De novo brown adipogenesis involves the proliferation and differentiation of progenitors, yet the mechanisms that guide these events in vivo are poorly understood. We previously demonstrated that treatment with a β3-adrenergic receptor (ADRB3) agonist triggers brown/beige adipogenesis in gonadal white adipose tissue following adipocyte death and clearance by tissue macrophages. The close physical relationship between adipocyte progenitors and tissue macrophages suggested that the macrophages that clear dying adipocytes might generate proadipogenic factors. Flow cytometric analysis of macrophages from mice treated with CL 316,243 identified a subpopulation that contained elevated lipid and expressed CD44. Lipidomic analysis of fluorescence-activated cell sorting-isolated macrophages demonstrated that CD44+ macrophages contained four- to five-fold higher levels of the endogenous peroxisome-proliferator activated receptor gamma (PPARγ) ligands 9-hydroxyoctadecadienoic acid (HODE), and 13-HODE compared with CD44- macrophages. Gene expression profiling and immunohistochemistry demonstrated that ADRB3 agonist treatment upregulated expression of ALOX15, the lipoxygenase responsible for generating 9-HODE and 13-HODE. Using an in vitro model of adipocyte efferocytosis, we found that IL-4-primed tissue macrophages accumulated lipid from dying fat cells and upregulated expression of Alox15. Furthermore, treatment of differentiating adipocytes with 9-HODE and 13-HODE potentiated brown/beige adipogenesis. Collectively, these data indicate that noninflammatory removal of adipocyte remnants and coordinated generation of PPARγ ligands by M2 macrophages provides localized adipogenic signals to support de novo brown/beige adipogenesis.

BackgroundThe higher prevalence of obesity-related metabolic disease in males suggests that female sex hormones provide protective mechanisms against the pathogenesis of metabolic syndrome. Because browning of white adipose tissue (WAT) is protective against obesity-related metabolic disease, we examined sex differences in β3-adrenergic remodeling of WAT in mice.MethodsEffects of the β3-adrenergic receptor agonist CL316,243 (CL) on browning of white adipose tissue were investigated in male and female C57BL mice. The role of ovarian hormones in female-specific browning was studied in control female C57BL mice and mice with ovarian failure induced by 4-vinylcyclohexene diepoxide treatment for 15 days.ResultsWe found that treatment with CL-induced upregulation of brown adipocyte markers and mitochondrial respiratory chain proteins in gonadal WAT (gWAT) of female mice, but was without effect in males. In contrast, CL treatment was equally effective in males and females in inducing brown adipocyte phenotypes in inguinal WAT. The tissue- and sex-specific differences in brown adipocyte recruitment were correlated with differences in sympathetic innervation, as determined by tyrosine hydroxylase immunostaining and western blotting. Levels of the neurotrophins NGF and BDNF were significantly higher in gWAT of female mice. CL treatment significantly increased NGF levels in gWAT of female mice but did not affect BDNF expression. In contrast, estradiol treatment doubled BDNF expression in female adipocytes differentiated in vitro. Ovarian failure induced by 4-vinylcyclohexene diepoxide treatment dramatically reduced BDNF and TH expression in gWAT, eliminated induction of UCP1 by CL, and reduced tissue metabolic rate.ConclusionsCollectively, these data demonstrate that female mice are more responsive than males to the recruitment of brown adipocytes in gonadal WAT and this difference corresponds to greater levels of estrogen-dependent sympathetic innervation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13293-016-0121-7) contains supplementary material, which is available to authorized users.

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We investigated the role of connexin 43 (Cx43) in maintaining the integrity of mitochondria in brown adipose tissue (BAT). The functional effects of Cx43 were evaluated using inducible, adipocyte-specific Cx43 knockout in mice (Gja1 adipoqKO) and by overexpression and knockdown of Cx43 in cultured adipocytes. Mitochondrial morphology was evaluated by electron microscopy and mitochondrial function and autophagy were assessed by immunoblotting, immunohistochemistry, and qPCR. The metabolic effects of adipocyte-specific knockout of Cx43 were assessed during cold stress and following high fat diet feeding. Cx43 expression was higher in BAT compared to white adipose tissue. Treatment with the β3-adrenergic receptor agonist CL316,243 increased Cx43 expression and mitochondrial localization. Gja1 adipoqKO mice reduced mitochondrial density and increased the presence of damaged mitochondria in BAT. Moreover, metabolic activation with CL316,243 further reduced mitochondrial integrity and upregulated autophagy in the BAT of Gja1 adipoqKO mice. Inhibition of Cx43 in cultured adipocytes increased the generation of reactive oxygen species and induction of autophagy during β-adrenergic stimulation. Gja1 adipoqKO mice were cold intolerant, expended less energy in response to β3-adrenergic receptor activation, and were more insulin resistant after a high-fat diet challenge. Collectively, our data demonstrate that Cx43 is required for maintaining the mitochondrial integrity and metabolic activity of BAT.

When injecting material into the skin using a pneumatic needle-free injector, higher-pressure injections result in a hole with smaller area than lower-pressure injections. The depth and shape of skin penetration vary according to the amount of pressure applied. For materials of low density and viscosity, there is a greater difference in penetration depth according to the degree of pressure. Lasers Surg. Med. 48:624-628, 2016. © 2016 Wiley Periodicals, Inc.