Pulmonary hypertension (PH) is a severe and progressive disease characterised by high pulmonary artery pressure, usually culminating in right heart failure. Current therapeutic approaches in PH largely provide symptomatic relief while the prognosis rate is lower due to the lack of specific molecular targets and the involvement of several factors in the development of PH. Numerous studies have suggested a crucial role of matrix metalloproteinase (MMP) axis during development and disease states, specifically with regard to extracellular matrix remodelling and vascular homeostasis. Increased MMP activity has been demonstrated in experimental animal models of PH, and MMP inhibition has been shown to either attenuate or enhance vascular remodelling. Moreover, several studies emphasise that restoration of deregulated MMPs to physiological MMP/tissue inhibitor of MMPs ratios would potentiate reverse remodelling in PH. This article will highlight the pathophysiological role of MMPs in vascular remodelling and the establishment of PH. In particular, we will focus on the MMP expression and regulation in pulmonary vasculature and pulmonary vascular remodelling. We will also provide an overview of recent clinical and experimental findings and their impact on achieving maximum reversal of PH, as well as current issues and future perspectives.

Remodeling of the distal pulmonary artery wall is a characteristic feature of pulmonary hypertension (PH). In hypoxic PH, the most substantial pathologic changes occur in the adventitia. Here, there is marked fibroblast proliferation and profound macrophage accumulation. These PH fibroblasts (PH-Fibs) maintain a hyperproliferative, apoptotic-resistant, and proinflammatory phenotype in ex vivo culture. Considering that a similar phenotype is observed in cancer cells, where it has been associated, at least in part, with specific alterations in mitochondrial metabolism, we sought to define the state of mitochondrial metabolism in PH-Fibs. In PH-Fibs, pyruvate dehydrogenase was markedly inhibited, resulting in metabolism of pyruvate to lactate, thus consistent with a Warburg-like phenotype. In addition, mitochondrial bioenergetics were suppressed and mitochondrial fragmentation was increased in PH-Fibs. Most importantly, complex I activity was substantially decreased, which was associated with down-regulation of the accessory subunit nicotinamide adenine dinucleotide reduced dehydrogenase (ubiquinone) Fe-S protein 4 (NDUFS4). Owing to less-efficient ATP synthesis, mitochondria were hyperpolarized and mitochondrial superoxide production was increased. This pro-oxidative status was further augmented by simultaneous induction of cytosolic nicotinamide adenine dinucleotide phosphate reduced oxidase 4. Although acute and chronic exposure to hypoxia of adventitial fibroblasts from healthy control vessels induced increased glycolysis, it did not induce complex I deficiency as observed in PH-Fibs. This suggests that hypoxia alone is insufficient to induce NDUFS4 down-regulation and constitutive abnormalities in complex I. In conclusion, our study provides evidence that, in the pathogenesis of vascular remodeling in PH, alterations in fibroblast mitochondrial metabolism drive distinct changes in cellular behavior, which potentially occur independently of hypoxia.

Epigenetic mechanisms, including DNA methylation and histone post‐translational modifications (PTMs), have been known to regulate chromatin structure and lineage‐specific gene expression during cardiovascular development and disease. However, alterations in the landscape of histone PTMs and their contribution to the pathogenesis of incurable cardiovascular diseases such as pulmonary hypertension (PH) and associated right heart failure (RHF) remain largely unexplored. This review focusses on the studies in PH and RHF that investigated the gene families that write (histone acetyltransferases), read (bromodomain‐containing proteins) or erase (histone deacetylases [HDACs] and sirtuins [SIRT]) acetyl moieties from the ε‐amino group of lysine residues of histones and non‐histone proteins. Analysis of cells and tissues isolated from the in vivo preclinical models of PH and human pulmonary arterial hypertension not only confirmed significant alterations in the expression levels of multiple HDACs, SIRT1, SIRT3 and BRD4 proteins but also demonstrated their strong association to proliferative, inflammatory and fibrotic phenotypes linked to the pathological vascular remodelling process. Due to the reversible nature of post‐translational protein acetylation, the therapeutic efficacy of numerous small‐molecule inhibitors (vorinostat, valproic acid, sodium butyrate, mocetinostat, entinostat, tubastatin A, apabetalone, JQ1 and resveratrol) have been evaluated in different preclinical models of cardiovascular disease, which revealed the promising therapeutic benefits of targeting histone acetylation pathways in the attenuation of cardiac hypertrophy, fibrosis, left heart dysfunction, PH and RHF. This review also emphasizes the need for deeper molecular insights into the contribution of epigenetic changes to PH pathogenesis and therapeutic evaluation of isoform‐specific modulation in ex vivo and in vivo models of PH and RHF. LINKED ARTICLES This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc