Caloric restriction, ageing and the liver sinusoidal endothelium: mechanisms and implications

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Old age is the major risk factor for many diseases yet the mechanism is unknown. We discovered age-related changes in the liver sinusoidal endothelial cell that provide a mechanism for the link between old age, lipid metabolism and vascular disease. The liver sinusoidal endothelial cell influences the transfer of substrates between the blood and liver cells, therefore changes in the liver sinusoidal endothelial cell affect liver function. We discovered major structural changes in the liver sinusoidal endothelial cell in old age called pseudocapillarization, consisting of loss of pores, increased thickness and deposition of collagen and basal lamina. We showed that the loss of pores prevented the uptake by the liver of some lipoproteins, with implications for age-related changes in lipid metabolism and vascular disease. We have now found that caloric restriction delays pseudocapillarization. Caloric restriction is the only intervention known to increase maximal life span. This effect of caloric restriction is mediated by a protein called SIRT1 through actions on mitochondria and cell death. A naturally occurring agonist of SIRT1 called resveratrol has been found to increase longevity in yeast, worms and flies. We hypothesize that caloric restriction prevents age-related cardiovascular disease by delaying pseudocapillarization and hence maintaining hepatic metabolism of lipoproteins, particularly chylomicron remnants. We propose that caloric restriction will prevent age-related pseudocapillarization via its effects on the SIRT1 pathways and therefore pseudocapillarization will be delayed by resveratrol. Confirmation of these hypotheses will generate a unique target - pores in the liver sinusoidal endothelial cell - for the prevention of vascular disease in older people and provide a platform for the development of novel pharmacological agents such as resveratrol that act by maintaining the porosity of the liver sinusoidal endothelial cell.