GFAP and Alzheimer disease: ROCK1 protein levels were at least 6-fold higher in human glial cells that overexpress the APOE4 allele than in the same cells expressing an APOE3 transgene (p < 0.0001; Figure 4a,b), potentially contributing to the additional GFAP phosphorylation sites observed in AD aggregates from ApoE(4,4) vs. ApoE(3,3) individuals (Figure 1b,c).