17beta-Estradiol reduces mitochondrial cAMP content and cytochrome oxidase activity in a phosphodiesterase 2-dependent manner

Background and Purpose: Mitochondria possess their own source of cAMP, that is, soluble adenylyl cyclase (sAC). Activation or expression of mitochondrial sAC promotes mitochondrial function. Oestrogen receptor signalling plays an essential role in the regulation of mitochondrial function. Here we aimed to determine whether 17?-estradiol may affect mitochondrial cAMP signalling. Experimental Approach: Expression of the intra-mitochondrial proteins (Western blot), mitochondrial cAMP content (FRET-based live imaging and MS assay), mitochondrial membrane potential and cytochrome oxidase activity were analysed in H9C2 and C2C12 cells. Key Results: A 24 h treatment with 17?-estradiol significantly reduced the basal level of mitochondrial cAMP, without affecting the intra-mitochondrial content of sAC, phosphodiesterase 2 (PDE2) or PKA and the activity of the intra-mitochondrial sAC. The effect of 17?-estradiol on mitochondrial cAMP was prevented by inhibition of a cGMP-activated PDE2 or soluble guanylyl cyclase (sGC), suggesting a role of NO signalling. Indeed, 17?-estradiol raised cellular levels of cGMP and the intra-mitochondrial expression of the catalytic subunit ? of sGC was found. The 17?-estradiol-induced reduction of the mitochondrial cAMP level was accompanied by decreased cytochrome oxidase activity and mitochondrial membrane potential in a PDE2-dependent manner. Conclusions and Implications: 17?-estradiol reduced the basal level of mitochondrial cAMP content and cytochrome oxidase activity in a sAC-independent but in a PDE2-dependent manner. The results suggest a role of 17?-estradiol-induced activation of NO signalling in the regulation of mitochondrial cAMP content. Our study adds a new aspect to the complex action of oestrogens on mitochondrial biology, that is relevant to hormone replacement therapy.