β2 adrenergic receptor, protein kinase A (PKA) and c-Jun N-terminal kinase (JNK) signaling pathways mediate tau pathology in Alzheimer disease models

Amyloid β production is regulated by β2-adrenergic signaling-mediated post-translational modifications of the ryanodine receptor

Alteration of ryanodine receptor (RyR)-mediated calcium (Ca²⁺) signaling has been reported in Alzheimer disease (AD) models. However, the molecular mechanisms underlying altered RyR-mediated intracellular Ca²⁺ release in AD remain to be fully elucidated. We report here that RyR2 undergoes post-translational modifications (phosphorylation, oxidation, and nitrosylation) in SH-SY5Y neuroblastoma cells expressing the β-amyloid precursor protein (βAPP) harboring the familial double Swedish mutations (APPswe). RyR2 macromolecular complex remodeling, characterized by depletion of the regulatory protein calstabin2, resulted in increased cytosolic Ca²⁺ levels and mitochondrial oxidative stress. We also report a functional interplay between amyloid β (Aβ), β-adrenergic signaling, and altered Ca²⁺ signaling via leaky RyR2 channels. Thus, post-translational modifications of RyR occur downstream of Aβ through a β2-adrenergic signaling cascade that activates PKA. RyR2 remodeling in turn enhances βAPP processing. Importantly, pharmacological stabilization of the binding of calstabin2 to RyR2 channels, which prevents Ca²⁺ leakage, or blocking the β2-adrenergic signaling cascade reduced βAPP processing and the production of Aβ in APPswe-expressing SH-SY5Y cells. We conclude that targeting RyR-mediated Ca²⁺ leakage may be a therapeutic approach to treat AD.

Peptide Antibodies in Clinical Laboratory Diagnostics

Peptide antibodies, with their high specificities and affinities, are invaluable reagents for peptide and protein recognition in biological specimens. Depending on the application and the assay, in which the peptide antibody is to used, several factors influence successful antibody production, including peptide selection and antibody screening. Peptide antibodies have been used in clinical laboratory diagnostics with great success for decades, primarily because they can be produced to multiple targets, recognizing native wildtype proteins, denatured proteins, and newly generated epitopes. Especially mutation-specific peptide antibodies have become important as diagnostic tools in the detection of various cancers. In addition to their use as diagnostic tools in malignant and premalignant conditions, peptide antibodies are applied in all other areas of clinical laboratory diagnostics, including endocrinology, hematology, neurodegenerative diseases, cardiovascular diseases, infectious diseases, and amyloidoses.

Locus Ceruleus Norepinephrine Release: A Central Regulator of CNS Spatio-Temporal Activation?

Norepinephrine (NE) is synthesized in the Locus Coeruleus (LC) of the brainstem, from where it is released by axonal varicosities throughout the brain via volume transmission. A wealth of data from clinics and from animal models indicates that this catecholamine coordinates the activity of the central nervous system (CNS) and of the whole organism by modulating cell function in a vast number of brain areas in a coordinated manner. The ubiquity of NE receptors, the daunting number of cerebral areas regulated by the catecholamine, as well as the variety of cellular effects and of their timescales have contributed so far to defeat the attempts to integrate central adrenergic function into a unitary and coherent framework. Since three main families of NE receptors are represented-in order of decreasing affinity for the catecholamine-by: α2 adrenoceptors (α2Rs, high affinity), α1 adrenoceptors (α1Rs, intermediate affinity), and β adrenoceptors (βRs, low affinity), on a pharmacological basis, and on the ground of recent studies on cellular and systemic central noradrenergic effects, we propose that an increase in LC tonic activity promotes the emergence of four global states covering the whole spectrum of brain activation: (1) sleep: virtual absence of NE, (2) quiet wake: activation of α2Rs, (3) active wake/physiological stress: activation of α2- and α1-Rs, (4) distress: activation of α2-, α1-, and β-Rs. We postulate that excess intensity and/or duration of states (3) and (4) may lead to maladaptive plasticity, causing-in turn-a variety of neuropsychiatric illnesses including depression, schizophrenic psychoses, anxiety disorders, and attention deficit. The interplay between tonic and phasic LC activity identified in the LC in relationship with behavioral response is of critical importance in defining the short- and long-term biological mechanisms associated with the basic states postulated for the CNS. While the model has the potential to explain a large number of experimental and clinical findings, a major challenge will be to adapt this hypothesis to integrate the role of other neurotransmitters released during stress in a centralized fashion, like serotonin, acetylcholine, and histamine, as well as those released in a non-centralized fashion, like purines and cytokines.

β2-Adrenergic receptor ablation modulates hepatic lipid accumulation and glucose tolerance in aging mice

Catecholamines acting through β-adrenergic receptors (β(1)-, β(2)-, β(3)-AR subtypes) modulate important biological responses in various tissues. Our previous studies suggest a role for increased hepatic β-AR-mediated signaling during aging as a mediator of hepatic steatosis, liver glucose output, and insulin resistance in rodents. In the current study, we have utilized β(2)-AR knockout (KO) and wildtype (WT) control mice to define further the role of β(2)-AR signaling during aging on lipid and glucose metabolism. Our results demonstrate for the first time that age-related increases in hepatic triglyceride accumulation and body weight are attenuated upon β(2)-AR ablation. Although no differences in plasma triglyceride, non-esterified fatty acids or insulin levels were detected between old WT and KO animals, an age-associated increase in hepatic expression of lipid homeostasis regulator Cidea was significantly reduced in old KO mice. Interestingly, we also observed a shift from reduced glucose tolerance in young adult KO animals to significantly improved glucose tolerance in old KO when compared to age-matched WT mice. These results provide evidence for an important role played by β(2)-ARs in the regulation of lipid and glucose metabolism during aging. The effect of β(2)-AR ablation on caloric intake during aging is currently not known and requires investigation. Future studies are also warranted to delineate the β(2)-AR-mediated mechanisms involved in the control of lipid and glucose homeostasis, especially in the context of a growing aging population.

Noradrenergic dysfunction in Alzheimer's disease

The brain noradrenergic system supplies the neurotransmitter norepinephrine throughout the brain via widespread efferent projections, and plays a pivotal role in modulating cognitive activities in the cortex. Profound noradrenergic degeneration in Alzheimer's disease (AD) patients has been observed for decades, with recent research suggesting that the locus coeruleus (where noradrenergic neurons are mainly located) is a predominant site where AD-related pathology begins. Mounting evidence indicates that the loss of noradrenergic innervation greatly exacerbates AD pathogenesis and progression, although the precise roles of noradrenergic components in AD pathogenesis remain unclear. The aim of this review is to summarize current findings on noradrenergic dysfunction in AD, as well as to point out deficiencies in our knowledge where more research is needed.

Bardoxolone methyl prevents high-fat diet-induced alterations in prefrontal cortex signalling molecules involved in recognition memory

High fat (HF) diets are known to induce changes in synaptic plasticity in the forebrain leading to learning and memory impairments. Previous studies of oleanolic acid derivatives have found that these compounds can cross the blood-brain barrier to prevent neuronal cell death. We examined the hypothesis that the oleanolic acid derivative, bardoxolone methyl (BM) would prevent diet-induced cognitive deficits in mice fed a HF diet. C57BL/6J male mice were fed a lab chow (LC) (5% of energy as fat), a HF (40% of energy as fat), or a HF diet supplemented with 10mg/kg/day BM orally for 21weeks. Recognition memory was assessed by performing a novel object recognition test on the treated mice. Downstream brain-derived neurotrophic factor (BDNF) signalling molecules were examined in the prefrontal cortex (PFC) and hippocampus of mice via Western blotting and N-methyl-d-aspartate (NMDA) receptor binding. BM treatment prevented HF diet-induced impairment in recognition memory (p<0.001). In HF diet fed mice, BM administration attenuated alterations in the NMDA receptor binding density in the PFC (p<0.05), however, no changes were seen in the hippocampus (p>0.05). In the PFC and hippocampus of the HF diet fed mice, BM administration improved downstream BDNF signalling as indicated by increased protein levels of BDNF, phosphorylated tropomyosin related kinase B (pTrkB) and phosphorylated protein kinase B (pAkt), and increased phosphorylated AMP-activated protein kinase (pAMPK) (p<0.05). BM administration also prevented the HF diet-induced increase in the protein levels of inflammatory molecules, phosphorylated c-Jun N-terminal kinase (pJNK) in the PFC, and protein tyrosine phosphatase 1B (PTP1B) in both the PFC and hippocampus. In summary, these findings suggest that BM prevents HF diet-induced impairments in recognition memory by improving downstream BDNF signal transduction, increasing pAMPK, and reducing inflammation in the PFC and hippocampus.

Dexmedetomidine increases tau phosphorylation under normothermic conditions in vivo and in vitro

There is developing interest in the potential association between anesthesia and the onset and progression of Alzheimer's disease. Several anesthetics have, thus, been demonstrated to induce tau hyperphosphorylation, an effect mostly mediated by anesthesia-induced hypothermia. Here, we tested the hypothesis that acute normothermic administration of dexmedetomidine (Dex), an intravenous sedative used in intensive care units, would result in tau hyperphosphorylation in vivo and in vitro. When administered to nontransgenic mice, Dex-induced tau hyperphosphorylation persisting up to 6 hours in the hippocampus for the AT8 epitope. Pretreatment with atipamezole, a highly specific α2-adrenergic receptor antagonist, blocked Dex-induced tau hyperphosphorylation. Furthermore, Dex dose-dependently increased tau phosphorylation at AT8 in SH-SY5Y cells, impaired mice spatial memory in the Barnes maze and promoted tau hyperphosphorylation and aggregation in transgenic hTau mice. These findings suggest that Dex: (1) increases tau phosphorylation, in vivo and in vitro, in the absence of anesthetic-induced hypothermia and through α2-adrenergic receptor activation, (2) promotes tau aggregation in a mouse model of tauopathy, and (3) impacts spatial reference memory.

c-Jun N-terminal kinase 3 expression in the retina of ocular hypertension mice: a possible target to reduce ganglion cell apoptosis

Glaucoma, a type of optic neuropathy, is characterized by the loss of retinal ganglion cells. It remains controversial whether c-Jun N-terminal kinase (JNK) participates in the apoptosis of retinal ganglion cells in glaucoma. This study sought to explore a possible mechanism of action of JNK signaling pathway in glaucoma-induced retinal optic nerve damage. We established a mouse model of chronic ocular hypertension by reducing the aqueous humor followed by photocoagulation using the laser ignition method. Results showed significant pathological changes in the ocular tissues after the injury. Apoptosis of retinal ganglion cells increased with increased intraocular pressure, as did JNK3 mRNA expression in the retina. These data indicated that the increased expression of JNK3 mRNA was strongly associated with the increase in intraocular pressure in the retina, and correlated positively with the apoptosis of retinal ganglion cells.

Ca(2+)/calmodulin-dependent protein kinase II interacts with group I metabotropic glutamate and facilitates receptor endocytosis and ERK1/2 signaling: role of β-amyloid

BACKGROUND

Agonist stimulation of Group I metabotropic glutamate receptors (mGluRs) initiates their coupling to the heterotrimeric G protein, Gαq/11, resulting in the activation of phospholipase C, the release of Ca(2+) from intracellular stores and the subsequent activation of protein kinase C. However, it is now recognized that mGluR5a also functions as a receptor for cellular prion protein (PrP(C)) and β-amyloid peptide (Aβ42) oligomers to facilitate intracellular signaling via the resulting protein complex. Intracellular mGluR5a signaling is also regulated by its association with a wide variety of intracellular regulation proteins.

RESULTS

In the present study, we utilized mass spectroscopy to identify calmodulin kinase IIα (CaMKIIα) as a protein that interacts with the second intracellular loop domain of mGluR5. We show that CaMKIIα interacts with both mGluR1a and mGluR5a in an agonist-independent manner and is co-immunoprecipitated with mGluR5a from hippocampal mouse brain. CaMKIIα positively regulates both mGluR1a and mGluR5a endocytosis, but selectively attenuates mGluR5a but not mGluR1a-stimulated ERK1/2 phosphorylation in a kinase activity-dependent manner. We also find that Aβ42 oligomers stimulate the association of CaMKIIα with mGluR5a and activate ERK1/2 in an mGluR5a-dependent manner. However, Aβ42 oligomer-stimulated ERK1/2 phosphorylation is not regulated by mGluR5a/CaMKIIα interactions suggesting that agonist and Aβ42 oligomers stabilize distinct mGluR5a activation states that are differentially regulated by CaMKIIα. The expression of both mGluR5a and PrP(C) together, but not alone resulted in the agonist-stimulated subcellular distribution of CaMKIIα into cytoplasmic puncta.

CONCLUSIONS

Taken together these results indicate that CaMKIIα selectively regulates mGluR1a and mGluR5a ERK1/2 signaling. As mGluR5 and CaMKIIα are involved in learning and memory and Aβ and mGluR5 are implicated in Alzheimer's disease, results of these studies could provide insight into potential pharmacological targets for treatment of Alzheimer's disease.

Compromised MAPK signaling in human diseases: an update

The mitogen-activated protein kinases (MAPKs) in mammals include c-Jun NH2-terminal kinase (JNK), p38 MAPK, and extracellular signal-regulated kinase (ERK). These enzymes are serine-threonine protein kinases that regulate various cellular activities including proliferation, differentiation, apoptosis or survival, inflammation, and innate immunity. The compromised MAPK signaling pathways contribute to the pathology of diverse human diseases including cancer and neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. The JNK and p38 MAPK signaling pathways are activated by various types of cellular stress such as oxidative, genotoxic, and osmotic stress as well as by proinflammatory cytokines such as tumor necrosis factor-α and interleukin 1β. The Ras-Raf-MEK-ERK signaling pathway plays a key role in cancer development through the stimulation of cell proliferation and metastasis. The p38 MAPK pathway contributes to neuroinflammation mediated by glial cells including microglia and astrocytes, and it has also been associated with anticancer drug resistance in colon and liver cancer. We here summarize recent research on the roles of MAPK signaling pathways in human diseases, with a focus on cancer and neurodegenerative conditions.

The Binding Receptors of Aβ: an Alternative Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders, which causes the deterioration of memory and other cognitive abilities of the elderly. Previous lines of research have shown that Aβ is an essential factor in AD pathology and the soluble oligomeric species of Aβ peptide is presumed to be the drivers of synaptic impairment in AD. However, the exact mechanisms underlying Aβ-induced synapse dysfunction are still not fully understood. Recently, increasing evidence suggests that some potential receptors which bind specifically with Aβ may play important roles in inducing the toxicity of the neurons in AD pathology. These receptors include the cellular prion protein (PrPc), the α7 nicotinic acetylcholine receptor (α7nAChR), the p75 neurotrophin receptor (p75(NTR)), the beta-adrenergic receptors (β-ARs), the Eph receptors, the paired immunoglobulin-like receptor B (PirB), the PirB's human ortholog receptor (LilrB2), and the Fcγ receptor II-b (FcγRIIb). This review summarizes the characters of these prominent receptors and how the bindings of them with Aβ inhibit the LTP, decrease the number of dendritic spine, damage the neurons, and so on in AD pathogenesis. Blocking or rescuing these receptors may have significant importance for AD treatments.

Isoform-specific interactions between meprin metalloproteases and the catalytic subunit of protein kinase A: significance in acute and chronic kidney injury

Meprin metalloproteases are abundantly expressed in the brush-border membranes of kidney proximal tubules. Meprins are implicated in ischemia-reperfusion (IR)-induced renal injury and diabetic nephropathy. The protein kinase A (PKA) signaling pathway modulates extracellular matrix metabolism in diabetic kidneys. The present study evaluated isoform-specific interactions between the catalytic subunit of PKA (PKA C) and meprins. To this end, cytosolic-enriched kidney proteins from meprin αβ double knockout mice, and purified forms of recombinant mouse PKA Cα, Cβ1, and Cβ2, were incubated with activated forms of either homomeric meprin A or meprin B. The cleaved protein products were subjected to SDS-PAGE and analyzed by Coomassie staining and Western blot analysis. While meprin A only cleaved PKA Cβ1, meprin B cleaved all three PKA C isoforms. Analysis of the proteolytic fragments by mass spectrometry revealed that meprin A and B cleave the PKA C isoforms at defined sites, resulting in unique cleavage products. Michaelis-Menten enzyme kinetics demonstrated that meprin B-mediated cleavage of PKA Cα occurs at a rate consistent with that of other physiologically relevant meprin substrates. Meprin cleavage decreased the kinase activity of PKA Cα, Cβ1, and Cβ2. PKA C levels were higher in diabetic kidneys, with evidence of in vivo fragmentation in wild-type diabetic kidneys. Confocal microscopy showed localization of meprin A in the glomeruli of diabetic kidneys. At 3 h post-IR, PKA C levels in proximal tubules decreased compared with distal tubules, which lack meprins. These data suggest that meprins may impact kidney injury, in part, via modulation of PKA signaling pathways.

Derailed intraneuronal signalling drives pathogenesis in sporadic and familial Alzheimer's disease

Although a wide variety of genetic and nongenetic Alzheimer's disease (AD) risk factors have been identified, their role in onset and/or progression of neuronal degeneration remains elusive. Systematic analysis of AD risk factors revealed that perturbations of intraneuronal signalling pathways comprise a common mechanistic denominator in both familial and sporadic AD and that such alterations lead to increases in Aβ oligomers (Aβo) formation and phosphorylation of TAU. Conversely, Aβo and TAU impact intracellular signalling directly. This feature entails binding of Aβo to membrane receptors, whereas TAU functionally interacts with downstream transducers. Accordingly, we postulate a positive feedback mechanism in which AD risk factors or genes trigger perturbations of intraneuronal signalling leading to enhanced Aβo formation and TAU phosphorylation which in turn further derange signalling. Ultimately intraneuronal signalling becomes deregulated to the extent that neuronal function and survival cannot be sustained, whereas the resulting elevated levels of amyloidogenic Aβo and phosphorylated TAU species self-polymerizes into the AD plaques and tangles, respectively.

Aβ1-42 monomers or oligomers have different effects on autophagy and apoptosis

The role of autophagy and its relationship with apoptosis in Alzheimer disease (AD) pathogenesis is poorly understood. Disruption of autophagy leads to buildup of incompletely digested substrates, amyloid-β (Aβ) peptide accumulation in vacuoles and cell death. Aβ, in turn, has been found to affect autophagy. Thus, Aβ might be part of a loop in which it is both the substrate of altered autophagy and its cause. Given the relevance of different soluble forms of Aβ1-42 in AD, we have investigated whether monomers and oligomers of the peptide have a differential role in causing altered autophagy and cell death. Using differentiated SK-N-BE neuroblastoma cells, we found that monomers hamper the formation of the autophagic BCL2-BECN1/Beclin 1 complex and activate the MAPK8/JNK1-MAPK9/JNK2 pathway phosphorylating BCL2. Monomers also inhibit apoptosis and allow autophagy with intracellular accumulation of autophagosomes and elevation of levels of BECN1 and LC3-II, resulting in an inhibition of substrate degradation due to an inhibitory action on lysosomal activity. Oligomers, in turn, favor the formation of the BCL2-BECN1 complex favoring apoptosis. In addition, they cause a less profound increase in BECN1 and LC3-II levels than monomers without affecting the autophagic flux. Thus, data presented in this work show a link for autophagy and apoptosis with monomers and oligomers, respectively. These studies are likely to help the design of novel disease modifying therapies.

Successful therapies for Alzheimer's disease: why so many in animal models and none in humans?

Peering into the field of Alzheimer’s disease (AD), the outsider realizes that many of the therapeutic strategies tested (in animal models) have been successful. One also may notice that there is a deficit in translational research, i.e., to take a successful drug in mice and translate it to the patient. Efforts are still focused on novel projects to expand the therapeutic arsenal to “cure mice.” Scientific reasons behind so many successful strategies are not obvious. This article aims to review the current approaches to combat AD and to open a debate on common mechanisms of cognitive enhancement and neuroprotection. In short, either the rodent models are not good and should be discontinued, or we should extract the most useful information from those models. An example of a question that may be debated for the advancement in AD therapy is: In addition to reducing amyloid and tau pathologies, would it be necessary to boost synaptic strength and cognition? The debate could provide clues to turn around the current negative output in generating effective drugs for patients. Furthermore, discovery of biomarkers in human body fluids, and a clear distinction between cognitive enhancers and disease modifying strategies, should be instrumental for advancing in anti-AD drug discovery.

Administration of a selective β2 adrenergic receptor antagonist exacerbates neuropathology and cognitive deficits in a mouse model of Alzheimer's disease

Currently, there are no available approaches to cure or slow down the progression of Alzheimer's disease (AD), which is characterized by the accumulation of extracellular amyloid-β (Aβ) deposits and intraneuronal tangles that comprised hyperphosphorylated tau. The β2 adrenergic receptors (β2ARs) are expressed throughout the cortex and hippocampus and play a key role in cognitive functions. Alterations in the function of these receptors have been linked to AD; however, these data remain controversial as apparent contradicting reports have been published. Given the current demographics of growing elderly population and the high likelihood of concurrent β-blocker use for other chronic conditions, more studies into the role of this receptor in AD animal models are needed. Here, we show that administration of ICI 118,551 (ICI), a selective β2AR antagonist, exacerbates cognitive deficits in a mouse model of AD, the 3xTg-AD mice. Neuropathologically, ICI increased Aβ levels and Aβ plaque burden. Concomitantly, ICI-treated 3xTg-AD mice showed an increase in tau phosphorylation and accumulation. Mechanistically, these changes were linked to an increase in amyloidogenic amyloid precursor protein processing. These results suggest that under the conditions used here, selective pharmacologic inhibition of β2ARs has detrimental effects on AD-like pathology in mice. Overall, these studies strengthen the notion that the link between β2ARs and AD is likely highly complex and suggest caution in generalizing the beneficial effects of β blockers on AD.

Transcriptomic analysis of the effects of a fish oil enriched diet on murine brains

The health benefits of fish oil enriched with high omega-3 polyunsaturated fatty acids (n-3 PUFA) are widely documented. Fish oil as dietary supplements, however, show moderate clinical efficacy, highlighting an immediate scope of systematic in vitro feedback. Our transcriptomic study was designed to investigate the genomic shift of murine brains fed on fish oil enriched diets. A customized fish oil enriched diet (FD) and standard lab diet (SD) were separately administered to two randomly chosen populations of C57BL/6J mice from their weaning age until late adolescence. Statistical analysis mined 1,142 genes of interest (GOI) differentially altered in the hemibrains collected from the FD- and SD-fed mice at the age of five months. The majority of identified GOI (∼40%) encodes proteins located in the plasma membrane, suggesting that fish oil primarily facilitated the membrane-oriented biofunctions. FD potentially augmented the nervous system's development and functions by selectively stimulating the Src-mediated calcium-induced growth cascade and the downstream PI3K-AKT-PKC pathways. FD reduced the amyloidal burden, attenuated oxidative stress, and assisted in somatostatin activation—the signatures of attenuation of Alzheimer's disease, Parkinson's disease, and affective disorder. FD induced elevation of FKBP5 and suppression of BDNF, which are often linked with the improvement of anxiety disorder, depression, and post-traumatic stress disorder. Hence we anticipate efficacy of FD in treating illnesses such as depression that are typically triggered by the hypoactivities of dopaminergic, adrenergic, cholinergic, and GABAergic networks. Contrastingly, FD's efficacy could be compromised in treating illnesses such as bipolar disorder and schizophrenia, which are triggered by hyperactivities of the same set of neuromodulators. A more comprehensive investigation is recommended to elucidate the implications of fish oil on disease pathomechanisms, and the result-driven repositioning of fish oil utilization may revitalize its therapeutic efficacy.

Genetic suppression of β2-adrenergic receptors ameliorates tau pathology in a mouse model of tauopathies

Accumulation of the microtubule-binding protein tau is a key event in several neurodegenerative disorders referred to as tauopathies, which include Alzheimer's disease, frontotemporal lobar degeneration, Pick's disease, progressive supranuclear palsy and corticobasal degeneration. Thus, understanding the molecular pathways leading to tau accumulation will have a major impact across multiple neurodegenerative disorders. To elucidate the pathways involved in tau pathology, we removed the gene encoding the beta-2 adrenergic receptors (β2ARs) from a mouse model overexpressing mutant human tau. Notably, the number of β2ARs is increased in brains of AD patients and epidemiological studies show that the use of beta-blockers decreases the incidence of AD. The mechanisms underlying these observations, however, are not clear. We show that the tau transgenic mice lacking the β2AR gene had a reduced mortality rate compared with the parental tau transgenic mice. Removing the gene encoding the β2ARs from the tau transgenic mice also significantly improved motor deficits. Neuropathologically, the improvement in lifespan and motor function was associated with a reduction in brain tau immunoreactivity and phosphorylation. Mechanistically, we provide compelling evidence that the β2AR-mediated changes in tau were linked to a reduction in the activity of GSK3β and CDK5, two of the major tau kinases. These studies provide a mechanistic link between β2ARs and tau and suggest the molecular basis linking the use of beta-blockers to a reduced incidence of AD. Furthermore, these data suggest that a detailed pharmacological modulation of β2ARs could be exploited to develop better therapeutic strategies for AD and other tauopathies.

Protein phosphorylation analysis based on proton release detection: potential tools for drug discovery

Phosphorylation is the most important post-translational modification of proteins in eukaryotic cells and it is catalysed by enzymes called kinases. The balance between protein phosphorylation and dephosphorylation is critical for the regulation of physiological processes and its unbalance is the cause of several diseases. Conventional assays used to analyse the kinase activity are limited as they rely heavily on phospho-specific antibodies and radioactive tags. This makes their use impractical for high throughput drug discovery platforms. We have developed two versatile methods to detect the release of protons (H(+)) associated with the protein phosphorylation catalysed by kinases. The first approach is based on the pH-sensitive response of oxide-semiconductor interfaces and the second method detects the pH changes in phosphorylation reaction using a commercial micro-pH electrode. The proposed methods successfully detected phosphorylation of myelin basic protein by PKC-α kinase. These techniques can be readily adopted for multiplexed arrays and high throughput analysis of kinase activity, which will represent an important innovation in biomedical research and drug discovery.

The importance of tau phosphorylation for neurodegenerative diseases

Fibrillar deposits of highly phosphorylated tau are a key pathological feature of several neurodegenerative tauopathies including Alzheimer's disease (AD) and some frontotemporal dementias. Increasing evidence suggests that the presence of these end-stage neurofibrillary lesions do not cause neuronal loss, but rather that alterations to soluble tau proteins induce neurodegeneration. In particular, aberrant tau phosphorylation is acknowledged to be a key disease process, influencing tau structure, distribution, and function in neurons. Although typically described as a cytosolic protein that associates with microtubules and regulates axonal transport, several additional functions of tau have recently been demonstrated, including roles in DNA stabilization, and synaptic function. Most recently, studies examining the trans-synaptic spread of tau pathology in disease models have suggested a potential role for extracellular tau in cell signaling pathways intrinsic to neurodegeneration. Here we review the evidence showing that tau phosphorylation plays a key role in neurodegenerative tauopathies. We also comment on the tractability of altering phosphorylation-dependent tau functions for therapeutic intervention in AD and related disorders.

β-Arrestins as potential therapeutic targets for Alzheimer's disease

β-arrestins represent a small family of G protein-coupled receptors (GPCRs) regulators, which provide modulating effects by facilitating desensitization and internalization of GPCRs as well as initiating their own signalings. Recent reports have demonstrated that β-arrestins levels were correlated with amyloid-β peptide (Aβ) pathology in brains of Alzheimer's disease (AD) patients and animal models. β-arrestins could enhance the activity of γ-secretase via interacting with anterior pharynx defective 1 subunit, which increased Aβ production and contributed to the pathogenesis of AD. In addition, Aβ-induced internalization of β2-adrenergic receptor internalization and loss of dendritic spine in neurons were proven to be mediated by β-arrestins, further establishing their pathogenic role in AD. More importantly, deletion of β-arrestins markedly attenuated AD pathology, without causing any gross abnormality. Here, we review the evidence about the roles of β-arrestins in the progression of AD. In addition, the established and postulated mechanisms by which β-arrestins mediated in AD pathogenesis are also discussed. Based on the role of β-arrestins in AD pathogenesis, genetically or pharmacologically targeting β-arrestins might provide new opportunities for AD treatment.