PI3K/Akt signaling pathway is required for neuroprotection of thalidomide on hypoxic–ischemic cortical neurons in vitro

Thalidomide, a derivative of glutamic acid, is used for immunomodulatory therapy in various diseases through inhibition of tumor necrotic factor-α (TNF-α) release. However, the effects of thalidomide in central nervous system (CNS) diseases such as stroke or hypoxic–ischemic encephalopathy (HIE) are unknown. In this study, we aimed to test whether thalidomide protects against hypoxic–ischemic neuronal damage and the possible signaling pathway involved in neuroprotection. Primary cultured cortical neurons of rats were treated with oxygen and glucose deprivation (OGD) for 3 h to mimic hypoxic–ischemic injury in vivo. Neuronal apoptosis was measured with terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. The expression of total caspase-3 (C3), cleaved caspase-3 (CC3), Akt, phosphorylated-Akt (p-Akt) and Bcl-2 protein were detected by Western blots. We found that OGD treatment increased the expression of CC3 and induced neuronal apoptosis. Both neuronal apoptosis and CC3 expression peaked at 24 h after OGD. Furthermore, we found that thalidomide protected neurons against apoptosis by decreasing CC3 and increasing Bcl-2 expression in a dose-dependent manner. Meanwhile, we found that thalidomide induced p-Akt expression, which could be inhibited by PI3K specific inhibitor, LY294002. In addition, inhibition of PI3K increased CC3 but decreased Bcl-2 expression. In summary, thalidomide has anti-apoptotic effects on cortical neurons after OGD by modulating CC3 and Bcl-2 expression through activation of PI3K/Akt pathway.

Research Highlights
► Hypoxia–ischemia increases cleaved caspase-3 expression and neuronal apoptosis.
► Thalidomide pretreatment inhibits cleaved caspase-3 and increases Bcl-2 expression.
► Thalidomide pretreatment inhibits neuronal apoptosis caused by hypoxia–ischemia.
► Thalidomide functions by activation of PI3K/Akt signaling pathway.