Dopamine and Aβ-Induced Stress Signaling and Decrements in Ca 2+ Buffering In Primary Neonatal Hippocampal Cells Are Antagonized by Blueberry Extract

Abstract

We have shown previously that dietary blueberry (BB) extract supplementation (S) reversed several parameters of neuronal and behavioral (e.g., cognition) aging in rodents. Additionally, findings indicate that COS-7 cells transfected with muscarinic receptor subtypes (e.g., M1) showed decrements in Ca²⁺ clearance following depolarization (Ca²⁺ Recovery time, Ca²⁺RT) that were antagonized by BB. Since it has been postulated that at least part of the loss of cognitive function in aging may be dependent upon a dysregulation in calcium homeostasis (i.e., Ca²⁺RT), we assessed whether: a) Ca²⁺RT would be altered in dopamine (DA)- or amyloid beta (Aβ)-exposed cultured primary hippocampal neuronal cells (HNC), and b) BB pre-treatment of the cells would prevent these deficits. Thus, control or BB (0.5 mg/ml)-treated HNC were exposed to DA (0.1 mM, 2 hrs), Aβ(40) (25 μM, 24 hrs), Aβ(42) (25 μM, 24 hrs), and Aβ(25–35) (25 μM, 24 hrs), and Ca²⁺RT following KCl-induced depolarization assessed. Ca²⁺RT was assessed as the % of HNC showing recovery to 50%–70% of control at 5, 10, or 15 min after depolarization. Results indicated that DA significantly lowered Ca²⁺RT in the HNC at all time points examined after depolarization. However, BB treatment selectively prevented these declines in Ca²⁺RT. In the case of Aβ, the greatest effects on Ca²⁺RT were seen when the hippocampal cells were Aβ(42)-treated. These effects were antagonized by BB treatment. Aβ(40) produced fewer deficits on Ca²⁺RT than those seen when the HNC were pre-treated with either A²⁺(42) or A²⁺(25–35), but BB was relatively ineffective in antagonizing the deficits in Ca²⁺RT produced by A²⁺(40) or A²⁺(25–35). Additional analyses indicated that BBs may be exerting their protective effects in the hippocampal cells by altering levels of phosphorylated MAPK, PKCγ, and phosphorylated CREB. Therefore it appears that at least part of the protective effect of BBs may involve alterations in stress signaling.