Abstract
Mitochondria play a pivotal role in co-ordinating cellular metabolic processes and bioenergetics and hence, the functioning of mitochondria are of key importance in maintaining cellular health. Mitochondrial dysfunction is a contributing factor in atherosclerosis, where reduced macrophage aerobic capacity potentiates ‘foam cell’ formation in atheromatous lesions. A key preventative strategy is therefore to sustain or enhance mitochondrial function and to mobilise cholesterol via cholesterol efflux pathways; a link between both factors has not yet been investigated and forms the basis of this study.Mitochondrial inhibitors/uncouplers such as nigericin and oligomycin alter aspects of mitochondrial function (AM-^; mitochondrial membrane potential, ApH and ATP production) by inhibition of ApH and inhibition of the ATP synthase at complex V respectively. Both these inhibitors caused a specific decrease to apoA-l mediated pathways (by 39% and 53%, respectively) with no alterations to HDL pathways. Oligomycin was also found to decrease cholesteryl esterification at the mitochondria-associated endoplasmic reticulum membrane (MAM), without a decrease to cholesterol biosynthesis. Thus, with a concurrent decrease in cholesterol efflux, the mitochondrial dysfunction potentiates ‘foam cell’ formation.
The action of the natural polyphenol compound, resveratrol, was also investigated. Beneficial effects of resveratrol include enhancement of mitochondrial function and is therefore of interest in the field of atherosclerosis. Resveratrol treatment led to a loss of viability, A'+'m and total cellular ATP levels in murine RAW 264.7 cells. Although there was an increase in cholesterol efflux, the result was found to be independent of the LXR (Liver X receptor); the key regulator of the cholesterol efflux pathway. The enhanced efflux was only attained at concentrations which impacted negatively on mitochondrial function, strengthening the hypothesis that resveratrol exerts dose dependent and cell specific
effects.
Finally, in atherosclerotic plaques, macrophages exist under a state of high oxidative stress, with the enzyme hexokinase 2 (HKII) playing a protective role by association with the mitochondrial membrane. In HKII overexpression studies, we found that HKII improved cell viability, ATP levels and was able to maintain A^m under hydrogen peroxide-induced stress. HKII showed a trend to increase cholesterol efflux to apoA-l. These data suggest that mitochondrial dysfunction impacts negatively on cholesterol efflux pathways but the converse may be possible by targeting key mitochondrial enzymes. The enhancement of mitochondrial function leads to increased cholesterol mobilisation via cholesterol efflux mechanisms. This study presents mitochondria as key targets for atheroma protection and regression.
| Date of Award | 2012 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Annette Graham (Supervisor) |