DUSP1 and Alzheimer disease: However, upregulation of MKP-1 expression by AAVMKP-1 significantly increased the total number of synapses to 18.85 ± 0.25, whereas knockdown of MKP-1 expression by AAVshMKP-1 further reduced the total number of synapses to 9.00 ± 2.36 in AD mice (p < 0.001; Fig. 6j, k).