Soluble mucus component CLCA1 modulates expression of leukotactic cytokines and BPIFA1 in murine alveolar macrophages but not in bone marrow-derived macrophages

Abstract

The secreted airway mucus cell protein chloride channel regulator, calcium-activated 1, CLCA1, plays a role in inflammatory respiratory diseases via as yet unidentified pathways. For example, deficiency of CLCA1 in a mouse model of acute pneumonia resulted in reduced cytokine expression with less leukocyte recruitment and the human CLCA1 was shown to be capable of activating macrophages in vitro. Translation of experimental data between human and mouse models has proven problematic due to several CLCA species-specific differences. We therefore characterized activation of macrophages by CLCA1 in detail in solely murine ex vivo and in vitro models. Only alveolar but not bone marrow-derived macrophages freshly isolated from C57BL6/J mice increased their expression levels of several pro-inflammatory and leukotactic cytokines upon CLCA1 stimulation. Among the most strongly regulated genes, we identified the host-protective and immunomodulatory airway mucus component BPIFA1, previously unknown to be expressed by airway macrophages. Furthermore, evidence from an in vivo Staphylococcus aureus pneumonia mouse model suggests that CLCA1 may also modify BPIFA1 expression in airway epithelial cells. Our data underscore and specify the role of mouse CLCA1 in inflammatory airway disease to activate airway macrophages. In addition to its ability to upregulate cytokine expression which explains previous observations in the Clca1-deficient S. aureus pneumonia mouse model, modulation of BPIFA1 expression expands the role of CLCA1 in airway disease to involvement in more complex downstream pathways, possibly including liquid homeostasis, airway protection, and antimicrobial defense.Electronic supplementary materialThe online version of this article (10.1007/s00418-018-1664-y) contains supplementary material, which is available to authorized users.

Genomic, biochemical and expressional properties reveal strong conservation of the CLCA2 gene in birds and mammals

“…CLCA2 seems to lack significant associations with human diseases, (OMIM Database entry #604003), which is usually the prime driver for generating animal models to investigate more complex functions in vivo . This is in contrast to ma CLCA1 , for which its proposed role as modifier in cystic fibrosis ( Hauber et al, 2003 ; Ritzka et al, 2004 ; Young et al, 2007 ) has stimulated the generation of several knockout models in mice ( Erickson et al, 2018 ; Erickson et al, 2015 ; Long et al, 2006 ; Mundhenk et al, 2012 ; Nyström et al, 2018 ; Patel et al, 2006 ; Robichaud et al, 2005 ). The lack of a relevant phenotype in any of these models raises general reservations regarding the suitability of deleting a gene for exploring its function, but in the case of CLCA , the interpretation was complicated even further.…”

“…It has been proposed that the CLCA2 protein is involved in epithelial differentiation, growth arrest and maturation of keratinocytes ( Connon et al, 2004 ; Koegel & Alzheimer, 2001 ; Ramena et al, 2016 ). Some species-specific differences regarding the expression, however, have been revealed in the mammalian respiratory tract, where human, porcine, and murine, but no feline CLCA2 has been detected in airway submucosal glands ( Dietert et al, 2015 ; Erickson et al, 2018 ). Further, additional protein expression has been found in a specific subset of respiratory epithelial cells of the bronchial bifurcation in mice ( Dietert et al, 2015 ).…”

CLCA1 mediates the regulatory effect of IL-13 on pediatric asthma

“…Studies have shown that CLCA1 plays an important role in a mouse model of dextran sulfate sodium-induced colitis by the modulation of early immune responses through altered cytokine secretion ( 27 ). Furthermore, CLCA1 deficiency resulted in decreased cytokine expression and decreased leukocyte recruitment in an acute pneumonia mouse model ( 28 ). Finally, CLCA1 has been shown to activate macrophages in vitro .…”

Calcium-activated chloride channel regulator 1 (CLCA1): More than a regulator of chloride transport and mucus production

“…Yet, mCLCA1-deficiency did not affect mucus cell number and mucin secretion in infected mice. In murine experimental acute pneumonia induced by S. aureus infection, the expression of airway mucus component bactericidal/permeability-increasing protein (BPI) fold-containing family A member 1 (Bpifa1), a secretory protein from the respiratory tract that has antimicrobial and anti-biofilm properties to regulate mucociliary clearance, 55 was significantly intensified in Clca1 −/− mice compared to that from WT mice at 24 hours post-infection 56 . Therefore, the role of CLCA1 in respiratory diseases might involve much more complicated downstream pathways, rather than just goblet cell mucus production and epithelial cell chloride ion secretion.…”