Molecular characterization of the grass carp bscl2 gene and its expression response to lipid accumulation, nutritional status, insulin and glucagon.

Bscl2 plays a role in lipid metabolism of mammals, however its role in teleost fish remains unclear. Using the grass carp (Ctenopharyngodon idella) as a model, the bscl2 gene was isolated from the brain and characterized. Thereafter, the tissue distribution of the gene was examined, before expression was analyzed as a function of fasting, refeeding, oral glucose administration and overfeeding. In addition, bscl2 mRNA levels were evaluated in grass carp primary hepatocytes treated with glucagon, insulin, oleic acid, and glucose. Results showed that the cloned bscl2 gene was 1341 bp, encoding 446 amino acids, and was highly expressed in the brain, heart, and gonad. Following oral glucose administration, bscl2 expression increased. Expression of bscl2 decreased in fasted fish but increased following refeeding. Overfeeding, which resulted in elevated lipid accumulation, also stimulated bscl2 expression. In primary hepatocytes, bscl2 levels were increased by glucose, oleic acid, and insulin treatments, and reduced by glucagon treatment. These data suggest that bscl2 may play an important role in nutrient metabolism in teleost fish.

A murine model of BSCL2-associated Celia's encephalopathy.

Celia's encephalopathy or progressive encephalopathy with/without lipodystrophy is a neurodegenerative disease with a fatal prognosis in childhood. It is generally caused by the c.985C > T variant in the BSCL2 gene, leading to the skipping of exon 7 and resulting in an aberrant seipin protein (Celia-seipin). To precisely define the temporal evolution and the mechanisms involved in neurodegeneration, lipodystrophy and fatty liver in Celia's encephalopathy, our group has generated the first global knock-in murine model for the aberrant human transcript of BSCL2 (Bscl2Celia/Celia) using a strategy based on the Cre/loxP recombination system. In order to carry out a characterization at the neurological, adipose tissue and hepatic level, behavioral studies, brain PET, metabolic, histological and molecular studies were performed. Around 12% of homozygous and 5.4% of heterozygous knock-in mice showed severe neurological symptoms early in life, and their life expectancy was dramatically reduced. Severe generalized lipodystrophy and mild hepatic steatosis were present in these affected animals, while serum triglycerides and glucose metabolism were normal, with no insulin resistance. Furthermore, the study revealed a reduction in brain glucose uptake, along with patchy loss of Purkinje cells and the presence of intranuclear inclusions in cerebellar cortex cells. Homozygous, non-severely-affected knock-in mice showed a decrease in locomotor activity and greater anxiety compared with their wild type littermates. Bscl2Celia/Celia is the first murine model of Celia's encephalopathy which partially recapitulates the phenotype and severe neurodegenerative picture suffered by these patients. This model will provide a helpful tool to investigate both the progressive encephalopathy with/without lipodystrophy and congenital generalized lipodystrophy.

The Effect of BSCL2 Gene on Fat Deposition Traits in Pigs.

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: Zlotnicka 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.

Metreleptin Treatment in a Boy with Congenital Generalized Lipodystrophy due to Homozygous c.465_468delGACT (p.T156Rfs*8) Mutation in the BSCL2 Gene: Results From the First-year

Congenital generalized lipodystrophy (CGL) is a rare, autosomal recessive disorder characterized by an almost complete absence of body fat. In CGL, patients may have hyperphagia due to leptin deficiency. Recombinant human leptin (metreleptin) has been suggested as an effective treatment option. We present successful treatment with metreleptin in a boy with CGL and results from the first year of follow-up. An eight-month-old boy presented with excessive hair growth and a muscular appearance. On examination he had hypertrichosis, decreased subcutaneous adipose tissue over the whole body and hepatomegaly. Laboratory investigations revealed hypertriglyceridemia, hyperinsulinemia, elevated liver transaminases and low leptin levels. Molecular genetic analysis detected a homozygous, c.465_468delGACT (p.T156Rfs*8) mutation in the BSCL2 gene. A diagnosis of CGL type 2 was considered. Despite dietary intervention, exercise, and treatment with additional omega-3 and metformin, the hypertriglyceridemia, hyperinsulinemia, and elevated liver transaminase levels worsened. Metreleptin treatment was started and after one year hyperphagia had disappeared, and there was dramatic improvement in levels of insulin, hemoglobin A1c, triglycerides and liver transaminases. Hepatosteatosis was lessened and hepatosplenomegaly was much improved. Metreleptin appears to be an effective treatment option in children with CGL that remarkably improved metabolic complications in the presented case. Initiation of metreleptin treatment in the early period may decrease mortality and morbidity, and increase the quality of life in children with CGL.

Features of BSCL2 related congenital generalized lipodystrophy in China: long-term follow-up of three patients and literature review.

OBJECTIVES: Congenital generalized lipodystrophy (CGL) is a group of rare autosomal inherited diseases characterized by a widespread loss of adipose tissue. The main purpose of this study was to evaluate the features of Chinese patients with CGL2. METHODS: Three patients diagnosed with CGL2 from our center were reviewed. Data on clinical features, results of laboratory analyses, and previous treatments were retrospectively collected. This study also reviewed studies that reported patients diagnosed with CGL2 in the last 30 years. RESULTS: All patients presented a lack of subcutaneous fat, hypertriglyceridemia, reversed triangular faces, acanthosis nigricans, and hepatomegaly within the first six months of life. All three patients developed splenomegaly, and mental retardation in later life. Dietary control dramatically lowered triglyceride levels in all patients. One patient presented with diabetes mellitus at 1 year-old. Although combined therapy with low fat diet and metformin maintained normal levels of blood lipid and glucose, this patient developed hypertrophic cardiomyopathy at the age of three. By a literature review on all Chinese cases with CGL2, it is known that classic manifestations such as hypertriglyceridemia, hepatomegaly and diabetes mellitus can occur shortly after birth, and early diagnosis and treatment can improve quality of life. In this cohort, the most frequent variations are c.782dupG and c.974dup in the BSCL2 gene. However, the same genotype may have different clinical phenotypes in patients with CGL2. CONCLUSIONS: This study not only described the clinical and genetic features of three patients with CGL2 in China, but also reviewed literature about CGL2 around the world.

A study of congenital generalized lipodystrophy (CGL) caused by BSCL2 gene mutation.

Congenital generalized lipodystrophy (CGL) is an extremely rare genetic disease mainly characterized by absence of whole-body adipose tissue and metabolic dysfunctions such as insulin resistance, diabetes mellitus, hypertriglyceridemia, hepatic steatosis, and acanthosis nigricans. In this study, we reported a novel case of a young woman patient with CGL. The patient came to the hospital for early-onset lipodystrophy and diabetes. She was 19-year-old with a height of 160 cm, a weight of 46 kg, BMI of 17.9 kg/m2, and a serum leptin level of 0.14 µg/L. Genomic DNA was extracted from blood samples of the patient and her family members, including her mother, father and brother. Genetic analysis revealed compound heterozygous mutations of the BSCL2 gene (c.560A>G and c.565G>T) in the patient. Her father carried a heterozygous mutation (c.565G>T), and her mother carried a heterozygous mutation (c.560A>G) in the BSCL2 gene. The mutant p.Y187C plasmid was transfected into HEK293T cells. The protein expression of SEIPIN and its interaction with glycerol-3-phosphate acyltransferase (GPAT3) were observed to be reduced. In addition, based on primary cultured skin fibroblasts from the patient, SEIPIN protein was decreased, and lipid droplets were much smaller when fatty acid was stimulated compared with those observed from healthy subject controls. However, histone deacetylase inhibitors (HDACis) was found capable of rescuing SEIPIN protein in fibroblasts of the patient. In addition, we further summarized and discussed gene mutations of BSCL2 reported in the current literature. Collectively, these findings have expanded the clinical phenotype and pathogenic gene spectrum of CGL, which might help clinicians to achieve better management of lipodystrophy.

Gene therapy restores adipose tissue and metabolic health in a pre-clinical mouse model of lipodystrophy.

Congenital generalized 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 generalized 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 that 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 generalized lipodystrophy type 2. Hyperglycemia was normalized within 2 weeks post-treatment together with normalization 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.

Role of Seipin in Human Diseases and Experimental Animal Models.

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.

BSCL2/Seipin deficiency in hearts causes cardiac energy deficit and dysfunction via inducing excessive lipid catabolism.

BACKGROUND: Heart failure (HF) is one of the leading causes of death worldwide and is associated with cardiac metabolic perturbations. Human Type 2 Berardinelli-Seip Congenital Lipodystrophy (BSCL2) disease is caused by mutations in the BSCL2 gene. Global lipodystrophic Bscl2-/- mice exhibit hypertrophic cardiomyopathy with reduced cardiac steatosis. Whether BSCL2 plays a direct role in regulating cardiac substrate metabolism and/or contractile function remains unknown. METHODS: We generated mice with cardiomyocyte-specific deletion of Bscl2 (Bscl2cKO ) and studied their cardiac substrate utilisation, bioenergetics, lipidomics and contractile function under baseline or after either a treatment regimen using fatty acid oxidation (FAO) inhibitor trimetazidine (TMZ) or a prevention regimen with high-fat diet (HFD) feeding. Mice with partial ATGL deletion and cardiac-specific deletion of Bscl2 were also generated followed by cardiac phenotyping. RESULTS: Different from hypertrophic cardiomyopathy in Bscl2-/- mice, mice with cardiac-specific deletion of Bscl2 developed systolic dysfunction with dilation. Myocardial BSCL2 deletion led to elevated ATGL expression and FAO along with reduced cardiac lipid contents. Cardiac dysfunction in Bscl2cKO mice was independent of mitochondrial dysfunction and oxidative stress, but associated with decreased metabolic reserve and ATP levels. Importantly, cardiac dysfunction in Bscl2cKO mice could be partially reversed by FAO inhibitor TMZ, or prevented by genetic abolishment of one ATGL allele or HFD feeding. Lipidomic analysis further identified markedly reduced glycerolipids, glycerophospholipids, NEFA and acylcarnitines in Bscl2cKO hearts, which were partially normalised by TMZ or HFD. CONCLUSIONS: We identified a new form of cardiac dysfunction with excessive lipid utilisation which ultimately causes cardiac substrate depletion and bioenergetics failure. Our findings also uncover a crucial role of BSCL2 in controlling cardiac lipid catabolism and contractile function and provide novel insights into metabolically treating energy-starved HF using FAO inhibitor or HFD.

The neonatal onset diabetes mellitus of Chinese neonate with congenital generalized lipodystrophy 2: a case report.

BACKGROUND: Congenital generalized lipodystrophy (CGL) is a clinically heterogeneous disorder characterized by near total absence of adipose tissue along with metabolic complications. Diabetes mellitus developed from CGL usually present between ages 15 and 20 years, and there are few reports in neonate. CASE PRESENTATION: In this report, we described a rare clinical presentation of CGL in a 12-day-old Chinese female neonates with hyperglycemia, hyperlipidemia, and subsequently appeared diabetes, hepatomegaly and fatty liver. The two clinical-exome sequencing identified heterozygous null mutations (c.793C > T and c.565G > T) in BSCL2 gene which was inherited from father and mother respectively. To date, it was the firstly reported CGL patient with neonatal onset diabetes. The neonate was treated with antibiotic, insulin and deeply hydrolyzed formula milk to significantly decrease FBG and serum trigylcerides levels.  CONCLUSIONS: Our case report analyzes the causes of early onset diabetes may relate with the locus of BSCL2 gene mutations and infection induction. It also suggests the importance of early identification, genetic analysis, and symptomatic treatment in the CGL, which are essential for improving the prognosis of children.

A De Novo BSCL2 Gene S90L Mutation in a Progressive Tetraparesis with Urinary Dysfunction and Corpus Callosum Involvement.

A Silver syndrome is a rare autosomal dominant spastic paraparesis in which spasticity of the lower limbs is accompanied by amyotrophy of the small hand muscles. The causative gene is the Berardinelli-Seip congenital lipodystrophy 2 ( BSCL2) , which is related to a spectrum of neurological phenotypes. In the current study, we presented a 14-year-old male with a slowly progressive spastic paraparesis with urinary incontinence that later on exhibited atrophy and weakness in the thenar and dorsal interosseous muscles. Magnetic resonance imaging (MRI) revealed discrete atrophy of the corpus callosum isthmus and an extended next-generation sequencing panel identified a de novo heterozygous mutation in BSCL2 gene, c.269C > T p.(S90L). Various clinical expression and incomplete penetrance of BSCL2 gene mutations complicate the establishment of a genetic etiology for these cases. Therefore, Silver syndrome should be included in the differential diagnosis if the initial presentation is a spastic paraparesis by urinary involvement with childhood-onset, even with MRI atypical findings. This report described the first Iberian Silver syndrome case carrying a de novo c.269C > T p. (S90L) BSCL2 gene mutation.

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

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

Lipid Droplet Contact Sites in Health and Disease.

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

Bscl2 Deficiency Does Not Directly Impair the Innate Immune Response in a Murine Model of Generalized Lipodystrophy.

Congenital Generalized Lipodystrophy type 2 (CGL2) is the most severe form of lipodystrophy and is caused by mutations in the BSCL2 gene. Affected patients exhibit a near complete lack of adipose tissue and suffer severe metabolic disease. A recent study identified infection as a major cause of death in CGL2 patients, leading us to examine whether Bscl2 loss could directly affect the innate immune response. We generated a novel mouse model selectively lacking Bscl2 in the myeloid lineage (LysM-B2KO) and also examined the function of bone-marrow-derived macrophages (BMDM) isolated from global Bscl2 knockout (SKO) mice. LysM-B2KO mice failed to develop lipodystrophy and metabolic disease, providing a model to study the direct role of Bscl2 in myeloid lineage cells. Lipopolysaccharide-mediated stimulation of inflammatory cytokines was not impaired in LysM-B2KO mice or in BMDM isolated from either LysM-B2KO or SKO mice. Additionally, intracellular fate and clearance of bacteria in SKO BMDM challenged with Staphylococcus aureus was indistinguishable from that in BMDM isolated from littermate controls. Overall, our findings reveal that selective Bscl2 deficiency in macrophages does not critically impact the innate immune response to infection. Instead, an increased susceptibility to infection in CGL2 patients is likely to result from severe metabolic disease.

Exercise Increases Bone in SEIPIN Deficient Lipodystrophy, Despite Low Marrow Adiposity.

Exercise, typically beneficial for skeletal health, has not yet been studied in lipodystrophy, a condition characterized by paucity of white adipose tissue, with eventual diabetes, and steatosis. We applied a mouse model of global deficiency of Bscl2 (SEIPIN), required for lipid droplet formation. Male twelve-week-old B6 knockouts (KO) and wild type (WT) littermates were assigned six-weeks of voluntary, running exercise (E) versus non-exercise (N=5-8). KO weighed 14% less than WT (p=0.01) and exhibited an absence of epididymal adipose tissue; KO liver Plin1 via qPCR was 9-fold that of WT (p=0.04), consistent with steatosis. Bone marrow adipose tissue (BMAT), unlike white adipose, was measurable, although 40.5% lower in KO vs WT (p=0.0003) via 9.4T MRI/advanced image analysis. SEIPIN ablation's most notable effect marrow adiposity was in the proximal femoral diaphysis (-56% KO vs WT, p=0.005), with relative preservation in KO-distal-femur. Bone via µCT was preserved in SEIPIN KO, though some quality parameters were attenuated. Running distance, speed, and time were comparable in KO and WT. Exercise reduced weight (-24% WT-E vs WT p<0.001) but not in KO. Notably, exercise increased trabecular BV/TV in both (+31%, KO-E vs KO, p=0.004; +14%, WT-E vs WT, p=0.006). The presence and distribution of BMAT in SEIPIN KO, though lower than WT, is unexpected and points to a uniqueness of this depot. That trabecular bone increases were achievable in both KO and WT, despite a difference in BMAT quantity/distribution, points to potential metabolic flexibility during exercise-induced skeletal anabolism.

Protein Arginine Methyltransferase PRMT5 Regulates Fatty Acid Metabolism and Lipid Droplet Biogenesis in White Adipose Tissues.

The protein arginine methyltransferase 5 (PRMT5) is an emerging regulator of cancer and stem cells including adipogenic progenitors. Here, a new physiological role of PRMT5 in adipocytes and systemic metabolism is reported. Conditional knockout mice were generated to ablate the Prmt5 gene specifically in adipocytes (Prmt5AKO). The Prmt5AKO mice exhibit sex- and depot-dependent progressive lipodystrophy that is more pronounced in females and in visceral (than subcutaneous) white fat. The lipodystrophy and associated energy imbalance, hyperlipidemia, hepatic steatosis, glucose intolerance, and insulin resistance are exacerbated by high-fat-diet. Mechanistically, Prmt5 methylates and releases the transcription elongation factor SPT5 from Berardinelli-Seip congenital lipodystrophy 2 (Bscl2, encoding Seipin) promoter, and Prmt5AKO disrupts Seipin-mediated lipid droplet biogenesis. Prmt5 also methylates Sterol Regulatory Element-Binding Transcription Factor 1a (SREBP1a) and promotes lipogenic gene expression, and Prmt5AKO suppresses SREBP1a-dependent fatty acid metabolic pathways in adipocytes. Thus, PRMT5 plays a critical role in regulating lipid metabolism and lipid droplet biogenesis in adipocytes.

Phenotypic correlations in a large single-center cohort of patients with BSCL2 nerve disorders: a clinical, neurophysiological and muscle magnetic resonance imaging study.

BACKGROUND AND PURPOSE: BSCL2 heterozygote mutations are a common cause of distal hereditary motor neuropathies (dHMNs). A series of BSCL2 patients is presented and clinical, neurophysiological and muscle magnetic resonance imaging (MRI) findings are correlated. METHODS: Twenty-six patients from five families carrying the p.N88S mutation were identified. Age of onset, clinical phenotype (dHMN, Charcot-Marie-Tooth, spastic paraplegia), physical examination, disability measured as a modified Rankin Scale score and neurophysiological findings were collected. A whole body muscle MRI had been performed in 18 patients. The pattern of muscle involvement on T1-weighted and short time inversion recovery sequences was analysed. Hierarchical analysis using heatmaps and an MRI Composite Score were generated. Statistical analysis was carried out with STATA SE v.15 (TX, USA). RESULTS: The mean age was 51.54 ± 19.94 years and 14 patients were men. dHMN was the most common phenotype (50%) and five patients (19.23%) showed no findings on examination. Disease onset was commonly in childhood and disability was low (modified Rankin Scale score 1.34 ± 1.13) although median time since onset of disease was 32 years (range 10-47). Charcot-Marie-Tooth-like patients were more disabled and disability correlated with age. On muscle MRI, thenar eminence, soleus and tibialis anterior were most frequently involved, irrespective of clinical phenotype. MRI Composite Score was strongly correlated with disability. CONCLUSION: Patients with the p.N88S BSCL2 gene mutation are phenotypically variable, although dHMN is most frequent and generally slowly progressive. Muscle MRI pattern is consistent regardless of phenotype and correlates with disease severity, probably serving as a reliable outcome measure for future clinical trials.

Novel compound heterozygous variant of BSCL2 identified by whole exome sequencing and multiplex ligation­dependent probe amplification in an infant with congenital generalized lipodystrophy.

Congenital generalized lipodystrophy (CGL) is a clinically and genetically heterogeneous condition with autosomal recessive inheritance. CGL is classified into four subtypes on the basis of causative genes. This study reported on a 2­month­old male infant diagnosed with CGL with generalized lipoatrophy and skin hyperpigmentation. Whole exome sequencing (WES) identified a heterozygous small insertion (c.545_546insCCG) in Berardinelli­Seip congenital lipodystrophy 2 (BSCL2) that was inherited from the infant's mother. Copy number variation analysis using exome data suggested a heterozygous deletion involving exon 3 that was inherited from the infant's father. This finding was confirmed by multiplex ligation­dependent probe amplification test. Gap­PCR revealed breakpoints and confirmed a 1274 bp heterozygous deletion encompassing exon 3 of BSCL2 (c.213­1081_c.294+111). This deletion is different from the founder 3.3 kb deletion involving exon 3 of BSCL2 in the Peruvian population. An 11­bp microhomology at the breakpoints may mediate the deletion, and its presence indicates the independent origins of the exon 3 deletion between Chinese and Peruvian populations. The present results expanded the mutational spectrum of the BSCL2 gene in the Chinese population and suggested that introns 2 and 3 of BSCL2 are prone to recombination. Thus, exon 3 deletion should be considered for patients with CGL2 when only one BSCL2 variant is detected through WES.

Berardinelli-Seip congenital lipodystrophy 2/SEIPIN determines brown adipose tissue maintenance and thermogenic programing.

OBJECTIVE: Understanding the mechanisms that control brown adipose tissue (BAT) mass and functionality is crucial for our understanding of how the disruption of energy homeostasis leads to obesity. Bernerdinali Seip Congenital Lipodystrophy (BSCL) type 2 (BSCL2, a.k.a. SEIPIN), a lipodystrophy-associated protein, has been shown to not be required for brown adipogenesis, but it has been shown to be essential for perinatal BAT development. However, its role in mature BAT maintenance and thermogenic programing remains poorly understood. METHODS: We subjected Bscl2f/f and Bscl2UCP1-BKO (BKO) mice with a brown adipose-specific loss of BSCL2 through UCP1 promoter-driven Cre to environmental, pharmacological and diet interventions to challenge BAT functionality and reprogramming. We carried out physiological, molecular and transcriptomic analyses of BAT. RESULTS: The deletion of BSCL2 in mature brown adipocytes increased sympathetic nervous system-independent cAMP/protein kinase A (PKA) signaling in BAT. Such activation reduced BAT triglyceride content and mass and was sufficient to reduce plasma triglyceride, but not enough to combat thermoneutral and high fat diet-induced obesity. Surprisingly, BKO mice displayed an impaired response to acute and chronic cold challenges despite cAMP/PKA activation. When subjected to chronic cold exposure or the administration of a ß3-adrenergic agonist, CL 316,243, BKO mice failed to induce BAT recruitment and underwent dramatic brown adipocyte loss. Transcriptomic analysis revealed pathological BAT remodeling with inflammation and fibrosis, which was further exacerbated by a chronic thermogenic challenge in BKO mice. Mechanistically, we found abnormal mitochondrial shapes and function in BAT of BKO mice housed at 21 °C; as well as mitochondrial DNA depletion and necroptotic-mediated brown adipocyte death after chronic thermogenic insult. CONCLUSION: BSCL2-mediated lipid catabolism within BAT is crucial for mature brown adipocyte function and survival both during times of activation and quiescence. BSCL2 is an important regulator of mature brown adipocyte mitochondrial metabolism, necroptosis and thus adaptive thermogenesis.

Clinical features of inherited neuropathy with BSCL2 mutations in Japan.

Heterozygous mutations in the Berardinelli-Seip congenital lipodystrophy 2 (BSCL2) gene have been reported with different clinical phenotypes including Silver syndrome (SS)/spastic paraplegia 17 (SPG17), distal hereditary motor neuropathy type V (dHMN-V), and Charcot-Marie-Tooth (CMT) disease type 2. We screened 407 Japanese patients who were clinically suspected of having CMT by exome sequencing and searched mutations in BSCL2. As a result, we identified five patients with heterozygous mutations in BSCL2. We confirmed three cases of known mutations (p.N88S and p.S90L) and two cases of novel mutations (p.N88T and p.S141A). The clinical features of the cases with known mutations in Japan were similar to those previously reported in other countries. In particular, there were many cases with sensory disturbance. The case with p.N88T mutation showed severe phenotype such as early onset age and prominent vocal cord paresis. The case with p.S141A mutation showed characteristics of demyelinating neuropathy such as CMT disease type 1 by electrophysiological examination. In this article, we report the clinical features and spread of cases with BSCL2 mutation in a Japanese cohort.