Expression of connexin 43 (Cx43), protein that forms communicating junctions, is increased in intrapulmonary arteries (IPA) from rats suffering from hypoxic pulmonary hypertension (PH).

In the present study, we compare heterozygous Cx43 knockout mice (Cx43^+/−) to their wild type littermate mice (Cx43^+/+) in normoxia (N) and chronic hypoxia (CH) in order to further address the role of Cx43 in PH.

Experiments were conducted on Cx43^+/+ and Cx43^+/− CD1 male mice, which were either housed in ambient room air (N) or exposed to CH (0.5atm during 3 weeks) to induce PH. Right ventricular systolic pressure (RVSP) was measured with a catheter. IPA remodelling was estimated by eosin-hematoxylin staining whereas right ventricular hypertrophy was estimated by fulton index (ratio of right ventricle to left ventricle plus septum weight).

In N, body weight, fulton index and RVSP were similar in Cx43^+/− and Cx43^+/+. In CH vs. N, body weight was decreased whereas fulton index as well as RVSP were increased in both Cx43^+/− and Cx43^+/+. In CH, fulton index was slightly smaller in Cx43^+/− vs. Cx43^+/+. Immunofluorescent labelling of IPA showed that Cx43 was expressed in endothelium as well as smooth muscle in Cx43^+/+ whereas it was strongly decreased in Cx43^+/−. Quantitative RT-PCR and Western Blot showed a decrease of Cx43 mRNA and proteins respectively, in IPA from both N and CH Cx43^+/− whereas Cx37 and Cx40 mRNA were stable. IPA wall thickness was increased in CH vs. N Cx43^+/+ but not Cx43^+/−. PCNA labelling experiments confirmed the presence of IPA cell proliferation in CH Cx43^+/+ and its absence in CH Cx43^+/−. With TUNEL methodology, we demonstrated the absence of lung tissue apoptosis. In both CH and N Cx43^+/− vs. Cx43^+/+, reactivity to endothelin-1 was increased and relaxation to carbachol was unchanged.

Altogether, Cx43 seems to play an important role in IPA remodelling and reactivity in CH-PH mice.