Control of P2X2 Channel Permeability by the Cytosolic Domain

ATP-gated P2X channels are the simplest of the three families of transmitter-gated ion channels. Some P2X channels display a time- and activation-dependent change in permeability as they undergo the transition from the relatively Na+-selective I1 state to the I2 state, which is also permeable to organic cations. We report that the previously reported permeability change of rat P2X2 (rP2X2) channels does not occur at mouse P2X2 (mP2X2) channels expressed in oocytes. Domain swaps, species chimeras, and point mutations were employed to determine that two specific amino acid residues in the cytosolic tail domain govern this difference in behavior between the two orthologous channels. The change in pore diameter was characterized using reversal potential measurements and excluded field theory for several organic ions; both rP2X2 and mP2X2 channels have a pore diameter of ~11 Å in the I1 state, but the transition to the I2 state increases the rP2X2 diameter by at least 3 Å. The I1 to I2 transition occurs with a rate constant of ~0.5 s^-1. The data focus attention on specific residues of P2X2 channel cytoplasmic domains as determinants of permeation in a state-specific manner

Uropathic Observations in Mice Expressing a Constitutively Active Point Mutation in the 5-HT_(3A) Receptor Subunit

Mutant mice with a hypersensitive serotonin (5-HT)_(3A) receptor were generated through targeted exon replacement. A valine to serine mutation (V13′S) in the channel-lining M2 domain of the 5-HT_(3A) receptor subunit rendered the 5-HT₃ receptor ∼70-fold more sensitive to serotonin and produced constitutive activity when combined with the 5-HT_(3B) subunit. Mice homozygous for the mutant allele (5-HT_(3A)^(vs/vs)) had decreased levels of 5-HT_(3A) mRNA. Measurements on sympathetic ganglion cells in these mice showed that whole-cell serotonin responses were reduced, and that the remaining 5-HT₃ receptors were hypersensitive. Male 5-HT_(3A)^(vs/vs) mice died at 2-3 months of age, and heterozygous (5-HT_(3A)^(vs/+)) males and homozygous mutant females died at 4-6 months of age from an obstructive uropathy. Both male and female 5-HT_(3A) mutant mice had urinary bladder mucosal and smooth muscle hyperplasia and hypertrophy, whereas male mutant mice had additional prostatic smooth muscle and urethral hyperplasia. 5-HT_(3A) mutant mice had marked voiding dysfunction characterized by a loss of micturition contractions with overflow incontinence. Detrusor strips from 5-HT_(3A)^(vs/vs) mice failed to contract to neurogenic stimulation, despite overall normal responses to a cholinergic agonist, suggestive of altered neuronal signaling in mutant mouse bladders. Consistent with this hypothesis, decreased nerve fiber immunoreactivity was observed in the urinary bladders of 5-HT_(3A)^(vs/vs) compared with 5-HT_(3A) wild-type (5-HT_(3A)^(+/+)) mice. These data suggest that persistent activation of the hypersensitive and constitutively active 5-HT_(3A) receptor in vivo may lead to excitotoxic neuronal cell death and functional changes in the urinary bladder, resulting in bladder hyperdistension, urinary retention, and overflow incontinence

The association of plasma biomarkers with computed tomography-assessed emphysema phenotypes

Rationale: Chronic obstructive pulmonary disease (COPD) is a phenotypically heterogeneous disease. In COPD, the presence of emphysema is associated with increased mortality and risk of lung cancer. High resolution computed tomography (HRCT) scans are useful in quantifying emphysema but are associated with radiation exposure and high incidence of false positive findings (i.e., nodules). Using a comprehensive biomarker panel, we sought to determine if there was a peripheral blood biomarker signature of emphysema. Methods: 114 plasma biomarkers were measured using a custom assay in 588 individuals enrolled in the COPDGene study. Quantitative emphysema measurements included percent low lung attenuation (%LAA) ≤ −950 HU, ≤ − 910 HU and mean lung attenuation at the 15th percentile on lung attenuation curve (LP15A). Multiple regression analysis was performed to determine plasma biomarkers associated with emphysema independent of covariates age, gender, smoking status, body mass index and FEV1. The findings were subsequently validated using baseline blood samples from a separate cohort of 388 subjects enrolled in the Treatment of Emphysema with a Selective Retinoid Agonist (TESRA) study. Results: Regression analysis identified multiple biomarkers associated with CT-assessed emphysema in COPDGene, including advanced glycosylation end-products receptor (AGER or RAGE, p < 0.001), intercellular adhesion molecule 1 (ICAM, p < 0.001), and chemokine ligand 20 (CCL20, p < 0.001). Validation in the TESRA cohort revealed significant associations with RAGE, ICAM1, and CCL20 with radiologic emphysema (p < 0.001 after meta-analysis). Other biomarkers that were associated with emphysema include CDH1, CDH 13 and SERPINA7, but were not available for validation in the TESRA study. Receiver operating characteristics analysis demonstrated a benefit of adding a biomarker panel to clinical covariates for detecting emphysema, especially in those without severe airflow limitation (AUC 0.85). Conclusions: Our findings, suggest that a panel of blood biomarkers including sRAGE, ICAM1 and CCL20 may serve as a useful surrogate measure of emphysema, and when combined with clinical covariates, may be useful clinically in predicting the presence of emphysema compared to just using covariates alone, especially in those with less severe COPD. Ultimately biomarkers may shed light on disease pathogenesis, providing targets for new treatments. Electronic supplementary material The online version of this article (doi:10.1186/s12931-014-0127-9) contains supplementary material, which is available to authorized users

The association of plasma biomarkers with computed tomography-assessed emphysema phenotypes

Abstract Rationale Chronic obstructive pulmonary disease (COPD) is a phenotypically heterogeneous disease. In COPD, the presence of emphysema is associated with increased mortality and risk of lung cancer. High resolution computed tomography (HRCT) scans are useful in quantifying emphysema but are associated with radiation exposure and high incidence of false positive findings (i.e., nodules). Using a comprehensive biomarker panel, we sought to determine if there was a peripheral blood biomarker signature of emphysema. Methods 114 plasma biomarkers were measured using a custom assay in 588 individuals enrolled in the COPDGene study. Quantitative emphysema measurements included percent low lung attenuation (%LAA)≤ - 950 HU, ≤ -910 HU and mean lung attenuation at the 15th percentile on lung attenuation curve (LP15A). Multiple regression analysis was performed to determine plasma biomarkers associated with emphysema independent of covariates age, gender, smoking status, body mass index and FEV1. The findings were subsequently validated using baseline blood samples from a separate cohort of 388 subjects enrolled in the Treatment of Emphysema with a Selective Retinoid Agonist (TESRA) study. Results Regression analysis identified multiple biomarkers associated with CT-assessed emphysema in COPDGene, including advanced glycosylation end-products receptor (AGER or RAGE, p < 0.001), intercellular adhesion molecule 1 (ICAM, p < 0.001), and chemokine ligand 20 (CCL20, p < 0.001). Validation in the TESRA cohort revealed significant associations with RAGE, ICAM1, and CCL20 with radiologic emphysema (p < 0.001 after meta-analysis). Other biomarkers that were associated with emphysema include CDH1, CDH 13 and SERPINA7, but were not available for validation in the TESRA study. Receiver operating characteristics analysis demonstrated a benefit of adding a biomarker panel to clinical covariates for detecting emphysema, especially in those without severe airflow limitation (AUC 0.85). Conclusions Our findings, suggest that a panel of blood biomarkers including sRAGE, ICAM1 and CCL20 may serve as a useful surrogate measure of emphysema, and when combined with clinical covariates, may be useful clinically in predicting the presence of emphysema compared to just using covariates alone, especially in those with less severe COPD. Ultimately biomarkers may shed light on disease pathogenesis, providing targets for new treatments.http://deepblue.lib.umich.edu/bitstream/2027.42/134591/1/12931_2014_Article_127.pd

Systemic Biomarkers of Neutrophilic Inflammation, Tissue Injury and Repair in COPD Patients with Differing Levels of Disease Severity

The identification and validation of biomarkers to support the assessment of novel therapeutics for COPD continues to be an important area of research. The aim of the current study was to identify systemic protein biomarkers correlated with measures of COPD severity, as well as specific protein signatures associated with comorbidities such as metabolic syndrome. 142 protein analytes were measured in serum of 140 patients with stable COPD, 15 smokers without COPD and 30 non-smoking controls. Seven analytes (sRAGE, EN-RAGE, NGAL, Fibrinogen, MPO, TGF-α and HB-EGF) showed significant differences between severe/very severe COPD, mild/moderate COPD, smoking and non-smoking control groups. Within the COPD subjects, univariate and multivariate analyses identified analytes significantly associated with FEV1, FEV1/FVC and DLCO. Most notably, a set of 5 analytes (HB-EGF, Fibrinogen, MCP-4, sRAGE and Sortilin) predicted 21% of the variability in DLCO values. To determine common functions/pathways, analytes were clustered in a correlation network by similarity of expression profile. While analytes related to neutrophil function (EN-RAGE, NGAL, MPO) grouped together to form a cluster associated with FEV1 related parameters, analytes related to the EGFR pathway (HB-EGF, TGF-α) formed another cluster associated with both DLCO and FEV1 related parameters. Associations of Fibrinogen with DLCO and MPO with FEV1/FVC were stronger in patients without metabolic syndrome (r  =  −0.52, p  = 0.005 and r  =  −0.61, p  = 0.023, respectively) compared to patients with coexisting metabolic syndrome (r  =  −0.25, p  = 0.47 and r  =  −0.15, p  = 0.96, respectively), and may be driving overall associations in the general cohort. In summary, our study has identified known and novel serum protein biomarkers and has demonstrated specific associations with COPD disease severity, FEV1, FEV1/FVC and DLCO. These data highlight systemic inflammatory pathways, neutrophil activation and epithelial tissue injury/repair processes as key pathways associated with COPD

Peristalsis is impaired in the small intestine of mice lacking the P2X3 subunit

P2X receptors are ATP-gated cation channels composed of one or more of seven different subunits. P2X receptors participate in intestinal neurotransmission but the subunit composition of enteric P2X receptors is unknown. In this study, we used tissues from P2X3 wild-type (P2X3+/+) mice and mice in which the P2X3 subunit gene had been deleted (P2X3−/−) to investigate the role of this subunit in neurotransmission in the intestine. RT-PCR analysis of mRNA from intestinal tissues verified P2X3 gene deletion. Intracellular electrophysiological methods were used to record synaptic and drug-induced responses from myenteric neurons in vitro. Drug-induced longitudinal muscle contractions were studied in vitro. Intraluminal pressure-induced reflex contractions (peristalsis) of ileal segments were studied in vitro using a modified Trendelenburg preparation. Gastrointestinal transit was measured as the progression in 30 min of a liquid radioactive marker administered by gavage to fasted mice. Fast excitatory postsynaptic potentials recorded from S neurons (motoneurons and interneurons) were similar in tissues from P2X3+/+ and P2X3−/− mice. S neurons from P2X3+/+ and P2X3−/− mice were depolarized by application of ATP but not α,β-methylene ATP, an agonist of P2X3 subunit-containing receptors. ATP and α,β-methylene ATP induced depolarization of AH (sensory) neurons from P2X3+/+ mice. ATP, but not α,β-methylene ATP, caused depolarization of AH neurons from P2X3−/− mice. Peristalsis was inhibited in ileal segments from P2X3−/− mice but longitudinal muscle contractions caused by nicotine and bethanechol were similar in segments from P2X3+/+ and P2X3−/− mice. Gastrointestinal transit was similar in P2X3+/+ and P2X3−/− mice. It is concluded that P2X3 subunit-containing receptors participate in neural pathways underlying peristalsis in the mouse intestine in vitro. P2X3 subunits are localized to AH (sensory) but not S neurons. P2X3 receptors may contribute to detection of distention or intraluminal pressure increases and initiation of reflex contractions