and to slow atrophy in several diseases. This review will describe the principal mechanisms that control mitochondrial quality and the pathways that link mitochondrial dysfunction to muscle mass regulation.