title: NAD blocks high glucose induced mesangial hypertrophy via activation of the sirtuins-AMPK-mTOR pathway.
abstract: OBJECTIVE
  Since the discovery of NAD-dependent deacetylases, Sirtuins, it has been recognized that maintaining intracellular levels of NAD is crucial for the management of stress-response of cells. Here we show that high glucose(HG)-induced mesangial hypertrophy is associated with loss of intracellular levels of NAD. This study was designed to investigate the effect of NAD on HG-induced mesangial hypertrophy.
  
  
  METHODS
  The rat glomerular mesangial cells (MCs) were incubated in HG medium with or without NAD. Afterwards, NAD(+)/NADH ratio and enzyme activity of Sirtuins was determined. In addition, the expression analyses of AMPK-mTOR signaling were evaluated by Western blot analysis.
  
  
  RESULTS
  We showed that HG induced the NAD(+)/NADH ratio and the levels of SIRT1 and SIRT3 activity decreased as well as mesangial hypertrophy, but NAD was capable of maintaining intracellular NAD(+)/NADH ratio and levels of SIRT1 and SIRT3 activity as well as of blocking the HG-induced mesangial hypertrophy in vitro. Activating Sirtuins by NAD blocked the activation of pro-hypertrophic Akt signaling, and augmented the activity of the antihypertrophic AMPK signaling in MCs, which prevented the subsequent induction of mTOR-mediated protein synthesis. By AMPK knockdown, we showed it upregulated phosphorylation of mTOR. In such, the NAD inhibited HG-induced mesangial hypertrophy whereas NAD lost its inhibitory effect in the presence of AMPK siRNA.
  
  
  CONCLUSIONS
  These results reveal a novel role of NAD as an inhibitor of mesangial hypertrophic signaling, and suggest that prevention of NAD depletion may be critical in the treatment of mesangial hypertrophy.
authors.affiliation: Department of Nephrology, Kidney Center and Key Lab of the People's Liberation Army, General Hospital of People's Liberation Army, Beijing, People's Republic of China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhuo
authors.forename: Bo
authors.initials: B
authors.lastname: Fu
authors.forename: Xueyuan
authors.initials: X
authors.lastname: Bai
authors.forename: Bin
authors.initials: B
authors.lastname: Zhang
authors.forename: Lingling
authors.initials: L
authors.lastname: Wu
authors.forename: Jing
authors.initials: J
authors.lastname: Cui
authors.forename: Shaoyuan
authors.initials: S
authors.lastname: Cui
authors.forename: Ribao
authors.initials: R
authors.lastname: Wei
authors.forename: Xiangmei
authors.initials: X
authors.lastname: Chen
authors.forename: Guangyan
authors.initials: G
authors.lastname: Cai
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D004789:Enzyme Activation; D005920:Glomerular Mesangium / Q000473:pathology / Q000502:physiology*; D005947:Glucose / Q000502:physiology*; D009243:NAD / Q000502:physiology*; D051381:Rats; D037761:Sirtuins / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000502:physiology*
chemical_list: D017931:DNA Primers; D009243:NAD; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases; D000263:Adenylate Kinase; D037761:Sirtuins; D005947:Glucose