Differential Roles of Cell Death-inducing DNA Fragmentation Factor-α-like Effector (CIDE) Proteins in Promoting Lipid Droplet Fusion and Growth in Subpopulations of Hepatocytes

Mechanisms coupling lipid droplets to MASLD pathophysiology

Hepatic steatosis, the buildup of neutral lipids in lipid droplets (LDs), is commonly referred to as metabolic dysfunction-associated steatotic liver disease when alcohol or viral infections are not involved. Metabolic dysfunction-associated steatotic liver disease encompasses simple steatosis and the more severe metabolic dysfunction-associated steatohepatitis, characterized by inflammation, hepatocyte injury, and fibrosis. Previously viewed as inert markers of disease, LDs are now understood to play active roles in disease etiology and have significant nonpathological and pathological functions in cell signaling and function. These dynamic properties of LDs are tightly regulated by hundreds of proteins that coat the LD surface, controlling lipid metabolism, trafficking, and signaling. The following review highlights various facets of LD biology with the primary goal of discussing key mechanisms through which LDs promote the development of advanced liver diseases, including metabolic dysfunction-associated steatohepatitis.

Unveiling Novel Mechanism of CIDEB in Fatty Acid Synthesis Through ChIP-Seq and Functional Analysis in Dairy Goat

Goat milk is abundant in nutrients, particularly in milk fats, which confer health benefits to humans. Exploring the regulatory mechanism of fatty acid synthesis is highly important to understand milk composition manipulation. In this study, we used chromatin immunoprecipitation sequencing (ChIP-seq) on goat mammary glands at different lactation stages which revealed a novel lactation regulatory factor: cell death-inducing DFFA-like effector B (CIDEB). RT-qPCR results revealed that CIDEB was significantly upregulated during lactation in dairy goats. CIDEB overexpression significantly increased the expression levels of genes involved in fatty acid synthesis (ACACA, SCD1, p < 0.05; ELOVL6, p < 0.01), lipid droplet formation (XDH, p < 0.05), and triacylglycerol (TAG) synthesis (DGAT1, p < 0.05; GPAM, p < 0.01) in goat mammary epithelial cells (GMECs). The contents of lipid droplets, TAG, and cholesterol were increased (p < 0.05) in CIDEB-overexpressing GMECs, and knockdown of CIDEB led to the opposite results. In addition, CIDEB knockdown significantly decreased the proportion of C16:0 and total C18:2. Luciferase reporter assays indicated that X-box binding protein 1 (XBP1) promoted CIDEB transcription via XBP1 binding sites located in the CIDEB promoter. Furthermore, CIDEB knockdown attenuated the stimulatory effect of XBP1 on lipid droplet accumulation. Collectively, these findings elucidate the critical regulatory roles of CIDEB in milk fat synthesis, thus providing new insights into improving the quality of goat milk.

Targeting lipid droplets and lipid droplet-associated proteins: a new perspective on natural compounds against metabolic diseases

BACKGROUND

Lipid droplet (LD) is a metabolically active organelle, which changes dynamically with the metabolic state and energy requirements of cells. Proteins that either insert into the LD phospholipid monolayer or are present in the cytoplasm, playing a crucial role in lipid homeostasis and signaling regulation, are known as LD-associated proteins.

METHODS

The keywords "lipid droplets" and "metabolic diseases" were used to obtain literature on LD metabolism and pathological mechanism. After searching databases including Scopus, OVID, Web of Science, and PubMed from 2013 to 2024 using terms like "lipid droplets", "lipid droplet-associated proteins", "fatty liver disease", "diabetes", "diabetic kidney disease", "obesity", "atherosclerosis", "hyperlipidemia", "natural drug monomers" and "natural compounds", the most common natural compounds were identified in about 954 articles. Eventually, a total of 91 studies of 10 natural compounds reporting in vitro or in vivo studies were refined and summarized.

RESULTS

The most frequently used natural compounds include Berberine, Mangostin, Capsaicin, Caffeine, Genistein, Epigallocatechin-3-gallate, Chlorogenic acid, Betaine, Ginsenoside, Resveratrol. These natural compounds interact with LD-associated proteins and help ameliorate abnormal LDs in various metabolic diseases.

CONCLUSION

Natural compounds involved in the regulation of LDs and LD-associated proteins hold promise for treating metabolic diseases. Further research into these interactions may lead to new therapeutic applications.

Unveiling the Multifaceted Role of CIDEB: From Apoptosis to Lipid Metabolism and Liver Health

Cell-death-inducing DNA fragmentation factor-alpha (DFFA)-like effector b (CIDEB) was first identified as an apoptosis-inducing protein. Further research revealed a pivotal role in lipid metabolism, regulating very-low-density lipoprotein (VLDL), lipid droplets (LD), sterol response element-binding protein (SREBP), and chylomicrons. Recent studies have uncovered that rare germline variants in CIDEB protect against liver diseases, including MAFLD, cirrhosis, and viral hepatitis. Furthermore, CIDEB influences steps of the hepatitis C virus (HCV) replication cycle. This review summarizes the current knowledge about CIDEB’s roles in apoptosis, lipid metabolism, and viral hepatitis, and highlights its critical role in liver diseases.

Establishment of a Steatosis Model in LMH Cells, Chicken Embryo Hepatocytes, and Liver Tissues Based on a Mixture of Sodium Oleate and Palmitic Acid

Research on hepatic steatosis in animal husbandry has been a prominent area of study. Developing an appropriate in vitro cellular steatosis model is crucial for comprehensively investigating the mechanisms involved in liver lipid deposition in poultry and for identifying potential interventions to address abnormalities in lipid metabolism. The research on the methods of in vitro liver steatosis in chickens, particularly the effects of different fat mixtures, is still lacking. In this study, LMH cells were utilized to investigate the effects of OA, SO, PA, SP, and their pairwise combinations on steatosis development, with the aim of identifying the optimal conditions for inducing steatosis. Analysis of triglyceride (TG) content in LMH cells revealed that OA and SP had limited efficacy in increasing TG content, while a combination of SO and PA in a 1:2 ratio exhibited the highest TG content. Moreover, Oil Red O staining results in LMH cells demonstrated that the combination treatment had a more pronounced induction effect compared to 0.375 mM SO. Additionally, RNA-seq analysis showed that 0.375 mM SO significantly influenced the expression of genes associated with fatty acid metabolism compared to the control group, whereas the combination of SO and PA led to an enrichment of key GO terms associated with programmed cell death. These findings suggest that varying conditions of cellular steatosis could lead to distinct disruptions in gene expression. The optimal conditions for inducing steatosis in LMH cells were also tested on chicken embryonic liver cells and embryos. TG detection and Oil Red O staining assays showed that the combination of SO and PA successfully induced steatosis. However, the gene expression pattern differed from that of LMH cells. This study lays the foundations for further investigations into avian hepatic steatosis.

Roles of lipid droplets and related proteins in metabolic diseases

Lipid droplets (LDs), which are active organelles, derive from the monolayer membrane of the endoplasmic reticulum and encapsulate neutral lipids internally. LD-associated proteins like RAB, those in the PLIN family, and those in the CIDE family participate in LD formation and development, and they are active players in various diseases, organelles, and metabolic processes (i.e., obesity, non-alcoholic fatty liver disease, and autophagy). Our synthesis on existing research includes insights from the formation of LDs to their mechanisms of action, to provide an overview needed for advancing research into metabolic diseases and lipid metabolism.

CIDE proteins and their regulatory mechanisms in lipid droplet fusion and growth

The cell death-inducing DFF45-like effector (CIDE) proteins, including Cidea, Cideb, and Cidec/Fsp27, regulate various aspects of lipid homeostasis, including lipid storage, lipolysis, and lipid secretion. This review focuses on the physiological roles of CIDE proteins based on studies on knockout mouse models and human patients bearing CIDE mutations. The primary cellular function of CIDE proteins is to localize to lipid droplets (LDs) and to control LD fusion and growth across different cell types. We propose a four-step process of LD fusion, characterized by (a) the recruitment of CIDE proteins to the LD surface and CIDE movement, (b) the enrichment and condensate formation of CIDE proteins to form LD fusion plates at LD-LD contact sites, (c) lipid transfer through lipid-permeable passageways within the fusion plates, and (d) the completion of LD fusion. Lastly, we outline CIDE-interacting proteins as regulatory factors, as well as their contribution in LD fusion.

Identification of potential pathogenic hepatic super-enhancers regulatory network in high-fat diet induced hyperlipidemia

Hyperlipidemia (HLP) is a prevalent metabolic disorder and a significant risk factor for cardiovascular disease. According to recent discoveries, super-enhancers (SEs) play a role in the increased expression of genes that encode important regulators of both cellular identity and the progression of diseases. However, the underlying function of SEs in the development of HLP is still unknown. We performed an integrative analysis of data on H3K27ac ChIP-seq and RNA sequencing obtained from liver tissues of mice under a low-fat diet (LFD) and high-fat diet (HFD) from GEO database. The rank ordering of super enhancers algorithm was employed for the computation and identification of SEs. A total of 1,877 and 1,847 SEs were identified in the LFD and HFD groups, respectively. The SE inhibitor JQ1 was able to potently reverse lipid deposition and the increased intracellular triglyceride and total cholesterol induced by oleic acid, indicating that SEs are involved in regulating lipid accumulation. Two hundred seventy-eight were considered as HFD-specific SEs (HSEs). GO and KEGG pathway enrichment analysis of the upregulated HSEs-associated genes revealed that they were mainly involved in lipid metabolic pathway. Four hub genes, namely Cd36, Pex11a, Ech1, and Cidec, were identified in the HSEs-associated protein-protein interaction network, and validated with two other datasets. Finally, we constructed a HSEs-specific regulatory network with Cidec and Cd36 as the core through the prediction and verification of transcription factors. Our study constructed a HSEs-associated regulatory network in the pathogenesis of HLP, providing new ideas for the underlying mechanisms and therapeutic targets of HLP.

Exploring the Multifaceted Landscape of MASLD: A Comprehensive Synthesis of Recent Studies, from Pathophysiology to Organoids and Beyond

Non-alcoholic fatty liver disease (NAFLD) is a widespread contributor to chronic liver disease globally. A recent consensus on renaming liver disease was established, and metabolic dysfunction-associated steatotic liver disease, MASLD, was chosen as the replacement for NAFLD. The disease's range extends from the less severe MASLD, previously known as non-alcoholic fatty liver (NAFL), to the more intense metabolic dysfunction-associated steatohepatitis (MASH), previously known as non-alcoholic steatohepatitis (NASH), characterized by inflammation and apoptosis. This research project endeavors to comprehensively synthesize the most recent studies on MASLD, encompassing a wide spectrum of topics such as pathophysiology, risk factors, dietary influences, lifestyle management, genetics, epigenetics, therapeutic approaches, and the prospective trajectory of MASLD, particularly exploring its connection with organoids.

Lipid droplets, autophagy, and ageing: A cell-specific tale

Lipid droplets are the essential organelle for storing lipids in a cell. Within the variety of the human body, different cells store, utilize and release lipids in different ways, depending on their intrinsic function. However, these differences are not well characterized and, especially in the context of ageing, represent a key factor for cardiometabolic diseases. Whole body lipid homeostasis is a central interest in the field of cardiometabolic diseases. In this review we characterize lipid droplets and their utilization via autophagy and describe their diverse fate in three cells types central in cardiometabolic dysfunctions: adipocytes, hepatocytes, and macrophages.

Concept of lipid droplet biogenesis

Lipid droplets (LD) are functionally conserved fat storage organelles found in all cell types. LDs have a unique structure comprising of a hydrophobic core of neutral lipids (fat), triacylglycerol (TAG) and cholesterol esters (CE) surrounded by a phospholipid monolayer. LD surface is decorated by a multitude of proteins and enzymes rendering this compartment functional. Accumulating evidence suggests that LDs originate from discrete ER-subdomains, demarcated by the lipodystrophy protein seipin, however, the mechanisms of which are not well understood. LD biogenesis factors together with biophysical properties of the ER membrane orchestrate spatiotemporal regulation of LD nucleation and growth at specific ER subdomains in response to metabolic cues. Defects in LD formation manifests in several human pathologies, including obesity, lipodystrophy, ectopic fat accumulation, and insulin resistance. Here, we review recent advances in understanding the molecular events during initial stages of eukaryotic LD assembly and discuss the critical role of factors that ensure fidelity of this process.

SUMO-specific protease 2 regulates lipid droplet size through ERRα-mediated CIDEA expression in adipocytes

Lipid droplets are not only lipid storage sites but also are closely related to lipid metabolism. Lipid droplet growth increases lipid storage capacity and suppresses lipolysis via lipase associated with the lipid droplet surface. The cell death-inducing DFF45-like effector (CIDE) family of proteins mediates lipid droplet fusion, which mainly contributes to lipid droplet growth. We previously demonstrated small ubiquitin-like modifier (SUMO)-specific protease 2 (SENP2) plays important roles in lipid metabolism and induction/maintenance of adipogenesis. In this study, we determined whether SENP2 regulates lipid droplet size in adipocytes. Overexpression of SENP2 increased lipid droplet size in differentiated 3T3-L1 adipocytes and facilitated CIDEA transcription. We found SENP2 increased CIDEA expression mainly through desumoylation of estrogen-related receptor α (ERRα), which acted in coordination with peroxisome proliferator-activated receptor γ-coactivator α. In addition, palmitate treatment increased SENP2 and CIDEA mRNA levels. Specific small interfering RNA-mediated knockdown of SENP2, as well as ERRα knockdown, eliminated palmitate-induced CIDEA expression. These results suggest SENP2 enhances CIDEA expression by modulating ERRα when SENP2 is upregulated, such as after palmitate treatment, to increase lipid droplet size in adipocytes.

Mechanisms of Lipid Droplet Accumulation in Steatotic Liver Diseases

The steatotic diseases of metabolic dysfunction-associated steatotic liver disease (MASLD), alcohol-associated liver disease (ALD), and chronic hepatitis C (HCV) account for the majority of liver disease prevalence, morbidity, and mortality worldwide. While these diseases have distinct pathogenic and clinical features, dysregulated lipid droplet (LD) organelle biology represents a convergence of pathogenesis in all three. With increasing understanding of hepatocyte LD biology, we now understand the roles of LD proteins involved in these diseases but also how genetics modulate LD biology to either exacerbate or protect against the phenotypes associated with steatotic liver diseases. Here, we review the history of the LD organelle and its biogenesis and catabolism. We also review how this organelle is critical not only for the steatotic phenotype of liver diseases but also for their advanced phenotypes. Finally, we summarize the latest attempts and challenges of leveraging LD biology for therapeutic gain in steatotic diseases. In conclusion, the study of dysregulated LD biology may lead to novel therapeutics for the prevention of disease progression in the highly prevalent steatotic liver diseases of MASLD, ALD, and HCV.

Spatial and single-cell profiling of the metabolome, transcriptome and epigenome of the aging mouse liver

Tissues within an organism and even cell types within a tissue can age with different velocities. However, it is unclear whether cells of one type experience different aging trajectories within a tissue depending on their spatial location. Here, we used spatial transcriptomics in combination with single-cell ATAC-seq and RNA-seq, lipidomics and functional assays to address how cells in the male murine liver are affected by age-related changes in the microenvironment. Integration of the datasets revealed zonation-specific and age-related changes in metabolic states, the epigenome and transcriptome. The epigenome changed in a zonation-dependent manner and functionally, periportal hepatocytes were characterized by decreased mitochondrial fitness, whereas pericentral hepatocytes accumulated large lipid droplets. Together, we provide evidence that changing microenvironments within a tissue exert strong influences on their resident cells that can shape epigenetic, metabolic and phenotypic outputs.

Therapeutic opportunities for the treatment of NASH with genetically validated targets

The identification of genetic variants associated with fatty liver disease (FLD) from genome-wide association studies started in 2008 when single nucleotide polymorphisms in PNPLA3, the gene encoding patatin-like phospholipase domain-containing 3, were found to be associated with altered hepatic fat content. Since then, several genetic variants associated with protection from, or an increased risk of, FLD have been identified. The identification of these variants has provided insight into the metabolic pathways that cause FLD and enabled the identification of potential therapeutic targets. In this mini-review, we will examine the therapeutic opportunities derived from genetically validated targets in FLD, including oligonucleotide-based therapies targeting PNPLA3 and HSD17B13 that are currently being evaluated in clinical trials for the treatment of NASH (non-alcoholic steatohepatitis).

Hepatocyte-specific loss of LAP2α protects against diet-induced hepatic steatosis, steatohepatitis, and fibrosis in male mice

There is increasing evidence for the importance of the nuclear envelope in lipid metabolism, nonalcoholic fatty liver disease (NAFLD), and nonalcoholic steatohepatitis (NASH). Human mutations in LMNA, encoding A-type nuclear lamins, cause early-onset insulin resistance and NASH, while hepatocyte-specific deletion of Lmna predisposes to NASH with fibrosis in male mice. Given that variants in the gene encoding LAP2α, a nuclear protein that regulates lamin A/C, were previously identified in patients with NAFLD, we sought to determine the role of LAP2α in NAFLD using a mouse genetic model. Hepatocyte-specific Lap2α-knockout (Lap2α(ΔHep)) mice and littermate controls were fed normal chow or high-fat diet (HFD) for 8 wk or 6 mo. Unexpectedly, male Lap2α(ΔHep) mice showed no increase in hepatic steatosis or NASH compared with controls. Rather, Lap2α(ΔHep) mice demonstrated reduced hepatic steatosis, with decreased NASH and fibrosis after long-term HFD. Accordingly, pro-steatotic genes including Cidea, Mogat1, and Cd36 were downregulated in Lap2α(ΔHep) mice, along with concomitant decreases in expression of pro-inflammatory and pro-fibrotic genes. These data indicate that hepatocyte-specific Lap2α deletion protects against hepatic steatosis and NASH in mice and raise the possibility that LAP2α could become a potential therapeutic target in human NASH.NEW & NOTEWORTHY The nuclear envelope and lamina regulate lipid metabolism and susceptibility to nonalcoholic steatohepatitis (NASH), but the role of the nuclear lamin-binding protein LAP2α in NASH has not been explored. Our data demonstrate that hepatocyte-specific loss of LAP2α protects against diet-induced hepatic steatosis, NASH, and fibrosis in male mice, with downregulation of pro-steatotic, pro-inflammatory, and pro-fibrotic lamin-regulated genes. These findings suggest that targeting LAP2α could have future potential as a novel therapeutic avenue in NASH.

Healthy lifestyle? or just the right genetic mutations

The development of genomic technologies over the past decades has enabled identification of genetic variants responsible of disease; occasionally however, protective rare variants emerged. Verweij et al have recently reported genetic variants in CIDEB gene that are protective from liver injury. Here, we briefly summarise the recent findings on the impact of CIDEB variants on liver disease, while emphasizing how phenotype-genotype studies tailored for the identification of "protective" mutations might direct development of prevention and therapeutic strategies for common diseases.

Lipid droplet biogenesis and functions in health and disease

Ubiquitous yet unique, lipid droplets are intracellular organelles that are increasingly being recognized for their versatility beyond energy storage. Advances uncovering the intricacies of their biogenesis and the diversity of their physiological and pathological roles have yielded new insights into lipid droplet biology. Despite these insights, the mechanisms governing the biogenesis and functions of lipid droplets remain incompletely understood. Moreover, the causal relationship between the biogenesis and function of lipid droplets and human diseases is poorly resolved. Here, we provide an update on the current understanding of the biogenesis and functions of lipid droplets in health and disease, highlighting a key role for lipid droplet biogenesis in alleviating cellular stresses. We also discuss therapeutic strategies of targeting lipid droplet biogenesis, growth or degradation that could be applied in the future to common diseases, such as cancer, hepatic steatosis and viral infection.

The rhythmic coupling of Egr-1 and Cidea regulates age-related metabolic dysfunction in the liver of male mice

The liver lipid metabolism of older individuals canbecome impaired and the circadian rhythm of genes involved in lipid metabolism is also disturbed. Although the link between metabolism and circadian rhythms is already recognized, how these processes are decoupled in liver during aging is still largely unknown. Here, we show that the circadian rhythm for the transcription factor Egr-1 expression is shifted forward with age in male mice. Egr-1 deletion accelerates liver age-related metabolic dysfunction, which associates with increased triglyceride accumulation, disruption of the opposite rhythmic coupling of Egr-1 and Cidea (Cell Death Inducing DFFA Like Effector A) at the transcriptional level and large lipid droplet formation. Importantly, adjustment of the central clock with light via a 4-hour forward shift in 6-month-old mice, leads to recovery the rhythm shift of Egr-1 during aging and largely ameliorated liver metabolic dysfunction. All our collected data suggest that liver Egr-1 might integrate the central and peripheral rhythms and regulate metabolic homeostasis in the liver.

The microglia-blood vessel interactions in the developing brain

Microglia are the immune cells in the central nervous system (CNS). Once microglial progenitors are generated in the yolk sac, these cells enter the CNS and colonize its structures by migrating and proliferating during development. Although the microglial population in the CNS is still low in this stage compared to adults, these cells can associate with many surrounding cells, such as neural lineage cells and vascular-structure-composing cells, by extending their filopodia and with their broad migration capacity. Previous studies revealed multifaceted microglial actions on neural lineage cells, such as regulating the differentiation of neural progenitors and modulating neuronal positioning. Notably, microglia not only act on neural lineage cells but also interact with blood vessels, for example, by supporting vascular formation and integrity. On the other hand, blood vessels contribute to microglial colonization into the CNS and their migration at local tissues. Importantly, pericytes, the cells that encompass vascular endothelial cells, have been suggested to play a profound role in microglial function. This review summarizes recent advances in the understanding of the interaction of microglia and blood vessels, especially focusing on the significance of this interaction in CNS development, and discusses how microglial and blood vessel dysfunction leads to developmental disorders.

Combinatorial therapy with BAR502 and UDCA resets FXR and GPBAR1 signaling and reverses liver histopathology in a model of NASH

Non-alcoholic steatosis (NAFLD) and steatohepatitis (NASH) are two highly prevalent human disorders for which therapy remains suboptimal. Bile acids are signaling molecules acting on two main receptors the Farnesoid-x-receptor (FXR) and G protein coupled receptor GPB AR1. Clinical trials have shown that FXR agonism might result in side effects along with lack of efficacy in restoring liver histopathology. For these reasons a multi-targets therapy combined FXR agonists with agent targeting additional molecular mechanisms might have improved efficacy over selective FXR agonists. In the present study we have compared the effects of BAR502, a dual FXR/GPBAR1 ligand) alone or in combination with ursodeoxycholic acid (UDCA) in a model of NAFLD/NASH induced by feeding mice with a Western diet for 10 weeks. The results demonstrated that while BAR502 and UDCA partially protected against liver damage caused by Western diet, the combination of the two, reversed the pro-atherogenic lipid profile and completely reversed the histopathology damage, attenuating liver steatosis, ballooning, inflammation and fibrosis. Additionally, while both agents increased insulin sensitivity and bile acid signaling, the combination of the two, modulated up top 85 genes in comparison of mice feed a Western diet, strongly reducing expression of inflammatory markers such as chemokines and cytokines. Additionally, the combination of the two agents redirected the bile acid metabolism toward bile acid species that are GPBAR1 agonist while reduced liver bile acid content and increased fecal excretion. Together, these data, highlight the potential role for a combinatorial therapy based on BAR502 and UDCA in treating of NAFLD.

Protective Effects of Glycyrrhiza Total Flavones on Liver Injury Induced by Streptococcus agalactiae in Tilapia (Oreochromis niloticus)

Clinical studies have confirmed that Glycyrrhiza total flavones (GTFs) have good anti-hepatic injury, but whether they have a good protective effect on anti-hepatic injury activity induced by Streptococcus agalactiae in tilapia (Oreochromis niloticus) is unknown. The aims of this study were to investigate the protective effects of Glycyrrhiza total flavones on liver injury induced by S. agalactiae (SA) and its underlying mechanism in fish. A total of 150 tilapia were randomly divided into five groups, each with three replicates containing 10 fish: normal control group, S. agalactiae infection group, and three Glycyrrhiza total flavone treatment groups (addition of 0.1, 0.5, or 1.0 g of GTF to 1 kg of feed). The normal control group was only fed with basic diet, after 60 d of feeding, and intraperitoneal injection of the same volume of normal saline (0.05 mL/10 g body weight); the S. agalactiae infection group was fed with basic diet, and the S. agalactiae solution was intraperitoneally injected after 60 d of feeding (0.05 mL/10 g body weight); the three GTF treatment groups were fed with a diet containing 0.1, 0.5, or 1.0 g/kg of GTF, and the S. agalactiae solution was intraperitoneally injected after 60 d of feeding (0.05 mL/10 g body weight). After 48 h injection, blood and liver tissues were collected to measure biochemical parameters and mRNA levels to evaluate the liver protection of GTFs. Compared with the control group, the serum levels of glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), alkaline phosphatase (AKP) and glucose (GLU) in the streptococcal infection group increased significantly, while the levels of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH) decreased significantly; observations of pathological sections showed obvious damage to the liver tissue structure in response to streptococcal infection. S. agalactiae can also cause fatty liver injury, affecting the function of fatty acid β-oxidation and biosynthesis in the liver of tilapia, and also causing damage to function of the immune system. The addition of GTFs to the diet could improve oxidative stress injury caused by S. agalactiae in tilapia liver tissue to different degrees, promote the β-oxidation of fatty acids in the liver, accelerate the lipid metabolism in the liver, and repair the damaged liver tissue. GTFs have a good protective effect on liver injury caused by streptococcus.

Inhibition of polyploidization in Pten-deficient livers reduces steatosis

The tumour suppressor PTEN is a negative regulator of the PI3K/AKT signalling pathway. Liver-specific deletion of Pten in mice results in the hyper-activation PI3K/AKT signalling accompanied by enhanced genome duplication (polyploidization), marked lipid accumulation (steatosis) and formation of hepatocellular carcinomas. However, it is unknown whether polyploidization in this model has an impact on the development of steatosis and the progression towards liver cancer. Here, we used a liver-specific conditional knockout approach to delete Pten in combination with deletion of E2f7/8, known key inducers of polyploidization. As expected, Pten deletion caused severe steatosis and liver tumours accompanied by enhanced polyploidization. Additional deletion of E2f7/8 inhibited polyploidization, alleviated Pten-induced steatosis without affecting lipid species composition and accelerated liver tumour progression. Global transcriptomic analysis showed that inhibition of polyploidization in Pten-deficient livers resulted in reduced expression of genes involved in energy metabolism, including PPAR-gamma signalling. However, we find no evidence that deregulated genes in Pten-deficient livers are direct transcriptional targets of E2F7/8, supporting that reduction in steatosis and progression towards liver cancer are likely consequences of inhibiting polyploidization. Lastly, flow cytometry and image analysis on isolated primary wildtype mouse hepatocytes provided further support that polyploid cells can accumulate more lipid droplets than diploid hepatocytes. Collectively, we show that polyploidization promotes steatosis and function as an important barrier against liver tumour progression in Pten-deficient livers.

Ban-xia-xie-xin-tang ameliorates hepatic steatosis by regulating Cidea and Cidec expression in HFD-fed mice

BACKGROUND

Ban-xia-xie-xin-tang (BXXXT) has been applied in treating metabolic diseases, such as nonalcohol fatty liver disease, diabetes mellitus, and obesity. However, the underlying molecular mechanism of BXXXT in treating diabetes mellitus is unknown.

PURPOSE

To clarify the underlying molecular mechanism of BXXXT in alleviating hepatic steatosis in high-fat diet (HFD)-fed mice.

METHODS

After 12 weeks of HFD treatment, mice were administered BXXXT for 4 weeks. The main chemical components of BXXXT were identified by UPLC-TQ-MS/MS. Indicators associated with insulin resistance and lipid metabolism were detected. The effect of improving glucose and lipid metabolism between BXXXT and the different components was compared. Differentially expressed genes (DEGs) were identified by hepatic transcriptomics. Key DEGs and proteins were further detected by real-time quantitative polymerase chain reaction, western blotting, immunohistochemistry, and immunofluorescence staining. LDs and mitochondria were detected by transmission electron microscopy.

RESULTS

First of all, our data demonstrated that the capacity to improve glucose and lipid metabolism for BXXXT was significantly superior to different components of BXXXT. BXXXT was found to improve HFD-induced insulin resistance. Moreover, BXXXT decreased weight, serum/hepatic triglycerides, total cholesterol, and FFAs to alleviate HFD-induced hepatic steatosis. According to the results of the hepatic transcription, Cidea and Cidec were identified as critical DEGs for promoting LD fusion and reducing FFAs β-oxidation in mitochondria and peroxisome resulting in hepatic steatosis, which was reversed by BXXXT.

CONCLUSION

BXXXT ameliorates HFD-induced hepatic steatosis and insulin resistance by increasing Cidea and Cidec-mediated mitochondrial and peroxisomal fatty acid oxidation, which may provide a potential strategy for therapy of NAFLD and T2DM.

Germline Mutations in CIDEB and Protection against Liver Disease

BACKGROUND

Exome sequencing in hundreds of thousands of persons may enable the identification of rare protein-coding genetic variants associated with protection from human diseases like liver cirrhosis, providing a strategy for the discovery of new therapeutic targets.

METHODS

We performed a multistage exome sequencing and genetic association analysis to identify genes in which rare protein-coding variants were associated with liver phenotypes. We conducted in vitro experiments to further characterize associations.

RESULTS

The multistage analysis involved 542,904 persons with available data on liver aminotransferase levels, 24,944 patients with various types of liver disease, and 490,636 controls without liver disease. We found that rare coding variants in APOB, ABCB4, SLC30A10, and TM6SF2 were associated with increased aminotransferase levels and an increased risk of liver disease. We also found that variants in CIDEB, which encodes a structural protein found in hepatic lipid droplets, had a protective effect. The burden of rare predicted loss-of-function variants plus missense variants in CIDEB (combined carrier frequency, 0.7%) was associated with decreased alanine aminotransferase levels (beta per allele, -1.24 U per liter; 95% confidence interval [CI], -1.66 to -0.83; P = 4.8×10^-9) and with 33% lower odds of liver disease of any cause (odds ratio per allele, 0.67; 95% CI, 0.57 to 0.79; P = 9.9×10^-7). Rare coding variants in CIDEB were associated with a decreased risk of liver disease across different underlying causes and different degrees of severity, including cirrhosis of any cause (odds ratio per allele, 0.50; 95% CI, 0.36 to 0.70). Among 3599 patients who had undergone bariatric surgery, rare coding variants in CIDEB were associated with a decreased nonalcoholic fatty liver disease activity score (beta per allele in score units, -0.98; 95% CI, -1.54 to -0.41 [scores range from 0 to 8, with higher scores indicating more severe disease]). In human hepatoma cell lines challenged with oleate, CIDEB small interfering RNA knockdown prevented the buildup of large lipid droplets.

CONCLUSIONS

Rare germline mutations in CIDEB conferred substantial protection from liver disease. (Funded by Regeneron Pharmaceuticals.).

Lipid droplet dynamics in healthy and pyometra-affected canine endometrium

BACKGROUND

Accumulation of lipid droplets (LDs) was recently observed in pyometra-affected uteri. As data about their nature and function are missing we intended to compare the localization, quality and quantity of LDs in canine healthy and pyometra-affected tissues and in an in vitro model.

METHODS AND RESULTS

We characterized LDs in healthy and pyometra uterine tissue samples as well as in canine endometrial epithelial cells (CEECs) in vitro by means of histochemistry, immunohistochemistry, transmission electron microscopy, western blot, and RT-qPCR. Oil Red O (ORO) staining and quantification as well as p-phenylenediamine staining showed a higher number of LDs in epithelial cells of pyometra samples. Immunohistochemistry revealed that the amount of LDs coated by perilipin2 (PLIN2) protein was also higher in pyometra samples. Transmission electron microscopy showed an increase of LD size in surface and glandular epithelial cells of pyometra samples. In cell culture experiments with CEECs, supplementation with oleic acid alone or in combination with cholesterol lead to an increased LD accumulation. The expression of PLIN2 at protein and mRNA level was also higher upon oleic acid supplementation. Most LDs were double positive for ORO and PLIN2. However, ORO positive LDs lacking PLIN2 coating or LDs positive for PLIN2 but containing a lipid class not detectable by ORO staining were identified.

CONCLUSIONS

We found differences in the healthy and pyometra-affected endometrium with respect to LDs size. Moreover, several kinds of LDs seem to be present in the canine endometrium. In vitro studies with CEECs could show their responsiveness to external lipids. Since epithelial cells reacted only to oleic acid stimulation, we assume that the cyclic lipid accumulation in the canine endometrium is based mainly on triglycerides and might serve as energy provision for the developing early embryo. Further studies are necessary to verify the complex role of lipids in the healthy and pyometra-affected canine endometrium.

Association of CIDEB gene promoter methylation with overweight or obesity in adults

Objective: To explore the association of the methylation level of cell death-inducing DFF45-like effector B (CIDEB) gene promoter with overweight or obesity in the abdominal subcutaneous adipose tissue (SAT) and omental adipose tissue (OAT) of adults.

Methods: A total of 61 patients undergoing abdominal surgery in the hospital were selected with an average age of 51.87 years. According to the diagnostic criteria of Chinese adult obesity, the subjects were divided into normal-weight group (n = 28) and overweight/obesity group (n = 33). CIDEB promoter methylation level in abdominal SAT and OAT was detected by the MethylTarget technology, then its relationship with overweight or obesity was analyzed.

Results: (1) There were no statistical differences between the normal-weight group and overweight/obesity group in Methylation levels of 16 CpG sites in the CIDEB gene promoter sequence. (2) The methylation level of OAT was higher than that of SAT, and there were significant differences in 16 CpG sites. (3) There were 3 statistically significant haplotypes between the normal-weight group and overweight/obesity group (2 in SAT and 1 in OAT).

Conclusions: The methylation level of CIDEB gene promoter in abdominal SAT and OAT may be related to overweight or obesity in adults, and the specific regulatory mechanism needs to be further studied.

A new perspective on NAFLD: Focusing on lipid droplets

Lipid droplets (LDs) are complex and metabolically active organelles. They are composed of a neutral lipid core surrounded by a monolayer of phospholipids and proteins. LD accumulation in hepatocytes is the distinctive characteristic of non-alcoholic fatty liver disease (NAFLD), which is a chronic, heterogeneous liver condition that can progress to liver fibrosis and hepatocellular carcinoma. Though recent research has improved our understanding of the mechanisms linking LD accumulation to NAFLD progression, numerous aspects of LD biology are either poorly understood or unknown. In this review, we provide a description of several key mechanisms that contribute to LD accumulation in hepatocytes, favouring NAFLD progression. First, we highlight the importance of LD architecture and describe how the dysregulation of LD biogenesis leads to endoplasmic reticulum stress and inflammation. This is followed by an analysis of the causal nexus that exists between LD proteome composition and LD degradation. Finally, we describe how the increase in size of LDs causes activation of hepatic stellate cells, leading to liver fibrosis and hepatocellular carcinoma. We conclude that acquiring a more sophisticated understanding of LD biology will provide crucial insights into the heterogeneity of NAFLD and assist in the development of therapeutic approaches for this liver disease.

Disruption of the circadian clock component BMAL1 elicits an endocrine adaption impacting on insulin sensitivity and liver disease

SignificanceWhile increasing evidence associates the disruption of circadian rhythms with pathologic conditions, including obesity, type 2 diabetes, and nonalcoholic fatty liver diseases (NAFLD), the involved mechanisms are still poorly described. Here, we show that, in both humans and mice, the pathogenesis of NAFLD is associated with the disruption of the circadian clock combined with perturbations of the growth hormone and sex hormone pathways. However, while this condition protects mice from the development of fibrosis and insulin resistance, it correlates with increased fibrosis in humans. This suggests that the perturbation of the circadian clock and its associated disruption of the growth hormone and sex hormone pathways are critical for the pathogenesis of metabolic and liver diseases.

Lipid Droplet-a New Target in Ischemic Heart Disease

Lipid droplet (LD) is a kind of subcellular organelle, which originates from the endoplasmic reticulum (ER). LDs can move flexibly between other organelles and store energy in the cells. In recent years, LDs and lipid droplet-associated proteins have attracted added attention at home and abroad, especially in cardiovascular diseases. Cardiovascular diseases, especially ischemic heart disease (IHD), have always been the focus of attention because of their high morbidity and mortality. Atherosclerosis and myocardial remodeling are two important pathologic processes of IHD, and LDs and other organelles are involved in the development of the disease. The interaction between LDs and ER is involved in the formation of foam cells in atherosclerosis. And LDs, mitochondria, and lysosomes also affect the remodeling of cardiomyocytes by affecting ROS production and regulating PI3K/AKT pathways. In this article, we will review the role of LDs in IHD.

Lipid droplets associated perilipins protein insights into finding a therapeutic target approach to cure non-alcoholic fatty liver disease (NAFLD)

Background

Non-alcoholic fatty liver disease (NAFLD) is now the most common form of chronic liver disease in the world, and it’s linked to a slew of other risk factors including diabetes, obesity, dysbiosis and inflammatory bowel disease. More than 30 years ago, a patient was diagnosed with fatty liver with excessive fat accumulation in hepatocytes, a disorder known as hepatosteatosis. There will be no promising therapeutic medicines available from 1980 to 2021 which can reverse the fatty liver to normal liver state. In this review, we highlighted on lipid droplet associated protein which play a major role in accumulation of fat in liver cells and how these cellular pathway could be a promising therapeutic approach to treat the fatty liver disease.

Main body

Over the last few decades, Western countries follow a high-fat diet and change their lifestyle pattern due to certain metabolic disorders prevalence rate is very high all over the world. NAFLD is a major health issue and burden globally nowadays. Researchers are trying to find out the potential therapeutic target to combat the disease. The exact pathophysiology of the disease is still unclear. In the present decades. There is no Food and Drug Administration approved drugs are available to reverse the chronic condition of the disease. Based on literature survey, lipid droplets and their associated protein like perilipins play an eminent role in body fat regulation. In this review, we explain all types of perilipins such as perilipin1-5 (PLIN1-5) and their role in the pathogenesis of fatty liver which will be helpful to find the novel pharmacological target to treat the fatty liver.

Conclusion

In this review, majorly focussed on how fat is get deposited into hepatocytes follow the cellular signalling involved during lipid droplet biogenesis and leads to NAFLD. However, up to date still there mechanism of action is unclear. In this review, we hypothesized that lipid droplets associated proteins like perilipins could be better pharmacological target to reverse the chronic stage of fatty liver disease and how these lipid droplets associated proteins hide a clue to maintain the normal lipid homeostasis in the human body.

A gel-like condensation of Cidec generates lipid-permeable plates for lipid droplet fusion

Membrane contact between intracellular organelles is important in mediating organelle communication. However, the assembly of molecular machinery at membrane contact site and its internal organization correlating with its functional activity remain unclear. Here, we demonstrate that a gel-like condensation of Cidec, a crucial protein for obesity development by facilitating lipid droplet (LD) fusion, occurs at the LD-LD contact site (LDCS) through phase separation. The homomeric interaction between the multivalent N terminus of Cidec is sufficient to promote its phase separation both in vivo and in vitro. Interestingly, Cidec condensation at LDCSs generates highly plastic and lipid-permeable fusion plates that are geometrically constrained by donor LDs. In addition, Cidec condensates are distributed unevenly in the fusion plate generating stochastic sub-compartments that may represent unique lipid passageways during LD fusion. We have thus uncovered the organization and functional significance of geometry-constrained Cidec phase separation in mediating LD fusion and lipid homeostasis.

The behavior and functions of embryonic microglia

Microglia are the resident immune cells of the central nervous system. Microglial progenitors are generated in the yolk sac during the early embryonic stage. Once microglia enter the brain primordium, these cells colonize the structure through migration and proliferation during brain development. Microglia account for a minor population among the total cells that constitute the developing cortex, but they can associate with many surrounding neural lineage cells by extending their filopodia and through their broad migration capacity. Of note, microglia change their distribution in a stage-dependent manner in the developing brain: microglia are homogenously distributed in the pallium in the early and late embryonic stages, whereas these cells are transiently absent from the cortical plate (CP) from embryonic day (E) 15 to E16 and colonize the ventricular zone (VZ), subventricular zone (SVZ), and intermediate zone (IZ). Previous studies have reported that microglia positioned in the VZ/SVZ/IZ play multiple roles in neural lineage cells, such as regulating neurogenesis, cell survival and neuronal circuit formation. In addition to microglial functions in the zones in which microglia are replenished, these cells indirectly contribute to the proper maturation of post-migratory neurons by exiting the CP during the mid-embryonic stage. Overall, microglial time-dependent distributional changes are necessary to provide particular functions that are required in specific regions. This review summarizes recent advances in the understanding of microglial colonization and multifaceted functions in the developing brain, especially focusing on the embryonic stage, and discuss the molecular mechanisms underlying microglial behaviors.

Lipid Droplet-Organelle Contact Sites as Hubs for Fatty Acid Metabolism, Trafficking, and Metabolic Channeling

Cells prepare for fluctuations in nutrient availability by storing energy in the form of neutral lipids in organelles called Lipid Droplets (LDs). Upon starvation, fatty acids (FAs) released from LDs are trafficked to different cellular compartments to be utilized for membrane biogenesis or as a source of energy. Despite the biochemical pathways being known in detail, the spatio-temporal regulation of FA synthesis, storage, release, and breakdown is not completely understood. Recent studies suggest that FA trafficking and metabolism are facilitated by inter-organelle contact sites that form between LDs and other cellular compartments such as the Endoplasmic Reticulum (ER), mitochondria, peroxisomes, and lysosomes. LD-LD contact sites are also sites where FAs are transferred in a directional manner to support LD growth and expansion. As the storage site of neutral lipids, LDs play a central role in FA homeostasis. In this mini review, we highlight the role of LD contact sites with other organelles in FA trafficking, channeling, and metabolism and discuss the implications for these pathways on cellular lipid and energy homeostasis.

The Propensity of the Human Liver to Form Large Lipid Droplets Is Associated with PNPLA3 Polymorphism, Reduced INSIG1 and NPC1L1 Expression and Increased Fibrogenetic Capacity

In nonalcoholic steatohepatitis animal models, an increased lipid droplet size in hepatocytes is associated with fibrogenesis. Hepatocytes with large droplet (Ld-MaS) or small droplet (Sd-MaS) macrovesicular steatosis may coexist in the human liver, but the factors associated with the predominance of one type over the other, including hepatic fibrogenic capacity, are unknown. In pre-ischemic liver biopsies from 225 consecutive liver transplant donors, we retrospectively counted hepatocytes with Ld-MaS and Sd-MaS and defined the predominant type of steatosis as involving ≥50% of steatotic hepatocytes. We analyzed a donor Patatin-like phospholipase domain-containing protein 3 (PNPLA3) rs738409 polymorphism, hepatic expression of proteins involved in lipid metabolism by RT-PCR, hepatic stellate cell (HSC) activation by α-SMA immunohistochemistry and, one year after transplantation, histological progression of fibrosis due to Hepatitis C Virus (HCV) recurrence. Seventy-four livers had no steatosis, and there were 98 and 53 with predominant Ld-MaS and Sd-MaS, respectively. In linear regression models, adjusted for many donor variables, the percentage of steatotic hepatocytes affected by Ld-MaS was inversely associated with hepatic expression of Insulin Induced Gene 1 (INSIG-1) and Niemann-Pick C1-Like 1 gene (NPC1L1) and directly with donor PNPLA3 variant M, HSC activation and progression of post-transplant fibrosis. In humans, Ld-MaS formation by hepatocytes is associated with abnormal PNPLA3-mediated lipolysis, downregulation of both the intracellular cholesterol sensor and cholesterol reabsorption from bile and increased hepatic fibrogenesis.

Lipid Droplet Contact Sites in Health and Disease

After having been disregarded for a long time as inert fat drops, lipid droplets (LDs) are now recognized as ubiquitous cellular organelles with key functions in lipid biology and beyond. The identification of abundant LD contact sites, places at which LDs are physically attached to other organelles, has uncovered an unexpected level of communication between LDs and the rest of the cell. In recent years, many disease factors mutated in hereditary disorders have been recognized as LD contact site proteins. Furthermore, LD contact sites are dramatically rearranged in response to infections with intracellular pathogens, as well as under pathological metabolic conditions such as hepatic steatosis. Collectively, it is emerging that LD-organelle contacts are important players in development and progression of disease.

Characterization of the Role of Rab18 in Mediating LD-ER Contact and LD Growth

Lipid droplets (LDs) are dynamic cellular organelles found in most eukaryotic cells. Lipid incorporation from endoplasmic reticulum (ER) to LD is important in controlling LD growth and intracellular lipid homeostasis. However, the molecular link that mediates ER and LD cross talk remains elusive. Here, we describe the methodology used to characterize the function of Rab18 in regulating LD homeostasis and LD-ER contact. First, we focus on the quantitative assay used to measure intracellular LDs morphological changes. This is followed by a detailed description of the use of the APEX-label technology in combination with electron microscope (EM) to visualize ER-LD contact sites. These assays are valuable for the investigation of LD-associated proteins such as Rab18 in establishing membrane contact sites between LDs and other subcellular organelles.

Hepatic lipid droplets: A balancing act between energy storage and metabolic dysfunction in NAFLD

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is defined by the abundance of lipid droplets (LDs) in hepatocytes. While historically considered simply depots for energy storage, LDs are increasingly recognized to impact a wide range of biological processes that influence cellular metabolism, signaling, and function. While progress has been made toward understanding the factors leading to LD accumulation (i.e. steatosis) and its progression to advanced stages of NAFLD and/or systemic metabolic dysfunction, much remains to be resolved.

SCOPE OF REVIEW

This review covers many facets of LD biology. We provide a brief overview of the major pathways of lipid accretion and degradation that contribute to steatosis and how they are altered in NAFLD. The major focus is on the relationship between LDs and cell function and the detailed mechanisms that couple or uncouple steatosis from the severity and progression of NAFLD and systemic comorbidities. The importance of specific lipids and proteins within or on LDs as key components that determine whether LD accumulation is linked to cellular and metabolic dysfunction is presented. We discuss emerging areas of LD biology and future research directions that are needed to advance our understanding of the role of LDs in NAFLD etiology.

MAJOR CONCLUSIONS

Impairments in LD breakdown appear to contribute to disease progression, but inefficient incorporation of fatty acids (FAs) into LD-containing triacylglycerol (TAG) and the consequential changes in FA partitioning also affect NAFLD etiology. Increased LD abundance in hepatocytes does not necessarily equate to cellular dysfunction. While LD accumulation is the prerequisite step for most NAFLD cases, the protein and lipid composition of LDs are critical factors in determining the progression from simple steatosis. Further defining the detailed molecular mechanisms linking LDs to metabolic dysfunction is important for designing effective therapeutic approaches targeting NAFLD and its comorbidities.

Acyl-Coenzyme A Thioesterase 9 Traffics Mitochondrial Short-Chain Fatty Acids Toward De Novo Lipogenesis and Glucose Production in the Liver

BACKGROUND AND AIMS

Obesity-induced pathogenesis of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) is associated with increased de novo lipogenesis (DNL) and hepatic glucose production (HGP) that is due to excess fatty acids. Acyl-coenzyme A (CoA) thioesterase (Acot) family members control the cellular utilization of fatty acids by hydrolyzing (deactivating) acyl-CoA into nonesterified fatty acids and CoASH.

APPROACH AND RESULTS

Using Caenorhabditis elegans, we identified Acot9 as the strongest regulator of lipid accumulation within the Acot family. Indicative of a maladaptive function, hepatic Acot9 expression was higher in patients with obesity who had NAFLD and NASH compared with healthy controls with obesity. In the setting of excessive nutrition, global ablation of Acot9 protected mice against increases in weight gain, HGP, steatosis, and steatohepatitis. Supportive of a hepatic function, the liver-specific deletion of Acot9 inhibited HGP and steatosis in mice without affecting diet-induced weight gain. By contrast, the rescue of Acot9 expression only in the livers of Acot9 knockout mice was sufficient to promote HGP and steatosis. Mechanistically, hepatic Acot9 localized to the inner mitochondrial membrane, where it deactivated short-chain but not long-chain fatty acyl-CoA. This unique localization and activity of Acot9 directed acetyl-CoA away from protein lysine acetylation and toward the citric acid (TCA) cycle. Acot9-mediated exacerbation of triglyceride and glucose biosynthesis was attributable at least in part to increased TCA cycle activity, which provided substrates for HGP and DNL. β-oxidation and ketone body production, which depend on long-chain fatty acyl-CoA, were not regulated by Acot9.

CONCLUSIONS

Taken together, our findings indicate that Acot9 channels hepatic acyl-CoAs toward increased HGP and DNL under the pathophysiology of obesity. Therefore, Acot9 represents a target for the management of NAFLD.

Loss of CD36 protects against diet-induced obesity but results in impaired muscle stem cell function, delayed muscle regeneration and hepatic steatosis

AIM

The prevalence of obesity is a major risk factor for cardiovascular and metabolic diseases including impaired skeletal muscle regeneration. Since skeletal muscle regenerative capacity is regulated by satellite cells, we aimed to investigate whether a high-fat diet impairs satellite cell function and whether this is linked to fatty acid uptake via CD36. We also aimed to determine whether loss of CD36 impacts on muscle redox homeostasis and skeletal muscle regenerative capacity.

METHODS

We studied the impact of a high-fat diet and CD36 deficiency on murine skeletal muscle morphology, redox homeostasis, satellite cell function, bioenergetics and lipid accumulation in the liver. We also determined the effect of CD36 deficiency on skeletal muscle regeneration.

RESULTS

High-fat diet increased body weight, intramuscular lipid accumulation and oxidative stress in wild-type mice that were significantly mitigated in CD36-deficient mice. High-fat diet and CD36 deficiency independently attenuated satellite cell function on single fibres and myogenic capacity on primary satellite cells. CD36 deficiency resulted in delayed skeletal muscle regeneration following acute injury with cardiotoxin. CD36-deficient and wild-type primary satellite cells had distinct bioenergetic profiles in response to palmitate. High-fat diet induced hepatic steatosis in both genotypes that was more pronounced in the CD36-deficient mice.

CONCLUSION

This study demonstrates that CD36 deficiency protects against diet-induced obesity, intramuscular lipid deposition and oxidative stress but results in impaired muscle satellite cell function, delayed muscle regeneration and hepatic steatosis. CD36 is a key mediator of fatty acid uptake in skeletal muscle, linking obesity with satellite cell function and muscle regeneration.

Mouse Fat-Specific Protein 27 (FSP27) expressed in plant cells localizes to lipid droplets and promotes lipid droplet accumulation and fusion

Fat-Specific Protein 27 (FSP27) belongs to a small group of vertebrate proteins containing a Cell-death Inducing DNA fragmentation factor-α-like Effector (CIDE)-C domain and is involved in lipid droplet (LD) accumulation and energy homeostasis. FSP27 is predominantly expressed in white and brown adipose tissues, as well as liver, and plays a key role in mediating LD-LD fusion. No orthologs have been identified in invertebrates or plants. In this study, we tested the function of mouse FSP27 in stably-transformed Arabidopsis thaliana leaves and seeds, as well as through transient expression in Nicotiana tabacum suspension-cultured cells and N. benthamiana leaves. Confocal microscopic analysis of plant cells revealed that, similar to ectopic expression in mammalian cells, FSP27 produced in plants 1) correctly localized to LDs, 2) accumulated at LD-LD contact sites, and 3) induced an increase in the number and size of LDs and also promoted LD clustering and fusion. Furthermore, FSP27 increased oil content in transgenic A. thaliana seeds. Given that plant oils have uses in human and animal nutrition as well as industrial uses such as biofuels and bioplastics, our results suggest that ectopic expression of FSP27 in plants represents a potential strategy for increasing oil content and energy density in bioenergy or oilseed crops.

Lipid droplet-associated kinase STK25 regulates peroxisomal activity and metabolic stress response in steatotic liver

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are emerging as leading causes of liver disease worldwide and have been recognized as one of the major unmet medical needs of the 21st century. Our recent translational studies in mouse models, human cell lines, and well-characterized patient cohorts have identified serine/threonine kinase (STK)25 as a protein that coats intrahepatocellular lipid droplets (LDs) and critically regulates liver lipid homeostasis and progression of NAFLD/NASH. Here, we studied the mechanism-of-action of STK25 in steatotic liver by relative quantification of the hepatic LD-associated phosphoproteome from high-fat diet-fed Stk25 knockout mice compared with their wild-type littermates. We observed a total of 131 proteins and 60 phosphoproteins that were differentially represented in STK25-deficient livers. Most notably, a number of proteins involved in peroxisomal function, ubiquitination-mediated proteolysis, and antioxidant defense were coordinately regulated in Stk25 ^-/- versus wild-type livers. We confirmed attenuated peroxisomal biogenesis and protection against oxidative and ER stress in STK25-deficient human liver cells, demonstrating the hepatocyte-autonomous manner of STK25's action. In summary, our results suggest that regulation of peroxisomal function and metabolic stress response may be important molecular mechanisms by which STK25 controls the development and progression of NAFLD/NASH.

DFCP1 associates with lipid droplets

Double FYVE-containing protein 1 (DFCP1) is ubiquitously expressed, participates in intracellular membrane trafficking and labels omegasomes through specific interactions with phosphatidylinositol-3-phosphate (PI3P). Previous studies showed that subcellular DFCP1 proteins display multi-organelle localization, including in the endoplasmic reticulum (ER), Golgi apparatus and mitochondria. However, its localization and function on lipid droplets (LDs) remain unclear. Here, we demonstrate that DFCP1 localizes to the LD upon oleic acid incubation. The ER-targeted domain of DFCP1 is indispensable for its LD localization, which is further enhanced by double FYVE domains. Inhibition of PI3P binding at the FYVE domain through wortmannin treatment or double mutation at C654S and C770S have no effect on DFCP1's LD localization. These show that the mechanisms for DFCP1 targeting the omegasome and LDs are different. DFCP1 deficiency in MEF cells causes an increase in LD number and reduces LD size. Interestingly, DFCP1 interacts with GTP-bound Rab18, an LD-associated protein. Taken together, our work demonstrates the dynamic localization of DFCP1 is regulated by nutritional status in response to cellular metabolism.

Plasticity of histone modifications around Cidea and Cidec genes with secondary bile in the amelioration of developmentally-programmed hepatic steatosis

We recently reported that a treatment with tauroursodeoxycholic acid (TUDCA), a secondary bile acid, improved developmentally-deteriorated hepatic steatosis in an undernourishment (UN, 40% caloric restriction) in utero mouse model after a postnatal high-fat diet (HFD). We performed a microarray analysis and focused on two genes (Cidea and Cidec) because they are enhancers of lipid droplet (LD) sizes in hepatocytes and showed the greatest up-regulation in expression by UN that were completely recovered by TUDCA, concomitant with parallel changes in LD sizes. TUDCA remodeled developmentally-induced histone modifications (dimethylation of H3K4, H3K27, or H3K36), but not DNA methylation, around the Cidea and Cidec genes in UN pups only. Changes in these histone modifications may contribute to the markedly down-regulated expression of Cidea and Cidec genes in UN pups, which was observed in the alleviation of hepatic fat deposition, even under HFD. These results provide an insight into the future of precision medicine for developmentally-programmed hepatic steatosis by targeting histone modifications.

Transcriptional insights into key genes and pathways controlling muscle lipid metabolism in broiler chickens

Background

Intramuscular fat (IMF) is one of the most important factors positively associated with meat quality. Triglycerides (TGs), as the main component of IMF, play an essential role in muscle lipid metabolism. This transcriptome analysis of pectoralis muscle tissue aimed to identify functional genes and biological pathways likely contributing to the extreme differences in the TG content of broiler chickens.

Results

The study included Jingxing-Huang broilers that were significantly different in TG content (5.81 mg/g and 2.26 mg/g, p < 0.01) and deposition of cholesterol also showed the same trend. This RNA sequencing analysis was performed on pectoralis muscle samples from the higher TG content group (HTG) and the lower TG content group (LTG) chickens. A total of 1200 differentially expressed genes (DEGs) were identified between two groups, of which 59 DEGs were related to TG and steroid metabolism. The HTG chickens overexpressed numerous genes related to adipogenesis and lipogenesis in pectoralis muscle tissue, including the key genes ADIPOQ, CD36, FABP4, FABP5, LPL, SCD, PLIN1, CIDEC and PPARG, as well as genes related to steroid biosynthesis (DHCR24, LSS, MSMO1, NSDHL and CH25H). Additionally, key pathways related to lipid storage and metabolism (the steroid biosynthesis and peroxisome proliferator activated receptor (PPAR) signaling pathway) may be the key pathways regulating differential lipid deposition between HTG group and LTG group.

Conclusions

This study showed that increased TG deposition accompanying an increase in steroid synthesis in pectoralis muscle tissue. Our findings of changes in gene expression of steroid biosynthesis and PPAR signaling pathway in HTG and LTG chickens provide insight into genetic mechanisms involved in different lipid deposition patterns in pectoralis muscle tissue.

Plin3 protects against alcoholic liver injury by facilitating lipid export from the endoplasmic reticulum

Hepatic lipid accumulation is the most common pathological characteristic of alcoholic liver disease (ALD). In mammalian cells, excess neutral lipids are stored in lipid droplets (LDs). As a member of perilipin family proteins, Plin3 was recently found to regulate the LD biogenesis. However, the roles and mechanism of Plin3 in ALD progression remain unclear. Herein, we found that alcohol stimulated Plin3 expression in both mouse livers and cultured AML12 mouse hepatic cells, which was accompanied by excess LD accumulation in hepatocytes. The elevations of Plin3 in alcohol-treated hepatocytes paralleled with the levels of both PPARα and γ, and the protein degradation of Plin3 was also reduced after alcohol exposure. Moreover, Plin3 knockdown increased cellular sensitivity to alcohol-induced apoptosis, endoplasmic reticulum (ER) stress, and inflammatory cytokines release, including TNF-α, IL-1, and IL-6β. Notably, alcohol exacerbated triglycerides (TG) accumulation in the ER and caused ER dilation in Plin3-knockdown AML12 cells. Finally, we observed that Plin3 interacted with dynein subunit Dync1i1 and mediated the colocalization of LDs and microtubules, while high concentration of alcohol disrupted microtubules and caused dispersion of excess small LDs in cytoplasm. Summarily, Plin3 promotes lipid export from the ER and reduces ER lipotoxic stress, thereby, protecting against alcoholic liver injury. Moreover, Plin3 could be an adapter protein mediating LD transport by microtubules. This study explored the roles of Plin3 in alcohol-induced hepatic injury, suggesting Plin3 as a potential target for the prevention of ALD progression.

Transcriptome Analysis of Dual FXR and GPBAR1 Agonism in Rodent Model of NASH Reveals Modulation of Lipid Droplets Formation

Non-alcoholic steatohepatitis (NASH) is a progressive, chronic, liver disease whose prevalence is growing worldwide. Despite several agents being under development for treating NASH, there are no drugs currently approved. The Farnesoid-x-receptor (FXR) and the G-protein coupled bile acid receptor 1 (GPBAR1), two bile acid activated receptors, have been investigated for their potential in treating NASH. Here we report that BAR502, a steroidal dual ligand for FXR/GPBAR1, attenuates development of clinical and liver histopathology features of NASH in mice fed a high fat diet (HFD) and fructose (F). By RNAseq analysis of liver transcriptome we found that BAR502 restores FXR signaling in the liver of mice feed HFD-F, and negatively regulates a cluster of genes including Srebf1 (Srepb1c) and its target genes-fatty acid synthase (Fasn) and Cell death-inducing DFF45-like effector (CIDE) genes, Cidea and Cidec-involved in lipid droplets formation and triglycerides storage in hepatocytes. Additionally, BAR502 increased the intestinal expression of Fgf15 and Glp1 and energy expenditure by white adipose tissues. Finally, exposure to BAR502 reshaped the intestinal microbiota by increasing the amount of Bacteroidaceae. In conclusion, we have shown that dual FXR/GPBAR1 agonism might have utility in treatment of NASH.