ATF6 and pulmonary arterial hypertension: In cutaneous systemic sclerosis patients with PAH, there is an increase in the expression of ER stress markers, including activating transcription factor 4 (ATF-4) and ATF-6, and the spliced form X- box binding protein 1 (sXBP1) in blood mononuclear cells, suggesting that this associated disease can be affected by ER disruption (78).