Adenylyl cyclases (AC), the principal control of cyclic AMP (cAMP) signaling pathway, are differently expressed in quiescent and remodeled vascular smooth muscle cells (SMCs). Particularly, the induction of AC8 isoform was reported in the inflammatory/migratory phenotype together with induction of metalloproteinases (MMPs 2 and 9) (Keuylian et al., 2012). Here, we investigated whether selective AC8 expression in VSMCs was sufficient to induce pulmonary hypertension (PH) in mice.

Transgenic mice carrying human AC8 cDNA under a-MHC promoter (AC8TG) were used (Lipskaia et al., 2000). We studied three groups of mice aged 3, 7 and 12months. Standard procedures were used to assess heart function and the morphologic characteristics of pulmonary muscular arteries. RNA expression was determined using real-time RT-PCR analysis.

No difference in basal cardiac function was detected in young mice (2–6-month-old). Starting from 8months echocardiographic analysis revealed progressive increase of contractile function evaluated by LVED and LVES diameters, ED and ES volumes; and decrease of EF (%) and FS (%) compared to their littermates. At the end point (12months) AC8TM exhibited an increased heart weight/tibia length ratio (1.02±0.13 vs. 0.77±0.11, P<0.01). Invasive hemodynamic measurements showed increased contractility and right ventricular systolic pressure (RVSP) at 3, 7 and 12-month-old AC8TG (in 3-month-old: 27.83±1.8 vs. 21.00±1.2, P<0.01; in 12-month-old: 27.07±0.4 vs. 20.33±0.2, P<0.01). Marker increase of AC8 expression was detected in lung, aorta and isolated cultured PA-SMC from AC8TG. In AC8TG aorta the expression of SMHC (smooth myosin heavy chain) and smoothelin was decreased, whereas the expression of MMP9 was increased, suggesting acquisition of proliferating/inflammatory/migratory phenotype by aortic SMC. By contrast, in lung RT-PCR analysis revealed an increase of SMHC expression and a decrease of MMP9 expression. These observations suggest acquisition of inflammatory/contractile phenotype by PH VSMC and highlight a difference between systemic and pulmonary vessels remodeling.

Adeylyl cyclase 8 over-expression in PA-SMC promotes the acquisition of inflammatory/migratory phenotype and development of pulmonary hypertension.