A Potential Role for α-Amylase in Amyloid-β-Induced Astrocytic Glycogenolysis and Activation.

Abstract

Astrocytes produce and store the energy reserve glycogen. However, abnormal large glycogen units accumulate if the production or degradation of glycogen is disturbed, a finding often seen in patients with Alzheimer's disease (AD). We have shown increased activity of glycogen degrading α-amylase in AD patients and α-amylase positive glial cells adjacent to AD characteristic amyloid-β (Aβ) plaques. Investigate the role of α-amylase in astrocytic glycogenolysis in presence of Aβ. Presence of α-amylase and large glycogen units in postmortem entorhinal cortex from AD patients and non-demented controls were analyzed by immunohistological stainings. Impact of different Aβ42 aggregation forms on enzymatic activity (α-amylase, pyruvate kinase, and lactate dehydrogenase), lactate secretion, and accumulation of large glycogen units in cultured astrocytes were analyzed by activity assays, ELISA, and immunocytochemistry, respectively. AD patients showed increased number of α-amylase positive glial cells. The glial cells co-expressed the astrocytic marker glial fibrillary acidic protein, displayed hypertrophic features, and increased amount of large glycogen units. We further found increased load of large glycogen units, α-amylase immunoreactivity and α-amylase activity in cultured astrocytes stimulated with fibril Aβ42, with increased pyruvate kinase activity, but unaltered lactate release as downstream events. The fibril Aβ42-induced α-amylase activity was attenuated by β-adrenergic receptor antagonist propranolol. We hypothesize that astrocytes respond to fibril Aβ42 in Aβ plaques by increasing their α-amylase production to either liberate energy or regulate functions needed in reactive processes. These findings indicate α-amylase as an important actor involved in AD associated neuroinflammation.