PPARγ agonist rosiglitazone prevents perinatal nicotine exposure-induced asthma in rat offspring

Perinatal nicotine vaping exposure induces pro-myofibroblastic phenotype in rat bone marrow-derived mesenchymal stem cells

Perinatal nicotine exposure via tobacco smoking results in increased proclivity to chronic lung disease (CLD); however, the underlying molecular mechanisms remain incompletely understood. We previously demonstrated that in addition to nicotine's direct effects on the developing lung, there are also adverse molecular alterations in bone marrow-derived mesenchymal stem cells (BMSCs), which are vital to lung injury repair. Whether perinatal nicotine exposure via electronic-cigarette (e-cig) vaping also adversely affects BMSCs is unknown. This is highly relevant due to marked increase in e-cig vaping including by pregnant women. Hypothesizing that perinatal nicotine exposure via e-cig vaping predisposes BMSCs to a pro-myofibroblastic phenotype, pregnant rat dams were exposed to fresh air (control), vehicle (e-cig without nicotine), or e-cig (e-cig with nicotine) daily during pregnancy and lactation. At postnatal day 21, offspring BMSCs were isolated and studied for cell proliferation, migration, wound healing response, and expression of key Wnt and PPARγ signaling intermediates (β-catenin, LEF-1, PPARγ, ADRP and C/EBPα) and myogenic markers (fibronectin, αSMA, calponin) proteins using immunoblotting. Compared to controls, perinatal e-cig exposure resulted in significant decrease in BMSC proliferation, migration, and wound healing response. The expression of key Wnt signaling intermediates (β-catenin, LEF-1) and myogenic markers (fibronectin, αSMA, calponin) increased significantly, while PPARγ signaling intermediates (PPARγ, ADRP, and C/EBPα) decreased significantly. Based on these data, we conclude that perinatally e-cig exposed BMSCs demonstrate pro-myofibroblastic phenotype and impaired injury-repair potential, indicating a potentially similar susceptibility to CLD following perinatal nicotine exposure via vaping as seen following parenteral perinatal nicotine exposure.

Perinatal Exposure to Nicotine Alters Sperm RNA Profiles in Rats

Perinatal exposure to smoking has been associated with childhood asthma, one of the most common pediatric conditions affecting millions of children globally. Of great interest, this disease phenotype appears heritable as it can persist across multiple generations even in the absence of persistent exposure to smoking in subsequent generations. Although the molecular mechanisms underlying childhood asthma induced by perinatal exposure to smoking or nicotine remain elusive, an epigenetic mechanism has been proposed, which is supported by the data from our earlier analyses on germline DNA methylation (5mC) and histone marks (H3 and H4 acetylation). To further investigate the potential epigenetic inheritance of childhood asthma induced by perinatal nicotine exposure, we profiled both large and small RNAs in the sperm of F1 male rats. Our data revealed that perinatal exposure to nicotine leads to alterations in the profiles of sperm-borne RNAs, including mRNAs and small RNAs, and that rosiglitazone, a PPARγ agonist, can attenuate the effect of nicotine and reverse the sperm-borne RNA profiles of F1 male rats to close to placebo control levels.

Rosiglitazone restores nitric oxide synthase-dependent reactivity of cerebral arterioles in rats exposed to prenatal alcohol

BACKGROUND

Prenatal exposure to alcohol leads to a greater incidence of many cardiovascular-related diseases, presumably via a mechanism that may involve increased oxidative stress. An agonist of peroxisome proliferator-activated receptor gamma (PPARγ; rosiglitazone) has been shown to suppress alcohol-induced neuroinflammation and oxidative stress. The goal of this study was to determine whether acute and chronic treatment with rosiglitazone could restore or prevent impaired nitric oxide synthase (NOS)-dependent responses of cerebral arterioles in male and female adult (14-16 weeks old) rats exposed to alcohol in utero.

METHODS

We fed Sprague-Dawley dams a liquid diet with or without 3% ethanol for the duration of their pregnancy (21-23 days). In the first series of studies, we examined the reactivity of cerebral arterioles to eNOS- (ADP), nNOS-dependent (NMDA), and NOS-independent agonists in male and female adult rats before and during acute (1 hour) topical application of rosiglitazone (1 µM). In a second series of studies, we examined the influence of chronic treatment with rosiglitazone (3 mg/kg/day in drinking water for 2-3 weeks) on the responses of cerebral arterioles in male and female adult rats exposed to alcohol in utero.

RESULTS

We found that in utero exposure to alcohol similarly reduced responses of cerebral arterioles to ADP and NMDA, but not to nitroglycerin in male and female adult rats. In addition, acute treatment of the male and female adult rats with rosiglitazone similarly restored this impairment in cerebral vascular function to that observed in controls. We also found that chronic treatment with rosiglitazone prevented impaired vascular function in male and female adult rats that were exposed to alcohol in utero.

CONCLUSIONS

PPARγ activation may be an effective and relevant treatment to reverse or prevent cerebral vascular abnormalities associated with prenatal exposure to alcohol.

Antenatal PPAR-γ agonist pioglitazone stimulates fetal lung maturation equally in males and females

Antenatal steroids (ANS) accelerate fetal lung maturation and reduce the incidence of respiratory distress syndrome. However, sex specificity, i.e., being less effective in males, and potential long-term neurodevelopmental sequelae, particularly with repeated courses, remain significant limitations. The differential sex response to ANS is likely mediated via the inhibitory effect of fetal androgens on steroid's stimulatory effect on alveolar epithelial-mesenchymal interactions. Since peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists accelerate lung maturation by stimulating alveolar epithelial-mesenchymal interactions, independent of fetal sex, we hypothesized that the effect of PPAR-γ agonist pioglitazone (PGZ) would be sex-independent. Pregnant Sprague-Dawley rat dams were intraperitoneally administered dexamethasone (DEX) or PGZ on embryonic day (e) 18 and e19. At e20, pups were delivered by cesarean section, and fetal lungs and brains were examined for markers of lung maturation and apoptosis, respectively. Mixed epithelial-fibroblast cell cultures were examined to gain mechanistic insights. Antenatal PGZ increased alveolar epithelial and mesenchymal maturation markers equally in males and females; in contrast, antenatal DEX had sex-specific effects. Additionally, unlike DEX, antenatal PGZ did not increase hippocampal apoptosis. We conclude that PPAR-γ agonist administration is an effective, and probably even a superior, alternative to ANS for accelerating fetal lung maturity equally in both males and females.

Developmental Timing Determines the Protective Effect of Maternal Electroacupuncture on Perinatal Nicotine Exposure-Induced Offspring Lung Phenotype

Introduction. Environmental exposure of the developing offspring to cigarette smoke or nicotine is an important predisposing factor for many chronic respiratory conditions, such as asthma, emphysema, pulmonary fibrosis, and so forth, in the exposed offspring. Studies showed that electroacupuncture (EA) applied to maternal "Zusanli" (ST36) acupoints during pregnancy and lactation protects against perinatal nicotine exposure- (PNE-) induced lung damage. However, the most effective time period, that is, prenatal vs. postnatal, to attain this effect has not been determined.

OBJECTIVE

To determine the most effective developmental timing of EA's protective effect against PNE-induced lung phenotype in the exposed offspring.

METHODS

Pregnant rats were given (1) saline ("S" group); (2) nicotine ("N" group); (3) nicotine + EA, exclusively prenatally ("Pre-EA" group); (4) nicotine + EA, exclusively postnatally ("Post-EA," group); and (5) nicotine + EA, administered both prenatally and postnatally ("Pre- and Post-EA" group). Nicotine was injected once daily (1 mg/kg, 100 μl) and EA was administered to bilateral ST36 acupoints once daily during the specified time-periods. At the end of the experimental periods, key hypothalamic pituitary adrenal (HPA) axis markers in pups and dams, and lung function, morphometry, and the central molecular markers of lung development in the offspring were determined.

RESULTS

After nicotine exposure, alveolar mean linear intercept (MLI) increased, but mean alveolar number (MAN) decreased and lung PPARγ level decreased, but glucocorticoid receptor (GR) and serum corticosterone (Cort) levels increased, in line with the known PNE-induced lung phenotype. In the nicotine exposed group, maternal hypothalamic corticotropin releasing hormone (CRH) level decreased, but pituitary adrenocorticotropic hormone (ACTH) and serum Cort levels increased. In the "Pre- and Post-EA" groups, PNE-induced alterations in lung morphometry, lung development markers, and HPA axis were blocked. In the "Pre-EA" group, PNE-induced changes in lung morphometry, GR, and maternal HPA axis improved; lung PPARγ level decreased, but glucocorticoid receptor (GR) and serum corticosterone (Cort) levels increased, in line with the known PNE-induced lung phenotype. In the nicotine exposed group, maternal hypothalamic corticotropin releasing hormone (CRH) level decreased, but pituitary adrenocorticotropic hormone (ACTH) and serum Cort levels increased. In the "Pre- and Post-EA" groups, PNE-induced alterations in lung morphometry, lung development markers, and HPA axis were blocked. In the "Pre-EA" group, PNE-induced changes in lung morphometry, GR, and maternal HPA axis improved; lung PPAR.

CONCLUSIONS

Maternal EA applied to ST36 acupoints during both pre- and postnatal periods preserves offspring lung structure and function despite perinatal exposure to nicotine. EA applied during the "prenatal period" affords only limited benefits, whereas EA applied during the "postnatal period" is ineffective, suggesting that the EA's effects in modulating PNE-induced lung phenotype are limited to specific time-periods during lung development.

The impact of perinatal nicotine exposure on fetal lung development and subsequent respiratory morbidity

Maternal smoking during pregnancy remains as a significant public health crisis as it did decades ago. Although its prevalence is decreasing in high-income countries, it has worsened globally, along with a concerning emergence of electronic-cigarette usage within the last two decades. Extensive epidemiologic and experimental evidence exists from both human and animal studies, demonstrating the detrimental long-term pulmonary outcomes in the offspring of mothers who smoke during pregnancy. Even secondhand and thirdhand smoke exposure to the developing lung might be as or even more harmful than firsthand smoke exposure. Furthermore, these effects are not limited only to the exposed progeny, but can also be transmitted transgenerationally. There is compelling evidence to support that the majority of the effects of perinatal smoke exposure on the developing lung, including the transgenerational transmission of asthma, is mediated by nicotine. Nicotine exposure induces cell-specific molecular changes in lungs, which offers a unique opportunity to prevent, halt, and/or reverse the resultant damage through targeted molecular interventions. Experimentally, the proposed interventions, such as administration of peroxisome proliferator-activated receptor gamma (PPARγ) agonists can not only block but also potentially reverse the perinatal nicotine exposure-induced respiratory morbidity in the exposed offspring. However, the development of a safe and effective intervention is still many years away. In the meantime, electropuncture at specific acupoints appears to be emerging as a more practical and safe physiologic approach to block the harmful pulmonary consequences of perinatal nicotine exposure.

The α3 and α4 nicotinic acetylcholine receptor (nAChR) subunits in the brainstem medulla of sudden infant death syndrome (SIDS)

SIDS occurs in early infancy and predominantly during a sleep period. Abnormalities in nicotine receptor binding and in the expression of the nicotinic acetylcholine receptor (nAChR) subunits α7 and β2 have been reported in the brainstem of SIDS infants. This study focuses on the α3 and α4 nAChR subunits as α3 is important for early postnatal survival while α4 is crucial for nicotine-elicited antinociception and sleep-wake cycle regulation. Tissue from the rostral medulla of infants who died with a known cause of death (eSUDI, n = 7), and from SIDS classified as SIDS I (n = 8) and SIDS II (n = 27), was immunohistochemically stained for the α3 and α4 nAChR subunits and quantified in 9 nuclei comparing amongst these groups. The association with risk factors of sex, cigarette smoke exposure, upper respiratory tract infection (URTI), prone sleeping and bedsharing was also evaluated. Results showed that only α4 changes (increase) were evident in SIDS, occurring in the hypoglossal and cuneate nuclei of SIDS II infants and the nucleus of the spinal trigeminal tract of SIDS I infants. Amongst the SIDS infants, cigarette smoke exposure was only associated with decreased α4 in cribriform fibre tracts, while sex and bedsharing were associated with increases in α3 in the dorsal motor nucleus of the vagus and solitary nucleus, respectively. Combined, these findings suggest that abnormalities in endogenous acetylcholine synthesis and regulation may underlie the altered α3 and α4 nAChR subunit expressions in the SIDS brainstem medulla since the changes were not related to cigarette smoke exposure.

Epigenetic impacts of maternal tobacco and e-vapour exposure on the offspring lung

In utero exposure to tobacco products, whether maternal or environmental, have harmful effects on first neonatal and later adult respiratory outcomes. These effects have been shown to persist across subsequent generations, regardless of the offsprings' smoking habits. Established epigenetic modifications induced by in utero exposure are postulated as the mechanism underlying the inherited poor respiratory outcomes. As e-cigarette use is on the rise, their potential to induce similar functional respiratory deficits underpinned by an alteration in the foetal epigenome needs to be explored. This review will focus on the functional and epigenetic impact of in utero exposure to maternal cigarette smoke, maternal environmental tobacco smoke, environmental tobacco smoke and e-cigarette vapour on foetal respiratory outcomes.

Prevention of perinatal nicotine-induced bone marrow mesenchymal stem cell myofibroblast differentiation by augmenting the lipofibroblast phenotype

Perinatal nicotine exposure drives the differentiation of alveolar lipofibroblasts (LIFs), which are critical for lung injury repair, to myofibroblasts (MYFs), which are the hallmark of chronic lung disease. Bone marrow-derived mesenchymal stem cells (BMSCs) are important players in lung injury repair; however, how these cells are affected with perinatal nicotine exposure and whether these can be preferentially driven to a lipofibroblastic phenotype are not known. We hypothesized that perinatal nicotine exposure would block offspring BMSCs lipogenic differentiation, driving these cells toward a MYF phenotype. Since peroxisome proliferator activated-receptor γ (PPARγ) agonists can prevent nicotine-induced MYF differentiation of LIFs, we further hypothesized that the modulation of PPARγ expression would inhibit nicotine's myogenic effect on BMSCs. Sprague Dawley dams were perinatally administered nicotine (1 mg/kg bodyweight) with or without the potent PPARγ agonist rosiglitazone (RGZ), both administered subcutaneously. At postnatal day 21, BMSCs were isolated and characterized morphologically, molecularly, and functionally for their lipogenic and myogenic potentials. Perinatal nicotine exposure resulted in decreased oil red O staining, triolein uptake, expression of PPARγ, and its downstream target gene adipocyte differentiation-related protein by BMSCs, but enhanced α-smooth muscle actin and fibronectin expression, and activated Wnt signaling, all features indicative of their inhibited lipogenic, but enhanced myogenic potential. Importantly, concomitant treatment with RGZ virtually blocked all of these nicotine-induced morphologic, molecular, and functional changes. Based on these data, we conclude that BMSCs can be directionally induced to differentiate into the lipofibroblastic phenotype, and PPARγ agonists can effectively block perinatal nicotine-induced MYF transdifferentiation, suggesting a possible molecular therapeutic approach to augment BMSC's lung injury/repair potential.

Protective effect of electro-acupuncture at maternal different points on perinatal nicotine exposure-induced pulmonary dysplasia in offspring based on HPA axis and signal transduction pathway

Perinatal nicotine exposure can not only lead to lung dysplasia in offspring, but also cause epigenetic changes and induce transgenerational asthma. Previous studies have shown that electro-acupuncture (EA) applied to "Zusanli" (ST 36) can improve the lung morphology and correct abnormal expression of lung development-related protein in perinatal nicotine exposure offspring. However, it is still unclear whether ST 36 has a specific therapeutic effect and how maternal acupuncture can protect the offspring from pulmonary dysplasia. In this study, we compared the different effect of ST 36 and "Fenglong" (ST 40), which belong to the same meridian, in terms of lung pulmonary function and morphology, PPARγ, β-catenin, GR levels in the lung tissues and CORT in the serum of perinatal nicotine exposure offspring, and explored the mechanism of acupuncture based on the maternal hypothalamus-pituitary-adrenal (HPA) axis. It is shown that EA applied to ST 36 could restore the normal function of maternal HPA axis and alleviate maternal glucocorticoid overexposure in offspring, thereby it can up-regulate the PTHrP/PPARγ and down-regulate the Wnt/β-catenin signaling pathways, and protects perinatal nicotine exposure-induced pulmonary dysplasia in offspring. Its effect is better than that of ST 40. These results are of great significance in preventing perinatal nicotine exposure-induced pulmonary dysplasia in offspring.

The Role of Nicotine in the Effects of Maternal Smoking during Pregnancy on Lung Development and Childhood Respiratory Disease. Implications for Dangers of E-Cigarettes

Use of e-cigarettes, especially among the young, is increasing at near-exponential rates. This is coupled with a perception that e-cigarettes are safe and with unlimited advertising geared toward vulnerable populations, the groups most likely to smoke or vape during pregnancy. There is now wide appreciation of the dangers of maternal smoking during pregnancy and the lifelong consequences this has on offspring lung function, including the increased risk of childhood wheezing and subsequent asthma. Recent evidence strongly supports that much of the effect of smoking during pregnancy on offspring lung function is mediated by nicotine, making it highly likely that e-cigarette use during pregnancy will have the same harmful effects on offspring lung function and health as do conventional cigarettes. In fact, the evidence for nicotine being the mediator of harm of conventional cigarettes may be most compelling for its effects on lung development. This raises concerns about both the combined use of e-cigarettes plus conventional cigarettes by smokers during pregnancy as well as the use of e-cigarettes by e-cigarette-only users who think them safe or by those sufficiently addicted to nicotine to not be able to quit e-cigarette usage during pregnancy. Thus, it is important for health professionals to be aware of the risks of e-cigarette usage during pregnancy, particularly as it pertains to offspring respiratory health.

Impaired Lung Mitochondrial Respiration Following Perinatal Nicotine Exposure in Rats

Perinatal smoke/nicotine exposure predisposes to chronic lung disease and morbidity. Mitochondrial abnormalities may contribute as the PPARγ pathway is involved in structural and functional airway deficits after perinatal nicotine exposure. We hypothesized perinatal nicotine exposure results in lung mitochondrial dysfunction that can be rescued by rosiglitazone (RGZ; PPARγ receptor agonist). Sprague-Dawley dams received placebo (CON), nicotine (NIC, 1 mg kg(-1)), or NIC + RGZ (3 mg kg(-1)) daily from embryonic day 6 to postnatal day 21. Parenchymal lung (~10 mg) was taken from adult male offspring for mitochondrial assessment in situ. ADP-stimulated O2 consumption was less in NIC and NIC + RGZ compared to CON (F[2,14] = 17.8; 4.5 ± 0.8 and 4.1 ± 1.4 vs. 8.8 ± 2.5 pmol s mg(-1); p < 0.05). The respiratory control ratio for ADP, an index of mitochondrial coupling, was reduced in NIC and remediated in NIC + RGZ (F[2,14] = 3.8; p < 0.05). Reduced mitochondrial oxidative capacity and abnormal coupling were evident after perinatal nicotine exposure. RGZ improved mitochondrial function through tighter coupling of oxidative phosphorylation.

Inter- and transgenerational epigenetic inheritance: evidence in asthma and COPD?

Evidence is now emerging that early life environment can have lifelong effects on metabolic, cardiovascular, and pulmonary function in offspring, a concept also known as fetal or developmental programming. In mammals, developmental programming is thought to occur mainly via epigenetic mechanisms, which include DNA methylation, histone modifications, and expression of non-coding RNAs. The effects of developmental programming can be induced by the intrauterine environment, leading to intergenerational epigenetic effects from one generation to the next. Transgenerational epigenetic inheritance may be considered when developmental programming is transmitted across generations that were not exposed to the initial environment which triggered the change. So far, inter- and transgenerational programming has been mainly described for cardiovascular and metabolic disease risk. In this review, we discuss available evidence that epigenetic inheritance also occurs in respiratory diseases, using asthma and chronic obstructive pulmonary disease (COPD) as examples. While multiple epidemiological as well as animal studies demonstrate effects of 'toxic' intrauterine exposure on various asthma-related phenotypes in the offspring, only few studies link epigenetic marks to the observed phenotypes. As epigenetic marks may distinguish individuals most at risk of later disease at early age, it will enable early intervention strategies to reduce such risks. To achieve this goal further, well designed experimental and human studies are needed.

Perinatal nicotine exposure suppresses PPARγ epigenetically in lung alveolar interstitial fibroblasts

Due to the active inhibition of the adipogenic programming, the default destiny of the developing lung mesenchyme is to acquire a myogenic phenotype. We have previously shown that perinatal nicotine exposure, by down-regulating PPARγ expression, accentuates this property, culminating in myogenic pulmonary phenotype, though the underlying mechanisms remained incompletely understood. We hypothesized that nicotine-induced PPARγ down-regulation is mediated by PPARγ promoter methylation, controlled by DNA methyltransferase 1 (DNMT1) and methyl CpG binding protein 2 (MeCP2), two known key regulators of DNA methylation. Using cultured alveolar interstitial fibroblasts and an in vivo perinatal nicotine exposure rat model, we found that PPARγ promoter methylation is strongly correlated with inhibition of PPARγ expression in the presence of nicotine. Methylation inhibitor 5-aza-2'-deoxycytidine restored the nicotine-induced down-regulation of PPARγ expression and the activation of its downstream myogenic marker fibronectin. With nicotine exposure, a specific region of PPARγ promoter was significantly enriched with antibodies against chromatin repressive markers H3K9me3 and H3K27me3, dose-dependently. Similar data were observed with antibodies against DNA methylation regulatory factors DNMT1 and MeCP2. The knock down of DNMT1 and MeCP2 abolished nicotine-mediated increases in DNMT1 and MeCP2 protein levels, and PPARγ promoter methylation, restoring nicotine-induced down regulation of PPARγ and upregulation of the myogenic protein, fibronectin. The nicotine-induced alterations in DNA methylation modulators DNMT1 and MeCP2, PPARγ promoter methylation, and its down-stream targets, were also validated in perinatally nicotine exposed rat lung tissue. These data provide novel mechanistic insights into nicotine-induced epigenetic silencing of PPARγ that could be exploited to design novel targeted molecular interventions against the smoke exposed lung injury in general and perinatal nicotine exposure induced lung damage in particular.

Nuclear receptors in transgenerational epigenetic inheritance

Nuclear Receptors are ligand-activated transcription factors that translate information about the lipid environment into specific genetic programs, a property that renders them good candidates to be mediators of rapid adaptation changes of a species. Lipid-based morphogens, endocrine hormones, fatty acids and xenobiotics might act through this class of transcription factors making them regulators able to fine-tune physiological processes. Here we review the basic concepts and current knowledge on the process whereby small molecules act through nuclear receptors and contribute to transgenerational changes. Several molecules shown to cause transgenerational changes like phthalates, BPA, nicotine, tributylin bind and activate nuclear receptors like ERs, androgen receptors, glucocorticoid receptors or PPARγ. A specific subset of observations involving nuclear receptors has focused on the effects of environmental stress or maternal behaviour on the development of transgenerational traits. While these effects do not involve environmental ligands, they change the expression levels of Estrogen and glucocorticoid receptors of the second generation and consequently initiate an altered genetic program in the second generation. In this review we summarize the available literature about the role of nuclear receptors in transgenerational inheritance.

PPAR-γ agonist rosiglitazone reverses perinatal nicotine exposure-induced asthma in rat offspring

In a rat model, downregulation of homeostatic mesenchymal peroxisome proliferator-activated receptor-γ (PPAR-γ) signaling following perinatal nicotine exposure contributes to offspring asthma, which can be effectively prevented by concomitant administration of PPAR-γ agonist rosiglitazone (RGZ). However, whether perinatal nicotine exposure-induced asthma can be reversed is not known. We hypothesized that perinatal nicotine exposure-induced asthma would be reversed by PPAR-γ agonist RGZ. Pregnant rat dams received either placebo or nicotine from embryonic day 6 until term. Following spontaneous delivery at term, dams were continued on the assigned treatments, up to postnatal day 21 (PND21). However, at delivery, pups were divided into two groups; one group received placebo, and the other group received RGZ from PND1 to PND21. At PND21, pulmonary function and the expression of mesenchymal markers of airway contractility (α-smooth muscle actin, calponin, fibronectin, collagen I, and collagen III) were determined by immunoblotting and immunostaining for the evidence of reversibility of perinatal nicotine exposure-induced lung effects. Compared with controls, perinatal nicotine exposure caused 1) a significant increase in airway resistance and a decrease in airway compliance following methacholine challenge, 2) a significant increase in acetylcholine-induced tracheal constriction, and 3) increased pulmonary and tracheal expression of the mesenchymal markers of contractility. Treatment with RGZ, starting on PND1, reversed all of the nicotine-induced molecular and functional pulmonary effects, virtually normalizing the pulmonary phenotype of the treated animals. We conclude that perinatal nicotine exposure-induced functional and molecular alterations in upper and lower airways can be reversed by PPAR-γ agonist RGZ, allowing an effective intervention even when started postnatally.

The PPARγ agonist, rosiglitazone, attenuates airway inflammation and remodeling via heme oxygenase-1 in murine model of asthma

AIM

Rosiglitazone is one of the specific PPARγ agonists showing potential therapeutic effects in asthma. Though PPARγ activation was considered protective in inhibiting airway inflammation and remodeling in asthma, the specific mechanisms are still unclear. This study was aimed to investigate whether heme oxygenase-1 (HO-1) related pathways were involved in rosiglitazone-activated PPARγ signaling in asthma treatment.

METHODS

Asthma was induced in mice by multiple exposures to ovalbumin (OVA) in 8 weeks. Prior to every OVA challenge, the mice received rosiglitazone (5 mg/kg, p.o.). After the mice were sacrificed, the bronchoalveolar lavage fluid (BALF), blood samples and lungs were collected for analyses. The activities of HO-1, MMP-2 and MMP-9 in airway tissue were assessed, and the expression of PPARγ, HO-1 and p21 proteins was also examined.

RESULTS

Rosiglitazone administration significantly attenuated airway inflammation and remodeling in mice with OVA-induced asthma, which were evidenced by decreased counts of total cells, eosinophils and neutrophils, and decreased levels of IL-5 and IL-13 in BALF, and by decreased airway smooth muscle layer thickness and reduced airway collagen deposition. Furthermore, rosiglitazone administration significantly increased PPARγ, HO-1 and p21 expression and HO-1 activity, decreased MMP-2 and MMP-9 activities in airway tissue. All the therapeutic effects of rosiglitazone were significantly impaired by co-administration of the HO-1 inhibitor ZnPP.

CONCLUSION

Rosiglitazone effectively attenuates airway inflammation and remodeling in OVA-induced asthma of mice by activating PPARγ/HO-1 signaling pathway.

The lung alveolar lipofibroblast: an evolutionary strategy against neonatal hyperoxic lung injury

SIGNIFICANCE

Oxygen, the main mode of support for premature infants with immature lungs, can cause toxicity by producing reactive oxygen species (ROS) that disrupt homeostasis; yet, these same molecules were entrained to promote vertebrate lung phylogeny. By providing a deeper understanding of this paradox, we propose physiologically rational strategies to prevent chronic lung disease (CLD) of prematurity.

RECENT ADVANCES

To prevent neonatal hyperoxic lung damage biologically, we have exploited the alveolar defense mechanism(s) that evolutionarily evolved to combat increased atmospheric oxygen during the vertebrate water to land transition.

CRITICAL ISSUES

Over the course of vertebrate lung evolution, ROS promoted the formation of lipofibroblasts, specialized adepithelial cells, which protect the alveoli against oxidant injury; peroxisome proliferator-activated receptor gamma (PPARγ), the master switch for lipofibroblast differentiation, prevents such oxidant lung injury, both by directly promoting mesodermal differentiation and its antioxidant defenses, and indirectly by stimulating the developmental epithelial-mesenchymal paracrine interactions that have physiologically determined lung surfactant production in accord with the lung's phylogenetic adaptation to atmospheric oxygen, preventing Respiratory Distress Syndrome at birth.

FUTURE DIRECTIONS

The molecular strategy (PPARγ agonists) to prevent CLD of prematurity, proposed by us, although seems to be robust, effective, and safe under experimental conditions, it awaits detailed pharmacokinetic and pharmacodynamic studies for its safe and effective clinical translation to human infants. Antioxid. Redox Signal. 21, 1893-1904. "I have procured air [oxygen]…between five and six times as good as the best common air that I have ever met with." -Joseph Priestley, 1775.

Nicotine stimulates nerve growth factor in lung fibroblasts through an NFκB-dependent mechanism

RATIONALE

Airway hyperresponsiveness (AHR) is classically found in asthma, and persistent AHR is associated with poor asthma control. Although airway smooth muscle (ASM) cells play a critical pathophysiologic role in AHR, the paracrine contributions of surrounding cells such as fibroblasts to the contractile phenotype of ASM cells have not been examined fully. This study addresses the hypothesis that nicotine promotes a contractile ASM cell phenotype by stimulating fibroblasts to increase nerve growth factor (NGF) secretion into the environment.

METHODS

Primary lung fibroblasts isolated from wild type and α7 nicotinic acetylcholine receptor (α7 nAChR) deficient mice were treated with nicotine (50 µg/ml) in vitro for 72 hours. NGF levels were measured in culture media and in bronchoalveolar lavage (BAL) fluid from asthmatic, smoking and non-smoking subjects by ELISA. The role of the NFκB pathway in nicotine-induced NGF expression was investigated by measuring NFκB nuclear translocation, transcriptional activity, chromatin immunoprecipitation assays, and si-p65 NFκB knockdown. The ability of nicotine to stimulate a fibroblast-mediated, contractile ASM cell phenotype was confirmed by examining expression of contractile proteins in ASM cells cultured with fibroblast-conditioned media or BAL fluid.

RESULTS

NGF levels were elevated in the bronchoalveolar lavage fluid of nicotine-exposed mice, current smokers, and asthmatic children. Nicotine increased NGF secretion in lung fibroblasts in vitro in a dose-dependent manner and stimulated NFκB nuclear translocation, p65 binding to the NGF promoter, and NFκB transcriptional activity. These responses were attenuated in α7 nAChR deficient fibroblasts and in wild type fibroblasts following NFκB inhibition. Nicotine-treated, fibroblast-conditioned media increased expression of contractile proteins in ASM cells.

CONCLUSION

Nicotine stimulates NGF release by lung fibroblasts through α7 nAChR and NFκB dependent pathways. These novel findings suggest that the nicotine-α7 nAChR-NFκB- NGF axis may provide novel therapeutic targets to attenuate tobacco smoke-induced AHR.

The electronic cigarette: a knight in shining armour or a Trojan horse?

Electronic cigarettes have caused a sharp debate in the public health community, with some promoting them as a means of harm reduction for tobacco users and some taking a strong stand against them because of fear of renormalising smoking behaviour and interrupting tobacco control progress. People with mental health problems smoke at high rates and e-cigarettes seem a potentially attractive method of cessation in this population, and their use should be studied carefully.

Cigarette smoking during pregnancy regulates the expression of specific nicotinic acetylcholine receptor (nAChR) subunits in the human placenta

Smoking during pregnancy is associated with low birth weight, premature delivery, and neonatal morbidity and mortality. Nicotine, a major pathogenic compound of cigarette smoke, binds to the nicotinic acetylcholine receptors (nAChRs). A total of 16 nAChR subunits have been identified in mammals (9 α, 4 β, and 1 δ, γ and ε subunits). The effect of cigarette smoking on the expression of these subunits in the placenta has not yet been determined, thus constituting the aim of this study. Using RT-qPCR and western blotting, this study investigated all 16 mammalian nAChR subunits in the normal healthy human placenta, and compared mRNA and protein expressions in the placentas from smokers (n = 8) to controls (n = 8). Our data show that all 16 subunit mRNAs are expressed in the normal, non-diseased human placenta and that the expression of α2, α3, α4, α9, β2 and β4 subunits is greater than the other subunits. For mRNA, cigarette smoke exposure was associated with increased expression of the α9 subunit, and decreased expression of the δ subunit. At the protein level, expression of both α9 and δ was increased. Thus, cigarette smoking in pregnancy is sufficient to regulate nAChR subunits in the placenta, specifically α9 and δ subunits, and could contribute to the adverse effects of vasoconstriction and decreased re-epithelialisation (α9), and increased calcification and apoptosis (δ), seen in the placentas of smoking women.

Peroxisome proliferator-activated receptor ligands regulate lipid content, metabolism, and composition in fetal lungs of diabetic rats

Maternal diabetes impairs fetal lung development. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors relevant in lipid homeostasis and lung development. This study aims to evaluate the effect of in vivo activation of PPARs on lipid homeostasis in fetal lungs of diabetic rats. To this end, we studied lipid concentrations, expression of lipid metabolizing enzymes and fatty acid composition in fetal lungs of control and diabetic rats i) after injections of the fetuses with Leukotriene B4 (LTB4, PPARα ligand) or 15deoxyΔ(12,14)prostaglandin J2 (15dPGJ2, PPARγ ligand) and ii) fed during pregnancy with 6% olive oil- or 6% safflower oil-supplemented diets, enriched with PPAR ligands were studied. Maternal diabetes increased triglyceride concentrations and decreased expression of lipid-oxidizing enzymes in fetal lungs of diabetic rats, an expression further decreased by LTB4 and partially restored by 15dPGJ2 in lungs of male fetuses in the diabetic group. In lungs of female fetuses in the diabetic group, maternal diets enriched with olive oil increased triglyceride concentrations and fatty acid synthase expression, while those enriched with safflower oil increased triglyceride concentrations and fatty acid transporter expression. Both olive oil- and safflower oil-supplemented diets decreased cholesterol and cholesteryl ester concentrations and increased the expression of the reverse cholesterol transporter ATP-binding cassette A1 in fetal lungs of female fetuses of diabetic rats. In fetal lungs of control and diabetic rats, the proportion of polyunsaturated fatty acids increased with the maternal diets enriched with olive and safflower oils. Our results revealed important changes in lipid metabolism in fetal lungs of diabetic rats, and in the ability of PPAR ligands to modulate the composition of lipid species relevant in the lung during the perinatal period.

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory, and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features, including 1) [Ca(2+)]i contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, and 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types, such as epithelium, fibroblasts, and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening, and fibrosis that influence compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard and helps set the stage for future research toward understanding the pathways regulating ASM and, in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.

The role of lipid-activated nuclear receptors in shaping macrophage and dendritic cell function: From physiology to pathology

Nuclear receptors are ligand-activated transcription factors linking lipid signaling to the expression of the genome. There is increasing appreciation of the involvement of this receptor network in the metabolic programming of macrophages and dendritic cells (DCs), essential members of the innate immune system. In this review we focus on the role of retinoid X receptor, retinoic acid receptor, peroxisome proliferator-associated receptor γ, liver X receptor, and vitamin D receptor in shaping the immune and metabolic functions of macrophages and DCs. We also provide an overview of the contribution of macrophage- and DC-expressed nuclear receptors to various immunopathologic conditions, such as rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, asthma, and some others. We suggest that systematic analyses of the roles of these receptors and their activating lipid ligands in immunopathologies combined with complementary and focused translational and clinical research will be crucial for the development of new therapies using the many molecules available to target nuclear receptors.

Perinatal nicotine-induced transgenerational asthma

Asthma is a major public health hazard worldwide. Its transgenerational inheritance has been inferred from epidemiological studies. More recently, using nicotine as a proxy for maternal smoking, we have demonstrated that an asthma-like phenotype can be inherited by rat offspring for up to two generations, i.e., multigenerationally, after the initial intrauterine exposure. We hypothesized that asthma transmission to offspring following perinatal nicotine exposure is not restricted up to F2 generation, but it also extends to subsequent generations. To test this hypothesis, using a well-established rat model of nicotine exposure-induced childhood asthma, we determined if perinatal nicotine exposure of F0 gestating dams would transmit asthma transgenerationally to F3 offspring. We now extend our findings to third-generation offspring, including abnormal pulmonary function, particularly as it relates to the occurrence in the upper airway exclusively in males, and to its effects on molecular functional markers (fibronectin and peroxisome proliferator-activated receptor γ), previously shown to be consistent with the asthma phenotype, herein expressed in fibroblasts isolated from the lung. These data, for the first time, demonstrate the transgenerational transmission of the asthma phenotype to F3 offspring following perinatal nicotine exposure of F0 dams.

Perinatal nicotine exposure induces asthma in second generation offspring

BACKGROUND

By altering specific developmental signaling pathways that are necessary for fetal lung development, perinatal nicotine exposure affects lung growth and differentiation, resulting in the offsprings' predisposition to childhood asthma; peroxisome proliferator-activated receptor gamma (PPARγ) agonists can inhibit this effect. However, whether the perinatal nicotine-induced asthma risk is restricted to nicotine-exposed offspring only; whether it can be transmitted to the next generation; and whether PPARγ agonists would have any effect on this process are not known.

METHODS

Time-mated Sprague Dawley rat dams received either placebo or nicotine (1 mg/kg, s.c.), once daily from day 6 of gestation to postnatal day (PND) 21. Following delivery, at PND21, generation 1 (F1) pups were either subjected to pulmonary function tests, or killed to obtain their lungs, tracheas, and gonads to determine the relevant protein markers (mesenchymal contractile proteins), global DNA methylation, histone 3 and 4 acetylation, and for tracheal tension studies. Some F1 animals were used as breeders to generate F2 pups, but without any exposure to nicotine in the F1 pregnancy. At PND21, F2 pups underwent studies similar to those performed on F1 pups.

RESULTS

Consistent with the asthma phenotype, nicotine affected lung function in both male and female F1 and F2 offspring (maximal 250% increase in total respiratory system resistance, and 84% maximal decrease in dynamic compliance following methacholine challenge; P < 0.01, nicotine versus control; P < 0.05, males versus females; and P > 0.05, F1 versus F2), but only affected tracheal constriction in males (51% maximal increase in tracheal constriction following acetylcholine challenge, P < 0.01, nicotine versus control; P < 0.0001, males versus females; P > 0.05, F1 versus F2); nicotine also increased the contractile protein content of whole lung (180% increase in fibronectin protein levels, P < 0.01, nicotine versus control, and P < 0.05, males versus females) and isolated lung fibroblasts (for example, 45% increase in fibronectin protein levels, P < 0.05, nicotine versus control), along with decreased PPARγ expression (30% decrease, P < 0.05, nicotine versus control), but only affected contractile proteins in the male trachea (P < 0.05, nicotine versus control, and P < 0.0001, males versus females). All of the nicotine-induced changes in the lung and gonad DNA methylation and histone 3 and 4 acetylation were normalized by the PPARγ agonist rosiglitazone except for the histone 4 acetylation in the lung.

CONCLUSIONS

Germline epigenetic marks imposed by exposure to nicotine during pregnancy can become permanently programmed and transferred through the germline to subsequent generations, a ground-breaking finding that shifts the current asthma paradigm, opening up many new avenues to explore.

Sex-specific perinatal nicotine-induced asthma in rat offspring

Recently, we have suggested that down-regulation of homeostatic mesenchymal peroxisome proliferator-activated receptor γ signaling after in utero nicotine exposure might contribute to asthma. Here, we have exploited an in vivo rat model of asthma to determine if the effects of perinatal nicotine exposure on offspring pulmonary function and mesenchymal markers of airway contractility in both tracheal and lung parenchymal tissue are sex specific, and whether the protection afforded by the peroxisome proliferator-activated receptor γ agonist, rosiglitazone (RGZ), against the perinatal nicotine-induced effect on offspring lung is also sex specific. Pregnant rat dams received placebo, nicotine, or nicotine plus RGZ daily from Embryonic Day 6 until Postnatal Day 21, at which time lung resistance, compliance, tracheal contractility, and the expression of structural and functional mesenchymal markers of pulmonary contractility were determined. Compared with control animals, perinatal nicotine exposure caused a significant increase in airway resistance and a decrease in airway compliance after a methacholine challenge in both male and female offspring, with more pronounced changes in the males. In contrast to this, the effects of perinatal nicotine exposure on acetylcholine-induced tracheal constriction, along with the expression of its mesenchymal markers, were observed exclusively in the male offspring. Concomitant treatment with RGZ normalized the nicotine-induced alterations in pulmonary function in both sexes, as well as the male-specific effects on acetylcholine-induced tracheal constriction, along with the affected mesenchymal markers. These data suggest that perinatal nicotine exposure causes sex-specific perinatal cigarette smoke exposure-induced asthma, providing a powerful phenotypic model for unequivocally determining the underlying nature of the cell molecular mechanism for this disease.

PPARγ Ligands Regulate Noncontractile and Contractile Functions of Airway Smooth Muscle: Implications for Asthma Therapy

In asthma, the increase in airway smooth muscle (ASM) can contribute to inflammation, airway wall remodeling and airway hyperresponsiveness (AHR). Targetting peroxisome proliferator-activated receptor γ (PPARγ), a receptor upregulated in ASM in asthmatic airways, may provide a novel approach to regulate these contributions. This review summarises experimental evidence that PPARγ ligands, such as rosiglitazone (RGZ) and pioglitazone (PGZ), inhibit proliferation and inflammatory cytokine production from ASM in vitro. In addition, inhaled administration of these ligands reduces inflammatory cell infiltration and airway remodelling in mouse models of allergen-induced airways disease. PPARγ ligands can also regulate ASM contractility, with acute treatment eliciting relaxation of mouse trachea in vitro through a PPARγ-independent mechanism. Chronic treatment can protect against the loss of bronchodilator sensitivity to β₂-adrenoceptor agonists and inhibit the development of AHR associated with exposure to nicotine in utero or following allergen challenge. Of particular interest, a small clinical trial has shown that oral RGZ treatment improves lung function in smokers with asthma, a group that is generally unresponsive to conventional steroid treatment. These combined findings support further investigation of the potential for PPARγ agonists to target the noncontractile and contractile functions of ASM to improve outcomes for patients with poorly controlled asthma.

PPARγ Signaling Mediates the Evolution, Development, Homeostasis, and Repair of the Lung

Epithelial-mesenchymal interactions mediated by soluble growth factors determine the evolution of vertebrate lung physiology, including development, homeostasis, and repair. The final common pathway for all of these positively adaptive properties of the lung is the expression of epithelial parathyroid-hormone-related protein, and its binding to its receptor on the mesenchyme, inducing PPARγ expression by lipofibroblasts. Lipofibroblasts then produce leptin, which binds to alveolar type II cells, stimulating their production of surfactant, which is necessary for both evolutionary and physiologic adaptation to atmospheric oxygen from fish to man. A wide variety of molecular insults disrupt such highly evolved physiologic cell-cell interactions, ranging from overdistention to oxidants, infection, and nicotine, all of which predictably cause loss of mesenchymal peroxisome-proliferator-activated receptor gamma (PPARγ) expression and the transdifferentiation of lipofibroblasts to myofibroblasts, the signature cell type for lung fibrosis. By exploiting such deep cell-molecular functional homologies as targets for leveraging lung homeostasis, we have discovered that we can effectively prevent and/or reverse the deleterious effects of these pathogenic agents, demonstrating the utility of evolutionary biology for the prevention and treatment of chronic lung disease. By understanding mechanisms of health and disease as an evolutionary continuum rather than as dissociated processes, we can evolve predictive medicine.

Prenatal nicotine exposure alters lung function and airway geometry through α7 nicotinic receptors

Maternal smoking during pregnancy has been associated with adverse effects on respiratory health. Whereas the epidemiologic link is incontrovertible, the mechanisms responsible for this association are still poorly understood. Although cigarette smoke has many toxic constituents, nicotine, the major addictive component in cigarette smoke, may play a more significant role than previously realized. The objectives of this study were to determine whether exposure to nicotine prenatally leads to alterations in pulmonary function and airway geometry in offspring, and whether α7 nicotinic acetylcholine receptors (nAChRs) mediate these effects. In a murine model of in utero nicotine exposure, pulmonary function, airway size and number, methacholine response, and collagen deposition were examined. Exposure periods included Gestation Days 7-21, Gestation Day 14 to Postnatal Day 7, and Postnatal Days 3-15. Prenatal nicotine exposure decreases forced expiratory flows in offspring through α7 nAChR-mediated signals, and the critical period of nicotine exposure was between Prenatal Day 14 and Postnatal Day 7. These physiologic changes were associated with increased airway length and decreased diameter. In addition, adult mice exposed to prenatal nicotine exhibit an increased response to methacholine challenge, even in the absence of allergic sensitization. Collagen expression was increased between adjacent airways and vessels, which was absent in α7 nAChR knockout mice. These observations provide a unified mechanism of how maternal smoking during pregnancy may lead to lifelong alterations in offspring pulmonary function and increased risk of asthma, and suggest potential targets to counteract those effects.

Harnessing opportunities in non-animal asthma research for a 21st-century science

The incidence of asthma is on the increase and calls for research are growing, yet asthma is a disease that scientists are still trying to come to grips with. Asthma research has relied heavily on animal use; however, in light of increasingly robust in vitro and computational models and the need to more fully incorporate the 'Three Rs' principles of Replacement, Reduction and Refinement, is it time to reassess the asthma research paradigm? Progress in non-animal research techniques is reaching a level where commitment and integration are necessary. Many scientists believe that progress in this field rests on linking disciplines to make research directly translatable from the bench to the clinic; a '21st-century' scientific approach to address age-old questions.