Biomarkers of the Pulmonary Complications of Scleroderma:
The SSc-PAH and SSc-ILD Phenotypes
PI – Harrison Farber, MD
Pulmonary hypertension (PH) is a well-recognized complication of systemic sclerosis (SSc) and occurs in 10-50% of patients depending on the study and mode of diagnosis. Incidence of PH increases with disease duration, with later age of disease onset, and is greater in males and in patients with limited SSc. PH is now a leading cause of mortality in these patients; moreover, incidence may be increasing due to the longer life span of SSc patients. Unlike the PH resulting from hypoxemia due to interstitial lung disease (ILD) with diffuse SSc (dcSSc), the PH associated predominantly with limited SSc (lcSSc) is histologically identical to other forms of pulmonary arterial hypertension (PAH). Whether SSc-PAH has similar predispositions, genetic or otherwise, to other populations predisposed to PAH and/or whether the molecular basis is similar is not known. Contrary to the excessive angiogenesis in vascular lesions of PAH, early vascular damage in SSc is characterized by endothelial cell (EC) injury; in addition, serum from SSc patients contains factors such as anti-endothelial cell antibodies (AECA) that can induce EC injury and are associated with the presence and severity of PH. Also, in contrast to other forms of PAH, with possible exception of HIV-associated PAH, connective tissue disease-associated PAH, such as SSc, is characterized by autoimmunity. Whether this inflammatory state contributes to development of PAH is not known. These observations raise the intriguing possibility that SSc-PAH arises from induction of EC injury, due to dysregulated autoimmunity, selection of an apoptosis-resistant population of EC and, ultimately, excessive angiogenesis observed in vascular lesions of established SSc-PAH. We have published data demonstrating that a molecular profile reflecting these processes exists in patients with SSc-PAH (see attached manuscripts) During the tenure of this grant, we will investigate the hypotheses that: 1) vascular changes in SSc-PAH result from EC dysfunction, initiated by interaction of autoimmunity and injury leading to subsequent excessive angiogenesis; and 2) specific markers of autoimmunity and EC injury and/or angiogenesis can define phenotypes in the SSc population and predict development and progression of PAH.
As such this project will:
1) Identify markers of inflammation/injury and angiogenesis in SSc patients with PAH (SSc-PAH phenotype). We will expand the markers of inflammation/injury and angiogenesis we have found to associate with established SSc-PAH. While this strategy may identify markers associated with established SSc-PAH, it is possible that there are different or additional markers associated with development of SSc-PAH. Thus, we will examine markers of inflammation/injury and angiogenesis annually in SSc patients who develop PAH during the tenure of this proposal. This strategy (both a cross-sectional and longitudinal study) will validate the markers identified in patients with established SSc-PAH and discover additional markers associated with development of SSc-PAH.
2) Compare markers identified in patients with SSc-PAH with those markers identified in patients with SSc-interstitial lung disease (SSc-ILD phenotype). (collaboration with Project #1). The cross-sectional and longitudinal studies above will identify candidate molecules of the “SSc-PAH phenotype”. We hypothesize that candidate molecules in these individuals will differ from candidate markers identified in individuals in whom interstitial lung disease is predominant, the “SSc-ILD phenotype”. Using candidate molecules from these two projects, we will compare and contrast them to designate the two phenotypes most associated with morbidity and mortality in SSc.
3) Determine the relationship between outcomes in patients with SSc-PAH and vascular endothelial endoplasmic reticulum (ER) stress and unfolded protein response (UPR). (collaboration with Project #3). Growing evidence suggests that inflammation contributes to development or progression of PAH; and we have demonstrated upregulation of inflammatory molecules in patients with SSc-PAH. In addition, inflammation is associated with development of endothelial ER stress. Whether outcomes in PAH are associated with the degree of endothelial ER stress has not been investigated. As such, we will: a) correlate multiple parameters of the clinical status of SSc-PAH patients with the degree of endothelial ER stress induced by their serum; and b) use our recently described model of spontaneous PH associated with inflammation, the adiponectin deficient mouse to provide EC from an inflammatory, pulmonary hypertensive model and to investigate candidate molecules and pathways of EC ER stress.