The Involvement of Upregulation and Translocation of Phospho-Rb in Early Neuronal Apoptosis Following Focal Cerebral Ischemia in Rats

Abstract

The aim of this study was to investigate the temporal and spatial relationship between phospho-Rb (ser 795) and neuronal apoptotic death in rats subjected to transient focal cerebral ischemia. We found increased phosphorylation of Rb and translocation from neuronal nucleus to cytoplasm in the penumbra zone at 12 h, 1 day, 3 days and 7 days after middle cerebral artery occlusion (MCAO)/reperfusion, compared with sham-operated controls. At 12 h and 1 day, phospho-Rb appeared to be colocalizated with TUNEL staining in neurons, but staining was not colocalizated at 3 days and 7 days. These results demonstrated that cytoplasmic translocation of phospho-Rb from nucleus of neurons occurs in potential apoptotic neurons in the early stages of ischemia/reperfusion, suggesting that the Rb pathway may only be involved in early neuronal apoptosis and may be not an apoptotic signal in the late stages of transient cerebral ischemia.

Phospho-Rb Mediating Cell Cycle Reentry Induces Early Apoptosis Following Oxygen–Glucose Deprivation in Rat Cortical Neurons

“…In this study, the percentage of colocalization between phospho-Rb and TUNEL staining was increased 6 h and 12 h after OGD treatment, but dramatically decreased 24 h after OGD. These in vitro findings are consistent with our previously reported in vivo findings [16]. The results strongly suggest that the Rb pathway is likely only involved in the early stages of neuronal apoptosis after ischemia/hypoxia.…”

“…In summary, our observations, presented here and reported previously [16], suggest that aberrant reentry of postmitotic neurons into the cell cycle through the G1/S checkpoint is regulated by phosphorylated Rb, and may contribute to the early apoptosis of neurons during an ischemia/hypoxia injury. Accordingly, our data provide compelling evidence for future examination of the phosphorylated Rb-mediated pathway as a potential therapeutic target for the treatment of stroke-induced neuronal apoptosis.…”

“…Mounting data suggest that aberrant cell cycle plays a prominent role in promoting neuronal cell death [2,27]; however, little is known about the regulation of neuronal Neurochem Res (2012) 37:503-511 507 cell cycle reentry during apoptosis induced by ischemia/ hypoxia. In a previous study, we found that increased expression of phospho-Rb is closely related to neuronal apoptosis in the penumbra zone in rats subjected to transient focal cerebral ischemia [16]. In the present study, we observed increasing phosphorylated Rb staining was colocalized with BrdU and TUNEL staining over the first 12 h after OGD.…”

“…One mechanism has been referred that postmitotic neurons reentering the cell cycle is through phosphorylation of Rb by cyclin D/CDK4 complex [8,13]. Consistent with this possibility, phosphoRb immunostaining in relevant neurons is increased in models of ischemia/stroke [4,[14][15][16]. We have also found that transient focal cerebral ischemia caused neuronal apoptosis in the penumbra of the ischemic cerebral cortex, which may involve increased phospho-Rb expression and translocation [16].…”

“…The phosphorylation of Rb results in the dissociation of Rb/E2F1 complex and the release of E2F1 that contributes to S phase entry and apoptosis [29]. Neuronal expression of phosphorylated Rb has been reported to be increased in models of ischemia/ stroke [4,16], superoxide dismutase (SOD)-induced amyotrophic lateral sclerosis (ALS) [30], and kainateinduced excitotoxicity [31] as well as in neurons from patients with Alzheimer disease (AD) [32] and ALS [25]. Phosphorylation of the cell cycle regulator, Rb, contributes to neuronal death in OGD [33].…”