Emerging roles of autophagy in metabolism and metabolic disorders

Exploring the key role of DNA methylation as an epigenetic modulator in oxidative stress related islet cell injury in patients with type 2 diabetes mellitus: a review

Type 2 diabetes mellitus (T2DM) is a multifactorial metabolic disorder characterised by impaired insulin secretion and action, often exacerbated by oxidative stress. Recent research has highlighted the intricate involvement of epigenetic mechanisms, particularly DNA methylation, in the pathogenesis of T2DM. This review aims to elucidate the role of DNA methylation as an epigenetic modifier in oxidative stress-mediated beta cell dysfunction, a key component of T2DM pathophysiology. Oxidative stress, arising from an imbalance between reactive oxygen species (ROS) production and antioxidant defence mechanisms, is a hallmark feature of T2DM. Beta cells, responsible for insulin secretion, are particularly vulnerable to oxidative damage due to their low antioxidant capacity. Emerging evidence suggests that oxidative stress can induce aberrant DNA methylation patterns in beta cells, leading to altered gene expression profiles associated with insulin secretion and cell survival. Furthermore, studies have identified specific genes involved in beta cell function and survival that undergo DNA methylation changes in response to oxidative stress in T2DM. These epigenetic modifications can perpetuate beta cell dysfunction by dysregulating key pathways essential for insulin secretion, such as the insulin signalling cascade and mitochondrial function. Understanding the interplay between DNA methylation, oxidative stress, and beta cell dysfunction holds promise for developing novel therapeutic strategies for T2DM. Targeting aberrant DNA methylation patterns may offer new avenues for restoring beta cell function and improving glycemic control in patients with T2DM. However, further research is needed to elucidate the complex mechanisms underlying epigenetic regulation in T2DM and to translate these findings into clinical interventions.

Fucoidan alleviated autoimmune diabetes in NOD mice by regulating pancreatic autophagy through the AMPK/mTOR1/TFEB pathway

Objectives

The present study investigated the effect and its underlying mechanisms of fucoidan on Type 1 diabetes mellitus (T1DM) in non-obese diabetic (NOD) mice.

Materials and Methods

Twenty 7-week-old NOD mice were used in this study, and randomly divided into two groups (10 mice in each group): the control group and the fucoidan treatment group (600 mg/kg. body weight). The weight gain, glucose tolerance, and fasting blood glucose level in NOD mice were detected to assess the development of diabetes. The intervention lasted for 5 weeks. The proportions of Th1/Th2 cells from spleen tissues were tested to determine the anti-inflammatory effect of fucoidan. Western blot was performed to investigate the expression levels of apoptotic markers and autophagic markers. Apoptotic cell staining was visualized through TdT-mediated dUTP nick-end labeling (TUNEL).

Results

The results suggested that fucoidan ameliorated T1DM, as evidenced by increased body weight and improved glycemic control of NOD mice. Fucoidan down-regulated the Th1/Th2 cells ratio and decreased Th1 type pro-inflammatory cytokines' level. Fucoidan enhanced the mitochondrial autophagy level of pancreatic cells and increased the expressions of Beclin-1 and LC3B II/LC3B I. The expression of p-AMPK was up-regulated and p-mTOR1 was inhibited, which promoted the nucleation of transcription factor EB (TFEB), leading to autophagy. Moreover, fucoidan induced apoptosis of pancreatic tissue cells. The levels of cleaved caspase-9, cleaved caspase-3, and Bax were up-regulated after fucoidan treatment.

Conclusion

Fucoidan could maintain pancreatic homeostasis and restore immune disorder through enhancing autophagy via the AMPK/mTOR1/TFEB pathway in pancreatic cells.

OR2H2 Activates CAMKKβ-AMPK-Autophagy Signaling Axis and Suppresses Senescence in VK2/E6E7 Cells

Olfactory receptors are expressed in multiple extra-nasal tissues and these ectopic olfactory receptors mediate tissue-specific functions and regulate cellular physiology. Ectopic olfactory receptors may play key roles in tissues constantly exposed to odorants, thus the functionality of these receptors in genital tissues is of particular interest. The functionality of ectopic olfactory receptors expressed in VK2/E6E7 human vaginal epithelial cells was investigated. OR2H2 was the most highly expressed olfactory receptor expressed in VK2/E6E7 cells, and activation of OR2H2 by aldehyde 13-13, a ligand of OR2H2, increased the intracellular calcium and cAMP concentrations. Immunoblotting demonstrated that activation of OR2H2 by aldehyde 13-13 stimulated the CAMKKβ-AMPK-mTORC1-autophagy signaling axis, and that these effects were negated by OR2H2 knockdown. AMPK is known to regulate senescence; consequently, we investigated further the effect of aldehyde 13-13 on senescence. In H2O2-induced senescent cells, activation of OR2H2 by aldehyde 13-13 restored proliferation, and reduced the expression of senescence markers, P16 and P19. Additionally, aldehyde 13-13 induced apoptosis of H2O2-induced senescent cells, compared with non-senescent normal cells. In vivo, aldehyde 13-13 increased the lifespan of Caenorhabditis elegans and budding yeast. These findings demonstrate that OR2H2 is a functional receptor in VK2/E6E7 cells, and that activation of OR2H2 activates the AMPK-autophagy axis, and suppresses cellular aging and senescence, which may increase cellular health.

Exercise-activated hepatic autophagy via the FN1-α5β1 integrin pathway drives metabolic benefits of exercise

How exercise elicits systemic metabolic benefits in both muscles and non-contractile tissues is unclear. Autophagy is a stress-induced lysosomal degradation pathway that mediates protein and organelle turnover and metabolic adaptation. Exercise activates autophagy in not only contracting muscles but also non-contractile tissues including the liver. However, the role and mechanism of exercise-activated autophagy in non-contractile tissues remain mysterious. Here, we show that hepatic autophagy activation is essential for exercise-induced metabolic benefits. Plasma or serum from exercised mice is sufficient to activate autophagy in cells. By proteomic studies, we identify fibronectin (FN1), which was previously considered as an extracellular matrix protein, as an exercise-induced, muscle-secreted, autophagy-inducing circulating factor. Muscle-secreted FN1 mediates exercise-induced hepatic autophagy and systemic insulin sensitization via the hepatic receptor α5β1 integrin and the downstream IKKα/β-JNK1-BECN1 pathway. Thus, we demonstrate that hepatic autophagy activation drives exercise-induced metabolic benefits against diabetes via muscle-secreted soluble FN1 and hepatic α5β1 integrin signaling.

Chromatin remodeler Activity-Dependent Neuroprotective Protein (ADNP) contributes to syndromic autism

BACKGROUND

Individuals affected with autism often suffer additional co-morbidities such as intellectual disability. The genes contributing to autism cluster on a relatively limited number of cellular pathways, including chromatin remodeling. However, limited information is available on how mutations in single genes can result in such pleiotropic clinical features in affected individuals. In this review, we summarize available information on one of the most frequently mutated genes in syndromic autism the Activity-Dependent Neuroprotective Protein (ADNP).

RESULTS

Heterozygous and predicted loss-of-function ADNP mutations in individuals inevitably result in the clinical presentation with the Helsmoortel-Van der Aa syndrome, a frequent form of syndromic autism. ADNP, a zinc finger DNA-binding protein has a role in chromatin remodeling: The protein is associated with the pericentromeric protein HP1, the SWI/SNF core complex protein BRG1, and other members of this chromatin remodeling complex and, in murine stem cells, with the chromodomain helicase CHD4 in a ChAHP complex. ADNP has recently been shown to possess R-loop processing activity. In addition, many additional functions, for instance, in association with cytoskeletal proteins have been linked to ADNP.

CONCLUSIONS

We here present an integrated evaluation of all current aspects of gene function and evaluate how abnormalities in chromatin remodeling might relate to the pleiotropic clinical presentation in individual"s" with Helsmoortel-Van der Aa syndrome.

Role of autophagy in tumor response to radiation: Implications for improving radiotherapy

Autophagy is an evolutionary conserved, lysosome-involved cellular process that facilitates the recycling of damaged macromolecules, cellular structures, and organelles, thereby generating precursors for macromolecular biosynthesis through the salvage pathway. It plays an important role in mediating biological responses toward various stress, including those caused by ionizing radiation at the cellular, tissue, and systemic levels thereby implying an instrumental role in shaping the tumor responses to radiotherapy. While a successful execution of autophagy appears to facilitate cell survival, abortive or interruptions in the completion of autophagy drive cell death in a context-dependent manner. Pre-clinical studies establishing its ubiquitous role in cells and tissues, and the systemic response to focal irradiation of tumors have prompted the initiation of clinical trials using pharmacologic modifiers of autophagy for enhancing the efficacy of radiotherapy. However, the outcome from the Phase I/II trials in many human malignancies has so far been equivocal. Such observations have not only precluded the advancement of these autophagy modifiers in the Phase III trial but have also raised concerns regarding their introduction as an adjuvant to radiotherapy. This warrants a thorough understanding of the biology of the cancer cells, including its spatio-temporal context, as well as its microenvironment all of which might be the crucial factors that determine the success of an autophagy modifier as an anticancer agent. This review captures the current understanding of the interplay between radiation induced autophagy and the biological responses to radiation damage as well as provides insight into the potentials and limitations of targeting autophagy for improving the radiotherapy of tumors.

Exocytosis Proteins: Typical and Atypical Mechanisms of Action in Skeletal Muscle

Insulin-stimulated glucose uptake in skeletal muscle is of fundamental importance to prevent postprandial hyperglycemia, and long-term deficits in insulin-stimulated glucose uptake underlie insulin resistance and type 2 diabetes. Skeletal muscle is responsible for ~80% of the peripheral glucose uptake from circulation via the insulin-responsive glucose transporter GLUT4. GLUT4 is mainly sequestered in intracellular GLUT4 storage vesicles in the basal state. In response to insulin, the GLUT4 storage vesicles rapidly translocate to the plasma membrane, where they undergo vesicle docking, priming, and fusion via the high-affinity interactions among the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) exocytosis proteins and their regulators. Numerous studies have elucidated that GLUT4 translocation is defective in insulin resistance and type 2 diabetes. Emerging evidence also links defects in several SNAREs and SNARE regulatory proteins to insulin resistance and type 2 diabetes in rodents and humans. Therefore, we highlight the latest research on the role of SNAREs and their regulatory proteins in insulin-stimulated GLUT4 translocation in skeletal muscle. Subsequently, we discuss the novel emerging role of SNARE proteins as interaction partners in pathways not typically thought to involve SNAREs and how these atypical functions reveal novel therapeutic targets for combating peripheral insulin resistance and diabetes.

Degradative and Non-Degradative Roles of Autophagy Proteins in Metabolism and Metabolic Diseases

Autophagy is a stress-induced lysosomal degradation pathway regulated by evolutionarily conserved autophagy-related (ATG) genes. Recent research has revealed that autophagy plays an important role in the regulation of energy metabolism, development of metabolic tissues, and pathogenesis of metabolic disorders. Bulk and selective degradation by autophagy helps maintain protein homeostasis and physiological function of cells. Aside from classical degradative roles, ATG proteins also carry out non-classical secretory functions of metabolic tissues. In this review, we summarize recent progresses and unanswered questions on the mechanisms of autophagy and ATG proteins in metabolic regulation, with a focus on organelle and nutrient storage degradation, as well as vesicular and hormonal secretion. Such knowledge broadens our understanding on the cause, pathophysiology, and prevention of metabolic diseases including obesity and diabetes.

Oxidative stress-mediated beta cell death and dysfunction as a target for diabetes management

The biggest drawback of a current diabetes therapy is the treatment of the consequences not the cause of the disease. Regardless of the diabetes type, preservation and recovery of functional pancreatic beta cells stands as the biggest challenge in the treatment of diabetes. Free radicals and oxidative stress are among the major mediators of autoimmune destruction of beta cells in type 1 diabetes (T1D) or beta cell malfunction and death provoked by glucotoxicity and insulin resistance in type 2 diabetes (T2D). Additionally, oxidative stress reduces functionality of beta cells in T2D by stimulating their de-/trans-differentiation through the loss of transcription factors critical for beta cell development, maturity and regeneration. This review summarizes up to date clarified redox-related mechanisms involved in regulating beta cell identity and death, underlining similarities and differences between T1D and T2D. The protective effects of natural antioxidants on the oxidative stress-induced beta cell failure were also discussed. Considering that oxidative stress affects epigenetic regulatory mechanisms involved in the regulation of pancreatic beta cell survival and insulin secretion, this review highlighted huge potential of epigenetic therapy. Special attention was paid on application of the state-of-the-art CRISPR/Cas9 technology, based on targeted epigenome editing with the purpose of changing the differentiation state of different cell types, making them insulin-producing with ability to attenuate diabetes. Clarification of the above-mentioned mechanisms could provide better insight into diabetes etiology and pathogenesis, which would allow development of novel, potentially more efficient therapeutic strategies for the prevention or reversion of beta cell loss.

The Role of Obesity-Induced Perivascular Adipose Tissue (PVAT) Dysfunction in Vascular Homeostasis

Perivascular adipose tissue (PVAT) is an additional special type of adipose tissue surrounding blood vessels. Under physiological conditions, PVAT plays a significant role in regulation of vascular tone, intravascular thermoregulation, and vascular smooth muscle cell (VSMC) proliferation. PVAT is responsible for releasing adipocytes-derived relaxing factors (ADRF) and perivascular-derived relaxing factors (PDRF), which have anticontractile properties. Obesity induces increased oxidative stress, an inflammatory state, and hypoxia, which contribute to PVAT dysfunction. The exact mechanism of vascular dysfunction in obesity is still not well clarified; however, there are some pathways such as renin-angiotensin-aldosterone system (RAAS) disorders and PVAT-derived factor dysregulation, which are involved in hypertension and endothelial dysfunction development. Physical activity has a beneficial effect on PVAT function among obese patients by reducing the oxidative stress and inflammatory state. Diet, which is the second most beneficial non-invasive strategy in obesity treatment, may have a positive impact on PVAT-derived factors and may restore the balance in their concentration.

Autophagy-dependent glutaminolysis drives superior IL21 production in HIV-1-specific CD4 T cells

The maintenance of a strong IL21 production in memory CD4 T cells, especially in HIV-1-specific cells, represents a major correlate of natural immune protection against the virus. However, the molecular mechanisms underlying IL21 production during HIV-1 infection, which is only elevated among the naturally protected elite controllers (EC), are still unknown. We recently found out that lipophagy is a critical immune mediator that control an antiviral metabolic state following CD8A T cell receptor engagement, playing an important role in the natural control of HIV-1 infection. This led us to investigate whether the beneficial role of a strong macroautophagy/autophagy, could also be used to ensure effective IL21 production as well. Herein, we confirm that after both polyclonal and HIV-1-specific activation, memory CD4 T cells (Mem) from EC display enhanced activity of the autophagy-mediated proteolysis compared to ART. Our results indicate that the enhanced autophagy activity in EC was controlled by the energy-sensing PRKAA1 (protein kinase AMP-activated catalytic subunit alpha 1). We further confirmed the critical role of the autophagy-mediated proteolysis in the strong IL21 production in EC by using BECN1 gene silencing as well as protease, PRKAA1, and lysosomal inhibitors. Finally, we established that high autophagy-mediated proteolysis in EC fuels their cellular rates of mitochondrial respiration due to glutaminolysis. Our data confirm the critical role of autophagy in dictating the metabolic input, which is required not only to ensure protective cytotoxic CD8A T cell responses, but also to provide strong IL21 production among antiviral CD4 T cells.Abbreviations: AKG: alpha-ketoglutarate; ART: patients under antiretroviral therapy; ATG7: autophagy related 7; BaF: bafilomycin A₁; BECN1: beclin 1; Chloro.: chloroquine; EC: elite controllers; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; FOXO3: forkhead box O3; GLS: glutaminase; GLUD1: glutamate dehydrogenase 1; HIV^neg: HIV-1-uninfected control donors; IFNG/IFN-γ: interferon gamma; IL21: interleukin 21; MTOR: mechanistic target of rapamycin kinase; PBMC: peripheral blood mononuclear cells; PRKAA1: protein kinase AMP-activated catalytic subunit alpha 1; SQSTM1: sequestosome 1; TCA: tricarboxylic acid cycle; ULK1: unc-51 like autophagy activating kinase.

The autophagy protein Becn1 improves insulin sensitivity by promoting adiponectin secretion via exocyst binding

Autophagy dysregulation is implicated in metabolic diseases, including type 2 diabetes. However, the mechanism by which the autophagy machinery regulates metabolism is largely unknown. Autophagy is generally considered a degradation process via lysosomes. Here, we unveil a metabolically important non-cell-autonomous, non-degradative mechanism regulated by the essential autophagy protein Becn1 in adipose tissue. Upon high-fat diet challenge, autophagy-hyperactive Becn1F121A mice show systemically improved insulin sensitivity and enhanced activation of AMP-activated protein kinase (AMPK), a central regulator of energy homeostasis, via a non-cell-autonomous mechanism mediated by adiponectin, an adipose-derived metabolic hormone. Adipose-specific Becn1F121A expression is sufficient to activate AMPK in non-adipose tissues and improve systemic insulin sensitivity by increasing adiponectin secretion. Further, Becn1 enhances adiponectin secretion by interacting with components of the exocyst complex via the coiled-coil domain. Together, our study demonstrates that Becn1 improves insulin sensitivity by facilitating adiponectin secretion through binding the exocyst in adipose tissue.

Autophagy Process in Trophoblast Cells Invasion and Differentiation: Similitude and Differences With Cancer Cells

Early human placental development begins with blastocyst implantation, then the trophoblast differentiates and originates the cells required for a proper fetal nutrition and placental implantation. Among them, extravillous trophoblast corresponds to a non-proliferating trophoblast highly invasive that allows the vascular remodeling which is essential for appropriate placental perfusion and to maintain the adequate fetal growth. This process involves different placental cell types as well as molecules that allow cell growth, cellular adhesion, tissular remodeling, and immune tolerance. Remarkably, some of the cellular processes required for proper placentation are common between placental and cancer cells to finally support tumor growth. Indeed, as in placentation trophoblasts invade and migrate, cancer cells invade and migrate to promote tumor metastasis. However, while these processes respond to a controlled program in trophoblasts, in cancer cells this regulation is lost. Interestingly, it has been shown that autophagy, a process responsible for the degradation of damaged proteins and organelles to maintain cellular homeostasis, is required for invasion of trophoblast cells and for vascular remodeling during placentation. In cancer cells, autophagy has a dual role, as it has been shown both as tumor promoter and inhibitor, depending on the stage and tumor considered. In this review, we summarized the similarities and differences between trophoblast cell invasion and cancer cell metastasis specifically evaluating the role of autophagy in both processes.

Activation of mitochondrial TUFM ameliorates metabolic dysregulation through coordinating autophagy induction

Disorders of autophagy, a key regulator of cellular homeostasis, cause a number of human diseases. Due to the role of autophagy in metabolic dysregulation, there is a need to identify autophagy regulators as therapeutic targets. To address this need, we conducted an autophagy phenotype-based screen and identified the natural compound kaempferide (Kaem) as an autophagy enhancer. Kaem promoted autophagy through translocation of transcription factor EB (TFEB) without MTOR perturbation, suggesting it is safe for administration. Moreover, Kaem accelerated lipid droplet degradation in a lysosomal activity-dependent manner in vitro and ameliorated metabolic dysregulation in a diet-induced obesity mouse model. To elucidate the mechanism underlying Kaem’s biological activity, the target protein was identified via combined drug affinity responsive target stability and LC–MS/MS analyses. Kaem directly interacted with the mitochondrial elongation factor TUFM, and TUFM absence reversed Kaem-induced autophagy and lipid degradation. Kaem also induced mitochondrial reactive oxygen species (mtROS) to sequentially promote lysosomal Ca²⁺ efflux, TFEB translocation and autophagy induction, suggesting a role of TUFM in mtROS regulation. Collectively, these results demonstrate that Kaem is a potential therapeutic candidate/chemical tool for treating metabolic dysregulation and reveal a role for TUFM in autophagy for metabolic regulation with lipid overload.

Kim, Hwang et al. use in vitro and in vivo models of autophagy disorder/metabolic dysfunction to show that in this context, the natural compound kaempferide is an autophagy enhancer and reveal that one of the underlying mechanisms governing this is mediated by the mitochondrial elongation factor TUFM. This insight may have therapeutic value in the treatment of metabolic disorders.

Cyclobutane pyrimidine dimers from UVB exposure induce a hypermetabolic state in keratinocytes via mitochondrial oxidative stress

Ultraviolet B radiation (UVB) is an environmental complete carcinogen, which induces and promotes keratinocyte carcinomas, the most common human malignancies. UVB induces the formation of cyclobutane pyrimidine dimers (CPDs). Repairing CPDs through nucleotide excision repair is slow and error-prone in placental mammals. In addition to the mutagenic and malignancy-inducing effects, UVB also elicits poorly understood complex metabolic changes in keratinocytes, possibly through CPDs. To determine the effects of CPDs, CPD-photolyase was overexpressed in keratinocytes using an N1-methyl pseudouridine-containing in vitro-transcribed mRNA. CPD-photolyase, which is normally not present in placental mammals, can efficiently and rapidly repair CPDs to block signaling pathways elicited by CPDs. Keratinocytes surviving UVB irradiation turn hypermetabolic. We show that CPD-evoked mitochondrial reactive oxygen species production, followed by the activation of several energy sensor enzymes, including sirtuins, AMPK, mTORC1, mTORC2, p53, and ATM, is responsible for the compensatory metabolic adaptations in keratinocytes surviving UVB irradiation. Compensatory metabolic changes consist of enhanced glycolytic flux, Szent-Györgyi-Krebs cycle, and terminal oxidation. Furthermore, mitochondrial fusion, mitochondrial biogenesis, and lipophagy characterize compensatory hypermetabolism in UVB-exposed keratinocytes. These properties not only support the survival of keratinocytes, but also contribute to UVB-induced differentiation of keratinocytes. Our results indicate that CPD-dependent signaling acutely maintains skin integrity by supporting cellular energy metabolism.

Challenges and Therapeutic Opportunities of Autophagy in Cancer Therapy

Simple Summary

Autophagy is a physiological process characterized by the degradation of the cell components through lysosomes due to stimuli/stress. In this study, we review the challenges and therapeutic opportunities that autophagy presents in the treatment of cancer. We discussed the results of several studies that evaluated autophagy as a therapeutic strategy in cancer, both through the modulation of therapeutic resistance and the death of cancer cells. Moreover, we discussed the role of autophagy in the biology of cancer stem cells and the inhibition of this process as a strategy to overcome resistance and progression of cancer stem cells.

Abstract

Autophagy is a physiological cellular process that is crucial for development and can occurs in response to nutrient deprivation or metabolic disorders. Interestingly, autophagy plays a dual role in cancer cells—while in some situations, it has a cytoprotective effect that causes chemotherapy resistance, in others, it has a cytotoxic effect in which some compounds induce autophagy-mediated cell death. In this review, we summarize strategies aimed at autophagy for the treatment of cancer, including studies of drugs that can modulate autophagy-mediated resistance, and/or drugs that cause autophagy-mediated cancer cell death. In addition, the role of autophagy in the biology of cancer stem cells has also been discussed.

The Mechanical Autophagy as a Part of Cellular Immunity; Facts and Features in Treating the Medical Disorders

Autophagy is a cellular housekeeping process that incorporates lysosomal-degradation to maintain cell survival and energy sources. In recent decades, the role of autophagy has implicated in the initiation and development of many diseases that affect humanity. Among these diseases are autoimmune diseases and neurodegenerative diseases, which connected with the lacking autophagy. Other diseases are connected with the increasing levels of autophagy such as cancers and infectious diseases. Therefore, controlling autophagy with sufficient regulators could represent an effective strategy to overcome such diseases. Interestingly, targeting autophagy can also provide a sufficient method to combat the current epidemic caused by the ongoing coronavirus. In this review, we aim to highlight the physiological function of the autophagic process to understand the circumstances surrounding its role in the cellular immunity associated with the development of human diseases.

Analysis of hepatic transcriptome modulation exerted by γ-conglutin from lupins in a streptozotocin-induced diabetes model

Lupinus albus γ-conglutin is proposed to positively affect glucose metabolism through inhibition of hepatic glucose production and insulin-mimetic activity; however, the action mechanism is not entirely known. Besides, most studies had focused on its effect on molecular targets directly related to glucose metabolism, and few studies have investigated how γ-conglutin may affect the liver gene expression or if it plays a role in other metabolic processes. Therefore, we investigated the influence of γ-conglutin on the liver transcriptome of streptozotocin-induced diabetic rats using DNA microarrays, ontological analyses, and quantitative PCR. Of the 22,000 genes evaluated, 803 and 173 were downregulated and upregulated, respectively. The ontological analyses of the differentially expressed genes revealed that among others, the mitochondria, microtubules, cytoskeleton, and oxidoreductase activity terms were enriched, implying a possible role of γ-conglutin on autophagy. To corroborate the microarray results, we selected and quantified, by PCR, the expression of two genes associated with autophagy (Atg7 and Snx18) and found their expression augmented two and threefold, respectively; indicating a higher autophagy activity in animals treated with γ-conglutin. Although complementary studies are required, our findings indicate for the first time that the hypoglycaemic effects of γ-conglutin may involve an autophagy induction mechanism, a pivotal process for the preservation of cell physiology and glucose homeostasis.

Compound Danshen Dripping Pills Prevented Leptin Deficiency-Induced Hepatic ER Stress, Stimulated Autophagy, and Improved Insulin Resistance of ob/ob Mice

Compound Danshen dripping pills (CDDP) is widely used for the treatment of coronary arteriosclerosis and ischemic heart diseases for decades of years. In our study, we interestingly discovered the effects and mechanism of CDDP on insulin resistance that increase the risk factor of cardiovascular diseases. Effects of CDDP on fasting blood glucose, the insulin tolerance test (ITT), the oral glucose tolerance test (OGTT), hepatic function, and underlying mechanism were analyzed in ob/ob mice. CDDP was found improving the impaired insulin signal sensitivity of ob/ob mice by ameliorating insulin and glucose tolerance, improving hepatic phosphorylation of the insulin receptor substrate-1 on Ser 307 (pIRS1) of ob/ob mice, and restoring hepatic function by decreasing serum ALT and AST, which increased in ob/ob mice serum. Decreasing hepatic phosphorylation of pancreatic ER kinase (PERK) and inositol-requiring enzyme-1 (IRE1) regulating hepatic ER stress in the liver of ob/ob mice were increased by CDDP. Furthermore, CDDP was also found stimulating ob/ob mice hepatic autophagy by increasing the expression of Beclin1 and LC3B, while decreasing P62 expression. Our study discovered an important role of CDDP on improving ob/ob mice insulin resistance and liver function probably through relieving hepatic ER stress and stimulating hepatic autophagy, which would broaden the application value and provide more benefits for treating cardiovascular patients. This trial is registered with NCT01659580.

Berberine represses human gastric cancer cell growth in vitro and in vivo by inducing cytostatic autophagy via inhibition of MAPK/mTOR/p70S6K and Akt signaling pathways

Berberine, an isoquinoline alkaloid from Coptidis Rhizoma, has been characterized as a potential anticancer drug due to its good anti-tumor effects. However, the molecular mechanisms involved in anti-gastric cancer remain poorly understood. Herein, the role of berberine in gastric cancer suppression by inducing cytostatic autophagy in vitro and in vivo was first investigated. Results showed that berberine induced an obvious growth inhibitory effect on gastric cancer BGC-823 cells without toxicity to human peripheral blood mononuclear cells. Treatment with berberine triggered cell autophagy, as demonstrated by the punctuate distribution of monodansylcadaverine staining and GFP-LC3, as well as the LC3-II, Beclin-1 and p-ULK1 promotion, and p62 degradation. Inhibition of autophagy by 3-MA, CQ, Baf-A1 and BECN1 siRNA obviously increased cell viability of berberine-exposed gastric cancer cells, which confirmed the anti-cancer role of autophagy induced by berberine. Mechanistic studies showed that berberine inhibited mTOR, Akt and MAPK (ERK, JNK and p38) pathways thereby inducing autophagy. Inhibition of above pathways increases berberine induced autophagy and cytotoxicity. Interestingly, mTOR/p70S6K was inhibited by the MAPK but not Akt. Furthermore, inhibition of autophagy reversed berberine down-regulated mTOR, Akt and MAPK. In xenografts, the berberine induced autophagy leads to suppression of tumor proliferation with no side-effect, and western blotting displayed an apparent attenuation of p-mTOR, p-p70S6K, p-Akt, p-ERK, p-JNK and p-p38 in tumors from berberine treated mice. Briefly, these results indicated that berberine repressed human gastric cancer cell growth in vitro and in vivo by inducing cytostatic autophagy via inhibition of MAPK/mTOR/p70S6K and Akt, and provided a molecular basis for the treatment of gastric cancer.

How autophagy can restore proteostasis defects in multiple diseases?

Cellular evolution develops several conserved mechanisms by which cells can tolerate various difficult conditions and overall maintain homeostasis. Autophagy is a well-developed and evolutionarily conserved mechanism of catabolism, which endorses the degradation of foreign and endogenous materials via autolysosome. To decrease the burden of the ubiquitin-proteasome system (UPS), autophagy also promotes the selective degradation of proteins in a tightly regulated way to improve the physiological balance of cellular proteostasis that may get perturbed due to the accumulation of misfolded proteins. However, the diverse as well as selective clearance of unwanted materials and regulations of several cellular mechanisms via autophagy is still a critical mystery. Also, the failure of autophagy causes an increase in the accumulation of harmful protein aggregates that may lead to neurodegeneration. Therefore, it is necessary to address this multifactorial threat for in-depth research and develop more effective therapeutic strategies against lethal autophagy alterations. In this paper, we discuss the most relevant and recent reports on autophagy modulations and their impact on neurodegeneration and other complex disorders. We have summarized various pharmacological findings linked with the induction and suppression of autophagy mechanism and their promising preclinical and clinical applications to provide therapeutic solutions against neurodegeneration. The conclusion, key questions, and future prospectives sections summarize fundamental challenges and their possible feasible solutions linked with autophagy mechanism to potentially design an impactful therapeutic niche to treat neurodegenerative diseases and imperfect aging.

Autophagy in metabolic syndrome: breaking the wheel by targeting the renin-angiotensin system

Metabolic syndrome (MetS) is a complex, emerging epidemic which disrupts the metabolic homeostasis of several organs, including liver, heart, pancreas, and adipose tissue. While studies have been conducted in these research areas, the pathogenesis and mechanisms of MetS remain debatable. Lines of evidence show that physiological systems, such as the renin-angiotensin system (RAS) and autophagy play vital regulatory roles in MetS. RAS is a pivotal system known for controlling blood pressure and fluid balance, whereas autophagy is involved in the degradation and recycling of cellular components, including proteins. Although RAS is activated in MetS, the interrelationship between RAS and autophagy varies in glucose homeostatic organs and their cross talk is poorly understood. Interestingly, autophagy is attenuated in the liver during MetS, whereas autophagic activity is induced in adipose tissue during MetS, indicating tissue-specific discordant roles. We discuss in vivo and in vitro studies conducted in metabolic tissues and dissect their tissue-specific effects. Moreover, our review will focus on the molecular mechanisms by which autophagy orchestrates MetS and the ways future treatments could target RAS in order to achieve metabolic homeostasis.

Resveratrol, an activator of SIRT1, improves ER stress by increasing clusterin expression in HepG2 cells

Endoplasmic reticulum stress (ER stress) is involved in lipid metabolism and lipotoxicity and can lead to apoptosis. Resveratrol, a sirtuin 1 (SIRT1) agonist, prevents ER stress and improves ER stress-induced hepatic steatosis and cell death. Clusterin is a secreted chaperone and has roles in various physiological processes. However, changes in the expression of clusterin upon ER stress and the connection between SIRT1 and clusterin in protection against ER stress are not well known. In cells treated with tunicamycin, resveratrol increased the expression of clusterin mRNA and protein and the secreted clusterin protein level in conditioned medium. Resveratrol decreased protein expression of the ER stress markers, p-PERK, p-IRE1α, and CHOP, and increased the expression of the ER-associated degradation (ERAD) factors, SEL1L and HRD1, in tunicamycin-treated cells. However, no changes in the expression of these genes were observed in clusterin siRNA-transfected cells. Moreover, increased LAMP2 and LC3 expression and decreased Rubicon expression were observed in cells treated with resveratrol or secreted clusterin. These data suggest that SIRT1 activation by resveratrol attenuates ER stress by promoting protective processes such as ERAD and autophagy pathways and that these protective effects are mediated by clusterin.

Targeting Autophagy to Overcome Human Diseases

Autophagy is an evolutionarily conserved cellular process, through which damaged organelles and superfluous proteins are degraded, for maintaining the correct cellular balance during stress insult. It involves formation of double-membrane vesicles, named autophagosomes, that capture cytosolic cargo and deliver it to lysosomes, where the breakdown products are recycled back to cytoplasm. On the basis of degraded cell components, some selective types of autophagy can be identified (mitophagy, ribophagy, reticulophagy, lysophagy, pexophagy, lipophagy, and glycophagy). Dysregulation of autophagy can induce various disease manifestations, such as inflammation, aging, metabolic diseases, neurodegenerative disorders and cancer. The understanding of the molecular mechanism that regulates the different phases of the autophagic process and the role in the development of diseases are only in an early stage. There are still questions that must be answered concerning the functions of the autophagy-related proteins. In this review, we describe the principal cellular and molecular autophagic functions, selective types of autophagy and the main in vitro methods to detect the role of autophagy in the cellular physiology. We also summarize the importance of the autophagic behavior in some diseases to provide a novel insight for target therapies.

Autophagy in Adipocyte Browning: Emerging Drug Target for Intervention in Obesity

Autophagy, lipophagy, and mitophagy are considered to be the major recycling processes for protein aggregates, excess fat, and damaged mitochondria in adipose tissues in response to nutrient status-associated stress, oxidative stress, and genotoxic stress in the human body. Obesity with increased body weight is often associated with white adipose tissue (WAT) hypertrophy and hyperplasia and/or beige/brown adipose tissue atrophy and aplasia, which significantly contribute to the imbalance in lipid metabolism, adipocytokine secretion, free fatty acid release, and mitochondria function. In recent studies, hyperactive autophagy in WAT was observed in obese and diabetic patients, and inhibition of adipose autophagy through targeted deletion of autophagy genes in mice improved anti-obesity phenotypes. In addition, active mitochondria clearance through activation of autophagy was required for beige/brown fat whitening – that is, conversion to white fat. However, inhibition of autophagy seemed detrimental in hypermetabolic conditions such as hepatic steatosis, atherosclerosis, thermal injury, sepsis, and cachexia through an increase in free fatty acid and glycerol release from WAT. The emerging concept of white fat browning–conversion to beige/brown fat–has been controversial in its anti-obesity effect through facilitation of weight loss and improving metabolic health. Thus, proper regulation of autophagy activity fit to an individual metabolic profile is necessary to ensure balance in adipose tissue metabolism and function, and to further prevent metabolic disorders such as obesity and diabetes. In this review, we summarize the effect of autophagy in adipose tissue browning in the context of obesity prevention and its potential as a promising target for the development of anti-obesity drugs.

Modulation of Autophagy Influences the Function and Survival of Human Pancreatic Beta Cells Under Endoplasmic Reticulum Stress Conditions and in Type 2 Diabetes

Autophagy is the major mechanism involved in degradation and recycling of intracellular components, and its alterations have been proposed to cause beta cell dysfunction. In this study, we explored the effects of autophagy modulation in human islets under conditions associated to endoplasmic reticulum (ER) stress. Human pancreatic islets were isolated by enzymatic digestion and density gradient purification from pancreatic samples of non-diabetic (ND; n = 17; age 65 ± 21 years; gender: 5 M/12 F; BMI 23.4 ± 3.3 kg/m²) and T2D (n = 9; age 76 ± 6 years; 4 M/5 F; gender: BMI 25.4 ± 3.7 kg/m²) organ donors. Nine ND organ donors were treated for hypertension and 1 for both hypertension and hypercholesterolemia. T2D organ donors were treated with metformin (1), oral hypoglycemic agents (2), diet + oral hypoglycemic agents (3), insulin (3) or insulin plus metformin (3) as for antidiabetic therapy and, of these, 3 were treated also for hypertension and 6 for both hypertension and hypercholesterolemia. Two days after isolation, they were cultured for 1-5 days with 10 ng/ml rapamycin (autophagy inducer), 5 mM 3-methyladenine or 1.0 nM concanamycin-A (autophagy blockers), either in the presence or not of metabolic (0.5 mM palmitate) or chemical (0.1 ng/ml brefeldin A) ER stressors. In ND islets palmitate exposure induced a 4 to 5-fold increase of beta cell apoptosis, which was significantly prevented by rapamycin and exacerbated by 3-MA. Similar results were observed with brefeldin treatment. Glucose-stimulated insulin secretion from ND islets was reduced by palmitate (-40 to 50%) and brefeldin (-60 to 70%), and rapamycin counteracted palmitate, but not brefeldin, cytotoxic actions. Both palmitate and brefeldin induced PERK, CHOP and BiP gene expression, which was partially, but significantly prevented by rapamycin. With T2D islets, rapamycin alone reduced the amount of p62, an autophagy receptor that accumulates in cells when macroautophagy is inhibited. Compared to untreated T2D cells, rapamycin-exposed diabetic islets showed improved insulin secretion, reduced proportion of beta cells showing signs of apoptosis and better preserved insulin granules, mitochondria and ER ultrastructure; this was associated with significant reduction of PERK, CHOP and BiP gene expression. This study emphasizes the importance of autophagy modulation in human beta cell function and survival, particularly in situations of ER stress. Tuning autophagy could be a tool for beta cell protection.

Autophagy as an emerging target in cardiorenal metabolic disease: From pathophysiology to management

Although advances in medical technology and health care have improved the early diagnosis and management for cardiorenal metabolic disorders, the prevalence of obesity, insulin resistance, diabetes, hypertension, dyslipidemia, and kidney disease remains high. Findings from numerous population-based studies, clinical trials, and experimental evidence have consolidated a number of theories for the pathogenesis of cardiorenal metabolic anomalies including resistance to the metabolic action of insulin, abnormal glucose and lipid metabolism, oxidative and nitrosative stress, endoplasmic reticulum (ER) stress, apoptosis, mitochondrial damage, and inflammation. Accumulating evidence has recently suggested a pivotal role for proteotoxicity, the unfavorable effects of poor protein quality control, in the pathophysiology of metabolic dysregulation and related cardiovascular complications. The ubiquitin-proteasome system (UPS) and autophagy-lysosomal pathways, two major although distinct cellular clearance machineries, govern protein quality control by degradation and clearance of long-lived or damaged proteins and organelles. Ample evidence has depicted an important role for protein quality control, particularly autophagy, in the maintenance of metabolic homeostasis. To this end, autophagy offers promising targets for novel strategies to prevent and treat cardiorenal metabolic diseases. Targeting autophagy using pharmacological or natural agents exhibits exciting new strategies for the growing problem of cardiorenal metabolic disorders.

Macroautophagy Regulates Nuclear NOTCH1 Activity Through Multiple p62 Binding Sites

NOTCH1 is the prototype of the NOTCH family of single-pass transmembrane receptors and regulates many basic processes during embryonic development and human pathogenesis. In core to NOTCH1 activation are proteolytic cleavages that release its intracellular domain (NICD1), which in turn translocates to the nucleus to regulate gene transcription. Macroautophagy (hereafter autophagy) has been shown to promote the degradation of NOTCH1, but the underlying mechanisms remain elusive. Here, we show that autophagy promotes the degradation of NOTCH1 by p62-dependent binding between NICD1 and LC3, a component of the autophagosomes that execute autophagy. Strikingly, deleting any of the structural NICD1 domains fails to block the degradation of NICD1 by autophagy, and p62 binds to almost all these domains independently, indicating that p62 binds to multiple sites on NICD1 to promote its degradation. Intriguingly, inhibition of autophagy induces the accumulation of NICD1 in not only the cytoplasm but also the nucleus and increases the transcriptional activity of NICD1, and such regulation of nuclear NICD1 by autophagy is unique to NICD1 and not observed for all other NICDs (NICD2-4). Collectively, our results suggest that autophagy tightly controls nuclear NOTCH1 activity through multiple p62 binding sites, and that modulating autophagy activity may be useful for treating NOTCH1 related human diseases. © 2018 IUBMB Life, 70(10):985-994, 2018.

Autophagy Differentially Regulates Insulin Production and Insulin Sensitivity

Autophagy, a stress-induced lysosomal degradative pathway, has been assumed to exert similar metabolic effects in different organs. Here, we establish a model where autophagy plays different roles in insulin-producing β cells versus insulin-responsive cells, utilizing knockin (Becn1F121A) mice manifesting constitutively active autophagy. With a high-fat-diet challenge, the autophagy-hyperactive mice unexpectedly show impaired glucose tolerance, but improved insulin sensitivity, compared to mice with normal autophagy. Autophagy hyperactivation enhances insulin signaling, via suppressing ER stress in insulin-responsive cells, but decreases insulin secretion by selectively sequestrating and degrading insulin granule vesicles in β cells, a process we term "vesicophagy." The reduction in insulin storage, insulin secretion, and glucose tolerance is reversed by transient treatment of autophagy inhibitors. Thus, β cells and insulin-responsive tissues require different autophagy levels for optimal function. To improve insulin sensitivity without hampering secretion, acute or intermittent, rather than chronic, activation of autophagy should be considered in diabetic therapy development.

The Steroid Hormone 20-Hydroxyecdysone Regulates the Conjugation of Autophagy-Related Proteins 12 and 5 in a Concentration and Time-Dependent Manner to Promote Insect Midgut Programmed Cell Death

Autophagy requires the conjugation of autophagy-related protein 12 (ATG12) to autophagy-related protein 5 (ATG5) through covalent attachment. However, the signals regulating ATG12-ATG5 conjugation are unclear. The larval midgut of lepidopteran insects performs autophagy and apoptosis sequentially during the transition of larvae to pupae under regulation by the steroid hormone 20-hydroxyecdysone (20E), thus representing a model to study steroid hormone regulation of ATG12-ATG5 conjugation. In the present study, using the lepidopteran insect Helicoverpa armigera as a model, we report that 20E regulates the conjugation of ATG12-ATG5 in a concentration and time-dependent manner. The ATG12-ATG5 conjugate was abundant in the epidermis, midgut, and fat body during metamorphosis from the larvae to the pupae; however, the ATG12-ATG5 conjugate level decreased at the time of pupation. At low concentrations (2-5 µM) over a short time course (1-48 h), 20E promoted the conjugation of ATG12-ATG5; however, at 10 µM and 72 h, 20E repressed the conjugation of ATG12-ATG5. ATG12 was localized in the larval midgut during metamorphosis. Knockdown of ATG12 in larvae caused death with delayed pupation, postponed the process of midgut programmed cell death (PCD), and repressed ATG8 (also called LC3-I) transformation to LC3-II and the cleavage of caspase-3; therefore, knockdown of ATG12 in larvae blocked both autophagy and apoptosis. Knockdown of ATG12 in H. armigera epidermis cell line cells also repressed 20E-induced autophagosome formation and caspase-3 activation. The results suggested that 20E plays key role in the regulation of ATG12-ATG5 conjugation in a concentration and time-dependent manner for autophagy or apoptosis, and that ATG12 is necessary by both autophagy and apoptosis during insect midgut PCD.

Pancreatic Beta Cell Death: Novel Potential Mechanisms in Diabetes Therapy

PURPOSE OF REVIEW

Describing the diverse molecular mechanisms (particularly immunological) involved in the death of the pancreatic beta cell in type 1 and type 2 diabetes mellitus.

RECENT FINDINGS

Beta cell death is the final event in a series of mechanisms that, up to date, have not been entirely clarified; it represents the pathophysiological mechanism in the natural history of diabetes mellitus. These mechanisms are not limited to an apoptotic process only, which is characteristic of the immune-mediated insulitis in type 1 diabetes mellitus. They also include the action of proinflammatory cytokines, the production of reactive oxygen species, DNA fragmentation (typical of necroptosis in type 1 diabetic patients), excessive production of islet amyloid polypeptide with the consequent endoplasmic reticulum stress, disruption in autophagy mechanisms, and protein complex formation, such as the inflammasome, capable of increasing oxidative stress produced by mitochondrial damage.

SUMMARY

Necroptosis, autophagy, and pyroptosis are molecular mechanisms that modulate the survival of the pancreatic beta cell, demonstrating the importance of the immune system in glucolipotoxicity processes and the potential role for immunometabolism as another component of what once known as the "ominous octet."

HMGB1-mediated autophagy confers resistance to gemcitabine in hormone-independent prostate cancer cells

As a main treatment of prostate cancer, castration therapy has been widely applied in the clinic. However, the therapeutic strategy for hormone-independent prostate cancer (HIPC) was not satisfied. Gemcitabine is an important chemotherapeutic agent that has been approved for the treatment of numerous human solid tumors, including HIPC, whereas the gemcitabine resistance has become a serious problem in clinical chemotherapy. In the present study, the mechanisms of resistance to gemcitabine were investigated in HIPC cell lines. The results demonstrated that the autophagy markers were induced significantly in HIPC cells subsequent to gemcitabine treatment. Meanwhile, administration of gemcitabine to HIPC cells increased the expression of high mobility group box1 (HMGB1). Furthermore, the gemcitabine-induced autophagy response was attenuated in stable HIPC cells harboring HMGB1 shRNA. Notably, the HIPC cells stably transfected with HMGB1 shRNA or treated with autophagy inhibitors were more sensitive to gemcitabine compared with the control group. These data suggested that inhibition of HMGB1 increased the sensitivity to gemcitabine by decreasing autophagy response in HIPC cells. Overall, the present findings demonstrate a new mechanism for the resistance to gemcitabine in HIPC cell lines.

Impaired autophagic flux and p62-mediated EMT are involved in arsenite-induced transformation of L-02 cells

Autophagy is a catabolic process essential for preserving cellular homeostasis, and the epithelial-to-mesenchymal transition (EMT) is involved during tissue development and cancer progression. In arsenite-treated human hepatic epithelial (L-02) cells, arsenite reduced the autophagic flux, which caused accumulation of p62, an adaptor and receptor of autophagy. Further, in arsenite-transformed L-02 cells, the levels of E-cadherin were attenuated, but the levels of vimentin, which is expressed in mesenchymal cells, and Snail, a transcription regulator of the EMT, were up-regulated. Thus, after chronic exposure of L-02 cells to arsenite, the impaired autophagic flux induced the accumulation of p62, which up-regulated the expression of Snail, a protein involved in arsenite-induced EMT of these cells. Knockdown of p62 by siRNA reversed the arsenite-induced EMT and decreased the capacities of arsenite-transformed L-02 cells for colony formation and invasion and migration. Therefore, in arsenite-induced transformation of L-02 cells, the accumulation of p62, by impairing autophagic flux, mediates the EMT via Snail. These results provide a previously unknown mechanism underlying arsenic toxicity and carcinogenicity.

A Becn1 mutation mediates hyperactive autophagic sequestration of amyloid oligomers and improved cognition in Alzheimer's disease

Impairment of the autophagy pathway has been observed during the pathogenesis of Alzheimer's disease (AD), a neurodegenerative disorder characterized by abnormal deposition of extracellular and intracellular amyloid β (Aβ) peptides. Yet the role of autophagy in Aβ production and AD progression is complex. To study whether increased basal autophagy plays a beneficial role in Aβ clearance and cognitive improvement, we developed a novel genetic model to hyperactivate autophagy in vivo. We found that knock-in of a point mutation F121A in the essential autophagy gene Beclin 1/Becn1 in mice significantly reduces the interaction of BECN1 with its inhibitor BCL2, and thus leads to constitutively active autophagy even under non-autophagy-inducing conditions in multiple tissues, including brain. Becn1F121A-mediated autophagy hyperactivation significantly decreases amyloid accumulation, prevents cognitive decline, and restores survival in AD mouse models. Using an immunoisolation method, we found biochemically that Aβ oligomers are autophagic substrates and sequestered inside autophagosomes in the brain of autophagy-hyperactive AD mice. In addition to genetic activation of autophagy by Becn1 gain-of-function, we also found that ML246, a small-molecule autophagy inducer, as well as voluntary exercise, a physiological autophagy inducer, exert similar Becn1-dependent protective effects on Aβ removal and memory in AD mice. Taken together, these results demonstrate that genetically disrupting BECN1-BCL2 binding hyperactivates autophagy in vivo, which sequestrates amyloid oligomers and prevents AD progression. The study establishes new approaches to activate autophagy in the brain, and reveals the important function of Becn1-mediated autophagy hyperactivation in the prevention of AD.

Regulation of Exercise-Induced Autophagy in Skeletal Muscle

PURPOSE OF REVIEW

Physical exercise is a highly effective method to prevent several pathogenic conditions, such as obesity, type 2 diabetes and cardiovascular diseases, largely due to metabolic adaptations induced by exercise in skeletal muscle. Yet how exercise induces the beneficial effects in muscle remains to be fully elucidated. Autophagy is a lysosomal degradation pathway that regulates nutrient recycling, energy production and organelle quality control. The autophagy pathway is upregulated in response to stress during exercise and muscle contraction, and may be an important mechanism mediating exercise-induced health benefits.

RECENT FINDINGS

A number of studies have indicated that physical exercise induces non-selective autophagy and selective mitophagy in skeletal muscle in animal models and humans. The AMPK-ULK1 and the FoxO3 signaling pathways play an essential role in the activation of the upstream autophagy machinery in skeletal muscle during exercise. The autophagy activity is required for health benefits of exercise, as in different autophagy-deficient mouse lines exercise-induced effects are abolished.

SUMMARY

This review aims to summarize and highlight the most recent findings on the role of autophagy in muscle maintenance, the molecular pathways that upregulate autophagy during exercise, and the potential functions of exercise-induced autophagy and mitophagy in skeletal muscle.

Mechanisms of Tanshinone II a inhibits malignant melanoma development through blocking autophagy signal transduction in A375 cell

Background

Malignant melanoma (MM) is one of the high degree of malignancy and early prone to blood and lymph node metastasis. There is not cured for MM. Tan II A has been reported to reduce cancer cell proliferation. But the mechanism by which Tan II A inhibited melanoma growth are not well characterized. We sought to explore the possible mechanism by which Tan II A regulated cell proliferation through autophagy signaling pathway in A375 cells.

Methods

We tested the effects of Tan II A on melanoma A375, MV3, M14, and other human cell lines including Hacat and HUVEC cells in cell culture model. Cell proliferation was assessed by using methyl thiazol tetrazolium (MTT) assay. Cell migration ability melanoma A375 was monitored by using cell scratch assay. Transwell chamber experimental was performed to assess the effect of Tan II A on A375 melanoma cell invasion ability. The autophagy body was examined by using flow cytometry. The expression of autophagy-associated protein beclin-1 and microtubule-associated protein 1 light chain 3(LC3)-II, as well as phosphatidylinositol 3-kinase(PI3K)、protein kinase B (Akt)、mammalian target of rapamycin (mTOR)、p70S6K1 signaling pathways were detected by using Western blotting. The effects of Tan II A on tumor progression was also examined in melanoma A375 induced tumor in mouse model.

Results

We found that Tan IIA inhibited melanoma A375, MV3, and M14 cell proliferation in dose and time dependent manner. Tan II A reduced CXCL12-induced A375 cell invasive ability and migration in a dose dependent manner. Tan IIA promoted autophagic body production and increased autophagy-associated protein beclin-1 and LC3-II expression in A375 cells. However, Tan IIA reduced the phosphorylation of PI3K, P-AKT, P-mTOR, and P-p7036k1. We also confirmed that Tan II A reduced melanoma A375 induced tumor volume and weight in mouse model.

Conclusions

We concluded that Tan II A reduced A375 cells proliferation by activation of autophagy production, blocked PI3K- Akt – mTOR - p70S6K1 signaling pathway, increased autophagic related gene beclin-1, LC3-II protein expressions and induced autophagocytosis. Tan II A inhibited melanoma A375 induced tumor development in mouse model.

Autophagy and hepatic lipid metabolism

Autophagy is initially thought to be a non-selective process in which intracellular proteins or damaged organelles are degraded. It is activated when cells lack nutrients and energy. Autophagy degrades cytoplasmic components within lysosomes and reuses the energy of amino acids to promote cell survival and maintain the cytoplasmic content. Current evidence implicates autophagy in the regulation of lipid stores within the two main organs involved in maintaining lipid homeostasis, the liver and adipose tissue. Upregulation of autophagy may lead to conversion of white adipose tissue into brown adipose tissue, thus regulating energy expenditure and obesity. Discovering new therapeutic interventions to treat lipid and lipoprotein disorders is of great interest and the discovery of autophagy as a regulator of lipid metabolism has opened up a new avenue for this area. In the liver, autophagy can play a role in some common metabolic disorders, which needs further research.

Activating Autophagy by Aerobic Exercise in Mice

Autophagy is a lysosomal degradation pathway essential for cell homeostasis, function and differentiation. Under stress conditions, autophagy is induced and targets various cargos, such as bulk cytosol, damaged organelles and misfolded proteins, for degradation in lysosomes. Resulting nutrient molecules are recycled back to the cytosol for new protein synthesis and ATP production. Upregulation of autophagy has beneficial effects against the pathogenesis of many diseases, and pharmacological and physiological strategies to activate autophagy have been reported. Aerobic exercise is recently identified as an efficient autophagy inducer in multiple organs in mice, including muscle, liver, heart and brain. Here we show procedures to induce autophagy in vivo by either forced treadmill exercise or voluntary wheel running. We also demonstrate microscopic and biochemical methods to quantitatively analyze autophagy levels in mouse tissues, using the marker proteins LC3 and p62 that are transported to and degraded in lysosomes along with autophagosomes.

Identification of natural products with neuronal and metabolic benefits through autophagy induction

Autophagy is a housekeeping lysosomal degradation pathway important for cellular survival, homeostasis and function. Various disease models have shown that upregulation of autophagy may be beneficial to combat disease pathogenesis. However, despite several recently reported small-molecule screens for synthetic autophagy inducers, natural chemicals of diverse structures and functions have not been included in the synthetic libraries, and characterization of their roles in autophagy has been lacking. To discover novel autophagy-regulating compounds and study their therapeutic mechanisms, we used analytic chemistry approaches to isolate natural phytochemicals from a reservoir of medicinal plants used in traditional remedies. From this pilot plant metabolite library, we identified several novel autophagy-inducing phytochemicals, including Rg2. Rg2 is a steroid glycoside chemical that activates autophagy in an AMPK-ULK1-dependent and MTOR-independent manner. Induction of autophagy by Rg2 enhances the clearance of protein aggregates in a cell-based model, improves cognitive behaviors in a mouse model of Alzheimer disease, and prevents high-fat diet-induced insulin resistance. Thus, we discovered a series of autophagy-inducing phytochemicals from medicinal plants, and found that one of the compounds Rg2 mediates metabolic and neurotrophic effects dependent on activation of the autophagy pathway. These findings may help explain how medicinal plants exert the therapeutic functions against metabolic diseases.