PTP1B, p-p38, p-MAPK and p-Akt protein levels. PTP1B, p-p38, p-MAPK and p-Akt levels were measured by Western blotting in 5-wk-old mice cochleae. P38α was used as a loading control to calculate the relative protein levels. Values are presented as mean ± SEM of at least three mice per condition. Statistical significance was estimated by t test; P values of <0.05 were considered significant. PTP1B expression levels were significantly increased in Irs2−/−Ptpn1+/+ mice compared with wild-type mice (*P < 0.05), and p-MAPK levels decreased when comparing the double mutant with the wild-type mice (*P < 0.05).