Modulation of autophagy affected tumorigenesis induced by the envelope glycoprotein of JSRV

Ovine pulmonary adenocarcinoma (OPA), caused by the jaagsiekte sheep retrovirus (JSRV), is a chronic, progressive, and contagious lung tumor that seriously affects sheep production. It also represents a valuable animal model for several human lung adenocarcinomas. However, little is known about the role of autophagy in OPA tumorigenesis. Here, Western blotting combined with transmission electron microscopy examination and Cyto-ID dye staining was employed for evaluation of changes of autophagic levels. The results of the present study showed that expression of the autophagy marker proteins Beclin-1 and LC3 was decreased in OPA lung tissues, as well as in cells overexpressing the envelope glycoprotein of JSRV (JSRV Env). Reduced numbers of autophagosomes were also observed in cells overexpressing JSRV Env, although assessment of autophagic flux showed that JSRV Env overexpression did not block the formation of autophagosomes, suggesting increased degradation of autolysosomes. Last, mouse xenograft experiments indicated that inhibition of autophagy by 3-methyladenine suppressed both tumor growth and the epithelial-to-mesenchymal transition. In conclusion, JSRV, through JSRV Env, takes advantage of the autophagy process, leading to the development of OPA.

Impaired autophagy following ex vivo cooling of simulated hypothermic temperatures in peripheral blood mononuclear cells from young and older adults

Hypothermia is a critical consequence of extreme cold exposure that increases the risk of cold-related injury and death in humans. While the initiation of cytoprotective mechanisms including the process of autophagy and the heat shock response (HSR) is crucial to cellular survival during periods of stress, age-related decrements in these systems may underlie cold-induced cellular vulnerability in older adults. Moreover, whether potential sex-related differences in autophagic regulation influence the human cold stress response remain unknown. We evaluated the effect of age and sex on mechanisms of cytoprotection (autophagy and the HSR) and cellular stress (apoptotic signaling and the acute inflammatory response) during ex vivo hypothermic cooling. Venous blood samples from 20 healthy young (10 females; mean [SD]: 22 [2] years) and 20 healthy older (10 females; 66 [5] years) adults were either isolated immediately (baseline) for peripheral blood mononuclear cells (PBMCs) or exposed to water bath temperatures maintained at 37, 35, 33, 31, or 4 °C for 90 min before PBMC isolation. Proteins associated with autophagy, apoptosis, the HSR, and inflammation were analyzed via Western blotting. Indicators of autophagic initiation and signaling (LC3, ULK1, and beclin-2) and the HSR (HSP90 and HSP70) increased when exposed to hypothermic temperatures in young and older adults (all p ≤ 0.007). Sex-related differences were only observed with autophagic initiation (ULK1; p = 0.015). However, despite increases in autophagic initiators ULK1 and beclin-2 (all p < 0.001), this was paralleled by autophagic dysfunction (increased p62) in all groups (all p < 0.001). Further, apoptotic (cleaved-caspase-3) and inflammatory (IL-6 and TNF-α) signaling increased in all groups (all p < 0.001). We demonstrated that exposure to hypothermic conditions is associated with autophagic dysfunction, irrespective of age or sex, although there may exist innate sex-related differences in cytoprotection in response to cold exposure as evidenced through altered autophagic initiation.

Autophagy-the crossword puzzle

It's April, so it is time to lighten up (think April Fools' Day). In this issue of the journal, I have two different sets of puzzles for you. Of course, these are not just for your amusement; there is an educational component as well. For example, the crossword puzzle requires you to think about autophagy and perhaps do some searching for names or terms that you are less familiar with (the Guidelines is always a good source of information in this regard). In addition, the crossword puzzle uses official HGNC nomenclature unless otherwise specified - another learning opportunity. Note that this is an alphabet-only puzzle, so dashes, spaces and numbers are omitted. Thus, the clue "The C. elegans homolog of ULK1" would have the answer "UNC". The second challenge is directly nomenclature based. The goal in this case is to identify as many nomenclature errors as you can in the puncta published in this issue. So, have fun, learn, impress your colleagues and take a break from lab work; unless you are working in my lab - in that case, you should be working at the bench or writing a paper (you know I don't go for this kind of tomfoolery).

The Role of ATG9 Vesicles in Autophagosome Biogenesis

Autophagy mediates the degradation and recycling of cellular material in the lysosomal system. Dysfunctional autophagy is associated with a plethora of diseases including uncontrolled infections, cancer and neurodegeneration. In macroautophagy (hereafter autophagy) this material is encapsulated in double membrane vesicles, the autophagosomes, which form upon induction of autophagy. The precursors to autophagosomes, referred to as phagophores, first appear as small flattened membrane cisternae, which gradually enclose the cargo material as they grow. The assembly of phagophores during autophagy initiation has been a major subject of investigation over the past decades. A special focus has been ATG9, the only conserved transmembrane protein among the core machinery. The majority of ATG9 localizes to small Golgi-derived vesicles. Here we review the recent advances and breakthroughs regarding our understanding of how ATG9 and the vesicles it resides in serve to assemble the autophagy machinery and to establish membrane contact sites for autophagosome biogenesis. We also highlight open questions in the field that need to be addressed in the years to come.

Age-related deficits in retinal autophagy following intraocular pressure elevation in autophagy reporter mouse model

This study quantified age-related changes to retinal autophagy using the CAG-RFP-EGFP-LC3 autophagy reporter mice and considered how aging impacts autophagic responses to acute intraocular pressure (IOP) stress. IOP was elevated to 50 mm Hg for 30 minutes in 3-month-old and 12-month-old CAG-RFP-EGFP-LC3 (n = 7 per age group) and Thy1-YFPh transgenic mice (n = 3 per age group). Compared with younger eyes, older eyes showed diminished basal autophagy in the outer retina, while the inner retina was unaffected. Autophagic flux (red:yellow puncta ratio) was elevated in the inner plexiform layer. Three days following IOP elevation, older eyes showed poorer functional recovery, most notably in ganglion cell responses compared to younger eyes (12 months old: -33.4 ± 5.3% vs. 3 months mice: -13.4 ± 4.5%). This paralleled a reduced capacity to upregulate autophagic puncta volume in the inner retina in older eyes, a response that was seen in younger eyes. Age-related decline in basal and stress-induced autophagy in the retina is associated with greater retinal ganglion cells' susceptibility to IOP elevation.

Mitochondrial dysfunction and mitophagy: crucial players in burn trauma and wound healing

Burn injuries are a significant cause of death worldwide, leading to systemic inflammation, multiple organ failure and sepsis. The progression of burn injury is explicitly correlated with mitochondrial homeostasis, which is disrupted by the hyperinflammation induced by burn injury, leading to mitochondrial dysfunction and cell death. Mitophagy plays a crucial role in maintaining cellular homeostasis by selectively removing damaged mitochondria. A growing body of evidence from various disease models suggest that pharmacological interventions targeting mitophagy could be a promising therapeutic strategy. Recent studies have shown that mitophagy plays a crucial role in wound healing and burn injury. Furthermore, chemicals targeting mitophagy have also been shown to improve wound recovery, highlighting the potential for novel therapeutic strategies based on an in-depth exploration of the molecular mechanisms regulating mitophagy and its association with skin wound healing.

Wild-type and pathogenic forms of ubiquilin 2 differentially modulate components of the autophagy-lysosome pathways

Missense mutations of ubiquilin 2 (UBQLN2) have been identified to cause X-linked amyotrophic lateral sclerosis (ALS). Proteasome-mediated protein degradation is reported to be impaired by ALS-associated mutations of UBQLN2. However, it remains unknown how these mutations affect autophagy-lysosome protein degradation, which consists of macroautophagy (MA), microautophagy (mA), and chaperone-mediated autophagy (CMA). Using a CMA/mA fluorescence reporter we found that overexpression of wild-type UBQLN2 impairs CMA. Conversely, knockdown of endogenous UBQLN2 increases CMA activity, suggesting that normally UBQLN2 negatively regulates CMA. ALS-associated mutant forms of UBQLN2 exacerbate this impairment of CMA. Using cells stably transfected with wild-type or ALS-associated mutant UBQLN2, we further determined that wild-type UBQLN2 increased the ratio of LAMP2A (a CMA-related protein) to LAMP1 (a lysosomal protein). This could represent a compensatory reaction to the impairment of CMA by wild-type UBQLN2. However, ALS-associated mutant UBQLN2 failed to show this compensation, exacerbating the impairment of CMA by mutant UBQLN2. We further demonstrated that ALS-associated mutant forms of UBQLN2 also impair MA, but wild-type UBQLN2 does not. These results support the view that ALS-associated mutant forms of UBQLN2 impair both CMA and MA which may contribute to the neurodegeneration observed in patients with UBQLN2-mediated ALS.

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

BACKGROUND

There are currently no disease-modifying therapeutics for Parkinson's disease (PD). Although extensive efforts were undertaken to develop therapeutic approaches to delay the symptoms of PD, untreated α-synuclein (α-syn) aggregates cause cellular toxicity and stimulate further disease progression. PROTAC (Proteolysis-Targeting Chimera) has drawn attention as a therapeutic modality to target α-syn. However, no PROTACs have yet shown to selectively degrade α-syn aggregates mainly owing to the limited capacity of the proteasome to degrade aggregates, necessitating the development of novel approaches to fundamentally eliminate α-syn aggregates.

METHODS

We employed AUTOTAC (Autophagy-Targeting Chimera), a macroautophagy-based targeted protein degradation (TPD) platform developed in our earlier studies. A series of AUTOTAC chemicals was synthesized as chimeras that bind both α-syn aggregates and p62/SQSTM1/Sequestosome-1, an autophagic receptor. The efficacy of Autotacs was evaluated to target α-syn aggregates to phagophores and subsequently lysosomes for hydrolysis via p62-dependent macroautophagy. The target engagement was monitored by oligomerization and localization of p62 and autophagic markers. The therapeutic efficacy to rescue PD symptoms was characterized in cultured cells and mice. The PK/PD (pharmacokinetics/pharmacodynamics) profiles were investigated to develop an oral drug for PD.

RESULTS

ATC161 induced selective degradation of α-syn aggregates at DC50 of ~ 100 nM. No apparent degradation was observed with monomeric α-syn. ATC161 mediated the targeting of α-syn aggregates to p62 by binding the ZZ domain and accelerating p62 self-polymerization. These p62-cargo complexes were delivered to autophagic membranes for lysosomal degradation. In PD cellular models, ATC161 exhibited therapeutic efficacy to reduce cell-to-cell transmission of α-syn and to rescue cells from the damages in DNA and mitochondria. In PD mice established by injecting α-syn preformed fibrils (PFFs) into brain striata via stereotaxic surgery, oral administration of ATC161 at 10 mg/kg induced the degradation of α-syn aggregates and reduced their propagation. ATC161 also mitigated the associated glial inflammatory response and improved muscle strength and locomotive activity.

CONCLUSION

AUTOTAC provides a platform to develop drugs for PD. ATC161, an oral drug with excellent PK/PD profiles, induces selective degradation of α-syn aggregates in vitro and in vivo. We suggest that ATC161 is a disease-modifying drug that degrades the pathogenic cause of PD.

ATG16L1 is equipped with two distinct WIPI2-binding sites to drive autophagy

The recruitment of ATG12-ATG5-ATG16L1 complex to phagophore mediated by the specific interaction between ATG16L1 and WIPI2, is pivotal to the formation of autophagosomes during macroautophagy. Recently, we reported that ATG16L1 contains two distinct WIPI2-binding sites, the previously reported WIPI2-binding site (WBS1), and the newly identified site (WBS2). By determining the crystal structures of WIPI2 with ATG16L1 WBS1 and WBS2 respectively, we uncovered that, unlike ATG16L1 WBS1, ATG16L1 WBS2 and its binding mechanism to WIPI2 are conserved from yeast to mammals. Using cell-based functional assays, we further demonstrated that the integrity of two WIPI2-binding sites of ATG16L1 is essential for normal autophagic flux. In summary, our study provided mechanistic insights into the interaction of two key autophagic proteins, ATG16L1 and WIPI2, and revealed a dual-binding-site mode adopted by ATG16L1 to associate with WIPI2.

CNTNAP2 Protein Is Degraded by the Ubiquitin-Proteasome System and the Macroautophagy-Lysosome Pathway

Contactin-associated protein-like 2 (CNTNAP2) gene, located on chromosome 7q35, is one of the largest genes in the human genome. CNTNAP2 protein is a type-I transmembrane protein specifically expressed in the nervous system, with versatile roles in the axonal organization, synaptic functions, neuronal migration, and functional connectivity. CNTNAP2 has been widely investigated as a risk gene for autism spectrum disorder (ASD), and recent studies also implicated CNTNAP2 in Alzheimer's disease (AD). Knowledge of the regulations on CNTNAP2's life cycle is necessary for understanding the related physiological functions and pathological conditions. However, the mechanisms underlying CNTNAP2 protein degradation remain elusive. Therefore, we systematically investigated the half-life and degradation pathway of the human CNTNAP2 protein. We discovered that CNTNAP2 has C-terminal fragments (CTF), which may have essential physiological functions. Our results demonstrated that CNTNAP2 full-length protein and CTF have a short half-life of about 3-4 h. CNTNAP2 proteins are degraded by the ubiquitin-proteasome system and the macroautophagy-lysosome pathway, while the lysosome pathway is more common for CNTNAP2 degradation. This study will provide novel insights and valuable tools for CNTNAP2 functional research in physiological and pathological scenarios.

Inhibition of autophagy in macrophage promotes IL-1β-mediated hepatocellular carcinoma progression via inflammasome accumulation and self-recruitment

Hepatocellular carcinoma (HCC) has a complex and changeable tumor microenvironment. Despite emerging evidence focusing on autophagy process within immune cells, the function and regulatory mechanism of macrophage autophagy in tumor progression remains unclear. Our results of multiplex-immunohistochemistry and RNA-sequencing identified the reduced levels of autophagy in tumor macrophages in the HCC microenvironment, associated with a poor prognosis and increased microvascular metastasis in HCC patients. Specifically, HCC suppressed the macrophage autophagy initiation through the up-regulation of mTOR and ULK1 phosphorylation at Ser757. Knockdown of autophagy-related proteins to further inhibit autophagy significantly boosted the metastatic potential of HCC. Mechanistically, the accumulation of NLRP3 inflammasome mediated by autophagy inhibition promoted the cleavage, maturation, and release of IL-1β, which facilitated the HCC progression, eventually accelerating HCC metastasis via the epithelial-mesenchymal transition. Autophagy inhibition provoked macrophage self-recruitment through the CCL20-CCR6 signaling was also a crucial account of HCC progression. Recruited macrophages mediated the cascade amplification of IL-1β and CCL20 to form a novel pro-metastatic positive feedback loop through promoting HCC metastasis and increased macrophage recruitment, respectively. Notably, targeting IL-1β/IL-1 receptor signaling impaired lung metastasis induced by macrophage autophagy inhibition in a mice HCC lung metastasis model. In summary, this study highlighted that inhibition of tumor macrophage autophagy facilitated HCC progression by increasing IL-1β secretion via NLRP3 inflammasome accumulation and by macrophage self-recruitment through the CCL20 signaling pathway. Interruption of this metastasis-promoting loop by IL-1β blockade may provide a promising therapeutic strategy for HCC patients.

Defective chaperone-mediated autophagy is a hallmark of joint disease in patients with knee osteoarthritis

OBJECTIVE

Defects in autophagy contribute to joint aging and Osteoarthritis (OA). Identifying specific autophagy types could be useful for developing novel treatments for OA.

DESIGN

An autophagy-related gene array was performed in blood from non-OA and knee OA subjects from the Prospective Cohort of A Coruña (PROCOAC). The differential expression of candidate genes was confirmed in blood and knee cartilage and a regression analysis was performed adjusting for age and BMI. HSP90A, a chaperone mediated autophagy (CMA) marker was validated in human knee joint tissues, as well as, in mice with aging-related and surgically-induced OA. The consequences of HSP90AA1 deficiency were evaluated on OA pathogenesis. Finally, the contribution of CMA to homeostasis was studied by assessing the capacity to restore proteostasis upon ATG5-mediated macroautophagy deficiency and genetic HSP90AA1 overexpression.

RESULTS

16 autophagy-related genes were significantly down-regulated in blood from knee OA subjects. Validation studies showed that HSP90AA1 was down-regulated in blood and human OA cartilage and correlated with risk incidence of OA. Moreover, HSP90A was reduced in human OA joints tissues and with aging and OA in mice. HSP90AA1 knockdown was linked to defective macroautophagy, inflammation, oxidative stress, senescence and apoptosis. However, macroautophagy deficiency increased CMA, highlighting the CMA-macroautophagy crosstalk. Remarkably, CMA activation was sufficient to protect chondrocytes from damage.

CONCLUSIONS

We show that HSP90A is a key chaperone for chondrocyte homeostasis, while defective CMA contributes to joint damage. We propose that CMA deficiency is a relevant disease mechanism and could represent a therapeutic target for OA.

Tributyltin activates the Keap1-Nrf2 pathway via a macroautophagy-independent reduction in Keap1

Tributyltin (TBT) is an environmental chemical, which was used as an antifouling agent for ships. Although its use has been banned, it is still persistently present in ocean sediments. Although TBT reportedly causes various toxicity in mammals, few studies on the mechanisms of biological response against TBT toxicity exist. The well-established Keap1-Nrf2 pathway is activated as a cytoprotective mechanism under stressful conditions. The relationship between TBT and the Keap1-Nrf2 pathway remains unclear. In the present study, we evaluated the effect of TBT on the Keap1-Nrf2 pathway. TBT reduced Keap1 protein expression in Neuro2a cells, a mouse neuroblastoma cell line, after 6 hr without altering mRNA expression levels. TBT also promoted the nuclear translocation of Nrf2, a transcription factor for antioxidant proteins, after 12 hr and augmented the expression of heme oxygenase 1, a downstream protein of Nrf2. Furthermore, TBT decreased Keap1 levels in mouse embryonic fibroblast (MEF) cells, with the knockout of Atg5, which is essential for macroautophagy, as well as in wild-type MEF cells. These results suggest that TBT activates the Keap1-Nrf2 pathway via the reduction in the Keap1 protein level in a macroautophagy-independent manner. The Keap1-Nrf2 pathway is activated by conformational changes in Keap1 induced by reactive oxygen species or electrophiles. Furthermore, any unutilized Keap1 protein is degraded by macroautophagy. Understanding the novel mechanism governing the macroautophagy-independent reduction in Keap1 by TBT may provide insights into the unresolved biological response mechanism against TBT toxicity and the activation mechanism of the Keap1-Nrf2 pathway.

Effects of high-fat diet-induced diabetes on autophagy in the murine liver: A systematic review and meta-analysis

AIMS

We conducted a meta-analysis to investigate whether diabetes induced by a high-fat diet (HFD) has the potential to alter the process of autophagy in the murine liver.

METHODS

A systematic literature search was performed with electronic databases (PubMed, EMBASE, Web of Science). Study design, population, intervention, outcome, and risk of bias were analyzed. Given the availability of studies, a quantitative meta-analysis including 23 studies was performed.

KEY FINDINGS

The search found 5754 articles, with 48 matching the eligibility criteria, comprising of 1033 animals. The meta-analysis showed that diabetic murines fed with HFD presented an absence of p62 degradation (SMD 4.63, 95 % CI 2.02 to 7.24, p = 0.0005; I² = 77 %), higher expression of p-mTOR/mTOR (SMD 5.20, 95 % CI 1.00 to 9.39, p = 0.01; I² = 78 %), and a decreased p-AMPK/AMPK ratio (SMD -2.02, 95 % CI -3.96 to -0.09, p = 0.04; I² = 85 %) when compared to nondiabetic murines. When associated with streptozotocin, the animals presented decreased ATG-7 and LC3-II. The meta-regression results showed a decrease in autophagy responses due to increased glycemic levels, fat content, and long-term exposure to HFD, and advanced animal age. The common and species-specific protein responses were also consistent with the inhibition of autophagy.

SIGNIFICANCE

The normal process of autophagy mechanisms in the liver is less competent after HFD consumption. The destabilization of (auto)phagolysosomes contributes to the perpetuation of diabetes, metabolic dysfunction-associated fatty liver disease, and cell death.

O-GlcNAcylation stabilizes the autophagy-initiating kinase ULK1 by inhibiting chaperone-mediated autophagy upon HPV infection

Human papillomaviruses (HPVs) cause a subset of head and neck squamous cell carcinomas (HNSCCs). Previously, we demonstrated that HPV16 oncogene E6 or E6/E7 transduction increases the abundance of O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT), but OGT substrates affected by this increase are unclear. Here, we focus on the effects of O-GlcNAcylation on HPV-positive HNSCCs. We found that upon HPV infection, Unc-51-like kinase 1 (ULK1), an autophagy-initiating kinase, is hyper-O-GlcNAcylated, stabilized, and linked with autophagy elevation. Through mass spectrometry, we identified that ULK1 is O-GlcNAcylated at Ser409, which is distinct from the previously reported Thr635/Thr754 sites. It has been demonstrated that PKCα mediates phosphorylation of ULK1 at Ser423, which attenuates its stability by shunting ULK1 to the chaperone-mediated autophagy (CMA) pathway. Using biochemical assays, we demonstrate that ULK1 Ser409Ser410 O-GlcNAcylation antagonizes its phosphorylation at Ser423. Moreover, mutations of Ser409A and its neighboring site Ser410A (2A) render ULK1 less stable by promoting interaction with the CMA chaperone HSC70 (heat shock cognate 70 kDa protein). Furthermore, ULK1-2A mutants attenuate the association of ULK1 with STX17, which is vital for the fusion between autophagosomes and lysosomes. Analysis of The Cancer Genome Atlas (TCGA) database reveals that ULK1 is upregulated in HPV-positive HNSCCs, and its level positively correlates with HNSCC patient survival. Overall, our work demonstrates that O-GlcNAcylation of ULK1 is altered in response to environmental changes. O-GlcNAcylation of ULK1 at Ser409 and perhaps Ser410 stabilizes ULK1, which might underlie the molecular mechanism of HPV-positive HNSCC patient survival.

Autophagy modulation by irbesartan mitigates the pulmonary fibrotic alterations in bleomycin challenged rats: Comparative study with rapamycin

AIMS

In pulmonary fibrosis, autophagy handles the maintenance of alveolar epithelial cells, prevents epithelial-mesenchymal transition (EMT), and controls collagen turnover. The mammalian target of rapamycin (mTOR) and its translational-dependent proteins are essential regulators of autophagy. Irbesartan (IRB) has earlier ameliorative effects in experimental pulmonary fibrosis. The current study aimed to explore therapeutic autophagy-modulated pulmonary fibrotic changes by IRB versus rapamycin (RAPA) in bleomycin (BLM)-challenged rats.

MATERIALS AND METHODS

A single intratracheal BLM dose at day (0), IRB in different doses (10, 20, and 40 mg/kg) or RAPA (2.5 mg/kg) was given daily for 14 continuous days.

KEY FINDINGS

IRB significantly diminished the fibrotic lung scores. Pulmonary levels of transforming growth factor (TGF)-β1 and hydroxyproline exhibited marked attenuation in IRB (40 mg/kg)-treated rats compared to other treated groups. IRB (40 mg/kg) was not significantly different from RAPA. It downregulated the fibrotic lung phosphorylated mammalian target of rapamycin (p-mTOR) levels and augmented lung Unc-51-like autophagy activating kinase 1 (ULK1), LC3-I and LC3-II more than IRB (10 and 20 mg/kg)-treated fibrotic groups.

SIGNIFICANCE

Autophagic effects via the mTOR signalling pathway may play a role in IRB's antifibrotic effects. Consideration of IRB as a therapeutic antifibrotic agent in pulmonary fibrosis needs further experimental and clinical long-term validation, especially in comorbid with primary hypertension, heart failure, and diabetic renal insults.

Vacuolar fragmentation promotes fluxes of microautophagy and micronucleophagy but not of macroautophagy

Vacuoles and lysosomes are organelles involved in the degradation of cytoplasmic proteins and organelles. Vacuolar morphology is dynamically regulated by fission and fusion in budding yeast. Vacuolar fusion is elicited in nutrient-depleted conditions and mediated by inactivation of target of rapamycin complex 1 (TORC1) protein kinase. However, it is unknown whether and how vacuolar morphology affects macroautophagy and microautophagy, which are induced by nutrient starvation and TORC1 inactivation. Here, we developed a system to control vacuolar fission in budding yeast. Vacuolar fragmentation promoted microautophagy but not macroautophagy. Vacuolar fragmentation caused multiple nucleus-vacuole junctions. Multiple vacuoles caused by vacuolar fragmentation also improved micronucleophagy (microautophagic degradation of a portion of the nucleus). However, vacuolar morphology did not impact nucleolar remodeling, condensation of the rDNA (rRNA gene) region, or separation of ribosomal DNA from nucleolar proteins, which is evoked by TORC1 inactivation. Thus, this study provides insights into the impacts of vacuolar/lysosomal morphology on macroautophagy and microautophagy.

mTOR signaling as a molecular target for the alleviation of Alzheimer's disease pathogenesis

Mechanistic/mammalian target of rapamycin (mTOR) belongs to the phosphatidylinositol kinase-related kinase (PIKK) family. mTOR signaling is required for the commencement of essential cell functions including autophagy. mTOR primarily governs cell growth in response to favourable nutrients and other growth stimuli. However, it also influences aging and other aspects of nutrient-related physiology such as protein synthesis, ribosome biogenesis, and cell proliferation in adults with very limited growth. The major processes for survival such as synaptic plasticity, memory storage and neuronal recovery involve a significant mTOR activity. mTOR dysregulation is becoming a prevalent motif in a variety of human diseases, including cancer, neurological disorders, and other metabolic syndromes. The use of rapamycin to prolong life in different animal models may be attributable to the multiple roles played by mTOR signaling in various processes involved in ageing, protein translation, autophagy, stem cell pool turnover, inflammation, and cellular senescence. mTOR activity was found to be altered in AD brains and rodent models, supporting the notion that aberrant mTOR activity is one of the key events contributing to the onset and progression of AD hallmarks This review assesses the molecular association between the mTOR signaling pathway and pathogenesis of Alzheimer's disease. The research data supporting this theme are also reviewed.

The dual roles of autophagy and the GPCRs-mediating autophagy signaling pathway after cerebral ischemic stroke

Ischemic stroke, caused by a lack of blood supply in brain tissues, is the third leading cause of human death and disability worldwide, and usually results in sensory and motor dysfunction, cognitive impairment, and in severe cases, even death. Autophagy is a highly conserved lysosome-dependent process in which eukaryotic cells removal misfolded proteins and damaged organelles in cytoplasm, which is critical for energy metabolism, organelle renewal, and maintenance of intracellular homeostasis. Increasing evidence suggests that autophagy plays important roles in pathophysiological mechanisms under ischemic conditions. However, there are still controversies about whether autophagy plays a neuroprotective or damaging role after ischemia. G-protein-coupled receptors (GPCRs), one of the largest protein receptor superfamilies in mammals, play crucial roles in various physiological and pathological processes. Statistics show that GPCRs are the targets of about one-fifth of drugs known in the world, predicting potential values as targets for drug research. Studies have demonstrated that nutritional deprivation can directly or indirectly activate GPCRs, mediating a series of downstream biological processes, including autophagy. It can be concluded that there are interactions between autophagy and GPCRs signaling pathway, which provides research evidence for regulating GPCRs-mediated autophagy. This review aims to systematically discuss the underlying mechanism and dual roles of autophagy in cerebral ischemia, and describe the GPCRs-mediated autophagy, hoping to probe promising therapeutic targets for ischemic stroke through in-depth exploration of the GPCRs-mediated autophagy signaling pathway.

Chaperon-mediated autophagy can regulate diquat-induced apoptosis by inhibiting α-synuclein accumulation cooperatively with macroautophagy

α-Synuclein, which is associated with Parkinson's disease, is cleared by the ubiquitin-proteasome system and autophagy lysosome system. Chaperon-mediated autophagy (CMA) and macroautophagy are major subtypes of autophagy and play a critical role in pesticide-induced α-synucleinopathy. In this study, we explored the role of CMA in diquat (DQ)-induced α-synucleinopathy and characterized the relationship between CMA and macroautophagy in the clearance of pathologic α-synuclein for the prevention of DQ neurotoxicity. DQ was cytotoxic to SH-SY5Y cells in a concentration-dependent manner, as shown by decreased cell viability and increased cytotoxicity. DQ treatment was also found to induce autophagy such as CMA and macroautophagy by monitoring the expression of Lamp2A and microtubule-associated protein 1A/1B light chain 3B (LC3-II) respectively. Following DQ treatment, SH-SY5Y cells were found to have induced phosphorylated and detergent-insoluble α-synuclein deposits, and MG132, a proteasome inhibitor, effectively potentiated both CMA and macroautophagy for preventing α-synuclein aggregation. Interestingly, CMA impairment by Lamp2A-knock down decreased the LC3II expression compared to in DQ-treated cells transfected with control siRNA. In Lamp2-knock down cells, pathologic α-synuclein was increased 12 h after DQ treatment, but there was no change observed at 24 h. In DQ-treated cells, macroautophagy by 3-methyladenine and bafilomycin inhibition increased Lamp2A expression, indicating an increase in CMA activity. In addition, CMA modulation affected apoptosis, and inhibiting lysosome activity by NH₄Cl increased apoptosis in DQ-treated cells. An increase in autophagy was confirmed to compensate for the decrease in lysosome activity. Pretreatment with z-VAD-fmk, a pan-caspase inhibitor, significantly enhanced the macroautophagy response of DQ-exposed cells without alterations in Lamp2A expression. Our results suggest that CMA can regulate DQ-induced α-synucleinopathy cooperatively with macroautophagy, and crosstalk between macroautophagy and CMA plays an important role in DQ-induced cytotoxicity. Taken together, autophagy modulation may be a useful treatment strategy in pesticide-induced neurodegenerative disorders through preventing α-synucleinopathy.

Neurons die with heightened but functional macro- and chaperone mediated autophagy upon increased amyloid-ß induced toxicity with region-specific protection in prolonged intermittent fasting

Alzheimer's disease (AD) is a devastating neurodegenerative condition with significant socio-economic impact that is exacerbated by the rapid increase in population aging, particularly impacting already burdened health care systems of poorly resourced countries. Accumulation of the amyloid-β (Aβ) peptide, generated through amyloid precursor protein (APP) processing, manifesting in senile plaques, is a well-established neuropathological feature. Aβ plays a key role in driving synaptic dysfunction, neuronal cell loss, glial cell activation and oxidative stress associated with the pathogenesis of AD. Thus, the enhanced clearance of Aβ peptide though modulation of the mechanisms that regulate intracellular Aβ metabolism and clearance during AD progression have received major attention. Autophagy, a lysosome-based major proteolytic pathway, plays a crucial role in intracellular protein quality control and has been shown to contribute to the clearance of Aβ peptide. However, to what extent autophagy activity remains upregulated and functional in the process of increasing Aβ neurotoxicity is largely unclear. Here, we investigated the extent of neuronal toxicity in vitro by characterising autophagic flux, the expression profile of key amyloidogenic proteins, and proteins associated with prominent subtypes of the autophagy pathway to dissect the interplay between the engagement of proteolytic pathways and cell death onset in the context of APP overexpression. Moreover, we assessed the neuroprotective effects of a caloric restriction regime in vivo on the modulation of autophagy in specific brain regions. Our results reveal that autophagy is upregulated in the presence of high levels of APP and Aβ and remains heightened and functional despite concomitant apoptosis induction, suggestive of a mismatch between autophagy cargo generation and clearance capacity. These findings were confirmed when implementing a prolonged intermittent fasting (IF) intervention in a model of paraquat-induced neuronal toxicity, where markers of autophagic activity were increased, while apoptosis onset and lipid peroxidation were robustly decreased in brain regions associated with neurodegeneration. This work highlights that especially caloric restriction mimetics and controlled prolonged IF may indeed be a highly promising therapeutic strategy at all stages of AD-associated pathology progression, for a cell-inherent and cell specific augmentation of Aβ clearance through the powerful engagement of autophagy and thereby robustly contributing to neuronal protection.

The impact of organic extracts of seasonal PM2.5 on primary human lung epithelial cells and their chemical characterization

Lung epithelial cells serve as the first line of defense against various inhaled pollutant particles. To investigate the adverse health effects of organic components of fine particulate matter (PM2.5) collected in Seoul, South Korea, we selected 12 PM2.5 samples from May 2016 to January 2017 and evaluated the effects of organic compounds of PM2.5 on inflammation, cellular aging, and macroautophagy in human lung epithelial cells isolated directly from healthy donors. Organic extracts of PM2.5 specifically induced neutrophilic chemokine and interleukin-8 expression via extracellular signal-regulated kinase activation. Moreover, PM2.5 significantly increased the expression of aging markers (p16, p21, and p27) and activated macroautophagy. Average mass concentrations of organic and elemental carbon had no significant correlations with PM2.5 effects. However, polycyclic aromatic hydrocarbons and n-alkanes were the most relevant components of PM2.5 that correlated with neutrophilic inflammation. Vegetative detritus and residential bituminous coal combustion sources strongly correlated with neutrophilic inflammation, aging, and macroautophagy activation. These data suggest that the chemical composition of PM2.5 is important for determining the adverse health effects of PM2.5. Our study provides encouraging evidence to regulate the harmful components of PM2.5 in Seoul.

Links between autophagy and tissue mechanics

Physical constraints, such as compression, shear stress, stretching and tension, play major roles during development, tissue homeostasis, immune responses and pathologies. Cells and organelles also face mechanical forces during migration and extravasation, and investigations into how mechanical forces are translated into a wide panel of biological responses, including changes in cell morphology, membrane transport, metabolism, energy production and gene expression, is a flourishing field. Recent studies demonstrate the role of macroautophagy in the integration of physical constraints. The aim of this Review is to summarize and discuss our knowledge of the role of macroautophagy in controlling a large panel of cell responses, from morphological and metabolic changes, to inflammation and senescence, for the integration of mechanical forces. Moreover, wherever possible, we also discuss the cell surface molecules and structures that sense mechanical forces upstream of macroautophagy.

Evidence Linking Protein Misfolding to Quality Control in Progressive Neurodegenerative Diseases

Several proteolytic systems including ubiquitin (Ub)-proteasome system (UPS), chaperonemediated autophagy (CMA), and macroautophagy are used by the mammalian cells to remove misfolded proteins (MPs). UPS mediates degradation of most of the MPs, where Ub-conjugated substrates are deubiquitinated, unfolded, and passed through the proteasome's narrow chamber, and eventually break into smaller peptides. It has been observed that the substrates that show a specific degradation signal, the KFERQ sequence motif, can be delivered to and go through CMA-mediated degradation in lysosomes. Macroautophagy can help in the degradation of substrates that are prone to aggregation and resistant to both the CMA and UPS. In the aforesaid case, cargoes are separated into autophagosomes before lysosomal hydrolase-mediated degradation. Even though the majority of the aggregated and MPs in the human proteome can be removed via cellular protein quality control (PQC), some mutant and native proteins tend to aggregate into β-sheet-rich oligomers that exhibit resistance to all identified proteolytic processes and can, therefore, grow into extracellular plaques or inclusion bodies. Indeed, the buildup of protease-resistant aggregated and MPs is a usual process underlying various protein misfolding disorders, including neurodegenerative diseases (NDs) for example Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and prion diseases. In this article, we have focused on the contribution of PQC in the degradation of pathogenic proteins in NDs.

Adaptive immunity at the crossroads of autophagy and metabolism

The function of lymphocytes is dependent on their plasticity, particularly their adaptation to energy availability and environmental stress, and their protein synthesis machinery. Lymphocytes are constantly under metabolic stress, and macroautophagy/autophagy is the primary metabolic pathway that helps cells overcome stressors. The intrinsic role of autophagy in regulating the metabolism of adaptive immune cells has recently gained increasing attention. In this review, we summarize and discuss the versatile roles of autophagy in regulating cellular metabolism and the implications of autophagy for immune cell function and fate, especially for T and B lymphocytes.

Involvement of lysosomal integral membrane protein-2 in the activation of autophagy

Lysosomal integral membrane protein-2 (LIMP-2) is a type III transmembrane protein that is highly glycosylated and mainly localized to the lysosomal membrane. The diverse functions of LIMP-2 are currently being uncovered; however, its participation in macroautophagy, usually described as autophagy, has not yet been well-investigated. To determine the possible involvement of LIMP-2 in autophagic activity, we examined the intracellular amount of microtubule-associated protein 1 light chain 3 (LC3)-II, which is well-correlated with autophagosome levels, in exogenous rat LIMP-2-expressing COS7 and HEK293 cells. Transient or stable expression of LIMP-2-myc significantly increased the levels of LC3-II. Conversely, knockdown of LIMP-2 decreased the LC3-II levels in NIH3T3 cells. Furthermore, approaches using lysosomal protease inhibitors and mCherry-GFP-LC3 fluorescence suggested that exogenous expression of LIMP-2 increased the biogenesis of autophagosomes rather than decreased the lysosomal turnover of LC3-II. Considering the results of the biochemical assay and the quantitative fluorescence assay together, it is suggested that LIMP-2 has a possible involvement in autophagic activity, especially autophagosome biogenesis.

Monitoring TFEB translocation

The transcription factor EB (TFEB) plays a critical role in autophagy induction and lysosomal biogenesis by orchestrating the expression of autophagy- and lysosome-related genes. In response to a series of stresses such as nutrient starvation, TFEB translocates from the cytoplasm to the nucleus, where it exerts its regulatory function. The activity of TFEB is tightly regulated by multiple phosphorylation and acetylation sites. Methods that rely on the analysis of posttranslational modification as a proxy for TFEB activation are often misleading. Here, we elaborate on protocols for monitoring nuclear translocation of TFEB by fluorescence microscopy.

Herbal cake-partitioned moxibustion inhibits colonic autophagy in Crohn’s disease via signaling involving distinct classes of phosphatidylinositol 3-kinases

BACKGROUND

Autophagy is an evolutionarily conserved biological process in eukaryotic cells that involves lysosomal-mediated degradation and recycling of related cellular components. Recent studies have shown that autophagy plays an important role in the pathogenesis of Crohn’s disease (CD). Herbal cake-partitioned moxibustion (HM) has been historically practiced to treat CD. However, the mechanism by which HM regulates colonic autophagy in CD remains unclear.

AIM

To observe whether HM can alleviate CD by regulating colonic autophagy and to elucidate the underlying mechanism.

METHODS

Rats were randomly divided into a normal control (NC) group, a CD group, an HM group, an insulin + CD (I + CD) group, an insulin + HM (I + HM) group, a rapamycin + CD (RA + CD) group, and a rapamycin + HM (RA + HM) group. 2,4,6-trinitrobenzenesulfonic acid was administered to establish a CD model. The morphology of the colonic mucosa was observed by hematoxylin-eosin staining, and the formation of autophagosomes was observed by electron microscopy. The expression of autophagy marker microtubule-associated protein 1 light chain 3 beta (LC3B) was observed by immunofluorescence staining. Insulin and rapamycin were used to inhibit and activate colonic autophagy, respectively. The mRNA expression levels of phosphatidylinositol 3-kinase class I (PI3KC1), Akt1, LC3B, sequestosome 1 (p62), and mammalian target of rapamycin (mTOR) were evaluated by RT-qPCR. The protein expression levels of interleukin 18 (IL-18), tumor necrosis factor-α (TNF-α), nuclear factor κB/p65 (NF-κB p65), LC3B, p62, coiled-coil myosin-like BCL2-interacting protein (Beclin-1), p-mTOR, PI3KC1, class III phosphatidylinositol 3-kinase (PI3KC3/Vps34), and p-Akt were evaluated by Western blot analysis.

RESULTS

Compared with the NC group, the CD group showed severe damage to colon tissues and higher expression levels of IL-18 and NF-κB p65 in colon tissues (P < 0.01 for both). Compared with the CD group, the HM group showed significantly lower levels of these proteins (P_IL-18 < 0.01 and P_p65 < 0.05). There were no significant differences in the expression of TNF-α protein in colon tissue among the rat groups. Typical autophagic vesicles were found in both the CD and HM groups. The expression of the autophagy proteins LC3B and Beclin-1 was upregulated (P < 0.01 for both) in the colon tissues of rats in the CD group compared with the NC group, while the protein expression of p62 and p-mTOR was downregulated (P < 0.01 for both). However, these expression trends were significantly reversed in the HM group compared with the CD group (P_LC3B < 0.01, P_Beclin-1 < 0.05, P_p62 < 0.05, and P_m-TOR < 0.05). Compared with those in the RA + CD group, the mRNA expression levels of PI3KC1, Akt1, mTOR, and p62 in the RA + HM group were significantly higher (P_PI3KC1 < 0.01 and P_{Akt1, mTOR, and p62} < 0.05), while those of LC3B were significantly lower (P < 0.05). Compared with the RA + CD group, the RA + HM group exhibited significantly higher PI3KC1, p-Akt1, and p-mTOR protein levels (P_PI3KC1 < 0.01, P_p-Akt1 < 0.05, and P_p-mTOR < 0.01), a higher p62 protein level (P = 0.057), and significantly lower LC3B and Vps34 protein levels (P < 0.01 for both) in colon tissue.

CONCLUSION

HM can activate PI3KC1/Akt1/mTOR signaling while inhibiting the PI3KC3 (Vps34)-Beclin-1 protein complex in the colon tissues of CD rats, thereby inhibiting overactivated autophagy and thus exerting a therapeutic effect.

Selective autophagy as a therapeutic target for neurological diseases

The neurological diseases primarily include acute injuries, chronic neurodegeneration, and others (e.g., infectious diseases of the central nervous system). Autophagy is a housekeeping process responsible for the bulk degradation of misfolded protein aggregates and damaged organelles through the lysosomal machinery. Recent studies have suggested that autophagy, particularly selective autophagy, such as mitophagy, pexophagy, ER-phagy, ribophagy, lipophagy, etc., is closely implicated in neurological diseases. These forms of selective autophagy are controlled by a group of important proteins, including PTEN-induced kinase 1 (PINK1), Parkin, p62, optineurin (OPTN), neighbor of BRCA1 gene 1 (NBR1), and nuclear fragile X mental retardation-interacting protein 1 (NUFIP1). This review highlights the characteristics and underlying mechanisms of different types of selective autophagy, and their implications in various forms of neurological diseases.

Stress and signaling pathways regulating autophagy: From behavioral models to psychiatric disorders

Autophagy is a process of degradation and recycling of cytoplasmatic components by the lysosomes. In the central nervous system (CNS), autophagy is involved in cell surveillance, neuroinflammation, and neuroplasticity. Neuropsychiatric conditions are associated with functional disturbances at molecular and cellular levels, causing significant impairments in cell homeostasis. Additionally, emerging evidence supports that dysfunctions in autophagy contribute to the pathophysiology of neurological diseases. However, the studies on autophagy in psychiatric disorders are highly heterogeneous and have several limitations, mainly to assess causality and determine the autophagy flux in animals and human samples. Besides, the role of this mechanism in non-neuronal cells in the CNS is only recently being explored. Thus, this review summarizes and discusses the changes in the autophagy pathway in animal models of psychiatric disorders and the limitations underlying the significant findings. Moreover, we compared these findings with clinical studies. Understanding the involvement of autophagy in psychiatric conditions, and the limitation of our current models may contribute to the development of more effective research approaches and possibly pharmacological therapies.

BECN1 promotes radiation-induced G2/M arrest through regulation CDK1 activity: a potential role for autophagy in G2/M checkpoint

Authophagy and G2/M arrest are two important mechanistic responses of cells to ionizing radiation (IR), in particular the IR-induced fibrosis. However, what interplayer and how it links the autophagy and the G2/M arrest remains elusive. Here, we demonstrate that the autophagy-related protein BECN1 plays a critical role in ionizing radiation-induced G2/M arrest. The treatment of cells with autophagy inhibitor 3-methyladenine (3-MA) at 0-12 h but not 12 h postirradiation significantly sensitized them to IR, indicating a radio-protective role of autophagy in the early response of cells to radiation. 3-MA and BECN1 disruption inactivated the G2/M checkpoint following IR by abrogating the IR-induced phosphorylation of phosphatase CDC25C and its target CDK1, a key mediator of the G2/M transition in coordination with CCNB1. Irradiation increased the nuclear translocation of BECN1, and this process was inhibited by 3-MA. We confirmed that BECN1 interacts with CDC25C and CHK2, and which is mediated the amino acids 89-155 and 151-224 of BECN1, respectively. Importantly, BECN1 deficiency disrupted the interaction of CHK2 with CDC25C and the dissociation of CDC25C from CDK1 in response to irradiation, resulting in the dephosphorylation of CDK1 and overexpression of CDK1. In summary, IR induces the translocation of BECN1 to the nucleus, where it mediates the interaction between CDC25C and CHK2, resulting in the phosphorylation of CDC25C and its dissociation from CDK1. Consequently, the mitosis-promoting complex CDK1/CCNB1 is inactivated, resulting in the arrest of cells at the G2/M transition. Our findings demonstrated that BECN1 plays a role in promotion of radiation-induced G2/M arrest through regulation of CDK1 activity. Whether such functions of BECN1 in G2/M arrest is dependent or independent on its autophagy-related roles is necessary to further identify.

Autophagic Pathways to Clear the Tau Aggregates in Alzheimer's Disease

Tau is a microtubule-associated protein with an intrinsically unstructured conformation. Tau is subjected to several pathological post-translational modifications (PTMs), leading to its loss of interaction with microtubules and accumulation as neurofibrillary tangles (NFTs) in neurons. Tau aggregates impede functions of endoplasmic reticulum and mitochondria leading to the generation of oxidative stress and in turn amplifying the Tau aggregation. Tau is channelled to chaperones for folding into their native form, which otherwise causes its degradation and clearance. Cellular response triggers the activation of ubiquitin-proteasome system or autophagy to facilitate Tau degradation, based on the PTMs or mutations associated with Tau. Further, autophagy can be selective where Hsc70 interacts with Tau in monomeric, oligomeric and aggregated form and drives its clearance by chaperone-mediated autophagy pathway (CMA). Lysosome-associated membrane proteins-2A (LAMP-2A) is the key player of CMA that recognises Hsc70-Tau complex and triggers the downstream cascade. Thus, it becomes challenging for mutant Tau to be cleared by CMA as it loses its affinity for Hsc70 and LAMP-2A. In such a scenario, Tau might be degraded by macroautophagy otherwise sequestered by aggresomes. Henceforth, the degradation of Tau and its blockage that is associated with various PTMs of Tau would explain the dynamics of Tau degradation or accumulation in AD. Further, unveiling the role of accessory proteins involved in these degradation pathways would help in understanding their loss of function and preventing Tau clearance.

Kinase inhibition of G2019S-LRRK2 enhances autolysosome formation and function to reduce endogenous alpha-synuclein intracellular inclusions

The Parkinson's disease (PD)-associated kinase Leucine-Rich Repeat Kinase 2 (LRRK2) is a crucial modulator of the autophagy-lysosome pathway, but unclarity exists on the precise mechanics of its role and the direction of this modulation. In particular, LRRK2 is involved in the degradation of pathological alpha-synuclein, with pathogenic mutations precipitating neuropathology in cellular and animal models of PD, and a significant proportion of LRRK2 patients presenting Lewy neuropathology. Defects in autophagic processing and lysosomal degradation of alpha-synuclein have been postulated to underlie its accumulation and onset of neuropathology. Thus, it is critical to obtain a comprehensive knowledge on LRRK2-associated pathology. Here, we investigated a G2019S-LRRK2 recombinant cell line exhibiting accumulation of endogenous, phosphorylated alpha-synuclein. We found that G2019S-LRRK2 leads to accumulation of LC3 and abnormalities in lysosome morphology and proteolytic activity in a kinase-dependent fashion, but independent from constitutively active Rab10. Notably, LRRK2 inhibition was ineffective upon upstream blockade of autophagosome-lysosome fusion events, highlighting this step as critical for alpha-synuclein clearance.

Vascular autophagy in health and disease

Homeostasis is maintained within organisms through the physiological recycling process of autophagy, a catabolic process that is intricately involved in the mobilization of nutrients during starvation, recycling of cellular cargo, as well as initiation of cellular death pathways. Specific to the cardiovascular system, autophagy responds to both chemical (e.g. free radicals) and mechanical stressors (e.g. shear stress). It is imperative to note that autophagy is not a static process, and measurement of autophagic flux provides a more comprehensive investigation into the role of autophagy. The overarching themes emerging from decades of autophagy research are that basal levels of autophagic flux are critical, physiological stressors may increase or decrease autophagic flux, and more importantly, aberrant deviations from basal autophagy may elicit detrimental effects. Autophagy has predominantly been examined within cardiac or vascular smooth muscle tissue within the context of disease development and progression. Autophagic flux within the endothelium holds an important role in maintaining vascular function, demonstrated by the necessary role for intact autophagic flux for shear-induced release of nitric oxide however the underlying mechanisms have yet to be elucidated. Within this review, we theorize that autophagy itself does not solely control vascular homeostasis, rather, it works in concert with mitochondria, telomerase, and lipids to maintain physiological function. The primary emphasis of this review is on the role of autophagy within the human vasculature, and the integrative effects with physiological processes and diseases as they relate to the vascular structure and function.

Autophagosome biogenesis and human health

Autophagy degrades the cytoplasmic contents engulfed by autophagosomes. Besides providing energy and building blocks during starvation via random degradation, autophagy selectively targets cytotoxic components to prevent a wide range of diseases. This preventive activity of autophagy is supported by many studies using animal models and reports identifying several mutations in autophagy-related genes that are associated with human genetic disorders, which have been published in the past decade. Here, we summarize the molecular mechanisms of autophagosome biogenesis involving the proteins responsible for these genetic disorders, demonstrating a role for autophagy in human health. These findings will help elucidate the underlying mechanisms of autophagy-related diseases and develop future medications.

SIRT1 directly activates autophagy in human chondrocytes

Osteoarthritis (OA) is the most common form of arthritis worldwide with no effective treatment. Ageing is the primary risk factor for OA. We sought to investigate if there is a distinct and functional convergence of ageing-related mechanisms SIRT1 and autophagy in chondrocytes. Our results show that, levels of SIRT1 are decreased in human normal aged and OA cartilage compared with young cartilage. Moreover, silencing SIRT1 in chondrocytes lead to decreased expression of chondrogenic markers but did not alter the expression of catabolic proteases. In contrast, activation of SIRT1 increased autophagy in chondrocytes by the deacetylation of lysine residues on crucial autophagy proteins (Beclin1, ATG5, ATG7, LC3). This activation was shown to be mTOR/ULK1 independent. Our results indicate that maintenance of autophagy in chondrocytes by SIRT1 is essential for preserving cartilage integrity throughout life and therefore is a target for drug intervention to protect against OA.

Mendelian neurodegenerative disease genes involved in autophagy

The lysosomal degradation pathway of macroautophagy (herein referred to as autophagy) plays a crucial role in cellular physiology by regulating the removal of unwanted cargoes such as protein aggregates and damaged organelles. Over the last five decades, significant progress has been made in understanding the molecular mechanisms that regulate autophagy and its roles in human physiology and diseases. These advances, together with discoveries in human genetics linking autophagy-related gene mutations to specific diseases, provide a better understanding of the mechanisms by which autophagy-dependent pathways can be potentially targeted for treating human diseases. Here, we review mutations that have been identified in genes involved in autophagy and their associations with neurodegenerative diseases.

Activation and targeting of ATG8 protein lipidation

ATG8 family proteins are evolutionary conserved ubiquitin-like modifiers, which become attached to the headgroup of the membrane lipid phosphatidylethanolamine in a process referred to as lipidation. This reaction is carried out analogous to the conjugation of ubiquitin to its target proteins, involving the E1-like ATG7, the E2-like ATG3 and the E3-like ATG12-ATG5-ATG16 complex, which determines the site of lipidation. ATG8 lipidation is a hallmark of autophagy where these proteins are involved in autophagosome formation, the fusion of autophagosomes with lysosomes and cargo selection. However, it has become evident that ATG8 lipidation also occurs in processes that are not directly related to autophagy. Here we discuss recent insights into the targeting of ATG8 lipidation in autophagy and other pathways with special emphasis on the recruitment and activation of the E3-like complex.

Dysfunction of ATG7-dependent autophagy dysregulates the antioxidant response and contributes to oxidative stress-induced biological impairments in human epidermal melanocytes

Autophagy is a process involving the self-digestion of components that participates in anti-oxidative stress responses and protects cells against oxidative damage. However, the role of autophagy in the anti-oxidative stress responses of melanocytes remains unclear. To investigate the role of autophagy in human epidermal melanocytes, we knocked down and overexpressed ATG7, the critical gene of autophagy, in normal human epidermal melanocytes. We demonstrated that ATG7-dependent autophagy could affect melanin content of melanocytes by regulating melanogenesis. Moreover, suppression of ATG7-dependent autophagy inhibits proliferation and promotes oxidative stress-induced apoptosis of melanocytes, whereas enhancement of ATG7-dependent autophagy protects melanocytes from oxidative stress-induced apoptosis. Meanwhile, deficiency of ATG7-dependent autophagy results in premature senescence of melanocytes under oxidative stress. Notably, we verified that ATG7-dependent autophagy could alter oxidative stress homeostasis by regulating reactive oxygen species (ROS) production, nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant pathway, and the activity of several antioxidant enzymes in melanocytes. In conclusion, our study suggested that ATG7-dependent autophagy is indispensable for redox homeostasis and the biological functions of melanocytes, such as melanogenesis, proliferation, apoptosis, and senescence, especially under oxidative stress.

The rise of T-type channels in melanoma progression and chemotherapeutic resistance

Hyperactivation of the Mitogen Activated Protein Kinase (MAPK) pathway is prevalent in melanoma, principally due to mutations in the BRAF and NRAS genes. MAPK inhibitors are effective only short-term, and recurrence occurs due to functional redundancies or intertwined pathways. The remodeling of Ca²⁺ signaling is also common in melanoma cells, partly through the increased expression of T-type channels (TTCCs). Here we summarize current knowledge about the prognostic value and molecular targeting of TTCCs. Furthermore, we discuss recent evidence pointing to TTCCs as molecular switches for melanoma chemoresistance, which set the grounds for novel combined therapies against the advanced disease.

Silymarin Protects Against Impaired Autophagy Associated with 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-Induced Parkinsonism

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exacerbates mitochondrial impairment and α-synuclein expression leading to Parkinsonism. Impaired mitochondria and over-expressed α-synuclein are degraded and eliminated via macroautophagy and chaperone-mediated autophagy. Owing to multiple properties, silymarin protects from oxidative stress-mediated cellular injury. However, its effect on MPTP-induced changes in autophagy is not yet known. The study aimed to decipher the effect of silymarin on MPTP-induced changes in autophagy. Male mice (20-25 g) were treated with silymarin (intraperitoneally, daily, 40 mg/kg) for 2 weeks. On day 7, a few animals were also administered with MPTP (intraperitoneally, 20 mg/kg, 4 injections at 2-h interval) along with vehicles. Striatal dopamine content was determined. Western blot analysis was done to assess α-synuclein, beclin-1, sequestosome, phosphorylated 5' adenosine monophosphate-activated protein kinase (p-AMPK), lysosome-associated membrane protein-2 (LAMP-2), heat shock cognate-70 (Hsc-70), LAMP-2A, phosphorylated unc-51-like autophagy activating kinase (p-Ulk1), and phosphorylated mechanistic target of rapamycin (p-mTOR) levels in the nigrostriatal tissue. Silymarin rescued from MPTP-induced increase in beclin-1, sequestosome, p-AMPK, and p-Ulk1 and decrease in LAMP-2, p-mTOR, and LAMP-2A levels. Silymarin defended against MPTP-induced increase in α-synuclein and reduction in dopamine content. The results demonstrate that silymarin protects against MPTP-induced changes in autophagy leading to Parkinsonism.

ER stress-linked autophagy stabilizes apoptosis effector PERP and triggers its co-localization with SERCA2b at ER-plasma membrane junctions

Specific molecular interactions that underpin the switch between ER stress-triggered autophagy-mediated cellular repair and cellular death by apoptosis are not characterized. This study reports the unexpected interaction elicited by ER stress between the plasma membrane (PM)-localized apoptosis effector PERP and the ER Ca²⁺ pump SERCA2b. We show that the p53 effector PERP, which specifically induces apoptosis when expressed above a threshold level, has a heterogeneous distribution across the PM of un-stressed cells and is actively turned over by the lysosome. PERP is upregulated following sustained starvation-induced autophagy, which precedes the onset of apoptosis indicating that PERP protein levels are controlled by a lysosomal pathway that is sensitive to cellular physiological state. Furthermore, ER stress stabilizes PERP at the PM and induces its increasing co-localization with SERCA2b at ER–PM junctions. The findings highlight a novel crosstalk between pro-survival autophagy and pro-death apoptosis pathways and identify, for the first time, accumulation of an apoptosis effector to ER–PM junctions in response to ER stress.

ATG5 cancer mutations and alternative mRNA splicing reveal a conjugation switch that regulates ATG12-ATG5-ATG16L1 complex assembly and autophagy. Cell Discov. 2019;5:42. [PMID: 31636955 PMCID: PMC6796855 DOI: 10.1038/s41421-019-0110-1]

Autophagy is critical for maintaining cellular homeostasis during times of stress, and is thought to play important roles in both tumorigenesis and tumor cell survival. Formation of autophagosomes, which mediate delivery of cytoplasmic cargo to lysosomes, requires multiple autophagy-related (ATG) protein complexes, including the ATG12–ATG5-ATG16L1 complex. Herein, we report that a molecular ATG5 “conjugation switch”, comprised of competing ATG12 and ubiquitin conjugation reactions, integrates ATG12–ATG5-ATG16L1 complex assembly with protein quality control of its otherwise highly unstable subunits. This conjugation switch is tightly regulated by ATG16L1, which binds to free ATG5 and mutually protects both proteins from ubiquitin conjugation and proteasomal degradation, thereby instead promoting the irreversible conjugation of ATG12 to ATG5. The resulting ATG12–ATG5 conjugate, in turn, displays enhanced affinity for ATG16L1 and thus fully stabilizes the ATG12–ATG5-ATG16L1 complex. Most importantly, we find in multiple tumor types that ATG5 somatic mutations and alternative mRNA splicing specifically disrupt the ATG16L1-binding pocket in ATG5 and impair the essential ATG5-ATG16L1 interactions that are initially required for ATG12–ATG5 conjugation. Finally, we provide evidence that ATG16L2, which is overexpressed in several cancers relative to ATG16L1, hijacks the conjugation switch by competing with ATG16L1 for binding to ATG5. While ATG16L2 stabilizes ATG5 and enables ATG12–ATG5 conjugation, this endogenous dominant-negative inhibitor simultaneously displaces ATG16L1, resulting in its proteasomal degradation and a block in autophagy. Thus, collectively, our findings provide novel insights into ATG12–ATG5-ATG16L1 complex assembly and reveal multiple mechanisms wherein dysregulation of the ATG5 conjugation switch inhibits autophagy.

Autophagy and vacuolar biogenesis during the nectary development

Different autophagy pathways are a driver of vacuolar biogenesis and are development stage specific during the extrafloral nectary development in Citharexylum myrianthum. Plant autophagy plays an important role in various developmental processes such as seed germination, pollen maturation and leaf senescence. However, studies that address the evidence of autophagy and its role in the development of plant glands are scarce and largely restricted to laticifers. Regarding nectary, studies have repeatedly pointed to signs of degradation associated with the end of the secretory cycle, without exploring autophagy. Likewise, the relationship between autophagy and biogenesis of vacuoles remains an unexplored issue. In this study, using conventional and microwave fixation in association with ultracytochemical methods for transmission electron microscopy, we investigated the occurrence of autophagy and its implication in the differentiation of extrafloral nectary in Citharexylum myrianthum (Verbenaceae) under natural conditions, focusing on the vacuole biogenesis. We described a variety of vacuole types associated with the stage of nectary epidermis development, which differs with respect to origin, function and nature of the products to be stored. Three distinct autophagy pathways were detected: macroautophagy, microautophagy (both restricted to the undifferentiated epidermal cells, at the presecretory stage) and megaautophagy (circumscribed to the differentiated epidermal cells, at the postsecretory stage). Our study clearly demonstrated that the vacuole variety and autophagy processes in the nectary epidermal cells are development specific. This study highlights the role of autophagy in vacuole biogenesis and its implications for the development of nectary and opens new venues for future studies on regulation mechanisms for autophagy in plant secretory structures under normal conditions.

Prosurvival autophagy is regulated by protein kinase CK1 alpha in multiple myeloma

Multiple myeloma (MM) is a tumor of plasma cells (PCs). Due to the intense immunoglobulin secretion, PCs are prone to endoplasmic reticulum stress and activate several stress-managing pathways, including autophagy. Indeed, autophagy deregulation is maladaptive for MM cells, resulting in cell death. CK1α, a pro-survival kinase in MM, has recently been involved as a regulator of the autophagic flux and of the transcriptional competence of the autophagy-related transcription factor FOXO3a in several cancers. In this study, we investigated the role of CK1α in autophagy in MM. To study the autophagic flux we generated clones of MM cell lines expressing the mCherry-eGFP-LC3B fusion protein. We observed that CK1 inhibition with the chemical ATP-competitive CK1 α/δ inhibitor D4476 resulted in an impaired autophagic flux, likely due to an alteration of lysosomes acidification. However, D4476 caused the accumulation of the transcription factor FOXO3a in the nucleus, and this was paralleled by the upregulation of mRNA coding for autophagic genes. Surprisingly, silencing of CK1α by RNA interference triggered the autophagic flux. However, FOXO3a did not shuttle into the nucleus and the transcription of autophagy-related FOXO3a-dependent genes was not observed. Thus, while the chemical inhibition with the dual CK1α/δ inhibitor D4476 induced cell death as a consequence of an accumulation of ineffective autophagic vesicles, on the opposite, CK1α silencing, although it also determined apoptosis, triggered a full activation of the early autophagic flux, which was then not supported by the upregulation of autophagic genes. Taken together, our results indicate that the family of CK1 kinases may profoundly influence MM cells survival also through the modulation of the autophagic pathway.

Autophagy dysfunction in peripheral blood mononuclear cells of Parkinson's disease patients

BACKGROUND

Alpha-synuclein aggregation is considered one of the main causes of Parkinson's Disease (PD). Malfunction of autophagy-lysosomal pathways is believed to be an underlying mechanism of α-synuclein aggregation. Although such malfunction has been observed in PD brains, it is unclear whether it may also occur in extraneuronal tissues.

OBJECTIVES

To assess lysosome-mediated protein degradation in cultured Peripheral Blood Mononuclear Cells (PBMCs) of PD patients and healthy controls.

METHODS

Total protein degradation in cultured PBMCs was measured by labelling the cells with ³H-leucine using pulse-chase experiments. Different inhibitors were used to measure a range of autophagic pathways.

RESULTS

Protein degradation through the main autophagic pathways is reduced in PD patients (n = 18) compared to age- and sex-matched healthy controls (n = 18), (macroautophagy, p = .018; Chaperone-Mediated autophagy, p = .04; and total lysosomal function, p = .007).

CONCLUSIONS

Lysosomal dysfunction is present in cultured PBMCs of PD patients, suggesting that it may reflect a systemic feature of the disease.

Axonal autophagy: Mini-review for autophagy in the CNS

Neurons are long-lived and highly polarized cells that depend on autophagy to maintain cellular homeostasis. The robust, constitutive biogenesis of autophagosomes in the distal axon occurs via a conserved pathway that is required to maintain functional synapses and prevent axon degeneration. Autophagosomes are formed de novo at the axon terminal in a stepwise assembly process, engulfing mitochondrial fragments, aggregated proteins, and bulk cytosol in what appears to be a nonselective uptake mechanism. Following formation, autophagosomes fuse with late endosomes/lysosomes and then are rapidly and efficiently transported along the axon toward the soma, driven by the microtubule motor cytoplasmic dynein. Motile autophagosomes mature to autolysosomes in transit by fusing with additional late endosomes/lysosomes, arriving at the soma as fully competent degradative organelles. Misregulation of neuronal autophagy leads to axonal degeneration and synaptic destabilization, and has been implicated in neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and ALS.

Impact of autophagic regulation on splenic red pulp macrophages during cerebral malarial infection

Splenic red pulp macrophages play a critical role infiltration of infected RBC and elimination of pathogens during malarial infection. However, the efficiency of pathogenic processing and the intricate pathway followed by them to boost the downstream immune response has not been studied in details. We checked the status of autophagic regulation within the cells both before and after the infection and also modulated the autophagic flux with either its inducer or inhibitor. We found that the upregulation of autophagic gene and the corresponding pathway is correlated with better parasite clearance and survivability, with an enhanced downstream immune response. It also increases their phagocytic potential with better Lysosomal associated protein I and II synthesis. The autophagolysosome formation increases as well, and more vacuole bound LC3B protein are detected. Chemokine synthesized from Red Pulp macrophage helps in mediating the induction for recruiting neutrophil and CD4 + T cells to the splenic red pulp region. The skewing of M1 macrophage polarity is observed post autophagic induction with a better costimulatory molecule like CD80, CD86 expression and antigen presenting molecule MHC I, MHC II is observed. This study shows the possibility of an alternative or adjuvant therapy regimen for the malarial patient by inducing the autophagic pathway that targets the red pulp macrophages. This might be helpful for better pathogen degradation and processing. The subsequent clearance of parasite will result in a better outcome for the patients.

Methods to Image Macroautophagy in the Brain In Vivo

Macroautophagy is the process to remove intracellular organelles or proteins by using autophagosome that is composed of autophagy proteins such as atg3, atg7, and atg8/LC3 (Mizushima, et al. Annu Rev Cell Dev Biol. 27:107-132, 2011). Here, we develop a useful method for in vivo imaging of autophagosome under the two-photon microscopy. Time-lapse imaging of LC3-ECFP enables us to quantify the dynamics of number, size, and signal intensity of autophagosomes in neurons or in other types of cells in the brain.