MNK1/2 contributes to periorbital hypersensitivity and hyperalgesic priming in preclinical migraine models

Abstract

Migraine is thought to involve sensitization of the trigeminal nociceptive system. In preclinical pain models, activation of MNK-eIF4E signalling contributes to nociceptor sensitization and the development of persistent pain. Despite these observations, the role of MNK signalling in migraine remains unclear. Here, we investigate whether activation of MNK contributes to hypersensitivity in two rodent models of migraine. Female and male wild-type (WT) and MNK1 knock-out mice were subjected to repeated restraint stress or a dural injection of interleukin-6 (IL-6) and tested for periorbital hypersensitivity and grimacing. Upon returning to baseline thresholds, stressed mice were administered a low dose of the nitric oxide donor sodium nitroprusside and mice previously injected with IL-6 were given a second dural injection of pH 7.0 to test for hyperalgesic priming. MNK1 knock-out mice were significantly less hypersensitive than the WT following dural IL-6 and did not prime to pH 7.0 or sodium nitroprusside. Furthermore, treatment with the selective MNK inhibitor, eFT508, in WT mice prevented hypersensitivity caused by dural IL-6 or pH 7.0. Together, these results implicate MNK-eIF4E signalling in the development of pain originating from the dura and strongly suggest that targeting MNK inhibition may have significant therapeutic potential as a treatment for migraine.

Keywords: MNK; eIF4E; headache; migraine; trigeminal.

Figure 1

Genetic inhibition of MNK1 partially attenuates facial hypersensitivity and hyperalgesic priming caused by dural IL-6. (A) Female and male WT or MNK1 KO mice were administered 5 µl of the proinflammatory cytokine, IL-6 (0.1 ng), or vehicle onto their dura mater and tested for acute facial hypersensitivity (B) and grimace measures (C). Following resolution of acute allodynia, all mice were tested for hyperalgesic priming by administering 5 µl of SIF (pH = 7.0) and tested again. WT mice were observed to have significantly reduced withdrawal thresholds and increased grimacing compared to MNK1 KO mice, in which these effects were partially attenuated. Likewise, contrary to WT mice, MNK1 KO mice did not prime to dural pH 7.0. No sex differences were observed. Comparisons were made via two-way ANOVA followed by Bonferroni post hoc analysis. Significance between WT/IL-6 and MNK1 KO/IL-6 groups (denoted by asterisk) and between MNK1 KO/Veh and MNK1KO/IL-6 groups (denoted by delta symbol) is shown. n ≥ 6 for all groups; *P ≤ 0.05; **^,ΔΔP ≤ 0.01; ^ΔΔΔP ≤ 0.001; ****^,ΔΔΔΔP ≤ 0.0001.

Figure 2

MNK1 KO mice do not prime to low-dose NO donor following repeated stress. (A) Following three consecutive days of restraint stress, female and male WT and MNK1 KO mice were tested for acute facial hypersensitivity and grimace measures. Upon resolution of hypersensitivity, mice were administered a low dose of the NO donor, SNP (0.1 mg/kg, IP), to test for the presence of priming. Following stress, WT and MNK1 KO mice showed similar levels of facial hypersensitivity (B) lasting up to 14 days, with MNK1 KO mice exhibiting significantly lower grimace scores (C) in the early time points measured. Interestingly, despite becoming acutely hypersensitive, MNK1 KO mice do not prime to low-dose SNP compared to WTs, suggesting a role for MNK1 activation in the development of stress-induced hyperalgesic priming. No sex differences were observed. Comparisons were made via two-way ANOVA followed by Bonferroni post hoc analysis. Significance between WT/Stress and MNK1 KO/Stress groups (denoted by asterisk) and MNK1KO/Ctrl and MNK1KO/Stress groups (denoted by delta symbol) is shown. n ≥ 7 for all groups; **P ≤ 0.01; ****^,ΔΔΔΔP ≤ 0.0001.

Figure 3

The MNK inhibitor, eFT508, reduces dural IL-6 -induced facial hypersensitivity and prevents priming to pH 7.0. Female and male WT mice were administered 5 µl of dural IL-6 (0.1 ng) or vehicle and tested for acute facial hypersensitivity and grimacing. Upon returning to baseline thresholds, mice were tested for priming with a 5 µl dural injection of SIF (pH = 7.0). Prior to IL-6 (A) or pH 7.0 (D), mice received 100 µl of the MNK inhibitor, eFT508 (10 mg/kg), or vehicle via oral gavage. In mice that received eFT508, dural IL-6 induced facial hypersensitivity (B) and grimace measures (C) were significantly attenuated compared to the vehicle group and these mice did not prime to dural pH 7.0. Similarly, mice that received eFT508 prior to dural pH 7.0 did not prime to pH 7.0 compared to the vehicle group (E–F), suggesting that activation of MNK is critical to transition to a primed state. No sex differences were observed. Comparisons were made via two-way ANOVA followed by Bonferroni post hoc analysis. Significance between IL-6/Vehicle and IL-6/eFT508 groups (denoted by asterisk) and SIF/eFT508 and IL-6/eFT508 groups (denoted by delta symbol) is shown. n = 7 for all groups; *^,ΔP ≤ 0.05; **^,ΔΔP ≤ 0.01; ***^,ΔΔΔP ≤ 0.001; ****^,ΔΔΔΔP ≤ 0.0001.