Objective: Pulmonary arterial hypertension (PAH) and interstitial lung disease (ILD) are major causes of mortality in systemic sclerosis (SSc). We used a previously identified microarray biomarker to determine if SSc-PAH and SSc-ILD patients demonstrate distinct gene expression profiles.
Methods: PBMCs were collected from healthy controls (n=10), SSc (SSc) patients without pulmonary hypertension [SSc-noPAH, n=39], and SSc-PAH patients (n=21; mPAP≥25, PCWP≤15, PVR≥3WU) diagnosed by right heart catheterization (RHC). SSc-ILD patients were defined as those with evidence of fibrosis on chest CT and significant restriction (FVC<70% predicted, n = 11). SSc-PAH biomarker included 69 genes selected by unbiased statistical screening of 3 publicly available microarray studies. RNA levels were measured by Nanostring. Gene expression levels that were significantly correlated with PAH (multiple statistical measures) were chosen as inputs into a forward selection logistic regression model.
Results: When ILD patients were included (n=64), 4 genes (S100P, CD8B1, CCL2, TIMP1) and male sex predicted PAH with a high level of accuracy (AUC = 0.83). Without ILD patients (n=53), 2 genes (THBS1, CD8B1) and male sex predicted PAH with a high level of accuracy (AUC = 0.80). When examining SSc patients with borderline elevated pulmonary pressures (mPAP = 21-24 mmHg), gene expression changes closely resembled the SSc-PAH group, except for THBS1.
Conclusion: SSc-PAH and SSc-ILD have similar, but distinct, gene expression profiles. Many gene expression changes occur early in the disease course, potentially allowing for early detection. THBS1 appears to be an important mediator in the development of PAH-predominant phenotype. Further prospective investigation is warranted.