Galectins and TRIMs directly interact and orchestrate autophagic response to endomembrane damage

Emerging Roles of Galectin-3 in Pulmonary Diseases

Galectin-3 is a multifunctional protein that is involved in various physiological and pathological events. Emerging evidence suggests that galectin-3 also plays a critical role in the pathogenesis of pulmonary diseases. Galectin-3 can be produced and secreted by various cell types in the lungs, and the overexpression of galectin-3 has been found in acute lung injury/acute respiratory distress syndrome (ALI/ARDS), pulmonary hypertension (PH), pulmonary fibrosis diseases, lung cancer, lung infection, chronic obstructive pulmonary disease (COPD), and asthma. Galectin-3 exerts diverse effects on the inflammatory response, immune cell activation, fibrosis and tissue remodeling, and tumorigenesis in these pulmonary disorders, and genetic and pharmacologic modulation of galectin-3 has therapeutic effects on the treatment of pulmonary illnesses. In this review, we summarize the structure and function of galectin-3 and the underlying mechanisms of galectin-3 in pulmonary disease pathologies; we also discuss preclinical and clinical evidence regarding the therapeutic potential of galectin-3 inhibitors in these pulmonary disorders. Additionally, targeting galectin-3 may be a very promising therapeutic approach for the treatment of pulmonary diseases.

TFEB ameliorates DEHP-induced neurotoxicity by activating GAL3/TRIM16 axis dependent lysophagy and alleviating lysosomal dysfunction

Di-(2-ethylhexyl) phthalate (DEHP) is a commonly used plasticizer with known neurotoxic effects. However, the specific mechanism underlying this neurotoxicity remains unclear. This study aimed to investigate the role of lysosomal function and lysophagy in DEHP-induced neurotoxicity, with a particular focus on the regulatory role of Transcription factor EB (TFEB). To achieve this, we utilized in vitro models of DEHP-exposed SH-SY5Y cells and HT22 cells. Our findings revealed that DEHP exposure led to lysosomal damage and dysfunction. Moreover, we observed impaired autophagic degradation, characterized by elevated levels of LC3II and p62. DEHP treatment downregulated the expression of TFEB, GAL3, and TRIM16, while upregulating the expression of PARP. This led to the inhibition of GAL3/TRIM16 axis dependent lysophagy and ultimately excessive apoptosis in neuronal cells. Importantly, TFEB overexpression alleviated lysosomal dysfunction, activated lysophagy, and mitigated DEHP-induced apoptosis. Overall, our results suggest that DEHP induces not only lysosomal dysfunction, but also inhibits lysophagy through the suppression of GAL3/TRIM16 axis. Consequently, impaired clearance of damaged lysosomes occurs, culminating in neuronal apoptosis. Taken together, our findings highlight the critical role of TFEB in regulating lysophagy and lysosomal function. Furthermore, TFEB may serve as a potential therapeutic target for mitigating DEHP-induced neuronal toxicity.

Activation of the lysosomal damage response and selective autophagy: the coordinated actions of galectins, TRIM proteins, and CGAS-STING1 in providing immunity against Mycobacterium tuberculosis

Autophagy is a crucial immune defense mechanism that controls the survival and pathogenesis of M. tb by maintaining cell physiology during stress and pathogen attack. The E3-Ub ligases (PRKN, SMURF1, and NEDD4) and autophagy receptors (SQSTM1, TAX1BP1, CALCOCO2, OPTN, and NBR1) play key roles in this process. Galectins (LGALSs), which bind to sugars and are involved in identifying damaged cell membranes caused by intracellular pathogens such as M. tb, are essential. These include LGALS3, LGALS8, and LGALS9, which respond to endomembrane damage and regulate endomembrane damage caused by toxic chemicals, protein aggregates, and intracellular pathogens, including M. tb. They also activate selective autophagy and de novo endolysosome biogenesis. LGALS3, LGALS9, and LGALS8 interact with various components to activate autophagy and repair damage, while CGAS-STING1 plays a critical role in providing immunity against M. tb by activating selective autophagy and producing type I IFNs with antimycobacterial functions. STING1 activates cGAMP-dependent autophagy which provides immunity against various pathogens. Additionally, cytoplasmic surveillance pathways activated by ds-DNA, such as inflammasomes mediated by NLRP3 and AIM2 complexes, control M. tb. Modulation of E3-Ub ligases with small regulatory molecules of LGALSs and TRIM proteins could be a novel host-based therapeutic approach for controlling TB.

PRKAA2, MTOR, and TFEB in the regulation of lysosomal damage response and autophagy

Lysosomes function as critical signaling hubs that govern essential enzyme complexes. LGALS proteins (LGALS3, LGALS8, and LGALS9) are integral to the endomembrane damage response. If ESCRT fails to rectify damage, LGALS-mediated ubiquitination occurs, recruiting autophagy receptors (CALCOCO2, TRIM16, and SQSTM1) and VCP/p97 complex containing UBXN6, PLAA, and YOD1, initiating selective autophagy. Lysosome replenishment through biogenesis is regulated by TFEB. LGALS3 interacts with TFRC and TRIM16, aiding ESCRT-mediated repair and autophagy-mediated removal of damaged lysosomes. LGALS8 inhibits MTOR and activates TFEB for ATG and lysosomal gene transcription. LGALS9 inhibits USP9X, activates PRKAA2, MAP3K7, ubiquitination, and autophagy. Conjugation of ATG8 to single membranes (CASM) initiates damage repair mediated by ATP6V1A, ATG16L1, ATG12, ATG5, ATG3, and TECPR1. ATG8ylation or CASM activates the MERIT system (ESCRT-mediated repair, autophagy-mediated clearance, MCOLN1 activation, Ca2+ release, RRAG-GTPase regulation, MTOR modulation, TFEB activation, and activation of GTPase IRGM). Annexins ANAX1 and ANAX2 aid damage repair. Stress granules stabilize damaged membranes, recruiting FLCN-FNIP1/2, G3BP1, and NUFIP1 to inhibit MTOR and activate TFEB. Lysosomes coordinate the synergistic response to endomembrane damage and are vital for innate and adaptive immunity. Future research should unveil the collaborative actions of ATG proteins, LGALSs, TRIMs, autophagy receptors, and lysosomal proteins in lysosomal damage response.

Multipronged regulation of autophagy and apoptosis: emerging role of TRIM proteins

TRIM proteins are characterized by their conserved N-terminal RING, B-box, and coiled-coil domains. These proteins are efficient regulators of autophagy, apoptosis, and innate immune responses and confer immunity against viruses and bacteria. TRIMs function as receptors or scaffold proteins that target substrates for autophagy-mediated degradation. Most TRIMs interact with the BECN1-ULK1 complex to form TRIMosomes, thereby efficiently targeting substrates to autophagosomes. They regulate the functions of ATG proteins through physical interactions or ubiquitination. TRIMs affect the lipidation of MAP1LC3B1 to form MAP1LC3B2, which is a prerequisite for phagophore and autophagosome formation. In addition, they regulate MTOR kinase and TFEB, thereby regulating the expression of ATG genes. TRIM proteins are efficient regulators of apoptosis and are crucial for regulating cell proliferation and tumor formation. Many TRIM proteins regulate intrinsic and extrinsic apoptosis via the cell surface receptors TGFBR2, TNFRSF1A, and FAS. Mitochondria modulate the anti- and proapoptotic functions of BCL2, BAX, BAK1, and CYCS. These proteins use a multipronged approach to regulate the intrinsic and extrinsic apoptotic pathways, culminating in coordinated activation or inhibition of the initiator and executor CASPs. Furthermore, TRIMs can have a dual effect in determining cell fate and are therefore crucial for cellular homeostasis. In this review, we discuss mechanistic insights into the role of TRIM proteins in regulating autophagy and apoptosis, which can be used to better understand cellular physiology. These findings can be used to develop therapeutic interventions to prevent or treat multiple genetic and infectious diseases.

The role of TRIM family in metabolic associated fatty liver disease

Metabolic associated fatty liver disease (MAFLD) ranks among the most prevalent chronic liver conditions globally. At present, the mechanism of MAFLD has not been fully elucidated. Tripartite motif (TRIM) protein is a kind of protein with E3 ubiquitin ligase activity, which participates in highly diversified cell activities and processes. It not only plays an important role in innate immunity, but also participates in liver steatosis, insulin resistance and other processes. In this review, we focused on the role of TRIM family in metabolic associated fatty liver disease. We also introduced the structure and functions of TRIM proteins. We summarized the TRIM family's regulation involved in the occurrence and development of metabolic associated fatty liver disease, as well as insulin resistance. We deeply discussed the potential of TRIM proteins as targets for the treatment of metabolic associated fatty liver disease.

The Functions of TRIM56 in Antiviral Innate Immunity and Tumorigenesis

As a member of the TRIM (tripartite motif) protein family, TRIM56 can function as an E3 ubiquitin ligase. In addition, TRIM56 has been shown to possess deubiquitinase activity and the ability to bind RNA. This adds to the complexity of the regulatory mechanism of TRIM56. TRIM56 was initially found to be able to regulate the innate immune response. In recent years, its role in direct antiviral and tumor development has also attracted the interest of researchers, but there is no systematic review on TRIM56. Here, we first summarize the structural features and expression of TRIM56. Then, we review the functions of TRIM56 in TLR and cGAS-STING pathways of innate immune response, the mechanisms and structural specificity of TRIM56 against different types of viruses, and the dual roles of TRIM56 in tumorigenesis. Finally, we discuss the future research directions regarding TRIM56.

Galectins and galectin-mediated autophagy regulation: new insights into targeted cancer therapy

Galectins are animal lectins with specific affinity for galactosides via the conserved carbohydrate recognition domains. Increasing studies recently have identified critical roles of galectin family members in tumor progression. Abnormal expression of galectins contributes to the proliferation, metastasis, epithelial-mesenchymal transformation (EMT), immunosuppression, radio-resistance and chemoresistance in various cancers, which has attracted cumulative clinical interest in galectin-based cancer treatment. Galectin family members have been reported to participate in autophagy regulation under physiological conditions and in non-tumoral diseases, and implication of galectins in multiple processes of carcinogenesis also involves regulation of autophagy, however, the relationship between galectins, autophagy and cancer remains largely unclear. In this review, we introduce the structure and function of galectins at the molecular level, summarize their engagements in autophagy and cancer progression, and also highlight the regulation of autophagy by galectins in cancer as well as the therapeutic potentials of galectin and autophagy-based strategies. Elaborating on the mechanism of galectin-regulated autophagy in cancers will accelerate the exploitation of galectins-autophagy targeted therapies in treatment for cancer.

Lysosomal dysfunction in diabetic cardiomyopathy

Diabetes is a major risk factor for a variety of cardiovascular complications, while diabetic cardiomyopathy, a disease specific to the myocardium independent of vascular lesions, is an important causative factor for increased risk of heart failure and mortality in diabetic populations. Lysosomes have long been recognized as intracellular trash bags and recycling facilities. However, recent studies have revealed that lysosomes are sophisticated signaling hubs that play remarkably diverse roles in adapting cell metabolism to an ever-changing environment. Despite advances in our understanding of the physiological roles of lysosomes, the events leading to lysosomal dysfunction and how they relate to the overall pathophysiology of the diabetic heart remain unclear and are under intense investigation. In this review, we summarize recent advances regarding lysosomal injury and its roles in diabetic cardiomyopathy.

TRIM family contribute to tumorigenesis, cancer development, and drug resistance

The tripartite-motif (TRIM) family represents one of the largest classes of putative single protein RING-finger E3 ubiquitin ligases. TRIM family is involved in a variety of cellular signaling transductions and biological processes. TRIM family also contributes to cancer initiation, progress, and therapy resistance, exhibiting oncogenic and tumor-suppressive functions in different human cancer types. Moreover, TRIM family members have great potential to serve as biomarkers for cancer diagnosis and prognosis. In this review, we focus on the specific mechanisms of the participation of TRIM family members in tumorigenesis, and cancer development including interacting with dysregulated signaling pathways such as JAK/STAT, PI3K/AKT, TGF-β, NF-κB, Wnt/β-catenin, and p53 hub. In addition, many studies have demonstrated that the TRIM family are related to tumor resistance; modulate the epithelial–mesenchymal transition (EMT) process, and guarantee the acquisition of cancer stem cells (CSCs) phenotype. In the end, we havediscussed the potential of TRIM family members for cancer therapeutic targets.

TBK1 is part of a galectin 8 dependent membrane damage recognition complex and drives autophagy upon Adenovirus endosomal escape

Intracellular pathogens cause membrane distortion and damage as they enter host cells. Cells perceive these membrane alterations as danger signals and respond by activating autophagy. This response has primarily been studied during bacterial invasion, and only rarely in viral infections. Here, we investigate the cellular response to membrane damage during adenoviral entry. Adenoviruses and their vector derivatives, that are an important vaccine platform against SARS-CoV-2, enter the host cell by endocytosis followed by lysis of the endosomal membrane. We previously showed that cells mount a locally confined autophagy response at the site of endosomal membrane lysis. Here we describe the mechanism of autophagy induction: endosomal membrane damage activates the kinase TBK1 that accumulates in its phosphorylated form at the penetration site. Activation and recruitment of TBK1 require detection of membrane damage by galectin 8 but occur independently of classical autophagy receptors or functional autophagy. Instead, TBK1 itself promotes subsequent autophagy that adenoviruses need to take control of. Deletion of TBK1 reduces LC3 lipidation during adenovirus infection and restores the infectivity of an adenovirus mutant that is restricted by autophagy. By comparing adenovirus-induced membrane damage to sterile lysosomal damage, we implicate TBK1 in the response to a broader range of types of membrane damage. Our study thus highlights an important role for TBK1 in the cellular response to adenoviral endosome penetration and places TBK1 early in the pathway leading to autophagy in response to membrane damage.

Rapid detection of invading pathogens is crucial for cell survival. Membrane alterations in this process are detected by cells but are rarely studied in the context of viral infections. TBK1 is an important kinase driving innate immunity and autophagy in response to pathogen invasion. Here we report that TBK1 promotes autophagy in response to membrane penetration by adenoviruses. We demonstrate that TBK1 is rapidly activated and recruited to virus membrane penetration sites, and promotes autophagy through its kinase activity. We show that TBK1 recruitment depends on membrane damage recognition via galectin 8 but occurs independently of classical autophagy receptors or functional autophagy. Moreover, we demonstrate that TBK1 activation is part of a wider cellular response to endo-lysosomal damage. Our work highlights a prominent role for TBK1 in the swift cellular response to membrane damage and the downstream activation of autophagy.

Membrane protective role of autophagic machinery during infection of epithelial cells by Candida albicans

Candida albicans (C. albicans) is an opportunistic pathogen causing infections ranging from superficial to life-threatening disseminated infections. In a susceptible host, C. albicans is able to translocate through the gut barrier, promoting its dissemination into deeper organs. C. albicans hyphae can invade human epithelial cells by two well-documented mechanisms: epithelial-driven endocytosis and C. albicans-driven active penetration. One mechanism by which host cells protect themselves against intracellular C. albicans is termed autophagy. The protective role of autophagy during C. albicans infection has been investigated in myeloid cells; however, far less is known regarding the role of this process during the infection of epithelial cells. In the present study, we investigated the role of autophagy-related proteins during the infection of epithelial cells, including intestinal epithelial cells and gut explants, by C. albicans. Using cell imaging, we show that key molecular players of the autophagy machinery (LC3-II, PI3P, ATG16L1, and WIPI2) were recruited at Candida invasion sites. We deepened these observations by electron microscopy analyses that reveal the presence of autophagosomes in the vicinity of invading hyphae. Importantly, these events occur during active penetration of C. albicans into host cells and are associated with plasma membrane damage. In this context, we show that the autophagy-related key proteins ATG5 and ATG16L1 contribute to plasma membrane repair mediated by lysosomal exocytosis and participate in protecting epithelial cells against C. albicans-induced cell death. Our findings provide a novel mechanism by which epithelial cells, forming the first line of defense against C. albicans in the gut, can react to limit C. albicans invasion.

LGALS3 (galectin 3) mediates an unconventional secretion of SNCA/α-synuclein in response to lysosomal membrane damage by the autophagic-lysosomal pathway in human midbrain dopamine neurons

Numerous lines of evidence support the premise that the misfolding and subsequent accumulation of SNCA/α-synuclein (synuclein alpha) is responsible for the underlying neuronal pathology observed in Parkinson disease (PD) and other synucleinopathies. Moreover, the cell-to-cell transfer of these misfolded SNCA species is thought to be responsible for disease progression and the spread of cellular pathology throughout the brain. Previous work has shown that when exogenous, misfolded SNCA fibrils enter cells through endocytosis, they can damage and rupture the membranes of their endocytotic vesicles in which they are trafficked. Rupture of these vesicular membranes exposes intralumenal glycans leading to galectin protein binding, subsequent autophagic protein recruitment, and, ultimately, their introduction into the autophagic-lysosomal pathway. Increasing evidence indicates that both pathological and non-pathological SNCA species undergo autophagy-dependent unconventional secretion. While other proteins have also been shown to be secreted from cells by autophagy, what triggers this release process and how these specific proteins are recruited to a secretory autophagic pathway is largely unknown. Here, we use a human midbrain dopamine (mDA) neuronal culture model to provide evidence in support of a cellular mechanism that explains the cell-to-cell transfer of pathological forms of SNCA that are observed in PD. We demonstrate that LGALS3 (galectin 3) mediates the release of SNCA following vesicular damage. SNCA release is also dependent on TRIM16 (tripartite motif containing 16) and ATG16L1 (autophagy related 16 like 1), providing evidence that secretion of SNCA is mediated by an autophagic secretory pathway.

TRIMs: selective recruitment at different steps of the NF-κB pathway-determinant of activation or resolution of inflammation

TNF-α-induced NF-κB pathway is an essential component of innate and adaptive immune pathway, and it is tightly regulated by various post-translational modifications including ubiquitination. Oscillations in NF-κB activation and temporal gene expression are emerging as critical determinants of inflammatory response, however, the regulators of unique outcomes in different patho-physiological conditions are not well understood. Tripartite Motif-containing proteins (TRIMs) are RING domain-containing E3 ligases involved in the regulation of cellular homeostasis, metabolism, cell death, inflammation, and host defence. Emerging reports suggest that TRIMs are recruited at different steps of TNF-α-induced NF-κB pathway and modulate via their E3 ligase activity. TRIMs show synergy and antagonism in the regulation of the NF-κB pathway and also regulate it in a feedback manner. TRIMs also regulate pattern recognition receptors (PRRs) mediated inflammatory pathways and may have evolved to directly regulate a specific arm of immune signalling. The review emphasizes TRIM-mediated ubiquitination and modulation of TNF-α-regulated temporal and NF-κB signaling and its possible impact on unique transcriptional and functional outcomes.

Galectin-3 is modulated in pancreatic cancer cells under hypoxia and nutrient deprivation

Pancreatic ductal adenocarcinoma is one of the most aggressive tumors with a microenvironment marked by hypoxia and starvation. Galectin-3 has been evaluated in solid tumors and seems to present both pro/anti-tumor effects. So, this study aims to characterize the expression of Galectin-3 from pancreatic tumor cells and analyze its influence for cell survive and motility in mimetic microenvironment. For this, cell cycle and cell death were accessed through flow cytometry. Characterization of inside and outside Galectin-3 was performed through Real-Time Quantitative Reverse Transcription PCR (qRT-PCR), immunofluorescence, Western blot, and ELISA. Consequences of Galectin-3 extracellular inhibition were investigated using cell death and scratch assays. PANC-1 showed increased Galectin-3 mRNA expression when cultivated in hypoxia for 24 and 48 h. After 24 h in simultaneously hypoxic/deprived incubation, PANC-1 shows increased Galectin-3 protein and secreted levels. For Mia PaCa-2, cultivation in deprivation was determinant for the increasing in Galectin-3 mRNA expression. When cultivated in simultaneously hypoxic/deprived condition, Mia PaCa-2 also presented increasing for the Galectin-3 secreted levels. Treatment of PANC-1 cells with lactose increased the death rate when cells were incubated simultaneously hypoxic/deprived condition. Therefore, it is possible to conclude that the microenvironmental conditions modulate the Galectin-3 expression on the transcriptional and translational levels for pancreatic cancer cells.

Selective Autophagy Receptors in Antiviral Defense

Autophagy ensures the degradation of cytosolic substrates by the lysosomal pathway. Cargoes destined to be eliminated are confined within double-membrane vesicles called autophagosomes, prior to fusion with endolysosomal vacuoles. Autophagy receptors selectively interact with cargoes and route them to elongating autophagic membranes, a process referred to as selective autophagy. Besides contributing to cell homeostasis, selective autophagy constitutes an important cell-autonomous defense mechanism against viruses. We review observations related to selective autophagy receptor engagement during host cell responses to virus infection. We examine the distinct roles of autophagy receptors in antiviral autophagy, consider the strategies viruses have evolved to escape or oppose such restrictions, and delineate the contributions of selective autophagy to the tailoring of antiviral innate responses. Finally, we mention some open and emerging questions in the field.

TRIM16 Promotes Osteogenic Differentiation of Human Periodontal Ligament Stem Cells by Modulating CHIP-Mediated Degradation of RUNX2

Bone regeneration is the ultimate goal of periodontal therapies, in which osteogenic differentiation of human periodontal ligament stem cells plays a critical role. The tripartite motif (TRIM)16, an E3 ubiquitin ligase, is downregulated in periodontal tissues of patients with periodontitis, while the role of TRIM16 in the osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) is largely unknown. Firstly, we found that TRIM16 was increased throughout the osteogenic media induced differentiation of hPDLSCs. Then overexpression plasmids and specific short-hairpin RNAs (shRNAs) were constructed to manipulate the expression of target molecules. TRIM16 significantly promoted alkaline phosphatase activity, mineralized nodule formation, and positively regulated the expression of osteo-specific markers RUNX2, COL1A1 and OCN except the mRNA of RUNX2. Mechanistically, TRIM16 serves as a pivotal factor that stabilizes RUNX2 protein levels by decreasing CHIP-mediated K48-linked ubiquitination degradation of the RUNX2 protein. This study identified a novel mechanism of TRIM16 in regulating stability of the RUNX2 protein, which promoted the osteogenic differentiation of hPDLSCs. TRIM16 may be a potential target of stem cell based-bone regeneration for periodontal therapies.

Galectin-3 Expression in Pancreatic Cell Lines Under Distinct Autophagy-Inducing Stimulus

Hypoxia and nutrient deprivation are responsible for inducing malignant behavior in neoplastic cells. In these conditions, metabolic stress leads the cells to enhance their autophagic flux and to activate key molecules for homeostasis maintenance. Galectin-3 (Gal-3) is upregulated in pancreatic cancer and it is activated under the hypoxic atmosphere. We aimed to analyze the most effective autophagic-inducing conditions in pancreatic ductal adenocarcinoma cells and the effect exerted under these conditions in association with hypoxia on the Gal-3 expression. Gal-3 and the microtubule-associated protein light chain 3 beta (LC3) were accessed through western blot and immunofluorescence. Degradative vacuole quantification was analyzed by transmission electronic microscopy, and inhibition of Gal-3 was performed using siRNA. According to the analyses, the most effective conditions in the inducement of autophagy for PANC-1 and MIA PaCa-2 cells were nutritional deprivation and complete amino acid/glucose deprivation, respectively. PANC-1 cells presented higher Gal-3 when they were submitted to 24 h of nutritional deprivation alone and simultaneously nutritional and oxygen deprivation. Inhibition of Gal-3 causes a decrease of LC3 levels in all experimental conditions. These results confirm that Gal-3 is modulated by microenvironment factors and the possibility of Gal-3 participating in an adaptive response from PDAC cells to extreme conditions.

Autophagy and Lc3-Associated Phagocytosis in Zebrafish Models of Bacterial Infections

Modeling human infectious diseases using the early life stages of zebrafish provides unprecedented opportunities for visualizing and studying the interaction between pathogens and phagocytic cells of the innate immune system. Intracellular pathogens use phagocytes or other host cells, like gut epithelial cells, as a replication niche. The intracellular growth of these pathogens can be counteracted by host defense mechanisms that rely on the autophagy machinery. In recent years, zebrafish embryo infection models have provided in vivo evidence for the significance of the autophagic defenses and these models are now being used to explore autophagy as a therapeutic target. In line with studies in mammalian models, research in zebrafish has shown that selective autophagy mediated by ubiquitin receptors, such as p62, is important for host resistance against several bacterial pathogens, including Shigella flexneri, Mycobacterium marinum, and Staphylococcus aureus. Furthermore, an autophagy related process, Lc3-associated phagocytosis (LAP), proved host beneficial in the case of Salmonella Typhimurium infection but host detrimental in the case of S. aureus infection, where LAP delivers the pathogen to a replication niche. These studies provide valuable information for developing novel therapeutic strategies aimed at directing the autophagy machinery towards bacterial degradation.

Assessing the role of SH3RF1 and SH3RF2 polymorphisms in susceptibility to tuberculosis: A case-control study in the Han Chinese population

BACKGROUND

Tuberculosis (TB) remains a major public health problem. SH3RF1 and SH3RF2 are candidate genes with multiple single-nucleotide polymorphisms (SNPs) that have the potential to participate in Mycobacterium infection via activation of the JNK signaling pathway. In this case-control study, we aimed to investigate the association of five SH3RF1 and SH3RF2 SNPs with susceptibility to TB in the Western Chinese population.

METHODS

A total of 900 TB patients and 1534 healthy control subjects were enrolled in our study. All samples used were obtained from the Bio-Bank of resources of Tuberculosis Research in the Department of Laboratory Medicine, West China Hospital, Sichuan University, China. SNP genotyping was conducted using a commercial custom-by-design 2 × 48-Plex SNPscan Kit.

RESULTS

The rs758037 variant of the SH3RF2 gene was found to be associated with decreased TB risk based on allelic effects (p = 0.00001, OR = 0.731, 95% CI = 0.641-0.833) and three genetic models (padd = 0.00001, pdom = 0.0003, prec = 0.0007) after the data were controlled for age and gender and underwent Bonferroni correction. The rs4913057 variant of the SH3RF2 gene was found to be associated with increased TB risk in a dominant model (p = 0.021, OR: 1.260, 95% CI: 1.065-1.490). No significant association was observed between other SNPs and TB risk.

CONCLUSION

These findings indicate that polymorphisms in the SH3RF2 gene are involved in susceptibility to TB in the Western Chinese population.

Restoration of lysosomal function after damage is accompanied by recycling of lysosomal membrane proteins

Lysosomes are central organelles for cellular degradation and energy homeostasis. In addition, lysosomal membrane permeabilization (LMP) and subsequent release of lysosomal content to the cytosol can initiate programmed cell death. The extent of LMP and available repair mechanisms determine the cell fate after lysosomal damage. In this study, we aimed to investigate the premises for lysosomal membrane repair after LMP and found that lysosomal membrane damage initiated by L-leucyl-L-leucine methyl ester (LLOMe) caused caspase-dependent apoptosis in almost 50% of the cells, while the rest recovered. Immediately after LLOMe addition, lysosomal proteases were detected in the cytosol and the ESCRT-components ALIX and CHMP4B were recruited to the lysosomal membrane. Next, lysophagic clearance of damaged lysosomes was evident and a concentration-dependent translocation of several lysosomal membrane proteins, including LAMP2, to the cytosol was found. LAMP2 was present in small vesicles with the N-terminal protein chain facing the lumen of the vesicle. We conclude that lysophagic clearance of damaged lysosomes results in generation of lysosomal membrane protein complexes, which constitute small membrane enclosed units, possibly for recycling of lysosomal membrane proteins. These lysosomal membrane complexes enable an efficient regeneration of lysosomes to regain cell functionality.

The Peroxisome Proliferator-Activated Receptor α- Agonist Gemfibrozil Promotes Defense Against Mycobacterium abscessus Infections

Peroxisome proliferator-activated receptor α (PPARα) shows promising potential to enhance host defenses against Mycobacterium tuberculosis infection. Herein we evaluated the protective effect of PPARα against nontuberculous mycobacterial (NTM) infections. Using a rapidly growing NTM species, Mycobacterium abscessus (Mabc), we found that the intracellular bacterial load and histopathological damage were increased in PPARα-null mice in vivo. In addition, PPARα deficiency led to excessive production of proinflammatory cytokines and chemokines after infection of the lung and macrophages. Notably, administration of gemfibrozil (GEM), a PPARα activator, significantly reduced the in vivo Mabc load and inflammatory response in mice. Transcription factor EB was required for the antimicrobial response against Mabc infection. Collectively, these results suggest that manipulation of PPARα activation has promising potential as a therapeutic strategy for NTM disease.

Galectin-3 and TRIM16 coregulate osteogenic differentiation of human bone marrow-derived mesenchymal stem cells at least partly via enhancing autophagy

BACKGROUND

The osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs) is critical for bone homeostasis. Here, we investigated the regulation of Galectin-3 and tripartite motif protein 16 (TRIM16) on osteogenic differentiation of hBMSCs through autophagy.

METHODS

Quantitative PCR (qPCR) and western blot were performed to determine the expression of osteogenic markers, autophagic markers, Galectin-3 and TRIM16. Short-hairpin RNAs (shRNAs) and overexpression plasmids were used to manipulate the expression of Galectin-3, TRIM16 and Unc-51 like autophagy activating kinase 1 (ULK1). Alkaline phosphatase (ALP) activity was measured by ALP staining assay. Calcium deposition in differentiated hBMSCs was assessed by Alizarin Red S staining. LC3 puncta formation was monitored by immunofluorescence staining. The interaction between indicated proteins was confirmed by co-immunoprecipitation (Co-IP) assay.

RESULTS

Either Galectin-3 or TRIM16 knockdown led to impaired ALP activity, reduced calcium deposition, down-regulation of pro-osteogenic markers as well as restrained autophagy in osteogenic-induced hBMSCs. However, overexpression of Galectin-3 or TRIM16 promoted osteogenic differentiation of hBMSCs, which was then compromised by autophagy inhibition. Co-IP experiment demonstrated that TRIM16 associated with Galectin-3 through ULK1. Meanwhile, osteogenic induction enhanced the association between TRIM16 and ULK1 or coiled-coil myosin-like BCL2-interacting protein (Beclin1), and TRIM16 increased the stability of ULK1 and Beclin1. Moreover, either TRIM16 or ULK1 knockdown dampened the pro-osteogenic effect of Galectin-3, which elucidated that Galectin-3 mediated osteogenic differentiation was at least partly dependent on TRIM16 and ULK1.

CONCLUSION

In summary, the present study revealed Galectin-3 and TRIM16 co-regulated osteogenic differentiation of hBMSCs at least partly via enhancing autophagy, which might provide a promising approach for osteoporosis treatment in future.

The Lysosome Signaling Platform: Adapting With the Times

Lysosomes are the terminal degradative compartment of autophagy, endocytosis and phagocytosis. What once was viewed as a simple acidic organelle in charge of macromolecular digestion has emerged as a dynamic organelle capable of integrating cellular signals and producing signal outputs. In this review, we focus on the concept that the lysosome surface serves as a platform to assemble major signaling hubs like mTORC1, AMPK, GSK3 and the inflammasome. These molecular assemblies integrate and facilitate cross-talk between signals such as amino acid and energy levels, membrane damage and infection, and ultimately enable responses such as autophagy, cell growth, membrane repair and microbe clearance. In particular, we review how molecular machinery like the vacuolar-ATPase proton pump, sestrins, the GATOR complexes, and the Ragulator, modulate mTORC1, AMPK, GSK3 and inflammation. We then elaborate how these signals control autophagy initiation and resolution, TFEB-mediated lysosome adaptation, lysosome remodeling, antigen presentation, inflammation, membrane damage repair and clearance. Overall, by being at the cross-roads for several membrane pathways, lysosomes have emerged as the ideal surveillance compartment to sense, integrate and elicit cellular behavior and adaptation in response to changing environmental and cellular conditions.

Trehalose induces autophagy via lysosomal-mediated TFEB activation in models of motoneuron degeneration

Macroautophagy/autophagy, a defense mechanism against aberrant stresses, in neurons counteracts aggregate-prone misfolded protein toxicity. Autophagy induction might be beneficial in neurodegenerative diseases (NDs). The natural compound trehalose promotes autophagy via TFEB (transcription factor EB), ameliorating disease phenotype in multiple ND models, but its mechanism is still obscure. We demonstrated that trehalose regulates autophagy by inducing rapid and transient lysosomal enlargement and membrane permeabilization (LMP). This effect correlated with the calcium-dependent phosphatase PPP3/calcineurin activation, TFEB dephosphorylation and nuclear translocation. Trehalose upregulated genes for the TFEB target and regulator Ppargc1a, lysosomal hydrolases and membrane proteins (Ctsb, Gla, Lamp2a, Mcoln1, Tpp1) and several autophagy-related components (Becn1, Atg10, Atg12, Sqstm1/p62, Map1lc3b, Hspb8 and Bag3) mostly in a PPP3- and TFEB-dependent manner. TFEB silencing counteracted the trehalose pro-degradative activity on misfolded protein causative of motoneuron diseases. Similar effects were exerted by trehalase-resistant trehalose analogs, melibiose and lactulose. Thus, limited lysosomal damage might induce autophagy, perhaps as a compensatory mechanism, a process that is beneficial to counteract neurodegeneration. Abbreviations: ALS: amyotrophic lateral sclerosis; AR: androgen receptor; ATG: autophagy related; AV: autophagic vacuole; BAG3: BCL2-associated athanogene 3; BECN1: beclin 1, autophagy related; CASA: chaperone-assisted selective autophagy; CTSB: cathepsin b; DAPI: 4',6-diamidino-2-phenylindole; DMEM: Dulbecco's modified Eagle's medium; EGFP: enhanced green fluorescent protein; fALS, familial amyotrophic lateral sclerosis; FRA: filter retardation assay; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GLA: galactosidase, alpha; HD: Huntington disease; hIPSCs: human induced pluripotent stem cells; HSPA8: heat shock protein A8; HSPB8: heat shock protein B8; IF: immunofluorescence analysis; LAMP1: lysosomal-associated membrane protein 1; LAMP2A: lysosomal-associated membrane protein 2A; LGALS3: lectin, galactose binding, soluble 3; LLOMe: L-leucyl-L-leucine methyl ester; LMP: lysosomal membrane permeabilization; Lys: lysosomes; MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; MCOLN1: mucolipin 1; mRNA: messenger RNA; MTOR: mechanistic target of rapamycin kinase; NDs: neurodegenerative diseases; NSC34: neuroblastoma x spinal cord 34; PBS: phosphate-buffered saline; PD: Parkinson disease; polyQ: polyglutamine; PPARGC1A: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; PPP3CB: protein phosphatase 3, catalytic subunit, beta isoform; RT-qPCR: real-time quantitative polymerase chain reaction; SBMA: spinal and bulbar muscular atrophy; SCAs: spinocerebellar ataxias; siRNA: small interfering RNA; SLC2A8: solute carrier family 2, (facilitated glucose transporter), member 8; smNPCs: small molecules neural progenitors cells; SOD1: superoxide dismutase 1; SQSTM1/p62: sequestosome 1; STED: stimulated emission depletion; STUB1: STIP1 homology and U-box containing protein 1; TARDBP/TDP-43: TAR DNA binding protein; TFEB: transcription factor EB; TPP1: tripeptidyl peptidase I; TREH: trehalase (brush-border membrane glycoprotein); WB: western blotting; ZKSCAN3: zinc finger with KRAB and SCAN domains 3.

Tuberculosis and the art of macrophage manipulation

Macrophages are first-line responders against microbes. The success of Mycobacterium tuberculosis (Mtb) rests upon its ability to convert these antimicrobial cells into a permissive cellular niche. This is a remarkable accomplishment, as the antimicrobial arsenal of macrophages is extensive. Normally bacteria are delivered to an acidic, degradative lysosome through one of several trafficking pathways, including LC3-associated phagocytosis (LAP) and autophagy. Once phagocytozed, the bacilli are subjected to reactive oxygen and nitrogen species, and they induce the expression of proinflammatory cytokines, which serve to augment host responses. However, Mtb hijacks these host defense mechanisms, manipulating host cellular trafficking, innate immune responses, and cell death pathways to its benefit. The complex series of measures and countermeasures between host and pathogen ultimately determines the outcome of infection. In this review, we focus on the diverse effectors that Mtb uses in its multipronged effort to subvert the innate immune responses of macrophages. We highlight recent advances in understanding the molecular interface of the Mtb-macrophage interaction.

The Role of Collectins and Galectins in Lung Innate Immune Defense

Different families of endogenous lectins use complementary defense strategies against pathogens. They may recognize non-self glycans typically found on pathogens and/or host glycans. The collectin and galectin families are prominent examples of these two lectin categories. Collectins are C-type lectins that contain a carbohydrate recognition domain and a collagen-like domain. Members of this group include surfactant protein A (SP-A) and D (SP-D), secreted by the alveolar epithelium to the alveolar fluid. Lung collectins bind to several microorganisms, which results in pathogen aggregation and/or killing, and enhances phagocytosis of pathogens by alveolar macrophages. Moreover, SP-A and SP-D influence macrophage responses, contributing to resolution of inflammation, and SP-A is essential for tissue-repair functions of macrophages. Galectins also function by interacting directly with pathogens or by modulating the immune system in response to the infection. Direct binding may result in enhanced or impaired infection of target cells, or can have microbicidal effects. Immunomodulatory effects of galectins include recruitment of immune cells to the site of infection, promotion of neutrophil function, and stimulation of the bactericidal activity of infected macrophages. Moreover, intracellular galectins can serve as danger receptors, promoting autophagy of the invading pathogen. This review will focus on the role of collectins and galectins in pathogen clearance and immune response activation in infectious diseases of the respiratory system.

TRIM16 controls assembly and degradation of protein aggregates by modulating the p62-NRF2 axis and autophagy

Sequestration of protein aggregates in inclusion bodies and their subsequent degradation prevents proteostasis imbalance, cytotoxicity, and proteinopathies. The underlying molecular mechanisms controlling the turnover of protein aggregates are mostly uncharacterized. Herein, we show that a TRIM family protein, TRIM16, governs the process of stress-induced biogenesis and degradation of protein aggregates. TRIM16 facilitates protein aggregate formation by positively regulating the p62-NRF2 axis. We show that TRIM16 is an integral part of the p62-KEAP1-NRF2 complex and utilizes multiple mechanisms for stabilizing NRF2. Under oxidative and proteotoxic stress conditions, TRIM16 activates ubiquitin pathway genes and p62 via NRF2, leading to ubiquitination of misfolded proteins and formation of protein aggregates. We further show that TRIM16 acts as a scaffold protein and, by interacting with p62, ULK1, ATG16L1, and LC3B, facilitates autophagic degradation of protein aggregates. Thus, TRIM16 streamlines the process of stress-induced aggregate clearance and protects cells against oxidative/proteotoxic stress-induced toxicity in vitro and in vivo Taken together, this work identifies a new mechanism of protein aggregate turnover, which could be relevant in protein aggregation-associated diseases such as neurodegeneration.

Role of autophagy in Zika virus infection and pathogenesis

Autophagy is an evolutionarily conserved cellular pathway that culminates in lysosomal degradation of selected substrates. Autophagy can serve dual roles in virus infection with either pro- or antiviral functions depending on the virus and the stage of the viral replication cycle. Recent studies have suggested a role for autophagy in Zika virus (ZIKV) replication by demonstrating the accumulation of autophagic vesicles following ZIKV infection in both in vitro and in vivo models. In human fetal neural stem cells, ZIKV inhibits Akt-mTOR signaling to induce autophagy, increase virus replication and impede neurogenesis. However, autophagy also has the potential to limit ZIKV replication, with separate studies demonstrating antiviral roles for autophagy at the maternal-placental-fetal interface, and more specifically, at the endoplasmic reticulum where virus replication is established in an infected cell. Interestingly, ZIKV (and related flaviviruses) has evolved specific mechanisms to overcome autophagy at the ER, thus demonstrating important roles for these autophagic pathways in virus replication and host response. This review summarizes the known roles of autophagy in ZIKV replication and how they might influence virus tissue tropism and disease.

TRIM50 regulates Beclin 1 proautophagic activity

Autophagy is a catabolic process needed for maintaining cell viability and homeostasis in response to numerous stress conditions. Emerging evidence indicates that the ubiquitin system has a major role in this process. TRIMs, an E3 ligase protein family, contribute to selective autophagy acting as receptors and regulators of the autophagy proteins recognizing endogenous or exogenous targets through intermediary autophagic tags, such as ubiquitin. Here we report that TRIM50 fosters the initiation phase of starvation-induced autophagy and associates with Beclin1, a central component of autophagy initiation complex. We show that TRIM50, via the RING domain, ubiquitinates Beclin 1 in a K63-dependent manner enhancing its binding with ULK1 and autophagy activity. Finally, we found that the Lys-372 residue of TRIM50, critical for its own acetylation, is necessary for its E3 ligase activity that governs Beclin1 ubiquitination. Our study expands the roles of TRIMs in regulating selective autophagy, revealing an acetylation-ubiquitination dependent control for autophagy modulation.

Enterovirus Transmission by Secretory Autophagy

Present in many cell types, non-degradative secretory autophagy is a newly discovered pathway in which autophagosomes fuse with the plasma membrane instead of lysosomes. Surprisingly, some viruses exploit secretory autophagy to exit cells non-lytically, shedding into the extracellular environment as particle populations contained within vesicles. As a result, this significantly enhances the infectivity of these viruses. In this paper, this novel cellular exit pathway is highlighted and its advantages for viral transmission discussed.

A Small Viral PPxY Peptide Motif To Control Antiviral Autophagy

Autophagy is an essential metabolic program that is also used for clearing intracellular pathogens. This mechanism, also termed selective autophagy, is well characterized for invasive bacteria but remains poorly documented for viral infections. Here we highlight our recent work showing that endosomolytic adenoviruses trigger autophagy when entering cells. Our study revealed how adenoviruses exploit a capsid-associated small PPxY peptide motif to manipulate the autophagic machinery to prevent autophagic degradation and to promote endosomal escape and nuclear trafficking.