5. protein kinase C beta repression and beneficial metabolic actions of exercise
It is generally accepted that high-fat diet intake and sedentary behavior
increase the risk of obesity and insulin resistance. There is also evidence
that exercise reduces the risk of these chronic diseases. The poten-tial mechanism by which
exercise attenuates high-fat diet-induced insulin resistance
involves increased insulin sensitivity and glucose transport in
contracting skeletal muscles. However, the underlying molecular and
cellular mechanisms are not fully understood because of the complicated
processes involved in exercise. Given the important regulatory
role of protein kinase C beta in obesity and insulin resistance, we postulated that
protein kinase C beta might also play a role in the exercise-induced improvement in
energy expenditure and insulin resistance.We performed physiological
studies to determine the extent to which the metabolic effects of exercise
were mediated by repression of protein kinase C beta and observed that protein kinase C beta
levels were significantly decreased in both skeletal muscle and liver
after exercise. Importantly, fat accumulation, mitochondrial dysfunction,
and insulin resistance induced by high-fat diet were ameliorated by exercise
in white tissue mice. In contrast, exercise had little effect on protein kinase C beta−/− mice.