Sex and Estrous Cycle Stage Influence the Efficiency of AAV-Mediated Gene Transfer in the Rodent Brain

Recent experiments completed in mice indicate that sex significantly influences adeno-associated virus (AAV) transduction efficiency in the liver suggesting that hormones may modulate the activity of AAV. The present study aimed to determine what influence sex and estrous cycle stage have on AAV transduction (as inferred from expression levels) in the rodent brain. Adult C57BL/6 mice and Sprague-Dawley rats were unilaterally injected within the thalamus, hippocampus and cortex with either AAV2/1-ASM or AAV2/2-ASM, and then sacrificed 4 weeks later. Vaginal smears were performed immediately following surgery to determine cycle stage at the time of vector delivery. A cohort of juvenile mice underwent a similar experimental procedure with AAV, but at an age (i.e., 3 weeks) when sex differences in circulating hormone levels are absent. Rodent brain homogenates were analyzed for ASM protein levels by ELISA. In both adult mice and rats, ASM protein levels (irrespective of AAV serotype vector used) were significantly higher in males than females. In adult mice, estrous cycle stage also significantly influenced AAV mouse brain transduction activity. ASM levels were highest in females in diestrus and lowest in females in proestrus. ASM protein levels in estrous female mice were intermediate between female mice classified in diestrus and proestrus |[ndash]| all groups were significantly different from each other. These results indicate that there is a negative relationship between AAV-mediated protein expression in the female mouse brain and circulating hormone levels. Consistent with hormonal influences on these results, non-cycling, juvenile mice did not exhibit sex differences in ASM protein expression levels within the CNS. Experiments are currently underway to determine which hormone(s) is/are responsible for the observed sex differences in AAV transduction in the rodent brain.