Alteration of ADP-ribosylation in aging rat brain astrocytes

Abstract

DNA damage and the enzyme poly (ADP-ribose) polymerase (PARP) associated with the pathogenesis of numerous age-related neurodegenerative disorders. Astrocytes play crucial roles in both support metabolic functions and cell viability of the brain. PARP regulates DNA damage and repair in the brain cells. In this study PARP activity and DNA strand break were investigated in the astrocytes isolated from young and aged rat brain. Three and 30-month-old rats were killed by decapitation and brains were removed onto an ice cooled glass plate. Astrocytes were isolated by sucrose density gradient centrifugation and glutamine synthetase (GS) served as a marker of the astrocytes lineage. The specific activity of PARP was assayed in permeabilized cells by measuring the incorporation of the ADPribose moiety of 3HNAD into the nuclear acceptor proteins. The rate of DNA strand breaks was determined using a fluorescent dye and monitored spectrofluorimetry. An increase (about 75%) in the PARP activity was observed in the whole homogenates of aged rats, whereas this rise was more pronounced (about 360%) when the reaction was measured in the purified astrocyte preparations. The amount of DNA strand breaks was also higher in the astrocytes isolated from the aged brain as compared to that of young levels. The close relationship between the level of DNA strand breaks and PARP activity in the astrocytes suggest that these cells are susceptible to the metabolic alterations in aging. It is concluded that the astrocytes PARP might be considered as a therapeutic target for combating age related neurodegenerative disorders.