G protein subunit levels in fibroblasts from familial Alzheimer's disease patients: lower levels of high molecular weight Gs alpha isoform in patients with decreased beta-adrenergic receptor stimulated cAMP formation

A Role for Phosphodiesterase 11A (PDE11A) in the Formation of Social Memories and the Stabilization of Mood

The most recently discovered 3',5'-cyclic nucleotide phosphodiesterase family is the Phosphodiesterase 11 (PDE11) family, which is encoded by a single gene PDE11A. PDE11A is a dual-specific PDE, breaking down both cAMP and cGMP. There are four PDE11A splice variants (PDE11A1-4) with distinct tissue expression profiles and unique N-terminal regulatory regions, suggesting that each isoform could be individually targeted with a small molecule or biologic. PDE11A4 is the PDE11A isoform expressed in brain and is found in the hippocampal formation of humans and rodents. Studies in rodents show that PDE11A4 mRNA expression in brain is, in fact, restricted to the hippocampal formation (CA1, possibly CA2, subiculum, and the adjacently connected amygdalohippocampal area). Within the hippocampal formation of rodents, PDE11A4 protein is expressed in neurons but not astrocytes, with a distribution across nuclear, cytoplasmic, and membrane compartments. This subcellular localization of PDE11A4 is altered in response to social experience in mouse, and in vitro studies show the compartmentalization of PDE11A4 is controlled, at least in part, by homodimerization and N-terminal phosphorylation. PDE11A4 expression dramatically increases in the hippocampus with age in the rodent hippocampus, from early postnatal life to late aging, suggesting PDE11A4 function may evolve across the lifespan. Interestingly, PDE11A4 protein shows a three to tenfold enrichment in the rodent ventral hippocampal formation (VHIPP; a.k.a. anterior in primates) versus dorsal hippocampal formation (DHIPP). Consistent with this enrichment in VHIPP, studies in knockout mice show that PDE11A regulates the formation of social memories and the stabilization of mood and is a critical mechanism by which social experience feeds back to modify the brain and subsequent social behaviors. PDE11A4 likely controls behavior by regulating hippocampal glutamatergic, oxytocin, and cytokine signaling, as well as protein translation. Given its unique tissue distribution and relatively selective effects on behavior, PDE11A may represent a novel therapeutic target for neuropsychiatric, neurodevelopmental, or age-related disorders. Therapeutically targeting PDE11A4 may be a way to selectively restore aberrant cyclic nucleotide signaling in the hippocampal formation while leaving the rest of the brain and periphery untouched, thus, relieving deficits while avoiding unwanted side effects.

Select 3',5'-cyclic nucleotide phosphodiesterases exhibit altered expression in the aged rodent brain

3',5'-cyclic nucleotide phosphodiesterases (PDEs) are the only known enzymes to compartmentalize cAMP and cGMP, yet little is known about how PDEs are dynamically regulated across the lifespan. We mapped mRNA expression of all 21 PDE isoforms in the adult rat and mouse central nervous system (CNS) using quantitative polymerase chain reaction (qPCR) and in situ hybridization to assess conservation across species. We also compared PDE mRNA and protein in the brains of old (26 months) versus young (5 months) Sprague-Dawley rats, with select experiments replicated in old (9 months) versus young (2 months) BALB/cJ mice. We show that each PDE isoform exhibits a unique expression pattern across the brain that is highly conserved between rats, mice, and humans. PDE1B, PDE1C, PDE2A, PDE4A, PDE4D, PDE5A, PDE7A, PDE8A, PDE8B, PDE10A, and PDE11A showed an age-related increase or decrease in mRNA expression in at least 1 of the 4 brain regions examined (hippocampus, cortex, striatum, and cerebellum). In contrast, mRNA expression of PDE1A, PDE3A, PDE3B, PDE4B, PDE7A, PDE7B, and PDE9A did not change with age. Age-related increases in PDE11A4, PDE8A3, PDE8A4/5, and PDE1C1 protein expression were confirmed in hippocampus of old versus young rodents, as were age-related increases in PDE8A3 protein expression in the striatum. Age-related changes in PDE expression appear to have functional consequences as, relative to young rats, the hippocampi of old rats demonstrated strikingly decreased phosphorylation of GluR1, CaMKIIα, and CaMKIIβ, decreased expression of the transmembrane AMPA regulatory proteins γ2 (a.k.a. stargazin) and γ8, and increased trimethylation of H3K27. Interestingly, expression of PDE11A4, PDE8A4/5, PDE8A3, and PDE1C1 correlate with these functional endpoints in young but not old rats, suggesting that aging is not only associated with a change in PDE expression but also a change in PDE compartmentalization.

Lymphocyte G-protein-coupled receptor kinase-2 is upregulated in patients with Alzheimer's disease

Alterations in signal transduction pathway of G-protein-coupled receptors (GPCRs) have been found in the cerebrocortex and in the peripheral cultured tissues of patients with Alzheimer's disease (AD). The G-protein-coupled receptor kinase-2 (GRK2) plays an important role in regulating the GPCRs signaling: its increased expression is associated with receptor desensitization. The aim of this study was to explore GRK2 levels in peripheral lymphocytes of AD patients and to establish a correlation between lymphocyte protein concentrations and the degree of cognitive impairment. GRK2 mRNA and protein expression were evaluated in the lymphocytes of AD patients with mild or moderate/severe cognitive impairment and in age-matched healthy subjects. Both GRK2 mRNA and protein expression were higher in AD patients lymphocytes compared to controls. Furthermore, lymphocyte GRK2 levels were significantly correlated to the degree of cognitive decline. Our preliminary data suggest that GRK2 is involved in GPCRs coupling dysfunction observed in AD patients. Further studies are needed in order to verify whether the lymphocyte GRK2 might be utilized as a novel biomarker in AD diagnosis and clinical monitoring.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

Phospholipid mass is increased in fibroblasts bearing the Swedish amyloid precursor mutation

Phospholipid changes occur in brain regions affected by Alzheimer disease (AD), including a marked reduction in plasmalogens, which could diminish brain function either by directly altering signaling events or by bulk membrane effects. However, model systems for studying the dynamics of lipid biosynthesis in AD are lacking. To determine if fibroblasts bearing the Swedish amyloid precursor protein (swAPP) mutation are a useful model to study the mechanism(s) associated with altered phospholipid biosynthesis in AD, we examined the steady-state phospholipid mass and composition of fibroblasts, including plasmalogens. We found a 15% increase in total phospholipid mass, accounted for by a 24% increase in the combined total of phosphatidylethanolamine and plasmanylethanolamine mass and a 19% increase in the combined total of phosphatidylcholine (PtdCho) and plasmanycholine (PakCho) mass in the swAPP mutant bearing fibroblasts. Cholesterol mass was unchanged in these cells. The changes in phospholipid mass did not alter the cellular molar composition of the phospholipids nor the cholesterol to phospholipid ratio. While plasmalogen mass was not altered, the ratio of choline plasmalogen (PlsCho) mass to PtdCho+PakCho mass was decreased 16% and there was a 14% reduction in the proportion of PlsCho as a percent of total phospholipids in the swAPP mutant bearing fibroblasts. This change in choline plasmalogen is consistent with the reported decreases in plasmalogen proportions in affected regions of AD brain, suggesting that these cells may serve as a useful model to determine the mechanism underlying changes in plasmalogen biosynthesis in AD brain.

Diphenhydramine-induced amnesia is mediated by Gi-protein activation

The effect of the i.c.v. administration of antisense oligodeoxynucleotides directed against the alpha subunit of different Gi-proteins (anti-Gialpha(1), anti-Gialpha(2), anti-Gialpha(3), anti-Goalpha(1), anti-Goalpha(2)) on the amnesia induced by the H(1)-antihistamine diphenhydramine (20 mg kg(-1) s.c.) was evaluated in the mouse passive avoidance test. Pretreatment with anti-Gialpha(1) (12.5-25 microg per mouse i.c.v.) and anti-Gialpha(2) (25 microg per mouse i.c.v.), administered 24 and 18 h before test, prevented antihistamine-induced amnesia. By contrast, pretreatment with an anti-Gialpha(3) (25 microg per mouse i.c.v.), anti-Goalpha(1) (25 microg per mouse i.c.v.) and anti-Goalpha(2) (25 microg per mouse i.c.v.) did not modify the detrimental effect induced by diphenhydramine. At the highest effective doses, none of the compounds used impaired motor coordination, as revealed by the rota rod test, nor modified spontaneous motility and inspection activity, as revealed by the hole board test. These results suggest the important role played by the Gi(1)- and Gi(2)-protein pathway in the transduction mechanism involved in the impairment of memory processes produced by the H(1)-antihistamine diphenhydramine.

α-2 agonists induce amnesia through activation of the Gi-protein signalling pathway

The post-receptorial mechanism of the amnesic action of the alpha2-agonists clonidine and guanabenz was investigated in the mouse passive avoidance test. Animals were i.c.v. injected with pertussis toxin (PTX) or with antisense oligonucleotides, complementary to the sequence of the alpha-subunit mRNA of Gi1, Gi2, Gi3, Go1 and Go2 proteins. The administration of PTX (0.25 microg per mouse i.c.v.) reversed the amnesia induced by both alpha2-agonists. Similarly, anti-Gialpha1 (6.25-12.5 microg per mouse i.c.v.), anti-Gialpha3 (3.12-12.5 microg per mouse i.c.v.), anti-Goalpha1 (12.5-25 microg per mouse i.c.v.) antagonised the detrimental effect induced by clonidine and guanabenz. By contrast, pretreatment with anti-Gialpha2 (3.12-25 microg per mouse i.c.v.) and anti-Goalpha2 (12.5-25 microg per mouse i.c.v.) never modified the impairment of memory processes induced by the alpha2-agonists. At the highest effective doses, none of the compounds used impaired motor coordination (rota rod test), nor modified spontaneous motility and inspection activity, (hole board test). These results indicate the involvement of Gi1, Gi3, and Go1, but not Gi2 and Go2, protein subtypes in the transduction mechanism responsible for the induction of amnesia by clonidine and guanabenz.

Differential prevention of morphine amnesia by antisense oligodeoxynucleotides directed against various Gi-protein alpha subunits

The effect of the i.c.v. administration of pertussis toxin (PTX) and antisense oligodeoxynucleotide directed against the alpha subunit of different Gi-proteins (anti-Gialpha1, anti-Gialpha2, anti-Gialpha3) on amnesia induced by morphine was evaluated in the mouse passive avoidance test. The administration of morphine (6 - 10 mg kg(-1) i.p.) immediately after the training session produced amnesia that was prevented by PTX (0.25 microg per mouse i.c.v.) administered 7 days before the passive avoidance test. Anti-Gialpha1 (6.25 microg per mouse i.c.v.) and anti-Gialpha3 (12.5 microg per mouse i.c.v.), administered 18 and 24 h before the training session, prevented the morphine amnesia. By contrast, pretreatment with anti-Gialpha2 (3.12 - 25 microg per mouse i.c.v.) never modified the impairment of memory processes induced by morphine. At the highest effective doses, none of the compounds used impaired motor coordination, as revealed by the rota rod test, nor modified spontaneous motility and inspection activity, as revealed by the hole board test. These results suggest the important role played by Gi1 and Gi3 protein subtypes in the transduction mechanism involved in the impairment of memory processes produced by morphine.

Phospholipid composition and levels are not altered in fibroblasts bearing presenilin-1 mutations

Lipid alterations have been reported in brain regions affected by Alzheimer disease (AD). The mechanisms causing these changes are poorly understood because it is difficult to study dynamic, biochemical processes in post-mortem brain. Fibroblasts derived from AD patients offer an alternative model to study disease-related alterations in lipid metabolism. Therefore, we measured the phospholipid levels and composition of fibroblasts from individuals bearing two different presenilin-1 mutations and compared these values to appropriate control fibroblasts. There were no differences between groups in phospholipid composition or in individual phospholipid levels, including the plasmalogens. Cholesterol levels and the cholesterol/phospholipid ratio were not different between presenilin-1 mutation bearing and control fibroblasts. Although these presenilin-1 mutation bearing fibroblasts have a number of biochemical changes related to AD, the absence of a change in phospholipid levels suggests that under these conditions, these cells are not useful in studying the mechanisms underlying the alterations in brain phospholipid levels associated with AD. However, these results do not preclude the possible use of other fibroblasts bearing AD-related mutations, e.g., APP mutations, to examine AD-related changes in brain lipid metabolism, or of these fibroblasts under different conditions.

Protein kinase C and amyloid precursor protein processing in skin fibroblasts from sporadic and familial Alzheimer's disease cases

Non-amyloidogenic alpha-secretase processing of amyloid precursor protein (APP) is stimulated by protein kinase C (PKC). Levels and activity of PKC are decreased in sporadic Alzheimer's disease skin fibroblasts. We investigated whether alterations in PKC and PKC-mediated APP processing occur also in fibroblasts established from individuals with familial Alzheimer's disease APP KM670/671NL, PS1 M146V and H163Y mutations. These pathogenic mutations are known to alter APP metabolism to increase Abeta. PKC activities, but not levels, were decreased by 50% in soluble fractions from sporadic Alzheimer's disease cases. In contrast, familial Alzheimer's disease fibroblasts showed no significant changes in PKC enzyme activity. Fibroblasts bearing the APP KM670/671NL mutation showed no significant differences in either PKC levels or PKC-mediated soluble APP (APPs) secretion, compared to controls. Fibroblasts bearing PS1 M146V and H163Y mutations showed a 30% increase in soluble PKC levels and a 40% decrease in PKC-mediated APPs secretion. These results indicate that PKC deficits are unlikely to contribute to increased Abeta seen with APP and PS1 mutations, and also that PS1 mutations decrease alpha-secretase derived APPs production independently of altered PKC activity.