Over the past few years, researchers have discovered that having type 2 diabetes and being overweight could raise the risk of Alzheimer’s. However, now they start talking about type 3 diabetes and the link it has with Alzheimer’s.
This newly discovered form of diabetes happens when the neurons can no longer respond to insulin which is crucial for things like learning, memory, and other basic tasks. According to some scientists, lack of insulin is the main cause of the cognitive decline related to Alzheimer’s.
Recently, researchers from the Mayo Clinic’s Campus in Florida and Rochester tested the effects of a new insulin nasal spray on symptoms of Alzheimer’s disease. The results of the multi-institution clinical study are forthcoming.
However, what has that got to do with the APOE gene (Alzheimer’s gene)?
The neuroscientist in Mayo Clinic Guojun Bu, and Professor of Medicine Mary Lowell Leary discovered that the root cause is APOE4. This is a variant of the APOE gene. Almost 20% of the general population and over 50% of Alzheimer’s patients have the APOE4 gene.
Researchers discovered that it’s responsible for interrupting the way the brain processes insulin. So, there was an insulin impairment in mice, especially old ones, with the APOE4 gene. What’s more, they saw a diet high in fats can speed up the process in middle-aged mice with APOE4.
Dr. Bu concluded that both APOE4 and the peripheral insulin resistance from the high-fat diet led to insulin resistance in the brain.
The gene produces an APOE4 protein which can attach to insulin receptors on the neuron surface more aggressively than APOE3 – its natural counterpart. What happens is something similar to a game of musical chairs.
The protein APOE4 blocks the receptor by outcompeting the normal protein. APOE4 aims to do one last brain cell damage. So, once it gets inside the neuron, the clumps trap within the machinery of cells. This, in turn, prevents the receptors to go back to the surface of the neuron to do their job.
All this impairs the insulin signal processing even more, resulting in brain cell starvation.
Dr. Bu explains that the research helped them understand the gene more than before. So, they are now even more convinced it’s the strongest genetic risk factor for Alzheimer’s.
However, he hopes the study could help in the invention of some treatment like insulin nasal spray that could help those without the APOE4 gene. And, those with the gene might require additional medication to prevent cognitive decline.