Timing of CNS cell generation: a programmed sequence of neuron and glial cell production from isolated murine cortical stem cells

Multipotent stem cells that generate both neurons and glia are widespread components of the early neuroepithelium. During CNS development, neurogenesis largely precedes gliogenesis: how is this timing achieved? Using clonal cell culture combined with long-term time-lapse video microscopy, we show that isolated stem cells from the embryonic mouse cerebral cortex exhibit a distinct order of cell-type production: neuroblasts first and glioblasts later. This is accompanied by changes in their capacity to make neurons versus glia and in their response to the mitogen EGF. Hence, multipotent stem cells alter their properties over time and undergo distinct phases of development that play a key role in scheduling production of diverse CNS cells.

Bace1 modulates myelination in the central and peripheral nervous system

Bace1 is an endopeptidase that cleaves the amyloid precursor protein at the beta-secretase site. Apart from this cleavage, the functional importance of Bace1 in other physiological events is unknown. We show here that Bace1 regulates the process of myelination and myelin sheath thickness in the central and peripheral nerves. In Bace1-null mice, the process of myelination was delayed and myelin thickness was markedly reduced, indicating that genetic deletion of Bace1 causes hypomyelination. Bace1-null mice also showed altered neurological behaviors such as elevated pain sensitivity and reduced grip strength. Further mechanistic studies showed an altered neuregulin-Akt signaling pathway in Bace1-null mice. Full-length neuregulin-1 was increased and its cleavage product was decreased in the CNS of Bace1-null mice. Furthermore, phosphorylated Akt was also reduced. Based upon these and previous studies, we postulate that neuronally enriched Bace1 cleaves neuregulin-1 and that processed neuregulin-1 regulates myelination by means of phosphorylation of Akt in myelin-forming cells.

Slowed recovery of rod photoresponse in mice lacking the GTPase accelerating protein RGS9-1

Timely deactivation of the alpha-subunit of the rod G-protein transducin (Galphat) is essential for the temporal resolution of rod vision. Regulators of G-protein signalling (RGS) proteins accelerate hydrolysis of GTP by the alpha-subunits of heterotrimeric G proteins in vitro. Several retinal RGS proteins can act in vitro as GTPase accelerating proteins (GAP) for Galphat. Recent reconstitution experiments indicate that one of these, RGS9-1, may account for much of the Galphat GAP activity in rod outer segments (ROS). Here we report that ROS membranes from mice lacking RGS9-1 hydrolyse GTP more slowly than ROS membranes from control mice. The Gbeta5-L protein that forms a complex with RGS9-1 was absent from RGS9-/- retinas, although Gbeta5-L messenger RNA was still present. The flash responses of RGS9-/- rods rose normally, but recovered much more slowly than normal. We conclude that RGS9-1, probably in a complex with Gbeta5-L, is essential for acceleration of hydrolysis of GTP by Galphat and for normal recovery of the photoresponse.

Yeast Sm-like proteins function in mRNA decapping and decay

One of the main mechanisms of messenger RNA degradation in eukaryotes occurs by deadenylation-dependent decapping which leads to 5'-to-3' decay. A family of Sm-like (Lsm) proteins has been identified, members of which contain the 'Sm' sequence motif, form a complex with U6 small nuclear RNA and are required for pre-mRNA splicing. Here we show that mutations in seven yeast Lsm proteins (Lsm1-Lsm7) also lead to inhibition of mRNA decapping. In addition, the Lsm1-Lsm7 proteins co-immunoprecipitate with the mRNA decapping enzyme (Dcp1), a decapping activator (Pat1/Mrt1) and with mRNA. This indicates that the Lsm proteins may promote decapping by interactions with the mRNA and the decapping machinery. In addition, the Lsm complex that functions in mRNA decay appears to be distinct from the U6-associated Lsm complex, indicating that Lsm proteins form specific complexes that affect different aspects of mRNA metabolism.

Improved insulin-sensitivity in mice heterozygous for PPAR-gamma deficiency

The thiazolidinedione class of insulin-sensitizing, antidiabetic drugs interacts with peroxisome proliferator-activated receptor gamma (PPAR-gamma). To gain insight into the role of this nuclear receptor in insulin resistance and diabetes, we conducted metabolic studies in the PPAR-gamma gene knockout mouse model. Because homozygous PPAR-gamma-null mice die in development, we studied glucose metabolism in mice heterozygous for the mutation (PPAR-gamma(+/-) mice). We identified no statistically significant differences in body weight, basal glucose, insulin, or FFA levels between the wild-type (WT) and PPAR-gamma(+/-) groups. Nor was there a difference in glucose excursion between the groups of mice during oral glucose tolerance test, but insulin concentrations of the WT group were greater than those of the PPAR-gamma(+/-) group, and insulin-induced increase in glucose disposal rate was significantly increased in PPAR-gamma(+/-) mice. Likewise, the insulin-induced suppression of hepatic glucose production was significantly greater in the PPAR-gamma(+/-) mice than in the WT mice. Taken together, these results indicate that - counterintuitively - although pharmacological activation of PPAR-gamma improves insulin sensitivity, a similar effect is obtained by genetically reducing the expression levels of the receptor.

Phosphotyrosine-dependent interaction of SHC and insulin receptor substrate 1 with the NPEY motif of the insulin receptor via a novel non-SH2 domain

The SHC proteins have been implicated in insulin receptor (IR) signaling. In this study, we used the sensitive two-hybrid assay of protein-protein interaction to demonstrate that SHC interacts directly with the IR. The interaction is mediated by SHC amino acids 1 to 238 and is therefore independent of the Src homology 2 domain. The interaction is dependent upon IR autophosphorylation, since the interaction is eliminated by mutation of the IR ATP-binding site. In addition, mutational analysis of the Asn-Pro-Glu-Tyr (NPEY) motif within the juxtamembrane domain of the IR showed the importance of the Asn, Pro, and Tyr residues to both SHC and IR substrate 1 (IRS-1) binding. We conclude that SHC interacts directly with the IR and that phosphorylation of Tyr-960 within the IR juxtamembrane domain is necessary for efficient interaction. This interaction is highly reminiscent of that of IRS-1 with the IR, and we show that the SHC IR-binding domain can substitute for that of IRS-1 in yeast and COS cells. We identify a homologous region within the IR-binding domains of SHC and IRS-1, which we term the SAIN (SHC and IRS-1 NPXY-binding) domain, which may explain the basis of these interactions. The SAIN domain appears to represent a novel motif which is able to interact with autophosphorylated receptors such as the IR.

RGS9, a GTPase accelerator for phototransduction

The rod outer segment phototransduction GAP (GTPase-accelerating protein) has been identified as RGS9, a member of the RGS family of G alpha GAPs. RGS9 mRNA expression is specific for photoreceptor cells, and RGS9 protein colocalizes with other phototransduction components to photoreceptor outer segment membranes. The RGS domain of RGS9 accelerates GTP hydrolysis by the visual G protein transducin (G alpha(t)), and this acceleration is enhanced by the gamma subunit of the phototransduction effector cGMP phosphodiesterase (PDEgamma). These unique properties of RGS9 match those of the rod outer segment GAP and implicate it as a key element in the recovery phase of visual transduction.

A randomized trial comparing fluconazole with clotrimazole troches for the prevention of fungal infections in patients with advanced human immunodeficiency virus infection. NIAID AIDS Clinical Trials Group

BACKGROUND

Cryptococcal meningitis and other serious fungal infections are common complications in patients infected with the human immunodeficiency virus (HIV). Fluconazole is effective for long-term suppression of many fungal infections, but its effectiveness as primary prophylaxis had not been adequately evaluated.

METHODS

We conducted a prospective, randomized trial that compared fluconazole (200 mg per day) with clotrimazole troches (10 mg taken five times daily) in patients who were also participating in a randomized trial of primary prophylaxis for Pneumocystis carinii pneumonia.

RESULTS

After a median follow-up of 35 months, invasive fungal infections had developed in 4.1 percent of the patients in the fluconazole group (9 of 217) and in 10.9 percent of those in the clotrimazole group (23 of 211; relative hazard, as adjusted for the CD4+ count, 3.3; 95 percent confidence interval, 1.5 to 7.6). Of the 32 invasive fungal infections, 17 were cryptococcosis (2 in the fluconazole group and 15 in the clotrimazole group; adjusted relative hazard, 8.5; 95 percent confidence interval, 1.9 to 37.6). The benefit of fluconazole was greater for the patients with 50 or fewer CD4+ cells per cubic millimeter than for the patients with higher counts. Fluconazole was also effective in preventing esophageal candidiasis (adjusted relative hazard, 5.8; 95 percent confidence interval, 1.7 to 20.0; P = 0.004) and confirmed and presumed oropharyngeal candidiasis (5.7 and 38.1 cases per 100 years of follow-up in the fluconazole and clotrimazole groups, respectively; P < 0.001). Survival was similar in the two groups.

CONCLUSIONS

Fluconazole taken prophylactically reduces the frequency of cryptococcosis, esophageal candidiasis, and superficial fungal infections in HIV-infected patients, especially those with 50 or fewer CD4+ lymphocytes per cubic millimeter, but the drug does not reduce overall mortality.

The human homologue of the yeast proteins Skb1 and Hsl7p interacts with Jak kinases and contains protein methyltransferase activity

To expand our understanding of the role of Jak2 in cellular signaling, we used the yeast two-hybrid system to identify Jak2-interacting proteins. One of the clones identified represents a human homologue of the Schizosaccaromyces pombe Shk1 kinase-binding protein 1, Skb1, and the protein encoded by the Saccharomyces cerevisiae HSL7 (histone synthetic lethal 7) gene. Since no functional motifs or biochemical activities for this protein or its homologues had been reported, we sought to determine a biochemical function for this human protein. We demonstrate that this protein is a protein methyltransferase. This protein, designated JBP1 (Jak-binding protein 1), and its homologues contain motifs conserved among protein methyltransferases. JBP1 can be cross-linked to radiolabeled S-adenosylmethionine (AdoMet) and methylates histones (H2A and H4) and myelin basic protein. Mutants containing substitutions within a conserved region likely to be involved in AdoMet binding exhibit little or no activity. We mapped the JBP1 gene to chromosome 14q11.2-21. In addition, JBP1 co-immunoprecipitates with several other proteins, which serve as methyl group acceptors and which may represent physiological targets of this methyltransferase. Messenger RNA for JBP1 is widely expressed in human tissues. We have also identified and sequenced a homologue of JBP1 in Drosophila melanogaster. This report provides a clue to the biochemical function for this conserved protein and suggests that protein methyltransferases may have a role in cellular signaling.

Reticulon family members modulate BACE1 activity and amyloid-β peptide generation

Inhibiting the activity of the beta-amyloid converting enzyme 1 (BACE1) or reducing levels of BACE1 in vivo decreases the production of amyloid-beta. The reticulon family of proteins has four members, RTN1, RTN2, RTN3 and RTN4 (also known as Nogo), the last of which is well known for its role in inhibiting neuritic outgrowth after injury. Here we show that reticulon family members are binding partners of BACE1. In brain, BACE1 mainly colocalizes with RTN3 in neurons, whereas RTN4 is more enriched in oligodendrocytes. An increase in the expression of any reticulon protein substantially reduces the production of Abeta. Conversely, lowering the expression of RTN3 by RNA interference increases the secretion of Abeta, suggesting that reticulon proteins are negative modulators of BACE1 in cells. Our data support a mechanism by which reticulon proteins block access of BACE1 to amyloid precursor protein and reduce the cleavage of this protein. Thus, changes in the expression of reticulon proteins in the human brain are likely to affect cellular amyloid-beta and the formation of amyloid plaques.

Total parenteral nutrition and bowel rest modify the metabolic response to endotoxin in humans

Intestinal mucosal atrophy, as induced by total parenteral nutrition (TPN) and/or prolonged bowel rest, is hypothesized to enhance bowel endotoxin (LPS) translocation and may alter host responses to infection. To examine the effect of TPN-induced bowel atrophy on the response to LPS, 12 healthy volunteers were randomized to receive either enteral feedings (ENT, n = 6) or seven days of TPN without oral intake (TPN, n = 6). Enteral or TPN feedings were terminated 12 hours before the study period when a constant dextrose infusion (50 mg/kg/hour) was initiated and continued throughout the subsequent study period. After placement of arterial, hepatic vein, and femoral vein catheters, metabolic parameters were determined before and for six hours after an intravenous E. coli LPS challenge (20 U/kg). Subsequent peak levels of arterial glucagon (ENT, 189 +/- 39 pg/mL; TPN, 428 +/- 48; p less than 0.01), arterial epinephrine (ENT, 236 +/- 52 pg/mL; TPN, 379 +/- 49; p less than 0.05) and hepatic venous cachectin/tumor necrosis factor (cachectin/TNF) (ENT, 250 +/- 56 pg/mL; TPN, 479 +/- 136; p less than 0.05) were significantly higher in the TPN group than in the ENT group. The extremity efflux of lactate (ENT, -16 +/- 4 micrograms/min-100cc tissue; TPN, -52 +/- 13; t = 2 hours; p less than 0.05) and of amino acids (ENT, -334 +/- 77 nmol/min-100cc tissue; TPN, -884 +/- 58; t = 4 hours; p less than 0.05) were higher in the TPN subjects after the endotoxin challenge. Circulating C-reactive Protein (CRP) levels measured 24 hours postendotoxin were also significantly higher in the TPN subjects (ENT, 1.7 +/- 0.2 mg/dL; TPN, 3.2 +/- 0.3; p less than 0.01). Hence the counter-regulatory hormone and splanchnic cytokine responses to LPS were enhanced after TPN and bowel rest. This is associated with a magnified acute-phase response, peripheral amino acid mobilization, and peripheral lactate production. Thus antecedent TPN may influence the metabolic alterations seen in infection and sepsis via both an exaggerated counter-regulatory hormone response as well as an enhanced systemic and splanchnic production of cytokines.

A controlled trial of trimethoprim-sulfamethoxazole or aerosolized pentamidine for secondary prophylaxis of Pneumocystis carinii pneumonia in patients with the acquired immunodeficiency syndrome. AIDS Clinical Trials Group Protocol 021

BACKGROUND

Pneumocystis carinii pneumonia (PCP) continues to be the most common index diagnosis in the acquired immunodeficiency syndrome (AIDS), but it is not clear which of several available agents is the most effective in preventing a recurrence of PCP.

METHODS

We conducted a comparative, open-label trial in 310 adults with AIDS who had recently recovered from an initial episode of PCP and had no treatment-limiting toxic effects of trimethoprim-sulfamethoxazole or pentamidine. All the patients were treated with zidovudine and were randomly assigned to receive either 800 mg of sulfamethoxazole and 160 mg of trimethoprim once daily or 300 mg of aerosolized pentamidine administered every four weeks by jet nebulizer. The participants were followed for a median of 17.4 months.

RESULTS

In the trimethoprim-sulfamethoxazole group (n = 154) there were 14 recurrences of PCP, as compared with 36 recurrences (including 1 extrapulmonary recurrence) in the aerosolized-pentamidine group (n = 156). The estimated recurrence rates at 18 months were 11.4 percent with trimethoprim-sulfamethoxazole and 27.6 percent with pentamidine (P < 0.001). The risk of a recurrence (adjusted for initial CD4 cell count) was 3.25 times higher in the pentamidine group (P < 0.001, 95 percent confidence interval, 1.72 to 6.16). There were no significant differences between the groups in survival or in hematologic or hepatic toxicity. Crossovers from trimethoprim-sulfamethoxazole to aerosolized pentamidine were more common than the reverse (27 vs. 4 percent), partly because of the study protocols for the management of leukopenia. There were 19 serious bacterial infections in the trimethoprim-sulfamethoxazole group and 38 in the pentamidine group. The time to a first bacterial infection was significantly greater for those assigned to trimethoprim-sulfamethoxazole (P = 0.017).

CONCLUSIONS

In patients with AIDS who are receiving zidovudine, trimethoprim-sulfamethoxazole is more effective than aerosolized pentamidine in conventional doses for the prevention of recurrent pneumocystis infection.

A randomized trial of three antipneumocystis agents in patients with advanced human immunodeficiency virus infection. NIAID AIDS Clinical Trials Group

BACKGROUND

We evaluated the effectiveness of three treatment strategies for the prevention of a first episode of Pneumocystis carinii pneumonia in patients infected with the human immunodeficiency virus (HIV).

METHODS

In an open-label trial, 843 patients with HIV infection and fewer than 200 CD4+ cells per cubic millimeter received zidovudine plus one of three randomly assigned prophylactic agents, beginning with trimethoprim-sulfamethoxazole, dapsone, or aerosolized pentamidine and followed by a defined sequence of other drugs to be used in cases of intolerance.

RESULTS

The estimated 36-month cumulative risks of P. carinii pneumonia were 18 percent, 17 percent, and 21 percent in the trimethoprim-sulfamethoxazole, dapsone, and aerosolized-pentamidine groups, respectively (P = 0.22). The difference in risk among treatment strategies was negligible in patients entering the study with 100 or more CD4+ lymphocytes per cubic millimeter. In those entering with fewer than 100 CD4+ cells per cubic millimeter, the risk was 33 percent with aerosolized pentamidine, as compared with 19 percent with trimethoprim-sulfamethoxazole and 22 percent with dapsone (P = 0.04). The lowest failure rates occurred in patients receiving trimethoprim-sulfamethoxazole, and failures were more common with 50 mg of dapsone than with 100 mg. Toxoplasmosis developed in less than 3 percent of patients. Of the patients assigned to the two systemic therapies, only 23 percent were receiving their assigned drug and dose when they completed the study. The median survival was approximately 39 months in all three groups, and the mortality attributable to P. carinii pneumonia was only 1 percent.

CONCLUSIONS

In patients with advanced HIV infection, the three treatment strategies we examined have similar effectiveness in preventing P. carinii pneumonia. Strategies that start with trimethoprim-sulfamethoxazole or with high-dose dapsone, rather than aerosolized pentamidine, are superior in patients with fewer than 100 CD4+ lymphocytes per cubic millimeter.

VPS35 haploinsufficiency increases Alzheimer's disease neuropathology

The retromer complex component VPS35 prevents activation of the BACE1 and Aβ production and thus plays an essential role in limiting Alzheimer’s disease neuropathology.

VPS35, a major component of the retromer complex, is important for endosome-to-Golgi retrieval of membrane proteins. Although implicated in Alzheimer’s disease (AD), how VPS35 regulates AD-associated pathology is unknown. In this paper, we show that hemizygous deletion of Vps35 in the Tg2576 mouse model of AD led to earlier-onset AD-like phenotypes, including cognitive memory deficits, defective long-term potentiation, and impaired postsynaptic glutamatergic neurotransmission in young adult age. These deficits correlated well with an increase of β-amyloid peptide (Aβ) level in the mutant hippocampus. We further demonstrate that VPS35 is predominantly expressed in pyramidal neurons of young adult hippocampus and interacts with BACE1, a protease responsible for Aβ production. Loss of VPS35 function in the mouse hippocampus increased BACE1 activity. Suppression of VPS35 expression in culture decreased BACE1 trans-Golgi localization but enriched it in endosomes. These results demonstrate an essential role for VPS35 in suppression of AD neuropathology and in inhibition of BACE1 activation and Aβ production by promoting BACE1 endosome-to-Golgi retrieval.

Structural determinants for regulation of phosphodiesterase by a G protein at 2.0 A

A multitude of heptahelical receptors use heterotrimeric G proteins to transduce signals to specific effector target molecules. The G protein transducin, Gt, couples photon-activated rhodopsin with the effector cyclic GMP phosophodiesterase (PDE) in the vertebrate phototransduction cascade. The interactions of the Gt alpha-subunit (alpha(t)) with the inhibitory PDE gamma-subunit (PDEgamma) are central to effector activation, and also enhance visual recovery in cooperation with the GTPase-activating protein regulator of G-protein signalling (RGS)-9 (refs 1-3). Here we describe the crystal structure at 2.0 A of rod transducin alpha x GDP x AlF4- in complex with the effector molecule PDEgamma and the GTPase-activating protein RGS9. In addition, we present the independently solved crystal structures of the RGS9 RGS domain both alone and in complex with alpha(t/i1) x GDP x AlF4-. These structures reveal insights into effector activation, synergistic GTPase acceleration, RGS9 specificity and RGS activity. Effector binding to a nucleotide-dependent site on alpha(t) sequesters PDEgamma residues implicated in PDE inhibition, and potentiates recruitment of RGS9 for hydrolytic transition state stabilization and concomitant signal termination.

Cabin 1, a negative regulator for calcineurin signaling in T lymphocytes

Calcineurin plays a pivotal role in the T cell receptor (TCR)-mediated signal transduction pathway and serves as a common target for the immunosuppressants FK506 and cyclosporin A. We report the identification of a novel endogenous calcineurin binding protein named Cabin 1 that inhibits calcineurin-mediated signal transduction. The interaction between Cabin 1 and calcineurin is dependent on PKC activation. Overexpression of Cabin 1 or its N-terminal truncation mutants inhibits the transcriptional activation of calcineurin-responsive elements in the interleukin-2 promoter and blocks dephosphorylation of NF-AT upon T cell activation. These results suggest a negative regulatory role for Cabin 1 in calcineurin signaling and provide a possible mechanism of feedback inhibition of TCR signaling through cross-talk between protein kinases and calcineurin.

The A beta 3-pyroglutamyl and 11-pyroglutamyl peptides found in senile plaque have greater beta-sheet forming and aggregation propensities in vitro than full-length A beta

A beta isolated from neuritic plaque and vascular walls of the brains of patients with Alzheimer's disease has been shown to contain significant quantities of A beta peptides which begin at residue 3Glu or 11Glu in the form of pyroglutamyl residues (A beta 3pE and A beta 11pE). To investigate the effects of these N-terminal modifications on the biophysical properties of A beta, peptides A beta 1-40, A beta 3pE-40, A beta 11pE-40, A beta 1-28, A beta 3pE-28, and A beta 11pE-28 were synthesized. Using circular dichroism spectroscopy, we determined that the pyroglutamyl-containing peptides form beta-sheet structure more readily than the corresponding full-length A beta peptides, both in aqueous solutions and in 10% sodium dodecyl sulfate micelles. Trifluoroethanol spectra indicated that the relative beta-sheet to alpha-helical stability is higher for the pyroglutamyl-containing peptides. Sedimentation experiments show that the pyroglutamyl-containing peptides have greater aggregation propensities than the corresponding full-length peptides. Comparison between the A beta 40 and the A beta 28 series indicated that the greater beta-sheet forming and aggregation propensities of the pyroglutamyl peptides are not simply due to an increase in hydrophobicity.

The type I serine/threonine kinase receptor ActRIA (ALK2) is required for gastrulation of the mouse embryo

ActRIA (or ALK2), one of the type I receptors of the transforming growth factor-beta (TGF-beta) superfamily, can bind both activin and bone morphogenetic proteins (BMPs) in conjunction with the activin and BMP type II receptors, respectively. In mice, ActRIA is expressed primarily in the extraembryonic visceral endoderm before gastrulation and later in both embryonic and extraembryonic cells during gastrulation. To elucidate its function in mouse development, we disrupted the transmembrane domain of ActRIA by gene targeting. We showed that embryos homozygous for the mutation were arrested at the early gastrulation stage, displaying abnormal visceral endoderm morphology and severe disruption of mesoderm formation. To determine in which germ layer ActRIA functions during gastrulation, we performed reciprocal chimera analyses. (1) Homozygous mutant ES cells injected into wild-type blastocysts were able to contribute to all three definitive germ layers in chimeric embryos. However, a high contribution of mutant ES cells in chimeras disrupted normal development at the early somite stage. (2) Consistent with ActRIA expression in the extraembryonic cells, wild-type ES cells failed to rescue the gastrulation defect in chimeras in which the extraembryonic ectoderm and visceral endoderm were derived from homozygous mutant blastocysts. Furthermore, expression of HNF4, a key visceral endoderm-specific transcription regulatory factor, was significantly reduced in the mutant embryos. Together, our results indicate that ActRIA in extraembryonic cells plays a major role in early gastrulation, whereas ActRIA function is also required in embryonic tissues during later development in mice.

An antagonist peptide-EPO receptor complex suggests that receptor dimerization is not sufficient for activation

Dimerization of the erythropoietin (EPO) receptor (EPOR), in the presence of either natural (EPO) or synthetic (EPO-mimetic peptides, EMPs) ligands is the principal extracellular event that leads to receptor activation. The crystal structure of the extracellular domain of EPOR bound to an inactive (antagonist) peptide at 2.7 A resolution has unexpectedly revealed that dimerization still occurs, but the orientation between receptor molecules is altered relative to active (agonist) peptide complexes. Comparison of the biological properties of agonist and antagonist EMPs with EPO suggests that the extracellular domain orientation is tightly coupled to the cytoplasmic signaling events and, hence, provides valuable new insights into the design of synthetic ligands for EPOR and other cytokine receptors.

Examination of reproductive aging milestones among women who carry the FMR1 premutation

BACKGROUND

The fragile X premutation is characterized by a large CGG repeat track (55-199 repeats) in the 5' UTR of the FMR1 gene. This X-linked mutation leads to an increased risk for premature ovarian failure; interestingly, the association of repeat size with risk is non-linear. We hypothesize that the premutation-associated ovarian insufficiency is due to a diminished oocyte pool and examined reproductive aging milestones by repeat size group to determine if the same non-linear association is observed.

METHODS

We analyzed cross-sectional reproductive history questionnaire data from 948 women with a wide range of repeat sizes.

RESULTS

We have confirmed the non-linear relationship among premutation carriers for ovarian insufficiency. The mid-range repeat size group (80-100 repeats), not the highest group, had an increased risk for: altered cycle traits (shortened cycle length, irregular cycles and skipped cycles), subfertility and dizygotic twinning. Smoking, a modifiable risk, decreased the reproductive lifespan of women with the premutation by about 1 year, similar to its effect on non-carriers. As expected, premutation carriers were found to be at an increased risk for osteoporosis.

CONCLUSIONS

Possible molecular mechanisms to explain the non-linear repeat size risk for ovarian insufficiency are discussed.

Elevated plasma chitotriosidase activity in various lysosomal storage disorders

Recently a striking elevation of the activity of chitotriosidase, an endo beta-glucosaminidase distinct from lysozyme, was found in plasma from patients with Gaucher type I disease (McKusick 230800). Plasma chitotriosidase originates from activated macrophages and this elevation is secondary to the basic defect in Gaucher disease. To investigate the specificity of this phenomenon, we have investigated 24 different lysosomal storage diseases. In 11 different diseases increased chitotriosidase activity in plasma was found (in 28% of the patients). None of these diseases showed elevations as high as in Gaucher disease. Chitotriosidase was not significantly elevated in plasma from 20 different non-lysosomal enzymopathies or in plasma from patients with infectious diseases associated with hepatomegaly. The results show that marked elevation of chitotriosidase activity in plasma appears to be specific for Gaucher disease. The data further suggest that elevated levels of chitotriosidase activity in plasma from patients with unexplained diseases may be indicative for a lysosomal disorder.

Patterns of nucleotide misincorporations during enzymatic amplification and direct large-scale sequencing of ancient DNA

Whereas evolutionary inferences derived from present-day DNA sequences are by necessity indirect, ancient DNA sequences provide a direct view of past genetic variants. However, base lesions that accumulate in DNA over time may cause nucleotide misincorporations when ancient DNA sequences are replicated. By repeated amplifications of mitochondrial DNA sequences from a large number of ancient wolf remains, we show that C/G-to-T/A transitions are the predominant type of such misincorporations. Using a massively parallel sequencing method that allows large numbers of single DNA strands to be sequenced, we show that modifications of C, as well as to a lesser extent of G, residues cause such misincorporations. Experiments where oligonucleotides containing modified bases are used as templates in amplification reactions suggest that both of these types of misincorporations can be caused by deamination of the template bases. New DNA sequencing methods in conjunction with knowledge of misincorporation processes have now, in principle, opened the way for the determination of complete genomes from organisms that became extinct during and after the last glaciation.

Genetic deletion of BACE1 in mice affects remyelination of sciatic nerves

BACE1 is a promising therapeutic and preventive target for Alzheimer's disease because it is essential for amyloid deposition. However, the recent demonstration of BACE1 in modulating developmental myelination in both peripheral and central nervous systems raises a concern of its effect on myelin maintenance or remyelination, and inhibition of these processes will potentially be detrimental to the BACE1 inhibitor users who are susceptible to myelination diseases such as adult peripheral nerve injury or multiple sclerosis. In this report, we investigated the role of BACE1 during peripheral nerve remyelination in wild-type (WT) and BACE1-null mice. We show here that genetic deletion of BACE1 affects sciatic nerve remyelination. The impaired remyelination appears to stem from the loss of neuregulin-1 cleavage by BACE1. To demonstrate a direct cleavage of neuregulin-1 by BACE1, we have identified a BACE1 cleavage site that turns out be highly conserved among neuregulin-1 paralogues. Moreover, we show that neuregulin-1 family member neuregulin-3 is also cleavable by BACE1. We hypothesize that the BACE1-cleaved extracellular domain of axonal neuregulin-1, perhaps neuregulin-3 as well, binds to Schwann cell ErbB receptors, which in turn regulate remyelination. Pharmacological inhibition of BACE1 should be carefully monitored to avoid alteration of signaling pathway that regulates remyelination.

LPS induces IL-8 expression through TLR4, MyD88, NF-kappaB and MAPK pathways in human dental pulp stem cells

AIM

To evaluate the effects of lipopolysaccharide (LPS) on interleukin-8 (IL-8) and related intracellular signalling pathways in human dental pulp stem cells (hDPSCs).

METHODOLOGY

Human pulp tissues were isolated from human impacted third molars, and the hDPSCs were cultured and characterized. The effects of LPS on IL-8 and Toll-like receptor 4 (TLR4) gene expression in hDPSCs were investigated using real-time quantitative RT-PCR and ELISA. Whether TLR4/MyD88/NF-кB was involved in the LPS-induced up-regulation of IL-8 in hDPSCs was determined using transient transfection, luciferase assay and ELISA. The involvement of MAPKs in the LPS-induced up-regulation of IL-8 in hDPSCs was investigated via transient transfection, luciferase assay, ELISA and western blot. The data were statistically analysed using Student's t-test or one-way anova followed by the Student-Neumann-Keuls test.

RESULTS

Cells exposed to LPS not only displayed an enhanced expression of TLR4 but also showed an elevated IL-8 gene expression; exposure to LPS also resulted in the induction of IL-8 gene transcription via promoter activation. The LPS-induced IL-8 promoter activation was inhibited through dominant-negative mutations in TLR4 and MyD88, but not in TLR2. The LPS-induced IL-8 protein release was attenuated through the administration of TLR4-neutralizing antibody or MyD88 inhibitory peptide and a dominant-negative mutation in IκBα. In contrast, IL-8 protein release was enhanced through the expression of NF-κB p65. Treatment with PDTC, TPCK or Bay117082 effectively antagonized LPS-induced IL-8 protein release. Moreover, both the promoter activity and the LPS-induced release of IL-8 were diminished upon the administration of U0126 and SB203580, but not SP600125. Moreover, the exposure to LPS activated ERK1/2 and p38 MAPK phosphorylation in cells.

CONCLUSIONS

This study reports the LPS-mediated transcriptional and post-translational up-regulation of IL-8, which is a process that also involves TLR4, MyD88, NF-κB and MAPK.

Functions of Lsm proteins in mRNA degradation and splicing

Recent results have identified a family of Lsm (Like Sm) proteins that are related to the Sm protein family. Seven Lsm proteins form a complex, which interacts with the U6 snRNA and functions in splicing. In addition, a different complex of Lsm proteins interacts with cytoplasmic mRNA and promotes its turnover. These diverse functions of Lsm proteins suggest that they are important modulators of RNA biogenesis and function.