Alzheimer disease is an age-related neurodegenerative disorder characterized by amyloid-β (Aβ) peptide deposition into cerebral amyloid plaques. The natural polyphenol resveratrol promotes anti-aging pathways via the activation of several metabolic sensors, including the AMP-activated protein kinase (AMPK). Resveratrol also lowers Aβ levels in cell lines; however, the underlying mechanism responsible for this effect is largely unknown. Moreover, the bioavailability of resveratrol in the brain remains uncertain. Here we show that AMPK signaling controls Aβ metabolism and mediates the anti-amyloidogenic effect of resveratrol in non-neuronal and neuronal cells, including in mouse primary neurons. Resveratrol increased cytosolic calcium levels and promoted AMPK activation by the calcium/calmodulin-dependent protein kinase kinase-β. Direct pharmacological and genetic activation of AMPK lowered extracellular Aβ accumulation, whereas AMPK inhibition reduced the effect of resveratrol on Aβ levels. Furthermore, resveratrol inhibited the AMPK target mTOR (mammalian target of rapamycin) to trigger autophagy and lysosomal degradation of Aβ. Finally, orally administered resveratrol in mice was detected in the brain where it activated AMPK and reduced cerebral Aβ levels and deposition in the cortex. These data suggest that resveratrol and pharmacological activation of AMPK have therapeutic potential against Alzheimer disease.

The voltage-gated ion channel CALHM1 is vital to taste-stimuli-evoked ATP release from sweet-, bitter- and umami-sensing taste bud cells in mice, but does not seem relevant to the recognition of sour and salty tastes. Perception of sweet, bitter and umami tastes relies on the non-vesicular release from taste bud cells of ATP, which acts as a neurotransmitter to activate the nerves sending gustatory signals to the brain. Now teams led by Kevin Foskett and Philippe Marambaud have used gene-knockout mice to show that the voltage-gated ion channel CALHM1 (calcium homeostasis modulator 1) acts as a voltage-gated ATP-release channel required for sweet, bitter and umami taste perception. CALHM1 deficiency affected taste perception without interfering with taste cell development or integrity, implying that it is a key functional component of the peripheral taste system. Recognition of sweet, bitter and umami tastes requires the non-vesicular release from taste bud cells of ATP, which acts as a neurotransmitter to activate afferent neural gustatory pathways1. However, how ATP is released to fulfil this function is not fully understood. Here we show that calcium homeostasis modulator 1 (CALHM1), a voltage-gated ion channel2,3, is indispensable for taste-stimuli-evoked ATP release from sweet-, bitter- and umami-sensing taste bud cells. Calhm1 knockout mice have severely impaired perceptions of sweet, bitter and umami compounds, whereas their recognition of sour and salty tastes remains mostly normal. Calhm1 deficiency affects taste perception without interfering with taste cell development or integrity. CALHM1 is expressed specifically in sweet/bitter/umami-sensing type II taste bud cells. Its heterologous expression induces a novel ATP permeability that releases ATP from cells in response to manipulations that activate the CALHM1 ion channel. Knockout of Calhm1 strongly reduces voltage-gated currents in type II cells and taste-evoked ATP release from taste buds without affecting the excitability of taste cells by taste stimuli. Thus, CALHM1 is a voltage-gated ATP-release channel required for sweet, bitter and umami taste perception.

J. Neurochem. (2012) 120, 461–472. Activation of microglia, the resident macrophages of the brain, around the amyloid plaques is a key hallmark of Alzheimer’s disease (AD). Recent evidence in mouse models indicates that microglia are required for the neurodegenerative process of AD. Amyloid‐β (Aβ) peptides, the core components of the amyloid plaques, can trigger microglial activation by interacting with several Toll‐like receptors (TLRs), including TLR4. In this study, we show that resveratrol, a natural polyphenol associated with anti‐inflammatory effects and currently in clinical trials for AD, prevented the activation of murine RAW 264.7 macrophages and microglial BV‐2 cells treated with the TLR4 ligand, lipopolysaccharide (LPS). Resveratrol preferentially inhibited nuclear factor κ‐light‐chain‐enhancer of activated B cells (NF‐κB) activation upon LPS stimulation by interfering with IKK and IκB phosphorylation, an effect that potently reduced the transcriptional stimulation of several NF‐κB target genes, including tumor necrosis factor‐α and interleukin‐6. Consequently, downstream phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3 upon LPS stimulation was also inhibited by resveratrol. We found that resveratrol acted upstream in the activation cascade by interfering with TLR4 oligomerization upon receptor stimulation. Resveratrol treatment also prevented the pro‐inflammatory effect of fibrillar Aβ on macrophages by potently inhibiting the effect of Aβ on IκB phosphorylation, activation of STAT1 and STAT3, and on tumor necrosis factor‐α and interleukin‐6 secretion. Importantly, orally administered resveratrol in a mouse model of cerebral amyloid deposition lowered microglial activation associated with cortical amyloid plaque formation. Together this work provides strong evidence that resveratrol has in vitro and in vivo anti‐inflammatory effects against Aβ‐triggered microglial activation. Further studies in cell culture systems showed that resveratrol acted via a mechanism involving the TLR4/NF‐κB/STAT signaling cascade.

Calcium is a key signaling ion involved in many different intracellular and extracellular processes ranging from synaptic activity to cell-cell communication and adhesion. The exact definition at the molecular level of the versatility of this ion has made overwhelming progress in the past several years and has been extensively reviewed. In the brain, calcium is fundamental in the control of synaptic activity and memory formation, a process that leads to the activation of specific calcium-dependent signal transduction pathways and implicates key protein effectors, such as CaMKs, MAPK/ERKs, and CREB. Properly controlled homeostasis of calcium signaling not only supports normal brain physiology but also maintains neuronal integrity and long-term cell survival. Emerging knowledge indicates that calcium homeostasis is not only critical for cell physiology and health, but also, when deregulated, can lead to neurodegeneration via complex and diverse mechanisms involved in selective neuronal impairments and death. The identification of several modulators of calcium homeostasis, such as presenilins and CALHM1, as potential factors involved in the pathogenesis of Alzheimer's disease, provides strong support for a role of calcium in neurodegeneration. These observations represent an important step towards understanding the molecular mechanisms of calcium signaling disturbances observed in different brain diseases such as Alzheimer's, Parkinson's, and Huntington's diseases.