Nucleotide oligomerization domain 1 ligation suppressed murine allergen-specific T-cell proliferation and airway hyperresponsiveness

Nanomedicine at the Pulmonary Frontier: Immune-Centric Approaches for Respiratory Disease Treatment

Respiratory diseases (RD) are a group of common ailments with a rapidly increasing global prevalence, posing a significant threat to humanity, especially the elderly population, and imposing a substantial burden on society and the economy. RD represents an unmet medical need that requires the development of viable pharmacotherapies. While various promising strategies have been devised to advance potential treatments for RD, their implementation has been hindered by difficulties in drug delivery, particularly in critically ill patients. Nanotechnology offers innovative solutions for delivering medications to the inflamed organ sites, such as the lungs. Although this approach is enticing, delivering nanomedicine to the lungs presents complex challenges that require sophisticated techniques. In this context, we review the potential of novel nanomedicine-based immunomodulatory strategies that could offer therapeutic benefits in managing this pressing health condition.

Synthesis and validation of click-modified NOD1/2 agonists

NOD1 and NOD2 sense small bacterial peptidoglycan fragments, often called muropeptides, that access the cytosol. These muropeptides include iE-DAP and MDP, the minimal agonists for NOD1 and NOD2, respectively. Here, we synthesized and validated alkyne-modified muropeptides, iE-DAP-Alk and MDP-Alk, for use in click-chemistry reactions. While it has long been known that many cell types respond to extracellular exposure to muropeptides, it is unclear how these innate immune activators access their cytosolic innate immune receptors, NOD1 and NOD2. The subcellular trafficking and transport mechanisms by which muropeptides access these cytosolic innate immune receptors are a major gap in our understanding of these critical host responses. The click-chemistry-enabled agonists developed here will be particularly powerful to decipher the underlying cell biology and biochemistry of NOD1 and NOD2 innate immune sensing.

NOD2 Agonism Counter-Regulates Human Type 2 T Cell Functions in Peripheral Blood Mononuclear Cell Cultures: Implications for Atopic Dermatitis

Atopic dermatitis (AD) is known as a skin disease; however, T cell immunopathology found in blood is associated with its severity. Skin Staphylococcus aureus (S. aureus) and associated host-pathogen dynamics are important to chronic T helper 2 (Th2)-dominated inflammation in AD, yet they remain poorly understood. This study sought to investigate the effects of S. aureus-derived molecules and skin alarmins on human peripheral blood mononuclear cells, specifically testing Th2-type cells, cytokines, and chemokines known to be associated with AD. We first show that six significantly elevated Th2-related chemokine biomarkers distinguish blood from adult AD patients compared to healthy controls ex vivo; in addition, TARC/CCL17, LDH, and PDGF-AA/AB correlated significantly with disease severity. We then demonstrate that these robust AD-associated biomarkers, as well as associated type 2 T cell functions, are readily reproduced from healthy blood mononuclear cells exposed to the alarmin TSLP and the S. aureus superantigen SEB in a human in vitro model, including IL-13, IL-5, and TARC secretion as well as OX-40-expressing activated memory T cells. We further show that the agonism of nucleotide-binding oligomerization domain-containing protein (NOD)2 inhibits this IL-13 secretion and memory Th2 and Tc2 cell functional activation while inducing significantly increased pSTAT3 and IL-6, both critical for Th17 cell responses. These findings identify NOD2 as a potential regulator of type 2 immune responses in humans and highlight its role as an endogenous inhibitor of pathogenic IL-13 that may open avenues for its therapeutic targeting in AD.

Endothelin B Receptor Immunodynamics in Pulmonary Arterial Hypertension

Introduction

Inflammation is a major pathological feature of pulmonary arterial hypertension (PAH), particularly in the context of inflammatory conditions such as systemic sclerosis (SSc). The endothelin system and anti-endothelin A receptor (ET_A) autoantibodies have been implicated in the pathogenesis of PAH, and endothelin receptor antagonists are routinely used treatments for PAH. However, immunological functions of the endothelin B receptor (ET_B) remain obscure.

Methods

Serum levels of anti-ET_B receptor autoantibodies were quantified in healthy donors and SSc patients with or without PAH. Age-dependent effects of overexpression of prepro-endothelin-1 or ET_B deficiency on pulmonary inflammation and the cardiovascular system were studied in mice. Rescued ET_B-deficient mice (ET_B^-/-) were used to prevent congenital Hirschsprung disease. The effects of pulmonary T-helper type 2 (Th2) inflammation on PAH-associated pathologies were analyzed in ET_B^-/- mice. Pulmonary vascular hemodynamics were investigated in isolated perfused mouse lungs. Hearts were assessed for right ventricular hypertrophy. Pulmonary inflammation and collagen deposition were assessed via lung microscopy and bronchoalveolar lavage fluid analyses.

Results

Anti-ET_B autoantibody levels were elevated in patients with PAH secondary to SSc. Both overexpression of prepro-endothelin-1 and rescued ET_B deficiency led to pulmonary hypertension, pulmonary vascular hyperresponsiveness, and right ventricular hypertrophy with accompanying lymphocytic alveolitis. Marked perivascular lymphocytic infiltrates were exclusively found in ET_B^-/- mice. Following induction of pulmonary Th2 inflammation, PAH-associated pathologies and perivascular collagen deposition were aggravated in ET_B^-/- mice.

Conclusion

This study provides evidence for an anti-inflammatory role of ET_B. ET_B seems to have protective effects on Th2-evoked pathologies of the cardiovascular system. Anti-ET_B autoantibodies may modulate ET_B-mediated immune homeostasis.

Pulmonary fibrosis in Fra-2 transgenic mice is associated with decreased numbers of alveolar macrophages and increased susceptibility to pneumococcal pneumonia

Idiopathic pulmonary fibrosis (IPF) is a deadly condition characterized by progressive respiratory dysfunction. Exacerbations due to airway infections are believed to promote disease progression, and presence of Streptococcus in the lung microbiome has been associated with the progression of IPF and mortality. The aim of this study was to analyze the effect of lung fibrosis on susceptibility to pneumococcal pneumonia and bacteremia. The effects of subclinical (low dose) infection with Streptococcus pneumoniae were studied in a well characterized fos-related antigen-2 (Fra-2) transgenic (TG) mouse model of spontaneous, progressive pulmonary fibrosis. Forty-eight hours after transnasal infection with S. pneumoniae, bacterial load was assessed in lung tissue, bronchoalveolar lavage (BAL), blood, and spleen. Leukocyte subsets and cytokine levels were analyzed in BAL and blood. Lung compliance and arterial blood gases were assessed. In contrast to wildtype mice, low dose lung infection with S. pneumoniae in Fra-2 TG mice resulted in substantial pneumonia including weight loss, increased lung bacterial load, and bacteremia. BAL alveolar macrophages were reduced in Fra-2 TG mice compared to the corresponding WT mice. Proinflammatory cytokines and chemokines (IL-1β, IL-6, TNF-α, and CXCL1) were elevated upon infection in BAL supernatant and plasma of Fra-2 TG mice. Lung compliance was decreased in Fra-2 TG mice following low dose infection with S. pneumoniae. Pulmonary fibrosis increases susceptibility to pneumococcal pneumonia and bacteremia possibly via impaired alveolar bacterial clearance.

Role of phosphatase and tensin homolog in hypoxic pulmonary vasoconstriction

Aims

Hypoxic pulmonary vasoconstriction (HPV) redistributes blood flow from poorly ventilated to better aerated areas in the lung, thereby optimizing ventilation-perfusion ratio (V/Q). Pulmonary artery smooth muscle cell (PASMC) contraction in response to hypoxia is triggered by Ca2+ influx via transient receptor potential canonical 6 (TRPC6) cation channels that have translocated to caveolae in the plasma membrane. Since phosphatase and tensin homolog (PTEN) was suggested to regulate TRPC6 in endothelial cells, we aimed to define its role in the hypoxic response of PASMCs and as a putative mediator of HPV.

Methods and results

In isolated perfused mouse lungs, smooth muscle specific PTEN deficiency attenuated pulmonary vasoconstriction in response to hypoxia but not to angiotensin II (Ang II). Analogously, siRNA-mediated knock down of PTEN in human PASMC inhibited the hypoxia-induced increase in cytosolic Ca2+ concentration ([Ca2+]i). Co-immunoprecipitation and proximity ligation assays revealed increased interaction of PTEN with TRPC6 in human PASMC and murine lungs in response to hypoxia. In hypoxic PASMC, both PTEN and TRPC6 translocated to caveolae, and this response was blocked by pharmacological inhibition of Rho-associated protein kinase (ROCK) which in parallel prevented PTEN-TRPC6 interaction, hypoxia-induced [Ca2+]i increase, and HPV in PASMC and murine lungs, respectively.

Conclusion

Our data indicate a novel interplay between ROCK and [Ca2+]i signalling in HPV via PTEN, in that ROCK mediates interaction of PTEN and TRPC6 which then conjointly translocate to caveolae allowing for Ca2+ influx into and subsequent contraction of PASMC.

Airway Epithelium Dysfunction in Cystic Fibrosis and COPD

Cystic fibrosis is a genetic disease caused by mutations in the CFTR gene, whereas chronic obstructive pulmonary disease (COPD) is mainly caused by environmental factors (mostly cigarette smoking) on a genetically susceptible background. Although the etiology and pathogenesis of these diseases are different, both are associated with progressive airflow obstruction, airway neutrophilic inflammation, and recurrent exacerbations, suggesting common mechanisms. The airway epithelium plays a crucial role in maintaining normal airway functions. Major molecular and morphologic changes occur in the airway epithelium in both CF and COPD, and growing evidence suggests that airway epithelial dysfunction is involved in disease initiation and progression in both diseases. Structural and functional abnormalities in both airway and alveolar epithelium have a relevant impact on alteration of host defences, immune/inflammatory response, and the repair process leading to progressive lung damage and impaired lung function. In this review, we address the evidence for a critical role of dysfunctional airway epithelial cells in chronic airway inflammation and remodelling in CF and COPD, highlighting the common mechanisms involved in the epithelial dysfunction as well as the similarities and differences of the two diseases.

Innate Immunity of the Lung: From Basic Mechanisms to Translational Medicine

The respiratory tract is faced daily with 10,000 L of inhaled air. While the majority of air contains harmless environmental components, the pulmonary immune system also has to cope with harmful microbial or sterile threats and react rapidly to protect the host at this intimate barrier zone. The airways are endowed with a broad armamentarium of cellular and humoral host defense mechanisms, most of which belong to the innate arm of the immune system. The complex interplay between resident and infiltrating immune cells and secreted innate immune proteins shapes the outcome of host-pathogen, host-allergen, and host-particle interactions within the mucosal airway compartment. Here, we summarize and discuss recent findings on pulmonary innate immunity and highlight key pathways relevant for biomarker and therapeutic targeting strategies for acute and chronic diseases of the respiratory tract.

The role of NOD1 and NOD2 in host defense against chlamydial infection

Chlamydial species are common intracellular parasites that cause various diseases, mainly characterized by persistent infection, which lead to inflammatory responses modulated by pattern recognition receptors (PRRs). The best understood PRRs are the extracellular Toll-like receptors, but recent significant advances have focused on two important proteins, NOD1 and NOD2, which are members of the intracellular nucleotide-binding oligomerization domain receptor family and are capable of triggering the host innate immune signaling pathways. This results in the production of pro-inflammatory cytokines, which is vital for an adequate host defense against intracellular chlamydial infection. NOD1/2 ligands are known to derive from peptidoglycan, and the latest research has resolved the paradox of whether chlamydial species possess this bacterial cell wall component; this finding is likely to promote in-depth investigations into the interaction between the NOD proteins and chlamydial pathogens. In this review, we summarize the basic characteristics and signal transduction functions of NOD1 and NOD2 and highlight the new research on the roles of NOD1 and NOD2 in the host defense against chlamydial infection.

PKCα Deficiency in Mice Is Associated with Pulmonary Vascular Hyperresponsiveness to Thromboxane A2 and Increased Thromboxane Receptor Expression

Pulmonary vascular hyperresponsiveness is a main characteristic of pulmonary arterial hypertension (PAH). In PAH patients, elevated levels of the vasoconstrictors thromboxane A2 (TXA2), endothelin (ET)-1 and serotonin further contribute to pulmonary hypertension. Protein kinase C (PKC) isozyme alpha (PKCα) is a known modulator of smooth muscle cell contraction. However, the effects of PKCα deficiency on pulmonary vasoconstriction have not yet been investigated. Thus, the role of PKCα in pulmonary vascular responsiveness to the TXA2 analog U46619, ET-1, serotonin and acute hypoxia was investigated in isolated lungs of PKCα-/- mice and corresponding wild-type mice, with or without prior administration of the PKC inhibitor bisindolylmaleimide I or Gö6976. mRNA was quantified from microdissected intrapulmonary arteries. We found that broad-spectrum PKC inhibition reduced pulmonary vascular responsiveness to ET-1 and acute hypoxia and, by trend, to U46619. Analogously, selective inhibition of conventional PKC isozymes or PKCα deficiency reduced ET-1-evoked pulmonary vasoconstriction. The pulmonary vasopressor response to serotonin was unaffected by either broad PKC inhibition or PKCα deficiency. Surprisingly, PKCα-/- mice showed pulmonary vascular hyperresponsiveness to U46619 and increased TXA2 receptor (TP receptor) expression in the intrapulmonary arteries. To conclude, PKCα regulates ET-1-induced pulmonary vasoconstriction. However, PKCα deficiency leads to pulmonary vascular hyperresponsiveness to TXA2, possibly via increased pulmonary arterial TP receptor expression.

CFTR and sphingolipids mediate hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) optimizes pulmonary ventilation-perfusion matching in regional hypoxia, but promotes pulmonary hypertension in global hypoxia. Ventilation-perfusion mismatch is a major cause of hypoxemia in cystic fibrosis. We hypothesized that cystic fibrosis transmembrane conductance regulator (CFTR) may be critical in HPV, potentially by modulating the response to sphingolipids as mediators of HPV. HPV and ventilation-perfusion mismatch were analyzed in isolated mouse lungs or in vivo. Ca(2+) mobilization and transient receptor potential canonical 6 (TRPC6) translocation were studied in human pulmonary (PASMCs) or coronary (CASMCs) artery smooth muscle cells. CFTR inhibition or deficiency diminished HPV and aggravated ventilation-perfusion mismatch. In PASMCs, hypoxia caused CFTR to interact with TRPC6, whereas CFTR inhibition attenuated hypoxia-induced TRPC6 translocation to caveolae and Ca(2+) mobilization. Ca(2+) mobilization by sphingosine-1-phosphate (S1P) was also attenuated by CFTR inhibition in PASMCs, but amplified in CASMCs. Inhibition of neutral sphingomyelinase (nSMase) blocked HPV, whereas exogenous nSMase caused TRPC6 translocation and vasoconstriction that were blocked by CFTR inhibition. nSMase- and hypoxia-induced vasoconstriction, yet not TRPC6 translocation, were blocked by inhibition or deficiency of sphingosine kinase 1 (SphK1) or antagonism of S1P receptors 2 and 4 (S1P2/4). S1P and nSMase had synergistic effects on pulmonary vasoconstriction that involved TRPC6, phospholipase C, and rho kinase. Our findings demonstrate a central role of CFTR and sphingolipids in HPV. Upon hypoxia, nSMase triggers TRPC6 translocation, which requires its interaction with CFTR. Concomitant SphK1-dependent formation of S1P and activation of S1P2/4 result in phospholipase C-mediated TRPC6 and rho kinase activation, which conjointly trigger vasoconstriction.