Blueberry extract alters oxidative stress-mediated signaling in COS-7 cells transfected with selectively vulnerable muscarinic receptor subtypes

Abstract

Previous research has indicated that selective vulnerability to oxidative stress may be important in determining regional differences in functional declines in neuronal aging. Oxidative stress vulnerability may involve selective deficits in Ca²⁺ buffering (Ca²⁺ recovery time following oxotremorine application) to oxidative stress, determined in-part by receptor subtype with M1, M2 and M4 AChR showing greater oxidative stress-induced loss [via dopamine (DA) exposure for 4 hrs] of Ca²⁺ recovery time than that seen in M3 or M5 cells. Deficits were antagonized by pre-treating M1, M2, or M4 AChR-transfected cells with blueberry (BB) extract. Thus, we assessed whether these differences in oxidative stress vulnerability might involve differential patterns of DA-induced protein kinase (PKCα, PKCγ) and/or cyclic AMP response element binding protein (CREB) activation, and whether these differences might be altered by BB treatment. M1 or M3 AChR-transfected COS-7 cells were exposed to 1 mM DA, and activation of phospho-(p) mitogen-activated protein kinase (MAPK) signaling was examined by immunoblotting analyses. The results showed that DA increased pCREB and pPKCγ for both M1- and M3-transfected cells, and BBs decreased these DA-induced alterations, when measured by immunoblotting techniques. Taken together these findings suggest that M1/M3 oxidative stress sensitivity differences may involve differential signaling in pMAPK and pCREB under oxidative stress conditions, suggesting that the native protection in these receptors against oxidative stress and inflammation may be derived from reduced activation. These findings also suggest that BB may antagonize oxidative stress effects induced by DA in M1-transfected cells by lowering activation of pCREB, and possibly pPKCγ.