Induction of autophagy contributes to the neuroprotection of nicotinamide phosphoribosyltransferase in cerebral ischemia

Abstract

Recent reports indicate that autophagy serves as a stress response and may participate in the pathophysiology of cerebral ischemia. Nicotinamide phosphoribosyltransferase (Nampt, also known as visfatin), the rate-limiting enzyme in mammalian NAD + biosynthesis, protects against ischemic stroke through inhibiting neuronal apoptosis and necrosis. This study sought to determine the involvement of autophagy in neuroprotection of Nampt in cerebral ischemia. Middle cerebral artery occlusion (MCAO) in rats and oxygen-glucose deprivation (OGD) in cultured cortical neurons were performed. Nampt was overexpressed or knocked down using lentivirus-mediated gene transfer in vivo and in vitro. Immunochemistry (LC3-II), electron microscope and immunoblotting assays (LC3-II, Beclin 1, mammalian target of rapamycin [mTOR], S6K1 and tuberous sclerosis complex-2 [TSC2]) were performed to assess autophagy. We found that overexpression of Nampt increased autophagy (LC3 puncta immunochemistry staining, LC3-II/Beclin 1 expression and autophagosomes number) both in vivo and in vitro at 2 h after MCAO. At the early stage of OGD, autophagy-inducer rapamycin protected against neuronal injury induced by Nampt knockdown, whereas autophagy-inhibitor 3-methyladenine partly abolished the neuroprotective effect of Nampt. Overexpression or knockdown of Nampt regulated the phosphorylation of mTOR and S6K1 signaling pathway upon OGD stress through enhancing phosphorylation of TSC2 at Ser1387 but not Thr1462 site. Furthermore, in cultured SIRT1-knockout neurons, the regulation of Nampt on autophagic proteins LC3-II and Beclin 1 was abolished. Our results demonstrate that Nampt promotes neuronal survival through inducing autophagy via regulating the TSC2-mTOR-S6K1 signaling pathway in a SIRT1-dependent manner during cerebral ischemia.

cPKCγ‐mediated down‐regulation ofUCHL1 alleviates ischaemic neuronal injuries by decreasing autophagyviaERK‐mTORpathway

“…However, the role of autophagy in ischaemic stroke is still controversial. Induction of autophagy by nicotinamide phosphoribosyltransferase increases the cell survival rate and simultaneously decreases the LDH leakage of primary neurons with 2‐hr OGD treatment 57. But other studies have reported that activation of autophagy can aggravate cortical neural cell injury following 1‐hr focal cerebral ischaemia/24‐hr R 58, 59.…”

Metformin Improves Neurologic Outcome Via AMP‐Activated Protein Kinase–Mediated Autophagy Activation in a Rat Model of Cardiac Arrest and Resuscitation

“…Autophagy is an essential degraded process that removes the damaged organelles and toxic proteins and subsequently recycles amino acids to facilitate cellular energy production, limit endoplasmic reticulum stress, and promote cell survival under subsequent ischemic exposure 8, 51, 52. Although controversies remain about the role of autophagic activation in stressful conditions, a great deal of studies have demonstrated that induction of autophagy contributes to the neuroprotection in response to cerebral ischemia8, 10, 52 or focal brain damage 9. As an AMPK activator, metformin has been revealed to induce autophagy through an AMPK‐dependent manner in heart tissue, which subsequently provides protection in response to stress 31.…”

“…A large pool of evidence has demonstrated that autophagy activation is neuroprotective in ischemic stroke 8, 9, 10. Despite the growing attention on autophagy as a novel target for ischemic brain injury, studies on agents that modulate autophagy and could be used clinically are still limited.…”

Identification of autophagy signaling network that contributes to stroke in the ischemic rodent brain via gene expression

“…The activation of autophagic and lysosomal pathways has been implicated in neuronal injury in a rat model of permanent focal cerebral ischemia [11] . Furthermore, by regulating the TSC2-mTOR-S6K1 signaling pathway, autophagy is induced and further promotes neuronal survival during cerebral ischemia [20] .…”