ULK1 and JNK are involved in mitophagy incurred by LRRK2 G2019S expression

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.

A patent review of UNC-51-like kinase 1/2 inhibitors (2019-present)

INTRODUCTION

UNC-51-like kinase 1/2 (ULK1/2) are serine/threonine kinases that play a crucial role in autophagy activation and maintaining cellular homeostasis. Given their broad physiological relevance, ULK1/2 are candidate targets for treating various diseases. In recent years, ULK1/2 inhibitors have made significant progress, and the highly potent ULK1/2 inhibitors have entered clinical trials.

AREA COVERED

This review aims to provide an updated analysis of patents describing ULK1/2 inhibitors and their potential therapeutic applications that were disclosed between 2019 and 2024.

EXPERT OPINION

Due to their crucial role in various diseases, the invention of small-molecule drugs targeting ULK1/2 is particularly important, especially in cancer treatment. Despite the great success of ULK1/2 inhibitors development, ULK1/2 inhibitors are ATP competitive inhibitors of aminopyrimidines currently, and most ULK1/2 inhibitors are still in the preclinical research stage, with only DCC-3116 entered clinical research. Therefore, developing highly selective ULK1/2 inhibitors with low side effects and high bioavailability remains a challenging and promising research direction.

Swimming short fibrous nasal drops achieving intraventricular administration

Adequate drug delivery across the blood-brain barrier (BBB) is a critical factor in treating central nervous system (CNS) disorders. Inspired by swimming fish and the microstructure of the nasal cavity, this study is the first to develop swimming short fibrous nasal drops that can directly target the nasal mucosa and swim in the nasal cavity, which can effectively deliver drugs to the brain. Briefly, swimming short fibrous nasal drops with charged controlled drug release were fabricated by electrospinning, homogenization, the π-π conjugation between indole group of fibers, the benzene ring of leucine-rich repeat kinase 2 (LRRK2) inhibitor along with charge-dipole interaction between positively charged poly-lysine (PLL) and negatively charged surface of fibers; this enabled these fibers to stick to nasal mucosa, prolonged the residence time on mucosa, and prevented rapid mucociliary clearance. In vitro, swimming short fibrous nasal drops were biocompatible and inhibited microglial activation by releasing an LRRK2 inhibitor. In vivo, luciferase-labelled swimming short fibrous nasal drops delivered an LRRK2 inhibitor to the brain through the nasal mucosa, alleviating cognitive dysfunction caused by sepsis-associated encephalopathy by inhibiting microglial inflammation and improving synaptic plasticity. Thus, swimming short fibrous nasal drops is a promising strategy for the treatment of CNS diseases.

Chaperone-mediated autophagy in neurodegenerative diseases: mechanisms and therapy

Chaperone-mediated autophagy (CMA) is the selective degradation process of intracellular components by lysosomes, which is required for the degradation of aggregate-prone proteins and contributes to proteostasis maintenance. Proteostasis is essential for normal cell function and survival, and it is determined by the balance of protein synthesis and degradation. Because postmitotic neurons are highly susceptible to proteostasis disruption, CMA is vital for the nervous system. Since Parkinson's disease (PD) was first linked to CMA dysfunction, an increasing number of studies have shown that CMA loss, as seen during aging, occurs in the pathogenetic process of neurodegenerative diseases. Here, we review the molecular mechanisms of CMA, as well as the physiological function and regulation of this autophagy pathway. Following, we highlight its potential role in neurodegenerative diseases, and the latest advances and challenges in targeting CMA in therapy of neurodegenerative diseases.

LRRK2 aggravates kidney injury through promoting MFN2 degradation and abnormal mitochondrial integrity

Mitochondrial dysfunction is one of the key features of acute kidney injury (AKI) and associated fibrosis. Leucine-rich repeat kinase 2 (LRRK2) is highly expressed in kidneys and regulates mitochondrial homeostasis. How it functions in AKI is unclear. Herein we reported that LRRK2 was dramatically downregulated in AKI kidneys. Lrrk2-/- mice exhibited less severity of AKI when compared to wild-type counterparts with less mitochondrial fragmentation and decreased reactive oxygen species (ROS) production in proximal renal tubular cells (PTCs) due to mitofusin 2 (MFN2) accumulation. Overexpression of LRRK2 in human PTC cell lines promoted LRRK2-MKK4/JNK-dependent phosphorylation of MFN2Ser27 and subsequently ubiquitination-mediated MFN2 degradation, which in turn exaggerated mitochondrial damage upon ischemia/reperfusion (I/R) mimicry treatment. Lrrk2 deficiency also alleviated AKI-to-chronic kidney disease (CKD) transition with less fibrosis. In vivo pretreatment of LRRK2 inhibitors attenuated the severity of AKI as well as CKD, potentiating LRRK2 as a novel target to alleviate AKI and fibrosis.

Multitarget inhibitors/probes that target LRRK2 and AURORA A kinases noncovalently and covalently

Herein, we report a salicylaldehyde-based, reversible covalent inhibitor (A2) that possesses moderate cellular activity against AURKA with a prolonged residence time and shows significant non-covalent inhibition towards LRRK2. Our results indicated that this multitarget kinase inhibitor may be used as the starting point for future development of more potent, selective and dual-targeting covalent kinase inhibitors against AURKA and LRRK2 for mitophagy.

Role of autophagy pathway in Parkinson's disease and related Genetic Neurological disorders

The elucidation of the function of the PINK1 protein kinase and Parkin ubiquitin E3 ligase in the elimination of damaged mitochondria by autophagy (mitophagy) has provided unprecedented understanding of the mechanistic pathways underlying Parkinson's disease (PD). We provide a comprehensive overview of the general importance of autophagy in Parkinson's disease and related disorders of the central nervous system. This reveals a critical link between autophagy and neurodegenerative and neurodevelopmental disorders and suggests that strategies to modulate mitophagy may have greater relevance in the CNS beyond PD.

Mitochondrial Control in Inflammatory Gastrointestinal Diseases

Mitochondria play a central role in the pathophysiology of inflammatory bowel disease (IBD) and colorectal cancer (CRC). The maintenance of mitochondrial function is necessary for a stable immune system. Mitochondrial dysfunction in the gastrointestinal system leads to the excessive activation of multiple inflammatory signaling pathways, leading to IBD and increased severity of CRC. In this review, we focus on the mitochondria and inflammatory signaling pathways and its related gastrointestinal diseases.

Autophagy and Its Association with Genetic Mutations in Parkinson Disease

Parkinson disease is the second most common neurodegenerative disorder, affecting 0.1-0.2% of the general population. It is a progressive debilitating disorder caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta. It is characterized by motor and non-motor symptoms. Parkinson disease can be caused by mutations in genes that encode proteins involved in the autophagic process, resulting in impaired autophagy. Indeed, autophagy has been implicated in the pathogenesis of Parkinson disease, particularly because its impairment causes the buildup of proteins. Thus, this review aims to provide an overview of Parkinson disease-related genetic mutations and their association with autophagy impairment in Parkinson disease, which can be helpful in improving the understanding of the pathogenesis of Parkinson disease, illustrating the potential therapeutic implications of agents that can enhance autophagy in Parkinson disease. Additionally, we will highlight the essential need for the development of highly sensitive and specific assays for gene-based diagnostic biomarkers. Finally, we will provide an overview on the potential gene-based therapeutic approaches for Parkinson disease, which have been most advanced and are associated with the most common targets being alpha-synuclein (SNCA), leucine-rich repeat kinase-2 (LRRK2), and glucocerebrosidase (GBA).

TRK-fused gene (TFG) regulates ULK1 stability via TRAF3-mediated ubiquitination and protects macrophages from LPS-induced pyroptosis

TRK-fused gene (TFG) is known to be involved in protein secretion and plays essential roles in an antiviral innate immune response. However, its function in LPS-induced inflammation and pyroptotic cell death is still unknown. Here, we reported that TFG promotes the stabilization of Unc-51 like autophagy activating kinase (ULK1) and participates in LPS plus nigericin (Ng) induced pyroptotic cell death. Our results showed that TFG-deficient THP-1 macrophages exhibit higher mitochondrial ROS production. LPS/Ng stimulation triggers a much higher level of ROS and induces pyroptotic cell death. ULK1 undergoes a rapid turnover in TFG-deficient THP-1 cells. TFG forms complex with an E3 ligase, tumor necrosis factor receptor-associated factor 3 (TRAF3), and stabilizes ULK1 via disturbing ULK1-TRAF3 interaction. Knockdown of TFG facilitates the interaction of ULK1 with TRAF3 and subsequent K48-linked ULK1 ubiquitination and proteasome degradation. Rescue of ULK1 expression blocks LPS/Ng-induced cell death in TFG-deficient THP-1 macrophages. Taken together, TFG plays an essential role in LPS/Ng-induced pyroptotic cell death via regulating K48-linked ULK1 ubiquitination in macrophages.

α-Synuclein Interactions in Mitochondria-ER Contacts: A Possible Role in Parkinson's Disease

Endoplasmic reticulum-mitochondria contact sites regulate various biological processes, such as mitochondrial dynamics, calcium homeostasis, autophagy and lipid metabolism. Notably, dysfunctions in these contact sites are closely related to neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis. However, details about the role of endoplasmic reticulum-mitochondria contact sites in neurodegenerative diseases remain unknown. In Parkinson's disease, interactions between α-synuclein in the contact sites and components of tether complexes that connect organelles can lead to various dysfunctions, especially with regards to calcium homeostasis. This review will summarize the main tether complexes present in endoplasmic reticulum-mitochondria contact sites, and their roles in calcium homeostasis and trafficking. We will discuss the impact of α-synuclein accumulation, its interaction with tethering complex components and the implications in Parkinson's disease pathology.

The Cross-Links of Endoplasmic Reticulum Stress, Autophagy, and Neurodegeneration in Parkinson's Disease

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder, and it is characterized by the selective loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc), as well as the presence of intracellular inclusions with α-synuclein as the main component in surviving DA neurons. Emerging evidence suggests that the imbalance of proteostasis is a key pathogenic factor for PD. Endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) and autophagy, two major pathways for maintaining proteostasis, play important roles in PD pathology and are considered as attractive therapeutic targets for PD treatment. However, although ER stress/UPR and autophagy appear to be independent cellular processes, they are closely related to each other. In this review, we focused on the roles and molecular cross-links between ER stress/UPR and autophagy in PD pathology. We systematically reviewed and summarized the most recent advances in regulation of ER stress/UPR and autophagy, and their cross-linking mechanisms. We also reviewed and discussed the mechanisms of the coexisting ER stress/UPR activation and dysregulated autophagy in the lesion regions of PD patients, and the underlying roles and molecular crosslinks between ER stress/UPR activation and the dysregulated autophagy in DA neurodegeneration induced by PD-associated genetic factors and PD-related neurotoxins. Finally, we indicate that the combined regulation of ER stress/UPR and autophagy would be a more effective treatment for PD rather than regulating one of these conditions alone.

The parkinsonian LRRK2 R1441G mutation shows macroautophagy-mitophagy dysregulation concomitant with endoplasmic reticulum stress

Autophagy is a mechanism responsible for the degradation of cellular components to maintain their homeostasis. However, autophagy is commonly altered and compromised in several diseases, including neurodegenerative disorders. Parkinson's disease (PD) can be considered a multifactorial disease because environmental factors, genetic factors, and aging are involved. Several genes are involved in PD pathology, among which the LRRK2 gene and its mutations, inherited in an autosomal dominant manner, are responsible for most genetic PD cases. The R1441G LRRK2 mutation is, after G2019S, the most important in PD pathogenesis. Our results demonstrate a relationship between the R1441G LRRK2 mutation and a mechanistic dysregulation of autophagy that compromises cell viability. This altered autophagy mechanism is associated with organellar stress including mitochondrial (which induces mitophagy) and endoplasmic reticulum (ER) stress, consistent with the fact that patients with this mutation are more vulnerable to toxins related to PD, such as MPP⁺.

Mitochondrial clearance: mechanisms and roles in cellular fitness

Mitophagy is one of the selective autophagy pathways that catabolizes dysfunctional or superfluous mitochondria. Under mitophagy-inducing conditions, mitochondria are labeled with specific molecular landmarks that recruit the autophagy machinery to the surface of mitochondria, enclosed into autophagosomes, and delivered to lysosomes (vacuoles in yeast) for degradation. As damaged mitochondria are the major sources of reactive oxygen species, mitophagy is critical for mitochondrial quality control and cellular health. Moreover, appropriate control of mitochondrial quantity via mitophagy is vital for the energy supply-demand balance in cells and whole organisms, cell differentiation, and developmental programs. Thus, it seems conceivable that defects in mitophagy could elicit pleiotropic pathologies such as excess inflammation, tissue injury, neurodegeneration, and aging. In this review, we will focus on the molecular basis and physiological relevance of mitophagy, and potential of mitophagy as a therapeutic target to overcome such disorders.

Mitophagy, a Form of Selective Autophagy, Plays an Essential Role in Mitochondrial Dynamics of Parkinson's Disease

Parkinson's disease (PD) is a severe neurodegenerative disorder caused by the progressive loss of dopaminergic neurons in the substantia nigra and affects millions of people. Currently, mitochondrial dysfunction is considered as a central role in the pathogenesis of both sporadic and familial forms of PD. Mitophagy, a process that selectively targets damaged or redundant mitochondria to the lysosome for elimination via the autophagy devices, is crucial in preserving mitochondrial health. So far, aberrant mitophagy has been observed in the postmortem of PD patients and genetic or toxin-induced models of PD. Except for mitochondrial dysfunction, mitophagy is involved in regulating several other PD-related pathological mechanisms as well, e.g., oxidative stress and calcium imbalance. So far, the mitophagy mechanisms induced by PD-related proteins, PINK1 and Parkin, have been studied widely, and several other PD-associated genes, e.g., DJ-1, LRRK2, and alpha-synuclein, have been discovered to participate in the regulation of mitophagy as well, which further strengthens the link between mitophagy and PD. Thus, in this view, we reviewed mitophagy pathways in belief and discussed the interactions between mitophagy and several PD's pathological mechanisms and how PD-related genes modulate the mitophagy process.

A pan-cancer assessment of alterations of the kinase domain of ULK1, an upstream regulator of autophagy

Autophagy is a key clearance process to recycle damaged cellular components. One important upstream regulator of autophagy is ULK1 kinase. Several three-dimensional structures of the ULK1 catalytic domain are available, but a comprehensive study, including molecular dynamics, is missing. Also, an exhaustive description of ULK1 alterations found in cancer samples is presently lacking. We here applied a framework which links -omics data to structural protein ensembles to study ULK1 alterations from genomics data available for more than 30 cancer types. We predicted the effects of mutations on ULK1 function and structural stability, accounting for protein dynamics, and the different layers of changes that a mutation can induce in a protein at the functional and structural level. ULK1 is down-regulated in gynecological tumors. In other cancer types, ULK2 could compensate for ULK1 downregulation and, in the majority of the cases, no marked changes in expression have been found. 36 missense mutations of ULK1, not limited to the catalytic domain, are co-occurring with mutations in a large number of ULK1 interactors or substrates, suggesting a pronounced effect of the upstream steps of autophagy in many cancer types. Moreover, our results pinpoint that more than 50% of the mutations in the kinase domain of ULK1, here investigated, are predicted to affect protein stability. Three mutations (S184F, D102N, and A28V) are predicted with only impact on kinase activity, either modifying the functional dynamics or the capability to exert effects from distal sites to the functional and catalytic regions. The framework here applied could be extended to other protein targets to aid the classification of missense mutations from cancer genomics studies, as well as to prioritize variants for experimental validation, or to select the appropriate biological readouts for experiments.

Enhancing mitophagy as a therapeutic approach for neurodegenerative diseases

Neurodegenerative diseases are highly debilitating illnesses and a growing cause of morbidity and mortality worldwide. Mitochondrial dysfunction and impairment of mitochondrial-specific autophagy, namely mitophagy, have emerged as important components of the cellular processes underlying neurodegeneration. Defective mitophagy has been highlighted as the cause of the accumulation of damaged mitochondria, which consequently leads to cellular dysfunction and/or death in neurodegenerative diseases. Here, we highlight the recent advances in the molecular mechanisms of mitochondrial homeostasis and mitophagy in neurodegenerative diseases. In particular, we evaluate how mitophagy is altered in Alzheimer's, Parkinson's, and Huntington's diseases, as well as in amyotrophic lateral sclerosis, and the potential of restoring mitophagy as a therapeutic intervention. We also discuss the interlinked connections between mitophagy and innate immunity (e.g., the involvement of Parkin, interferons and TRIM21) as well as the opportunity these pathways provide to develop combinational therapeutic strategies targeting them and related molecular mechanisms in such neurodegenerative diseases.

Autophagy in Parkinson's Disease

Impaired protein homeostasis and accumulation of damaged or abnormally modified protein are common disease mechanisms in many neurodegenerative disorders, including Parkinson's disease (PD). As one of the major degradation pathways, autophagy plays a pivotal role in maintaining effective turnover of proteins and damaged organelles in cells. Several decades of research efforts led to insights into the potential contribution of impaired autophagy machinery to α-synuclein accumulation and the degeneration of dopaminergic neurons, two major features of PD pathology. In this review, we summarize recent pathological, genetic, and mechanistic findings that link defective autophagy with PD pathogenesis in human patients, animals, and cellular models and discuss current challenges in the field.

Mechanisms and roles of mitophagy in neurodegenerative diseases

Mitochondria are double‐membrane‐encircled organelles existing in most eukaryotic cells and playing important roles in energy production, metabolism, Ca²⁺ buffering, and cell signaling. Mitophagy is the selective degradation of mitochondria by autophagy. Mitophagy can effectively remove damaged or stressed mitochondria, which is essential for cellular health. Thanks to the implementation of genetics, cell biology, and proteomics approaches, we are beginning to understand the mechanisms of mitophagy, including the roles of ubiquitin‐dependent and receptor‐dependent signals on damaged mitochondria in triggering mitophagy. Mitochondrial dysfunction and defective mitophagy have been broadly associated with neurodegenerative diseases. This review is aimed at summarizing the mechanisms of mitophagy in higher organisms and the roles of mitophagy in the pathogenesis of neurodegenerative diseases. Although many studies have been devoted to elucidating the mitophagy process, a deeper understanding of the mechanisms leading to mitophagy defects in neurodegenerative diseases is required for the development of new therapeutic interventions, taking into account the multifactorial nature of diseases and the phenotypic heterogeneity of patients.

Emerging views of mitophagy in immunity and autoimmune diseases

Mitophagy is a vital form of autophagy for selective removal of dysfunctional or redundant mitochondria. Accumulating evidence implicates elimination of dysfunctional mitochondria as a powerful means employed by autophagy to keep the immune system in check. The process of mitophagy may restrict inflammatory cytokine secretion and directly regulate mitochondrial antigen presentation and immune cell homeostasis. In this review, we describe distinctive pathways of mammalian mitophagy and highlight recent advances relevant to its function in immunity. In addition, we further discuss the direct and indirect evidence linking mitophagy to inflammation and autoimmunity underlying the pathogenesis of autoimmune diseases including inflammatory bowel diseases (IBD), systemic lupus erythematosus (SLE) and primary biliary cirrhosis (PBC).Abbreviations: AICD: activation induced cell death; AIM2: absent in melanoma 2; ALPL/HOPS: alkaline phosphatase, biomineralization associated; AMA: anti-mitochondrial antibodies; AMFR: autocrine motility factor receptor; ATG: autophagy-related; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CARD: caspase recruitment domain containing; CASP1: caspase 1; CD: Crohn disease; CGAS: cyclic GMP-AMP synthase; CXCL1: C-X-C motif chemokine ligand 1; DEN: diethylnitrosamine; DLAT/PDC-E2: dihydrolipoamide S-acetyltransferase; DNM1L/Drp1: dynamin 1 like; ESCRT: endosomal sorting complexes required for transport; FKBP8: FKBP prolyl isomerase 8; FUNDC1: Fun14 domain containing 1; GABARAP: GABA type A receptor-associated protein; HMGB1: high mobility group box 1; HPIV3: human parainfluenza virus type 3; IBD: inflammatory bowel diseases; IEC: intestinal epithelial cell; IFN: interferon; IL1B/IL-1β: interleukin 1 beta; iNK: invariant natural killer; IRGM: immunity related GTPase M; LIR: LC3-interacting region; LPS: lipopolysaccharide; LRRK2: leucine rich repeat kinase 2; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARCH5: membrane associated ring-CH-type finger 5; MAVS: mitochondrial antiviral signaling protein; MDV: mitochondria-derived vesicle; MFN1: mitofusin 1; MHC: major histocompatibility complex; MIF: macrophage migration inhibitory factor; mtAP: mitochondrial antigen presentation; mtDNA: mitochondrial DNA; MTOR: mechanistic target of rapamycin kinase; mtROS: mitochondrial ROS; MUL1: mitochondrial E3 ubiquitin protein ligase 1; NBR1: NBR1 autophagy cargo receptor; NFKB/NF-ĸB: nuclear factor kappa B subunit; NK: natural killer; NLR: NOD-like receptor; NLRC4: NLR family CARD domain containing 4; NLRP3: NLR family pyrin domain containing 3; OGDH: oxoglutarate dehydrogenase; OMM: outer mitochondrial membrane; OPTN: optineurin; ox: oxidized; PARK7: Parkinsonism associated deglycase; PBC: primary biliary cirrhosis; PEX13: peroxisomal biogenesis factor 13; PHB/PHB1: prohibitin; PHB2: prohibitin 2; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PINK1: PTEN induced kinase 1; PLEKHM1: pleckstrin homology and RUN domain containing M1; PRKN/PARK2: parkin RBR E3 ubiquitin protein ligase; RAB: member RAS oncogene family; RHEB: Ras homolog: mTORC1 binding; RIPK2: receptor interacting serine/threonine kinase 2; RLR: DDX58/RIG-I like receptor; ROS: reactive oxygen species; SBD: small bile ducts; SLC2A1/GLUT1: solute carrier family 2 member 1; SLE: systemic lupus erythematosus; SMURF1: SMAD specific E3 ubiquitin protein ligase 1; SQSTM1/p62: sequestosome 1; TAX1BP1: Tax1 binding protein 1; TCR: T cell receptor; TFAM: transcription factor A: mitochondrial; Th17: T helper 17; TLR9: toll like receptor 9; TMEM173/STING: transmembrane protein 173; TNF/TNF-α: tumor necrosis factor; Ub: ubiquitin; UC: ulcerative colitis; ULK1: unc-51 like autophagy activating kinase 1; WIPI: WD repeat domain: phosphoinositide interacting; ZFYVE1/DFCP1: zinc finger FYVE-type containing 1.

LRRK2 mutations impair depolarization-induced mitophagy through inhibition of mitochondrial accumulation of RAB10

Parkinson disease (PD) is a disabling, incurable disorder with increasing prevalence in the western world. In rare cases PD is caused by mutations in the genes for PINK1 (PTEN induced kinase 1) or PRKN (parkin RBR E3 ubiquitin protein ligase), which impair the selective autophagic elimination of damaged mitochondria (mitophagy). Mutations in the gene encoding LRRK2 (leucine rich repeat kinase 2) are the most common monogenic cause of PD. Here, we report that the LRRK2 kinase substrate RAB10 accumulates on depolarized mitochondria in a PINK1- and PRKN-dependent manner. RAB10 binds the autophagy receptor OPTN (optineurin), promotes OPTN accumulation on depolarized mitochondria and facilitates mitophagy. In PD patients with the two most common LRRK2 mutations (G2019S and R1441C), RAB10 phosphorylation at threonine 73 is enhanced, while RAB10 interaction with OPTN, accumulation of RAB10 and OPTN on depolarized mitochondria, depolarization-induced mitophagy and mitochondrial function are all impaired. These defects in LRRK2 mutant patient cells are rescued by LRRK2 knockdown and LRRK2 kinase inhibition. A phosphomimetic RAB10 mutant showed less OPTN interaction and less translocation to depolarized mitochondria than wild-type RAB10, and failed to rescue mitophagy in LRRK2 mutant cells. These data connect LRRK2 with PINK1- and PRKN-mediated mitophagy via its substrate RAB10, and indicate that the pathogenic effects of mutations in LRRK2, PINK1 and PRKN may converge on a common pathway.Abbreviations : ACTB: actin beta; ATP5F1B: ATP synthase F1 subunit beta; CALCOCO2: calcium binding and coiled-coil domain 2; CCCP: carbonyl cyanide m-chlorophenylhydrazone; Co-IP: co-immunoprecipitation; EBSS: Earle's balanced salt solution; GFP: green fluorescent protein; HSPD1: heat shock protein family D (Hsp60) member 1; LAMP1: lysosomal associated membrane protein 1; LRRK2: leucine rich repeat kinase 2; IF: immunofluorescence; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MFN2: mitofusin 2; OMM: outer mitochondrial membrane; OPTN: optineurin; PD: Parkinson disease; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RHOT1: ras homolog family member T1; ROS: reactive oxygen species; TBK1: TANK binding kinase 1; WB: western blot.

Hallmarks of Aging: An Autophagic Perspective

Autophagy is a major protein turnover pathway by which cellular components are delivered into the lysosomes for degradation and recycling. This intracellular process is able to maintain cellular homeostasis under stress conditions, and its dysregulation could lead to the development of physiological alterations. The autophagic activity has been found to decrease with age, likely contributing to the accumulation of damaged macromolecules and organelles during aging. Interestingly, failure of the autophagic process has been reported to worsen aging-associated diseases, such as neurodegeneration or cancer, among others. Likewise, it has been proposed in different organisms that maintenance of a proper autophagic activity contributes to extending longevity. In this review, we discuss recent papers showing the impact of autophagy on cell activity and age-associated diseases, highlighting the relevance of this process to the hallmarks of aging. Thus, understanding how autophagy plays an important role in aging opens new avenues for the discovery of biochemical and pharmacological targets and the development of novel anti-aging therapeutic approaches.

Activation of CD137 Signaling Enhances Vascular Calcification through c-Jun N-Terminal Kinase-Dependent Disruption of Autophagic Flux

Background

Vascular calcification is widespread and clinically significant, contributing to substantial morbidity and mortality. Calcifying vascular cells are partly derived from local vascular smooth muscle cells (VSMCs), which can undergo chondrogenic or osteogenic differentiation under inflammatory environment. Recently, we have found activation of CD137 signaling accelerated vascular calcification. However, the underlying mechanism remains unknown. This study aims to identify key mediators involved in CD137 signaling-induced vascular calcification in vivo and in vitro.

Methods

Autophagy flux was measured through mRFP-GFP-LC3 adenovirus and transmission electron microscopy. Von Kossa assay and alkaline phosphatase (ALP) activity were used to observe calcification in vivo and in vitro, respectively. Autophagosome-containing vesicles were collected and identified by flow cytometry and Western blot. Autophagy or calcification-associated targets were measured by Western blot, quantitative real-time PCR, and immunohistochemistry.

Results

Treatment with the agonist-CD137 displayed c-Jun N-terminal kinase- (JNK-) dependent increase in the expression of various markers of autophagy and the number of autophagosomes relative to the control group. Autophagy flux experiments suggested that agonist-CD137 blocked the fusion of autophagosomes with lysosomes in cultured VSMCs. Calcium deposition, ALP activity, and the expression of calcification-associated proteins also increased in agonist-CD137 group compared with anti-CD137 group, which could be recovered by autophagy stimulator rapamycin. Autophagosome-containing vesicles collected from agonist-CD137 VSMCs supernatant promoted VSMC calcification.

Conclusion

The present study identified a new pathway in which CD137 promotes VSMC calcification through the activation of JNK signaling, subsequently leading to the disruption of autophagic flux, which is responsible for CD137-induced acceleration of vascular calcification.

Mechanisms of selective autophagy and mitophagy: Implications for neurodegenerative diseases

Over the past 20 years, the concept of mammalian autophagy as a nonselective degradation system has been repudiated, due in part to important discoveries in neurodegenerative diseases, which opened the field of selective autophagy. Protein aggregates and damaged mitochondria represent key pathological hallmarks shared by most neurodegenerative diseases. The landmark discovery in 2007 of p62/SQSTM1 as the first mammalian selective autophagy receptor defined a new family of autophagy-related proteins that serve to target protein aggregates, mitochondria, intracellular pathogens and other cargoes to the core autophagy machinery via an LC3-interacting region (LIR)-motif. Notably, mutations in the LIR-motif proteins p62 (SQSTM1) and optineurin (OPTN) contribute to familial forms of frontotemporal dementia and amyotrophic lateral sclerosis. Moreover, a subset of LIR-motif proteins is involved in selective mitochondrial degradation initiated by two recessive familial Parkinson's disease genes. PTEN-induced kinase 1 (PINK1) activates the E3 ubiquitin ligase Parkin (PARK2) to mark depolarized mitochondria for degradation. An extensive body of literature delineates key mechanisms in this pathway, based mostly on work in transformed cell lines. However, the potential role of PINK1-triggered mitophagy in neurodegeneration remains a conundrum, particularly in light of recent in vivo mitophagy studies. There are at least three major mechanisms by which mitochondria are targeted for mitophagy: transmembrane receptor-mediated, ubiquitin-mediated and cardiolipin-mediated. This review summarizes key features of the major cargo recognition pathways for selective autophagy and mitophagy, highlighting their potential impact in the pathogenesis or amelioration of neurodegenerative diseases.

Deficiency of unc-51 like kinase 1 (Ulk1) protects against mice traumatic brain injury (TBI) by suppression of p38 and JNK pathway

Unc-51 like autophagy activating kinase 1 (Ulk1) is a serine/threonine kinase that plays a key role in regulating autophagy processes. We attempted to investigate the effects of Ulk1 on traumatic brain injury (TBI) progression by using wild type (WT) mice and Ulk1-knockout (KO) mice suffered with or not TBI. The results were verified using LPS-treated primary astrocyte (AST). Here, Ulk1 was over-expressed in hippocampus of WT mice after TBI, as well as in lipopolysaccharide (LPS)-stimulated AST. Ulk1-deletion improved cognitive ability and hippocampus histological changes in TBI mice. Nissl and neuronal nuclei (NeuN) staining indicated that Ulk1-deletion increased the number of surviving neurons in hippocampus of TBI mice. Ulk1-ablation alleviated neuroinflammation, as evidenced by the reduced expression of hippocampus pro-inflammatory cytokines in TBI mice. TBI-induced apoptosis was also ameliorated by Ulk1-ablation, as proved by the reduced number of TUNEL-staining cells, and cleaved Caspase-3 and poly (ADP-ribose) polymerase (PARP) expressions. Moreover, Ulk1-knockout suppressed TBI-stimulated activation of astrocytes and microglia cells. Additionally, hippocampus autophagy induced by TBI was attenuated by Ulk1-knockout. Further, TBI-activated p38/c-Jun N-terminal Kinase (JNK) pathway was repressed by Ulk1-deletion in hippocampus of mice. The findings above were confirmed in LPS-stimulated AST with or without Ulk1 siRNA transfection. Intriguingly, pre-treatment of p38 or JNK activator markedly abolished the anti-inflammation, anti-apoptosis and anti-autophagy effects of Ulk1-knockdown on LPS-incubated AST. In conclusion, our results demonstrated that Ulk1 might be a potential target for developing therapeutic strategy against TBI in future.

Multiple pathways for mitophagy: A neurodegenerative conundrum for Parkinson's disease

It has been nearly a decade since the first landmark studies implicating familial recessive Parkinson's disease genes in the regulation of selective mitochondrial autophagy. The PTEN-induced kinase 1 (PINK1) and the E3 ubiquitin ligase Parkin (encoded by the PARK2 gene) act together to mark depolarized mitochondria for degradation. There is now an extensive body of literature detailing key mediators and steps in this pathway, based mostly on work in transformed cell lines. However, the degree to which PINK1-triggered mitophagy contributes to mitochondrial quality control in the mammalian brain, and the extent to which its disruption contributes to Parkinson's disease pathogenesis remain uncertain. In recent years, it has become clear that there are multiple, potentially redundant, pathways of cargo specification for mitophagy. Important mitophagy-independent functions of PINK1 and Parkin are also emerging. This review summarizes key features of three major mitophagy cargo recognition systems: receptor-mediated, ubiquitin-mediated and cardiolipin-mediated. New animal models that may be useful for tracking the delivery of mitochondria into lysosomes in different neuronal populations will be highlighted. Combining these research tools with methods to selectively disrupt specific mitophagy pathways may lead to a better understanding of the potential role of mitophagy in modulating neuronal vulnerability in Parkinson's spectrum (PD/PDD/DLB) and other neurodegenerative diseases.

AMPK: guardian of metabolism and mitochondrial homeostasis

Cells constantly adapt their metabolism to meet their energy needs and respond to nutrient availability. Eukaryotes have evolved a very sophisticated system to sense low cellular ATP levels via the serine/threonine kinase AMP-activated protein kinase (AMPK) complex. Under conditions of low energy, AMPK phosphorylates specific enzymes and growth control nodes to increase ATP generation and decrease ATP consumption. In the past decade, the discovery of numerous new AMPK substrates has led to a more complete understanding of the minimal number of steps required to reprogramme cellular metabolism from anabolism to catabolism. This energy switch controls cell growth and several other cellular processes, including lipid and glucose metabolism and autophagy. Recent studies have revealed that one ancestral function of AMPK is to promote mitochondrial health, and multiple newly discovered targets of AMPK are involved in various aspects of mitochondrial homeostasis, including mitophagy. This Review discusses how AMPK functions as a central mediator of the cellular response to energetic stress and mitochondrial insults and coordinates multiple features of autophagy and mitochondrial biology.

LRRK2 enhances Nod1/2-mediated inflammatory cytokine production by promoting Rip2 phosphorylation

The innate immune system is critical for clearing infection, and is tightly regulated to avert excessive tissue damage. Nod1/2-Rip2 signaling, which is essential for initiating the innate immune response to bacterial infection and ER stress, is subject to many regulatory mechanisms. In this study, we found that LRRK2, encoded by a gene implicated in Crohn's disease, leprosy and familial Parkinson's disease, modulates the strength of Nod1/2-Rip2 signaling by enhancing Rip2 phosphorylation. LRRK2 deficiency markedly reduces cytokine production in macrophages upon Nod2 activation by muramyl dipeptide (MDP), Nod1 activation by D-gamma-Glu-meso-diaminopimelic acid (iE-DAP) or ER stress. Our biochemical study shows that the presence of LRRK2 is necessary for optimal phosphorylation of Rip2 upon Nod2 activation. Therefore, this study reveals that LRRK2 is a new positive regulator of Rip2 and promotes inflammatory cytokine induction through the Nod1/2-Rip2 pathway.

Candidate genes for Parkinson disease: Lessons from pathogenesis

Parkinson disease (PD) is a multifactorial neurodegenerative disease characterized by the progressive loss of specific neuronal populations and accumulation of Lewy bodies in the brain, leading to motor and non-motor symptoms. In a small subset of patients, PD is dominantly or recessively inherited, while a number of susceptibility genetic loci have been identified through genome wide association studies. The discovery of genes mutated in PD and functional studies on their protein products have provided new insights into the molecular events leading to neurodegeneration, suggesting that few interconnected molecular pathways may be deranged in all forms of PD, triggering neuronal loss. Here, we summarize the most relevant findings implicating the main PD-related proteins in biological processes such as mitochondrial dysfunction, misfolded protein damage, alteration of cellular clearance systems, abnormal calcium handling and altered inflammatory response, which represent key targets for neuroprotection.

UNC-51-like kinase 1 blocks S6k1 phosphorylation contributes to neurodegeneration in Parkinson's disease model in vitro

OBJECTIVE

This study was aim to determine the role and underling mechanism of ribosomal protein S6 kinases 1 (S6k1) phosphorylation in Parkinson's disease (PD).

METHODS

The dopaminergic neuron MN9D was employed and 1-methyl-4-phenylpyridium (MPP) iodide (MPP(+)) was used to generate PD model in vitro. The S6k1 phosphorylation and UNC-51-like kinase 1 (ULK1) protein levels were analyzed by western blot. The ULK1 mRNA level was evaluated by Real-time RT-PCR. The S6k1 threonine 389 (T389) site-directed mutagenesis, the phosphodeficit T389A (threonine to alanine) and the phosphomimetic T389D (threonine to aspartate) were generated to examine the phosphorylation site of S6k1.

RESULTS

An increase in the ULK1 mRNA and protein levels were detected in the MPP(+)-treated MN9D cells compared to control. ULK1 knockdown increased neuronal cell viability, and enhanced S6k1 phosphorylation. Further investigation demonstrated ULK1 knockdown promoted the S6k1 T389 phosphorylation in particular. T389A enhanced the viability of MPP iodide-treated MN9D, whereas T389D decreased the cell viability.

CONCLUSION

ULK1 acts to inhibit S6k1 phosphorylation at T389, leading to MN9D viability reduction under MPP(+) treatment. These results provide evidence for a novel mechanism by which the ULK1 inhibit S6k1 T389 phosphorylation contributes to neurodegeneration in MPP(+) treated-MN9D, and suggests a new therapeutic strategy for PD.

Association of the LRRK2 genetic polymorphisms with leprosy in Han Chinese from Southwest China

Leprosy is a chronic infectious and neurological disease that is caused by infection of Mycobacterium leprae (M. leprae). A recent genome-wide association study indicated a suggestive association of LRRK2 genetic variant rs1873613 with leprosy in Chinese population. To validate this association and further identify potential causal variants of LRRK2 with leprosy, we genotyped 13 LRRK2 variants in 548 leprosy patients and 1078 healthy individuals from Yunnan Province and (re-)analyzed 3225 Han Chinese across China. Variants rs1427267, rs3761863, rs1873613, rs732374 and rs7298930 were significantly associated with leprosy per se and/or paucibacillary leprosy (PB). Haplotype A-G-A-C-A was significantly associated with leprosy per se (P=0.018) and PB (P=0.020). Overexpression of the protective allele (Thr2397) of rs3761863 in HEK293 cells led to a significantly increased nuclear factor of activated T-cells' activity compared with allele Met2397 after lipopolysaccharides stimulation. Allele Thr2397 could attenuate 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine-induced autophagic activity in U251 cells. These data suggest that the protective effect of LRRK2 variant p.M2397T on leprosy might be mediated by increasing immune response and decreasing neurotoxicity after M. leprae loading. Our findings confirm that LRRK2 is a susceptible gene to leprosy in Han Chinese population.

The complex relationships between microglia, alpha-synuclein, and LRRK2 in Parkinson's disease

The proteins alpha-synuclein (αSyn) and leucine rich repeat kinase 2 (LRRK2) are both key players in the pathogenesis of the neurodegenerative disorder Parkinson's disease (PD), but establishing a functional link between the two proteins has proven elusive. Research studies for these two proteins have traditionally and justifiably focused in neuronal cells, but recent studies indicate that each protein could play a greater pathological role elsewhere. αSyn is expressed at high levels within neurons, but they also secrete the protein into the extracellular milieu, where it can have broad ranging effects in the nervous system and relevance to disease etiology. Similarly, low neuronal LRRK2 expression and activity suggests that LRRK2-related functions could be more relevant in cells with higher expression, such as brain-resident microglia. Microglia are monocytic immune cells that protect neurons from noxious stimuli, including pathological αSyn species, and microglial activation is believed to contribute to neuroinflammation and neuronal death in PD. Interestingly, both αSyn and LRRK2 can be linked to microglial function. Secreted αSyn can directly activate microglia, and can be taken up by microglia for clearance, while LRRK2 has been implicated in the intrinsic regulation of microglial activation and of lysosomal degradation processes. Based on these observations, the present review will focus on how PD-associated mutations in LRRK2 could potentially alter microglial biology with respect to neuronally secreted αSyn, resulting in cell dysfunction and neurodegeneration.