Endogenous galanin protects mouse hippocampal neurons against amyloid toxicity in vitro via activation of galanin receptor-2

Abstract

Expression of the neuropeptide galanin is known to be upregulated in the brain of patients with Alzheimer's disease (AD). We and others have shown that galanin plays a neuroprotective role in a number of excitotoxic injury paradigms, mediated by activation of the second galanin receptor subtype (GAL2). In the present study, we investigated whether galanin/GAL2 plays a similar protective role against amyloid-β(Aβ) toxicity. Here we report that galanin or the GAL2/3-specific peptide agonist Gal2-11, both equally protect primary dispersed mouse wildtype (WT) neonatal hippocampal neurons from 250 nM Aβ1-42 toxicity in a dose dependent manner. The amount of Aβ1-42 induced cell death was significantly greater in mice with loss-of-function mutations in galanin (Gal-KO) or GAL2 (GAL2-MUT) compared to strain-matched WT controls. Conversely, cell death was significantly reduced in galanin over-expressing (Gal-OE) transgenic mice compared to strain-matched WT controls. Exogenous galanin or Gal2-11 rescued the deficits in the Gal-KO but not the GAL2-MUT cultures, confirming that the protective effects of endogenous or exogenous galanin are mediated by activation of GAL2. Despite the high levels of endogenous galanin in the Gal-OE cultures, the addition of exogenous 100 nM or 50 nM galanin or 100 nM Gal2-11 further significantly reduced cell death, implying that GAL2-mediated neuroprotection is not at maximum in the Gal-OE mice. These data further support the hypothesis that galanin over-expression in AD is a neuroprotective response and imply that the development of a drug-like GAL2 agonist might reduce the progression of symptoms in patients with AD.

Fig. 1

Percentage cell death in (A) Gal-KO and (B) GAL2-MUT both compared to strain matched WT hippocampal cultures, treated with 250 nM fA_1-42 in the presence of varying concentrations of galanin or Gal2-11. In both loss-of-function mutations there is a significant increase in fA_1–42 and glutamate-induced cell death compared to strain-matched WT cultures. Addition of galanin or Gal2-11 significantly rescues the deficits in the Gal-KO but not the GAL2-MUT cultures. **p < 0.01 treatment versus control. §p < 0.05 Gal-KO or GAL2-MUT versus WT. §§p < 0.01 GAL2-MUT versus WT. +p < 0.05 treatment different to fA_1–42 or glutamate alone. ++p < 0.01 treatment different to fA_1–42 or glutamate alone.

Fig. 2

Percentage cell death in Gal-OE and strain matched WT hippocampal cultures treated with 250 nM fA_1–42 in the presence of varying concentrations of galanin or Gal2-11. In the Gal-OE mice there is a significant decrease in fA_1–42 and glutamate-induced cell death compared to strain-matched WT cultures. Addition of 100 nM and 50 nM galanin or 100 nM Gal2-11 further and significantly rescues the cell death. **p < 0.01 treatment versus control. §§p < 0.01 Gal-OE versus WT. +p < 0.05 treatment different to fA_1–42 or glutamate alone. ++p < 0.01 treatment different to fA_1–42 or glutamate alone.