TMBIM4 and pulmonary arterial hypertension: The present results showed that (1) Sigma 1 receptor (S1R) was expressed in the RV and was downregulated in PAH rats; (2) pharmacologically activated S1R alleviated right ventricular dysfunction and structural remodeling induced by pulmonary hypertension; (3) S1R activation did not reduce pulmonary vessel remodeling in rats with PAH; and (4) S1R exerted its protective effects partly through oxidative stress mediated by the NRF 2/HO 1 pathway.