👤 Catherine Labbé

Adipokines regulate body weight and metabolism by targeting the hypothalamus, influencing feeding, energy expenditure (EE) and insulin sensitivity. Angiopoietin-like 2 (Angptl2) is a pro-inflammatory adipokine linking obesity to insulin resistance. Both Angptl2 and its receptor are expressed in the central nervous system. Yet, the contribution of Angptl2 to the regulation of energy metabolism and relevant hypothalamic neuropeptides in male and female mice is unknown. We aim at determining the impact of Angptl2 knockdown (KD) on energy balance, nutrient partitioning and hypothalamic responses to a standard (STD) or high-fat diet (HFD) in mice. Three-month-old male and female Angptl2-KD mice and wildtype (WT) littermates were fed 16 weeks either a STD or a HFD. Body weight, food consumption and insulin sensitivity were assessed along with measurements of EE, respiratory exchange ratio (RER) and locomotor activity. We quantified the expression of Angptl2 and its receptors itga5, mag and pirb in the medio-basal hypothalamus (MBH) of WT mice, and MBH neuropeptide Y (NPY), agouti-related neuropeptide (AgRP) and proopiomelanocortin (POMC) gene expression in both KD and control fasting mice. Lack of Angptl2 reduced food intake in males on both diets, and in females on HFD. In KD males, this anorexigenic effect was associated with lower body weight, increased EE, improved insulin sensitivity and lower hypothalamic orexigenic NPY expression compared to controls. Female Angptl2-KD mice however, exhibited unaltered body weight, EE and insulin sensitivity, and elevated NPY, AgRP and MC4R expression compared to controls. Fasting caused an increase in the MBH of mag expression in males and females but Angptl2 expression only in female mice. Angptl2 KD improved diet-induced obesity and associated metabolic dysfunction in male mice. The lack of similar changes in female mice and divergent MBH neuropeptide profile suggest that sex-dependent mechanisms underly the anabolic effects of this proinflammatory adipokine. Show less

Bacterial lipopolysaccharides (LPSs or endotoxins) can bind most proteins of the lipid transfer/LPS-binding protein (LT/LBP) family in host organisms. The LPS-bound LT/LBP proteins then trigger either an LPS-induced proinflammatory cascade or LPS binding to lipoproteins that are involved in endotoxin inactivation and detoxification. Cholesteryl ester transfer protein (CETP) is an LT/LBP member, but its impact on LPS metabolism and sepsis outcome is unclear. Here, we performed fluorescent LPS transfer assays to assess the ability of CETP to bind and transfer LPS. The effects of intravenous (iv) infusion of purified LPS or polymicrobial infection (cecal ligation and puncture [CLP]) were compared in transgenic mice expressing human CETP and wild-type mice naturally having no CETP activity. CETP displayed no LPS transfer activity in vitro, but it tended to reduce biliary excretion of LPS in vivo. The CETP expression in mice was associated with significantly lower basal plasma lipid levels and with higher mortality rates in both models of endotoxemia and sepsis. Furthermore, CETPTg plasma modified cytokine production of macrophages in vitro. In conclusion, despite having no direct LPS binding and transfer property, human CETP worsens sepsis outcomes in mice by altering the protective effects of plasma lipoproteins against endotoxemia, inflammation, and infection. Show less

The microtubule-associated protein tau (MAPT) gene is considered a strong genetic risk factor for Parkinson's disease (PD) in Caucasians. MAPT is located within an inversion region of high linkage disequilibrium designated as H1 and H2 haplotype, and contains eight other genes which have been implicated in neurodegeneration. The aim of the current study was to identify common coding variants in strong linkage disequilibrium (LD) within the associated loci on chr17q21 harboring MAPT. Sanger sequencing of coding exons in 90 Caucasian late-onset PD (LOPD) patients was performed. Specific gene sequencing for LRRC37A, LRRC37A2, ARL17A and ARL17B was not possible given the high homology, presence of pseudogenes and copy number variants that are in the region, and therefore four genes (NSF, KANSL1, SPPL2C, and CRHR1) were included in the analysis. Coding variants from these four genes that did not perfectly tag (r In the 90 LOPD cases we identified 30 coding variants. Eleven non-synonymous variants tagged the MAPT H1/H2 haplotype, including two SPPL2C variants (rs12185233 and rs12373123) that had high pathogenic combined annotation dependent depletion (CADD) scores of >20. In the replication series, the non-synonymous KANSL1 rs17585974 variant was in very strong LD with MAPT H1/H2 and had a high CADD score of 24.7. We have identified several non-synonymous variants across neighboring genes of MAPT that may warrant further genetic and functional investigation within the biological etiology of PD. Show less

Crohn's disease (CD) and ulcerative colitis (UC) are inflammatory bowel diseases (IBDs) presumably caused by dysregulated immune responses to the gut microbiota. Genetic association studies have implicated dozens of chromosomal regions or loci in IBD susceptibility. The next challenge is to explain the individual role of each of these modest effect loci in the disease state. We have previously identified MAST3 as an IBD susceptibility gene through genetic fine-mapping of the 19p linkage region. Testing MAST3 in a reporter assay provided preliminary evidence that MAST3 modulates the activity of inflammation-related transcription factor nuclear factor kappa B. Here we characterized the function of MAST3 through an examination of the influence of the modulation of MAST3 expression on endogenous genome-wide expression patterns. More specifically, we looked at differential gene expression resulting from overexpression and knockdown of the MAST3 gene in epithelial and macrophage cell lines. From we highlight a group of genes whose expression is modulated by MAST3 and correlate their expression with NF-jB activity. Their expression was found to be enriched in inflamed mucosal tissue of UC patients, confirming the importance of these genes in IBD. We highlight a group of genes whose expression is modulated by MAST3 and correlate their expression with NF-κB activity. Their expression was found to be enriched in inflamed mucosal tissue of UC patients, confirming the importance of these genes in IBD. These MAST3-regulated genes are central to mucosal immune responses. Among them are proinflammatory cytokines (e.g., CCL20, IL8), regulators of NF-κB (e.g., TNFAIP3, LY96, NFKBIA), genes involved in interferon-induced defense against pathogen invasion (e.g., IFIT1, ISG15), and genes involved in cell adhesion and/or migration (e.g., CD44, TMOD1). Taken together, these results confirm MAST3 as a modulator of the inflammatory response through regulation of immune gene expression in the gut of IBD patients. Show less

Inflammatory bowel disease (IBD) is a chronic disorder caused by multiple factors in a genetically susceptible host. Significant advances in the study of genetic susceptibility have highlighted the importance of the innate immune system in this disease. We previously completed a genome-wide linkage study and found a significant locus (IBD6) on chromosome 19p. We were interested in identifying the causal variant in IBD6. We performed a two-stage association mapping study. In stage 1, 1530 single-nucleotide polymorphisms (SNPs) were selected from the HapMap database and genotyped in 761 patients with IBD. Among the SNPs that passed the threshold for replication, 26 were successfully genotyped in 754 additional patients (stage 2). One intronic variant, rs273506, located in the microtubule-associated serine/threonine-protein kinase gene-3 (MAST3), was found to be associated in both stages (pooled P=1.8 x 10(-4)). We identified four MAST3 coding variants, including a non-synonymous SNP rs8108738, correlated to rs273506 and associated with IBD. To test whether MAST3 was expressed in cells of interest, we performed expression assays, which showed abundant expression of MAST3 in antigen-presenting cells and in lymphocytes. The knockdown of MAST3 specifically decreased Toll-like receptor-4-dependent NF-kappaB activity. Our findings are additional proofs of the pivotal role played by modulators of NF-kappaB activity in IBD pathogenesis. Show less