Age-dependent increased expression and activity of inorganic pyrophosphatase in the liver of male mice and its further enhancement with short- and long-term dietary restriction.

Intracellular orthophosphate and inorganic pyrophosphate (PPi) are by-products of multiple biosynthetic reactions. PPi hydrolysis by soluble inorganic pyrophosphatase (iPPase) has been considered as an important homeostatic mechanism. We investigated the expression and activities (U/mg protein) of iPPase in the liver of young and old mice subjected to short- and long-term dietary restriction. The expression level of iPPase was ascertained by the Western blot analysis using anti-iPPase and differential polymerase chain reaction using iPPase specific primer. Older mice showed a significant increase in the expression and activity of iPPase as compared to younger ones. Short-term fasting of 24 h increased the expression and activity of iPPase in the liver of both young and old mice which were reversed upon 24 h of re-feeding them. However, both young and old mice on long-term dietary restriction showed a cumulative increase in the expression and activity of iPPase when compared with their age-matched controls. This might be due to accumulative adaptation to refill energy deficiency of long-term dietary restricted mice for ATP generation via oxidative phosphorylation, where fatty acid activation could be driven by elevated iPPase.