Alternative autophagy: mechanisms and roles in different diseases

Anti-Cancer Strategy Based on Changes in the Role of Autophagy Depending on the Survival Environment and Tumorigenesis Stages

Autophagy is a crucial mechanism for recycling intracellular materials, and under normal metabolic conditions, it is maintained at low levels in cells. However, when nutrients are deficient or under hypoxic conditions, the level of autophagy significantly increases. Particularly in cancer cells, which grow more rapidly than normal cells and tend to grow in a three-dimensional manner, cells inside the cell mass often face limited oxygen supply, leading to inherently higher levels of autophagy. Therefore, the initial development of anticancer drugs targeting autophagy was based on a strategy to suppress these high levels of autophagy. However, anticancer drugs that inhibit autophagy have not shown promising results in clinical trials, as it has been revealed that autophagy does not always play a role that favors cancer cell survival. Hence, this review aims to suggest anticancer strategies based on the changes in the role of autophagy according to survival conditions and tumorigenesis stage.

Insights into molecular and cellular functions of the Golgi calcium/manganese-proton antiporter TMEM165

The Golgi compartment performs a number of crucial roles in the cell. However, the exact molecular mechanisms underlying these actions are not fully defined. Pathogenic mutations in genes encoding Golgi proteins may serve as an important source for expanding our knowledge. For instance, mutations in the gene encoding Transmembrane protein 165 (TMEM165) were discovered as a cause of a new type of congenital disorder of glycosylation (CDG). Comprehensive studies of TMEM165 in different model systems, including mammals, yeast, and fish uncovered the new realm of Mn2+ homeostasis regulation. TMEM165 was shown to act as a Ca2+/Mn2+:H+ antiporter in the medial- and trans-Golgi network, pumping the metal ions into the Golgi lumen and protons outside. Disruption of TMEM165 antiporter activity results in defects in N- and O-glycosylation of proteins and glycosylation of lipids. Impaired glycosylation of TMEM165-CDG arises from a lack of Mn2+ within the Golgi. Nevertheless, Mn2+ insufficiency in the Golgi is compensated by the activity of the ATPase SERCA2. TMEM165 turnover has also been found to be regulated by Mn2+ cytosolic concentration. Besides causing CDG, recent investigations have demonstrated the functional involvement of TMEM165 in several other pathologies including cancer and mental health disorders. This systematic review summarizes the available information on TMEM165 molecular structure, cellular function, and its roles in health and disease.

Chemotherapy's effects on autophagy in the treatment of Hodgkin's lymphoma: a scoping review

BACKGROUND

Classical Hodgkin Lymphomas (HL) are a unique malignant growth with an excellent initial prognosis. However, 10-30% of patients will still relapse after remission. One primary cellular function that has been the focus of tumor progression is autophagy. This process can preserve cellular homeostasis under stressful conditions. Several studies have shown that autophagy may play a role in developing HL. Therefore, this review aimed to explore chemotherapy's effect on autophagy in HL, and the effects of autophagy on HL.

METHODS

A scoping review in line with the published PRISMA extension for scoping reviews (PRISMA-ScR) was conducted. A literature search was conducted on the MEDLINE database and the Cochrane Central Register of Controlled Trials (CENTRAL). All results were retrieved and screened, and the resulting articles were synthesized narratively.

RESULTS

The results showed that some cancer chemotherapy also induces autophagic flux. Although the data on HL is limited, since the mechanisms of action of these drugs are similar, we can infer a similar relationship. However, this increased autophagy activity may reflect a mechanism for increasing tumor growth or a cellular compensation to inhibit its growth. Although evidence supports both views, we argued that autophagy allowed cancer cells to resist cell death, mainly due to DNA damage caused by cytotoxic drugs.

CONCLUSION

Autophagy reflects the cell's adaptation to survive and explains why chemotherapy generally induces autophagy functions. However, further research on autophagy inhibition is needed as it presents a viable treatment strategy, especially against drug-resistant populations that may arise from HL chemotherapy regimens.

Autophagy in Its (Proper) Context: Molecular Basis, Biological Relevance, Pharmacological Modulation, and Lifestyle Medicine

Autophagy plays a critical role in maintaining cellular homeostasis and responding to various stress conditions by the degradation of intracellular components. In this narrative review, we provide a comprehensive overview of autophagy's cellular and molecular basis, biological significance, pharmacological modulation, and its relevance in lifestyle medicine. We delve into the intricate molecular mechanisms that govern autophagy, including macroautophagy, microautophagy and chaperone-mediated autophagy. Moreover, we highlight the biological significance of autophagy in aging, immunity, metabolism, apoptosis, tissue differentiation and systemic diseases, such as neurodegenerative or cardiovascular diseases and cancer. We also discuss the latest advancements in pharmacological modulation of autophagy and their potential implications in clinical settings. Finally, we explore the intimate connection between lifestyle factors and autophagy, emphasizing how nutrition, exercise, sleep patterns and environmental factors can significantly impact the autophagic process. The integration of lifestyle medicine into autophagy research opens new avenues for promoting health and longevity through personalized interventions.

Establishment of a high-content imaging assay for tau aggregation in hiPSC-derived neurons differentiated from two protocols to routinely evaluate compounds and genetic perturbations

Aberrant protein aggregation is a pathological cellular hallmark of many neurodegenerative diseases, such as Alzheimer's disease (AD) and frontotemporal dementia (FTD), where the tau protein is aggregating, forming neurofibrillary tangles (NFTs), and propagating from neuron to neuron. These processes have been linked to disease progression and a decline in cognitive function. Various therapeutic approaches aim at the prevention or reduction of tau aggregates in neurons. Human induced pluripotent stem cells (hiPSCs) are a very valuable tool in neuroscience discovery, as they offer access to potentially unlimited amounts of cell types that are affected in disease, including cortical neurons, for in vitro studies. We have generated an in vitro model for tau aggregation that uses hiPSC - derived neurons expressing an aggregation prone, fluorescently tagged version of the human tau protein after lentiviral transduction. Upon addition of tau seeds in the form of recombinant sonicated paired helical filaments (sPHFs), the neurons show robust, disease-like aggregation of the tau protein. The model was developed as a plate-based high content screening assay coupled with an image analysis algorithm to evaluate the impact of small molecules or genetic perturbations on tau. We show that the assay can be used to evaluate small molecules or screen targeted compound libraries. Using siRNA-based gene knockdown, genes of interest can be evaluated, and we could show that a targeted gene library can be screened, by screening nearly 100 deubiquitinating enzymes (DUBs) in that assay. The assay uses an imaging-based readout, a relatively short timeline, quantifies the extent of tau aggregation, and also allows the assessment of cell viability. Furthermore, it can be easily adapted to different hiPSC lines or neuronal subtypes. Taken together, this complex and highly relevant approach can be routinely applied on a weekly basis in the screening funnels of several projects and generates data with a turnaround time of approximately five weeks.

Melatonin alleviates renal injury in diabetic rats by regulating autophagy

Melatonin (MLT) is a biologically active indoleamine involved in regulating various biological rhythms, which is deficient in individuals with Type 2 diabetes. The present study examined the effects of MLT on diabetic neuropathy (DN). Diabetic rats received MLT treatment for 12 weeks, after which changes in kidney histology, oxidative damage, mitochondrial morphology and autophagy were measured. The glucose tolerance‑ and isoflurane tolerance‑area under the curve (AUC) values and the relative renal weight index (RI) in the diabetes mellitus (DM) group of rats were significantly higher compared with those in the control group. A significant increase in malondialdehyde (MDA) content, and decreases in the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH‑Px) and GSH were demonstrated in the kidneys of DM rats compared with those in the control rats. Histological staining of DM rat kidney tissue with hematoxylin and eosin, Masson's trichome and Periodic acid‑Schiff demonstrated glomerular and tubule lesions, and an increase in collagen compared with control rats. Protein expression levels of LC3II, P62, collagen IV (COL‑IV) and α‑SMA were increased in DM rats and HG‑induced NRK‑52E cells compared with those in the control groups. Phosphorylation of AMPK was reduced, whereas phosphorylation of PI3K, Akt and mTOR were increased in vivo and in vitro. Notably, MLT treatment significantly reduced glucose tolerance‑AUC and RI, decreased MDA content, and increased SOD, CAT, GSH‑Px and GSH activity. Glomerular and tubule lesions improved, collagen was decreased and mitochondrial damage was alleviated by MLT treatment. MLT treatment also decreased the protein expression levels of LC3II, P62 and COL‑IV, whereas the phosphorylation of AMPK was significantly increased, which inhibited the phosphorylation of PI3K, AKT and mTOR in vivo and in vitro. These results demonstrated that MLT protects against DN and NRK‑52E cell injury through inhibiting oxidative damage and regulating autophagy via the PI3K/AKT/mTOR signaling pathway.

Systems Biology and Cytokines Potential Role in Lung Cancer Immunotherapy Targeting Autophagic Axis

Lung cancer accounts for the highest number of deaths among men and women worldwide. Although extensive therapies, either alone or in conjunction with some specific drugs, continue to be the principal regimen for evolving lung cancer, significant improvements are still needed to understand the inherent biology behind progressive inflammation and its detection. Unfortunately, despite every advancement in its treatment, lung cancer patients display different growth mechanisms and continue to die at significant rates. Autophagy, which is a physiological defense mechanism, serves to meet the energy demands of nutrient-deprived cancer cells and sustain the tumor cells under stressed conditions. In contrast, autophagy is believed to play a dual role during different stages of tumorigenesis. During early stages, it acts as a tumor suppressor, degrading oncogenic proteins; however, during later stages, autophagy supports tumor cell survival by minimizing stress in the tumor microenvironment. The pivotal role of the IL6-IL17-IL23 signaling axis has been observed to trigger autophagic events in lung cancer patients. Since the obvious roles of autophagy are a result of different immune signaling cascades, systems biology can be an effective tool to understand these interconnections and enhance cancer treatment and immunotherapy. In this review, we focus on how systems biology can be exploited to target autophagic processes that resolve inflammatory responses and contribute to better treatment in carcinogenesis.

Inhibition of ERK downregulates autophagy via mitigating mitochondrial fragmentation to protect SH-SY5Y cells from OGD/R injury

BACKGROUND

Cerebral ischemia-reperfusion injury (CIRI) is the main cause leading to high mortality and neurological disability in patients with cardiac arrest/cardiopulmonary resuscitation (CA/CPR). Our previous study found that extracellular signal-regulated kinase (ERK) activation, dynamin-related protein1 (Drp1)/Mitofusin2 (Mfn2)-dependent mitochondrial dynamics imbalance, and excessive autophagy were involved in the mechanism of nerve injury after CA/CPR. However, the specific pathological signaling pathway is still unknown. This study aimed to explore the molecular function changes of ERK-Drp1/Mfn2-autophagy signaling pathway in SH-SY5Y cell oxygen-glucose deprivation/reoxygenation (OGD/R) model, to further clarify the pathophysiological mechanism of CIRI, and to provide a new strategy for cerebral protection after CIRI.

METHODS

SH-SY5Y cells were pretreated with drugs 24 h before OGD/R. The Drp1 and Mfn2 knockdown were adopted small interfering RNAs. The overexpression of p-Drp1S616 and Mfn2 were used recombinant plasmids. The expression levels of mitochondrial dynamics proteins (p-Drp1, Drp1, Mfn2, Mfn1 and Opa1) and autophagy markers (LC3, Beclin1 and p62) were measured with the Western blotting. The mRNA levels after transfection were determined by PCR. Cell injury and viability were evaluated with released LDH activity and CCK8 assay kits. Mitochondria morphology and autophagosome were observed under transmission electron microscopy. Mitochondrial function was detected by the mitochondrial permeability transition pore assay kit. The co-expression of p-ERK, p-Drp1 and LC3 was assessed with multiple immunofluorescences. One-way analysis of variance followed by least significance difference post hoc analysis (for equal homogeneity) or Dunnett's T3 test (for unequal homogeneity) were used for statistical tests.

RESULTS

ERK inhibitor-PD98059 (PD) protects SH-SY5Y cells from OGD/R-induced injury; while ERK activator-TPA had the opposite effect. Similar to autophagy inhibitor 3-MA, PD downregulated autophagy to improve cell viability; while autophagy activator-rapamycin further aggravated cell death. PD and Drp1-knockdown synergistically attenuated OGD/R-induced Drp1 activation, mPTP opening and cell injury; overexpression of Drp1S616E or ablating Mfn2 partly abolished the protective effects of PD. Multiple immunofluorescences showed that p-ERK, p-Drp1 and LC3 were co-expressed.

CONCLUSION

Inhibition of ERK downregulates autophagy via reducing Drp1/Mfn2-dependent mitochondrial fragmentation to antagonize mitochondrial dysfunction and promotes cell survival in the SH-SY5Y cells OGD/R model. Video Abstract.

Development of small fluorescent probes for the analysis of autophagy kinetics

Autophagy is a dynamic process that degrades subcellular constituents, and its activity is measured by autophagic flux. The tandem proteins RFP-GFP-LC3 and GFP-LC3-RFP-LC3ΔG, which enable the visualization of autophagic vacuoles of different stages by differences in their fluorescent color, are useful tools to monitor autophagic flux, but they require plasmid transfection. In this study, we hence aimed to develop a new method to monitor autophagic flux using small cell-permeable fluorescent probes. We previously developed two green-fluorescent probes, DALGreen and DAPGreen, which detect autolysosomes and multistep autophagic vacuoles, respectively. We here developed a red-fluorescent autophagic probe, named DAPRed, which recognizes various autophagic vacuoles. By the combinatorial use of these green- and red-fluorescent probes, we were able to readily detect autophagic flux. Furthermore, these probes were useful not only for the visualization of canonical autophagy but also for alternative autophagy. DAPRed was also applicable for the detection of autophagy in living organisms.

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.

FLIP-based autophagy-detecting technique reveals closed autophagic compartments

Autophagy results in the degradation of cytosolic components via two major membrane deformations. First, the isolation membrane sequesters components from the cytosol and forms autophagosomes, by which open structures become closed compartments. Second, the outer membrane of the autophagosomes fuses with lysosomes to degrade the inner membrane and its contents. The efficiency of the latter degradation process, namely autophagic flux, can be easily evaluated using lysosomal inhibitors, whereas the dynamics of the former process is difficult to analyze because of the challenges in identifying closed compartments of autophagy (autophagosomes and autolysosomes). To resolve this problem, we here developed a method to detect closed autophagic compartments by applying the FLIP technique, and named it FLIP-based Autophagy Detection (FLAD). This technique visualizes closed autophagic compartments and enables differentiation of open autophagic structures and closed autophagic compartments in live cells. In addition, FLAD analysis detects not only starvation-induced canonical autophagy but also genotoxic stress-induced alternative autophagy. By the combinational use of FLAD and LC3, we were able to distinguish the structures of canonical autophagy from those of alternative autophagy in a single cell.

Autophagy in Hematological Malignancies

Simple Summary

Autophagy is a dynamic and tightly regulated process that seems to have dual effects in cancer. In some contexts, it can induce carcinogenesis and promote cancer cell survival, whereas in others, it acts preventing tumor cell growth and tumor progression. Thus, autophagy functions seem to strictly depend on cancer ontogenesis, progression, and type. Here, we will dive into the current knowledge of autophagy in hematological malignancies and will highlight the main genetic components involved in each cancer type.

Abstract

Autophagy is a highly conserved metabolic pathway via which unwanted intracellular materials, such as unfolded proteins or damaged organelles, are digested. It is activated in response to conditions of oxidative stress or starvation, and is essential for the maintenance of cellular homeostasis and other vital functions, such as differentiation, cell death, and the cell cycle. Therefore, autophagy plays an important role in the initiation and progression of tumors, including hematological malignancies, where damaged autophagy during hematopoiesis can cause malignant transformation and increase cell proliferation. Over the last decade, the importance of autophagy in response to standard pharmacological treatment of hematological tumors has been observed, revealing completely opposite roles depending on the tumor type and stage. Thus, autophagy can promote tumor survival by attenuating the cellular damage caused by drugs and/or stabilizing oncogenic proteins, but can also have an antitumoral effect due to autophagic cell death. Therefore, autophagy-based strategies must depend on the context to create specific and safe combination therapies that could contribute to improved clinical outcomes. In this review, we describe the process of autophagy and its role on hematopoiesis, and we highlight recent research investigating its role as a potential therapeutic target in hematological malignancies. The findings suggest that genetic variants within autophagy-related genes modulate the risk of developing hemopathies, as well as patient survival.