Glycogen synthase kinase-3␤ (GSK-3␤) is a critical activator of neuronal apoptosis induced by a diverse array of neurotoxic insults.However, the downstream substrates of GSK-3␤ that ultimately induce neuronal death are unknown. Here, we show that GSK-3␤ phosphorylates and regulates the activity of Bax, a pro-apoptotic Bcl-2 family member that stimulates the intrinsic (mitochondrial) death pathway by eliciting cytochrome c release from mitochondria. In cerebellar granule neurons undergoing apoptosis, inhibition of GSK-3␤ suppressed both the mitochondrial translocation of an expressed green fluorescent protein (GFP)-Bax ␣ fusion protein and the conformational activation of endogenous Bax. GSK-3␤ directly phosphorylated Bax ␣ on Ser163, a residue found within a species-conserved, putative GSK-3␤ phosphorylation motif. Coexpression of GFP-Bax ␣ with a constitutively active mutant of GSK-3␤, GSK-3␤(Ser9Ala), enhanced the in vivo phosphorylation of wild-type Bax ␣ , but not a Ser163Ala mutant of Bax ␣ , in transfected human embryonic kidney 293 (HEK293) cells. Moreover, cotransfection with constitutively active GSK-3␤ promoted the localization of Bax ␣ to mitochondria and induced apoptosis in both transfected HEK293 cells and cerebellar granule neurons. In contrast, neither a Ser163Ala point mutant of Bax ␣ nor a naturally occurring splice variant that lacks 13 amino acids encompassing Ser163 (Bax ) were driven to mitochondria in HEK293 cells coexpressing constitutively active GSK-3␤. In a similar manner, either mutation or deletion of the identified GSK-3␤ phosphorylation motif prevented the localization of Bax to mitochondria in cerebellar granule neurons undergoing apoptosis. Our results indicate that GSK-3␤ exerts some of its pro-apoptotic effects in neurons by regulating the mitochondrial localization of Bax, a key component of the intrinsic apoptotic cascade.

A variety of antioxidant compounds derived from natural products (nutraceuticals) have demonstrated neuroprotective activity in either in vitro or in vivo models of neuronal cell death or neurodegeneration, respectively. These natural antioxidants fall into several distinct groups based on their chemical structures: (1) flavonoid polyphenols like epigallocatechin 3-gallate (EGCG) from green tea and quercetin from apples; (2) non-flavonoid polyphenols such as curcumin from tumeric and resveratrol from grapes; (3) phenolic acids or phenolic diterpenes such as rosmarinic acid or carnosic acid, respectively, both from rosemary; and (4) organosulfur compounds including the isothiocyanate, L-sulforaphane, from broccoli and the thiosulfonate allicin, from garlic. All of these compounds are generally considered to be antioxidants. They may be classified this way either because they directly scavenge free radicals or they indirectly increase endogenous cellular antioxidant defenses, for example, via activation of the nuclear factor erythroid-derived 2-related factor 2 (Nrf2) transcription factor pathway. Alternative mechanisms of action have also been suggested for the neuroprotective effects of these compounds such as modulation of signal transduction cascades or effects on gene expression. Here, we review the literature pertaining to these various classes of nutraceutical antioxidants and discuss their potential therapeutic value in neurodegenerative diseases.

The Rho family of GTPases belongs to the Ras superfamily of low molecular weight (∼21 kDa) guanine nucleotide binding proteins. The most extensively studied members are RhoA, Rac1, and Cdc42. In the last few decades, studies have demonstrated that Rho family GTPases are important regulatory molecules that link surface receptors to the organization of the actin and microtubule cytoskeletons. Indeed, Rho GTPases mediate many diverse critical cellular processes, such as gene transcription, cell–cell adhesion, and cell cycle progression. However, Rho GTPases also play an essential role in regulating neuronal morphology. In particular, Rho GTPases regulate dendritic arborization, spine morphogenesis, growth cone development, and axon guidance. In addition, more recent efforts have underscored an important function for Rho GTPases in regulating neuronal survival and death. Interestingly, Rho GTPases can exert either a pro-survival or pro-death signal in neurons depending upon both the cell type and neurotoxic insult involved. This review summarizes key findings delineating the involvement of Rho GTPases and their effectors in the regulation of neuronal survival and death. Collectively, these results suggest that dysregulation of Rho family GTPases may potentially underscore the etiology of some forms of neurodegenerative disease such as amyotrophic lateral sclerosis.