Neuropathological changes in the nucleus basalis of Meynert in people with type 1 or type 2 diabetes mellitus

People with type 1 or type 2 diabetes mellitus (T1DM or T2DM) often experience cognitive impairment. We profiled cells in the nucleus basalis of Meynert (NBM) in postmortem human brain tissue to investigate the neuropathological changes. Sixty-eight postmortem NBM samples were grouped as T1DM, T2DM, and controls without diabetes, with Braak stage 0–II or III–VI. T1DM subjects had only Braak stage 0–II and were thus compared only to controls with a similar Braak stage and not subjects with Braak stage III–VI. We analyzed neurons expressing choline acetyltransferase (ChAT), phosphorylated tau, amyloid-beta, glial cells, and vasculature with their respective markers. We found significantly lower neuronal expression of ChAT in T1DM individuals than in controls and T2DM individuals with Braak stage 0–II. Later-stage hyperphosphorylated tau levels were higher in T2DM compared to controls with Braak stage III–VI. Our results suggest that reduced acetylcholine production by NBM neurons may underlie the cognitive complaints of people with T1DM. In contrast, T2DM may exacerbate neuropathological changes associated with Alzheimer’s disease-like alterations.