GABAB receptors, the most abundant inhibitory G protein-coupled receptors in the mammalian brain, display pronounced diversity in functional properties, cellular signaling and subcellular distribution. We used high-resolution functional proteomics to identify the building blocks of these receptors in the rodent brain. Our analyses revealed that native GABAB receptors are macromolecular complexes with defined architecture, but marked diversity in subunit composition: the receptor core is assembled from GABAB1a/b, GABAB2, four KCTD proteins and a distinct set of G-protein subunits, whereas the receptor's periphery is mostly formed by transmembrane proteins of different classes. In particular, the periphery-forming constituents include signaling effectors, such as Cav2 and HCN channels, and the proteins AJAP1 and amyloid-β A4, both of which tightly associate with the sushi domains of GABAB1a. Our results unravel the molecular diversity of GABAB receptors and their postnatal assembly dynamics and provide a roadmap for studying the cellular signaling of this inhibitory neurotransmitter receptor.

Alzheimer disease is a neurodegenerative process that leads to severe cognitive impairment as a consequence of selective death of neuronal populations. The molecular pathogenesis of Alzheimer disease involves the participation of the ␤-amyloid peptide (A␤) and oxidative stress. We report here that peroxisomal proliferation attenuated A␤-dependent toxicity in hippocampal neurons. Pretreatment with Wy-14.463 (Wy), a peroxisome proliferator, prevent the neuronal cell death and neuritic network loss induced by the A␤ peptide. Moreover, the hippocampal neurons treated with this compound, showed an increase in the number of peroxisomes, with a concomitant increase in catalase activity. Additionally, we evaluate the Wy protective effect on ␤-catenin levels, production of intracellular reactive oxygen species, cytoplasmic calcium uptake, and mitochondrial potential in hippocampal neurons exposed to H 2 O 2 and A␤ peptide. Results show that the peroxisomal proliferation prevents ␤-catenin degradation, reactive oxygen species production, cytoplasmic calcium increase, and changes in mitochondrial viability. Our data suggest, for the first time, a direct link between peroxisomal proliferation and neuroprotection from A␤-induced degenerative changes.Peroxisomes are subcellular organelles found in most animal cells that perform diverse metabolic functions, including detoxification of reactive oxygen species (ROS) 2 through their matrix enzyme catalase (1-3) and regulation of the oxidative balance and fatty acid oxidation (4 -6). Peroxisomes are present in the cell bodies, dendrites, and presynaptic axon terminals of neuronal cells (7,8) as well as in growing neurites (9). Tau overexpression inhibits kinesin-dependent transport of peroxisomes, neurofilaments, and Golgi-derived vesicles into neurites (10), and it has been suggested that a loss of peroxisomes apparently makes neurons more vulnerable to oxidative stress (10). Peroxisome proliferators (PPs) are a class of structurally dissimilar industrial and pharmaceutical chemicals that were originally identified as inducers of peroxisome proliferation in rat and mouse hepatocytes (11,12). Several PPs have shown to bind to peroxisome proliferator-activated receptors (PPARs), these include Wy-14.643 (Wy), which binds with great affinity to PPAR␣ and induces a strong activation of this receptor (11). 4-Phenyl butyric (4-PB) is a PP that, in contrast to other PPs, is able to induce human peroxisome proliferation (13); however, the mechanism of peroxisome proliferation remains to be elucidated. According to Liu et al. (14), 4-PB activates PPARs in astrocytes; nevertheless, they suggested that peroxisome proliferation may be independent of PPAR␣ activation.Alzheimer disease (AD) is characterized by a progressive neurodegeneration associated with extracellular deposits of amyloid ␤-peptide (A␤) in the form of senile plaques (15,16). A␤ peptide acquires neurotoxic properties when it forms homo-oligomeric species (17) or heterooligomeric species with molecules associated with mature ...

GABAB receptors (GBRs) are key regulators of synaptic release but little is known about trafficking mechanisms that control their presynaptic abundance. We now show that sequence-related epitopes in APP, AJAP-1 and PIANP bind with nanomolar affinities to the N-terminal sushi-domain of presynaptic GBRs. Of the three interacting proteins, selectively the genetic loss of APP impaired GBR-mediated presynaptic inhibition and axonal GBR expression. Proteomic and functional analyses revealed that APP associates with JIP and calsyntenin proteins that link the APP/GBR complex in cargo vesicles to the axonal trafficking motor. Complex formation with GBRs stabilizes APP at the cell surface and reduces proteolysis of APP to Aβ, a component of senile plaques in Alzheimer’s disease patients. Thus, APP/GBR complex formation links presynaptic GBR trafficking to Aβ formation. Our findings support that dysfunctional axonal trafficking and reduced GBR expression in Alzheimer’s disease increases Aβ formation.

Acetylcholinesterase is an enzyme associated with senile plaques. Biochemical studies have indicated that acetylcholinesterase induces amyloid fibril formation by interaction throughout the peripherical anionic site of the enzyme forming highly toxic acetylcholinesterase–amyloid‐β peptide (Aβ) complexes. The pro‐aggregating acetylcholinesterase effect is associated with the intrinsic amyloidogenic properties of the corresponding Aβ peptide. The neurotoxicity induced by acetylcholinesterase–Aβ complexes is higher than the that induced by the Aβ peptide alone, both in vitro and in vivo. The fact that acetylcholinesterase accelerates amyloid formation and the effect is sensitive to peripherical anionic site blockers of the enzyme, suggests that specific and new acetylcholinesterase inhibitors may well provide an attractive possibility for treating Alzheimer’s disease. Recent studies also indicate that acetylcholinesterase induces the aggregation of prion protein with a similar dependence on the peripherical anionic site.

The major protein constituent of amyloid deposits in Alzheimer's disease (AD) is the amyloid b-peptide (Ab). In the present work, we have determined the effect of hyperforin an acylphloroglucinol compound isolated from Hypericum perforatum (St John's Wort), on Ab-induced spatial memory impairments and on Ab neurotoxicity. We report here that hyperforin: (1) decreases amyloid deposit formation in rats injected with amyloid fibrils in the hippocampus; (2) decreases the neuropathological changes and behavioral impairments in a rat model of amyloidosis; (3) prevents Ab-induced neurotoxicity in hippocampal neurons both from amyloid fibrils and Ab oligomers, avoiding the increase in reactive oxidative species associated with amyloid toxicity. Both effects could be explained by the capacity of hyperforin to disaggregate amyloid deposits in a dose and time-dependent manner and to decrease Ab aggregation and amyloid formation. Altogether these evidences suggest that hyperforin may be useful to decrease amyloid burden and toxicity in AD patients, and may be a putative therapeutic agent to fight the disease.