Val⁸-GLP-1 remodels synaptic activity and intracellular calcium homeostasis impaired by amyloid β peptide in rats.

Type 2 diabetes mellitus (T2DM) is a risk factor for Alzheimer's disease (AD) in the elderly. Glucagon-like peptide-1 (GLP-1), a modulator in T2DM therapy, has been shown to have neuroprotective properties. However, the native GLP-1 can be rapidly degraded by the enzyme dipeptidyl peptidase IV (DPP IV); the neuroprotective mechanism of GLP-1 in the central nervous system is still an open question, and whether GLP-1 can prevent amyloid β (Aβ)-induced synaptic dysfunction and calcium disorder is still unclear. The present study, by using patch clamp and calcium imaging techniques, investigated the effects of Val⁸-GLP-1(7-36), a GLP-1 analogue with profound resistance to DPP IV, on the excitatory and inhibitory synaptic transmission and intracellular calcium concentration ([Ca²⁺](i) ) in the absence or presence of Aβ1-40. The results showed that 1) Aβ1-40 significantly reduced the frequency of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) in CA1 pyramidal neurons of rat brain slices; 2) Val⁸-GLP-1(7-36) did not affect the activity of miniature postsynaptic currents but effectively protected against the Aβ1-40-induced decrease in mEPSC and mIPSC frequency; 3) Aβ1-40 significantly increased [Ca²⁺](i) in primary neuronal cultures; and 4) Val⁸-GLP-1(7-36) alone did not change the intracellular calcium level but prevented Aβ1-40-induced persistent elevation of [Ca²⁺](i). These findings demonstrate for the first time that central application of Val⁸-GLP-1(7-36) could protect against Aβ-induced synaptic dysfunction and intracellular calcium overloading, suggesting that the neuroprotection of GLP-1 may be involved in the remodeling of synaptic activity and intracellular calcium homeostasis in the brain.