Roles of N-myc downstream-regulated gene 2 in the central nervous system: molecular basis and relevance to pathophysiology

Inhibition of PI3K/Akt/mTOR signaling by NDRG2 contributes to neuronal apoptosis and autophagy in ischemic stroke

BACKGROUND

Astrocytic N-myc downstream-regulated gene 2 (NDRG2), a differentiation- and stress-associated molecule, has been involved in the cause of ischemic stroke (IS). However, its downstream effector in IS remains unclear. This study aimed to characterize expression of NDRG2 in IS patients and rats and to investigate the underlying mechanism.

METHODS

The protein expression of NDRG2 and mammalian target of the rapamycin (mTOR) and the extent of mTOR phosphorylation in plasma of IS patients were detected by ELISA. An oxygen-glucose deprivation model was established in mouse neuronal cells CATH.a, followed by cell counting kit-8, flow cytometry, TUNEL, and western blot assays to examine cell viability, apoptosis and autophagy. Finally, the effect of NDRG2-mediated phosphatidylinositol 3-kinase/protein kinase-B/mTOR (PI3K/AKT/mTOR) pathway on neuronal apoptosis and autophagy was verified in rats treated with middle cerebral artery occlusion.

RESULTS

NDRG2 was highly expressed in the plasma of IS patients, while the extent of mTOR phosphorylation was reduced in IS patients. NDRG2 blocked the PI3K/Akt/mTOR signaling through dephosphorylation. Depletion of NDRG2 suppressed apoptosis and autophagy in CATH.a cells, which was reversed by a dual inhibitor of PI3K and mTOR, BEZ235. In vivo experiments confirmed that NDRG2 promoted neuronal apoptosis and autophagy by dephosphorylating and blocking the PI3K/Akt/mTOR signaling.

CONCLUSION

The present study has shown that NDRG2 impairs the PI3K/Akt/mTOR pathway via dephosphorylation to promote neuronal apoptosis and autophagy in IS. These findings provide potential targets for future clinical therapies for IS.

[Astrocytes in the pathogenesis of multiple sclerosis]

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS), and is designated as an intractable disease in Japan. It is characterized by dissemination of plaque-like sclerosis in space and time, accompanied with various symptoms corresponding to the CNS lesion site. Typically, neurological symptoms chronically progress accompanied with relapses and remissions, and there is still no curative therapy. A number of studies using MS specimen and the animal MS model experimental autoimmune encephalomyelitis (EAE) have shown that MS is an autoimmune disease that targets myelin sheath in the CNS. Autoreactive T cells and B cells play a central role in pathogenesis of MS. MS comprise relapsing-remitting MS and progressive MS, the latter accumulates clinical disability without relapse. Based on the importance of adaptive immunity, various disease-modifying drugs have been developed to treat relapsing-remitting MS. On the other hand, an effective treatment for progressive MS has not yet been established. Increasing evidence have been recognized glial cells as key components of MS immunopathology, in addition to innate immunity and adaptive immunity. However, molecular mechanisms of crosstalk between immune cells, glial cells and neurons remain to be elucidated. Here, we review MS pathology and recent advances in the disease-modifying therapy that efficiently reduce disease activity in relapsing-remitting MS and introduce an update of recent evidence that astrocyte is involved in the MS pathology with including our research analyzed in mouse EAE model.