As a relatively healthy person, insulin is something that I rarely consider, I do not consider how my intake of sugar may affect my body, I also do not consider what would happen if I did not have the necessary insulin in my body. Insulin is involved in many processes in the body, more than I have ever really considered. Deficiencies in insulin lead to diabetes, and in turn obesity, but also with links to Alzheimer’s disease. Insulin is highly involved in metabolic as well as cognitive regulations. Thus, when the insulin pathway is not working properly, the brain and energy homeostasis are thrown off. Insulin is the key player in glucose homeostasis, meaning it is the thing that keeps our body’s sugar and energy levels under control. In the central nervous system, insulin is largely found, but in patients with diabetes or Alzheimer’s disease, there are lower levels of insulin or insulin receptors. Thus, we see a link of insulin to Alzheimer’s disease (which makes sense as insulin has a part in cognitive part of the brain, especially in learning and memory). We also can see a link to obesity when insulin is not functioning properly. This change in food intake is changed as within the insulin signaling pathway, we see the PI3-K pathway, which when activated will send signals for decrease of food intake. The neurons that are involved in this regulation of food intake are the AgRP/NPY neuron (which tells the body to eat more) and the POMC neuron (which sends the signals that the body is full) and if insulin is not functioning fully, then there is excess glucose, leading to these two neurons getting signals screwed up. Thus, if the insulin is not working properly, then there is no signal to decrease food intake, which will then lead to over ingestion and set the body up for obesity. Another interesting part of these neurons is that in a high fat diet, the POMC neuron is tricked, and instead of recognizing high fat food as something that should satiate our bodies, it instead still thinks we are hungry (in the figure below we see this pathway and that fatty food cause the same pathway as hunger).
It really took me by surprise learning that this is why it is so easy to eat lots of fatty foods without ever really feeling full, and explains why problems with insulin can lead to obesity.
The other pathway that insulin signals through is the MAP-K cascade, which is involved in cognition (especially learning and memory). Thus, we can see how Alzheimer’s disease has a link to poor insulin function, as there would be decreased memory when there is less signaling coming from the insulin pathway. In addition to causing the memory issues, the PI3-K pathway (from insulin pathway) causes a descrease in phosphorylated tau, so as PI3K stops functioning appropriately, phosphorylated tau increases, which is a large player in AD. In addition to the tau, we see an increase in Aβ plaques, which inhibits the insulin pathway, thus causing loss of the cognition that is gained. I find it extremely interesting that AD is linked to insulin. It is not something that I had ever considered to be related to each other. I also found myself wondering if having diabetes earlier on would pretty much mean that one will end up with AD or if there are ways to prevent AD when someone has type II diabetes. It is kind of a foreboding thought, just because a large possibility for the future of people who have this type of diabetes is AD, which is a scary thought to know that you will slowly forget who you are. However, I think it is interesting that we have found such a link, and how insulin may be the link in curing AD as effectively as it is in helping with diabetes. All in all, I found that I really should put more thought towards how insulin is working in my body and how what I may be eating may hurt the insulin or its receptors. What I am trying to get across is that insulin plays such a crucial role in our lives, and that maybe we should consider how to keep the insulin in our body functioning appropriately (by eating healthy) so we don’t have to be worried about whether our sugar will be metabolized and our body will function properly in the future.
Insulin: A Sometimes Under Appreciated Key Player in the Brain
