Absence of perilipin results in leanness and reverses obesity in Lepr(db/db) mice

Involvement of a battery of investigated genes in lipid droplet pathophysiology and associated comorbidities

Lipid droplets (LDs) are highly specialized energy storage organelles involved in the maintenance of lipid homoeostasis by regulating lipid flux within white adipose tissue (WAT). The physiological function of adipocytes and LDs can be compromised by mutations in several genes, leading to NEFA-induced lipotoxicity, which ultimately manifests as metabolic complications, predominantly in the form of dyslipidemia, ectopic fat accumulation, and insulin resistance. In this review, we delineate the effects of mutations and deficiencies in genes - CIDEC, PPARG, BSCL2, AGPAT2, PLIN1, LIPE, LMNA, CAV1, CEACAM1, and INSR - involved in lipid droplet metabolism and their associated pathophysiological impairments, highlighting their roles in the development of lipodystrophies and metabolic dysfunction.

Perilipin2 depletion causes lipid droplet enlargement in the ovarian corpus luteum in mice

Lipid droplets (LDs) are endoplasmic reticulum-derived organelles that store neutral lipids (mostly triglycerides and cholesterol esters) within a phospholipid monolayer and appear in most eukaryotic cells. Perilipins (PLINs, comprising PLIN1-5) are abundant LD-associated proteins with highly variable expression levels among tissues. Although PLINs are expressed in the mammalian ovaries, little is known about their subcellular localization and physiological functions. In this study, we investigated the localization of PLIN1-3 and their relationship with LD synthesis using mCherry-HPos reporter mice, thereby enabling the visualization of LD biogenesis in vivo. PLIN2 and PLIN3 were localized as puncta in granulosa cells with low levels of LD synthesis in developing follicles. This localization pattern was quite different from that of PLIN1, which was mainly localized in the theca and interstitial cells with high levels of LD synthesis. In the corpus luteum, where LD synthesis is highly induced, PLIN2 and PLIN3 are abundant in the particulate structures, whereas PLIN1 is poorly distributed. We also generated global Plin2-deficient mice using the CRSPR/Cas9 system and demonstrated that the lack of PLIN2 did not alter the distribution of PLIN1 and PLIN3 but unexpectedly induced LD enlargement in the corpus luteum. Collectively, our results suggest that the localization of PLIN1-3 is spatiotemporally regulated and that PLIN2 deficiency influences LD mobilization in the corpus luteum within the ovaries.

Persistent organic pollutants and metabolic diseases: From the perspective of lipid droplets

The characteristic of semi-volatility enables persistent organic pollutants (POPs) almost ubiquitous in the environment. There is increasing concern about the potential risks of exposure to POPs due to their lipophilicity and readily bioaccumulation. Lipid droplets (LDs) are highly dynamic lipid storage organelles, alterations of intracellular LDs play a vital role in the progression of many prevalent metabolic diseases, such as type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD). This article systematically reviewed the biological processes involved in LDs metabolism, the role of LDs proteins and LDs in metabolic diseases, and summarized updating researches on involvement of POPs in the progression of LDs-related metabolic diseases and potential mechanisms. POPs might change the physiological functions of LDs, also interfere the processes of adipogenesis and lipolysis by altering LDs synthesis, decomposition and function. However, further studies are still needed to explore the underlying mechanism of POPs-induced metabolic diseases, which can offer scientific evidences for metabolic disease prevention.

Drosophila models of the anti-inflammatory and anti-obesity mechanisms of kombucha tea produced by Camellia sinensis leaf fermentation

Kombucha tea is a traditional beverage originating from China and has recently gained popularity worldwide. Kombucha tea is produced by the fermentation of tea leaves and is characterized by its beneficial properties and varied chemical content produced during the fermentation process, which includes organic acids, amino acids, vitamins, minerals, and other biologically active compounds. Kombucha tea is often consumed as a health drink to combat obesity and inflammation; however, the bioactive effects of kombucha tea have not been thoroughly researched. In this study, we reveal the underlying mechanisms of the beneficial properties of kombucha tea and how they protect against obesity and inflammation by studying Drosophila models. We established an inflammatory Drosophila model by knocking down the lipid storage droplet-1 gene, a human perilipin-1 ortholog. In this model, dysfunction of lipid storage droplet-1 induces inflammation by enhancing the infiltration of hemocytes into adipose tissues, increasing reactive oxygen species production, elevating levels of proinflammatory cytokines, and promoting the differentiation of hemocytes into macrophages. These processes are regulated by the c-Jun N-terminal Kinase (JNK) pathway. Using this unique Drosophila model that mimics mammalian inflammation, we verified the beneficial effects of kombucha tea on reducing tissue inflammation. Our data confirms that kombucha tea effectively improves inflammatory conditions by suppressing the expression of cytokines and proinflammatory responses induced by lipid storage droplet-1 dysfunction. It was found that kombucha tea consumption alleviated the production of reactive oxygen species and activated the JNK signaling pathway, signifying its potential as an anti-inflammatory agent against systemic inflammatory responses connected to the JNK pathway. Kombucha tea reduced triglyceride accumulation by increasing the activity of Brummer (a lipase), thereby promoting lipolysis in third-instar larvae. Therefore, kombucha tea could be developed as a novel, functional beverage to protect against obesity and inflammation. Our study also highlights the potential use of this innovative model to evaluate the effects of bioactive compounds derived from natural products.

The Role of Adipocytes Recruited as Part of Tumor Microenvironment in Promoting Colorectal Cancer Metastases

Adipose tissue dysfunction, which is associated with an increased risk of colorectal cancer (CRC), is a significant factor in the pathophysiology of obesity. Obesity-related inflammation and extracellular matrix (ECM) remodeling promote colorectal cancer metastasis (CRCM) by shaping the tumor microenvironment (TME). When CRC occurs, the metabolic symbiosis of tumor cells recruits adjacent adipocytes into the TME to supply energy. Meanwhile, abundant immune cells, from adipose tissue and blood, are recruited into the TME, which is stimulated by pro-inflammatory factors and triggers a chronic local pro-inflammatory TME. Dysregulated ECM proteins and cell surface adhesion molecules enhance ECM remodeling and further increase contractibility between tumor and stromal cells, which promotes epithelial-mesenchymal transition (EMT). EMT increases tumor migration and invasion into surrounding tissues or vessels and accelerates CRCM. Colorectal symbiotic microbiota also plays an important role in the promotion of CRCM. In this review, we provide adipose tissue and its contributions to CRC, with a special emphasis on the role of adipocytes, macrophages, neutrophils, T cells, ECM, and symbiotic gut microbiota in the progression of CRC and their contributions to the CRC microenvironment. We highlight the interactions between adipocytes and tumor cells, and potential therapeutic approaches to target these interactions.

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.

Mitochondrial fractions located in the cytoplasmic and peridroplet areas of white adipocytes have distinct roles

The role of mitochondria in white adipocytes (WAs) has not been fully explored. A recent study revealed that brown adipocytes contain functionally distinct mitochondrial fractions, cytoplasmic mitochondria, and peridroplet mitochondria. However, it is not known whether such a functional division of mitochondria exists in WA. Herein, we observed that mitochondria could be imaged and mitochondrial DNA and protein detected in pellets obtained from the cytoplasmic layer and oil layer of WAs after centrifugation. The mitochondria in each fraction were designated as cytoplasmic mitochondria (CMw) and peridroplet mitochondria (PDMw) in WAs, respectively. CMw had higher β-oxidation activity than PDMw, and PDMw was associated with diacylglycerol acyltransferase 2. Therefore, CMw may be involved in β-oxidation and PDMw in droplet expansion in WAs.

Perilipin 1: a systematic review on its functions on lipid metabolism and atherosclerosis in mice and humans

The function of perilipin 1 in human metabolism was recently highlighted by the description of PLIN1 variants associated with various pathologies. These include severe familial partial lipodystrophy and early onset acute coronary syndrome. Additionally, certain variants have been reported to have a protective effect on cardiovascular diseases. The role of this protein remains controversial in mice and variant interpretation in humans is still conflicting. This literature review has two primary objectives (i) to clarify the function of the PLIN1 gene in lipid metabolism and atherosclerosis by examining functional studies performed in cells (adipocytes) and mice and (ii) to understand the impact of PLIN1 variants identified in humans based on the variant's location within the protein and the type of variant (missense or frameshift). To achieve these objectives, we conducted an extensive analysis of the relevant literature on perilipin 1, its function in cellular models and mice, and the consequences of its mutations in humans. We also utilized bioinformatics tools and consulted the Human Genetics Cardiovascular Disease Knowledge Portal to enhance the pathogenicity assessment of PLIN1 missense variants.

Equisetin inhibits adiposity through AMPK-dependent regulation of brown adipocyte differentiation

Obesity has a significant impact on endocrine function, which leads to metabolic diseases including diabetes, insulin resistance, and other complications associated with obesity. Development of effective and safe anti-obesity drugs is imperative and necessary. Equisetin (EQST), a tetramate-containing marine fungal product, was reported to inhibit bacterial fatty acid synthesis and affect mitochondrial metabolism. It is tempting to speculate that EQST might have anti-obesity effects. This study was designed to explore anti-obesity effects and underlying mechanism of EQST on 3T3-L1 adipocytes differentiated from 3T3-L1 cells. Oil Red O staining showed that EQST reduced lipid accumulation in 3T3-L1 adipocytes. Quantitative real-time polymerase chain reaction and Western blot analysis revealed that EQST significantly inhibited expression of adipogenesis/lipogenesis-related genes C/ebp-α, Ppar-γ, Srebp1c, Fas, and reduced protein levels. There was also increased expression of key genes and protein levels involved in lipolysis (Perilipin, Atgl, Hsl), brown adipocyte differentiation (Prdm16, Ucp1), mitochondrial biogenesis (Pgc1α, Tfam) and β-oxidation Acsl1, Cpt1. Moreover, mitochondrial content, their membrane potential ΔΨM, and respiratory chain genes Mt-Co1, Cox7a1, Cox8b, and Cox4 (and protein) exhibited marked increase in expression upon EQST treatment, along with increased protein levels. Importantly, EQST induced expression and activation of AMPK, which was compromised by the AMPK inhibitor dorsomorphin, leading to rescue of EQST-downregulated Fas expression and a reduction of the EQST-increased expression of Pgc1α, Ucp1, and Cox4. Together, EQST robustly promotes fat clearance through the AMPK pathway, these results supporting EQST as a strong candidate for the development into an anti-obesity therapeutic agent.

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.

DIDO is necessary for the adipogenesis that promotes diet-induced obesity

The prevalence of overweight and obesity continues to rise in the population worldwide. Because it is an important predisposing factor for cancer, cardiovascular diseases, diabetes mellitus, and COVID-19, obesity reduces life expectancy. Adipose tissue (AT), the main fat storage organ with endocrine capacity, plays fundamental roles in systemic metabolism and obesity-related diseases. Dysfunctional AT can induce excess or reduced body fat (lipodystrophy). Dido1 is a marker gene for stemness; gene-targeting experiments compromised several functions ranging from cell division to embryonic stem cell differentiation, both in vivo and in vitro. We report that mutant mice lacking the DIDO N terminus show a lean phenotype. This consists of reduced AT and hypolipidemia, even when mice are fed a high-nutrient diet. DIDO mutation caused hypothermia due to lipoatrophy of white adipose tissue (WAT) and dermal fat thinning. Deep sequencing of the epididymal white fat (Epi WAT) transcriptome supported Dido1 control of the cellular lipid metabolic process. We found that, by controlling the expression of transcription factors such as C/EBPα or PPARγ, Dido1 is necessary for adipocyte differentiation, and that restoring their expression reestablished adipogenesis capacity in Dido1 mutants. Our model differs from other lipodystrophic mice and could constitute a new system for the development of therapeutic intervention in obesity.

ApoL6 associates with lipid droplets and disrupts Perilipin1-HSL interaction to inhibit lipolysis

Adipose tissue stores triacylglycerol (TAG) in lipid droplets (LD) and release fatty acids upon lipolysis during energy shortage. We identify ApoL6 as a LD-associated protein mainly found in adipose tissue, specifically in adipocytes. ApoL6 expression is low during fasting but induced upon feeding. ApoL6 knockdown results in smaller LD with lower TAG content in adipocytes, while ApoL6 overexpression causes larger LD with higher TAG content. We show that the ApoL6 affects adipocytes through inhibition of lipolysis. While ApoL6, Perilipin 1 (Plin1), and HSL can form a complex on LD, C-terminal ApoL6 directly interacts with N-terminal Plin1 to prevent Plin1 binding to HSL, to inhibit lipolysis. Thus, ApoL6 ablation decreases white adipose tissue mass, protecting mice from diet-induced obesity, while ApoL6 overexpression in adipose brings obesity and insulin resistance, making ApoL6 a potential future target against obesity and diabetes.

TGS1/PIMT knockdown reduces lipid accumulation in adipocytes, limits body weight gain and promotes insulin sensitivity in mice

PRIP Interacting protein with Methyl Transferase domain (PIMT/TGS1) is an integral upstream coactivator in the peroxisome proliferator-activated receptor gamma (PPARγ) transcriptional apparatus. PPARγ activation alleviates insulin resistance but promotes weight gain. Herein, we show how PIMT regulates body weight while promoting insulin sensitivity in diet induced obese mice. In vitro, we observed enhanced PIMT levels during adipogenesis. Knockdown of PIMT in 3T3-L1 results in reduced lipid accumulation and alters PPARγ regulated gene expression. Intraperitoneal injection of shPIMT lentivirus in high fat diet (HFD)-fed mice caused reduced adipose tissue size and decreased expression of lipid markers. This was accompanied by significantly lower levels of inflammation, hypertrophy and hyperplasia in the different adipose depots (eWAT and iWAT). Notably, PIMT depletion limits body weight gain in HFD-fed mice along with improved impaired oral glucose clearance. It also enhanced insulin sensitivity revealed by assessment of important insulin resistance markers and increased adiponectin levels. In addition, reduced PIMT levels did not alter the serum free fatty acid and TNFα levels. Finally, the relevance of our studies to human obesity is suggested by our finding that PIMT was upregulated in adipose tissue of obese patients along with crucial fat marker genes. We speculate that PIMT may be a potential target in maintaining energy metabolism, thus regulating obesity.

From scarcity to solutions: Therapeutic strategies to restore adipose tissue functionality in rare disorders of lipodystrophy

AIMS

Lipodystrophy is a rare disorder characterised by abnormal or deficient adipose tissue formation and distribution. It poses significant challenges to affected individuals, including the development of severe metabolic complications like diabetes and fatty liver disease. These conditions are often chronic, debilitating and life-threatening, with limited treatment options and a lack of specialised expertise. This review aims to raise awareness of lipodystrophy disorders and highlights therapeutic strategies to restore adipose tissue functionality.

METHODS

Extensive research has been conducted, including both historical and recent advances. We have examined and summarised the literature to provide an overview of potential strategies to restore adipose tissue functionality and treat/reverse metabolic complications in lipodystrophy disorders.

RESULTS

A wealth of basic and clinical research has investigated various therapeutic approaches for lipodystrophy. These include ground-breaking methods such as adipose tissue transplantation, innovative leptin replacement therapy, targeted inhibition of lipolysis and cutting-edge gene and cell therapies. Each approach shows great potential in addressing the complex challenges posed by lipodystrophy.

CONCLUSIONS

Lipodystrophy disorders require urgent attention and innovative treatments. Through rigorous basic and clinical research, several promising therapeutic strategies have emerged that could restore adipose tissue functionality and reverse the severe metabolic complications associated with this condition. However, further research and collaboration between academics, clinicians, patient advocacy groups and pharmaceutical companies will be crucial in transforming these scientific breakthroughs into effective and viable treatment options for individuals and families affected by lipodystrophy. Fostering such interdisciplinary partnerships could pave the way for a brighter future for those battling this debilitating disorder.

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.

Cellular plasticity of the bone marrow niche promotes hematopoietic stem cell regeneration

Hematopoietic stem cells (HSCs) regenerate after myeloablation, a procedure that adversely disrupts the bone marrow and drives leptin receptor-expressing cells, a key niche component, to differentiate extensively into adipocytes. Regeneration of the bone marrow niche is associated with the resolution of adipocytes, but the mechanisms remain poorly understood. Using Plin1-creER knock-in mice, we followed the fate of adipocytes in the regenerating niche in vivo. We found that bone marrow adipocytes were highly dynamic and dedifferentiated to leptin receptor-expressing cells during regeneration after myeloablation. Bone marrow adipocytes could give rise to osteolineage cells after skeletal injury. The cellular fate of steady-state bone marrow adipocytes was also plastic. Deletion of adipose triglyceride lipase (Atgl) from bone marrow stromal cells, including adipocytes, obstructed adipocyte dedifferentiation and led to severely compromised regeneration of HSCs as well as impaired B lymphopoiesis after myeloablation, but not in the steady state. Thus, the regeneration of HSCs and their niche depends on the cellular plasticity of bone marrow adipocytes.

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.

Dysregulation of Lipid Droplet Protein Expression in Adipose Tissues and Association with Metabolic Risk Factors in Adult Females with Obesity and Type 2 Diabetes

BACKGROUND

Adipocyte dysregulation of lipid droplet (LD) metabolism caused by altered expression of LD proteins contributes to obesity-related metabolic diseases.

OBJECTIVES

We aimed to investigate whether expression levels of PLIN1, CIDEA, and CIDEC were altered in adipose tissues of women with obesity and type 2 diabetes and whether their alterations were associated with metabolic risk factors.

METHODS

Normal-weight (NW; 18.5 kg/m² < BMI ≤ 25 kg/m²; n = 43), nondiabetic obese (OB; BMI > 30 kg/m²; n = 38), and diabetic obese (OB/DM; BMI > 30 kg/m², fasting glucose ≥ 126 mg/dL, HbA1c ≥ 6.5%; n = 22) women were recruited. Metabolic parameters were measured, and expressions of PLIN1, CIDEA, CIDEC, and obesity-related genes were quantified in abdominal subcutaneous (SAT) and visceral adipose tissues (VAT). Effects of proinflammatory cytokines, endoplasmic reticulum (ER) stress inducers, and metabolic improvement agents on LD protein gene expressions were investigated in human adipocytes.

RESULTS

PLIN1, CIDEA, and CIDEC expressions were lower in SAT and higher in VAT in OB subjects relative to NW subjects; however, they were suppressed in both fat depots in OB/DM subjects relative to OB (P < 0.05). Across the entire cohort, whereas VAT PLIN1 (r = 0.349) and CIDEC expressions (r = 0.282) were positively associated with BMI (P < 0.05), SAT PLIN1 (r = -0.390) and CIDEA expressions (r = -0.565) were inversely associated. After adjustment for BMI, some or all of the adipose LD protein gene expressions were negatively associated with fasting glucose (r = -0.259 or higher) and triglyceride levels (r = -0.284 or higher) and positively associated with UCP1 expression (r = 0.353 or higher) (P < 0.05). In adipocytes, LD protein gene expressions were 55-70% downregulated by increased proinflammatory cytokines and ER stress but 2-4-fold upregulated by the metabolic improvement agents exendin-4 and dapagliflozin (P < 0.05).

CONCLUSIONS

The findings suggest that reduction of adipose LD protein expression is involved in the pathogenesis of metabolic disorders in women with obesity and type 2 diabetes and that increasing LD protein expression in adipocytes could control development of metabolic disorders.

Prenylcysteine Oxidase 1 Is a Key Regulator of Adipogenesis

The process of adipogenesis involves the differentiation of preadipocytes into mature adipocytes. Excessive adipogenesis promotes obesity, a condition that increasingly threatens global health and contributes to the rapid rise of obesity-related diseases. We have recently shown that prenylcysteine oxidase 1 (PCYOX1) is a regulator of atherosclerosis-disease mechanisms, which acts through mechanisms not exclusively related to its pro-oxidant activity. To address the role of PCYOX1 in the adipogenic process, we extended our previous observations confirming that Pcyox1−/−/Apoe−/− mice fed a high-fat diet for 8 or 12 weeks showed significantly lower body weight, when compared to Pcyox1+/+/Apoe−/− mice, due to an evident reduction in visceral adipose content. We herein assessed the role of PCYOX1 in adipogenesis. Here, we found that PCYOX1 is expressed in adipose tissue, and, independently from its pro-oxidant enzymatic activity, is critical for adipogenesis. Pcyox1 gene silencing completely prevented the differentiation of 3T3-L1 preadipocytes, by acting as an upstream regulator of several key players, such as FABP4, PPARγ, C/EBPα. Proteomic analysis, performed by quantitative label-free mass spectrometry, further strengthened the role of PCYOX1 in adipogenesis by expanding the list of its downstream targets. Finally, the absence of Pcyox1 reduces the inflammatory markers in adipose tissue. These findings render PCYOX1 a novel adipogenic factor with possible pathophysiological or therapeutic potential.

Lipid Droplet Protein PLIN1 Regulates Inflammatory Polarity in Human Macrophages and is Involved in Atherosclerotic Plaque Development by Promoting Stable Lipid Storage

AIM

Perilipins (PLINs), peripheral lipid droplet (LD) proteins, play important roles in lipid accumulation and maturation in adipocytes. The relationship between PLIN family proteins and macrophage polarization in atherosclerosis has not been elucidated.

METHODS

The experiments used tissues from human arteries of 65 patients who had undergone a carotid endarterectomy, and cultured macrophages generated from healthy human peripheral blood mononuclear cells.

RESULTS

Plaque immunohistochemistry demonstrated co-expression of PLIN1 and PLIN2 in both symptomatic (n=31) and asymptomatic patients (n=34). PLIN2 mRNA expression increased 3.38-fold in the symptomatic group compared with those from asymptomatic. PLIN1 was not expressed on small LDs at a shorter incubation but was on large LDs at longer incubation with oxidized LDL and VLDL, while PLIN2 was observed after 24 h and increased with a longer incubation in cultured M1 macrophage. In M2 macrophages, PLIN1 was seen as early as 24 h following incubation with VLDL, and LD size increased with longer incubation. PLIN1 overexpression increased the size of LDs in M1 macrophages, even after a short incubation, and reduced the RNA expression of TNFA, MMP2, ABCA1, and ABCG1 versus the M1 control. Conversely, silencing of PLIN1 in M2 macrophages had the opposite effects on LD size and RNA expression.

CONCLUSION

There was a relationship between macrophage polarity, cytosolic LD size, and PLIN1/PLIN2 expression levels. PLIN2 was mainly expressed in arterial plaques in symptomatic stroke patients, and associated with the inflammatory phenotype of human macrophages, while PLIN1 expression is closely associated with plaque stability and the anti-inflammatory phenotype.

Effects of PLIN1 Gene Knockout on the Proliferation, Apoptosis, Differentiation and Lipolysis of Chicken Preadipocytes

Perilipin 1 (PLIN1) is one of the most abundant lipid droplet-related proteins on the surface of adipocytes. Our previous results showed that PLIN1 plays an important role in chicken lipid metabolism. To further reveal the role of PLIN1 in the growth and development of adipocytes, a chicken preadipocyte line with a PLIN1 gene knockout was established by the CRISPR/Cas9 gene editing technique, and the effects of the PLIN1 gene on the proliferation, apoptosis, differentiation and lipolysis of chicken preadipocytes were detected. The results showed that the CRISPR/Cas9 system effectively mediated knockout of the PLIN1 gene. After the deletion of PLIN1, the differentiation ability and early apoptotic activity of chicken preadipocytes decreased, and their proliferation ability increased. Moreover, knockout of PLIN1 promoted chicken preadipocyte lipolysis under basal conditions and inhibited chicken preadipocyte lipolysis under hormone stimulation. Taken together, our results inferred that PLIN1 plays a regulatory role in the process of proliferation, apoptosis, differentiation and lipolysis of chicken preadipocytes.

PNPLA3(I148M) Inhibits Lipolysis by Perilipin-5-Dependent Competition with ATGL

The single nucleotide polymorphism I148M of the lipase patatin-like phospholipase domain containing 3 (PNPLA3) is associated with an unfavorable prognosis in alcoholic and non-alcoholic steatohepatitis (ASH, NASH), with progression to liver cirrhosis and development of hepatocellular carcinoma. In this study, we investigated the mechanistic interaction of PNPLA3 with lipid droplet (LD)-associated proteins of the perilipin family, which serve as gatekeepers for LD degradation. In a collective of 106 NASH, ASH and control liver samples, immunohistochemical analyses revealed increased ballooning, inflammation and fibrosis, as well as an accumulation of PNPLA3-perilipin 5 complexes on larger LDs in patients homo- and heterozygous for PNPLA3(I148M). Co-immunoprecipitation demonstrated an interaction of PNPLA3 with perilipin 5 and the key enzyme of lipolysis, adipose triglyceride lipase (ATGL). Localization studies in cell cultures and human liver showed colocalization of perilipin 5, ATGL and PNPLA3. Moreover, the lipolytic activity of ATGL was negatively regulated by PNPLA3 and perilipin 5, whereas perilipin 1 displaced PNPLA3 from the ATGL complex. Furthermore, ballooned hepatocytes, the hallmark of steatohepatitis, were positive for PNPLA3 and perilipins 2 and 5, but showed decreased perilipin 1 expression with respect to neighboured hepatocytes. In summary, PNPLA3- and ATGL-driven lipolysis is significantly regulated by perilipin 1 and 5 in steatohepatitis.

Lipid Droplet Formation Is Regulated by Ser/Thr Phosphatase PPM1D via Dephosphorylation of Perilipin 1

Hypertrophy and hyperplasia of white adipocytes induce obesity, leading to diseases such as type 2 diabetes and hypertension, and even cancer. Hypertrophy of white adipocytes is attributed to the excessive storage of the energy form of triglycerides in lipid droplets (LDs). LDs are fat storage organelles that maintain whole-body energy homeostasis. It is important to understand the mechanism of LD formation for the development of obesity therapy; however, the regulatory mechanisms of LD size and formation are not fully understood. In this study, we demonstrated that the PPM family phosphatase PPM1D regulates LD formation. PPM1D specific inhibitor, SL-176 significantly decreased LD formation via two different pathways: dependent of and independent of adipocyte-differentiation processes. In the mature white adipocytes after differentiation, LD formation was found to be controlled by PPM1D via dephosphorylation of Ser511 of perilipin 1. We found that inhibition of PPM1D in mature white adipocytes significantly reduced the size of the LDs via dephosphorylation of Ser511 of perilipin 1 but did not change the lipolysis sensitivity and the total amount of lipid in cells. Collectively, the results of this study provide evidence that PPM1D plays an important role in LD formation in mature adipocytes.

The Colletotrichum siamense Hydrophobin CsHydr1 Interacts with the Lipid Droplet-Coating Protein CsCap20 and Regulates Lipid Metabolism and Virulence

Previous studies of the lipid droplet-coating protein Cap20 in Colletotrichum show that it plays a key role in appressorium development and virulence. In this study, the hydrophobin CsHydr1, which contains a signal peptide of 19 amino acids and a hydrophobic domain (HYDRO), was shown to interact with CsCap20 in Colletotrichum siamense. The CsHydr1 deletion mutant showed slightly enhanced mycelial growth, small conidia, slow spore germination and appressoria formation, cell wall integrity and virulence. Like CsCAP20, CsHydr1 is also localized on the lipid droplet surface of C. siamense. However, when CsCap20 was absent, some CsHydr1 was observed in other parts. Quantitative lipid determination showed that the absence of either CsHydr1 or CsCap20 reduced the content of lipids in mycelia and conidia, while the effect of CsCap20 was more obvious; these results suggest that an interaction protein CsHydr1 of CsCap20 is localized on the lipid droplet surface and involved in lipid metabolism, which affects appressorium formation and virulence in C. siamense.

Caffeic Acid Phenethyl Ester Inhibits Basal Lipolysis by Activating PPAR-Gamma and Increasing Lipid Droplet-Associated Perilipin in Mature Rat Adipocytes

Abnormal lipolysis is correlated with metabolic syndrome. Caffeic acid phenethyl ester (CAPE), a natural product from honeybee hives, has been reported to improve metabolic syndrome. However, the effects of CAPE on lipolysis and perilipin-1 (the major lipid droplet-associated protein) in mature adipocytes were not clarified. In this study, mature adipocytes were isolated from the epididymal fat pads of male rats and incubated with CAPE to estimate lipolysis by measuring glycerol release. It was found that the basal lipolysis was inhibited by CAPE in a dose- and time-dependent manner. The lipid droplet-associated perilipin-1 and phosphorylated peroxisome proliferator-activated receptor (PPAR) gamma levels increased following CAPE treatment by Western blot analysis. Moreover, a specific PPAR-gamma inhibitor (T0070907) could partly reverse the effect of CAPE on basal lipolysis. Furthermore, treatment of adipocytes with dibutyryl-cAMP (db-cAMP) or isoproterenol (ISO) increased lipolysis, but the drug-induced lipolysis was abrogated by combination treatment with CAPE. The lipid droplet-associated perilipin-1 level was also decreased in the drug-induced groups but increased when combined treatment with CAPE. In conclusion, our results revealed that a decrease in basal lipolysis and an increase in lipid droplet-associated perilipin-1 levels induced by CAPE may be involved in the regulation of lipid metabolism through activation of PPAR-gamma in mature adipocytes.

Trends in insulin resistance: insights into mechanisms and therapeutic strategy

The centenary of insulin discovery represents an important opportunity to transform diabetes from a fatal diagnosis into a medically manageable chronic condition. Insulin is a key peptide hormone and mediates the systemic glucose metabolism in different tissues. Insulin resistance (IR) is a disordered biological response for insulin stimulation through the disruption of different molecular pathways in target tissues. Acquired conditions and genetic factors have been implicated in IR. Recent genetic and biochemical studies suggest that the dysregulated metabolic mediators released by adipose tissue including adipokines, cytokines, chemokines, excess lipids and toxic lipid metabolites promote IR in other tissues. IR is associated with several groups of abnormal syndromes that include obesity, diabetes, metabolic dysfunction-associated fatty liver disease (MAFLD), cardiovascular disease, polycystic ovary syndrome (PCOS), and other abnormalities. Although no medication is specifically approved to treat IR, we summarized the lifestyle changes and pharmacological medications that have been used as efficient intervention to improve insulin sensitivity. Ultimately, the systematic discussion of complex mechanism will help to identify potential new targets and treat the closely associated metabolic syndrome of IR.

Metformin Prevents Key Mechanisms of Obesity-Related Complications in Visceral White Adipose Tissue of Obese Pregnant Mice

With the gaining prevalence of obesity, related risks during pregnancy are rising. Inflammation and oxidative stress are considered key mechanisms arising in white adipose tissue (WAT) sparking obesity-associated complications and diseases. The established anti-diabetic drug metformin reduces both on a systemic level, but only little is known about such effects on WAT. Because inhibiting these mechanisms in WAT might prevent obesity-related adverse effects, we investigated metformin treatment during pregnancy using a mouse model of diet-induced maternal obesity. After mating, obese mice were randomised to metformin administration. On gestational day G15.5, phenotypic data were collected and perigonadal WAT (pgWAT) morphology and proteome were examined. Metformin treatment reduced weight gain and visceral fat accumulation. We detected downregulation of perilipin-1 as a correlate and observed indications of recovering respiratory capacity and adipocyte metabolism under metformin treatment. By regulating four newly discovered potential adipokines (alpha-1 antitrypsin, Apoa4, Lrg1 and Selenbp1), metformin could mediate anti-diabetic, anti-inflammatory and oxidative stress-modulating effects on local and systemic levels. Our study provides an insight into obesity-specific proteome alterations and shows novel modulating effects of metformin in pgWAT of obese dams. Accordingly, metformin therapy appears suitable to prevent some of obesity’s key mechanisms in WAT.

Perilipin Genetic Variation Correlated with Obesity and Lipid Profile in Metabolic Syndrome

BACKGROUND: Perilipin is very important for the regulation of the deposition and mobilization of fats. The human perilipin gene (PLIN) is near the locus for risk of obesity and hypertriglyceridemia. The PLIN gene is thought to be involved in the occurrence of metabolic syndrome. AIM: The aim of this research is to determine the role of variations of the PLIN gene (PLN4 11482 G>A) as a risk factor for component of metabolic syndrome. METHODS: This study involved a total of 160 subjects consisting of 80 with metabolic syndrome and 80 controls. Genotype analysis was done with the polymerase chain reaction-restriction fragment length polymorphism method. The data were analyzed with t-tests to compare the subjects’ characteristics between metabolic syndrome groups and controls. Risk factors of PLIN genotypes were calculated with odds ratio and multivariate regression analysis was used to determine the role of the PLIN gene with each biochemical characteristic. RESULTS: The result was significant differences between the characteristics of the metabolic syndrome subjects with controls (p < 0.05). There was no difference in genotypes between patients with metabolic syndrome and controls. The multivariate analysis of the genetic role with biochemical components showed the PLIN gene in AA carriers as a risk factor for metabolic syndrome compare GA+GG, risk of obesity, and hypercholesterolemia with p < 0.05. CONCLUSION: It can be concluded that PLIN variation has a role in the incidence of metabolic syndrome, especially in relation to obesity and hypercholesterolemia. Further study is needed to determine the role of other gene variations as a risk factor for metabolic syndrome.

Dysfunction of lipid storage droplet-2 suppresses endoreplication and induces JNK pathway-mediated apoptotic cell death in Drosophila salivary glands

The lipid storage droplet-2 (LSD-2) protein of Drosophila is a homolog of mammalian perilipin 2, which is essential for promoting lipid accumulation and lipid droplet formation. The function of LSD-2 as a regulator of lipolysis has also been demonstrated. However, other LSD-2 functions remain unclear. To investigate the role of LSD-2, we performed tissue-specific depletion in the salivary glands of Drosophila using a combination of the Gal4-upstream activating sequence system and RNA interference. LSD-2 depletion inhibited the entry of salivary gland cells into the endoreplication cycle and delayed this process by enhancing CycE expression, disrupting the development of this organ. The deficiency of LSD-2 expression enhanced reactive oxygen species production in the salivary gland and promoted JNK-dependent apoptosis by suppressing dMyc expression. This phenomenon did not result from lipolysis. Therefore, LSD-2 is vital for endoreplication cell cycle and cell death programs.

Perilipins at a glance

Lipid droplets (LDs) are ubiquitous organelles that store and supply lipids for energy metabolism, membrane synthesis and production of lipid-derived signaling molecules. While compositional differences in the phospholipid monolayer or neutral lipid core of LDs impact their metabolism and function, the proteome of LDs has emerged as a major influencer in all aspects of LD biology. The perilipins (PLINs) are the most studied and abundant proteins residing on the LD surface. This Cell Science at a Glance and the accompanying poster summarize our current knowledge of the common and unique features of the mammalian PLIN family of proteins, the mechanisms through which they affect cell metabolism and signaling, and their links to disease.

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.

Tropolone-Bearing Sesquiterpenes from Juniperus chinensis: Structures, Photochemistry and Bioactivity

The tropolone-bearing sesquiterpenes juniperone A (1) and norjuniperone A (2) were isolated from the folk medicinal plant Juniperus chinensis, and their structures were determined by a combination of spectroscopic and crystallographic methods. Photojuniperones A1 (3) and A2 (4), bearing bicyclo[3,2,0]heptadienones derived from tropolone, were photochemically produced and structurally identified by spectroscopic methods. Predicted by the machine learning-based assay, 1 significantly inhibited the action of tyrosinase. The new compounds also inhibited lipid accumulation and enhanced the extracellular glycerol excretion.

Involvement of TRP Channels in Adipocyte Thermogenesis: An Update

Obesity prevalence became a severe global health problem and it is caused by an imbalance between energy intake and expenditure. Brown adipose tissue (BAT) is a major site of mammalian non-shivering thermogenesis or energy dissipation. Thus, modulation of BAT thermogenesis might be a promising application for body weight control and obesity prevention. TRP channels are non-selective calcium-permeable cation channels mainly located on the plasma membrane. As a research focus, TRP channels have been reported to be involved in the thermogenesis of adipose tissue, energy metabolism and body weight regulation. In this review, we will summarize and update the recent progress of the pathological/physiological involvement of TRP channels in adipocyte thermogenesis. Moreover, we will discuss the potential of TRP channels as future therapeutic targets for preventing and combating human obesity and related-metabolic disorders.

MED1 is a lipogenesis coactivator required for postnatal adipose expansion

In this study, Jang et al. investigated the role of MED1 in adipose development and expansion in vivo, and they show that MED1 is not generally required for transcription during adipogenesisin culture and that MED1 is dispensable for adipose development in mice. Instead, MED1 is required for postnatal adipose expansion and the induction of fatty acid and triglyceride synthesis genes after pups switch diet from high-fat maternal milk to carbohydrate-based chow. Their findings identify a cell- and gene-specific regulatory role of MED1 as a lipogenesis coactivator required for postnatal adipose expansion.

MED1 often serves as a surrogate of the general transcription coactivator complex Mediator for identifying active enhancers. MED1 is required for phenotypic conversion of fibroblasts to adipocytes in vitro, but its role in adipose development and expansion in vivo has not been reported. Here, we show that MED1 is not generally required for transcription during adipogenesis in culture and that MED1 is dispensable for adipose development in mice. Instead, MED1 is required for postnatal adipose expansion and the induction of fatty acid and triglyceride synthesis genes after pups switch diet from high-fat maternal milk to carbohydrate-based chow. During adipogenesis, MED1 is dispensable for induction of lineage-determining transcription factors (TFs) PPARγ and C/EBPα but is required for lipid accumulation in the late phase of differentiation. Mechanistically, MED1 controls the induction of lipogenesis genes by facilitating lipogenic TF ChREBP- and SREBP1a-dependent recruitment of Mediator to active enhancers. Together, our findings identify a cell- and gene-specific regulatory role of MED1 as a lipogenesis coactivator required for postnatal adipose expansion.

A Dual Omics Approach to Evaluate Transcriptional and Metabolic Responses During Lipid Deprivation in an Oyster Parasite, Perkinsus marinus

Perkinsus marinus, a protozoan and the causative agent of perkinsosis (dermo disease) is a prevalent parasite found within the eastern oyster (Crassostrea virginica). In this study, we explore metabolic processes of P. marinus cells under lipid-depleted medium conditions to elucidate the interchanging flux of lipid and carbohydrate metabolism. Although P. marinus can synthesize their own lipids from available nutrients, they display a slower growth in medium not supplemented with lipids as opposed to medium with lipids. Under these conditions, using transcriptomics, we surprisingly observed evidence of stimulated lipid degradation through increased transcription of two core β-oxidation pathway enzymes. Simultaneously, phospholipid biosynthetic pathways were downregulated. Metabolomic analysis supported the transcriptomic results. Most fatty acids were decreased in lipid-deplete medium as opposed to lipid-replete medium, and available glucose was fermented to lactate. A significant increase in the cholesterol derivative zymosterol further supported a downregulation of membrane synthesis under the experimental conditions. A robust tricarboxylic acid (TCA) cycle was apparent by enhanced citrate synthase transcription, and a simultaneous reduction in branched chain amino acids. It is concluded that although P. marinus has the capacity for synthesizing its own lipids, it can respond to lipid deprivation in medium by oxidizing readily available stores, and likely transitioning into a resting stage.

Identification of SCARA3 with potential roles in metabolic disorders

Obesity is characterized by the expansion of adipose tissue which is partially modulated by adipogenesis. In the present study, we identified five differentially expressed genes by incorporating two adipogenesis-related datasets from the GEO database and their correlation with adipogenic markers. However, the role of scavenger receptor class A member 3 (SCARA3) in obesity-related disorders has been rarely reported. We found that Scara3 expression in old adipose tissue-derived mesenchymal stem cells (Ad-MSCs) was lower than it in young Ad-MSCs. Obese mice caused by deletion of the leptin receptor gene (db/db) or by a high-fat diet both showed reduced Scara3 expression in inguinal white adipose tissue. Moreover, hypermethylation of SCARA3 was observed in patients with type 2 diabetes and atherosclerosis. Data from the CTD database indicated that SCARA3 is a potential target for metabolic diseases. Mechanistically, JUN was predicted as a transcriptional factor of SCARA3 in different databases which is consistent with our further bioinformatics analysis. Collectively, our study suggested that SCARA3 is potentially associated with age-related metabolic dysfunction, which provided new insights into the pathogenesis and treatment of obesity as well as other obesity-associated metabolic complications.

Lipodystrophies-Disorders of the Fatty Tissue

Lipodystrophies are a heterogeneous group of physiological changes characterized by a selective loss of fatty tissue. Here, no fat cells are present, either through lack of differentiation, loss of function or premature apoptosis. As a consequence, lipids can only be stored ectopically in non-adipocytes with the major health consequences as fatty liver and insulin resistance. This is a crucial difference to being slim where the fat cells are present and store lipids if needed. A simple clinical classification of lipodystrophies is based on congenital vs. acquired and generalized vs. partial disturbance of fat distribution. Complications in patients with lipodystrophy depend on the clinical manifestations. For example, in diabetes mellitus microangiopathic complications such as nephropathy, retinopathy and neuropathy may develop. In addition, due to ectopic lipid accumulation in the liver, fatty liver hepatitis may also develop, possibly with cirrhosis. The consequences of extreme hypertriglyceridemia are typically acute pancreatitis or eruptive xanthomas. The combination of severe hyperglycemia with dyslipidemia and signs of insulin resistance can lead to premature atherosclerosis with its associated complications of coronary heart disease, peripheral vascular disease and cerebrovascular changes. Overall, lipodystrophy is rare with an estimated incidence for congenital (<1/1.000.000) and acquired (1-9/100.000) forms. Due to the rarity of the syndrome and the phenotypic range of metabolic complications, only studies with limited patient numbers can be considered. Experimental animal models are therefore useful to understand the molecular mechanisms in lipodystrophy and to identify possible therapeutic approaches.

Transcriptional regulation of adipogenic marker genes for the improvement of intramuscular fat in Qinchuan beef cattle

The intramuscular fat content plays a crucial role in meat quality traits. Increasing the degree of adipogenesis in beef cattle leads to an increase in the content of intramuscular fat. Adipogenesis a complex biochemical process which is under firm genetic control. Over the last three decades, the Qinchuan beef cattle have been extensively studied for the improvement of meat production and quality traits. In this study, we reviewed the literature regarding adipogenesis and intramuscular fat deposition. Then, we summarized the research conducted on the transcriptional regulation of key adipogenic marker genes, and also reviewed the roles of adipogenic marker genes in adipogenesis of Qinchuan beef cattle. This review will elaborate our understanding regarding transcriptional regulation which is a vital physiological process regulated by a cascade of transcription factors (TFs), key target marker genes, and regulatory proteins. This synergistic action of TFs and target genes ensures the accurate and diverse transmission of the genetic information for the accomplishment of central physiological processes. This information will provide an insight into the transcriptional regulation of the adipogenic marker genes and its role in bovine adipogenesis for the breed improvement programs especially for the trait of intramuscular fat deposition.

Overexpression of PLIN1 Promotes Lipid Metabolism in Bovine Adipocytes

Perilipin 1 (PLIN1) is a protein encoded by the PLIN1 gene in eukaryotes. PLIN1 is a member of the PAT protein family, a family of proteins related to lipid droplet (LD) surface proteins. PLIN1 phosphorylation plays a vital role during fat metabolism of adipose tissue lipolysis and fat storage in adipocytes. However, to further explore the regulation of the PLIN1 gene on the proliferation, differentiation and lipid metabolism of bovine adipocytes. In this study, the mRNA expression of PLIN1, at day six, was the highest during bovine adipocyte differentiation. Moreover, PLIN1 can promote the proliferation and differentiation of preadipocytes in cattle. On the sixth day, after transfection with, and overexpression of, the PLIN1 gene in bovine preadipocytes via adenovirus, cell samples were collected, and transcriptome sequencing was performed. A total of 1923 differentially expressed genes were detected. Through GO and KEGG pathway analysis, the differentially expressed genes were established to be mainly enriched in the AMPK, Wnt, and PPAR signaling pathways related to fat proliferation and differentiation. In conclusion, at the transcriptional level, PLIN1 plays an important role in regulating fat proliferation and metabolism. Additionally, the sequencing results screened new differentially expressed genes related to fat metabolism, providing theoretical support for molecular breeding of Qinchuan beef cattle.

The "discovery" of lipid droplets: A brief history of organelles hidden in plain sight

Mammalian lipid droplets (LDs), first described as early as the 1880s, were virtually ignored for more than 100 years. Between 1991 and the early 2000s, however, a series of discoveries and conceptual breakthroughs led to a resurgent interest in obesity as a disease, in the metabolism of intracellular triacylglycerol (TAG), and in the physical locations of LDs as cellular structures with their associated proteins. Insights included the recognition that obesity underlies major chronic diseases, that appetite is hormonally controlled, that hepatic steatosis is not a benign finding, and that diabetes might fundamentally be a disorder of lipid metabolism. In this brief review, I describe the metamorphosis of LDs from overlooked globs of stored fat to dynamic organelles that control insulin resistance, mitochondrial oxidation, and viral replication.

Perilipin LDP1 coordinates lipid droplets formation and utilization for appressorium-mediated infection in Magnaporthe oryzae

Lipid droplets (LDs) serve as one of the major reservoirs in conidia of Magnaporthe oryzae and are quickly utilized during appressorium formation. Here, we identified a gene, LDP1, encoding a perilipin that is important for LD formation and utilization during appressorium maturation. LDP1 is highly expressed in conidium and immature appressorium. Disruption mutants of LDP1 were significantly reduced in virulence, due to appressorial turgor reduction and difficulty in penetration. LDs were significantly reduced in the Δldp1 mutant, indicating LDP1 was required for LDs formation. LDP1 was colocalized with the LDs in conidium and immature appressorium but was gradually separated during appressorium maturation. A typical intracellular triacylglycerol lipase, TGL1-2, was clearly separated with LDs in conidium and immature appressorium but was well colocalized with LDs during appressorium maturation. The subcellular localization of TGL1-2 was affected by LDP1. These data suggested that LDP1 was bound to LDs for protecting from utilization in conidia and at the early appressorium stage but was separated from LDs for lipase entering and degradation. LDP1 was phosphorylated by CPKA at Thr96, which was essential for its localization and functions. These data indicate perilipin LDP1 can coordinate LD formation and utilization for appressorium-mediated infection of M. oryzae.

Systemic TNF-α blockade attenuates anxiety and depressive-like behaviors in db/db mice through downregulation of inflammatory signaling in peripheral immune cells

Research studies have indicated that the comorbidity burden of mood disorders and obesity is reasonably high. Insulin signaling has been shown to modulate multiple physiological functions in the brain, indicating its association with neuropsychiatric diseases, including mood disorders. Leptin is a hormone responsible for regulating body weight and insulin homeostasis. Previous studies on db/db mice (a mouse model that carries a spontaneous genetic mutation in leptin receptor Lepr^db) have shown that they exhibit inflammation as well as neurobehavioral traits associated with mood. Therefore, targeting inflammatory pathways such as TNF-α may be an effective strategy in the treatment of obesity-linked mood disorders. The objective of this study was to investigate the effect of long-term administration of etanercept (a TNF-α blocker) on anxiety and depressive-like behaviors in db/db mice. This was performed using light/dark box, forced swim, and open field tests with lean littermate wild type (WT) mice serving as a control group. Using flow cytometry in peripheral blood, we further examined the molecular effects of etanercept on NF-κB p65, TNF-α, IL-17A, and TLR-4 expressing CD4+, CD8+, and CD14+ cells in the peripheral blood. Our data show that peripheral administration of etanercept decreased these cells in db/db mice. Furthermore, our results indicated that peripheral administration of etanercept reduced anxiety and depressive-like behaviors. Therefore, targeting TNF-α signaling might be an effective strategy for modulating obesity-associated depression and anxiety.

Eicosapentaenoic acid-enriched phospholipids suppressed lipid accumulation by specific inhibition of lipid droplet-associated protein FSP27 in mice

BACKGROUND

Sea cucumber is a rich source of eicosapentaenoic acid in the form of eicosapentaenoic acid-enriched phospholipids (EPA-PL). It is known to be efficacious in preventing obesity. However, few studies have focused on the role of EPA-PL in inhibiting lipid accumulation by lipid droplets (LDs). This study first investigated the effect of EPA-PL from sea cucumber on the formation of LDs and the underlying mechanism in C57BL/6J mice. The mice were randomly divided into two groups and treated for 8 weeks or 3, 7, and 14 days with either (i) a high-sucrose diet (model group), (ii) a high-sucrose diet plus 2% EPA-PL (EPA-PL group).

RESULTS

Eight-week EPA-PL supplementation significantly reduced lipid accumulation and LD size in liver and white adipose tissue (WAT), which was accompanied by the decreased expression of LDs-associated protein FSP27. A 3-day EPA-PL treatment suppressed the mRNA expression of Fsp27. The mRNA level of Fsp27 reached its 'normal level' after withdrawing EPA-PL for 7 days, suggesting that EPA-PL might serve as a rapid regulator of FSP27. Furthermore, EPA-PL increased the expression of lipolysis genes Hsl and Atgl accompanied by the regulation of Pparγ in WAT.

CONCLUSIONS

Dietary EPA-PL from sea cucumber (Cucumaria frondosa) protected against lipid accumulation by regulating LDs-associated protein FSP27, which might provide novel evidence for the anti-obesity action of EPA-PL. © 2020 Society of Chemical Industry.

A comparative metabolomics study on anadromous clupeid Tenualosa ilisha for better understanding the influence of habitat on nutritional composition

INTRODUCTION

Fish inhabiting different aquatic habitats adapts to the environment by metabolomic readjustments. Understanding the combined activities of all the metabolic pathways (metabolome) helps in better understanding the complex interactions between gene and environment.

OBJECTIVES

The anadromous migratory Tenualosa ilisha is a high value food fish comprising the dominant fishery of the rivers Padma and Hooghly. The present study aimed at understanding the influence of the two habitats on the nutritional composition of hilsa.

METHODS

Metabolite profiling was carried out by GC/MS. De novo assembly of hilsa liver transcriptome was generated under Illumina HiSeq platform and multivariate analysis was employed for correlation and comparison.

RESULTS

GC/MS fingerprinting showed C16:0, C18:1, C20:5 and C22:6 to be the predominant fatty acids present in hilsa liver, which were also found to be significantly higher in Hooghly hilsa. Comparative transcriptome analysis revealed that the differentially expressed genes were mainly associated with 'lipid metabolism' and 'amino acid metabolism' pathways. Multivariate analysis between the metabolites amino acid, fatty acid and corresponding gene expression showed that few genes of amino acid metabolism (EZH1, ALAS2 and ALDH4A1) positively correlated with individual amino acids (lysine, glycine and glutamate) in Hooghly hilsa. Similarly, the key genes for LC-PUFA biosynthesis (ELOVL5, FADS2, CPT1) showed positive correlation with individual LC-PUFAs (C18:3, C20:4, C20:5, C22:6), indicating higher LC-PUFA biosynthesis potential in Hooghly hilsa.

CONCLUSION

Comparative metabolomic study in hilsa from the two different habitats showed that the habitats influence the nutritional composition as evidenced by high abundance of amino acids lysine, leucine and arginine and LC-PUFAs C18:3, C20:4, C20:5, C22:6 in Hooghly hilsa.

Cathepsin B overexpression induces degradation of perilipin 1 to cause lipid metabolism dysfunction in adipocytes

Obesity, caused by the dysfunction of white adipose tissue (WAT), is reportedly accompanied by exacerbation of lipolysis. Perilipin 1 (PLIN1), which forms a coat around lipid droplets, interacts with several lipolysis proteins to regulate lipolysis. While it is known that perilipin family proteins are degraded in lysosomes, the underlying molecular mechanisms related to the downregulated expression of PLIN1 in obese WAT remain unknown. Recently, we found that lysosomal dysfunction originating from an abnormality of cathepsin B (CTSB), a lysosomal representative protease, occurs in obese WAT. Therefore, we investigated the effect of CTSB alterations on PLIN1 expression in obese WAT. PLIN1 protein disappeared and CTSB protein appeared in the cytoplasm of adipocytes in the early stage of obese WAT. Overexpression of CTSB reduced PLIN1 protein in 3T3L1 adipocytes, and treatment with a CTSB inhibitor significantly recovered this reduction. In addition, CTSB overexpression induced the dysfunction of lipolysis in 3T3L1 adipocytes. Therefore, we concluded that upregulation of CTSB induced the reduction of PLIN1 protein in obese WAT, resulting in lipolysis dysfunction. This suggests a novel pathology of lipid metabolism involving PLIN1 in adipocytes and that CTSB might be a therapeutic candidate molecule for obese WAT.

Anti-Lipolysis Induced by Insulin in Diverse Pathophysiologic Conditions of Adipose Tissue

As an important energy reservoir, adipose tissue maintains lipid balance and regulates energy metabolism. When the body requires energy, adipocytes provide fatty acids to peripheral tissues through lipolysis. Insulin plays an important role in regulating normal fatty acid levels by inhibiting lipolysis. When the morphology of adipose tissue is abnormal, its microenvironment changes and the lipid metabolic balance is disrupted, which seriously impairs insulin sensitivity. As the most sensitive organ to respond to insulin, lipolysis levels in adipose tissue are affected by impaired insulin function, which results in serious metabolic diseases. However, the specific underlying mechanisms of this process have not yet been fully elucidated, and further study is required. The purpose of this review is to discuss the effects of adipose tissue on the anti-lipolysis process triggered by insulin under different conditions. In particular, the functional changes of this process respond to inconsonantly morphological changes of adipose tissue.

Childhood Obesity Risk in Relationship to Perilipin 1 (PLIN1) Gene Regulation by Circulating microRNAs

Childhood obesity is a growing public health burden in many countries. The lipid perilipin 1 (PLIN1) gene is involved in regulation of lipolysis, and thus represents a viable candidate mechanism for obesity genetics research in children. In addition, the regulation of candidate gene expression by circulating microRNAs (miRNAs) offers a new research venue for diagnostic innovation. We report new findings on associations among circulating miRNAs, regulation of the PLIN1 gene, and susceptibility to childhood obesity. In a sample of 135 unrelated subjects, 35 children with obesity (between ages 3 and 13) and 100 healthy controls (between ages 4 and 16), we examined the expression levels of four candidate miRNAs (hsa-miR-4777-3p, hsa-miR-642b-3p, hsa-miR-3671-1, and hsa-miR-551b-2) targeting the PLIN1 as measured by real-time polymerase chain reaction in whole blood samples. We found that the full genetic model, including the four candidate miRNAs and the PLIN1 gene, explained a statistically significant 12.7% of the variance in childhood obesity risk (p = 0.0034). The four miRNAs together explained 10.1% of the risk (p = 0.008). The percentage of variation in childhood obesity risk explained by hsa-miR-642b-3p and age was 19%. In accordance with biological polarity of the observed association, for example, hsa-miR-642b-3p was upregulated, while the PLIN1 expression decreased in obese participants compared to healthy controls. To the best of our knowledge, this is the first clinical association study of these candidate miRNAs targeting the PLIN1 in childhood obesity. These data offer new molecular leads for future clinical biomarker and diagnostic discovery for childhood obesity.

High prevalence of mutations in perilipin 1 in patients with precocious acute coronary syndrome

BACKGROUND AND AIMS

Genetic partial lipodystrophies are rare heterogeneous disorders characterized by abnormalities of fat distribution and associated metabolic complications including a predisposition for atherosclerotic cardiovascular disease. We hypothesized that the milder forms of these diseases might be underdiagnosed and might result in early acute coronary syndrome (ACS) as the first sign of the pathology.

METHODS

We performed targeted sequencing on a panel of 8 genes involved in genetic lipodystrophy for 62 patients with premature ACS, and selected heterozygous missense variations with low frequency. To confirm those results, we analyzed a second independent group of 60 additional patients through Sanger sequencing, and compared to a control group of 120 healthy patients.

RESULTS

In the first cohort, only PLIN1 exhibited variants in more than 1 patient. In PLIN1, 3 different variants were found in 6 patients. We then analyzed PLIN1 sequence in the second cohort with premature ACS and found 2 other patients. Altogether, 8 patients were carriers of 4 different mutations in PLIN1. The variant frequencies in the total cohort of 122 patients were compared to frequencies observed in a local control cohort and in 2 different public databases showing a significant difference between patient vs control group frequencies for two mutations out of 4 (c.245C > T p = 10^-4; c.839G > A p = 0.014).

DISCUSSION

This is the first study that identifies a high frequency of potential pathogenic mutations in PLIN1 related to early onset ACS. These findings could contribute to the prevention and care of precocious ACS in families carrying those mutations.