PDE1A and pulmonary arterial hypertension: Accordingly, the current study set out to investigate the specific mechanisms by which BMSC-EVs influence macrophage polarization in PAH, and the obtained findings revealed that BMSC-EVs carrying miR-200b could induce PKA phosphorylation by repressing the expression of PDE1A, whereby promoting M2 polarization of macrophages and ultimately attenuating PAH.