Blocking a Cell-Cycle Pathway to Protect Neurons After Spinal Cord Injury

Wu J, Kharebava G, Piao C, Stoica BA, Dinizo M, Sabirzhanov B, Hanscom M, Guanciale K, Faden AI. Inhibition of E2F1/CDK1 pathway attenuates neuronal apoptosis in vitro and confers neuroprotection after spinal cord injury in vivo. PLoS One 2012;7(7):e42129. doi: 10.1371/journal.pone.0042129.

Background: Neuronal apoptosis contributes significantly to secondary tissue damage after spinal cord injury (SCI). The E2F1/CDK1 signaling pathway, known to regulate both cell proliferation and apoptosis, is implicated in neuronal death in various neurodegenerative models, but its specific role after SCI has not been established. Understanding how this pathway influences neuronal apoptosis could identify potential therapeutic targets for SCI.

Hypothesis: This study hypothesized that activation of the E2F1/CDK1 signaling pathway contributes to neuronal apoptosis after spinal cord injury and that inhibition of this pathway would attenuate neuronal death and improve neuroprotection.

Methods: The authors used both in vitro neuronal cultures and an in vivo rat contusion SCI model. Protein expression and apoptosis were assessed by Western blotting, immunohistochemistry and TUNEL staining. Neuronal survival was quantified using unbiased stereological cell counts analyzed with Stereo Investigator. E2F1 or CDK1 expression was manipulated with shRNA, and apoptosis was pharmacologically modulated with CDK inhibitors such as roscovitine and CR8.

Results: SCI rapidly upregulated E2F1 and CDK1 protein expression, which remained elevated for several days. Their downstream targets, Bim and c-Myb, as well as biochemical markers of apoptosis, were increased. Inhibition of E2F1/CDK1 by shRNA or CR8 reduced apoptotic markers, decreased TUNEL-positive neurons and significantly increased surviving neurons five weeks after injury.

Conclusions: Activation of the E2F1/CDK1 pathway promotes neuronal apoptosis after spinal cord injury, while its inhibition confers significant neuroprotection. Targeting this signaling cascade may represent an effective therapeutic strategy for SCI.