Autophagic Receptor Research Articles

Ksp1 is an autophagic receptor protein for the Snx4-assisted autophagy of Ssn2/Med13

ABSTRACT Ksp1 is a casein II-like kinase whose activity prevents aberrant macroautophagy/autophagy induction in nutrient-rich conditions in yeast. Here, we describe a kinase-independent role of Ksp1 as a novel autophagic receptor protein for Ssn2/Med13, a known cargo of Snx4-assisted autophagy of transcription factors. In this pathway, a subset of conserved transcriptional regulators, Ssn2/Med13, Rim15, and Msn2, are selectively targeted for vacuolar proteolysis following nitrogen starvation, assisted by the sorting nexin heterodimer Snx4-Atg20. Here we show that phagophores also engulf Ksp1 alongside its cargo for vacuolar proteolysis. Ksp1 directly associates with Atg8 following nitrogen starvation at the interface of an Atg8-family interacting motif (AIM)/LC3-interacting region (LIR) in Ksp1 and the LIR/AIM docking site (LDS) in Atg8. Mutating the LDS site prevents the autophagic degradation of Ksp1. However, deletion of the C terminal canonical AIM still permitted Ssn2/Med13 proteolysis, suggesting that additional non-canonical AIMs may mediate the Ksp1-Atg8 interaction. Ksp1 is recruited to the perivacuolar phagophore assembly site by Atg29, a member of the trimeric scaffold complex. This interaction is independent of Atg8 and Snx4, suggesting that Ksp1 is recruited early to phagophores, with Snx4 delivering Ssn2/Med13 thereafter. Finally, normal cell survival following prolonged nitrogen starvation requires Ksp1. Together, these studies define a kinase-independent role for Ksp1 as an autophagic receptor protein mediating Ssn2/Med13 degradation. They also suggest that phagophores built by the trimeric scaffold complex are capable of receptor-mediated autophagy. These results demonstrate the dual functionality of Ksp1, whose kinase activity prevents autophagy while it plays a scaffolding role supporting autophagic degradation. Abbreviations: 3-AT: 3-aminotriazole; 17C: Atg17-Atg31-Atg29 trimeric scaffold complex; AIM: Atg8-family interacting motif; ATG: autophagy related; CKM: CDK8 kinase module; Cvt: cytoplasm-to-vacuole targeting; IDR: intrinsically disordered region; LIR: LC3-interacting region; LDS: LIR/AIM docking site; MoRF: molecular recognition feature; NPC: nuclear pore complex; PAS: phagophore assembly site; PKA: protein kinase A; RBP: RNA-binding protein; UPS: ubiquitin-proteasome system. SAA-TF: Snx4-assisted autophagy of transcription factors; Y2H: yeast two-hybrid.

Comprehensive transcriptional analysis unveils salt stress-regulated key pathways in Suaeda salsa leaves

Suaeda salsa represents a promising halophyte model for investigating the mechanisms underlying salt tolerance in plants. However, the molecular mechanisms regulating seedling establishment of Suaeda salsa remain unknown. Thus, the current study was conducted to understand the underlying regulatory mechanisms in Suaeda salsa leaves exposed to 0 mM, 200 mM, 400 mM, and 800 mM NaCl using high-throughput RNA sequencing. The number of differentially expressed transcripts substantially increased when the salinity level elevated, suggesting major transcriptional reorganization in response to salinity stress. Importantly, the differentially identified transcripts were mostly salt responsive genes belonging to specific categories like plant hormone signaling, solute transport and nutrient uptake, protein metabolism, and transcriptional regulation. Specifically, higher level of salt changed 339 genes markedly implicated in transcriptional regulation such as MYB, MADS-box, NAC, ERF, WRKY, HB families, as well as genes involved in protein metabolism such as the tyrosine-like protein and ATG members and autophagic cargo receptor protein. This indicated important key players to high salt tolerance. Collectively, our findings revealed the crucial regulatory pathways underlying the salt tolerance of Suaeda salsa through a cascade that includes signal perception and transduction, and transcription factors that regulate the downstream response genes such as those involved in protein metabolism, solute and nutrient transport for salt stress adaptation.

The N-degron pathway mediates lipophagy: The chemical modulation of lipophagy in obesity and NAFLD.

Central to the pathogenesis of nonalcoholic fatty liver disease (NAFLD) is the accumulation of lipids in the liver and various fat tissues. We aimed to elucidate the mechanisms by which lipid droplets (LDs) in the liver and adipocytes are degraded by the autophagy-lysosome system and develop therapeutic means to modulate lipophagy, i.e., autophagic degradation of LDs. We monitored the process in which LDs are pinched off by autophagic membranes and degraded by lysosomal hydrolases in cultured cells and mice. The autophagic receptor p62/SQSTM-1/Sequestosome-1 was identified as a key regulator and used as a target to develop drugs to induce lipophagy. The efficacy of p62 agonists was validated in mice to treat hepatosteatosis and obesity. We found that the N-degron pathway modulates lipophagy. This autophagic degradation initiates when the molecular chaperones including BiP/GRP78, retro-translocated from the endoplasmic reticulum, is N-terminally (Nt-) arginylated by ATE1 R-transferase. The resulting Nt-arginine (Nt-Arg) binds the ZZ domain of p62 associated with LDs. Upon binding to Nt-Arg, p62 undergoes self-polymerization and recruits LC3+ phagophores to the site of lipophagy, leading to lysosomal degradation. Liver-specific Ate1 conditional knockout mice under high fat diet developed severe NAFLD. The Nt-Arg was modified into small molecule agonists to p62 that facilitate lipophagy in mice and exerted therapeutic efficacy in obesity and hepatosteatosis of wild-type but not p62 knockout mice. Our results show that the N-degron pathway modulates lipophagy and provide p62 as a drug target to treat NAFLD and other diseases related with metabolic syndrome.

Targeted degradation of ⍺-synuclein aggregates in Parkinson’s disease using the AUTOTAC technology

BackgroundThere are currently no disease-modifying therapeutics for Parkinson’s disease (PD). Although extensive efforts were undertaken to develop therapeutic approaches to delay the symptoms of PD, untreated α-synuclein (α-syn) aggregates cause cellular toxicity and stimulate further disease progression. PROTAC (Proteolysis-Targeting Chimera) has drawn attention as a therapeutic modality to target α-syn. However, no PROTACs have yet shown to selectively degrade α-syn aggregates mainly owing to the limited capacity of the proteasome to degrade aggregates, necessitating the development of novel approaches to fundamentally eliminate α-syn aggregates.MethodsWe employed AUTOTAC (Autophagy-Targeting Chimera), a macroautophagy-based targeted protein degradation (TPD) platform developed in our earlier studies. A series of AUTOTAC chemicals was synthesized as chimeras that bind both α-syn aggregates and p62/SQSTM1/Sequestosome-1, an autophagic receptor. The efficacy of Autotacs was evaluated to target α-syn aggregates to phagophores and subsequently lysosomes for hydrolysis via p62-dependent macroautophagy. The target engagement was monitored by oligomerization and localization of p62 and autophagic markers. The therapeutic efficacy to rescue PD symptoms was characterized in cultured cells and mice. The PK/PD (pharmacokinetics/pharmacodynamics) profiles were investigated to develop an oral drug for PD.ResultsATC161 induced selective degradation of α-syn aggregates at DC50 of ~ 100 nM. No apparent degradation was observed with monomeric α-syn. ATC161 mediated the targeting of α-syn aggregates to p62 by binding the ZZ domain and accelerating p62 self-polymerization. These p62-cargo complexes were delivered to autophagic membranes for lysosomal degradation. In PD cellular models, ATC161 exhibited therapeutic efficacy to reduce cell-to-cell transmission of α-syn and to rescue cells from the damages in DNA and mitochondria. In PD mice established by injecting α-syn preformed fibrils (PFFs) into brain striata via stereotaxic surgery, oral administration of ATC161 at 10 mg/kg induced the degradation of α-syn aggregates and reduced their propagation. ATC161 also mitigated the associated glial inflammatory response and improved muscle strength and locomotive activity.ConclusionAUTOTAC provides a platform to develop drugs for PD. ATC161, an oral drug with excellent PK/PD profiles, induces selective degradation of α-syn aggregates in vitro and in vivo. We suggest that ATC161 is a disease-modifying drug that degrades the pathogenic cause of PD.

Quercetin Alleviates Acrylamide-Induced Liver Injury by Inhibiting Autophagy-Dependent Ferroptosis

Acrylamide (ACR) generated in carbohydrate-rich foods during thermal processing has been demonstrated to exhibit hepatotoxicity. As one of the most consumed flavonoids with diet, quercetin (QCT) possesses the ability to protect against ACR-induced toxicity, albeit its mechanism is unclear. Herein, we discovered that QCT alleviated ACR-induced elevated levels of reactive oxygen species (ROS), AST, and ALT in mice. RNA-seq analysis revealed that QCT reversed the ferroptosis signaling pathway upregulated by ACR. Subsequently, experiments indicated that QCT inhibited ACR-induced ferroptosis through the reduction of oxidative stress. With autophagy inhibitor chloroquine, we further confirmed that QCT suppressed ACR-induced ferroptosis by inhibiting oxidative stress-driven autophagy. Additionally, QCT specifically reacted with autophagic cargo receptor NCOA4, blocked the degradation of iron storage protein FTH1, and eventually downregulated the intracellular iron levels and the consequent ferroptosis. Collectively, our results presented a unique approach to alleviate ACR-induced liver injury by targeting ferroptosis with QCT.

Host factor TNK2 is required for influenza virus infection.

Host factors are required for Influenza virus infection and have great potential to become antiviral target. Here we demonstrate the role of TNK2 in influenza virus infection. CRISPR/Cas9 induced TNK2 deletion in A549 cells. CRISPR/Cas9-mediated deletion of TNK2. Western blotting and qPCR was used to measure the expression of TNK2 and other proteins. CRISPR/Cas9-mediated deletion of TNK2 decreased the replication of influenza virus and significantly inhibited the ex-pression of viral proteins and TNK2 inhibitors (XMD8-87 and AIM-100) reduced the expression of influenza M2, while over-expression of TNK2 weakened the resistance of TNK2-knockout cells to influenza virus infection. Furthermore, a decrease of nuclear import of IAV in the infected TNK2 mutant cells was observed in 3h post-infection. Interestingly, TNK2 deletion enhanced the colocalization of LC3 with autophagic receptor p62 and led to the attenuation of influenza virus-caused accumulation of autophagosomes in TNK2 mutant cells. Further, confocal microscopy visualization result showed that influenza viral matrix 2 (M2) was colocalized with Lamp1 in the infected TNK2 mutant cells in early infection, while almost no colocalization between M2 and Lamp1 was observed in IAV-infected wild-type cells. Moreover, TNK2 depletion also affected the trafficking of early endosome and the movement of influenza viral NP and M2. Our results identified TNK2 as a critical host factor for influenza viral M2 protein trafficking, suggesting that TNK2 will be an attractive target for the development of antivirals therapeutics.

Autophagy Receptor p62 Regulates SARS-CoV-2-Induced Inflammation in COVID-19.

As autophagy can promote or inhibit inflammation, we examined autophagy-inflammation interplay in COVID-19. Autophagy markers in the blood of 19 control subjects and 26 COVID-19 patients at hospital admission and one week later were measured by ELISA, while cytokine levels were examined by flow cytometric bead immunoassay. The antiviral IFN-α and proinflammatory TNF, IL-6, IL-8, IL-17, IL-33, and IFN-γ were elevated in COVID-19 patients at both time points, while IL-10 and IL-1β were increased at admission and one week later, respectively. Autophagy markers LC3 and ATG5 were unaltered in COVID-19. In contrast, the concentration of autophagic cargo receptor p62 was significantly lower and positively correlated with TNF, IL-10, IL-17, and IL-33 at hospital admission, returning to normal levels after one week. The expression of SARS-CoV-2 proteins NSP5 or ORF3a in THP-1 monocytes caused an autophagy-independent decrease or autophagy-inhibition-dependent increase, respectively, of intracellular/secreted p62, as confirmed by immunoblot/ELISA. This was associated with an NSP5-mediated decrease in TNF/IL-10 mRNA and an ORF3a-mediated increase in TNF/IL-1β/IL-6/IL-10/IL-33 mRNA levels. A genetic knockdown of p62 mimicked the immunosuppressive effect of NSP5, and a p62 increase in autophagy-deficient cells mirrored the immunostimulatory action of ORF3a. In conclusion, the proinflammatory autophagy receptor p62 is reduced inacute COVID-19, and the balance between autophagy-independent decrease and autophagy blockade-dependent increase of p62 levels could affect SARS-CoV-induced inflammation.

Quantitative omics analyses of NCOA4 deficiency reveal an integral role of ferritinophagy in iron homeostasis of hippocampal neuronal HT22 cells.

Neurons require iron to support their metabolism, growth, and differentiation, but are also susceptible to iron-induced oxidative stress and cytotoxicity. Ferritin, a cytosolic iron storage unit, mediates cellular adaptation to fluctuations in iron delivery. NCOA4 has been characterized as a selective autophagic cargo receptor facilitating the mobilization of intracellular iron from ferritin. This process named ferritinophagy results in the degradation of ferritin and the consequent release of iron into the cytosol. Here we demonstrate that NCOA4 is important for the adaptation of the HT22 mouse hippocampal neuronal cell line to cellular iron restriction. Additionally, we determined the pathophysiological implications of impaired ferritinophagy via functional analysis of the omics profile of HT22 cells deficient in NCOA4. NCOA4 silencing impaired ferritin turnover and was cytotoxic when cells were restricted of iron. Quantitative proteomics identified IRP2 accumulation among the most prominent protein responses produced by NCOA4 depletion in HT22 cells, which is indicative of functional iron deficiency. Additionally, proteins of apoptotic signaling pathway were enriched by those responsive to NCOA4 deficiency. Transcriptome profiles of NCOA4 depletion revealed neuronal cell death, differentiation of neurons, and development of neurons as potential diseases and bio functions affected by impaired ferritinophagy, particularly, when iron was restricted. These findings identify an integral role of NCOA4-mediated ferritinophagy in the maintenance of iron homeostasis by HT22 cells, and its potential implications in controlling genetic pathways of neurodevelopment and neurodegenerative diseases.

Copper-dependent autophagic degradation of GPX4 drives ferroptosis

ABSTRACT Ferroptosis is a type of iron-dependent regulated cell death characterized by unrestricted lipid peroxidation and membrane damage. Although GPX4 (glutathione peroxidase 4) plays a master role in blocking ferroptosis by eliminating phospholipid hydroperoxides, the regulation of GPX4 remains poorly understood. Here, we report an unexpected role for copper in promoting ferroptotic cell death, but not cuproptosis, by inducing macroautophagic/autophagic degradation of GPX4. Copper chelators reduce ferroptosis sensitivity but do not inhibit other types of cell death, such as apoptosis, necroptosis, and alkaliptosis. Conversely, exogenous copper increases GPX4 ubiquitination and the formation of GPX4 aggregates by directly binding to GPX4 protein cysteines C107 and C148. TAX1BP1 (Tax1 binding protein 1) then acts as an autophagic receptor for GPX4 degradation and subsequent ferroptosis in response to copper stress. Consequently, copper enhances ferroptosis-mediated tumor suppression in a mouse model of pancreatic cancer tumor, whereas copper chelators attenuate experimental acute pancreatitis associated with ferroptosis. Taken together, these findings provide new insights into the link between metal stress and autophagy-dependent cell death. Abbreviations: CALCOCO2, calcium binding and coiled-coil domain 2; GPX4, glutathione peroxidase 4; MAP1LC3A/B, microtubule associated protein 1 light chain 3 alpha/beta; MPO, myeloperoxidase; NCOA4, nuclear receptor coactivator 4; OPTN, optineurin; PDAC, pancreatic ductal adenocarcinoma; RIPK1, receptor interacting serine/threonine kinase 1; ROS, reactive oxygen species; SLC40A1, solute carrier family 40 member 1; SQSTM1, sequestosome 1; TAX1BP1, Tax1 binding protein 1; TEPA, tetraethylenepentamine; TM, tetrathiomolybdate.

Mitophagy and endoplasmic reticulum-phagy accelerated by a p62 ZZ ligand alleviates paracetamol-induced hepatotoxicity.

Paracetamol (acetaminophen)-induced hepatotoxicity is the leading cause of drug-induced liver injury worldwide. Autophagy is a degradative process by which various cargoes are collected by the autophagic receptors such as p62/SQSTM1/Sequestosome-1 for lysosomal degradation. Here, we investigated the protective role of p62-dependent autophagy in paracetamol-induced liver injury. Paracetamol-induced hepatotoxicity was induced by a single i.p. injection of paracetamol (500 mg·kg-1 ) in C57/BL6 male mice. YTK-2205 (20 mg·kg-1 ), a p62 agonist targeting ZZ domain, was co- or post-administered with paracetamol. Western blotting and immunocytochemistry were performed to explore the mechanism. N-terminal arginylation of the molecular chaperone calreticulin retro-translocated from the endoplasmic reticulum (ER) was induced in the livers undergoing paracetamol-induced hepatotoxicity, and YTK-2205 exhibited notable therapeutic efficacy in acute hepatotoxicity as assessed by the levels of serum alanine aminotransferase and hepatic necrosis. This efficacy was significantly attributed to accelerated degradation of ubiquitin (Ub) conjugates as well as damaged mitochondria (mitophagy) and endoplasmic reticulum (ER-phagy). In primary murine hepatocytes treated with paracetamol, YTK-2205 induced the co-localization of p62+ LC3+ phagophores to the sites of mitophagy and ER-phagy. A similar activity of YTK-2205 was observed with N-acetyl-p-benzoquinone imine, a putative toxic metabolite of paracetamol in Hep3B cells. Our results elucidated that p62-dependent autophagy plays a key role in the removal of cytotoxic materials such as damaged mitochondria in paracetamol-induced hepatotoxicity. Small molecule ligands to p62 may be developed into drugs to treat this pathological condition.

Characterization and chemical modulation of p62/SQSTM1/Sequestosome-1 as an autophagic N-recognin.

In the Arg/N-degron pathway, single N-terminal (Nt) residues function as N-degrons recognized by UBR box-containing N-recognins that induce substrate ubiquitination and proteasomal degradation. Recent studies led to the discovery of the autophagic Arg/N-degron pathway, in which the autophagic receptor p62/SQSTM1/Sequestosome-1 acts as an N-recognin that binds the Nt-Arg and other destabilizing residues as N-degrons. Upon binding to Nt-Arg, p62 undergoes self-polymerization associated with its cargoes, accelerating the macroautophagic delivery of p62-cargo complexes to autophagosomes leading to degradation by lysosomal hydrolases. This autophagic mechanism is emerging as an important pathway that modulates the lysosomal degradation of various biomaterial ranging from protein aggregates and subcellular organelles to invading pathogens. Chemical mimics of the physiological N-degrons were developed to exert therapeutic efficacy in pathophysiological processes associated with neurodegeneration and other related diseases. Here, we describe the methods to monitor the activities of p62 in a dual role as an N-recognin and an autophagic receptor. The topic includes self-polymerization (for cargo condensation), its interaction with LC3 on autophagic membranes (for cargo targeting), and the degradation of p62-cargo complexes by lysosomal hydrolases. We also discuss the development and use of small molecule mimics of N-degrons that modulate p62-dependent macroautophagy in biological and pathophysiological processes.

Glutamine Produces Ammonium to Tune Lysosomal pH and Regulate Lysosomal Function.

Glutamine is one of the most abundant amino acids in the cell. In mitochondria, glutaminases 1 and 2 (GLS1/2) hydrolyze glutamine to glutamate, which serves as the precursor of multiple metabolites. Here, we show that ammonium generated during GLS1/2-mediated glutaminolysis regulates lysosomal pH and in turn lysosomal degradation. In primary human skin fibroblasts BJ cells and mouse embryonic fibroblasts, deprivation of total amino acids for 1 h increased lysosomal degradation capacity as shown by the increased turnover of lipidated microtubule-associated proteins 1A/1B light chain 3B (LC3-II), several autophagic receptors, and endocytosed DQ-BSA. Removal of glutamine but not any other amino acids from the culture medium enhanced lysosomal degradation similarly as total amino acid starvation. The presence of glutamine in regular culture media increased lysosomal pH by >0.5 pH unit and the removal of glutamine caused lysosomal acidification. GLS1/2 knockdown, GLS1 antagonist, or ammonium scavengers reduced lysosomal pH in the presence of glutamine. The addition of glutamine or NH4Cl prevented the increase in lysosomal degradation and curtailed the extension of mTORC1 function during the early time period of amino acid starvation. Our findings suggest that glutamine tunes lysosomal pH by producing ammonium, which regulates lysosomal degradation to meet the demands of cellular activities. During the early stage of amino acid starvation, the glutamine-dependent mechanism allows more efficient use of internal reserves and endocytosed proteins to extend mTORC1 activation such that the normal anabolism is not easily interrupted by a brief disruption of the amino acid supply.

Catalpol inhibits hepatic stellate cell activation by reducing the formation and changing the contents of hepatocyte-derived extracellular vesicles.

Hepatic stellate cell (HSC) activation is the central event in hepatic fibrosis. The cross-talk between HSCs and hepatocytes, which is mediated by extracellular vesicles (EVs), affects HSC activation. This study aimed to investigate whether Catalpol (CTP) attenuated hepatic fibrosis via modulating EVs. Mice were injected intraperitoneally with CCl4 for 4weeks to induce hepatic fibrosis. They were gavaged with CTP daily. Mouse serum EVs were isolated and identified using nanoparticle tracking analysis and transmission electron microscopy. Mouse hepatocytes (AML12) and primary HSCs were used to investigate the cell-to-cell crosstalk. The autophagosome-autolysosome fusion was determined using the autophagic flux assay. Hepatic fibrosis was attenuated by CTP, with a decrease of the myofibroblast marker, alpha-smooth muscle actin. The CTP treatment lowered the serum EVs. The co-culture of HSCs and the EVs derived from the CTP-treated mice or hepatocytes reduced HSC proliferation and the expressions of ACTA2 and Col1a1. After the CCl4 treatment, the autophagosomes in AML12 cells were increased, while the autolysosomes were reduced. The decrease of autophagic cargo receptor SQSTM1 in the CTP group suggested that autophagic degradation was sustained. After inhibiting the endogenous Rac1-GTP of hepatocytes, the co-culture of EVs and HSCs reduced Rac1-GTP. The Rac1-GTP level in serum EVs from the CTP-treated mice was reduced in vivo. CTP inhibited autophagy in hepatocytes by reducing Rac1-GTP and thus affect the amount of Rac1-GTP in hepatocyte-derived EVs and the formation of EVs, which attenuated hepatic fibrosis via inhibiting HSC activation.

Dysregulated Autophagy in Platelets from JAK2V617F-Positive Polycythemia Vera and Essential Thrombocythemia Underlies Bioenergetic Failure As a Possible Mechanism for Thrombohemorrhagic Complications

Background: JAK2V617F-positive polycythemia vera (PV) and essential thrombocythemia (ET) are the most common Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). ET/PV patients have high levels of inflammation and are at increased risk of thrombosis. Platelets from patients with ET/PV are characterized by hyperreactivity (low activation threshold), contributing to the increased incidence of thrombosis in the MPNs. We previously described that platelets from PV patients accumulate dysmorphic mitochondria. Autophagy is a housekeeping and an inducible cellular process that eliminates damaged proteins and organelles (such as mitochondria and endoplasmic reticulum), providing biosynthetic and bioenergetic substrates for the cell. Dysregulated autophagy has been described in cancer, aging, and neurodegenerative, cardiac, and muscular diseases. We hypothesized that impairment of the platelet autophagic flux in ET/PV Jak2V617F alters platelet metabolism and function at the early and late stages of platelet activation. Methods: Platelets from sex and age-matched healthy subjects and patients with PV were analyzed. Platelets were incubated for two hours with chloroquine (CQ) [50 and 100 µM] to inhibit autophagy. CQ blocks the late stage of the autophagy process; therefore, functional autophagy was assessed by quantifying the accumulation of autophagic-related proteins by western blot. Oxidative stress (4-hydroxynonenal protein adducts) was measured by western blot. Platelet bioenergetics was studied by the Seahorse extracellular flux analyzer. Semi-quantitative metabolomics was performed using the Vanquish UHPLC system. Clot retraction was assessed by measuring the weight of serum extruded from the clot. Results: Platelets from healthy patients showed basal and inducible autophagy characterized by the accumulation of autophagic markers such as LC3II (p<0.0024), GABARAP, the autophagic cargo receptor p62 and the mitochondrial marker TOM20 (p<0.021). However, ET/PV platelets showed dysfunctional basal and inducible autophagy. Moreover, PV platelets and platelets treated with CQ had higher levels of ROS-damaged proteins (p<0.0001) compared to healthy platelets. Platelets from PV patients exhibited hyperreactivity by flow cytometry (PAC-1 binding, p<0.05) and under flow conditions (p<0.03). Moreover, platelets from ET/PV patients showed marked bioenergetic failure characterized by increased mitochondrial depolarization, higher intracellular calcium, depressed mitochondrial respiration, and lower levels of ADP and ATP. Pharmacological inhibition of autophagy of platelets from healthy individuals with CQ recapitulated the bioenergetic and functional profiles of platelets from patients with ET/PV. Bioenergetically, autophagy inhibition resulted in depressed basal (p<0.03) and ATP-linked respiration (p<0.01). Functionally, pharmacological inhibition of the autophagic flux led to significantly decreased clot retraction, as observed with the platelets from patients with ET/PV. Conclusion: Our results suggest that impairment of autophagy in platelets from ET/PV patients might exert a negative bioenergetic effect on platelet function, promoting platelet hyperreactivity and dysfunctional clot retraction, which would likely favor the formation of unstable clots. Our findings may explain why patients with Jak2V617F ET and PV are at increased risk for both thrombosis and hemorrhage and suggest that targeting autophagy might lower this risk. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Impaired autophagy flux by lncRNA NEAT1 is critical for inflammation factors production in human periodontal ligament stem cells with nicotine treatment.

Periodontitis is the top reason for tooth loss, and smoking significantly increases severe periodontitis risk. Defective autophagy has been reported to play a vital role in periodontitis. This study aimed to elucidate the relationship between autophagy and inflammation factors production in nicotine-treated periodontal ligament stem cells (PDLSCs) and the underlying mechanism. In this study, transmission electron microscopy, immunofluorescence, and the mCherry-GFP-LC3 plasmid were used to study autophagy flux. The gene levels of inflammation factors and long noncoding RNA nuclear paraspeckle assembly transcript 1 (lncRNA NEAT1) were detected by quantitative real-time PCR (qRT-PCR). Western blot was performed to assess the protein levels of autophagic markers and α7 nicotinic acetylcholine receptor (α7nAChR). We found that nicotine impaired autophagosome-lysosome fusion and lysosome functions to block autophagy flux, contributing to inflammatory factors production in nicotine-treated PDLSCs. Moreover, nicotine upregulated NEAT1 by activating α7nAChR. NEAT1 decreased autophagy flux by downregulating syntaxin 17 (STX17). Our data indicate that NEAT1-decreased autophagy flux is pivotal for inflammation factors production in nicotine-treated PDLSCs.

Parkin coordinates mitochondrial lipid remodeling to execute mitophagy.

Autophagy has emerged as the prime machinery for implementing organelle quality control. In the context of mitophagy, the ubiquitin E3 ligase Parkin tags impaired mitochondria with ubiquitin to activate autophagic degradation. Although ubiquitination is essential for mitophagy, it is unclear how ubiquitinated mitochondria activate autophagosome assembly locally to ensure efficient destruction. Here, we report that Parkin activates lipid remodeling on mitochondria targeted for autophagic destruction. Mitochondrial Parkin induces the production of phosphatidic acid (PA) and its subsequent conversion to diacylglycerol (DAG) by recruiting phospholipase D2 and activating the PA phosphatase, Lipin-1. The production of DAG requires mitochondrial ubiquitination and ubiquitin-binding autophagy receptors, NDP52 and optineurin (OPTN). Autophagic receptors, via Golgi-derived vesicles, deliver an autophagic activator, EndoB1, to ubiquitinated mitochondria. Inhibition of Lipin-1, NDP52/OPTN, or EndoB1 results in a failure to produce mitochondrial DAG, autophagosomes, and mitochondrial clearance, while exogenous cell-permeable DAG can induce autophagosome production. Thus, mitochondrial DAG production acts downstream of Parkin to enable the local assembly of autophagosomes for the efficient disposal of ubiquitinated mitochondria.

NCOA4 Regulates Iron Recycling and Responds to Hepcidin Activity and Lipopolysaccharide in Macrophages.

Macrophages, via erythrophagocytosis, recycle iron from effete erythrocytes to newly developing red blood cells. Conversion of potentially cytotoxic levels of iron from its heme into nonheme form during iron recycling is safely accomplished via coordinated regulations of cellular iron transport and homeostasis. Herein, we demonstrate the roles and regulation of NCOA4 (nuclear receptor coactivator 4)-mediated ferritinophagy in macrophages after erythrophagocytosis using the mouse macrophage cell line J774 cells. Ferritin in J774 cells increased with the rise of nonheme iron by erythrocyte ingestion and declined when total cellular iron contents subsequently decreased. NCOA4, a selective autophagic cargo receptor for ferritin, was responsible for the control of cellular ferritin and total iron contents at the later stage of erythrophagocytosis. A hepcidin analog, which limits the flux of iron through iron-recycling by inhibiting iron export at the plasma membrane, repressed NCOA4 expression and led to accumulation of ferritin in the mouse macrophages. Transcriptome analyses revealed a functional association of immune response with NCOA4-dependent gene expressions, and we confirmed repression of Ncoa4 by lipopolysaccharide (LPS) in J774 cells and the spleen of mice. Collectively, our studies indicate that NCOA4 facilitates cellular ferritin turnover and the release of iron by macrophages after erythrophagocytosis and functions as a regulatory target for molecular signals of systemic iron overload and inflammation. These identify macrophage NCOA4 as a potential therapeutic target for disorders of systemic iron dysregulation, including anemia of inflammation and hemochromatosis.

Autophagic sequestration of SQSTM1 disrupts the aggresome formation of ubiquitinated proteins during proteasome inhibition

Aggresome formation is a protective cellular response to counteract proteasome dysfunction by sequestering misfolded proteins and reducing proteotoxic stress. Autophagic degradation of the protein aggregates is considered to be a key compensating mechanism for balancing proteostasis. However, the precise role of autophagy in proteasome inhibition-induced aggresome biogenesis remains unclear. Herein, we demonstrate that in the early stage of proteasome inhibition, the maturation of the autophagosome is suppressed, which facilitates aggresome formation of misfolded proteins. Proteasome inhibition-induced phosphorylation of SQSTM1 T269/S272 inhibits its autophagic receptor activity and promotes aggresome formation of misfolded proteins. Inhibiting SQSTM1 T269/S272 phosphorylation using Doramapimod aggravates proteasome inhibitor-mediated cell damage and tumor suppression. Taken together, our data reveal a negative effect of autophagy on aggresome biogenesis and cell damage upon proteasome inhibition. Our study suggests a novel therapeutic intervention for proteasome inhibitor-mediated tumor treatment.

Spatiotemporal Patterns of Substance P-Bound MRGPRX2 Reveal a Novel Connection Between Macropinosome Resolution and Secretory Granule Regeneration in Mast Cells.

MRGPRX2, the human member of the MAS-related G protein coupled receptors (Mrgprs), serves as the cellular target of human mast cells (MCs) for innate ligands, including neuropeptides and antimicrobial peptides. In addition, MRGPRX2 also functions as the receptor for multiple FDA-approved drugs. As such, MRGPRX2 is a mediator of MC responses in neurogenic inflammation, host defense and pseudoallergy. We analyzed the spatiotemporal patterns of MRGPRX2 following its binding of the neuropeptide substance P (SP). Herein, we show that MRGPRX2 internalizes via both endocytosis and macropinocytosis, followed by its distribution between a perinuclear region and the secretory granules (SGs). Further, we show that MRGPRX2-containing macropinosomes undergo resolution by a mechanism that involves dynamin and LC3, giving rise to the incorporation of both LC3 and MRGPRX2 into the SGs. SP then promotes the acidification of the LC3-associated SGs, presumably by stimulating their fusion with lysosomes. Taken together, our results reveal a unique mode of MRGPRX2 trafficking that complements endocytosis and involves macropinocytosis, autophagic machinery-assisted macropinosome resolution and receptor delivery to the SGs.

Hepatocyte nuclear factor 1A suppresses innate immune response by inducing degradation of TBK1 to inhibit steatohepatitis

Non-alcoholic steatohepatitis (NASH), a progressive form of non-alcoholic fatty liver disease (NAFLD), is characterised by chronic liver inflammation, which can further progress into complications such as liver cirrhosis and NASH-associated hepatocellular carcinoma (HCC) and therefore has become a growing health problem worldwide. The type I interferon (IFN) signaling pathway plays a pivotal role in chronic inflammation; however, the molecular mechanisms underlying NAFLD/NASH from the perspective of innate immune response has not yet been fully explored. In this study, we elucidated the mechanisms of how innate immune response modulates NAFLD/NASH pathogenesis, and demonstrated that hepatocyte nuclear factor-1alpha (HNF1A) was suppressed and the type I IFN production pathway was activated in liver tissues of patients with NAFLD/NASH. Further experiments suggested that HNF1A negatively regulates the TBK1-IRF3 signaling pathway by promoting autophagic degradation of phosphorylated-TBK1, which constrains IFN production, thereby inhibiting the activation of type I IFN signaling. Mechanistically, HNF1A interacts with the phagophore membrane protein LC3 through its LIR-docking sites, and mutations of LIRs (LIR2, LIR3, LIR4, and LIRs) block the HNF1A-LC3 interaction. In addition, HNF1A was identified not only as a novel autophagic cargo receptor but also to specifically induce K33-linked ubiquitin chains on TBK1 at Lys670, thereby resulting in autophagic degradation of TBK1. Collectively, our study illustrates the crucial function of the HNF1A-TBK1 signaling axis in NAFLD/NASH pathogenesis via cross-talk between autophagy and innate immunity.