APOE and pulmonary arterial hypertension: Cluster #0 (interstitial lung diseases) represents the earliest and largest research focus, initially emphasizing basic mechanisms like “cells” and “tumorigenesis.” Recent keywords have shifted toward micro-mechanisms and potential targets such as “pulmonary arterial hypertension,” “myofibroblast differentiation,” and “apolipoprotein E.” Cluster #1 (acute exacerbation) primarily addresses clinical management strategies.