Adiponectin improves long-term potentiation in the 5XFAD mouse brain

Abstract

Adiponectin is an adipokine that regulates apoptosis, glucose and lipid metabolism, and insulin sensitivity in metabolic diseases. As recent studies have associated changes in adipokines and other metabolites in the central nervous system with a risk for Alzheimer's disease (AD), we investigated the effects of adiponectin treatment on hippocampal cells in the 5XFAD mouse model of AD and neuronal SH-SY5Y cells under amyloid beta toxicity. Adiponectin treatment reduced levels of cleaved caspase 3 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) apoptosis signalling and decreased glycogen synthase kinase 3 beta (GSK3β) activation. Moreover, adiponectin treatment triggered long-term potentiation in the hippocampi of 5XFAD mice, which was associated with reduced expression of N-methyl-D-aspartate and its receptor as well as surface expression of the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor. These findings suggest that adiponectin inhibits neuronal apoptosis and inflammatory mechanisms and promotes hippocampal long-term potentiation. Thus, adiponectin exhibits beneficial effect on hippocampal synaptic plasticity in Alzheimer's disease mouse model.

Figure 1

Electrophysiological recordings in the CA1 hippocampal region, and ionotropic glutamate receptor, AdipoR1, AdipoR2 and PSD-95 protein expression after adiponectin/ACRP30 treatment. (a) Schematic diagrams of the experimental procedure and field recordings in hippocampal slices. (b,c) High-frequency stimulation (HFS; two trains of 100 Hz, 100 pulses) failed to induce LTP in 5XFAD mice (n = 4). However, HFS induced robust LTP in slices following adiponectin/ACRP30 perfusion (10 min) and incubation (2 h) (closed circles). (d) In vitro surface expression of GluA1, GluN1 and GluN2B decreased in the 5XFAD mouse hippocampus compared with that in wild-type mice; however, these decreases were reversed by adiponectin/ACRP30 treatment under both conditions (n = 3). No change in GluA1 (AMPA receptor subunit), GluN1 (NMDA receptor subunit) or GluN2B (NMDA receptor subunit) expression was observed (n = 3). (e) AdipoR1, AdipoR2 and PSD-95 protein levels were decreased in 5XFAD mouse hippocampus compared with those in wild-type mice; however, adiponectin/ACRP30 significantly increased protein levels under both treatment conditions. Data are expressed as means ± SEMs. *p < 0.05, **p < 0.001, ***p < 0.0001; adiponectin/ACRP30 perfusion, 2.7 nM adiponectin/ACRP30 perfusion for 10 min; adiponectin/ACRP30 incubation, 2.7 nM adiponectin/ACRP30 incubation for 2 h; a.10, adiponectin/ACRP30 treatment for 10 min; a.2, adiponectin/ACRP30 treatment for 2 h.

Figure 2

Adiponectin/ACRP30 alleviates aberrant GSK3β and NF-κB signalling in the 5XFAD mouse hippocampus. (a) GSK3β activation and cleaved caspase 3 protein levels were increased in 5XFAD mouse hippocampus compared with those in wild-type mice; these were alleviated by adiponectin/ACRP30 treatment for 10 min and 2 h. (b) Phosphorylated p65 (p-p65) protein levels were significantly increased in 5XFAD mouse hippocampus compared with those in the control; this increase was suppressed by adiponectin/ACRP30 treatment for 10 min and 2 h. (c) Analysis of IL-1β, IL-6 and IL-10 expression by Western blotting (n = 4 in each group). Data are expressed as means ± SEMs. *p < 0.05, **p < 0.001, ***p < 0.0001; a.10 and a.2 indicate 2.7 nM adiponectin/ACRP30 treatment for 10 min and 2 h, respectively; C, 5XFAD control mouse hippocampus.

Figure 3

Altered activation of NF-κB and GSK3β signalling in neuronal SH-SY5Y cells under Aβ toxicity by adiponectin/ACRP30 treatment. Western blot analysis of protein expression levels in neuronal SH-SY5Y cells under Aβ₄₂ toxicity (a–c) and following the transfection with AdipoR1-specific siRNAs (d). (a) AdipoR1, AdipoR2 and PSD-95 protein levels decreased after Aβ₄₂ treatment compared with those in the control. However, except for AdipoR2, these decreases were rescued by adiponectin/ACRP30 treatment. (b) GSK3β activation and cleaved caspase 3 protein levels increased after Aβ₄₂ treatment compared with those in the control but were reversed by adiponectin/ACRP30 treatment. (c) p-p65 levels were significantly increased after Aβ₄₂ treatment compared with those in the control and were suppressed by adiponectin/ACRP30 treatment. (d) Adiponectin treatment prevented the effect of Aβ₄₂ toxicity on PSD-95, p-GSK3β (ser9), p-p65 and cleaved caspase 3 protein levels. However, AdipoR1 siRNAs fully reversed these effects. Data are expressed as means ± SEMs. *p < 0.05 compare with control, **p < 0.001 compare with control, ***p < 0.0001 compare with control; ^#p < 0.05, ^##p < 0.001, ^###p < 0.0001; adiponectin/ACRP30, 20 nM treatment for 12 h; Aβ₄₂, treatment with 10 μM Aβ₄₂ peptide for 24 h in neuronal SH-SY5Y cells; adiponectin/ACRP30 + Aβ₄₂, SH-SY5Y cells were treated with adiponectin/ACRP30 (20 nM) for 12 h and then incubated with Aβ₄₂ peptide (10 μM) for 24 h; siAdipoR1 + adiponectin/ACRP30 + Aβ₄₂, SH-SY5Y cells were transfected with siAdipoR1 (5 μM) for 48 h and then treated with Aβ₄₂ and adiponectin/ACRP30; siAdipoR1 + adiponectin/ACRP30, SH-SY5Y cells were transfected with siAdipoR1 (5 μM) for 48 h and then treated with adiponectin/ACRP30; C.C3, cleaved caspase 3.