Translocation of interleukin-1β into a vesicle intermediate in autophagy-mediated secretion

Unraveling the potential of neuroinflammation and autophagy in schizophrenia

Schizophrenia (SCZ) is a complex and chronic psychiatric disorder that affects a significant proportion of the global population. Although the precise etiology of SCZ remains uncertain, recent studies have underscored the involvement of neuroinflammation and autophagy in its pathogenesis. Neuroinflammation, characterized by hyperactivated microglia and markedly elevated pro-inflammatory cytokines, has been observed in postmortem brain tissues of SCZ patients and is closely associated with disease severity. Autophagy, a cellular process responsible for eliminating damaged components and maintaining cellular homeostasis, is believed to play a pivotal role in neuronal health and the onset of SCZ. This review explores the roles and underlying mechanisms of neuroinflammation and autophagy in SCZ, with a particular focus on their intricate interplay. Additionally, we provide an overview of potential therapeutic strategies aimed at modulating neuroinflammation and autophagy, including nutritional interventions, anti-inflammatory drugs, antipsychotics, and plant-derived natural compounds. The review also addresses the dual effects of antipsychotics on autophagy. Our objective is to translate these insights into clinical practice, expanding the therapeutic options available to improve the overall health and well-being of individuals with SCZ.

Endocytic tethers modulate unconventional GAPDH secretion

Yeast cell walls contain both classically-secreted and unconventionally-secreted proteins. The latter class lacks the signal sequence for translocation into the ER, therefore these proteins are transported to the wall by uncharacterized mechanisms. One such protein is the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) which is abundant in the cytosol, but also found in the yeast cell wall where it is enzymatically active. We screened diploid Saccharomyces cerevisiae homozygous gene deletions for changes in cell wall GAPDH activity. Deletions targeting endocytic tethers in the endolysosomal system had the largest effects on GAPDH secretion, including vps21, bro1, vps41, and pep12. The predominant GAPDH isoform Tdh3 was partially localized to endolysosomal compartments, including multivesicular bodies, which are common entry points to unconventional protein secretion pathways. Yeast lacking the endosomal Rab5-GTPase Vps21 had defects in GAPDH secretion as well as delayed entry into to the endolysosomal compartments. Therefore, we conclude that entry into the endolysosomal compartment facilitates non-conventional secretion of GAPDH.

Crosstalk between autophagy and other forms of programmed cell death

Cell death occurs continuously throughout individual development. By removing damaged or senescent cells, cell death not only facilitates morphogenesis during the developmental process, but also contributes to maintaining homeostasis after birth. In addition, cell death reduces the spread of pathogens by eliminating infected cells. Cell death is categorized into two main forms: necrosis and programmed cell death. Programmed cell death encompasses several types, including autophagy, pyroptosis, apoptosis, necroptosis, ferroptosis, and PANoptosis. Autophagy, a mechanism of cell death that maintains cellular equilibrium via the breakdown and reutilization of proteins and organelles, is implicated in regulating almost all forms of cell death in pathological contexts. Notably, necroptosis, ferroptosis, and PANoptosis are directly classified as autophagy-mediated cell death. Therefore, regulating autophagy presents a therapeutic approach for treating diseases such as inflammation and tumors that arise from abnormalities in other forms of programmed cell death. This review focuses on the crosstalk between autophagy and other programmed cell death modalities, providing new perspectives for clinical interventions in inflammatory and neoplastic diseases.

Unconventional secretion of PARK7 requires lysosomal delivery via chaperone-mediated autophagy and specialized SNARE complex

PARK7/DJ-1, a redox-sensitive protein implicated in neurodegeneration, cancer, and inflammation, exhibits increased secretion under stress. We previously demonstrated that, as a leaderless protein, PARK7 relies on an unconventional autophagy pathway for stress-induced secretion. The current study delves deeper into the mechanisms governing PARK7 secretion under oxidative stress triggered by the neurotoxin 6-hydroxydopamine (6-OHDA). Here, we revealed that 6-OHDA-induced autophagic flux is critical for PARK7 secretion. Downregulation of syntaxin 17 (STX17), a SNARE protein crucial for autophagosome-lysosome fusion and cargo degradation, hindered PARK7 secretion. Likewise, impairing lysosomal function with bafilomycin A1 (BafA1) or chloroquine (CQ) diminished PARK7 release, highlighting the importance of functional lysosomes, potentially in the form of secretory autolysosomes, in PARK7 release. We also found that 6-OHDA appeared to promote the unfolding of PARK7, allowing its selective recognition by the chaperone HSPA8 via KFERQ-like motifs, leading to PARK7 translocation to the lysosomal membrane through LAMP2 via chaperone-mediated autophagy (CMA). Additionally, a dedicated SNARE complex comprising Qabc-SNAREs (STX3/4, VTI1B, and STX8) and R-SNARE SEC22B mediates the fusion of PARK7-containing autolysosomes with the plasma membrane, facilitating the extracellular release of PARK7. Hence, this study uncovers a mechanism where 6-OHDA-induced autophagic flux drives the unconventional secretion of PARK7, involving CMA for PARK7 translocation to lysosomes and specialized SNARE complexes for membrane fusion events.

Autophagy-independent role of ATG9A vesicles as carriers for galectin-9 secretion

Galectins play vital roles in cellular processes such as adhesion, communication, and survival, yet the mechanisms underlying their unconventional secretion remain poorly understood. This study identifies ATG9A, a core autophagy protein, as a key regulator of galectin-9 secretion via a mechanism independent of classical autophagy, secretory autophagy, or the LC3-dependent extracellular vesicle loading and secretion pathway. ATG9A vesicles function as specialized carriers, with the N-terminus of ATG9A and both carbohydrate recognition domains of galectin-9 being critical for the process. TMED10 mediates the incorporation of galectin-9 into ATG9A vesicles, which then fuse with the plasma membrane via the STX13-SNAP23-VAMP3 SNARE complex. Furthermore, ATG9A regulates the secretion of other proteins, including galectin-4, galectin-8, and annexin A6, but not IL-1β, galectin-3, or FGF2. This mechanism is potentially conserved across other cell types, including monocytic cells, which underscores its broader significance in unconventional protein secretion.

Oxidative stress induced by combined glyphosate and TBBPA exposure promotes gill autophagy and inflammation via the PI3K/AKT/mTOR pathway

Glyphosate and tetrabromobisphenol A (TBBPA) are pollutants that pose a serious threat to the ecological safety of aquatic environments. However, there has been no report on the effects of combined exposure on the toxicity of carp fish gills in water. Therefore, we constructed a model of carp gill tissue and the carp epithelioma cells (EPC) cells exposed to glyphosate and/or TBBPA in vitro and in vivo, established a control group, a glyphosate group, a TBBPA group, and a glyphosate + TBBPA group, and added PI3K/AKT pathway activator musk ketone in vitro to verify the relationship between toxins and pathways. qRT-PCR and western blotting methods were used to detect the expression of oxidative stress-related indicators (CAT, GSH-Px, T-AOC, H2O2) and related genes. In vitro and in vivo results showed that glyphosate and/or TBBPA exposure resulted in overproduction of ROS, decreased activity of CAT, GSH-Px, T-AOC, and increased H2O2 content. Glyphosate and/or TBBPA exposure inhibited the PI3K/AKT/mTOR signaling pathway, further resulting in increased autophagy related genes LC3, ATG-5, Beclin-1, and decreased p62 expression. Inflammation related genes TNF-α, IL-1β, IL-6, IL-18 increased. And it was more significant when exposed in combination than when exposed alone. The addition of PI3K/AKT signaling pathway activator musk ketone in vitro can significantly alleviate the changes of autophagy and inflammation-related indicators. In summary, glyphosate and/or TBBPA induce oxidative stress by promoting gill autophagy and inflammation via the PI3K/AKT/mTOR pathway.

p.Phe508del-CFTR Trafficking: A Protein Quality Control Perspective Through UPR, UPS, and Autophagy

Cystic fibrosis (CF) is a genetic disease due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The most frequent mutation (p.Phe508del) results in a misfolded protein (p.Phe508del-CFTR) with an altered transport to the membrane of the cells via the conventional protein secretion (CPS) pathway. Nevertheless, it can use unconventional protein secretion (UPS). Indeed, p.Phe508del-CFTR forms a complex with GRASP55 to assist its direct trafficking from the endoplasmic reticulum to the plasma membrane. While GRASP55 is a key player of UPS, it is also a key player of stress-induced autophagy. In parallel, the unfolded protein response (UPR), which is activated in the presence of misfolded proteins, is tightly linked to UPS and autophagy through the key effectors IRE1, PERK, and ATF6. A better understanding of how UPS, UPR, and stress-induced autophagy interact to manage protein trafficking in CF and other conditions could lead to novel therapeutic strategies. By enhancing or modulating these pathways, it may be possible to increase p.Phe508del-CFTR surface expression. In summary, this review highlights the critical roles of UPS- and UPR-induced autophagy in managing protein transport, offering new perspectives for therapeutic approaches.

Amphisome plays a role in HBV production and release through the endosomal and autophagic pathways

BACKGROUND

Autophagic and endosomal pathways coordinately contribute to HBV virions and subviral particles (SVPs) production. To date, limited evidence supports that HBV and exosomes have a common pathway for their biogenesis and secretion. The final steps of HBV production and release have not yet been well studied.

METHODS

We examined the production and release of HBV virions and SVPs by using GW4869 (N,N'-Bis[4-(4,5-dihydro-1H-imidazol-2-yl)phenyl]-3,3'-pht hal amide dihydrochloride), a small molecule inhibiting ceramide-mediated inward membrane budding. Neutral sphingomyelinase, the target of GW4869, and RAB27A and -B,  2 small GTPases involved in exosome release control, were silenced using gene silencing to confirm the results obtained. Western blot, immunofluorescence staining, and confocal microscopy were applied.

RESULTS

GW4869 inhibited HBV virion release, causing their accumulation along with SVPs in hepatocytes. This triggered cellular endoplasmic reticulum stress, leading to protein kinase B-mechanistic target of rapamycin kinase signaling pathway inactivation. GW4869 treatment increased autophagosome formation and impaired autophagic degradation by blocking autophagosome-lysosome fusion. Consequently, HBsAg is increasingly localized to autophagosomes and late endosomes/multivesicular bodies. Silencing neutral sphingomyelinase yielded consistent results. Similarly, RAB27A silencing inhibited HBV virion and SVP secretion, causing their accumulation within hepatoma cells. Notably, GW4869 treatment, as well as RAB27A and -B silencing, increased the presence of LC3+CD63+HBsAg+ complexes.

CONCLUSIONS

Our results demonstrate the involvement of the autophagosome-late endosome/multivesicular bodies-exosome axis in regulating HBV production and release, highlighting amphisomes as a potential platform for HBV release.

NEDD4 E3 ligase-catalyzed NAMPT ubiquitination and autophagy activation are essential for pyroptosis-independent NAMPT secretion in human monocytes

NAMPT is an important intracellular metabolic enzyme (iNAMPT) regulating the NAD+ salvage pathway. However, increased cellular stress (infection, inflammation, hypoxia) promotes the secretion of extracellular NAMPT (eNAMPT), a TLR4 ligand and damage-associated molecular pattern protein (DAMP) that directly drives amplification of innate immune-mediated inflammatory, fibrotic, and neoplastic responses to influence disease severity. We sought to examine the mechanisms underlying pyroptotic eNAMPT release from human monocytic THP-1 cells, evoked by Nigericin, and non-pyroptotic eNAMPT secretion elicited by lipopolysaccharide (LPS). Our data indicate eNAMPT secretion/release requires NLRP3 inflammasome activation with substantial attenuation by either NLRP3 inhibition (MCC-950) or targeted genetic deletion of key inflammasome components, including NLRP3, caspase-1, or gasdermin D (GSDMD). Pyroptosis-associated eNAMPT release involved cleavage of the pore-forming GSDMD protein resulting in plasma membrane rupture (PMR) whereas non-pyroptotic LPS-induced eNAMPT secretion involved neither GSDMD cleavage nor PMR, verified utilizing non-cleavable GSDMD mutant constructs. LPS-induced eNAMPT secretion, however, was highly dependent upon NAMPT ubiquitination catalyzed by a complex containing the NEDD4 E3 ligase, Hsp90 (a selective chaperone), and intact GSDMD verified by enzymatic inhibition or silencing of NEDD4, GSDMD, or Hsp90. NAMPT ubiquitination and secretion involves autophagy activation as super-resolution microscopy analyses demonstrate NAMPT co-localization with autophagosome marker LC3B and eNAMPT secretion was significantly reduced by targeted ATG5 and ATG7 inhibition, critical components of the autophagy E3-like complex. These studies provide key insights into eNAMPT secretion that may accelerate the development of therapeutic strategies that address unmet therapeutic needs in inflammatory, fibrotic and neoplastic disorders.

The Life and Times of Brain Autophagic Vesicles

Most of the knowledge on the mechanisms and functions of autophagy originates from studies in yeast and other cellular models. How this valuable information is translated to the brain, one of the most complex and evolving organs, has been intensely investigated. Fueled by the tight dependence of the mammalian brain on autophagy, and the strong links of human brain diseases with autophagy impairment, the field has revealed adaptations of the autophagic machinery to the physiology of neurons and glia, the highly specialized cell types of the brain. Here, we first provide a detailed account of the tools available for studying brain autophagy; we then focus on the recent advancements in understanding how autophagy is regulated in brain cells, and how it contributes to their homeostasis and integrated functions. Finally, we discuss novel insights and open questions that the new knowledge has raised in the field.

Acanthamoeba castellanii-Mediated Reduction of Interleukin-1β Secretion and Its Association With Macrophage Autophagy

Noncanonical autophagy including unconventional protein secretion has been extensively studied. Our work focused on a leaderless IL-1β protein secretion from human macrophage in response to Acanthamoeba castellanii components, Acanthamoeba culture supernatant (CS) and cell lysate (CL), as well as its association with macrophage autophagy. Phorbol 12-myristate 13-acetate (PMA)-induced THP-1 macrophages were treated with Acanthamoeba components of pathogenic (ATCC50739) and nonpathogenic (ATCC30010) strains in vitro. The data showed that Acanthamoeba treatment resulted in low IL-1β secretion from macrophages. In addition, Acanthamoeba CL of both strains was able to upregulate autophagy-related (Atg) protein 8, an autophagy marker, whereas Acanthamoeba CS downregulated Atg8 expression. We further manipulated autophagy and found that autophagy induction by starvation diminished IL-1β secretion while autophagy inhibition by 3-methyladenine (3MA) increased IL-1β secretion. Interestingly, in the presence of Acanthamoeba components either under starvation or 3MA treatment, IL-1β secretion was significantly reduced. Transcriptional expression of other ATG genes, i.e., ATG6, ATG7, and ATG5, were investigated and showed that their mRNA expression was maintained at the basal level under A. castellanii CS or CL treatment. Inflammasome-related genes, NLRP3 and CASPASE1, were upregulated following A. castellanii 50739 CS treatment but not in A. castellanii 50739 CL-treated condition. However, both conditions were able to increase IL-1β mRNA expression. TEM micrographs revealed that 3MA treatment induced the formation of large vacuoles and accumulation of autophagosome at the edge of THP-1 macrophages. However, the number and size of their structures were declined in the presence of A. castellanii 50739 CS with 3MA. Furthermore, immunofluorescence staining demonstrated the association between Atg8/LC3 and IL-1β expression, where downregulation of Atg8 by A. castellanii 50739 CS led to the upregulation of IL-1β. Altogether, the data indicate that Acanthamoeba can manipulate macrophage autophagy, thereby controlling low IL-1β secretion. The expression of autophagy- and inflammasome-related genes also indicates multiple mechanisms in IL-1β secretion in response to Acanthamoeba components. However, further characterization of Atg proteins and investigations into other intracellular pathways or defense mechanisms are needed to fully understand the unconventional secretion of IL-1β in macrophages. This knowledge could eventually lead to the development of innovative therapeutic strategies against Acanthamoeba infection by modulating autophagy or macrophage responses.

HSP70 chaperones IL-33 in chronic airway disease

RATIONALE

IL-33 is a key driver of type 2 inflammation relevant to airway epithelial biology. However, the mechanisms for IL-33 secretion and regulation in the context of chronic airway disease is poorly understood.

OBJECTIVES

We sought to define how a disease associated isoform IL-33d34 that escapes nuclear sequestration and is tonically secreted from epithelial cells can be recruited to non-canonical secretory pathways.

METHODS

IL-33d34 interaction with HSP70 was assessed and validated by affinity purification, mass-spectrometry and miniTurboID proximity labeling. Secretion and activity reporter assays were used to probe the effect of HSP70 on epithelial IL-33d34 secretion and receptor binding. Human airway disease biospecimens were analyzed for dysregulation of heat shock pathways revealing modulation of TCP1 complex intermediates.

MEASUREMENTS AND MAIN RESULTS

We confirmed that HSP70 interacts directly with IL-33d34, recruits the cytokine to a vesicular compartment and enhances stability upon secretion. IL-33, HSP70 and other key mediators of proteostasis were found to be dysregulated in airway disease biospecimens and secreted extracellular vesicles. The IL-33d34 interactome was characterized and novel secretion modulators were identified.

CONCLUSIONS

This study confirms a role for HSP70 in non-canonical IL-33d34 secretion and function that may be amenable for therapeutic targeting in airway diseases.

Uncovering layer by layer the risk of nanoplastics to the environment and human health

Nanoplastics (NPs), defined as plastic particles with dimensions less than 100 nm, have emerged as a persistent environmental contaminant with potential risk to both environment and human health. Nanoplastics might translocate across biological barriers and accumulate in vital organs, leading to inflammatory responses, oxidative stress, and genotoxicity, already reported in several organisms. Disruptions to cellular functions, hormonal balance, and immune responses were also linked to NPs exposure in in vitro assays. Further, NPs have been found to adsorb other pollutants, such as persistent organic pollutants (POPs), and leach additives potentially amplifying their advere impacts, increasing the threat to organisms greater than NPs alone. However, NPs toxic effects remain largely unexplored, requiring further research to elucidate potential risks to human health, especially their accumulation, degradation, migration, interactions with the biological systems and long-term consequences of chronic exposure to these compounds. This review provides an overview of the current state-of-art regarding NPs interactions with environmental pollutants and with biological mechanisms and toxicity within cells.

Molecular mechanisms and pathological implications of unconventional protein secretion in human disease: from cellular stress to therapeutic targeting

Unconventional protein secretion (UcPS) encompasses diverse non-canonical cellular export mechanisms that operate independently of the classical secretory pathway, representing a crucial cellular response to various physiological and pathological conditions. This comprehensive review synthesizes current understanding of UcPS mechanisms, particularly focusing on their roles in disease pathogenesis and progression. Recent advances in proteomics and cellular biology have revealed that UcPS facilitates the secretion of various biomedically significant proteins, including inflammatory mediators, growth factors, and disease-associated proteins, through multiple pathways such as membrane translocation, secretory lysosomes, and membrane-bound organelles. Notably, dysregulation of UcPS mechanisms has been implicated in various pathological conditions, including chronic inflammation, neurodegenerative disorders, and malignant transformation. We critically evaluate the molecular machinery governing UcPS, its regulation under cellular stress, and its contribution to disease mechanisms. Furthermore, we examine emerging therapeutic strategies targeting UcPS pathways, highlighting both opportunities and challenges in developing novel interventional approaches.

Autophagy in Tissue Repair and Regeneration

Autophagy is a cellular recycling system that, through the sequestration and degradation of intracellular components regulates multiple cellular functions to maintain cellular homeostasis and survival. Dysregulation of autophagy is closely associated with the development of physiological alterations and human diseases, including the loss of regenerative capacity. Tissue regeneration is a highly complex process that relies on the coordinated interplay of several cellular processes, such as injury sensing, defense responses, cell proliferation, differentiation, migration, and cellular senescence. These processes act synergistically to repair or replace damaged tissues and restore their morphology and function. In this review, we examine the evidence supporting the involvement of the autophagy pathway in the different cellular mechanisms comprising the processes of regeneration and repair across different regenerative contexts. Additionally, we explore how modulating autophagy can enhance or accelerate regeneration and repair, highlighting autophagy as a promising therapeutic target in regenerative medicine for the development of autophagy-based treatments for human diseases.

The interplay between probiotics and host autophagy: mechanisms of action and emerging insights

Autophagy, a lysosome-dependent protein degradation mechanism, is a highly conserved catabolic process seen in all eukaryotes. This cell protection system, which is present in all tissues and functions at a basic level, can be up- or downregulated in response to various stresses. A disruption in the natural route of the autophagy process is frequently followed by an interruption in the inherent operation of the body's cells and organs. Probiotics are live bacteria that protect the host through various mechanisms. One of the processes through which probiotics exert their beneficial effects on various cells and tissues is autophagy. Autophagy can assist in maintaining host homeostasis by stimulating the immune system and affecting numerous physiological and pathological responses. In this review, we particularly focus on autophagy impairments occurring in several human illnesses and investigate how probiotics affect the autophagy process under various circumstances.Abbreviation: AD: Alzheimer disease; AKT: AKT serine/threonine kinase; AMPK: 5'AMP-activated protein kinase; ATG: autophagy related; CCl4: carbon tetrachloride; CFS: cell-free supernatant; CMA: chaperone-mediated autophagy; CRC: colorectal cancer; EPS: L. plantarum H31 exopolysaccharide; HD: Huntington disease; HFD: high-fat diet; HPV: human papillomavirus; IFNG/IFN-γ: interferon gamma; IL6: interleukin 6; LGG: L. rhamnosus GG; LPS: lipopolysaccharide; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; PD: Parkinson disease; Pg3G: pelargonidin-3-O-glucoside; PI3K: phosphoinositide 3-kinase; PolyQ: polyglutamine; ROS: reactive oxygen species; SCFAs: short-chain fatty acids; SLAB51: a novel formulation of lactic acid bacteria and bifidobacteria; Slp: surface layer protein (of acidophilus NCFM); SNCA: synuclein alpha; ULK1: unc-51 like autophagy-activating kinase 1; YB: B. longum subsp. infantis YB0411; YFP: yeast fermentate prebiotic.

Canonical and noncanonical autophagy: involvement in Parkinson's disease

Autophagy is the major degradation process in cells and is involved in a variety of physiological and pathological functions. While macroautophagy, which employs a series of molecular cascades to form ATG8-coated double membrane autophagosomes for degradation, remains the well-known type of canonical autophagy, microautophagy and chaperon-mediated autophagy have also been characterized. On the other hand, recent studies have focused on the functions of autophagy proteins beyond intracellular degradation, including noncanonical autophagy, also known as the conjugation of ATG8 to single membranes (CASM), and autophagy-related extracellular secretion. In particular, CASM is unique in that it does not require autophagy upstream mechanisms, while the ATG8 conjugation system is involved in a manner different from canonical autophagy. There have been many reports on the involvement of these autophagy-related mechanisms in neurodegenerative diseases, with Parkinson's disease (PD) receiving particular attention because of the important roles of several causative and risk genes, including LRRK2. In this review, we will summarize and discuss the contributions of canonical and noncanonical autophagy to cellular functions, with a special focus on the pathogenesis of PD.

Yip1 interacting factor homolog B mediates the unconventional secretion of ORF8 during SARS-CoV-2 infection

Severe cases of COVID-19 are associated with immune responses that lead to a surge in inflammatory molecules, resulting in multi-organ failure and death. This significant increase in inflammatory factors is triggered by viral proteins. Open reading frame 8 (ORF8) has received particular attention as a unique accessory protein of SARS-CoV-2. In a previous study, we have examined the role of unconventionally released ORF8 during cytokine storm associated with SARS-CoV-2 infection. Here, after mass spectrometry analysis and gene knockout/knockdown in cell/hamster models, we further discovered that Yip1 interacting factor homolog B (YIF1B) directly translocates unglycosylated ORF8 into vesicles that mediate cargo transport; specifically, the α4 helix of YIF1B interacts with the β8 sheet. Blocking ORF8 unconventional secretion via YIF1B knockdown attenuates inflammation and yields reduced mortality. Our study suggests that YIF1B directs ORF8 translocation into an unconventional secretion pathway, which has significant implications for the pathogenesis and treatment of COVID-19.

Pellino 3 E3 ligase promotes starvation-induced autophagy to prevent hepatic steatosis

Nutrient deprivation is a major trigger of autophagy, a conserved quality control and recycling process essential for cellular and tissue homeostasis. In a high-content image-based screen of the human ubiquitome, we here identify the E3 ligase Pellino 3 (PELI3) as a crucial regulator of starvation-induced autophagy. Mechanistically, PELI3 localizes to autophagic membranes, where it interacts with the ATG8 proteins through an LC3-interacting region (LIR). This facilitates PELI3-mediated ubiquitination of ULK1, driving ULK1's subsequent proteasomal degradation. PELI3 depletion leads to an aberrant accumulation and mislocalization of ULK1 and disrupts the early steps of autophagosome formation. Genetic deletion of Peli3 in mice impairs fasting-induced autophagy in the liver and enhances starvation-induced hepatic steatosis by reducing autophagy-mediated clearance of lipid droplets. Notably, PELI3 expression is decreased in the livers of patients with metabolic dysfunction-associated steatotic liver disease (MASLD), suggesting its role in hepatic steatosis development in humans. The findings suggest that PELI3-mediated control of autophagy plays a protective role in liver health.

Redundant role of PAD2 and PAD4 in the development of cardiovascular lesions in a mouse model of Kawasaki disease vasculitis

Kawasaki disease (KD) is the leading cause of acquired heart disease in children. While circulating neutrophils are increased and activated during acute KD, it is unclear whether neutrophils and neutrophil extracellular traps (NETs) contribute to the pathogenesis of KD. Peptidylarginine deiminase 4 (PAD4), an enzyme involved in protein citrullination and essential for NETs formation, is implicated in the pathogenesis of various diseases. Here, we used the Lactobacillus casei cell wall extract (LCWE)-induced mouse model of KD vasculitis to determine the contribution of PAD4 in KD vasculitis. We found that the pan-PADs inhibitor, Cl-amidine, significantly reduced LCWE-induced cardiovascular lesions, but neutrophil-specific Padi4 KO mice did not impact the development of KD vasculitis. While in vitro treatment of macrophages, which highly express Padi4, with Cl-amidine inhibited IL-1β secretion, macrophage-specific Padi4 KO mice did not reduce the lesions. Padi4-/- mice also developed KD vasculitis, AFM30a, a PAD2 inhibitor, significantly reduced KD vasculitis in Padi4-/- mice, indicating a compensatory role of PAD2 in PAD4 deficiency. We also identified several citrullinated proteins in macrophages with constitutively active NLRP3 inflammasome that were inhibited by Cl-amidine treatment, suggesting that protein citrullination participates in NLRP3 inflammasome activation. These data indicate a dispensable role for PAD4-dependent NETs formation, and a redundant role of PAD2 and PAD4 in this murine KD vasculitis. The cardioprotective effects of Cl-amidine to reduce the severity of murine KD vasculitis are not limited to PAD4 inhibition and may include decreased citrullination in the inflammasome pathway.

Type I IFN drives unconventional IL-1β secretion in lupus monocytes

Opsonization of red blood cells that retain mitochondria (Mito+ RBCs), a feature of systemic lupus erythematosus (SLE), triggers type I interferon (IFN) production in macrophages. We report that monocytes (Mos) co-produce IFN and mature interleukin-1β (mIL-1β) upon Mito+ RBC opsonization. IFN expression depended on cyclic GMP-AMP synthase (cGAS) and RIG-I-like receptors' (RLRs) sensing of Mito+ RBC-derived mitochondrial DNA (mtDNA) and mtRNA, respectively. Interleukin-1β (IL-1β) production was initiated by the RLR antiviral signaling adaptor (MAVS) pathway recognition of Mito+ RBC-derived mtRNA. This led to the cytosolic release of Mo mtDNA, which activated the inflammasome. Importantly, mIL-1β secretion was independent of gasdermin D (GSDMD) and pyroptosis but relied on IFN-inducible myxovirus-resistant protein 1 (MxA), which facilitated the incorporation of mIL-1β into a trans-Golgi network (TGN)-mediated secretory pathway. RBC internalization identified a subset of blood Mo expressing IFN-stimulated genes (ISGs) that released mIL-1β and expanded in SLE patients with active disease.

Autophagic stress activates distinct compensatory secretory pathways in neurons

Autophagic dysfunction is a hallmark of neurodegenerative disease, leaving neurons vulnerable to the accumulation of damaged organelles and proteins. However, the late onset of diseases suggests that compensatory quality control mechanisms may be engaged to delay the deleterious effects induced by compromised autophagy. Neurons expressing common familial Parkinson's disease (PD)-associated mutations in LRRK2 kinase exhibit defective autophagy. Here, we demonstrate that both primary murine neurons and human iPSC-derived neurons harboring pathogenic LRRK2 upregulate the secretion of extracellular vesicles. We used unbiased proteomics to characterize the secretome of LRRK2G2019S neurons and found that autophagic cargos including mitochondrial proteins were enriched. Based on these observations, we hypothesized that autophagosomes are rerouted toward secretion when cell-autonomous degradation is compromised, likely to mediate clearance of undegraded cellular waste. Immunoblotting confirmed the release of autophagic cargos and immunocytochemistry demonstrated that secretory autophagy was upregulated in LRRK2G2019S neurons. We also found that LRRK2G2019S neurons upregulate the release of exosomes containing miRNAs. Live-cell imaging confirmed that this upregulation of exosomal release was dependent on hyperactive LRRK2 activity, while pharmacological experiments indicate that this release staves off apoptosis. Finally, we show that markers of both vesicle populations are upregulated in plasma from mice expressing pathogenic LRRK2. In sum, we find that neurons expressing pathogenic LRRK2 upregulate the compensatory release of secreted autophagosomes and exosomes, to mediate waste disposal and transcellular communication, respectively. We propose that this increased secretion contributes to the maintenance of cellular homeostasis, delaying neurodegenerative disease progression over the short term while potentially contributing to increased neuroinflammation over the longer term.

Immune modulation through secretory autophagy

Autophagy is a central mechanism of cellular homeostasis through the degradation of a wide range of cellular constituents. However, recent evidence suggests that autophagy actively provides information to neighboring cells via a process called secretory autophagy. Secretory autophagy couples the autophagy machinery to the secretion of cellular content via extracellular vesicles (EVs). EVs carry a variety of cargo, that reflect the pathophysiological state of the originating cells and have the potential to change the functional profile of recipient cells, to modulate cell biology. The immune system has evolved to maintain local and systemic homeostasis. It is able to sense a wide array of molecules signaling disturbed homeostasis, including EVs and their content. In this review, we explore the emerging concept of secretory autophagy as a means to communicate cellular, and in total tissue pathophysiological states to the immune system to initiate the restoration of tissue homeostasis. Understanding how autophagy mediates the secretion of immunogenic factors may hold great potential for therapeutic intervention.

Proteomic Characterization of Ubiquitin Carboxyl-Terminal Hydrolase 19 Deficient Cells Reveals a Role for USP19 in the Secretion of Lysosomal Proteins

Ubiquitin carboxyl-terminal hydrolase 19 (USP19) is a unique deubiquitinase, characterized by multiple variants generated by alternative splicing. Several variants bear a C-terminal transmembrane domain that anchors them to the endoplasmic reticulum. Other than regulating protein stability by preventing proteasome degradation, USP19 has been reported to rescue substrates from endoplasmic reticulum-associated protein degradation in a catalytic-independent manner, promote autophagy, and address proteins to lysosomal degradation via endosomal microautophagy. USP19 has recently emerged as the protein responsible for the unconventional secretion of misfolded proteins including Parkinson's disease-associated protein α-synuclein. Despite mounting evidence that USP19 plays crucial roles in several biological processes, the underlying mechanisms are unclear due to lack of information on the physiological substrates of USP19. Herein, we used high-resolution quantitative proteomics to analyze changes in the secretome and cell proteome induced by the loss of USP19 to identify proteins whose secretion or turnover is regulated by USP19. We found that ablation of USP19 induced significant proteomic alterations both in and out of the cell. Loss of USP19 impaired the release of several lysosomal proteins, including legumain (LGMN) and several cathepsins. In order to understand the underlaying mechanism, we dissected the USP19-regulated secretion of LGMN in several cell types. We found that LGMN was not a deubiquitinase substrate of USP19 and that its USP19-dependent release did not require their direct interaction. LGMN secretion occurred by a mechanism that involved the Golgi apparatus, autophagosome formation, and lysosome function. This mechanism resembled the recently described "lysosomal exocytosis," by which lysosomal hydrolases are secreted, when ubiquitination of p62 is increased in cells lacking deubiquitinases such as USP15 and USP17. In conclusion, our proteomic characterization of USP19 has identified a collection of proteins in the secretome and within the cell that are regulated by USP19, which link USP19 to the secretion of lysosomal proteins, including LGMN.

New Insights into the Fanconi Anemia Pathogenesis: A Crosstalk Between Inflammation and Oxidative Stress

Fanconi anemia (FA) represents a rare hereditary disease; it develops due to germline pathogenic variants in any of the 22 currently discovered FANC genes, which interact with the Fanconi anemia/breast cancer-associated (FANC/BRCA) pathway to maintain genome integrity. FA is characterized by a triad of clinical traits, including congenital anomalies, bone marrow failure (BMF) and multiple cancer susceptibility. Due to the complex genetic background and a broad spectrum of FA clinical symptoms, the diagnostic process is complex and requires the use of classical cytogenetic, molecular cytogenetics and strictly molecular methods. Recent findings indicate the interplay of inflammation, oxidative stress, disrupted mitochondrial metabolism, and impaired intracellular signaling in the FA pathogenesis. Additionally, a shift in the balance towards overproduction of proinflammatory cytokines and prooxidant components in FA is associated with advanced myelosuppression and ultimately BMF. Although the mechanism of BMF is very complex and needs further clarification, it appears that mutual interaction between proinflammatory cytokines and redox imbalance causes pancytopenia. In this review, we summarize the available literature regarding the clinical phenotype, genetic background, and diagnostic procedures of FA. We also highlight the current understanding of disrupted autophagy process, proinflammatory state, impaired signaling pathways and oxidative genotoxic stress in FA pathogenesis.

Distinct trafficking routes of polarized and non-polarized membrane cargoes in Aspergillus nidulans

Membrane proteins are sorted to the plasma membrane via Golgi-dependent trafficking. However, our recent studies challenged the essentiality of Golgi in the biogenesis of specific transporters. Here, we investigate the trafficking mechanisms of membrane proteins by following the localization of the polarized R-SNARE SynA versus the non-polarized transporter UapA, synchronously co-expressed in wild-type or isogenic genetic backgrounds repressible for conventional cargo secretion. In wild-type, the two cargoes dynamically label distinct secretory compartments, highlighted by the finding that, unlike SynA, UapA does not colocalize with the late-Golgi. In line with early partitioning into distinct secretory carriers, the two cargoes collapse in distinct ER-Exit Sites (ERES) in a sec31ts background. Trafficking via distinct cargo-specific carriers is further supported by showing that repression of proteins essential for conventional cargo secretion does not affect UapA trafficking, while blocking SynA secretion. Overall, this work establishes the existence of distinct, cargo-dependent, trafficking mechanisms, initiating at ERES and being differentially dependent on Golgi and SNARE interactions.

Coronavirus envelope protein activates TMED10-mediated unconventional secretion of inflammatory factors

The precise cellular mechanisms underlying heightened proinflammatory cytokine production during coronavirus infection remain incompletely understood. Here we identify the envelope (E) protein in severe coronaviruses (SARS-CoV-2, SARS, or MERS) as a potent inducer of interleukin-1 release, intensifying lung inflammation through the activation of TMED10-mediated unconventional protein secretion (UcPS). In contrast, the E protein of mild coronaviruses (229E, HKU1, or OC43) demonstrates a less pronounced effect. The E protein of severe coronaviruses contains an SS/DS motif, which is not present in milder strains and facilitates interaction with TMED10. This interaction enhances TMED10-oligomerization, facilitating UcPS cargo translocation into the ER-Golgi intermediate compartment (ERGIC)-a pivotal step in interleukin-1 UcPS. Progesterone analogues were identified as compounds inhibiting E-enhanced release of proinflammatory factors and lung inflammation in a Mouse Hepatitis Virus (MHV) infection model. These findings elucidate a molecular mechanism driving coronavirus-induced hyperinflammation, proposing the E-TMED10 interaction as a potential therapeutic target to counteract the adverse effects of coronavirus-induced inflammation.

Plekhg5 controls the unconventional secretion of Sod1 by presynaptic secretory autophagy

Increasing evidence suggests an essential function for autophagy in unconventional protein secretion (UPS). However, despite its relevance for the secretion of aggregate-prone proteins, the mechanisms of secretory autophagy in neurons have remained elusive. Here we show that the lower motoneuron disease-associated guanine exchange factor Plekhg5 drives the UPS of Sod1. Mechanistically, Sod1 is sequestered into autophagosomal carriers, which subsequently fuse with secretory lysosomal-related organelles (LROs). Exocytosis of LROs to release Sod1 into the extracellular milieu requires the activation of the small GTPase Rab26 by Plekhg5. Deletion of Plekhg5 in mice leads to the accumulation of Sod1 in LROs at swollen presynaptic sites. A reduced secretion of toxic ALS-linked SOD1G93A following deletion of Plekhg5 in SOD1G93A mice accelerated disease onset while prolonging survival due to an attenuated microglia activation. Using human iPSC-derived motoneurons we show that reduced levels of PLEKHG5 cause an impaired secretion of ALS-linked SOD1. Our findings highlight an unexpected pathophysiological mechanism that converges two motoneuron disease-associated proteins into a common pathway.

The endolysosomal system in conventional and unconventional protein secretion

Most secreted proteins are transported through the "conventional" endoplasmic reticulum-Golgi apparatus exocytic route for their delivery to the cell surface and release into the extracellular space. Nonetheless, formative discoveries have underscored the existence of alternative or "unconventional" secretory routes, which play a crucial role in exporting a diverse array of cytosolic proteins outside the cell in response to intrinsic demands, external cues, and environmental changes. In this context, lysosomes emerge as dynamic organelles positioned at the crossroads of multiple intracellular trafficking pathways, endowed with the capacity to fuse with the plasma membrane and recognized for their key role in both conventional and unconventional protein secretion. The recent recognition of lysosomal transport and exocytosis in the unconventional secretion of cargo proteins provides new and promising insights into our understanding of numerous physiological processes.

Effect of α7 nAChR-autophagy axis of deciduous tooth pulp stem cells in regulating IL-1β in the process of physiological root resorption of deciduous teeth

Physiological root resorption of deciduous teeth is a normal phenomenon occurring during the developmental stages of children. Previous research has indicated the pivotal role of the inflammatory microenvironment in this process, although the specific mechanisms remain unclear. This study is aimed at elucidating the involvement of the alpha7 nicotinic acetylcholine receptors (α7 nAChR)-autophagy axis in the regulation of the inflammatory microenvironment during physiological root resorption in deciduous teeth. Samples were collected from deciduous teeth at various stages of physiological root resorption, and deciduous dental pulp stem cells (DDPSCs) were isolated and cultured during the mid-phase of root resorption. The findings revealed a substantial infiltration of the pulp of deciduous teeth at the mid-phase of root resorption, characterized by elevated expression levels of α7 nAChR and IL-1β. Significantly increased IL-1β and α7 nAChR expressions were observed in DDPSCs during the mid-phase of root resorption, with α7 nAChR demonstrating a regulatory effect on IL-1β. Moreover, evidence suggested that mechanical stress may act as a trigger, regulating autophagy and IL-1 expression via α7 nAChR. In conclusion, mechanical stress was identified as a regulator of autophagy in DDPSCs through α7 nAChR, influencing the expression of IL-1β and contributing to the formation of the inflammatory microenvironment. This mechanism plays a crucial role in the physiological root resorption of deciduous teeth. KEY MESSAGES: The pulp of deciduous teeth at mid-phase of root resorption was heavily infiltrated with high expression of α7nAChR and IL-1β. α7 nAChR acts as an initiating factor to regulate IL-1β through autophagy in DDPSCs. Mechanical stress can regulate autophagy of DDPSCs through α7 nAChR and thus affect IL-1β expression and inflammatory microenvironment formation in physiological root resorption in deciduous teeth.

Gasdermin D and Gasdermin E Are Dispensable for Silica-Mediated IL-1β Secretion from Mouse Macrophages

Silica crystals activate the NLRP3 inflammasome in macrophages, resulting in the caspase-1-dependent secretion of the proinflammatory cytokine IL-1β. Caspase-1-mediated cleavage of gasdermin D (GSDMD) triggers the formation of GSDMD pores, which drive pyroptotic cell death and facilitate the rapid release of IL-1β. However, the role of GSDMD in silica-induced lung injury is unclear. In this study, we show that although silica-induced lung injury is dependent on the inflammasome adaptor ASC and IL-1R1 signaling, GSDMD is dispensable for acute lung injury. Although the early rapid secretion of IL-1β in response to ATP and nigericin was GSDMD dependent, GSDMD was not required for IL-1β release at later time points. Similarly, secretion of IL-1β from macrophages in response to silica and alum proceeded in a GSDMD-independent manner. We further found that gasdermin E did not contribute to macrophage IL-1β secretion in the absence of GSDMD in vitro and was also not necessary for silica-induced acute lung injury in vivo. These findings demonstrate that GSDMD and gasdermin E are dispensable for IL-1β secretion in response to silica in vitro and in silica-induced acute lung injury in vivo.

Atg8/LC3 controls systemic nutrient surplus signaling in flies and humans

Organisms experience constant nutritional flux. Mechanisms at the interface of opposing nutritional states-scarcity and surplus-enable organismal energy homeostasis. Contingent on nutritional stores, adipocytes secrete adipokines, such as the fat hormone leptin, to signal nutrient status to the central brain. Increased leptin secretion underlies metabolic dysregulation during common obesity, but the molecular mechanisms regulating leptin secretion from human adipocytes are poorly understood. Here, we report that Atg8/LC3 family proteins, best known for their role in autophagy during nutrient scarcity, play an evolutionarily conserved role during nutrient surplus by promoting adipokine secretion. We show that in a well-fed state, Atg8/LC3 promotes the secretion of the Drosophila functional leptin ortholog unpaired 2 (Upd2) and leptin from human adipocytes. Proteomic analyses reveal that LC3 directs leptin to a secretory pathway in human cells. We identified LC3-dependent extracellular vesicle (EV) loading and secretion (LDELS) as a required step for leptin release, highlighting a unique secretory route adopted by leptin in human adipocytes. In Drosophila, mutations to Upd2's Atg8 interaction motif (AIM) result in constitutive adipokine retention. Atg8-mediated Upd2 retention alters lipid storage and hunger response and rewires the bulk organismal transcriptome in a manner conducive to starvation survival. Thus, Atg8/LC3's bidirectional role in nutrient sensing-conveying nutrient surplus and responding to nutrient deprivation-enables organisms to manage nutrient flux effectively. We posit that decoding how bidirectional molecular switches-such as Atg8/LC3-operate at the nexus of nutritional scarcity and surplus will inform therapeutic strategies to tackle chronic metabolic disorders.

A dual role of ERGIC-localized Rabs in TMED10-mediated unconventional protein secretion

Cargo translocation across membranes is a crucial aspect of secretion. In conventional secretion signal peptide-equipped proteins enter the endoplasmic reticulum (ER), whereas a subset of cargo lacking signal peptides translocate into the ER-Golgi intermediate compartment (ERGIC) in a process called unconventional protein secretion (UcPS). The regulatory events at the ERGIC in UcPS are unclear. Here we reveal the involvement of ERGIC-localized small GTPases, Rab1 (Rab1A and Rab1B) and Rab2A, in regulating UcPS cargo transport via TMED10 on the ERGIC. Rab1 enhances TMED10 translocator activity, promoting cargo translocation into the ERGIC, whereas Rab2A, in collaboration with KIF5B, regulates ERGIC compartmentalization, establishing a UcPS-specific compartment. This study highlights the pivotal role of ERGIC-localized Rabs in governing cargo translocation and specifying the ERGIC's function in UcPS.

Intraluminal vesicle trafficking is involved in the secretion of base excision repair protein APE1

The apurinic/apyrimidinic endodeoxyribonuclease 1 (APE1) is an essential enzyme of the base excision repair pathway of non-distorting DNA lesions. In response to genotoxic treatments, APE1 is highly secreted (sAPE1) in association with small-extracellular vesicles (EVs). Interestingly, its presence in the serum of patients with hepatocellular or non-small-cell-lung cancers may represent a prognostic biomarker. The mechanism driving APE1 to associate with EVs is unknown, but is of paramount importance in better understanding the biological roles of sAPE1. Because APE1 lacks an endoplasmic reticulum-targeting signal peptide, it can be secreted through an unconventional protein secretion endoplasmic reticulum-Golgi-independent pathway, which includes an endosome-based secretion of intraluminal vesicles, mediated by multivesicular bodies (MVBs). Using HeLa and A549 cell lines, we investigated the role of endosomal sorting complex required for transport protein pathways (either-dependent or -independent) in the constitutive or trichostatin A-induced secretion of sAPE1, by means of manumycin A and GW 4869 treatments. Through an in-depth biochemical analysis of late-endosomes (LEs) and early-endosomes (EEs), we observed that the distribution of APE1 on density gradient corresponded to that of LE-CD63, LE-Rab7, EE-EEA1 and EE-Rab 5. Interestingly, the secretion of sAPE1, induced by cisplatin genotoxic stress, involved an autophagy-based unconventional secretion requiring MVBs. The present study enlightens the central role played by MVBs in the secretion of sAPE1 under various stimuli, and offers new perspectives in understanding the biological relevance of sAPE1 in cancer cells.

Function of autophagy genes in innate immune defense against mucosal pathogens

Mucosal immunity is posed to constantly interact with commensal microbes and invading pathogens. As a fundamental cell biological pathway affecting immune response, autophagy regulates the interaction between mucosal immunity and microbes through multiple mechanisms, including direct elimination of microbes, control of inflammation, antigen presentation and lymphocyte homeostasis, and secretion of immune mediators. Some of these physiologically important functions do not involve canonical degradative autophagy but rely on certain autophagy genes and their 'autophagy gene-specific functions.' Here, we review the relationship between autophagy and important mucosal pathogens, including influenza virus, Mycobacterium tuberculosis, Salmonella enterica, Citrobacter rodentium, norovirus, and herpes simplex virus, with a particular focus on distinguishing the canonical versus gene-specific mechanisms of autophagy genes.

AGR2-mediated unconventional secretion of 14-3-3ε and α-actinin-4, responsive to ER stress and autophagy, drives chemotaxis in canine mammary tumor cells

BACKGROUND

Canine mammary tumors (CMTs) in intact female dogs provide a natural model for investigating metastatic human cancers. Our prior research identified elevated expression of Anterior Gradient 2 (AGR2), a protein disulfide isomerase (PDI) primarily found in the endoplasmic reticulum (ER), in CMT tissues, highly associated with CMT progression. We further demonstrated that increased AGR2 expression actively influences the extracellular microenvironment, promoting chemotaxis in CMT cells. Unraveling the underlying mechanisms is crucial for assessing the potential of therapeutically targeting AGR2 as a strategy to inhibit a pro-metastatic microenvironment and impede tumor metastasis.

METHODS

To identify the AGR2-modulated secretome, we employed proteomics analysis of the conditioned media (CM) from two CMT cell lines ectopically expressing AGR2, compared with corresponding vector-expressing controls. AGR2-regulated release of 14-3-3ε (gene: YWHAE) and α-actinin 4 (gene: ACTN4) was validated through ectopic expression, knockdown, and knockout of the AGR2 gene in CMT cells. Extracellular vesicles derived from CMT cells were isolated using either differential ultracentrifugation or size exclusion chromatography. The roles of 14-3-3ε and α-actinin 4 in the chemotaxis driven by the AGR2-modulated CM were investigated through gene knockdown, antibody-mediated interference, and recombinant protein supplement. Furthermore, the clinical relevance of the release of 14-3-3ε and α-actinin 4 was assessed using CMT tissue-immersed saline and sera from CMT-afflicted dogs.

RESULTS

Proteomics analysis of the AGR2-modulated secretome revealed increased abundance in 14-3-3ε and α-actinin 4. Ectopic expression of AGR2 significantly increased the release of 14-3-3ε and α-actinin 4 in the CM. Conversely, knockdown or knockout of AGR2 expression remarkably reduced their release. Silencing 14-3-3ε or α-actinin 4 expression diminished the chemotaxis driven by AGR2-modulated CM. Furthermore, AGR2 controls the release of 14-3-3ε and α-actinin 4 primarily via non-vesicular routes, responding to the endoplasmic reticulum (ER) stress and autophagy activation. Knockout of AGR2 resulted in increased α-actinin 4 accumulation and impaired 14-3-3ε translocation in autophagosomes. Depletion of extracellular 14-3-3ε or α-actinin 4 reduced the chemotaxis driven by AGR2-modulated CM, whereas supplement with recombinant 14-3-3ε in the CM enhanced the CM-driven chemotaxis. Notably, elevated levels of 14-3-3ε or α-actinin 4 were observed in CMT tissue-immersed saline compared with paired non-tumor samples and in the sera of CMT dogs compared with healthy dogs.

CONCLUSION

This study elucidates AGR2's pivotal role in orchestrating unconventional secretion of 14-3-3ε and α-actinin 4 from CMT cells, thereby contributing to paracrine-mediated chemotaxis. The insight into the intricate interplay between AGR2-involved ER stress, autophagy, and unconventional secretion provides a foundation for refining strategies aimed at impeding metastasis in both canine mammary tumors and potentially human cancers.

Tau fibrils induce nanoscale membrane damage and nucleate cytosolic tau at lysosomes

The prion-like spread of protein aggregates is a leading hypothesis for the propagation of neurofibrillary lesions in the brain, including the spread of tau inclusions associated with Alzheimer's disease. The mechanisms of cellular uptake of tau seeds and subsequent nucleated polymerization of cytosolic tau are major questions in the field, and the potential for coupling between the entry and nucleation mechanisms has been little explored. We found that in primary astrocytes and neurons, endocytosis of tau seeds leads to their accumulation in lysosomes. This in turn leads to lysosomal swelling, deacidification, and recruitment of ESCRT proteins, but not Galectin-3, to the lysosomal membrane. These observations are consistent with nanoscale damage of the lysosomal membrane. Live cell imaging and STORM superresolution microscopy further show that the nucleation of cytosolic tau occurs primarily at the lysosome membrane under these conditions. These data suggest that tau seeds escape from lysosomes via nanoscale damage rather than wholesale rupture and that nucleation of cytosolic tau commences as soon as tau fibril ends emerge from the lysosomal membrane.

The incorporation of acetylated LAP-TGF-β1 proteins into exosomes promotes TNBC cell dissemination in lung micro-metastasis

Triple-negative breast cancer (TNBC) stands as the breast cancer subtype with the highest recurrence and mortality rates, with the lungs being the common site of metastasis. The pulmonary microenvironment plays a pivotal role in the colonization of disseminated tumor cells. Herein, this study highlights the crucial role of exosomal LAP-TGF-β1, the principal form of exosomal TGF-β1, in reshaping the pulmonary vascular niche, thereby facilitating TNBC lung metastasis. Although various strategies have been developed to block TGF-β signaling and have advanced clinically, their significant side effects have limited their therapeutic application. This study demonstrates that in lung metastatic sites, LAP-TGF-β1 within exosomes can remarkably reconfigure the pulmonary vascular niche at lower doses, bolstering the extravasation and colonization of TNBC cells in the lungs. Mechanistically, under the aegis of the acetyltransferase TIP60, a non-canonical KFERQ-like sequence in LAP-TGF-β1 undergoes acetylation at the K304 site, promoting its interaction with HSP90A and subsequent transport into exosomes. Concurrent inhibition of both HSP90A and TIP60 significantly diminishes the exosomal burden of LAP-TGF-β1, presenting a promising therapeutic avenue for TNBC lung metastasis. This study not only offers fresh insights into the molecular underpinnings of TNBC lung metastasis but also lays a foundation for innovative therapeutic strategies.

A cilia-bound unconventional secretory pathway for Drosophila odorant receptors

BACKGROUND

Post-translational transport is a vital process which ensures that each protein reaches its site of function. Though most do so via an ordered ER-to-Golgi route, an increasing number of proteins are now shown to bypass this conventional secretory pathway.

RESULTS

In the Drosophila olfactory sensory neurons (OSNs), odorant receptors (ORs) are trafficked from the ER towards the cilia. Here, we show that Or22a, a receptor of various esters and alcoholic compounds, reaches the cilia partially through unconventional means. Or22a frequently present as puncta at the somatic cell body exit and within the dendrite prior to the cilia base. These rarely coincide with markers of either the intermediary ER-Golgi-intermediate-compartment (ERGIC) or Golgi structures. ERGIC and Golgi also displayed axonal localization biases, a further indication that at least some measure of OR transport may occur independently of their involvement. Additionally, neither the loss of several COPII genes involved in anterograde trafficking nor ERGIC itself affected puncta formation or Or22a transport to the cilium. Instead, we observed the consistent colocalization of Or22a puncta with Grasp65, the sole Drosophila homolog of mammalian GRASP55/Grh1, a marker of the unconventional pathway. The numbers of both Or22a and Grasp65-positive puncta were furthermore increased upon nutritional starvation, a condition known to enhance Golgi-bypassing secretory activity.

CONCLUSIONS

Our results demonstrate an alternative route of Or22a transport, thus expanding the repertoire of unconventional secretion mechanisms in neurons.

Role for Caspase-8 in the Release of IL-1β and Active Caspase-1 from Viable Human Monocytes during Toxoplasma gondii Infection

Monocytes are actively recruited to sites of infection and produce the potent proinflammatory cytokine IL-1β. We previously showed that IL-1β release during Toxoplasma gondii infection of primary human monocytes requires the NLRP3 inflammasome and caspase-1 but is independent of gasdermin D and pyroptosis. To investigate mechanisms of IL-1β release, we generated caspase-1, -4, -5, or -8 knockout (KO) THP-1 monocytic cells. Genetic ablation of caspase-1 or -8, but not caspase-4 or -5, decreased IL-1β release during T. gondii infection without affecting cell death. In contrast, TNF-α and IL-6 secretion were unperturbed in caspase-8 KO cells during T. gondii infection. Dual pharmacological inhibition of caspase-8 and RIPK1 in primary monocytes also decreased IL-1β release without affecting cell viability or parasite infection. Caspase-8 was also required for the release of active caspase-1 from T. gondii-infected cells and for IL-1β release during infection with the related apicomplexan parasite Neospora caninum. Surprisingly, caspase-8 deficiency did not impair synthesis or cleavage of pro-IL-1β, but resulted in the retention of mature IL-1β within cells. Generation of gasdermin E KO and ATG7 KO THP-1 cells revealed that the release of IL-1β was not dependent on gasdermin E or ATG7. Collectively, our data indicate that during T. gondii Infection of human monocytes, caspase-8 functions in a novel gasdermin-independent mechanism controlling IL-1β release from viable cells. This study expands on the molecular pathways that promote IL-1β in human immune cells and provides evidence of a role for caspase-8 in the mechanism of IL-1β release during infection.

Tumor cell-derived LC3B+extracellular vesicles mediate the crosstalk between tumor microenvironment and immunotherapy efficacy in hepatocellular carcinoma via the HSP90α-IL-6/IL-8 signaling axis

BACKGROUND

Inflammatory factors are being recognized as critical modulators of host antitumor immunity in liver cancer. We have previously shown that tumor cell-released LC3B positive extracellular vesicles (LC3B+ EVs) are responsible for malignant progression by dampening antitumor immunity. However, the relationship between LC3B+ EVs and inflammatory factors in the regulation of the liver cancer microenvironment remains unclear.

METHODS

Flow cytometry analyses were performed to examine the panel of 12 cytokines, the main source of positive cytokines, and plasma LC3B+ EVs carrying HSP90α in peripheral blood of liver cancer patients. We correlated the levels of plasma IL-6, IL-8 with LC3B+ EVs carrying HSP90α and with prognosis. In vitro culture of healthy donor leukocytes with liver cancer-derived LC3B+ EVs was performed to evaluate the potential effect of blocking HSP90α, IL-6 or IL-8 alone or in combination with PD-1 inhibitor on CD8+ T cell function. We also investigated the potential associations of MAP1LC3B, HSP90AA1, IL6 or IL8 with immunotherapy efficacy using the TCGA databases.

RESULTS

In liver cancer patients, plasma IL-6 and IL-8 levels were significantly higher than in healthy controls and associated with poor clinical outcome. In peripheral blood, levels of plasma LC3B+ EVs carrying HSP90α were significantly elevated in HCC patients and positively associated with IL-6 and IL-8 levels, which are predominantly secreted by monocytes and neutrophils. Moreover, LC3B+ EVs from human liver cancer cells promoted the secretion of IL-6 and IL-8 by leukocytes through HSP90α. Besides, we show that the cytokines IL-6 and IL-8 secreted by LC3B+ EVs-induced leukocytes were involved in the inhibition of CD8+ T-cell function, while blockade of the HSP90α on the LC3B+ EVs, IL-6, or IL-8 could enhance anti-PD-1-induced T cell reinvigoration. Finally, patients who received anti-PD-1/PD-L1 immunotherapy with high MAP1LC3B, HSP90AA1, IL6, or IL8 expression had a lower immunotherapy efficacy.

CONCLUSIONS

Our data suggest that liver cancer-derived LC3B+ EVs promote a pro-oncogenic inflammatory microenvironment by carrying membrane-bound HSP90α. Targeting HSP90α on the LC3B+ EVs, IL-6, or IL-8 may synergize with anti-PD-1 treatment to enhance the CD8+ T-cell functions, which may provide novel combination strategies in the clinic for the treatment of liver cancer.

Autophagy as a new player in the regulation of clock neurons physiology of Drosophila melanogaster

Axonal terminals of the small ventral lateral neurons (sLNvs), the circadian clock neurons of Drosophila, show daily changes in their arborization complexity, with many branches in the morning and their shrinkage during the night. This complex phenomenon is precisely regulated by several mechanisms. In the present study we describe that one of them is autophagy, a self-degradative process, also involved in changes of cell membrane size and shape. Our results showed that autophagosome formation and processing in PDF-expressing neurons (both sLNv and lLNv) are rhythmic and they have different patterns in the cell bodies and terminals. These rhythmic changes in the autophagy activity seem to be important for neuronal plasticity. We found that autophagosome cargos are different during the day and night, and more proteins involved in membrane remodeling are present in autophagosomes in the morning. In addition, we described for the first time that Atg8-positive vesicles are also present outside the sLNv terminals, which suggests that secretory autophagy might be involved in regulating the clock signaling network. Our data indicate that rhythmic autophagy in clock neurons affect the pacemaker function, through remodeling of terminal membrane and secretion of specific proteins from sLNvs.

Autophagy-Dependent Secretion: Crosstalk between Autophagy and Exosome Biogenesis

The cellular secretome is pivotal in mediating intercellular communication and coordinating responses to stressors. Exosomes, initially recognized for their role in waste disposal, have now emerged as key intercellular messengers with significant therapeutic and diagnostic potential. Similarly, autophagy has transcended its traditional role as a waste removal mechanism, emerging as a regulator of intracellular communication pathways and a contributor to a unique autophagy-dependent secretome. Secretory authophagy, initiated by various stress stimuli, prompts the selective release of proteins implicated in inflammation, including leaderless proteins that bypass the conventional endoplasmic reticulum-Golgi secretory pathway. This reflects the significant impact of stress-induced autophagy on cellular secretion profiles, including the modulation of exosome release. The convergence of exosome biogenesis and autophagy is exemplified by the formation of amphisomes, vesicles that integrate autophagic and endosomal pathways, indicating their synergistic interplay. Regulatory proteins common to both pathways, particularly mTORC1, emerge as potential therapeutic targets to alter cellular secretion profiles involved in various diseases. This review explores the dynamic interplay between autophagy and exosome formation, highlighting the potential to influence the secretome composition. While the modulation of exosome secretion and cytokine preconditioning is well-established in regenerative medicine, the strategic manipulation of autophagy is still underexplored, presenting a promising but uncharted therapeutic landscape.

SARS-CoV-2 NSP2 as a Potential Delivery Vehicle for Proteins

The development of biomolecule delivery systems is essential for the treatment of various diseases such as cancer, immunological diseases, and metabolic disorders. For the first time, we found that SARS-CoV-2-encoded nonstructural protein 2 (NSP2) can be secreted from the cells, where it is synthesized. Brefeldin A and H89, inhibitors of ER/Golgi secretion pathways, did not inhibit NSP2 secretion. NSP2 is likely secreted via an unconventional secretory pathway. Moreover, both secreted and purified NSP2 proteins were able to traverse the plasma membrane barrier and enter both immortalized human umbilical vein endothelial cells and tumor cell lines. After entry, the NSP2 protein was localized in only the cytoplasm. Cytochalasin D, a potent inhibitor of actin polymerization, inhibited the entry of NSP2. NSP2 can carry other molecules into cells. Burkholderia lethal factor 1, a monomeric toxin from the intracellular pathogen Burkholderia pseudomallei, has demonstrated antitumor activity by targeting host eukaryotic initiation translation factor 4A. An NSP2-BLF1 fusion protein was translocated across the cellular membranes of Huh7 cells and mediated cell killing. By using different approaches, including protein purification, chemical inhibition, and cell imaging, we confirm that NSP2 is able to deliver heterologous proteins into cells. NSP2 can act as a potential delivery vehicle for proteins.

[Unconventional protein secretion - new perspectives in protein trafficking]

The characterization of the structural and functional organization of eukaryotic cells has revealed the membrane compartments and machinery required for vesicular protein transport. Most proteins essential for intercellular communication contain an N-terminal signal sequence enabling them to be incorporated into the biosynthetic or conventional secretory pathway, in which proteins are sequentially transported through the endoplasmic reticulum (ER) and the Golgi apparatus. However, major research studies have shown the existence of alternative secretory routes that are independent of the ER-Golgi and designated as unconventional secretory pathways. These pathways involve a large number of players that may divert specific compartments from their primary function in favor of secretory roles. The comprehensive description of these processes is therefore of utmost importance to unveil how proteins secreted through these alternative pathways control cell homeostasis or contribute to disease development.

Myristoylated GRASP55 dimerizes in the presence of model membranes

The Golgi Reassembly and Stacking Proteins (GRASPs) are engaged in various functions within the cell, both in unconventional secretion mechanisms and structuring and organizing the Golgi apparatus. Understanding their specific role in each situation still requires more structural and functional data at the molecular level. GRASP55 is one of the GRASP members in mammals, anchored to the membrane via the myristoylation of a Gly residue at its N-terminus. Therefore, co-translational modifications, such as myristoylation, are fundamental when considering a strategy to obtain detailed information on the interactions between GRASP55 and membranes. Despite its functional relevance, the N-terminal myristoylation has been underappreciated in the studies reported to date, compromising the previously proposed models for GRASP-membrane interactions. Here, we investigated the synergy between the presence of the membrane and the formation of oligomeric structures of myristoylated GRASP55, using a series of biophysical techniques to perform the structural characterization of the lipidated GRASP55 and its interaction with biological lipid model membranes. Our data fulfill an unexplored gap: the adequate evaluation of the presence of lipidations and lipid membranes on the structure-function dyad of GRASPs.

Coordination of RAB-8 and RAB-11 during unconventional protein secretion

Multiple physiology-pertinent transmembrane proteins reach the cell surface via the Golgi-bypassing unconventional protein secretion (UcPS) pathway. By employing C. elegans-polarized intestine epithelia, we recently have revealed that the small GTPase RAB-8/Rab8 serves as an important player in the process. Nonetheless, its function and the relevant UcPS itinerary remain poorly understood. Here, we show that deregulated RAB-8 activity resulted in impaired apical UcPS, which increased sensitivity to infection and environmental stress. We also identified the SNARE VTI-1/Vti1a/b as a new RAB-8-interacting factor involved in the apical UcPS. Besides, RAB-11/Rab11 was capable of recruiting RABI-8/Rabin8 to reduce the guanine nucleotide exchange activity of SMGL-1/GEF toward RAB-8, indicating the necessity of a finely tuned RAB-8/RAB-11 network. Populations of RAB-8- and RAB-11-positive endosomal structures containing the apical UcPS cargo moved toward the apical side. In the absence of RAB-11 or its effectors, the cargo was retained in RAB-8- and RAB-11-positive endosomes, respectively, suggesting that these endosomes are utilized as intermediate carriers for the UcPS.

Mitochondria isolated from lipid droplets of white adipose tissue reveal functional differences based on lipid droplet size

Recent studies in brown adipose tissue (BAT) described a unique subpopulation of mitochondria bound to lipid droplets (LDs), which were termed PeriDroplet Mitochondria (PDM). PDM can be isolated from BAT by differential centrifugation and salt washes. Contrary to BAT, this approach has so far not led to the successful isolation of PDM from white adipose tissue (WAT). Here, we developed a method to isolate PDM from WAT with high yield and purity by an optimized proteolytic treatment that preserves the respiratory function of mitochondria. Using this approach, we show that, contrary to BAT, WAT PDM have lower respiratory and ATP synthesis capacities compared with WAT cytoplasmic mitochondria (CM). Furthermore, by isolating PDM from LDs of different sizes, we found a negative correlation between LD size and the respiratory capacity of their PDM in WAT. Thus, our new isolation method reveals tissue-specific characteristics of PDM and establishes the existence of heterogeneity in PDM function determined by LD size.