Cyclic Nucleotide Phosphodiesterases (PDEs) in Smooth Muscle : Expression, Function and Mechanism

The aim of the present thesis was to characterize the role of the different families of phosphodiesterases (PDEs), the enzymes degrading 3'-5'-cyclic adenosine monophosphate (cAMP), in controlling the cAMP signalling in two distinct smooth muscle cells (SMCs), the rat aorta SMC (RASMCs) and the rat bladder SMC (RBSMCs).In cultured RASMCs, we firstly characterized the pattern of cAMP-PDE expression and activity. We then showed, by using a FRET-based cAMP sensor to explore cAMP signals in living cells, that PDE4 inhibition unmasks an effect of PDE1 and PDE3 on cytosolic cAMP hydrolyzis, whereas PDE3 and PDE4 act synergistically at the submembrane compartment. The mechanisms of this subcellular compartmentation need to be characterized. In neonatal RBSMCs, we showed that both PDE3 and PDE4 are involved in regulating the phasic contractions albeit through distinct mechanisms. PDE4 inhibition inhibits the carbachol-enhanced contractions through a protein kinase A-dependent pathway involving an increase in Ca2+ sparks frequency which activates BK channels to ultimately decrease Ca2+ transients, whereas PDE3 inhibition acts through a protein kinase G-dependent pathway through a still unknown mechanism.In conclusion, our work shows that in the SMC, the different cAMP-PDE families exhibit a specificity in their function and/or mechanism of action, thus participating to a subcellular signaling compartmentation.