The role of bioactive lipids and lipid binding proteins in skeletal muscle

Mohd Noor, Mohd Fadly (2019) The role of bioactive lipids and lipid binding proteins in skeletal muscle. PhD thesis, University of Nottingham.

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Obesity and diabetes mellitus have been identified as major worldwide health problems. There is a growing body of evidence which suggests lipid signalling molecules including fatty acids, endocannabinoids and fatty acid amides may play a role in the development of obesity and insulin resistance. Much of the current research has focused upon the synthesis and release of such molecules by adipose tissue and their effects upon the endocrine system. Interestingly, cannabinoid (CB) receptors and other endocannabinoid components are also found to be expressed in human and animal skeletal muscle cells. However, there is minimal information regarding the role of these fatty acid derivatives in skeletal muscle and the lack of these data represents a significant gap in our knowledge. The aims of this thesis were to investigate the effects of cannabinoid receptor CB1 modulation upon insulin-stimulated glucose uptake and its effects upon regulation of selected genes expression in primary skeletal muscle myotubes. In addition, we would like to investigate the synthesis and secretion of Lipocalin 2 (LCN2), a type of lipid binding protein as a novel myokine.

Our previous laboratory data demonstrated that the level of GLUT4 was expressed at approximately 3000-fold lower in non-contracting primary skeletal muscle cell cultures as compared to skeletal muscle tissue. Since the mechanism of glucose uptake in contracting skeletal muscle is determined by the translocation of GLUT4 to the surface membrane, we have developed a contractile model of skeletal muscle myotubes by electrical pulse stimulation (EPS) which is sensitive to insulin-stimulated glucose uptake for further studies on CB1 receptor characteristics. CB1 activation demonstrated a significant reduction in insulin-stimulated glucose uptake in contractile primary skeletal muscle myotubes by inhibition of Akt phosphorylation and alteration in p85/p110 ratio in insulin signalling cascade. Apart from that, CB1 modulation in primary skeletal muscle showed no effects on regulations of selected genes that known to be related to obesity and insulin resistance namely LCN2, Neuropeptide Y, NR4A1, NR4A2 and NR4A3. On the other hand, the upregulation of these genes were influenced by low free fatty acid levels and muscle contractions. In addition, this study also demonstrated that LCN2, a lipid binding protein was found to be expressed in skeletal muscle. LCN2 protein were synthesized and secreted by rat myotubes post-EPS and human skeletal muscle cells following acute eccentric exercise in vivo.

In conclusion, the development of this contractile myotubes model provides an important tool not only for the study on CB1 receptor characteristics as in this thesis, but also for other aspect in future such as oxidative phosphorylation and exercise. This thesis provides a new understanding of the CB1 characteristic in skeletal muscle, in which it inhibit insulin-stimulated glucose uptake by interrupting the important steps in insulin signalling cascade. Even though the current study has demonstrated that skeletal muscle is able to synthesize and secrete LCN2, further future works need to be done to investigate its role in mediating other metabolic changes or exerting specific endocrine effects to other organs such as the liver and the adipose tissue, in order to classify LCN2 as a novel myokine.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Bennett, Andrew
Tsintzas, Kostas
Keywords: Cannabinoid receptor CB1 modulation; Insulin-stimulated glucose uptake; Gene expression; Skeletal muscle; Lipocalin 2; Novel myokine
Subjects: Q Science > QP Physiology
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Life Sciences
Item ID: 55762
Depositing User: Mohd Noor, Mohd
Date Deposited: 01 Aug 2019 10:27
Last Modified: 15 Mar 2021 04:30

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