Amy M. Pastva

Aerobic Exercise Attenuates Airway Inflammatory Responses in a Mouse Model of Atopic Asthma

Recent reports indicate that aerobic exercise improves the overall physical fitness and health of asthmatic patients. The specific exercise-induced improvements in the pathology of asthma and the mechanisms by which these improvements occur, however, are ill-defined; thus, the therapeutic potential of exercise in the treatment of asthma remains unappreciated. Using an OVA-driven mouse model, we examined the role of aerobic exercise in modulating inflammatory responses associated with atopic asthma. Data demonstrate that moderate intensity aerobic exercise training decreased leukocyte infiltration, cytokine production, adhesion molecule expression, and structural remodeling within the lungs of OVA-sensitized mice (n = 6–10; p < 0.05). Because the transcription factor NF-κB regulates the expression of a variety of genes that encode inflammatory mediators, we monitored changes in NF-κB activation in the lungs of exercised/sensitized mice. Results show that exercise decreased NF-κB nuclear translocation and IκBα phosphorylation, indicating that exercise decreased NF-κB activation in the lungs of sensitized mice (n = 6). Taken together, these results suggest that aerobic exercise attenuates airway inflammation in a mouse model of atopic asthma via modulation of NF-κB activation. Potential exists, therefore, for the amelioration of asthma-associated chronic airway inflammation through the use of aerobic exercise training as a non-drug therapeutic modality.

RU486 blocks the anti-inflammatory effects of exercise in a murine model of allergen-induced pulmonary inflammation

In an ovalbumin (OVA)-driven murine model of allergic pulmonary inflammation, we have shown previously that moderate-intensity aerobic exercise training attenuates inflammatory responses, disease progression, and NF-kappaB activation within the sensitized lung. Glucocorticoids (GCs), potent anti-inflammatory agents, have been shown to alter transcriptional events that are important in asthmatic pathogenesis, such as NF-kappaB activation. Notably, exercise training can alter the production and signaling capacity of endogenous GCs. Because GCs exert their anti-inflammatory effects through binding to intracellular glucocorticoid receptors (GRs), we examined the role of the GR in facilitating the anti-inflammatory effects of exercise. Results show that, in exercised OVA-sensitized mice, treatment with the GR antagonist RU486 blocked the exercise-induced reductions in cellular infiltration of the airways (p < .05), KC and soluble VCAM-1 protein levels in the bronchoalveloar lavage fluid (p < .05), and NF-kappaB translocation and DNA binding within the lung to levels similar to those observed in sedentary OVA-sensitized mice. Importantly, RU486 treatment also blocked exercise-induced increases in GR nuclear translocation to the levels seen in sensitized control mice. Together, these results suggest that GR nuclear translocation and NF-kappaB activation play roles in mediating the anti-inflammatory effects of exercise in allergen-mediated lung pathology.

Surfactant Protein A Modulates Induction of Regulatory T Cells via TGF-β

TCR signaling plays a critical role in regulatory T cell (Treg) development. However, the mechanism for tissue-specific induction of Tregs in the periphery remains unclear. We observed that surfactant protein A (SP-A)–deficient mice have impaired expression of Foxp3 and fewer CD25+Foxp3+ Tregs after ex vivo stimulation and after stimulation with LPS in vivo. The addition of exogenous SP-A completely reversed this phenotype. Although SP-A is known to inhibit T cell proliferation under certain activation conditions, both IL-2 levels as well as active TGF-β levels increase on extended culture with exogenous SP-A, providing a key mechanism for the maintenance and induction of Tregs. In addition, kinetic suppression assays demonstrate that SP-A enhances the frequency of functional Foxp3+ Tregs in responder T cell populations in a TGF-β–dependent manner. In mice treated with LPS in vivo, Tregs increased ∼160% in wild-type mice compared with only a 50% increase in LPS-treated SP-A−/− mice 8 d after exposure. Taken together, these findings support the hypothesis that SP-A affects T cell immune function by the induction of Tregs during activation.

Lung Effector Memory and Activated CD4+ T Cells Display Enhanced Proliferation in Surfactant Protein A-Deficient Mice during Allergen-Mediated Inflammation

Although many studies have shown that pulmonary surfactant protein (SP)-A functions in innate immunity, fewer studies have addressed its role in adaptive immunity and allergic hypersensitivity. We hypothesized that SP-A modulates the phenotype and prevalence of dendritic cells (DCs) and CD4+ T cells to inhibit Th2-associated inflammatory indices associated with allergen-induced inflammation. In an OVA model of allergic hypersensitivity, SP-A−/− mice had greater eosinophilia, Th2-associated cytokine levels, and IgE levels compared with wild-type counterparts. Although both OVA-exposed groups had similar proportions of CD86+ DCs and Foxp3+ T regulatory cells, the SP-A−/− mice had elevated proportions of CD4+ activated and effector memory T cells in their lungs compared with wild-type mice. Ex vivo recall stimulation of CD4+ T cell pools demonstrated that cells from the SP-A−/− OVA mice had the greatest proliferative and IL-4–producing capacity, and this capability was attenuated with exogenous SP-A treatment. Additionally, tracking proliferation in vivo demonstrated that CD4+ activated and effector memory T cells expanded to the greatest extent in the lungs of SP-A−/− OVA mice. Taken together, our data suggested that SP-A influences the prevalence, types, and functions of CD4+ T cells in the lungs during allergic inflammation and that SP deficiency modifies the severity of inflammation in allergic hypersensitivity conditions like asthma.

Review: Collectins link innate and adaptive immunity in allergic airway disease

Although the lipoprotein complex of pulmonary surfactant has long been recognized as essential for reducing lung surface tension, its role in lung immune host defense has only relatively recently been elucidated. Surfactant-associated proteins A (SP-A) and D (SP-D) can attenuate bacterial and viral infection and inflammation by acting as opsonins and by regulating innate immune cell functions. Surfactant-associated protein A and D also interact with antigen-presenting cells and T cells, thereby linking the innate and adaptive immune systems. A recent study from our laboratory demonstrated that mice deficient in SP-A have enhanced susceptibility to airway hyper-responsiveness and lung inflammation induced by Mycoplasma pneumonia, an atypical bacterium present in the airways of approximately 50% of asthmatics experiencing their first episode, and further supports an important role for SP-A in the host response to allergic airway disease. Animal and human studies suggest that alterations in the functions or levels of SP-A and SP-D are associated with both infectious and non-infectious chronic lung diseases such as asthma. Future studies are needed to elucidate whether alterations in SP-A and SP-D are a consequence and/or cause of allergic airway disease.

Rehabilitation Therapy in Older Acute Heart Failure Patients (REHAB-HF) trial: Design and rationale

Background Acute decompensated heart failure (ADHF) is a leading cause of hospitalization in older persons in the United States. Reduced physical function and frailty are major determinants of adverse outcomes in older patients with hospitalized ADHF. However, these are not addressed by current heart failure (HF) management strategies and there has been little study of exercise training in older, frail HF patients with recent ADHF. Hypothesis Targeting physical frailty with a multi‐domain structured physical rehabilitation intervention will improve physical function and reduce adverse outcomes among older patients experiencing a HF hospitalization. Study design REHAB‐HF is a multi‐center clinical trial in which 360 patients ≥60 years hospitalized with ADHF will be randomized either to a novel 12‐week multi‐domain physical rehabilitation intervention or to attention control. The goal of the intervention is to improve balance, mobility, strength and endurance utilizing reproducible, targeted exercises administered by a multi‐disciplinary team with specific milestones for progression. The primary study aim is to assess the efficacy of the REHAB‐HF intervention on physical function measured by total Short Physical Performance Battery score. The secondary outcome is 6‐month all‐cause rehospitalization. Additional outcome measures include quality of life and costs. Conclusions REHAB‐HF is the first randomized trial of a physical function intervention in older patients with hospitalized ADHF designed to determine if addressing deficits in balance, mobility, strength and endurance improves physical function and reduces rehospitalizations. It will address key evidence gaps concerning the role of physical rehabilitation in the care of older patients, those with ADHF, frailty, and multiple comorbidities.

Surfactant Protein A Integrates Activation Signal Strength To Differentially Modulate T Cell Proliferation

Pulmonary surfactant lipoproteins lower the surface tension at the alveolar–airway interface of the lung and participate in host defense. Previous studies reported that surfactant protein A (SP-A) inhibits lymphocyte proliferation. We hypothesized that SP-A–mediated modulation of T cell activation depends upon the strength, duration, and type of lymphocyte activating signals. Modulation of T cell signal strength imparted by different activating agents ex vivo and in vivo in different mouse models and in vitro with human T cells shows a strong correlation between strength of signal (SoS) and functional effects of SP-A interactions. T cell proliferation is enhanced in the presence of SP-A at low SoS imparted by exogenous mitogens, specific Abs, APCs, or in homeostatic proliferation. Proliferation is inhibited at higher SoS imparted by different doses of the same T cell mitogens or indirect stimuli such as LPS. Importantly, reconstitution with exogenous SP-A into the lungs of SP-A−/− mice stimulated with a strong signal also resulted in suppression of T cell proliferation while elevating baseline proliferation in unstimulated T cells. These signal strength and SP-A–dependent effects are mediated by changes in intracellular Ca2+ levels over time, involving extrinsic Ca2+-activated channels late during activation. These effects are intrinsic to the global T cell population and are manifested in vivo in naive as well as memory phenotype T cells. Thus, SP-A appears to integrate signal thresholds to control T cell proliferation.

Novel role for surfactant protein A in gastrointestinal graft-versus-host disease.

Graft-versus-host disease (GVHD) is a severe and frequent complication of allogeneic bone marrow transplantation (BMT) that involves the gastrointestinal (GI) tract and lungs. The pathobiology of GVHD is complex and involves immune cell recognition of host Ags as foreign. We hypothesize a central role for the collectin surfactant protein A (SP-A) in regulating the development of GVHD after allogeneic BMT. C57BL/6 (H2b; WT) and SP-A–deficient mice on a C57BL/6 background (H2b; SP-A−/−) mice underwent allogeneic or syngeneic BMT with cells from either C3HeB/FeJ (H2k; SP-A–deficient recipient mice that have undergone an allogeneic BMT [SP-A−/−alloBMT] or SP-A–sufficient recipient mice that have undergone an allogeneic BMT) or C57BL/6 (H2b; SP-A–deficient recipient mice that have undergone a syngeneic BMT or SP-A–sufficient recipient mice that have undergone a syngeneic BMT) mice. Five weeks post-BMT, mice were necropsied, and lung and GI tissue were analyzed. SP-A−/− alloBMT or SP-A–sufficient recipient mice that have undergone an allogeneic BMT had no significant differences in lung pathology; however, SP-A−/−alloBMT mice developed marked features of GI GVHD, including decreased body weight, increased tissue inflammation, and lymphocytic infiltration. SP-A−/−alloBMT mice also had increased colon expression of IL-1β, IL-6, TNF-α, and IFN-γ and as well as increased Th17 cells and diminished regulatory T cells. Our results demonstrate the first evidence, to our knowledge, of a critical role for SP-A in modulating GI GVHD. In these studies, we demonstrate that mice deficient in SP-A that have undergone an allogeneic BMT have a greater incidence of GI GVHD that is associated with increased Th17 cells and decreased regulatory T cells. The results of these studies demonstrate that SP-A protects against the development of GI GVHD and establishes a role for SP-A in regulating the immune response in the GI tract.

Nitric Oxide Mediates Relative Airway Hyporesponsiveness to Lipopolysaccharide in Surfactant Protein A–Deficient Mice

Surfactant protein A (SP-A) mediates innate immune cell responses to LPS, a cell wall component of gram-negative bacteria that is found ubiquitously in the environment and is associated with adverse health effects. Inhaled LPS induces lung inflammation and increases airway responsiveness (AR). However, the role of SP-A in mediating LPS-induced AR is not well-defined. Nitric oxide (NO) is described as a potent bronchodilator, and previous studies showed that SP-A modulates the LPS-induced production of NO. Hence, we tested the hypothesis that increased AR, observed in response to aerosolized LPS exposure, would be significantly reduced in an SP-A-deficient condition. Wild-type (WT) and SP-A null (SP-A(-/-)) mice were challenged with aerosolized LPS. Results indicate that despite similar inflammatory indices, LPS-treated SP-A(-/-) mice had attenuated AR after methacholine challenge, compared with WT mice. The attenuated AR could not be attributed to inherent differences in SP-D concentrations or airway smooth muscle contractile and relaxation properties, because these measures were similar between WT and SP-A(-/-) mice. LPS-treated SP-A(-/-) mice, however, had elevated nitrite concentrations, inducible nitric oxide synthase (iNOS) expression, and NOS activity in their lungs. Moreover, the administration of the iNOS-specific inhibitor 1400W completely abrogated the attenuated AR. Thus, when exposed to aerosolized LPS, SP-A(-/-) mice demonstrate a relative airway hyporesponsiveness that appears to be mediated at least partly via an iNOS-dependent mechanism. These findings may have clinical significance, because recent studies reported associations between surfactant protein polymorphisms and a variety of lung diseases.

Increased Nitric Oxide Production Prevents Airway Hyperresponsiveness in Caveolin-1 Deficient Mice Following Endotoxin Exposure.

BACKGROUND Caveolin-1, the hallmark protein of caveolae, is highly expressed within the lung in the epithelium, endothelium, and in immune cells. In addition to its classical roles in cholesterol metabolism and endocytosis, caveolin-1 has also been shown to be important in inflammatory signaling pathways. In particular, caveolin-1 is known to associate with the nitric oxide synthase enzymes, downregulating their activity. Endotoxins, which are are composed mainly of lipopolysaccharide (LPS), are found ubiquitously in the environment and can lead to the development of airway inflammation and increased airway hyperresponsiveness (AHR). METHODS We compared the acute responses of wild-type and caveolin-1 deficient mice after LPS aerosol, a well-accepted mode of endotoxin exposure, to investigate the role of caveolin-1 in the development of environmental lung injury. RESULTS Although the caveolin-1 deficient mice had greater lung inflammatory indices compared to wild-type mice, they exhibited reduced AHR following LPS exposure. The uncoupling of inflammation and AHR led us to investigate the role of caveolin-1 in the production of nitric oxide, which is known to act as a bronchodilator. The absence of caveolin-1 resulted in increased nitrite levels in the lavage fluid in both sham and LPS treated mice. Additionally, inducible nitric oxide synthase expression was increased in the lung tissue of caveolin-1 deficient mice following LPS exposure and administration of the potent and specific inhibitor 1400W increased AHR to levels comparable to wild-type mice. CONCLUSIONS We attribute the relative airway hyporesponsiveness in the caveolin-1 deficient mice after LPS exposure to the specific role of caveolin-1 in mediating nitric oxide production.