Cideb regulates diet-induced obesity, liver steatosis, and insulin sensitivity by controlling lipogenesis and fatty acid oxidation

CIDEB promotes lipid deposition in goat intramuscular adipocytes

OBJECTIVE

Cell death-inducing DNA fragmentation factor alpha-like effector B (CIDEB), a family member of Cell death-inducing DFF45-like effectors (CIDEs), is well known as a crucial regulator for lipid metabolic signaling pathways in various metabolic tissues and secretory glands. However, its role in regulating intramuscular fat (IMF) deposition in goat remains unclear.

METHODS

The expression vector pcDNA3.1-CIDEB was constructed and transfected into goat intramuscular preadipocytes; the overexpression and interference efficiency and expression of genes related to lipid metabolism were measured by Real-time polymerase chain reaction; the effect of overexpression of CIDEB and interfering with CIDEB on lipid droplet formation was observed by Oil Red O staining and glycerol phosphate oxidase-Trinder enzymatic reaction. Then RNA-Seq was used to investigate the metabolic pathway of CIDEB affecting adipocyte deposition in goat intramuscular preadipocytes.

RESULTS

Overexpression of CIDEB significantly promoted the lipid droplets accumulation and the triglyceride deposition, and significantly upregulated the expression of genes related to lipid metabolism. After overexpression of CIDEB in goat intramuscular preadipocytes, 171 differentially expressed genes (DEGs) were found, including 122 up-regulated and 49 down-regulated DEGs, and the top three significantly changed pathways filtered by Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were Cocaine addiction, Amphetamine addiction and Malaria pathways. Conversely, the silencing of CIDEB significantly reduced lipid accumulation in goat intramuscular preadipocytes, meanwhile changing the expression of lipid metabolism genes. For CIDEB silencing, a total of 2140 DEGs were found, including 1252 up-regulated and 888 down-regulated DEGs, and the top three significantly changed pathways filtered by KEGG analysis were Ribosome, Thyroid hormone signaling pathway and Alzheimer disease.

CONCLUSION

The expression of CIDEB can significantly promote lipid deposition of intramuscular adipocytes in goats, and these results provide important data to support further clarifying the mechanism of CIDEB gene on the regulation of intramuscular adipogenesis, and the IMF formation in goats.

PPARα regulates ER-lipid droplet protein Calsyntenin-3β to promote ketogenesis in hepatocytes

Ketogenesis requires fatty acid flux from intracellular (lipid droplets) and extrahepatic (adipose tissue) lipid stores to hepatocyte mitochondria. However, whether interorganelle contact sites regulate this process is unknown. Recent studies have revealed a role for Calsyntenin-3β (CLSTN3β), an endoplasmic reticulum-lipid droplet contact site protein, in the control of lipid utilization in adipose tissue. Here, we show that Clstn3b expression is induced in the liver by the nuclear receptor PPARα in settings of high lipid utilization, including fasting and ketogenic diet feeding. Hepatocyte-specific loss of CLSTN3β in mice impairs ketogenesis independent of changes in PPARα activation. Conversely, hepatic overexpression of CLSTN3β promotes ketogenesis in mice. Mechanistically, CLSTN3β affects LD-mitochondria crosstalk, as evidenced by changes in fatty acid oxidation, lipid-dependent mitochondrial respiration, and the mitochondrial integrated stress response. These findings define a function for CLSTN3β-dependent membrane contacts in hepatic lipid utilization and ketogenesis.

Growth, fusion and degradation of lipid droplets: advances in lipid droplet regulatory protein

Context: An adequate supply of energy is essential for the proper functioning of all life activities in living organisms. As organelles that store neutral lipids, lipid droplets (LDs) are involved in the synthesis and metabolism of lipids in cells and are also an important source of energy supply.

Methods and mechanisms: A comprehensive summary of the literature was first carried out to screen for relevant proteins affecting the morphological size of LDs. The size of milk fat globules (MFGs) is directly influenced by the morphological size of LDs, which also controls the energy storage capacity of LDs. In this review, we detail the progress of research into the role of some protein in regulating the morphological size of LDs.

Conclusion: It has been discovered that the number of protein are involved in the control of LD growth and degradation, such as Rab18-mediated local synthesis of triacylglycerol (TAG), cell death-inducing DFF45-like effector family proteins (CIDEs)-mediated atypical fusion between LDs, Stomatin protein-mediated LD fusion and autophagy-related proteins (ATGs)-mediated autophagic degradation of LDs. However, more studies are needed in the future to enrich the network of mechanisms that regulate the morphological size of LDs.

Liver-specific inactivation of Cideb improves metabolic profiles and ameliorates steatohepatitis and fibrosis in animal models for MASH

Germline mutations of CIDEB, a lipid droplets (LDs)-associated protein, confer protection against various liver diseases in humans. It remains to be determined whether liver-specific inhibition of CIDEB will bring clinical benefits. We aim to establish pharmacological proof of concept by testing GalNAc-conjugated Cideb surrogate siRNAs in respective animal models of obesity and MASH and to develop siRNA drug candidates for clinical investigations. Surrogate siRNAs targeting mouse Cideb were designed and evaluated via a panel of assays. Concurrently, humanized CIDEB knock-in mice were generated as a research tool to facilitate human therapeutic siRNA discovery. In vivo administration of the surrogate siRNAs was conducted in the diet-induced obesity (DIO) model and CDAA-HFD model of MASH. In the DIO model, Cideb knockdown led to significant reductions of serum total cholesterol (TC) and triglyceride (TG) levels, a significant decrease in hepatic macro-steatosis and notable weight loss. In the CDAA-HFD model, Cideb siRNA treatment significantly reduced liver TC and TG levels. Furthermore, remarkable reductions of hepatic steatosis and the composite NAS score were observed with a concomitant amelioration of liver fibrosis. Transcriptome analyses revealed that integrin pathways may contribute to the major pharmacological activities upon Cideb inactivation beyond lipid metabolism. CIDEB exhibits significant potential as a therapeutic target for the treatment of MASH. Liver-targeting siRNA candidates are under development for therapeutic hypothesis testing in humans.

Unraveling Mechanisms of Genetic Risks in Metabolic Dysfunction-Associated Steatotic Liver Diseases: A Pathway to Precision Medicine

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a growing global health problem, affecting ∼1 billion people. This condition is well established to have a heritable component with strong familial clustering. With the extraordinary breakthroughs in genetic research techniques coupled with their application to large-scale biobanks, the field of genetics in MASLD has expanded rapidly. In this review, we summarize evidence regarding genetic predisposition to MASLD drawn from family and twin studies. Significantly, we delve into detailed genetic variations associated with diverse pathogenic mechanisms driving MASLD. We highlight the interplay between these genetic variants and their connections with metabolic factors, the gut microbiome, and metabolites, which collectively influence MASLD progression. These discoveries are paving the way for precise medicine, including noninvasive diagnostics and therapies. The promising landscape of novel genetically informed drug targets such as RNA interference is explored. Many of these therapies are currently under clinical validation, raising hopes for more effective MASLD treatment.

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.

In vivo selection of hepatocytes

The liver is a highly regenerative organ capable of significant proliferation and remodeling during homeostasis and injury responses. Experiments of nature in rare genetic diseases have illustrated that healthy hepatocytes may have a selective advantage, outcompete diseased cells, and result in extensive liver replacement. This observation has given rise to the concept of therapeutic liver repopulation by providing an engineered selective advantage to a subpopulation of beneficial hepatocytes. In vivo selection can greatly enhance the efficiency of both gene and cell transplantation therapies for hepatic diseases. In vivo hepatocyte selection has also enabled the expansion of human hepatocytes in animals, creating novel models of human liver disease and biology. Finally, recent work has shown that somatic mutations produce clonal expansion of injury-resistant hepatocytes in most chronic liver diseases. In this review, we will address the role of hepatocyte selection in disease pathophysiology and therapeutic strategies.

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.

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.

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.

The Extremely-Low-Frequency Electromagnetic Field Affects Apoptosis and Oxidative-Stress-Related Genes and Proteins in the Porcine Endometrium-An In Vitro Study

Nowadays, the extremely-low-frequency electromagnetic field (ELF-EMF) is recognized as environmental pollution. The data indicate that the ELF-EMF may affect factors related to epigenetic regulation and alter important biological processes in the uterus. The impact of the ELF-EMF on apoptosis and oxidative-stress-related genes has not been documented in porcine endometrium. This raises the question of whether the exposure to the ELF-EMF can induce apoptosis and/or oxidative stress in the endometrium of pigs during the peri-implantation period. Porcine endometrial slices (100 ± 5 mg) collected (n = 5) during the peri-implantation period were treated in vitro with ELF-EMF at a frequency of 50 Hz and flux density of 8 × 104 mG for 2 h. To determine the effect of ELF-EMF on apoptosis and oxidative stress in the endometrium, CASP3, CASP7, CIDEB, GADD45G, NOS1, NOS2, NOS3, and TP53I3 mRNA transcript were analyzed using real-time PCR, and protein abundance of CASP3, CASP7 using Western blot, and eNOS using ELISA were determined. Moreover, CASP3/7 and NOS activity was analyzed using flow cytometry and colorimetry, respectively. The decreased CASP7 and increased NOS3 mRNA transcript and protein abundance in ELF-EMF-treated endometrium were observed. Moreover, CIDEB, GADD45G, and TP53I3 mRNA transcript abundance was increased. Only p ≤ 0.05 was considered a statistically significant difference. The documented alterations indicate the potential of the ELF-EMF to affect apoptosis and generate oxidative stress in the endometrium. The insight into observed consequences documents for the first time the fact that the ELF-EMF may influence endometrial cell proliferation, angiogenesis, and/or tissue receptivity during peri-implantation.

The role of lipid droplet associated proteins in inherited human disorders

Proteins which associate with the surface of lipid droplets are intimately involved in the regulation of the droplets. Several human inherited disorders have now been linked to loss- and, in some cases, likely gain-of-function mutations in the genes encoding these proteins. These are summarised in this Graphical Review.

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.

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.

VLDL Biogenesis and Secretion: It Takes a Village

The production and secretion of VLDLs (very-low-density lipoproteins) by hepatocytes has a direct impact on liver fat content, as well as the concentrations of cholesterol and triglycerides in the circulation and thus affects both liver and cardiovascular health, respectively. Importantly, insulin resistance, excess caloric intake, and lack of physical activity are associated with overproduction of VLDL, hepatic steatosis, and increased plasma levels of atherogenic lipoproteins. Cholesterol and triglycerides in remnant particles generated by VLDL lipolysis are risk factors for atherosclerotic cardiovascular disease and have garnered increasing attention over the last few decades. Presently, however, increased risk of atherosclerosis is not the only concern when considering today's cardiometabolic patients, as they often also experience hepatic steatosis, a prevalent disorder that can progress to steatohepatitis and cirrhosis. This duality of metabolic risk highlights the importance of understanding the molecular regulation of the biogenesis of VLDL, the lipoprotein that transports triglycerides and cholesterol out of the liver. Fortunately, there has been a resurgence of interest in the intracellular assembly, trafficking, degradation, and secretion of VLDL by hepatocytes, which has led to many exciting new molecular insights that are the topic of this review. Increasing our understanding of the biology of this pathway will aid to the identification of novel therapeutic targets to improve both the cardiovascular and the hepatic health of cardiometabolic patients. This review focuses, for the first time, on this duality.

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.

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).

Mammalian lipid droplets: structural, pathological, immunological and anti-toxicological roles

Mammalian lipid droplets (LDs) are specialized cytosolic organelles consisting of a neutral lipid core surrounded by a membrane made up of a phospholipid monolayer and a specific population of proteins that varies according to the location and function of each LD. Over the past decade, there have been significant advances in the understanding of LD biogenesis and functions. LDs are now recognized as dynamic organelles that participate in many aspects of cellular homeostasis plus other vital functions. LD biogenesis is a complex, highly-regulated process with assembly occurring on the endoplasmic reticulum although aspects of the underpinning molecular mechanisms remain elusive. For example, it is unclear how many enzymes participate in the biosynthesis of the neutral lipid components of LDs and how this process is coordinated in response to different metabolic cues to promote or suppress LD formation and turnover. In addition to enzymes involved in the biosynthesis of neutral lipids, various scaffolding proteins play roles in coordinating LD formation. Despite their lack of ultrastructural diversity, LDs in different mammalian cell types are involved in a wide range of biological functions. These include roles in membrane homeostasis, regulation of hypoxia, neoplastic inflammatory responses, cellular oxidative status, lipid peroxidation, and protection against potentially toxic intracellular fatty acids and lipophilic xenobiotics. Herein, the roles of mammalian LDs and their associated proteins are reviewed with a particular focus on their roles in pathological, immunological and anti-toxicological processes.

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.

New insights into the role of dietary triglyceride absorption in obesity and metabolic diseases

The incidence of obesity and associated metabolic diseases is increasing globally, adversely affecting human health. Dietary fats, especially triglycerides, are an important source of energy for the body, and the intestine absorbs lipids through a series of orderly and complex steps. A long-term high-fat diet leads to intestinal dysfunction, inducing obesity and metabolic disorders. Therefore, regulating dietary triglycerides absorption is a promising therapeutic strategy. In this review, we will discuss diverse aspects of the dietary triglycerides hydrolysis, fatty acid uptake, triglycerides resynthesis, chylomicron assembly, trafficking, and secretion processes in intestinal epithelial cells, as well as potential targets in this process that may influence dietary fat-induced obesity and metabolic diseases. We also mention the possible shortcomings and deficiencies in modulating dietary lipid absorption targets to provide a better understanding of their administrability as drugs in obesity and related metabolic disorders.

CLSTN3β enforces adipocyte multilocularity to facilitate lipid utilization

Multilocular adipocytes are a hallmark of thermogenic adipose tissue1,2, but the factors that enforce this cellular phenotype are largely unknown. Here, we show that an adipocyte-selective product of the Clstn3 locus (CLSTN3β) present in only placental mammals facilitates the efficient use of stored triglyceride by limiting lipid droplet (LD) expansion. CLSTN3β is an integral endoplasmic reticulum (ER) membrane protein that localizes to ER-LD contact sites through a conserved hairpin-like domain. Mice lacking CLSTN3β have abnormal LD morphology and altered substrate use in brown adipose tissue, and are more susceptible to cold-induced hypothermia despite having no defect in adrenergic signalling. Conversely, forced expression of CLSTN3β is sufficient to enforce a multilocular LD phenotype in cultured cells and adipose tissue. CLSTN3β associates with cell death-inducing DFFA-like effector proteins and impairs their ability to transfer lipid between LDs, thereby restricting LD fusion and expansion. Functionally, increased LD surface area in CLSTN3β-expressing adipocytes promotes engagement of the lipolytic machinery and facilitates fatty acid oxidation. In human fat, CLSTN3B is a selective marker of multilocular adipocytes. These findings define a molecular mechanism that regulates LD form and function to facilitate lipid utilization in thermogenic adipocytes.

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.

Association of COVID-19 with hepatic metabolic dysfunction

The coronavirus disease 2019 (COVID-19) pandemic continues to be a global problem with over 438 million cases reported so far. Although it mostly affects the respiratory system, the involvement of extrapulmonary organs, including the liver, is not uncommon. Since the beginning of the pandemic, metabolic com-orbidities, such as obesity, diabetes, hypertension, and dyslipidemia, have been identified as poor prognostic indicators. Subsequent metabolic and lipidomic studies have identified several metabolic dysfunctions in patients with COVID-19. The metabolic alterations appear to be linked to the course of the disease and inflammatory reaction in the body. The liver is an important organ with high metabolic activity, and a significant proportion of COVID-19 patients have metabolic comorbidities; thus, this factor could play a key role in orchestrating systemic metabolic changes during infection. Evidence suggests that metabolic dysregulation in COVID-19 has both short- and long-term metabolic implications. Furthermore, COVID-19 has adverse associations with metabolic-associated fatty liver disease. Due to the ensuing effects on the renin-angiotensin-aldosterone system and ammonia metabolism, COVID-19 can have significant implications in patients with advanced chronic liver disease. A thorough understanding of COVID-19-associated metabolic dysfunction could lead to the identification of important plasma biomarkers and novel treatment targets. In this review, we discuss the current understanding of metabolic dysfunction in COVID-19, focusing on the liver and exploring the underlying mechanistic pathogenesis and clinical implications.

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.).

Suppression of cideb under endoplasmic reticulum stress exacerbated hepatic inflammation by inducing hepatic steatosis and oxidative stress

Previous studies have shown that endoplasmic reticulum (ER) stress contributes to inflammation in several manners. However, whether cell death inducing DFF45-like effector b (Cideb), a lipid droplet (LD) associated protein that plays an important role in hepatic lipid metabolism, participates in this process has not been reported. In the present study, we demonstrated that deficiency of cideb alone did not trigger violent inflammation in the liver. However, the expression of cideb was suppressed by Chop (C/EBP homologous protein) under ER stress, which inhibited the transport of lipoproteins in the liver and led to the exacerbation of hepatic steatosis and oxidative stress, and ultimately exacerbated inflammation. Our results might provide a novel mechanism explaining inflammation triggered by ER stress.

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.

Molecular basis of apoptotic DNA fragmentation by DFF40

Although the functions of CIDE domain-containing proteins, including DFF40, DFF45, CIDE-A, CIDE-B, and FSP27, in apoptotic DNA fragmentation and lipid homeostasis have been studied extensively in mammals, the functions of four CIDE domain-containing proteins identified in the fly, namely DREP1, 2, 3, and 4, have not been explored much. Recent structural study of DREP4, a fly orthologue of mammalian DFF40 (an endonuclease involved in apoptotic DNA fragmentation), showed that the CIDE domain of DREP4 (and DFF40) forms filament-like assembly, which is critical for the corresponding function. The current study aimed to investigate the mechanism of filament formation of DREP4 CIDE and to characterize the same. DREP4 CIDE was shown to specifically bind to histones H1 and H2, an event important for the nuclease activity of DREP4. Based on the current experimental results, we proposed the mechanism underlying the process of apoptotic DNA fragmentation.

The protective effects of Aster yomena (Kitam.) Honda on high-fat diet-induced obese C57BL/6J mice

BACKGROUND/OBJECTIVES

Aster yomena (Kitam.) Honda (AY) has remarkable bioactivities, such as antioxidant, anti-inflammation, and anti-cancer activities. On the other hand, the effects of AY against obesity-induced insulin resistance have not been reported. Therefore, this study examined the potential of AY against obesity-associated insulin resistance in high-fat diet (HFD)-fed mice.

MATERIALS/METHODS

An obesity model was established by feeding C57BL/6J mice a 60% HFD for 16 weeks. The C57BL6/When ethyl acetate fraction from AY (EFAY) at doses of 100 and 200 mg/kg/day was administered orally to mice fed a HFD for the last 4 weeks. Normal and control groups were administered water orally. The body weight and fasting blood glucose were measured every week. Dietary intake was measured every other day. After dissection, blood and tissues were collected from the mice.

RESULTS

The administration of EFAY reduced body and organ weights significantly compared to HFD-fed control mice. The EFAY-administered groups also improved the serum lipid profile by decreasing the triglyceride, total cholesterol, and low-density lipoprotein compared to the control group. In addition, EFAY ameliorated the insulin resistance-related metabolic dysfunctions, including the fasting blood glucose and serum insulin level, compared to the HFD-fed control mice. The EFAY inhibited lipid synthesis and insulin resistance by down-regulation of hepatic fatty acid synthase and up-regulation of the AMP-activated protein kinase pathway. EFAY also reduced lipid peroxidation in the liver, indicating that EFAY protected hepatic injury induced by obesity.

CONCLUSIONS

These results suggest that EFAY improved obesity-associated insulin resistance by regulating the lipid and glucose metabolism, suggesting that AY could be used as a functional food to prevent obesity and insulin resistance.

Convergent somatic mutations in metabolism genes in chronic liver disease

The progression of chronic liver disease to hepatocellular carcinoma is caused by the acquisition of somatic mutations that affect 20-30 cancer genes1-8. Burdens of somatic mutations are higher and clonal expansions larger in chronic liver disease9-13 than in normal liver13-16, which enables positive selection to shape the genomic landscape9-13. Here we analysed somatic mutations from 1,590 genomes across 34 liver samples, including healthy controls, alcohol-related liver disease and non-alcoholic fatty liver disease. Seven of the 29 patients with liver disease had mutations in FOXO1, the major transcription factor in insulin signalling. These mutations affected a single hotspot within the gene, impairing the insulin-mediated nuclear export of FOXO1. Notably, six of the seven patients with FOXO1S22W hotspot mutations showed convergent evolution, with variants acquired independently by up to nine distinct hepatocyte clones per patient. CIDEB, which regulates lipid droplet metabolism in hepatocytes17-19, and GPAM, which produces storage triacylglycerol from free fatty acids20,21, also had a significant excess of mutations. We again observed frequent convergent evolution: up to fourteen independent clones per patient with CIDEB mutations and up to seven clones per patient with GPAM mutations. Mutations in metabolism genes were distributed across multiple anatomical segments of the liver, increased clone size and were seen in both alcohol-related liver disease and non-alcoholic fatty liver disease, but rarely in hepatocellular carcinoma. Master regulators of metabolic pathways are a frequent target of convergent somatic mutation in alcohol-related and non-alcoholic fatty liver disease.

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.

Down-Regulation of CIDEA Promoted Tumor Growth and Contributed to Cisplatin Resistance by Regulating the JNK-p21/Bad Signaling Pathways in Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies with poor prognosis and lack of effective targeted therapies. In this study, we investigated the tumor suppressive role of the cell death inducing DFF like effector A (CIDEA) in ESCC. Firstly, public datasets and ESCC tissue microarray analysis showed that CIDEA was frequently down-regulated at both the mRNA and protein level. This was significantly associated with low differentiation and TNM stage in ESCC, and indicated poor prognosis for ESCC patients. Bisulfite genomic sequencing (BGS) and methylation-specific PCR (MSP) analysis revealed that the down-regulation of CIDEA was associated with hypermethylation of its promoter, which was also correlated with the poor prognosis in ESCC patients. In vitro and in vivo functional studies demonstrated that CIDEA decreased cell growth, foci formation, DNA replication, and tumorigenesis in nude mice. Further study revealed that, during starvation or cisplatin induced DNA damage, CIDEA facilitated the G1-phase arrest or caspase-dependent mitochondrial apoptosis through the JNK-p21/Bad pathway. Therefore, CIDEA is a novel tumor suppressor gene that plays an important role in the development and progression of ESCC, and may provide a potential therapeutic target for patients with ESCC.

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.

Synergistic regulation of hepatic Fsp27b expression by HNF4α and CREBH

The CIDE (cell death-inducing DFF45-like effector) family composed of CIDEA, CIDEB, CIDEC/FSP27 (fat-specific protein 27), has a critical role in growth of lipid droplets. Of these, CIDEB and CIDEC2/FSP27B are abundant in the liver, and the steatotic livers, respectively. Hepatocyte nuclear factor 4α (HNF4α) has an important role in lipid homeostasis because liver-specific HNF4α-null mice (Hnf4a^ΔHep mice) exhibit hepatosteatosis. We investigated whether HNF4α directly regulates expression of CIDE family genes. Expression of Cideb and Fsp27b was largely decreased in Hnf4a^ΔHep mice, while expression of Cidea was increased. Similar results were observed only in CIDEC2, the human orthologue of the Fsp27b, in human hepatoma cell lines in which HNF4α expression was knocked down. Conversely, overexpression of HNF4α strongly induced CIDEC2 expression in hepatoma cell lines. Furthermore, HNF4α transactivated Fsp27b by direct binding to an HNF4α response element in the Fsp27b promoter. In addition, Fsp27b is known to be transactivated by CREBH that is regulated by HNF4α, and expression of CREBH was induced by HNF4α in human hepatoma cells. Co-transfection of HNF4α and CREBH resulted in synergistic transactivation and induction of Fsp27b compared to that of HNF4α or CREBH alone. These results suggest that HNF4α, in conjunction with CREBH, plays an important role in regulation of Fsp27b expression.

Assembly of platforms for signal transduction in the new era: dimerization, helical filament assembly, and beyond

Supramolecular organizing center (SMOC)-mediated signal transduction is an emerging concept in the field of signal transduction that is ushering in a new era. The formation of location-specific, higher-order SMOCs is particularly important for cell death and innate immune signaling processes. Several protein interaction domains, including the death domain (DD) superfamily and the CIDE domain, are representative mediators of SMOC assembly in cell death and innate immune signaling pathways. DD superfamily- and CIDE domain-containing proteins form SMOCs that activate various caspases and provide signaling scaffold platforms. These assemblies can lead to signal transduction and amplification during signaling events. In this review, we summarize recent findings on the molecular basis of DD superfamily- and CIDE domain-mediated SMOC formation.

Improved understanding of large molecular signaling complexes that form during innate (nonspecific) immune responses could help develop treatments for multiple diseases including cancer. Correct cell signaling requires precise protein interactions and binding, which are mediated by specific sites on the surface of the protein molecules involved. Innate immune responses and cell death mechanisms rely on such protein interactions, and defects can cause signaling abnormalities and trigger disease. Hyun Ho Park and co-workers at Chung-Ang University in Seoul, South Korea, reviewed recent insights into the presence of supramolecular organizing centers (SMOCs), localized complexes of signaling proteins that form during immune responses. The researchers highlight existing understanding of SMOC assembly processes. A better understanding of SMOCs will help to explain enzyme activation, signal amplification and cell signaling control mechanisms.

The Role of Lipophagy in the Development and Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) or metabolic (dysfunction) associated liver disease (MAFLD), is, with a global prevalence of 25%, the most common liver disorder worldwide. NAFLD comprises a spectrum of liver disorders ranging from simple steatosis to steatohepatitis, fibrosis, cirrhosis and eventually end-stage liver disease. The cause of NAFLD is multifactorial with genetic susceptibility and an unhealthy lifestyle playing a crucial role in its development. Disrupted hepatic lipid homeostasis resulting in hepatic triglyceride accumulation is an hallmark of NAFLD. This disruption is commonly described based on four pathways concerning 1) increased fatty acid influx, 2) increased de novo lipogenesis, 3) reduced triglyceride secretion, and 4) reduced fatty acid oxidation. More recently, lipophagy has also emerged as pathway affecting NAFLD development and progression. Lipophagy is a form of autophagy (i.e. controlled autolysosomal degradation and recycling of cellular components), that controls the breakdown of lipid droplets in the liver. Here we address the role of hepatic lipid homeostasis in NAFLD and specifically review the current literature on lipophagy, describing its underlying mechanism, its role in pathophysiology and its potential as a therapeutic target.

The Differential Expression of Cide Family Members is Associated with Nafld Progression from Steatosis to Steatohepatitis

Improved understanding of the molecular mechanisms responsible for the progression from a “non-pathogenic” steatotic state to Non-Alcoholic Steatohepatitis is an important clinical requirement. The cell death-inducing DFF45 like effector (CIDE) family members (A, B and FSP27) regulate hepatic lipid homeostasis by controlling lipid droplet growth and/or VLDL production. However, CIDE proteins, particularly FSP27, have a dual role in that they also regulate cell death. We here report that the hepatic expression of CIDEA and FSP27 (α/β) was similarly upregulated in a dietary mouse model of obesity-mediated hepatic steatosis. In contrast, CIDEA expression decreased, but FSP27-β expression strongly increased in a dietary mouse model of steatohepatitis. The inverse expression pattern of CIDEA and FSP27β was amplified with the increasing severity of the liver inflammation and injury. In obese patients, the hepatic CIDEC2 (human homologue of mouse FSP27β) expression strongly correlated with the NAFLD activity score and liver injury. The hepatic expression of CIDEA tended to increase with obesity, but decreased with NAFLD severity. In hepatic cell lines, the downregulation of FSP27β resulted in the fractionation of lipid droplets, whereas its overexpression decreased the expression of the anti-apoptotic BCL2 marker. This, in turn, sensitized cells to apoptosis in response to TNF α and saturated fatty acid. Considered together, our animal, human and in vitro studies indicate that differential expression of FSP27β/CIDEC2 and CIDEA is related to NAFLD progression and liver injury.

CIDEA and CIDEC are regulated by CREB and are not induced during fasting in grass carp Ctenopharyngodon idella adipocytes

Cell death-inducing DNA fragmentation factor 45-like effector family proteins, including CIDEA, CIDEB and CIDEC, play an important role in energy metabolism. In the present study, CIDEA, CIDEB and CIDEC cDNAs were firstly isolated and characterized from grass carp Ctenopharyngodon idella, encoding peptides of 205, 208 and 238 amino acids, respectively. Analysis of the exon-intron structures clarified that grass carp CIDEA, CIDEB and CIDEC consisted of 5 coding exons, 5 coding exons and 6 coding exons, respectively, which is similar with human and mouse. Both CIDE family genes mRNAs were expressed in a wide range of tissues, but the abundance of each CIDE family gene mRNA showed the tissue-dependent expression patterns. Time-course analysis of CIDE family expressions indicated that their expression were enhanced significantly from day 0 to day 8 after differentiation. Forskolin caused an increase in CIDEA and CIDEC expression, and the effects were attenuated by treatment with CREB inhibitor, revealing that CIDEA and CIDEC are regulated by CREB. Further study found that CIDEA and CIDEC mRNA levels did not show significant changes during fasting. These results provide the groundwork to elucidate the gene structure and physiological function of CIDE family in fish.

Ces1d deficiency protects against high-sucrose diet-induced hepatic triacylglycerol accumulation

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease. Triacylglycerol accumulation in the liver is a hallmark of NAFLD. Metabolic studies have confirmed that increased hepatic de novo lipogenesis (DNL) in humans contributes to fat accumulation in the liver and to NAFLD progression. Mice deficient in carboxylesterase (Ces)1d expression are protected from high-fat diet-induced hepatic steatosis. To investigate whether loss of Ces1d can also mitigate steatosis induced by over-activated DNL, WT and Ces1d-deficient mice were fed a lipogenic high-sucrose diet (HSD). We found that Ces1d-deficient mice were protected from HSD-induced hepatic lipid accumulation. Mechanistically, Ces1d deficiency leads to activation of AMP-activated protein kinase and inhibitory phosphorylation of acetyl-CoA carboxylase. Together with our previous demonstration that Ces1d deficiency attenuated high-fat diet-induced steatosis, this study suggests that inhibition of CES1 (the human ortholog of Ces1d) might represent a novel pharmacological target for prevention and treatment of NAFLD.

CIDE Proteins in Human Health and Disease

Cell death-Inducing DNA Fragmentation Factor Alpha (DFFA)-like Effector (CIDE) proteins have emerged as lipid droplet-associated proteins that regulate fat metabolism. There are three members in the CIDE protein family—CIDEA, CIDEB, and CIDEC (also known as fat-specific protein 27 (FSP27)). CIDEA and FSP27 are primarily expressed in adipose tissue, while CIDEB is expressed in the liver. Originally, based upon their homology with DNA fragmentation factors, these proteins were identified as apoptotic proteins. However, recent studies have changed the perception of these proteins, redefining them as regulators of lipid droplet dynamics and fat metabolism, which contribute to a healthy metabolic phenotype in humans. Despite various studies in humans and gene-targeting studies in mice, the physiological roles of CIDE proteins remains elusive. This review will summarize the known physiological role and metabolic pathways regulated by the CIDE proteins in human health and disease.

Cideb controls sterol-regulated ER export of SREBP/SCAP by promoting cargo loading at ER exit sites

SREBPs are master regulators of lipid homeostasis and undergo sterol‐regulated export from ER to Golgi apparatus for processing and activation via COPII‐coated vesicles. While COPII recognizes SREBP through its escort protein SCAP, factor(s) specifically promoting SREBP/SCAP loading to the COPII machinery remains unknown. Here, we show that the ER/lipid droplet‐associated protein Cideb selectively promotes the loading of SREBP/SCAP into COPII vesicles. Sterol deprivation releases SCAP from Insig and enhances ER export of SREBP/SCAP by inducing SCAP‐Cideb interaction, thereby modulating sterol sensitivity. Moreover, Cideb binds to the guanine nucleotide exchange factor Sec12 to enrich SCAP/SREBP at ER exit sites, where assembling of COPII complex initiates. Loss of Cideb inhibits the cargo loading of SREBP/SCAP, reduces SREBP activation, and alleviates diet‐induced hepatic steatosis. Our data point to a linchpin role of Cideb in regulated ER export of SREBP and lipid homeostasis.

A high-fat diet increases body fat mass and up-regulates expression of genes related to adipogenesis and inflammation in a genetically lean pig

Because of their physiological similarity to humans, pigs provide an excellent model for the study of obesity. This study evaluated diet-induced adiposity in genetically lean pigs and found that body weight and energy intake did not differ between controls and pigs fed the high-fat (HF) diet for three months. However, fat mass percentage, adipocyte size, concentrations of total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C), insulin, and leptin in plasma were significantly higher in HF pigs than in controls. The HF diet increased the expression in backfat tissue of genes responsible for cholesterol synthesis such as Insig-1 and Insig-2. Lipid metabolism-related genes including sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase 1 (FASN1), diacylglycerol O-acyltransferase 2 (DGAT2), and fatty acid binding protein 4 (FABP4) were significantly up-regulated in backfat tissue, while the expression of proliferator-activated receptor-α (PPAR-α) and carnitine palmitoyl transferase 2 (CPT2), both involved in fatty acid oxidation, was reduced. In liver tissue, HF feeding significantly elevated the expression of SREBP-1c, FASN1, DGAT2, and hepatocyte nuclear factor-4α (HNF-4α) mRNAs. Microarray analysis further showed that the HF diet had a significant effect on the expression of 576 genes. Among these, 108 genes were related to 21 pathways, with 20 genes involved in adiposity deposition and 26 related to immune response. Our results suggest that an HF diet can induce genetically lean pigs into obesity with body fat mass expansion and adipose-related inflammation.

Crystal structure and mutation analysis revealed that DREP2 CIDE forms a filament-like structure with features differing from those of DREP4 CIDE

Cell death-inducing DFF45-like effect (CIDE) domain-containing proteins, DFF40, DFF45, CIDE-A, CIDE-B, and FSP27, play important roles in apoptotic DNA fragmentation and lipid homeostasis. The function of DFF40/45 in apoptotic DNA fragmentation is mediated by CIDE domain filament formation. Although our recent structural study of DREP4 CIDE revealed the first filament-like structure of the CIDE domain and its functional importance, the filament structure of DREP2 CIDE is unclear because this structure was not helical in the asymmetric unit. In this study, we present the crystal structure and mutagenesis analysis of the DREP2 CIDE mutant, which confirmed that DREP2 CIDE also forms a filament-like structure with features differing from those of DREP4 CIDE.

Polybasic RKKR motif in the linker region of lipid droplet (LD)-associated protein CIDEC inhibits LD fusion activity by interacting with acidic phospholipids

Lipid droplets (LDs) are intracellular organelles and a central site for lipid synthesis, storage, and mobilization. The size of LDs reflects the dynamic regulation of lipid metabolism in cells. Previously, we found that cell death-inducing DFFA-like effector C (CIDEC) mediates LD fusion and growth by lipid transfer through LD-LD contact sites in adipocytes and hepatocytes. The CIDE-N domains of CIDEC molecules form homodimers, whereas the CIDE-C domain plays an important role in LD targeting and enrichment. Here, using targeted protein deletions and GFP expression coupled with fluorescence microscopy, we identified a polybasic RKKR motif in the linker region that connects the CIDE-N and CIDE-C domains of CIDEC and functions as a regulatory motif for LD fusion. We found that deletion of the linker region or mutation of the RKKR motif increases the formation of supersized LDs compared with LD formation in cells with WT CIDEC. This enhanced LD fusion activity required the interaction between CIDE-N domains. Mechanistically, we found that the RKKR motif interacts with acidic phospholipids via electrostatic attraction. Loss of this motif disrupted the protein-lipid interaction, resulting in enhanced lipid droplet fusion activity and thus formation of larger LDs. In summary, we have uncovered a CIDEC domain that regulates LD fusion activity, a finding that provides insights into the inhibitory regulation of LD fusion through CIDEC-lipid interactions.

Coordination Among Lipid Droplets, Peroxisomes, and Mitochondria Regulates Energy Expenditure Through the CIDE-ATGL-PPARα Pathway in Adipocytes

Metabolic homeostasis is maintained by an interplay among tissues, organs, intracellular organelles, and molecules. Cidea and Cidec are lipid droplet (LD)-associated proteins that promote lipid storage in brown adipose tissue (BAT) and white adipose tissue (WAT). Using ob/ob/Cidea^-/- , ob/ob/Cidec^-/- , and ob/ob/Cidea^-/-/Cidec^-/- mouse models and CIDE-deficient cells, we studied metabolic regulation during severe obesity to identify ways to maintain metabolic homeostasis and promote antiobesity effects. The phenotype of ob/ob/Cidea^-/- mice was similar to that of ob/ob mice in terms of serum parameters, adipose tissues, lipid storage, and gene expression. Typical lipodystrophy accompanied by insulin resistance occurred in ob/ob/Cidec^-/- mice, with ectopic storage of lipids in the BAT and liver. Interestingly, double deficiency of Cidea and Cidec activated both WAT and BAT to consume more energy and to increase insulin sensitivity compared with their behavior in the other three mouse models. Increased lipolysis, which occurred on the LD surfaces and released fatty acids, led to activated β-oxidation and oxidative phosphorylation in peroxisomes and mitochondria in CIDE-deficient adipocytes. The coordination among LDs, peroxisomes, and mitochondria was regulated by adipocyte triglyceride lipase (ATGL)-peroxisome proliferator-activated receptor α (PPARα). Double deficiency of Cidea and Cidec activated energy consumption in both WAT and BAT, which provided new insights into therapeutic approaches for obesity and diabetes.