THE ROLE OF PONTIN IN MODULATING ADVERSE CARDIAC REMODELLING VIA REGULATION OF HIPPO PATHWAY

  • Bayu Lestari

Student thesis: Phd

Abstract

Cardiac remodelling is a crucial process in the development of heart failure (HF). Previous observations confirmed that inhibiting the Hippo pathway or activating YAP (the main effector of this pathway) showed beneficial effects in reducing cardiac remodelling following myocardial infarction. However, targeting the Hippo core components for therapeutic purposes is challenging due to the limited understanding of its upstream regulatory mechanism. Pontin is an AAA+ ATPase, which is important in regulating several cellular functions, such as cell proliferation, survival, and transcriptional regulation. Studies in zebrafish showed that Pontin plays an important role in embryonic heart development. However, the role of Pontin in the postnatal mammalian heart is unknown. Therefore, this study aimed to investigate the role of Pontin in the regulation of cardiac remodelling in vitro and in vivo and to examine its association with the Hippo pathway. Cellular models of Pontin knockdown and overexpression were generated in neonatal rat cardiomyocytes by using siRNA and adenoviral systems, respectively. Furthermore, inducible cardiac-specific Pontin knock-out (PontinicKO) mice were generated to investigate the cardiac phenotype and molecular features in this model. In neonatal rat cardiomyocytes, Pontin knockdown reduced YAP activity, whereas Pontin overexpression induced YAP activity as indicated by YAP phosphorylation, nuclear translocation, and transcriptional activity. Phenotypically, Pontin knockdown was negatively associated with cardiomyocyte proliferation and survival, whereas Pontin overexpression demonstrated the opposite effects. In vivo experiments showed that PontinicKO mice displayed severe cardiomyopathy, characterised by a significant reduction of ejection fraction, increased hypertrophy, fibrosis, and massive cardiomyocyte apoptosis at the 24th day following the induction of Pontin gene deletion. Meanwhile, Angiotensin treatment accelerates the development of HF in these mice. Molecular analysis indicated that apoptosis inducers (Bax, Bad, Caspase-3) and MST1 were significantly upregulated in Pontin-deficient mice, suggesting that Pontin regulates programmed cell death in cardiomyocytes via MST1 upregulation. Further analysis of RNA sequencing data revealed that Pontin gene ablation was associated with the upregulation of Hippo core components and their positive upstream regulators. Interestingly, the transcriptomic analysis indicated that Pontin is strongly associated with the Myc target genes, which are linked with epigenetic regulation of MST1 expression. However, further study is still required to confirm this notion. In conclusion, our findings identified Pontin as a novel regulator of adverse cardiac remodelling via regulating the Hippo pathway in cardiomyocytes, specifically MST1-mediated cardiomyocyte apoptosis. This study may lead to the development of a new approach to control cardiac remodelling by targeting Pontin.
Date of Award1 Aug 2024
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorDelvac Oceandy (Supervisor) & Alicia D'Souza (Supervisor)

Keywords

  • Pontin
  • Hippo pathway
  • cardiac remodelling

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