Proinflammatory Cytokines Impair Vitamin D-Induced Host Defense in Cultured Airway Epithelial Cells

In vitro modelling of bacterial pneumonia: a comparative analysis of widely applied complex cell culture models

Bacterial pneumonia greatly contributes to the disease burden and mortality of lower respiratory tract infections among all age groups and risk profiles. Therefore, laboratory modelling of bacterial pneumonia remains important for elucidating the complex host-pathogen interactions and to determine drug efficacy and toxicity. In vitro cell culture enables for the creation of high-throughput, specific disease models in a tightly controlled environment. Advanced human cell culture models specifically, can bridge the research gap between the classical two-dimensional cell models and animal models. This review provides an overview of the current status of the development of complex cellular in vitro models to study bacterial pneumonia infections, with a focus on air-liquid interface models, spheroid, organoid, and lung-on-a-chip models. For the wide scale, comparative literature search, we selected six clinically highly relevant bacteria (Pseudomonas aeruginosa, Mycoplasma pneumoniae, Haemophilus influenzae, Mycobacterium tuberculosis, Streptococcus pneumoniae, and Staphylococcus aureus). We reviewed the cell lines that are commonly used, as well as trends and discrepancies in the methodology, ranging from cell infection parameters to assay read-outs. We also highlighted the importance of model validation and data transparency in guiding the research field towards more complex infection models.

Exploring the Influence of VDR Genetic Variants TaqI, ApaI, and FokI on COVID-19 Severity and Long-COVID-19 Symptoms

There is increasing evidence regarding the importance of vitamin D in the prognosis of coronavirus disease 2019 (COVID-19). Genetic variants in the vitamin D receptor (VDR) gene affect the response to vitamin D and have been linked to various diseases. This study investigated the associations of the major VDR genetic variants ApaI, FokI, and TaqI with the severity and long post-infection symptoms of COVID-19. In total, 100 Jordanian patients with confirmed COVID-19 were genotyped for the VDR ApaI, FokI, and TaqI variants using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. COVID-19 severity, the most commonly reported long-COVID-19 symptoms that lasted for >4 weeks from the onset of infection, and other variables were analyzed according to VDR genetic variants. In this study, ApaI and FokI polymorphisms showed no significant associations with COVID-19 severity (p > 0.05). However, a significant association was detected between the TaqI polymorphism and the severity of symptoms after infection with the SARS-CoV-2 virus (p = 0.04). The wild-type TaqI genotype was typically present in patients with mild illness, whereas the heterozygous TaqI genotype was present in asymptomatic patients. With regard to long-COVID-19 symptoms, the VDR heterozygous ApaI and wild-type TaqI genotypes were significantly associated with persistent fatigue and muscle pain after COVID-19 (p ˂ 0.05). Most carriers of the heterozygous ApaI genotype and carriers of the wild-type TaqI genotype reported experiencing fatigue and muscle pain that lasted for more than 1 month after the onset of COVID-19. Furthermore, the TaqI genotype was associated with persistent shortness of breath after COVID-19 (p = 0.003). Shortness of breath was more common among individuals with homozygous TaqI genotype than among individuals with the wild-type or heterozygous TaqI genotype. VDR TaqI is a possible genetic variant related to both COVID-19 severity and long-COVID-19 symptoms among Jordanian individuals. The associations between VDR TaqI polymorphisms and long-COVID-19 symptoms should be investigated in larger and more diverse ethnic populations.

Vitamin D promotes epithelial tissue repair and host defense responses against influenza H1N1 virus and Staphylococcus aureus infections

BACKGROUND

Early studies indicated that vitamin D (VD) exerted pleiotropic extra-skeletal effects in the airway, but the definite linkage between VD deficiency and airway host responses remains unclear.

METHODS

142 cases of clinical data from Department of Otolaryngology, the Seventh Affiliated Hospital of Sun Yat-sen University, were collected to characterize the relationship between VD deficiency and chronic rhinosinusitis (CRS). Based on the clinical observations, 2.5-D airway epithelial organoids cultured at the air-liquid interface (ALI) were used to simulate the effects of VD treatment in the development of airway epithelium and the modulation of the host responses against influenza H1N1 virus (representing viral infections) and Staphylococcus aureus (representing bacterial infections) infections in the airway. The intrinsic mechanisms of VD deficiency underlying epithelial remodeling were mapped by transcriptomic as well as proteomic analyses.

RESULTS

In this study we observed prevailing VD deficiency among inpatients suffering from CRS, a common disease predominantly characterized by epithelial impairment and remodeling. Relative to control organoids cultured without VD, long-term incubation with VD accelerated basal cell proliferation during nasal epithelial development. Under infectious conditions, VD treatment protected the organoids against influenza H1N1 virus and Staphylococcus aureus invasions by reinforcing the respiratory host defenses, including upregulation of LL37, suppression (or inhibition) of proinflammatory cytokines, strengthening of epithelial integrity, and mucociliary clearance. In silico analysis of transcriptomics and proteomics suggested that VD modulated the epithelial development and remodeling, involving epithelial cell proliferation/differentiation, epithelial-mesenchymal transition (EMT), and cytokine signaling in the immune system, as well as responses to microbe, cell junction organization, and extracellular matrix organization via PTEN signaling, independent of TGF-β signaling.

CONCLUSIONS

Our findings emphasize the importance of managing VD deficiency in clinical settings for the sake of alleviating pathological epithelial remodeling. Vitamin D promotes epithelial tissue repair and host defense responses against influenza H1N1 and Staphylococcus aureus infections.

Immunomodulatory Properties of Vitamin D in the Intestinal and Respiratory Systems

Vitamin D plays a crucial role in modulating the innate immune response by interacting with its intracellular receptor, VDR. In this review, we address vitamin D/VDR signaling and how it contributes to the regulation of intestinal and respiratory microbiota. We additionally review some components of the innate immune system, such as the barrier function of the pulmonary and intestinal epithelial membranes and secretion of mucus, with their respective modulation by vitamin D. We also explore the mechanisms by which this vitamin D/VDR signaling mounts an antimicrobial response through the transduction of microbial signals and the production of antimicrobial peptides that constitute one of the body’s first lines of defense against pathogens. Additionally, we highlight the role of vitamin D in clinical diseases, namely inflammatory bowel disease and acute respiratory distress syndrome, where excessive inflammatory responses and dysbiosis are hallmarks. Increasing evidence suggests that vitamin D supplementation may have potentially beneficial effects on those diseases.

Shared mechanisms and crosstalk of COVID-19 and osteoporosis via vitamin D

Recently accumulated evidence implicates a close association of vitamin D (VitD) insufficiency to the incidence and clinical manifestations of the COVID-19 caused by severe acute respiratory syndrome coronavirus-2 (SARS-COV-2). Populations with insufficient VitD including patients with osteoporosis are more susceptible to SARS-COV-2 infection and patients with COVID-19 worsened or developed osteoporosis. It is currently unknown, however, whether osteoporosis and COVID-19 are linked by VitD insufficiency. In this study, 42 common targets for VitD on both COVID-19 and osteoporosis were identified among a total of 243 VitD targets. Further bioinformatic analysis revealed 8 core targets (EGFR, AR, ESR1, MAPK8, MDM2, EZH2, ERBB2 and MAPT) in the VitD-COVID-19-osteoporosis network. These targets are involved in the ErbB and MAPK signaling pathways critical for lung fibrosis, bone structural integrity, and cytokines through a crosstalk between COVID-19 and osteoporosis via the VitD-mediated conventional immune and osteoimmune mechanisms. Molecular docking confirmed that VitD binds tightly to the predicted targets. These findings support that VitD may target common signaling pathways in the integrated network of lung fibrosis and bone structural integrity as well as the immune systems. Therefore, VitD may serve as a preventive and therapeutic agent for both COVID-19 and osteoporosis.

Role of C3a as a Novel Regulator of 25(OH)D3 to 1α,25-Dihydroxyvitamin D3 Metabolism in Upper Airway Epithelial Cells

In patients with chronic rhinosinusitis with nasal polyps, primary human sinonasal epithelial cell (HSNEC) 1α-hydroxylase levels are reduced, as is their ability to metabolize 25-hydroxycholecalciferol [25(OH)D₃] to its active metabolite, 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃]. In this study, we sought to identify the factor responsible for the regulation of HSNEC metabolism of 25(OH)D₃, focusing on C3 and C3a. Multiple inhaled irritants trigger the release of complement components, C3 and C3a, leading to suppression of 1α-hydroxylase levels in HSNECs. Recombinant C3a was able to decrease 1α-hydroxylase and impair 25(OH)D₃ to 1,25(OH)₂D₃ metabolism, while addition of a C3a receptor antagonist restored conversion. Conversely, 1,25(OH)₂D₃ suppressed Aspergillus fumigatus-induced C3 and C3a levels in HSNEC supernatant. Given the ability of 1,25(OH)₂D₃ to modulate LL37 in other cell types, we examined its regulation in HSNECs and relationship to C3a. 1,25(OH)₂D₃ stimulated the secretion of LL37, whereas A. fumigatus and C3a suppressed it. Conversely, LL37 reduced the release of C3/C3a by HSNECs. Lastly, oral steroid use and in vitro dexamethasone application both failed to increase 1α-hydroxylase or reduce C3a levels. In summary, in this article, we describe for the first time a novel relationship between complement activation and local vitamin D metabolism in airway epithelial cells. The presence of elevated C3/C3a in patients with asthma and/or chronic rhinosinusitis with nasal polyps may account for their impaired HSNEC 25(OH)D₃ to 1,25(OH)₂D₃ metabolism and explain why they receive limited therapeutic benefit from oral vitamin D₃ supplementation.

Calcifediol for Use in Treatment of Respiratory Disease

Calcifediol is the prohormone of the vitamin D endocrine system (VDES). It requires hydroxylation to move to 1,25(OH)2D3 or calcitriol, the active form that exerts its functions by activating the vitamin D receptor (VDR) that is expressed in many organs, including the lungs. Due to its rapid oral absorption and because it does not require first hepatic hydroxylation, it is a good option to replace the prevalent deficiency of vitamin D (25 hydroxyvitamin D; 25OHD), to which patients with respiratory pathologies are no strangers. Correcting 25OHD deficiency can decrease the risk of upper respiratory infections and thus improve asthma and COPD control. The same happens with other respiratory pathologies and, in particular, COVID-19. Calcifediol may be a good option for raising 25OHD serum levels quickly because the profile of inflammatory cytokines exhibited by patients with inflammatory respiratory diseases, such as asthma, COPD or COVID-19, can increase the degradation of the active metabolites of the VDES. The aim of this narrative revision is to report the current evidence on the role of calcifediol in main respiratory diseases. In conclusion, good 25OHD status may have beneficial effects on the clinical course of respiratory diseases, including COVID-19. This hypothesis should be confirmed in large, randomized trials. Otherwise, a rapid correction of 25(OH)D deficiency can be useful for patients with respiratory disease.

Local nebulization of 1α,25(OH)2D3 attenuates LPS-induced acute lung inflammation

Background

Evidence supports a critical role of vitamin D status on exacerbation in chronic obstructive pulmonary disease, indicating the need to avoid vitamin D deficiency in these patients. However, oral vitamin D supplementation is limited by the potential risk for hypercalcemia. In this study, we investigated if local delivery of vitamin D to the lungs improves vitamin D-mediated anti-inflammatory action in response to acute inflammation without inducing hypercalcemia.

Methods

We studied vitamin D sufficient (VDS) or deficient (VDD) mice in whom 1α,25(OH)₂D₃ (0.2 μg/kg) or a vehicle followed by lipopolysaccharide (LPS 25 µg) were delivered to the lung as a micro-spray.

Results

Local 1α,25(OH)₂D₃ reduced LPS-induced inflammatory cells in bronchoalveolar lavage (BAL) in VDS (absolute number of cells: − 57% and neutrophils − 51% p < 0.01) and tended to diminish LPS-increased CXCL5 BAL levels in VDS (− 40%, p = 0.05) while it had no effect on CXCL1 and CXCL2 in BAL and mRNA in lung of VDS and VDD. It also significantly attenuated the increased IL-13 in BAL and lung, especially in VDD mice (− 41 and − 75%, respectively). mRNA expression of Claudin-18 in lung was significantly lower in VDS mice with local 1α,25(OH)₂D₃ while Claudin-3, -5 and -8 mRNA levels remained unchanged. Finally, in VDD mice only, LPS reduced lung mRNA expression of adhesion junction Zona-occludens-1, in addition to increasing uric acid and total protein in BAL, which both were prevented by local 1α,25(OH)₂D₃.

Conclusion

Under normal levels of vitamin D, local 1α,25(OH)₂D₃ nebulization into the lung efficiently reduced LPS induction of inflammatory cells in BAL and slightly attenuated LPS-increase in CXCL5. In case of severe vitamin D deficiency, although local 1α,25(OH)₂D₃ nebulization failed to significantly minimize cellular inflammation in BAL at this dose, it prevented epithelial barrier leakage and damage in lung. Additional research is needed to determine the potential long-term beneficial effects of local 1α,25(OH)2D3 nebulization on lung inflammation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-01997-9.

Vitamin D Supplementation: Association With Serum Cytokines in Pediatric Hematopoietic Stem Cell Transplantation

Vitamin D deficiency is prevalent in pediatric patients presenting for hematopoietic stem cell transplantation (HSCT) and has been linked to poor clinical outcomes. Using the data from a randomized control trial, in this paper we explore the effects of vitamin D supplementation on circulating cytokine levels during pediatric HSCT (www.clinicaltrials.gov as NCT03176849). A total of 41 children, 20 received Stoss therapy and 21 children received standard of care vitamin D supplementation. Levels of 25(OH)D and 20 cytokines were assessed at baseline and day +30. Significantly (P < 0.05) higher levels of mostly proinflammatory cytokines, FGF, GCSF, TNFα, IL-2, IL-6, IP10 were detected pre-transplant for patients with low compared to those with normal vitamin D levels. In sex stratified models that compare changes in cytokines between Stoss vs. standard of care, females in the Stoss group show greater changes in mostly pro -inflammatory cytokines- IP-10 (P = 0.0047), MIG (P = 0.009), and RANTES (P = 0.0047), IL-2R (P = 0.07) and IL-6(P = 0.069). Despite a small sample size, these findings suggest vitamin D deficiency affects the pre-transplant cytokine milieu and higher doses of vitamin D (Stoss therapy) appears to influence proinflammatory cytokine responses in a sex specific manner during pediatric HSCT. Larger clinical trials are warranted to validate these results.

Vitamin D Actions: The Lung Is a Major Target for Vitamin D, FGF23, and Klotho

Vitamin D is well known for its role as a calcium regulator and in maintenance of phosphate homeostasis in musculoskeletal health, and fibroblast growth factor 23 (FGF23) and its coreceptor α-klotho are known for their roles as regulators of serum phosphate levels. However, apart from these classical actions, recent data point out a relevant role of vitamin D and FGF23/klotho in lung health. The expression of the vitamin D receptor by different cell types in the lung and the fact that those cells respond to vitamin D or can locally produce vitamin D indicate that the lung represents a target for vitamin D actions. Similarly, the presence of the four FGF receptor isoforms in the lung and the ability of FGF23 to stimulate pulmonary cells support the concept that the lung is a target for FGF23 actions, whereas the contribution of klotho is still undetermined. This review will give an overview on how vitamin D or FGF23/klotho may act on the lung and interfere positively or negatively with lung health. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Vitamin D Metabolism Is Dysregulated in Asthma and Chronic Obstructive Pulmonary Disease

Rationale: Vitamin D deficiency is common in patients with asthma and chronic obstructive pulmonary disease (COPD). Low 25-hydroxyvitamin D (25[OH]D) levels may represent a cause or a consequence of these conditions.Objectives: To determine whether vitamin D metabolism is altered in asthma or COPD.Methods: We conducted a longitudinal study in 186 adults to determine whether the 25(OH)D response to six oral doses of 3 mg vitamin D₃, administered over 1 year, differed between those with asthma or COPD versus control subjects. Serum concentrations of vitamin D₃, 25(OH)D₃, and 1α,25-dihydroxyvitamin D₃ (1α,25[OH]₂D₃) were determined presupplementation and postsupplementation in 93 adults with asthma, COPD, or neither condition, and metabolite-to-parent compound molar ratios were compared between groups to estimate hydroxylase activity. Additionally, we analyzed 14 datasets to compare expression of 1α,25(OH)₂D₃-inducible gene expression signatures in clinical samples taken from adults with asthma or COPD versus control subjects.Measurements and Main Results: The mean postsupplementation 25(OH)D increase in participants with asthma (20.9 nmol/L) and COPD (21.5 nmol/L) was lower than in control subjects (39.8 nmol/L; P = 0.001). Compared with control subjects, patients with asthma and COPD had lower molar ratios of 25(OH)D₃-to-vitamin D₃ and higher molar ratios of 1α,25(OH)₂D₃-to-25(OH)D₃ both presupplementation and postsupplementation (P ≤ 0.005). Intergroup differences in 1α,25(OH)₂D₃-inducible gene expression signatures were modest and variable if statistically significant.Conclusions: Attenuation of the 25(OH)D response to vitamin D supplementation in asthma and COPD associated with reduced molar ratios of 25(OH)D₃-to-vitamin D₃ and increased molar ratios of 1α,25(OH)₂D₃-to-25(OH)D₃ in serum, suggesting that vitamin D metabolism is dysregulated in these conditions.

Shining Light on the COVID-19 Pandemic: A Vitamin D Receptor Checkpoint in Defense of Unregulated Wound Healing

SARS-CoV-2 pneumonitis can quickly strike to incapacitate the lung, leading to severe disease and sometimes death. In this perspective, we suggest that vitamin D deficiency and the failure to activate the vitamin D receptor (VDR) can aggravate this respiratory syndrome by igniting a wounding response in stellate cells of the lung. The FDA-approved injectable vitamin D analog, paricalcitol, suppresses stellate cell-derived murine hepatic and pancreatic pro-inflammatory and pro-fibrotic changes. Therefore, we suggest a possible parallel program in the pulmonary stellate cells of COVID-19 patients and propose repurposing paricalcitol infusion therapy to restrain the COVID-19 cytokine storm. This proposed therapy could prove important to people of color who have higher COVID-19 mortality rates and lower vitamin D levels.

Inhaled corticosteroid suppression of cathelicidin drives dysbiosis and bacterial infection in chronic obstructive pulmonary disease

Bacterial infection commonly complicates inflammatory airway diseases such as chronic obstructive pulmonary disease (COPD). The mechanisms of increased infection susceptibility and how use of the commonly prescribed therapy inhaled corticosteroids (ICS) accentuates pneumonia risk in COPD are poorly understood. Here, using analysis of samples from patients with COPD, we show that ICS use is associated with lung microbiota disruption leading to proliferation of streptococcal genera, an effect that could be recapitulated in ICS-treated mice. To study mechanisms underlying this effect, we used cellular and mouse models of streptococcal expansion with Streptococcus pneumoniae, an important pathogen in COPD, to demonstrate that ICS impairs pulmonary clearance of bacteria through suppression of the antimicrobial peptide cathelicidin. ICS impairment of pulmonary immunity was dependent on suppression of cathelicidin because ICS had no effect on bacterial loads in mice lacking cathelicidin (Camp ^-/-) and exogenous cathelicidin prevented ICS-mediated expansion of streptococci within the microbiota and improved bacterial clearance. Suppression of pulmonary immunity by ICS was mediated by augmentation of the protease cathepsin D. Collectively, these data suggest a central role for cathepsin D/cathelicidin in the suppression of antibacterial host defense by ICS in COPD. Therapeutic restoration of cathelicidin to boost antibacterial immunity and beneficially modulate the lung microbiota might be an effective strategy in COPD.

Impact of the Local Inflammatory Environment on Mucosal Vitamin D Metabolism and Signaling in Chronic Inflammatory Lung Diseases

Vitamin D plays an active role in the modulation of innate and adaptive immune responses as well as in the protection against respiratory pathogens. Evidence for this immunomodulatory and protective role is derived from observational studies showing an association between vitamin D deficiency, chronic airway diseases and respiratory infections, and is supported by a range of experimental studies using cell culture and animal models. Furthermore, recent intervention studies have now shown that vitamin D supplementation reduces exacerbation rates in vitamin D-deficient patients with chronic obstructive pulmonary disease (COPD) or asthma and decreases the incidence of acute respiratory tract infections. The active vitamin D metabolite, 1,25-dihydroxy-vitamin D (1,25(OH)₂D), is known to contribute to the integrity of the mucosal barrier, promote killing of pathogens (via the induction of antimicrobial peptides), and to modulate inflammation and immune responses. These mechanisms may partly explain its protective role against infections and exacerbations in COPD and asthma patients. The respiratory mucosa is an important site of local 1,25(OH)₂D synthesis, degradation and signaling, a process that can be affected by exposure to inflammatory mediators. As a consequence, mucosal inflammation and other disease-associated factors, as observed in e.g., COPD and asthma, may modulate the protective actions of 1,25(OH)₂D. Here, we discuss the potential consequences of various disease-associated processes such as inflammation and exposure to pathogens and inhaled toxicants on vitamin D metabolism and local responses to 1,25(OH)₂D in both immune- and epithelial cells. We furthermore discuss potential consequences of disturbed local levels of 25(OH)D and 1,25(OH)₂D for chronic lung diseases. Additional insight into the relationship between disease-associated mechanisms and local effects of 1,25(OH)₂D is expected to contribute to the design of future strategies aimed at improving local levels of 1,25(OH)₂D and signaling in chronic inflammatory lung diseases.

Local expression profiles of vitamin D-related genes in airways of COPD patients

Treatment of Chronic Obstructive Pulmonary Disease (COPD) is based on bronchodilation, with inhaled corticosteroids or azithromycin associated when frequent exacerbations occur. Despite the proven benefits of current treatment regimens, the need for new interventions in delineated subgroups remains. There is convincing evidence for oral vitamin D supplementation in reducing exacerbations in COPD patients severely deficient for circulating vitamin D. However, little is known about local vitamin D metabolism in the airways and studies examining expression of the vitamin D receptor (VDR), the activating enzyme (CYP27B1) and inactivating enzyme (CYP24A1) of vitamin D in lung tissue of COPD patients are lacking. Therefore, the expression and localization of key enzymes and the receptor of the vitamin D pathway were examined in tissue of 10 unused donor lungs and 10 COPD explant lungs. No differences in the expression of CYP27B1 and CYP24A1 were found. Although protein expression of VDR was significantly lower in COPD explant tissue, there was no difference in downstream expression of the antimicrobial peptide cathelicidin. Whereas CYP27B1 and CYP24A1 were present in all layers of the bronchial epithelium, VDR was only expressed at the apical layer of a fully differentiated bronchial epithelium with no expression in vascular endothelial cells. By contrast, CYP24A1 expression was highly present in lung endothelial cells suggesting that systemic vitamin D can be inactivated before reaching the epithelial compartment and the tissue immune cells. These data support the idea of exploring the role of vitamin D inhalation in patients with COPD.

Vitamin D attenuates lung injury via stimulating epithelial repair, reducing epithelial cell apoptosis and inhibits TGF-β induced epithelial to mesenchymal transition

Vitamin D regulates cell proliferation, inhibits cytokines release at sites of inflammation and reduces inflammatory responses. In this study, the aim was to investigate whether exogenous vitamin D attenuates LPS-induced lung injury via modulating epithelial cell proliferation, migration, apoptosis and epithelial mesenchymal transition (EMT). Murine and in vitro primary type II alveolar epithelial cell work were included in this study. In vivo, mice were mildly vitamin D deficient, 0.1, 1.5, 10 mg/kg 1,25(OH)₂-vitamin D₃ or 25(OH)-vitamin D₃ was administrated by means of an intra-gastric injection for 14 days pre-intra-tracheal (IT) LPS, which remarkedly promoted alveolar epithelial type II cells proliferation, inhibited ATII cells apoptosis and inhibited EMT, with the outcome of attenuated LPS-induced lung injury. In vitro, vitamin D stimulated epithelial cell scratch wound repair, reduced primary ATII cells apoptosis as well. Vitamin D promoted primary human ATII cells proliferation through the PI3K/AKT signaling pathway and activation of vitamin D receptor (VDR). Moreover, vitamin D inhibited EMT in response to TGF-β, which was vitamin D receptor dependent. In conclusion, vitamin D attenuates lung injury via stimulating ATII cells proliferation and migration, reducing epithelial cell apoptosis and inhibits TGF-β induced EMT. Together, these results suggest that vitamin D has therapeutic potential for the resolution of ARDS.

Vitamin D-Cathelicidin Axis: at the Crossroads between Protective Immunity and Pathological Inflammation during Infection

Vitamin D signaling plays an essential role in innate defense against intracellular microorganisms via the generation of the antimicrobial protein cathelicidin. In addition to directly binding to and killing a range of pathogens, cathelicidin acts as a secondary messenger driving vitamin D-mediated inflammation during infection. Recent studies have elucidated the biological and clinical functions of cathelicidin in the context of vitamin D signaling. The vitamin D-cathelicidin axis is involved in the activation of autophagy, which enhances antimicrobial effects against diverse pathogens. Vitamin D studies have also revealed positive and negative regulatory effects of cathelicidin on inflammatory responses to pathogenic stimuli. Diverse innate and adaptive immune signals crosstalk with functional vitamin D receptor signals to enhance the role of cathelicidin action in cell-autonomous effector systems. In this review, we discuss recent findings that demonstrate how the vitamin D-cathelicidin pathway regulates autophagy machinery, protective immune defenses, and inflammation, and contributes to immune cooperation between innate and adaptive immunity. Understanding how the vitamin D-cathelicidin axis operates in the host response to infection will create opportunities for the development of new therapeutic approaches against a variety of infectious diseases.

Antiviral immunity is impaired in COPD patients with frequent exacerbations

Patients with frequent exacerbations represent a chronic obstructive pulmonary disease (COPD) subgroup requiring better treatment options. The aim of this study was to determine the innate immune mechanisms that underlie susceptibility to frequent exacerbations in COPD. We measured sputum expression of immune mediators and bacterial loads in samples from patients with COPD at stable state and during virus-associated exacerbations. In vitro immune responses to rhinovirus infection in differentiated primary bronchial epithelial cells (BECs) sampled from patients with COPD were additionally evaluated. Patients were stratified as frequent exacerbators (≥2 exacerbations in the preceding year) or infrequent exacerbators (<2 exacerbations in the preceding year) with comparisons made between these groups. Frequent exacerbators had reduced sputum cell mRNA expression of the antiviral immune mediators type I and III interferons and reduced interferon-stimulated gene (ISG) expression when clinically stable and during virus-associated exacerbation. A role for epithelial cell-intrinsic innate immune dysregulation was identified: induction of interferons and ISGs during in vitro rhinovirus (RV) infection was also impaired in differentiated BECs from frequent exacerbators. Frequent exacerbators additionally had increased sputum bacterial loads at 2 wk following virus-associated exacerbation onset. These data implicate deficient airway innate immunity involving epithelial cells in the increased propensity to exacerbations observed in some patients with COPD. Therapeutic approaches to boost innate antimicrobial immunity in the lung could be a viable strategy for prevention and treatment of frequent exacerbations.

Modulation of cathelicidins, IFNβ and TNFα by bovine alpha-herpesviruses is dependent on the stage of the infectious cycle

Production of antimicrobial peptides cathelicidins, interferons and cytokines is an important feature in airway epithelial host defense. The innate immune response to alpha-herpesvirus infection at the sites of primary replication has not been fully studied. Thus, the aim of this study was to determine the expression of innate immune components, cathelicidins, IFNβ, TNFα and TNF receptors (TNFRI and TNFRII) during acute infection and reactivation of bovine herpesvirus type 1 (BoHV-1) and 5 (BoHV-5) in the respiratory tract and lymphoid tissue of their natural host. We found that BoHV infection modulates mainly the expression of BMAP28, a key cathelicidin in cattle. It was downregulated by both viruses in retropharyngeal lymph nodes of acutely infected-calves, and it was accompanied by a lower expression of IFNβ, TNFα and TNFRI. BoHV-5 showed a pronounced role in the downregulation of BMAP28, even in nasal mucosa and lung. However, during reactivation, BoHV-5 upregulated both BMAP28 and IFNβ in retropharyngeal lymph nodes. Acute replication induced also TNFα mRNA and protein synthesis, and expression of TNFRI and II was positively regulated during both acute infection and reactivation, particularly in the trachea. Moreover, BMAP27 was detected during BoHV-1 reactivation suggesting a potential role at this stage. Thus, cathelicidins are implicated in alpha-herpesvirus infections of the bovine respiratory system and the response is distinct during BoHV-1 and BoHV-5 acute infection and reactivation. This demonstrates that these viruses modulate differentially the components of innate immune response, possibly influencing their pathogenesis. This study provides an initial pilot analysis of factors that might be implicated in alpha-herpesvirus infection of the bovine respiratory system.

Involvement of multiple transcription factors in regulation of IL-β-induced MCP-1 expression in alveolar type II epithelial cells

During acute lung injury, a large number of monocytes are recruited into the pulmonary tissue, which is mainly mediated by local production of monocyte chemotactic protein 1 (MCP-1). As an essential component of the lung tissues, alveolar type II epithelial cells are one of the major sources of MCP-1. Therefore, uncovering the mechanism whereby MCP-1 production is regulated in the alveolar type II cells will provide a pivotal theoretical basis for clinical intervention in acute lung injury. In the current study, we find that there is a κB binding site in the MCP-1 promoter region, and mutation of the site leads to reduced production of MCP-1 in alveolar type II epithelial cells. In contrast, overexpression of NF-κB p65 significantly increases MCP-1 expression. Furthermore, we elucidate that IKKα/β-NF-κB p65 signaling pathway and phosphorylation of serine 534 in NF-κB p65 are required for the maximal expression of MCP-1. Also, Activator protein 1 (AP-1) site in the promoter region and JNK1/2-c-Jun signaling are required for MCP-1 generation in alveolar type II epithelial cells. Moreover, a CCAAT/enhancer-binding protein (C/EBP) element is identified in the MCP-1 promoter region through the point mutation technique, and further experiments demonstrate that both C/EBPβ and C/EBPδ are involved in basic and IL-1β-mediated MCP-1 expression. Of note, specificity protein 1-Sp1 expression is not changed in alveolar type II epithelial cells incubated with IL-1β, but it still control MCP-1 production by binding to the consensus sequence in the promoter region. More importantly, we find that the results derived from the cell line-MLE-12 cells and primary cells are consistent. Taken together, our data provide insights into the molecular mechanism how MCP-1 expression in inflammatory alveolar type II epithelial cells is regulated at transcription level.

TGF-β1 Impairs Vitamin D-Induced and Constitutive Airway Epithelial Host Defense Mechanisms

Airway epithelium is an important site for local vitamin D (VD) metabolism; this can be negatively affected by inflammatory mediators. VD is an important regulator of respiratory host defense, for example, by increasing the expression of hCAP18/LL-37. TGF-β1 is increased in chronic obstructive pulmonary disease (COPD), and known to decrease the expression of constitutive host defense mediators such as secretory leukocyte protease inhibitor (SLPI) and polymeric immunoglobulin receptor (pIgR). VD has been shown to affect TGF-β1-signaling by inhibiting TGF-β1-induced epithelial-to-mesenchymal transition. However, interactions between VD and TGF-β1, relevant for the understanding host defense in COPD, are incompletely understood. Therefore, the aim of the present study was to investigate the combined effects of VD and TGF-β1 on airway epithelial cell host defense mechanisms. Exposure to TGF-β1 reduced both baseline and VD-induced expression of hCAP18/LL-37, partly by increasing the expression of the VD-degrading enzyme CYP24A1. TGF-β1 alone decreased the number of secretory club and goblet cells and reduced the expression of constitutive host defense mediators SLPI, s/lPLUNC and pIgR, effects that were not modulated by VD. These results suggest that TGF-β1 may decrease the respiratory host defense both directly by reducing the expression of host defense mediators, and indirectly by affecting VD-mediated effects such as expression of hCAP18/LL-37.

Plasma cathelicidin and longitudinal lung function in current and former smokers

INTRODUCTION

Cathelicidin (also known as LL-37 in humans) is an antimicrobial peptide secreted by epithelial and immune cells and regulated by vitamin D. The immunological roles of cathelicidin make it a putative biomarker to identify individuals at risk for reduced lung function. The objective of this study is to determine potential independent associations between low plasma cathelicidin and longitudinal lung function in current or former smokers without COPD.

METHODS

In a nested analysis of 308 participants from an observational cohort study, plasma cathelicidin and serum 25-hydroxy-vitamin D measurements were obtained at baseline, years three and five. The independent association between lowest quartile cathelicidin (<35 ng/ml) and forced-expiratory-volume-in-1-second (FEV1) at baseline, six and 18 months from each cathelicidin measurement was assessed with generalized estimating equations after adjusting for age, sex, race, smoking status and intensity. The long-term stability of cathelicidin and relationship with vitamin D was evaluated.

RESULTS

The cohort was 91% African-American, mean age 48.6 years, 32% female, and 81% current smokers. Participants with low cathelicidin were more likely to be female and have lower FEV1. Low cathelicidin was not independently associated with baseline FEV1. There was an independent association between low cathelicidin and reduced FEV1 at six months [-72 ml (95% CI, -140 to -8ml); p = 0.027] and 18 months [-103 ml (95% CI, -180 to -27 ml); p = 0.007]. Cathelicidin was stable over time and not correlated with vitamin D level.

CONCLUSION

In current and former smokers with preserved lung function, low cathelicidin is associated with sustained lung function reductions at six and 18 months, suggesting that cathelicidin may be an informative biomarker to predict persistent lung function disparities among at-risk individuals.

Contribution of Host Defence Proteins and Peptides to Host-Microbiota Interactions in Chronic Inflammatory Lung Diseases

The respiratory tract harbours a variety of microorganisms, collectively called the respiratory microbiota. Over the past few years, alterations in respiratory and gut microbiota composition have been associated with chronic inflammatory diseases of the lungs. How these changes influence disease development and progression is an active field of investigation. Identifying and understanding host-microbiota interactions and factors contributing to these interactions could promote the development of novel therapeutic strategies aimed at restoring host-microbiota homeostasis. In this review, we discuss recent literature on host-microbiota interactions in the respiratory tract, with a specific focus on the influence of endogenous host defence peptides and proteins (HDPs) on the composition of microbiota populations in vivo and explore possible HDPs-related therapeutic approaches targeting microbiota dysbiosis in chronic inflammatory lung diseases.

Antiviral therapeutic approaches for human rhinovirus infections

Human rhinoviruses are the primary etiological agent of the common cold. This infection can be mild and self-limiting in immunocompetent hosts, but can be associated with bronchiolitis in infants, pneumonia in the immunosuppressed and exacerbations of pre-existing pulmonary conditions such as asthma or chronic obstructive pulmonary disease. Many of these conditions can place significant economic costs upon healthcare infrastructure. There is currently no licensed vaccine for rhinovirus, as the large variety of rhinovirus serotypes has posed significant challenges for research. In this review, we discuss current knowledge around antiviral drugs and small molecule inhibitors of rhinovirus infection, as well as antiviral host defense peptides as exciting prospects to approach the development of novel therapeutics which target human rhinovirus.

Vitamin D status and its influence on outcomes following major burn injury and critical illness

Vitamin D deficiency is common among the general population. It is also observed in up to 76% of critically ill patients. Despite the high prevalence of hypovitaminosis D in critical illness, vitamin D is often overlooked by medical staff as the clinical implications and consequences of vitamin D deficiency in acute contexts remain to be fully understood. Vitamin D has a broad range of pleotropic effects on various processes and systems including the immune-inflammatory response. 1α,25-dihydroxyvitamin D (1,25(OH)₂D), has been shown to promote a tolerogenic immune response limiting deleterious inflammatory effects, modulation of the innate immune system, and enhancement of anti-microbial peptides. Vitamin D deficiency is frequently observed in critically ill patients and has been related to extrinsic causes (i.e., limited sunlight exposure), magnitude of injury/illness, or the treatment started by medical doctors including fluid resuscitation. Low levels of vitamin D in critically ill patients have been associated with sepsis, organ failure, and mortality. Despite this, there are subpopulations of critical illness, such as burn patients, where the literature regarding vitamin D status and its influence on outcomes remain insufficient. Thermal injury results in damage to both burned and non-burned tissues, as well as induces an exaggerated and persistent immune-inflammatory and hypermetabolic response. In this review, we propose potential mechanisms in which burn injury affects the vitamin D status and summarizes current literature investigating the influence of vitamin D status on outcomes. In addition, we reviewed the literature and trials investigating vitamin D supplementation in critically ill patients and discuss the therapeutic potential of vitamin D supplementation in burn and critically ill patients. We also highlight current limitations of studies that have investigated vitamin D status and supplementation in critical illness. Thermal injury influences vitamin D status. More studies investigating vitamin D depletion in burn patients and its influence on prognosis, via standardized methodology, are required to reach definitive conclusions and influence clinical practice.

Aberrant epithelial differentiation by cigarette smoke dysregulates respiratory host defence

It is currently unknown how cigarette smoke-induced airway remodelling affects highly expressed respiratory epithelial defence proteins and thereby mucosal host defence.

Localisation of a selected set of highly expressed respiratory epithelial host defence proteins was assessed in well-differentiated primary bronchial epithelial cell (PBEC) cultures. Next, PBEC were cultured at the air–liquid interface, and during differentiation for 2–3 weeks exposed daily to whole cigarette smoke. Gene expression, protein levels and epithelial cell markers were subsequently assessed. In addition, functional activities and persistence of the cigarette smoke-induced effects upon cessation were determined.

Expression of the polymeric immunoglobulin receptor, secretory leukocyte protease inhibitor and long and short PLUNC (palate, lung and nasal epithelium clone protein) was restricted to luminal cells and exposure of differentiating PBECs to cigarette smoke resulted in a selective reduction of the expression of these luminal cell-restricted respiratory host defence proteins compared to controls. This reduced expression was a consequence of cigarette smoke-impaired end-stage differentiation of epithelial cells, and accompanied by a significant decreased transepithelial transport of IgA and bacterial killing.

These findings shed new light on the importance of airway epithelial cell differentiation in respiratory host defence and could provide an additional explanation for the increased susceptibility of smokers and patients with chronic obstructive pulmonary disease to respiratory infections.