Lithium-mediated protection of hippocampal cells involves enhancement of DNA-PK–dependent repair in mice
Eddy S. Yang, … , Dennis E. Hallahan, Fen Xia
Eddy S. Yang, … , Dennis E. Hallahan, Fen Xia
Published April 1, 2009
Citation Information: J Clin Invest. 2009;119(5):1124-1135. https://doi.org/10.1172/JCI34051.
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Research Article Neuroscience

Lithium-mediated protection of hippocampal cells involves enhancement of DNA-PK–dependent repair in mice

Abstract

Long-term neurological deficiencies resulting from hippocampal cytotoxicity induced by cranial irradiation (IR) present a challenge in the treatment of primary and metastatic brain cancers, especially in children. Previously, we showed that lithium protected hippocampal neurons from IR-induced apoptosis and improved neurocognitive function in treated mice. Here, we demonstrate accelerated repair of IR-induced chromosomal double-strand breaks (DSBs) in lithium-treated neurons. Lithium treatment not only increased IR-induced DNA-dependent protein kinase (DNA-PK) threonine 2609 foci, a surrogate marker for activated nonhomologous end-joining (NHEJ) repair, but also enhanced double-strand DNA end-rejoining activity in hippocampal neurons. The increased NHEJ repair coincided with reduced numbers of IR-induced γ-H2AX foci, well-characterized in situ markers of DSBs. These findings were confirmed in vivo in irradiated mice. Consistent with a role of NHEJ repair in lithium-mediated neuroprotection, attenuation of IR-induced apoptosis of hippocampal neurons by lithium was dramatically abrogated when DNA-PK function was abolished genetically in SCID mice or inhibited biochemically by the DNA-PK inhibitor IC86621. Importantly, none of these findings were evident in glioma cancer cells. These results support our hypothesis that lithium protects hippocampal neurons by promoting the NHEJ repair–mediated DNA repair pathway and warrant future investigation of lithium-mediated neuroprotection during cranial IR, especially in the pediatric population.

Authors

Eddy S. Yang, Hong Wang, Guochun Jiang, Somaira Nowsheen, Allie Fu, Dennis E. Hallahan, Fen Xia

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Figure 8

Lithium-mediated effects are not apparent in glioma tumor cells.

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Lithium-mediated effects are not apparent in glioma tumor cells. Cells o...
Cells of the glioma cancer cell line GL261 were treated with 3 mM lithium for 7 days. Following the treatment period, cells were exposed to 3 Gy. At the indicated times after IR, cells were processed for immunofluorescence staining for γ-H2AX (A), DNA-PK T2609 (B), or Rad51 (C). Data (mean ± SEM from 3 independent experiments) show the percentage of cells containing greater than 10 foci. Experiments were performed simultaneously with HT-22 cells (γ-H2AX, Figure 2A; T2609, Figure 3A; Rad51, Figure 5A). (D and E) Neuroprotection by lithium is not evident in glioma tumor cells and is unaffected by the addition of the DNA-PK inhibitor IC86621. Cells of the glioma cancer cell line GL261 were treated with 3 mM lithium for 7 days. At 24 hours before IR, cells were exposed to the DNA-PK inhibitor IC86621 for 24 hours and subsequently irradiated with 3 Gy. At the indicated times after IR, cells were processed for immunofluorescence staining with DAPI and cleaved caspase-3, indicative of apoptosis activation. Data (mean ± SEM from 3 independent experiments) show percentage of cells with positive cleaved caspase-3 staining and pyknotic or condensed nuclei after subtracting respective basal apoptotic levels from each condition.