Research On The Relationship Between The Expression Of UCP₂ In The Livers Of Old-aged Rats And Ageing

Objectives: Uncoupling protein 2 (UCP₂ ), discovered recently to be distributed in manifold organs in rodent, is one member of the UCP family which lie in mitochondrial inner membrane. Acting as a proton pump, it may reduce the production of reactive oxygen species(ROS) in mitochondria, and perform the protective function when cells suffer from oxidative damage.Many research results prove that ROS is the decisive element of ageing. The ageing of the living organism appears with the reduction of mitochondrial adenosine triphosphate (ATP), the increase of ROS, the sharpening of its damage, and a series of changes of the turbulence of neuroendocrine system.There are many theories about the mechanism of ageing, among which the relationship between free radical and ageing is widely attended. Respecting UCP₂ can depress the level of ROS, we suppose that UCP₂ may participate in the anti-oxidative damage, consequently perform the function of staving off ageing by reducing the oxidative damage of mediate ROS cells. On the other hand, UCP₂ can reduce the proton gradients across in mitochondria membrane, so proton can enter grass roots directly instead of participating in the synthesrs of ATP, leading to the expenditure of the free energy in electrochemistrial protential energy restored in proton by uncoupling oxidative phosphoylation. The level of ATP descends. AS the relationships between UCP₂ and ROS and ATP are still not clear, so are the relationships between UCP₂, ROS, ATP and ageing respectively, we make use of livers of old rats to be as the researching object to illustrates the relationships between UCP₂ and ROS and ATP in rats of different age and physiologic state, explore the effect of UCP₂ on ageing and try to offer theoretical clues for clinical treatment of the disease concerned with ageing and starving off the ageing of organs.Methods: Male SD rats of different ages were divided into three groups: the infancy group (21 days after birth, n=10), adult group (three months after birth, n=10) and old-aged group (eighteen months after birth, n=10). These rats were bred for three days in different cages in room temprature and natural day and night. The rats were fasted for 12 hours before the operation. After executing the rats, malondialdehyde, glutathione and adenosine triphosphate in hepatic tissue were measured, and UCP₂ expression was tested by chemical coloration in immuagte and western blot method. These figures were then used to make quantitative analysis.Results:1. The change of MDA contents in the hepatic tissue in difference age rats.The content of MDA in hepatic tissue in infancy group is 4.84±0.16nmol/mg, the content of adult group is 1.88±0.21 nmol/mg, while the content in old-aged group is 17.62±7.36 nmol/mg. The MDA content of old-aged group increased remarkably compared with the infancy group and adult group ( p<0.01).2. The changes of GSH level in the hepatic tissue in difference age rats.The content of GSH in liver organization in infancy group is 100.19±7.29 mg/g, the content in adult group is 98.76±5.06 mg/g, while the content of old-aged group is 76.93±13.88 mg/g. The GSH content of old-aged group went down compared with the infancy group and adult group ( p<0.01).3. The change of levels ATP in the hepatic tissue in difference age rats.The levels of ATP in liver organization in infancy group is 0.24±0.06 nmol/L, the content in adult group is 0.19±0.10 nmol/L, while the content of old-aged group is 0.06±0.03 nmol/L. The ATP level of old-aged group decreased remarkably compared with the infancy group and adult group ( p<0.01).4. The correlative change of the expression of UCP₂ in the hepatic tissue in difference age rats.The result of immunohistochemistry show that the UCP₂ in parenchymal cells in the livers of old-aged group express the most, the expression of UCP₂ in infancy group is less, its expression in the adult group is the lest. The western blot experiment can prove the result of immunohistochemistry further. The quantivative analysis show that the expression of UCP₂ in the infancy group is 110.53±0.59(relative gray level, %), while the old-aged group 160.74±0.80 (relative gray level, %). It showed that the average relative photodensity was obviously increased in old-aged group compared with the infancy group and adult group ( p<0.01).Conclusions:1. The content of MDA descends while the content of GSH rises in the livers of old-aged rats. The results suggest that the level of ROS is relatively higher and causes the increase of UCP₂ expression. UCP₂ may perform important function in staving off the ageing of liver cells.2. The higher expression of UCP₂ may be one of the reasons of the decrease of ATP in old-aged rats.3. The expression of UCP₂ in hepatic tissue is mainly regulated by the content of ROS. The level of ATP is not only regulated by UCP₂ but also influenced by the metabolic state of cells.