.....Since a detailed study of NAD+ metabolism in the healthy ageing mammalian brain is nascent, we examined the effect of ageing on intracellular NAD+ metabolism in different brain regions in female Wistar rats in young (3 months), middle aged (12 months) and older adults (24 months).
Our results are the first to show a significant decline in intracellular NAD+ levels and NAD:NADH ratio with ageing in the CNS, occurring in parallel to an increase in lipid peroxidation and protein oxidation (o- and m-tyrosine) and a decline in total antioxidant capacity. Hyperphosphorylation of H2AX levels was also observed together with increased PARP-1 and PARP-2 expression, and CD38 activity, concomitantly with reduced NAD+ and ATP levels and SIRT1 function in the cortex, brainstem, hippocampus and cerebellum. Reduced activity of mitochondrial complex I-IV and impaired maximum mitochondrial respiration rate were also observed in the ageing rat brain
. Among the multiple physiological pathways associated with NAD+ catabolism, our discovery of CD38 as the major regulator of cellular NAD+ levels in rat neurons indicates that CD38 is a promising therapeutic target for the treatment of age-related neurodegenerative diseases.