Role of bile acid receptor FXR in development and function of brown adipose tissue

Bile acids act as signalling molecules that contribute to maintenance of energy homeostasis in mice and humans. Activation of G-protein-coupled bile acid receptor TGR5 induces energy expenditure in brown adipose tissue (BAT). However, a role for the nuclear bile acid receptor Farnesoid X receptor (FXR) in BAT has remained ambiguous. We aimed to study the potential role of FXR in BAT development and functioning. Here we demonstrate low yet detectable expression of the α1/2 isoforms of FXR in murine BAT that markedly decreases upon cold exposure. Moderate adipose tissue-specific FXR overexpression in mice induces pronounced BAT whitening, presenting with large intracellular lipid droplets and extracellular collagen deposition. Expression of thermogenic marker genes including the target of Tgr5, Dio2, was significantly lower in BAT of chow-fed aP2-hFXR mice compared to wild-type controls. Transcriptomic analysis revealed marked up-regulation of extracellular matrix formation and down-regulation of mitochondrial functions in BAT from aP2-hFXR mice. In addition, markers of cell type lineages deriving from the dermomyotome, such as myocytes, as well as markers of cellular senescence were strongly induced. The response to cold and β3-adrenergic receptor agonism was blunted in these mice, yet resolved BAT whitening. Newborn cholestatic Cyp2c70-/- mice with a human-like bile acid profile also showed distinct BAT whitening and upregulation of myocyte-specific genes, while thermogenic markers were down-regulated. Ucp1 expression inversely correlated with plasma bile acid levels. Therefore, bile acid signalling via FXR has a role in BAT function already early in tissue development. Functionally, FXR activation appears to oppose TGR5-mediated thermogenesis

Prdm1 functions in the mesoderm of the second heart field, where it interacts genetically with Tbx1, during outflow tract morphogenesis in the mouse embryo

International audienceCongenital heart defects affect at least 0.8% of newborn children and are a major cause of lethality prior to birth. Malformations of the arterial pole are particularly frequent. The myocardium at the base of the pulmonary trunk and aorta and the arterial tree associated with these great arteries are derived from splanchnic mesoderm of the second heart field (SHF), an important source of cardiac progenitor cells. These cells are controlled by a gene regulatory network that includes Fgf8, Fgf10 and Tbx1. Prdm1 encodes a transcriptional repressor that we show is also expressed in the SHF. In mouse embryos, mutation of Prdm1 affects branchial arch development and leads to persistent truncus arteriosus (PTA), indicative of neural crest dysfunction. Using conditional mutants, we show that this is not due to a direct function of Prdm1 in neural crest cells. Mutation of Prdm1 in the SHF does not result in PTA, but leads to arterial pole defects, characterized by mis-alignment or reduction of the aorta and pulmonary trunk, and abnormalities in the arterial tree, defects that are preceded by a reduction in outflow tract size and loss of caudal pharyngeal arch arteries. These defects are associated with a reduction in proliferation of progenitor cells in the SHF. We have investigated genetic interactions with Fgf8 and Tbx1, and show that on a Tbx1 heterozygote background, conditional Prdm1 mutants have more pronounced arterial pole defects, now including PTA. Our results identify PRDM1 as a potential modifier of phenotypic severity in TBX1 haploinsufficient DiGeorge syndrome patients

Production of Innervated Skeletal Muscle Fibers Using Human Induced Pluripotent Stem Cells

International audienceOnly a limited number of large-scale protocols describe the production of mature skeletal muscle fibers from human induced pluripotent stem cells (hiPSCs). Here we describe a novel procedure for simultaneous differentiation of hiPSC into muscle cells and motor neurons, that generates innervated and contractile multinucleated skeletal muscle fibers with sarcomeric organization. Our protocol permits the production of expandable skeletal muscle progenitor cells and mature skeletal muscle fibers that can be used for the exploration of skeletal muscle differentiation for basic research, disease modeling, and drug discovery

Metabolipidomic profiling reveals an age‐related deficiency of skeletal muscle pro‐resolving mediators that contributes to maladaptive tissue remodeling

Specialized pro- resolving mediators actively limit inflammation and support tissue regeneration, but their role in age- related muscle dysfunction has not been explored. We profiled the mediator lipidome of aging muscle via liquid chromatography- tandem mass spectrometry and tested whether treatment with the pro- resolving mediator resolvin D1 (RvD1) could rejuvenate the regenerative ability of aged muscle. Aged mice displayed chronic muscle inflammation and this was associated with a basal deficiency of pro- resolving mediators 8- oxo- RvD1, resolvin E3, and maresin 1, as well as many anti- inflammatory cytochrome P450- derived lipid epoxides. Following muscle injury, young and aged mice produced similar amounts of most pro- inflammatory eicosanoid metabolites of cyclooxygenase (e.g., prostaglandin E2) and 12- lipoxygenase (e.g., 12- hydroxy- eicosatetraenoic acid), but aged mice produced fewer markers of pro- resolving mediators including the lipoxins (15- hydroxy- eicosatetraenoic acid), D- resolvins/protectins (17- hydroxy- docosahexaenoic acid), E- resolvins (18- hydroxy- eicosapentaenoic acid), and maresins (14- hydroxy- docosahexaenoic acid). Similar absences of downstream pro- resolving mediators including lipoxin A4, resolvin D6, protectin D1/DX, and maresin 1 in aged muscle were associated with greater inflammation, impaired myofiber regeneration, and delayed recovery of strength. Daily intraperitoneal injection of RvD1 had minimal impact on intramuscular leukocyte infiltration and myofiber regeneration but suppressed inflammatory cytokine expression, limited fibrosis, and improved recovery of muscle function. We conclude that aging results in deficient local biosynthesis of specialized pro- resolving mediators in muscle and that immunoresolvents may be attractive novel therapeutics for the treatment of muscular injuries and associated pain in the elderly, due to positive effects on recovery of muscle function without the negative side effects on tissue regeneration of non- steroidal anti- inflammatory drugs.Chronic low- grade inflammation of aging muscle was associated with a basal deficiency of maresin 1, resolvin E3, 8- oxo- resolvin D1, and anti- inflammatory fatty acid epoxides. Aged mice produced normal amounts of most prostaglandins following muscle injury but were deficient in local biosynthesis of markers of the lipoxins, E- resolvins, D- resolvins, and maresins. Systemic treatment with resolvin D1 suppressed inflammatory cytokine expression, limited muscle fibrosis, and improved functional recovery.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/168317/1/acel13393-sup-0002-TableS1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168317/2/acel13393-sup-0003-TableS2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168317/3/acel13393_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168317/4/acel13393-sup-0001-FigS1-S4.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168317/5/acel13393.pd