The Goblet Cell Protein Clca1 (Alias mClca3 or Gob-5) Is Not Required for Intestinal Mucus Synthesis, Structure and Barrier Function in Naive or DSS-Challenged Mice

Abstract

The secreted, goblet cell-derived protein Clca1 (chloride channel regulator, calcium-activated-1) has been linked to diseases with mucus overproduction, including asthma and cystic fibrosis. In the intestine Clca1 is found in the mucus with an abundance and expression pattern similar to Muc2, the major structural mucus component. We hypothesized that Clca1 is required for the synthesis, structure or barrier function of intestinal mucus and therefore compared wild type and Clca1-deficient mice under naive and at various time points of DSS (dextran sodium sulfate)-challenged conditions. The mucus phenotype in Clca1-deficient compared to wild type mice was systematically characterized by assessment of the mucus protein composition using proteomics, immunofluorescence and expression analysis of selected mucin genes on mRNA level. Mucus barrier integrity was assessed in-vivo by analysis of bacterial penetration into the mucus and translocation into sentinel organs combined analysis of the fecal microbiota and ex-vivo by assessment of mucus penetrability using beads. All of these assays revealed no relevant differences between wild type and Clca1-deficient mice under steady state or DSS-challenged conditions in mouse colon. Clca1 is not required for mucus synthesis, structure and barrier function in the murine colon.

Loss of Bcl-G, a Bcl-2 family member, augments the development of inflammation-associated colorectal cancer

“…While we observed no significant differences in Ki67+ proliferating cells in any of our models, loss of Bcl-g was linked to decreased Clca1, which is also decreased in CRC patients and is associated with inhibition of CRC epithelial differentiation when knocked down in cell lines [37,54]. Similar to Bcl-g −/− mice, Clca1 −/− mice display no overt phenotype in the acute DSS model, although mucous composition is not associated specifically with Clca1 expression [37,54]. Alternatively, changes in the mucin network in Bcl-g −/− mice may reflect changes in goblet cell restitution, a process that is not well understood.…”

“…We believe that the contribution of Bcl-G to the mucin network is a reflection of a potential difference in the transition from proliferation to differentiation of colonic epithelial cells. While we observed no significant differences in Ki67+ proliferating cells in any of our models, loss of Bcl-g was linked to decreased Clca1, which is also decreased in CRC patients and is associated with inhibition of CRC epithelial differentiation when knocked down in cell lines [37,54]. Similar to Bcl-g −/− mice, Clca1 −/− mice display no overt phenotype in the acute DSS model, although mucous composition is not associated specifically with Clca1 expression [37,54].…”

“…7d). Chloride accessory channel 1 (Clca1), which has a similar expression pattern to Muc2 [37], was also significantly decreased in naïve Bcl-g −/− mice (1.32 Log 2 fold) and following DSS treatment (2.04 Log 2 fold; Fig. 7b, c).…”

Role of goblet cell protein CLCA1 in murine DSS colitis

“…We chose the dextran sodium sulfate (DSS) challenge model which is commonly used to study early immune reactions in mouse intestine [ 9 ]. In a previous DSS colitis study, we failed to observe any effects of Clca1-deficiency on mucus barrier integrity and mucin gene expression [ 10 ] which likely would have affected secondary immune responses. Additionally, recent studies have indicated that CLCA1 does not play a role in calcium-activated chloride secretion in the respiratory tract nor does restoration of reduced Clca1 expression rectify the cystic fibrosis electrophysiology defect in the intestine [ 11 , 12 ].…”

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

“…The originally confusing nomenclature of murine CLCA1, previously termed mCLCA3 or goblet cell protein-5 (gob-5), was harmonized with respect to the human and rat nomenclature in accordance with the Human Gene Nomenclature Committee and the Rat Genome Database (Erickson et al 2015). The soluble heterodimer consists of two posttranslational cleavage products, a 75 kDa amino- and a 35 kDa carboxy-terminal protein, that are processed and glycosylated from a primary 125 kDa translation product (Mundhenk et al 2006).…”