Functional, proteomic and bioinformatic analyses of Nrf2- and Keap1- null skeletal muscle.

Although Nrf2 has been recognized as a master regulator of cytoprotection, its functional significance remains to be completely defined. We hypothesized that proteomic/bioinformatic analyses from Nrf2-deficient or overexpressed skeletal muscle tissues will provide a broader spectrum of Nrf2 targets and downstream pathways than are currently known. To this end, we created two transgenic mouse models; the iMS-Nrf2flox/flox and iMS-Keap1flox/flox , employing which we demonstrated that selective deletion of skeletal muscle Nrf2 or Keap1 separately impaired or improved skeletal muscle function. Mass spectrometry revealed that Nrf2-KO changed expression of 114 proteins while Keap1-KO changed expression of 117 proteins with 10 proteins in common between the groups. Gene ontology analysis suggested that Nrf2 KO-changed proteins are involved in metabolism of oxidoreduction coenzymes, purine ribonucleoside triphosphate, ATP and propanoate, which are considered as the basal function of Nrf2, while Keap1 KO-changed proteins are involved in cellular detoxification, NADP metabolism, glutathione metabolism and the electron transport chain, which belong to the induced effect of Nrf2. Canonical pathway analysis suggested that Keap1-KO activated four pathways, whereas Nrf2-KO did not. Ingenuity pathway analysis further revealed that Nrf2-KO and Keap1-KO impacted different signal proteins and functions. Finally, we validated the proteomic and bioinformatics data by analysing glutathione metabolism and mitochondrial function. In conclusion, we found that Nrf2-targeted proteins are assigned to two groups: one mediates the tonic effects evoked by a low level of Nrf2 at basal condition; the other is responsible for the inducible effects evoked by a surge of Nrf2 that is dependent on a Keap1 mechanism.