I think the main progression is lymphatic dysfunction > chemical build-up > BBB damage > neurodegenerative plaques and tangles.

My mother died from Alzheimer's at 77 but was the picture of health and happiness for many years prior, but never slept well to the point she had to have her own room away from Dad for many years.

Maybe the trick is going to be repairing the BBB and stimulating lymphatic function rather than chasing down every factor that explains why the BBB and/or lymphatic function is compromised in the first place.