Nutrient starvation elicits an acute autophagic response mediated by Ulk1 dephosphorylation and its subsequent dissociation from AMPK

PP2Ac Regulates Autophagy via Mediating mTORC1 and ULK1 During Osteoclastogenesis in the Subchondral Bone of Osteoarthritis

The molecular mechanism underlying abnormal osteoclastogenesis triggering subchondral bone remodeling in osteoarthritis (OA) is still unclear. Here, single-cell and bulk transcriptomics sequencing analyses are performed on GEO datasets to identify key molecules and validate them using knee joint tissues from OA patients and rat OA models. It is found that the catalytic subunit of protein phosphatase 2A (PP2Ac) is highly expressed during osteoclastogenesis in the early stage of OA and is correlated with autophagy. Knockdown or inhibition of PP2Ac weakened autophagy during osteoclastogenesis. Furthermore, the ULK1 expression of the downstream genes is significantly increased when PP2Ac is knocked down. PP2Ac-mediated autophagy is dependent on ULK1 phosphorylation activity during osteoclastogenesis, which is associated with enhanced dephosphorylation of ULK1 Ser637 residue regulating at the post-translational level. Additionally, mTORC1 inhibition facilitated the expression level of PP2Ac during osteoclastogenesis. In animal OA models, decreasing the expression of PP2Ac ameliorated early OA progression. The findings suggest that PP2Ac is also a promising therapeutic target in early OA.

New developments in AMPK and mTORC1 cross-talk

Metabolic homeostasis and the ability to link energy supply to demand are essential requirements for all living cells to grow and proliferate. Key to metabolic homeostasis in all eukaryotes are AMPK and mTORC1, two kinases that sense nutrient levels and function as counteracting regulators of catabolism (AMPK) and anabolism (mTORC1) to control cell survival, growth and proliferation. Discoveries beginning in the early 2000s revealed that AMPK and mTORC1 communicate, or cross-talk, through direct and indirect phosphorylation events to regulate the activities of each other and their shared protein substrate ULK1, the master initiator of autophagy, thereby allowing cellular metabolism to rapidly adapt to energy and nutritional state. More recent reports describe divergent mechanisms of AMPK/mTORC1 cross-talk and the elaborate means by which AMPK and mTORC1 are activated at the lysosome. Here, we provide a comprehensive overview of current understanding in this exciting area and comment on new evidence showing mTORC1 feedback extends to the level of the AMPK isoform, which is particularly pertinent for some cancers where specific AMPK isoforms are implicated in disease pathogenesis.

Antibiotic synergistic effect surge bioenergy potential and pathogen resistance of Chlorella variabilis biofilm

Tetracycline (TC) and ciprofloxacin (CF) induce a synergistic effect that alters the biochemical composition, leading to a decrease in the growth and photosynthetic efficiency of microalgae. But the current study provides a novel insight into stress-inducing techniques that trigger a change in macromolecules, leading to an increase in the bioenergy potential and pathogen resistance of Chlorella variabilis biofilm. The study revealed that in a closed system, a light intensity of 167 μmol/m2/s causes 93.5% degradation of TC and 16% degradation of CF after 7 days of exposure, hence availing the products for utilization by C. variabilis biofilm. The resistance to pathogens invasion was linked to 85% and 40% increase in the expression level of photosystem II oxygen-evolving enhancer protein 3 (PsbQ), and mitogen activated kinase (MAK) respectively. The results also indicate that a surge in light intensity triggers 49% increase in the expression level of lysophosphatidylcholine (LPC) (18:2), which is an important lipidomics that can easily undergo transesterification into bioenergy. The thermogravimetric result indicates that the biomass sample of C. variabilis biofilm cultivated under light intensity of 167 μmol/m2/s produces a higher residual mass of 45.5% and 57.5 under air and inert conditions, respectively. The Fourier transform infrared (FTIR) indicates a slight shift in the major functional groups, while the energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence (XRF) indicate clear differences in the morphology and elemental composition of the biofilm biomass in support of the increase bioenergy potential of C. variabilis biofilm. The current study provides a vital understanding of a innovative method of cultivation of C. variabilis biofilm, which is resistant to pathogens and controls the balance between fatty acid and TAG synthesis leading to surge in bioenergy potential and environmental sustainability.

Cellular response during cellular starvation: A battle for cellular survivability

Cellular starvation occurs when a cell is deprived of nutrition and oxygen availability. The genesis of this state of deprivation is exclusively contingent upon the inadequacy in the supply of essential components, namely amino acids, glucose, and oxygen. Consequently, the impact of this altered condition manifests in the regulation of cellular respiratory, metabolic, and stress responses. Subsequently, as a reactive outcome, cell death may transpire through mechanisms such as autophagy or apoptosis, particularly under prolonged circumstances. However, the cell combats such situations by evolving altered activity in their metabolic and protein level. Modulated signaling cascades help them to conquer starvation. But as in a prolonged condition, the battle that a cell has to evolve will come into and result in the form of cellular death. Therefore, in cancer therapy, cellular starvation may also act as a possible way out so that the cancer cell can undergo its death pathway in an induced starved condition. This review has collectively depicted the mechanism of cellular starvation. Besides this, the cellular response in this starved condition has also been summarized. Gaining such knowledge of the causation of cell starvation and cellular response during starvation not only generates new insight into the mechanism of cell survivability but also may act as a beneficial role in combating cellular diseases like cancer.

Unexpected roles for AMPK in the suppression of autophagy and the reactivation of MTORC1 signaling during prolonged amino acid deprivation

AMPK promotes catabolic and suppresses anabolic cell metabolism to promote cell survival during energetic stress, in part by inhibiting MTORC1, an anabolic kinase requiring sufficient levels of amino acids. We found that cells lacking AMPK displayed increased apoptotic cell death during nutrient stress caused by prolonged amino acid deprivation. We presumed that impaired macroautophagy/autophagy explained this phenotype, as a prevailing view posits that AMPK initiates autophagy (often a pro-survival response) through phosphorylation of ULK1. Unexpectedly, however, autophagy remained unimpaired in cells lacking AMPK, as monitored by several autophagic readouts in several cell lines. More surprisingly, the absence of AMPK increased ULK1 signaling and MAP1LC3B/LC3B lipidation during amino acid deprivation while AMPK-mediated phosphorylation of ULK1 S555 (a site proposed to initiate autophagy) decreased upon amino acid withdrawal or pharmacological MTORC1 inhibition. In addition, activation of AMPK with compound 991, glucose deprivation, or AICAR blunted autophagy induced by amino acid withdrawal. These results demonstrate that AMPK activation and glucose deprivation suppress autophagy. As AMPK controlled autophagy in an unexpected direction, we examined how AMPK controls MTORC1 signaling. Paradoxically, we observed impaired reactivation of MTORC1 in cells lacking AMPK upon prolonged amino acid deprivation. Together these results oppose established views that AMPK promotes autophagy and inhibits MTORC1 universally. Moreover, they reveal unexpected roles for AMPK in the suppression of autophagy and the support of MTORC1 signaling in the context of prolonged amino acid deprivation. These findings prompt a reevaluation of how AMPK and its control of autophagy and MTORC1 affect health and disease.

Autophagic Regulation of Adipogenesis Through TP53INP2: Insights from In Silico and In Vitro Analysis

Obesity is an epidemic disease associated with multimorbidity resulting in higher mortality risk. The imbalance between energy storage and expenditure is the prime factor in the prognosis of the disease. Specifically, excessive lipid storage through adipogenesis leads to obesity. Adipogenesis is the process that converts preadipocytes into mature adipocytes by regulating major transcription factors like PPARγ and C/EBPα, contributes to lipid storage in adipose tissue. On the contrary, autophagy is a self-degradative process that maintains homeostasis in adipose tissue by regulating adipogenesis and lipolysis. TP53INP2 is a key player that regulates the autophagy process, and it negatively regulates adipogenesis and lipid storage. The gene expression profile GSE93637 was retrieved from the GEO database and analyzed using an integrated bioinformatics approach. The differentially expressed genes (DEGs) were analyzed using R-Bioconductor for TP53INP2 knockdown microarray dataset of 3T3L1 cells, and the DEGs were analyzed for the functional enrichment analysis. Further, the genes involved in the potential biological and molecular functions were evaluated for pathway enrichment analysis by KEGG (Kyoto Encyclopedia of Genes and Genomes). A total of 726 DEGs were found including 391 upregulated and 335 downregulated genes. Further, the functional and pathway enrichment analysis was employed to identify the highly interacting genes, and we identified a total of 56 genes that are highly interacting through a protein-protein interaction network. The DEGs mainly regulate the Peroxisome proliferator-activated receptor (PPAR) signaling pathway, lipolysis, and autophagy. Further, we investigated the associated Hub genes for enriched pathway genes and found the involvement of two autophagic genes ATG7 and sequestosome 1 (p62). In addition, in vitro studies of qRT-PCR (Quantitative real-time polymerase chain reaction) and Western blot analysis revealed that increased autophagy resulted in reduced lipid storage through down-regulation of the adipogenic gene. Moreover, increased expression of autophagic gene TP53INP2 and ATG7 facilitates the down-regulation of p62 and PPARγ gene resulting in lipolysis in mature adipocytes through autophagy. There is no specific treatment to reduce obesity other than a caloric diet and exercise. Hence, this study provides sufficient evidence to conclude that TP53INP2 negatively regulates adipogenesis and increases the degradation of lipids in mature adipocytes which is crucial for reducing obesity. Therefore, it is plausible to consider TP53INP2 as a promising therapeutic target for managing adipogenesis and obesity. However, further studies are necessary to validate their functional and molecular pathway analysis in the regulation of adipogenesis and obesity.

Unexpected roles for AMPK in the suppression of autophagy and the reactivation of mTORC1 signaling during prolonged amino acid deprivation

AMPK promotes catabolic and suppresses anabolic cell metabolism to promote cell survival during energetic stress, in part by inhibiting mTORC1, an anabolic kinase requiring sufficient levels of amino acids. We found that cells lacking AMPK displayed increased apoptotic cell death during nutrient stress caused by prolonged amino acid deprivation. We presumed that impaired autophagy explained this phenotype, as a prevailing view posits that AMPK initiates autophagy (often a pro-survival response) through phosphorylation of ULK1. Unexpectedly, however, autophagy remained unimpaired in cells lacking AMPK, as monitored by several autophagic readouts in several cell lines. More surprisingly, the absence of AMPK increased ULK1 signaling and LC3b lipidation during amino acid deprivation while AMPK-mediated phosphorylation of ULK1 S555 (a site proposed to initiate autophagy) decreased upon amino acid withdrawal or pharmacological mTORC1 inhibition. In addition, activation of AMPK with compound 991, glucose deprivation, or AICAR blunted autophagy induced by amino acid withdrawal. These results demonstrate that AMPK activation and glucose deprivation suppress autophagy. As AMPK controlled autophagy in an unexpected direction, we examined how AMPK controls mTORC1 signaling. Paradoxically, we observed impaired reactivation of mTORC1 in cells lacking AMPK upon prolonged amino acid deprivation. Together these results oppose established views that AMPK promotes autophagy and inhibits mTORC1 universally. Moreover, they reveal unexpected roles for AMPK in the suppression of autophagy and the support of mTORC1 signaling in the context of prolonged amino acid deprivation. These findings prompt a reevaluation of how AMPK and its control of autophagy and mTORC1 impact health and disease.

Post-translational modifications linked to preclinical Alzheimer's disease-related pathological and cognitive changes

INTRODUCTION

In this study, we leverage proteomic techniques to identify communities of proteins underlying Alzheimer's disease (AD) risk among clinically unimpaired (CU) older adults.

METHODS

We constructed a protein co-expression network using 3869 cerebrospinal fluid (CSF) proteins quantified by SomaLogic, Inc., in a cohort of participants along the AD clinical spectrum. We then replicated this network in an independent cohort of CU older adults and related these modules to clinically-relevant outcomes.

RESULTS

We discovered modules enriched for phosphorylation and ubiquitination that were associated with abnormal amyloid status, as well as p-tau181 (M4: β = 2.44, p < 0.001, M7: β = 2.57, p < 0.001) and executive function performance (M4: β = -2.00, p = 0.005, M7: β = -2.39, p < 0.001).

DISCUSSION

In leveraging CSF proteomic data from individuals spanning the clinical spectrum of AD, we highlight the importance of post-translational modifications for early cognitive and pathological changes.

The Multiple Roles of Autophagy in Neural Function and Diseases

Autophagy involves the sequestration and delivery of cytoplasmic materials to lysosomes, where proteins, lipids, and organelles are degraded and recycled. According to the way the cytoplasmic components are engulfed, autophagy can be divided into macroautophagy, microautophagy, and chaperone-mediated autophagy. Recently, many studies have found that autophagy plays an important role in neurological diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, neuronal excitotoxicity, and cerebral ischemia. Autophagy maintains cell homeostasis in the nervous system via degradation of misfolded proteins, elimination of damaged organelles, and regulation of apoptosis and inflammation. AMPK-mTOR, Beclin 1, TP53, endoplasmic reticulum stress, and other signal pathways are involved in the regulation of autophagy and can be used as potential therapeutic targets for neurological diseases. Here, we discuss the role, functions, and signal pathways of autophagy in neurological diseases, which will shed light on the pathogenic mechanisms of neurological diseases and suggest novel targets for therapies.

Contrasting views on the role of AMPK in autophagy

Efficient management of low energy states is vital for cells to maintain basic functions and metabolism and avoid cell death. While autophagy has long been considered a critical mechanism for ensuring survival during energy depletion, recent research has presented conflicting evidence, challenging the long-standing concept. This recent development suggests that cells prioritize preserving essential cellular components while restraining autophagy induction when cellular energy is limited. This essay explores the conceptual discourse on autophagy regulation during energy stress, navigating through the studies that established the current paradigm and the recent research that has challenged its validity while proposing an alternative model. This exploration highlights the far-reaching implications of the alternative model, which represents a conceptual departure from the established paradigm, offering new perspectives on how cells respond to energy stress.

mTORC1 activity oscillates throughout the cell cycle promoting mitotic entry and differentially influencing autophagy induction

Mechanistic Target of Rapamycin Complex 1 (mTORC1) is a master metabolic regulator that stimulates anabolic cell growth while suppressing catabolic processes such as autophagy. mTORC1 is active in most, if not all, proliferating eukaryotic cells. However, it remains unclear whether and how mTORC1 activity changes from one cell cycle phase to another. Here we tracked mTORC1 activity through the complete cell cycle and uncover oscillations in its activity. We find that mTORC1 activity peaks in S and G2, and is lowest in mitosis and G1. We further demonstrate that multiple mechanisms are involved in controlling this oscillation. The interphase oscillation is mediated through the TSC complex, an upstream negative regulator of mTORC1, but is independent of major known regulatory inputs to the TSC complex, including Akt, Mek/Erk, and CDK4/6 signaling. By contrast, suppression of mTORC1 activity in mitosis does not require the TSC complex, and instead involves CDK1-dependent control of the subcellular localization of mTORC1 itself. Functionally, we find that in addition to its well-established role in promoting progression through G1, mTORC1 also promotes progression through S and G2, and is important for satisfying the Wee1- and Chk1- dependent G2/M checkpoint to allow entry into mitosis. We also find that low mTORC1 activity in G1 sensitizes cells to autophagy induction in response to partial mTORC1 inhibition or reduced nutrient levels. Together these findings demonstrate that mTORC1 is differentially regulated throughout the cell cycle, with important phase-specific functional consequences in proliferating cells.

Recent advances of vacuolar protein-sorting 34 inhibitors targeting autophagy

Autophagy is a ubiquitous pathological/physiological antioxidant cellular reaction in eukaryotic cells. Vacuolar protein sorting 34 (Vps34 or PIK3C3), which plays a crucial role in autophagy, has received much attention. As the only Class III phosphatidylinositol-3 kinase in mammals, Vps34 participates in vesicular transport, nutrient signaling and autophagy. Dysfunctionality of Vps34 induces carcinogenesis, and abnormal autophagy mediated by dysfunction of Vps34 is closely related to the pathological progression of various human diseases, which makes Vps34 a novel target for tumor immunotherapy. In this review, we summarize the molecular mechanisms underlying macroautophagy, and further discuss the structure-activity relationship of Vps34 inhibitors that have been reported in the past decade as well as their potential roles in anticancer immunotherapy to better understand the antitumor mechanism underlying the effects of these inhibitors.

DENND6A links Arl8b to a Rab34/RILP/dynein complex, regulating lysosomal positioning and autophagy

Lysosomes help maintain cellular proteostasis, and defects in lysosomal positioning and function can cause disease, including neurodegenerative disorders. The spatiotemporal distribution of lysosomes is regulated by small GTPases including Rabs, which are activated by guanine nucleotide exchange factors (GEFs). DENN domain proteins are the largest family of Rab GEFs. Using a cell-based assay, we screened DENND6A, a member of the DENN domain protein family against all known Rabs and identified it as a potential GEF for 20 Rabs, including Rab34. Here, we demonstrate that DENND6A activates Rab34, which recruits a RILP/dynein complex to lysosomes, promoting lysosome retrograde transport. Further, we identify DENND6A as an effector of Arl8b, a major regulatory GTPase on lysosomes. We demonstrate that Arl8b recruits DENND6A to peripheral lysosomes to activate Rab34 and initiate retrograde transport, regulating nutrient-dependent lysosomal juxtanuclear repositioning. Loss of DENND6A impairs autophagic flux. Our findings support a model whereby Arl8b/DENND6A/Rab34-dependent lysosomal retrograde trafficking controls autophagy.

Autophagy in spinal muscular atrophy: from pathogenic mechanisms to therapeutic approaches

Spinal muscular atrophy (SMA) is a devastating neuromuscular disorder caused by the depletion of the ubiquitously expressed survival motor neuron (SMN) protein. While the genetic cause of SMA has been well documented, the exact mechanism(s) by which SMN depletion results in disease progression remain elusive. A wide body of evidence has highlighted the involvement and dysregulation of autophagy in SMA. Autophagy is a highly conserved lysosomal degradation process which is necessary for cellular homeostasis; defects in the autophagic machinery have been linked with a wide range of neurodegenerative disorders, including amyotrophic lateral sclerosis, Alzheimer's disease and Parkinson's disease. The pathway is particularly known to prevent neurodegeneration and has been suggested to act as a neuroprotective factor, thus presenting an attractive target for novel therapies for SMA patients. In this review, (a) we provide for the first time a comprehensive summary of the perturbations in the autophagic networks that characterize SMA development, (b) highlight the autophagic regulators which may play a key role in SMA pathogenesis and (c) propose decreased autophagic flux as the causative agent underlying the autophagic dysregulation observed in these patients.

Lasmiditan restores mitochondrial quality control mechanisms and accelerates renal recovery after ischemia-reperfusion injury

BACKGROUND

Mitochondrial dysfunction is a well-established result of acute kidney injury (AKI). Previously, we identified that 5-hydroxytryptamine 1F (5-HT1F) receptor agonism with lasmiditan induces mitochondrial biogenesis (MB) and improves renal vasculature and function in an AKI mouse model. We hypothesize that lasmiditan also modulates mitochondrial dynamics and mitophagy in a mouse model of AKI.

METHODS

Male mice were subjected to renal ischemia/reperfusion (I/R) and treated daily with lasmiditan (0.3 mg/kg) or vehicle beginning 24 h after injury for 3 or 6d. Serum creatinine was measured to estimate glomerular filtration. Electron microscopy was used to assess mitochondrial morphology and mitophagy. Mitochondrial-related protein were confirmed with immunoblotting. Mitochondrial function was assessed with ATP measurements.

RESULTS

Lasmiditan treatment improved mitochondrial and kidney recovery as early as 3d post-AKI, as evidenced by increased ATP, and decreased serum creatinine, respectively. Electron micrographs of renal cortices revealed that lasmiditan also decreased mitochondrial damage and increased mitochondrial area and size by 6d after I/R injury. Additionally, lasmiditan treatment increased mitolysosomes by 3d, indicating induction of mitophagy. Phosphorylation of mitophagy-related proteins were also increased in the renal cortices of lasmiditan-treated AKI mice 3d after I/R injury, whereas fusion-related proteins were increased at 6d after I/R injury.

CONCLUSION

These data reveal that lasmiditan accelerates renal recovery, restores normal mitochondrial membrane and cristae morphology, decreases excessive mitochondrial fission, and accelerates mitophagy post-AKI in a time-dependent manner, establishing mitochondrial function and recovery from AKI.

Growth or death? Control of cell destiny by mTOR and autophagy pathways

One of the central regulators of cell growth, proliferation, and metabolism is the mammalian target of rapamycin, mTOR, which exists in two structurally and functionally different complexes: mTORC1 and mTORC2; unlike m TORC2, mTORC1 is activated in response to the sufficiency of nutrients and is inhibited by rapamycin. mTOR complexes have critical roles not only in protein synthesis, gene transcription regulation, proliferation, tumor metabolism, but also in the regulation of the programmed cell death mechanisms such as autophagy and apoptosis. Autophagy is a conserved catabolic mechanism in which damaged molecules are recycled in response to nutrient starvation. Emerging evidence indicates that the mTOR signaling pathway is frequently activated in tumors. In addition, dysregulation of autophagy was associated with the development of a variety of human diseases, such as cancer and aging. Since mTOR can inhibit the induction of the autophagic process from the early stages of autophagosome formation to the late stage of lysosome degradation, the use of mTOR inhibitors to regulate autophagy could be considered a potential therapeutic option. The present review sheds light on the mTOR and autophagy signaling pathways and the mechanisms of regulation of mTOR-autophagy.

Unraveling the Intricacies of Autophagy and Mitophagy: Implications in Cancer Biology

Autophagy is an essential lysosome-mediated degradation pathway that maintains cellular homeostasis and viability in response to various intra- and extracellular stresses. Mitophagy is a type of autophagy that is involved in the intricate removal of dysfunctional mitochondria during conditions of metabolic stress. In this review, we describe the multifaceted roles of autophagy and mitophagy in normal physiology and the field of cancer biology. Autophagy and mitophagy exhibit dual context-dependent roles in cancer development, acting as tumor suppressors and promoters. We also discuss the important role of autophagy and mitophagy within the cancer microenvironment and how autophagy and mitophagy influence tumor host-cell interactions to overcome metabolic deficiencies and sustain the activity of cancer-associated fibroblasts (CAFs) in a stromal environment. Finally, we explore the dynamic interplay between autophagy and the immune response in tumors, indicating their potential as immunomodulatory targets in cancer therapy. As the field of autophagy and mitophagy continues to evolve, this comprehensive review provides insights into their important roles in cancer and cancer microenvironment.

Rhabdomyosarcoma: Current Therapy, Challenges, and Future Approaches to Treatment Strategies

Rhabdomyosarcoma is a rare cancer arising in skeletal muscle that typically impacts children and young adults. It is a worldwide challenge in child health as treatment outcomes for metastatic and recurrent disease still pose a major concern for both basic and clinical scientists. The treatment strategies for rhabdomyosarcoma include multi-agent chemotherapies after surgical resection with or without ionization radiotherapy. In this comprehensive review, we first provide a detailed clinical understanding of rhabdomyosarcoma including its classification and subtypes, diagnosis, and treatment strategies. Later, we focus on chemotherapy strategies for this childhood sarcoma and discuss the impact of three mechanisms that are involved in the chemotherapy response including apoptosis, macro-autophagy, and the unfolded protein response. Finally, we discuss in vivo mouse and zebrafish models and in vitro three-dimensional bioengineering models of rhabdomyosarcoma to screen future therapeutic approaches and promote muscle regeneration.

Mitophagy for cardioprotection

Mitochondrial function is maintained by several strictly coordinated mechanisms, collectively termed mitochondrial quality control mechanisms, including fusion and fission, degradation, and biogenesis. As the primary source of energy in cardiomyocytes, mitochondria are the central organelle for maintaining cardiac function. Since adult cardiomyocytes in humans rarely divide, the number of dysfunctional mitochondria cannot easily be diluted through cell division. Thus, efficient degradation of dysfunctional mitochondria is crucial to maintaining cellular function. Mitophagy, a mitochondria specific form of autophagy, is a major mechanism by which damaged or unnecessary mitochondria are targeted and eliminated. Mitophagy is active in cardiomyocytes at baseline and in response to stress, and plays an essential role in maintaining the quality of mitochondria in cardiomyocytes. Mitophagy is mediated through multiple mechanisms in the heart, and each of these mechanisms can partially compensate for the loss of another mechanism. However, insufficient levels of mitophagy eventually lead to mitochondrial dysfunction and the development of heart failure. In this review, we discuss the molecular mechanisms of mitophagy in the heart and the role of mitophagy in cardiac pathophysiology, with the focus on recent findings in the field.

DIRAS3 regulates autophagy in an endometriosis epithelial cell line

RESEARCH QUESTION

What is the role of DIRAS3 in endometriosis pathogenesis?

DESIGN

Prospective patient cohort study combined with experiments in the 12Z human endometriosis epithelial cell line model to determine the role of DIRAS3 in endometriosis. Endometrium and endometriosis lesion samples were collected from premenopausal women from 24 control and 40 endometriosis patients by laparoscopic surgery. The role of DIRAS3 in endometriosis was assessed by siRNA knockdown in 12Z cells followed by proliferation, apoptosis, invasion and autophagy assays. Autophagy was induced by serum starvation and the levels of autophagy determined by assessing changes in the expression levels and localization of autophagy marker proteins, such as LC3.

RESULTS

DIRAS3 mRNA showed a large increase in expression in ectopic endometriosis lesions compared with endometrium from control patients, with expression largely localized to the epithelium. DIRAS3 knockdown in 12Z endometriosis epithelial cells caused a significant reduction in the number of proliferating cells (1.6-fold, adjusted P = 0.0007) and increased apoptosis (AnnexinV/7AAD double-positive cells +48%, P = 0.01), indicating an effect on cell proliferation. Induction of autophagy by serum starvation caused significant upregulation in DIRAS3 expression after 24 h (mRNA +2.4-fold [adjusted P = 0.017], protein +8.1-fold (adjusted P = 0.029), reduced LC3I/LC3II ratio (-2.2-fold, adjusted P = 0.044) and an increase in the number of double positive LC3/DIRAS3 puncta (+2.3-fold, P = 0.02). Knockdown of DIRAS3 in serum-starved cells led to a reduction in autophagy, indicated by an overall decrease in LC3 expression and significant increase in LC3I/LC3II ratio.

CONCLUSIONS

DIRAS3 is highly upregulated in endometriosis lesions. Studies in an endometriosis epithelial cell line indicate that DIRAS3 facilitates cell survival in this context by inducing autophagy.

LncRNA SNHG6 role in clinicopathological parameters in cancers

RNA sequencing has revealed that a substantial portion of the human genome undergoes transcription, yet a minimal fraction of these transcripts translates into proteins. LncRNAs, RNA molecules less than 200 nt in length, once deemed as transcriptional noise, have now emerged as crucial regulators of numerous cellular processes. This review focuses on the lncRNA SNHG6, aiming to elucidate its biogenesis, the pivotal roles it plays, and its mechanisms in facilitating the hallmarks of cancer. A comprehensive literature review and analysis were undertaken to delve into the biogenesis of SNHG6, its roles in cellular processes, and the mechanisms through which it contributes to the hallmarks of cancer. SNHG6 is a notable lncRNA, observed to be overexpressed in various cancer types; its perturbation has been linked to tumor progression, emphasizing its significance in oncogenesis. This lncRNA contributes to a range of cellular aberrations, influencing transcriptional, post-transcriptional, and epigenetic processes of mRNA, ultimately driving cancerous transformations. LncRNA SNHG6 serves as a potential biomarker and therapeutic target due to its association with tumorigenesis. Understanding its mechanism and role in cancer can pave the way for novel diagnostic and therapeutic strategies.

miR-30a-3p Regulates Autophagy in the Involution of Mice Mammary Glands

The mammary gland undergoes intensive remodeling during the lactation cycle, and the involution process of mammary gland contains extensive epithelial cells involved in the process of autophagy. Our studies of mice mammary glands suggest that miR-30a-3p expression was low during involution compared with its high expression in the mammary glands of lactating mice. Then, we revealed that miR-30a-3p negatively regulated autophagy by autophagy related 12 (Atg12) in mouse mammary gland epithelial cells (MMECs). Restoring ATG12, knocking down autophagy related 5 (Atg5), starvation, and Rapamycin were used to further confirm this conclusion. Overexpression of miR-30a-3p inhibited autophagy and altered mammary structure in the involution of the mammary glands of mice, which was indicative of alteration in mammary remodeling. Taken together, these results elucidated the molecular mechanisms of miR-30a-3p as a key induction mediator of autophagy by targeting Atg12 within the transition period between lactation and involution in mammary glands.

Phosphorylation of Bcl-2 by JNK confers gemcitabine resistance in lung cancer cells by reducing autophagy-mediated cell death

The most common cancer-related death in the world is non-small cell lung cancer (NSCLC). Gemcitabine (GEM) is a common and effective first-line chemotherapeutic drug for the treatment of NSCLC. However, the long-term use of chemotherapeutic drugs in patients usually induces cancer cell drug resistance, leading to poor survival, and prognosis. In this study, to observe and explore the key targets and potential mechanisms of NSCLC resistance to GEM, we first cultured lung cancer CL1-0 cells in a GEM-containing medium to induce CL1-0 cells to develop GEM resistance. Next, we compared protein expression between the parental and GEM-R CL1-0 cell groups. We observed significantly lower expression of autophagy-related proteins in GEM-R CL1-0 cells than in parental CL1-0 cells, indicating that autophagy is associated with GEM resistance in CL1-0 cells. Furthermore, a series of autophagy experiments revealed that GEM-R CL1-0 cells had significantly reduced GEM-induced c-Jun N-terminal kinase phosphorylation, which further affected the phosphorylation of Bcl-2, thereby reducing the dissociation of Bcl-2 and Beclin-1 and ultimately reducing the generation of GEM-induced autophagy-dependent cell death. Our findings suggest that altering the expression of autophagy is a promising therapeutic option for drug-resistant lung cancer.

Autophagy inhibitors for cancer therapy: Small molecules and nanomedicines

Autophagy is a conserved process in which the cytosolic materials are degraded and eventually recycled for cellular metabolism to maintain homeostasis. The dichotomous role of autophagy in pathogenesis is complicated. Accumulating reports have suggested that cytoprotective autophagy is responsible for tumor growth and progression. Autophagy inhibitors, such as chloroquine (CQ) and hydroxychloroquine (HCQ), are promising for treating malignancies or overcoming drug resistance in chemotherapy. With the rapid development of nanotechnology, nanomaterials also show autophagy-inhibitory effects or are reported as the carriers delivering autophagy inhibitors. In this review, we summarize the small-molecule compounds and nanomaterials inhibiting autophagic flux as well as the mechanisms involved. The nanocarrier-based drug delivery systems for autophagy inhibitors and their distinct advantages are also described. The progress of autophagy inhibitors for clinical applications is finally introduced, and their future perspectives are discussed.

Altered Expression of Autophagy Biomarkers in Hippocampal Neurons in a Multiple Sclerosis Animal Model

Multiple Sclerosis (MS) is a chronic inflammatory disease that affects the brain and spinal cord. Inflammation, demyelination, synaptic alteration, and neuronal loss are hallmarks detectable in MS. Experimental autoimmune encephalomyelitis (EAE) is an animal model widely used to study pathogenic aspects of MS. Autophagy is a process that maintains cell homeostasis by removing abnormal organelles and damaged proteins and is involved both in protective and detrimental effects that have been seen in a variety of human diseases, such as cancer, neurodegenerative diseases, inflammation, and metabolic disorders. This study is aimed at investigating the autophagy signaling pathway through the analysis of the main autophagic proteins including Beclin-1, microtubule-associated protein light chain (LC3, autophagosome marker), and p62 also called sequestosome1 (SQSTM1, substrate of autophagy-mediated degradation) in the hippocampus of EAE-affected mice. The expression levels of Beclin-1, LC3, and p62 and the Akt/mTOR pathway were examined by Western blot experiments. In EAE mice, compared to control animals, significant reductions of expression levels were detectable for Beclin-1 and LC3 II (indicating the reduction of autophagosomes), and p62 (suggesting that autophagic flux increased). In parallel, molecular analysis detected the deregulation of the Akt/mTOR signaling. Immunofluorescence double-labeling images showed co-localization of NeuN (neuronal nuclear marker) and Beclin-1, LC3, and p62 throughout the CA1 and CA3 hippocampal subfields. Taken together, these data demonstrate that activation of autophagy occurs in the neurons of the hippocampus in this experimental model.

Role of Mitochondria-ER Contact Sites in Mitophagy

Mitochondria are often referred to as the "powerhouse" of the cell. However, this organelle has many more functions than simply satisfying the cells' metabolic needs. Mitochondria are involved in calcium homeostasis and lipid metabolism, and they also regulate apoptotic processes. Many of these functions require contact with the ER, which is mediated by several tether proteins located on the respective organellar surfaces, enabling the formation of mitochondria-ER contact sites (MERCS). Upon damage, mitochondria produce reactive oxygen species (ROS) that can harm the surrounding cell. To circumvent toxicity and to maintain a functional pool of healthy organelles, damaged and excess mitochondria can be targeted for degradation via mitophagy, a form of selective autophagy. Defects in mitochondria-ER tethers and the accumulation of damaged mitochondria are found in several neurodegenerative diseases, including Parkinson's disease and amyotrophic lateral sclerosis, which argues that the interplay between the two organelles is vital for neuronal health. This review provides an overview of the different mechanisms of mitochondrial quality control that are implicated with the different mitochondria-ER tether proteins, and also provides a novel perspective on how MERCS are involved in mediating mitophagy upon mitochondrial damage.

Targeting PP2A-dependent autophagy enhances sensitivity to ruxolitinib in JAK2V617F myeloproliferative neoplasms

The Janus kinase 2 (JAK2)-driven myeloproliferative neoplasms (MPNs) are chronic malignancies associated with high-risk complications and suboptimal responses to JAK inhibitors such as ruxolitinib. A better understanding of cellular changes induced by ruxolitinib is required to develop new combinatory therapies to improve treatment efficacy. Here, we demonstrate that ruxolitinib induced autophagy in JAK2^V617F cell lines and primary MPN patient cells through the activation of protein phosphatase 2A (PP2A). Inhibition of autophagy or PP2A activity along with ruxolitinib treatment reduced proliferation and increased the death of JAK2^V617F cells. Accordingly, proliferation and clonogenic potential of JAK2^V617F-driven primary MPN patient cells, but not of normal hematopoietic cells, were markedly impaired by ruxolitinib treatment with autophagy or PP2A inhibitor. Finally, preventing ruxolitinib-induced autophagy with a novel potent autophagy inhibitor Lys05 improved leukemia burden reduction and significantly prolonged the mice's overall survival compared with ruxolitinib alone. This study demonstrates that PP2A-dependent autophagy mediated by JAK2 activity inhibition contributes to resistance to ruxolitinib. Altogether, our data support that targeting autophagy or its identified regulator PP2A could enhance sensitivity to ruxolitinib of JAK2^V617F MPN cells and improve MPN patient care.

Downregulation of Claudin5 promotes malignant progression and radioresistance through Beclin1-mediated autophagy in esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a highly prevalent and aggressive cancer with poor treatment outcomes. Despite the critical role of tight junction proteins in tumorigenesis, the involvement of Claudin5 in ESCC remains poorly understood. Thus, this study aimed to investigate the role of Claudin5 in ESCC malignant progression and radioresistance, as well as the underlying regulatory mechanisms.

METHODS

The expression of Claudin5 was evaluated in esophageal cancer tissue using both public databases and 123 clinical samples. CCK-8, transwell invasion, wound healing and clonogenic survival assays were used to examine the proliferation, invasion, migration and radiosensitivity of ESCC cells in vitro. Xenograft and animal lung metastasis experiments were conducted to examine the impact of Claudin5 on tumor growth and lung metastasis in vivo. The effect of Claudin5 on autophagy was detected via transmission electron microscopy, western blotting and autophagy flux. Immunohistochemical staining was used to detect Claudin5 expression in ESCC patient samples. The statistical difference was assessed with Student t test or one-way ANOVA. The correlation between Claudin5 expression and radiotherapy response rate was performed by the Chi-square test. The significance of Kaplan-Meier curves was evaluated by the Logrank test.

RESULTS

Claudin5 expression was downregulated in ESCC tissues. Downregulation of Claudin5 promoted ESCC cell proliferation, invasion, and migration both in vitro and in vivo. Downregulation of Claudin5 decreased the radiosensitivity of ESCC cells. Moreover, downregulation of Claudin5 promoted autophagy and the expression of Beclin1. Beclin1 knockdown reversed the effect of Claudin5 downregulation on autophagy induction and the promotion of ESCC cell malignant progression and radioresistance. Additionally, low expression of Claudin5 in ESCC cancer tissues was associated with poor radiotherapy response and prognosis.

CONCLUSIONS

In summary, these findings suggest that downregulation of Claudin5 promotes ESCC malignant progression and radioresistance via Beclin1-autophagy activation and may serve as a promising biomarker for predicting radiotherapy response and patient outcome in ESCC.

Redefining the role of AMPK in autophagy and the energy stress response

Autophagy maintains cellular homeostasis during low energy states. According to the current understanding, glucose-depleted cells induce autophagy through AMPK, the primary energy-sensing kinase, to acquire energy for survival. However, contrary to the prevailing concept, our study demonstrates that AMPK inhibits ULK1, the kinase responsible for autophagy initiation, thereby suppressing autophagy. We found that glucose starvation suppresses amino acid starvation-induced stimulation of ULK1-Atg14-Vps34 signaling via AMPK activation. During an energy crisis caused by mitochondrial dysfunction, the LKB1-AMPK axis inhibits ULK1 activation and autophagy induction, even under amino acid starvation. Despite its inhibitory effect, AMPK protects the ULK1-associated autophagy machinery from caspase-mediated degradation during energy deficiency, preserving the cellular ability to initiate autophagy and restore homeostasis once the stress subsides. Our findings reveal that dual functions of AMPK, restraining abrupt induction of autophagy upon energy shortage while preserving essential autophagy components, are crucial to maintain cellular homeostasis and survival during energy stress.

Adenosine Monophosphate-Activated Protein Kinase (AMPK) Phosphorylation Is Required for 20-Hydroxyecdysone Regulates Ecdysis in Apolygus lucorum

The plant mirid bug Apolygus lucorum is an omnivorous pest that can cause considerable economic damage. The steroid hormone 20-hydroxyecdysone (20E) is mainly responsible for molting and metamorphosis. The adenosine monophosphate-activated protein kinase (AMPK) is an intracellular energy sensor regulated by 20E, and its activity is regulated allosterically through phosphorylation. It is unknown whether the 20E-regulated insect's molting and gene expression depends on the AMPK phosphorylation. Herein, we cloned the full-length cDNA of the AlAMPK gene in A. lucorum. AlAMPK mRNA was detected at all developmental stages, whereas the dominant expression was in the midgut and, to a lesser extent, in the epidermis and fat body. Treatment with 20E and AMPK activator 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AlCAR) or only AlCAR resulted in activation of AlAMPK phosphorylation levels in the fat body, probed with an antibody directed against AMPK phosphorylated at Thr172, enhancing AlAMPK expression, whereas no phosphorylation occurred with compound C. Compared to compound C, 20E and/or AlCAR increased the molting rate, the fifth instar nymphal weight and shortened the development time of A. lucorum in vitro by inducing the expression of EcR-A, EcR-B, USP, and E75-A. Similarly, the knockdown of AlAMPK by RNAi reduced the molting rate of nymphs, the weight of fifth-instar nymphs and blocked the developmental time and the expression of 20E-related genes. Moreover, as observed by TEM, the thickness of the epidermis of the mirid was significantly increased in 20E and/or AlCAR treatments, molting spaces began to form between the cuticle and epidermal cells, and the molting progress of the mirid was significantly improved. These composite data indicated that AlAMPK, as a phosphorylated form in the 20E pathway, plays an important role in hormonal signaling and, in short, regulating insect molting and metamorphosis by switching its phosphorylation status.

The interaction between Hsp90-mediated unfolded protein response and autophagy contributes to As3+/ Se4+ combination-induced apoptosis of acute promyelocytic leukemia cells

The interaction between the unfolded protein response (UPR) and autophagy plays either pro-survival or pro-apoptotic roles in the treatment of acute promyelocytic leukemia (APL). Our previous study has shown that the combination therapy of arsenite (As³⁺) and selenite (Se⁴⁺) induces apoptosis in APL NB4 cells, although the mechanisms are not clear. Here, we demonstrate that the interaction between heat shock protein 90 (Hsp90)-mediated UPR and autophagy is the core module for As³⁺/Se⁴⁺ combination-induced apoptosis. Hsp90 overexpression and knockdown assays indicate that Hsp90 inhibition by PERK modulates two branches of the UPR, leading to the activation of ATF4 and CHOP, causing the degradation of IRE1α and the dephosphorylation of eIF2α, thereby contributing to switching the cytoprotective UPR into an apoptotic pathway. Assays using pretreatment with inducers and inhibitors of endoplasmic reticulum stress (ERS) and autophagy reveal that autophagy is stimulated by ERS but suppressed by As³⁺/Se⁴⁺ combination via the mTOR signaling pathway. However, inhibition of autophagy decreases GRP78 expression and eIF2α phosphorylation, thereby further promoting ERS-induced apoptosis. Moreover, As³⁺/Se⁴⁺ combination blocks hepatic infiltration in an APL-NCG mouse model of extramedullary infiltration. Taken together, these findings provide novel agents and therapeutic approaches for APL.

Early Growth Response-1: Friend or Foe in the Heart?

Cardiovascular disease is a major cause of mortality and morbidity worldwide. Early growth response-1 (Egr-1) plays a critical regulatory role in a range of experimental models of cardiovascular diseases. Egr-1 is an immediate-early gene and is upregulated by various stimuli including shear stress, oxygen deprivation, oxidative stress and nutrient deprivation. However, recent research suggests a new, underexplored cardioprotective side of Egr-1. The main purpose of this review is to explore and summarise the dual nature of Egr-1 in cardiovascular pathobiology.

Trehalose attenuates abdominal aortic aneurysm formation by inducing autophagy in smooth muscle cells

BACKGROUND

Trehalose is a naturally occurring disaccharide, which has been identified as an autophagy inducer and exhibits protective effect in cardiovascular diseases such as myocardial infraction and atherosclerosis. However, the functional role of trehalose in abdominal aortic aneurysm (AAA) remains undefined.

METHODS

To study the effect of trehalose in AAA, trehalose (1 g/kg per day) were given for 14 continuous days in a mouse model of elastase-induced abdominal aortic aneurysm. On day 14, ultrasound was performed to measure aortic diameter before the abdominal aortas were harvested and processed for further analysis. Verhoeff-Van Gieson staining and TUNEL staining were performed on paraffin sections to evaluate vascular histology and apoptosis, immunofluorescence staining and Western-blot were performed to evaluate expression of autophagy markers.

RESULTS

Echocardiography and in situ pictures demonstrated that trehalose attenuated infrarenal aorta dilation. Verhoeff-Van Gieson staining showed elastin degradation was improved in trehalose-treated group. Compared with vehicle-treated mice, trehalose treatment restored smooth muscle cell contractile phenotype with increased α-SMA, Calponin and Myh11 expression. Furthermore, trehalose also attenuated cell apoptosis and leukocytes infiltration. Importantly, trehalose induced autophagy with decrease SQSTM1/p62 accumulation, increased lamp2 expression and LC3B conversion.

CONCLUSION

Trehalose attenuated AAA progression with decreased inflammation and restored SMC contractile phenotype by inducing autophagy. These results demonstrated the therapeutic potential of trehalose in AAA.

The Role of Alternative Mitophagy in Heart Disease

Autophagy is essential for maintaining cellular homeostasis through bulk degradation of subcellular constituents, including misfolded proteins and dysfunctional organelles. It is generally governed by the proteins Atg5 and Atg7, which are critical regulators of the conventional autophagy pathway. However, recent studies have identified an alternative Atg5/Atg7-independent pathway, i.e., Ulk1- and Rab9-mediated alternative autophagy. More intensive studies have identified its essential role in stress-induced mitochondrial autophagy, also known as mitophagy. Alternative mitophagy plays pathophysiological roles in heart diseases such as myocardial ischemia and pressure overload. Here, this review discusses the established and emerging mechanisms of alternative autophagy/mitophagy that can be applied in therapeutic interventions for heart disorders.

Autophagy and neurodegeneration: Unraveling the role of C9ORF72 in the regulation of autophagy and its relationship to ALS-FTD pathology

The proper functioning of the cell clearance machinery is critical for neuronal health within the central nervous system (CNS). In normal physiological conditions, the cell clearance machinery is actively involved in the elimination of misfolded and toxic proteins throughout the lifetime of an organism. The highly conserved and regulated pathway of autophagy is one of the important processes involved in preventing and neutralizing pathogenic buildup of toxic proteins that could eventually lead to the development of neurodegenerative diseases (NDs) such as Alzheimer’s disease or Amyotrophic lateral sclerosis (ALS). The most common genetic cause of ALS and frontotemporal dementia (FTD) is a hexanucleotide expansion consisting of GGGGCC (G4C2) repeats in the chromosome 9 open reading frame 72 gene (C9ORF72). These abnormally expanded repeats have been implicated in leading to three main modes of disease pathology: loss of function of the C9ORF72 protein, the generation of RNA foci, and the production of dipeptide repeat proteins (DPRs). In this review, we discuss the normal physiological role of C9ORF72 in the autophagy-lysosome pathway (ALP), and present recent research deciphering how dysfunction of the ALP synergizes with C9ORF72 haploinsufficiency, which together with the gain of toxic mechanisms involving hexanucleotide repeat expansions and DPRs, drive the disease process. This review delves further into the interactions of C9ORF72 with RAB proteins involved in endosomal/lysosomal trafficking, and their role in regulating various steps in autophagy and lysosomal pathways. Lastly, the review aims to provide a framework for further investigations of neuronal autophagy in C9ORF72-linked ALS-FTD as well as other neurodegenerative diseases.

Mitochondrial Lon-induced mitophagy benefits hypoxic resistance via Ca2+-dependent FUNDC1 phosphorylation at the ER-mitochondria interface

During hypoxia, FUNDC1 acts as a mitophagy receptor and accumulates at the ER (endoplasmic reticulum)-mitochondria contact sites (EMC), also called mitochondria-associated membranes (MAM). In mitophagy, the ULK1 complex phosphorylates FUNDC1(S17) at the EMC site. However, how mitochondria sense the stress and send the signal from the inside to the outside of mitochondria to trigger mitophagy is still unclear. Mitochondrial Lon was reported to be localized at the EMC under stress although the function remained unknown. In this study, we explored the mechanism of how mitochondrial sensors of hypoxia trigger and stabilize the FUNDC1-ULK1 complex by Lon in the EMC for cell survival and cancer progression. We demonstrated that Lon is accumulated in the EMC and associated with FUNDC1-ULK1 complex to induce mitophagy via chaperone activity under hypoxia. Intriguingly, we found that Lon-induced mitophagy is through binding with mitochondrial Na⁺/Ca²⁺ exchanger (NCLX) to promote FUNDC1-ULK1-mediated mitophagy at the EMC site in vitro and in vivo. Accordingly, our findings highlight a novel mechanism responsible for mitophagy initiation under hypoxia by chaperone Lon in mitochondria through the interaction with FUNDC1-ULK1 complex at the EMC site. These findings provide a direct correlation between Lon and mitophagy on cell survival and cancer progression.

Thymoquinone attenuates hepatic lipid accumulation by inducing autophagy via AMPK/mTOR/ULK1-dependent pathway in nonalcoholic fatty liver disease

Thymoquinone (TQ) has been proved to exert wide-ranging pharmacological activities, with anti-inflammatory, antioxidant, anticonvulsant, antimicrobial, anti-tumor, and antidiabetic properties. In this study, we investigated the beneficial effects of TQ on a high-fat diet (HFD)-induced nonalcoholic fatty liver disease (NAFLD) in C57BL/6 N mice in vivo and free fatty acid (FFA)-induced human hepatocellular carcinoma HepG2 cells in vitro. Further, the underlying mechanisms of TQ to promote hepatic autophagy were also discovered. Data showed that TQ caused (p < 0.01) body weight reduction, improved glucose homeostasis, alleviated hepatosteatosis, and decreased hepatic lipid accumulation related to the induction of autophagy in HFD-fed mice. In vitro, TQ obviously increased (p < 0.01) autophagic flux in FFA-induced HepG2 cells and consequently reduced the lipid accumulation in combination with activation of AMPK/mTOR/ULK1 signaling pathways. Moreover, pharmacological inhibition of the AMPK pathway by addition with AMPK inhibitor Compound C (CC) or silence of ULK1 by transfection with siRNA(ULK1) into HepG2 cells reversed these beneficial effects of TQ on triggering hepatic autophagy and reducing lipid accumulation (p < 0.01). Taken together, these results suggested that TQ alleviated hepatic lipid accumulation by triggering autophagy through the AMPK/mTOR/ULK1-dependent signaling pathway. Our study supports a potential role for TQ in ameliorating NAFLD.

BL-918, a small-molecule activator of ULK1, induces cytoprotective autophagy for amyotrophic lateral sclerosis therapy

Amyotrophic lateral sclerosis (ALS) is one of the most common fatal neurodegenerative diseases in adults. ALS pathogenesis is associated with toxic SOD1 aggregates generated by mutant SOD1. Since autophagy is responsible for the clearance of toxic protein aggregates including SOD1 aggregates, autophagy induction has been considered as a potential strategy for treating ALS. Autophagic signaling is initiated by unc-51 like autophagy activating kinase 1 (ULK1) complex. We previously identified that BL-918 as a specific ULK1 activator, which exerted cytoprotective effect against Parkinson's disease in vitro and in vivo. In this study we investigated whether BL-918 exerted a therapeutic effect against ALS, and characterized its pharmacokinetic profile in rats. In hSODG93A-NSC34 cells, treatment with BL-918 (5, 10 μM) dose-dependently induced ULK1-dependent autophagy, and eliminated toxic SOD1 aggregates. In SODG93A mice, administration of BL-918 (40, 80 mg/kg, b.i.d., i.g.) dose-dependently prolonged lifespan and improved the motor function, and enhanced the clearance of SOD1 aggregates in spinal cord and cerebral cortex through inducing autophagy. In the pharmacokinetic study conducted in rats, we found BL-918 and its 2 metabolites (M8 and M10) present in spinal cord and brain; after intragastric and intravenous administration, BL-918 reached the highest blood concentration compared to M8 and M10. Collectively, ULK1 activator BL-918 displays a therapeutic potential on ALS through inducing cytoprotective autophagy. This study provides a further clue for autophagic dysfunction in ALS pathogenesis.

Lack of COL6/collagen VI causes megakaryocyte dysfunction by impairing autophagy and inducing apoptosis

Endoplasmic reticulum stress is an emerging significant player in the molecular pathology of connective tissue disorders. In response to endoplasmic reticulum stress, cells can upregulate macroautophagy/autophagy, a fundamental cellular homeostatic process used by cells to degrade and recycle proteins or remove damaged organelles. In these scenarios, autophagy activation can support cell survival. Here we demonstrated by in vitro and in vivo approaches that megakaryocytes derived from col6a1^-⁄- (collagen, type VI, alpha 1) null mice display increased intracellular retention of COL6 polypeptides, endoplasmic reticulum stress and apoptosis. The unfolded protein response is activated in col6a1^-⁄- megakaryocytes, as evidenced by the upregulation of molecular chaperones, by the increased splicing of Xbp1 mRNA and by the higher level of the pro-apoptotic regulator DDIT3/CHOP. Despite the endoplasmic reticulum stress, basal autophagy is impaired in col6a1^-⁄- megakaryocytes, which show lower BECN1 levels and reduced autophagosome maturation. Starvation and rapamycin treatment rescue the autophagic flux in col6a1^-⁄- megakaryocytes, leading to a decrease in intracellular COL6 polypeptide retention, endoplasmic reticulum stress and apoptosis. Furthermore, megakaryocytes cultured from peripheral blood hematopoietic progenitors of patients affected by Bethlem myopathy and Ullrich congenital muscular dystrophy, two COL6-related disorders, displayed increased apoptosis, endoplasmic reticulum stress and impaired autophagy. These data demonstrate that genetic disorders of collagens, endoplasmic reticulum stress and autophagy regulation in megakaryocytes may be interrelated.Abbreviations: 7-AAD: 7-amino-actinomycin D; ATF: activating transcriptional factor; BAX: BCL2 associated X protein; BCL2: B cell leukemia/lymphoma 2; BCL2L1/Bcl-xL: BCL2-like 1; BM: bone marrow; COL6: collagen, type VI; col6a1^-⁄-: mice that are null for Col6a1; DDIT3/CHOP/GADD153: DNA-damage inducible transcript 3; EGFP: enhanced green fluorescent protein; ER: endoplasmic reticulum; reticulophagy: endoplasmic reticulum-selective autophagy; HSPA5/Bip: heat shock protein 5; HSP90B1/GRP94: heat shock protein 90, beta (Grp94), member 1; LAMP2: lysosomal associated membrane protein 2; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; Mk: megakaryocytes; MTOR: mechanistic target of rapamycin kinase; NIMV: noninvasive mechanical ventilation; PI3K: phosphoinositide 3-kinase; PPP1R15A/GADD34: protein phosphatase 1, regulatory subunit 15A; RT-qPCR: reverse transcription-quantitative real-time PCR; ROS: reactive oxygen species; SERPINH1/HSP47: serine (or cysteine) peptidase inhibitor, clade H, member 1; sh-RNA: short hairpin RNA; SOCE: store operated calcium entry; UCMD: Ullrich congenital muscular dystrophy; UPR: unfolded protein response; WIPI2: WD repeat domain, phosphoinositide-interacting 2; WT: wild type; XBP1: X-box binding protein 1.

TBK1-medicated DRP1 phosphorylation orchestrates mitochondrial dynamics and autophagy activation in osteoarthritis

Mitochondrial dynamics, including mitochondrial fission and fusion, are critical for maintaining mitochondrial functions. Evidence shows that TANK-binding kinase 1 (TBK1) regulates mitochondrial fusion and fission and then mitophagy. Since a previous study demonstrates a strong correlation between mitophagy and osteoarthritis (OA), we herein investigated the potential role of TBK1 in OA process and mitochondrial functions. We demonstrated a strong correlation between TBK1 and OA, evidenced by significantly downregulated expression of TBK1 in cartilage tissue samples of OA patients and in the chondrocytes of aged mice, as well as TNF-α-stimulated phosphorylation of TBK1 in primary mouse chondrocytes. TBK1 overexpression significantly attenuated TNF-α-induced apoptosis and abnormal mitochondrial function in primary mouse chondrocytes. Furthermore, TBK1 overexpression induced remodeling of mitochondrial morphology by directly phosphorylating dynamin-related protein 1 (DRP1) at Ser637, abolishing the fission of DRP1 and preventing its fragmentation function. Moreover, TBK1 recruitment and DRP1 phosphorylation at Ser637 was necessary for engulfing damaged mitochondria by autophagosomal membranes during mitophagy. Moreover, we demonstrated that APMK/ULK1 signaling contributed to TBK1 activation. In OA mouse models established by surgical destabilization of the medial meniscus, intraarticular injection of lentivirus-TBK1 significantly ameliorated cartilage degradation via regulation of autophagy and alleviation of cell apoptosis. In conclusion, our results suggest that the TBK1/DRP1 pathway is involved in OA and pharmacological targeting of the TBK1-DRP1 cascade provides prospective therapeutic benefits for the treatment of OA.

Autophagy/Mitophagy Regulated by Ubiquitination: A Promising Pathway in Cancer Therapeutics

Autophagy is essential for organismal development, maintenance of energy homeostasis, and quality control of organelles and proteins. As a selective form of autophagy, mitophagy is necessary for effectively eliminating dysfunctional mitochondria. Both autophagy and mitophagy are linked with tumor progression and inhibition. The regulation of mitophagy and autophagy depend upon tumor type and stage. In tumors, mitophagy has dual roles: it removes damaged mitochondria to maintain healthy mitochondria and energy production, which are necessary for tumor growth. In contrast, mitophagy has been shown to inhibit tumor growth by mitigating excessive ROS production, thus preventing mutation and chromosomal instability. Ubiquitination and deubiquitination are important modifications that regulate autophagy. Multiple E3 ubiquitin ligases and DUBs modulate the activity of the autophagy and mitophagy machinery, thereby influencing cancer progression. In this review, we summarize the mechanistic association between cancer development and autophagy/mitophagy activities regulated by the ubiquitin modification of autophagic proteins. In addition, we discuss the function of multiple proteins involved in autophagy/mitophagy in tumors that may represent potential therapeutic targets.

Interplays of AMPK and TOR in Autophagy Regulation in Yeast

Cells survey their environment and need to balance growth and anabolism with stress programmes and catabolism towards maximum cellular bioenergetics economy and survival. Nutrient-responsive pathways, such as the mechanistic target of rapamycin (mTOR) interact and cross-talk, continuously, with stress-responsive hubs such as the AMP-activated protein kinase (AMPK) to regulate fundamental cellular processes such as transcription, protein translation, lipid and carbohydrate homeostasis. Especially in nutrient stresses or deprivations, cells tune their metabolism accordingly and, crucially, recycle materials through autophagy mechanisms. It has now become apparent that autophagy is pivotal in lifespan, health and cell survival as it is a gatekeeper of clearing damaged macromolecules and organelles and serving as quality assurance mechanism within cells. Autophagy is hard-wired with energy and nutrient levels as well as with damage-response, and yeasts have been instrumental in elucidating such connectivities. In this review, we briefly outline cross-talks and feedback loops that link growth and stress, mainly, in the fission yeast Schizosaccharomyces pombe, a favourite model in cell and molecular biology.

BRG1: Promoter or Suppressor of Cancer? The Outcome of BRG1's Interaction with Specific Cellular Pathways

BRG1 is one of two catalytic subunits of the SWI/SNF ATP-dependent chromatin-remodeling complex. In cancer, it has been hypothesized that BRG1 acts as a tumor suppressor. Further study has shown that, under certain circumstances, BRG1 acts as an oncogene. Targeted knockout of BRG1 has proven successful in most cancers in suppressing tumor growth and proliferation. Furthermore, BRG1 effects cancer proliferation in oncogenic KRAS mutated cancers, with varying directionality. Thus, dissecting BRG1's interaction with various cellular pathways can highlight possible intermediates that can facilitate the design of different treatment methods, including BRG1 inhibition. Autophagy and apoptosis are two important cellular responses to stress. BRG1 plays a direct role in autophagy and apoptosis and likely promotes autophagy and suppresses apoptosis, supporting unfettered cancer growth. PRMT5 inhibits transcription by interacting with ATP-dependent chromatin remodeling complexes, such as SWI/SNF. When PRMT5 associates with the SWI/SNF complex, including BRG1, it represses tumor suppressor genes. The Ras/Raf/MAPK/ERK1/2 pathway in cancers is a signal transduction pathway involved in the transcription of genes related to cancer survival. BRG1 has been shown to effect KRAS-driven cancer growth. BRG1 associates with several proteins within the signal transduction pathway. In this review, we analyze BRG1 as a promising target for cancer inhibition and possible synergy with other cancer treatments.

Lysosome signaling in cell survival and programmed cell death for cellular homeostasis

Recent developments in lysosome biology have transformed our view of lysosomes from static garbage disposals that can also act as suicide bags to decidedly dynamic multirole adaptive operators of cellular homeostasis. Lysosome-governed signaling pathways, proteins, and transcription factors equilibrate the rate of catabolism and anabolism (autophagy to lysosomal biogenesis and metabolite pool maintenance) by sensing cellular metabolic status. Lysosomes also interact with other organelles by establishing contact sites through which they exchange cellular contents. Lysosomal function is critically assessed by lysosomal positioning and motility for cellular adaptation. In this setting, mechanistic target of rapamycin kinase (MTOR) is the chief architect of lysosomal signaling to control cellular homeostasis. Notably, lysosomes can orchestrate explicit cell death mechanisms, such as autophagic cell death and lysosomal membrane permeabilization-associated regulated necrotic cell death, to maintain cellular homeostasis. These lines of evidence emphasize that the lysosomes serve as a central signaling hub for cellular homeostasis.

Metabolic adaptations of cancer in extreme tumor microenvironments

Cancer cells are highly heterogeneous to adapt to extreme tumor microenvironments (TMEs). TMEs challenge cancer cells via hypoxia, nutrition starvation, and acidic pH, promoting invasion and metastasis concomitant with genetic, epigenetic, and metabolic alterations. Metabolic adaptation to an extreme TME could allow cancer cells to evade cell death and immune responses, as well as resulting in drug resistance, recurrence, and poor patient prognosis. Therefore, elucidation of the metabolic adaptation of malignant cancer cells within TMEs is necessary, however, most are still elusive. Recently, adaptation of cancer cells within the TME can be analyzed via cell-cell interactions at the single-cell level. In addition, information into organelle-organelle interactions has recently been obtained. These cell-cell, and organelle-organelle interactions demonstrate the potential as new cancer therapy targets, as they play essential roles in the metabolic adaptation of cancer cells to the TME. In this manuscript, we review (1) metabolic adaptations within tumor microenvironments through (2) cell-to-cell, and (3) organelle-organelle metabolic interactions.

Autophagy activation attenuates the circadian clock oscillators in U2OS cells via the ATG5 pathway

The circadian clock and autophagy are essential biological mechanisms involved in regulating many physiological processes. Accumulating evidence has revealed that autophagic activity is regulated by the circadian clock system. However, whether autophagy regulates the circadian clock system remains unclear. In this study, rapamycin and AICAR, two classical activators of autophagy, were used to create autophagy activation models in BMAL1-dLuc U2OS cell line. The results showed that the mRNA expression of MAP1LC3B and ATG5 were significantly upregulated after autophagy activation, whereas the mRNA expression of circadian clock genes (BMAL1, PER2, REV-ERBα, and DBP) were significantly decreased. Consistent with these data, the relative ratio of LC3-II/LC3-I and the protein level of ATG5 were increased after rapamycin or AICAR treatment. In contrast, BMAL1 and REV-ERBα levels were decreased. Notably, the mRNA expression of circadian clock genes (BMAL1, PER2, REV-ERBα, and DBP) and autophagy-related genes (MAP1LC3B and ATG5) showed rhythmic expression patterns in both untreated and rapamycin/AICAR-treated U2OS cells. Moreover, the autophagy inhibitor 3-methyladenine partially reversed the inhibitory effects of autophagy on circadian clock genes expression and BMAL1-Luc oscillations. Another critical finding was that ATG5 knockout alleviates the inhibitory effect of rapamycin-mediated autophagy activation on the circadian clock oscillators in U2OS cells. Collectively, our data indicate that autophagy activation attenuates the circadian clock oscillators in U2OS cells via the ATG5 pathway.

Ratiometric and Discriminative Visualization of Autophagy and Apoptosis with a Single Fluorescent Probe Based on the Aggregation/Monomer Principle

Autophagy and apoptosis play a central role in maintaining homeostasis in mammals. Therefore, discriminative visualization of the two cellular processes is an important and challenging task. However, fluorescent probes enabling ratiometric visualization of both autophagy and apoptosis with different sets of fluorescence signals have not been developed yet. In this work, we constructed a versatile single fluorescent probe (NKLR) based on the aggregation/monomer principle for the ratiometric and discriminative visualization of autophagy and apoptosis. NKLR can simultaneously perform two-color imaging of RNA (deep red channel) and lysosomes (yellow channel) in aggregation and monomer states, respectively. During autophagy, NKLR migrated from cytoplasmic RNA and nuclear RNA to lysosomes, showing enhanced yellow emission and sharply decreased deep red fluorescence. Moreover, this migration process was reversible upon the recovery of autophagy. Comparatively, during apoptosis, NKLR immigrated from lysosomes to RNA, and the yellow emission decreased and even disappeared, while the fluorescence of the deep red channel slightly increased. Overall, autophagy and apoptosis could be discriminatively visualized via the fluorescence intensity ratios of the two channels. Meanwhile, the cells in three different states (healthy, autophagic, apoptotic) could be distinguished by three point-to-point fluorescence images via the localization and emission color of NKLR. Therefore, the probe NKLR can serve as a desirable molecular tool to reveal the in-depth relation between autophagy and apoptosis and facilitate the study on the two cellular processes.

The Importance of mTORC1-Autophagy Axis for Skeletal Muscle Diseases

The mechanistic target of rapamycin (mTOR) complex 1, mTORC1, integrates nutrient and growth factor signals with cellular responses and plays critical roles in regulating cell growth, proliferation, and lifespan. mTORC1 signaling has been reported as a central regulator of autophagy by modulating almost all aspects of the autophagic process, including initiation, expansion, and termination. An increasing number of studies suggest that mTORC1 and autophagy are critical for the physiological function of skeletal muscle and are involved in diverse muscle diseases. Here, we review recent insights into the essential roles of mTORC1 and autophagy in skeletal muscles and their implications in human muscle diseases. Multiple inhibitors targeting mTORC1 or autophagy have already been clinically approved, while others are under development. These chemical modulators that target the mTORC1/autophagy pathways represent promising potentials to cure muscle diseases.

The Greatwall-Endosulfine Switch Accelerates Autophagic Flux during the Cell Divisions Leading to G1 Arrest and Entry into Quiescence in Fission Yeast

Entry into quiescence in the fission yeast Schizosaccharomyces pombe is induced by nitrogen starvation. In the absence of nitrogen, proliferating fission yeast cells divide twice without cell growth and undergo cell cycle arrest in G1 before becoming G0 quiescent cells. Under these conditions, autophagy is induced to produce enough nitrogen for the two successive cell divisions that take place before the G1 arrest. In parallel to the induction of autophagy, the Greatwall-Endosulfine switch is activated upon nitrogen starvation to down-regulate protein phosphatase PP2A/B55 activity, which is essential for cell cycle arrest in G1 and implementation of the quiescent program. Here we show that, although inactivation of PP2A/B55 by the Greatwall-Endosulfine switch is not required to promote autophagy initiation, it increases autophagic flux at least in part by upregulating the expression of a number of autophagy-related genes.