Jian Hu

Novel Targets of Drug Treatment for Pulmonary Hypertension

Biomedical advances over the last decade have identified the central role of proliferative pulmonary arterial smooth muscle cells (PASMCs) in the development of pulmonary hypertension (PH). Furthermore, promoters of proliferation and apoptosis resistance in PASMCs and endothelial cells, such as aberrant signal pathways involving growth factors, G protein-coupled receptors, kinases, and microRNAs, have also been described. As a result of these discoveries, PH is currently divided into subgroups based on the underlying pathology, which allows focused and targeted treatment of the condition. The defining features of PH, which subsequently lead to vascular wall remodeling, are dysregulated proliferation of PASMCs, local inflammation, and apoptosis-resistant endothelial cells. Efforts to assess the relative contributions of these factors have generated several promising targets. This review discusses recent novel targets of therapies for PH that have been developed as a result of these advances, which are now in pre-clinical and clinical trials (e.g., imatinib [phase III]; nilotinib, AT-877ER, rituximab, tacrolimus, paroxetine, sertraline, fluoxetine, bardoxolone methyl [phase II]; and sorafenib, FK506, aviptadil, endothelial progenitor cells (EPCs) [phase I]). While substantial progress has been made in recent years in targeting key molecular pathways, PH still remains without a cure, and these novel therapies provide an important conceptual framework of categorizing patients on the basis of molecular phenotype(s) for effective treatment of the disease.

Development of a Mouse Model of Metabolic Syndrome, Pulmonary Hypertension, and Heart Failure with Preserved Ejection Fraction

&NA; Pulmonary hypertension (PH) associated with heart failure with preserved ejection fraction (PH‐HFpEF; World Health Organization Group II) secondary to left ventricular (LV) diastolic dysfunction is the most frequent cause of PH. It is an increasingly recognized clinical complication of the metabolic syndrome. To date, no effective treatment has been identified, and no genetically modifiable mouse model is available for advancing our understanding for PH‐HFpEF. To develop a mouse model of PH‐HFpEF, we exposed 36 mouse strains to 20 weeks of high‐fat diet (HFD), followed by systematic evaluation of right ventricular (RV) and LV pressure‐volume analysis. The HFD induces obesity, glucose intolerance, insulin resistance, hyperlipidemia, as well as PH, in susceptible strains. We observed that certain mouse strains, such as AKR/J, NON/shiLtJ, and WSB/EiJ, developed hemodynamic signs of PH‐HFpEF. Of the strains that develop PH‐HFpEF, we selected AKR/J for further model validation, as it is known to be prone to HFD‐induced metabolic syndrome and had low variability in hemodynamics. HFD‐treated AKR/J mice demonstrate reproducibly higher RV systolic pressure compared with mice fed with regular diet, along with increased LV end‐diastolic pressure, both RV and LV hypertrophy, glucose intolerance, and elevated HbA1c levels. Time course assessments showed that HFD significantly increased body weight, RV systolic pressure, LV end‐diastolic pressure, biventricular hypertrophy, and HbA1c throughout the treatment period. Moreover, we also identified and validated 129S1/SvlmJ as a resistant mouse strain to HFD‐induced PH‐HFpEF. These studies validate an HFD/AKR/J mouse model of PH‐HFpEF, which may offer a new avenue for testing potential mechanisms and treatments for this disease.

Targeting Pulmonary Endothelial Hemoglobin α Improves Nitric Oxide Signaling and Reverses Pulmonary Artery Endothelial Dysfunction

&NA; Pulmonary hypertension is characterized by pulmonary endothelial dysfunction. Previous work showed that systemic artery endothelial cells (ECs) express hemoglobin (Hb) &agr; to control nitric oxide (NO) diffusion, but the role of this system in pulmonary circulation has not been evaluated. We hypothesized that up‐regulation of Hb &agr; in pulmonary ECs contributes to NO depletion and pulmonary vascular dysfunction in pulmonary hypertension. Primary distal pulmonary arterial vascular smooth muscle cells, lung tissue sections from unused donor (control) and idiopathic pulmonary artery (PA) hypertension lungs, and rat and mouse models of SU5416/hypoxia‐induced pulmonary hypertension (PH) were used. Immunohistochemical, immunocytochemical, and immunoblot analyses and transfection, infection, DNA synthesis, apoptosis, migration, cell count, and protein activity assays were performed in this study. Cocultures of human pulmonary microvascular ECs and distal pulmonary arterial vascular smooth muscle cells, lung tissue from control and pulmonary hypertensive lungs, and a mouse model of chronic hypoxia‐induced PH were used. Immunohistochemical, immunoblot analyses, spectrophotometry, and blood vessel myography experiments were performed in this study. We find increased expression of Hb &agr; in pulmonary endothelium from humans and mice with PH compared with controls. In addition, we show up‐regulation of Hb &agr; in human pulmonary ECs cocultured with PA smooth muscle cells in hypoxia. We treated pulmonary ECs with a Hb &agr; mimetic peptide that disrupts the association of Hb &agr; with endothelial NO synthase, and found that cells treated with the peptide exhibited increased NO signaling compared with a scrambled peptide. Myography experiments using pulmonary arteries from hypoxic mice show that the Hb &agr; mimetic peptide enhanced vasodilation in response to acetylcholine. Our findings reveal that endothelial Hb &agr; functions as an endogenous scavenger of NO in the pulmonary endothelium. Targeting this pathway may offer a novel therapeutic target to increase endogenous levels of NO in PH.

Nitrite Prevents Right Ventricular Failure and Remodeling Induced by Pulmonary Artery Banding.

Background: Nitrite has been shown to reduce right ventricle (RV) remodeling in experimental pulmonary hypertension. However, whether this effect is due to a reduction in RV afterload (ie, reduction in pulmonary artery pressure) or a direct effect on the RV itself remains unanswered. We hypothesize that nitrite has direct effects on RV remodeling and studied its effects in mice with pulmonary artery banding (PAB). Methods and Results: PAB decreased exercise tolerance and reduced RV systolic and diastolic function. Nitrite treatment attenuated the decrease in RV systolic function and improved the RV diastolic function. Nitrite-treated mice with PAB had similar exercise tolerance compared with a control group. PAB induced RV hypertrophy and fibrosis which were associated with increased expression of phospho-Akt. Interestingly, nitrite treatment attenuated PAB-induced RV hypertrophy and reduced the expression of phospho-Akt in RV tissue from mice with PAB. In neonatal rat cardiac fibroblast, nitrite also attenuated hypoxia-induced increase in expression of phospho-Akt. Conclusion: Our study indicates that nitrite treatment has direct beneficial effects on RV and improves function and attenuates remodeling in RV exposed to chronic pressure overload. These beneficial effects, at least in part, could be due to the inhibition of the phospho-Akt (p-Akt) pathway activation.