Cellular and subcellular localization of PDE10A, a striatum-enriched phosphodiesterase

PDE10A is a recently identified phosphodiesterase that is highly expressed by the GABAergic medium spiny projection neurons of the mammalian striatum. Inhibition of PDE10A results in striatal activation and behavioral suppression, suggesting that PDE10A inhibitors represent a novel class of antipsychotic agents. In the present studies we further elucidate the localization of this enzyme in striatum of rat and cynomolgus monkey. We find by confocal microscopy that PDE10A-like immunoreactivity is excluded from each class of striatal interneuron. Thus, the enzyme is restricted to the medium spiny neurons. Subcellular fractionation indicates that PDE10A is primarily membrane bound. The protein is present in the synaptosomal fraction but is separated from the postsynaptic density upon solubilization with 0.4% Triton X-100. Immuno-electron microscopy of striatum confirms that PDE10A is most often associated with membranes in dendrites and spines. Immuno-gold particles are observed on the edge of the postsynaptic density but not within this structure. Our studies indicate that PDE10A is associated with post-synaptic membranes of the medium spiny neurons, suggesting that the specialized compartmentation of PDE10A enables the regulation of intracellular signaling from glutamatergic and dopaminergic inputs to these neurons.

A luciferase transgenic mouse model: visualization of prostate development and its androgen responsiveness in live animals

Numerous mouse models of prostate carcinogenesis have been developed, but hitherto there has been no model in which the prostate gland could be imaged in live animals. The transgenic model generated here targeted mouse prostate gland using a firefly luciferase enzyme under the control of a small but highly active and specific supra prostate-specific antigen (sPSA) promoter. We evaluated postnatal prostate development, involution and androgen-induced restoration of prostate growth in adult transgenic mice using bioluminescence imaging. Results of our study showed that: (i) the prostate gland of male offspring did not yield a significant bioluminescence signal until after sexual maturity. Luciferase was detected in the luminal epithelial cells of the ventral and dorsolateral lobes of the prostate gland and caput epididymis, with little or no activity in 18 other organs evaluated. (ii) While a constant high level of bioluminescence was detected in the mouse prostate from 5 to 35 weeks of age, a slight drop in bioluminescence was detected at 36 to 54 weeks. (iii) Upon castration, the luciferase activity signal associated with mouse prostate detected by a cooled charge-coupled device camera was dramatically reduced. This signal could be rapidly restored to pre-castration levels after androgen administration. Androgen-induced luciferase activity subsided to nearly basal levels 5 days following the last injection. These data demonstrate that a bioluminescent mouse model with luciferase activity restricted to the prostate gland under the control of a (sPSA) promoter can be used on a real-time basis in live animals to investigate the development and responsiveness of the prostate gland to exogenously administered androgen. This model can be extended to detect the responsiveness of the prostate gland to therapy and used as a founder strain to visualize tumors in hosts with different genetic backgrounds.

Enhanced Maturation and Functional Capacity of Dendritic Cells Induced by Mannosylated L2 Domain of ErbB2 Receptor

The nature of antigens and functional state of dendritic cells (DC) are important in antigen presentation. The ability of DC for the induction of T-cell responses is promoted by maturation. It has been confirmed that mannose receptors mediate highly efficient endocytosis and presentation of mannosylated proteins. In the present study, L2 domain of ErbB2 ectodomain was expressed in Escherichia coli, purified and mannosylated. The maturation and functional capacity of DC induced by mannosylated L2 (mL2) protein were investigated. The results showed that L2 protein could induce DC maturation, which was accompanied by elevated expression of MHC and co-stimulatory molecules. The effect of mL2 protein on DC maturation was more remarkable than that of non-mL2 proteins. Uptake of mL2 antigens by DC was more efficient. Furthermore, the T cells can be stimulated to proliferate in vitro and secrete Th1 and Th2 cytokines. Higher levels of both IFN-gamma and IL-10 were detected from the T cells stimulated by mL2-pulsed DC, suggesting a concurrent activation of CD4+ and CD8+ T cells. The results demonstrated that L2 domain of ErbB2 receptor is an immunodominant molecule. The mL2 domain of ErbB2 can induce an enhanced maturation and functional capacity of DC. It may become an effective strategy to induce anti-ErbB2 response.

Apolipoprotein J (clusterin) activates rodent microglia in vivo and in vitro

Apolipoprotein J (apoJ; also known as clusterin and sulfated glycoprotein (SGP)-2) is associated with senile plaques in degenerating regions of Alzheimer's disease brains, where activated microglia are also prominent. We show a functional link between apoJ and activated microglia by demonstrating that exogenous apoJ activates rodent microglia in vivo and in vitro. Intracerebroventricular infusion of purified human plasma apoJ ( approximately 4 microg over 28 days) activated parenchymal microglia to a phenotype characterized by enlarged cell bodies and processes (phosphotyrosine immunostaining). In vitro, primary rat microglia were also activated by apoJ, with changes in morphology and induction of major histocompatibility complex class II (MHCII) antigen. ApoJ increased the secretion of reactive nitrogen intermediates in a dose-dependent manner (EC(50) 112 nm), which was completely blocked by aminoguanidine (AG), a nitric oxide synthase inhibitor. However, AG did not block the increased secretion of tumor necrosis factor-alpha by apoJ (EC(50) 55 nm). Microglial activation by apoJ was also blocked by an anti-apoJ monoclonal antibody (G7), and by chemical cleavage of apoJ with 2-nitro-5-thiocyanobenzoate. The mitogen-activated protein kinase kinase and protein kinase C inhibitors PD98059 and H7 inhibited apoJ-mediated induction of reactive nitrogen intermediate secretion from cultured microglia. As a functional measure, apoJ-activated microglia secreted neurotoxic agents in a microglia-neuron co-culture model. We hypothesize that ApoJ contributes to chronic inflammation and neurotoxicity through direct effects on microglia.

The negative cell cycle regulator, Tob (transducer of ErbB-2), is a multifunctional protein involved in hippocampus-dependent learning and memory

Tob (transducer of ErbB2) is a negative cell cycle regulator with anti-proliferative activity in the periphery. Using a behavioral screening paradigm to look for novel gene functions in the brain, we identified Tob as a brain-expressed protein involved in learning and memory. Behavioral training of fear-conditioning triggered a transient elevation of Tob protein, which preceded the formation of long-term memory. Functional perturbation of Tob by intra-CA1 infusion of antisense oligonucleotides in rats impaired spatial learning and memory in the Morris water maze and long-term memory for contextual fear conditioning, two behavioral paradigms that require the hippocampus. Furthermore, long-term potentiation was suppressed by Tob antisense infusion into the CA1 region. Together, these results indicate that the negative cell cycle regulator Tob is a multifunctional protein involved in hippocampus-dependent learning and memory.

Young investigator award recipient

Dr. Zhongcong Xie started his research career in 1989 with graduate studies in behavioral pharmacology at Wayne State University, Detroit, Michigan.He moved to Harvard Medical School, Boston, Massachusetts in 1994 as a postdoctoral research fellow in both human and animal behavioral research. After years of research training, he returned to the clinical arena in 1997 as an Anesthesiology resident at Massachusetts General Hospital and Harvard Medical School. After completing anesthesia residency training, he decided to become a physician-scientist and continue his research in neuroscience. He joined the Genetics and Aging Research Unit at Massachusetts General Hospital and Harvard Medical School supervised by Dr. Rudolph Tanzi in the year 2000 to study Alzheimer's disease. His research on the neuropathogenesis of Alzheimer's disease has focused primarily on the molecular mechanisms underlying beta-amyloid precursor protein processing and beta-amyloid protein production, especially regarding regulation of the gamma-secretase complex.Additionally, his work has addressed the role of presenilin-related apoptosis in Alzheimer's disease.

Etomidate elevates intracellular calcium levels and promotes catecholamine secretion in bovine chromaffin cells

Etomidate, an intravenous imidazole general anaesthetic, is thought to produce anaesthesia by modulating or activating ionotropic Cl(-)-permeable GABA(A) receptors. Chromaffin cells are known to express functional GABA(A) receptors with properties similar to their neuronal counterparts. We have shown that activation of the GABA(A) receptors, with specific GABA(A) agonists, leads to cellular excitation. Our goal was to determine whether etomidate mimicked this response and to explore the functional consequences of this activation. Imaging experiments with the Ca(2+)-indicator dye fura-2 were used to assay [Ca(2+)](i). Bovine adrenal chromaffin cells were superfused with a variety of GABA(A)-selective drugs to determine their effects on [Ca(2+)](i). Amperometric measurements were used to assay catecholamine release in real-time. We show that bovine adrenal chromaffin cells were excited by etomidate at clinically relevant concentrations. Etomidate directly activated GABA(A) receptors found in chromaffin cells thereby elevating [Ca(2+)](i). The effects of etomidate were mimicked by the specific GABA(A) agonist muscimol and blocked by the specific antagonist bicuculline. Our data show that low concentrations of etomidate modulated GABA(A) receptor activation by muscimol. Blockade of voltage-dependent Ca(2+) channels prevented the elevation of [Ca(2+)](i) by GABA. Application of etomidate directly to the chromaffin cells elicited robust catecholamine secretion from these cells. The data indicate that clinically relevant concentrations of etomidate can directly activate GABA(A) receptors, which, due to the positive anion equilibrium potential, depolarizes chromaffin cells. This depolarization activates voltage-dependent Ca(2+) channels thereby stimulating catecholamine release. Our data suggest that circulating catecholamine levels may be elevated after etomidate application.

Sensitivity of 14-3-3 protein test varies in subtypes of sporadic Creutzfeldt-Jakob disease

BACKGROUND

The increase of the 14-3-3 protein in CSF is used as a diagnostic test in Creutzfeldt-Jakob disease (CJD), but the sensitivity and specificity of the 14-3-3 test are disputed. One reason for the dispute may be the recently established heterogeneity of sporadic CJD. The relationship between CSF 14-3-3 protein and sporadic CJD subtypes, distinguished by electrophoretic mobility of proteinase K-resistant prion protein (PrP(Sc)) and genotype at codon 129 of the prion protein gene, has not been elucidated.

METHODS

The authors examined the 14-3-3 protein test in 90 patients with sporadic CJD. PrP(Sc) type (type 1 or type 2) and the genotype at polymorphic codon 129 were determined in each patient. Mutations were excluded by prion gene sequencing.

RESULTS

The authors' findings indicate that the sensitivity of the 14-3-3 test is higher in patients with molecular features of the classic sporadic CJD than in patients with the nonclassic CJD subtypes. The difference appears to be related to the PrP(Sc) type and not to the codon 129 genotype. Disease duration before 14-3-3 testing might also have an influence because it was shorter in classic sporadic CJD.

CONCLUSION

The Creutzfeldt-Jakob disease clinical subtype should be considered when interpreting results of the 14-3-3 test.

25 Hydroxyvitamin D 1 alpha-hydroxylase is required for optimal epidermal differentiation and permeability barrier homeostasis

Keratinocytes express high levels of 25OHD 1alpha-hydroxylase (1OHase). The product of this enzyme, 1,25-dihydroxyvitamin D (1,25(OH)(2)D), promotes the differentiation of keratinocytes in vitro suggesting an important role for this enzyme in epidermal differentiation. To test whether 1OHase activity is essential for keratinocyte differentiation in vivo we examined the differentiation process in mice null for the expression of the 1alphaOHase gene (1alphaOHase(-/-)). Heterozygotes for the null allele were bred, and the progeny genotyped by PCR. The epidermis of the 1alphaOHase(-/-) animals and their wild-type littermates (1alphaOHase(+/+)) were examined by histology at the light and electron microscopic level, by immunocytochemistry for markers of differentiation, and by function examining the permeability barrier using transepidermal water loss (TEWL). No gross epidermal phenotype was observed; however, immunocytochemical assessment of the epidermis revealed a reduction in involucrin, filaggrin, and loricrin-markers of differentiation in the keratinocyte and critical for the formation of the cornified envelope. These observations were confirmed at the electron microscopic level, which showed a reduction in the F (containing filaggrin) and L (containing loricrin) granules and a reduced calcium gradient. The functional significance of these observations was tested using TEWL to evaluate the permeability barrier function of the epidermis. Although TEWL was normal in the basal state, following disruption of the barrier using tape stripping, the 1alphaOHase(-/-) animals displayed a markedly delayed recovery of normal barrier function. This delay was associated with a reduction in lamellar body secretion and a failure to reform the epidermal calcium gradient. Thus, the 25OHD 1OHase is essential for normal epidermal differentiation, most likely by producing the vitamin D metabolite, 1,25(OH)(2)D, responsible for inducing the proteins regulating calcium levels in the epidermis that are critical for the generation and maintenance of the barrier.

Calcium and 1,25(OH)2D: interacting drivers of epidermal differentiation

Both calcium and 1,25(OH)(2)D promote the differentiation of keratinocytes in vitro. The autocrine or paracrine production of 1,25(OH)(2)D by keratinocytes combined with the critical role of the epidermal calcium gradient in regulating keratinocyte differentiation in vivo suggest the physiologic importance of this interaction. The interactions occur at a number of levels. Calcium and 1,25(OH)(2)D synergistically induce involucrin, a protein critical for cornified envelope formation. The involucrin promoter contains an AP-1 site essential for calcium and 1,25(OH)(2)D induction and an adjacent VDRE essential for 1,25(OH)(2)D but not calcium induction. Calcium regulates coactivator complexes that bind to the Vitamin D receptor (VDR). Nuclear extracts from cells grown in low calcium contain an abundance of DRIP(205), whereas calcium induced differentiation leads to reduced DRIP(205) and increased SRC 3 which replaces DRIP in its binding to the VDR. In vivo models support the importance of 1,25(OH)(2)D-calcium interactions in epidermal differentiation. The epidermis of 1alphaOHase null mice fails to form a normal calcium gradient, has reduced expression of proteins critical for barrier function, and shows little recovery of the permeability barrier when disrupted. Thus in vivo and in vitro, calcium and 1,25(OH)(2)D interact at multiple levels to regulate epidermal differentiation.

Mice lacking 25OHD 1alpha-hydroxylase demonstrate decreased epidermal differentiation and barrier function

Keratinocytes express high levels of 25OHD 1alpha-hydroxylase (1OHase). The product of this enzyme, 1,25(OH)(2)D, promotes the differentiation of keratinocytes in vitro. To test whether 1OHase activity is essential for keratinocyte differentiation in vivo we examined the differentiation process in mice null for the expression of the 1alphaOHase gene (1alphaOHase(-/-)) by light and electron microscopy, by immunocytochemistry for markers of differentiation, by ion capture cytochemistry for calcium localization, and by function using transepidermal water loss (TEWL) to assess barrier integrity. Levels of involucrin, filaggrin, and loricrin-markers of differentiation in the keratinocyte and critical for the formation of the cornified envelope-were reduced in the epidermis of 1alphaOHase(-/-) mice. Calcium in the outer epidermis was reduced with loss of the calcium gradient from stratum basale to stratum granulosum. TEWL was normal in the resting state, but following disruption of the barrier, 1alphaOHase(-/-) mice had a markedly prolonged recovery of barrier function associated with a reduction in lamellar body secretion and a failure to reform the calcium gradient. Thus 1,25(OH)(2)D is essential for normal epidermal differentiation, most likely by inducing the proteins and mediating the calcium signaling in the epidermis required for the generation and maintenance of the barrier.

Role of Cl- co-transporters in the excitation produced by GABAA receptors in juvenile bovine adrenal chromaffin cells

GABA is the primary inhibitory neurotransmitter in the adult mammalian brain. However, in neonatal animals, activation of Cl(-)-permeable GABA receptors is excitatory and appears to depend on the expression of a Na(+)-K(+)-2Cl- cotransporter (NKCC) that elevates intracellular Cl- levels, leading to a depolarized Cl- equilibrium potential (ECl). The change from excitation to inhibition appears to involve the expression of the K+/Cl- co-transporter, KCC2, which lowers intracellular Cl- levels resulting in a hyperpolarized ECl. In this study, we show that bovine chromaffin cells from 4- to 5-mo-old animals are excited by GABA. Activation of GABAA receptors depolarizes the cells, opens voltage-dependent Ca2+ channels, elevates [Ca2+]i, and promotes the release of catecholamines. Blockade of voltage-dependent Ca2+ channels prevents the elevation of [Ca2+]i by GABA. The extrapolated anion reversal potential in these cells is approximately -28 mV, indicating a resting intracellular anion concentration of approximately 50 mM. Expression of KCC2 protein was not detected in the juvenile chromaffin cells. In contrast, clear expression of NKCC1 was observed. Blockade of NKCC1 should reduce the intracellular Cl- concentration and hyperpolarize ECl. Bumetanide, an NKCC1 blocker, reduced the elevation of [Ca2+]i by GABA. In some cells, activation of GABAA receptors inhibits responses to excitatory neurotransmitters, even though GABA itself is depolarizing. Co-activation of cholinergic and GABAA receptors in chromaffin cells produced elevations in [Ca2+]i that were comparable to those produced by cholinergic receptors alone. Our data showing the selective expression of chloride co-transporters and the resulting strongly depolarized anion reversal potential may help explain how activation of GABAA receptors causes sufficient excitation to elicit catecholamine release from chromaffin cells.

Inhibition of phosphatidylinositol 3-kinase dephosphorylates BAD and promotes apoptosis in myeloid leukemias

The phosphatidylinositol 3-kinase (PI3K)/AKT protein kinase pathway is involved in cell growth, proliferation, and apoptosis. The functional activation of PI3K/AKT provides survival signals and blockade of this pathway may facilitate cell death. Downstream targets of PI3K-AKT include the proapoptotic protein BAD, caspase-9, NF-kappaB, and Forkhead. We have previously reported that BAD is constitutively phosphorylated in primary acute myeloid leukemia (AML) cells, a post-transcriptional modification, which inactivates its proapoptotic function. In this study, we tested the hypothesis that the inhibition of PI3K by LY294002 results in the dephosphorylation of AKT and BAD, and thus promote leukemia cell apoptosis. We investigated the effects of LY294002 in megakaryocytic leukemia-derived MO7E cells, primary AML and normal bone marrow progenitor cells. In MO7E cells, LY294002 reduced AKT kinase activity, induced dephosphorylation of AKT and BAD, and increased apoptosis. Concomitant inhibition of mitogen-activated protein kinase signaling or combination with all-trans retinoic acid further enhanced apoptosis of leukemic cells. In primary AML samples, clonogenic cell growth was significantly reduced. Normal hematopoietic progenitors were less affected, suggesting preferential targeting of leukemia cells. In conclusion, the data suggest that the inhibition of the PI3K/AKT signaling pathway restores apoptosis in AML and may be explored as a novel target for molecular therapeutics in AML.

Vitamin D regulated keratinocyte differentiation: role of coactivators

1,25 Dihydroxyvitamin D (1,25(OH)(2)D) regulates the differentiation of keratinocytes. 1,25(OH)(2)D raises intracellular free calcium (Cai) as a necessary early step toward stimulating differentiation. 1,25(OH)(2)D induces the calcium sensing receptor (CaR) in keratinocytes and enhances the calcium response of these cells. Activation of the CaR by calcium increases intracellular free calcium by a mechanism involving phospholipase C (PLC) cleavage of phosphatidylinositolbisphosphate into inositoltrisphosphate (IP(3)) and diacylglycerol (DG). 1,25(OH)(2)D induces the family of PLCs. PLC-gamma1 has a DR6 VDRE in its promoter which binds and is activated by VDR/RAR rather than VDR/RXR. The involucrin gene, which encodes a critical component of the cornified envelope, contains a DR3 VDRE in its promoter that acts in conjunction with a nearby AP-1 site. The sequential regulation of these genes is critical for the differentiation process. In undifferentiated keratinocytes, the VDR binds preferentially to the DRIP complex of coactivators. However, with differentiation DRIP 205 is no longer produced, and the VDR switches partners to the SRC family (SRC2 and 3). These studies suggest that at least part of the sequential activation of genes required during keratinocyte differentiation is regulated by the change (availability) of these different coactivator complexes.

[Antagonism of the novel cholinolytic tricyclopinate on nicotinic and muscarinic cholinergic receptors]

Tricyclopinate hydrochloride(TCPN.HCl) and methiodide(TCPN.CH3I) have been identified as new chemical entities. The effects of these two compounds on central and peripheral nicotinic and muscarinic cholinergic receptor activities were investigated. Excitation of the central nicotinic receptors by nicotine produced convulsions in mice. The dose-response curves of nicotine for producing convulsions were shifted rightward by TCPN.CH3I in a paralled manner. Excitation of the central muscarinic receptors by arecoline produced tremors in mice. TCPN.HCl was shown to prevent arecoline-induced tremors. In isolated guinea-pig ileum preparations. TCPN.HCl was found to antagonize nicotine-induced contractions due to excitation of ganglionic nicotinic receptors. In xenopus laevis embryo neuron-muscle co-cultured cells, TCPN.HCl blocked spontaneous miniature endplate currents, and showed preference to blocking the nicotinic receptor ion channels, which had a long open time, and high current amplitude. The anticholinergic effects of TCPN.CH3I were weaker than those of TCPN.HCl. In conclusion, TCPN.HCl has potent effects against nicotinic and muscarinic receptors in the central and periphery nervous systems.

[Protective effects of ischemic preconditioning on ischemia reperfusion injuries of kidney: experimental studies]

We studied the serum levels of SOD and creatinine(Cr) of venous blood and changes in renal tissue structures under electromicroscope in the ischemia referfusion(I/R), the ischemic preconditioning(PC1, PC2, PC3), and the control groups in rabbits. The results were that the serum levels of SOD and Cr in the I/R group were obviously higher than that in the PC and control groups after one-hour ischemia and one-hour reperfusion(P < 0.001). There were no significant difference in Cr levels between the PC2 and control groups; there were significant degenerate and necrotic changes under the electromicroscope in renal tissues in the I/R group, but there were no significant change in the PC and control groups. The results suggest that PC plays a role in protecting the kidney from injury induced by ischemia and reperfusion.