Early behavioral changes and quantitative analysis of neuropathological features in murine prion disease: Stereological analysis in the albino Swiss mice model

Behavioral and neuropathological changes have been widely investigated in murine prion disease but stereological based unbiased estimates of key neuropathological features have not been carried out. After injections of ME7 infected (ME7) or normal brain homogenates (NBH) into dorsal CA1 of albino Swiss mice and C57BL6, we assessed behavioral changes on hippocampal-dependent tasks. We also estimated by optical fractionator at 15 and 18 weeks post-injections (w.p.i.) the total number of neurons, reactive astrocytes, activated microglia and perineuronal nets (PN) in the polymorphic layer of dentate gyrus (PolDG), CA1 and septum in albino Swiss mice. On average, early behavioral changes in albino Swiss mice start four weeks later than in C57BL6. Cluster and discriminant analysis of behavioral data in albino Swiss mice revealed that four of nine subjects start to change their behavior at 12 w.p.i. and reach terminal stage at 22 w.p.i and the remaining subjects start at 22 w.p.i. and reach terminal stage at 26 w.p.i. Biotinylated dextran-amine BDA-tracer experiments in mossy fiber pathway confirmed axonal degeneration and stereological data showed that early astrocytosis, microgliosis and reduction in the perineuronal nets are independent of a change in the number of neuronal cell bodies. Statistical analysis revealed that the septal region had greater levels of neuroinflammation and extracellular matrix damage than CA1. This stereological and multivariate analysis at early stages of disease in an outbred model of prion disease provided new insights connecting behavioral changes and neuroinflammation and seems to be important to understand the mechanisms of prion disease progression.Key words: prion disease, optical fractionator, neuropathology, behavioral changes, albino Swiss mice     

Mutations in LRP5 or FZD4 underlie the common familial exudative vitreoretinopathy locus on chromosome 11q

Familial exudative vitreoretinopathy (FEVR) is an inherited blinding disorder of the retinal vascular system. Autosomal dominant FEVR is genetically heterogeneous, but its principal locus, EVR1, is on chromosome 11q13-q23. The gene encoding the Wnt receptor frizzled-4 (FZD4) was recently reported to be the EVR1 gene, but our mutation screen revealed fewer patients harboring mutations than expected. Here, we describe mutations in a second gene at the EVR1 locus, low-density-lipoprotein receptor-related protein 5 (LRP5), a Wnt coreceptor. This finding further underlines the significance of Wnt signaling in the vascularization of the eye and highlights the potential dangers of using multiple families to refine genetic intervals in gene-identification studies.     

Characterization of a Glutamate Transporter Operon,glnQHMP, in Streptococcus mutans and Its Role in Acid Tolerance

Glutamate contributes to the acid tolerance response (ATR) of many Gram-negative and Gram-positive bacteria, but its role in the ATR of the oral bacterium Streptococcus mutans is unknown. This study describes the discovery and characterization of a glutamate transporter operon designated glnQHMP (Smu.1519 to Smu.1522) and investigates its potential role in acid tolerance. Deletion of glnQHMP resulted in a 95% reduction in transport of radiolabeled glutamate compared to the wild-type UA159 strain. The addition of glutamate to metabolizing UA159 cells resulted in an increased production of acidic end products, whereas the glnQHMP mutant produced less lactic acid than UA159, suggesting a link between glutamate metabolism and acid production and possible acid tolerance. To investigate this possibility, we conducted a microarray analysis with glutamate and under pH 5.5 and pH 7.5 conditions which showed that expression of the glnQHMP operon was downregulated by both glutamate and mild acid. We also measured the growth kinetics of UA159 and its glnQHMP-negative derivative at pH 5.5 and found that the mutant doubled at a much slower rate than the parent strain but survived at pH 3.5 significantly better than the wild type. Taken together, these findings support the involvement of the glutamate transporter operon glnQHMP in the acid tolerance response in S. mutans.Streptococcus mutans is 1 of over 700 bacterial species commonly found in the oral environment (1). Its ability to rapidly metabolize dietary carbohydrates to acid end products causes demineralization of the tooth enamel, leading to caries formation (19). Acidogenicity (the ability to produce acid end products via glycolysis) and aciduricity (the ability to survive and grow in acidic environments) are two important virulence factors of S. mutans. Maintenance of a pH gradient across the cell membrane by increasing intracellular pH by 0.5 to 1.0 relative to the extracellular pH (ΔpH) when exposed to a low pH environment is critical for the survival of S. mutans at low pH. This is primarily accomplished by acid-induced mechanisms that facilitate proton extrusion via the proton-translocating ATPase (5, 20) and by acid end product efflux (8, 12). S. mutans also possesses an acid tolerance response (ATR) mechanism, whereby preexposure to sublethal pH environments (e.g., pH 5.5) affords protection from killing under lethal pH values as low as pH 3.0 (7). This adaptive process is characterized by increased acid resistance (4), increased glycolytic capacities (20), and increased proton-translocating enzyme F₁F₀-ATPase activity (44). The ATR is enhanced by sugar starvation and the addition of amino acids (48), the addition of potassium ions (12), growth in biofilms, and activity of multiple two-component signal transduction systems that include the ComDE, HK11/RR11 (also designated LiaS/LiaR), VicKR, CiaHR, LevSR, ScnKR, and HK1037/RR1038 (6, 17, 31, 32, 46).Previously, Noji et al. and Sato et al. described a glutamate/aspartate transporter in S. mutans (38, 45). Those researchers showed that the presence of potassium ions was required for transport and that, in environments of pH 6.0 or below, the activity of the H⁺-ATPase system was required (38, 45). Potassium ions are the main cations in plaque (50), and potassium uptake is associated with intracellular pH homeostasis in S. mutans (24, 35). In addition, expression of several genes involved in the glutamate synthesis pathway (icd, citZ, and acn) are downregulated under low pH (10), suggesting a link between glutamate metabolism, potassium levels, and aciduricity in S. mutans. Since acid tolerance is an important virulence property of S. mutans, we aimed to investigate a possible link between glutamate uptake and acid resistance in this oral pathogen. In bacteria, intracellular glutamate and glutamine levels are closely linked with nitrogen metabolism of the cell. Glutamine is synthesized from glutamate and ammonium, which is a major way for cells to assimilate the nitrogen required for biosynthesis of all amino acids, thus affecting protein synthesis and the structural and functional integrity of the cell. Notably, nitrogen metabolism, especially glutamine metabolism, has been linked to virulence in a number of microorganisms, including Streptococcus pneumoniae (26, 42), Staphylococcus aureus (41), Candida albicans (33), and Pseudomonas aeruginosa (51). Glutamate uptake and metabolism are known to be involved in the ATR of Gram-negative bacteria such as Escherichia coli via the use of glutamate decarboxylase and the glutamate/gamma-amino butyrate (glutamate/GABA) antiporter (9). Similarly, the homologous proteins of these systems in Lactococcus lactis, encoded by the gadBC genes, were shown to assist in a glutamate-dependent acid-resistance mechanism in that Gram-positive bacterium (44).In this study, we searched the S. mutans UA159 genome for potential glutamine transporter operons. We constructed a deletion mutant (SmuGLT) of the glnQHMP operon (Smu.1519 to Smu.1522) and confirmed its role as a glutamate transporter. The inability of SmuGLT to take up glutamate resulted in a general growth deficiency, especially at pH 5.5, as well as an increased tolerance to acid. Results from this study provide insight into the ATR of S. mutans, including a potential link between glutamate metabolism and acid resistance in S. mutans.     

Desferoxamine and ethyl-3,4-dihydroxybenzoate protect myocardium by activating NOS and generating mitochondrial ROS

Protection from a prolyl hydroxylase domain-containing enzyme (PHD) inhibitor, desferoxamine (DFO), was recently reported to be dependent on production of reactive oxygen species (ROS). Ischemic preconditioning triggers the protected state by stimulating nitric oxide (NO) production to open mitochondrial ATP-sensitive K+ (mitoK(ATP)) channels, generating ROS required for protection. We tested whether DFO and a second PHD inhibitor, ethyl-3,4-dihydroxybenzoate (EDHB), might have similar mechanisms. EDHB and DFO increased ROS generation by 50-75% (P < 0.001) in isolated rabbit cardiomyocytes. This increase after EDHB exposure was blocked by N(omega)-nitro-L-arginine methyl ester (L-NAME), an NO synthase (NOS) inhibitor; ODQ, a guanylyl cyclase antagonist; and Rp-8-bromoguanosine-3',5'-cyclic monophosphorothioate Rp isomer, a PKG blocker, thus implicating the NO pathway in EDHB's signaling. Glibenclamide, a nonselective K(ATP) channel blocker, or 5-hydroxydecanoate, a selective mitoK(ATP) channel antagonist, also prevented EDHB's ROS production, as did blockade of mitochondrial electron transport with myxothiazol. NOS is activated by Akt. However, neither wortmannin, an inhibitor of phosphatidylinositol-3-kinase, nor Akt inhibitor blocked EDHB-induced ROS generation, indicating that EDHB initiates signaling downstream of Akt. DFO also increased ROS production, and this effect was blocked by ODQ, 5-hydroxydecanoate, and N-(2-mercaptopropionyl)glycine, an ROS scavenger. DFO increased cardiomyocyte production of nitrite, a metabolite of NO, and this effect was blocked by an inhibitor of NOS. DFO also spared ischemic myocardium in intact hearts. This infarct-sparing effect was blocked by ODQ, L-NAME, and N-(2-mercaptopropionyl)glycine. Hence, DFO and EDHB stimulate NO-dependent activation of PKG to open mitoK(ATP) channels and produce ROS, which act as second messengers to trigger entrance into the preconditioned state.     

Tyrosine phosphatase SHP-2 regulates IL-1 signaling in fibroblasts through focal adhesions

Interleukin-1beta (IL-1beta) mediates destruction of matrix collagens in diverse inflammatory diseases including arthritis, periodontitis, and pulmonary fibrosis by activating fibroblasts, cells that interact with matrix proteins through integrin-based adhesions. In vitro, IL-1beta signaling is modulated by focal adhesions, supramolecular protein complexes that are enriched with tyrosine kinases and phosphatases. We assessed the importance of tyrosine phosphatases in regulating cell-matrix interactions and IL-1beta signaling. In human gingival fibroblasts plated on fibronectin, IL-1beta enhanced the maturation of focal adhesions as defined by morphology and enrichment with paxillin and alpha-actinin. IL-1beta also induced activation of ERK and recruitment of phospho-ERK to focal complexes/adhesions. Treatment with the potent tyrosine phosphatase inhibitor pervanadate, in the absence of IL-1beta, recapitulated many of these responses indicating the importance of tyrosine phosphatases. Immunoblotting of collagen bead-associated complexes revealed that the tyrosine phosphatase, SHP-2, was also enriched in focal complexes/adhesions. Depletion of SHP-2 by siRNA or by homologous recombination markedly altered IL-1beta-induced ERK activation and maturation of focal adhesions. IL-1beta-induced tyrosine phosphorylation of SHP-2 on residue Y542 promoted focal adhesion maturation. Association of Gab1 with SHP-2 in focal adhesions correlated temporally with activation of ERK and was abrogated in cells expressing mutant (Y542F) SHP-2. We conclude that IL-1beta mediated maturation of focal adhesions is dependent on tyrosine phosphorylation of SHP-2 at Y542, leading to recruitment of Gab1, a process that may influence the downstream activation of ERK.