LC3B is lipidated to large lipid droplets during prolonged starvation for noncanonical autophagy

An immunocompetent mouse model revealed that congenital Zika virus infection disrupted hippocampal function by activating autophagy

Congenital Zika virus (ZIKV) infection significantly affects neurological development in infants and subsequently induces neurodevelopmental abnormality symptoms; however, the potential mechanism is still unknown. Therefore, in order to effectively intervene in neurodevelopmental abnormalities in infected infants, it is necessary to identify the main brain regions affected by congenital infection. In this study, we constructed a congenital ZIKV-infected murine model using immunocompetent human STAT2 knock-in mice, which presented long-term neurodevelopmental abnormalities with abnormal neurodevelopmental symptoms. We found that the hippocampus, which regulates cognitive behaviour and processes spatial information and navigation, was the main brain region affected by congenital infection and that hippocampal cells were more prone to autophagy during the growth period of these mice at the transcriptional and pathological levels. These findings highlighted that congenital ZIKV infection could interrupt hippocampal function by activating autophagy, thus providing a theoretical basis for the clinical treatment of congenital ZIKV-infected infants.

Causal validation between 179 lipids and hyperparathyroidism: A bidirectional Mendelian randomization combined meta-analysis with mediation factors

Hyperparathyroidism, an endocrine disorder linked to hypercalcemia, increases with age, particularly in those over 60. Abnormal lipid metabolism may be closely related to its occurrence and progression. The study used Mendelian randomization (MR) analysis on 179 lipid traits against hyperparathyroidism in the Finngen and UK Biobank (UKB) databases. Meta-analysis of inverse variance weighted results followed, with significance P-values corrected for multiple comparisons. Causal validation was performed between positive lipids and renal failure, and MR analysis examined the link between renal failure and hyperparathyroidism. Reverse causal validation was also conducted between lipids and hyperparathyroidism, positive lipids and renal failure, and renal failure and hyperparathyroidism. The study conducted causal validation between 179 lipid traits and hyperparathyroidism, also exploring intermediary factors. Ultimately, MR analysis was performed on triacylglycerol (52:3) levels with hyperparathyroidism in both Finngen and UKB databases, followed by meta-analysis and multiple corrections. The results showed an odds ratio (OR) of 1.147 (95% confidence interval [CI]: 1.065-1.235, P = .040). The MR results for triacylglycerol (52:3) levels and renal failure indicated an OR of 1.054 (95% CI: 1.004-1.106, P = .032). For the intermediary factor renal failure, MR analysis with hyperparathyroidism in both Finngen and UKB databases followed by meta-analysis showed an OR of 1.336 (95% CI: 1.193-1.495, P = 4.78 × 10-7). Notably, no significant associations were found in the reverse validation of each analysis process. Furthermore, the mediation effect was β12 = 0.0153, and the direct effect was β3 = 0.1207 (0.1183, 0.1230). The mediation effect accounted for 11.25%, while the direct effect accounted for 88.75% of the total effect, Z = 12.5, indicating that the direct effect predominantly influences the overall impact. The research shows that triacylglycerol (52:3) levels can directly increase the risk of hyperparathyroidism. It also raises the risk indirectly by increasing the likelihood of renal failure, an intermediary factor. About one-tenth of the lipid's effect on hyperparathyroidism is mediated through renal failure, while the direct effect constitutes roughly nine-tenths of the total effect.

New Potential Agent in Ovarian Ischemia Reperfusion Injury: Alpha Pinene

Ovarian torsion causes problems such as infertility in women due to ischemia-reperfusion (I/R) injury. α-Pinene (AP) is a monoterpene with known anti-inflammatory, antioxidant, and antiapoptotic impacts. In the present investigation, the protective impact of AP was examined in the ovarian I/R model. 28 Wistar-Albino female rats were used in the study. TNF-α, IL-1β, IL-10, MDA, IMA, SOD, and SIRT-1 levels were determined in ovarian tissue by ELISA method. Histopathological and immunohistochemical analyses were conducted to determine Bcl-2, Caspase-3, LC3B, and NFκB levels in ovarian tissues. TNF-α, IL-1β, IMA, and MDA levels were reduced in the treatment groups than the I/R group dose-dependent, while IL-10, SOD, and SIRT-1 levels increased substantially. Caspase-3 immunoreactivity declined in the treatment groups while Bcl-2 levels increased. LC3B and NFκB levels, which rise with I/R injury, were reduced considerably in the treatment groups. In addition, hemorrhage, edema, vascular congestion, and follicular degeneration due to I/R injury decreased in the treatment groups. The present investigation shows that AP has anti-inflammatory, antiapoptotic, and autophagy inhibitory effects against I/R damage in ovarian tissues and reduces oxidative stress. The results indicate that AP may be a potential protective agent in clinical use. Further research is needed before AP can be used in the clinic.

High glucose levels promote glycolysis and cholesterol synthesis via ERRα and suppress the autophagy-lysosomal pathway in endometrial cancer

Endometrial cancer (EC) patients with Diabetes Mellitus (DM) always have a poor prognosis. Estrogen-related receptor α (ERRα) is known as the metabolic-related prognostic factor for EC. However, the mechanism linking glycolipid metabolism dysfunction mediated by ERRα to poor prognosis of EC with DM is still unclear. In vitro, high-glucose (HG) levels showed enhancement of ERRα expression, cell proliferation, and inhibition of the autophagic lysosomes and apoptosis by flow cytometry analysis, transmission electron microscopy, and CCK-8 assays. Mechanistically, lose-and-gain function assay, DNA sequencing, and CO-IP revealed HG increased ERRα expression to promote the transcription of HK2 and HMGCS1, which were the key rate-limiting enzyme of glycolysis-cholesterol synthesis and their metabolites suppressed the autophagy-lysosomal pathway in an ERRα-dependent manner. Furthermore, CO-IP and molecular dynamics simulation uncovered the protein residues (ARG 769HK2 vs. ARG 313HMGCS1) of HK2 and HMGCS1 could bind to p62 to form stable protein complexes involved in the autophagy-lysosomal pathway. In EC tissue from patients with comorbid DM, ERRα was significantly higher expressed compared to EC tissue from patients without evidence for DM (p < 0.05). The 3D EC organoid model with HG stimulation showed that the cell viability of XCT790 + carboplatin treatment was similar to that of metformin+carboplatin treatment, while the obviously bigger volume of organoids was more visible in the metformin+carboplatin group, indicating the therapy of XCT790 + carboplatin had the better inhibition of EC organoids with the same carboplatin dose. Besides insights into the interaction of HG and the autophagy-lysosomal pathway via ERRα, our present study points out the potential benefit of targeting ERRα in patients with EC with dysregulation of glucose and cholesterol metabolism.

Targeting membrane contact sites to mediate lipid dynamics: innovative cancer therapies

Membrane contact sites (MCS) are specialized regions where organelles are closely interconnected through membrane structures, facilitating the transfer and exchange of ions, lipids, and other molecules. This proximity enables a synergistic regulation of cellular homeostasis and functions. The formation and maintenance of these contact sites are governed by specific proteins that bring organelle membranes into close apposition, thereby enabling functional crosstalk between cellular compartments. In eukaryotic cells, lipids are primarily synthesized and metabolized within distinct organelles and must be transported through MCS to ensure proper cellular function. Consequently, MCS act as pivotal platforms for lipid synthesis and trafficking, particularly in cancer cells and immune cells within the tumor microenvironment, where dynamic alterations are critical for maintaining lipid homeostasis. This article provides a comprehensive analysis of how these cells exploit membrane contact sites to modulate lipid synthesis, metabolism, and transport, with a specific focus on how MCS-mediated lipid dynamics influence tumor progression. We also examine the differences in MCS and associated molecules across various cancer types, exploring novel therapeutic strategies targeting MCS-related lipid metabolism for the development of anticancer drugs, while also addressing the challenges involved.

A comparison of lipid diffusive dynamics in monolayers and bilayers in the context of interleaflet coupling

Cellular membranes are composed of lipids typically organized in a double-leaflet structure. Interactions between these two leaflets - often referred to as interleaflet coupling - play a crucial role in various cellular processes. Despite extensive study, the mechanisms governing such interactions remain incompletely understood. Here, we investigate the effects of interleaflet coupling from a specific point of view, i.e. by comparing diffusive dynamics in bilayers and monolayers, focusing on potential lipid-specific interactions between opposing leaflets. Through quantitative fluorescence microscopy techniques, we characterize lipid diffusion and mean molecular area in monolayers and bilayers composed of different lipids. Our results suggest that the observed decrease in bilayer lipid diffusion compared to monolayers depends on lipid identity. Furthermore, our analysis suggests that lipid acyl chain structure and spatial configuration at the bilayer may strongly influence interleaflet interactions and dynamics in bilayers. These findings provide insights into the role of lipid structure in mediating interleaflet coupling and underscore the need for further experimental investigations to elucidate the underlying mechanisms.

An update on autophagy disorders

Macroautophagy is a highly conserved cellular pathway for the degradation and recycling of defective cargo including proteins, organelles, and macromolecular complexes. As autophagy is particularly relevant for cellular homeostasis in post-mitotic tissues, congenital disorders of autophagy, due to monogenic defects in key autophagy genes, share a common "clinical signature" including neurodevelopmental, neurodegenerative, and neuromuscular features, as well as variable abnormalities of the eyes, skin, heart, bones, immune cells, and other organ systems, depending on the expression pattern and the specific function of the defective proteins. Since the clinical and genetic resolution of EPG5-related Vici syndrome, the paradigmatic congenital disorder of autophagy, the widespread use of massively parallel sequencing has resulted in the identification of a growing number of autophagy-associated disease genes, encoding members of the core autophagy machinery as well as related proteins. Recently identified monogenic disorders linking selective autophagy, vesicular trafficking, and other pathways have further expanded the molecular and phenotypical spectrum of congenital disorders of autophagy as a clinical disease spectrum. Moreover, significant advances in basic research have enhanced the understanding of the underlying pathophysiology as a basis for therapy development. Here, we review (i) autophagy in the context of other intracellular trafficking pathways; (ii) the main congenital disorders of autophagy and their typical clinico-pathological signatures; and (iii) the recommended primary health surveillance in monogenic disorders of autophagy based on available evidence. We further discuss recently identified molecular mechanisms that inform the current understanding of autophagy in health and disease, as well as perspectives on future therapeutic approaches.

Mechanisms of lipid droplet degradation

Lipid droplets (LDs) are subcellular organelles that play an integral role in lipid metabolism by regulating the storage and release of fatty acids, which are essential for energy production and various cellular processes. Lipolysis and lipophagy are the two major LD degradation pathways that mediate the utilization of lipids stored in these organelles. Recent studies have further uncovered alternative pathways, including direct lysosomal LD degradation and LD exocytosis. Here, we highlight recent findings that dissect the molecular basis of these diverse LD degradation pathways. Then, we discuss speculations on the crosstalk among these pathways and the potential unconventional roles of LD degradation.

Membrane atg8ylation in Canonical and Noncanonical Autophagy

Membrane atg8ylation is a homeostatic process responding to membrane remodeling and stress signals. Membranes are atg8ylated by mammalian ATG8 ubiquitin-like proteins through a ubiquitylation-like cascade. A model has recently been put forward which posits that atg8ylation of membranes is conceptually equivalent to ubiquitylation of proteins. Like ubiquitylation, membrane atg8ylation involves E1, E2 and E3 enzymes. The E3 ligases catalyze the final step of atg8ylation of aminophospholipids in membranes. Until recently, the only known E3 ligase for membrane atg8ylation was ATG16L1 in a noncovalent complex with the ATG12-ATG5 conjugate. ATG16L1 was first identified as a factor in canonical autophagy. During canonical autophagy, the ATG16L1-based E3 ligase complex includes WIPI2, which in turn recognizes phosphatidylinositiol 3-phosphate and directs atg8ylation of autophagic phagophores. As an alternative to WIPIs, binding of ATG16L1 to the proton pump V-ATPase guides atg8ylation of endolysosomal and phagosomal membranes in response to lumenal pH changes. Recently, a new E3 complex containing TECPR1 instead of ATG16L1, has been identified that responds to sphingomyelin's presence on the cytofacial side of perturbed endolysosomal membranes. In present review, we cover the principles of membrane atg8ylation, catalog its various presentations, and provide a perspective on the growing repertoire of E3 ligase complexes directing membrane atg8ylation at diverse locations.

Giant organelle vesicles to uncover intracellular membrane mechanics and plasticity

Tools for accessing and studying organelles remain underdeveloped. Here, we present a method by which giant organelle vesicles (GOVs) are generated by submitting cells to a hypotonic medium followed by plasma membrane breakage. By this means, GOVs ranging from 3 to over 10 µm become available for micromanipulation. GOVs are made from organelles such as the endoplasmic reticulum, endosomes, lysosomes and mitochondria, or in contact with one another such as giant mitochondria-associated ER membrane vesicles. We measure the mechanical properties of each organelle-derived GOV and find that they have distinct properties. In GOVs procured from Cos7 cells, for example, bending rigidities tend to increase from the endoplasmic reticulum to the plasma membrane. We also found that the mechanical properties of giant endoplasmic reticulum vesicles (GERVs) vary depending on their interactions with other organelles or the metabolic state of the cell. Lastly, we demonstrate GERVs' biochemical activity through their capacity to synthesize triglycerides and assemble lipid droplets. These findings underscore the potential of GOVs as valuable tools for studying the biophysics and biology of organelles.

Lipid droplets and cellular lipid flux

Lipid droplets are dynamic organelles that store neutral lipids, serve the metabolic needs of cells, and sequester lipids to prevent lipotoxicity and membrane damage. Here we review the current understanding of the mechanisms of lipid droplet biogenesis and turnover, the transfer of lipids and metabolites at membrane contact sites, and the role of lipid droplets in regulating fatty acid flux in lipotoxicity and cell death.

LC3 conjugation to lipid droplets

Macroautophagy/autophagy and lipid droplet (LD) biology are intricately linked, with autophagosome-dependent degradation of LDs in response to different signals. LDs play crucial roles in forming autophagosomes possibly by providing essential lipids and serving as a supportive autophagosome assembly platform at the endoplasmic reticulum (ER)-LD interface. LDs and autophagosomes share common proteins, such as VPS13, ATG2, ZFYVE1/DFCP1, and ATG14, but their dual functions remain poorly understood. In our recent study, we found that prolonged starvation leads to ATG3 localizing to large LDs and lipidating LC3B, revealing a non-canonical autophagic role on LDs. In vitro, ATG3 associates with purified and artificial LDs, and conjugated Atg8-family proteins. In long-term starved cells, only LC3B is found on the specific large LDs, positioned near LC3B-positive membranes that undergo lysosome-mediated acidification. This implies that LD-lipidated LC3B acts as a tethering factor, connecting phagophores to LDs and promoting degradation. Our data also support the notion that certain LD surfaces may function as lipidation stations for LC3B, which may move to nearby sites of autophagosome formation. Overall, our study unveils an unknown non-canonical implication of LDs in autophagy processes.Abbreviation: ATG: autophagy-related enzyme, ATP: adenosine triphosphate, E2 enzyme: ubiquitin-conjugating enzyme, ER: endoplasmic reticulum, LD: lipid droplet, LIR motif: LC3-interacting region, MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta, PE: phosphatidylethanolamine, PLIN1: perilipin 1, PNPLA2/ATGL: patatin-like phospholipase domain containing 2, SQSTM1/p62: sequestosome 1, VSP13: vacuolar protein sorting 13, ZFYVE1/DFCP1: zinc finger, FYVE domain containing 1.

ARL8B mediates lipid droplet contact and delivery to lysosomes for lipid remobilization

Lipid droplets (LDs) play a crucial role in maintaining cellular lipid balance by storing and delivering lipids as needed. However, the intricate lipolytic pathways involved in LD turnover remain poorly described, hindering our comprehension of lipid catabolism and related disorders. Here, we show a function of the small GTPase ARL8B in mediating LD turnover in lysosomes. ARL8B-GDP localizes to LDs, while ARL8-GTP predominantly favors lysosomes. GDP binding induces a conformation with an exposed N-terminal amphipathic helix, enabling ARL8B to bind to LDs. By associating with LDs and lysosomes, and with its property to form a heterotypic complex, ARL8B mediates LD-lysosome contacts and efficient lipid transfer between these organelles. In human macrophages, this ARL8B-dependent LD turnover mechanism appears as the major lipolytic pathway. Our finding opens exciting possibilities for understanding the molecular mechanisms underlying LD degradation and its potential implications for inflammatory disorders.

Atg8ylation as a host-protective mechanism against Mycobacterium tuberculosis

Nearly two decades have passed since the first report on autophagy acting as a cell-autonomous defense against Mycobacterium tuberculosis. This helped usher a new area of research within the field of host-pathogen interactions and led to the recognition of autophagy as an immunological mechanism. Interest grew in the fundamental mechanisms of antimicrobial autophagy and in the prophylactic and therapeutic potential for tuberculosis. However, puzzling in vivo data have begun to emerge in murine models of M. tuberculosis infection. The control of infection in mice affirmed the effects of certain autophagy genes, specifically ATG5, but not of other ATGs. Recent studies with a more complete inactivation of ATG genes now show that multiple ATG genes are indeed necessary for protection against M. tuberculosis. These particular ATG genes are involved in the process of membrane atg8ylation. Atg8ylation in mammalian cells is a broad response to membrane stress, damage and remodeling of which canonical autophagy is one of the multiple downstream outputs. The current developments clarify the controversies and open new avenues for both fundamental and translational studies.