Pancreatic β-cell growth and survival in the onset of type 2 diabetes: a role for protein kinase B in the Akt?

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Abstract
The control of pancreatic β-cell growth and survival in the adult plays a pivotal role in the pathogenesis of type 2 diabetes. In certain insulin-resistant states, such as obesity, the increased insulin-secretory demand can often be compensated for by an increase in β-cell mass, so that the onset of type 2 diabetes is avoided. This is why approximately two-thirds of obese individuals do not progress to type 2 diabetes. However, the remaining one-third of obese subjects that do acquire type 2 diabetes do so because they have inadequate compensatory β-cell mass and function. As such, type 2 diabetes is a disease of insulin insufficiency. Indeed, it is now realized that, in the vast majority of type 2 diabetes cases, there is a decreased β-cell mass caused by a marked increase in β-cell apoptosis that outweighs rates of β-cell mitogenesis and neogenesis. Thus a means of promoting β-cell survival has potential therapeutic implications for treating type 2 diabetes. However, understanding the control of β-cell growth and survival at the molecular level is a relatively new subject area of research and still in its infancy. Notwithstanding, recent advances have implicated signal transduction via insulin receptor substrate-2 (IRS-2) and downstream via protein kinase B (PKB, also known as Akt) as critical to the control of β-cell survival. In this review, we highlight the mechanism of IRS-2, PKB, and anti-apoptotic PKB substrate control of β-cell growth and survival, and we discuss whether these may be targeted therapeutically to delay the onset of type 2 diabetes.