Temporal expression pattern of Bardet-Biedl syndrome genes in adipogenesis

Bardet-Biedl syndrome: A focus on genetics, mechanisms and metabolic dysfunction

Bardet-Biedl syndrome (BBS) is a rare, monogenic, multisystem disorder characterized by retinal dystrophy, renal abnormalities, polydactyly, learning disabilities, as well as metabolic dysfunction, including obesity and an increased risk of type 2 diabetes. It is a primary ciliopathy, and causative mutations in more than 25 different genes have been described. Multiple cellular mechanisms contribute to the development of the metabolic phenotype associated with BBS, including hyperphagia as a consequence of altered hypothalamic appetite signalling as well as alterations in adipocyte biology promoting adipocyte proliferation and adipogenesis. Within this review, we describe in detail the metabolic phenotype associated with BBS and discuss the mechanisms that drive its evolution. In addition, we review current approaches to the metabolic management of patients with BBS, including the use of weight loss medications and bariatric surgery. Finally, we evaluate the potential of targeting hypothalamic appetite signalling to limit hyperphagia and induce clinically significant weight loss.

Dietary macronutrient composition impacts gene regulation in adipose tissue

Diet is a key lifestyle component that influences metabolic health through several factors, including total energy intake and macronutrient composition. While the impact of caloric intake on gene expression and physiological phenomena in various tissues is well described, the influence of dietary macronutrient composition on these parameters is less well studied. Here, we use the Nutritional Geometry framework to investigate the role of macronutrient composition on metabolic function and gene regulation in adipose tissue. Using ten isocaloric diets that vary systematically in their proportion of energy from fat, protein, and carbohydrates, we find that gene expression and splicing are highly responsive to macronutrient composition, with distinct sets of genes regulated by different macronutrient interactions. Specifically, the expression of many genes associated with Bardet-Biedl syndrome is responsive to dietary fat content. Splicing and expression changes occur in largely separate gene sets, highlighting distinct mechanisms by which dietary composition influences the transcriptome and emphasizing the importance of considering splicing changes to more fully capture the gene regulation response to environmental changes such as diet. Our study provides insight into the gene regulation plasticity of adipose tissue in response to macronutrient composition, beyond the already well-characterized response to caloric intake.

BBS genes are involved in accelerated proliferation and early differentiation of BBS-related tissues

Bardet-Biedl syndrome (BBS) is an inherited disorder primarily ciliopathy with pleiotropic multi-systemic phenotypic involvement, including adipose, nerve, retinal, kidney, Etc. Consequently, it is characterized by obesity, cognitive impairment and retinal, kidney and cutaneous abnormalities. Initial studies, including ours have shown that BBS genes play a role in the early developmental stages of adipocytes and β-cells. However, this role in other BBS-related tissues is unknown. We investigated BBS genes involvement in the proliferation and early differentiation of different BBS cell types. The involvement of BBS genes in cellular proliferation were studied in seven in-vitro and transgenic cell models; keratinocytes (hHaCaT) and Ras-transfected keratinocytes (Ras-hHaCaT), neuronal cell lines (hSH-SY5Y and rPC-12), silenced BBS4 neural cell lines (siBbs4 hSH-SY5Y and siBbs4 rPC-12), adipocytes (m3T3L1), and ex-vivo transformed B-cells obtain from BBS4 patients, using molecular and biochemical methodologies. RashHaCaT cells showed an accelerated proliferation rate in parallel to significant reduction in the transcript levels of BBS1, 2, and 4. BBS1, 2, and 4 transcripts linked with hHaCaT cell cycle arrest (G1 phase) using both chemical (CDK4 inhibitor) and serum deprivation methodologies. Adipocyte (m3T3-L1) Bbs1, 2 and 4 transcript levels corresponded to the cell cycle phase (CDK4 inhibitor and serum deprivation). SiBBS4 hSH-SY5Y cells exhibited early cell proliferation and differentiation (wound healing assay) rates. SiBbs4 rPC-12 models exhibited significant proliferation and differentiation rate corresponding to Nestin expression levels. BBS4 patients-transformed B-cells exhibited an accelerated proliferation rate (LPS-induced methodology). In conclusions, the BBS4 gene plays a significant, similar and global role in the cellular proliferation of various BBS related tissues. These results highlight the universal role of the BBS gene in the cell cycle, and further deepen the knowledge of the mechanisms underlying the development of BBS.

Adipose Tissue Hyperplasia and Hypertrophy in Common and Syndromic Obesity-The Case of BBS Obesity

Obesity is a metabolic state generated by the expansion of adipose tissue. Adipose tissue expansion depends on the interplay between hyperplasia and hypertrophy, and is mainly regulated by a complex interaction between genetics and excess energy intake. However, the genetic regulation of adipose tissue expansion is yet to be fully understood. Obesity can be divided into common multifactorial/polygenic obesity and monogenic obesity, non-syndromic and syndromic. Several genes related to obesity were found through studies of monogenic non-syndromic obesity models. However, syndromic obesity, characterized by additional features other than obesity, suggesting a more global role of the mutant genes related to the syndrome and, thus, an additional peripheral influence on the development of obesity, were hardly studied to date in this regard. This review summarizes present knowledge regarding the hyperplasia and hypertrophy of adipocytes in common obesity. Additionally, we highlight the scarce research on syndromic obesity as a model for studying adipocyte hyperplasia and hypertrophy, focusing on Bardet-Biedl syndrome (BBS). BBS obesity involves central and peripheral mechanisms, with molecular and mechanistic alternation in adipocyte hyperplasia and hypertrophy. Thus, we argue that using syndromic obesity models, such as BBS, can further advance our knowledge regarding peripheral adipocyte regulation in obesity.

Adipose tissue function and insulin sensitivity in syndromic obesity of Bardet-Biedl syndrome

BACKGROUND

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive syndromic obesity of childhood onset among many other features. To date, the excess risk of metabolic complications of severe early-onset obesity in BBS remains controversial. In-depth investigation of adipose tissue structure and function with detailed metabolic phenotype has not been investigated yet.

OBJECTIVE

To investigate adipose tissue function in BBS.

DESIGN

A prospective cross-sectional study.

MAIN OUTCOME MEASURE

To determine if there are differences in insulin resistance, metabolic profile, adipose tissue function and gene expression in patients with BBS compared to BMI-matched polygenic obese controls.

METHOD

9 adults with BBS and 10 controls were recruited from the national centre for BBS, Birmingham, UK. An in-depth study of adipose tissue structure and function along with insulin sensitivity was performed using hyperinsulinemic-euglycemic clamp studies, adipose tissue microdialysis, histology and RNA sequencing, and measurement of circulating adipokines and inflammatory biomarkers.

RESULTS

Adipose tissue structure, gene expression and in vivo functional analysis between BBS and polygenic obesity cohorts were similar. Using hyperinsulinemic-euglycemic clamp and surrogate markers of insulin resistance, we found no significant differences in insulin sensitivity between BBS and obese controls. Furthermore, no significant changes were noted in an array of adipokines, cytokines, pro-inflammatory markers and adipose tissue RNA transcriptomic.

CONCLUSION

Although childhood-onset extreme obesity is a feature of BBS, detailed studies of insulin sensitivity and adipose tissue structure and function are similar to common polygenic obesity. This study adds to the literature by suggesting that it is the quality and quantity of adiposity not the duration that drives the metabolic phenotype.

A 5′ UTR Mutation Contributes to Down-Regulation of Bbs7 in the Berlin Fat Mouse

The Bardet–Biedl Syndrome 7 (Bbs7) gene was identified as the most likely candidate gene causing juvenile obesity in the Berlin Fat Mouse Inbred (BFMI) line. Bbs7 expression is significantly lower in the brain, adipose tissue, and liver of BFMI mice compared to lean C57BL/6NCrl (B6N) mice. A DNA sequence comparison between BFMI and B6N revealed 16 sequence variants in the Bbs7 promoter region. Here, we tested if these mutations contribute to the observed differential expression of Bbs7. In a cell-based dual-luciferase assay, we compared the effects of the BFMI and the B6N haplotypes of different regions of the Bbs7 promotor on the reporter gene expression. A single-nucleotide polymorphism (SNP) was identified causing a significant reduction in the reporter gene expression. This SNP (rs29947545) is located in the 5′ UTR of Bbs7 at Chr3:36.613.350. The SNP is not unique to BFMI mice but also occurs in several other mouse strains, where the BFMI allele is not associated with lower Bbs7 transcript amounts. Thus, we suggest a compensatory mutation in the other mouse strains that keeps Bbs7 expression at the normal level. This compensatory mechanism is missing in BFMI mice and the cell lines tested.

Loss of the ciliary gene Bbs4 results in defective thermogenesis due to metabolic inefficiency and impaired lipid metabolism

Adipose tissue is central to the regulation of energy balance. While white adipose tissue (WAT) is responsible for triglyceride storage, brown adipose tissue specializes in energy expenditure. Deterioration of brown adipocyte function contributes to the development of metabolic complications like obesity and diabetes. These disorders are also leading symptoms of the Bardet-Biedl syndrome (BBS), a hereditary disorder in humans which is caused by dysfunctions of the primary cilium and which therefore belongs to the group of ciliopathies. The cilium is a hair-like organelle involved in cellular signal transduction. The BBSome, a supercomplex of several Bbs gene products, localizes to the basal body of cilia and is thought to be involved in protein sorting to and from the ciliary membrane. The effects of a functional BBSome on energy metabolism and lipid mobilization in brown and white adipocytes were tested in whole-body Bbs4 knockout mice that were subjected to metabolic challenges. Chronic cold exposure reveals cold-intolerance of knockout mice but also ameliorates the markers of metabolic pathology detected in knockouts prior to cold. Hepatic triglyceride content is markedly reduced in knockout mice while circulating lipids are elevated, altogether suggesting that defective lipid metabolism in adipose tissue creates increased demand for systemic lipid mobilization to meet energetic demands of reduced body temperatures. These findings taken together suggest that Bbs4 is essential for the regulation of adipose tissue lipid metabolism, representing a potential target to treat metabolic disorders.

Potential Roles of O-GlcNAcylation in Primary Cilia- Mediated Energy Metabolism

The primary cilium, an antenna-like structure on most eukaryotic cells, functions in transducing extracellular signals into intracellular responses via the receptors and ion channels distributed along it membrane. Dysfunction of this organelle causes an array of human diseases, known as ciliopathies, that often feature obesity and diabetes; this indicates the primary cilia's active role in energy metabolism, which it controls mainly through hypothalamic neurons, preadipocytes, and pancreatic β-cells. The nutrient sensor, O-GlcNAc, is widely involved in the regulation of energy homeostasis. Not only does O-GlcNAc regulate ciliary length, but it also modifies many components of cilia-mediated metabolic signaling pathways. Therefore, it is likely that O-GlcNAcylation (OGN) plays an important role in regulating energy homeostasis in primary cilia. Abnormal OGN, as seen in cases of obesity and diabetes, may play an important role in primary cilia dysfunction mediated by these pathologies.

Identification of strong candidate genes for backfat and intramuscular fatty acid composition in three crosses based on the Iberian pig

Meat quality has an important genetic component and can be modified by the fatty acid (FA) composition and the amount of fat contained in adipose tissue and muscle. The present study aimed to find genomic regions associated with the FA composition in backfat and muscle (longissimus dorsi) in 439 pigs with three different genetic backgrounds but having the Iberian breed in common. Genome-wide association studies (GWAS) were performed between 38,424 single-nucleotide polymorphisms (SNPs) covering the pig genome and 60 phenotypic traits related to backfat and muscle FA composition. Nine significant associated regions were found in backfat on the Sus scrofa chromosomes (SSC): SSC1, SSC2, SSC4, SSC6, SSC8, SSC10, SSC12, and SSC16. For the intramuscular fat, six significant associated regions were identified on SSC4, SSC13, SSC14, and SSC17. A total of 52 candidate genes were proposed to explain the variation in backfat and muscle FA composition traits. GWAS were also reanalysed including SNPs on five candidate genes (ELOVL6, ELOVL7, FADS2, FASN, and SCD). Regions and molecular markers described in our study may be useful for meat quality selection of commercial pig breeds, although several polymorphisms were breed-specific, and further analysis would be needed to evaluate possible causal mutations.

Bardet-Biedl syndrome obesity: BBS4 regulates cellular ER stress in early adipogenesis

BACKGROUND

Bardet-Biedl syndrome (BBS) is an autosomal recessive ciliopathy, presenting with early obesity onset. The etiology of BBS obesity involves both central and peripheral defects, through mechanisms mostly yet to be deciphered. We previously showed BBS4 expression in adipogenesis, peaking at day 3 of differentiation. Obesity is characterized by cellular stress which promotes pathological consequences.

AIMS

We set out to test a possible role of BBS4 in adipocyte endoplasmic reticulum (ER) stress-induced unfolding protein response (UPR).

METHODS

BBS4 silenced (SiBBS4) and overexpressing (OEBBS4) pre-adipocyte murine cell lines were subjected to ER-stress induction (Tunicamycin, TM) during adipogenesis. ER-stress UPR was analyzed at the transcript, protein and biochemical levels (microscopy, immunocytochemistry, western blotting, quantitative RT-PCR and X-box binding protein 1 (XBP-1) splicing).

RESULTS

In silico analysis showed that BBS4 harbors an ER localization sequences indicative of ER localization. We verified BBS4's ER localization in adipocytes by immunocytochemistry and cellular protein fractionation. Furthermore, we demonstrated that BBS4 expression is significantly up-regulated by ER-stress, as indicated by protein and transcript levels. SiBBS4 adipocytes exhibited swollen ER typical to ER-stress and significant XBP-1 down-regulation at day 3 of differentiation. Following ER-stress, SiBBS4 adipocytes exhibited XBP-1 ER retention, failure to translocate to the nucleus and depletion of the nuclear active cleaved ATF6α. BBS4 did not alter ATF6α processing by S1P and S2P in the Golgi. Notably, SiBBS4 cells demonstrated significant reduction in the downstream activated phospho-IRE1α, independent of ER-stress.

CONCLUSIONS

At day 3 of adipogenesis, coinciding with the timing of its peak expression, BBS4 is localized to the ER and is involved in the ER stress response and trafficking. BBS4 depletion results in swollen ER with impaired intracellular nucleus translocation of XBP-1 and ATF6α. Thus, BBS4 affects the ER stress response in early adipogenesis, altering ER stress responsiveness and the adipocyte ER phenotype.

Genetic Architecture and Selection of Chinese Cattle Revealed by Whole Genome Resequencing

The bovine genetic resources in China are diverse, but their value and potential are yet to be discovered. To determine the genetic diversity and population structure of Chinese cattle, we analyzed the whole genomes of 46 cattle from six phenotypically and geographically representative Chinese cattle breeds, together with 18 Red Angus cattle genomes, 11 Japanese black cattle genomes and taurine and indicine genomes available from previous studies. Our results showed that Chinese cattle originated from hybridization between Bos taurus and Bos indicus. Moreover, we found that the level of genetic variation in Chinese cattle depends upon the degree of indicine content. We also discovered many potential selective sweep regions associated with domestication related to breed-specific characteristics, with selective sweep regions including genes associated with coat color (ERCC2, MC1R, ZBTB17, and MAP2K1), dairy traits (NCAPG, MAPK7, FST, ITFG1, SETMAR, PAG1, CSN3, and RPL37A), and meat production/quality traits (such as BBS2, R3HDM1, IGFBP2, IGFBP5, MYH9, MYH4, and MC5R). These findings substantially expand the catalogue of genetic variants in cattle and reveal new insights into the evolutionary history and domestication traits of Chinese cattle.

BBS4 regulates the expression and secretion of FSTL1, a protein that participates in ciliogenesis and the differentiation of 3T3-L1

Bardet-Biedl syndrome is a model ciliopathy. Although the characterization of BBS proteins has evidenced their involvement in cilia, extraciliary functions for some of these proteins are also being recognized. Importantly, understanding both cilia and cilia-independent functions of the BBS proteins is key to fully dissect the cellular basis of the syndrome. Here we characterize a functional interaction between BBS4 and the secreted protein FSTL1, a protein linked to adipogenesis and inflammation among other functions. We show that BBS4 and cilia regulate FSTL1 mRNA levels, but BBS4 also modulates FSTL1 secretion. Moreover, we show that FSTL1 is a novel regulator of ciliogenesis thus underscoring a regulatory loop between FSTL1 and cilia. Finally, our data indicate that BBS4, cilia and FSTL1 are coordinated during the differentiation of 3T3-L1 cells and that FSTL1 plays a role in this process, at least in part, by modulating ciliogenesis. Therefore, our findings are relevant to fully understand the development of BBS-associated phenotypes such as obesity.

Insulin regulates Bbs4 during adipogenesis

Bardet-Biedl syndrome (BBS) is a pleiotropic autosomal recessive disorder associated with marked obesity, increased susceptibility to insulin resistance and type 2 diabetes. However, it is unknown whether the link between BBS and diabetes is indirect or direct. Adipogenesis and adipocyte function are regulated by hormonal stimuli, with insulin and insulin growth factor (IGF) playing an important role both in normal and impaired conditions. We have previously shown augmented transcript levels of BBS genes upon induction of adipogenesis. The aim of this study was to investigate the role of insulin in BBS. Through in vitro studies in adipocytes in which Bbs4 expression was either silenced (SiBbs4) or overexpressed (OEBbs4), we showed that insulin and IGF dose- and time-dependently decrease transcription and protein expression of BBS genes during adipogenesis. Silencing of Bbs4 expression in adipocytes significantly impaired and reduced glucose uptake. This effect was reversed by Bbs4 overexpression. Inhibition of PI 3-kinase resulted in upregulation of Bbs transcripts, suggesting that the PI3K pathway is involved in the regulation of these genes. In conclusion, we showed that insulin is a direct regulator of Bbs1, 2, 4 and 6. This hormonal regulation might indicate a metabolic link of these genes to obesity and metabolic syndrome. © 2017 IUBMB Life, 69(7):489-499, 2017.

Bardet-Biedl syndrome: Is it only cilia dysfunction?

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous, pleiotropic disorder, characterized by both congenital and late onset defects. From the analysis of the mutational burden in patients to the functional characterization of the BBS proteins, this syndrome has become a model for both understanding oligogenic patterns of inheritance and the biology of a particular cellular organelle: the primary cilium. Here we briefly review the genetics of BBS to then focus on the function of the BBS proteins, not only in the context of the cilium but also highlighting potential extra-ciliary roles that could be relevant to the etiology of the disorder. Finally, we provide an overview of how the study of this rare syndrome has contributed to the understanding of cilia biology and how this knowledge has informed on the cellular basis of different clinical manifestations that characterize BBS and the ciliopathies.

Metabolic regulation and energy homeostasis through the primary Cilium

Obesity and diabetes represent a significant healthcare concern. In contrast to genome-wide association studies that, some exceptions notwithstanding, have offered modest clues about pathomechanism, the dissection of rare disorders in which obesity represents a core feature have highlighted key molecules and structures critical to energy regulation. Here we focus on the primary cilium, an organelle whose roles in energy homeostasis have been underscored by the high incidence of obesity and type II diabetes in patients and mouse mutants with compromised ciliary function. We discuss recent evidence linking ciliary dysfunction to metabolic defects and we explore the contribution of neuronal and nonneuronal cilia to these phenotypes.

BBS4 directly affects proliferation and differentiation of adipocytes

BBS4 is one of several proteins whose defects cause Bardet-Biedl syndrome (BBS), a multi-systemic disorder, manifesting with marked obesity. BBS4 polymorphisms have been associated with common non-syndromic morbid obesity. BBS4 obesity molecular mechanisms, and the role of the BBS4 gene in adipocyte differentiation and function are not entirely known. We now show that Bbs4 plays a direct and essential role in proliferation and adipogenesis: silencing of Bbs4 in 3T3F442A preadipocytes induced accelerated cell division and aberrant differentiation, evident through morphologic studies (light, scanning and transmission electron microscopy), metabolic analyses (fat accumulation, fatty acid profile and lipolysis) and adipogenic markers transcripts (Cebpα, Pparγ, aP2, ADRP, Perilipin). Throughout adipogenesis and when challenged with fat load, Bbs4 silenced cells accumulate significantly more triglycerides than control adipocytes, albeit in smaller (yet greater in number) droplets containing modified fatty acid profiles. Thus, greater fat accumulation in the silenced cells is a consequence of both a higher rate of adipocyte proliferation and of aberrant differentiation leading to augmented aberrant accumulation of fat per cell. Our findings suggest that the BBS obesity might be partly due to a direct role of BBS4 in physiological and pathophysiological mechanisms that underlie adipose tissue formation relevant to obesity.

Transcriptional background of beef marbling - novel genes implicated in intramuscular fat deposition

The purpose of this study was to identify novel marbling-related genes by comparison of the global gene expression in semitendinosus muscle of 15-month-old Limousin (LIM), Holstein-Friesian (HF) and Hereford (HER) bulls. Muscle of LIM was lean with low intramuscular fat (IMF) content (0.53%) unlike the marbled muscles of HER and HF characterized by higher amounts of IMF (1.10 and 0.81%, respectively). The comparison of muscle transcriptional profile between marbled and lean beef revealed significant differences in expression of 144 genes, presumably involved in consecutive stages of adipose tissue development, such as preadipocyte proliferation and differentiation, adipocyte maturation, lipid filling and lipid metabolism leading to increased IMF deposition and marbling development. Correlation coefficients and regression analysis for nine of them (gadd45a, pias3, ccrn4l, diras3, pou5f1, hoxa9, atp2a2 and pim1) validated by real-time qPCR confirmed their moderate-high correlation with IMF% and explained up to 70.5% of the total variability in IMF deposition in the bulls.

Common FSNP variants of fourteen Bardet-Biedl syndrome genes and adult body mass

OBJECTIVE

Bardet-Biedl syndrome (BBS) is a rare monogenic multi-systemic disorder manifesting with marked obesity. Fourteen BBS genes have been identified to date and additional loci are expected. Mutations of several BBS genes were shown to affect fat cell differentiation. The purpose was to Investigate the association between common polymorphisms in all 14 genes as a group and body weight.

DESIGN AND METHODS

We investigated association between tagging single nucleotide polymorphisms (tSNPs) located between 10 kb upstream and downstream from the transcribed sequences of each of 14 BBS genes, and body weight and fat in 2462 adult women from the UK Twins study. Significant results were further tested in a confirmation sample of 2003 women from the same cohort and additionally in the GIANT consortium population (n = 123,865).

RESULTS

105 SNPs in 14 BBS genes were selected and tested in the first cohort of women for association with the body weight and fat related phenotypes, i.e. weight, body mass index (BMI), total body fat (assessed by DEXA), total fat/height(2), and total fat/weight. We used principal component (PC) derived using the latter five traits as a primary phenotype for this study. Of the 105 SNPs, 3 variants in BBS9 and BBS11 showed evidence of nominally significant association with elevated body weight and fat. However, none of the associations survived multiple-testing correction.

CONCLUSIONS

The results suggest that common variation in 14 BBS genes (within or adjacent to the genes) are unlikely to have a substantial effect on body weight and fat in the European population.

BBS-induced ciliary defect enhances adipogenesis, causing paradoxical higher-insulin sensitivity, glucose usage, and decreased inflammatory response

Studying ciliopathies, like the Bardet-Biedl syndrome (BBS), allow the identification of signaling pathways potentially involved in common diseases, sharing phenotypic features like obesity or type 2 diabetes. Given the close association between obesity and insulin resistance, obese BBS patients would be expected to be insulin resistant. Surprisingly, we found that a majority of obese BBS patients retained normal glucose tolerance and insulin sensitivity. Patient's adipose tissue biopsies revealed upregulation of adipogenic genes and decrease of inflammatory mediators. In vitro studies on human primary mesenchymal stem cells (MSCs) showed that BBS12 inactivation facilitated adipogenesis, increased insulin sensitivity, and glucose utilization. We generated a Bbs12(-/-) mouse model to assess the impact of Bbs12 inactivation on adipocyte biology. Despite increased obesity, glucose tolerance was increased with specific enhanced insulin sensitivity in the fat. This correlated with an active recruitment of MSCs resulting in adipose tissue hyperplasia and decreased in inflammation.

Molecular basis of the obesity associated with Bardet-Biedl syndrome

Bardet-Biedl Syndrome (BBS) is a rare human hereditary disorder associated with several features including obesity, retinopathy, renal defects, polydactyly, learning disabilities and hypogenitalism. This article discusses the abnormalities accounting for energy imbalance leading to obesity in BBS, with emphasis on the recent evidence pointing to aberrations in hypothalamic action of leptin. Indeed, BBS proteins have emerged as important mediators of leptin receptor trafficking, and loss of BBS genes results in leptin resistance that could be due to abnormal leptin receptor handling in a subset of leptin-responsive neurons. These recent discoveries hold promise for improved clinical management of BBS patients. The relevance of these findings to non-syndromic common obesity is also discussed.

End stage renal disease, differential diagnosis, a rare genetic disorder: bardet-biedl syndrome: case report and review

End stage renal disease (ESRD) represents a clinical condition in which there is an irreversible loss of endogenous renal function. Both structural and functional abnormalities of the kidney are associated with increased morbidity, mortality. Bardet-Biedel syndrome (BBS) is one of the rare genetic disorders with prevalence of 1 in 1, 40,000-1 in 1,60,000 worldwide. ESRD in BBS patients is the final stage of the disease, increasing mortality in youth.

Utilization of conditional alleles to study the role of the primary cilium in obesity

Ciliopathies are a group of human diseases that involve dysfunction of the cilium. Human patients with mutations in ciliary proteins can exhibit a wide range of phenotypes, one of which is obesity. This is seen in patients with Bardet-Biedl syndrome (BBS) and Alström syndrome (ALMS). Both of these disorders are caused by mutations in proteins that localize to the cilium or the basal body at the base of the cilium. These rare human disorders and their corresponding mouse models together with genetic approaches to disrupt cilia on specific cell types are beginning to uncover the connection between the cilium and energy homeostasis. Here we will review the current data on how cilia are thought to be involved in energy homeostatic pathways and discuss several key factors to consider when utilizing conditional approaches to evaluate ciliary function and their link to obesity.

The nonmotile ciliopathies

Over the last 5 years, disorders of nonmotile cilia have come of age and their study has contributed immeasurably to our understanding of cell biology and human genetics. This review summarizes the main features of the ciliopathies, their underlying genetics, and the functions of the proteins involved. We describe some of the key findings in the field, including new animal models, the role of ciliopathy proteins in signaling pathways and development, and the unusual genetics of these diseases. We also discuss the therapeutic potential for these diseases and finally, discuss important future work that will extend our understanding of this fascinating organelle and its associated pathologies.

Mechanistic insights into Bardet-Biedl syndrome, a model ciliopathy

Bardet-Biedl syndrome (BBS) is a multisystemic disorder typified by developmental and progressive degenerative defects. A combination of genetic, in vitro, and in vivo studies have highlighted ciliary dysfunction as a primary cause of BBS pathology, which has in turn contributed to the improved understanding of the functions of the primary cilium in humans and other vertebrates. Here we discuss the evidence linking the clinical BBS phenotype to ciliary defects, highlight how the genetic and cellular characteristics of BBS overlap with and inform other ciliary disorders, and explore the possible mechanistic underpinnings of ciliary dysfunction.

Transient ciliogenesis involving Bardet-Biedl syndrome proteins is a fundamental characteristic of adipogenic differentiation

Bardet-Biedl syndrome (BBS) is an inherited ciliopathy generally associated with severe obesity, but the underlying mechanism remains hypothetical and is generally proposed to be of neuroendocrine origin. In this study, we show that while the proliferating preadipocytes or mature adipocytes are nonciliated in culture, a typical primary cilium is present in differentiating preadipocytes. This transient cilium carries receptors for Wnt and Hedgehog pathways, linking this organelle to previously described regulatory pathways of adipogenesis. We also show that the BBS10 and BBS12 proteins are located within the basal body of this primary cilium and inhibition of their expression impairs ciliogenesis, activates the glycogen synthase kinase 3 pathway, and induces peroxisome proliferator-activated receptor nuclear accumulation, hence favoring adipogenesis. Moreover, adipocytes derived from BBS-patients' dermal fibroblasts in culture exhibit higher propensity for fat accumulation when compared to controls. This strongly suggests that a peripheral primary dysfunction of adipogenesis participates to the pathogenesis of obesity in BBS.

Genes and pathways differentially expressed in the brains of Fxr2 knockout mice

Fragile X syndrome is a common inherited form of mental retardation and originates from the absence of expression of the FMR1 gene. This gene and its two homologues, FXR1 and FXR2, encode for a family of fragile X related (FXR) proteins with similar tissue distribution, together with sequence and functional homology. Based on these characteristics, it has been suggested that these proteins might partly complement one another. To unravel the function of Fxr2 protein, the expression pattern of 12,588 genes was studied in the brains of wild-type and Fxr2 knockout mice, an animal model which shows behavioral abnormalities partly similar to those observed in Fmr1-knockout mice. By genome expression profiling and stringent significance tests we identify genes and gene groups de-regulated in the brains of Fxr2 knockout mice. Differential expression of candidate genes was validated by real-time PCR, in situ hybridization, immunohistochemistry and western blot analysis. A number of differentially expressed genes associated with the Fxr2 phenotype have been previously involved in other memory or cognitive disorders.

Association between BBS6/MKKS gene polymorphisms, obesity and metabolic syndrome in the Greek population

OBJECTIVE

To investigate the relationship between MKKS gene variations, obesity-related traits and features of the metabolic syndrome (MS) in the Greek population.

DESIGN AND SUBJECTS

Genotype and haplotype analysis was carried out for six known MKKS gene polymorphisms (534C>T, 985+16T>G, 985+33C>G, 986-29A>T, 1161+58A>G and 1595G>T) in 220 obese subjects (body mass index > or =30 kg/m(2)) and 330 non-obese controls.

RESULTS

Genotype frequencies of the 985+16T>G, 986-29A>T and 1595G>T SNPs were significantly different between obese and non-obese individuals (P=0.0016, 0.0196 and 0.0069, respectively). Obese carriers of the risk alleles of the above three polymorphisms had a significantly increased prevalence of arterial hypertension. Furthermore, obese carriers of the G allele for the 985+16T>G polymorphism had an increased prevalence of type 2 diabetes mellitus and of MS component traits. A new polymorphism was detected, namely a C to T substitution at position 1129 (1129C>T or N377N). Frequency of the T allele for the 1129C>T polymorphism was significantly higher in control individuals than in obese subjects (P=0.0253). Haplotype TGTGT was more prevalent in obese than in controls (P=0.0002) and was associated with increased prevalence of the MS in obese subjects (P<0.0001).

CONCLUSION

Our results suggest that genetic variation in the MKKS gene may play a role in the development of obesity and the metabolic syndrome.