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Title: Protective mechanisms of resveratrol in ageing muscle and muscle disorders
Authors: Sin, Ka Wai Thomas
Degree: Ph.D.
Issue Date: 2015
Abstract: The present thesis aims to test the hypothesis that long-term supplementation with resveratrol, a natural polyphenolic antioxidant in grapes and red wine, would attenuate the ageing-related reductions in cardiac systolic function, endurance to exercise and basal activity by modulating the SIRT1/Foxo1-related apoptotic and insulin signalling in the heart and skeletal muscle. This thesis also examines whether acute resveratrol administration would protect 1) the skeletal muscle from compression-induced injury through the attenuation of oxidative stress and apoptotic signalling and 2) against the deterioration of cardiac systolic function in senescent hearts induced by the chemotherapeutics doxorubicin through the deacetylase activity of SIRT1 to suppress concomitantly the activation of apoptotic and catabolic machineries. Understanding the precise molecular mechanisms of cardiac ageing is essential due to the general consensus that cardiovascular diseases often develop secondary to cardiac ageing. The ageing heart is characterised by age-dependent reductions of cardiac function and elevations of cardiomyocyte apoptosis, which is an elegantly controlled cell-death programme and cardiac fibrotic collagen deposition, which is thought as a pathogenic remodelling mechanism to compensate for the considerable loss of cardiomyocytes. The present thesis is the first to reveal that an 8-month supplementation with resveratrol improves cardiac systolic function in aged mice, an observation attributable to the activation of SIRT1 deacetylase activity to suppress acetylation of Foxo1 and transactivation of Bim, which is a pro-apoptotic protein. Interestingly, acute resveratrol treatment has been shown to increase the expression and membranous localisation of glucose transporter 4 (GLUT4) to increase glucose uptake in the skeletal muscle whereas the reduction of Akt activity in diabetic muscles can be mimicked by SIRT1 deficiency in-vitro. Provided that the skeletal muscle mediates ~65% of glucose clearance in response to insulin stimulation and ~25% of the senior population experiences significant loss of skeletal muscle mass and function, it is postulated that insulin signalling would be impaired in the senescent skeletal muscle. This thesis has presented the novel data that chronic resveratrol intervention enhances SIRT1 deacetylase activity and mitigates signs of impaired insulin signalling including blunted Akt phosphorylation, PDH activity and membrane trafficking of GLUT4 and elevated phosphorylation of IRS1 in the senescent skeletal muscle. It is worth-noting that these resveratrol-related alterations correlate significantly with the inhibition of Foxo1 acetylation. Furthermore, analyses of apoptotic signalling unravelled that the age-related increases in Bim transactivation and apoptotic DNA fragmentation were ameliorated in the skeletal muscle of resveratrol-treated aged mice. Resveratrol has been shown to improve skeletal muscle strength through the attenuation of oxidative stress/apoptosis in rodent models of muscle disuse including hindlimb suspension and dystrophin deficiency but not in pressure ulcer, which is a complication often observed in individuals with frailty and diminished spontaneous activity. The absence of effective diagnosis, management and treatment strategies is largely owing to the lack of understanding in the underlying pathognenic mechanisms, although prolonged exposure to mechanical pressure exerted by supporting interfaces in combination with shear and friction by daily nursing activities have been proposed as plausible risk factors. Previous studies have demonstrated that the expression of Bax and number of TUNEL-positive cells were increased in ulcerated subdermal tissues and skeletal muscle exhibiting pathohistological damages after moderate compression. This thesis is the first attempt to demonstrate that resveratrol alleviates the increases in oxidative damages to DNA, lipids and proteins measured as 8OHdG, 4HNE and nitrotyrosine respectively, aberrant muscle morphology and pro-apoptotic markers p53 and Bax induced by compression injury in the skeletal muscle.
Inhibition of apoptosis by natural compounds/antioxidants including resveratrol has been shown to mitigate the cardiotoxicity induced by the chemotherapeutic doxorubicin. These findings have important implications in cancer/cardiovascular research due to the fact that the anti-tumour efficacy of doxorubicin is often limited by the undesired consequence of development of heart failure in cancer patients post-treatment. It is noteworthy that senior patients are of higher vulnerability to doxorubicin-related cardiomyopathy, suggesting that the identification of aberrant signalling in the ageing heart in response to doxorubicin challenge is pivotal for devising cardioprotective adjuvant therapy. The current thesis showed that 1) doxorubicin reduced further the cardiac systolic function in senescent hearts but this reduction was prevented by acute resveratrol treatment and 2) the doxorubicin-induced elevations of protein ubiquitination and pro-apoptotic signalling measured as p53, Bax and caspase 3 activity in the aged heart were ameliorated by activation of SIRT1 deacetylase activity following treatment with resveratrol, but not in combination with either inhibitors of SIRT1 namely sirtinol and EX527. Taken together, long-term resveratrol intervention reduces the ageing-associated reductions in physical traits measured as cardiac systolic function, endurance to exercise and basal activity. These effects are at least in part attributed to the activation of SIRT1 deacetylase activity to repress acetylation and activity of Foxo1, reduce pro-apoptotic signalling and augment insulin signalling in the ageing cardiac and skeletal muscle. In addition, acute resveratrol intervention protects against muscle disorders induced by compression injury and doxorubicin challenge. Resveratrol mitigates pathohistological damages, oxidative damages to macromolecules and pro-apoptotic markers in the skeletal muscle in response to prolonged, moderate compression. Resveratrol also prevents the doxorubicin-induced aggravation of cardiac systolic function in senescent hearts through the restoration of SIRT1 deacetylase activity to repress concomitantly the activation of apoptotic cell death and catabolic mechanism. These data thereby raise the possibilities that 1) modulation of the SIRT1/Foxo1-related apoptotic/insulin signalling axis may represent a novel anti-ageing mechanism of life-long resveratrol intervention in the cardiac and skeletal muscle, 2) alleviation of oxidative stress by resveratrol may reduce compression-induced injury in the skeletal muscle of pressure ulcer patients and 3) resveratrol may serve as a promising candidate for cardioprotective adjuvant therapy in senior patients treated with doxorubicin through the SIRT1-mediated suppression of apoptotic and catabolic signalling.
Subjects: Resveratrol -- Health aspects.
Musculoskeletal system -- Diseases.
Musculoskeletal system -- Aging.
Hong Kong Polytechnic University -- Dissertations
Pages: xx, 268 pages : illustrations ; 30 cm
Appears in Collections:Thesis

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