Differential Sensitivity of Oligodendrocyte Precursor Cells and Microglia to Methotrexate in Grey Versus White Matter (P7.011)

OBJECTIVE: We hypothesize that oligodendroglial progenitor cell (OPC) dysfunction is responsible for neurocognitive deficits that many children experience following chemotherapy exposure. BACKGROUND: Cancer chemotherapy improves and saves lives but frequently causes debilitating neurocognitive consequences, including attention and concentration, particularly in children and when it is directed at the brain. DESIGN/METHODS: Human pediatric autopsy cases of chemotherapy exposure were age-matched to controls. Frontal lobe samples were formalin-fixed paraffin-embedded, stained using immunohistochemistry, and analyzed using light microscopy. CD-1 mice were administered methotrexate (MTX) at “standard” (50 mg/kg) or “high” (150 mg/kg) dosages; EdU was injected concurrently. Animals were perfused at acute, subacute and chronic time points following MTX administration. Immunofluorescence was performed, and cells quantified under confocal microscopy. RESULTS: Frontal lobes of human patients exposed to chemotherapy compared to age-matched controls demonstrated a three-fold decrease in OPC lineage (Olig2+), site-specific to the grey-white junction, with relative sparing in the grey matter. In mice, the “standard” dose MTX demonstrated a selective depletion of non-dividing OPCs (PDGFRa+/EdU-) at acute and chronic time points in the corpus callosum (CC); frontal lobe deep cortical grey matter (fGM) was preserved. In the CC, OPC lineage cells decreased two-fold acutely, and dividing OPC lineage cells increased three-fold subacutely. With “high” dosage MTX, the CC demonstrated a 25% depletion of OPCs acutely, and a 25% depletion of dividing OPCs (PDGFRa+/EdU+) subacutely; the frontal fGM was spared. We observed a two-fold increase in activated microglia (CD68+/Iba1+) subacutely in the CC, and a more robust (3-fold) and earlier increase in the fGM. CONCLUSIONS: This research demonstrates a differential response of both OPCs and microglia in grey versus white matter to methotrexate. A proliferation of OPC lineage cells subacutely suggests a compensatory response to the acute depletion of OPCs. The heightened microglial response to MTX in the more resistant fGM may suggest a possible neuroprotective role. Study Supported by: California Institute for Regenerative Medicine; Stanford MedScholars Disclosure: Dr. Wood has nothing to disclose. Dr. Miller has nothing to disclose. Dr. Vogel has nothing to disclose. Dr. Monje has nothing to disclose.