Role of autophagy in IL-1β export and release from cells

Molecular mechanisms of secretory autophagy and its potential role in diseases

Autophagy is a cellular degradation system that recycles or degrades damaged organelles, viral particles, and aggregated proteins through the lysosomal pathway. Autophagy plays an indispensable role in cellular homeostasis and communication processes. An interesting aspect is that autophagy also mediates the secretion of cellular contents, a process known as secretory autophagy. Secretory autophagy differs from macroautophagy, which sequesters recruited proteins, organelles, or viral particles into autophagosomes and degrades these sequesters in lysosomes, while the secretory autophagy pathway participates in the extracellular export of cellular contents sequestered by autophagosomes through autophagy and endosomal modulators. Recent evidence reveals that secretory autophagy is pivotal in the occurrence and progression of diseases. In this review, we summarize the molecular mechanisms of secretory autophagy. Furthermore, we review the impact of secretory autophagy on diseases, including cancer, viral infectious diseases, neurodegenerative diseases, and cardiovascular diseases. Considering the pleiotropic actions of secretory autophagy on diseases, studying the mechanism of secretory autophagy may help to understand the relevant pathophysiological processes.

The multifaceted role of extracellular vesicles (EVs) in colorectal cancer: metastasis, immune suppression, therapy resistance, and autophagy crosstalk

Extracellular vesicles (EVs) are lipid bilayer structures released by all cells and widely distributed in all biological fluids. EVs are implicated in diverse physiopathological processes by orchestrating cell-cell communication. Colorectal cancer (CRC) is one of the most common cancers worldwide, with metastasis being the leading cause of mortality in CRC patients. EVs contribute significantly to the advancement and spread of CRC by transferring their cargo, which includes lipids, proteins, RNAs, and DNAs, to neighboring or distant cells. Besides, they can serve as non-invasive diagnostic and prognostic biomarkers for early detection of CRC or be harnessed as effective carriers for delivering therapeutic agents. Autophagy is an essential cellular process that serves to remove damaged proteins and organelles by lysosomal degradation to maintain cellular homeostasis. Autophagy and EV release are coordinately activated in tumor cells and share common factors and regulatory mechanisms. Although the significance of autophagy and EVs in cancer is well established, the exact mechanism of their interplay in tumor development is obscure. This review focuses on examining the specific functions of EVs in various aspects of CRC, including progression, metastasis, immune regulation, and therapy resistance. Further, we overview emerging discoveries relevant to autophagy and EVs crosstalk in CRC.

Progress in the study of molecular mechanisms of intervertebral disc degeneration

Degenerative intervertebral disc disease (IVDD) is one of the main spinal surgery, conditions, which markedly increases the incidence of low back pain and deteriorates the patient's quality of life, and it imposes significant social and economic burdens. The molecular pathology of IVDD is highly complex and multilateral however still not ompletely understood. New findings indicate that IVDD is closely associated with inflammation, oxidative stress, cell injury and extracellular matrix metabolismdysregulation. Symptomatic management is the main therapeutic approach adopted for IVDD, but it fails to address the basic pathological changes and the causes of the disease. However, research is still focusing on molecular aspects in terms of gene expression, growth factors and cell signaling pathways in an attempt to identify specific molecular targets for IVDD treatment. The paper summarizes the most recent achievements in molecularunderstanding of the pathogenesis of IVDD and gives evidence-based recommendations for clinical practice.

SKA2 regulated hyperactive secretory autophagy drives neuroinflammation-induced neurodegeneration

High levels of proinflammatory cytokines induce neurotoxicity and catalyze inflammation-driven neurodegeneration, but the specific release mechanisms from microglia remain elusive. Here we show that secretory autophagy (SA), a non-lytic modality of autophagy for secretion of vesicular cargo, regulates neuroinflammation-mediated neurodegeneration via SKA2 and FKBP5 signaling. SKA2 inhibits SA-dependent IL-1β release by counteracting FKBP5 function. Hippocampal Ska2 knockdown in male mice hyperactivates SA resulting in neuroinflammation, subsequent neurodegeneration and complete hippocampal atrophy within six weeks. The hyperactivation of SA increases IL-1β release, contributing to an inflammatory feed-forward vicious cycle including NLRP3-inflammasome activation and Gasdermin D-mediated neurotoxicity, which ultimately drives neurodegeneration. Results from protein expression and co-immunoprecipitation analyses of male and female postmortem human brains demonstrate that SA is hyperactivated in Alzheimer's disease. Overall, our findings suggest that SKA2-regulated, hyperactive SA facilitates neuroinflammation and is linked to Alzheimer's disease, providing mechanistic insight into the biology of neuroinflammation.

Agomelatine improves memory and learning impairments in a rat model of LPS-induced neurotoxicity by modulating the ERK/SorLA/BDNF/TrkB pathway

The mutual interplay between neuroinflammation, synaptic plasticity, and autophagy has piqued researchers' interest, particularly when it comes to linking their impact and relationship to cognitive deficits. Being able to reduce inflammation and apoptosis, melatonin has shown to have positive neuroprotective effects; that is why we thought to check the possible role of agomelatine (AGO) as a promising candidate that could have a positive impact on cognitive deficits. In the current study, AGO (40 mg/kg/day, p.o., 7 days) successfully ameliorated the cognitive and learning disabilities caused by lipopolysaccharide (LPS) in rats (250 μg/kg/day, i.p., 7 days). This positive impact was supported by improved histopathological findings and improved spatial memory as assessed using Morris water maze. AGO showed a strong ability to control BACE1 activity and to rein in the hippocampal amyloid beta (Aβ) deposition. Also, it improved neuronal survival, neuroplasticity, and neurogenesis by boosting BDNF levels and promoting its advantageous effects and by reinforcing the pTrkB expression. In addition, it upregulated the pre- and postsynaptic neuroplasticity biomarkers resembled in synapsin I, synaptophysin, and PSD-95. Furthermore, AGO showed a modulatory action on Sortilin-related receptor with A-type repeats (SorLA) pathway and adjusted autophagy. It is noteworthy that all of these actions were abolished by administering PD98059 a MEK/ERK pathway inhibitor (0.3 mg/kg/day, i.p., 7 days). In conclusion, AGO administration significantly improves memory and learning disabilities associated with LPS administration by modulating the ERK/SorLA/BDNF/TrkB signaling pathway parallel to its capacity to adjust the autophagic process.

Role of Autophagy and Pyroptosis in Intervertebral Disc Degeneration

Intervertebral disc degeneration is a chronic degenerative disease caused by the interaction of genetic and environmental factors, mainly manifested as lower back pain. At present, the diagnosis of intervertebral disc degeneration mainly relies on imaging. However, early intervertebral disc degeneration is usually insidious, and there is currently a lack of relevant clinical biomarkers that can reliably reflect early disease progression. Pyroptosis is a regulatory form of cell death triggered by the activation of inflammatory bodies and caspase, which can induce the formation of plasma membrane pores and cell swelling or lysis. Previous studies have shown that during the progression of intervertebral disc degeneration, sustained activation of inflammasomes leads to nuclear cell pyroptosis, which can occur in the early stages of intervertebral disc degeneration. Moreover, intervertebral disc nucleus pulposus cells adapt to the external environment through autophagy and maintain cellular homeostasis and studying the mechanism of autophagy in IDD and intervening in its pathological and physiological processes can provide new ideas for the clinical treatment of IDD. This review analyzes the effects of pyroptosis and autophagy on IDD by reviewing relevant literature in recent years, in order to explore the relationship between pyroptosis, autophagy and IDD.

Biomarkers of aging in frailty and age-associated disorders: State of the art and future perspective

According to the Geroscience concept that organismal aging and age-associated diseases share the same basic molecular mechanisms, the identification of biomarkers of age that can efficiently classify people as biologically older (or younger) than their chronological (i.e. calendar) age is becoming of paramount importance. These people will be in fact at higher (or lower) risk for many different age-associated diseases, including cardiovascular diseases, neurodegeneration, cancer, etc. In turn, patients suffering from these diseases are biologically older than healthy age-matched individuals. Many biomarkers that correlate with age have been described so far. The aim of the present review is to discuss the usefulness of some of these biomarkers (especially soluble, circulating ones) in order to identify frail patients, possibly before the appearance of clinical symptoms, as well as patients at risk for age-associated diseases. An overview of selected biomarkers will be discussed in this regard, in particular we will focus on biomarkers related to metabolic stress response, inflammation, and cell death (in particular in neurodegeneration), all phenomena connected to inflammaging (chronic, low-grade, age-associated inflammation). In the second part of the review, next-generation markers such as extracellular vesicles and their cargos, epigenetic markers and gut microbiota composition, will be discussed. Since recent progresses in omics techniques have allowed an exponential increase in the production of laboratory data also in the field of biomarkers of age, making it difficult to extract biological meaning from the huge mass of available data, Artificial Intelligence (AI) approaches will be discussed as an increasingly important strategy for extracting knowledge from raw data and providing practitioners with actionable information to treat patients.

A brown fat-enriched adipokine, ASRA, is a leptin receptor antagonist that stimulates appetite

The endocrine control of food intake remains incompletely understood, and whether the leptin receptor-mediated anorexigenic pathway in the hypothalamus is negatively regulated by a humoral factor is unknown. Here we identify an appetite-stimulating factor - ASRA - that acts as a leptin receptor antagonist. ASRA encodes an 8 kD protein that is abundantly and selectively expressed in adipose tissue and to a lesser extent, in liver, and is upregulated during fasting and cold. ASRA protein associates with autophagosomes and its secretion is induced by energy deficiency. Overexpression of ASRA in mice attenuates leptin receptor signaling leading to elevated blood glucose and development of severe hyperphagic obesity, whereas either adipose- or liver-specific ASRA knockout mice display increased leptin sensitivity, improved glucose homeostasis, reduced food intake, and resistance to high fat diet-induced obesity. Furthermore, ASRA is indispensable for cold-evoked feeding response. Recombinant ASRA (rASRA) protein binds to leptin receptor and suppresses leptin receptor signaling in cultured cells. In vivo, rASRA promotes food intake and increases blood glucose in a leptin receptor signaling-dependent manner. Our studies collectively show that ASRA, acting as a peripheral signal of energy deficit, stimulates appetite and regulates glucose metabolism by antagonizing leptin receptor signaling, thus revealing a previously unknown endocrine mechanism that has important implications for our understanding of leptin resistance.

Proteomics Studies Suggest That Nitric Oxide Donor Furoxans Inhibit In Vitro Vascular Smooth Muscle Cell Proliferation by Nitric Oxide-Independent Mechanisms

Physiologically, smooth muscle cells (SMC) and nitric oxide (NO) produced by endothelial cells strictly cooperate to maintain vasal homeostasis. In atherosclerosis, where this equilibrium is altered, molecules providing exogenous NO and able to inhibit SMC proliferation may represent valuable antiatherosclerotic agents. Searching for dual antiproliferative and NO-donor molecules, we found that furoxans significantly decreased SMC proliferation in vitro, albeit with different potencies. We therefore assessed whether this property is dependent on their thiol-induced ring opening. Indeed, while furazans (analogues unable to release NO) are not effective, furoxans' inhibitory potency parallels with the electron-attractor capacity of the group in 3 of the ring, making this effect tunable. To demonstrate whether their specific block on G1-S phase could be NO-dependent, we supplemented SMCs with furoxans and inhibitors of GMP- and/or of the polyamine pathway, which regulate NO-induced SMC proliferation, but they failed in preventing the antiproliferative effect. To find the real mechanism of this property, our proteomics studies revealed that eleven cellular proteins (with SUMO1 being central) and networks involved in cell homeostasis/proliferation are modulated by furoxans, probably by interaction with adducts generated after degradation. Altogether, thanks to their dual effect and pharmacological flexibility, furoxans may be evaluated in the future as antiatherosclerotic molecules.

SKA2 regulated hyperactive secretory autophagy drives neuroinflammation-induced neurodegeneration

High levels of proinflammatory cytokines induce neurotoxicity and catalyze inflammation-driven neurodegeneration, but the specific release mechanisms from microglia remain elusive. We demonstrate that secretory autophagy (SA), a non-lytic modality of autophagy for secretion of vesicular cargo, regulates neuroinflammation-mediated neurodegeneration via SKA2 and FKBP5 signaling. SKA2 inhibits SA-dependent IL-1β release by counteracting FKBP5 function. Hippocampal Ska2 knockdown in mice hyperactivates SA resulting in neuroinflammation, subsequent neurodegeneration and complete hippocampal atrophy within six weeks. The hyperactivation of SA increases IL-1β release, initiating an inflammatory feed-forward vicious cycle including NLRP3-inflammasome activation and Gasdermin D (GSDMD)-mediated neurotoxicity, which ultimately drives neurodegeneration. Results from protein expression and co-immunoprecipitation analyses of postmortem brains demonstrate that SA is hyperactivated in Alzheimer's disease. Overall, our findings suggest that SKA2-regulated, hyperactive SA facilitates neuroinflammation and is linked to Alzheimer's disease, providing new mechanistic insight into the biology of neuroinflammation.

hASCs-derived exosomal miR-155-5p targeting TGFβR2 promotes autophagy and reduces pyroptosis to alleviate intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration (IDD) is a complex chronic disease involving nucleus pulposus cells (NPCs) senescence, apoptosis, autophagy and extracellular matrix (ECM) degradation. In this study, we aimed to investigate the role of human adipose tissue stem cells (hASCs)-derived exosomal miR-155-5p targeting TGFβR2 in IDD and the mechanisms involved. Then miRNA sequencing was performed, and hASCs-derived Exo (hASCs-Exo) was extracted and characterized.

METHODS

First, NPCs were treated with different concentrations of LPS. Then miRNA sequencing was performed, and hASCs-Exo was extracted and characterized. NPCs were treated with PBS or autophagy inhibitor 3-MA. NPCs were transfected with miR-155-5p mimic, si-TGFβR2 and negative control. Cell viability, apoptosis, ROS, caspase-1+PI, pyroptosis markers, inflammatory cytokines, autophagy markers, Aggrecan, MMP13, and Akt/mTOR pathway-related factors were measured. Bioinformatics prediction and dual-luciferase were performed to verify the binding sites of miR-155-5p to TGFβR2. Finally, we validated the role of hASCs-derived exosomal miR-155-5p on IDD in vivo.

RESULTS

LPS promoted pyroptosis of NPCs, and inhibited autophagy and ECM synthesis. MiR-155-5p was characterized as an inflammation-related miRNA in NPCs. HASCs-derived exosomal miR-155-5p inhibited pyroptosis of NPCs and promoted autophagy and ECM synthesis. After bioinformatics prediction and verification, it was found that miR-155-5p targeted TGFβR2. Moreover, miR-155-5p targeted TGFβR2 to promote autophagy and inhibit pyroptosis in NPCs. In vivo experiments revealed that hASCs-derived exosomal miR-155-5p alleviated IDD in rats.

CONCLUSIONS

HASCs-derived exosomal miR-155-5p alleviated IDD by targeting TGFβR2 to promote autophagy and reduce pyroptosis. Our study may provide a new therapeutic target for IDD.

TRANSLATIONAL POTENTIAL OF THIS ARTICLE

HASCs-derived exosomal miR-155-5p is expected to be a biomarker for clinical treatment of IDD. Our study may provide a new therapeutic target for IDD.

Pyruvate dehydrogenase kinase supports macrophage NLRP3 inflammasome activation during acute inflammation

Activating the macrophage NLRP3 inflammasome can promote excessive inflammation with severe cell and tissue damage and organ dysfunction. Here, we show that pharmacological or genetic inhibition of pyruvate dehydrogenase kinase (PDHK) significantly attenuates NLRP3 inflammasome activation in murine and human macrophages and septic mice by lowering caspase-1 cleavage and interleukin-1β (IL-1β) secretion. Inhibiting PDHK reverses NLRP3 inflammasome-induced metabolic reprogramming, enhances autophagy, promotes mitochondrial fusion over fission, preserves crista ultrastructure, and attenuates mitochondrial reactive oxygen species (ROS) production. The suppressive effect of PDHK inhibition on the NLRP3 inflammasome is independent of its canonical role as a pyruvate dehydrogenase regulator. Our study suggestsa non-canonical role of mitochondrial PDHK in promoting mitochondrial stress and supporting NLRP3 inflammasome activation during acute inflammation.

IL-1β, an important cytokine affecting Helicobacter pylori-mediated gastric carcinogenesis

Infection with Helicobacter pylori (H. pylori) is prevalent around the world and responsible for gastric cancer (GC). The development of GC from gastritis is closely associated with the bacterial virulence and the body's immune response ability. In this process, interleukin-1β (IL-1β) plays an important role. Under H. pylori infection, IL-1β is highly expressed that result in gastric acid inhibition, GC-related gene methylations and disfunctions, angiogenesis. Nod-like receptor pyrin domain containing 3 (NLRP3) inflammasome mediates IL-1β maturation in cells such as macrophages, neutrophils and dendritic cells. But how does IL-1β get released across the cell membrane still unclear. In this review, we focus on the secretion mechanism of IL-1β across the membrane, and to explore the role of IL-1β in the progression of GC.

Pyroptosis and Intervertebral Disc Degeneration: Mechanistic Insights and Therapeutic Implications

Low back pain (LBP) is a common problem worldwide, resulting in great patient suffering and great challenges for the social health system. Intervertebral disc (IVD) degeneration (IVDD) is widely acknowledged as one of the key causes of LBP. Accumulating evidence suggests that aberrant pyroptosis of IVD cells is involved in the pathogenesis of IVDD progression, however, the comprehensive roles of pyroptosis in IVDD have not been fully established, leaving attempts to treat IVDD with anti-pyroptosis approaches questionable. In this review, we summarize the characteristics of pyroptosis and emphasize the effects of IVD cell pyroptosis on the pathological progression of IVDD, including secretion of cytokines, nucleus pulposus cell apoptosis and autophagy, accelerated extracellular matrix degradation, annulus fibrosus rupture, cartilage endplate calcification, vascularization, sensory and sympathetic fiber neoinnervation, and infiltrating lymphatic vessels. Finally, we discuss several interventions used to treat IVDD by targeting pyroptosis. This review provides novel insights into the crucial role of IVD cell pyroptosis in IVDD pathogenesis, and could be informative for developing novel therapeutic approaches for IVDD and LBP.

Exosomes, autophagy and ER stress pathways in human diseases: Cross-regulation and therapeutic approaches

Exosomal release pathway and autophagy together maintain homeostasis and survival of cells under stressful conditions. Autophagy is a catabolic process through which cell entities, such as malformed biomacromolecules and damaged organelles, are degraded and recycled via the lysosomal-dependent pathway. Exosomes, a sub-type of extracellular vesicles (EVs) formed by the inward budding of multivesicular bodies (MVBs), are mostly involved in mediating communication between cells. The unfolded protein response (UPR) is an adaptive response that is activated to sustain survival in the cells faced with the endoplasmic reticulum (ER) stress through a complex network that involves protein synthesis, exosomes secretion and autophagy. Disruption of the critical crosstalk between EVs, UPR and autophagy may be implicated in various human diseases, including cancers and neurodegenerative diseases, yet the molecular mechanism(s) behind the coordination of these communication pathways remains obscure. Here, we review the available information on the mechanisms that control autophagy, ER stress and EV pathways, with the view that a better understanding of their crosstalk and balance may improve our knowledge on the pathogenesis and treatment of human diseases, where these pathways are dysregulated.

Recent advances in conventional and unconventional vesicular secretion pathways in the tumor microenvironment

All cells in the changing tumor microenvironment (TME) need a class of checkpoints to regulate the balance among exocytosis, endocytosis, recycling and degradation. The vesicular trafficking and secretion pathways regulated by the small Rab GTPases and their effectors convey cell growth and migration signals and function as meditators of intercellular communication and molecular transfer. Recent advances suggest that Rab proteins govern conventional and unconventional vesicular secretion pathways by trafficking widely diverse cargoes and substrates in remodeling TME. The mechanisms underlying the regulation of conventional and unconventional vesicular secretion pathways, their action modes and impacts on the cancer and stromal cells have been the focus of much attention for the past two decades. In this review, we discuss the current understanding of vesicular secretion pathways in TME. We begin with an overview of the structure, regulation, substrate recognition and subcellular localization of vesicular secretion pathways. We then systematically discuss how the three fundamental vesicular secretion processes respond to extracellular cues in TME. These processes are the conventional protein secretion via the endoplasmic reticulum-Golgi apparatus route and two types of unconventional protein secretion via extracellular vesicles and secretory autophagy. The latest advances and future directions in vesicular secretion-involved interplays between tumor cells, stromal cell and host immunity are also described.

The Regulation and Modification of GSDMD Signaling in Diseases

Gasdermin D (GSDMD) serves as a key executor to trigger pyroptosis and is emerging as an attractive checkpoint in host defense, inflammatory, autoimmune diseases, and many other systemic diseases. Although canonical and non-canonical inflammasome-mediated classic GSDMD cleavage, GSDMD-NT migration to cell membrane, GSDMD-NT oligomerization, and pore forming have been well recognized, a few unique features of GSDMD in specific condition beyond its classic function, including non-lytic function of GSDMD, the modification and regulating mechanism of GSDMD signaling have also come to great attention and played a crucial role in biological processes and diseases. In the current review, we emphasized the GSDMD protein expression, stabilization, modification, activation, pore formation, and repair during pyroptosis, especially the regulation and modification of GSDMD signaling, such as GSDMD complex in polyubiquitination and non-pyroptosis release of IL-1β, ADP-riboxanation, NINJ1 in pore forming, GSDMD binding protein TRIM21, GSDMD succination, and Regulator-Rag-mTOR-ROS regulation of GSDMD. We also discussed the novel therapeutic strategies of targeting GSDMD and summarized recently identified inhibitors with great prospect.

Dying by fire: noncanonical functions of autophagy proteins in neuroinflammation and neurodegeneration

Neuroinflammation and neurodegeneration are key components in the establishment and progression of neurodegenerative diseases including Alzheimer's Disease (AD). Over the past decade increasing evidence is emerging for the use of components of the canonical autophagy machinery in pathways that are characterized by LC3 lipidation yet are distinct from traditional macro-autophagy. One such pathway that utilizes components of the autophagy machinery to target LC3 to endosomes, a process termed LC3-associated endocytosis (LANDO), has recently been identified and regulates neuroinflammation. Abrogation of LANDO in microglia cells results in a propensity for elevated neuroinflammatory cytokine production. Using the well-established 5xFAD model of AD to interrogate neuroinflammatory regulation, impairment of LANDO through deletion of a key upstream regulator Rubicon or other downstream autophagy components, exacerbated disease onset and severity, while deletion of microglial autophagy alone had no measurable effect. Mice presented with robust deposition of the neurotoxic AD protein β-amyloid (Aβ), microglial activation and inflammatory cytokine production, tau phosphorylation, and aggressive neurodegeneration culminating in severe memory impairment. LANDO-deficiency impaired recycling of receptors that recognize Aβ, including TLR4 and TREM2. LANDO-deficiency alone through deletion of the WD-domain of the autophagy protein ATG16L, revealed a role for LANDO in the spontaneous establishment of age-associated AD. LANDO-deficient mice aged to 2 years presented with advanced AD-like disease and pathology correlative to that observed in human AD patients. Together, these studies illustrate an important role for microglial LANDO in regulating CNS immune activation and protection against neurodegeneration. New evidence is emerging that demonstrates a putative linkage between pathways such as LANDO and cell death regulation via apoptosis and possibly necroptosis. Herein, we provide a review of the use of the autophagy machinery in non-canonical mechanisms that alter immune regulation and could have significant impact in furthering our understanding of not only CNS diseases like AD, but likely beyond.

Lysosomal potassium channels

The lysosome is an important membrane-bound acidic organelle that is regarded as the degradative center as well as multifunctional signaling hub. It digests unwanted macromolecules, damaged organelles, microbes, and other materials derived from endocytosis, autophagy, and phagocytosis. To function properly, the ionic homeostasis and membrane potential of the lysosome are strictly regulated by transporters and ion channels. As the most abundant cation inside the cell, potassium ions (K⁺) are vital for lysosomal membrane potential and lysosomal calcium (Ca²⁺) signaling. However, our understanding about how lysosomal K⁺homeostasis is regulated and what are the functions of K⁺in the lysosome is very limited. Currently, two lysosomal K⁺channels have been identified: large-conductance Ca²⁺-activated K⁺channel (BK) and transmembrane Protein 175 (TMEM175). In this review, we summarize recent development in our understanding of K⁺ homeostasis and K⁺channels in the lysosome. We hope to guide the readers into a more in-depth discussion of lysosomal K⁺ channels in lysosomal physiology and human diseases.

Nicotine regulates autophagy of human periodontal ligament cells through α7 nAchR that promotes secretion of inflammatory factors IL-1β and IL-8

Background

Nicotine is an important risk factor and the main toxic component associated with periodontitis. However, the mechanism of nicotine induced periodontitis is not clear. To investigated the mechanism through which nicotine regulates autophagy of human periodontal ligament cells (hPDLCs) through the alpha7 nicotinic acetylcholine receptor (α7 nAChR) and how autophagy further regulates the release of IL-1β and IL-8 secretion in hPDLCs.

Methods

HPDLCs were obtained from root of extracted teeth and pre-incubated in alpha-bungarotoxin (α-BTX) or 3-Methyladenine (3-MA), followed by culturing in nicotine. We used a variety of experimental detection techniques including western blotting, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), transmission electron microscopy (TEM) and RT-qPCR to assess the expression of the LC3 protein, autolysosome, and release of IL-1β and IL-8 from hPDLCs.

Results

Western blots, immunofluorescence and TEM results found that the nicotine significantly increased the autophagy expression in hPDLCs that was time and concentration dependent and reversed by α-BTX treatment (p < 0.05). RT-qPCR and ELISA results revealed a noticeable rise in the release of inflammatory factors IL-1β and IL-8 from hPDLCs in response to nicotine. RT-qPCR and ELISA results showed that nicotine can significantly up-regulate the release of inflammatory factors IL-1β and IL-8 in hPDLCs, and this effect can be inhibited by 3-MA (p < 0.05).

Conclusions

Nicotine regulated autophagy of hPDLCs through α7 nAChR and in turn the regulation of the release of inflammatory factors 1L-1β and 1L-8 by hPDLCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01894-5.

Tumor-Derived Extracellular Vesicles: Modulation of Cellular Functional Dynamics in Tumor Microenvironment and Its Clinical Implications

Cancer can be described as a dynamic disease formed by malignant and stromal cells. The cellular interaction between these components in the tumor microenvironment (TME) dictates the development of the disease and can be mediated by extracellular vesicles secreted by tumor cells (TEVs). In this review, we summarize emerging findings about how TEVs modify important aspects of the disease like continuous tumor growth, induction of angiogenesis and metastasis establishment. We also discuss how these nanostructures can educate the immune infiltrating cells to generate an immunosuppressive environment that favors tumor progression. Furthermore, we offer our perspective on the path TEVs interfere in cancer treatment response and promote tumor recurrence, highlighting the need to understand the underlying mechanisms controlling TEVs secretion and cargo sorting. In addition, we discuss the clinical potential of TEVs as markers of cell state transitions including the acquisition of a treatment-resistant phenotype, and their potential as therapeutic targets for interventions such as the use of extracellular vesicle (EV) inhibitors to block their pro-tumoral activities. Some of the technical challenges for TEVs research and clinical use are also presented.

Non-autophagy Role of Atg5 and NBR1 in Unconventional Secretion of IL-12 Prevents Gut Dysbiosis and Inflammation

Intestinal myeloid cells play a critical role in balancing intestinal homeostasis and inflammation. Here, we report that expression of the autophagy-related 5 [Atg5] protein in myeloid cells prevents dysbiosis and excessive intestinal inflammation by limiting IL-12 production. Mice with a selective genetic deletion of Atg5 in myeloid cells [Atg5ΔMye] showed signs of dysbiosis preceding colitis, and exhibited severe intestinal inflammation upon colitis induction that was characterised by increased IFNγ production. The exacerbated colitis was linked to excess IL-12 secretion from Atg5-deficient myeloid cells and gut dysbiosis. Restoration of the intestinal microbiota or genetic deletion of IL-12 in Atg5ΔMye mice attenuated the intestinal inflammation in Atg5ΔMye mice. Additionally, Atg5 functions to limit IL-12 secretion through modulation of late endosome [LE] acidity. Last, the autophagy cargo receptor NBR1, which accumulates in Atg5-deficient cells, played a role by delivering IL-12 to LE. In summary, Atg5 expression in intestinal myeloid cells acts as an anti-inflammatory brake to regulate IL-12, thus preventing dysbiosis and uncontrolled IFNγ-driven intestinal inflammation.

Interconnections among major forms of regulated cell death

As a basic biological phenomenon of cells, regulated cell death (RCD) has irreplaceable influence on the occurrence and development of many processes of life and diseases. RCD plays an important role in the stability of the homeostasis, the development of multiple systems and the evolution of organisms. Thus comprehensively understanding of RCD is undoubtedly helpful in the innovation of disease treatment. Recently, research on the underlying mechanisms of the major forms of RCD, such as apoptosis, autophagy, necroptosis, pyroptosis, paraptosis and neutrophils NETosis has made significant breakthroughs. In addition, the interconnections among them have attracted increasing attention from global scholars in the field of life sciences. Here, recent advances in RCD research field are discussed.

The Pathways Underlying the Multiple Roles of p62 in Inflammation and Cancer

p62 is a highly conserved, multi-domain, and multi-functional adaptor protein critically involved in several important cellular processes. Via its pronounced domain architecture, p62 binds to numerous interaction partners, thereby influencing key pathways that regulate tissue homeostasis, inflammation, and several common diseases including cancer. Via binding of ubiquitin chains, p62 acts in an anti-inflammatory manner as an adaptor for the auto-, xeno-, and mitophagy-dependent degradation of proteins, pathogens, and mitochondria. Furthermore, p62 is a negative regulator of inflammasome complexes. The transcription factor Nrf2 regulates expression of a bundle of ROS detoxifying genes. p62 activates Nrf2 by interaction with and autophagosomal degradation of the Nrf2 inhibitor Keap1. Moreover, p62 activates mTOR, the central kinase of the mTORC1 sensor complex that controls cell proliferation and differentiation. Through different mechanisms, p62 acts as a positive regulator of the transcription factor NF-κB, a central player in inflammation and cancer development. Therefore, p62 represents not only a cargo receptor for autophagy, but also a central signaling hub, linking several important pro- and anti-inflammatory pathways. This review aims to summarize knowledge about the molecular mechanisms underlying the roles of p62 in health and disease. In particular, different types of tumors are characterized by deregulated levels of p62. The elucidation of how p62 contributes to inflammation and cancer progression at the molecular level might promote the development of novel therapeutic strategies.

Acankoreagenin and acankoreosides, a family of lupane triterpenoids with anti-inflammatory properties: an overview

Acankoreagenin (ACK, also known as acankoreanogenin and HLEDA) and impressic acid are two lupane-type triterpenes that can be isolated from various Acanthopanax and Schefflera species. They efficiently block activation of the NF-κB signaling pathway and the release of proinflammatory cytokines and/or the action of inflammation mediators (HMGB1, iNOS, and NO). These effects are the basis for the antiviral and anticancer activities reported with these pentacyclic compounds or their various glycoside derivatives. More than 15 acankoreosides (Ack-A to -O, and -R) and a few other mono- and bidesmosidic saponins (acantrifoside A and acangraciliside S) derive from the ACK aglycone. Compounds like Ack-A and -B are remarkable anti-inflammatory agents, inhibiting cytokine release from activated macrophages. Despite their effectiveness, ACK and impressic acid are far much less known and studied than the structurally related compounds betulinic acid and 23-hydroxybetulinic acid (anemosapogenin). The structural differences (notably the R/S stereoisomerism of the 3-hydroxyl group) and functional similarities of these compounds are discussed. The complete series of acankoreosides is presented for the first time. These natural products deserve further attention as anti-inflammatory agents, and ACK is recommended as a template for the design of new anticancer and antiviral drugs.

Autophagic Degradation of Gasdermin D Protects against Nucleus Pulposus Cell Pyroptosis and Retards Intervertebral Disc Degeneration In Vivo

Intervertebral disc degeneration (IDD) is the primary culprit of low back pain and renders heavy social burden worldwide. Pyroptosis is a newly discovered form of programmed cell death, which is also involved in nucleus pulposus (NP) cells during IDD progression. Moderate autophagy activity is critical for NP cell survival, but its relationship with pyroptosis remains unknown. This study is aimed at investigating the relationship between autophagy and pyroptotic cell death. The pyroptosis executor N-terminal domain of gasdermin D (GSDMD-N) and inflammation-related proteins were measured in lipopolysaccharide- (LPS-) treated human NP cells. Inhibition of autophagy by siRNA transfection and chemical drugs aggravated human NP cell pyroptosis. Importantly, we found that the autophagy-lysosome pathway and not the proteasome pathway mediated the degradation of GSDMD-N as lysosome dysfunction promoted the accumulation of cytoplasmic GSDMD-N. Besides, P62/SQSTM1 colocalized with GSDMD-N and mediated its degradation. The administration of the caspase-1 inhibitor VX-765 could reduce cell pyroptosis as confirmed in a rat disc IDD model in vivo, whereas ATG5 knockdown significantly accelerated the progression of IDD. In conclusion, our study indicated that autophagy protects against LPS-induced human NP cell pyroptosis via a P62/SQSTM1-mediated degradation mechanism and the inhibition of pyroptosis retards IDD progression in vivo. These findings deepen the understanding of IDD pathogenesis and hold implications in unraveling therapeutic targets for IDD treatment.

Carbon monoxide alleviates senescence in diabetic nephropathy by improving autophagy

OBJECTIVES

Senescence, characterized by permanent cycle arrest, plays an important role in diabetic nephropathy (DN). However, the mechanism of renal senescence is still unclear, and the treatment targeting it remains to be further explored.

MATERIALS AND METHODS

The DN mice were induced by HFD and STZ, and 3 types of renal cells were treated with high glucose (HG) to establish in vitro model. Senescence-related and autophagy-related markers were detected by qRT-PCR and Western blot. Further, autophagy inhibitors and co-immunoprecipitation were used to clarify the mechanism of CO. Additionally, the specific relationship between autophagy and senescence was explored by immunofluorescence triple co-localization and ELISA.

RESULTS

We unravelled that senescence occurred in vivo and in vitro, which could be reversed by CO. Mechanistically, we demonstrated that CO inhibited the dysfunction of autophagy in DN mice partly through dissociating Beclin-1-Bcl-2 complex. Further results showed that autophagy inhibitors blocked the improvement of CO on senescence. In addition, the data revealed that autophagy regulated the degradation of senescence-related secretory phenotype (SASP) including Il-1β, Il-6, Tgf-β and Vegf.

CONCLUSIONS

These results suggested that CO protects DN mice from renal senescence and function loss via improving autophagy partly mediated by dissociating Beclin-1-Bcl-2 complex, which is possibly ascribed to the degradation of SASP. These findings bring new ideas for the prevention and treatment of DN and the regulation of senescence.

NRG4-ErbB4 signaling represses proinflammatory macrophage activity

Proinflammatory macrophages are essential drivers of colitis and express the growth factor receptor ErbB4. This study tested the role of ErbB4 and its specific ligand, NRG4, in regulating macrophage function. We show that endogenous NRG4-ErbB4 signaling limits macrophage production of proinflammatory cytokines in vitro and limits colitis severity in vivo and thus is a potential target for therapeutic intervention.

β-Glucan-stimulated neutrophil secretion of IL-1α is independent of GSDMD and mediated through extracellular vesicles

Neutrophils are an important source of interleukin (IL)-1β and other cytokines because they are recruited to sites of infection and inflammation in high numbers. Although secretion of processed, bioactive IL-1β by neutrophils is dependent on NLRP3 and Gasdermin D (GSDMD), IL-1α secretion by neutrophils has not been reported. In this study, we demonstrate that neutrophils produce IL-1α following injection of Aspergillus fumigatus spores that express cell-surface β-Glucan. Although IL-1α secretion by lipopolysaccharide (LPS)/ATP-activated macrophages and dendritic cells is GSDMD dependent, IL-1α secretion by β-Glucan-stimulated neutrophils occurs independently of GSDMD. Instead, we found that bioactive IL-1α is in exosomes that were isolated from cell-free media of β-Glucan-stimulated neutrophils. Further, the exosome inhibitor GW4869 significantly reduces IL-1α in extracellular vesicles (EVs) and total cell-free supernatant. Together, these findings identify neutrophils as a source of IL-1α and demonstrate a role for EVs, specifically exosomes, in neutrophil secretion of bioactive IL-1α.

Neutrophils have functional NLRP3 and NLRC4 and are recognized as an important source of IL-1β. Ratitong et al. demonstrate that murine neutrophils also produce IL-1α. Unlike macrophages, neutrophil IL-1α is secreted in extracellular vesicles and is released independently of gasdermin D and cell death.

Hierarchical cluster analysis in the study of the effect of cytokine expression patterns on endometrial repair and receptivity after hysteroscopic adhesiolysis

Background

In a previous study, we reported that amnion promotes endometrial cell growth by regulating cytokines. In this study, hierarchical cluster analysis enabled the evaluation of cytokine expression changes after amnion treatment to be explored by cluster patterns. The role of IL1B on endometrial repair and receptivity was revealed.

Methods

A total of 30 patients were recruited in this clinical trial (NCT02496052) of hysteroscopic adhesiolysis. They were randomly allocated into an amnion grafts group (amnion group) and a control group. After hysteroscopic adhesiolysis, a Foley catheter covered with a sterilized freeze-dried amnion graft was inserted into the uterine cavity of the participants in the amnion group, whereas for the control group, a Foley catheter without amnion graft was inserted. After surgery, patient follow-up was done for a year. Uterine exudates were collected every day for seven days after surgery, and analyzed by enzyme-linked immunosorbent assays. Hierarchical cluster analysis was performed to compare expression patterns of each cytokine. Single-gene gene set enrichment analysis and differentially expressed genes enrichment analysis of IL1B were performed using NCBI GEO (N=151) to evaluate its potential mechanisms and impact on endometrial receptivity.

Results

Compared to the control group, cytokine expression patterns of the amnion group revealed significant stratifications, which were highly correlated with the expression levels of IL1B on the sixth to seventh day after surgery, improving the pregnant rate. Wilcoxon test revealed significantly low expression levels of IL1B in the reduced endometrial receptivity group compared to the normal group. Moreover, gene set enrichment analysis showed that lysosomes, cell cycle, and calcium signaling pathways were associated with the biological processes in which IL1B plays a role. Screening and enrichment analyses of differentially expressed genes further verified the mechanisms of action of IL1B on endometrial repair and receptivity recovery.

Conclusions

Amnion promotes endometrial repair and receptivity by altering the expression levels and patterns of IL1B. Furthermore, by affecting lysosomal, cell cycle, and calcium signaling pathways, IL1B may be one of the factors involved in endometrial repair and receptivity recovery.

The P2X7 Receptor in Osteoarthritis

Osteoarthritis (OA) is the most common joint disease. With the increasing aging population, the associated socio-economic costs are also increasing. Analgesia and surgery are the primary treatment options in late-stage OA, with drug treatment only possible in early prevention to improve patients' quality of life. The most important structural component of the joint is cartilage, consisting solely of chondrocytes. Instability in chondrocyte balance results in phenotypic changes and cell death. Therefore, cartilage degradation is a direct consequence of chondrocyte imbalance, resulting in the degradation of the extracellular matrix and the release of pro-inflammatory factors. These factors affect the occurrence and development of OA. The P2X7 receptor (P2X7R) belongs to the purinergic receptor family and is a non-selective cation channel gated by adenosine triphosphate. It mediates Na⁺, Ca²⁺ influx, and K⁺ efflux, participates in several inflammatory reactions, and plays an important role in the different mechanisms of cell death. However, the relationship between P2X7R-mediated cell death and the progression of OA requires investigation. In this review, we correlate potential links between P2X7R, cartilage degradation, and inflammatory factor release in OA. We specifically focus on inflammation, apoptosis, pyroptosis, and autophagy. Lastly, we discuss the therapeutic potential of P2X7R as a potential drug target for OA.

lncRNA NEAT1 ameliorates LPS‑induced inflammation in MG63 cells by activating autophagy and suppressing the NLRP3 inflammasome

The mechanisms of inflammation in bone and joint tissue are complex and involve long non‑coding RNAs (lncRNAs), which play an important role in this process. The aim of the present study was to screen out differentially expressed genes in human osteoblasts stimulated by inflammation, and to further explore the mechanisms underlying inflammatory responses and the functional activity of human osteoblasts through bioinformatics methods and in vitro experiments. For this purpose, MG63 cells were stimulated with various concentrations of lipopolysaccharide (LPS) for different periods of time to construct an optimal inflammatory model and RNA sequencing was then performed on these cells. The levels of nuclear enriched abundant transcript 1 (NEAT1), various inflammatory factors, Nod‑like receptor protein 3 (NLRP3) protein and osteogenesis‑related proteins, as well as the levels of cell apoptosis‑ and cell cycle‑related markers were measured in MG63 cells stimulated with LPS, transfected with NEAT1 overexpression plasmid and treated with bexarotene by western blot analysis, RT‑qPCR, immunofluorescence, FISH, TEM and flow cytometry. There were 427 differentially expressed genes in the LPS‑stimulated MG63 cells, in which NEAT1 was significantly downregulated. LPS upregulated the expression of inflammatory cytokines and NLRP3, inhibited the expression of autophagy‑related and osteogenesis‑related proteins, promoted apoptosis and altered the cell cycle, which was partially inhibited by NEAT1 overexpression and promoted by bexarotene. LPS stimulated inflammation in the MG63 cells and inhibited the retinoid X receptor (RXR)‑α to downregulate the expression of NEAT1 and decrease levels of autophagy, which promoted the activation of NLRP3 and the release of inflammatory factors, and impaired the functional activity of osteoblasts, thus promoting the development of inflammation.

Interleukin-1β weakens paclitaxel sensitivity through regulating autophagy in the non-small cell lung cancer cell line A549

Non-small cell lung cancer (NSCLC) poses a threat to human health and paclitaxel chemotherapy has been approved for the treatment of this type of cancer. However, resistance to treatment severely compromises the survival rate and prognosis of patients with NSCLC. The aim of the present study was to investigate the role of IL-1β in paclitaxel sensitivity of NSCLC cells and elucidate the underlying mechanism. The expression of IL-1β was found to be upregulated in NSCLC tissues and cells compared with healthy adjacent tissues and a normal epithelial cell line, respectively, as detected by reverse transcription-quantitative PCR and western blot analyses. Subsequently, Cell Counting Kit-8 assay and flow cytometry revealed that IL-1β weakened the sensitivity of A549 cells to paclitaxel. It was subsequently demonstrated that IL-1β induced A549 cell autophagy, while tunicamycin-induced autophagy increased the IL-1β expression level and weakened paclitaxel sensitivity. Thus, the results revealed that IL-1β reduced the sensitivity to paclitaxel in A549 cells by promoting autophagy and suggested that IL-1β may be of value for improving the therapeutic efficacy of paclitaxel chemotherapy in NSCLC.

Involvement of autophagy in MHC class I antigen presentation

MHC class I molecules on the cellular surface display peptides that either derive from endogenous proteins (self or viral), or from endocytosis of molecules, dying cells or pathogens. The conventional antigen‐processing pathway for MHC class I presentation depends on proteasome‐mediated degradation of the protein followed by transporter associated with antigen‐processing (TAP)‐mediated transport of the generated peptides into the endoplasmic reticulum (ER). Here, peptides are loaded onto MHC I molecules before transportation to the cell surface. However, several alternative mechanisms have emerged. These include TAP‐independent mechanisms, the vacuolar pathway and involvement of autophagy. Autophagy is a cell intrinsic recycling system. It also functions as a defence mechanism that removes pathogens and damaged endocytic compartments from the cytosol. Therefore, it appears likely that autophagy would intersect with the MHC class I presentation pathway to alarm CD8⁺ T cells of an ongoing intracellular infection. However, the importance of autophagy as a source of antigen for presentation on MHC I molecules remains to be defined. Here, original research papers which suggest involvement of autophagy in MHC I antigen presentation are reviewed. The antigens are from herpesvirus, cytomegalovirus and chlamydia. The studies point towards autophagy as important in MHC class I presentation of endogenous proteins during conditions of immune evasion. Because autophagy is a regulated process which is induced upon activation of, for example, pattern recognition receptors (PRRs), it will be crucial to use relevant stimulatory conditions together with primary cells when aiming to confirm the importance of autophagy in MHC class I antigen presentation in future studies.

Regulation of Innate Immune Responses by Autophagy: A Goldmine for Viruses

Autophagy is a lysosomal degradation pathway for intracellular components and is highly conserved across eukaryotes. This process is a key player in innate immunity and its activation has anti-microbial effects by directly targeting pathogens and also by regulating innate immune responses. Autophagy dysfunction is often associated with inflammatory diseases. Many studies have shown that it can also play a role in the control of innate immunity by preventing exacerbated inflammation and its harmful effects toward the host. The arms race between hosts and pathogens has led some viruses to evolve strategies that enable them to benefit from autophagy, either by directly hijacking the autophagy pathway for their life cycle, or by using its regulatory functions in innate immunity. The control of viral replication and spread involves the production of anti-viral cytokines. Controlling the signals that lead to production of these cytokines is a perfect way for viruses to escape from innate immune responses and establish successful infection. Published reports related to this last viral strategy have extensively grown in recent years. In this review we describe several links between autophagy and regulation of innate immune responses and we provide an overview of how viruses exploit these links for their own benefit.

Hacking the host: exploitation of macrophage polarization by intracellular bacterial pathogens

Macrophages play an integral role in host defenses against intracellular bacterial pathogens. A remarkable plasticity allows for adaptation to the needs of the host to orchestrate versatile innate immune responses to a variety of microbial threats. Several bacterial pathogens have adapted to macrophage plasticity and modulate the classical (M1) or alternative (M2) activation bias towards a polarization state that increases fitness for intracellular survival. Here, we summarize the current understanding of the host macrophage and intracellular bacterial interface; highlighting the roles of M1/M2 polarization in host defense and the mechanisms employed by several important intracellular pathogens to modulate macrophage polarization to favor persistence or proliferation. Understanding macrophage polarization in the context of disease caused by different bacterial pathogens is important for the identification of targets for therapeutic intervention.

The Autophagy-RNA Interplay: Degradation and Beyond

Autophagy is a highly conserved degradation pathway that ensures nutrient recycling and removal of unwanted substrates. This process has a fundamental role in stress adaptation and maintenance of cellular homeostasis. Here, we discuss emerging aspects of the autophagy-RNA interplay, including autophagy-mediated degradation of RNA, RNA-binding proteins (RBPs), and ribonucleoprotein (RNP) complexes. Beyond degradation, we review new roles for autophagy players in the secretion and intracellular transport of RNA and related complexes. We discuss the physiological importance of these events for RNA homeostasis and gene expression programs, as well as their implications for disease, including cancer and neurodegeneration. Lastly, we examine how post-transcriptional regulation of autophagy, through specialized processing and selective translation of key transcripts, challenges and updates our current view of autophagy complexity.

The flavonoids of Sophora flavescens exerts anti-inflammatory activity via promoting autophagy of Bacillus Calmette-Guérin-stimulated macrophages

Tuberculosis (TB), a highly infectious air-borne disease, has remained a global health problem. Conventional treatment and preventions such as antibiotics and Bacilli Calmette-Guerin (BCG) vaccine can be unreliable. In view of the increasing prevalence of anti-TB drug resistance, adjunctive therapy may be necessary to shorten the recovery time. We have previously shown that flavonoids in the medicinal herb Sophora flavescens exhibit anti-inflammatory and bactericidal activities. The aim of this study was to investigate the molecular and cellular characteristics of flavonoids of S. flavescens (FSF) in BCG-stimulated macrophages for assessing their roles in anti-inflammation and autophagy. Mouse alveolar macrophage (MH-S) cell line and primary mouse peritoneal macrophages were stimulated in vitro with heat-inactivated BCG and treated with FSF, with or without autophagy inhibitor Bafilomycin A1 (BafA1). Gene expression was analyzed using quantitative PCR, and cytokine/chemokine release was analyzed by Milliplex assay and ELISA. Autophagy-related proteins were quantified by Western blot and flow cytometry, and autophagolysosomes were detected using fluorescence microscopy. In both MH-S cell line and mouse peritoneal macrophages stimulated by heat-inactivated BCG, FSF was found to up-regulate autophagy-related proteins microtubule-associated protein 1A/1B-light chain 3 (LC3) and protein 62 (p62), and suppress the induced proinflammatory cytokine TNF-α, CCL5, and IL-6. FSF actively modulates immune processes through suppressing BCG-mediated inflammation by promoting autophagy in MH-S cells and mouse peritoneal macrophages. We suggest that FSF may be useful as an adjunctive therapeutic agent for TB infection by modulating cell survival through autophagy and reducing inflammation.

Epithelial-derived gasdermin D mediates nonlytic IL-1β release during experimental colitis

Gasdermin D (GSDMD) induces pyroptosis via the pore-forming activity of its N-terminal domain, cleaved by activated caspases associated with the release of IL-1β. Here, we report a nonpyroptotic role of full-length GSDMD in guiding the release of IL-1β-containing small extracellular vesicles (sEVs) from intestinal epithelial cells (IECs). In response to caspase-8 inflammasome activation, GSDMD, chaperoned by Cdc37/Hsp90, recruits the E3 ligase, NEDD4, to catalyze polyubiquitination of pro-IL-1β, serving as a signal for cargo loading into secretory vesicles. GSDMD and IL-1β colocalize with the exosome markers CD63 and ALIX intracellularly, and GSDMD and NEDD4 are required for release of CD63+ sEVs containing IL-1β, GSDMD, NEDD4, and caspase-8. Importantly, increased expression of epithelial-derived GSDMD is observed both in patients with inflammatory bowel disease (IBD) and those with experimental colitis. While GSDMD-dependent release of IL-1β-containing sEVs is detected in cultured colonic explants from colitic mice, GSDMD deficiency substantially attenuates disease severity, implicating GSDMD-mediated release of IL-1β sEVs in the pathogenesis of intestinal inflammation, such as that observed in IBD.

Osteocyte-Related Cytokines Regulate Osteoclast Formation and Bone Resorption

The process of bone remodeling is the result of the regulated balance between bone cell populations, namely bone-forming osteoblasts, bone-resorbing osteoclasts, and the osteocyte, the mechanosensory cell type. Osteoclasts derived from the hematopoietic stem cell lineage are the principal cells involved in bone resorption. In osteolytic diseases such as rheumatoid arthritis, periodontitis, and osteoporosis, the balance is lost and changes in favor of bone resorption. Therefore, it is vital to elucidate the mechanisms of osteoclast formation and bone resorption. It has been reported that osteocytes express Receptor activator of nuclear factor κΒ ligand (RANKL), an essential factor for osteoclast formation. RANKL secreted by osteocytes is the most important factor for physiologically supported osteoclast formation in the developing skeleton and in pathological bone resorption such as experimental periodontal bone loss. TNF-α directly enhances RANKL expression in osteocytes and promotes osteoclast formation. Moreover, TNF-α enhances sclerostin expression in osteocytes, which also increases osteoclast formation. These findings suggest that osteocyte-related cytokines act directly to enhance osteoclast formation and bone resorption. In this review, we outline the most recent knowledge concerning bone resorption-related cytokines and discuss the osteocyte as the master regulator of bone resorption and effector in osteoclast formation.

Cathepsin regulation on microglial function

Microglia, the resident mononuclear phagocyte population in the brain, have long been implicated in the pathology of neurodegenerative age-associated disorders. However, activated microglia have now been identified as homeostatic keepers in the brain, because they are involved in the initiation and resolution of neuropathology. The complex roles of activated microglia appear to be linked to change from inflammatory and neurotoxic to anti-inflammatory and neuroprotective phenotypes. Increased expression and secretion of various cathepsins support roles of activated microglia in chronic neuroinflammation, the neurotoxic M1-like polarization and neuronal death. Moreover, changes in expression and localization of microglial cathepsin B play a critical role in the acceleration of the brain aging. Beyond the role as brain-resident macrophages, many lines of evidence have shown that microglia have essential roles in the maturation and maintenance of neuronal circuits in the developing and adult brain. Cathepsin S secreted from microglia induces the diurnal variation of spine density of cortical neurons though proteolytic modification of peri-synaptic extracellular matrix molecules. In this review, I highlight the emerging roles of cathepsins that support the roles of microglia in both normal healthy and pathological brains. In addition, I discuss cathepsin inhibitors as potential therapeutic targets for brain disorders.

N-GSDMD trafficking to neutrophil organelles facilitates IL-1β release independently of plasma membrane pores and pyroptosis

Gasdermin-D (GSDMD) in inflammasome-activated macrophages is cleaved by caspase-1 to generate N-GSDMD fragments. N-GSDMD then oligomerizes in the plasma membrane (PM) to form pores that increase membrane permeability, leading to pyroptosis and IL-1β release. In contrast, we report that although N-GSDMD is required for IL-1β secretion in NLRP3-activated human and murine neutrophils, N-GSDMD does not localize to the PM or increase PM permeability or pyroptosis. Instead, biochemical and microscopy studies reveal that N-GSDMD in neutrophils predominantly associates with azurophilic granules and LC3+ autophagosomes. N-GSDMD trafficking to azurophilic granules causes leakage of neutrophil elastase into the cytosol, resulting in secondary cleavage of GSDMD to an alternatively cleaved N-GSDMD product. Genetic analyses using ATG7-deficient cells indicate that neutrophils secrete IL-1β via an autophagy-dependent mechanism. These findings reveal fundamental differences in GSDMD trafficking between neutrophils and macrophages that underlie neutrophil-specific functions during inflammasome activation.

tert-Butyl-p-benzoquinone induces autophagy by inhibiting the Akt/mTOR signaling pathway in RAW 264.7 cells

tert-Butyl-p-benzoquinone (TBBQ), a metabolite of tert-butylhydroquinone from food, has cytotoxicity, the underlying mechanism of which is not clear. In this study, the viability of RAW 264.7 cells exposed to TBBQ at concentrations of 0.5-10 μg mL^-1 was assayed by MTT. Results suggest that TBBQ decreased the viability in a dose-dependent manner. Monodansylcadaverine (MDC) staining results indicate the occurrence of autophagy induced by TBBQ, which was manifested by activation of LC3-II concurrent with the increased levels of Beclin1 and reduced levels of p62. Elevated lipid peroxide and decreased SOD activity by TBBQ exposure suggest the overproduction of ROS, which may account for the increase in the genotoxic stress protein p53. Both upregulation of p53 and reduction of Akt levels inhibited mTOR, which activated autophagy. Addition of 3-MA counteracted the impact of TBBQ on ATG proteins and cell viability. All of these results suggest that TBBQ induces autophagy of RAW 264.7 cells principally by inhibition of the Akt/mTOR signaling pathway, and they implicate ROS in this regulation.

A Translocation Pathway for Vesicle-Mediated Unconventional Protein Secretion

Many cytosolic proteins lacking a signal peptide, called leaderless cargoes, are secreted through unconventional secretion. Vesicle trafficking is a major pathway involved. It is unclear how leaderless cargoes enter into the vesicle. Here, we find a translocation pathway regulating vesicle entry and secretion of leaderless cargoes. We identify TMED10 as a protein channel for the vesicle entry and secretion of many leaderless cargoes. The interaction of TMED10 C-terminal region with a motif in the cargo accounts for the selective release of the cargoes. In an in vitro reconstitution assay, TMED10 directly mediates the membrane translocation of leaderless cargoes into the liposome, which is dependent on protein unfolding and enhanced by HSP90s. In the cell, TMED10 localizes on the endoplasmic reticulum (ER)-Golgi intermediate compartment and directs the entry of cargoes into this compartment. Furthermore, cargo induces the formation of TMED10 homo-oligomers which may act as a protein channel for cargo translocation.

Lysosomal Exocytosis, Exosome Release and Secretory Autophagy: The Autophagic- and Endo-Lysosomal Systems Go Extracellular

Beyond the consolidated role in degrading and recycling cellular waste, the autophagic- and endo-lysosomal systems play a crucial role in extracellular release pathways. Lysosomal exocytosis is a process leading to the secretion of lysosomal content upon lysosome fusion with plasma membrane and is an important mechanism of cellular clearance, necessary to maintain cell fitness. Exosomes are a class of extracellular vesicles originating from the inward budding of the membrane of late endosomes, which may not fuse with lysosomes but be released extracellularly upon exocytosis. In addition to garbage disposal tools, they are now considered a cell-to-cell communication mechanism. Autophagy is a cellular process leading to sequestration of cytosolic cargoes for their degradation within lysosomes. However, the autophagic machinery is also involved in unconventional protein secretion and autophagy-dependent secretion, which are fundamental mechanisms for toxic protein disposal, immune signalling and pathogen surveillance. These cellular processes underline the crosstalk between the autophagic and the endosomal system and indicate an intersection between degradative and secretory functions. Further, they suggest that the molecular mechanisms underlying fusion, either with lysosomes or plasma membrane, are key determinants to maintain cell homeostasis upon stressing stimuli. When they fail, the accumulation of undigested substrates leads to pathological consequences, as indicated by the involvement of autophagic and lysosomal alteration in human diseases, namely lysosomal storage disorders, age-related neurodegenerative diseases and cancer. In this paper, we reviewed the current knowledge on the functional role of extracellular release pathways involving lysosomes and the autophagic- and endo-lysosomal systems, evaluating their implication in health and disease.

TRIM proteins in autophagy: selective sensors in cell damage and innate immune responses

Autophagy, a main intracellular catabolic process, is induced in response to a variety of cellular stresses to promptly degrade harmful agents and to coordinate the activity of prosurvival and prodeath processes in order to determine the fate of the injured cells. While the main components of the autophagy machinery are well characterized, the molecular mechanisms that confer selectivity to this process both in terms of stress detection and cargo engulfment have only been partly elucidated. Here, we discuss the emerging role played by the E3 ubiquitin ligases of the TRIM family in regulating autophagy in physiological and pathological conditions, such as inflammation, infection, tumorigenesis, and muscle atrophy. TRIM proteins employ different strategies to regulate the activity of the core autophagy machinery, acting either as scaffold proteins or via ubiquitin-mediated mechanisms. Moreover, they confer high selectivity to the autophagy-mediated degradation as described for the innate immune response, where TRIM proteins mediate both the engulfment of pathogens within autophagosomes and modulate the immune response by controlling the stability of signaling regulators. Importantly, the elucidation of the molecular mechanisms underlying the regulation of autophagy by TRIMs is providing important insights into how selective types of autophagy are altered under pathological conditions, as recently shown in cancer and muscular dystrophy.

Autophagy and Protein Secretion

Autophagy - conventional for macroautophagy - is a major recycling strategy that ensures cellular homeostasis through the selective engulfment of cytoplasmic supramolecular cargos in double membrane vesicles and their rapid dispatch to the lysosome for digestion. As autophagy operates in the cytoplasm, its interference with secretory proteins, that is, proteins destined to the plasma membrane or the extracellular space, generally synthesized and routed within the endoplasmic reticulum (ER), has been relatively overlooked in the past. However, mounting evidence reveals that autophagy in fact heavily regulates protein secretion through diverse mechanisms. First, autophagy is closely involved in the unconventional secretion of leaderless proteins, a pool of proteins destined extracellularly, but lacking an ER-targeted leader sequence, and thus manufactured in the cytosol. Autophagy-related (ATG) genes now appear instrumental to the underlying pathways, hence the recently coined concept of secretory autophagy, or better ATG gene-dependent secretion. Indeed, ATG genes regulate unconventional protein secretion at multiple levels, ranging from intracellular inflammatory signaling, for example, through the control of mitochondrial health and inflammasome activity, to trafficking of leaderless proteins. Moreover, perhaps less expectedly, autophagy also participates in the control of conventional secretion, intersecting the secretory apparatus at multiple points, though with surprising differences among professional secretory cell types that disclose remarkable and unpredicted specificity. This review synopsizes the multiple mechanisms whereby autophagy interfaces with conventional and unconventional protein secretory pathways and discusses the relative teleology. Altogether, the diverse controls exerted on protein secretion broaden and deepen the homeostatic significance of autophagy within the cell.

Secretory Autophagy and Its Relevance in Metabolic and Degenerative Disease

Proteins to be secreted through so-called "conventional mechanisms" are characterized by the presence of an N-terminal peptide that is a leader or signal peptide, needed for access to the endoplasmic reticulum and the Golgi apparatus for further secretion. However, some relevant cytosolic proteins lack of this signal peptides and should be secreted by different unconventional or "non-canonical" processes. One form of this unconventional secretion was named secretory autophagy (SA) because it is specifically associated with the autophagy pathway. It is defined by ATG proteins that regulate the biogenesis of the autophagosome, its representative organelle. The canonical macroautophagy involves the fusion of the autophagosomes with lysosomes for content degradation, whereas the SA pathway bypasses this degradative process to allow the secretion. ATG5, as well as other factors involved in autophagy such as BCN1, are also activated as part of the secretory pathway. SA has been recognized as a new mechanism that is becoming of increasing relevance to explain the unconventional secretion of a series of cytosolic proteins that have critical biological importance. Also, SA may play a role in the release of aggregation-prone protein since it has been related to the autophagosome biogenesis machinery. SA requires the autophagic pathway and both, secretory autophagy and canonical degradative autophagy are at the same time, integrated and highly regulated processes that interact in ultimate cross-talking molecular mechanisms. The potential implications of alterations in SA, its cargos, pathways, and regulation in human diseases such as metabolic/aging pathological processes are predictable. Further research of SA as potential target of therapeutic intervention is deserved.

Sirt6-induced autophagy restricted TREM-1-mediated pyroptosis in ox-LDL-treated endothelial cells: relevance to prognostication of patients with acute myocardial infarction

Inflammation mediated by myeloid cells trigger receptors 1 (TREM-1) is important for atherosclerosis development, while sirtuin 6 (Sirt6) levels decrease in atheroscleoritc plaque. Here we demonstrate that oxidatively modified low density lipoprotein (ox-LDL)-treated endothelial cells (ECs) exhibited increased TREM-1-mediated pyroptosis and decreased Sirt6-induced autophagy. We show that high sTREM-1 and low sSirt6 levels were independent predictors of boosted endothelial microparticles (EMPs) on admission, and were associated with increased risk for all-cause mortality and major adverse cardiovascular events (MACE) at median 24 months (interquartile range, 18–26) follow-up in acute myocardial infarction (AMI) patients. Additionally, blockage of Sirt6-induced autophagy led to augmented TREM-1-mediated pyroptosis, whereas Sirt6 overexpression attenuated ECs inflammation and pyroptosis following ox-LDL treatment. Our findings indicate that TREM-1 and in a reversed trend Sirt6 appeared to be markers of endothelial inflammation with potential for use in risk stratification.