A brown fat-enriched adipokine Adissp controls adipose thermogenesis and glucose homeostasis.
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Endogenous mouse Adissp is present in brown-adipocyte conditioned medium, and a Flag knock-in at the native locus confirms the endogenous protein is secreted.
"we were able to detect endogenous Adissp present in conditioned medium of mouse brown adipocyte culture"
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Secretion is non-classical. Brefeldin A plus monensin, which blocks the ER-to-Golgi route, increased Adissp secretion while inhibiting adiponectin in the same experiment.
"While adiponectin secretion was inhibited by brefeldin A and monensin as expected, Adissp secretion was instead increased"
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The human protein was itself shown to be secreted: adenoviral expression of human ADISSP in mouse liver put it into the circulation at about 0.45 ug/mL.
"this injection resulted in acute expression of ADISSP in the liver and its secretion into circulation with a concentration of about 0.45 μg/mL"
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The receptor is inferred from binding but never identified; the authors describe it as putative throughout.
"Together, our data suggest that Adissp activates PKA signaling through binding to a putative receptor at adipocyte surface"
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The link to a heterotrimeric G protein rests on a single melittin experiment; melittin is a membrane-active bee-venom peptide rather than a selective Gs inhibitor.
"induction of Ucp1 expression by Adissp was reduced by a merely 2-h treatment with the PKA inhibitor H89 and was blocked by Melittin, an inhibitor for Gαs subunit of the heterotrimeric G protein"
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Adipose-specific knockout impairs white-fat browning and produces diet-induced obesity and hyperglycaemia.
"Adipose-specific Adissp knockout mice are defective in WAT browning, and are susceptible to high fat diet-induced obesity and hyperglycemia"
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The thermogenic phenotype persists at thermoneutrality, so the process regulated is not specifically cold-induced thermogenesis.
"Thus, Adissp-regulated thermogenesis is still maintained at thermoneutral condition."
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To purify secreted protein the authors had to graft a heterologous signal peptide onto the construct, which is independent evidence that the native protein has none.
"To increase the yield and facilitate the purification of secreted Adissp, we added a signal peptide at the N-terminus of Adissp and a 6×His tag at its C-terminus"