Diabetes is a growing global epidemic currently affecting 537 million adults worldwide, with 90% of these cases attributed to type 2 diabetes mellitus. Individuals with diabetes suffer from glucose intolerance, hyperinsulinaemia and hyperglycaemia. Additionally, target tissues and organs of insulin have a diminished response to insulin, known as insulin resistance, which results in the dysregulation of insulin signalling. Prolonged insulin resistance, in turn, leads to pancreatic β cell dysfunction leading to decreased insulin production and ultimately the cessation of insulin secretion. Several target tissues and organs are implicated in type 2 diabetes mellitus namely the liver, brain, skeletal muscle and adipose tissue. Skeletal muscle cells are primarily responsible for insulin-dependent glucose uptake and homeostasis. Ergo, in vitro models of skeletal muscle cells often are utilised in studies examining insulin signalling and glucose uptake. In the highly complex insulin signalling pathway, protein kinase B more commonly known as Akt, plays an essential role where its dysregulation has been implicated in several deceases. Specifically, the overactivation of Akt can result in tumour growth, whereas metabolic conditions such as insulin resistance can occur when Akt phosphorylation is impaired. Thus, inhibitors of this enzyme are of interest as a tool for research into Akt phosphorylation and insulin signalling.
Recently, our group has developed a kinetic mechanistic model to describe the dynamics of insulin signalling, glucose uptake and its metabolism in C2C12 mouse skeletal muscle. The activities of these modules were analysed dose- and time-dependently upon induction with insulin. This model serves as the reference state to further study mechanisms leading to insulin resistance as a function of known agents causing type 2 diabetes mellitus.
Accordingly, the effect of Akt inhibition on insulin signalling, glucose uptake and glycolytic flux was investigated in C2C12 mouse skeletal muscle myotubes. The current phase II trial Akt allosteric inhibitor, MK-2206, was utilised. The inhibitory effect of MK-2206 on Akt phosphorylation was analysed using our group’s minimal mathematical model. As before, 100 nM insulin stimulation of untreated cells increased Akt Ser473 and Thr308 phosphorylation dose- and time-dependently. Treatment with MK-2206 decreased the dose-dependent increase of Akt phosphorylation of both Ser473 and Thr308 regulatory sites after stimulation with 100 nM insulin. In addition, MK-2206 treatment delayed the time dynamics of insulin-induced Akt phosphorylation. Model simulations were able to describe the delay and decrease of Akt phosphorylation that was observed experimentally. In control cells, stimulation with 100 nM insulin increased glucose uptake rate and lactate production rate by 2-fold and 1.9-fold, respectively. MK-2206 treatment did not affect the basal rate of glucose uptake or lactate production, but a strong decrease of insulin stimulation of glucose metabolism was observed in MK-2206 treated cells.