Polyglucosan neurotoxicity caused by glycogen branching enzyme deficiency can be reversed by inhibition of glycogen synthase

Uncontrolled elongation of glycogen chains, not adequately balanced by their branching, leads to the formation of an insoluble, presumably neurotoxic, form of glycogen called polyglucosan. To test the suspected pathogenicity of polyglucosans in neurological glycogenoses, we have modeled the typical glycogenosis Adult Polyglucosan Body Disease (APBD) by suppressing glycogen branching enzyme 1 (GBE1, EC 2.4.1.18) expression using lentiviruses harboring short hairpin RNA (shRNA). GBE1 suppression in embryonic cortical neurons led to polyglucosan accumulation and associated apoptosis, which were reversible by rapamycin or starvation treatments. Further analysis revealed that rapamycin and starvation led to phosphorylation and inactivation of glycogen synthase (GS, EC 2.4.1.11), dephosphorylated and activated in the GBE1‐suppressed neurons. These protective effects of rapamycin and starvation were reversed by overexpression of phosphorylation site mutant GS only if its glycogen binding site was intact. While rapamycin and starvation induce autophagy, autophagic maturation was not required for their corrective effects, which prevailed even if autophagic flux was inhibited by vinblastine. Furthermore, polyglucosans were not observed in any compartment along the autophagic pathway. Our data suggest that glycogen branching enzyme repression in glycogenoses can cause pathogenic polyglucosan buildup, which might be corrected by GS inhibition.

     

Formaldehyde induces hyperphosphorylation and polymerization of Tau protein both in vitro and in vivo

Background

Chronic formaldehyde exposure leads to memory impairment and abnormal elevation of endogenous formaldehyde has been found in the brains of Alzheimer's disease (AD) patients. Hyperphosphorylated Tau protein with subsequent aggregates as neurofibrillary tangles (NFTs) is one of the typical pathological characteristics in AD brains. The mechanism underlying abnormally elevated concentrations of endogenous formaldehyde that induce Tau hyperphosphorylation is unknown.

Methods

N2a cells and mice were treated with formaldehyde for different time points, then Western blotting and immunocytochemistry were utilized to determine the phosphorylation and polymerization of Tau protein. HPLC was used to detect the concentration of formaldehyde in cell media.

Results

Under formaldehyde stress, Tau became hyperphosphorylated, not only in the cytoplasm, but also in the nucleus of neuroblastoma (N2a) cells, and mouse brains. Polymers of cellular phospho-Tau were also detected. Significant accumulation of glycogen synthase kinase-3β (GSK-3β) in the nucleus of N2a and mouse brain cells, and elevation of its phosphorylation at Y216, was observed under formaldehyde stress. Formaldehyde-induced Tau hyperphosphorylation was blocked in the presence of LiCl and CT99021, inhibitors of GSK-3β, and by RNAi interference.

Conclusions

Formaldehyde, which may cause age-related memory loss, can act as a factor triggering Tau hyperphosphorylation via GSK-3β catalysis and induces polymerization of Tau.

General significance

Investigation of formaldehyde-induced Tau hyperphosphorylation may provide novel insights into mechanisms underlying tauopathies.     

PEP-1-PEA-15 protects against toxin-induced neuronal damage in a mouse model of Parkinson's disease

Background

PEA-15 is abundantly expressed in both neurons and astrocytes throughout the brain. It is a multifunctional protein with the ability to increase cell survival via anti-apoptotic and anti-proliferative properties. However, the function of PEA-15 in neuronal diseases such as Parkinson's disease (PD) remains unclear. In this study, we investigated the protective effects of PEA-15 on neuronal damage induced by MPP⁺ in neuroblastoma SH-SY5Y and BV2 microglia cells and in a MPTP-induced PD mouse model using cell-permeable PEP-1-PEA-15.

Methods

PEP-1-PEA-15 was purified using affinity chromatography. Cell viability and DNA fragmentation were examined by MTT assay and TUNEL staining. Dopaminergic neuronal cell death in the animal model was examined by immunohistochemistry.

Results

PEP-1-PEA-15 transduced into the SH-SY5Y and BV2 cells in a time- and dose-dependent manner. Transduced PEP-1-PEA-15 protected against MPP⁺-induced toxicity by inhibiting intracellular ROS levels and DNA fragmentation. Further, it enhanced the expression levels of Bcl-2 and caspase-3 while reducing the expression levels of Bax and cleaved caspase-3. We found that PEP-1-PEA-15 transduced into the substantia nigra and prevented dopaminergic neuronal cell death in a MPTP-induced PD mouse. Also, we showed the neuroprotective effects in the model by demonstrating that treatment with PEP-1-PEA-15 ameliorated MPTP-induced behavioral dysfunctions and increased dopamine levels in the striatum.

Conclusions

PEP-1-PEA-15 can efficiently transduce into cells and protects against neurotoxin-induced neuronal cell death in vitro and in vivo.

General significance

These results demonstrate the potential for PEP-1-PEA-15 to provide a new strategy for protein therapy treatment of a variety of neurodegenerative diseases including PD.     

3β-taraxerol of Mangifera indica, a PI3K dependent dual activator of glucose transport and glycogen synthesis in 3T3-L1 adipocytes

Background

The present study focuses on identifying and developing an anti-diabetic molecule from plant sources that would effectively combat insulin resistance through proper channeling of glucose metabolism involving glucose transport and storage.

Methods

Insulin-stimulated glucose uptake formed the basis for isolation of a bioactive molecule through column chromatography followed by its characterization using NMR and mass spectroscopic analysis. Mechanism of glucose transport and storage was evaluated based on the expression profiling of signaling molecules involved in the process.

Results

The study reports (i) the isolation of a bioactive compound 3β-taraxerol from the ethyl acetate extract (EAE) of the leaves of Mangifera indica (ii) the bioactive compound exhibited insulin-stimulated glucose uptake through translocation and activation of the glucose transporter (GLUT4) in an IRTK and PI3K dependent fashion. (iii) the fate of glucose following insulin-stimulated glucose uptake was ascertained through glycogen synthesis assay that involved the activation of PKB and suppression of GSK3β.

General significance

This study demonstrates the dual activity of 3β-taraxerol and the ethyl acetate extract of Mangifera indica as a glucose transport activator and stimulator of glycogen synthesis. 3β-taraxerol can be validated as a potent candidate for managing the hyperglycemic state.     

Age-dependent guanine oxidation in DNA of different brain regions of Wistar rats and prematurely aging OXYS rats

Background

Oxidative damage to the cell, including the formation of 8-oxoG, has been regarded as a significant factor in carcinogenesis and aging. An inbred prematurely aging rat strain (OXYS) is characterized by high sensitivity to oxidative stress, lipid peroxidation, protein oxidation, DNA rearrangements, and pathological conditions paralleling several human degenerative diseases including learning and memory deterioration.

Methods

We have used monoclonal antibodies against a common pre-mutagenic base lesion 8-oxoguanine (8-oxoG) and 8-oxoguanine DNA glycosylase (OGG1) in combination with indirect immunofluorescence microscopy and image analysis to follow the relative amounts and distribution of 8-oxoG and OGG1 in various cells of different brain regions from OXYS and control Wistar rats.

Results

It was shown that 8-oxoG increased with age in mature neurons, nestin- and glial fibrillary acidic protein (GFAP)-positive cells of hippocampus and frontal cortex in both strains of rats, with OXYS rats always displaying statistically significantly higher levels of oxidative DNA damage than Wistar rats. The relative content of 8-oxoG and OGG1 in nestin- and GFAP-positive cells was higher than in mature neurons in both Wistar and OXYS rats. However, there was no significant interstrain difference in the content of OGG1 for all types of cells and brain regions analyzed, and no difference in the relative content of 8-oxoG between different brain regions.

Conclusions

Oxidation of guanine may play an important role in the development of age-associated decrease in memory and learning capability of OXYS rats.

General significance

The findings are important for validation of the OXYS rat strain as a model of mammalian aging.     

Biochemical characterization of tau protein and its associated syndapin 1 and protein kinase Cɛ for their functional regulation in rat brain

Background

We recently reported that both sulfatide and cholesterol-3-sulfate (SCS) function as potent stimulators for the GSK-3β-mediated phosphorylation of tau protein (TP) in vitro [J. Biochem. 143 (2008) 359–367].

Methods

By means of successive gel filtration on a Superdex 200 pg column and three distinct ion-exchange column chromatographies, TP and its associated proteins were highly purified from the extract of rat brain.

Results

We found that (i) syndapin 1 and novel protein kinase C? (nPKC?) were identified as the TP-associated proteins; (ii) SCS highly stimulated the phosphorylation of TP and syndapin 1 by nPKC? as well as CK1; (iii) the full phosphorylation of TP and syndapin 1 by nPKC? in the presence of sulfatide resulted in their dissociation; (iv) TP primed by CK1 functioned as an effective phosphate acceptor for GSK-3β; (v) syndapin 1 highly stimulated the GSK-3β-mediated phosphorylation of TP; and (vi) TP isoforms were highly expressed in aged brain, whereas syndapin 1 was consistently detected in adult brain, but not in newborn brain.

General significance

These results provided here suggest that (i) TP-associated nPKC? suppresses the GSK-3β-mediated phosphorylation of TP through the phosphorylation of GSK-3β by the kinase in vitro; and (ii) SCS act as effective sole mediators to induce the GSK-3β-mediated high phosphorylation of both TP and its associated syndapin 1 involved in the biochemical processes of neuronal diseases, including Alzheimer's disease.     

P-glycoprotein (Mdr1a/1b) and breast cancer resistance protein (Bcrp) decrease the uptake of hydrophobic alkyl triphenylphosphonium cations by the brain

Background

Mitochondrial dysfunction contributes to degenerative neurological disorders, consequently there is a need for mitochondria-targeted therapies that are effective within the brain. One approach to deliver pharmacophores is by conjugation to the lipophilic triphenylphosphonium (TPP) cation that accumulates in mitochondria driven by the membrane potential. While this approach has delivered TPP-conjugated compounds to the brain, the amounts taken up are lower than by other organs.

Methods

To discover why uptake of hydrophobic TPP compounds by the brain is relatively poor, we assessed the role of the P-glycoprotein (Mdr1a/b) and breast cancer resistance protein (Bcrp) ATP binding cassette (ABC) transporters, which drive the efflux of lipophilic compounds from the brain thereby restricting the uptake of lipophilic drugs. We used a triple transgenic mouse model lacking two isoforms of P-glycoprotein (Mdr1a/1b) and the Bcrp.

Results

There was a significant increase in the uptake into the brain of two hydrophobic TPP compounds, MitoQ and MitoF, in the triple transgenics following intra venous (IV) administration compared to control mice. Greater amounts of the hydrophobic TPP compounds were also retained in the liver of transgenic mice compared to controls. The uptake into the heart, white fat, muscle and kidneys was comparable between the transgenic mice and controls.

Conclusion

Efflux of hydrophobic TPP compounds by ABC transporters contributes to their lowered uptake into the brain and liver.

General significance

These findings suggest that strategies to bypass ABC transporters in the BBB will enhance delivery of mitochondria-targeted antioxidants, probes and pharmacophores to the brain.     

Could a dysfunction of ferritin be a determinant factor in the aetiology of some neurodegenerative diseases?

Background

The concentration of iron in the brain increases with aging. Furthermore, it has also been observed that patients suffering from neurological diseases (e.g. Parkinson, Alzheimer…) accumulate iron in the brain regions affected by the disease. Nevertheless, it is still not clear whether this accumulation is the initial cause or a secondary consequence of the disease. Free iron excess may be an oxidative stress source causing cell damage if it is not correctly stored in ferritin cores as a ferric iron oxide redox-inert form.

Scope

Both, the composition of ferritin cores and their location at subcellular level have been studied using analytical transmission electron microscopy in brain tissues from progressive supranuclear palsy (PSP) and Alzheimer disease (AD) patients.

Major conclusions

Ferritin has been mainly found in oligodendrocytes and in dystrophic myelinated axons from the neuropili in AD. In relation to the biomineralization of iron inside the ferritin shell, several different crystalline structures have been observed in the study of physiological and pathological ferritin. Two cubic mixed ferric–ferrous iron oxides are the major components of pathological ferritins whereas ferrihydrite, a hexagonal ferric iron oxide, is the major component of physiological ferritin. We hypothesize a dysfunction of ferritin in its ferroxidase activity.

General significance

The different mineralization of iron inside ferritin may be related to oxidative stress in olygodendrocites, which could affect myelination processes with the consequent perturbation of information transference.     

Characterization of the in vitro binding and inhibition kinetics of primary amine oxidase/vascular adhesion protein-1 by glucosamine

Background

Primary-amine oxidase (PrAO) catalyzes the oxidative deamination of endogenous and exogenous primary amines and also functions, in some tissues, as an inflammation-inducible endothelial factor, known as vascular adhesion protein-1. VAP-1 mediates the slow rolling and adhesion of lymphocytes to endothelial cells in a number of inflammatory conditions, including inflammation of the synovium.

Methods

Glucosamine binding to the enzyme was assessed spectrofluorometrically and the kinetics of inhibition of PrAO were determined spectrophotometrically through the use of direct or coupled assays, in the presence of different substrates.

Results

Glucosamine is not a substrate for PrAO, but acts as a time-dependent inhibitor of PrAO activity, displaying mixed inhibition kinetics. The observed inhibition and binding were augmented in the presence of H₂O₂.

Conclusions

Significant in vitro effects on PrAO require glucosamine in the millimolar concentration range and it is not clear at this stage whether a low but persistent level of PrAO inhibition might contribute to the anti-arthritic response.

General significance

This work was aimed at characterizing the interactions of PrAO/VAP-1 with glucosamine, a widely used “over-the-counter” supplement for the treatment of osteoarthritis.     

Peroxiredoxins as biomarkers of oxidative stress

Background

Peroxiredoxins (Prxs) are a class of abundant thiol peroxidases that degrade hydroperoxides to water. Prxs are sensitive to oxidation, and it is hypothesized that they also act as redox sensors. The accumulation of oxidized Prxs may indicate disruption of cellular redox homeostasis.

Scope of review

This review discusses the biochemical properties of the Prxs that make them suitable as endogenous biomarkers of oxidative stress, and describes the methodology available for measuring Prx oxidation in biological systems.

Major conclusions

Two Prx oxidation products accumulate in cells under increased oxidative stress: an intermolecular disulfide and a hyperoxidized form. Methodologies are available for measuring both of these redox states, and oxidation has been reported in cells and tissues under oxidative stress from external or internal sources.

General significance

Monitoring the oxidation state of Prxs provides insight into disturbances of cellular redox homeostasis, and complements the use of exogenous probes of oxidative stress. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.     

Aquaporin and brain diseases

Background

The presence of water channel proteins, aquaporins (AQPs), in the brain led to intense research in understanding the underlying roles of each of them under normal conditions and pathological conditions.

Scope of review

In this review, we summarize some of the recent knowledge on the 3 main AQPs (AQP1, AQP4 and AQP9), with a special focus on AQP4, the most abundant AQP in the central nervous system.

Major conclusions

AQP4 was most studied in several brain pathological conditions ranging from acute brain injuries (stroke, traumatic brain injury) to the chronic brain disease with autoimmune neurodegenerative diseases. To date, no specific therapeutic agents have been developed to either inhibit or enhance water flux through these channels. However, experimental results strongly underline the importance of this topic for future investigation. Early inhibition of water channels may have positive effects in prevention of edema formation in brain injuries but at later time points during the course of a disease, AQP is critical for clearance of water from the brain into blood vessels.

General significance

Thus, AQPs, and in particular AQP4, have important roles both in the formation and resolution of edema after brain injury. The dual, complex function of these water channel proteins makes them an excellent therapeutic target. This article is part of a Special Issue entitled Aquaporins.     

Inhibition of formation of α-synuclein inclusions by mannosylglycerate in a yeast model of Parkinson's disease

Background

Protein aggregation in the brain is a central hallmark in many neurodegenerative diseases. In Parkinson's disease, α-synuclein (α-Syn) is the major component of the intraneuronal inclusions found in the brains of patients. Current therapeutics is merely symptomatic, and there is a pressing need for developing novel therapies. Previously we showed that mannosylglycerate (MG), a compatible solute typical of marine microorganisms thriving in hot environments, is highly effective in protecting a variety of model proteins against thermal denaturation and aggregation in vitro.

Methods

Saccharomyces cerevisiae cells expressing eGFP-tagged α-Syn, were further engineered to synthesize MG. The number of cells with fluorescent foci was assessed by fluorescence microscopy. Fluorescence spectroscopy and transmission electron microscopy were used to monitor fibril formation in vitro.

Results

We observed a 3.3-fold reduction in the number of cells with α-Syn foci and mild attenuation of α-Syn-induced toxicity. Accordingly, sucrose gradient analysis confirmed a clear reduction in the size-range of α-Syn species in the cells. MG did not affect the expression levels of α-Syn or its degradation rate. Moreover, MG did not induce molecular chaperones (Hsp104, Hsp70 and Hsp40), suggesting the implication of other mechanisms for α-Syn stabilization. MG also inhibited α-Syn fibrillation in vitro.

Conclusions

MG acts as a chemical chaperone and the stabilization mechanism involves direct solute/protein interactions.

General significance

This is the first demonstration of the anti-aggregating ability of MG in the intracellular milieu. The work shows that MG is a good candidate to inspire the development of new drugs for protein-misfolding diseases.     

Decline in mitochondrial bioenergetics and shift to ketogenic profile in brain during reproductive senescence

Background

We have previously demonstrated that mitochondrial bioenergetic deficits precede Alzheimer's pathology in the female triple transgenic Alzheimer's (3xTgAD) mouse model. Herein, we sought to determine the impact of reproductive senescence on mitochondrial function in the normal non-transgenic (nonTg) and 3xTgAD female mouse model of AD.

Methods

Both nonTg and 3xTgAD female mice at 3, 6, 9, and 12 months of age were sacrificed and mitochondrial bioenergetic profile as well as oxidative stress markers were analyzed.

Results

In both nonTg and 3xTgAD mice, reproductive senescence paralleled a significant decline in PDH, and Complex IV cytochrome c oxidase activity and mitochondrial respiration. During the reproductive senescence transition, both nonTg and 3xTgAD mice exhibited greater individual variability in bioenergetic parameters suggestive of divergent bioenergetic phenotypes. Following transition through reproductive senescence, enzymes required for long-chain fatty acid (HADHA) and ketone body (SCOT) metabolism were significantly increased and variability in cytochrome c oxidase (Complex IV) collapsed to cluster at a ∼ 40% decline in both the nonTg and 3xTgAD brain which was indicative of alternative fuel generation with concomitant decline in ATP generation.

Conclusions

These data indicate that reproductive senescence in the normal nonTg female brain parallels the shift to ketogenic/fatty acid substrate phenotype with concomitant decline in mitochondrial function and exacerbation of bioenergetic deficits in the 3xTgAD brain.

General significance

These findings provide a plausible mechanism for increased life-time risk of AD in postmenopausal women and suggest an optimal window of opportunity to prevent or delay decline in bioenergetics during reproductive senescence.     

Molecular composition and function of integrin-based collagen glues—Introducing COLINBRIs

Background

Despite detailed knowledge about the structure and signaling properties of individual collagen receptors, much remains to be learned about how these receptors participate in linking cells to fibrillar collagen matrices in tissues. In addition to collagen-binding integrins, a group of proteins with affinity both for fibrillar collagens and integrins link these two protein families together. We have introduced the name COLINBRI (COLlagen INtegrin BRIdging) for this set of molecules. Whereas collagens are the major building blocks in tissues and defects in these structural proteins have severe consequences for tissue integrity, the mild phenotypes of the integrin type of collagen receptors have raised questions about their importance in tissue biology and pathology.

Scope of review

We will discuss the two types of cell linkages to fibrillar collagen (direct- versus indirect COLINBRI-mediated) and discuss how the parallel existence of direct and indirect linkages to collagens may ensure tissue integrity.

Major conclusions

The observed mild phenotypes of mice deficient in collagen-binding integrins and the relatively restricted availability of integrin-binding sequences in mature fibrillar collagen matrices support the existence of indirect collagen-binding mechanisms in parallel with direct collagen binding in vivo.

General significance

A continued focus on understanding the molecular details of cell adhesion mechanisms to collagens will be important and will benefit our understanding of diseases like tissue- and tumor fibrosis where collagen dynamics are disturbed. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.     

Mitochondrial dysfunction enhances the migration of vascular smooth muscles cells via suppression of Akt phosphorylation

Background

Atherosclerosis is one of the major complications of diabetes, which may result from insulin resistance via mitochondrial dysfunction. Although a strong association between insulin resistance and cardiovascular disease has been suggested, it is not clear yet whether stress-inducing factors damage mitochondria and insulin signaling pathway in cardiovascular tissues.

Methods

We investigated whether stress-induced mitochondrial dysfunction might alter the insulin/Akt signaling pathway in A10 rat vascular smooth muscle cells (VSMC).

Results

The treatment of oxidized low density lipoprotein (oxLDL) decreased ATP contents, mitochondrial respiration activity, mRNA expressions of OXPHOS subunits and IRS-1/2 and insulin-mediated phosphorylations of Akt and AMP-activated protein kinase (AMPK). Similarly, dideoxycytidine (ddC), the mtDNA replication inhibitor, or rotenone, OXPHOS complex I inhibitor, inhibited the insulin-mediated pAkt while increased pAMPK regardless of insulin. Reciprocally, an inhibitor of Akt, triciribine (TCN), decreased cellular ATP contents. Overexpression of Akt dominant positive reversed the oxLDL- or ddC-mediated ATP decrease but AMPK activator did not. Akt activation also normalized the aberrant VSMC migration induced by ddC.

Conclusions

Defective insulin signaling and mitochondrial function may collectively contribute to developing cardiovascular disease.

General significance

Akt may be a possible therapeutic target for treating insulin resistance-associated atherosclerosis.     

PEP-1–metallothionein-III protein ameliorates the oxidative stress-induced neuronal cell death and brain ischemic insults

Background

Oxidative stress is considered to be involved in a number of human diseases including ischemia. Metallothioneins (MT)-III can protect neuronal cells from the cytotoxicity of reactive oxygen species (ROS). However, MT-III proteins biological function is unclear in ischemia. Thus, we examined the protective effects of MT-III proteins on oxidative stress-induced neuronal cell death and brain ischemic insult.

Methods

A human MT-III gene was fused with a protein transduction domain, PEP-1 peptide, to construct a cell permeable PEP-1–MT-III protein. PEP-1–MT-III protein was purified using affinity chromatograph. Transduced PEP-1–MT-III proteins were detected by Western blotting and immunoflourescence. Cell viability and DNA fragmentation were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-dipheyltetrazolium bromide (MTT) assay and terminal dexoynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining, respectively. Brain ischemic injury was detected with immunohistochemistry.

Results

Purified PEP-1–MT-III proteins transduced into astrocytes in a time- and dose-dependent manner and protected against oxidative stress-induced cell death. Also, transduced PEP-1–MT-III proteins efficiently protected cells against DNA fragmentation. Furthermore, immunohistochemical analysis revealed that PEP-1–MT-III prevented neuronal cell death in the CA1 region of the hippocampus induced by transient forebrain ischemia. We demonstrated that transduced PEP-1–MT-III protein protects against oxidative stress induced cell death in vitro and in vivo.

General significance

Transduced PEP-1–MT-III protein has neuroprotective roles as an antioxidant in vitro and in vivo. PEP-1–MT-III protein is a potential therapeutic agent for various human brain diseases such as stroke, Alzheimer's disease, and Parkinson's disease.     

Water channel structures analysed by electron crystallography

Background

The mechanisms underlying water transport through aquaporin (AQP) have been debated for two decades. The water permeation phenomenon of AQP seems inexplicable because the Grotthuss mechanism does not allow for simultaneous fast water permeability and inhibition of proton transfer through the hydrogen bonds of water molecules.

Scope of review

The AQP1 structure determined by electron crystallography provided the first insights into the proton exclusion mechanism despite fast water permeation. Although several studies have provided clues about the mechanism based on the AQP structure, each proposed mechanism remains incomplete. The present review is focused on AQP function and structure solved by electron crystallography in an attempt to fill the gaps between the findings in the absence and presence of lipids.

Major conclusions

Many AQP structures can be superimposed regardless of the determination method. The AQP fold is preserved even under conditions lacking lipids, but the water arrangement in the channel pore differs. The differences might be explained by dipole moments formed by the two short helices in the lipid bilayer. In addition, structure analyses of double-layered two-dimensional crystals of AQP suggest an array formation and cell adhesive function.

General significance

Electron crystallography findings not only have contributed to resolve some of the water permeation mechanisms, but have also elucidated the multiple functions of AQPs in the membrane. The roles of AQPs in the brain remain obscure, but their multiple activities might be important in the regulation of brain and other biological functions. This article is part of a Special Issue entitled Aquaporins.