A09

A09

In the 1^st funding period, project A09 identified several chemokines/chemokine receptors that are differentially regulated in BAT by diet (13% fat vs 60% fat) or housing temperature (23°C vs 4°C), e.g.: Cxcl12, Cxcl10, Ccr10, Cxcl14, Ccl2, Ccl5, Ccl6, Ccl7, Cxcr4 and Cxcr5.  Cxcl12 (C-X-C motif chemokine ligand-12) was significantly upregulated in BAT from mice exposed to cold. Upon treatment of mature brown adipocytes with CXCL12, a reduction of Ucp-1 mRNA expression (the major thermogenic marker) was observed. In contrast to Cxcl12, Cxcl10 (C-X-C motif chemokine ligand-10) transcript was downregulated in BAT isolated from mice exposed to cold. Interestingly, Cxcl10 mRNA levels were significantly upregulated in BAT upon HFD diet and in brown adipocytes treated with TNFα to mimic adipose tissue inflammation. Collectively, project A09’s results suggest that Cxcl10 might be a possible macrophage-recruiting factor released by BAT. Further, in project A09 the spatiotemporal organization of cAMP signaling in adipocytes was studied by real-time live cell imaging in pre- and mature brown adipocytes in close collaboration with Prof. Nikolaev (project A06). Cytosolic cAMP microdomains generated during stimulation of individual β-adrenoceptor subtypes (β₁, β₂ and β₃) as well as cAMP degradation by PDEs were visualized revealing PDE3 or 4 differentially regulate cAMP microdomains initiated by β1 or β3 adrenoceptors depending on the stage of adipocytes differentiation (pre- versus mature). Functionally, β_1/2 receptor-induced lipolysis was controlled more by PDE3/4 than β₃-receptor-induced lipolysis, which might be explained by the changes of both PDE3- and 4-mediated regulation of individual β adrenoceptor-dependent cAMP pools. Project A09 also studies the downstream effectors of cAMP-mediated regulation of BAT, and discovered a so far unknown biological role of the effector receptor EPAC1 in thermogenic fat. Using pharmacological and genetic tools EPAC1 was identified as a potent enhancer of BAT thermogenic capacity that significantly reduces diet-induced obesity and enhances human brown adipocyte differentiation. Thus, EPAC1 is apotentially promising target for obesity prevention and treatment. Also, project A09 studied ADO signaling and found that ADO receptor A_2B induces BAT activation and browning of white fat. Human data also revealed that A_2BAdoR expression correlates inversely with obesity. Further preliminary data of project A09relate to cAMP signaling organization in murine and human brown/beige adipocytes, the role of A-kinase anchoring proteins for the cAMP signaling architecture, and ADO signaling in adipocyte-macrophage communication.