Finally, we demonstrated enhanced activation of AKT, a downstream
signaling molecule of insulin, in skeletal muscle and liver of exercised
WT mice, whereas PKCβ deficiency decreased the difference between
sedentary and exercised mice. It is important to note that increasing
PKCβ activity in muscle alone is associated with both muscle and
systemic insulin resistance. Muscle-specific overexpression of PKCβII
in the transgenic mice not only induced insulin resistance, but also
affected expression levels of several genes involved in lipid metabolism
[88]. Decreased expression of PGC-1α, acyl CoA oxidase, and hormonesensitive
lipase, together with enhanced expression of the lipogenic
transcription factor SREBP-1c, in the skeletal muscle of these mice was
associated with decreased lipid oxidation and increased intramyocellular
lipid deposition. This is concordant with thewell-established correlation
between intramyocellular triglyceride and insulin resistance in obese
and prediabetic individuals [89]. The above data led us to propose that
downregulation of PKCβ expression contributes to exercise-induced
improvement in insulin resistance.