The neuronal insulin receptor in its environment

Insulin is known mainly for its effects in peripheral tissues, such as the liver, skeletal muscles and adipose tissue, where the activation of the insulin receptor (IR) has both short-term and long-term effects. Insulin and the IR are also present in the brain, and since there is evidence that neuronal insulin signaling regulates synaptic plasticity and that it is impaired in disease, this pathway might be the key to protection or reversal of symptoms, especially in Alzheimer's disease. However, there are controversies about the importance of the neuronal IR, partly because biophysical data on its activation and signaling are much less complete than for the peripheral IR. This review briefly summarizes the neuronal IR signaling in health and disease, and then focuses on known differences between the neuronal and peripheral IR with regard to alternative splicing and glycosylation, and lack of data with respect to phosphorylation and membrane subdomain localization. Particularities in the neuronal IR itself and its environment may have consequences for downstream signaling and impact synaptic plasticity. Furthermore, establishing the relative importance of insulin signaling through IR or through hybrids with its homolog, the insulin-like growth factor 1 receptor, is crucial for evaluating the consequences of brain IR activation. An improved biophysical understanding of the neuronal IR may help predict the consequences of insulin-targeted interventions.