Reduced phospholipase C-beta activity and isoform expression in the cerebellum of TS65Dn mouse: a model of Down syndrome

Proteomic analysis of six- and twelve-month hippocampus and cerebellum in a murine Down syndrome model

This study was designed to investigate the brain proteome of the Ts65Dn mouse model of Down syndrome. We profiled the cerebellum and hippocampus proteomes of 6- and 12-month-old trisomic and disomic mice by difference gel electrophoresis. We quantified levels of 2082 protein spots and identified 272 (170 unique UniProt accessions) by mass spectrometry. Four identified proteins are encoded by genes trisomic in the Ts65Dn mouse. Three of these (CRYZL11, EZR, and SOD1) were elevated with p-value <0.05, and 2 proteins encoded by disomic genes (MAPRE3 and PHB) were reduced. Intergel comparisons based on age (6 vs. 12 months) and brain region (cerebellum vs. hippocampus) revealed numerous differences. Specifically, 132 identified proteins were different between age groups, and 141 identified proteins were different between the 2 brain regions. Our results suggest that compensatory mechanisms exist, which ameliorate the effect of trisomy in the Ts65Dn mice. Differences observed during aging may play a role in the accelerated deterioration of learning and memory seen in Ts65Dn mice.

Nuclear phospholipase C-β1 and diacylglycerol LIPASE-α in brain cortical neurons

Phosphoinositide (PtdIns) signaling involves the generation of lipid second messengers in response to stimuli in a receptor-mediated manner at the plasma membrane. In neuronal cells of adult brain, the standard model proposes that activation of metabotropic receptors coupled to Phospholipase C-β1 (PLC-β1) is linked to endocannabinoid signaling through the production of diacylglycerol (DAG), which could be systematically metabolized by 1,2-diacylglycerol Lipases (DAGL) to produce an increase of 2-arachidonoyl-glycerol (2-AG), the most abundant endocannabinoid in the brain. However, the existence of a nuclear PtdIns metabolism independent from that occurring elsewhere in the cell is now widely accepted, suggesting that the nucleus constitutes both a functional and a distinct compartment for PtdIns metabolism. In this review, we shall highlight the main achievements in the field of neuronal nuclear inositol lipid metabolism with particular attention to progress made linked to the 2-AG biosynthesis. Our aim has been to identify potential sites of 2-AG synthesis other than the neuronal cytoplasmic compartment by determining the subcellular localization of PLC-β1 and DAGL-α, which is much more abundant than DAGL-β in brain. Our data show that PLC-β1 and DAGL-α are detected in discrete brain regions, with a marked predominance of pyramidal morphologies of positive cortical cells, consistent with their role in the biosynthesis and release of 2-AG by pyramidal neurons to control their synaptic inputs. However, as novelty, we showed here an integrated description of the localization of PLC-β1 and DAGL-α in the neuronal nuclear compartment. We discuss our comparative analysis of the expression patterns of PLC-β1 and DAGL-α, providing some insight into the potential autocrine role of 2-AG production in the neuronal nuclear compartment that probably subserve additional roles to the recognized activation of the CB1 cannabinoid receptor.

G-protein-associated signal transduction processes are restored after postweaning environmental enrichment in Ts65Dn, a Down syndrome mouse model

Individuals with Down syndrome (DS) present cognitive deficits that can be improved by early implementation of special care programs. However, they showed limited and temporary cognitive effects. We previously demonstrated that postnatal environmental enrichment (EE) improved clearly, though temporarily, the execution of visuospatial memory tasks in Ts65Dn mice, a DS model bearing a partial trisomy of murine chromosome 16; but in contrast to wild-type littermates, there was a lack of structural plasticity in pyramidal cell structure in the trisomic cerebral cortex. In the present study, we have investigated the impact of EE on the function of adenylyl cyclase and phospholipase C as a possible mechanism underlying the time-limited improvements observed. Basal production of cyclic adenosine monophosphate (cAMP) was not affected, but responses to GTPγS, isoprenaline, noradrenaline, SKF 38393 and forskolin were depressed in the Ts65Dn hippocampus. In EE conditions, cAMP accumulation was not significantly modified in control animals with respect to nonenriched controls. However, EE had a marked effect in Ts65Dn mice, in which cAMP production was significantly increased. Similarly, EE increased phospholipase C activity in Ts65Dn mice, in response to carbachol and calcium. We conclude that EE restores the G-protein-associated signal transduction systems that are altered in Ts65Dn mice.

Levels of Gsα(short and long), Gα(olf) and Gβ(common) subunits, and calcium-sensitive adenylyl cyclase isoforms (1, 5/6, 8) in post-mortem human brain caudate and cortical membranes: comparison with rat brain membranes and potential stoichiometric relationships

The levels of expression of Gsα(short and long), Gα(olf) and Gβ(common) subunits, and calcium-sensitive adenylyl cyclases isoforms (AC1, 5/6, and 8) in human brain cortical and caudate membranes were quantified by western blot analysis in order to establish their contribution to the patterns of AC functioning. Both areas expressed Gsα(long) (52 kDa) with values ranging from about 1400 ng/mg of membrane protein in cerebral cortex to close to 600 ng/mg of membrane protein in caudate nucleus. In contrast, Gsα(short) and Gsα(olf) were expressed separately, Gsα(short) in cortical membranes with values around 500 ng/mg of membrane protein and Gα(olf) in caudate membranes with values around 1300 ng/mg of membrane protein. Quantitative measurements of Gβ, revealed a similar expression level in cortical and caudate membranes (5444±732 versus 5511±394 ng/mg protein; p=0.966). The B(max) values of GTPγS-dependent [(3)H]-forskolin binding show the following descending order: rat striatal membranes>rat cortical membranes=human caudate membranes>human cortical membranes. Therefore, as measured immunochemically and by [(3)H]-forskolin binding, there seems to be a vast excess of Gsα subunits over catalytic units of AC. The highest levels of AC5/6 expression were detected in caudate membranes. AC8 was little expressed, and there were no significant differences in the relative values between both human brain regions. Finally, the levels of the AC1 isoform were significantly lower in caudate than in cortical membranes. It is concluded that these stoichiometric data contribute nonetheless to explain the significant differences observed in signalling capacities through the AC system in both human brain regions.

Increased NR2A expression and prolonged decay of NMDA-induced calcium transient in cerebellum of TgDyrk1A mice, a mouse model of Down syndrome

Transgenic mice overexpressing Dyrk1A (TgDyrk1A), a Down syndrome (DS) candidate gene, exhibit motor and cognitive alterations similar to those observed in DS individuals. To gain new insights into the molecular consequences of Dyrk1A overexpression underlying TgDyrk1A and possibly DS motor phenotypes, microarray studies were performed. Transcriptome analysis showed an upregulation of the NR2A subunit of the NMDA type of glutamate receptors in TgDyrk1A cerebellum. NR2A protein overexpression was also detected in TgDyrk1A cerebellar homogenates, in the synaptosome-enriched fraction and in TgDyrk1A primary cerebellar granular neuronal cultures (CGNs). In TgDyrk1A synaptosomes, calcium-imaging experiments showed a higher calcium uptake after NMDA stimulation. Similarly, NMDA administration promoted longer calcium transients in TgDyrk1A CGNs. Taken together, these results show that NMDA-induced calcium rise is altered in TgDyrk1A cerebellar neurons and indicate that calcium signaling is dysregulated in TgDyrk1A mice cerebella. These findings suggest that DYRK1A overexpression might contribute to the dysbalance in the excitatory transmission found in the cerebellum of DS individuals and DS mouse models.

Molecular responses of the Ts65Dn and Ts1Cje mouse models of Down syndrome to MK-801

Down syndrome (DS), caused by trisomy of human chromosome 21 (chr21), is the most common genetic cause of intellectual disability. The Ts65Dn mouse model of DS is trisomic for orthologs of 94 chr21-encoded, confirmed protein-coding genes and displays a number of behavioral deficits. Recently, Ts65Dn mice were shown to be hypersensitive to the locomotor stimulatory effects of the high-affinity N-methyl-d-aspartate (NMDA) receptor (NMDAR) channel blocker, MK-801. This is consistent with the functions of several chr21 proteins that are predicted directly or indirectly to impact NMDAR function or NMDAR-mediated signaling. In this study, we show that a second mouse model of DS, the Ts1Cje, which is trisomic for 70 protein-coding genes, is also hypersensitive to MK-801. To investigate the molecular basis for the responses to MK-801, we have measured levels of a subset of chr21 and phosphorylated non-chr21 proteins, in the cortex and hippocampus of Ts65Dn and Ts1Cje mice and euploid controls, with and without treatment with MK-801. We show that in euploid mice, the chr21-encoded proteins, TIAM1 and DYRK1A, and phosphorylation of AKT, ERK1/2 and the transcription factor ELK are involved in the MK-801 response. However, in both Ts65Dn and Ts1Cje mice, levels of phosphorylation are constitutively elevated in naïve, unstimulated mice, and the MK-801-induced changes in TIAM1 and DYRK1A and in phosphorylation are either absent or abnormal, with both genotype and brain-region-specific patterns. These results emphasize the complexities of the pathway perturbations that arise with segmental trisomy.

Effects of chronic administration of SGS-111 during adulthood and during the pre- and post-natal periods on the cognitive deficits of Ts65Dn mice, a model of Down syndrome

The Ts65Dn mouse is the most commonly used model of Down syndrome. This mouse shows many phenotypic characteristics present in people with Down syndrome, including behavioral and cognitive deficits. SGS-111 is a novel analogue of the nootropic piracetam, which prevents oxidative damage and apoptosis in both normal and Down syndrome human cortical neurons. In this work we tested the ability of chronic administration of SGS-111 to adult Ts65Dn mice to reverse the cognitive deficit found in these mice. Moreover, since oxidative stress has been reported as early as the fetal stage, SGS-111 was also administered to pregnant Ts65Dn females from the day of conception throughout the pregnancy and to Ts65Dn pups during their entire life (5 months), from birth to the end of the behavioral testing period. A characterization of the effects of SGS-111 treatment on Ts65Dn and control mice sensorimotor abilities, motor coordination, spontaneous activity, activity in the open field, exploration, anxiety and spatial and non-spatial short- and long-term learning and memory was performed. The behavioral characterization showed that chronic administration of the antioxidant SGS-111 reduced the hyperactivity shown by Ts65Dn mice in their home cage, in the open field and in the hole board test. SGS-111 administration during adulthood improved performance in the first session in the Morris water maze in control mice, and when administered during the pre- and post-natal periods, improved spatial learning in the control mice but not in Ts65Dn mice. Chronic SGS-111 administration failed to affect behavior and cognition in Ts65Dn mice.

Transmembrane signaling through phospholipase C-beta in the developing human prefrontal cortex

To investigate changes in muscarinic receptor-stimulated phospholipase C-beta (PLC-beta) activity during brain development, we examined the functional coupling of each of the three major protein components of the phosphoinositide system (M1, M3, and M5 muscarinic receptor subtypes; Gq/11 proteins; PLC-beta1-4 isoforms) in membrane preparations from post-mortem human prefrontal cerebral cortex collected at several stages of prenatal and postnatal development. In human prenatal brain membranes, PLC was found to be present and could be activated by calcium, but the ability of guanosine-5'-o-3 thiotriphosphate (GTPgammaS) or carbachol (in the presence of GTPgammaS) to modulate prenatal PLC-beta was significantly weaker than that associated with postnatal PLC-beta. Western blot analysis revealed that the levels of Galphaq/11 did not change significantly during development. In contrast, dramatically higher levels of expression of PLC-beta1-4 isoforms and of M1, M3, and M5 muscarinic receptors were detected in the child vs. the fetal brain, a finding that might underlie the observed increased activity of PLC. Thus, inositol phosphate production may be more efficiently regulated by altering the amount of effectors (PLC-beta1-4) and receptors (M1,3,5 subtypes) than by altering the level of Galphaq/11 subunits. These results demonstrate that different PLC isoforms are expressed in the prefrontal cortex of the developing human brain in an age-specific manner, suggesting specific roles not only in synaptic transmission but also in the differentiation and maturation of neurons in the developing brain.

Anxiety and panic responses to a predator in male and female Ts65Dn mice, a model for Down syndrome

Hyperactivity is a feature frequently reported in behavioral studies on the Ts65Dn (TS) mouse, the most widely accepted model of Down syndrome, when tested in anxiety-provoking situations such as the plus-maze and the open-field tests. Although this behavior could be considered as an expression of reduced anxiety, it has been considered as a consequence of a lack of behavioral inhibition and/or reduced attention. This study addressed anxiety and panic behavior of male and female TS mice by evaluating serum biochemical parameters and behavioral responses to a predator in the Mouse Defense Test Battery. Flight, risk assessment, defensive threat/attack and escape attempts were measured during and after rat confrontation. When confronted to a rat, male TS mice showed similar biochemical and behavioral responses as control mice. However, female control and TS mice presented lower serum adrenocorticotropic hormone (ACTH) levels under basal conditions and higher corticosterone levels after predator exposure than male mice. Thus, there was a larger increase in ACTH and corticosterone levels after predator exposure with respect to the undisturbed condition in females than in males. In addition, TS females showed some alterations in defensive behaviors after predator exposure. The results emphasize the need to consider gender as a confounding factor in the behavioral assessment of TS mice.

Brain G protein-dependent signaling pathways in Down syndrome and Alzheimer's disease

Premature aging and neuropathological features of Alzheimer's disease (AD) are commonly observed in Down syndrome (DS). Based on previous findings in a DS mouse model, the function of signaling pathways associated with adenylyl cyclase (AC) and phospholipase C (PLC) was assessed in cerebral cortex and cerebellum of age-matched adults with DS, AD, and controls. Basal production of cAMP was reduced in DS but not in AD cortex, and in both, DS and AD cerebellum. Responses to GTPgammaS, noradrenaline, SKF 38393 and forskolin were more depressed in DS than in AD cortex and cerebellum. Although no differences in PLC activity among control, DS and AD cortex were observed under basal and GTPgammaS- or Ca-stimulated conditions, the response of DS cortex to serotonergic and cholinergic stimulation was depressed, and that of AD was only impaired at cholinergic stimulation. No differences were documented in cerebellum. Our results demonstrate that PLC and AC were severely disturbed in the aged DS and AD brains, but the alterations in DS were more severe, and differed to some extent from those observed in AD.

Levels of G-protein alpha q/11 subunits and of phospholipase C-beta(1-4), -gamma, and -delta1 isoforms in postmortem human brain caudate and cortical membranes: potential functional implications

The levels of expression of G-protein alpha(q/11) (Galpha(q/11)) subunits and PLC-beta(1-4), -gamma, and -delta(1) isoforms were quantified by Western blot analysis in order to establish their contribution to the patterns of PLC functioning reported here. Quantitative measurements of the levels of Galpha(q/11) subunits in each region were obtained by comparison with known amounts of Escherichia coli expressed recombinant Galpha(q) subunits. Quantitative analysis indicated that Galpha(q/11) subunits are abundant polypeptides in human brain, with values ranging from about 1200 ng/mg in cerebral cortex to close to 900 ng/mg of membrane protein in caudate. In cerebral cortical membranes, the PLC-beta(1) isoform was more abundant than in caudate membranes. The highest levels of PLC-beta(2) expression were detected in caudate membranes. PLC-beta(3) was little expressed, and there were no significant differences in the relative values between both brain regions. Finally, the levels of the PLC-beta(4) isoform were significantly lower in caudate than in cortical membranes. It is concluded that although most of these data represent relative, not absolute, measures of protein levels within these regions, they contribute nonetheless to the significant differences observed in signaling capacities through the PLC system in both human brain regions.

Complementary stripes of phospholipase Cβ3 and Cβ4 expression by Purkinje cell subsets in the mouse cerebellum

Transverse boundaries divide the cerebellar cortex into four transverse zones, and within each zone the cortex is further subdivided into a symmetrical array of parasagittal stripes. Several molecules believed to mediate long-term depression at the parallel fiber-Purkinje cell synapse are known to be expressed in stripes. We have therefore explored the distributions of phospholipase Cbeta3 and phospholipase Cbeta4, key components in the transduction of type 1 metabotropic glutamate receptor-mediated responses. The data reveal that both phospholipase Cbeta isotypes are expressed strongly in the mouse cerebellum in subsets of Purkinje cells. The two distributions are distinct and largely nonoverlapping. The pattern of phospholipase Cbeta3 expression is unique, revealing stripes in three of the four transverse zones and a uniform distribution in the fourth. In contrast, phospholipase Cbeta4 appears to be confined largely to the Purkinje cells that are phospholipase Cbeta3-negative. PLCbeta3 is restricted to the zebrin II-immunopositive Purkinje cell subset. Not all zebrin II-immunoreactive Purkinje cells express PLCbeta3: in lobules IX and X it is restricted to that zebrin II-immunopositive subset that also expresses the small heat shock protein HSP25. PLCbeta4 expression is restricted to, and coextensive with, the zebrin II-immunonegative Purkinje cell subset. These nonoverlapping expression patterns suggest that long-term depression may be manifested differently between cerebellar modules.

Behavioral, cognitive and biochemical responses to different environmental conditions in male Ts65Dn mice, a model of Down syndrome

Ts65Dn mouse is the most widely accepted model for Down syndrome. We previously showed that environmental enrichment improved spatial learning in female but deteriorated it in male Ts65Dn mice. This study analyzed the factors contributing to the disturbed cognition of male Ts65Dn mice after enriched housing, by allocating male control and Ts65Dn mice in four conditions after weaning: small (n = 2-3) and large group (n = 8-10) housing, and enriched housing in small (2-3) and large groups (8-10). Learning, aggressive behavior, anxiety-like behavior and biochemical correlates of stress were evaluated when Ts65Dn and control mice were 4-5 months old. Environmental enrichment in large mixed colonies of Ts65Dn and diploid littermates disturbed behavioral and learning skills of Ts65Dn mice in the Morris water maze. ACTH and testosterone levels were not modified in any group of mice. Ts65Dn and control mice subjected to enriched housing in large groups and Ts65Dn mice housed in large groups showed higher corticosterone levels. Aggressive behavior was evaluated by measuring the number of attacks performed in the presence of an intruder. Ts65Dn mice performed less attacks than controls in all conditions, especially after enriched housing, indicating subordination. In the plus maze, cognitive aspects (i.e. risk assessment) and motor components (open arm avoidance) of anxiety behavior were evaluated; no difference in any condition was found. It is suggested that an excess of social and/or physical stimulation in Ts65Dn mice may affect cognition by disturbing the emotional and behavioral components of the learning process.

A potentially critical role of phospholipases in central nervous system ischemic, traumatic, and neurodegenerative disorders

Phospholipases are a diverse group of enzymes whose activation may be responsible for the development of injury following insult to the brain. Amongst the numerous isoforms of phospholipase proteins expressed in mammals are 19 different phospholipase A2's (PLA2s), classified functionally as either secretory, calcium dependent, or calcium independent, 11 isozymes belonging to three structural groups of PLC, and 3 PLD gene products. Many of these phospholipases have been identified in selected brain regions. Under normal conditions, these enzymes regulate the turnover of free fatty acids (FFAs) in membrane phospholipids affecting membrane stability, fluidity, and transport processes. The measurement of free fatty acids thus provides a convenient method to follow phospholipase activity and their regulation. Phospholipase activity is also responsible for the generation of an extensive list of intracellular messengers including arachidonic acid metabolites. Phospholipases are regulated by many factors including selective phosphorylation, intracellular calcium and pH. However, under abnormal conditions, excessive phospholipase activation, along with a decreased ability to resynthesize membrane phospholipids, can lead to the generation of free radicals, excitotoxicity, mitochondrial dysfunction, and apoptosis/necrosis. This review evaluates the critical contribution of the various phospholipases to brain injury following ischemia and trauma and in neurodegenerative diseases.

Role of PRIP-1, a novel Ins(1,4,5)P3 binding protein, in Ins(1,4,5)P3-mediated Ca2+ signaling

PRIP-1 was isolated as a novel inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] binding protein with a domain organization similar to phospholipase C-delta1 (PLC-delta1) but lacking the enzymatic activity. Further studies revealed that the pleckstrin homology (PH) domain of PRIP-1 is the region responsible for binding Ins(1,4,5)P3. In this study we aimed to clarify the role of PRIP-1 at the physiological concentration in Ins(1,4,5)P3-mediated Ca2+ signaling, as we had previously used COS-1 cells overexpressing PRIP-1 (Takeuchi et al., 2000, Biochem J 349:357-368). For this purpose we employed PRIP-1 knock out (PRIP-1-/-) mice generated previously (Kanematsu et al., 2002, EMBO J 21:1004-1011). The increase in free Ca2+ concentration in response to purinergic receptor stimulation was lower in primary cultured cortical neurons prepared from PRIP-1-/- mice than in those from wild type mice. The relative amounts of [3H]Ins(1,4,5)P3 measured in neurons labeled with [3H]inositol was also lower in cells from PRIP-1-/- mice. In contrast, PLC activities in brain cortex samples from PRIP-1-/- mice were not different from those in the wild type mice, indicating that the hydrolysis of Ins(1,4,5)P3 is enhanced in cells from PRIP-1-/- mice. In vitro analyses revealed that type1 inositol polyphosphate 5-phosphatase physically interacted with a PH domain of PRIP-1 (PRIP-1PH) and its enzyme activity was inhibited by PRIP-1PH. However, physical interaction with these two proteins did not appear to be the reason for the inhibition of enzyme activity, indicating that binding of Ins(1,4,5)P3 to the PH domain prevented its hydrolyzation. Together, these results indicate that PRIP-1 plays an important role in regulating the Ins(1,4,5)P3-mediated Ca2+ signaling by modulating type1 inositol polyphosphate 5-phosphatase activity through binding to Ins(1,4,5)P3.

Differential effects of environmental enrichment on behavior and learning of male and female Ts65Dn mice, a model for Down syndrome

We have assessed the effects of enriched environment (EE) upon behavioral and cognitive performances of partially trisomic Ts65Dn (TS) mice and their control (CO) littermates. Enriched environment was applied to pups for 7 weeks after weaning. Circadian spontaneous activity (actimetry), exploratory behavior (hole board), activity in the open field and spatial memory (Morris Water Maze, repeated acquisition and cued paradigms) were analyzed in 86 female and 75 male mice, starting 15 days after completing enrichment. For each gender, mice were distributed in non-enriched and enriched control and trisomic groups. Enriched environment reduced in trisomic females and enhanced in trisomic males' circadian activity. Exploratory behavior was increased by enrichment in all groups, regardless of gender or presence of trisomy. In the Morris Water Maze, a significant improvement of the spatial memory was observed in enriched-control females, but not in enriched-control male mice, as assessed by distances traveled. Performances in the four groups of control animals were also consistently and significantly better than those of matching trisomic mice. In the acquisition trials, enrichment improved performance in trisomic female animals, but deteriorated in trisomic male mice. In all groups, changes in escape latencies and distances induced by enrichment were accounted for by changes in the total time spent in the periphery of the pool, indicating changes in learning strategy. Working memory was the function more affected by enrichment. It is concluded that enriched environment induces behavioral and learning changes in trisomic mice, although gender plays a significant modulatory role.