Aims: Protein kinase C epsilon (PKCε) has been causally linked to diet-induced glucose intolerance, with emphasis on a direct role for the kinase in impaired hepatic insulin signalling. However, we have previously demonstrated (i) that PKCε deletion specifically in the liver has no effect on insulin action, and (ii) that the kinase is activated in skeletal muscle of fat-fed rodents. We therefore investigated the effects of PKCε deletion in muscle tissue on glucose tolerance, as well as on mitochondrial function, insulin signalling and the muscle proteome.
Methods: “Floxed” PKCε mice were bred with HSA-CreT2 transgenic mice to generate tamoxifen-inducible MEpsKO mice and littermate controls. Mice, treated with tamoxifen at 10 weeks, were then fed normal chow or a high fat/sucrose diet (HFSD) for 6 weeks and were either sedentary or housed in cages with voluntary running wheels for the final 3 weeks (n=7-9). Mice were subjected to ECHO-MRI and glucose tolerance tests. Permeabilised fibres from fresh gastrocnemius muscles were subjected to Oroboros high resolution respirometry. Proximal insulin signalling was examined after in vivo insulin challenge by immunoblotting and the muscle proteome was analysed by ZenoTOF mass spectrometry.
Results: MepsKO mice exhibited improved glucose tolerance on a HFSD compared to controls, with no change in body composition. Both voluntary exercise and the HFSD increased muscle mitochondrial capacity, and this was unaffected by PKCε deletion. Voluntary exercise also protected against glucose intolerance caused by HFSD so that the genotype effect was no longer evident. PKCε-dependent alterations in the muscle proteome may provide insights into the mechanisms involved, which were independent of changes in insulin signalling.
Conclusions: PKCε deletion specifically in skeletal muscle protects against diet-induced glucose intolerance, independently of proximal insulin signalling. The non-additive effects of PKCε deletion and exercise suggest a convergence of the pathways involved.