Heart failure is associated with a high mortality rate and is one of the most prevalent diseases worldwide whereby susceptibility increases with age. The development of heart failure occurs over an extensive period of time in which arrhythmias and hypertrophy are both very prevalent manifestations throughout this progression. Arrhythmias are defined as an irregular rhythm originating from intracellular calcium dysregulation, which can be fatal. Cardiac hypertrophy is a compensatory condition induced by increased workload involving augmented cardiomyocyte growth accompanied by myocardial remodelling. However, under prolonged periods of increased stress this compensatory mechanism can lead to cardiac dysfunction. The current treatments for heart failure are mainly aimed at relieving symptoms or itself possess proarrhythmic ability. Therefore it is fundamental to elucidate the pathways involved in arrhythmias and hypertrophy for the development of more effective treatment. p21 activated protein kinase (Pak1) is a novel gene involved in the regulation of cardiac function, however, the mechanisms involved remain inconclusive. This study has demonstrated Pak1 to be both antiarrhythmic and antihypertrophic, emphasizing Pak1 as a credible therapeutic target for simultaneously treating both manifestations. The antiarrhythmic properties of Pak1 were demonstrated through cardiomyocyte-specific Pak1 knockout (Pak1cko) mouse model which underwent Isoproterenol (ISO) stimulation for 2 weeks. Compared with ISO treated control group, the Pak1cko group had increased calcium irregularities and particularly a prolongation in sarcoplasmic reticulum (SR) calcium refill. The absence of Pak1 abrogated the transcriptional up-regulation of sarcoplasmic reticulum calcium ATPase 2a (SERCA2a) under stressed conditions. Further analysis in neonatal rat cardiomyocytes (NRCMs) revealed this regulation to be through activation of the transcription factor, SRF. The antihypertrophic effects of Pak1 were further illustrated through cardiomyocyte-specific overexpressed constitutively-active Pak1 (Pak1cTG) mice which were subjected to transverse aortic constriction (TAC) for 3 weeks. Compared to TAC control group, Pak1cTG mice had improved cardiac performance accompanied with diminished fibrosis. Further analysis led to the discovery of a novel antihypertrophic pathway of Pak1 involving positive regulation of the E3ligase, Fbxo32 through activation of Smad3. This pathway is vital in the prevention of calcineurin (PP2B) accretion. Berberine administration in TAC treated mice corroborated that Fbxo32 up-regulation is sufficient in the prevention of hypertrophy. In conclusion, my study has demonstrated that Pak1 conveys antiarrhythmic influence through the up-regulation of SERCA2a. In the prevention of pathological hypertrophy, Pak1 inhibits PP2B through positive regulation of Fbxo32. Overall, my thesis has advanced the knowledge about cardioprotective pathways initiated by Pak1 under stressed conditions, presenting Pak1 as a promising therapeutic target.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:764368 |
| Date | January 2015 |
| Creators | Tsui, Hoyee |
| Contributors | Wang, Xin |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/the-role-of-p21activated-kinase-1-pak1-in-the-heart(8c34d7bc-a2aa-4ae0-a197-91ed905212f5).html |
Page generated in 0.0039 seconds