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Mutations in BSCL2 underlie human congenital generalized lipodystrophy. We inactivated Bscl2 in mice to examine the mechanisms
whereby absence of Bscl2 leads to adipose tissue loss and metabolic disorders. Bscl2−/− mice develop severe lipodystrophy of white adipose tissue (WAT), dyslipidemia, insulin resistance, and hepatic steatosis.
In vitro diff...
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The study herein determined the role of nuclear factor erythoid 2-related factor 2 (Nrf2) in the pathogenesis of hepatic steatosis, insulin resistance, obesity, and type 2 diabetes. Lep(ob/ob)-Keap1-knockdown (KD) mice, which have increased Nrf2 activity, were generated. Markers of obesity and type 2 diabetes were measured in C57Bl/6J, Keap1-KD, Le...
Citations
... Seipin, a conserved endoplasmic reticulum transmembrane protein, is highly expressed in adipose tissues and the brain. Seipin affects cellular lipid homeostasis directly by regulating the enzyme machinery of fatty acid (FA) synthesis, phosphatidic acid (PA) metabolism, or sphingolipid production [1][2][3][4], mediating phosphatidylcholine (PC) synthesis [5], or regulating lipolysis [6]. Lipid droplets (LDs), crucial dynamic organelles for lipid homeostasis. ...
... The content and size of LDs in undifferentiated OLN cells was significantly decreased in undifferentiated OLN cells, while increased in differentiated OLN cells. There were literatures reported that LDs size was influenced by lipid metabolism, of which Seipin was a key mediator [6,62,63]. These findings indicated that Seipin deficiency obstructed the degradation and utilization of LDs in OPCs, which compromised OPC differentiation. ...
Seipin is one key mediator of lipid metabolism that is highly expressed in adipose tissues as well as in the brain. Lack of Seipin gene, Bscl2 , leads to not only severe lipid metabolic disorders but also cognitive impairments and motor disabilities. Myelin, composed mainly of lipids, facilitates nerve transmission and is important for motor coordination and learning. Whether Seipin deficiency-leaded defects in learning and motor coordination is underlined by lipid dysregulation and its consequent myelin abnormalities remains to be elucidated. In the present study, we verified the expression of Seipin in oligodendrocytes (OLs) and their precursors, oligodendrocyte precursor cells (OPCs), and demonstrated that Seipin deficiency compromised OPC differentiation, which led to decreased OL numbers, myelin protein, myelinated fiber proportion and thickness of myelin. Deficiency of Seipin resulted in impaired spatial cognition and motor coordination in mice. Mechanistically, Seipin deficiency suppressed sphingolipid metabolism-related genes in OPCs and caused morphological abnormalities in lipid droplets (LDs), which markedly impeded OPC differentiation. Importantly, rosiglitazone, one agonist of PPAR-gamma, substantially restored phenotypes resulting from Seipin deficiency, such as aberrant LDs, reduced sphingolipids, obstructed OPC differentiation, and neurobehavioral defects. Collectively, the present study elucidated how Seipin deficiency-induced lipid dysregulation leads to neurobehavioral deficits via impairing myelination, which may pave the way for developing novel intervention strategy for treating metabolism-involved neurological disorders.
... We examined the effect of liraglutide administration on food intake, water consumption, body composition and non-fasted blood glucose levels, assessed over 8 consecutive days. In accordance with clinical features observed in CGL2 patients, SKO mice were hyperphagic (Figure 2A), attributable to the low circulating levels of leptin (28)(29)(30)(31)(32). Water intake was also significantly elevated in SKO mice when compared to WT mice ( Figure 2B), which is consistent with polydipsia, a recognised feature of diabetes (33). ...
... This likely reflects an anti-diabetic treatment effect of liraglutide on SKO mice. As shown previously (19,28,29,34), lipodystrophic SKO mice display significantly reduced fat mass ( Figures 2E; Supplementary Figure S1A) and increased lean mass ( Figure 2F; Supplementary Figure S1B) relative to WT mice. When comparing metabolic parameters pre and post the 2-week treatment, we observed that liraglutide significantly lowered fat mass in male WT mice, however similar changes failed to reach statistical significance in female WT mice ( Figure 2E). ...
... Here we demonstrate that the GLP-1R agonist liraglutide is highly effective at improving multiple aspects of metabolic disease in a mouse model of generalised lipodystrophy. SKO mice recapitulate key features of generalised lipodystrophy seen in individuals with disruption of the corresponding gene, BSCL2 (19,(28)(29)(30)34). This includes insulin resistance, glucose intolerance, hepatic steatosis, very low adiponectin and leptin levels and hyperphagia, although not the hypertriglyceridemia observed in CGL2 patients. ...
Aims
Individuals with lipodystrophies typically suffer from metabolic disease linked to adipose tissue dysfunction including lipoatrophic diabetes. In the most severe forms of lipodystrophy, congenital generalised lipodystrophy, adipose tissue may be almost entirely absent. Better therapies for affected individuals are urgently needed. Here we performed the first detailed investigation of the effects of a glucagon like peptide-1 receptor (GLP-1R) agonist in lipoatrophic diabetes, using mice with generalised lipodystrophy.
Methods
Lipodystrophic insulin resistant and glucose intolerant seipin knockout mice were treated with the GLP-1R agonist liraglutide either acutely preceding analyses of insulin and glucose tolerance or chronically prior to metabolic phenotyping and ex vivo studies.
Results
Acute liraglutide treatment significantly improved insulin, glucose and pyruvate tolerance. Once daily injection of seipin knockout mice with liraglutide for 14 days led to significant improvements in hepatomegaly associated with steatosis and reduced markers of liver fibrosis. Moreover, liraglutide enhanced insulin secretion in response to glucose challenge with concomitantly improved glucose control.
Conclusions
GLP-1R agonist liraglutide significantly improved lipoatrophic diabetes and hepatic steatosis in mice with generalised lipodystrophy. This provides important insights regarding the benefits of GLP-1R agonists for treating lipodystrophy, informing more widespread use to improve the health of individuals with this condition.
... In the absence of ER-LD contact site proteins like Seipin, lipid droplets show significant morphological abnormalities and alterations in their proteome [11,12]. In mammals, Seipin deficiency leads to increased lipolysis and marked loss of adipocytes, which can be partially rescued by the suppression of the lipase ATGL that is homologous to Drosophila Brummer [37,38]. Thus, disruption of LD biogenesis can eventually lead to LD loss due to increased triglyceride catabolism. ...
Lipid dyshomeostasis has been implicated in a variety of diseases ranging from obesity to neurodegenerative disorders such as Neurodegeneration with Brain Iron Accumulation (NBIA). Here, we uncover the physiological role of Nazo, the Drosophila melanogaster homolog of the NBIA-mutated protein–c19orf12, whose function has been elusive. Ablation of Drosophila c19orf12 homologs leads to dysregulation of multiple lipid metabolism genes. nazo mutants exhibit markedly reduced gut lipid droplet and whole-body triglyceride contents. Consequently, they are sensitive to starvation and oxidative stress. Nazo is required for maintaining normal levels of Perilipin-2, an inhibitor of the lipase–Brummer. Concurrent knockdown of Brummer or overexpression of Perilipin-2 rescues the nazo phenotype, suggesting that this defect, at least in part, may arise from diminished Perilipin-2 on lipid droplets leading to aberrant Brummer-mediated lipolysis. Our findings potentially provide novel insights into the role of c19orf12 as a possible link between lipid dyshomeostasis and neurodegeneration, particularly in the context of NBIA.
... Examination of mouse embryonic fibroblasts and stromal vascular cells from global and adipose tissue-specific SKO mice revealed uncontrolled lipolysis was present and responsible for the failure of terminal adipocyte differentiation. [36][37][38] This was found to be due to uncontrolled cyclic AMP-dependent protein kinase A-activated lipolysis, leading to lipid droplet depletion and the down-regulation of the adipogenic transcription cascade. Intriguingly, Chen and colleagues revealed that inhibition of lipolysis was able to correct defects in adipogenesis in vitro, an effect that was not replicated with the use of a peroxisome proliferator-activated receptor gamma agonist, the master regulator of adipogenesis. ...
... Intriguingly, Chen and colleagues revealed that inhibition of lipolysis was able to correct defects in adipogenesis in vitro, an effect that was not replicated with the use of a peroxisome proliferator-activated receptor gamma agonist, the master regulator of adipogenesis. 36 In 2019, additional research from the Chen laboratory confirmed that pharmacological inhibition of lipolysis, using Atglistatin, could rescue adipocyte differentiation in vitro. They also revealed that genetic inactivation of lipolysis in vivo was able to rescue lipodystrophy in SKO mice. ...
Aims:
Lipodystrophy is a rare disorder characterised by abnormal or deficient adipose tissue formation and distribution. It poses significant challenges to affected individuals, including 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 highlight 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 researchers, 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.
... This observation could support the hypothesis that BSCL2 plays a crucial role during adipogenesis. BSCL2, through the cAMP/PKA pathway, participates in regulating the processes in WAT and the differentiation and maintenance of adipocytes [32]. Zhou et al. [33] suggest that in vivo BSCL2 controls, at least to some extent, the adipogenesis process through the enzyme ATGL (adipose triglyceride lipase), which is involved in the initial phase of lipogenesis. ...
... Moreover, the present study found that the expression of particular BSCL2 isoforms in SAT varied dependent on fat deposition level. Regarding BSCL2 mutations investigated in the present study, two missense variants (rs330154033 and rs81333153) are located in the IPR009617 protein domain, which is the seipin family domain, whose primary function is to control the adipogenesis process by regulating lipolysis in a cell-independent manner [32]. Therefore, these mutations can play a crucial role in the proper function of BSCL2 protein; in addition, one of them (rs330154033) was defined by SIFT and GERP as highly unfavorable or deleterious. ...
Simple Summary
The study evaluated the mutation effects of BSCL2 variants on slaughter and fattening characteristics and meat quality traits. These mutations were selected based on variant calling analysis and χ test results within subcutaneous fat RNA-seq data. Potential genetic markers revealed significant genotype/allele distribution variations between high- and low-fat pigs. We suggested that the proposed variant calling derived from RNA-seq data might help develop genetic markers for complex pig traits. The results pinpoint that the selection of the BSCL2 G allele (rs341493267) could increase backfat thickness in pigs. In addition, observed polymorphisms also affected meat percentage, loin mass, and eye area.
Abstract
BSCL2 encodes seipin, a transmembrane endoplasmic reticulum protein associated with lipodystrophy and severe metabolic complications, including diabetes and hepatic steatosis. In pigs, BSCL2 expression increases during adipocyte differentiation. In the present study, we identified significant gene variants associated with fat deposition (FD)-related processes based on subcutaneous fat tissue RNA-seq data. In the association study, to prove our hypothesis, three Polish pig breeds were included: Złotnicka White (ZW, n = 72), Polish Landrace (PL, n = 201), and Polish Large White (PLW, n = 169). Based on variant calling analysis and χ² tests, BSCL2 mutations showing significantly different genotype/allele distribution between high- and low-fat pigs were selected for a comprehensive association study. Four interesting BSCL2 variants (rs346079334, rs341493267, rs330154033, and rs81333153) belonging to downstream and missense mutations were investigated. Our study showed a significant decrease in minor allele frequency for two BSCL2 variants (rs346079334 and rs341493267) in PL pigs in 2020–2021. In ZW, BSCL2 mutations significantly affected loin and ham fats, meat redness, and growth performance traits, such as feed conversion and daily feed intake. Similar observations were noted for PLW and PL, where BSCL2 mutations influenced fat depositions and meat traits, such as loin eye area, loin mass and fat, carcass yield, and growth performance traits. Based on the observation in pigs, our study supports the theory that BSCL2 expressed in subcutaneous fat is involved in the FD process.
... Animal studies were performed in accordance with the National Institutes of Health guidelines, and all procedures were approved by the institutional animal care and use committee of VA Palo Alto Health Care System. Bscl2 f/f mice on a C57BL/6J background in which exon 3 of mouse Bscl2 gene and its flanking intronic region was flanked by two loxP sites were generated as previously described (16). Deletion of exon 3 not only removes a portion of the coding gene but also leads to a frameshift mutation generating a premature stop codon one amino acid after the presumed exon skipping (16). ...
... Bscl2 f/f mice on a C57BL/6J background in which exon 3 of mouse Bscl2 gene and its flanking intronic region was flanked by two loxP sites were generated as previously described (16). Deletion of exon 3 not only removes a portion of the coding gene but also leads to a frameshift mutation generating a premature stop codon one amino acid after the presumed exon skipping (16). The animals carrying the floxed Bscl2 were crossed with transgenic mice expressing Cre recombinase under control of the Cyp11a1 promoter on a C57BL/6J background, obtained from Jackson Laboratories (stock number: 010988). ...
Cholesteryl ester-rich lipid droplets accumulate in steroidogenic tissues under physiological conditions and constitute an important source of cholesterol as the precursor for the synthesis of all steroid hormones. The mechanisms specifically involved in cholesteryl ester-rich lipid droplet formation have not been directly studied and are assumed by most to occur in a fashion analogous to triacylglycerol-rich lipid droplets. Seipin is an ER protein that forms oligomeric complexes at ER-lipid droplet contact sites, and seipin deficiency results in severe alterations in lipid droplet maturation and morphology as seen in Berardinelli-Seip congenital lipodystrophy type 2. While seipin is critical for triacylglycerol-rich lipid droplet formation, no studies have directly addressed whether seipin is important for cholesteryl ester-rich lipid droplet biogenesis. To address this issue, mice with deficient expression of seipin specifically in adrenal, testis and ovary, steroidogenic tissues that accumulate cholesteryl ester-rich lipid droplets under normal physiological conditions were generated. We found that the steroidogenic-specific seipin deficient mice displayed a marked reduction in lipid droplet and cholesterol/cholesteryl ester accumulation in the adrenals, demonstrating the pivotal role of seipin in cholesteryl ester-rich lipid droplet accumulation/formation. Moreover, the reduction in cholesteryl ester-rich lipid droplets was associated with significant defects in adrenal and gonadal steroid hormone production that could not be completely reversed by addition of exogenous lipoprotein cholesterol. We conclude that seipin has a heretofore unappreciated role in intracellular cholesterol trafficking.
... [4][5][6] The most severe form of lipodystrophy is CGL type 2 (CGL2), which is caused by mutations affecting BSCL2/seipin. 7 Multiple groups have generated seipin knockout (SKO) mouse models, [8][9][10][11] which broadly recapitulate the metabolic phenotype observed in patients with CGL2. Previous studies have revealed that the restoration of adipose tissue is sufficient to reverse metabolic disease in SKO mice. ...
... Weight gain in wild-type (WT) and AAV-EGFP mice increased 25%-30% compared with levels prior to AAV administration, and no significant differences were observed. This has been observed previously [8][9][10][11] and is likely attributable to increased hepatomegaly/lean mass gain observed in SKO mice. In contrast, AAV-hBSCL2 mice gained less weight, which became apparent 3 weeks post-treatment, with significant differences observed in AAV-hBSCL2 compared with WT and AAV-EGFP from 8 and 14 weeks, respectively ( Figure 2A). ...
... Gene therapy prevents hepatomegaly and restores WAT development AAV-EGFP mice had significantly increased liver weights compared with WT controls, as expected given the substantial hepatic steatosis known to occur in this model of CGL2, mimicking the human condition. [8][9][10][11] Liver weights in AAV-hBSCL2 mice were significantly decreased compared with AAV-EGFP 19 weeks after AAV-hBSCL2 injection. H&E staining also appeared to indicate lower lipid accumulation within the livers of AAV-hBSCL2 compared with AAV-eGFP. ...
Congenital generalised lipodystrophy type 2 is a serious multisystem disorder with limited treatment options. It is caused by mutations affecting the BSCL2 gene, which encodes the protein seipin. Patients with congenital generalised lipodystrophy type 2 lack both metabolic and mechanical adipose tissue and develop severe metabolic complications including hepatic steatosis, lipoatrophic diabetes and cardiovascular disease. Gene therapies are becoming viable treatments, helping to alleviate inherited and acquired human disorders. We aimed to determine whether gene therapy could offer an effective form of medical intervention for lipodystrophy. We examined whether systemic adeno-associated virus delivery of human BSCL2 could reverse metabolic disease in seipin knockout mice, where white adipose tissue is absent. We reveal adeno-associated virus gene therapy targets adipose progenitor cells in vivo and substantially restores white adipose tissue development in adult seipin knockout mice. This resulted in both rapid and prolonged beneficial effects to metabolic health in this pre-clinical mouse model of congenital generalised lipodystrophy type 2. Hyperglycaemia was normalised within two weeks post-treatment, together with normalisation of severe insulin resistance. We propose that gene therapy offers great potential as a therapeutic strategy to correct multiple metabolic complications in patients with congenital lipodystrophy.
... Interestingly, the muscular phenotype that we describe here is unique to this mouse among lipodystrophic models. Across mouse models where lean mass has been reported, none exhibit a deficit (Chen et al., 2012;Cortes et al., 2009;Guo et al., 2012). This aligns with lipodystrophy in humans which is not typically characterized by a loss of lean mass (Akinci et al., 2017;Figure 8. Exogenous leptin treatment increases muscle protein synthesis in vivo but not ex vivo A, seven days of leptin injections partially rescues mass of FF EDL and gastrocnemius muscles (red) compared with saline treated FF (grey) and WT littermate controls (white). ...
Adipose tissue secretes numerous cytokines (termed ‘adipokines’) that have known or hypothesized actions on skeletal muscle. The majority of adipokines have been implicated in the pathological link between excess adipose and muscle insulin resistance, but approximately half also have documented in vitro effects on myogenesis and/or hypertrophy. This complexity suggests a potential dual role for adipokines in the regulation of muscle mass in homeostasis and the development of pathology. In this study, we used lipodystrophic ‘fat‐free’ mice to demonstrate that adipose tissue is indeed necessary for the development of normal muscle mass and strength. Fat‐free mice had significantly reduced mass (∼15%) and peak contractile tension (∼20%) of fast‐twitch muscles, a slowing of contractile dynamics and decreased cross‐sectional area of fast twitch fibres compared to wild‐type littermates. These deficits in mass and contractile tension were fully rescued by reconstitution of ∼10% of normal adipose mass, indicating that this phenotype is the direct consequence of absent adipose. We then showed that the rescue is solely mediated by the adipokine leptin, as similar reconstitution of adipose from leptin‐knockout mice fails to rescue mass or strength. Together, these data indicate that the development of muscle mass and strength in wild‐type mice is dependent on adipose‐secreted leptin. This finding extends our current understanding of the multiple roles of adipokines in physiology as well as disease pathophysiology to include a critical role for the adipokine leptin in muscle homeostasis. image
Key points
Adipose‐derived cytokines (adipokines) have long been implicated in the pathogenesis of insulin resistance in obesity but likely have other under‐appreciated roles in muscle physiology.
Here we use a fat‐free mouse to show that adipose tissue is necessary for the normal development of muscle mass and strength.
Through add‐back of genetically modified adipose tissue we show that leptin is the key adipokine mediating this regulation.
This expands our understanding of leptin's role in adipose–muscle signalling to include development and homeostasis and adds the surprising finding that leptin is the sole mediator of the maintenance of muscle mass and strength by adipose tissue.
... While ketosis (outside of diabetic ketoacidosis) is not a known feature of FRDA, we reasoned that the relative deficiency of OXCT1 might elevate blood ketones in selected situations. We identified two siblings with FRDA who exhibit recurrent ketosis when exposed to a high-fat diet found in both patients suggest that relative deficiency of seipin, which leads to dysregulated fatty acid breakdown and dysfunction in the initial steps in lipid droplet synthesis (23)(24), could contribute to their overall phenotype in combination with other aspects of FRDA. Fibroblasts from patient 1 had an 80% decrease in seipin levels compared to control while buccal cells had a 30% decrease in such levels. ...
Friedreich's ataxia (FRDA) is an autosome recessive neurodegenerative disease caused by the deficiency of mitochondrial protein frataxin which plays a crucial role in iron-sulphur cluster formation and ATP production. The cellular function of frataxin is not entirely known. Here, we demonstrate that frataxin controls ketone body metabolism through regulation of 3-Oxoacid CoA-Transferase 1 (OXCT1), a rate limiting enzyme catalyzing the conversion of ketone bodies to aceto-acetyl-CoA that is then fed into the Krebs cycle. Biochemical studies show a physical interaction between frataxin and OXCT1 both in vivo and in vitro. Frataxin overexpression also increases OXCT1 protein levels in human skin fibroblasts while frataxin deficiency decreases OXCT1 in multiple cell types including cerebellum and skeletal muscle both acutely and chronically, suggesting that frataxin directly regulates OXCT1. This regulation is mediated by frataxin-dependent suppression of ubiquitin-proteasome system-dependent OXCT1 degradation. Concomitantly, plasma ketone bodies are significantly elevated in frataxin deficient knock-in/knockout (KIKO) mice with no change in the levels of other enzymes involved in ketone body production. In addition, ketone bodies fail to be metabolized to acetyl-CoA accompanied by increased succinyl-CoA in vitro in frataxin deficient cells, suggesting that ketone body elevation is caused by frataxin-dependent reduction of OXCT1 leading to deficits in tissue utilization of ketone bodies. Considering the potential role of metabolic abnormalities and deficiency of ATP production in FRDA, our results suggest a new role for frataxin in ketone body metabolism and also suggest modulation of OXCT1 may be a potential therapeutic approach for FRDA.
... This phenomenon is only observed during the early stage of seipin loss because there are rare TAGs left after this period [43,45,46]. Elevated adipose triglyceride lipase (ATGL) stability and expression, increased phosphorylation of hormone-sensitive lipase (HSL) and perilipin 1 (PLIN1) contribute to seipin deficiency-induced lipolysis acceleration [47,48]. Additionally, seipin has been found to participate in maintaining metabolic homeostasis via recruiting remodelling actin cytoskeleton of adipocytes [49], protecting mature adipocyte tissue [44,46], and restricting lipogenesis as well as LD accumulation in non-adipocyte tissue [50]. ...
Seipin, a protein encoded by the Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) gene, is famous for its key role in the biogenesis of lipid droplets and type 2 congenital generalised lipodystrophy (CGL2). BSCL2 gene mutations result in genetic diseases including CGL2, progressive encephalopathy with or without lipodystrophy (also called Celia’s encephalopathy), and BSCL2-associated motor neuron diseases. Abnormal expression of seipin has also been found in hepatic steatosis, neurodegenerative diseases, glioblastoma stroke, cardiac hypertrophy, and other diseases. In the current study, we comprehensively summarise phenotypes, underlying mechanisms, and treatment of human diseases caused by BSCL2 gene mutations, paralleled by animal studies including systemic or specific Bscl2 gene knockout, or Bscl2 gene overexpression. In various animal models representing diseases that are not related to Bscl2 mutations, differential expression patterns and functional roles of seipin are also described. Furthermore, we highlight the potential therapeutic approaches by targeting seipin or its upstream and downstream signalling pathways. Taken together, restoring adipose tissue function and targeting seipin-related pathways are effective strategies for CGL2 treatment. Meanwhile, seipin-related pathways are also considered to have potential therapeutic value in diseases that are not caused by BSCL2 gene mutations.
