Adipose tissue secretes a variety of bioactive signaling molecules, termed adipokines, which regulate numerous biological functions including appetite, energy balance, glucose homeostasis, and ...inflammation. Chemerin is a novel adipokine that regulates adipocyte differentiation and metabolism by binding to and activating the G protein-coupled receptor, chemokine like receptor-1 (CMKLR1). In the present study, we investigated the impact of CMKLR1 deficiency on adipose development, glucose homeostasis, and inflammation in vivo. Herein we report that regardless of diet (low or high fat), CMKLR1−/− mice had lower food consumption, total body mass, and percent body fat compared with wild-type controls. CMKLR1−/− mice also exhibited decreased hepatic and white adipose tissue TNFα and IL-6 mRNA levels coincident with decreased hepatic dendritic cell infiltration, decreased adipose CD3+ T cells, and increased adipose natural killer cells. CMKLR1−/− mice were glucose intolerant compared with wild-type mice, and this was associated with decreased glucose stimulated insulin secretion as well as decreased skeletal muscle and white adipose tissue glucose uptake. Collectively these data provide compelling evidence that CMKLR1 influences adipose tissue development, inflammation, and glucose homeostasis and may contribute to the metabolic derangement characteristic of obesity and obesity-related diseases.
Chemerin is an adipocyte derived signalling molecule (adipokine) that serves as a ligand activator of Chemokine-like receptor 1(CMKLR1). Chemerin/CMKLR1 signalling is well established to regulate ...fundamental processes in metabolism and inflammation. The composition and function of gut microbiota has also been shown to impact the development of metabolic and inflammatory diseases such as obesity, diabetes and inflammatory bowel disease. In this study, we assessed the microbiome composition of fecal samples isolated from wildtype, chemerin, or CMKLR1 knockout mice using Illumina-based sequencing. Moreover, the knockout mice and respective wildtype mice used in this study were housed at different universities allowing us to compare facility-dependent effects on microbiome composition. While there was no difference in alpha diversity within samples when compared by either facility or genotype, we observed a dramatic difference in the presence and abundance of numerous taxa between facilities. There were minor differences in bacterial abundance between wildtype and chemerin knockout mice, but significantly more differences in taxa abundance between wildtype and CMKLR1 knockout mice. Specifically, CMKLR1 knockout mice exhibited decreased abundance of
and
, which correlated with body weight in CMKLR1 knockout, but not wildtype mice. This is the first study to investigate a linkage between chemerin/CMKLR1 signaling and microbiome composition. The results of our study suggest that chemerin/CMKLR1 signaling influences metabolic processes through effects on the gut microbiome. Furthermore, the dramatic difference in microbiome composition between facilities might contribute to discrepancies in the metabolic phenotype of CMKLR1 knockout mice reported by independent groups. Considered altogether, these findings establish a foundation for future studies to investigate the relationship between chemerin signaling and the gut microbiome on the development and progression of metabolic and inflammatory disease.
Cyp26b1, a retinoic acid (RA)-metabolising enzyme, is expressed in the developing limb bud, and Cyp26b1(-/-) mice present with severe limb defects. These malformations might be attributable to an ...RA-induced patterning defect; however, recent reports suggest that RA is dispensable for limb patterning. In this study, we examined the role of endogenous retinoid signalling in skeletogenesis using Cyp26b1(-/-) mice and transgenic mice in which Cyp26b1 is conditionally deleted under control of the Prrx1 promoter beginning at ~E9.5 (Prrx1Cre(+)/Cyp26b1(fl/fl)). We found that the limb phenotype in Prrx1Cre(+)/Cyp26b1(fl/fl) mice was less severe than that observed in Cyp26b1(-/-) animals and that a change in retinoid signalling contributed to the difference in phenotypes. We systematically examined the role of endogenous RA signalling in chondrogenesis and found that Cyp26b1(-/-) cells and limb mesenchymal cells treated with a CYP inhibitor, are maintained in a pre-chondrogenic state, exhibit reduced chondroblast differentiation and have modestly accelerated chondrocyte hypertrophy. Furthermore, Cyp26b1(-/-) mesenchyme exhibited an increase in expression of genes in a closely related tendogenic lineage, indicating that retinoid signals in the limb interfere with differentiation and maintain progenitor status. Together, these findings support an important function for RA in regulating the behaviour of mesenchymal progenitors, and their subsequent differentiation and maturation.
Brachydactyly type A1 is an autosomal dominant disorder primarily characterized by hypoplasia/aplasia of the middle phalanges of digits 2-5. Human and mouse genetic perturbations in the BMP-SMAD ...signaling pathway have been associated with many brachymesophalangies, including BDA1, as causative mutations in IHH and GDF5 have been previously identified. GDF5 interacts directly as the preferred ligand for the BMP type-1 receptor BMPR1B and is important for both chondrogenesis and digit formation. We report pathogenic variants in BMPR1B that are associated with complex BDA1. A c.975A>C (p.(Lys325Asn)) was identified in the first patient displaying absent middle phalanges and shortened distal phalanges of the toes in addition to the significant shortening of middle phalanges in digits 2, 3 and 5 of the hands. The second patient displayed a combination of brachydactyly and arachnodactyly. The sequencing of BMPR1B in this individual revealed a novel c.447-1G>A at a canonical acceptor splice site of exon 8, which is predicted to create a novel acceptor site, thus leading to a translational reading frameshift. Both mutations are most likely to act in a dominant-negative manner, similar to the effects observed in BMPR1B mutations that cause BDA2. These findings demonstrate that BMPR1B is another gene involved with the pathogenesis of BDA1 and illustrates the continuum of phenotypes between BDA1 and BDA2.
Inflammatory bowel disease (IBD) is a family of disorders including ulcerative colitis and Crohn's disease that are characterized by chronic and relapsing intestinal inflammation. Increased ...production of proinflammatory mediators, possibly combined with low expression of anti‐inflammatory mediators, is thought to promote the development and progression of IBD. In the current study, we demonstrate that expression, secretion, and processing of chemerin, a potent chemoattractant for cells expressing chemokine‐like receptor 1 (CMKLR1), increased in the cecum and colon along a gradient positively associated with the severity of inflammation in dextran sodium sulfate (DSS)‐induced colitis. We also show that levels of circulating bioactive chemerin increased following DSS treatment. At both 6–8 and 14–16 weeks of age, CMKLR1 knockout mice developed signs of clinical illness more slowly than wild type and had changes in circulating cytokine levels, increased spleen weight, and increased local chemerin secretion following DSS treatment. However, knockout mice ultimately developed similar levels of clinical illness and local inflammation as wild type. Finally, contrary to previous reports, intraperitoneal injection of bioactive chemerin had no effect on the severity of DSS‐induced colitis. This suggests that local chemerin levels have a greater impact than circulating levels in the pathogenesis of colitis. Considered altogether, bioactive chemerin represents a novel biomarker for IBD severity, although strategies to modulate endogenous chemerin signaling other than chronic CMKLR1 loss are necessary in order to exploit chemerin as a therapeutic target for the treatment of IBD.
Chemerin is a small secreted protein implicated in several inflammatory and metabolic disorders. While circulating chemerin levels were altered in an animal model of colitis, loss of the receptor for chemerin (CMKLR1) does not substantially alter disease severity. Thus, chemerin may be more useful as a biomarker of inflammatory bowel disease rather than a therapeutic target.
Obesity and diabetes are associated with increased chronic low-grade inflammation and elevated plasma glucose levels. Although inflammation in the fat and liver are established features of ...obesity-associated insulin resistance, the intestine is emerging as a new site for immunologic changes that affect whole-body metabolism. Specifically, microbial and dietary factors incurred by diet-induced obesity influence underlying innate and adaptive responses of the intestinal immune system. These responses affect the maintenance of the intestinal barrier, systemic inflammation, and glucose metabolism. In this Review we propose that an understanding of the changes to the intestinal immune system, and how these changes influence systemic immunity and glucose metabolism in a whole-body integrative and a neuronal-dependent network, will unveil novel intestinal pathologic and therapeutic targets for diabetes and obesity.
Long chain acyl CoA synthetase (ACSL)-dependent upper small intestinal lipid metabolism activates preabsorptive pathways to regulate metabolic homeostasis, but whether changes in the upper small ...intestinal microbiota alter specific fatty acid-dependent pathways to impact glucose homeostasis remains unknown. We here first find that upper small intestinal infusion of Intralipid, oleic acid, or linoleic acid preabsorptively increases glucose tolerance and lowers glucose production in rodents. High-fat feeding impairs preabsorptive fatty acid sensing and reduces upper small intestinal Lactobacillus gasseri levels and ACSL3 expression. Transplantation of healthy upper small intestinal microbiota to high-fat fed rodents restores Lactobacillus gasseri levels and fatty acid sensing via increased ACSL3 expression, while Lactobacillus gasseri probiotic administration to non-transplanted high-fat fed rodents is sufficient to restore upper small intestinal ACSL3 expression and fatty acid sensing.
In summary, we unveil a glucoregulatory role of upper small intestinal Lactobacillus gasseri that impacts an ACSL3-dependent glucoregulatory fatty acid sensing pathway.
Disclosure
P.V. Bauer: None. F. Duca: None. T. Waise: None. H.J. Dranse: None. B.A. Rasmussen-Small: None. A. Puri: None. M. Rasti: None. T.K.T. Lam: None.
Abstract only
BACKGROUND
Chemerin is a recently identified adipocyte‐secreted signalling molecule (adipokine) that plays local and systemic roles in the regulation of adipocyte differentiation, ...metabolism, and inflammation. Chemerin levels are increased in obese patients, however little is known regarding the signal transduction pathways coupled to chemerin signalling and how altered chemerin levels in obesity affect adipose function.
OBJECTIVE
To identify key signalling pathways and molecular targets influenced by chemerin signalling.
RESULTS
Microarray analysis revealed that a number of genes with important roles in adipose tissue remodeling were up‐regulated following treatment of murine adipocytes with a neutralizing chemerin antibody. Functionally, this resulted in increased matrix metalloproteinase activity and recruitment of macrophages towards adipocyte‐conditioned medium. Treatment with a NFkB inhibitor was able to reverse these effects, suggesting a NFkB‐dependent mechanism.
CONCLUSIONS
Chemerin mediates the expression of genes involved in adipose tissue remodeling and inflammation through a NFkB‐dependent pathway. This novel role for chemerin signalling likely has important effects on adipose tissue when chemerin levels are modified in obesity.
Supported by CIHR, NSERC, and Killam Trusts.
High-density micromass cultures of embryonic mesenchymal cells have proved to be an invaluable model for studying the entire chondrogenic program, from precartilaginous condensations through to ...chondrocyte hypertrophy. This culture model also provides a powerful system in which to explore the function of various factors in the commitment and differentiation of mesenchymal cells to the chondrogenic lineage. In this regard, micromass cultures provide a consistent and robust model for investigating the effects of genetic manipulations on skeletal phenotypes and for delineating their molecular basis. In this methods chapter, the derivation and use of micromass cultures from murine limb buds are described, but these techniques are also applicable to other organisms and mesenchymal cell sources.
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