A.I. Berro

Regulator of G protein signaling 2 is a key modulator of airway hyperresponsiveness

BACKGROUND Drugs targeting individual G protein-coupled receptors are used as asthma therapies, but this strategy is limited because of G protein-coupled receptor signal redundancy. Regulator of G protein signaling 2 (RGS2), an intracellular selective inhibitor of multiple bronchoconstrictor receptors, may play a central role in the pathophysiology and treatment of asthma. OBJECTIVE We defined functions and mechanisms of RGS2 in regulating airway hyperresponsiveness (AHR), the pathophysiologic hallmark of asthma. METHODS Real-time PCR and Western blot were used to determine changes in RGS2 expression in ovalbumin-sensitized/-challenged mice. We also used immunohistochemistry and real-time PCR to compare RGS2 expression between human asthmatic and control subjects. The AHR of RGS2 knockout mice was assessed by using invasive tracheostomy and unrestrained plethysmography. Effects of loss of RGS2 on mouse airway smooth muscle (ASM) remodeling, contraction, intracellular Ca(2+), and mitogenic signaling were determined in vivo and in vitro. RESULTS RGS2 was highly expressed in human and murine bronchial epithelium and ASM and was markedly downregulated in lungs of ovalbumin-sensitized/-challenged mice. Lung tissues and blood monocytes from asthma patients expressed significantly lower RGS2 protein (lung) and mRNA (monocytes) than from nonasthma subjects. The extent of reduction of RGS2 on human monocytes correlated with increased AHR. RGS2 knockout caused spontaneous AHR in mice. Loss of RGS2 augmented Ca(2+) mobilization and contraction of ASM cells. Loss of RGS2 also increased ASM mass and stimulated ASM cell growth via extracellular signal-regulated kinase and phosphatidylinositol 3-kinase pathways. CONCLUSION We identified RGS2 as a potent modulator of AHR and a potential novel therapeutic target for asthma.

Time-dependent effects of inhaled corticosteroids on lung function, bronchial hyperresponsiveness, and airway inflammation in asthma.

BACKGROUND Exhaled nitric oxide (F(ENO)) and exhaled breath condensate (EBC) are noninvasive markers that directly measure airway inflammation and may potentially be useful in assessing asthma control and response to therapy. OBJECTIVE To examine the time-dependent effects of inhaled corticosteroids on F(ENO) and EBC markers concomitantly with lung function and bronchial hyperresponsiveness. METHODS Eleven steroid-naive adults with mild-to-moderate persistent asthma were treated with mometasone furoate dry powder inhaler, 400 microg/d, for 8 weeks, followed by a 4-week washout. Forced expiratory volume in 1 second (FEV1), the concentration of methacholine calculated to cause a 20% decline in FEV1 (PC20), F(ENO), EBC pH, and EBC nitrite measurements before, during, and after treatment were analyzed and compared. RESULTS The mean (SEM) FEV1 increased from 3.01 (0.13) L (82% predicted) to 3.24 (0.18) L (87% predicted) by week 8 (P < .05). The PC20 level increased from 1.28 (0.31) mg/mL to 2.99 (0.51) mg/mL by treatment week 8 (P < .05) and remained relatively stable through washout week 4 (P < .05). The F(ENO) level decreased from 31.1 (4.1) ppb to 20.6 (4.5) ppb by treatment week 1 (P < .01), remained low through treatment week 8 (P < .01), then trended back to the baseline level by washout week 1 (P < .01). The median EBC pH increased from 7.81 (interquartile range, 7.49-8.09) to 8.02 (interquartile range, 7.87-8.12) by treatment week 4, but did not achieve statistical significance. The EBC nitrite level decreased from 17.6 (1.6) microM to 9.3 (0.9) microM by treatment week 8 (P < .01), and remained low throughout washout week 4 (P < .05). There was a negative correlation between F(ENO) and PC20 (Spearman rank correlation coefficient = -0.50, P < .001). CONCLUSION The F(ENO) level responded the earliest to treatment and withdrawal of inhaled corticosteroids, whereas changes in EBC markers were delayed but more sustained.

Expression and Function of a Novel Variant of Estrogen Receptor–α36 in Murine Airways

Evidence suggests that estrogen signaling is involved in sex differences in the prevalence rates and control of asthma, but the expression patterns of estrogen receptor variants and estrogen function in the lung are not well established. We investigated the expression of major estrogen receptor variants occurring naturally and after the development of allergen-induced airway hyperreactivity in a murine model of allergic asthma, along with the role of estrogen signaling in small-airway ciliary motion and smooth muscle contraction. Female BALB/c mice were sensitized with ovalbumin, and estrogen receptor expression patterns were examined by immunofluorescence and Western blot analysis. Time-lapse video and photodiode-based displacement measurement systems were used to assess the effects of estrogen signaling on airway ciliary beat frequency and smooth muscle contraction. We found that a novel variant of estrogen receptor (ER)-α, ER-α36, is expressed in airway epithelial and smooth muscle cells. ER-α36 was predominately localized on the plasma membranes of airway cells. After sensitization to allergen, the expression levels of ER-α36 increased significantly (P < 0.01), whereas the expression of ER-β and ER-α66 did not significantly change. Estrogen treatment in vitro resulted in a rapid increase in airway cilia motion in a dose-dependent fashion, but did not exert any effect on airway smooth muscle contraction. We speculate that the up-regulation of estrogen receptor expression associated with allergen-induced airway hyperresponsiveness may constitute a protective mechanism to facilitate the clearance of mucus. The identification and localization of specific estrogen receptor subtypes in the lung could lead to newer therapeutic avenues aimed at addressing sex differences of asthma susceptibility.