Inositol hexakisphosphate kinase-1 regulates behavioral responses via GSK3 signaling pathways

Glycogen synthase kinase 3 (GSK3), a prominent enzyme in carbohydrate metabolism, also has a major role in brain function. It is physiologically regulated by the kinase Akt, which phosphorylates GSK3 to inhibit catalytic activity. Inositol hexakisphosphate-1 (IP6K1) generates the inositol pyrophosphate diphosphoinositol pentakisphosphate (IP7), which physiologically inhibits Akt leading to enhanced GSK3 activity. We report that IP6K1 binds and stimulates GSK3 enzymatic activity in a non-catalytic fashion. Physiological relevance is evident in the inhibition of GSK3 activity in the brains of IP6K1-deleted mice. Behavioral alterations of IP6K1 knockout mice resemble those of GSK3 mutants. Accordingly, modulation of IP6K1-GSK3β interaction may exert beneficial effects in psychiatric disorders involving GSK3.

The unusual amino acid L-ergothioneine is a physiologic cytoprotectant

Ergothioneine (ET) is an unusual sulfur-containing derivative of the amino acid, histidine, which is derived exclusively through the diet. Although ET was isolated a century ago, its physiologic function has not been clearly established. Recently, a highly specific transporter for ET (ETT) was identified in mammalian tissues, which explains abundant tissue levels of ET and implies a physiologic role. Using RNA interference, we depleted cells of its transporter. Cells lacking ETT are more susceptible to oxidative stress, resulting in increased mitochondrial DNA damage, protein oxidation and lipid peroxidation. ETT is concentrated in mitochondria, suggesting a specific role in protecting mitochondrial components such as DNA from oxidative damage associated with mitochondrial generation of superoxide. In combating cytotoxic effects of pyrogallol, a known superoxide generator, ET is as potent as glutathione. Because of its dietary origin and the toxicity associated with its depletion, ET may represent a new vitamin whose physiologic roles include antioxidant cytoprotection.

Serine racemase binds to PICK1: potential relevance to schizophrenia

Accumulating evidence from both genetic and clinico-pharmacological studies suggests that D-serine, an endogenous coagonist to the NMDA subtype glutamate receptor, may be implicated in schizophrenia (SZ). Although an association of genes for D-serine degradation, such as D-amino acid oxidase and G72, has been reported, a role for D-serine in SZ has been unclear. In this study, we identify and characterize protein interacting with C-kinase (PICK1) as a protein interactor of the D-serine synthesizing enzyme, serine racemase (SR). The binding of endogenous PICK1 and SR requires the PDZ domain of PICK1. The gene coding for PICK1 is located at chromosome 22q13, a region frequently linked to SZ. In a case-control association study using well-characterized Japanese subjects, we observe an association of the PICK1 gene with SZ, which is more prominent in disorganized SZ. Our findings implicating PICK1 as a susceptibility gene for SZ are consistent with a role for D-serine in the disease.

Species, strain and developmental variations in hippocampal neuronal and endothelial nitric oxide synthase clarify discrepancies in nitric oxide-dependent synaptic plasticity

Nitric oxide (NO) has been implicated in long-term potentiation (LTP) in pyramidal neurons in cellular area 1 (CA1) of the hippocampus. However, considerable confusion exists about the exact role of NO, and the contribution of the endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) isoforms of NO synthase to NO-dependent LTP (NO-LTP), with results often varying, depending on the organism and experimental paradigm used. Using immunohistochemistry and in situ hybridization, we contrast NO synthase expression and activity in rat, mouse, and human hippocampus. nNOS is prominently expressed in all CA1 pyramidal cells of C57B6 mice and humans, while in rats and SV129 mice, its levels are much lower and restricted to the caudal hippocampus. By contrast, eNOS is restricted to endothelial cells. We observe N-methyl-D-aspartate-dependent citrulline production in pyramidal cells of mouse hippocampus, which is absent in nNOS(Delta/Delta) animals. Finally, we observe robust nNOS expression in human CA1 pyramidal cells.The considerable axial, developmental, strain and species-dependent variations in nNOS expression in CA1 pyramidal neurons can explain much of the variation observed in reports of NO-dependent LTP. Moreover, our data suggest that NO produced by eNOS in endothelial cells may play a paracrine role in modulating LTP.

Naturally occurring free D-aspartate is a nuclear component of cells in the mammalian hypothalamo-neurohypophyseal system

It is generally believed that only L-amino acids have a physiological role in species other than bacteria. Recently, the existence of some D-amino acids, particularly D-aspartate, in various organs of several higher animals has been reported. Here we demonstrate that naturally occurring free D-aspartate is localized subcellularly to the heterochromatin in the nucleoli (but not in either the dendrites or axonal terminals) of magnocellular neurosecretory neurons in the rat hypothalamus, and also of microglia and pericytes in the posterior pituitary. Our results imply that naturally occurring free D-aspartate might have a physiological role in nuclear function in mammals. The findings provide new insight for the biological function of D-stereoisomers of amino acids as well as the organization of the nucleus of at least some eukaryotic cells.

Identification and characterization of a novel inositol hexakisphosphate kinase

The inositol pyrophosphate disphosphoinositol pentakisphosphate (PP-InsP(3)/InsP(7)) is formed in mammals by two recently cloned inositol hexakiphosphate kinases, InsP(6)K1 and InsP(6)K2 (Saiardi, A., Erdjument-Bromage, H., Snowman, A. M., Tempst, P., and Snyder, S. H. (1999) Curr. Biol. 9, 1323-1326). We now report the identification, cloning, and characterization of a third InsP(7) forming enzyme designated InsP(6)K3. InsP(6)K3 displays 50 and 45% sequence identity to InsP(6)K1 and InsP(6)K2, respectively, with a smaller mass (46 kDa) and a more basic character than the other two enzymes. InsP(6)K3 is most enriched in the brain where its localization resembles InsP(6)K1 and InsP(6)K2. Intracellular disposition discriminates the three enzymes with InsP(6)K2 being exclusively nuclear, InsP(6)K3 predominating in the cytoplasm, and InsP(6)K1 displaying comparable nuclear and cytosolic densities.

Neural roles for heme oxygenase: contrasts to nitric oxide synthase

The heme oxygenase (HO) and nitric oxide (NO) synthase (NOS) systems display notable similarities as well as differences. HO and NOS are both oxidative enzymes using NADPH as an electron donor. The constitutive forms of the enzyme are differentially activated, with calcium entry stimulating NOS by binding to calmodulin, whereas calcium entry activates protein kinase C to phosphorylate and activate HO2. Although both NO and carbon monoxide (CO) stimulate soluble guanylyl cyclase to form cGMP, NO also S-nitrosylates selected protein targets. Both involve constitutive and inducible biosynthetic enzymes. However, functions of the inducible forms are virtual opposites. Macrophage-inducible NOS generates NO to kill other cells, whereas HO1 generates bilirubin to exert antioxidant cytoprotective effects and also provides cytoprotection by facilitating iron extrusion from cells. The neuronal form of HO, HO2, is also cytoprotective. Normally, neural NO in the brain seems to exert some sort of behavioral inhibition. However, excess release of NO in response to glutamate's N-methyl-d-aspartate receptor activation leads to stroke damage. On the other hand, massive neuronal firing during a stroke presumably activates HO2, leading to neuroprotective actions of bilirubin. Loss of this neuroprotection after HO inhibition by mutant forms of amyloid precursor protein may mediate neurotoxicity in Familial Alzheimer's Disease. NO and CO both appear to be neurotransmitters in the brain and peripheral autonomic nervous system. They also are physiologic endothelial-derived relaxing factors for blood vessels. In the gastrointestinal pathway, NO and CO appear to function as coneurotransmitters, both stimulating soluble guanylyl cyclase to cause smooth muscle relaxation.

GRAB: a physiologic guanine nucleotide exchange factor for Rab3A, which interacts with inositol hexakisphosphate kinase

Diphosphoinositol-pentakisphosphate (InsP7) and bis-diphosphoinositol tetrakisphosphate (InsP8) possess pyrophosphate bonds. InsP7 is formed from inositol hexakisphosphate (InsP6) by recently identified InsP6 kinases designated InsP6K1 and InsP6K2. We now report the identification, cloning, and characterization of a novel protein, GRAB (guanine nucleotide exchange factor for Rab3A), which interacts with both InsP6K1 and Rab3A, a Ras-like GTPase that regulates synaptic vesicle exocytosis. GRAB is a physiologic GEF (guanine nucleotide exchange factor) for Rab3A. Consistent with a role of Rab3A in synaptic vesicle exocytosis, GRAB regulates depolarization-induced release of dopamine from PC12 cells and nicotinic agonist-induced hGH release from bovine adrenal chromaffin cells. The association of InsP6K1 with GRAB fits with a role for InsP7 in vesicle exocytosis.

The biotin switch method for the detection of S-nitrosylated proteins

Many of the effects of nitric oxide are mediated by the direct modification of cysteine residues resulting in an adduct called a nitrosothiol. Here, we describe a novel method for detecting proteins that contain nitrosothiols. In this three-step procedure, nitrosylated cysteines are converted to biotinylated cysteines. Biotinylated proteins can then be detected by immunoblotting or can be purified by avidin-affinity chromatography. We include examples of the detection of S-nitrosylated proteins in brain lysates after in vitro S-nitrosylation, as well as the detection of endogenous S-nitrosothiols in selected neuronal proteins.

Differential neuronal localizations and dynamics of phosphorylated and unphosphorylated type 1 inositol 1,4,5-trisphosphate receptors

Type 1 inositol 1,4,5-trisphosphate receptors are phosphorylated by cyclic-AMP-dependent protein kinase A at serines 1589 and 1755, with serine 1755 phosphorylation greatly predominating in the brain. Inositol 1,4,5-trisphosphate receptor protein kinase A phosphorylation augments Ca(2+) release. To assess type 1 protein kinase A phosphorylation dynamics in the intact organism, we developed antibodies selective for either serine 1755 phosphorylated or unphosphorylated species. Immunohistochemical studies reveal marked variation in localization. For example, in the hippocampus the phosphorylated type 1 inositol 1,4,5-trisphosphate receptor is restricted to CA1, while the unphosphorylated receptor occurs ubiquitously in CA1-CA3 and dentate gyrus granule cells. Throughout the brain the phosphorylated type 1 inositol 1,4,5-trisphosphate receptor is selectively enriched in dendrites, while the unphosphorylated receptor predominates in cell bodies. Focal cerebral ischemia in rats and humans is associated with dephosphorylation of type 1 inositol 1,4,5-trisphosphate receptors, and glutamatergic excitation of cerebellar Purkinje cells mediated by ibogaine elicits dephosphorylation of type 1 inositol 1,4,5-trisphosphate receptors that precedes evidence of excitotoxic neuronal degeneration. We have demonstrated striking variations in regional and subcellular distribution of inositol 1,4,5-trisphosphate receptor phosphorylation that may influence normal physiological intracellular Ca(2+) signaling in rat and human brain. We have further shown that the subcellular distribution of inositol 1,4,5-trisphosphate receptor phosphorylation in neurons is regulated by excitatory neurotransmission, as well as excitotoxic insult and neuronal ischemia-reperfusion. Phosphorylation dynamics of type 1 inositol 1,4,5-trisphosphate receptors may modulate intracellular Ca(2+) release and influence the cellular response to neurotoxic insults.

Pharmacologic inhibition of poly(ADP-ribose) polymerase is neuroprotective following traumatic brain injury in rats

The nuclear enzyme poly(ADP-ribose) polymerase (PARP), which has been shown to be activated following experimental traumatic brain injury (TBI), binds to DNA strand breaks and utilizes nicotinamide adenine dinucleotide (NAD) as a substrate. Since consumption of NAD may be deleterious to recovery in the setting of CNS injury, we examined the effect of a potent PARP inhibitor, GPI 6150, on histological outcome following TBI in the rat. Rats (n = 16) were anesthetized, received a preinjury dose of GPI 6150 (30 min; 15 mg/kg, i.p.), subjected to lateral fluid percussion (FP) brain injury of moderate severity (2.5-2.8 atm), and then received a second dose 3 h postinjury (15 mg/kg, i.p.). Lesion area was examined using Nissl staining, while DNA fragmentation and apoptosis-associated cell death was assessed with terminal deoxynucleotidyl-transferase-mediated biotin-dUTP nick end labeling (TUNEL) with stringent morphological evaluation. Twenty-four hours after brain injury, a significant cortical lesion and number of TUNEL-positive/nonapoptotic cells and TUNEL-positive/apoptotic cells in the injured cortex of vehicle-treated animals were observed as compared to uninjured rats. The size of the trauma-induced lesion area was significantly attenuated in the GPI 6150-treated animals versus vehicle-treated animals (p < 0.05). Treatment of GPI 6150 did not significantly affect the number of TUNEL-positive apoptotic cells in the injured cortex. The observed neuroprotective effects on lesion size, however, offer a promising option for further evaluation of PARP inhibition as a means to reduce cellular damage associated with TBI.

Poly(ADP-ribose) polymerase-1 is required for efficient HIV-1 integration

Poly(ADP-ribose) polymerase-1 (PARP-1; EC ) is an abundant nuclear enzyme, activated by DNA strand breaks to attach up to 200 ADP-ribose groups to nuclear proteins. As retroviral infection requires integrase-catalyzed DNA strand breaks, we examined infection of pseudotyped HIV type I in fibroblasts from mice with a targeted deletion of PARP-1. Viral infection is almost totally abolished in PARP-1 knockout fibroblasts. This protection from infection reflects prevention of viral integration into the host genome. These findings suggest a potential for PARP inhibitors in therapy of HIV type I infection.

D-aspartate disposition in neuronal and endocrine tissues: ontogeny, biosynthesis and release

High levels of D-aspartate occur in the brain and endocrine glands, such as pineal, adrenal and pituitary. In the brain, D-aspartate levels are highest in embryonic and early postnatal stages. Notably high levels occur in the early postnatal cortical plate and subventricular zone of the cerebral cortical cultures, implying a role in development. In embryonic neuronal primary culture cells, we detected high levels of endogenous D-aspartate and demonstrated biosynthesis of [14C]D-aspartate using [14C]L-aspartate as precursor. Synthesis of D-aspartate in cell cultures is inhibited by amino-oxyacetic acid, an inhibitor of pyridoxal phosphate-dependent enzymes. In the rat adrenal medulla, D-aspartate is depleted by treatment of the animals with intraperitoneal nicotine injections. In adrenal slices, D-aspartate is released by depolarization with KCl or acetylcholine, implying physiological release by activation of the cholinergic innervation of the adrenal. Our characterization of D-aspartate ontogeny, biosynthesis and depolarization-induced release implies specific physiological roles for this amino acid.

Heme oxygenase-2 acts to prevent neuronal death in brain cultures and following transient cerebral ischemia

Heme oxygenase (HO) cleaves the heme ring to form biliverdin, which is rapidly reduced to bilirubin, carbon monoxide, and iron. HO1, the first form of the enzyme discovered, is an inducible protein, concentrated in tissues that are exposed to degrading red blood cells and stimulated by hemolysis and numerous other toxic perturbations to eliminate potentially toxic heme. By contrast, HO2 is constitutive and most highly concentrated in neural tissues. Carbon monoxide, formed from HO2, is a putative neurotransmitter in the brain and peripheral autonomic nervous system. HO1 regulates the efflux of potentially toxic iron from cells, as iron efflux is deficient in mice with targeted deletion of HO1 (HO1(-/-)), and transfection of HO1 facilitates iron efflux. Bilirubin appears to be a physiologic neuroprotectant. Activation of HO2 by phorbol esters, that stimulate protein kinase C to phosphorylate HO2, augments production of bilirubin which protects brain cultures from oxidative stress. Bilirubin itself in nanomolar concentrations is neuroprotective, while HO2 deletion (HO2(-/-)) leads to increased neurotoxicity in brain cultures and increased neural damage following transient cerebral ischemia in intact mice. Mechanisms whereby HO2 provides neuroprotection have not been clarified including whether protection is primarily associated with apoptotic or necrotic cell death. Moreover, the generality of neurotoxic stimuli influenced by HO2 has been unclear. We now demonstrate increased neuronal death in cerebellar granule cultures of HO2(-/-) mice with a selective augmentation of apoptotic death. We also demonstrate that HO2 transfection rescues apoptotic death. In intact mice, we show an increased incidence of apoptotic morphology in the penumbra area surrounding the infarct core in HO2(-/-) mice undergoing transient focal ischemia.

Mammalian inositol polyphosphate multikinase synthesizes inositol 1,4,5-trisphosphate and an inositol pyrophosphate

Using a consensus sequence in inositol phosphate kinase, we have identified and cloned a 44-kDa mammalian inositol phosphate kinase with broader catalytic capacities than any other member of the family and which we designate mammalian inositol phosphate multikinase (mIPMK). By phosphorylating inositol 4,5-bisphosphate, mIPMK provides an alternative biosynthesis for inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)]. mIPMK also can form the pyrophosphate disphosphoinositol tetrakisphosphate (PP-InsP(4)) from InsP(5). Additionally, mIPMK forms InsP(4) from Ins(1,4,5)P(3) and InsP(5) from Ins(1,3,4,5)P(4).

FKBP12, the 12-kDa FK506-binding protein, is a physiologic regulator of the cell cycle

FKBP12, the 12-kDa FK506-binding protein, is a ubiquitous abundant protein that acts as a receptor for the immunosuppressant drug FK506, binds tightly to intracellular calcium release channels and to the transforming growth factor beta (TGF-beta) type I receptor. We now demonstrate that cells from FKBP12-deficient (FKBP12(-/-)) mice manifest cell cycle arrest in G(1) phase and that these cells can be rescued by FKBP12 transfection. This arrest is mediated by marked augmentation of p21(WAF1/CIP1) levels, which cannot be further augmented by TGF-beta1. The p21 up-regulation and cell cycle arrest derive from the overactivity of TGF-beta receptor signaling, which is normally inhibited by FKBP12. Cell cycle arrest is prevented by transfection with a dominant-negative TGF-beta receptor construct. TGF-beta receptor signaling to gene expression can be mediated by SMAD, p38, and ERK/MAP kinase (extracellular signal-regulated kinase/mitogen-activated protein kinase) pathways. SMAD signaling is down-regulated in FKBP12(-/-) cells. Inhibition of ERK/MAP kinase fails to affect p21 up-regulation. By contrast, activated phosphorylated p38 is markedly augmented in FKBP12(-/-) cells and the p21 up-regulation is prevented by an inhibitor of p38. Thus, FKBP12 is a physiologic regulator of cell cycle acting by normally down-regulating TGF-beta receptor signaling.

Atypical neural messengers

Notions of what constitutes a neurotransmitter have changed markedly with the advent in the past decade of synaptic molecules, which satisfy key neurotransmitter criteria but differ radically from classical transmitters. Thus, NO and carbon monoxide are neither stored in synaptic vesicles nor released by exocytosis. These gases do not act via traditional receptors on postsynaptic membranes. In addition, zinc, stored together with glutamate in synaptic vesicles, appears to act as an 'antagonist' co-transmitter at the NMDA receptor, and although localized exclusively to glia, D-serine fulfills most neurotransmitter criteria as an endogenous ligand for the 'glycine' site of NMDA receptors.

Protein S-nitrosylation: a physiological signal for neuronal nitric oxide

Nitric oxide (NO) has been linked to numerous physiological and pathophysiological events that are not readily explained by the well established effects of NO on soluble guanylyl cyclase. Exogenous NO S-nitrosylates cysteine residues in proteins, but whether this is an important function of endogenous NO is unclear. Here, using a new proteomic approach, we identify a population of proteins that are endogenously S-nitrosylated, and demonstrate the loss of this modification in mice harbouring a genomic deletion of neuronal NO synthase (nNOS). Targets of NO include metabolic, structural and signalling proteins that may be effectors for neuronally generated NO. These findings establish protein S-nitrosylation as a physiological signalling mechanism for nNOS.

Pike. A nuclear gtpase that enhances PI3kinase activity and is regulated by protein 4.1N

While cytoplasmic PI3Kinase (PI3K) is well characterized, regulation of nuclear PI3K has been obscure. A novel protein, PIKE (PI3Kinase Enhancer), interacts with nuclear PI3K to stimulate its lipid kinase activity. PIKE encodes a 753 amino acid nuclear GTPase. Dominant-negative PIKE prevents the NGF enhancement of PI3K and upregulation of cyclin D1. NGF treatment also leads to PIKE interactions with 4.1N, which has translocated to the nucleus, fitting with the initial identification of PIKE based on its binding 4.1N in a yeast two-hybrid screen. Overexpression of 4.1N abolishes PIKE effects on PI3K. Activation of nuclear PI3K by PIKE is inhibited by the NGF-stimulated 4.1N translocation to the nucleus. Thus, PIKE physiologically modulates the activation by NGF of nuclear PI3K.

The calcineurin-binding protein cain is a negative regulator of synaptic vesicle endocytosis

During neurotransmitter release, exocytosed neurotransmitter vesicles are recycled by endocytosis, which involves the assembly of a complex of endocytic proteins. Assembly of endocytic proteins into a functional complex depends on their dephosphorylation by calcineurin, a calcium-sensitive protein phosphatase and the inhibitory target of immunosuppressive drugs cyclosporin A and FK506. Cain is a recently identified protein inhibitor of calcineurin. We now provide evidence that cain is a component of the endocytic protein complex. The proline-rich region of cain forms a stable association with the SH3 domain of amphiphysin 1. Using a transferrin uptake assay, we found that overexpression of cain in HEK293 cells blocks endocytosis as potently as expression of a dominant negative dynamin 1 construct. The use of other calcineurin inhibitors such as cyclosporin A and FK506 also blocks endocytosis. Since binding of cain to amphiphysin 1 does not affect amphiphysin's interaction with other endocytic proteins, our results suggest that cain negatively regulates synaptic vesicle endocytosis by inhibiting calcineurin activity, rather than sterically interfering with the assembly of the endocytic protein complex.

Novel neurotransmitters and their neuropsychiatric relevance

OBJECTIVE

The purpose of this review is to integrate insights regarding novel neurotransmitters or neuromodulators of neuropsychiatric significance.

METHOD

Evolving concepts of neurotransmitter criteria are reviewed in light of the unexpected properties displayed by recently identified transmitters.

RESULTS

Classic criteria for transmitters were based on the properties of acetylcholine but were markedly revised with the recognition of the catecholamines, serotonin, gamma-aminobutyric acid (GABA), and other amino acid transmitters and neuropeptides. Nitric oxide and carbon monoxide are notably atypical, as they are not stored in synaptic vesicles, are not released by exocytosis, and do not act at postsynaptic membrane receptor proteins. D-Serine, recently appreciated as the endogenous ligand for the glycine site of the glutamate N-methyl-D-aspartate (NMDA) receptor, overturns fundamental axioms of biology as well as those of neuroscience. It is a D-amino acid, and it is synthesized and stored in glia rather than neurons. Released glutamate acts on receptors on the protoplasmic astrocytes closely apposed to the synapse to release D-serine, which coactivates postsynaptic NMDA receptors together with glutamate. D-Serine is formed by serine racemase, which directly converts L-serine to D-serine. Inhibitors of this enzyme should reduce NMDA neurotransmission and might be therapeutic in stroke and other conditions associated with glutamate excitotoxicity.

CONCLUSIONS

The diversity of novel neurotransmitters and venues of their activity afford multiple opportunities for therapeutic intervention.

Regulation of rat magnocellular neurosecretory system by D-aspartate: evidence for biological role(s) of a naturally occurring free D-amino acid in mammals

Little evidence is available for the physiological function of D-amino acids in species other than bacteria. Here we demonstrate that naturally occurring freed -aspartate (D-Asp) is present in all magnocellular neurons of rat hypothalamus. The levels of this naturally occurring D-amino acid were elevated during lactation and returned to normal thereafter in the magnocellular neurosecretory system, which produces oxytocin, a hormone responsible for milk ejection during lactation. Intraperitoneal injections of D-Asp reproducibly increased oxytocin gene expression and decreased the concentration of circulating oxytocin in vivo. Similar changes were observed in the vasopressin system. These results provide evidence for the role(s) of naturally occurring free D-Asp in mammalian physiology. The findings argue against the conventional concept that only L-stereoisomers of amino acids are functional in higher species.

Amyloid precursor proteins inhibit heme oxygenase activity and augment neurotoxicity in Alzheimer's disease

Amyloid precursor protein (APP) generates the beta-amyloid peptide, postulated to participate in the neurotoxicity of Alzheimer's disease. We report that APP and APLP bind to heme oxygenase (HO), an enzyme whose product, bilirubin, is antioxidant and neuroprotective. The binding of APP inhibits HO activity, and APP with mutations linked to the familial Alzheimer's disease (FAD) provides substantially greater inhibition of HO activity than wild-type APP. Cortical cultures from transgenic mice expressing Swedish mutant APP have greatly reduced bilirubin levels, establishing that mutant APP inhibits HO activity in vivo. Oxidative neurotoxicity is markedly greater in cerebral cortical cultures from APP Swedish mutant transgenic mice than wild-type cultures. These findings indicate that augmented neurotoxicity caused by APP-HO interactions may contribute to neuronal cell death in Alzheimer's disease.

Interaction of amyloid precursor proteins and heme oxygenase

Amyloid precursor protein generates the beta-amyloid peptide and is a member of a multigene family that contains at least two other gene products, known as amyloid precursor-like proteins. Heme oxygenase is an enzyme whose products are antioxidant and neuroprotective. The authors report that amyloid precursor protein and amyloid precursor-like protein bind to heme oxygenase to inhibit its enzymatic activity. Our findings suggest that decreased neuroprotection caused by amyloid precursor protein-heme oxygenase interactions influences neurotoxicity in Alzheimer disease.

Dexras1: a G protein specifically coupled to neuronal nitric oxide synthase via CAPON

Because nitric oxide (NO) is a highly reactive signaling molecule, chemical inactivation by reaction with oxygen, superoxide, and glutathione competes with specific interactions with target proteins. NO signaling may be enhanced by adaptor proteins that couple neuronal NO synthase (nNOS) to specific target proteins. Here we identify a selective interaction of the nNOS adaptor protein CAPON with Dexras1, a brain-enriched member of the Ras family of small monomeric G proteins. We find that Dexras1 is activated by NO donors as well as by NMDA receptor-stimulated NO synthesis in cortical neurons. The importance of Dexras1 as a physiologic target of nNOS is established by the selective decrease of Dexras1 activation, but not H-Ras or four other Ras family members, in the brains of mice harboring a targeted genomic deletion of nNOS (nNOS-/-). We also find that nNOS, CAPON, and Dexras1 form a ternary complex that enhances the ability of nNOS to activate Dexras1. These findings identify Dexras1 as a novel physiologic NO effector and suggest that anchoring of nNOS to specific targets is a mechanism by which NO signaling is enhanced.

The inositol hexakisphosphate kinase family. Catalytic flexibility and function in yeast vacuole biogenesis

Saiardi et al. (Saiardi, A., Erdjument-Bromage, H., Snowman, A., Tempst, P., and Snyder, S. H. (1999) Curr. Biol. 9, 1323-1326) previously described the cloning of a kinase from yeast and two kinases from mammals (types 1 and 2), which phosphorylate inositol hexakisphosphate (InsP(6)) to diphosphoinositol pentakisphosphate, a "high energy" candidate regulator of cellular trafficking. We have now studied the significance of InsP(6) kinase activity in Saccharomyces cerevisiae by disrupting the kinase gene. These ip6kDelta cells grew more slowly, their levels of diphosphoinositol polyphosphates were 60-80% lower than wild-type cells, and the cells contained abnormally small and fragmented vacuoles. Novel activities of the mammalian and yeast InsP(6) kinases were identified; inositol pentakisphosphate (InsP(5)) was phosphorylated to diphosphoinositol tetrakisphosphate (PP-InsP(4)), which was further metabolized to a novel compound, tentatively identified as bis-diphosphoinositol trisphosphate. The latter is a new substrate for human diphosphoinositol polyphosphate phosphohydrolase. Kinetic parameters for the mammalian type 1 kinase indicate that InsP(5) (K(m) = 1.2 micrometer) and InsP(6) (K(m) = 6.7 micrometer) compete for phosphorylation in vivo. This is the first time a PP-InsP(4) synthase has been identified. The mammalian type 2 kinase and the yeast kinase are more specialized for the phosphorylation of InsP(6). Synthesis of the diphosphorylated inositol phosphates is thus revealed to be more complex and interdependent than previously envisaged.

Insulin restores neuronal nitric oxide synthase expression and function that is lost in diabetic gastropathy

Gastrointestinal dysfunction is common in diabetic patients. In genetic (nonobese diabetic) and toxin-elicited (streptozotocin) models of diabetes in mice, we demonstrate defects in gastric emptying and nonadrenergic, noncholinergic relaxation of pyloric muscle, which resemble defects in mice harboring a deletion of the neuronal nitric oxide synthase gene (nNOS). The diabetic mice manifest pronounced reduction in pyloric nNOS protein and mRNA. The decline of nNOS in diabetic mice does not result from loss of myenteric neurons. nNOS expression and pyloric function are restored to normal levels by insulin treatment. Thus diabetic gastropathy in mice reflects an insulin-sensitive reversible loss of nNOS. In diabetic animals, delayed gastric emptying can be reversed with a phosphodiesterase inhibitor, sildenafil. These findings have implications for novel therapeutic approaches and may clarify the etiology of diabetic gastropathy.

Poly(ADP-ribose) polymerase-1 in the nervous system

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme, activated by DNA strand breaks to participate in DNA repair. Overactivation of PARP by cellular insults depletes its substrate NAD(+) and then ATP, leading to a major energy deficit and cell death. This mechanism appears to be prominent in vascular stroke and other neurodegenerative processes in which PARP gene deletion and PARP-inhibiting drugs provide major protection. Cell death associated with PARP-1 overactivation appears to be predominantly necrotic while apoptosis is associated with PARP-1 cleavage, which may conserve energy needed for the apoptotic process. Novel forms of PARP derived from distinct genes and lacking classic DNA-binding domains may have nonnuclear functions, perhaps linked to cellular energy dynamics.

Type 3 inositol 1,4,5-trisphosphate receptor modulates cell death

Mechanisms accounting for the cellular entry of calcium that mediates cellular proliferation and apoptosis have been obscure. Previously we reported selective augmentation of type 3 inositol (1,4,5) trisphosphate receptors (IP(3)R3) in lymphocytes undergoing programmed cell death, which was prevented by antisense constructs to IP(3)R3. We now report increases in mRNA and protein levels for IP(3)R3 associated with cell death in several apoptotic paradigms in diverse tissues. Elevations of IP(3)R3 occur during developmental apoptosis in early postnatal cerebellar granule cells, dorsal root ganglia, embryonic hair follicles, and intestinal villi. Neurotoxic damage elicited by the glutamate agonist kainate is also associated with IP(3)R3 augmentation. In chick dorsal root ganglia neurons undergoing apoptosis due to deprivation of nerve growth factor, levels of IP(3)R3 are selectively increased and cell death is selectively prevented by antisense oligonucleotides to IP(3)R3. Thus, IP(3)R3 appears to participate actively in cell death in a diversity of tissues.

A mammalian iron ATPase induced by iron

While molecular mechanisms for iron entry and storage within cells have been elucidated, no system to mediate iron efflux has been heretofore identified. We now describe an ATP requiring iron transporter in mammalian cells. (55)Fe is transported into microsomal vesicles in a Mg-ATP-dependent fashion. The transporter is specific for ferrous iron, is temperature- and time-dependent, and detected only with hydrolyzable nucleotides. It differs from all known ATPases and appears to be a P-type ATPase. The Fe-ATPase is localized together with heme oxygenase-1 to microsomal membranes with both proteins greatly enriched in the spleen. Iron treatment markedly induces ATP-dependent iron transport in RAW 264.7 macrophage cells with an initial phase that is resistant to cycloheximide and actinomycin D and a later phase that is inhibited by these agents. Iron release, elicited in intact rats by glycerol-induced rhabdomyolysis, induces ATP-dependent iron transport in the kidney. Mice with genomic deletion of heme oxygenase-1 have selective tissue iron accumulation and display augmented ATP-dependent iron transport in those tissues that accumulate iron.

D-amino acids as putative neurotransmitters: focus on D-serine

Of the twenty amino acids in the mammalian body, only serine and aspartate occur in D-configuration as well as L-configuration in significant amount. D-serine is selectively concentrated in the brain, localized to protoplasmic astrocytes that ensheath synapses and distributed similarly to N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. D-serine has been found to function as an endogenous ligand for the "glycine" site of the NMDA receptor. Evidences for this include the greater potency of D-serine to activate this site than glycine, and D-amino acid oxidase, which degrades D-serine as well as other neutral D-amino acids, markedly attenuates NMDA neurotransmission. D-serine is also formed by serine racemase, a recently cloned enzyme that converts L-serine to D-serine. Thus, in many ways D-serine fulfills criteria for defining its functionality as a neurotransmitter and challenges the dogma relating to neurotransmission, for it is the "unnatural" isomeric form of an amino acid derived from glia rather than neurons.

D-serine is an endogenous ligand for the glycine site of the N-methyl-D-aspartate receptor

Functional activity of N-methyl-D-aspartate (NMDA) receptors requires both glutamate binding and the binding of an endogenous coagonist that has been presumed to be glycine, although D-serine is a more potent agonist. Localizations of D-serine and it biosynthetic enzyme serine racemase approximate the distribution of NMDA receptors more closely than glycine. We now show that selective degradation of d-serine with D-amino acid oxidase greatly attenuates NMDA receptor-mediated neurotransmission as assessed by using whole-cell patch-clamp recordings or indirectly by using biochemical assays of the sequelae of NMDA receptor-mediated calcium flux. The inhibitory effects of the enzyme are fully reversed by exogenously applied D-serine, which by itself did not potentiate NMDA receptor-mediated synaptic responses. Thus, D-serine is an endogenous modulator of the glycine site of NMDA receptors and fully occupies this site at some functional synapses.

Myocardial postischemic injury is reduced by polyADPripose polymerase-1 gene disruption

BACKGROUND

PolyADPribose polymerase (PARP) is activated by DNA strand breaks to catalyze the addition of ADPribose groups to nuclear proteins, especially PARP-1. Excessive polyADPribosylation leads to cell death through depletion of NAD+ and ATP.

MATERIALS AND METHODS

In vivo PARP activation in heart tissue slices was assayed through conversion of [33P]NAD+ into polyADPribose (PAR) following ischemia-reperfusion (I/R) and also monitored by immunohistochemical staining for PAR. Cardiac contractility, nitric oxide (NO), reactive oxygen species (ROS), NAD+ and ATP levels were examined in wild type (WT) and in PARP-1 gene-deleted (PARP-1(-/-)) isolated, perfused mouse hearts. Myocardial infarct size was assessed following coronary artery occlusion in rats treated with PARP inhibitors.

RESULTS

Ischemia-reperfusion (I/R) augmented formation of nitric oxide, oxygen free radicals and PARP activity. I/R induced decreases in cardiac contractility and NAD+ levels were attenuated in PARP-1(-/-) mouse hearts. PARP inhibitors reduced myocardial infarct size in rats. Residual polyADPribosylation in PARP-1(-/-) hearts may reflect alternative forms of PARP.

CONCLUSIONS

PolyADPribosylation from PARP-1 and other sources of enzymatic PAR synthesis is associated with cardiac damage following myocardial ischemia. PARP inhibitors may have therapeutic utility in myocardial disease.

Inositol polyphosphate multikinase (ArgRIII) determines nuclear mRNA export in Saccharomyces cerevisiae

The ARGRIII gene of Saccharomyces cerevisiae encodes a transcriptional regulator that also has inositol polyphosphate multikinase (ipmk) activity [Saiardi et al. (1999) Curr. Biol. 9, 1323-1326]. To investigate how inositol phosphates regulate gene expression, we disrupted the ARGRIII gene. This mutation impaired nuclear mRNA export, slowed cell growth, increased cellular [InsP(3)] 170-fold and decreased [InsP(6)] 100-fold, indicating reduced phosphorylation of InsP(3) to InsP(6). Levels of diphosphoinositol polyphosphates were decreased much less dramatically than was InsP(6). Low levels of InsP(6), and considerable quantities of Ins(1,3,4,5)P(4), were synthesized by an ipmk-independent route. Transcriptional control by ipmk reflects that it is a pivotal regulator of nuclear mRNA export via inositol phosphate metabolism.

Carbon monoxide and nitric oxide as coneurotransmitters in the enteric nervous system: evidence from genomic deletion of biosynthetic enzymes

Nitric oxide (NO) and carbon monoxide (CO) seem to be neurotransmitters in the brain. The colocalization of their respective biosynthetic enzymes, neuronal NO synthase (nNOS) and heme oxygenase-2 (HO2), in enteric neurons and altered intestinal function in mice with genomic deletion of the enzymes (nNOS(Delta/Delta) and HO2(Delta/Delta)) suggest neurotransmitter roles for NO and CO in the enteric nervous system. We now establish that NO and CO are both neurotransmitters that interact as cotransmitters. Small intestinal smooth muscle cells from nNOS(Delta/Delta) and HO2(Delta/Delta) mice are depolarized, with apparent additive effects in the double knockouts (HO2(Delta/Delta)/nNOS(Delta/Delta)). Muscle relaxation and inhibitory neurotransmission are reduced in the mutant mice. In HO2(Delta/Delta) preparations, responses to electrical field stimulation are nearly abolished despite persistent nNOS expression, whereas exogenous CO restores normal responses, indicating that the NO system does not function in the absence of CO generation.

Poly(ADP-ribosyl)ation basally activated by DNA strand breaks reflects glutamate-nitric oxide neurotransmission

Poly(ADP-ribose) polymerase (PARP) transfers ADP ribose groups from NAD(+) to nuclear proteins after activation by DNA strand breaks. PARP overactivation by massive DNA damage causes cell death via NAD(+) and ATP depletion. Heretofore, PARP has been thought to be inactive under basal physiologic conditions. We now report high basal levels of PARP activity and DNA strand breaks in discrete neuronal populations of the brain, in ventricular ependymal and subependymal cells and in peripheral tissues. In some peripheral tissues, such as skeletal muscle, spleen, heart, and kidney, PARP activity is reduced only partially in mice with PARP-1 gene deletion (PARP-1(-/-)), implicating activity of alternative forms of PARP. Glutamate neurotransmission involving N-methyl-d-aspartate (NMDA) receptors and neuronal nitric oxide synthase (nNOS) activity in part mediates neuronal DNA strand breaks and PARP activity, which are diminished by NMDA antagonists and NOS inhibitors and also diminished in mice with targeted deletion of nNOS gene (nNOS(-/-)). An increase in NAD(+) levels after treatment with NMDA antagonists or NOS inhibitors, as well as in nNOS(-/-) mice, indicates that basal glutamate-PARP activity regulates neuronal energy dynamics.

Molecular and functional characterization of protein 4.1B, a novel member of the protein 4.1 family with high level, focal expression in brain

Brain-enriched isoforms of skeletal proteins in the spectrin and ankyrin gene families have been described. Here we characterize protein 4.1B, a novel homolog of erythrocyte protein 4.1R that is encoded by a distinct gene. In situ hybridization revealed high level, focal expression of 4.1B mRNA in select neuronal populations within the mouse brain, including Purkinje cells of the cerebellum, pyramidal cells in hippocampal regions CA1-3, thalamic nuclei, and olfactory bulb. Expression was also detected in adrenal gland, kidney, testis, and heart. 4.1B protein exhibits high homology to the membrane binding, spectrin-actin binding, and C-terminal domains of 4.1R, including motifs for interaction with NuMA and FKBP13. cDNA characterization and Western blot analysis revealed multiple spliceoforms of protein 4.1B, with functionally relevant heterogeneity in the spectrin-actin and NuMA binding domains. Regulated alternative splicing events led to expression of unique 4. 1B isoforms in brain and muscle; only the latter possessed a functional spectrin-actin binding domain. By immunofluorescence, 4. 1B was localized specifically at the plasma membrane in regions of cell-cell contact. Together these results indicate that 4.1B transcription is selectively regulated among neuronal populations and that alternative splicing regulates expression of 4.1B isoforms possessing critical functional domains typical of other protein 4.1 family members.

Drugs for a new millennium

A millennium, a century, even a decade is a long time-frame for speculation about anything. Advances in biomedical research in the last few decades have been so extraordinary and escalating at an ever-accelerating pace that any prophecy is a risky proposition. However, it is possible to divine the big, unanswered questions and envisage ways in which they might reasonably be approached in the next few decades, a task which I will try to essay. So many drugs treat so many different medical conditions that a detailed and comprehensive coverage would probably be tiresome. Instead, I will address certain broad themes and diseases that offer both immense challenges and great potential for advances. Rather than review detailed experimental issues, I will confine myself to the 'big picture' issues, providing examples of specific research only in a few instances drawing largely from areas I know best.

Protein 4.1N binding to nuclear mitotic apparatus protein in PC12 cells mediates the antiproliferative actions of nerve growth factor

Protein 4.1N is a neuronal selective isoform of the erythrocyte membrane cytoskeleton protein 4.1R. In the present study, we demonstrate an interaction between 4.1N and nuclear mitotic apparatus protein (NuMA), a nuclear protein required for mitosis. The binding involves the C-terminal domain of 4.1N. In PC12 cells treatment with nerve growth factor (NGF) elicits translocation of 4. 1N to the nucleus and promotes its association with NuMA. Specific targeting of 4.1N to the nucleus arrests PC12 cells at the G1 phase and produces an aberrant nuclear morphology. Inhibition of 4.1N nuclear translocation prevents the NGF-mediated arrest of cell division, which can be reversed by overexpression of 4.1N. Thus, nuclear 4.1N appears to mediate the antiproliferative actions of NGF by antagonizing the role of NuMA in mitosis.