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Autophagy is an essential physiological process that maintains cellular homeostasis by eliminating harmful protein aggregates, damaged organelles and certain pathogens through lysosomal degradation. During autophagy specialized structures, known as autophagosomes are formed that recruit the cargo through autophagy receptors, and deliver it to lysosomes. Optineurin (Optn) is an autophagy receptor that mediates cargo selective autophagy. Recently, we have identified a novel function of Optn that promotes autophagosome formation during non-selective autophagy. Optn-deficient cells show reduced formation of autophagosomal protein LC3-II and lower number of autophagosomes as well as autolysosomes. Interestingly, formation of phagophores is increased in Optn-deficient cells. This suggests that Optn promotes autophagosome formation by potentiating LC3-II production and phagophore maturation. Phosphorylation of Optn at Ser-177 is required for promoting autophagosome formation. Here, we discuss various aspects of the role of Optn in the formation of autophagosomes and Atg16L1-positive vesicles. We also discuss the potential role of Rab1a-Optn interaction.

Background Diabetic nephropathy (DN) is one of the most important medical complications of diabetes mellitus. Autophagy is an important mediator of pathological response and plays a critical role in inflammation during the progression of diabetic nephropathy. Interleukin (IL)-17A favorably modulates inflammatory disorders including DN. In this study, we examined whether IL-17A deficiency affected the autophagy process in the kidneys of mice with streptozotocin (STZ)-induced DN. Methods The autophagic response of IL-17A to STZ-induced nephrotoxicity was evaluated by analyzing STZ-induced functional and histological renal injury in IL-17A knockout (KO) mice. Results IL-17A KO STZ-treated mice developed more severe nephropathy than STZ-treated wild-type (WT) mice, with increased glomerular damage and renal interstitial fibrosis at 12 weeks. IL-17A deficiency also increased the up-regulation of proinflammatory cytokines and fibrotic gene expression after STZ treatment. Meanwhile, autophagy-associated proteins were induced in STZ-treated WT mice. However, IL-17A KO STZ-treated mice displayed a significant decrease in protein expression. Especially, the levels of LC3 and ATG7, which play crucial roles in autophagosome formation, were notably decreased in the IL-17A KO STZ-treated mice compared with their WT counterparts. Conclusions IL-17 deficiency aggravates of STZ-induced DN via attenuation of autophagic response. Our study demonstrated that IL-17A mediates STZ-induced renal damage and represents a potential therapeutic target in DN.

Tobacco products vary widely in their chemical composition and potential harm, yet their impact on oral tissue remains insufficiently characterized. This study comparatively investigated the cytotoxic, oxidative, and inflammatory responses, along with apoptotic/necrotic cell death, autophagosome formation, and tissue remodeling capacity, in human gingival fibroblasts (hGFs) exposed to total particulate matter (TPM) derived from a conventional cigarette (TPM-c) and a heated tobacco product (TPM-h). TPMs were chemically characterized by inductively coupled plasma mass spectrometry (ICP-MS) for heavy metal content. TPM-c induced notable cytotoxicity, necrosis, and impaired wound healing compared to TPM-h, although both products compromised hGF viability and function. In addition, higher levels of Cadmium (Cd), Lead (Pb), and Zinc (Zn) were detected in TPM-c. Triggered vascular endothelial growth factor-A (VEGF-A) upregulation as a defensive reaction to cellular stress was observed in hGFs via TPM-c, while TPM-h reduced autophagic response via Microtubule-associated protein 1 A/1 B-light chain 3-phosphatidyl ethanolamine conjugate/LC3-II (LC3β) expression. Both TPMs elevated interleukin-6 (IL-6) release, notably at intermediate and high doses. In summary, TPM-c demonstrated a greater capacity than TPM-h to induce cytotoxicity, oxidative and inflammatory damage, and disrupted tissue remodeling. Nonetheless, TPM-h was not devoid of toxicity, eliciting pro-inflammatory/ angiogenic responses concentration-dependently. These findings highlight the necessity of further investigation into the long-term effects of emerging tobacco products on periodontal disease progression and development.

Macroautophagy/autophagy is a lysosome-dependent catabolic process induced by various cellular stress conditions, maintaining the homeostasis of cells, tissues and organs. Autophagy is a series of membrane-related events involving multiple autophagy-related (ATG) proteins. Most studies to date have focused on various signaling pathways affecting ATG proteins to control autophagy. However, mounting evidence reveals that the actin cytoskeleton acts on autophagy-associated membranes to regulate different events of autophagy. The actin cytoskeleton assists in vesicle formation and provides the mechanical forces for cellular activities that involve membrane deformation. Although the interaction between the actin cytoskeleton and membrane makes the role of actin in autophagy recognized, how the actin cytoskeleton is recruited and assembles on membranes during autophagy needs to be detailed. Nucleation-promoting factors (NPFs) activate the Arp2/3 complex to produce actin cytoskeleton. In this review, we summarize the important roles of the actin cytoskeleton in autophagy regulation and focus on the effect of NPFs on actin cytoskeleton assembly during autophagy, providing new insights into the occurrence and regulatory mechanisms of autophagy. 3faFZQ-LH-sD4jatu9NQ53 Video Abstract

Maintenance of skeletal muscle structure and function requires efficient and precise metabolic control. Autophagy plays a key role in metabolic homeostasis of diverse tissues by recycling cellular constituents, particularly under conditions of caloric restriction, thereby normalizing cellular metabolism. Here we show that histone deacetylases (HDACs) 1 and 2 control skeletal muscle homeostasis and autophagy flux in mice. Skeletal muscle-specific deletion of both HDAC1 and HDAC2 results in perinatal lethality of a subset of mice, accompanied by mitochondrial abnormalities and sarcomere degeneration. Mutant mice that survive the first day of life develop a progressive myopathy characterized by muscle degeneration and regeneration, and abnormal metabolism resulting from a blockade to autophagy. HDAC1 and HDAC2 regulate skeletal muscle autophagy by mediating the induction of autophagic gene expression and the formation of autophagosomes, such that myofibers of mice lacking these HDACs accumulate toxic autophagic intermediates. Strikingly, feeding HDAC1/2 mutant mice a high-fat diet from the weaning age releases the block in autophagy and prevents myopathy in adult mice. These findings reveal an unprecedented and essential role for HDAC1 and HDAC2 in maintenance of skeletal muscle structure and function and show that at least in some pathological conditions, myopathy may be mitigated by dietary modifications.

ATG9A is the only transmembrane protein among the components required for autophagosome formation and participates in multiple cellular biological processes. ATG9A undergoes intracellular transport via microtubules and actin. As a lipid scramblase, ATG9A facilitates the random movement of lipid molecules between the inner and outer leaflets of lipid bilayers. Additionally, it can influence the homeostasis of the plasma membrane and membranous organelles. In autophagy, ATG9A is recruited to autophagic initiation sites to initiate cellular autophagy and subsequently participates in the process by promoting lipid transfer. Moreover, ATG9A also plays roles in maintaining neuronal homeostasis and is involved in embryonic development, infection, and immune responses. In this review, we comprehensively and systematically summarize the roles and mechanisms of ATG9A, aiming to provide a new perspective for understanding its functions.

Abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs) is one of the critical pathological mechanisms of pulmonary hypertension (PH), and therefore is gradually being adopted as an important direction for the treatment of PH. Metallothioneins (MTs) have been reported to be associated with PH, but the underlying mechanisms are not fully understood. Here, we demonstrated that the expression level of metallothionein 3 (MT3) was significantly increased in pulmonary arterioles from PH patients and chronic hypoxia-induced rat and mouse PH models, as well as in hypoxia-treated human PASMCs. Knockdown of MT3 significantly inhibited the proliferation of human PASMCs by arresting the cell cycle in the G1 phase, while overexpression of MT3 had the opposite effect. Mechanistically, we found that MT3 increased the intracellular zinc (Zn ) concentration to enhance the transcriptional activity of metal-regulated transcription factor 1 (MTF1), which promoted the expression of autophagy-related gene 5 (ATG5), facilitating autophagosome formation. More importantly, MT3-induced autophagy and proliferation of human PASMCs were largely prevented by knockdown of MTF1 and ATG5. Therefore, in this study, we identified MT3-Zinc-MTF1-ATG5 as a novel pathway that affects PASMC proliferation by regulating autophagosome formation, suggesting that MT3 may be a novel target for the treatment of PH.

Autophagy plays an important role in determining stem‐cell differentiation. During the osteogenic differentiation of mesenchymal stem cells (MSCs), autophagosome formation is upregulated but the reason is unknown. A long‐standing quest in the autophagy field is to find the membrane origin of autophagosomes. In this study, cytoplasmic coat protein complex II (COPII) vesicles, endoplasmic reticulum‐derived vesicles responsible for the transport of storage proteins to the Golgi, are demonstrated to be a critical source of osteoblastic autophagosomal membrane. A significant correlation between the number of COPII vesicle and the autophagy level is identified in the rat bone tissues. Disruption of COPII vesicles restrained osteogenesis and decreased the number and size of autophagosomes. SEC31a (an outer coat protein of COPII vesicle) is found to be vital to regulate COPII vesicle‐dependent autophagosome formation via interacting with ATG9a of autophagosomal seed vesicles. The interference of Sec31a inhibited autophagosome formation and osteogenesis in vitro and in vivo. These results identified a novel mechanism of autophagosome formation in osteogenic differentiation of stem cells and identified SEC31a as a critical protein that mediates the interplay between COPII and ATG9a vesicles. These findings broaden the understanding of the regulatory mechanism in the osteogenic differentiation of MSCs. During osteogenic differentiation of MSCs, autophagosome formation is upregulated but the reason is unknown. Here, COPII vesicles are demonstrated to be a critical source of osteoblastic autophagosomal membrane. The interact between SEC31a (COPII vesicles coat protein) and ATG9a regulates the formation of autophagosome. These findings broaden the understanding of the regulatory mechanism in osteogenic differentiation of MSCs.