Long-term depression activates transcription of immediate early transcription factor genes: involvement of serum response factor/Elk-1

Long-term depression (LTD) is one of the paradigms used in vivo or ex vivo for studying memory formation. In order to identify genes with potential relevance for memory formation we used mouse organotypic hippocampal slice cultures in which chemical LTD was induced by applications of 3,5-dihydroxyphenylglycine (DHPG). The induction of chemical LTD was robust, as monitored electrophysiologically. Gene expression analysis after chemical LTD induction was performed using cDNA microarrays containing >7,000 probes. The DHPG-induced expression of immediate early genes (c-fos, junB, egr1 and nr4a1) was subsequently verified by TaqMan polymerase chain reaction. Bioinformatic analysis suggested a common regulator element [serum response factor (SRF)/Elk-1 binding sites] within the promoter region of these genes. Indeed, here we could show a DHPG-dependent binding of SRF at the SRF response element (SRE) site within the promoter region of c-fos and junB. However, SRF binding to egr1 promoter sites was constitutive. The phosphorylation of the ternary complex factor Elk-1 and its localization in the nucleus of hippocampal neurones after DHPG treatment was shown by immunofluorescence using a phosphospecific antibody. We suggest that LTD leads to SRF/Elk-1-regulated gene expression of immediate early transcription factors, which could in turn promote a second broader wave of gene expression.

Effect of maternal protein restriction during pregnancy and postweaning high-fat feeding of diet-induced thermogenesis in adult mouse offspring

Purpose Prenatal undernutrition followed by postweaning feeding of a high-fat diet results in obesity in the adult offspring. In this study, we investigated whether diet-induced thermogenesis is altered as a result of such nutritional mismatch. Methods Female MF-1 mice were fed a normal protein (NP, 18 % casein) or a protein-restricted (PR, 9 % casein) diet throughout pregnancy and lactation. After weaning, male offspring of both groups were fed either a high-fat diet (HF; 45 % kcal fat) or standard chow (C, 7 % kcal fat) to generate the NP/C, NP/HF, PR/C and PR/HF adult offspring groups (n = 7–11 per group). Results PR/C and NP/C offspring have similar body weights at 30 weeks of age. Postweaning HF feeding resulted in significantly heavier NP/HF offspring (P < 0.01), but not in PR/HF offspring, compared with their chow-fed counterparts. However, the PR/HF offspring exhibited greater adiposity (P < 0.01) v the NP/HF group. The NP/HF offspring had increased energy expenditure and increased mRNA expression of uncoupling protein-1 and β-3 adrenergic receptor in the interscapular brown adipose tissue (iBAT) compared with the NP/C mice (both at P < 0.01). No such differences in energy expenditure and iBAT gene expression were observed between the PR/HF and PR/C offspring. Conclusions These data suggest that a mismatch between maternal diet during pregnancy and lactation, and the postweaning diet of the offspring, can attenuate diet-induced thermogenesis in the iBAT, resulting in the development of obesity in adulthood.

The N-terminal SH2 domain of Syk is required for (hem)ITAM, but not integrin, signaling in mouse platelets

We have used a novel knockin mouse to investigate the effect of disruption of phosphotyrosine binding of the N-terminal SH2 domain of Syk on platelet activation by GPVI, CLEC-2, and integrin αIIbβ3. The Syk(R41Afl/fl) mouse was crossed to a PF4-Cre(+) mouse to induce expression of the Syk mutant in the megakaryocyte/platelet lineage. Syk(R41Afl/fl;PF4-Cre) mice are born at approximately 50% of the expected frequency and have a similar phenotype to Syk(fl/fl;PF4-Cre) mice, including blood-lymphatic mixing and chyloascites. Anastomosis of the venous and lymphatic vasculatures can be seen in the mesenteric circulation accounting for rapid and continuous mixing of the 2 vasculatures. Platelet activation by CLEC-2 and GPVI is abolished in Syk(R41Afl/fl;PF4-Cre) platelets. Syk phosphorylation on Tyr519/20 is blocked in CLEC-2-stimulated platelets, suggesting a model in which binding of Syk via its N-terminal SH2 domain regulates autophosphorylation. In contrast, outside-in signaling by integrin αIIbβ3 is not altered, but it is inhibited in the presence of inhibitors of Src and Syk tyrosine kinases. These results demonstrate that αIIbβ3 regulates Syk through an ITAM-independent pathway in mice and provide novel insight into the course of events underlying Syk activation and hemITAM phosphorylation by CLEC-2.

Differential roles of the PKC novel isoforms, PKCδ and PKCε, in mouse and human platelets

Background Increasing evidence suggests that individual isoforms of protein kinase C (PKC) play distinct roles in regulating platelet activation. Methodology/Principal Findings In this study, we focus on the role of two novel PKC isoforms, PKCδ and PKCε, in both mouse and human platelets. PKCδ is robustly expressed in human platelets and undergoes transient tyrosine phosphorylation upon stimulation by thrombin or the collagen receptor, GPVI, which becomes sustained in the presence of the pan-PKC inhibitor, Ro 31-8220. In mouse platelets, however, PKCδ undergoes sustained tyrosine phosphorylation upon activation. In contrast the related isoform, PKCε, is expressed at high levels in mouse but not human platelets. There is a marked inhibition in aggregation and dense granule secretion to low concentrations of GPVI agonists in mouse platelets lacking PKCε in contrast to a minor inhibition in response to G protein-coupled receptor agonists. This reduction is mediated by inhibition of tyrosine phosphorylation of the FcRγ-chain and downstream proteins, an effect also observed in wild-type mouse platelets in the presence of a PKC inhibitor. Conclusions These results demonstrate a reciprocal relationship in levels of the novel PKC isoforms δ and ε in human and mouse platelets and a selective role for PKCε in signalling through GPVI.

Three dimensional analysis of cardiovascular development in mouse embryos using X-ray microcomputed tomography

Micro-computed tomography (μCT) has been successfully used to study the cardiovascular system of mouse embryos in situ. With the use of barium as a suitable contrast agent, blood vessels have been imaged and analysed quantitatively such as blood volume and vessel sizes on embryos of ages 14.5 to 16.5 days old. The advantage of using this imaging modality is that it has provided three dimensional information whilst leaving samples intact for further study.

CLEC-2-dependent activation of mouse platelets is weakly inhibited by cAMP but not by cGMP

The present results demonstrate that platelet adhesion and activation on CLEC-2 ligands or LECs is maintained in the presence of PGI2 and NO.

Investigating mechanisms underpinning the detrimental impact of a high-fat diet in the developing and adult hypermuscular myostatin null mouse

Background: Obese adults are prone to develop metabolic and cardiovascular diseases. Furthermore, over-weight expectant mothers give birth to large babies who also have increased likelihood of developing metabolic and cardiovascular diseases. Fundamental advancements to better understand the pathophysiology of obesity are critical in the development of anti-obesity therapies not only for this but also future generations. Skeletal muscle plays a major role in fat metabolism and much work has focused in promoting this activity in order to control the development of obesity. Research has evaluated myostatin inhibition as a strategy to prevent the development of obesity and concluded in some cases that it offers a protective mechanism against a high-fat diet. Results: We hypothesised that myostatin inhibition should protect not only the mother but also its developing foetus from the detrimental effects of a high-fat diet. Unexpectedly, we found muscle development was attenuated in the foetus of myostatin null mice raised on a high-fat diet. We therefore re-examined the effect of the high-fat diet on adults and found myostatin null mice were more susceptible to diet-induced obesity through a mechanism involving impairment of inter-organ fat utilization. Conclusions: Loss of myostatin alters fatty acid uptake and oxidation in skeletal muscle and liver. We show that abnormally high metabolic activity of fat in myostatin null mice is decreased by a high-fat diet resulting in excessive adipose deposition and lipotoxicity. Collectively, our genetic loss-of-function studies offer an explanation of the lean phenotype displayed by a host of animals lacking myostatin signalling. Keywords: Muscle, Obesity, High-fat diet, Metabolism, Myostatin

Muscular weakness in the mdx mouse.

mdx mice are believed to be virtually free from neuromuscular symptoms, despite the presence of a degenerative/regenerative process that involves all skeletal muscles. We analyzed both the spontaneous motility and treadmill motor activity of mdx mice aged 15 days to 6 months. Our results indicate that there is an early period, between the end of the second and up to the fifth week of life, when mdx mice experience extreme weakness. After this critical period, both spontaneous motility and endurance of mdx mice, although lower than those of controls, do not show statistically significant differences up to 6 months of age. We also carried out a detailed histological analysis of proximal and distal muscle groups in mdx mice during this early critical motility period. The occurrence of extensive necrosis followed by regeneration and involving proximal muscles before distal ones was documented in mice as young as 16-17 days of age and reached a peak at day 18. We conclude that dystrophin deficiency induces muscle degeneration and significant weakness in mdx mice, but only in an early period. Later on, during development, mdx mice adapt to the lack of this protein and do not show detectable in vivo functional muscle impairment up to 6 months of age.

Thyroid hormones regulate anxiety in the male mouse

Thyroid hormone levels are implicated in mood disorders in the adult human but the mechanisms remain unclear partly because, in rodent models, more attention has been paid to the consequences of perinatal hypo and hyperthyroidism. Thyroid hormones act via the thyroid hormone receptor (TR) alpha and beta isoforms, both of which are expressed in the limbic system. TR's modulate gene expression via both unliganded and liganded actions. Though the thyroid hormone receptor (TR) knockouts and a transgenic TRalpha1 knock-in mouse have provided us valuable insight into behavioral phenotypes such as anxiety and depression, it is not clear if this is because of the loss of unliganded actions or liganded actions of the receptor or due to locomotor deficits. We used a hypothyroid mouse model and supplementation with tri-iodothyronine (T3) or thyroxine (T4) to investigate the consequences of dysthyroid hormone levels on behaviors that denote anxiety. Our data from the open field and the light-dark transition tests suggest that adult onset hypothyroidism in male mice produces a mild anxiogenic effect that is possibly due to unliganded receptor actions. T3 or T4 supplementation reverses this phenotype and euthyroid animals show anxiety that is intermediate between the hypothyroid and thyroid hormone supplemented groups. In addition, T3 but not T4 supplemented animals have lower spine density in the CA1 region of the hippocampus and in the central amygdala suggesting that T3-mediated rescue of the hypothyroid state might be due to lower neuronal excitability in the limbic circuit.

Consumption of mate tea (Ilex paraguariensis) decreases the oxidation of unsaturated fatty acids in mouse liver

Mate (Ilex paraguariensis) is rich in polyphenolic compounds, which are thought to contribute to the health benefits of tea. Mate tea was administered orally to mice at a dose of 0.5, 1.0 or 2.0 g/kg for 60 d, and changes both in serum lipid concentration and fatty acid composition of liver and kidney were examined. The effects of mate tea on serum and tissue lipid peroxidation were assessed by the evaluation of thiobarbituric acid-reactive substances (TBARS). In tea-consuming mice, both MUFA (18: 1n-9) and PUFA (18: 2n-6 and 20: 4n-6) were increased (P<0.05) in the liver lipid (approximately 90 and 60%, respectively), whereas only MUFA (approximately 20%) were increased in the kidney lipid. The most altered PUFA class was n-6 PUFA, which increased by approximately 60-75 % (P<0.05). This difference in the fatty acid profile in the liver is reflected in the increased PUFA:SFA ratio. Consistent with these results, mice fed with mate tea had much lower TBARS in the liver. No differences (P>0.05) were found in the levels of serum cholesterol, HDL-cholesterol and TAG under the conditions of the present study. These results suggest that treatment with mate tea was able to protect unsaturated fatty acids from oxidation and may have selective protective effects within the body, especially on the liver.

Role of alpha 7 Nicotinic Acetylcholine Receptor in Calcium Signaling Induced by Prion Protein Interaction with Stress-inducible Protein 1

The prion protein (PrP(C)) is a conserved glycosylphosphatidyl-inositol-anchored cell surface protein expressed by neurons and other cells. Stress-inducible protein 1 (STI1) binds PrP(C) extracellularly, and this activated signaling complex promotes neuronal differentiation and neuroprotection via the extracellular signal-regulated kinase 1 and 2 (ERK1/2) and cAMP-dependent protein kinase 1 (PKA) pathways. However, the mechanism by which the PrPC-STI1 interaction transduces extracellular signals to the intracellular environment is unknown. We found that in hippocampal neurons, STI1-PrP(C) engagement induces an increase in intracellular Ca(2+) levels. This effect was not detected in PrP(C)-null neurons or wild-type neurons treated with an STI1 mutant unable to bind PrP(C). Using a best candidate approach to test for potential channels involved in Ca(2+) influx evoked by STI1-PrP(C), we found that alpha-bungarotoxin, a specific inhibitor for alpha 7 nicotinic acetylcholine receptor (alpha 7nAChR), was able to block PrP(C)-STI1-mediated signaling, neuroprotection, and neuritogenesis. Importantly, when alpha 7nAChR was transfected into HEK 293 cells, it formed a functional complex with PrP(C) and allowed reconstitution of signaling by PrP(C)-STI1 interaction. These results indicate that STI1 can interact with the PrP(C).alpha 7nAChR complex to promote signaling and provide a novel potential target for modulation of the effects of prion protein in neurodegenerative diseases.

Regulation of Multidrug Resistance-Associated Protein 2 by Calcium Signaling in Mouse Liver

Mu hiding resistance associated protein 2 (Mrp2) is a canalicular transporter responsible for organic anion secretion into bile. Mrp2 activity is regulated by insertion into the plasma membrane; however, the factors that control this are not understood. Calcium (Ca(2+)) signaling regulates exocytosis of vesicles in most cell types, and the type II inositol 1,4,5-triphosphate receptor (InsP(3)R2) regulates Ca(2+) release in the canalicular region of hepatocytes. However, the role of InsP(3)R2 and of Ca(2+) signals in canalicular insertion and function of Mrp2 is not known. The aim of this study was to determine the role of InsP(3)R2-mediated Ca(2+) signals in targeting Mrp2 to the canalicular membrane. Livers, isolated hepatocytes, and hepatocytes in collagen sandwich culture from wild-type (WT) and InsP(3)R2 knockout (KO) mice were used for western blots, confocal immunofluorescence, and time-lapse imaging of Ca(2+) signals and of secretion of a fluorescent organic anion. Plasma membrane insertion of green fluorescent protein (GFP)-Mrp2 expressed in HepG2 cells was monitored by total internal reflection microscopy. InsP(3)R2 was concentrated in the canalicular region of WT mice but absent in InsP(3)R2 KO livers, whereas expression and localization of InsP(3)R1 was preserved, and InsP(3)R3 was absent from both WT and KO livers. Ca(2+) signals induced by either adenosine triphosphate (ATP) or vasopressin were impaired in hepatocytes lacking InsP(3)R2. Canalicular secretion of the organic anion 5-chloromethylfluorescein diacetate (CMFDA) was reduced in KO hepatocytes, as well as in WT hepatocytes treated with 1,2-bis(o-aminophenoxy)ethane-N,N,N`,N`-tetra-acetic acid (BAPTA). Moreover, the choleretic effect of tauroursodeoxycholic acid (TUDCA) was impaired in InsP(3)R2 KO mice. Finally, ATP increased GFP-Mrp2 fluorescence in the plasma membrane of HepG2 cells, and this also was reduced by BAPTA. Conclusion: InsP(3)R2-mediated Ca(2+) signals enhance organic anion secretion into bile by targeting Mrp2 to the canalicular membrane. (HEPATOLOGY 2010;52:327-337)

Age-dependent changes in adenosine A(1) receptor distribution and density within the nucleus tractus solitarii of normotensive and hypertensive rats

This study shows the distribution and density of adenosine A1 receptor (A(1)R) within the nucleus tractus solitarii (NTS) of Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) from birth to adulthood (1, 15, 30 and 90 days old). The NTS shows heterogeneous distribution of A(1)R in dorsomedial/dorsolateral, subpostremal and medial/intermediate subnuclei. A(1)R decrease from rostral to caudal within dorsomedial/dorsolateral subnucleus in 15-, 30- and 90-day-old WKY and SHR. A(1)R increase from rostral to caudal subpostremal subnucleus in 30- and 90-day-old WKY, and in 15-, 30- and 90-day-old SHR. Furthermore, A(1)Rs are increased in SHR as compared with WKY within dorsomedial/dorsolateral in 30- and 90-day-old and within subpostremal of 15-, 30- and 90-day-old rats. Finally, A(1)Rs increase from 1- to 30-day-old rats. Medial/intermediate did not show any changes in A(1)R from rostral to caudal levels, age or strain. In summary, our result highlights the importance of A1 adenosine system regarding the neural control of blood pressure and the development of hypertension.

Variety matters: adaptive genetic diversity and parasite load in two mouse opossums from the Brazilian Atlantic forest

The adaptive potential of a species to a changing environment and in disease defence is primarily based on genetic variation. Immune genes, such as genes of the major histocompatibility complex (MHC), may thereby be of particular importance. In marsupials, however, there is very little knowledge about natural levels and functional importance of MHC polymorphism, despite their key role in the mammalian evolution. In a previous study, we discovered remarkable differences in the MHC class II diversity between two species of mouse opossums (Gracilinanus microtarsus, Marmosops incanus) from the Brazilian Atlantic forest, which is one of the most endangered hotspots for biodiversity conservation. Since the main forces in generating MHC diversity are assumed to be pathogens, we investigated in this study gastrointestinal parasite burden and functional associations between the individual MHC constitution and parasite load. We tested two contrasting scenarios, which might explain differences in MHC diversity between species. We predicted that a species with low MHC diversity would either be under relaxed selection pressure by low parasite diversity (`Evolutionary equilibrium` scenario), or there was a recent loss in MHC diversity leading to a lack of resistance alleles and increased parasite burden (`Unbalanced situation` scenario). In both species it became apparent that the MHC class II is functionally important in defence against gastrointestinal helminths, which was shown here for the first time in marsupials. On the population level, parasite diversity did not markedly differ between the two host species. However, we did observe considerable differences in the individual parasite load (parasite prevalence and infection intensity): while M. incanus revealed low MHC DAB diversity and high parasite load, G. microtarsus showed a tenfold higher population wide MHC DAB diversity and lower parasite burden. These results support the second scenario of an unbalanced situation.

Cell coupling in mouse pancreatic beta-cells measured in intact islets of Langerhans

The perforated whole-cell configuration of the patch-clamp technique was applied to functionally identified beta-cells in intact mouse pancreatic islets to study the extent of cell coupling between adjacent beta-cells. Using a combination of current- and voltage-clamp recordings, the total gap junctional conductance between beta-cells in an islet was estimated to be 1.22 nS. The analysis of the current waveforms in a voltage-clamped cell ( due to the. ring of an action potential in a neighbouring cell) suggested that the gap junctional conductance between a pair of beta-cells was 0.17 nS. Subthreshold voltage-clamp depolarization (to -55 mV) gave rise to a slow capacitive current indicative of coupling between beta-cells, but not in non-beta-cells, with a time constant of 13.5 ms and a total charge movement of 0.2 pC. Our data suggest that a superficial beta-cell in an islet is in electrical contact with six to seven other beta-cells. No evidence for dye coupling was obtained when cells were dialysed with Lucifer yellow even when electrical coupling was apparent. The correction of the measured resting conductance for the contribution of the gap junctional conductance indicated that the whole-cell K(ATP) channel conductance (G(K,ATP)) falls from approximately 2.5 nS in the absence of glucose to 0.1 nS at 15 mM glucose with an estimated IC(50) of approximately 4 mM. Theoretical considerations indicate that the coupling between beta-cells within the islet is sufficient to allow propagation of [Ca(2+)](i) waves to spread with a speed of approximately 80 mu m s(-1), similar to that observed experimentally in confocal [Ca(2+)](i) imaging.