Inhibition of pJNK improves the structural and functional deficits caused by inhibition of USP14’s DUB activity. (A) Representative immunoblots of pJNK1/2 and JNK1/2 in spinal cords from 5-week-old wild type or TgUsp14CA mice following 2 weeks of IP injections of the JNK inhibitor SP600125 (SP, +) or vehicle control (DMSO, -). β-tubulin was used as a loading control. Wild type mice given SP had pJNK levels that were 71.2 ± 10.3% (p < 0.01, Mann-Whitney test) of what was observed in vehicle-treated wild type controls and SP-treated TgUsp14CA mice had pJNK levels that were 66.6 ± 19.4% (p < 0.01, Mann-Whitney test) of vehicle-treated TgUsp14CA mice. (B) Gastrocnemius muscle masses from male wild type or TgUsp14CA mice treated with vehicle alone (-) or SP (+) as described above. The same effect was observed in female mice. (C) Relative AChR-γ mRNA abundance in gastrocnemius muscles. (D) Total distance travelled and (E) ambulatory velocity during 10 min in an open field. (F) Latency to fall from beam in the rotarod assay. For (B)-(F), all data are shown as mean ± SEM and n = 5 to 7 animals per condition. Symbols represent Mann-Whitney tests corrected for multiple comparisons with a Bonferonni adjustment, where *p < 0.05, **p < 0.01, and ***p < 0.001. (G) High magnification images of whole-mount immunostaining of TA muscles from mice described above. AChRs were labeled with rhodamine-conjugated α-BTX (red), and motor neuron axons were visualized via expression of YFP under the Thy1.2 promoter (green). Scale bars = 20 μm.