Repopulating microglia rapidly return to a cuprizone-induced activated state with area-dependent kinetics

ANABELLA A. DI PIETRO; LAURA A PASQUINI

Buenos Aires

Congreso; FIRST MEETING GLIA CLUB SOUTHERN CONE The good, the bad, the nice and the ugly of glial cells; 2022

Prolonged cuprizone (CPZ) administration can model progressive multiple sclerosis in triggering chronic demyelination, neurodegeneration, astrogliosis and exacerbated microglia (MG) activation. MG can be almost completely eliminated from the brain using colony-stimulating factor 1 receptor inhibitors like BLZ945 (BLZ). Our previous results show that continuous BLZ treatment attenuates demyelination but exacerbates axonal degeneration. The present work characterizes MG as they repopulate and determines whether these new cells ameliorate CPZ-induced pathology. Two-month-old mice were fed CPZ chow for 11 weeks, orally gavaged vehicle or BLZ for 3 weeks from the 5th week of CPZ treatment, and evaluated after 0, 1, 2 and 3 weeks of BLZ withdrawal (T0, T1, T2 and T3). Results showed a reduction in the Iba1-positive area at T0 in the cortex (CX) and at T1 in the corpus callosum (CC), reaching repopulation at T3. CPZ induced a more ramified microglial phenotype, while branches were shorter than control only in the CC. BLZ inverted this phenotype in the CX at T0, but the number of branches equaled CPZ very early from T1 and longer process length was maintained until T3. In the CC, BLZ did not change the phenotype induced by CPZ. Pro- and anti-inflammatory gene expression tended to change with treatment, brain area and repopulation time. BLZ attenuated demyelination at T0, concomitant with a reduced number of GFAP+ cells, but showed no differences from CPZ at T3 in the CX. In the CC, no differences were found between CPZ and CPZ+BLZ at any time. Axonal neurodegeneration was unaltered by BLZ at T0 but increased at T3 accompanied by an increased number of GFAP+ cells. These results show that the kinetics of MG depletion/repopulation differs between CX and CC and that new MG quickly reactivate due to the pathological state generated by CPZ.