Cell-autonomous expression of Rett-associated MeCP2 mutations leads to dendritic spine pathologies in pyramidal hippocampal neurons

C. A. CHAPLEAU, G. D. CALFA, J. M. RUTHERFORD, M. LANE, J. L. LARIMORE, S. KUDO, C. SCHANEN, A. K. PERCY, L. POZZO-MILLER

Congreso; Society for Neroscience - Neuroscience 2007; 2007

The structure and density of dendritic spines are modulated during synaptic plasticity as well as learning and memory. Anomalies in dendritic spines have been observed in many neurological disorders associated with mental retardation. One X chromosomelinked mental retardation where reduced cortical spine density has been observed is Rett Syndrome (RTT), which results from mutations in the transcriptional repressor MeCP2. While altered synaptic transmission and plasticity has been demonstrated in mouse models of RTT, observations regarding dendritic pathologies have produced varying results. Considering that human RTT postmortem tissue shows clear dendritic anomalies, we investigated the consequences of MeCP2 dysfunction on dendritic spine structure by overexpressing MeCP2-GFP constructs encoding the wildtype (WT) protein, or missense mutations associated with RTT. Pyramidal neurons within hippocampal slice cultures expressing WT or mutant MeCP2 for 48hrs by biolistic gene-transfer (2X the endogenous levels) showed a significant reduction in total spine density. Interestingly, when the WT protein was expressed for 96hrs the total spine density recovered to that observed in control neurons, while neurons expressing mutant MeCP2 failed to recover spine density. To determine whether these effects result from a loss of MeCP2 function, we explored the effect of siRNA-mediated MeCP2
knockdown on dendritic spines. While the effects were not as dramatic as that observed when expressing mutant MeCP2, we observed a significant reduction in stubby (Type-1) dendritic spines after 96hrs of MeCP2 siRNA expression. Though it remains to be determined whether these structural deficits occur in the hippocampus of RTT patients, these results provide novel insights into the consequence of cell-autonomous expression of mutant MeCP2 in postmitotic CNS neurons.