Abstract T P206: Mkp-1 Inhibition Increases Stroke Injury via JNK Pathway Activation

Background: MKP-1, a negative modulator of several MAP kinases including JNK and p38, is a critical regulator of inflammation and apoptosis in the CNS. Inhibition of MKP-1 worsens stroke outcome in mice, suggesting that MKP-1 is an endogenous protective molecule, although the underlying mechanisms remain unclear. Here we investigated the downstream mediators of MKP-1’s effects in stroke. Methods: Stroke was induced by 60 min transient middle cerebral artery occlusion (tMCAO) in male mice. Levels of p-JNK and p-p38 in MKP-1 KO mice and WT littermates 6 hours after stroke were assessed by Western blots. In a second cohort, the selective JNK inhibitor (SP600125) was administered intraperitoneally to both MKP-1 KO and WT mice 30 min before stroke then infarcts were analyzed at 72 hours post ischemia. In a third cohort, WT mice were intraperitoneally administrated the inhibitor or vehicle 30 min before stroke and sacrificed at 6 hours for protein analysis. Results: MKP-1 deletion produced significantly higher levels of p-JNK 6 hours after stroke (0.71±0.12 WT vs. 1.32± 0.14 KO, p0.05, n=3 p/g). There was no additive deleterious effects of pharmacological JNK inhibition in MKP-1 KO mice as measured by infarcts at 72 hours (cortex: 25.84±2.44%WT vs. 22.32±1.91%KO, striatum: 33.10±3.61% WT vs. 26.52±1.92% KO, total: 27.85±2.95% WT vs. 26.75±1.61% KO, p>0.05, n=6 p/g). In WT mice, JNK inhibition significantly decreased p-JNK (0.99 ± 0.14 vehicle vs. 0.44 ± 0.13 drug, p0.05, n=3 p/g). Conclusions: JNK is an important downstream mediator of MKP-1’s effects in stroke. In the ischemic brain, activating MKP-1 may restrain JNK activity, thereby producing neuroprotective effects.