Mapping NAD+ metabolism in the brain of ageing Wistar rats: potential targets for influencing brain senescence

Abstract

Over the last decade, the importance of NAD(+) has expanded beyond its role as an essential cofactor for energy metabolism. NAD(+) has emerged as a major signalling molecule that serves as the sole substrate for several enzymatic reactions including the DNA repair enzyme, poly(ADP-ribose) polymerase (PARP), NAD-dependent protein deacetylases or CD38, and transcriptional factors by a new class of histone deacetylases known as sirtuins. NAD(+) levels are regulated by the metabolic status and cellular stress caused by oxidative stress and DNA damage. 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.

In vivo NAD assay reveals the intracellular NAD contents and redox state in healthy human brain and their age dependences

“…The strong age dependences of intracellular [NAD + ], [NADH], RX, and RP observed in this study provide the first in vivo evidence, to our knowledge, that connects human aging to the changes in cerebral NAD contents and redox state. This finding is in agreement with ex vivo studies showing the same trends of NAD changes found in rodent brains of different age groups (34,35).…”

SIRT1 in Neurodevelopment and Brain Senescence

“…However much still needs to be learned about the safety and efficacy profiles of sirtuin activators. One exciting new finding in the field of aging research is that the levels of NAD+, the cosubstrate for SIRT1-7, decreases with aging in mice (Mouchiroud et al, 2013; Ramsey et al, 2008), rats (Braidy et al, 2013), worms (Mouchiroud et al, 2013), and even humans (Massudi et al, 2012). This reduction in NAD+ is expected to reduce the activities of SIRT1-7, and may thus compromise protection against neurological decline and neurodegenerative diseases.…”

“…SIRT1 was initially described as a nuclear protein (Mouchiroud et al, 2013) that may also shuttle to the cytoplasm during neuronal differentiation and neurite outgrowth (Hisahara et al, 2008; Sugino et al, 2010; Tanno et al, 2007), tumor progression (Byles et al, 2010; Ramsey et al, 2008) and apoptosis (Jin et al, 2007). SIRT2 is a cytoplasmic protein that can deacetylate tubulin (North et al, 2003) but has also been described in the nucleus during cell cycle progression (Canto et al, 2012), cancer (Braidy et al, 2013), and bacterial infection (Eskandarian et al, 2013). SIRT3, SIRT4 and SIRT5 are mitochondrial sirtuins, however they each have distinct enzymatic activities within this organelle (Du et al, 2011; Haigis et al, 2006; Nakagawa et al, 2009).…”

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States

“…Comparisons of mitochondria isolated from brain tissue of animals reveal numerous age-related alterations, including mitochondrial enlargement or fragmentation (Stahon et al, 2016; Morozov et al, 2017), increased oxidative damage to mitochondrial DNA (Kim and Chan, 2001; Santos et al, 2013), impaired function of the electron transport chain (ETC) (Yao et al, 2010; Pandya et al, 2015, 2016; Pollard et al, 2016), increased numbers of mitochondria with depolarized membranes (Lores-Arnaiz et al, 2016), impaired Ca 2+ handling (Leslie et al, 1985; Pandya et al, 2015), and a reduced threshold for triggering mPTP formation (Brown et al, 2004). The decrement in mitochondrial function during brain aging involves a decline in cellular NAD + levels and the NAD:NADH ratio (Braidy et al, 2014), which would be expected to compromise the activities of NAD + -dependent enzymes critical for neuronal function and viability, including protein deacetylases of the sirtuin family (Fang et al, 2017). Most cell types in the brain likely experience the accumulation of dysfunctional mitochondria during aging as suggested from studies of neurons and astrocytes established from brains of young and old mice, or allowed to “age” in culture (Lin et al, 2007; Ghosh et al, 2012).…”