SPP1 and pulmonary arterial hypertension: It is expressed and upregulated during inflammation and expressed in high levels in patients with fibrotic lung disorders, and it has been demonstrated that OPN is one of the most upregulated genes in the lungs of patients with severe PAH, while the SPP1 gene shows a strong correlation with mPAP (mean pulmonary arterial pressure), which should be less than 20 mmHg [70].