Posttranslational modification impact on the mechanism by which amyloid-β induces synaptic dysfunction

Oligomeric amyloid-beta (A) 1-42 disrupts synaptic function at an early stage of Alzheimer's disease (AD). Multiple posttranslational modifications of A have been identified, among which N-terminally truncated forms are the most abundant. It is not clear, however, whether modified species can induce synaptic dysfunction on their own and how altered biochemical properties can contribute to the synaptotoxic mechanisms. Here, we show that a prominent isoform, pyroglutamated A beta 3(pE)- 42, induces synaptic dysfunction to a similar extent like A1-42 but by clearly different mechanisms. In contrast to A beta 1-42, A3(pE)-42 does not directly associate with synaptic membranes or the prion protein but is instead taken up by astrocytes and potently induces glial release of the proinflammatory cytokine TNF alpha. Moreover, A beta 3(pE)-42-induced synaptic dysfunction is not related to NMDAR signalling and A beta 3(pE)-42-induced impairment of synaptic plasticity cannot be rescued by D1-agonists. Collectively, the data point to a scenario where neuroinflammatory processes together with direct synaptotoxic effects are caused by posttranslational modification of soluble oligomeric A and contribute synergistically to the onset of synaptic dysfunction in AD.