Advances in Autophagy Regulatory Mechanisms

The Current Landscape of Pharmacotherapies for Sarcopenia

Sarcopenia is a skeletal muscle disorder characterized by progressive and generalized decline in muscle mass and function. Although it is mostly known as an age-related disorder, it can also occur secondary to systemic diseases such as malignancy or organ failure. It has demonstrated a significant relationship with adverse outcomes, e.g., falls, disabilities, and even mortality. Several breakthroughs have been made to find a pharmaceutical therapy for sarcopenia over the years, and some have come up with promising findings. Yet still no drug has been approved for its treatment. The key factor that makes finding an effective pharmacotherapy so challenging is the general paradigm of standalone/single diseases, traditionally adopted in medicine. Today, it is well known that sarcopenia is a complex disorder caused by multiple factors, e.g., imbalance in protein turnover, satellite cell and mitochondrial dysfunction, hormonal changes, low-grade inflammation, senescence, anorexia of aging, and behavioral factors such as low physical activity. Therefore, pharmaceuticals, either alone or combined, that exhibit multiple actions on these factors simultaneously will likely be the drug of choice to manage sarcopenia. Among various drug options explored throughout the years, testosterone still has the most cumulated evidence regarding its effects on muscle health and its safety. A mas receptor agonist, BIO101, stands out as a recent promising pharmaceutical. In addition to the conventional strategies (i.e., nutritional support and physical exercise), therapeutics with multiple targets of action or combination of multiple therapeutics with different targets/modes of action appear to promise greater benefit for the prevention and treatment of sarcopenia.

The endoplasmic reticulum: Homeostasis and crosstalk in retinal health and disease

The endoplasmic reticulum (ER) is the largest intracellular organelle carrying out a broad range of important cellular functions including protein biosynthesis, folding, and trafficking, lipid and sterol biosynthesis, carbohydrate metabolism, and calcium storage and gated release. In addition, the ER makes close contact with multiple intracellular organelles such as mitochondria and the plasma membrane to actively regulate the biogenesis, remodeling, and function of these organelles. Therefore, maintaining a homeostatic and functional ER is critical for the survival and function of cells. This vital process is implemented through well-orchestrated signaling pathways of the unfolded protein response (UPR). The UPR is activated when misfolded or unfolded proteins accumulate in the ER, a condition known as ER stress, and functions to restore ER homeostasis thus promoting cell survival. However, prolonged activation or dysregulation of the UPR can lead to cell death and other detrimental events such as inflammation and oxidative stress; these processes are implicated in the pathogenesis of many human diseases including retinal disorders. In this review manuscript, we discuss the unique features of the ER and ER stress signaling in the retina and retinal neurons and describe recent advances in the research to uncover the role of ER stress signaling in neurodegenerative retinal diseases including age-related macular degeneration, inherited retinal degeneration, achromatopsia and cone diseases, and diabetic retinopathy. In some chapters, we highlight the complex interactions between the ER and other intracellular organelles focusing on mitochondria and illustrate how ER stress signaling regulates common cellular stress pathways such as autophagy. We also touch upon the integrated stress response in retinal degeneration and diabetic retinopathy. Finally, we provide an update on the current development of pharmacological agents targeting the UPR response and discuss some unresolved questions and knowledge gaps to be addressed by future research.

Inhibition of autophagy and induction of glioblastoma cell death by NEO214, a perillyl alcohol-rolipram conjugate

Glioblastoma (GBM) is the most aggressive primary brain tumor, exhibiting a high rate of recurrence and poor prognosis. Surgery and chemoradiation with temozolomide (TMZ) represent the standard of care, but, in most cases, the tumor develops resistance to further treatment and the patients succumb to disease. Therefore, there is a great need for the development of well-tolerated, effective drugs that specifically target chemoresistant gliomas. NEO214 was generated by covalently conjugating rolipram, a PDE4 (phosphodiesterase 4) inhibitor, to perillyl alcohol, a naturally occurring monoterpene related to limonene. Our previous studies in preclinical models showed that NEO214 harbors anticancer activity, is able to cross the blood-brain barrier (BBB), and is remarkably well tolerated. In the present study, we investigated its mechanism of action and discovered inhibition of macroautophagy/autophagy as a key component of its anticancer effect in glioblastoma cells. We show that NEO214 prevents autophagy-lysosome fusion, thereby blocking autophagic flux and triggering glioma cell death. This process involves activation of MTOR (mechanistic target of rapamycin kinase) activity, which leads to cytoplasmic accumulation of TFEB (transcription factor EB), a critical regulator of genes involved in the autophagy-lysosomal pathway, and consequently reduced expression of autophagy-lysosome genes. When combined with chloroquine and TMZ, the anticancer impact of NEO214 is further potentiated and unfolds against TMZ-resistant cells as well. Taken together, our findings characterize NEO214 as a novel autophagy inhibitor that could become useful for overcoming chemoresistance in glioblastoma.Abbreviations: ATG: autophagy related; BAFA1: bafilomycin A1; BBB: blood brain barrier; CQ: chloroquine; GBM: glioblastoma; LAMP1: lysosomal associated membrane protein 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MGMT: O-6-methylguanine-DNA methyltransferase; MTOR: mechanistic target of rapamycin kinase; MTORC: MTOR complex; POH: perillyl alcohol; SQSTM1/p62: sequestosome 1; TFEB: transcription factor EB; TMZ: temozolomide.

Reactive nitrogen species as therapeutic targets for autophagy/mitophagy modulation to relieve neurodegeneration in multiple sclerosis: Potential application for drug discovery

Multiple sclerosis (MS) is a neuroinflammatory disease with limited therapeutic effects, eventually developing into handicap. Seeking novel therapeutic strategies for MS is timely important. Active autophagy/mitophagy could mediate neurodegeneration, while its roles in MS remain controversial. To elucidate the exact roles of autophagy/mitophagy and reveal its in-depth regulatory mechanisms, we conduct a systematic literature study and analyze the factors that might be responsible for divergent results obtained. The dynamic change levels of autophagy/mitophagy appear to be a determining factor for final neuron fate during MS pathology. Excessive neuronal autophagy/mitophagy contributes to neurodegeneration after disease onset at the active MS phase. Reactive nitrogen species (RNS) serve as key regulators for redox-related modifications and participate in autophagy/mitophagy modulation in MS. Nitric oxide (•NO) and peroxynitrite (ONOO-), two representative RNS, could nitrate or nitrosate Drp1/parkin/PINK1 pathway, activating excessive mitophagy and aggravating neuronal injury. Targeting RNS-mediated excessive autophagy/mitophagy could be a promising strategy for developing novel anti-MS drugs. In this review, we highlight the important roles of RNS-mediated autophagy/mitophagy in neuronal injury and review the potential therapeutic compounds with the bioactivities of inhibiting RNS-mediated autophagy/mitophagy activation and attenuating MS progression. Overall, we conclude that reactive nitrogen species could be promising therapeutic targets to regulate autophagy/mitophagy for multiple sclerosis treatment.

Protective role of autophagy in triptolide-induced apoptosis of TM3 Leydig cells

Background and Objectives

Triptolide (TP) is known to impair testicular development and spermatogenesis in mammals, but the mechanism of the side effects still needs to be investigated. The aim of the research is to confirm whether TP can cause autophagy in TM3 Leydig cells and the potential molecular pathway in vitro.

Methods

TM3 Leydig cells are used to investigate the molecular pathway through Western blot, detection of apoptosis, transmission electron microscopy for autophagosomes and so on.

Results

The data show that TP treatment resulted in the decreasing of the viability of TM3 cells due to the increased apoptosis. Treated with TP, the formation of autophagosomes, the decrease in P62, and the increase in the conversion of LC3-I to LC3-II suggested the induction of autophagy. The induction of autophagy has accompanied the activation of the mTOR/P70S6K signal pathway. The viability of the TM3 cells was further inhibited when they were co-treated with autophagy inhibitor, chloroquine (CQ).

Conclusion

All these data suggest that autophagy plays a very important role in antagonizing TM3 cell apoptosis during the TP exposure.

High-content analysis of testicular toxicity of BPA and its selected analogs in mouse spermatogonial, Sertoli cells, and Leydig cells revealed BPAF induced unique multinucleation phenotype associated with the increased DNA synthesis

Bisphenol A is an endocrine disruptor that has been shown to have testicular toxicity in animal models. Its structural analog, including bisphenol S (BPS), bisphenol AF (BPAF), and tetrabromobisphenol A (TBBPA) have been introduced to the market as BPA alternatives. Previously, we developed high-content analysis (HCA) assays and applied machine learning to compare the testicular toxicity of BPA and its analogs in spermatogonial cells and testicular cell co-culture models. There are diverse cell populations in the testis to support spermatogenesis, but their cell type-specific toxicities are still not clear. The purpose of this study is to examine the selective toxicity of BPA, BPS), BPAF, and TBBPA on these testicular cells, including Sertoli cells, Leydig cells, and spermatogonia cells. We developed a high-content image-based single-cell analysis and measured a broad spectrum of adverse endpoints related to the development of reproductive toxicology, including cell number, nuclear morphology, DNA synthesis, cell cycle progression, early DNA damage response, cytoskeleton structure, DNA methylation status, and autophagy. We introduced an HCA index and spectrum to reveal multiple HCA parameters and observed distinct toxicity profiling of BPA and its analogs among three testicular types. The HCA spectrum shows the dynamic, chemical-specific, dose-dependent changes of each HCA parameter. Each chemical displayed a unique dose-dependent profile within each type of cell. All three types of cells showed the highest response to BPAF at 10 μM across all endpoints measured. BPAF targeted spermatogonial cell (C18) more significantly at 5 μM. BPS more likely targeted Sertoli cell (TM4) and Leydig cell (TM3) and less at spermatogonia cells. TBBPA targeted spermatogonia, Sertoli cells, and less at TM3 cells. BPA is mainly targeted at TM4, followed by TM3 cells, and less at spermatogonial cells. Most importantly, we observed that BPAF induced a dose-dependent increase in spermatogonia cells, not in Sertoli and Leydig cells. In summary, our current HCA assays revealed the cell-type-specific toxicities of BPA and its analogs in different testicular cells. Multinucleation induced by BPAF, along with increased DNA damage and synthesis at low doses, could possibly have a profound long-term effect on reproductive systems.

Oxidative stress-induced apoptosis and autophagy: Balancing the contrary forces in spermatogenesis

Spermatogenesis is a complex process in the testis and is a cornerstone of male infertility. The abundance of unsaturated fatty acid and high cell division rate make male germs cells prone to DNA deterioration. ROS-mediated oxidative stress triggers DNA damage, autophagy, and apoptosis in male germ cells, which are critical causative factors that lead to male infertility. The complex connection and molecular crosstalk between apoptosis and autophagy is seen at multifaceted levels that interconnect the signaling pathways of these two processes. Multilevel interaction between apoptosis and autophagy is a seamless state of survival and death in response to various stressors. Interaction between multiple genes and proteins such as the mTor signaling pathway, Atg12 proteins, and the death adapter proteins, such as Beclin 1, p53, and Bcl-2 family proteins, validates such a link between these two phenomena. Testicular cells being epigenetically different from somatic cells, undergo numerous significant epigenetic transitions, and ROS modulates the epigenetic framework of mature sperm. Epigenetic deregulation of apoptosis and autophagy under oxidative stress conditions can cause sperm cell damage. The current review recapitulates the current role of prevailing stressors that generate oxidative stress leading to the induction of apoptosis and autophagy in the male reproductive system. Considering the pathophysiological consequences of ROS-mediated apoptosis and autophagy, a combinatorial approach, including apoptosis inhibition and autophagy activation, a therapeutic strategy to treat male idiopathic infertility. Understanding the crosslink between apoptosis and autophagy under stress conditions in male germ cells may play an essential role in developing therapeutic strategies to treat infertility.

Photodynamic therapy reduces cell viability, migration and triggers necroptosis in prostate tumor cells

Prostate cancer is the most common cancer in American men, aside from skin cancer. As an alternative cancer treatment, photodynamic laser therapy (PDT) can be used to induce cell death. We evaluated the PDT effect, using methylene blue as a photosensitizer, in human prostate tumor cells (PC3). PC3 were subjected to four different conditions: DMEM (control); laser treatment (L-660 nm, 100 mW, 100 J.cm^-2); methylene blue treatment (MB-25 μM, 30 min), and MB treatment followed by low-level red laser irradiation (MB-PDT). Groups were evaluated after 24 h. MB-PDT treatment reduced cell viability and migration. However, because MB-PDT did not significantly increase the levels of active caspase-3 and BCL-2, apoptosis was not the primary mode of cell death. MB-PDT, on the other hand, increased the acid compartment by 100% and the LC3 immunofluorescence (an autophagy marker) by 254%. Active MLKL level, a necroptosis marker, was higher in PC3 cells after MB-PDT treatment. Furthermore, MB-PDT resulted in oxidative stress due to a decrease in total antioxidant potential, catalase levels, and increased lipid peroxidation. According to these findings, MB-PDT therapy is effective at inducing oxidative stress and reducing PC3 cell viability. In such therapy, necroptosis is also an important mechanism of cell death triggered by autophagy.

Electroconvulsive Seizure Normalizes Motor Deficits and Induces Autophagy Signaling in the MPTP-Induced Parkinson Disease Mouse Model

OBJECTIVE

Electroconvulsive seizure (ECS) is a potent treatment modality for various neuropsychiatric diseases, including Parkinson disease (PD). Recent animal studies showed that repeated ECS activates autophagy signaling, the impairment of which is known to be involved in PD. However, the effectiveness of ECS on PD and its therapeutic mechanisms have not yet been investigated in detail.

METHODS

Systemic injection of a neurotoxin 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP), which destroys dopaminergic neurons in the substantia nigra compacta (SNc), in mice was utilized to induce an animal model of PD. Mice were treated with ECS 3 times per week for 2 weeks. Behavioral changes were measured with a rotarod test. Molecular changes related to autophagy signaling in midbrain including SNc, striatum, and prefrontal cortex were analyzed with immunohistochemistry and immunoblot analyses.

RESULTS

Repeated ECS treatments normalized the motor deficits and the loss of dopamiergic neurons in SNc of the MPTP PD mouse model. In the mouse model, LC3-II, an autophagy marker, was increased in midbrain while decreased in prefrontal cortex, both of which were reversed by repeated ECS treatments. In the prefrontal cortex, ECS-induced LC3-II increase was accompanied with AMP-activated protein kinase (AMPK)-Unc-51-like kinase 1-Beclin1 pathway activation and inhibition of mamalian target of rapamycin signaling which promotes autophagy initiation.

CONCLUSION

The findings revealed the therapeutic effects of repeated ECS treatments on PD, which could be attributed to the neuroprotective effect of ECS mediated by AMPK-autophagy signaling.

Mitochondrial-Endoplasmic Reticulum Communication-Mediated Oxidative Stress and Autophagy

Oxidative stress is an imbalance between free radicals and the antioxidant system causing overgeneration of free radicals (oxygen-containing molecules) ultimately leading to oxidative damage in terms of lipid peroxidation, protein denaturation, and DNA mutation. Oxidative stress can activate autophagy to alleviate oxidative damage and maintain normal physiological activities of cells by degrading damaged organelles or local cytoplasm. When oxidative stress is not eliminated by autophagy, it activates the apoptosis cascade. This review provides a brief summary of mitochondrial-endoplasmic reticulum communication-mediated oxidative stress and autophagy. Mitochondria and endoplasmic reticulum being important organelles in cells are directly or indirectly connected to each other through mitochondria-associated endoplasmic reticulum membranes and jointly regulate oxidative stress and autophagy. The reactive oxygen species (ROS) produced by the mitochondrial respiratory chain are the main inducers of oxidative stress. Damaged mitochondria can be effectively cleared by the process of mitophagy mediated by PINK1/parkin pathway, Nix/BNIP3 pathways, and FUNDC1 pathway, avoiding excessive ROS production. However, the mechanism of mitochondrial-endoplasmic reticulum communication in the regulation of oxidative stress and autophagy is rarely known. For this reason, this review explores the mutual connection of mitochondria and endoplasmic reticulum in mediating oxidative stress and autophagy through ROS and Ca²⁺ and aims to provide part of the theoretical basis for alleviating oxidative stress through autophagy mediated by mitochondrial-endoplasmic reticulum communication.

Molecular and cellular mechanisms in diabetic heart failure: Potential therapeutic targets

Diabetes Mellitus (DM) is a worldwide health issue that can lead to a variety of complications. DM is a serious metabolic disorder that causes long-term microvascular and macro-vascular complications, as well as the failure of various organ systems. Diabetes-related cardiovascular diseases (CVD) including heart failure cause significant morbidity and mortality worldwide. Concurrent hypertensive heart disease and/or coronary artery disease have been thought to be the causes of diabetic heart failure in DM patients. However, heart failure is extremely common in DM patients even in the absence of other risk factors such as coronary artery disease and hypertension. The occurrence of diabetes-induced heart failure has recently received a lot of attention. Understanding how diabetes increases the risk of heart failure and how it mediates major cellular and molecular alteration will aid in the development of therapeutics to prevent these changes. Hence, this review aimed to summarize the current knowledge and most recent findings in cellular and molecular mechanisms of diabetes-induced heart failure.

Ursolic Acid Enhances the Sensitivity of MCF-7 and MDA-MB-231 Cells to Epirubicin by Modulating the Autophagy Pathway

Breast cancer is the leading cause of cancer death among women in the world, and its morbidity and mortality are increasing year by year. Epirubicin (EPI) is a commonly used drug for the treatment of breast cancer but unfortunately can cause cardiac toxicity in patients because of dose accumulation. Therefore, there is an urgent need for new therapies to enhance the sensitivity of breast cancer cells to EPI. In this study, we found ursolic acid (UA) can significantly improve the drug sensitivity of human breast cancer MCF-7/MDA-MB-231 cells to EPI. Next, we observed that the co-treatment of UA and EPI can up-regulate the expression of autophagy-related proteins Beclin-1, LC3-II/LC3-I, Atg5, and Atg7, and decrease the expression levels of PI3K and AKT, which indicates that the potential mechanism should be carried out by the regulating class III PI3K(VPS34)/Beclin-1 pathway and PI3K/AKT/mTOR pathway. Furthermore, we found the autophagy inhibitor 3-methyladenine (3-MA) could significantly reverse the inhibitory effect of co-treatment of UA and EPI on MCF-7 and MDA-MB-231 cells. These findings indicate that UA can dramatically enhance the sensitivity of MCF-7 and MDA-MB-231 cells to EPI by modulating the autophagy pathway. Our study may provide a new therapeutic strategy for combination therapy.

Biomarkers of everolimus efficacy in breast cancer therapy

OBJECTIVE

Everolimus is an inhibitor of serine/ threonine kinase mTOR. The drug is approved for the treatment of metastatic ER positive, HER2 negative breast cancers and benefits a subset of patients with these breast cancers in combination with hormonal therapies. Despite extensive efforts, no additional predictive biomarkers to guide therapeutic decisions for everolimus have been introduced in clinical practice.

DATA SOURCES

This paper discusses predictive biomarkers for everolimus efficacy in breast cancer. A search of the medline and web of science databases was performed using the words "everolimus" and "biomarkers". References of retrieved articles were manually scanned for additional relevant articles.

DATA SUMMARY

Everolimus benefits a subset of patients with metastatic ER positive, HER2 negative breast cancers in combination with hormonal therapies. Despite extensive efforts no additional predictive biomarkers to guide therapeutic decisions for everolimus therapy have been confirmed for use in clinical practice. However, promising biomarker leads for everolimus efficacy in breast cancer have been suggested and include expression of proteins in the mTOR pathway in ER positive, HER2 negative breast cancers. In HER2 positive cancers PIK3CA mutations, and PTEN expression loss are prognostic. Other clinical predictive biomarkers with more limited data include characteristics derived from whole genome sequencing, subsets of circulating leukocytes and changes in Standardized Uptake Values (SUV) of Positron Emission Tomography (PET) scans.

CONCLUSIONS

Putative predictive biomarkers for everolimus efficacy in breast cancer patients, both genomic and clinical, deserve further study and could lead to a better selection of responsive patients.

Evaluation of Sertoli cell autophagy associated with laminin, fibronectin, and caspase-3 proteins' alteration, following testicular torsion rat

Autophagy is a vital process that maintains cellular homeostasis by joining lysosomes and providing energy production substrates. In testicular tissue, Sertoli cells play functional roles in spermatogenesis and steroidogenesis. It is well known that autophagy physiologically occurs in the Sertoli cells. Under pathological conditions, such as testicular torsion, autophagy can be activated under high-stress stimuli. It is worth noting that Sertoli cells receive autophagy-induced signals through some extracellular matrix proteins, e.g. laminin and fibronectin. The present study aims to evaluate Sertoli cells' autophagy-associated extracellular matrix proteins' alteration following testicular torsion in rat model. The animals were divided into two groups as sham and testicular torsion/detorsion groups. In the testicular torsion/detorsion group, testicular torsion was maintained for 6 hr, followed by detorsion for 14 days. The obtained results revealed that testicular torsion-induced oxidative stress leads to increased autophagy in Sertoli cells as well as the whole testicular tissue. Moreover, extracellular matrix proteins including laminin and fibronectin act as autophagy-regulating proteins, in which their expression levels are reduced and increased respectively. In addition, the level of caspase-3, as an autophagy inhibitory protein, did not increase significantly in the cytoplasm of Sertoli cells as opposed to whole testicular tissue, indicating that autophagy is active after testicular torsion in these cells.

Regulation of mitochondrial cargo-selective autophagy by posttranslational modifications

Mitochondria are important organelles in eukaryotes. Turnover and quality control of mitochondria are regulated at the transcriptional and posttranslational level by several cellular mechanisms. Removal of defective mitochondrial proteins is mediated by mitochondria resident proteases or by proteasomal degradation of individual proteins. Clearance of bulk mitochondria occurs via a selective form of autophagy termed mitophagy. In yeast and some developing metazoan cells (e.g., oocytes and reticulocytes), mitochondria are largely removed by ubiquitin-independent mechanisms. In such cases, the regulation of mitophagy is mediated via phosphorylation of mitochondria-anchored autophagy receptors. On the other hand, ubiquitin-dependent recruitment of cytosolic autophagy receptors occurs in situations of cellular stress or disease, where dysfunctional mitochondria would cause oxidative damage. In mammalian cells, a well-studied ubiquitin-dependent mitophagy pathway induced by mitochondrial depolarization is regulated by the mitochondrial protein kinase PINK1, which upon activation recruits the ubiquitin ligase parkin. Here, we review mechanisms of mitophagy with an emphasis on posttranslational modifications that regulate various mitophagy pathways. We describe the autophagy components involved with particular emphasis on posttranslational modifications. We detail the phosphorylations mediated by PINK1 and parkin-mediated ubiquitylations of mitochondrial proteins that can be modulated by deubiquitylating enzymes. We also discuss the role of accessory factors regulating mitochondrial fission/fusion and the interplay with pro- and antiapoptotic Bcl-2 family members. Comprehensive knowledge of the processes of mitophagy is essential for the understanding of vital mitochondrial turnover in health and disease.

Chemoprotective and chemosensitizing effects of apigenin on cancer therapy

Background

Therapeutic resistance to radiation and chemotherapy is one of the major obstacles in cancer treatment. Although synthetic radiosensitizers are pragmatic solution to enhance tumor sensitivity, they pose concerns of toxicity and non-specificity. In the last decades, scientists scrutinized novel plant-derived radiosensitizers and chemosensitizers, such as flavones, owing to their substantial physiological effects like low toxicity and non-mutagenic properties on the human cells. The combination therapy with apigenin is potential candidate in cancer therapeutics. This review explicates the combinatorial strategies involving apigenin to overcome drug resistance and boost the anti-cancer properties.

Methods

We selected full-text English papers on international databases like PubMed, Web of Science, Google Scholar, Scopus, and ScienceDirect from 1972 up to 2020. The keywords included in the search were: Apigenin, Chemoprotective, Chemosensitizing, Side Effects, and Molecular Mechanisms.

Results

In this review, we focused on combination therapy, particularly with apigenin augmenting the anti-cancer effects of chemo drugs on tumor cells, reduce their side effects, subdue drug resistance, and protect healthy cells. The reviewed research data implies that these co-therapies exhibited a synergistic effect on various cancer cells, where apigenin sensitized the chemo drug through different pathways including a significant reduction in overexpressed genes, AKT phosphorylation, NFκB, inhibition of Nrf2, overexpression of caspases, up-regulation of p53 and MAPK, compared to the monotherapies. Meanwhile, contrary to the chemo drugs alone, combined treatments significantly induced apoptosis in the treated cells.

Conclusion

Briefly, our analysis proposed that the combination therapies with apigenin could suppress the unwanted toxicity of chemotherapeutic agents. It is believed that these expedient results may pave the path for the development of drugs with a high therapeutic index. Nevertheless, human clinical trials are a prerequisite to consider the potential use of apigenin in the prevention and treatment of various cancers. Conclusively, the clinical trials to comprehend the role of apigenin as a chemoprotective agent are still in infancy.

Graphical Abstract

Insights into the Interaction of Lysosomal Amino Acid Transporters SLC38A9 and SLC36A1 Involved in mTORC1 Signaling in C2C12 Cells

Amino acids are critical for mammalian target of rapamycin complex 1 (mTORC1) activation on the lysosomal surface. Amino acid transporters SLC38A9 and SLC36A1 are the members of the lysosomal amino acid sensing machinery that activates mTORC1. The current study aims to clarify the interaction of SLC38A9 and SLC36A1. Here, we discovered that leucine increased expressions of SLC38A9 and SLC36A1, leading to mTORC1 activation. SLC38A9 interacted with SLC36A1 and they enhanced each other's expression levels and locations on the lysosomal surface. Additionally, the interacting proteins of SLC38A9 in C2C12 cells were identified to participate in amino acid sensing mechanism, mTORC1 signaling pathway, and protein synthesis, which provided a resource for future investigations of skeletal muscle mass.

γ-Linolenic Acid Prevents Lipid Metabolism Disorder in Palmitic Acid-Treated Alpha Mouse Liver-12 Cells by Balancing Autophagy and Apoptosis via the LKB1-AMPK-mTOR Pathway

Excessive fat deposition is the main character in nonalcoholic fatty liver disease (NAFLD), while γ-linolenic acid (GLA) is a polyunsaturated fatty acid that can reduce lipid deposition. This study investigated the effect and regulatory mechanism of GLA (100 μM) on lipid metabolism in alpha mouse liver 12 (AML-12) cells treated by 400 μM palmitic acid (PA). GLA reduced lipid content and increased fatty acid β oxidation, as indicated by decreasing triglyceride and cholesterol contents and increasing mRNA and protein expressions of CPT1α and PPARα. GLA relieved oxidative stress caused by PA, upregulated mRNA levels of superoxide dismutase and glutathione peroxidase, and decreased reactive oxygen species content. GLA reduced apoptosis, as indicated by decreases in the BAX/BCL2 expression level and apoptosis percentage. GLA activated autophagy, autophagosome-lysosome fusion, and LKB1-AMPK-mTOR signaling and upregulated mRNA and protein expressions of Beclin-1, autophagy-related 5, and liver kinase B1 (LKB1). These effects of GLA on lipid metabolism disorders of PA-treated hepatocytes were reversed by autophagy inhibitor 3MA and AMPK inhibitor compound C, confirming our conclusions. Overall, GLA can protect AML-12 cells from lipid metabolism disorder caused by PA via balancing autophagy and apoptosis mediated by the LKB1-AMPK-mTOR pathway. Consequently, GLA, as a dietary supplement, can help to prevent and treat NAFLD by regulating lipid metabolism and autophagy.

By restoring autophagic flux and improving mitochondrial function, corosolic acid protects against Dox-induced cardiotoxicity

Despite effective anticancer effects, the use of doxorubicin (Dox) is limited due to its side effects as cardiotoxicity. Corosolic acid (CRA) is a pentacyclic triterpene acid isolated from Lagerstroemia speciosa L. (Banaba) leaves, and it has also been shown to improve myocardial hypertrophy and myocardial infarction which expected to be used in clinical pharmaceuticals. The purpose of this study was to explore whether CRA can improve myocardial injury caused by Dox and to clarify potential mechanisms. C57 BL/6J mice and AMPKα2 knockout mice were given a single intraperitoneal (i.p.) injection of Dox (5 mg/kg) every week for 4 weeks, while normal saline (NS) was used as control. Mice were given CRA (10 mg/kg or 20 mg/kg) or equal volumes of normal saline daily after the first time i.p. injection of Dox. After 4 weeks, echocardiography, gravimetric, hemodynamic, histological, and biochemical analyses were conducted. After Dox injury, compared with the control group, CRA increased the survival rate of mice, improved the cardiac function, decreased the oxidative stress, and reduced the apoptosis. CRA may function by promoting transcription factor EB (TFEB) nuclear translocation and thus restoring autophagic flux. We also observed that CRA protected mitochondrial structure and function, which may benefit from oxidative stress reduction or TFEB activation. In vitro, the protective effect of CRA is reversed by TFEB deletion. Then, we evaluated the expression of AMPKα2/mTOR C1 signaling pathway, the main pathway of TFEB activation. In vivo and in vitro, CRA promoted TFEB nuclear translocation by activating AMPKα2/mTOR C1 signaling, while ablating AMPKα2 reversed these results and accompanied with a decrease in the ability of CRA to resist Dox-induced cardiotoxicity. Thus, we suggested that CRA activated TFEB in an AMPKα2-dependent manner to protect against Dox cardiotoxicity. This study confirms the role and mechanism of CRA in the treatment of Dox-induced cardiac injury. Dox-induced damage to autophagy includes autophagosomes maturation disorders and autophagolysosomes acidification defects, CRA restored autophagic flux, and promoted lysosomal degradation by activating TFEB in an AMPKα2-depended manner, stabilized mitochondrial function, ultimately protected against Dox-induced cardiotoxicity.

Autophagosome Trafficking

Autophagy is a major intracellular degradation/recycling system that ubiquitously exists in eukaryotic cells. Autophagy contributes to the turnover of cellular components through engulfing portions of the cytoplasm or organelles and delivering them to the lysosomes/vacuole to be degraded. The trafficking of autophagosomes and their fusion with lysosomes are important steps that complete their maturation and degradation. In cells such as neuron, autophagosomes traffic long distances along the axon, while in other specialized cells such as cardiomyocytes, it is unclear how and even whether autophagosomes are transported. Therefore, it is important to learn more about the processes and mechanisms of autophagosome trafficking to lysosomes/vacuole during autophagy. The mechanisms of autophagosome trafficking are similar to those of other organelles trafficking within cells. The machinery mainly includes cytoskeletal systems such as actin and microtubules, motor proteins such as myosins and the dynein-dynactin complex, and other proteins like LC3 on the membrane of autophagosomes. Factors regulating autophagosome trafficking have not been widely studied. To date the main reagents identified for disrupting autophagosome trafficking include: 1. Microtubule polymerization reagents, which disrupt microtubules by interfering with microtubule dynamics, thus directly influence microtubule-dependent autophagosome trafficking 2. F-actin-depolymerizing drugs, which inhibit autophagosome formation, and also subsequently inhibit autophagosome trafficking 3. Motor protein regulators, which directly affect autophagosome trafficking.

ROS and metabolomics-mediated autophagy in rat's testicular tissue alter after exercise training; Evidence for exercise intensity and outcomes

AIMS

Oxidative damage and altered metabolic reactions are suspected to initiate the autophagy. The exercise training significantly impacts testicular antioxidant and metabolic potentials. However, the underlying mechanism(s) that the exercise-induced alterations can affect the autophagy markers remained unknown. This study explored the effect of exercise training on antioxidant and metabolic statuses of testicular tissue and uncovered the possible cross-link between these statuses and autophagy-inducers expression.

MAIN METHODS

Wistar rats were divided into sedentary control, low (LICT), moderate (MICT), and high (HICT) intensity continuous training groups. Following 8 weeks of training, the testicular total antioxidant capacity (TAC), total oxidant status (TOS), glutathione (GSH), and NADP⁺/NADPH as oxidative biomarkers along with intracytoplasmic carbohydrate and lipid droplet patterns, lactate dehydrogenase (LDH) activity, and lactate as metabolic elements were assessed. Finally, the autophagy-inducers expression and sperm count were examined.

KEY FINDINGS

With no significant impact on the oxidative biomarkers and metabolic elements, the LICT and MICT groups exhibited statistically unremarkable (p < 0.05) impacts on spermatogenesis differentiation, spermiogenesis ratio, and sperm count while increased the autophagy-inducers expression. Reversely, the HICT group, simultaneous with suppressing the antioxidant biomarkers (TAC↓, GSH↓, TOS↑, NADP⁺/NADPH↑), significantly (p < 0.05) reduced the testicular LDH activity and lactate level, changed the intracytoplasmic carbohydrate and lipid droplet's pattern, and amplified the classical autophagy-inducers p62, Beclin-1, autophagy-related gene (ATG)-7, and light chain 3 (LC3)-II/I expression.

SIGNIFICANCE

The autophagy-inducers overexpression has occurred after HICT induction, most probably to eliminate the oxidative damage cargoes, while increased to maintain the metabolic homeostasis in the LICT and MICT groups.

Targeting autophagy to modulate hepatic ischemia/reperfusion injury: A comparative study between octreotide and melatonin as autophagy modulators through AMPK/PI3K/AKT/mTOR/ULK1 and Keap1/Nrf2 signaling pathways in rats

Hepatic ischemia-reperfusion (HIR) injury is a common pathophysiological process in many clinical settings. This study was designed to compare the protective role of octreotide (somatostatin analogue, OCT) and melatonin (N-acetyl-5-methoxytryptamine, MLT) through the modulation of autophagy against HIR injury in rats. Male albino rats were divided into sham, HIR, OCT at three doses (50, 75, and 100 μg/kg), MLT, MLT + OCT75, compound C (AMPK inhibitor, CC), and CC + OCT75 groups. Ischemia was induced for 30 min followed by 24 h reperfusion. Biochemical, histopathological, immunohistochemical, lipid peroxidation, ELISA, qPCR, and western blot techniques were performed in our study. Liver autophagy was restored by OCT at doses (50 or 75 μg/kg) as indicated by elevating the expressions of Beclin-1, ATG7, and LC3 accompanied by the reduction of p62 expression through induction of AMPK/S317-ULK1 and inhibition of PI3K/AKT/mTOR/S757-ULK1 signaling pathways. As well, OCT maintained the integrity of the Keap1-Nrf2 system for the normal hepatic functions via controlling the Keap1 turnover through autophagy in a p62-dependent manner, resulting in upholding a series of anti-oxidant and anti-inflammatory cascades. These effects were abolished by compound C. On the other hand, MLT showed a decrease in the autophagy markers via inhibiting AMPK/pS317-ULK1 and activating PI3K/AKT/mTOR/pS757-ULK1 pathways. Autophagy inhibition with MLT markedly reversed the hepatoprotective effects of OCT75 after HIR injury. Finally, our results proved for the first time that OCT75 was more effective than MLT as it was sufficient to induce protective autophagy in our HIR model, which led to the induction of Nrf2-dependent AMPK/autophagy pathways.

Quercetin Covalently Linked Lipid Nanoparticles: Multifaceted Killing Effect on Tumor Cells

The encapsulation of hydrophobic drugs is a problem that many researchers are working on. The goal of this study is to achieve the delivery of hydrophobic drugs by means of prodrugs and nanoformulations for a stronger tumor cell-killing effect and explore related killing mechanisms. Lipophilic quercetin (Qu) was covalently linked to glyceryl caprylate-caprate (Gcc) via disulfide bonds-containing 3,3'-dithiodipropionic acid (DTPA) to synthesize novel lipid Qu-SS-Gcc. Qu-SS-Gcc lipid nanoparticles (Qu-SS-Gcc LNPs) were fabricated using the solvent diffusion technique. The intracellular release of Qu by cleavage of nanocarriers was determined by liquid chromatography and compared with the uptake of free Qu. Detection methods, such as fluorescent quantitation, flow cytometry, and western blot were applied to explore the action mechanism induced by Qu. It was revealed that Qu-SS-Gcc LNPs could be cleaved by the high concentrations of reduction molecules in MCF-7/ADR (human multidrug-resistant breast cancer) cells, followed by the release of Qu. The intracellular Qu content produced by dissociation of Qu-SS-Gcc LNPs was higher than that produced by internalization of free Qu. The resulting release of Qu exerted superior cell-killing effects on MCF-7/ADR cells, such as P-gp inhibition by binding to P-gp binding sites, blocking the cell cycle in the G2 phase, and causing cell apoptosis and autophagy. Moreover, it was revealed autophagy triggered by a low concentration of Qu-SS-Gcc LNPs was beneficial to cell survival, while at a higher concentration, it acted as a cell killer. Qu-SS-Gcc LNPs can realize massive accumulation of Qu in tumor cells and exert a multifaceted killing effect on tumor cells, which is a reference for the delivery of hydrophobic drugs.

Low-Dose Berberine Attenuates the Anti-Breast Cancer Activity of Chemotherapeutic Agents via Induction of Autophagy and Antioxidation

Berberine (BBR), a major active component of Rhizoma coptidis, is one of the most promising agents for breast cancer adjuvant therapy. It is well accepted that BBR could exhibit remarkable anticancer efficacy with few side effects, and when treated with chemotherapeutic agents in combination, BBR could enhance the chemosensitivity of cancer cells. Our previous study reported that low-dose BBR (LDB) induced hormetic effect and attenuated the anticancer activity of chemotherapeutic agents. However, the underlying mechanisms are still unclear. In this study, we confirmed that LDB could promote cancer cell proliferation and antagonize the anti-breast cancer activities of chemotherapeutic agents. And the mechanisms were proved to be induction of autophagy and antioxidation by LDB. Our results showed that LDB could mildly induce reactive oxygen species, raise the level of autophagy by promoting the phosphorylation of adenosine monophosphate-activated protein kinase, and promote antioxidant enzymes expression through activating nuclear factor erythroid 2-related factor 2 in breast cancer cells. These findings revealed a potential negative impact of BBR on its adjuvant anti-breast cancer therapy, providing guidance for a safe and effective use of naturally originated medicines in the clinic.

Hypoglycemic effects of polysaccharides from Gomphidiaceae rutilus fruiting bodies and their mechanisms

Insulin resistance is the main cause of type 2 diabetes, fatty liver and obesity. Our previous study found that mushroom polysaccharides improved insulin resistance in vitro, but the underlying mechanisms were still unknown. Thus, we investigate the hypoglycemic effects of polysaccharides from Gomphidiaceae rutilus fruiting bodies and their mechanisms. The total polysaccharides (AGRP) from Gomphidiaceae rutilus fruiting bodies and the neutral polysaccharide (AGRP-N) fraction both enhance insulin-stimulated glucose uptake in an autophagy-dependent manner in high glucose and fatty acid-treated hepatic cells, but not the acidic polysaccharide (AGRP-A) fraction. Further, we elucidate the oral hypoglycemic effects of polysaccharides on ob/ob mice. AGRP and AGRP-N lower blood glucose and improve insulin sensitivity. They inhibit liver lipid deposition, not only by activating AMPK to increase autophagy but also by increasing the expressions of PPARα and CPT-1a to enhance lipolysis. Our results provide a basis for the development of polysaccharides from Gomphidiaceae rutilus as a hypoglycemic healthy food.

Regular Aerobic Exercise-Alleviated Dysregulation of CAMKIIα Carbonylation to Mitigate Parkinsonism via Homeostasis of Apoptosis With Autophagy

This study investigated carbonylation of proteins with oxidative modification profiling in the striatum of aging and Parkinson disease (PD) rats, as well as the long-term effects of regular aerobic exercise on the carbonylation process and the damaging effects of PD vs habitual sedentary behavior. Regular aerobic exercise improved the PD rats' rotational behavior, increased tyrosine hydroxylase expression in both the striatum and substantia nigra pars compacta, and decreased α-synuclein expression significantly. Interestingly, apoptotic nuclei and autophagosomes were increased in the aerobic exercise PD rat striatum. Carbonylated protein Ca2+/calmodulin-dependent protein kinase alpha (CAMKIIα) was present in the middle-aged and aged groups but only in the sedentary, not the exercise, PD rat striatum. Notably, CAMKIIα was characterized by a 4-hydroxynonenal adduct. Regular aerobic exercise upregulated CAMKIIα expression level, activated the CAMK signaling pathway, and promoted the expression of autophagy markers Beclin1 and microtubule-associated proteins 1 A/1B light chain 3II. Aberrant carbonylation of CAMKII initiated age-related changes and might be useful as a potential biomarker of PD. Regular aerobic exercise alleviated protein carbonylation modification of CAMKIIα and regulated the CAMK signaling pathway, thereby affecting and regulating the homeostasis of apoptosis and autophagy in the striatum to alleviate the neurodegenerative process of PD lesions.

Citrate pretreatment attenuates hypoxia/reoxygenation-induced cardiomyocyte injury via regulating microRNA-142-3p/Rac1 aix

Purpose: Citrate has a positive effect on improving the pathophysiological changes of cardiomyocytes such as cardiac failure and auricular fibrillation. However, the underlying mechanism remains still unclear.Methods: Rat cardiomyocytes were used to establish hypoxia/reoxygenation (H/R) cell model. Citrate was conduct to pretreat with cardiomyocytes, and microRNA-142-3p (miR-142-3p) knockdown and overexpression were used to determine the underlying mechanism of their functions in cardiomyocytes. Cell viability and apoptosis were respectively detected by CCK-8 and flow cytometry. Protein and mRNA levels were determined by Western blot and qRT-PCR. Luciferase reporter assay and Targetscan were performed to study the regulation of miR-142-3p and Rac1.Results: The level of miR-142-3p was down-regulated in H/R model, but up-regulated in cardiomyocytes following citrate treatment. Citrates attenuated H/R injury induced miR-142-3p level and cell viability, and also inhibited H/R injury induced apoptosis, LDH, MDA and autophagy. Cell viability was improved, and autophagy was suppressed by miR-142-3p mimic, while inhibitor had opposite results. Compared with H/R + miR-142-3p inhibitor group, cell viability was higher, and apoptosis and autophagy were lower in Cit + H/R + miR-142-3p inhibitor group. Furthermore, Rac1 was target gene of miR-142-3p, and decreased by citrate, in comparison with H/R + miR-142-3p inhibitor group.Conclusion: Taken together, our findings indicated that citrate ameliorates H/R injury-induced cardiomyocytes autophagy by regulating miR-142-3p/Rac1 aix.

A global view of the miRNA-mitophagy connexion

Mitochondria are highly dynamics organelles that provide the necessary energy for cellular functions. However, when they are dysfunctional, they can, by contrast, be very harmful for the cell. Mitophagy ensures their recycling and preserves cell performance. This mechanism is particularly important in neurons because they use a lot of energy. Failed mitophagy can thus affect the development of neurons and lead to brain problems. In this regard, a tight regulation of this process is needed. In recent years microRNAs, as regulators of several biological processes, have attracted attention in the field of mitophagy. In this review, we focused on the studies that highlight the miRNAs implicated in the regulation of mitophagic pathways. In particular, we described the first study carried out 7 years ago, in the context of mitophagy during erythroid differentiation. Next, we have cited all the other works to date on microRNAs and mitophagy regulation. Finally, we have underlined the importance of these discoveries in order to define new therapeutic approaches in the context of age-related diseases involving mitochondrial dysfunctions, such as cancers and neurodegenerative diseases.

The roles of apoptosis, autophagy and unfolded protein response in arbovirus, influenza virus, and HIV infections

Virus infection induces different cellular responses in infected cells. These include cellular stress responses like autophagy and unfolded protein response (UPR). Both autophagy and UPR are connected to programed cell death I (apoptosis) in chronic stress conditions to regulate cellular homeostasis via Bcl2 family proteins, CHOP and Beclin-1. In this review article we first briefly discuss arboviruses, influenza virus, and HIV and then describe the concepts of apoptosis, autophagy, and UPR. Finally, we focus upon how apoptosis, autophagy, and UPR are involved in the regulation of cellular responses to arboviruses, influenza virus and HIV infections.

Abbreviation: AIDS: Acquired Immunodeficiency Syndrome; ATF6: Activating Transcription Factor 6; ATG6: Autophagy-specific Gene 6; BAG3: BCL Associated Athanogene 3; Bak: BCL-2-Anatagonist/Killer1; Bax; BCL-2: Associated X protein; Bcl-2: B cell Lymphoma 2x; BiP: Chaperon immunoglobulin heavy chain binding Protein; CARD: Caspase Recruitment Domain; cART: combination Antiretroviral Therapy; CCR5: C-C Chemokine Receptor type 5; CD4: Cluster of Differentiation 4; CHOP: C/EBP homologous protein; CXCR4: C-X-C Chemokine Receptor Type 4; Cyto c: Cytochrome C; DCs: Dendritic Cells; EDEM1: ER-degradation enhancing-a-mannosidase-like protein 1; ENV: Envelope; ER: Endoplasmic Reticulum; FasR: Fas Receptor;G2: Gap 2; G2/M: Gap2/Mitosis; GFAP: Glial Fibrillary Acidic Protein; GP120: Glycoprotein120; GP41: Glycoprotein41; HAND: HIV Associated Neurodegenerative Disease; HEK: Human Embryonic Kidney; HeLa: Human Cervical Epithelial Carcinoma; HIV: Human Immunodeficiency Virus; IPS-1: IFN-β promoter stimulator 1; IRE-1: Inositol Requiring Enzyme 1; IRGM: Immunity Related GTPase Family M protein; LAMP2A: Lysosome Associated Membrane Protein 2A; LC3: Microtubule Associated Light Chain 3; MDA5: Melanoma Differentiation Associated gene 5; MEF: Mouse Embryonic Fibroblast; MMP: Mitochondrial Membrane Permeabilization; Nef: Negative Regulatory Factor; OASIS: Old Astrocyte Specifically Induced Substrate; PAMP: Pathogen-Associated Molecular Pattern; PERK: Pancreatic Endoplasmic Reticulum Kinase; PRR: Pattern Recognition Receptor; Puma: P53 Upregulated Modulator of Apoptosis; RIG-I: Retinoic acid-Inducible Gene-I; Tat: Transactivator Protein of HIV; TLR: Toll-like receptor; ULK1: Unc51 Like Autophagy Activating Kinase 1; UPR: Unfolded Protein Response; Vpr: Viral Protein Regulatory; XBP1: X-Box Binding Protein 1

Dexmedetomidine Alleviated Endoplasmic Reticulum Stress via Inducing ER-phagy in the Spinal Cord of Neuropathic Pain Model

Studies demonstrated that spinal autophagy was impaired in spinal nerve ligation (SNL) rats. However, the relationship of endoplasmic reticulum (ER) stress and ER-phagy and whether dexmedetomidine (DEX) modulates ER-phagy remain unclear. In this study, male Sprague-Dawley (SD) rats and the SNL animal model were used. 4-Phenylbutyric acid (4-PBA), tunicamycin (TM), rapamycin (RAP), and 3-methyladenine (3-MA) were intrathecally administered, respectively to demonstrate the relationship of ER stress and ER-phagy. Dexmedetomidine (30 μg/kg) was administered as treatment. Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) tests were performed to evaluate nociceptive hypersensitivity. Protein expressions were examined by Western blot, and the location of glucose-regulated protein 78 (Grp78) was examined by immunofluorescence staining. SNL induced ER stress and ER-phagy impairment. ER stress was altered in rostral ventromedial medulla (RVM); 4-phenylbutyric acid induced analgesic effect via inhibiting ER stress and unfolded protein response (UPR) pathways to induce ER-phagy; tunicamycin led to worsening pain through enhancing ER stress and UPR pathways to further impair ER-phagy. Rapamycin provided analgesic effect through enhancing ER-phagy to relieve SNL-induced ER stress and UPR pathway activation; 3-methyladenine deteriorated pain via further impairing ER-phagy to aggravate ER stress. Dexmedetomidine provided analgesic effect through elevating ER-phagy. In conclusion, ER stress led to ER-phagy impairment in the spinal cord of SNL rats and participated in the nociceptive descending system. ER-phagy impairment was both a trigger and an effector of ER stress via UPR pathways in SNL rats. Dexmedetomidine targeted ER-phagy to provide analgesic effect.

AMPK-dependent activation of the Cyclin Y/CDK16 complex controls autophagy

The AMP-activated protein kinase (AMPK) is a master sensor of the cellular energy status that is crucial for the adaptive response to limited energy availability. AMPK is implicated in the regulation of many cellular processes, including autophagy. However, the precise mechanisms by which AMPK controls these processes and the identities of relevant substrates are not fully understood. Using protein microarrays, we identify Cyclin Y as an AMPK substrate that is phosphorylated at Serine 326 (S326) both in vitro and in cells. Phosphorylation of Cyclin Y at S326 promotes its interaction with the Cyclin-dependent kinase 16 (CDK16), thereby stimulating its catalytic activity. When expressed in cells, Cyclin Y/CDK16 is sufficient to promote autophagy. Moreover, Cyclin Y/CDK16 is necessary for efficient AMPK-dependent activation of autophagy. This functional interaction is mediated by AMPK phosphorylating S326 of Cyclin Y. Collectively, we define Cyclin Y/CDK16 as downstream effector of AMPK for inducing autophagy.

Crosstalks of GSK3 signaling with the mTOR network and effects on targeted therapy of cancer

The introduction of therapeutics targeting specific tumor-promoting oncogenic or non-oncogenic signaling pathways has revolutionized cancer treatment. Mechanistic (previously mammalian) target of rapamycin (mTOR), a highly conserved Ser/Thr kinase, is a central hub of the phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR network, one of the most frequently deregulated signaling pathways in cancer, that makes it an attractive target for therapy. Numerous mTOR inhibitors have progressed to clinical trials and two of them have been officially approved as anticancer therapeutics. However, mTOR-targeting drugs have met with a very limited success in cancer patients. Frequently, the primary impediment to a successful targeted therapy in cancer is drug-resistance, either from the very beginning of the therapy (innate resistance) or after an initial response and upon repeated drug treatment (evasive or acquired resistance). Drug-resistance leads to treatment failure and relapse/progression of the disease. Resistance to mTOR inhibitors depends, among other reasons, on activation/deactivation of several signaling pathways, included those regulated by glycogen synthase kinase-3 (GSK3), a protein that targets a vast number of substrates in its repertoire, thereby orchestrating many processes that include cell proliferation and survival, metabolism, differentiation, and stemness. A detailed knowledge of the rewiring of signaling pathways triggered by exposure to mTOR inhibitors is critical to our understanding of the consequences such perturbations cause in tumors, including the emergence of drug-resistant cells. Here, we provide the reader with an updated overview of intricate circuitries that connect mTOR and GSK3 and we relate them to the efficacy (or lack of efficacy) of mTOR inhibitors in cancer cells.

MicroRNA-Based Combinatorial Cancer Therapy: Effects of MicroRNAs on the Efficacy of Anti-Cancer Therapies

The susceptibility of cancer cells to different types of treatments can be restricted by intrinsic and acquired therapeutic resistance, leading to the failure of cancer regression and remission. To overcome this problem, a combination therapy has been proposed as a fundamental strategy to improve therapeutic responses; however, resistance is still unavoidable. MicroRNA (miRNAs) are associated with cancer therapeutic resistance. The modulation of dysregulated miRNA levels through miRNA-based therapy comprising a replacement or inhibition approach has been proposed to sensitize cancer cells to other anti-cancer therapies. The combination of miRNA-based therapy with other anti-cancer therapies (miRNA-based combinatorial cancer therapy) is attractive, due to the ability of miRNAs to target multiple genes associated with the signaling pathways controlling therapeutic resistance. In this article, we present an overview of recent findings on the role of therapeutic resistance-related miRNAs in different types of cancer. We review the feasibility of utilizing dysregulated miRNAs in cancer cells and extracellular vesicles as potential candidates for miRNA-based combinatorial cancer therapy. We also discuss innate properties of miRNAs that need to be considered for more effective combinatorial cancer therapy.

Rasal2 suppresses breast cancer cell proliferation modulated by secretory autophagy

Rasal2, a Ras-GTPase-activating protein (RasGAP), is a tumor suppressor in Luminal B breast cancer, frequently metastatic and recurrent. Exosomes (Exos) are small membrane vesicles secreted by various cell types, including tumor cells, recognized as vehicles for cell-to-cell communication. Our study aimed to investigate whether Rasal2 regulates breast cancer cell growth via affecting this process. In this paper, we described that Rasal2 knockout (KO) in MCF-7 cells enhanced exosomal release and increased autophagy-related proteins in exosomal fraction, while attenuated by exosome release inhibitor GW4869. Moreover, MCF-7 cells with chloroquine (CQ) treatment boosted Rasal2 KO-induced secretory autophagy. In addition, we presented that exosomes derived from KO MCF-7 cells (KO-exo) significantly promoted breast cancer cell proliferation compared to those from MCF-7 cells transfected with an empty crispr-cas9 plasmid serving as controls (sgNT-exo); however, exosomes purified from KO MCF-7 cells co-cultured with 3-methyladenine ((3-MA + KO)-exo)/CQ ((CQ + KO)-exo) dramatically inhibited/facilitated MCF-7 cell proliferation in contrast to KO-exo group, separately. In conclusion, our findings revealed a new mechanism of Rasal2 in the regulation of breast cancer cell proliferation via autophagy-exo-mediated pathway.

Estrogen inhibits autophagy and promotes growth of endometrial cancer by promoting glutamine metabolism

Background

Excessive estrogen exposure is an important pathogenic factor in uterine endometrial cancer (UEC). Recent studies have reported the metabolic properties can influence the progression of UEC. However, the underlying mechanisms have not been fully elucidated.

Methods

Glutaminase (GLS), MYC and autophagy levels were detected. The biological functions of estrogen-MYC-GLS in UEC cells (UECC) were investigated both in vivo and in vitro.

Results

Our study showed that estrogen remarkably increased GLS level through up-regulating c-Myc, and enhanced glutamine (Gln) metabolism in estrogen-sensitive UEC cell (UECC), whereas fulvestrant (an ER inhibitor antagonist) could reverse these effects. Estrogen remarkably promoted cell viability and inhibited autophagy of estrogen sensitive UECC. However, CB-839, a potent selective oral bioavailable inhibitor of both splice variants of GLS, negatively regulated Gln metabolism, and inhibited the effects of Gln and estrogen on UECC’s growth and autophagy in vitro and / or in vivo.

Conclusions

CB-839 triggers autophagy and restricts growth of UEC by suppressing ER/Gln metabolism, which provides new insights into the potential value of CB-839 in clinical treatment of estrogen-related UEC.

Proteomic Profile of Carbonylated Proteins Screen the Regulation of Calmodulin-Dependent Protein Kinases-AMPK-Beclin1 in Aerobic Exercise-Induced Autophagy in Middle-Aged Rat Hippocampus

BACKGROUND

Carbonylation is an oxidative modification of the proteins and a marker of oxidative stress. The accumulation of toxic carbonylated proteins might be one of the onsets of pathogenesis in hippocampal aging or neurodegeneration. Enormous evidence indicates that regular aerobic exercise might alleviate the dysfunction of carbonylated proteins, but the adaptational mechanisms in response to exercise are unclear.

OBJECTIVE

This study explored the carbonyl stress mechanism in the hippocampus using proteomics and the role of calmodulin-dependent protein kinases (CAMK)-AMP-activated protein kinase (AMPK)-Beclin1 signaling pathways in alleviating aging or improving function with regular aerobic exercise.

METHODS

Twenty-four healthy 13-month-old male Sprague-Dawley rats (average 693.21 ± 68.85 g) were randomly divided into middle-aged sedentary control group (M-SED, n = 12) and middle-aged aerobic exercise runner group (M-EX, n = 12). The M-EX group participated in regular aerobic exercise - treadmill running - with exercise intensity increasing gradually from 50-55% to 65-70% of maximum oxygen consumption (V˙O2max) over 10 weeks. The targeted proteins of oxidative modification were profiled by avidin magnetic beads and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q-TOF-MS). Western blots were used to test for molecular targets.

RESULTS

Regular aerobic exercise restores the intersessional habituation and rescues the hippocampus morphological structure in middle-aged rats. -ESI-Q-TOF-MS screened 56 carbonylated proteins only found in M-SED and 16 carbonylated proteins only found in M-EX, indicating aerobic exercise decreased carbonyl stress. Intriguingly, Ca2+/CAMK II alpha (CAMKIIα) was carbonylated only in the M-SED group at the oxidative modification site of 4-hydroxynonenal adducts, while regular aerobic exercise alleviated CAMKIIα carbonylation. Regular aerobic exercise significantly increased the expression and phosphorylated, active levels of CAMKIIα and AMPKα1. It also upregulated the expression of Beclin1 and microtubule-associated protein1-light chain 3 in the hippocampus.

CONCLUSION

Quantification of CAMKIIα carbonylation may be a potential biomarker of the hippocampal senescence. Additionally, regular aerobic exercise-induced autophagy via the activation of CAMK-AMPK-Beclin1 signaling pathway may mitigate the hippocampal neurodegeneration or pathological changes by alleviating protein carbonylation (carbonyl stress).

Sarcopenia targeting with autophagy mechanism by exercise

The loss of skeletal muscle, called sarcopenia, is an inevitable event during the aging process, and significantly impacts quality of life. Autophagy is known to reduce muscle atrophy caused by dysfunctional organelles, even though the molecular mechanism remains unclear. Here, we have discuss the current understanding of exercise-induced autophagy activation in skeletal muscle regeneration and remodeling, leading to sarcopenia intervention. With aging, dysregulation of autophagy flux inhibits lysosomal storage processes involved in muscle biogenesis. AMPK-ULK1 and the FoxO/PGC-1α signaling pathways play a critical role in the induction of autophagy machinery in skeletal muscle, thus these pathways could be targets for therapeutics development. Autophagy has been also shown to be a critical regulator of stem cell fate, which determines satellite cell differentiation into muscle fiber, thereby increasing muscle mass. This review aims to provide a comprehensive understanding of the physiological role of autophagy in skeletal muscle aging and sarcopenia.

Autophagy in pulmonary hypertension: Emerging roles and therapeutic implications

Autophagy is an important mechanism for cellular self-digestion and basal homeostasis. This gene- and modulator-regulated pathway is conserved in cells. Recently, several studies have shown that autophagic dysfunction is associated with pulmonary hypertension (PH). However, the relationship between autophagy and PH remains controversial. In this review, we mainly introduce the effects of autophagy-related genes and some regulatory molecules on PH and the relationship between autophagy and PH under the conditions of hypoxia, monocrotaline injection, thromboembolic stress, oxidative stress, and other drugs and toxins. The effects of other autophagy-related drugs, such as chloroquine, 3-methyladenine, rapamycin, and other potential therapeutic drugs and targets, in PH are also described.

Autophagy: Supporting cellular and organismal homeostasis by self-eating

Autophagy is a conserved catabolic process that delivers cytoplasmic components and organelles to lysosomes for degradation and recycling. This pathway serves to degrade nonfunctional organelles and aggregate-prone proteins, as well as to produce substrates for energy production and biosynthesis. Autophagy is especially important for the maintenance of stem cells, and for the survival and homeostasis of post-mitotic cells like neurons. Functional autophagy promotes longevity in several model organisms. Autophagy regulates immunity and inflammation at several levels and has both anti- and pro-tumorigenic roles in cancer. This review provides a concise overview of autophagy and its importance in cellular and organismal homeostasis, with emphasis on aging, stem cells, neuronal cells, immunity, inflammation, and cancer.

Advances in understanding the mechanisms of evasive and innate resistance to mTOR inhibition in cancer cells

The development of drug-resistance by neoplastic cells is recognized as a major cause of targeted therapy failure and disease progression. The mechanistic (previously mammalian) target of rapamycin (mTOR) is a highly conserved Ser/Thr kinase that acts as the catalytic subunit of two structurally and functionally distinct large multiprotein complexes, referred to as mTOR complex 1 (mTORC1) and mTORC2. Both mTORC1 and mTORC2 play key roles in a variety of healthy cell types/tissues by regulating physiological anabolic and catabolic processes in response to external cues. However, a body of evidence identified aberrant activation of mTOR signaling as a common event in many human tumors. Therefore, mTOR is an attractive target for therapeutic targeting in cancer and this fact has driven the development of numerous mTOR inhibitors, several of which have progressed to clinical trials. Nevertheless, mTOR inhibitors have met with a very limited success as anticancer therapeutics. Among other reasons, this failure was initially ascribed to the activation of several compensatory signaling pathways that dampen the efficacy of mTOR inhibitors. The discovery of these regulatory feedback mechanisms greatly contributed to a better understanding of cancer cell resistance to mTOR targeting agents. However, over the last few years, other mechanisms of resistance have emerged, including epigenetic alterations, compensatory metabolism rewiring and the occurrence of mTOR mutations. In this article, we provide the reader with an updated overview of the mechanisms that could explain resistance of cancer cells to the various classes of mTOR inhibitors.

Dexmedetomidine restores autophagy and cardiac dysfunction in rats with streptozotocin-induced diabetes mellitus

AIMS

Dexmedetomidine (DEX), a highly selective and potent α2-adrenergic receptor agonist, has anti-apoptotic, anti-inflammatory, and anti-oxidative stress effects in diabetes mellitus (DM) rats. The underlying molecular mechanisms and signaling pathways of diabetic cardiomyopathy remain poorly understood. This study aimed to elucidate the effect of DEX on cardiac function in DM rats.

METHODS

Eight-week-old male Sprague Dawley rats were divided into three groups: control (n = 5), diabetes (DM, n = 7), and diabetes + DEX (DM + DEX, n = 10). DM was induced via intraperitoneal injection of streptozotocin (70 mg/kg); at 3 days later, DEX (1 µg/kg/h) was administered for 4 weeks. Cardiac function was evaluated using pressure-volume loop analysis and echocardiography. Left ventricular (LV) histological sections were used to analyze the interstitial collagen fraction. Using the LV samples, we performed a western blot analysis to evaluate signaling pathways and autophagic markers.

RESULTS

The DM group had lower body weight and higher blood glucose level and heart weight/body weight ratio than the control group. However, metabolic changes did not differ between the DM and DM + DEX groups. Pressure-volume loop analysis and echocardiography showed impaired cardiac function, evidenced by a decrease in systolic and diastolic function, in both DM groups. DEX treatment in DM rats was associated with increased LV end-systolic pressure, LV contractility, cardiac output, and relaxed LV function compared with that in non-treated DM rats. LC3B and autophagy-related gene (ATG) proteins increased in the hearts of DM rats compared with the hearts of control rats. However, DEX reduced the expression of LC3B and ATG proteins in the hearts of DM rats. Increased p-ERK and decreased p-AKT were reduced in the hearts of DEX-treated DM rats.

CONCLUSIONS

DEX reduces cardiac dysfunction and impaired autophagy in DM rats. This study reinforces our understanding of the potential anti-autophagic effect of DEX in patients with diabetic cardiomyopathy.

Autophagy Pathway Mapping to Elucidate the Function of Novel Autophagy Regulators Identified by High-Throughput Screening

Autophagy is an evolutionarily conserved degradative pathway, and the core autophagy machinery acts in a highly regulated, hierarchical manner to engulf cytoplasmic material in a double-membrane-bound organelle and deliver it to the lysosome. High-throughput screening approaches lead to the identification of novel autophagy regulators, and we describe an autophagy pathway mapping strategy to determine the stage of the autophagy pathway at which these novel candidate proteins function.

Identification and Validation of Novel Autophagy Regulators Using an Endogenous Readout siGENOME Screen

Autophagy is a highly regulated process, and its deregulation can contribute to various diseases, including cancer, immune diseases, and neurodegenerative disorders. Here we describe the design, protocol, and analysis of an imaging-based high-throughput screen with an endogenous autophagy readout. The screen uses a genome-wide siRNA library to identify autophagy regulators in mammalian cells.

Autophagy: novel insights into therapeutic target of electroacupuncture against cerebral ischemia/ reperfusion injury

Electroacupuncture is known as an effective adjuvant therapy in ischemic cerebrovascular disease. However, its underlying mechanisms remain unclear. Studies suggest that autophagy, which is essential for cell survival and cell death, is involved in cerebral ischemia reperfusion injury and might be modulate by electroacupuncture therapy in key ways. This paper aims to provide novel insights into a therapeutic target of electroacupuncture against cerebral ischemia/reperfusion injury from the perspective of autophagy. Here we review recent studies on electroacupuncture regulation of autophagy-related markers such as UNC-51-like kinase-1 complex, Beclin1, microtubule-associated protein-1 light chain 3, p62, and autophagosomes for treating cerebral ischemia/reperfusion injury. The results of these studies show that electroacupuncture may affect the initiation of autophagy, vesicle nucleation, expansion and maturation of autophagosomes, as well as fusion and degradation of autophagolysosomes. Moreover, studies indicate that electroacupuncture probably modulates autophagy by activating the mammalian target of the rapamycin signaling pathway. This review thus indicates that autophagy is a therapeutic target of electroacupuncture treatment against ischemic cerebrovascular diseases.

Ethanol acutely antagonizes the refeeding-induced increase in mTOR-dependent protein synthesis and decrease in autophagy in skeletal muscle

The purpose of this study was to determine the impact of acute ethanol administration on the major signal transduction pathways in skeletal muscle responsible for regulating the protein synthetic and degradative response to refeeding. Adult male C57Bl/6 mice were fasted overnight; mice were then either refed normal rodent chow for 30 min or a separate group of mice remained food deprived (i.e., fasted). Thereafter, mice were administered either 3 g/kg ethanol or saline. Gastrocnemius/plantaris was collected 1 h later and analyzed. Acute ethanol decreased basal and prevented the refeeding-induced increase in muscle protein synthesis. While ethanol prevented a nutrient-stimulated increase in S6K1 phosphorylation, it did not alter the increase in 4E-BP1 phosphorylation. Downstream of S6K1, ethanol also attenuated the refeeding-induced increase in S6 and eIF4B phosphorylation, as well as the decrease in eEF2 phosphorylation. Although ethanol decreased ERK and p90 RSK phosphorylation, activation of this signaling pathway was not altered by refeeding in either control or ethanol-treated mice. Related to protein degradation, in vitro-determined proteasome activity and the content of total ubiquitinated proteins were not altered by ethanol and/or refeeding. Control mice appeared to exhibit a refeeding-induced decrease in autophagy as suggested by the increased FoxO3 and ULK1 phosphorylation and total p62 protein as well as decreased LC3B-II; however, ethanol blunted these refeeding-induced changes. These data suggest that ethanol can acutely prevent the normally observed mTOR-dependent increase in protein synthesis and reduction in autophagy in response to nutrient stimulation, but does not appear to acutely alter proteasome activity.

Neuroprotective Autophagic Flux Induced by Hyperbaric Oxygen Preconditioning is Mediated by Cystatin C

We have previously reported that Cystatin C (CysC) is a pivotal mediator in the neuroprotection induced by hyperbaric oxygen (HBO) preconditioning; however, the underlying mechanism and how CysC changes after stroke are not clear. In the present study, we demonstrated that CysC expression was elevated as early as 3 h after reperfusion, and this was further enhanced by HBO preconditioning. Concurrently, LC3-II and Beclin-1, two positive-markers for autophagy induction, exhibited increases similar to CysC, while knockdown of CysC blocked these elevations. As a marker of autophagy inhibition, p62 was downregulated by HBO preconditioning and this was blocked by CysC knockdown. Besides, the beneficial effects of preserving lysosomal membrane integrity and enhancing autolysosome formation induced by HBO preconditioning were abolished in CysC^−/− rats. Furthermore, we demonstrated that exogenous CysC reduced the neurological deficits and infarct volume after brain ischemic injury, while 3-methyladenine partially reversed this neuroprotection. In the present study, we showed that CysC is biochemically and morphologically essential for promoting autophagic flux, and highlighted the translational potential of HBO preconditioning and CysC for stroke treatment.

Acute alcohol prevents the refeeding-induced decrease in autophagy but does not alter the increased protein synthetic response in heart

Ethanol produces a state of anabolic resistance in skeletal muscle; however, whether the heart displays a similar defect is unknown. Hence, the purpose of this study was to determine the impact of acute ethanol administration on the major signal transduction pathways in the heart that are responsible for regulating the protein synthetic and degradative response to refeeding. Adult male C57Bl/6 mice were fasted for 12 h. Mice were then either refed normal rodent chow for 30 min or a separate group of mice remained food deprived prior to administration of 3-g/kg ethanol. Cardiac tissue and blood were collected 1 h thereafter and analyzed. Acute ethanol prevented the nutrient-induced stimulation of S6K1 phosphorylation in heart, but did not alter the phosphorylation of S6, eIF4B, and eEF2, known downstream substrates for this kinase. The refeeding-induced redistribution of eIF4E into the active eIF4F complex was also not changed by acute ethanol. Consistent with the above-mentioned changes in signaling proteins, ethanol did not impair the refeeding-induced increase in cardiac protein synthesis. Proteasome activity was not altered by alcohol and/or refeeding. In contrast, ethanol antagonized the refeeding-induced increase in ULK1 phosphorylation and p62 as well as the reduction in LC3B-II and Atg5/12 complex proteins. These data indicate that acute ethanol prevents the normally observed inhibition of autophagy seen after refeeding, while the mTOR-dependent increase in protein synthesis remains largely unaltered by alcohol.

Regulatory effects of lncRNAs and miRNAs on autophagy in malignant tumorigenesis

Autophagy is an important process in endogenous substrate degradation by lysosomes within cells, with a degree of evolutionary conservation. Like apoptosis and cell senescence, cell autophagy is a very important biological phenomenon involving the development and growth of biological processes. Abnormal autophagy may lead to tumorigenesis. In recent years, increasing studies have demonstrated that long non-coding RNAs (lncRNAs) and miRNAs can regulate cell autophagy by modulating targetting gene expression. In this review, we will provide an overview of lncRNAs and miRNAs in autophagy modulation and new insights into the underlying mechanisms, as well as their potential utilization in disease diagnosis, prognosis, and therapy.