ACI (Acta Cardiologia Indonesiana) (Vol.5 No.2): 145-149

The BMPR2, ALK1 and ENG Genes Mutation in Congenital Heart Disease- Associated Pulmonary Artery Hypertension

Anggoro Budi Hartopo1,*, Dyah Wulan Anggrahini1, Noriaki Emoto2, Lucia Kris Dinarti1

1 Department of Cardiology and Vascular Medicine, Faculty of Medicine, Public Health and Nursing, Universitas Gadjah Mada / Dr. Sardjito Hospital, Yogyakarta, Indonesia 2 Laboratory of Clinical Pharmaceutical Science, Kobe Pharmaceutical University, Kobe, Japan

*Corresponding author: Anggoro Budi Hartopo MD, PhD. –email: [email protected] Address: Department of Cardiology and Vascular Medicine, Faculty of Medicine, Public Health and Nursing, Universitas Gadjah Mada / Dr. Sardjito Hospital, Yogyakarta, Indonesia, Jalan Farmako Sekip Utara, Yogyakarta, 55281, Indonesia

Manuscript submitted: September 11, 2019; Revised and accepted: September 18, 2019

ABSTRACT

The gene mutation is one of the background underlie the pathogenesis of pulmonary artery hypertension (PAH). Several genes have been recognized to be responsible for the development of PAH. The mutation in transforming growth factor-β (TGF-β) pathway is considered to be major genotype background in heritable PAH. The genetic mutation in bone morphogenetic protein -2 (BMPR2), -like 1 (ALK-1) and (ENG) are known to cause heritable PAH. In congenital heart disease–associated PAH (CHD- APAH), their mutation are also presence.

Keywords: gene mutation; pulmonary artery hypertension; congenital heart disease– associated PAH

INTISARI

Mutasi genetik merupakan salah satu kondisi yang mendasari patogenesis hipertensi arteri paru (HAP). Beberapa gene telah dikenal bertanggungjawab terhadap terjadinya HAP. Mutasi pada gen jalur transforming growth factor-β (TGF-β) diduga merupakan melatarbelakangi HAP yang diwariskan. Mutasi gen pada bone morphogenetic protein receptor-2 (BMPR2), activin receptor- like kinase 1 (ALK-1) dan endoglin (ENG) diketahui menyebabkan HAP yang diwariskan. Pada HAP yang terkait penyakit jantung kongenital, mutasi pada gen tersebut juga terjadi.

INTRODUCTION an increased level of pulmonary vascular resistance (> 3 Wood units).2 Clinically, the Pulmonary artery hypertension PAH can be divided into idiopathic PAH, (PAH) is a disease of pulmonary artery heritable PAH, or associated with other obstruction, due to complex plexyform conditions (APAH). lesions in the distal artery, with subsequent 1 Several diseases can be associated elevation in pulmonary vascular resistance. with PAH, such as such as drug-induced, Right ventricular failure will develop in the 1 toxin exposures, connective tissue eventual process of PAH. The PAH is diseases, human immunodeficiency virus characterized by a persistent increase in infection, portal hypertension, congenital mean pulmonary artery pressure (≥ 25 mm heart disease and schistosomiasis.2 Hg at rest), a normal value of pulmonary Heritable PAH is recognized by the capillary wedge pressure (≤ 15 mmHg) and presence of genetic mutation.

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Hartopo et al., 2019 ACI (Acta Cardiologia Indonesiana) (Vol.5 No.2): 145-149

The genetic mutation in bone The BMPR2 mutations in PAH result morphogenetic protein receptor-2 (BMPR2) in derangement of Smad signaling gene has been reported in about 75% of pathways, which increases the tendency of heritable PAH and nearly 25% of sporadic endothelial and artery smooth muscle cells PAH.3 Other mutations of gene encoding to proliferate and reduce their apoptotic activin receptor-like kinase 1 (ALK-1) and capacity.4 BMPR2 receptor-activated Smads endoglin (ENG) have been recognized in forms a complex with Smad4 (canonical PAH with a history of hereditary pathway) and translocatesinto the nucleus, haemorrhagic telangiectasia.3 where it regulates gene transcription.1 Other Pathophysiology of PAH is Smad4-independent pathways are related multifactorials and can be attributed to to Smad8 pathway, in which mutation of various pathologies. One of the important SMAD9 gene (gene encodes Smad8) leads aspects of pathophysiology of PAH is the to significant loss of function in microRNA role of genetic factors such as mutations in maturation and is implicated in PAH BMPR2, ALK1 and ENG genes. The pathogenesis.4 SMAD9 mutation BMPR2, ALK1 and ENG gene mutations demonstrates a cellular hyperproliferative have been determined to have a high level state, blunted BMP signaling, and of evidence as a causal role in PAH.4 The dysregulated Smad-mediated microRNA congenital heart disease–associated PAH activity.6 Drake et al. reported the case of (CHD-APAH) most commonly occurs with dyregulated SMAD9 pathway in CHD- septal defect and systemic-to-pulmonary APAH.6 The majority of the patients with shunt lesions. It accounts for around 10% of heritable PAH have mutations in BMPR2 all patients with PAH.5 Pulmonary which causes increased cellular hypertension in this condition is due to proliferation.7 Furthermore, BMPR2 mutation increasing blood flow in pulmonary vascular patients with PAH have more severe clinical systems and subsequent endothelial condition and low response to acute damage and pulmonary vascular vasodilator testing.7 remodeling. The pulmonary vascular lesions The prevalence of PAH-associated in CHD-APAH are similar with lesions in mutations in the CHD-APAH population idiopathic PAH and heritable PAH.5 In CHD- indicate that up to 10% have a APAH), the role of genetics mutations has germline BMPR2 mutation.8 Robert et al. been reported, however the result until reported six missense BMPR2 mutations in currently cannot be completely concluded exons 2 and 3 (an extracellular domain of yet. BMPR2), exon 5 (kinase domain for phosporylation) and exon 11 (cytoplasmic THE BMPR2 GENE MUTATION IN tail with unknown function), which CHD-APAH associated with altered protein sequence at evolutionary conserved amino acids and Mutation in BMPR2 genes has been 8 recognized in 70-80% of familial PAH and deranged BMPR2 function. Patients with 10-20% of idiopathic PAH. BMPR2 is gene BMPR2 mutations were identified as having that encode BMPR2 protein, a member of atrioventricular septal defects (AVSD) and multiple defects (ASD+PDA, ASD+PDA and the transforming growth factor-β (TGF-β) 8 receptor superfamily.4 The BMPR2 is an PAPVD, and AP window+VSD). A study in active serine-threonine kinase receptor 11 children with CHD-APAH (10 ASD and 1 VSD) indicated 1 subject (female, VSD) with which is expressed constitutively in the 9 lung.1 Ligation of BMPR2 by its ligands BMPR2 mutation (deletion in exon 1). (BMP2, BMP4, BMP6, BMP7, BMP9 and Study in Chinese CHD-APAH population BMP10), triggers BMPR2 phosphorylation indicated mutation rate of 7.5% in BMPR2 and Smad protein-signaling activation.1 gene among CHD-APAH, whereas in CHD

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Hartopo et al., 2019 ACI (Acta Cardiologia Indonesiana) (Vol.5 No.2): 145-149 with no PAH the mutation rate of BMPR2 is THE ALK1 GENE MUTATION IN 10 much lower (1.2 %). Females have CHD-APAH increased BMPR2 mutation rate and the Mutation in ALK1, which is also a dominant mutation type is missense member of the TGF-β receptor superfamily, 10 mutation. The type of defects were not is currently reported in PAH patients, 10 associated with BMPR2 mutation. although the mutation rate is not as high as BMPR2 is highly expressed on the BMPR2 gene mutation.11 In a European 4 pulmonary vascular endothelial cells. It cohort of adult-onset PAH, the mutation rate forms a complex with the type I receptors, of ALK1 gene was 0.9%.4 However this 4 ALK1. The complex of ALK1/BMPR2 collaborative research did not include CHD- receptor signaling pathway requires the APAH. The ALK1 is located on 4 utilization of ENG as a co-receptor. This 12q13 and plays a role in membrane bound receptor complex various tissues such as cell proliferation and regulates various cellular processes differentiation, cell migration, cell survival including cell differentiation, proliferation, and angiogenesis.4 Its missense mutations and apoptosis in embryonic and mature are located in the serine-threonine kinase 4 cells. Similar with BMPR2 expression, the domain, which is responsible for PAH ALK1 and ENG are also abundantly development in patients with hereditary expressed in the pulmonary endothelial hemorrhagic telangiectasia (HHT) as well as 4,5 cells. Figure 1 shows the diagram of familial and idiopathic PAH.12 BMPR2/ALK1/ENG complex receptors in The HHT and heritable PAH endothelial cells. The mutation of ALK1 and represent inherited diseases caused by ENG also deranges the BMPR2 mutation of the TGF-β receptor-mediated downstream signaling and is implicated in signalling, particularly involving ALK1, in the the presence of PVD in CHD-APAH. vasculatures.

Figure 1. The diagram of BMPR2/ALK1/ENG complex receptor in surface membrane of endothelial cells which exhibit its role on endothelial cell differentiation, proliferation, and apoptosis upon ligation by BMPs.

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The TGF-β signaling in endothelial only found one branch-site ENG mutation in cells modulates vascular remodeling, a subject with HHT and IPAH.14 The study therefore mutation in ALK-1 gene may by Pfarr et al. described a small number of induce derangement of remodeling of the pathogenic mutations in patients with CHD- vascular bed.13 A mutation analysis in 18 APAH.9 In 11 children with CHD-APAH children with PAH (16 idiopathic PAH and 2 without history of HHT, 1 patient with CHD-APAH), detected a missence mutation secundum ASD had mutation in the ENG in idiopatic PAH subject but not in CHD- gene (missense mutation in exon 12).9 APAH (BMPR2 mutation instead).14 Another study involved 11 children with CHD-APAH CONCLUSION (10 ASD and 1 VSD) and performed PCR amplification of the entire coding regions In CHD-APAH patients, mutation in and the exon/intron of the ALK1 gene did the TGF-β pathway genes involving not find ALK1 mutation.9 BMPR2/ALK1/ENG complex receptors is needed to be explored. Unlike idiopathic THE ENG GENE MUTATION IN PAH and heritable PAH, the genetic mutation in CHD-APAH is quite rare and its CHD-APAH clinical implication need further Endoglin is a homodimeric corroboration. glycoprotein ubiquitously located in the vascular endothelial cells of human body.4 It is an integral membrane glycoprotein in the ACKNOWLEDGEMENT 4 celular membranes. The ENG gene Authors acknowledge the research encodes a type I integral membrane grant from Universitas Gadjah Mada. This 4 glycoprotein receptor. It belongs to the review article is part of the outcome of 4 TGF-β signaling superfamily. This receptor research grant Penelitian Dasar 2019 from is expressed on proliferating vascular Universitas Gadjah Mada (No: endothelial cells and other cell types 2798/UN1.DITLIT/DIT-LIT/LT/2019) to associated with cardiovascular system, in Principal Investigator Anggoro Budi which indicate its important of endothelial Hartopo. and vascular function. It promotes cell differentiation, proliferation, angiogenesis, REFERENCES inflammation, and also induce wound healings.15 The ENG gene is located on 1. Archer S.L., Weir E.K., Wilkins M.R. chromosome 9q33-34 and the encoded 2010. Basic science of pulmonary protein demonstrates an extracellular arterial hypertension for clinicians: domain, hydrophobic transmembrane new concepts and experimental domain and a cytosolic domain.15 therapies. Circulation, 121:2045- Similar with the mutation on ALK1 2066. gene, the mutation on ENG gene is 2. Galiè N., Humbert M., Vachiery J.L., associated with HHT, in which the mutation Gibbs S., Lang I., Torbicki A., et al. involved are missense, splicing mutations, 2015. 2015 ESC/ERS Guidelines for and novel protein-truncating mutations.13 In the diagnosis and treatment of a European cohort of adult-onset PAH, the : The Joint mutation rate of ALK1 gene was 0.6%.4 Task Force for the Diagnosis and Unfortunately, this collaborative research Treatment of Pulmonary did not include CHD-APAH. The study by Hypertension of the European Harrison et al. in 18 children with PAH, Society of Cardiology (ESC) and the found no ENG mutation in CHD-APAH European Respiratory Society patients (only two subjects in this study), but (ERS): Endorsed by: Association for

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