The metabolic basis of cell identity in the pulmonary arteries and the right ventricle in pulmonary arterial hypertension
Creators: Zhang, Yongneng
Publisher: name: University of Alberta Library
Year: 2023

<p>Pulmonary arterial hypertension (PAH) is an incurable disease characterized by profound pulmonary vascular remodeling, including the development of plexogenic lesions (which is the hallmark of PAH) that results in lumen obliteration, raising the pulmonary vascular resistance (PVR) and the right ventricle (RV) afterload. While initially this leads to RV hypertrophy, it eventually advances to RV dilatation, decompensation and death. </p>

<p>One of the biggest challenges in PAH research is the lack of good animal models that mimic human PAH with severe high mean PA pressure (mPAP) and plexogenic lesions.  In Chapter 2, we studied a cohort of 60 PAH patients and found Sirtuin 3 (Sirt3, a mitochondrial deacetylase) and uncoupling protein 2 (Ucp2, an atypical uncoupling protein enabling mitochondrial calcium entry) loss of function SNPs, often both found in the same patient in a homozygous or heterozygous manner. The presence of these SNPs correlated positively with PAH severity and 10 years outcomes (death and transplantation). We then generated a mouse model lacking both Sirt3 and Ucp2. We found that the double KO mice have an increasing severity of PAH (mPAP, right ventricular hypertrophy/dilatation and extensive vascular remodeling, including inflammatory plexogenic lesions as removed from wildtype to heterozygous to KO for both genes), along with insulin resistance. The suppressed mitochondrial function (decreased respiration, increased mitochondrial membrane potential) also exhibited a similar gene-dose dependent effect. This was the first mouse model ever described exhibiting spontaneous severe PAH with frequent plexogenic lesions and provided further support to the metabolic theory of PAH that our group had recently proposed. </p>

<p>In Chapter 3, we focused on the transition from compensated RV hypertrophy (cRVH) to decompensated RV hypertrophy (dRVH), because the main driver of mortality and morbidity in PAH is not the degree of PA pressure increase, but rather the function of the RV. What makes the transition from cRVH to dRVH and how one RV is more prone to failure than another RV is unknown. We hypothesized that a transition from cardiac fibroblasts (cFB) to cardiac myofibroblasts (cMFB) underlies this mechanism. We studied a cohort of rats with monocrotaline-induced pulmonary hypertension (PHT). Compared to cRVH, dRVH rats still kept high mPAP, but had lower RV systolic pressure, higher right atrial pressure, lower cardiac output, lower TAPSE and higher RV end-diastolic diameter. We found that the dRVH has an increased myofibroblast number compared with normal RV and cRVH. The dRVH myofibroblasts had increased proliferation indices and decreased mitochondrial function and mitochondrial calcium (mCa++) compared with normal and cRVH cFB. It has been shown that the decrease in mCa++ is related to mitochondrial calcium uptake 1 (MICU1) methylation and lack of UCP2. The dRVH cMFB had increased MICU1 methylation (shown by protein arginine methyltransferase 1 (PRMT1) and asymmetric dimethylarginine (ADMA) levels) and decreased UCP2, compared to normal RV and cRVH cFB. In human RV tissue (Control, cRVH, dRVH, n=5 for each), we confirmed the result of cMFB numbers, PRMT1 and UCP2 levels as what we found in the rat model. In a cohort of 25 patients with PHT (secondary PHT vs Pulmonary Arterial Hypertension) undergoing both catheterization and echocardiography, we found that carriers of this germline UCP2 loss of function SNP, had decreased TAPSE to non-carriers despite similar PA pressures. </p>

<p>This thesis made two contributions to the PAH field. First, it showed a provocative correlation between the loss-of-function SNPs of SIRT3 and UCP2 with the severity of disease in patients with PAH. We also created a novel mouse model in which to explore the true pathology of PAH since it was the first animal model with spontaneous plexogenic lesions and insulin resistance, both features of human PAH not presented in any other models. Second, we explored the mechanism of the transition from cRVH to dRVH in PAH, and we found the transformation from cFB to cMFB underlines this transition. We confirmed these findings in human RVs. This was important because we showed that this transition was not due to cardiomyocyte failure as thought until now. Furthermore, we showed that the loss-of-function SNP of UCP2 correlates with worse RV function in PAH patients regardless of the degree of mPAP, making this UCP2 SNP a potential biomarker that could predict RV function in PAH patients, if confirmed in larger cohorts. </p>