Inflammation in Pulmonary Arterial Hypertension: Where Can the Sugen/Hypoxia Rodent Model Take Us?
Pulmonary Hypertension (PH) is a complex, multifactorial disease that results in right heart failure and premature death. Since the initial reports of PH in the late 1800s, the diagnosis of PH has evolved with respect to its definition, screening tools, and diagnostic techniques. Early detection of PH and the proper determination of etiology are vital for the early therapeutic intervention that can prolong life expectancy and improve quality of life. Group 1 of PH, Pulmonary Arterial Hypertension (PAH) remains a difficult disease to diagnose and despite new therapeutics, patient morbidity and mortality remain high. The search for a non-invasive screening tool for the identification and classification of PAH is ongoing. However, limited patient samples and a lack of an animal model that recapitulates human disease have hindered new therapeutics from translating to clinical use. The SUGEN/Hypoxia rat model is progressive with worsening hemodynamics and pulmonary vascular remodeling. This model is unique in its ability to replicate the characteristic complex vascular lesions of human disease. We have adopted an experimental design to study the progression of disease over multiple time points. This dissertation will highlight our findings in the study of plasma isolated over the progression of disease.
Plasma Extracellular Vesicles (EVs) are a submicron heterogenous group of circulating membrane bound packages that are released from nearly all cell types. EVs are altered with respect to disease and can serve as plasma biomarkers in PAH. In addition, EVs participate in cell signaling that facilitates PAH disease progression. Previously, our lab identified that PAH plasma derived EVs contribute to pulmonary vascular inflammation. Preliminary investigators led us to investigate leukocyte derived (CD45+) EV populations isolated via fluorescence-activated cell sorting (FACS) flow cytometry. Inconsistencies, in our functional data led to a critical view of traditional flow cytometry biomarker studies performed in plasma EVs. Overall, we found a lack of detail in EV literature utilizing flow cytometry. Our studies have led to the development of several strategies to improve technical rigor and reproducibility of EV flow cytometry studies. Further, our findings align with and complement the current standing of the International Society of Extracellular Vesicles (ISEV) flow cytometry working group.
In addition to EVs, we analyzed the plasma cytokine levels of PAH rats over the progression of disease. Overall, we found that plasma cytokines are altered with respect to disease severity. Interestingly, our inclusion of female PAH rats revealed that the cytokine profile throughout disease is entirely unique to their male counterparts. Sex dimorphism is prominent in PAH patient registries and our understanding of this phenomenon remains elusive. Our findings suggest that the SUGEN/Hypoxia rat model can offer insight into how sex dimorphism in inflammation influences the formation and progression of pulmonary arterial hypertension.