Brown adipose tissue (BAT) is a metabolically active organ that exhibits sex-differential features, that is, being generally more abundant and active in females than in males. Although sex steroids, particularly estrogens, have been shown to regulate BAT thermogenic function, the underlying molecular mechanisms contributing to sexual dimorphism in basal BAT activity have not been elucidated. Therefore, we assessed the transcriptome of interscapular BAT of male and female C57BL/6J mice by RNA sequencing and identified 295 genes showing ≥2-fold differential expression (adjusted P < 0.05). In silico functional annotation clustering suggested an enrichment of genes encoding proteins involved in cell–cell contact, interaction, and adhesion. Ovariectomy reduced the expression of these genes in female BAT toward a male pattern whereas orchiectomy had marginal effects on the transcriptional pattern, indicating a prominent role of female gonadal hormones in this sex-differential expression pattern. Progesterone was identified as a possible upstream regulator of the sex-differentially expressed genes. Studying the direct effects of progesterone in vitro in primary adipocytes showed that progesterone significantly altered the transcription of several of the identified genes, possibly via the glucocorticoid receptor. In conclusion, this study reveals a sexually dimorphic transcription profile in murine BAT at general housing conditions and demonstrates a role for progesterone in the regulation of the interscapular BAT transcriptome.
Kasiphak Kaikaew, Aldo Grefhorst, Jacobie Steenbergen, Sigrid M A Swagemakers, Anke McLuskey, and Jenny A Visser
Patric J D Delhanty, Martin Huisman, Karina Prins, Cobie Steenbergen, Rosinda Mies, Sebastian J C M M Neggers, A J van der Lely, and Jenny A Visser
Acylated ghrelin (AG) is a gut-derived peptide with growth hormone secretagogue (GHS), orexigenic and other physiological activities mediated by GHS receptor-1a (GHSR). Ghrelin occurs in unacylated form (UAG) with activities opposing AG, although its mechanism of action is unknown. UAG does not antagonize AG at GHSR, and has biological effects on cells that lack this receptor. Because UAG binds to cells, it has been hypothesized that UAG acts via a cell-surface receptor, although this has not been confirmed. This study aimed to identify cell surface proteins to which UAG binds that could modulate or mediate its biological effects. The MCF7 cell-line was used as a model because UAG induces ERK signaling in these cells in the absence of GHSR. Using ligand–receptor capture and LC-MS/MS we identified specific heparan-sulfate proteoglycans (HSPGs) to which UAG interacts on cell surfaces. In line with this, UAG, as well as AG, bind with high affinity to heparin, and heparin and heparinase treatment suppress, whereas HSPG overexpression increases, UAG binding to MCF7 cell surfaces. Moreover, heparin suppresses the ERK response to UAG. However, conversion of the lysines in UAG to alanine, which prevents its binding to heparin and cell surface HSPGs, does not prevent its activation of ERK. Our data show that the interaction of UAG with HSPGs modulates its biological activity in cells. More broadly, the interaction of UAG and AG with HSPGs could be important for the specificity and potency of their biological action in vivo.