Chronic itch, or pruritus, is associated with a wide range of skin abnormalities. The mechanisms responsible for chronic itch induction and persistence remain unclear. We developed a mouse model in ...which a constitutively active form of the serine/threonine kinase BRAF was expressed in neurons gated by the sodium channel Nav1.8 (BRAF(Nav1.8) mice). We found that constitutive BRAF pathway activation in BRAF(Nav1.8) mice results in ectopic and enhanced expression of a cohort of itch-sensing genes, including gastrin-releasing peptide (GRP) and MAS-related GPCR member A3 (MRGPRA3), in nociceptors expressing transient receptor potential vanilloid 1 (TRPV1). BRAF(Nav1.8) mice showed de novo neuronal responsiveness to pruritogens, enhanced pruriceptor excitability, and heightened evoked and spontaneous scratching behavior. GRP receptor expression was increased in the spinal cord, indicating augmented coding capacity for itch subsequent to amplified pruriceptive inputs. Enhanced GRP expression and sustained ERK phosphorylation were observed in sensory neurons of mice with allergic contact dermatitis– or dry skin–elicited itch; however, spinal ERK activation was not required for maintaining central sensitization of itch. Inhibition of either BRAF or GRP signaling attenuated itch sensation in chronic itch mouse models. These data uncover RAF/MEK/ERK signaling as a key regulator that confers a subset of nociceptors with pruriceptive properties to initiate and maintain long-lasting itch sensation.
Intracerebral hemorrhage (ICH) is the stroke subtype with the worst prognosis and has no established acute treatment. ICH is classified as lobar or nonlobar based on the location of ruptured blood ...vessels within the brain. These different locations also signal different underlying vascular pathologies. Heritability estimates indicate a substantial genetic contribution to risk of ICH in both locations. We report a genome-wide association study of this condition that meta-analyzed data from six studies that enrolled individuals of European ancestry. Case subjects were ascertained by neurologists blinded to genotype data and classified as lobar or nonlobar based on brain computed tomography. ICH-free control subjects were sampled from ambulatory clinics or random digit dialing. Replication of signals identified in the discovery cohort with p < 1 × 10−6 was pursued in an independent multiethnic sample utilizing both direct and genome-wide genotyping. The discovery phase included a case cohort of 1,545 individuals (664 lobar and 881 nonlobar cases) and a control cohort of 1,481 individuals and identified two susceptibility loci: for lobar ICH, chromosomal region 12q21.1 (rs11179580, odds ratio OR = 1.56, p = 7.0 × 10−8); and for nonlobar ICH, chromosomal region 1q22 (rs2984613, OR = 1.44, p = 1.6 × 10−8). The replication included a case cohort of 1,681 individuals (484 lobar and 1,194 nonlobar cases) and a control cohort of 2,261 individuals and corroborated the association for 1q22 (p = 6.5 × 10−4; meta-analysis p = 2.2 × 10−10) but not for 12q21.1 (p = 0.55; meta-analysis p = 2.6 × 10−5). These results demonstrate biological heterogeneity across ICH subtypes and highlight the importance of ascertaining ICH cases accordingly.
The T2Rs belong to a multi-gene family of G-protein-coupled receptors responsible for the detection of ingested bitter-tasting compounds. The T2Rs are conserved among mammals with the human and mouse ...gene families consisting of about 25 members. In the present study we address the signalling properties of human and mouse T2Rs using an in vitro reconstitution system in which both the ligands and G-proteins being assayed can be manipulated independently and quantitatively assessed. We confirm that the mT2R5, hT2R43 and hT2R47 receptors respond selectively to micromolar concentrations of cycloheximide, aristolochic acid and denatonium respectively. We also demonstrate that hT2R14 is a receptor for aristolochic acid and report the first characterization of the ligand specificities of hT2R7, which is a broadly tuned receptor responding to strychnine, quinacrine, chloroquine and papaverine. Using these defined ligand-receptor interactions, we assayed the ability of the ligand-activated T2Rs to catalyse GTP binding on divergent members of the G(alpha) family including three members of the G(alphai) subfamily (transducin, G(alphai1) and G(alphao)) as well as G(alphas) and G(alphaq). The T2Rs coupled with each of the three G(alphai) members tested. However, none of the T2Rs coupled to either G(alphas) or G(alphaq), suggesting the T2Rs signal primarily through G(alphai)-mediated signal transduction pathways. Furthermore, we observed different G-protein selectivities among the T2Rs with respect to both G(alphai) subunits and G(betagamma) dimers, suggesting that bitter taste is transduced by multiple G-proteins that may differ among the T2Rs.
Positional cloning of hereditary deafness genes is a direct approach to identify molecules and mechanisms underlying auditory function. Here we report a locus for dominant deafness, DFNA36, which ...maps to human chromosome 9q13-21 in a region overlapping the DFNB7/B11 locus for recessive deafness. We identified eight mutations in a new gene, transmembrane cochlear-expressed gene 1 (TMC1), in a DFNA36 family and eleven DFNB7/B11 families. We detected a 1.6-kb genomic deletion encompassing exon 14 of Tmc1 in the recessive deafness (dn) mouse mutant, which lacks auditory responses and has hair-cell degeneration. TMC1 and TMC2 on chromosome 20p13 are members of a gene family predicted to encode transmembrane proteins. Tmc1 mRNA is expressed in hair cells of the postnatal mouse cochlea and vestibular end organs and is required for normal function of cochlear hair cells.
Taste receptors cells are responsible for detecting a wide variety of chemical stimuli. Several molecules including both G protein coupled receptors and ion channels have been shown to be involved in ...the detection and transduction of tastants. We report on the expression of two members of the transient receptor potential (TRP) family of ion channels, PKD1L3 and PKD2L1, in taste receptor cells. Both of these channels belong to the larger polycystic kidney disease (PKD or TRPP) subfamily of TRP channels, members of which have been demonstrated to be non‐selective cation channels and permeable to both Na+ and Ca2+. Pkd1l3 and Pkd2l1 are co‐expressed in a select subset of taste receptor cells and therefore may, like other PKD channels, function as a heteromer. We found the taste receptor cells expressing Pkd1l3 and Pkd2l1 to be distinct from those that express components of sweet, bitter and umami signal transduction pathways. These results provide the first evidence for a role of TRPP channels in taste receptor cell function.
We identified the
Grp gene, encoding gastrin-releasing peptide, as being highly expressed both in the lateral nucleus of the amygdala, the nucleus where associations for Pavlovian learned fear are ...formed, and in the regions that convey fearful auditory information to the lateral nucleus. Moreover, we found that GRP receptor (GRPR) is expressed in GABAergic interneurons of the lateral nucleus. GRP excites these interneurons and increases their inhibition of principal neurons. GRPR-deficient mice showed decreased inhibition of principal neurons by the interneurons, enhanced long-term potentiation (LTP), and greater and more persistent long-term fear memory. By contrast, these mice performed normally in hippocampus-dependent Morris maze. These experiments provide genetic evidence that GRP and its neural circuitry operate as a negative feedback regulating fear and establish a causal relationship between
Grpr gene expression, LTP, and amygdala-dependent memory for fear.
In the gustatory system, the recognition of sugars, amino acids and bitter‐tasting compounds is the function of specialized G protein‐coupled receptors. Recently, two members of novel subfamily of G ...protein‐coupled receptors were proposed to function as taste receptors based on their specific expression in taste receptor cells. Here, we report the identification of a third member, T1R3, of this family of receptors. T1R3 maps near the telomere of mouse chromosome 4 rendering it a candidate for the Sac locus, a primary determinant of sweet preference in mice. Consistent with its candidacy for the Sac locus, T1R3 displays taste receptor cell‐specific expression. In addition, taster and non‐taster strains of mouse harbor different alleles of T1R3.
We aimed to assess the effect of APOE ε variants on warfarin-related intracerebral hemorrhage (wICH), evaluated their predictive power, and tested for interaction with warfarin in causing wICH.
This ...was a prospective, 2-stage (discovery and replication), case-control study. wICH was classified as lobar or nonlobar based on the location of the hematoma. Controls were sampled from ambulatory clinics (discovery) and random digit dialing (replication). APOE ε variants were directly genotyped. A case-control design and logistic regression analysis were utilized to test for association between APOE ε and wICH. A case-only design and logistic regression analysis were utilized to test for interaction between APOE ε and warfarin. Receiver operating characteristic curves were implemented to evaluate predictive power.
The discovery stage included 319 wICHs (44% lobar) and 355 controls. APOE ε2 was associated with lobar (odds ratio OR 2.46; p < 0.001) and nonlobar wICH (OR 1.67; p = 0.04), whereas ε4 was associated with lobar (OR 2.09; p < 0.001) but not nonlobar wICH (p = 0.35). The replication stage (63 wICHs and 1,030 controls) confirmed the association with ε2 (p = 0.03) and ε4 (p = 0.003) for lobar but not for nonlobar wICH (p > 0.20). Genotyping information on APOE ε variants significantly improved case/control discrimination of lobar wICH (C statistic 0.80). No statistical interaction between warfarin and APOE was found (p > 0.20).
APOE ε variants constitute strong risk factors for lobar wICH. APOE exerts its effect independently of warfarin, although power limitations render this absence of interaction preliminary. Evaluation of the predictive ability of APOE in cohort studies is warranted.
Intracerebral hemorrhage has a substantial genetic component. We performed a preliminary search for rare coding variants associated with intracerebral hemorrhage.
A total of 757 cases and 795 ...controls were genotyped using the Illumina HumanExome Beadchip (Illumina, Inc, San Diego, CA). Meta-analyses of single-variant and gene-based association were computed.
No rare coding variants were associated with intracerebral hemorrhage. Three common variants on chromosome 19q13 at an established susceptibility locus, encompassing TOMM40, APOE, and APOC1, met genome-wide significance (P<5e-08). After adjusting for the APOE epsilon alleles, this locus was no longer convincingly associated with intracerebral hemorrhage. No gene reached genome-wide significance level in gene-based association testing.
Although no coding variants of large effect were detected, this study further underscores a major challenge for the study of genetic susceptibility loci; large sample sizes are required for sufficient power except for loci with large effects.
Stem cells have two remarkable properties. They can either renew themselves or they can differentiate into one or more adult cell types. Stem cells derived from a human embryo appear to have an ...unlimited capacity to self‐renew in cell culture, and they are also able to differentiate into hundreds of adult cell types. Human embryonic stem cell lines offer a platform technology that has the potential to elucidate the molecular mechanisms that determine adult cell fate, generate cellular models for discovery of new drugs, and create populations of differentiated cells for novel transplantation therapies. The National Institutes of Health (NIH) has identified some of the rate‐limiting steps toward realizing this potential, and has forged funding initiatives to accelerate research progress. Given the remarkable potential, NIH support for research using stem cells is an important priority for the foreseeable future. Developmental Dynamics 236:3193–3198, 2007. Published 2007 Wiley‐Liss, Inc.
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