O4+ oligodendrocyte cultures from PAR1+/+, PAR1−/− or PAR2−/− mice were treated with active recombinant Klk6 for 24 h. A, B, Klk6 (30 nM) promoted significant process retraction in PAR1+/+ (SNK, p = 9.0 × 10−4) or PAR2−/− (SNK, p = 0.002) oligodendrocytes, but not in the absence of PAR1−/−. C, Klk6 treatment had no significant effect on oligodendrocyte number in cultures isolated from either PAR1+/+, PAR1−/− or PAR2−/− mice. Error bars indicate SEM. *p = < 0.005, **p = < 0.001, SNK. Scale bar = 100 μm.