Optineurin is an autophagy receptor for damaged mitochondria in parkin-mediated mitophagy that is disrupted by an ALS-linked mutation

The mitophagy receptors BNIP3 and NIX mediate tight attachment and expansion of the isolation membrane to mitochondria

BNIP3 and NIX are the main receptors for mitophagy, but their mechanisms of action remain elusive. Here, we used correlative light EM (CLEM) and electron tomography to reveal the tight attachment of isolation membranes (IMs) to mitochondrial protrusions, often connected with ER via thin tubular and/or linear structures. In BNIP3/NIX-double knockout (DKO) HeLa cells, the ULK1 complex and nascent IM formed on mitochondria, but the IM did not expand. Artificial tethering of LC3B to mitochondria induced mitophagy that was equally efficient in DKO cells and WT cells. BNIP3 and NIX accumulated at the segregated mitochondrial protrusions via binding with LC3 through their LIR motifs but did not require dimer formation. Finally, the average distance between the IM and the mitochondrial surface in receptor-mediated mitophagy was significantly smaller than that in ubiquitin-mediated mitophagy. Collectively, these results indicate that BNIP3 and NIX are required for the tight attachment and expansion of the IM along the mitochondrial surface during mitophagy.

Rab GTPases are evolutionarily conserved signals mediating selective autophagy

Selective autophagy plays a crucial role in maintaining cellular homeostasis by specifically targeting unwanted cargo labeled with "autophagy cues" signals for autophagic degradation. In this study, we identify Rab GTPases as a class of such autophagy cues signals involved in selective autophagy. Through biochemical and imaging screens, we reveal that human Rab GTPases are common autophagy substrates. Importantly, we confirm the conservation of Rab GTPase autophagic degradation in different model organisms. Rab GTPases translocate to damaged mitochondria, lipid droplets, and invading Salmonella-containing vacuoles (SCVs) to serve as degradation signals. Furthermore, they facilitate mitophagy, lipophagy, and xenophagy, respectively, by recruiting receptors. This interplay between Rab GTPases and receptors may ensure the de novo synthesis of isolation membranes around Rab-GTPase-labeled cargo, thereby mediating selective autophagy. These processes are further influenced by upstream regulators such as LRRK2, GDIs, and RabGGTase. In conclusion, this study unveils a conserved mechanism involving Rab GTPases as autophagy cues signals and proposes a model for the spatiotemporal control of selective autophagy.

Potential of autophagy in subretinal fibrosis in neovascular age-related macular degeneration

Age-related macular degeneration (AMD) is an eye disease that can lead to legal blindness and vision loss. In its advanced stages, it is classified into dry and neovascular AMD. In neovascular AMD, the formation of new blood vessels disrupts the structure of the retina and induces an inflammatory response. Treatment for neovascular AMD involves antibodies and fusion proteins targeting vascular endothelial growth factor A (VEGFA) and its receptors to inhibit neovascularization and slow vision loss. However, a fraction of patients with neovascular AMD do not respond to therapy. Many of these patients exhibit a subretinal fibrotic scar. Thus, retinal fibrosis may contribute to resistance against anti-VEGFA therapy and the cause of irreversible vision loss in neovascular AMD patients. Retinal pigment epithelium cells, choroidal fibroblasts, and retinal glial cells are crucial in the development of the fibrotic scar as they can undergo a mesenchymal transition mediated by transforming growth factor beta and other molecules, leading to their transdifferentiation into myofibroblasts, which are key players in subretinal fibrosis. Autophagy, a process that removes cellular debris and contributes to the pathogenesis of AMD, regardless of its type, may be stimulated by epithelial-mesenchymal transition and later inhibited. The mesenchymal transition of retinal cells and the dysfunction of the extracellular matrix-the two main aspects of fibrotic scar formation-are associated with impaired autophagy. Nonetheless, the causal relationship between autophagy and subretinal fibrosis remains unknown. This narrative/perspective review presents information on neovascular AMD, subretinal fibrosis, and autophagy, arguing that impaired autophagy may be significant for fibrosis-related resistance to anti-VEGFA therapy in neovascular AMD.

Inborn errors of canonical autophagy in neurodegenerative diseases

Neurodegenerative disorders (NDDs), characterized by a progressive loss of neurons and cognitive function, are a severe burden to human health and mental fitness worldwide. A hallmark of NDDs such as Alzheimer's disease, Huntington's disease, Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and prion diseases is disturbed cellular proteostasis, resulting in pathogenic deposition of aggregated protein species. Autophagy is a major cellular process maintaining proteostasis and integral to innate immune defenses that mediates lysosomal protein turnover. Defects in autophagy are thus frequently associated with NDDs. In this review, we discuss the interplay between NDDs associated proteins and autophagy and provide an overview over recent discoveries in inborn errors in canonical autophagy proteins that are associated with NDDs. While mutations in autophagy receptors seems to be associated mainly with the development of ALS, errors in mitophagy are mainly found to promote PD. Finally, we argue whether autophagy may impact progress and onset of the disease, as well as the potential of targeting autophagy as a therapeutic approach. Concludingly, understanding disorders due to inborn errors in autophagy-"autophagopathies"-will help to unravel underlying NDD pathomechanisms and provide unique insights into the neuroprotective role of autophagy, thus potentially paving the way for novel therapeutic interventions.

Rab32 regulates Golgi structure and cell migration through Protein Kinase A-mediated phosphorylation of Optineurin

Rab32 is a small GTPase and molecular switch implicated in vesicular trafficking. Rab32 is also an A-Kinase Anchoring Protein (AKAP), which anchors cAMP-dependent Protein Kinase (PKA) to specific subcellular locations and specifies PKA phosphorylation of nearby substrates. Surprisingly, we found that a form of Rab32 deficient in PKA binding (Rab32 L188P) relocalized away from the Golgi apparatus and induced a marked disruption in Golgi organization, assembly, and dynamics. Although Rab32 L188P did not cause a global defect in PKA activity, our data indicate that Rab32 facilitates the phosphorylation of a specific PKA substrate. We uncovered a direct interaction between Rab32 and the adaptor protein optineurin (OPTN), which regulates Golgi dynamics. Further, our data indicate that optineurin is phosphorylated by PKA at Ser342 in a Rab32-dependent manner. Critically, blocking phosphorylation at OPTN Ser342 leads to Golgi fragmentation, and a phospho-mimetic version of OPTN rescues Golgi defects induced by Rab32 L188P. Finally, Rab32 AKAP function and OPTN phosphorylation are required for Golgi repositioning during cell migration, contributing to tumor cell invasion. Together, these data reveal a role for Rab32 in regulating Golgi dynamics through PKA-mediated phosphorylation of OPTN.

Mitophagy in Neurons: Mechanisms Regulating Mitochondrial Turnover and Neuronal Homeostasis

Mitochondrial quality control is instrumental in regulating neuronal health and survival. The receptor-mediated clearance of damaged mitochondria by autophagy, known as mitophagy, plays a key role in controlling mitochondrial homeostasis. Mutations in genes that regulate mitophagy are causative for familial forms of neurological disorders including Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). PINK1/Parkin-dependent mitophagy is the best studied mitophagy pathway, while more recent work has brought to light additional mitochondrial quality control mechanisms that operate either in parallel to or independent of PINK1/Parkin mitophagy. Here, we discuss our current understanding of mitophagy mechanisms operating in neurons to govern mitochondrial homeostasis. We also summarize progress in our understanding of the links between mitophagic dysfunction and neurodegeneration, and highlight the potential for therapeutic interventions to maintain mitochondrial health and neuronal function.

Miro1- a key player in β-cell function and mitochondrial dynamics under diabetes mellitus

Mitochondrial health is crucial for the survival and function of β-cells, preserving glucose homeostasis and effective insulin production. Miro1, a mitochondrial Rho GTPase1 protein, plays an essential role in maintaining thequality of mitochondria by regulating calcium homeostasis and mitophagy. In this review, we aim to explore the dysfunction of Miro1 in type 2 diabetes mellitus (T2DM) and its contribution to impaired Ca2+ signaling, which increases oxidative stress in β-cells. This dysfunction is the hallmark of T2DM pathogenesis, leading to insufficient insulin production and poor glycemic control. Additionally, we discuss the role of Miro1 in modulating insulin secretion and inflammation, highlighting its effect on modulating key signaling cascades in β-cells. Altogether, enhancing Miro1 function and activity could alleviate mitochondrial dysfunction, reducing oxidative stress-mediated damage, and improving pancreatic β-cell survival. Targeting Miro1 with small molecules or gene-editing approaches could provide effective strategies for restoring cell function and insulin secretion in diabetic individuals. Exploring the deeper knowledge of Miro1 functions and interactions could lead to novel therapeutic advances in T2DM management.

Amyotrophic Lateral Sclerosis: Focus on Cytoplasmic Trafficking and Proteostasis

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal motor neuron disease characterized by the pathological loss of upper and lower motor neurons. Whereas most ALS cases are caused by a combination of environmental factors and genetic susceptibility, in a relatively small proportion of cases, the disorder results from mutations in genes that are inherited. Defects in several different cellular mechanisms and processes contribute to the selective loss of motor neurons (MNs) in ALS. Prominent among these is the accumulation of aggregates of misfolded proteins or peptides which are toxic to motor neurons. These accumulating aggregates stress the ability of the endoplasmic reticulum (ER) to function normally, cause defects in the transport of proteins between the ER and Golgi, and impair the transport of RNA, proteins, and organelles, such as mitochondria, within axons and dendrites, all of which contribute to the degeneration of MNs. Although dysfunction of a variety of cellular processes combines towards the pathogenesis of ALS, in this review, we focus on recent advances concerning the involvement of defective ER stress, vesicular transport between the ER and Golgi, and axonal transport.

Targeting mitophagy in neurodegenerative diseases

Mitochondrial dysfunction is a hallmark of idiopathic neurodegenerative diseases, including Parkinson disease, amyotrophic lateral sclerosis, Alzheimer disease and Huntington disease. Familial forms of Parkinson disease and amyotrophic lateral sclerosis are often characterized by mutations in genes associated with mitophagy deficits. Therefore, enhancing the mitophagy pathway may represent a novel therapeutic approach to targeting an underlying pathogenic cause of neurodegenerative diseases, with the potential to deliver neuroprotection and disease modification, which is an important unmet need. Accumulating genetic, molecular and preclinical model-based evidence now supports targeting mitophagy in neurodegenerative diseases. Despite clinical development challenges, small-molecule-based approaches for selective mitophagy enhancement - namely, USP30 inhibitors and PINK1 activators - are entering phase I clinical trials for the first time.

Region-specific mitophagy in nucleus pulposus, annulus fibrosus, and cartilage endplate of intervertebral disc degeneration: mechanisms and therapeutic strategies

Intervertebral disc degeneration (IVDD) is a prevalent condition contributing to various spinal disorders, posing a significant global health burden. Mitophagy plays a crucial role in maintaining mitochondrial quantity and quality and is closely associated with the onset and progression of IVDD. Well-documented region-specific mitophagy mechanisms in IVDD are guiding the development of therapeutic strategies. In the nucleus pulposus (NP), impaired mitochondria lead to apoptosis, oxidative stress, senescence, extracellular matrix degradation and synthesis, excessive autophagy, inflammation, mitochondrial instability, and pyroptosis, with key regulatory targets including AMPK, PGC-1α, SIRT1, SIRT3, Progerin, p65, Mfn2, FOXO3, NDUFA4L2, SLC39A7, ITGα5/β1, Nrf2, and NLRP3 inflammasome. In the annulus fibrosus (AF), mitochondrial damage induces apoptosis and oxidative stress mediated by PGC-1α, while in the cartilage endplate (CEP), mitochondrial dysfunction similarly triggers apoptosis and oxidative stress. These mechanistic insights highlight therapeutic strategies such as activating Parkin-dependent and Ub-independent mitophagy pathways for NP, enhancing Parkin-dependent mitophagy for AF, and targeting Parkin-mediated mitophagy for CEP. These strategies include the use of natural ingredients, hormonal modulation, gene editing technologies, targeted compounds, and manipulation of related proteins. This review summarizes the mechanisms of mitophagy in different regions of the intervertebral disc and highlights therapeutic approaches using mitophagy modulators to ameliorate IVDD. It discusses the complex mechanisms of mitophagy and underscores its potential as a therapeutic target. The objective is to provide valuable insights and a scientific basis for the development of mitochondrial-targeted drugs for anti-IVDD.

Fam163a knockdown and mitochondrial stress in the arcuate nucleus of hypothalamus reduce AgRP neuron activity and differentially regulate mitochondrial dynamics in mice

AIM

Mitochondria play key roles in neuronal activity, particularly in modulating agouti-related protein (AgRP) and proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARC), which regulates food intake. FAM163A, a newly identified protein, is suggested to be part of the mitochondrial proteome, though its functions remain largely unknown. This study aimed to investigate the effects of Fam163a knockdown and mitochondrial dysfunction on food intake, AgRP neuron activity, and mitochondrial function in the hypothalamus.

METHODS

Male C57BL/6 and AgRP-Cre mice received intracranial injections of either Fam163a shRNA, rotenone, or appropriate controls. Behavioral assessments included food intake, locomotor activity, and anxiety-like behaviors. qRT-PCR was used to quantify the expression of the genes related to food intake, mitochondrial biogenesis, dynamics, and oxidative stress. Blood glucose, serum insulin, and leptin levels were measured. Electrophysiological patch-clamp recordings were used to assess the AgRP neuronal activity.

RESULTS

Fam163a knockdown in the ARC increased the cumulative food intake in short term (first 7 days) without altering the 25-day food intake and significantly increased the Pomc mRNA expression. Fam163a silencing significantly reduced leptin levels. Both Fam163a knockdown and rotenone significantly reduced the firing frequency of AgRP neurons. Neither Fam163a silencing nor rotenone altered locomotor or anxiety-like behaviors. Fam163a knockdown and rotenone differentially altered the expression of mitochondrial biogenesis-, mitophagy-, fusion-, and oxidative stress-related genes.

CONCLUSION

Hypothalamic FAM163A may play a role in modulating AgRP neuronal activity through regulating mitochondrial biogenesis, dynamics, and redox state. These findings provide insights into the role of FAM163A and mitochondrial stress in the central regulation of metabolism.

In situ cryo-ET visualization of mitochondrial depolarization and mitophagic engulfment

Defective mitochondrial quality control in response to loss of mitochondrial membrane polarization is implicated in Parkinson's disease by mutations in PINK1 and PRKN. Application of in situ cryo-electron tomography (cryo-ET) made it possible to visualize the consequences of mitochondrial depolarization at higher resolution than heretofore attainable. Parkin-expressing U2OS cells were treated with the depolarizing agents oligomycin and antimycin A (OA), subjected to cryo-FIB milling, and mitochondrial structure was characterized by in situ cryo-ET. Phagophores were visualized in association with mitochondrial fragments. Bridge-like lipid transporter (BLTP) densities potentially corresponding to ATG2A were seen connected to mitophagic phagophores. Mitochondria in OA-treated cells were fragmented and devoid of matrix calcium phosphate crystals. The intermembrane gap of cristae was narrowed and the intermembrane volume reduced, and some fragments were devoid of cristae. A subpopulation of ATP synthases re-localized from cristae to the inner boundary membrane (IBM) apposed to the outer membrane (OMM). The structure of the dome-shaped prohibitin complex, a dodecamer of PHB1-PHB2 dimers, was determined in situ by sub-tomogram averaging in untreated and treated cells and found to exist in open and closed conformations, with the closed conformation is enriched by OA treatment. These findings provide a set of native snapshots of the manifold nano-structural consequences of mitochondrial depolarization and provide a baseline for future in situ dissection of Parkin-dependent mitophagy.

Mitochondria transplantation transiently rescues cerebellar neurodegeneration improving mitochondrial function and reducing mitophagy in mice

Cerebellar ataxia is the primary manifestation of cerebellar degenerative diseases, and mitochondrial dysfunction in Purkinje cells (PCs) plays a critical role in disease progression. In this study, we investigated the feasibility of mitochondria transplantation as a potential therapeutic approach to rescue cerebellar neurodegeneration and elucidate the associated mechanisms. We constructed a conditional Drp1 knockout model in PCs (PCKO mice), characterized by progressive ataxia. Drp1 knockout resulted in pervasive and progressive apoptosis of PCs and significant activation of surrounding glial cells. Mitochondrial dysfunction, which triggers mitophagy, is a key pathogenic factor contributing to morphological and functional damage in PCs. Transplanting liver-derived mitochondria into the cerebellum of 1-month-old PCKO mice improved mitochondrial function, reduced mitophagy, delayed apoptosis of PCs, and alleviated cerebellar ataxia for up to 3 weeks. These findings demonstrate that mitochondria transplantation holds promise as a therapeutic approach for cerebellar degenerative diseases.

Proteomic profiling uncovers sexual dimorphism in the muscle response to wheel running exercise in the FLExDUX4 murine model of facioscapulohumeral muscular dystrophy

FLExDUX4 is a murine experimental model of facioscapulohumeral muscular dystrophy (FSHD) characterized by chronic, low levels of leaky expression of the human full-length double homeobox 4 gene (DUX4-fl). FLExDUX4 mice exhibit mild pathologies and functional deficits similar to people affected by FSHD. Proteomic studies in FSHD could offer new insights into disease mechanisms underpinned by post-transcriptional processes. We used mass spectrometry-based proteomics to quantify the abundance of 1322 proteins in triceps brachii muscle, encompassing both male and female mice in control and free voluntary wheel running (VWR) in Wild-type (n=3) and FLExDUX4 (n=3) genotypes. We report the triceps brachii proteome of FLExDUX4 mice recapitulates key skeletal muscle clinical characteristics of human FSHD, including alterations to mitochondria, RNA metabolism, oxidative stress, and apoptosis. RNA-binding proteins exhibit a sex-specific difference in FLExDUX4 mice. Sexual dimorphism of mitochondrial protein adaptation to exercise was uncovered specifically in FLExDUX4 mice, where females increased, but males decreased mitochondrial proteins after a 6-week of VWR. Our results highlight the importance of identifying sex-specific diagnostic biomarkers to enable more reliable monitoring of FSHD therapeutic targets. Our data provides a resource for the FSHD research community to explore the burgeoning aspect of sexual dimorphism in FSHD.

The Role of Autophagy in Excitotoxicity, Synaptic Mitochondrial Stress and Neurodegeneration

Brain and nervous system functions depend upon maintaining the integrity of synaptic structures over the lifetime. Autophagy, a key homeostatic quality control system, plays a central role not only in neuronal development and survival/cell death, but also in regulating synaptic activity and plasticity. Glutamate is the major excitatory neurotransmitter that activates downstream targets, with a key role in learning and memory. However, an excess of glutamatergic stimulation is pathological in stroke, epilepsy and neurodegeneration, triggering excitotoxic cell death or a sublethal process of excitatory mitochondrial calcium toxicity (EMT) that triggers dendritic retraction. Markers of autophagy and mitophagy are often elevated following excitatory neuronal injuries, with the potential to influence cell death or neurodegenerative outcomes of these injuries. Interestingly, leucine-rich repeat kinase 2 (LRRK2) and PTEN-induced kinase 1 (PINK1), two kinases linked to autophagy, mitophagy and Parkinson disease, play important roles in regulating mitochondrial calcium handling, synaptic density and function, and maturation of dendritic spines. Mutations in LRRK2, PINK1, or proteins linked to Alzheimer's disease perturb mitochondrial calcium handling to sensitize neurons to excitatory injury. While autophagy and mitophagy can play both protective and harmful roles, studies in various excitotoxicity and stroke models often implicate autophagy in a pathogenic role. Understanding the role of autophagic degradation in regulating synaptic loss and cell death following excitatory neuronal injuries has important therapeutic implications for both acute and chronic neurological disorders.

Phosphorylation of optineurin by TBK1 drives fragmentation of Golgi apparatus

Optineurin (OPTN) is a multifunctional adaptor protein involved in various cellular processes. One critical function is maintaining the Golgi complex, as OPTN depletion or its disease-associated mutations leads to Golgi fragmentation. On the other hand, OPTN is known to be phosphorylated by TBK1 to regulate specific cellular processes; however, its role in Golgi regulation remains unclear. Here, we show that expression of a phosphomimetic OPTN mutant, S177E, but not its phospho-deficient mutant, S177A, in HeLa cells effectively results in fragmentation of the Golgi apparatus. Although the effect of S177E appears similar to that of disease-associated OPTN mutations such as E50K, experiments using OPTN double mutants suggest that S177E induces Golgi fragmentation possibly through an E50K-independent pathway. Furthermore, we found that Ser177 phosphorylation in OPTN is enhanced by TBK1, and co-expression of TBK1 with wild-type OPTN induces Golgi fragmentation. Notably, Ser177 phosphorylation leads to the formation of cytoplasmic OPTN puncta, correlating with Golgi fragmentation. Taken together, our data suggest that OPTN phosphorylation by TBK1 induces ectopic OPTN accumulation, leading to Golgi disassembly, possibly via a novel pathway distinct from those associated with disease-related OPTN mutations.

Molecular aspects of cytoprotection by Optineurin during stress and disease

Optineurin/OPTN is an adapter protein that plays a crucial role in mediating many cellular functions, including autophagy, vesicle trafficking, and various signalling pathways. Mutations of OPTN are linked with neurodegenerative disorders, glaucoma, and amyotrophic lateral sclerosis (ALS). Recent work has shown that OPTN provides cytoprotection from many types of stress, including oxidative stress, endoplasmic reticulum stress, protein homeostasis stress, tumour necrosis factor α, and microbial infection. Here, we discuss the mechanisms involved in cytoprotective functions of OPTN, which possibly depend on its ability to modulate various stress-induced signalling pathways. ALS- and glaucoma-causing mutants of OPTN are altered in this regulation, which may affect cell survival, particularly under various stress conditions. We suggest that OPTN deficiency created by mutations may cooperate with stress-induced signalling to enhance or cause neurodegeneration. Other functions of OPTN, such as neurotrophin secretion and vesicle trafficking, may also contribute to cytoprotection.

Optineurin-facilitated axonal mitochondria delivery promotes neuroprotection and axon regeneration

Optineurin (OPTN) mutations are linked to amyotrophic lateral sclerosis (ALS) and normal tension glaucoma (NTG), but a relevant animal model is lacking, and the molecular mechanisms underlying neurodegeneration are unknown. We find that OPTN C-terminus truncation (OPTN∆C) causes late-onset neurodegeneration of retinal ganglion cells (RGCs), optic nerve (ON), and spinal cord motor neurons, preceded by a decrease of axonal mitochondria in mice. We discover that OPTN directly interacts with both microtubules and the mitochondrial transport complex TRAK1/KIF5B, stabilizing them for proper anterograde axonal mitochondrial transport, in a C-terminus dependent manner. Furthermore, overexpressing OPTN/TRAK1/KIF5B prevents not only OPTN truncation-induced, but also ocular hypertension-induced neurodegeneration, and promotes robust ON regeneration. Therefore, in addition to generating animal models for NTG and ALS, our results establish OPTN as a facilitator of the microtubule-dependent mitochondrial transport necessary for adequate axonal mitochondria delivery, and its loss as the likely molecular mechanism of neurodegeneration.

Novel reporter of the PINK1-Parkin mitophagy pathway identifies its damage sensor in the import gate

Damaged mitochondria can be cleared from the cell by mitophagy, using a pathway formed by the recessive Parkinson's disease genes PINK1 and Parkin. How mitochondrial damage is sensed by the PINK1-Parkin pathway, however, remains uncertain. Here, using a Parkin substrate-based reporter in genome-wide screens, we identified that diverse forms of mitochondrial damage converge on loss of mitochondrial membrane potential (MMP) to activate PINK1. Consistently, the MMP but not the presequence translocase-associated motor (PAM) import motor provided the essential driving force for endogenous PINK1 import through the inner membrane translocase TIM23. In the absence of TIM23, PINK1 arrested in the translocase of the outer membrane (TOM) during import. The energy-state outside of the mitochondria further modulated the pathway by controlling the rate of new PINK1 synthesis. Our results identify separation of PINK1 from TOM by the MMP, as the key damage-sensing switch in the PINK1-Parkin mitophagy pathway.

Highlights

MFN2-Halo is a quantitative single-cell reporter of PINK1-Parkin activation.Diverse forms of mitochondrial damage, identified in whole-genome screens, activate the PINK1-Parkin pathway by disrupting the mitochondrial membrane potential (MMP).The primary driving force for endogenous PINK1 import through the TIM23 translocase is the MMP with the PAM import motor playing a supporting role.Loss of TIM23 is sufficient to stabilize PINK1 in the TOM complex and activate Parkin.

Magnetic control of membrane damage in early endosomes using internalized magnetic nanoparticles

Membrane stiffness is essential for cell migration, tumorigenesis, and development; however, the physical properties of intracellular membrane are poorly characterized. In this study, we internalized 20 nm magnetic nanoparticles (MNPs) into MCF7 human breast cancer cells and applied a magnetic field. We investigated whether magnetic field could induce membrane damage of the early endosomes by analyzing the colocalization of MNPs with galectin 3 (Gal3), a cytosolic protein recruited to the lumen of damaged organelles. We first tried to apply magnetic field by electromagnet, and found a direct-current (DC) magnetic field for five minutes increased the colocalization of the MNPs with Gal3, suggesting that the magnetic field damaged the endosomal membrane. We used a neodymium magnet to apply longer and stronger static magnetic fields. The static magnetic field more than 50 mT for five minutes started to damage endosomes, while 100 mT was the most effective. Longer exposure or higher magnetic field strengths did not induce further membrane damage. We confirmed that a Gal3 positive compartment was also positive for the early endosome marker, EEA1, suggesting that the external magnetic field induced membrane damage in the early endosomes. Our results indicate that a static magnetic field can control the membrane damage in early endosomes using internalized MNPs.Key words: magnetic nanoparticles, endosomes, membrane damage, organelle.

Diverse routes to mitophagy governed by ubiquitylation and mitochondrial import

The selective removal of mitochondria by mitophagy proceeds via multiple mechanisms and is essential for human well-being. The PINK1/Parkin and NIX/BNIP3 pathways are strongly linked to mitochondrial dysfunction and hypoxia, respectively. Both are regulated by ubiquitylation and mitochondrial import. Recent studies have elucidated how the ubiquitin kinase PINK1 acts as a sensor of mitochondrial import stress through stable interaction with a mitochondrial import supercomplex. The stability of BNIP3 and NIX is regulated by the SCFFBXL4 ubiquitin ligase complex. Substrate recognition requires an adaptor molecule, PPTC7, whose availability is limited by mitochondrial import. Unravelling the functional implications of each mode of mitophagy remains a critical challenge. We propose that mitochondrial import stress prompts a switch between these two pathways.

Calcium-mediated regulation of mitophagy: implications in neurodegenerative diseases

Calcium signaling plays a pivotal role in diverse cellular processes through precise spatiotemporal regulation and interaction with effector proteins across distinct subcellular compartments. Mitochondria, in particular, act as central hubs for calcium buffering, orchestrating energy production, redox balance and apoptotic signaling, among others. While controlled mitochondrial calcium uptake supports ATP synthesis and metabolic regulation, excessive accumulation can trigger oxidative stress, mitochondrial membrane permeabilization, and cell death. Emerging findings underscore the intricate interplay between calcium homeostasis and mitophagy, a selective type of autophagy for mitochondria elimination. Although the literature is still emerging, this review delves into the bidirectional relationship between calcium signaling and mitophagy pathways, providing compelling mechanistic insights. Furthermore, we discuss how disruptions in calcium homeostasis impair mitophagy, contributing to mitochondrial dysfunction and the pathogenesis of common neurodegenerative diseases.

Targeting common disease pathomechanisms to treat amyotrophic lateral sclerosis

The motor neuron disease amyotrophic lateral sclerosis (ALS) is a devastating condition with limited treatment options. The past few years have witnessed a ramping up of translational ALS research, offering the prospect of disease-modifying therapies. Although breakthroughs using gene-targeted approaches have shown potential to treat patients with specific disease-causing mutations, the applicability of such therapies remains restricted to a minority of individuals. Therapies targeting more general mechanisms that underlie motor neuron pathology in ALS are therefore of considerable interest. ALS pathology is associated with disruption to a complex array of key cellular pathways, including RNA processing, proteostasis, metabolism and inflammation. This Review details attempts to restore cellular homeostasis by targeting these pathways in order to develop effective, broadly-applicable ALS therapeutics.

Autophagic signatures in peripheral blood mononuclear cells from Parkinson's disease patients

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor impairments and the accumulation of misfolded α-synuclein. Dysregulation of the autophagy-lysosomal pathway (ALP), responsible for degrading misfolded proteins, has been implicated in PD pathogenesis. However, current diagnostic approaches rely heavily on motor symptoms, which occur due to substantial neurodegeneration, limiting early detection and intervention. This study investigated the potential of ALP-associated proteins in peripheral blood mononuclear cells (PBMCs) as diagnostic biomarkers for early-stage PD. Quantitative analysis revealed a significant reduction in optineurin levels in PBMCs from PD patients, and the expression levels of various ALP-associated proteins were tightly correlated, suggesting a coordinated dysregulation of the pathway. Correlation analyses revealed associations between ALP-associated features and clinical characteristics, such as age of onset and motor impairment. Furthermore, the study identified multiple positive correlations among ALP-associated proteins and functional readouts, highlighting the interconnectivity within the pathway. Notably, a PBMC biomarker model incorporating lysosomal-associated membrane protein 1 and optineurin exhibited high diagnostic accuracy (86%) in distinguishing PD patients from controls. These findings highlight the potential of ALP-associated protein signatures in PBMCs as novel diagnostic biomarkers for early detection and intervention in PD, offering insights into the systemic manifestations of the disease.

Oxidative stress of mitophagy in neurodegenerative diseases: Mechanism and potential therapeutic targets

Neurodegenerative diseases are now significant chronic progressive neurological conditions that affect individuals' physical health. Oxidative stress is crucial in the development of these diseases. Among the various neurodegenerative diseases, mitochondrial damage has become a major factor in oxidative stress and disease advancement. During this process, oxidative stress and mitophagy plays an important role. In this paper, we introduced the role of mitophagy and oxidative stress in detail, and expounded the relationship between them. In addition, we summarized the pathogenesis of some neurodegenerative diseases and the mechanism of three antioxidants. The former includes AD, PD, HD and ALS, while the latter includes carnosine, adiponectin and resveratrol. Provide goals and directions for further research and treatment of neurodegenerative diseases. This review summarizes the impact of oxidative stress on neurodegenerative diseases by regulating mitophagy, provides a deeper understanding of their pathological mechanisms, and suggests potential new therapeutic targets.

Mitochondrial Dysfunction in Neurodegenerative Diseases: Mechanisms and Corresponding Therapeutic Strategies

Neurodegenerative disease (ND) refers to the progressive loss and morphological abnormalities of neurons in the central nervous system (CNS) or peripheral nervous system (PNS). Examples of neurodegenerative diseases include Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Recent studies have shown that mitochondria play a broad role in cell signaling, immune response, and metabolic regulation. For example, mitochondrial dysfunction is closely associated with the onset and progression of a variety of diseases, including ND, cardiovascular diseases, diabetes, and cancer. The dysfunction of energy metabolism, imbalance of mitochondrial dynamics, or abnormal mitophagy can lead to the imbalance of mitochondrial homeostasis, which can induce pathological reactions such as oxidative stress, apoptosis, and inflammation, damage the nervous system, and participate in the occurrence and development of degenerative nervous system diseases such as AD, PD, and ALS. In this paper, the latest research progress of this subject is detailed. The mechanisms of oxidative stress, mitochondrial homeostasis, and mitophagy-mediated ND are reviewed from the perspectives of β-amyloid (Aβ) accumulation, dopamine neuron damage, and superoxide dismutase 1 (SOD1) mutation. Based on the mechanism research, new ideas and methods for the treatment and prevention of ND are proposed.

Autophagy, aging, and age-related neurodegeneration

Autophagy is a conserved mechanism that degrades damaged or superfluous cellular contents and enables nutrient recycling under starvation conditions. Many neurodegeneration-associated proteins are autophagy substrates, and autophagy upregulation ameliorates disease in many animal models of neurodegeneration by enhancing the clearance of toxic proteins, proinflammatory molecules, and dysfunctional organelles. Autophagy inhibition also induces neuronal and glial senescence, a phenomenon that occurs with increasing age in non-diseased brains as well as in response to neurodegeneration-associated stresses. However, aging and many neurodegeneration-associated proteins and mutations impair autophagy. This creates a potentially detrimental feedback loop whereby the accumulation of these disease-associated proteins impairs their autophagic clearance, facilitating their further accumulation and aggregation. Thus, understanding how autophagy interacts with aging, senescence, and neurodegenerative diseases in a temporal, cellular, and genetic context is important for the future clinical application of autophagy-modulating therapies in aging and neurodegeneration.

A Multi-Omics Analysis of a Mitophagy-Related Signature in Pan-Cancer

Mitophagy, an essential process within cellular autophagy, has a critical role in regulating key cellular functions such as reproduction, metabolism, and apoptosis. Its involvement in tumor development is complex and influenced by the cellular environment. Here, we conduct a comprehensive analysis of a mitophagy-related gene signature, composed of PRKN, PINK1, MAP1LC3A, SRC, BNIP3L, BECN1, and OPTN, across various cancer types, revealing significant differential expression patterns associated with molecular subtypes, stages, and patient outcomes. Pathway analysis revealed a complex interplay between the expression of the signature and potential effects on the activity of various cancer-related pathways in pan-cancer. Immune infiltration analysis linked the mitophagy signature with certain immune cell types, particularly OPTN with immune infiltration in melanoma. Methylation patterns correlated with gene expression and immune infiltration. Mutation analysis also showed frequent alterations in PRKN (34%), OPTN (21%), PINK1 (28%), and SRC (15%), with implications for the tumor microenvironment. We also found various correlations between the expression of the mitophagy-related genes and sensitivity in different drugs, suggesting that targeting this signature could improve therapy efficacy. Overall, our findings underscore the importance of mitophagy in cancer biology and drug resistance, as well as its potential for informing treatment strategies.

Molecular Symphony of Mitophagy: Ubiquitin-Specific Protease-30 as a Maestro for Precision Management of Neurodegenerative Diseases

INTRODUCTION

Mitochondrial dysfunction stands as a pivotal feature in neurodegenerative disorders, spurring the quest for targeted therapeutic interventions. This review examines Ubiquitin-Specific Protease 30 (USP30) as a master regulator of mitophagy with therapeutic promise in Alzheimer's disease (AD) and Parkinson's disease (PD). USP30's orchestration of mitophagy pathways, encompassing PINK1-dependent and PINK1-independent mechanisms, forms the crux of this exploration.

METHOD

A systematic literature search was conducted in PubMed, Scopus, and Web of Science, selecting studies that investigated USP's function, inhibitor design, or therapeutic efficacy in AD and PD. Inclusion criteria encompassed mechanistic and preclinical/clinical data, while irrelevant or duplicate references were excluded. Extracted findings were synthesized narratively.

RESULTS

USP30 modulates interactions with translocase of outer mitochondrial membrane (TOM) 20, mitochondrial E3 ubiquitin protein ligase 1 (MUL1), and Parkin, thus harmonizing mitochondrial quality control. Emerging novel USP30 inhibitors, racemic phenylalanine derivatives, N-cyano pyrrolidine, and notably, benzosulphonamide class compounds, restore mitophagy, and reduce neurodegenerative phenotypes across diverse models with minimal off-target effects. Modulation of other USPs also influences neurodegenerative disease pathways, offering additional therapeutic avenues.

CONCLUSIONS

In highlighting the nuanced regulation of mitophagy by USP30, this work heralds a shift toward more precise and effective treatments, paving the way for a new era in the clinical management of neurodegenerative disorders.

Adaptor-Mediated Trafficking of Tank Binding Kinase 1 During Diverse Cellular Processes

The serine/threonine kinase, Tank Binding Kinase 1 (TBK1), drives distinct cellular processes like innate immune signaling, selective autophagy, and mitosis. It is suggested that the translocation and activation of TBK1 at different subcellular locations within the cell, downstream of diverse stimuli, are driven by TBK1 adaptor proteins forming a complex directly or indirectly with TBK1. Various TBK1 adaptors and associated proteins like NAP1, TANK, SINTBAD, p62, optineurin (OPTN), TAX1BP1, STING, and NDP52 have been identified in facilitating TBK1 activation and recruitment with varying overlapping redundancy. This review focuses on what is known about these proteins, their interactions with TBK1, and the functional consequences of these associations. We shed light on underexplored areas of research on these TBK1 binding partners while emphasizing how future research is required to understand the function and flexibility of TBK1 signaling and crosstalk or regulation between different biological processes.

The autophagy-lysosome pathway: a potential target in the chemical and gene therapeutic strategies for Parkinson's disease

Parkinson's disease is a common neurodegenerative disease with movement disorders associated with the intracytoplasmic deposition of aggregate proteins such as α-synuclein in neurons. As one of the major intracellular degradation pathways, the autophagy-lysosome pathway plays an important role in eliminating these proteins. Accumulating evidence has shown that upregulation of the autophagy-lysosome pathway may contribute to the clearance of α-synuclein aggregates and protect against degeneration of dopaminergic neurons in Parkinson's disease. Moreover, multiple genes associated with the pathogenesis of Parkinson's disease are intimately linked to alterations in the autophagy-lysosome pathway. Thus, this pathway appears to be a promising therapeutic target for treatment of Parkinson's disease. In this review, we briefly introduce the machinery of autophagy. Then, we provide a description of the effects of Parkinson's disease-related genes on the autophagy-lysosome pathway. Finally, we highlight the potential chemical and genetic therapeutic strategies targeting the autophagy-lysosome pathway and their applications in Parkinson's disease.

Phosphorylation of Optineurin by protein kinase D regulates Parkin-dependent mitophagy

Degradation of damaged mitochondria, a process called mitophagy, plays a role in mitochondrial quality control and its dysfunction has been linked to neurodegenerative pathologies. The PINK1 kinase and the ubiquitin ligase Parkin-mediated mitophagy represents the most common pathway in which specific receptors, including Optineurin (Optn), target ubiquitin-labeled mitochondria to autophagosomes. Here, we show that Protein Kinases D (PKD) are activated and recruited to damaged mitochondria. Subsequently, PKD phosphorylate Optn to promote a complex with Parkin leading to enhancement of its ubiquitin ligase activity. Paradoxically, inhibiting PKD activity enhances the interaction between Optn and LC3, promotes the recruitment of Parkin to mitochondria, and increases the mitophagic function of Optn. This enhancement of mitophagy is characterized by increased production of mitochondrial ROS and a reduction in mitochondrial mass. The PKD kinases may therefore regulate Optn-dependent mitophagy by amplifying the Parkin-mediated degradation signals to improve the cell response against oxidative stress damage.

Preserving mitochondrial homeostasis protects against drug-induced liver injury via inducing OPTN (optineurin)-dependent Mitophagy

Disruption of mitochondrial function is observed in multiple drug-induced liver injuries (DILIs), a significant global health threat. However, how the mitochondrial dysfunction occurs and whether maintain mitochondrial homeostasis is beneficial for DILIs remains unclear. Here, we show that defective mitophagy by OPTN (optineurin) ablation causes disrupted mitochondrial homeostasis and aggravates hepatocytes necrosis in DILIs, while OPTN overexpression protects against DILI depending on its mitophagic function. Notably, mass spectrometry analysis identifies a new mitochondrial substrate, GCDH (glutaryl-CoA dehydrogenase), which can be selectively recruited by OPTN for mitophagic degradation, and a new cofactor, VCP (valosin containing protein) that interacts with OPTN to stabilize BECN1 during phagophore assembly, thus boosting OPTN-mediated mitophagy initiation to clear damaged mitochondria and preserve mitochondrial homeostasis in DILIs. Then, the accumulation of OPTN in different DILIs is further validated with a protective effect, and pyridoxine is screened and established to alleviate DILIs by inducing OPTN-mediated mitophagy. Collectively, our findings uncover a dual role of OPTN in mitophagy initiation and implicate the preservation of mitochondrial homeostasis via inducing OPTN-mediated mitophagy as a potential therapeutic approach for DILIs.Abbreviation: AILI: acetaminophen-induced liver injury; ALS: amyotrophic lateral sclerosis; APAP: acetaminophen; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CHX: cycloheximide; Co-IP: co-immunoprecipitation; DILI: drug-induced liver injury; FL: full length; GCDH: glutaryl-CoA dehydrogenase; GOT1/AST: glutamic-oxaloacetic transaminase 1; GO: gene ontology; GSEA: gene set enrichment analysis; GPT/ALT: glutamic - pyruvic transaminase; INH: isoniazid; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MMP: mitochondrial membrane potential; MST: microscale thermophoresis; MT-CO2/COX-II: mitochondrially encoded cytochrome c oxidase II; OPTN: optineurin; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; TIMM23: translocase of inner mitochondrial membrane 23; TOMM20: translocase of outer mitochondrial membrane 20; TSN: toosendanin; VCP: valosin containing protein, WIPI2: WD repeat domain, phosphoinositide interacting 2.

Mitophagy and its regulatory mechanisms in the biological effects of nanomaterials

Mitophagy is a selective cellular process critical for the removal of damaged mitochondria. It is essential in regulating mitochondrial number, ensuring mitochondrial functionality, and maintaining cellular equilibrium, ultimately influencing cell destiny. Numerous pathologies, such as neurodegenerative diseases, cardiovascular disorders, cancers, and various other conditions, are associated with mitochondrial dysfunctions. Thus, a detailed exploration of the regulatory mechanisms of mitophagy is pivotal for enhancing our understanding and for the discovery of novel preventive and therapeutic options for these diseases. Nanomaterials have become integral in biomedicine and various other sectors, offering advanced solutions for medical uses including biological imaging, drug delivery, and disease diagnostics and therapy. Mitophagy is vital in managing the cellular effects elicited by nanomaterials. This review provides a comprehensive analysis of the molecular mechanisms underpinning mitophagy, underscoring its significant influence on the biological responses of cells to nanomaterials. Nanoparticles can initiate mitophagy via various pathways, among which the PINK1-Parkin pathway is critical for cellular defense against nanomaterial-induced damage by promoting mitophagy. The role of mitophagy in biological effects was induced by nanomaterials, which are associated with alterations in Ca2+ levels, the production of reactive oxygen species, endoplasmic reticulum stress, and lysosomal damage.

Therapeutic potential of Parkin and its regulation in Parkinson's disease

Parkinson's disease (PD) is a debilitating neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the midbrain substantia nigra, resulting in motor and non-motor symptoms. While the exact etiology of PD remains elusive, a growing body of evidence suggests that dysfunction in the parkin protein plays a pivotal role in the pathogenesis of the disease. Parkin is an E3 ubiquitin ligase that ubiquitinates substrate proteins to control a number of crucial cellular processes including protein catabolism, immune response, and cellular apoptosis.While autosomal recessive mutations in the PARK2 gene, which codes for parkin, are linked to an inherited form of early-onset PD, heterozygous mutations in PARK2 have also been reported in the more commonly occurring sporadic PD cases. Impairment of parkin's E3 ligase activity is believed to play a pathogenic role in both familial and sporadic forms of PD.This article provides an overview of the current understanding of the mechanistic basis of parkin's E3 ligase activity, its major physiological role in controlling cellular functions, and how these are disrupted in familial and sporadic PD. The second half of the manuscript explores the currently available and potential therapeutic strategies targeting parkin structure and/or function in order to slow down or mitigate the progressive neurodegeneration in PD.

Calreticulin-driven autophagy enhances cell proliferation in laryngeal squamous cell carcinoma

BACKGROUND

Calreticulin (CALR) is a multifunctional calcium-binding protein. Recent studies have revealed that CALR contributes to tumor development and promotes cancer cell proliferation. However, how CALR affects the development of laryngeal squamous cell carcinoma (LSCC) remains mysterious. Thus, this study aimed to explore the effect of CALR on LSCC development and uncover its underlying mechanisms.

METHODS

CALR expression in LSCC cell lines and tissues was examined by qRT-PCR and western blot analysis and its functional role was detected via in vivo and in vitro assays. Cell proliferation was discriminated with CCK-8 and colony formation assays, while apoptosis was analyzed using flow cytometry. Autophagy levels were measured via LC3 immunofluorescence, and western blot assay was conducted to assess apoptosis- and autophagy-related proteins. Additionally, a mouse xenograft model was employed to determine the impact of CALR knockdown on tumor growth.

RESULTS

We found that CALR knockdown reduced LSCC cell viability and proliferation while enhancing apoptosis, whereas CALR overexpression showed opposite effects. In vivo experiments verified that CALR knockdown suppressed tumor growth. In addition, elevated CALR expression induced autophagy in LSCC cells, while autophagy inhibitor 3-MA (2.5 mM) reversed the anti-apoptosis effects of CALR overexpression.

CONCLUSION

Our study identifies CALR as an oncogene in LSCC, where it promotes tumor progression by inducing autophagy and inhibiting apoptosis. Targeting CALR or modulating autophagy may represent novel therapeutic strategies for LSCC.

Control of mitophagy initiation and progression by the TBK1 adaptors NAP1 and SINTBAD

Mitophagy preserves overall mitochondrial fitness by selectively targeting damaged mitochondria for degradation. The regulatory mechanisms that prevent PTEN-induced putative kinase 1 (PINK1) and E3 ubiquitin ligase Parkin (PINK1/Parkin)-dependent mitophagy and other selective autophagy pathways from overreacting while ensuring swift progression once initiated are largely elusive. Here, we demonstrate how the TBK1 (TANK-binding kinase 1) adaptors NAP1 (NAK-associated protein 1) and SINTBAD (similar to NAP1 TBK1 adaptor) restrict the initiation of OPTN (optineurin)-driven mitophagy by competing with OPTN for TBK1. Conversely, they promote the progression of nuclear dot protein 52 (NDP52)-driven mitophagy by recruiting TBK1 to NDP52 and stabilizing its interaction with FIP200. Notably, OPTN emerges as the primary recruiter of TBK1 during mitophagy initiation, which in return boosts NDP52-mediated mitophagy. Our results thus define NAP1 and SINTBAD as cargo receptor rheostats, elevating the threshold for mitophagy initiation by OPTN while promoting the progression of the pathway once set in motion by supporting NDP52. These findings shed light on the cellular strategy to prevent pathway hyperactivity while still ensuring efficient progression.

Age-related effects of optineurin deficiency in the mouse eye

Optineurin (OPTN) is a gene associated with familial normal tension glaucoma (NTG). While NTG involves intraocular pressure (IOP)-independent neurodegeneration of the visual pathway that progresses with age, how OPTN dysfunction leads to NTG remains unclear. Here, we generated an OPTN knockout mouse (Optn-/-) model to test the hypothesis that a loss-of-function mechanism induces structural and functional eye deterioration with aging. Eye anatomy, visual function, IOP, retinal histology, and retinal ganglion cell survival were compared to littermate wild-type (WT) control mice. Consistent with OPTN's role in NTG, loss of OPTN did not increase IOP or alter gross eye anatomy in young (2-3 months) or aged (12 months) mice. When retinal layers were quantitated, young Optn-/- mice had thinner retina in the peripheral regions than young WT mice, primarily due to thinner ganglion cell-inner plexiform layers. Despite this, visual function in Optn-/- mice was not severely impaired, even with aging. We also assessed relative abundance of retinal cell subtypes, including amacrine cells, bipolar cells, cone photoreceptors, microglia, and astrocytes. While many of these cellular subtypes were unaffected by Optn deletion, more dopaminergic amacrine cells were observed in aged Optn-/- mice. Taken together, our findings showed that complete loss of Optn resulted in mild retinal changes and less visual function impairment, supporting the possibility that OPTN-associated glaucoma does not result from a loss-of-function disease mechanism. Further research using these Optn mice will elucidate detailed molecular pathways involved in NTG and identify clinical or environmental risk factors that can be targeted for glaucoma treatment.

Autophagy adaptors mediate Parkin-dependent mitophagy by forming sheet-like liquid condensates

During PINK1- and Parkin-mediated mitophagy, autophagy adaptors are recruited to damaged mitochondria to promote their selective degradation. Autophagy adaptors such as optineurin (OPTN) and NDP52 facilitate mitophagy by recruiting the autophagy-initiation machinery, and assisting engulfment of damaged mitochondria through binding to ubiquitinated mitochondrial proteins and autophagosomal ATG8 family proteins. Here, we demonstrate that OPTN and NDP52 form sheet-like phase-separated condensates with liquid-like properties on the surface of ubiquitinated mitochondria. The dynamic and liquid-like nature of OPTN condensates is important for mitophagy activity, because reducing the fluidity of OPTN-ubiquitin condensates suppresses the recruitment of ATG9 vesicles and impairs mitophagy. Based on these results, we propose a dynamic liquid-like, rather than a stoichiometric, model of autophagy adaptors to explain the interactions between autophagic membranes (i.e., ATG9 vesicles and isolation membranes) and mitochondrial membranes during Parkin-mediated mitophagy. This model underscores the importance of liquid-liquid phase separation in facilitating membrane-membrane contacts, likely through the generation of capillary forces.

Acquisition of neurodegenerative features in isogenic OPTN(E50K) human stem cell-derived retinal ganglion cells associated with autophagy disruption and mTORC1 signaling reduction

The ability to derive retinal ganglion cells (RGCs) from human pluripotent stem cells (hPSCs) has led to numerous advances in the field of retinal research, with great potential for the use of hPSC-derived RGCs for studies of human retinal development, in vitro disease modeling, drug discovery, as well as their potential use for cell replacement therapeutics. Of all these possibilities, the use of hPSC-derived RGCs as a human-relevant platform for in vitro disease modeling has received the greatest attention, due to the translational relevance as well as the immediacy with which results may be obtained compared to more complex applications like cell replacement. While several studies to date have focused upon the use of hPSC-derived RGCs with genetic variants associated with glaucoma or other optic neuropathies, many of these have largely described cellular phenotypes with only limited advancement into exploring dysfunctional cellular pathways as a consequence of the disease-associated gene variants. Thus, to further advance this field of research, in the current study we leveraged an isogenic hPSC model with a glaucoma-associated mutation in the Optineurin (OPTN) protein, which plays a prominent role in autophagy. We identified an impairment of autophagic-lysosomal degradation and decreased mTORC1 signaling via activation of the stress sensor AMPK, along with subsequent neurodegeneration in OPTN(E50K) RGCs differentiated from hPSCs, and have further validated some of these findings in a mouse model of ocular hypertension. Pharmacological inhibition of mTORC1 in hPSC-derived RGCs recapitulated disease-related neurodegenerative phenotypes in otherwise healthy RGCs, while the mTOR-independent induction of autophagy reduced protein accumulation and restored neurite outgrowth in diseased OPTN(E50K) RGCs. Taken together, these results highlighted that autophagy disruption resulted in increased autophagic demand which was associated with downregulated signaling through mTORC1, contributing to the degeneration of RGCs.

Optineurin regulates motor and learning behaviors by affecting dopaminergic neuron survival in mice

Optineurin (OPTN) is an autophagy receptor that participates in the degradation of damaged mitochondria, protein aggregates, and invading pathogens. OPTN is closely related to various types of neurodegenerative diseases. However, the role of OPTN in the central nervous system is unclear. Here, we found that OPTN dysregulation in the compact part of substantia nigra (SNc) led to motor and learning deficits in animal models. Knockdown of OPTN increased total and phosphorylated α-synuclein levels which induced microglial activation and dopaminergic neuronal loss in the SNc. Overexpression of OPTN can't reverse the motor and learning phenotypes. Mechanistic analysis revealed that upregulation of OPTN increased α-synuclein phosphorylation independent of its autophagy receptor activity, which further resulted in microglial activation and dopaminergic neuronal loss similar to OPTN downregulation. Our study uncovers the crucial role of OPTN in maintaining dopaminergic neuron survival and motor and learning functions which are disrupted in PD patients.

The Integrated Stress Response Suppresses PINK1-dependent Mitophagy by Preserving Mitochondrial Import Efficiency

Mitophagy is crucial for maintaining mitochondrial health, but how its levels adjust to different stress conditions remains unclear. In this study, we investigated the role of the DELE1-HRI axis of integrated stress response (ISR) in regulating mitophagy, a key mitochondrial stress pathway. Our findings show that the ISR suppresses mitophagy under non-depolarizing mitochondrial stress by positively regulating mitochondrial protein import, independent of ATF4 activation. Mitochondrial protein import is regulated by the rate of protein synthesis under both depolarizing and non-depolarizing stress. Without ISR, increased protein synthesis overwhelms the mitochondrial import machinery, reducing its efficiency. Under depolarizing stress, mitochondrial import is heavily impaired even with active ISR, leading to significant PINK1 accumulation. In contrast, non-depolarizing stress allows more efficient protein import in the presence of ISR, resulting in lower mitophagy. Without ISR, mitochondrial protein import becomes severely compromised, causing PINK1 accumulation to reach the threshold necessary to trigger mitophagy. These findings reveal a novel link between ISR-regulated protein synthesis, mitochondrial import, and mitophagy, offering potential therapeutic targets for diseases associated with mitochondrial dysfunction.

Mitophagy in Cell Death Regulation: Insights into Mechanisms and Disease Implications

Mitophagy, a selective form of autophagy, plays a crucial role in maintaining optimal mitochondrial populations, normal function, and intracellular homeostasis by monitoring and removing damaged or excess mitochondria. Furthermore, mitophagy promotes mitochondrial degradation via the lysosomal pathway, and not only eliminates damaged mitochondria but also regulates programmed cell death-associated genes, thus preventing cell death. The interaction between mitophagy and various forms of cell death has recently gained increasing attention in relation to the pathogenesis of clinical diseases, such as cancers and osteoarthritis, neurodegenerative, cardiovascular, and renal diseases. However, despite the abundant literature on this subject, there is a lack of understanding regarding the interaction between mitophagy and cell death. In this review, we discuss the main pathways of mitophagy, those related to cell death mechanisms (including apoptosis, ferroptosis, and pyroptosis), and the relationship between mitophagy and cell death uncovered in recent years. Our study offers potential directions for therapeutic intervention and disease diagnosis, and contributes to understanding the molecular mechanism of mitophagy.

The role of PINK1-Parkin in mitochondrial quality control

Mitophagy mediated by the recessive Parkinson's disease genes PINK1 and Parkin responds to mitochondrial damage to preserve mitochondrial function. In the pathway, PINK1 is the damage sensor, probing the integrity of the mitochondrial import pathway, and activating Parkin when import is blocked. Parkin is the effector, selectively marking damaged mitochondria with ubiquitin for mitophagy and other quality-control processes. This selective mitochondrial quality-control pathway may be especially critical for dopamine neurons affected in Parkinson's disease, in which the mitochondrial network is widely distributed throughout a highly branched axonal arbor. Here we review the current understanding of the role of PINK1-Parkin in the quality control of mitophagy, including sensing of mitochondrial distress by PINK1, activation of Parkin by PINK1 to induce mitophagy, and the physiological relevance of the PINK1-Parkin pathway.

Iron chelators as mitophagy agents: Potential and limitations

Mitochondrial autophagy (mitophagy) is very important process for the maintenance of cellular homeostasis, functionality and survival. Its dysregulation is associated with high risk and progression numerous serious diseases (e.g., oncological, neurodegenerative and cardiovascular ones). Therefore, targeting mitophagy mechanisms is very hot topic in the biological and medicinal research. The interrelationships between the regulation of mitophagy and iron homeostasis are now becoming apparent. In short, mitochondria are central point for the regulation of iron homeostasis, but change in intracellular cheatable iron level can induce/repress mitophagy. In this review, relationships between iron homeostasis and mitophagy are thoroughly discussed and described. Also, therapeutic applicability of mitophagy chelators in the context of individual diseases is comprehensively and critically evaluated.

Evidence for the potential role of m6A modification in regulating autophagy in models of amyotrophic lateral sclerosis

Objective

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease. Research indicates that N6-methyladenosine (m6A) modification plays a crucial role in cellular autophagy during ALS development. This study investigates the role of autophagy in ALS, with a focus on the effect of messenger ribonucleic acid m6A methylation modification on disease progression.

Material and Methods

We compared m6A levels and regulatory molecule expressions in transgenic superoxide dismutase (SOD1)-G93A and non-transgenic mice, categorized into end-stage and control groups, using quantitative polymerase chain reaction and Western blotting. The NSC-34 cell line, which was modified to model ALS, enabled the investigation of apoptosis, autophagy, and autophagy disruption through terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling assays, Western blotting, and fluorescent staining.

Results

Our findings indicate significantly elevated m6A methylation levels in ALS mice (0.262 ± 0.005) compared with the controls (0.231 ± 0.003) and in the ALS model cells (0.242±0.005) relative to those belonging to the wild-type control group (0.183 ± 0.007). Furthermore, the proteins involved in m6A RNA modification differed between groups, which suggest impaired autophagy flux in the ALS models.

Conclusion

These results suggest that m6A methylation may accelerate ALS progression through the disruption of autophagic processes. Our study underscores the role of m6A methylation in the pathology of ALS and proposes the targeting of m6A methylation as a potential therapeutic strategy for disease treatment. Although this study primarily used transgenic SOD1-G93A mice and NSC-34 cell models to investigate ALS pathology, potential differences in disease mechanisms between animal models and humans must be considered. Although a correlation was detected between m6A methylation levels and autophagy disruption in ALS, the study primarily established an association rather than provided detailed mechanistic insights.

Transcriptome analysis reveals hepatic disordered lipid metabolism, lipotoxic injury, and abnormal development in IUGR sheep fetuses due to maternal undernutrition during late pregnancy

Although lipid metabolism in fetal livers under intrauterine growth restriction (IUGR) conditions has been widely studied, the implications of maternal undernutrition on fetal hepatic lipid metabolism, lipotoxic injury, and abnormal development remain largely unknown. Therefore, this study investigated the effects of maternal undernutrition on disordered hepatic lipid metabolism, lipotoxic injury, and abnormal development in IUGR sheep fetuses using transcriptome analysis. Seventeen singleton ewes were randomly divided into three groups on day 90 of pregnancy: a control group (CG; 0.63 MJ metabolic energy/body weight (ME/BW)0.75/day, n = 5), maternal undernutrition group 1 (MU1; 0.33 MJ ME/BW0.75/day, n = 6), and maternal undernutrition group 2 (MU2; 0.20 MJ ME/BW0.75/day, n = 6). The fetuses were euthanized and recovered on day 130 of pregnancy. The levels of free fatty acids (FFA) in maternal blood (P < 0.01), fetal blood (P < 0.01), and fetal livers (P < 0.05) were increased in the MU1 and MU2 groups, but fetal hepatic triglyceride (TG) levels in the MU2 group (P < 0.01) and β-hydroxybutyrate levels in the MU1 and MU2 groups (P < 0.01) were decreased compared to the CG. Severe inflammatory cell infiltration and increased non-alcoholic fatty liver disease activity scores were observed in MU1 and MU2 fetuses (P < 0.01). Progressive deposition of fetal hepatic reticular fibers and collagen fibers in the fetal livers of the MU1 and MU2 groups and significant hepatic fibrosis were observed in the MU2 fetuses (P < 0.05). Gene set enrichment analysis showed that genes involved in lipid accumulation and FFA beta oxidation were downregulated in both MU groups compared to those in the controls. The fetal liver mRNA expression of the β-oxidation regulator, acetyl-CoA acetyltransferase 1, and the TCA regulator, isocitrate dehydrogenase were reduced in MU1 (P < 0.05) and MU2 (P < 0.01) fetuses, and downregulated mRNA expression of long chain fatty acid CoA ligase 1 (P < 0.05) and glycerol-3-phosphate acyltransferase (P < 0.01) was observed in MU2 fetuses. Differentially expressed genes (DEGs) in MU1 versus CG (360 DEGs) and MU2 versus CG (746 DEGs) were identified using RNA sequencing. Bioinformatics analyses of the 231 intersecting DEGs between MU1 versus CG and MU2 versus CG indicated that neutrophil extracellular traps (NETs) were induced and played a central role in fetal hepatic injury in IUGR sheep. Increased maternal blood myeloperoxidase (MPO) levels (P < 0.01), NE (Elane)-positive areas in fetal liver sections (P < 0.05), and fetal liver MPO protein expression (P < 0.01) were found in the MU1 and MU2 groups; however, MPO levels were reduced in the fetal membrane (P < 0.01) and fetal blood (P < 0.05) in the MU1 group, and in the maternal-fetal placenta and fetal blood in the MU2 group (P < 0.01). Analysis of gene expression trends in the intersecting DEGs between MU1 versus CG (129 DEGs) and MU2 versus CG (515 DEGs) further revealed that 30 hub genes were essential regulators of the G2/M cell cycle, all of which were associated with hepatocellular carcinoma. G0/G1 phase cells of the fetal liver were reduced in the MU1 (P < 0.05) and MU2 (P < 0.01) groups, whereas G2/M phase cells were elevated in the MU1 and MU2 groups (P < 0.01). The representatives of upregulated hub genes and fetal liver protein expression of maternal embryonic leucine zipper kinase and protein regulator of cytokinesis 1 were progressively enhanced in the MU1 and MU2 groups (P < 0.01), and topoisomerase II alpha protein expression in the MU2 group (P < 0.05), as expected. These results indicate that FFA overload, severe lipotoxic injury, and NETs were induced, and disease-promoting regulators of the G2/M cell cycle were upregulated in the fetal liver of IUGR sheep. These findings provide new insights into the pathogenesis of impaired hepatic lipid metabolism and abnormal development and the molecular origin of post-natal liver disease in IUGR due to maternal undernutrition. This information can support the development of new therapeutic strategies.

The interplay between mitochondrial dynamics and autophagy: From a key homeostatic mechanism to a driver of pathology

The complex relationship between mitochondrial dynamics and autophagy illustrates how two cellular housekeeping processes are intimately linked, illuminating fundamental principles of cellular homeostasis and shedding light on disparate pathological conditions including several neurodegenerative disorders. Here we review the basic tenets of mitochondrial dynamics i.e., the concerted balance between fusion and fission of the organelle, and its interplay with macroautophagy and selective mitochondrial autophagy, also dubbed mitophagy, in the maintenance of mitochondrial quality control and ultimately in cell viability. We illustrate how conditions of altered mitochondrial dynamics reverberate on autophagy and vice versa. Finally, we illustrate how altered interplay between these two key cellular processes participates in the pathogenesis of human disorders affecting multiple organs and systems.

The effects of light emitting diodes on mitochondrial function and cellular viability of M-1 cell and mouse CD1 brain cortex neurons

The invention of Light Emitting Diode (LED) revolutionized energy-efficient illumination, but concerns persist regarding the potential harm of blue light to our eyes. In this study, we scrutinized the impact of LED light characteristics on eyes using two cell types: M-1 (rich in mitochondria) and CD-1 (neuronal). Variations in color rendering index (CRI) and correlated color temperature (CCT) were investigated, alongside exposure durations ranging from 0 to 24 hours. The findings illuminated the potential benefits of high-quality LED lighting, characterized by a high CRI and low CCT, which emits a greater proportion of red light. This form of lighting was associated with enhanced cell proliferation, elevated ATP levels, and reduced oxidative stress. In contrast, LEDs with low CRI and high CCT exhibited adverse effects, diminishing cell viability and increasing oxidative stress. These results suggest that high-quality LED lighting may have neuroprotective potential as a treatment option, such as for retinal ganglion cells.

Molecular Mechanisms of Autophagy Decline during Aging

Macroautophagy (hereafter autophagy) is a cellular recycling process that degrades cytoplasmic components, such as protein aggregates and mitochondria, and is associated with longevity and health in multiple organisms. While mounting evidence supports that autophagy declines with age, the underlying molecular mechanisms remain unclear. Since autophagy is a complex, multistep process, orchestrated by more than 40 autophagy-related proteins with tissue-specific expression patterns and context-dependent regulation, it is challenging to determine how autophagy fails with age. In this review, we describe the individual steps of the autophagy process and summarize the age-dependent molecular changes reported to occur in specific steps of the pathway that could impact autophagy. Moreover, we describe how genetic manipulations of autophagy-related genes can affect lifespan and healthspan through studies in model organisms and age-related disease models. Understanding the age-related changes in each step of the autophagy process may prove useful in developing approaches to prevent autophagy decline and help combat a number of age-related diseases with dysregulated autophagy.