Friend or Foe: Lipid Droplets as Organelles for Protein and Lipid Storage in Cellular Stress Response, Aging and Disease

ER nests are specialized ER subdomains in Arabidopsis where peroxisomes and lipid droplets form

Organelles are defining features of eukaryotic cells, yet much remains to be learned about organelle biogenesis. Lipid droplets and peroxisomes, which play opposing roles in storing and catabolizing fats, form from a mysterious domain in the endoplasmic reticulum (ER). We used live-cell fluorescence microscopy to visualize peroxisome and lipid droplet biogenesis in young Arabidopsis seedlings, where lipid catabolism is active, and peroxisomes can be unusually large. We found that the ER domains where these organelles are born, which we term ER nests, are complex, dynamic structures that exclude general ER proteins but accumulate other proteins, including lipid biosynthetic enzymes and the COPII component SAR1. Furthermore, ER nests appear to define peroxisome-lipid droplet contact sites. Our findings provide a framework for understanding how these domains form and sort their protein components, illuminate eukaryotic lipid biosynthesis, and elucidate how distinct organelles arise from the ER.

The many faces of DGAT1

Acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) is a multifaced enzyme with a wide spectrum of substrates, from lipids through waxes to retinoids, which makes it an interesting therapeutic target. DGAT1 inhibitors are currently at various stages of preclinical and clinical trials, mostly related to metabolic diseases. Interestingly, in recent years, a growing amount of research has shown the influence of DGAT1 on immune cell metabolism and functions, highlighting its important role during infections and tumorigenesis. In this review, we aim to elucidate the potential immunomodulatory effect of DGAT1 in physiological and pathological conditions.

Lipid droplet specific BODIPY based rotors with viscosity sensitivity to distinguish normal and cancer cells: impact of molecular conformation

Lipid droplets (LDs) are dynamic, multifunctional organelles critical for regulating energy balance, cell signaling, membrane formation, and trafficking. Recent studies have highlighted LDs as emerging cancer biomarkers, with cancer cells typically exhibiting a higher number and viscosity of LDs compared to normal cells. This discovery paves the way for developing molecular probes that can monitor intracellular viscosity changes within LDs, offering a powerful tool for early cancer diagnosis, recurrence monitoring, and therapeutic interventions. In this study, we designed and synthesized two series of donor-acceptor (D-A) conjugated BODIPY-cyanostilbene based fluorophores (5a-c and 6a-c) by fine-tuning the cyanostilbene unit with three distinct substituents (OMe, H, Cl) and modulating the molecular conformation via rigidifying the indacene core. While the terminal substituents had a minimal effect on the optical properties, changes in molecular conformation significantly impacted the photophysical behavior of the fluorophores. Compounds 5a-c function as molecular rotors, with the free rotation of the meso-biphenyl rings leading to non-radiative deactivation of the excited state, resulting in weak emission. Additionally, this structural feature makes them highly responsive to changes in viscosity. As the glycerol concentration increased from 0% to 99%, the fluorescence intensity of compounds 5a, 5b, and 5c increased dramatically by 17-fold, 78-fold, and 43-fold, respectively. In contrast, compounds 6a-c, with restricted phenyl ring rotation due to tetra-methyls on the indacene unit, showed only a modest 2-3-fold increment in fluorescence intensity under similar conditions. These fluorophores possess several key advantages, including high selectivity for LDs, good photostability, sensitivity to viscosity, and responsiveness to polarity and pH. Moreover, they effectively differentiate between normal and cancer cells, making them valuable tools for cancer diagnosis and potential therapeutic applications.

An activatable "AIE + ESIPT" fluorescent probe for dual-imaging of lipid droplets and hydrogen peroxide in drug-induced liver injury model

BACKGROUND

Drug-induced liver injury (DILI) is one of the most common liver diseases. The crucial role of lipid droplets (LDs) and hydrogen peroxide (H2O2), two important biomarkers in the pathophysiology of DILI, has spurred considerable efforts to accurately visualize H2O2 and LDs for elucidating their functions in the progression of DILI. However, construction of a single fluorescent probe that is able to simultaneously image H2O2 and LDs dynamics remains to be a challenging task. Therefore, it is of great demand to develop a novel fluorescent probe for tracking the LDs status and H2O2 fluctuation in drug-induced liver injury.

RESULTS

We developed an "AIE + ESIPT" fluorescent probe TPEHBT for dual-imaging of LDs and H2O2 during DILI process. TPEHBT displayed greatly enhanced fluorescent response to H2O2 by generating an excited state intramolecular proton transfer (ESIPT) fluorophore TPEHBT-OH with aggregation induced emission (AIE) properties. TPEHBT exhibits high selectivity, sensitivity (LOD = 4.73 nM) and large Stokes shift (320 nm) to H2O2. Interestingly, TPEHBT can light up LDs with high specificity. The probe was favorably applied in the detection of endogenous and exogenous H2O2 in living cells, and notably in the simultaneous real-time visualization of H2O2 generation and LDs accumulation during DILI process. Moreover, TPEHBT was able to image H2O2 generation in zebrafish animal model with APAP-induced liver injury.

SIGNIFICANCE

For the first time, probe TPEHBT was applied in the dual-imaging of H2O2 fluctuation and LDs status in APAP-induced liver injury model in vitro and in vivo. The present findings strongly suggest that TPEHBT is a promising tool for monitoring H2O2 and LDs dynamics in DILI progression.

From Adipose to Ailing Kidneys: The Role of Lipid Metabolism in Obesity-Related Chronic Kidney Disease

Obesity has emerged as a significant public health crisis, closely linked to the pathogenesis and progression of chronic kidney disease (CKD). This review explores the intricate relationship between obesity-induced lipid metabolism disorders and renal health. We discuss how excessive free fatty acids (FFAs) lead to lipid accumulation in renal tissues, resulting in cellular lipotoxicity, oxidative stress, and inflammation, ultimately contributing to renal injury. Key molecular mechanisms, including the roles of transcriptional regulators like PPARs and SREBP-1, are examined for their implications in lipid metabolism dysregulation. The review also highlights the impact of glomerular and tubular lipid overload on kidney pathology, emphasizing the roles of podocytes and tubular cells in maintaining kidney function. Various therapeutic strategies targeting lipid metabolism, including pharmacological agents such as statins and SGLT2 inhibitors, as well as lifestyle modifications, are discussed for their potential to mitigate CKD progression in obese individuals. Future research directions are suggested to better understand the mechanisms linking lipid metabolism to kidney disease and to develop personalized therapeutic approaches. Ultimately, addressing obesity-related lipid metabolism disorders may enhance kidney health and improve outcomes for individuals suffering from CKD.

Plasma Lipidomics Reveals Lipid Signatures of Early Pregnancy in Mares

Understanding the systemic biochemistry of early pregnancy in the mare is essential for developing new diagnostics and identifying causes for pregnancy loss. This study aimed to elucidate the dynamic lipidomic changes occurring during the initial stages of equine pregnancy, with a specific focus on days 7 and 14 post-ovulation. By analysing and comparing the plasma lipid profiles of pregnant and non-pregnant mares, the objective of this study was to identify potential biomarkers for pregnancy and gain insights into the biochemical adaptations essential for supporting maternal recognition of pregnancy and early embryonic development. Employing discovery lipidomics, we analysed plasma samples from pregnant and non-pregnant mares on days 7 and 14 post-conception using the SCIEX ZenoTOF 7600 system. This high-resolution mass spectrometry approach enabled us to comprehensively profile and compare the lipidomes across these critical early gestational timepoints. Our analysis revealed significant lipidomic alterations between pregnant and non-pregnant mares and between days 7 and 14 of pregnancy. Key findings include the upregulation of bile acids, sphingomyelins, phosphatidylinositols, and triglycerides in pregnant mares. These changes suggest enhanced lipid synthesis and mobilization, likely associated with the embryo's nutritional requirements and the establishment of embryo-maternal interactions. There were significant differences in lipid metabolism between pregnant and non-pregnant mares, with a notable increase in the sterol lipid BA 24:1;O5 in pregnant mares as early as day 7 of gestation, suggesting it as a sensitive biomarker for early pregnancy detection. Notably, the transition from day 7 to day 14 in pregnant mares is characterized by a shift towards lipids indicative of membrane biosynthesis, signalling activity, and preparation for implantation. The study demonstrates the profound lipidomic shifts that occur in early equine pregnancy, highlighting the critical role of lipid metabolism in supporting embryonic development. These findings provide valuable insights into the metabolic adaptations during these period and potential biomarkers for early pregnancy detection in mares.

Contribution of impaired autophagy, mitochondrial dysfunction and abnormal lipolysis to epididymal aging in mice

With the increase of the aged population in modern society, research on aging and aging-related diseases has attracted increasing attention. Unlike women, men experience changes gradually in the reproductive system during aging. The epididymis is an important organ for sperm maturation and storage, but less study has been conducted to investigate cellular senescence in aging epididymis and the corresponding influences on sperm. This study aims to explore cellular and molecular mechanisms underlying aging changes in epididymal tissues. Cellular senescence in the epididymis of 18-month-old C57BL/6 J mice was evaluated with SA (senescence-associated)-β-galactosidase staining and molecular markers such as P21 and Lamin B, compared to the 2-month-old young group. Western blot analysis and immunofluorescence staining were performed to examine the proteins expressions involved in AMPKα/SIRT1 pathway, autophagy/mitophagy, mitochondrial dynamics and lipolysis. The results showed that in old mice AMPKα/ SIRT1 pathway was downregulated with increased acetylation in the epididymal tissues. Reduced expressions of autophagy related genes and PINK1/PARK2 were detected as well as increased P62 protein level and decreased colocalization of LC3 and LAMP2, which indicated deficient autophagy and mitophagy occurred in aging epididymal tissues. Significant decreased expressions of MFN1, MFN2, p-DRP1(Ser637) and FIS1 showed an imbalance in mitochondrial dynamics in aging epididymal tissues. Additionally, intracellular lipid droplets accumulation occurred in epididymal epithelial cells in old mice, with reduced expressions of the lipolysis enzymes ATGL, HSL and Ascl4. Lipophagy impairment was further detected by minimal colocalization of lipid droplets with either LC3 or LAMP2 in the epididymal ductal epithelial cells of old mice. Our study provides new insights into the molecular mechanisms of impaired autophagy, imbalanced mitochondrial dynamics and disrupted lipolysis, which together contribute to senescent changes and may be detrimental to the epididymal function during aging.

Hepatic miR-149-5p upregulation fosters steatosis, inflammation and fibrosis development in mice and in human liver organoids

Background & Aims

The incidence of metabolic dysfunction-associated steatotic liver disease (MASLD) is increasing worldwide. Alterations of hepatic microRNA (miRNA) expression/activity significantly contribute to the development and progression of MASLD. Genetic polymorphisms of miR-149 are associated with an increased susceptibility to MASLD development in humans. Aberrant expression of miR-149 was also associated with metabolic alterations in several organs, but the impact of hepatic miR-149-5p deregulation in MASLD remains poorly characterized.

Methods

MiR-149-5p was downregulated in the livers of mice by in vivo transduction with hepatotropic adeno-associated virus 8 harboring short-hairpin RNAs (shRNAs) specific for miR-149-5p (shmiR149) or scrambled shRNAs (shCTL). MASLD was then induced with a methionine/choline-deficient (MCD, n = 7 per group) diet or a fructose/palmitate/cholesterol-enriched (FPC, n = 8-12 per group, per protocol) diet. The impact of miR-149-5p modulation on MASLD development was assessed in vivo and in vitro using multi-lineage 3D human liver organoids (HLOs) and Huh7 cells.

Results

MiR-149-5p expression was strongly upregulated in mouse livers from different models of MASLD (2-4-fold increase in ob/ob, db/db mice, high-fat and FPC-fed mice). In vivo downregulation of miR-149-5p led to an amelioration of diet-induced hepatic steatosis, inflammation/fibrosis, and to increased whole-body fatty acid consumption. In HLOs, miR-149-5p overexpression promoted lipid accumulation, inflammation and fibrosis. In vitro analyses of human Huh7 cells overexpressing miR-149-5p indicated that glycolysis and intracellular lipid accumulation was promoted, while mitochondrial respiration was impaired. Translatomic analyses highlighted deregulation of multiple potential miR-149-5p targets in hepatocytes involved in MASLD development.

Conclusions

MiR-149-5p upregulation contributes to MASLD development by affecting multiple metabolic/inflammatory/fibrotic pathways in hepatocytes. Our results further demonstrate that HLOs are a relevant 3D in vitro model to investigate hepatic steatosis and inflammation/fibrosis development.

Impact and implications

Our research shows compelling evidence that miR-149-5p plays a pivotal role in the development and progression of MASLD. By employing in vivo and innovative in vitro models using multi-lineage human liver organoids, we demonstrate that miR-149-5p upregulation significantly impacts hepatocyte energy metabolism, exacerbating hepatic steatosis and inflammation/fibrosis by modulating a wide network of target genes. These findings not only shed light on the intricate miR-149-5p-dependent molecular mechanisms underlying MASLD, but also underscore the importance of human liver organoids as valuable 3D in vitro models for studying the disease's pathogenesis.

Unveiling the intersection: ferroptosis in influenza virus infection

The influenza virus (IFV) imposes a considerable health and economic burden globally, requiring a comprehensive understanding of its pathogenic mechanisms. Ferroptosis, an iron-dependent lipid peroxidation cell death pathway, holds unique implications for the antioxidant defense system, with possible contributions to inflammation. This exploration focuses on the dynamic interplay between ferroptosis and the host defense against viruses, emphasizing the influence of IFV infections on the activation of the ferroptosis pathway. IFV causes different types of cell death, including apoptosis, necrosis, and ferroptosis. IFV-induced ferroptotic cell death is mediated by alterations in iron homeostasis, intensifying the accumulation of reactive oxygen species and promoting lipid peroxidation. A comprehensive investigation into the mechanism of ferroptosis in viral infections, specifically IFV, has great potential to identify therapeutic strategies. This understanding may pave the way for the development of drugs using ferroptosis inhibitors, presenting an effective approach to suppress viral infections.

Molecular Basis for Surface-Initiated Non-Thrombin-Generated Clot Formation Following Viral Infection

In this paper, we propose a model that connects two standard inflammatory responses to viral infection, namely, elevation of fibrinogen and the lipid drop shower, to the initiation of non-thrombin-generated clot formation. In order to understand the molecular basis for the formation of non-thrombin-generated clots following viral infection, human epithelial and Madin-Darby Canine Kidney (MDCK, epithelial) cells were infected with H1N1, OC43, and adenovirus, and conditioned media was collected, which was later used to treat human umbilical vein endothelial cells and human lung microvascular endothelial cells. After direct infection or after exposure to conditioned media from infected cells, tissue surfaces of both epithelial and endothelial cells, exposed to 8 mg/mL fibrinogen, were observed to initiate fibrillogenesis in the absence of thrombin. No fibers were observed after direct viral exposure of the endothelium or when the epithelium cells were exposed to SARS-CoV-2 isolated spike proteins. Heating the conditioned media to 60 °C had no effect on fibrillogenesis, indicating that the effect was not enzymatic but rather associated with relatively thermally stable inflammatory factors released soon after viral infection. Spontaneous fibrillogenesis had previously been reported and interpreted as being due to the release of the alpha C domains due to strong interactions of the interior of the fibrinogen molecule in contact with hydrophobic material surfaces rather than cleavage of the fibrinopeptides. Contact angle goniometry and immunohistochemistry were used to demonstrate that the lipids produced within the epithelium and released in the conditioned media, probably after the death of infected epithelial cells, formed a hydrophobic residue responsible for fibrillogenesis. Hence, the standard inflammatory response constitutes the ideal conditions for surface-initiated clot formation.

Impact of Seipin in cholesterol mediated lipid droplet maturation; status of endoplasmic reticulum stress and lipophagy

The global prevalence of nonalcoholic fatty liver disease (NAFLD) defined by the increased number of lipid droplets (LDs) in hepatocytes, have risen continuously in parallel with the obesity. LDs and related proteins are known to affect cellular metabolism and signaling. Seipin, one of the most important LD-related proteins, plays a critical role in LD biogenesis. Although the role of adipose tissue-specific Seipin silencing is known, hepatocyte-specific silencing upon cholesterol-mediated lipid accumulation has not been investigated. In our study, we investigated the effect of Seipin on endoplasmic reticulum (ER) stress and lipophagy in cholesterol accumulated mouse hepatocyte cells. In this direction, cholesterol accumulation was induced by cholesterol-containing liposome, while Seipin mRNA and protein levels were reduced by siRNA. Our findings show that cholesterol containing liposome administration in hepatocytes increases both Seipin protein and number of large LDs. However Seipin silencing reduced the increase of cholesterol mediated large LDs and Glucose-regulated protein 78 (GRP78) mRNA. Additionally, lysosome-LD colocalization increased only in cells treated with cholesterol containing liposome, while the siRNA against Seipin did not lead any significant difference. According to our findings, we hypothesize that Seipin silencing in hepatocytes reduced cholesterol mediated LD maturation as well as GRP78 levels, but not lipophagy.

Physiological and Pathogenesis Significance of Chorein in Health and Disease

This comprehensive review explores the physiological and pathophysiological significance of VPS13A, a protein encoded by the VPS13A gene. The VPS13A gene is associated with Chorea-acanthocytosis (ChAc), a rare hereditary neurodegenerative disorder. The review covers essential aspects, beginning with the genetics of VPS13A, highlighting its role in the pathogenesis of ChAc, and addressing the spectrum of genetic variants involved. It delves into the structure and function of the VPS13A protein, emphasizing its presence in various tissues and its potential involvement in protein trafficking and lipid homeostasis. Molecular functions of VPS13A in the brain tissue and other cell types or tissues with respect to their role in cytoskeletal regulation and autophagy are explored. Finally, it explores the intriguing link between VPS13A mutations, lipid imbalances, and neurodegeneration, shedding light on future research directions. Overall, this review serves as a comprehensive resource for understanding the pivotal role of VPS13A in health and disease, particularly in the context of ChAc. Key words: Chorein , Tumor, Actin, Microfilament, Gene expression, Chorea-acanthocytosis.

BHLHE40/41 regulate microglia and peripheral macrophage responses associated with Alzheimer's disease and other disorders of lipid-rich tissues

Genetic and experimental evidence suggests that Alzheimer's disease (AD) risk alleles and genes may influence disease susceptibility by altering the transcriptional and cellular responses of macrophages, including microglia, to damage of lipid-rich tissues like the brain. Recently, sc/nRNA sequencing studies identified similar transcriptional activation states in subpopulations of macrophages in aging and degenerating brains and in other diseased lipid-rich tissues. We collectively refer to these subpopulations of microglia and peripheral macrophages as DLAMs. Using macrophage sc/nRNA-seq data from healthy and diseased human and mouse lipid-rich tissues, we reconstructed gene regulatory networks and identified 11 strong candidate transcriptional regulators of the DLAM response across species. Loss or reduction of two of these transcription factors, BHLHE40/41, in iPSC-derived microglia and human THP-1 macrophages as well as loss of Bhlhe40/41 in mouse microglia, resulted in increased expression of DLAM genes involved in cholesterol clearance and lysosomal processing, increased cholesterol efflux and storage, and increased lysosomal mass and degradative capacity. These findings provide targets for therapeutic modulation of macrophage/microglial function in AD and other disorders affecting lipid-rich tissues.

Ola1p trafficking indicates an interaction network between mitochondria, lipid droplets, and stress granules in times of stress

Protein aggregates arise naturally under normal physiological conditions, but their formation is accelerated by age or stress-induced protein misfolding. When the stressful event dissolves, these aggregates are removed by mechanisms, such as aggrephagy, chaperone-mediated autophagy, refolding attempts, or the proteasome. It was recently shown that mitochondria in yeast cells may support these primarily cytosolic processes. Protein aggregates attach to mitochondria, and misfolded proteins are transported into the matrix and degraded by mitochondria-specific proteases. Using a proximity labeling method and colocalization with an established stress granule (SG) marker, we were able to show that these mitochondria-localized aggregates that harbor the "super aggregator" Ola1p are, in fact, SGs. Our in vivo and in vitro studies have revealed that Ola1p can be transferred from mitochondria to lipid droplets (LDs). This "mitochondria to LD" aggregate transfer dampens proteotoxic effects. The LD-based protein aggregate removal system gains importance when other proteolytic systems fail. Furthermore, we were able to show that the distribution of SGs is drastically altered in LD-deficient yeast cells, demonstrating that LDs play a role in the SG life cycle.

Two Polarity-Sensitive Fluorescent Probes Based on Curcumin Analogs for Visualizing Polarity Changes in Lipid Droplets

As a class of highly dynamic organelles, lipid droplets (LDs) are involved in numerous physiological functions, and the changes in polarity of LDs are closely related to a variety of diseases. In this work, we developed two polarity-sensitive fluorescent probes (CC-CH and CC-Cl) based on curcumin analogs. CC-CH and CC-Cl with a donor-acceptor-donor (D-A-D) structure exhibited the property of intramolecular charge transfer (ICT); thus, their fluorescence emissions were significantly attenuated with increasing ambient polarity. Cell experiments indicated that CC-CH and CC-Cl showed excellent photostability, a low cytotoxicity, and a superior targeting ability regarding LDs. After treatment with oleic acid (OA) and methyl-β-cyclodextrin (M-β-CD), the polarity changes of LDs in living cells could be visualized by using CC-CH and CC-Cl. In addition, CC-CH and CC-Cl could monitor polarity changes of LDs in different pathological processes, including inflammatory responses, nutrient deprivation, and H2O2-induced oxidative stress. Therefore, CC-CH and CC-Cl are promising potential fluorescent probes for tracking intracellular LD polarity changes.

Atherosclerosis, Diabetes Mellitus, and Cancer: Common Epidemiology, Shared Mechanisms, and Future Management

The involvement of cardiovascular disease in cancer onset and development represents a contemporary interest in basic science. It has been recognized, from the most recent research, that metabolic syndrome-related conditions, ranging from atherosclerosis to diabetes, elicit many pathways regulating lipid metabolism and lipid signaling that are also linked to the same framework of multiple potential mechanisms for inducing cancer. Otherwise, dyslipidemia and endothelial cell dysfunction in atherosclerosis may present common or even interdependent changes, similar to oncogenic molecules elevated in many forms of cancer. However, whether endothelial cell dysfunction in atherosclerotic disease provides signals that promote the pre-clinical onset and proliferation of malignant cells is an issue that requires further understanding, even though more questions are presented with every answer. Here, we highlight the molecular mechanisms that point to a causal link between lipid metabolism and glucose homeostasis in metabolic syndrome-related atherosclerotic disease with the development of cancer. The knowledge of these breakthrough mechanisms may pave the way for the application of new therapeutic targets and for implementing interventions in clinical practice.

Exploring the microscopic changes of lipid droplets and mitochondria in alcoholic liver disease via fluorescent probes with high polarity specificity

Alcoholic liver disease (ALD) has received extensive attention because of the increasing alcohol consumption globally as well as its high morbidity. It is reported that absorbed alcohol can cause lipid metabolism disorder and mitochondria dysfunction, so here in this work, we planned to study the microscopic changes of the two organelles, lipid droplets (LDs) and mitochondria in hepatocyte, under the stimulation of alcohol, hoping to present some meaningful information for the theranostics of ALD by the technique of fluorescence imaging. Guided by theoretical calculation, two fluorescent probes, named CBu and CBuT, were rationally designed. Although constructed by the same chromophore scaffold, they stained different organelles efficiently and emitted distinctively. CBu with high lipophilicity, ascribed to the two butyl groups, can selectively localize in LDs with green fluorescence, while CBuT bearing a triphenylphosphine unit can specifically target mitochondria due to electrostatic interactions with near-infrared (NIR) fluorescence. Both probes displayed remarkable selectivity and sensitivity to polarity, free from the environmental interferences including viscosity, pH and other bio-species. With these two probes, the accumulation of LDs and polarity decrease in mitochondria were clearly monitored at the green and red channels, respectively, in the ALD cell model. CBuT was further applied to image the mice with ALD in vivo. In short, we have confirmed the valuable organelles, LDs and mitochondria, for ALD study and provided two potent molecular tools to visualize their changes through fluorescence imaging, which would be favorable for the further development of theranostics for ALD.

The Janus-Faced Role of Lipid Droplets in Aging: Insights from the Cellular Perspective

It is widely accepted that nine hallmarks-including mitochondrial dysfunction, epigenetic alterations, and loss of proteostasis-exist that describe the cellular aging process. Adding to this, a well-described cell organelle in the metabolic context, namely, lipid droplets, also accumulates with increasing age, which can be regarded as a further aging-associated process. Independently of their essential role as fat stores, lipid droplets are also able to control cell integrity by mitigating lipotoxic and proteotoxic insults. As we will show in this review, numerous longevity interventions (such as mTOR inhibition) also lead to strong accumulation of lipid droplets in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, and mammalian cells, just to name a few examples. In mammals, due to the variety of different cell types and tissues, the role of lipid droplets during the aging process is much more complex. Using selected diseases associated with aging, such as Alzheimer's disease, Parkinson's disease, type II diabetes, and cardiovascular disease, we show that lipid droplets are "Janus"-faced. In an early phase of the disease, lipid droplets mitigate the toxicity of lipid peroxidation and protein aggregates, but in a later phase of the disease, a strong accumulation of lipid droplets can cause problems for cells and tissues.

Lipid droplets and peroxisomes are co-regulated to drive lifespan extension in response to mono-unsaturated fatty acids

Dietary mono-unsaturated fatty acids (MUFAs) are linked to longevity in several species. But the mechanisms by which MUFAs extend lifespan remain unclear. Here we show that an organelle network involving lipid droplets and peroxisomes is critical for MUFA-induced longevity in Caenorhabditis elegans. MUFAs upregulate the number of lipid droplets in fat storage tissues. Increased lipid droplet number is necessary for MUFA-induced longevity and predicts remaining lifespan. Lipidomics datasets reveal that MUFAs also modify the ratio of membrane lipids and ether lipids-a signature associated with decreased lipid oxidation. In agreement with this, MUFAs decrease lipid oxidation in middle-aged individuals. Intriguingly, MUFAs upregulate not only lipid droplet number but also peroxisome number. A targeted screen identifies genes involved in the co-regulation of lipid droplets and peroxisomes, and reveals that induction of both organelles is optimal for longevity. Our study uncovers an organelle network involved in lipid homeostasis and lifespan regulation, opening new avenues for interventions to delay aging.

Automated Segmentation and Morphological Characterization of Hepatic Steatosis and Correlation with Histopathology

Background/objectives

Prevalence of nonalcoholic fatty liver disease (NAFLD) has increased to 25% of the world population. Hepatic steatosis is a hallmark feature of NAFLD and is assessed histologically using visual and ordinal fat grading criteria (0-3) from the Nonalcoholic Steatohepatitis (NASH) Clinical Research Network (CRN) scoring system. The purpose of this study is to automatically segment and extract morphological characteristics and distributions of fat droplets (FDs) on liver histology images and find associations with severity of steatosis.

Methods

A previously published human cohort of 68 NASH candidates was graded for steatosis by an experienced pathologist using the Fat CRN grading system. The automated segmentation algorithm quantified fat fraction (FF) and fat-affected hepatocyte ratio (FHR), extracted fat morphology by calculating radius and circularity of FDs, and examined FDs distribution and heterogeneity using nearest neighbor distance and regional isotropy.

Results

Regression analysis and Spearman correlation (ρ) yielded high correlations for radius (R2 = 0.86, ρ = 0.72), nearest neighbor distance (R2 = 0.82, ρ = -0.82), regional isotropy (R2 = 0.84, ρ = 0.74), and FHR (R2 = 0.90, ρ = 0.85), and low correlation for circularity (R2 = 0.48, ρ = -0.32) with FF and pathologist grades, respectively. FHR showed a better distinction between pathologist Fat CRN grades compared to conventional FF measurements, making it a potential surrogate measure for Fat CRN scores. Our results showed variation in distribution of morphological features and steatosis heterogeneity within the same patient's biopsy sample as well as between patients of similar FF.

Conclusions

The fat percentage measurements, specific morphological characteristics, and patterns of distribution quantified with the automated segmentation algorithm showed associations with steatosis severity; however, future studies are warranted to evaluate the clinical significance of these steatosis features in progression of NAFLD and NASH.

NLRP3-dependent lipid droplet formation contributes to posthemorrhagic hydrocephalus by increasing the permeability of the blood-cerebrospinal fluid barrier in the choroid plexus

Hydrocephalus is a severe complication that can result from intracerebral hemorrhage, especially if this hemorrhage extends into the ventricles. Our previous study indicated that the NLRP3 inflammasome mediates cerebrospinal fluid hypersecretion in the choroid plexus epithelium. However, the pathogenesis of posthemorrhagic hydrocephalus remains unclear, and therapeutic strategies for prevention and treatment are lacking. In this study, an Nlrp3^-/- rat model of intracerebral hemorrhage with ventricular extension and primary choroid plexus epithelial cell culture were used to investigate the potential effects of NLRP3-dependent lipid droplet formation and its role in the pathogenesis of posthemorrhagic hydrocephalus. The data indicated that NLRP3-mediated dysfunction of the blood-cerebrospinal fluid barrier (B-CSFB) accelerated neurological deficits and hydrocephalus, at least in part, through the formation of lipid droplets in the choroid plexus; these lipid droplets interacted with mitochondria and increased the release of mitochondrial reactive oxygen species that destroyed tight junctions in the choroid plexus after intracerebral hemorrhage with ventricular extension. This study broadens the current understanding of the relationship among NLRP3, lipid droplets and the B-CSFB and provides a new therapeutic target for the treatment of posthemorrhagic hydrocephalus. Strategies to protect the B-CSFB may be effective therapeutic approaches for posthemorrhagic hydrocephalus.

BHLHE40/41 regulate macrophage/microglia responses associated with Alzheimer's disease and other disorders of lipid-rich tissues

Background

Genetic and experimental evidence strongly implicates myeloid cells in the etiology of AD and suggests that AD-associated alleles and genes may modulate disease risk by altering the transcriptional and cellular responses of macrophages (like microglia) to damage of lipid-rich tissues (like the brain). Specifically, recent single-cell/nucleus RNA sequencing (sc/nRNA-seq) studies identified a transcriptionally distinct state of subsets of macrophages in aging or degenerating brains (usually referred to as disease-associated microglia or DAM) and in other diseased lipid-rich tissues (e.g., obese adipose tissue, fatty liver, and atherosclerotic plaques). We collectively refer to these subpopulations as lipid-associated macrophages or LAMs. Importantly, this particular activation state is characterized by increased expression of genes involved in the phagocytic clearance of lipid-rich cellular debris (efferocytosis), including several AD risk genes.

Methods

We used sc/nRNA-seq data from human and mouse microglia from healthy and diseased brains and macrophages from other lipid-rich tissues to reconstruct gene regulatory networks and identify transcriptional regulators whose regulons are enriched for LAM response genes (LAM TFs) across species. We then used gene knock-down/knock-out strategies to validate some of these LAM TFs in human THP-1 macrophages and iPSC-derived microglia in vitro, as well as mouse microglia in vivo.

Results

We nominate 11 strong candidate LAM TFs shared across human and mouse networks (BHLHE41, HIF1A, ID2, JUNB, MAF, MAFB, MEF2A, MEF2C, NACA, POU2F2 and SPI1). We also demonstrate a strong enrichment of AD risk alleles in the cistrome of BHLHE41 (and its close homolog BHLHE40), thus implicating its regulon in the modulation of disease susceptibility. Loss or reduction of BHLHE40/41 expression in human THP-1 macrophages and iPSC-derived microglia, as well as loss of Bhlhe40/41 in mouse microglia led to increased expression of LAM response genes, specifically those involved in cholesterol clearance and lysosomal processing, with a concomitant increase in cholesterol efflux and storage, as well as lysosomal mass and degradative capacity.

Conclusions

Taken together, this study nominates transcriptional regulators of the LAM response, experimentally validates BHLHE40/41 in human and mouse macrophages/microglia, and provides novel targets for therapeutic modulation of macrophage/microglia function in AD and other disorders of lipid-rich tissues.

Effect of atorvastatin on lipoxygenase pathway-related gene expression in an in vitro model of lipid accumulation in hepatocytes

Lipid accumulation in hepatocytes can result from an imbalance between lipid acquisition and lipid catabolism. In recent years, it has been discovered that eicosanoids derived from arachidonic acid (AA) have the potential to create specialized pro-resolving lipid mediators to actively resolve inflammation, but it is not clear whether AA and lipoxygenases exert effects on hepatic inflammation. Here, the effects of atorvastatin on the expression of cytoplasmic phospholipase A2 (cPLA2) and lipoxygenase pathway genes (ALOX5, ALOX12, ALOX15, and ALOX15B) were evaluated in an in vitro model of palmitic acid (PA)-induced hepatocyte lipid accumulation in McA-RH7777 (McA) cells. Palmitic acid increased cPLA2 expression, intracellular AA levels, and ALOX12 expression (P < 0.05). Atorvastatin at various concentrations had no significant effects on AA levels or on cPLA2, ALOX15, and ALOX15B expressions. ALOX5 was not detected, despite multiple measurements. Pro-inflammatory IL-1β expression levels were upregulated by PA (P < 0.01) and attenuated by atorvastatin (P < 0.001). TNFα did not differ among groups. The expression levels of anti-inflammatory IL-10 decreased in response to PA (P < 0.05), but were not affected by atorvastatin. In conclusion, in an in vitro model of lipid accumulation in McA cells, atorvastatin reduced IL-1β; however, its effect was not mediated by AA and the lipoxygenase pathway at the established doses and treatment duration. Further research is required to investigate time-response data, as well as other drugs and integrated cell systems that could influence the lipoxygenase pathway and modulate inflammation in liver diseases.

A novel sulfur dioxide probe inhibits high glucose-induced endothelial cell senescence

Sulfur dioxide (SO₂) is an important gas signal molecule produced in the cardiovascular system, so it has an important regulatory effect on human umbilical vascular endothelial cells (HUVECs). Studies have shown that high glucose (HG) has become the main cause of endothelial dysfunction and aging. However, the mechanism by which SO₂ regulates the senescence of vascular endothelial cells induced by HG has not yet been clarified, so it is necessary to find effective tools to elucidate the effect of SO₂ on senescence of HUVECs. In this paper, we identified a novel sulfur dioxide probe (2-(4-(dimethylamino)styryl)-1,1,3-trimethyl-1H-benzo [e]indol-3-ium, DLC) that inhibited the senescence of HUVECs. Our results suggested that DLC facilitated lipid droplets (LDs) translocation to lysosomes and triggered upregulation of LAMP1 protein levels by targeting LDs. Further study elucidated that DLC inhibited HG-induced HUVECs senescence by promoting the decomposition of LDs and protecting the proton channel of V-ATPase on lysosomes. In conclusion, our study revealed the regulatory effect of lipid droplet-targeted sulfur dioxide probes DLC on HG-induced HUVECs senescence. At the same time, it provided the new experimental evidence for elucidating the regulatory mechanism of intracellular gas signaling molecule sulfur dioxide on vascular endothelial fate.

Silencing SIRT5 induces the senescence of UCB-MSCs exposed to TNF-α by reduction of fatty acid β-oxidation and anti-oxidation

Tumor necrosis factor-α (TNF-α) is an inflammatory cytokine involved in cell survival, apoptosis, and homeostasis. However, the regulatory effect of TNF-α on mesenchymal stem cell (MSC) redox regulation remains unknown. The process of delaying the senescence of MSCs and maintaining antioxidation mechanism is important in transplantation therapy to treat inflammatory diseases that result from restricted immunomodulatory effects of senescent MSCs. Thus, we examined the role of TNF-α-mediated signaling and its regulatory mechanisms on the senescence of umbilical cord blood-derived MSCs (UCB-MSCs) and identified its therapeutic efficacy in a collagen-induced arthritis (CIA) mouse model. We found that TNF-α increased fatty acid synthesis and lipid droplet (LD) formation through NF-κB/SREBP1-mediated FASN, SCD1, and DGAT2 expression, which protects UCB-MSCs from oxidative stress against accumulated toxic lipids. Additionally, DGAT2-mediated LD formation was regulated by TNF-α-activated TNF receptor (TNFR)1 signaling. We also found that storage of unsaturated FAs in LDs is regulated by SIRT5-dependent β-oxidation of FAs, which reduces mitochondrial ROS (mtROS) accumulation. Particularly, mtROS homeostasis was maintained by superoxide dismutase 2 (SOD2) upregulation through TNFR2-mediated SIRT5/Nrf2 signaling. In a CIA mouse model, UCB-MSCs transfected with SIRT5 siRNA exhibited reduced therapeutic effects compared with UCB-MSCs transfected with NT siRNA. Overall, the results indicated that SIRT5 plays a central role in protecting TNF-α-induced UCB-MSC senescence through FA β-oxidation and SOD2-mediated antioxidation.

Finding intracellular lipid droplets from the single-cell biolens' signature in a holographic flow-cytometry assay

In recent years, intracellular LDs have been discovered to play an important role in several pathologies. Therefore, detection of LDs would provide an in-demand diagnostic tool if coupled with flow-cytometry to give significant statistical analysis and especially if the diagnosis is made in full non-invasive mode. Here we combine the experimental results of in-flow tomographic phase microscopy with a suited numerical simulation to demonstrate that intracellular LDs can be easily detected through a label-free approach based on the direct analysis of the 2D quantitative phase maps recorded by a holographic flow cytometer. In fact, we demonstrate that the presence of LDs affects the optical focusing lensing features of the embracing cell, which can be considered a biological lens. The research was conducted on white blood cells (i.e., lymphocytes and monocytes) and ovarian cancer cells. Results show that the biolens properties of cells can be a rapid biomarker that aids in boosting the diagnosis of LDs-related pathologies by means of the holographic flow-cytometry assay for fast, non-destructive, and high-throughput screening of statistically significant number of cells.

The uniformity and stability of cellular mass density in mammalian cell culture

Cell dry mass is principally determined by the sum of biosynthesis and degradation. Measurable change in dry mass occurs on a time scale of hours. By contrast, cell volume can change in minutes by altering the osmotic conditions. How changes in dry mass and volume are coupled is a fundamental question in cell size control. If cell volume were proportional to cell dry mass during growth, the cell would always maintain the same cellular mass density, defined as cell dry mass dividing by cell volume. The accuracy and stability against perturbation of this proportionality has never been stringently tested. Normalized Raman Imaging (NoRI), can measure both protein and lipid dry mass density directly. Using this new technique, we have been able to investigate the stability of mass density in response to pharmaceutical and physiological perturbations in three cultured mammalian cell lines. We find a remarkably narrow mass density distribution within cells, that is, significantly tighter than the variability of mass or volume distribution. The measured mass density is independent of the cell cycle. We find that mass density can be modulated directly by extracellular osmolytes or by disruptions of the cytoskeleton. Yet, mass density is surprisingly resistant to pharmacological perturbations of protein synthesis or protein degradation, suggesting there must be some form of feedback control to maintain the homeostasis of mass density when mass is altered. By contrast, physiological perturbations such as starvation or senescence induce significant shifts in mass density. We have begun to shed light on how and why cell mass density remains fixed against some perturbations and yet is sensitive during transitions in physiological state.

Implications of High-Density Cholesterol Metabolism for Oocyte Biology and Female Fertility

Cholesterol is an essential component of animal cells. Different regulatory mechanisms converge to maintain adequate levels of this lipid because both its deficiency and excess are unfavorable. Low cell cholesterol content promotes its synthesis and uptake from circulating lipoproteins. In contrast, its excess induces the efflux to high-density lipoproteins (HDL) and their transport to the liver for excretion, a process known as reverse cholesterol transport. Different studies suggest that an abnormal HDL metabolism hinders female fertility. HDL are the only lipoproteins detected in substantial amounts in follicular fluid (FF), and their size and composition correlate with embryo quality. Oocytes obtain cholesterol from cumulus cells via gap junctions because they cannot synthesize cholesterol de novo and lack HDL receptors. Recent evidence has supported the possibility that FF HDL play a major role in taking up excess unesterified cholesterol (UC) from the oocyte. Indeed, genetically modified mouse models with disruptions in reverse cholesterol transport, some of which show excessive circulating UC levels, exhibit female infertility. Cholesterol accumulation can affect the egg´s viability, as reported in other cell types, and activate the plasma membrane structure and activity of membrane proteins. Indeed, in mice deficient for the HDL receptor Scavenger Class B Type I (SR-B1), excess circulating HDL cholesterol and UC accumulation in oocytes impairs meiosis arrest and hinders the developmental capacity of the egg. In other cells, the addition of cholesterol activates calcium channels and dysregulates cell death/survival signaling pathways, suggesting that these mechanisms may link altered HDL cholesterol metabolism and infertility. Although cholesterol, and lipids in general, are usually not evaluated in infertile patients, one study reported high circulating UC levels in women showing longer time to pregnancy as an outcome of fertility. Based on the evidence described above, we propose the existence of a well-regulated and largely unexplored system of cholesterol homeostasis controlling traffic between FF HDL and oocytes, with significant implications for female fertility.

Microbiota mitochondria disorders as hubs for early age-related macular degeneration

Age-related macular degeneration (AMD) is a progressive neurodegenerative disease affecting the central area (macula lutea) of the retina. Research on the pathogenic mechanism of AMD showed complex cellular contribution governed by such risk factors as aging, genetic predisposition, diet, and lifestyle. Recent studies suggested that microbiota is a transducer and a modifier of risk factors for neurodegenerative diseases, and mitochondria may be one of the intracellular targets of microbial signaling molecules. This review explores studies supporting a new concept on the contribution of microbiota-mitochondria disorders to AMD. We discuss metabolic, vascular, immune, and neuronal mechanism in AMD as well as key alterations of photoreceptor cells, retinal pigment epithelium (RPE), Bruch's membrane, choriocapillaris endothelial, immune, and neuronal cells. Special attention was paid to alterations of mitochondria contact sites (MCSs), an organelle network of mitochondria, endoplasmic reticulum, lipid droplets (LDs), and peroxisomes being documented based on our own electron microscopic findings from surgically removed human eyes. Morphometry of Bruch's membrane lipids and proteoglycans has also been performed in early AMD and aged controls. Microbial metabolites (short-chain fatty acids, polyphenols, and secondary bile acids) and microbial compounds (lipopolysaccharide, peptidoglycan, and bacterial DNA)-now called postbiotics-in addition to local effects on resident microbiota and mucous membrane, regulate systemic metabolic, vascular, immune, and neuronal mechanisms in normal conditions and in various common diseases. We also discuss their antioxidant, anti-inflammatory, and metabolic effects as well as experimental and clinical observations on regulating the main processes of photoreceptor renewal, mitophagy, and autophagy in early AMD. These findings support an emerging concept that microbiota-mitochondria disorders may be a crucial pathogenic mechanism of early AMD; and similarly, to other age-related neurodegenerative diseases, new treatment approaches should be targeted at these disorders.

Protein misfolding and clearance in the pathogenesis of a new infantile onset ataxia caused by mutations in PRDX3

Peroxiredoxin 3 (PRDX3) encodes a mitochondrial antioxidant protein which is essential for the control of reactive oxidative species (ROS) homeostasis. So far, PRDX3 mutations are involved in mild-to-moderate progressive juvenile onset cerebellar ataxia. We aimed to unravel the molecular bases underlying the disease in an infant suffering from cerebellar ataxia that started at 19 months old and presented severe cerebellar atrophy and peripheral neuropathy early in the course of disease. By whole exome sequencing, we identified a novel homozygous mutation, PRDX3 p.D163E, which impaired the mitochondrial ROS defense system. In mouse primary cortical neurons, the exogenous expression of PRDX3 p.D163E was reduced and triggered alterations in neurite morphology and in mitochondria. Mitochondrial computational parameters showed that p.D163E led to serious mitochondrial alterations. In transfected HeLa cells expressing the mutation, mitochondria accumulation was detected by correlative light electron microscopy (CLEM). Mitochondrial morphology showed severe changes, including extremely damaged outer and inner membranes with a notable cristae disorganization. Moreover, spherical structures compatible with lipid droplets were identified, which can be associated with a generalized response to stress and can be involved in the removal of unfolded proteins. In the patient's fibroblasts, PRDX3 expression was nearly absent. The biochemical analysis suggested that the mutation p.D163E would result in an unstable structure tending to form aggregates that trigger unfolded protein responses via mitochondria and endoplasmic reticulum. Altogether, our findings broaden the clinical spectrum of the recently described PRDX3-associated neurodegeneration and provide new insight into the pathological mechanisms underlying this new form of cerebellar ataxia.

Trappc9 Deficiency Impairs the Plasticity of Stem Cells

Genetic mutations of trappc9 cause intellectual disability with the atrophy of brain structures and variable obesity by poorly understood mechanisms. Trappc9-deficient mice develop phenotypes resembling pathological changes in humans and appear overweight shortly after weaning, and thus are useful for studying the pathogenesis of obesity. Here, we investigated the effects of trappc9 deficiency on the proliferation and differentiation capacity of adipose-derived stem cells (ASCs). We isolated ASCs from mice before overweight was developed and found that trappc9-null ASCs exhibited signs of premature senescence and cell death. While the lineage commitment was retained, trappc9-null ASCs preferred adipogenic differentiation. We observed a profound accumulation of lipid droplets in adipogenic cells derived from trappc9-deficient ASCs and marked differences in the distribution patterns and levels of calcium deposited in osteoblasts obtained from trappc9-null ASCs. Biochemical studies revealed that trappc9 deficiency resulted in an upregulated expression of rab1, rab11, and rab18, and agitated autophagy in ASCs. Moreover, we found that the content of neural stem cells in both the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus vastly declined in trappc9-null mice. Collectively, our results suggest that obesity, as well as brain structure hypoplasia induced by the deficiency of trappc9, involves an impairment in the plasticity of stem cells.

Functions of Stress-Induced Lipid Droplets in the Nervous System

Lipid droplets are highly dynamic intracellular organelles that store neutral lipids such as cholesteryl esters and triacylglycerols. They have recently emerged as key stress response components in many different cell types. Lipid droplets in the nervous system are mostly observed in vivo in glia, ependymal cells and microglia. They tend to become more numerous in these cell types and can also form in neurons as a consequence of ageing or stresses involving redox imbalance and lipotoxicity. Abundant lipid droplets are also a characteristic feature of several neurodegenerative diseases. In this minireview, we take a cell-type perspective on recent advances in our understanding of lipid droplet metabolism in glia, neurons and neural stem cells during health and disease. We highlight that a given lipid droplet subfunction, such as triacylglycerol lipolysis, can be physiologically beneficial or harmful to the functions of the nervous system depending upon cellular context. The mechanistic understanding of context-dependent lipid droplet functions in the nervous system is progressing apace, aided by new technologies for probing the lipid droplet proteome and lipidome with single-cell type precision.

Lipid Droplets' Role in the Regulation of β-Cell Function and β-Cell Demise in Type 2 Diabetes

During development of type 2 diabetes (T2D), excessive nutritional load is thought to expose pancreatic islets to toxic effects of lipids and reduce β-cell function and mass. However, lipids also play a positive role in cellular metabolism and function. Thus, proper trafficking of lipids is critical for β cells to maximize the beneficial effects of these molecules while preventing their toxic effects. Lipid droplets (LDs) are organelles that play an important role in the storage and trafficking of lipids. In this review, we summarize the discovery of LDs in pancreatic β cells, LD lifecycle, and the effect of LD catabolism on β-cell insulin secretion. We discuss factors affecting LD formation such as age, cell type, species, and nutrient availability. We then outline published studies targeting critical LD regulators, primarily in rat and human β-cell models, to understand the molecular effect of LD formation and degradation on β-cell function and health. Furthermore, based on the abnormal LD accumulation observed in human T2D islets, we discuss the possible role of LDs during the development of β-cell failure in T2D. Current knowledge indicates that proper formation and clearance of LDs are critical to normal insulin secretion, endoplasmic reticulum homeostasis, and mitochondrial integrity in β cells. However, it remains unclear whether LDs positively or negatively affect human β-cell demise in T2D. Thus, we discuss possible research directions to address the knowledge gap regarding the role of LDs in β-cell failure.

Touch and Go: Membrane Contact Sites Between Lipid Droplets and Other Organelles

Lipid droplets (LDs) have emerged not just as storage sites for lipids but as central regulators of metabolism and organelle quality control. These critical functions are achieved, in part, at membrane contact sites (MCS) between LDs and other organelles. MCS are sites of transfer of cellular constituents to or from LDs for energy mobilization in response to nutrient limitations, as well as LD biogenesis, expansion and autophagy. Here, we describe recent findings on the mechanisms underlying the formation and function of MCS between LDs and mitochondria, ER and lysosomes/vacuoles and the role of the cytoskeleton in promoting LD MCS through its function in LD movement and distribution in response to environmental cues.

Recent insights into the role of glia and oxidative stress in Alzheimer's disease gained from Drosophila

Here, we discuss findings made using Drosophila on Alzheimer's disease (AD) risk and progression. Recent studies have investigated the mechanisms underlying glia-mediated neuroprotection in AD. First, we discuss a novel mechanism of glial lipid droplet formation that occurs in response to elevated reactive oxygen species in neurons. The data suggest that disruptions to this process contribute to AD risk. We further discuss novel mechanistic insights into glia-mediated Aβ42-clearance made using the fly. Finally, we highlight work that provides evidence that the aberrant accumulation of reactive oxygen species in AD may not just be a consequence of disease but contribute to disease progression as well. Cumulatively, the discussed studies highlight recent, relevant discoveries in AD made using Drosophila.

Caveolin-1 Regulates Cellular Metabolism: A Potential Therapeutic Target in Kidney Disease

The kidney is an energy-consuming organ, and cellular metabolism plays an indispensable role in kidney-related diseases. Caveolin-1 (Cav-1), a multifunctional membrane protein, is the main component of caveolae on the plasma membrane. Caveolae are represented by tiny invaginations that are abundant on the plasma membrane and that serve as a platform to regulate cellular endocytosis, stress responses, and signal transduction. However, caveolae have received increasing attention as a metabolic platform that mediates the endocytosis of albumin, cholesterol, and glucose, participates in cellular metabolic reprogramming and is involved in the progression of kidney disease. It is worth noting that caveolae mainly depend on Cav-1 to perform the abovementioned cellular functions. Furthermore, the mechanism by which Cav-1 regulates cellular metabolism and participates in the pathophysiology of kidney diseases has not been completely elucidated. In this review, we introduce the structure and function of Cav-1 and its functions in regulating cellular metabolism, autophagy, and oxidative stress, focusing on the relationship between Cav-1 in cellular metabolism and kidney disease; in addition, Cav-1 that serves as a potential therapeutic target for treatment of kidney disease is also described.

Lipotoxicity Downstream of α-Synuclein Imbalance: A Relevant Pathomechanism in Synucleinopathies?

Neuronal loss in Parkinson's disease and related brain diseases has been firmly linked to the abundant neuronal protein α-synuclein (αS). However, we have gained surprisingly little insight into how exactly αS exerts toxicity in these diseases. Hypotheses of proteotoxicity, disturbed vesicle trafficking, mitochondrial dysfunction and other toxicity mechanisms have been proposed, and it seems possible that a combination of different mechanisms may drive pathology. A toxicity mechanism that has caught increased attention in the recent years is αS-related lipotoxicity. Lipotoxicity typically occurs in a cell when fatty acids exceed the metabolic needs, triggering a flux into harmful pathways of non-oxidative metabolism. Genetic and experimental approaches have revealed a significant overlap between lipid storage disorders, most notably Gaucher's disease, and synucleinopathies. There is accumulating evidence for lipid aberrations causing synuclein misfolding as well as for αS excess and misfolding causing lipid aberration. Does that mean the key problem in synucleinopathies is lipotoxicity, the accumulation of harmful lipid species or alteration in lipid equilibrium? Here, we review the existing literature in an attempt to get closer to an answer.

Cellular and molecular pathways underlying the nephrotoxicity of gadolinium

Mounting evidence on the short- and long-term adverse effects associated with gadolinium [Gd (III)]-based contrast agents used in magnetic resonance imaging have emerged in the past three decades. Safety issues arise from the release of Gd (III) from chelates and its deposition in tissues, which is exacerbated in patients with renal disease, since the kidney is the major excretion organ of most of these agents. This study aimed at unveiling the cellular and molecular mechanisms of nephrotoxicity of Gd (III), using an in vitro model of human proximal tubular cells (HK-2 cell line). Cell viability declined in a concentration- and time-dependent manner after exposure to GdCl3·6H2O. The estimated inhibitory concentrations (ICs) eliciting 1 to 50% of cell death, after 24 h of exposure, ranged from 3.4 to 340.5 µM. At toxic concentrations, exposure to Gd (III) led to disruption of the oxidative status, mitochondrial dysfunction, cell death by apoptosis, switching to necrosis at higher levels, and autophagic activation. Disturbance of the lipid metabolism was already observed at low-toxicity ICs, with accumulation of lipid droplets, and upregulation of genes related to both lipogenesis and lipolysis. Gd (III)-exposure, even at the subtoxic IC01, increased the expression of modulators of various signaling pathways involved in the development and progression of renal disease, including inflammation, hypoxia and fibrosis. Our results give new insights into the mechanisms underlying the nephrotoxic potential of Gd (III) and highlight the need to further clarify the risks versus benefits of the Gd (III)-based contrast agents currently in use.

Lipid Droplets Protect Aging Mitochondria and Thus Promote Lifespan in Yeast Cells

Besides their role as a storage for neutral lipids and sterols, there is increasing evidence that lipid droplets (LDs) are involved in cellular detoxification. LDs are in close contact to a broad variety of organelles where protein- and lipid exchange is mediated. Mitochondria as a main driver of the aging process produce reactive oxygen species (ROS), which damage several cellular components. LDs as highly dynamic organelles mediate a potent detoxification mechanism by taking up toxic lipids and proteins. A stimulation of LDs induced by the simultaneously overexpression of Lro1p and Dga1p (both encoding acyltransferases) prolongs the chronological as well as the replicative lifespan of yeast cells. The increased number of LDs reduces mitochondrial fragmentation as well as mitochondrial ROS production, both phenotypes that are signs of aging. Strains with an altered LD content or morphology as in the sei1∆ or lro1∆ mutant lead to a reduced replicative lifespan. In a yeast strain defective for the LON protease Pim1p, which showed an enhanced ROS production, increased doubling time and an altered mitochondrial morphology, a LRO1 overexpression resulted in a partially reversion of this "premature aging" phenotype.

In Vitro and In Vivo Antifungal Activity of Buparvaquone against Sporothrix brasiliensis

Sporotrichosis has become an important zoonosis in Brazil, and Sporothrix brasiliensis is the primary species transmitted by cats. Improvement of animal treatment will help control and limit the spread and geographic expansion of sporotrichosis. Accordingly, buparvaquone, an antiprotozoal hydroxynaphthoquinone agent marketed as Butalex, was evaluated in vitro and in vivo against feline-borne isolates of S. brasiliensis. Buparvaquone inhibited in vitro fungal growth at concentrations 4-fold lower than itraconazole (the first-choice antifungal used for sporotrichosis) and was 408 times more selective for S. brasiliensis than mammalian cells. Yeasts treated with a subinhibitory concentration of buparvaquone exhibited mitochondrial dysfunction, reactive oxygen species and neutral lipid accumulation, and impaired plasma membranes. Scanning electron microscopy images also revealed buparvaquone altered cell wall integrity and induced cell disruption. In vivo experiments in a Galleria mellonella model revealed that buparvaquone (single dose of 5 mg/kg of body weight) is more effective than itraconazole against infections with S. brasiliensis yeasts. Combined, our results indicate that buparvaquone has a great in vitro and in vivo antifungal activity against S. brasiliensis, revealing the potential application of this drug as an alternative treatment for feline sporotrichosis.

Lipid droplets and the host-pathogen dynamic: FATal attraction?

In the ongoing conflict between eukaryotic cells and pathogens, lipid droplets (LDs) emerge as a choke point in the battle for nutrients. While many pathogens seek the lipids stored in LDs to fuel an expensive lifestyle, innate immunity rewires lipid metabolism and weaponizes LDs to defend cells and animals. Viruses, bacteria, and parasites directly and remotely manipulate LDs to obtain substrates for metabolic energy, replication compartments, assembly platforms, membrane blocks, and tools for host colonization and/or evasion such as anti-inflammatory mediators, lipoviroparticles, and even exosomes. Host LDs counterattack such advances by synthesizing bioactive lipids and toxic nucleotides, organizing immune signaling platforms, and recruiting a plethora of antimicrobial proteins to provide a front-line defense against the invader. Here, we review the current state of this conflict. We will discuss why, when, and how LDs efficiently coordinate and precisely execute a plethora of immune defenses. In the age of antimicrobial resistance and viral pandemics, understanding innate immune strategies developed by eukaryotic cells to fight and defeat dangerous microorganisms may inform future anti-infective strategies.

Loss of swiss cheese in Neurons Contributes to Neurodegeneration with Mitochondria Abnormalities, Reactive Oxygen Species Acceleration and Accumulation of Lipid Droplets in Drosophila Brain

Various neurodegenerative disorders are associated with human NTE/PNPLA6 dysfunction. Mechanisms of neuropathogenesis in these diseases are far from clearly elucidated. Hereditary spastic paraplegia belongs to a type of neurodegeneration associated with NTE/PNLPLA6 and is implicated in neuron death. In this study, we used Drosophila melanogaster to investigate the consequences of neuronal knockdown of swiss cheese (sws)-the evolutionarily conserved ortholog of human NTE/PNPLA6-in vivo. Adult flies with the knockdown show longevity decline, locomotor and memory deficits, severe neurodegeneration progression in the brain, reactive oxygen species level acceleration, mitochondria abnormalities and lipid droplet accumulation. Our results suggest that SWS/NTE/PNPLA6 dysfunction in neurons induces oxidative stress and lipid metabolism alterations, involving mitochondria dynamics and lipid droplet turnover in neurodegeneration pathogenesis. We propose that there is a complex mechanism in neurological diseases such as hereditary spastic paraplegia, which includes a stress reaction, engaging mitochondria, lipid droplets and endoplasmic reticulum interplay.

Lipid Droplets as Regulators of Metabolism and Immunity

Abstract

A hallmark of sterile and nonsterile inflammation is the increased accumulation of cytoplasmic lipid droplets (LDs) in non-adipose cells. LDs are ubiquitous organelles specialized in neutral lipid storage and hydrolysis. Originating in the ER, LDs are comprised of a core of neutral lipids (cholesterol esters, triglycerides) surrounded by a phospholipid monolayer and several LD-associated proteins. The perilipin (PLIN1-5) family are the most abundant structural proteins present on the surface of LDs. While PLIN1 is primarily expressed in adipocytes, PLIN2 and PLIN3 are ubiquitously expressed. LDs also acquire a host of enzymes and proteins that regulate LD metabolism. Amongst these are neutral lipases and selective lipophagy factors that promote hydrolysis of LD-associated neutral lipid. In addition, LDs physically associate with other organelles such as mitochondria through inter-organelle membrane contact sites that facilitate lipid transport. Beyond serving as a source of energy storage, LDs participate in inflammatory and infectious diseases, regulating both innate and adaptive host immune responses. Here, we review recent studies on the role of LDs in the regulation of immunometabolism.

Celia's Encephalopathy (BSCL2-Gene-Related): Current Understanding

Seipin, encoded by the BSCL2 gene, is a protein that in humans is expressed mainly in the central nervous system. Uniquely, certain variants in BSCL2 can cause both generalized congenital lipodystrophy type 2, upper and/or lower motor neuron diseases, or progressive encephalopathy, with a poor prognosis during childhood. The latter, Celia's encephalopathy, which may or may not be associated with generalized lipodystrophy, is caused by the c.985C >T variant. This cytosine to thymine transition creates a cryptic splicing zone that leads to intronization of exon 7, resulting in an aberrant form of seipin, Celia seipin. It has been proposed that the accumulation of this protein, both in the endoplasmic reticulum and in the nucleus of neurons, might be the pathogenetic mechanism of this neurodegenerative condition. In recent years, other variants in BSCL2 associated with generalized lipodystrophy and progressive epileptic encephalopathy have been reported. Interestingly, most of these variants could also lead to the loss of exon 7. In this review, we analyzed the molecular bases of Celia's encephalopathy and its pathogenic mechanisms, the clinical features of the different variants, and a therapeutic approach in order to slow down the progression of this fatal neurological disorder.