Role of Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN-1) in pulmonary hypertension
Pulmonary arterial hypertension (PAH) is a condition that is characterized by an increased pulmonary vascular resistance due to prolonged pulmonary vascular remodeling. It encompasses complex pathological mechanisms including dysregulated proliferation and resistance to apoptosis of all three vascular cell types, leading to the emergence and ... development of PAH. Clinical trials of various therapeutic products targeting vascular remodeling are underway, although effective and successful therapeutical treatment of the disease currently remains a major challenge. Existing evidence strongly supports the involvement of Pin1 signaling in vascular homoeostasis. However, the role of Pin1 in PAH has not been studied, and this led us to investigate the expression and potential contribution of Pin1 signaling in PAH and Juglone as an attractive future therapy for PAH. Pin1 is a unique enzyme, which induces cis/trans conformational changes by interacting with specific Ser/thr-Pro motifs present in its phosphorylated substrates. Pin1 guided isomerization of various substrates results in different biological outcomes, offering an alternative signaling pathway under different cellular conditions. Pin1 is involved in the cell cycle regulation in various diseases. This study provides evidence for the first time that Pin1 is upregulated in clinical and experimental models of PAH, specifically in a mouse model of chronic-hypoxia and rat model SU5416/hypoxia-induced PAH. Pin1 expression is correlated with clinical characteristics of patients with PAH such as CI and might correlate with disease severity. In vasculature, Pin1 expression is observed in both pulmonary artery smooth muscle cells (PASMCs) as well as pulmonary artery endothelial cells (PAECs). Here we show, that genetic and pharmacological inhibition of Pin1 resulted in downregulation of proliferating cell nuclear antigen (PCNA) and Ki-67, leading to a marked decrease in proliferative responses of human PASMCs and PAECs. Thus, endogenous Pin1 is a significant contributor in cancer-like proliferation of vascular cells. Apoptotic resistant vascular cell growth exhibits an alternative paradigm of the PAH phenotype. Pin1 modulates various signaling pathways including the regulation of cell death signaling and contributes to the pathogenesis of various diseases. In our study, Pin1 deletion led to an initiation of apoptosis in human vascular cells as evidenced by an increase in Cleaved Caspase-3 and cleaved PARP in both PASMCs and PAECs. Pin1 was induced by growth factors in PASMCs, and siRNA-mediated deletion of Pin1 resulted in a strong decrease of the activity of key TFs, which have been previously implicated in chronic inflammation, tissue remodeling, and PH, such as STAT3, HIF, EGR, OCT4 and SMADs. In-vivo, Juglone administration lowered pulmonary vascular resistance, enhanced RV function, improved pulmonary vascular and cardiac remodeling in the SU5416/hypoxia rat model of PAH and the chronic hypoxia-induced PH model in mice. Pin1 inhibition in vascular cells of the lung resulted in inhibition of proliferative (PCNA) and activation of pro-apoptotic responses (Cleaved Caspase-3), implicating Pin1 for PH emergence. The unique ability of Pin1 to bind with phosphorylated trans forms of Ser/Thr‐containing proteins either enhances degradation and/or stabilizes the protein and makes it an effective molecular switch of multiple downstream cellular functions. To establish personalized therapeutic approaches based on Pin1 inhibition, a thorough understanding of the upstream and downstream molecular mechanisms driving Pin1 regulation and the molecular and cellular effects driven by Pin1 in diseased vascular cells is important. Taken together, this study puts forward a role of Pin1 signaling in the regulation of proliferation and apoptosis of smooth muscle and endothelial cells contributing to PAH pathogenesis. Thus, Pin1 represents a novel target, and Juglone a potential new strategy for the prevention of cardiovascular diseases, including pulmonary arterial hypertension.