The Mst1/2-BNIP3 axis is required for mitophagy induction and neuronal viability under mitochondrial stress.

Mitophagy induction upon mitochondrial stress is critical for maintaining mitochondrial homeostasis and cellular function. Here, we found that Mst1/2 (Stk3/4), key regulators of the Hippo pathway, are required for the induction of mitophagy under various mitochondrial stress conditions. Knockdown of Mst1/2 or pharmacological inhibition by XMU-MP-1 treatment led to impaired mitophagy induction upon CCCP and DFP treatment. Mechanistically, Mst1/2 induces mitophagy independently of the PINK1-Parkin pathway and the canonical Hippo pathway. Moreover, our results suggest the essential involvement of BNIP3 in Mst1/2-mediated mitophagy induction upon mitochondrial stress. Notably, Mst1/2 knockdown diminishes mitophagy induction, exacerbates mitochondrial dysfunction, and reduces cellular survival upon neurotoxic stress in both SH-SY5Y cells and Drosophila models. Conversely, Mst1 and Mst2 expression enhances mitophagy induction and cell survival. In addition, AAV-mediated Mst1 expression reduced the loss of TH-positive neurons, ameliorated behavioral deficits, and improved mitochondrial function in an MPTP-induced Parkinson's disease mouse model. Our findings reveal the Mst1/2-BNIP3 regulatory axis as a novel mediator of mitophagy induction under conditions of mitochondrial stress and suggest that Mst1/2 play a pivotal role in maintaining mitochondrial function and neuronal viability in response to neurotoxic treatment.

Selective induction of Rab9-dependent alternative mitophagy using a synthetic derivative of isoquinoline alleviates mitochondrial dysfunction and cognitive deficits in Alzheimer's disease models.

Rationale: Promotion of mitophagy is considered a promising strategy for the treatment of neurodegenerative diseases including Alzheimer's disease (AD). The development of mitophagy-specific inducers with low toxicity and defined molecular mechanisms is essential for the clinical application of mitophagy-based therapy. The aim of this study was to investigate the potential of a novel small-molecule mitophagy inducer, ALT001, as a treatment for AD. Methods: ALT001 was developed through chemical optimization of an isoquinolium scaffold, which was identified from a chemical library screening using a mitophagy reporter system. In vitro and in vivo experiments were conducted to evaluate the potential of ALT001 as a mitophagy-targeting therapeutic agent and to investigate the molecular mechanisms underlying ALT001-induced mitophagy. The therapeutic effect of ALT001 was assessed in SH-SY5Y cells expressing mutant APP and mouse models of AD (5×FAD and PS2APP) by analyzing mitochondrial dysfunction and cognitive defects. Results: ALT001 specifically induces mitophagy both in vitro and in vivo but is nontoxic to mitochondria. Interestingly, we found that ALT001 induces mitophagy through the ULK1-Rab9-dependent alternative mitophagy pathway independent of canonical mitophagy pathway regulators such as ATG7 and PINK1. Importantly, ALT001 reverses mitochondrial dysfunction in SH-SY5Y cells expressing mutant APP in a mitophagy-dependent manner. ALT001 induces alternative mitophagy in mice and restores the decreased mitophagy level in a 5×FAD AD model mouse. In addition, ALT001 reverses mitochondrial dysfunction and cognitive defects in the PS2APP and 5×FAD AD mouse models. AAV-mediated silencing of Rab9 in the hippocampus further confirmed that ALT001 exerts its therapeutic effect through alternative mitophagy. Conclusion: Our results highlight the therapeutic potential of ALT001 for AD via alleviation of mitochondrial dysfunction and indicate the usefulness of the ULK1-Rab9 alternative mitophagy pathway as a therapeutic target.

Varicella zoster virus glycoprotein E facilitates PINK1/Parkin-mediated mitophagy to evade STING and MAVS-mediated antiviral innate immunity.

Viruses have evolved to control mitochondrial quality and content to facilitate viral replication. Mitophagy is a selective autophagy, in which the damaged or unnecessary mitochondria are removed, and thus considered an essential mechanism for mitochondrial quality control. Although mitophagy manipulation by several RNA viruses has recently been reported, the effect of mitophagy regulation by varicella zoster virus (VZV) remains to be fully determined. In this study, we showed that dynamin-related protein-1 (DRP1)-mediated mitochondrial fission and subsequent PINK1/Parkin-dependent mitophagy were triggered during VZV infection, facilitating VZV replication. In addition, VZV glycoprotein E (gE) promoted PINK1/Parkin-mediated mitophagy by interacting with LC3 and upregulating mitochondrial reactive oxygen species. Importantly, VZV gE inhibited MAVS oligomerization and STING translocation to disrupt MAVS- and STING-mediated interferon (IFN) responses, and PINK1/Parkin-mediated mitophagy was required for VZV gE-mediated inhibition of IFN production. Similarly, carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-mediated mitophagy induction led to increased VZV replication but attenuated IFN production in a three-dimensional human skin organ culture model. Our results provide new insights into the immune evasion mechanism of VZV gE via PINK1/Parkin-dependent mitophagy.

Glucose-mediated mitochondrial reprogramming by cholesterol export at TM4SF5-enriched mitochondria-lysosome contact sites.

BACKGROUND: Transmembrane 4 L six family member 5 (TM4SF5) translocates subcellularly and functions metabolically, although it is unclear how intracellular TM4SF5 translocation is linked to metabolic contexts. It is thus of interests to understand how the traffic dynamics of TM4SF5 to subcellular endosomal membranes are correlated to regulatory roles of metabolisms. METHODS: Here, we explored the metabolic significance of TM4SF5 localization at mitochondria-lysosome contact sites (MLCSs), using in vitro cells and in vivo animal systems, via approaches by immunofluorescence, proximity labelling based proteomics analysis, organelle reconstitution etc. RESULTS: Upon extracellular glucose repletion following depletion, TM4SF5 became enriched at MLCSs via an interaction between mitochondrial FK506-binding protein 8 (FKBP8) and lysosomal TM4SF5. Proximity labeling showed molecular clustering of phospho-dynamic-related protein I (DRP1) and certain mitophagy receptors at TM4SF5-enriched MLCSs, leading to mitochondrial fission and autophagy. TM4SF5 bound NPC intracellular cholesterol transporter 1 (NPC1) and free cholesterol, and mediated export of lysosomal cholesterol to mitochondria, leading to impaired oxidative phosphorylation but intact tricarboxylic acid (TCA) cycle and ß-oxidation. In mouse models, hepatocyte Tm4sf5 promoted mitophagy and cholesterol transport to mitochondria, both with positive relations to liver malignancy. CONCLUSIONS: Our findings suggested that TM4SF5-enriched MLCSs regulate glucose catabolism by facilitating cholesterol export for mitochondrial reprogramming, presumably while hepatocellular carcinogenesis, recapitulating aspects for hepatocellular carcinoma metabolism with mitochondrial reprogramming to support biomolecule synthesis in addition to glycolytic energetics.

The Natural Alkaloid Palmatine Selectively Induces Mitophagy and Restores Mitochondrial Function in an Alzheimer's Disease Mouse Model.

Palmatine, a natural alkaloid found in various plants, has been reported to have diverse pharmacological and biological effects, including anti-inflammatory, antioxidant, and cardiovascular effects. However, the role of palmatine in mitophagy, a fundamental process crucial for maintaining mitochondrial function, remains elusive. In this study, we found that palmatine efficiently induces mitophagy in various human cell lines. Palmatine specifically induces mitophagy and subsequently stimulates mitochondrial biogenesis. Palmatine did not interfere with mitochondrial function, similar to CCCP, suggesting that palmatine is not toxic to mitochondria. Importantly, palmatine treatment alleviated mitochondrial dysfunction in PINK1-knockout MEFs. Moreover, the administration of palmatine resulted in significant improvements in cognitive function and restored mitochondrial function in an Alzheimer's disease mouse model. This study identifies palmatine as a novel inducer of selective mitophagy. Our results suggest that palmatine-mediated mitophagy induction could be a potential strategy for Alzheimer's disease treatment and that natural alkaloids are potential sources of mitophagy inducers.

PINK1 and Parkin Ameliorate the Loss of Motor Activity and Mitochondrial Dysfunction Induced by Peripheral Neuropathy-Associated HSPB8 Mutants in Drosophila Models.

Charcot-Marie-Tooth disease (CMT) is a group of inherited peripheral nerve disorders characterized by progressive muscle weakness and atrophy, sensory loss, foot deformities and steppage gait. Missense mutations in the gene encoding the small heat shock protein HSPB8 (HSP22) have been associated with hereditary neuropathies, including CMT. HSPB8 is a member of the small heat shock protein family sharing a highly conserved α-crystallin domain that is critical to its chaperone activity. In this study, we modeled HSPB8 mutant-induced neuropathies in Drosophila. The overexpression of human HSPB8 mutants in Drosophila neurons produced no significant defect in fly development but led to a partial reduction in fly lifespan. Although these HSPB8 mutant genes failed to induce sensory abnormalities, they reduced the motor activity of flies and the mitochondrial functions in fly neuronal tissue. The motor defects and mitochondrial dysfunction were successfully restored by PINK1 and parkin, which are Parkinson's disease-associated genes that have critical roles in maintaining mitochondrial function and integrity. Consistently, kinetin riboside, a small molecule amplifying PINK1 activity, also rescued the loss of motor activity in our HSPB8 mutant model.

COUP-TFII plays a role in cAMP-induced Schwann cell differentiation and in vitro myelination by up-regulating Krox20.

Schwann cells (SCs) are known to produce myelin for saltatory nerve conduction in the peripheral nervous system (PNS). Schwann cell differentiation and myelination processes are controlled by several transcription factors including Sox10, Oct6/Pou3f1, and Krox20/Egr2. Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII/NR2F2) is an orphan receptor that plays a role in the development and differentiation. However, the role of COUP-TFII in the transcriptional regulatory network of SC differentiation has not been fully identified yet. Thus, the objective of this study was to investigate the role and molecular hierarchy of COUP-TFII during cAMP-induced SC differentiation. Our results showed that dibutyryl-cAMP (db-cAMP) increased expression levels of COUP-TFII along with the expressions of Oct6, Krox20, and myelin-related genes known to be related to SC differentiation. Our mechanistic studies showed that COUP-TFII acted downstream of Hsp90/ErbB2/Gab1/ERK-AKT pathway during db-cAMP-induced SC differentiation. In addition, we found that COUP-TFII induced Krox20 expression by directly binding to Krox20-MSE8 as revealed by chromatin immunoprecipitation assay and promoter activity assay. In line with this, the expression of COUP-TFII was increased before up-regulation of Oct6, Krox20, and myelin-related genes in the sciatic nerves during early postnatal myelination period. Finally, COUP-TFII knockdown by COUP-TFII siRNA or via AAV-COUP-TFII shRNA in SCs inhibited db-cAMP-induced SC differentiation and in vitro myelination of sensory axons, respectively. Taken together, these findings indicate that COUP-TFII might be involved in postnatal myelination through induction of Krox20 in SCs. Our results present a new insight into the transcriptional regulatory mechanism in SC differentiation and myelination.

Berberine Induces Mitophagy through Adenosine Monophosphate-Activated Protein Kinase and Ameliorates Mitochondrial Dysfunction in PINK1 Knockout Mouse Embryonic Fibroblasts.

Mitophagy stimulation has been shown to have a therapeutic effect on various neurodegenerative diseases. However, nontoxic mitophagy inducers are still very limited. In this study, we found that the natural alkaloid berberine exhibited mitophagy stimulation activity in various human cells. Berberine did not interfere with mitochondrial function, unlike the well-known mitophagy inducer carbonyl cyanide m-chlorophenyl hydrazone (CCCP), and subsequently induced mitochondrial biogenesis. Berberine treatment induced the activation of adenosine monophosphate-activated protein kinase (AMPK), and the AMPK inhibitor compound C abolished berberine-induced mitophagy, suggesting that AMPK activation is essential for berberine-induced mitophagy. Notably, berberine treatment reversed mitochondrial dysfunction in PINK1 knockout mouse embryonic fibroblasts. Our results suggest that berberine is a mitophagy-specific inducer and can be used as a therapeutic treatment for neurodegenerative diseases, including Parkinson's disease, and that natural alkaloids are potential sources of mitophagy inducers.

Emerging role of LETM1/GRP78 axis in lung cancer.

The selective autophagy of damaged mitochondria is called mitophagy. Mitochondrial dysfunction, mitophagy, and apoptosis have been suggested to be interrelated in various human lung carcinomas. Leucine zipper EF-hand-containing transmembrane protein-1 (LETM1) was cloned in an attempt to identify candidate genes for Wolf-Hirschhorn syndrome. LETM1 plays a role in mitochondrial morphology, ion homeostasis, and cell viability. LETM1 has also been shown to be overexpressed in different human cancer tissues, including lung cancer. In the current study, we have provided clear evidence that LETM1 acts as an anchoring protein for the mitochondria-associated ER membrane (MAM). Fragmented mitochondria have been found in lung cancer cells with LETM1 overexpression. In addition, a reduction of mitochondrial membrane potential and significant accumulation of microtubule-associated protein 1 A/1B-light chain 3 punctate, which localizes with Red-Mito, was found in LETM1-overexpressed cells, suggesting that mitophagy is upregulated in these cells. Interestingly, glucose-regulated protein 78 kDa (GRP78; an ER chaperon protein) and glucose-regulated protein 75 kDa (GRP75) were posited to interact with LETM1 in the immunoprecipitated LETM1 of H460 cells. This interaction was enhanced in cells treated with carbonyl cyanide m-chlorophenylhydrazone, a chemical mitophagy inducer. Treatment of cells with honokiol (a GRP78 inhibitor) blocked LETM1-mediated mitophagy, and CRISPR/Cas9-mediated GRP75 knockout inhibited LETM1-induced autophagy. Thus, GRP78 interacts with LETM1. Taken together, these observations support the notion that the complex formation of LETM1/GRP75/GRP78 might be an important step in MAM formation and mitophagy, thus regulating mitochondrial quality control in lung cancer.

The PINK1 Activator Niclosamide Mitigates Mitochondrial Dysfunction and Thermal Hypersensitivity in a Paclitaxel-Induced Drosophila Model of Peripheral Neuropathy.

Paclitaxel is a widely used anticancer drug that induces dose-limiting peripheral neuropathy. Mitochondrial dysfunction has been implicated in paclitaxel-induced neuronal damage and in the onset of peripheral neuropathy. We have previously shown that the expression of PINK1, a key mediator of mitochondrial quality control, ameliorated the paclitaxel-induced thermal hyperalgesia phenotype and restored mitochondrial homeostasis in Drosophila larvae. In this study, we show that the small-molecule PINK1 activator niclosamide exhibits therapeutic potential for paclitaxel-induced peripheral neuropathy. Specifically, niclosamide cotreatment significantly ameliorated the paclitaxel-induced thermal hyperalgesia phenotype in Drosophila larvae in a PINK1-dependent manner. Paclitaxel-induced alteration of the dendrite structure of class IV dendritic arborization (C4da) neurons was not reduced upon niclosamide treatment. In contrast, paclitaxel treatment-induced increases in both mitochondrial ROS and aberrant mitophagy levels in C4da neurons were significantly suppressed by niclosamide. In addition, niclosamide suppressed paclitaxel-induced mitochondrial dysfunction in human SH-SY5Y cells in a PINK1-dependent manner. These results suggest that niclosamide alleviates thermal hyperalgesia by attenuating paclitaxel-induced mitochondrial dysfunction. Taken together, our results suggest that niclosamide is a potential candidate for the treatment of paclitaxel-induced peripheral neuropathy with low toxicity in neurons and that targeting mitochondrial dysfunction is a promising strategy for the treatment of chemotherapy-induced peripheral neuropathy.

Peroxiredoxin 3 deficiency induces cardiac hypertrophy and dysfunction by impaired mitochondrial quality control.

Mitochondrial quality control (MQC) consists of multiple processes: the prevention of mitochondrial oxidative damage, the elimination of damaged mitochondria via mitophagy and mitochondrial fusion and fission. Several studies proved that MQC impairment causes a plethora of pathological conditions including cardiovascular diseases. However, the precise molecular mechanism by which MQC reverses mitochondrial dysfunction, especially in the heart, is unclear. The mitochondria-specific peroxidase Peroxiredoxin 3 (Prdx3) plays a protective role against mitochondrial dysfunction by removing mitochondrial reactive oxygen species. Therefore, we investigated whether Prdx3-deficiency directly leads to heart failure via mitochondrial dysfunction. Fifty-two-week-old Prdx3-deficient mice exhibited cardiac hypertrophy and dysfunction with giant and damaged mitochondria. Mitophagy was markedly suppressed in the hearts of Prdx3-deficient mice compared to the findings in wild-type and Pink1-deficient mice despite the increased mitochondrial damage induced by Prdx3 deficiency. Under conditions inducing mitophagy, we identified that the damaged mitochondrial accumulation of PINK1 was completely inhibited by the ablation of Prdx3. We propose that Prdx3 interacts with the N-terminus of PINK1, thereby protecting PINK1 from proteolytic cleavage in damaged mitochondria undergoing mitophagy. Our results provide evidence of a direct association between MQC dysfunction and cardiac function. The dual function of Prdx3 in mitophagy regulation and mitochondrial oxidative stress elimination further clarifies the mechanism of MQC in vivo and thereby provides new insights into developing a therapeutic strategy for mitochondria-related cardiovascular diseases such as heart failure.

Corrigendum: CVB3-Mediated Mitophagy Plays an Important Role in Viral Replication via Abrogation of Interferon Pathways.

[This corrects the article DOI: 10.3389/fcimb.2021.704494.].

Correction: PINK1 alleviates thermal hypersensitivity in a paclitaxel-induced Drosophila model of peripheral neuropathy.

[This corrects the article DOI: 10.1371/journal.pone.0239126.].

Nonstructural Protein NS1 of Influenza Virus Disrupts Mitochondrial Dynamics and Enhances Mitophagy via ULK1 and BNIP3.

Nonstructural protein 1 (NS1) of influenza virus (IFV) is essential for evading interferon (IFN)-mediated antiviral responses, thereby contributing to the pathogenesis of influenza. Mitophagy is a type of autophagy that selectively removes damaged mitochondria. The role of NS1 in IFV-mediated mitophagy is currently unknown. Herein, we showed that overexpression of NS1 protein led to enhancement of mitophagy. Mitophagy induction via carbonyl cyanide 3-chlorophenylhydrazone treatment in IFV-infected A549 cells led to increased viral replication efficiency, whereas the knockdown of PTEN-induced kinase 1 (PINK1) led to the opposite effect on viral replication. Overexpression of NS1 protein led to changes in mitochondrial dynamics, including depolarization of mitochondrial membrane potential. In contrast, infection with NS1-deficient virus resulted in impaired mitochondrial fragmentation, subsequent mitolysosomal formation, and mitophagy induction, suggesting an important role of NS1 in mitophagy. Meanwhile, NS1 protein increased the phosphorylation of Unc-51-like autophagy activating kinase 1 (ULK1) and the mitochondrial expression of BCL2- interacting protein 3 (BNIP3), both of which were found to be important for IFV-mediated mitophagy. Overall, these data highlight the importance of IFV NS1, ULK1, and BNIP3 during mitophagy activation.

CVB3-Mediated Mitophagy Plays an Important Role in Viral Replication via Abrogation of Interferon Pathways.

Coxsackievirus B3 (CVB3) is a common enterovirus that causes systemic inflammatory diseases, such as myocarditis, meningitis, and encephalitis. CVB3 has been demonstrated to subvert host cellular responses via autophagy to support viral replication in neural stem cells. Mitophagy, a specialized form of autophagy, contributes to mitochondrial quality control via degrading damaged mitochondria. Here, we show that CVB3 infection induces mitophagy in human neural progenitor cells, HeLa and H9C2 cardiomyocytes. In particular, CVB3 infection triggers mitochondrial fragmentation, loss of mitochondrial membrane potential, and Parkin/LC3 translocation to the mitochondria. Rapamycin or carbonyl cyanide m-chlorophenyl hydrazone (CCCP) treatment led to increased CVB3 RNA copy number in a dose-dependent manner, suggesting enhanced viral replication via autophagy/mitophagy activation, whereas knockdown of PTEN-induced putative kinase protein 1(PINK1) led to impaired mitophagy and subsequent reduction in viral replication. Furthermore, CCCP treatment inhibits the interaction between mitochondrial antiviral signaling protein (MAVS) and TANK-binding kinase 1(TBK1), thus contributing to the abrogation of type I and III interferon (IFN) production, suggesting that mitophagy is essential for the inhibition of interferon signaling. Our findings suggest that CVB3-mediated mitophagy suppresses IFN pathways by promoting fragmentation and subsequent sequestration of mitochondria by autophagosomes.

Magneto mitochondrial dysfunction mediated cancer cell death using intracellular magnetic nano-transducers.

Mitochondria are crucial regulators of the intrinsic pathway of cancer cell death. The high sensitivity of cancer cells to mitochondrial dysfunction offers opportunities for emerging targets in cancer therapy. Herein, magnetic nano-transducers, which convert external magnetic fields into physical stress, are designed to induce mitochondrial dysfunction to remotely kill cancer cells. Spindle-shaped iron oxide nanoparticles were synthesized to maximize cellular internalization and magnetic transduction. The magneto-mechanical transduction of nano-transducers in mitochondria enhances cancer cell apoptosis by promoting a mitochondrial quality control mechanism, referred to as mitophagy. In the liver cancer animal model, nano-transducers are infused into the local liver tumor via the hepatic artery. After treatment with a magnetic field, in vivo mitophagy-mediated cancer cell death was also confirmed by mitophagy markers, mitochondrial DNA damage assay, and TUNEL staining of tissues. This study is expected to contribute to the development of nanoparticle-mediated mitochondria-targeting cancer therapy and biological tools, such as magneto-genetics.

STK3/STK4 signalling in adipocytes regulates mitophagy and energy expenditure.

Obesity reduces adipocyte mitochondrial function, and expanding adipocyte oxidative capacity is an emerging strategy to improve systemic metabolism. Here, we report that serine/threonine-protein kinase 3 (STK3) and STK4 are key physiological suppressors of mitochondrial capacity in brown, beige and white adipose tissues. Levels of STK3 and STK4, kinases in the Hippo signalling pathway, are greater in white than brown adipose tissues, and levels in brown adipose tissue are suppressed by cold exposure and greatly elevated by surgical denervation. Genetic inactivation of Stk3 and Stk4 increases mitochondrial mass and function, stabilizes uncoupling protein 1 in beige adipose tissue and confers resistance to metabolic dysfunction induced by high-fat diet feeding. Mechanistically, STK3 and STK4 increase adipocyte mitophagy in part by regulating the phosphorylation and dimerization status of the mitophagy receptor BNIP3. STK3 and STK4 expression levels are elevated in human obesity, and pharmacological inhibition improves metabolic profiles in a mouse model of obesity, suggesting STK3 and STK4 as potential targets for treating obesity-related diseases.

p53-mediated regulation of mitochondrial dynamics plays a pivotal role in the senescence of various normal cells as well as cancer cells.

The tumor suppressor p53 is known as a critical mediator of many cellular processes, including cellular senescence, but its role in mitochondrial dynamics is not fully understood. We have previously shown that p53 regulates mitochondrial dynamics via the PKA-Drp1 pathway to induce cellular senescence. In this study, to further understand the role of p53-dependent regulation of mitochondrial dynamics, the effect of p53 expression on mitochondrial morphology was examined in various cancer cell lines and normal human cells. We found that p53 induced remarkable mitochondrial elongation and cellular senescence in various cancer cells regardless of their p53 status. p53 also induced mitochondrial elongation in various human primary normal cells, suggesting that p53-mediated mitochondrial elongation is a general phenomenon. Moreover, we found that p53 plays an essential role in mitochondrial elongation in H-Ras-induced cellular senescence and in the replicative senescence of normal human cells. Treatment with the MDM-2 antagonist Nutlin-3a also induced mitochondrial elongation through the PKA-Drp1 pathway in IMR90 normal human cells. Furthermore, the inhibition of PKA activity in late-passage normal cells significantly reduced both mitochondrial elongation and cellular senescence, suggesting that the p53-PKA pathway is essential for maintaining the senescence phenotype in normal cells. Together, these results further confirm the direct regulation of mitochondrial dynamics by p53 and the important role of p53-mediated mitochondrial elongation in cellular senescence.

PINK1 alleviates thermal hypersensitivity in a paclitaxel-induced Drosophila model of peripheral neuropathy.

Paclitaxel is a representative anticancer drug that induces chemotherapy-induced peripheral neuropathy (CIPN), a common side effect that limits many anticancer chemotherapies. Although PINK1, a key mediator of mitochondrial quality control, has been shown to protect neuronal cells from various toxic treatments, the role of PINK1 in CIPN has not been investigated. Here, we examined the effect of PINK1 expression on CIPN using a recently established paclitaxel-induced peripheral neuropathy model in Drosophila larvae. We found that the class IV dendritic arborization (C4da) sensory neuron-specific expression of PINK1 significantly ameliorated the paclitaxel-induced thermal hyperalgesia phenotype. In contrast, knockdown of PINK1 resulted in an increase in thermal hypersensitivity, suggesting a critical role for PINK1 in sensory neuron-mediated thermal nociceptive sensitivity. Interestingly, analysis of the C4da neuron morphology suggests that PINK1 expression alleviates paclitaxel-induced thermal hypersensitivity by means other than preventing alterations in sensory dendrites in C4da neurons. We found that paclitaxel induces mitochondrial dysfunction in C4da neurons and that PINK1 expression suppressed the paclitaxel-induced increase in mitophagy in C4da neurons. These results suggest that PINK1 mitigates paclitaxel-induced sensory dendrite alterations and restores mitochondrial homeostasis in C4da neurons and that improvement in mitochondrial quality control could be a promising strategy for the treatment of CIPN.

Rubrofusarin Attenuates Chronic Restraint Stress-Induced Depressive Symptoms.

The aim of this study was to examine whether rubrofusarin, an active ingredient of the Cassia species, has an antidepressive effect in chronic restraint stress (CRS) mouse model. Although acute treatment using rubrofusarin failed, chronic treatment using rubrofusarin ameliorated CRS-induced depressive symptoms. Rubrofusarin treatment significantly reduced the number of Fluoro-Jade B-positive cells and caspase-3 activation within the hippocampus of CRS-treated mice. Moreover, rubrofusarin treatment significantly increased the number of newborn neurons in the hippocampus of CRS-treated mice. CRS induced activation of glycogen synthase kinase-3ß and regulated development and DNA damage responses, and reductions in the extracellular-signal-regulated kinase pathway activity were also reversed by rubrofusarin treatment. Microglial activation and inflammasome markers, including nod-like receptor family pyrin domain containing 3 and adaptor protein apoptosis-associated speck-like protein containing CARD, which were induced by CRS, were ameliorated by rubrofusarin. Synaptic plasticity dysfunction within the hippocampus was also rescued by rubrofusarin treatment. Within in vitro experiments, rubrofusarin blocked corticosterone-induced long-term potentiation impairments. These were blocked by LY294002, which is an Akt inhibitor. Finally, we found that the antidepressant effects of rubrofusarin were blocked by an intracerebroventricular injection of LY294002. These results suggest that rubrofusarin ameliorated CRS-induced depressive symptoms through PI3K/Akt signaling.