Differential Muc2 and Muc5ac secretion by stimulated guinea pig tracheal epithelial cells in vitro.
BACKGROUND
Mucus overproduction is a characteristic of inflammatory pulmonary diseases including asthma, chronic bronchitis, and cystic fibrosis. Expression of two mucin genes, MUC2 and MUC5AC, and their protein products (mucins), is modulated in certain disease states. Understanding the signaling mechanisms that regulate the production and secretion of these major mucus components may contribute significantly to development of effective therapies to modify their expression in inflamed airways.


METHODS
To study the differential expression of Muc2 and Muc5ac, a novel monoclonal antibody recognizing guinea pig Muc2 and a commercially-available antibody against human MUC5AC were optimized for recognition of specific guinea pig mucins by enzyme-linked immunosorbent assay (ELISA), Western blot, and immunohistochemistry (IHC). These antibodies were then used to analyze expression of Muc2 and another mucin subtype (likely Muc5ac) in guinea pig tracheal epithelial (GPTE) cells stimulated with a mixture of pro-inflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha), interleukin 1beta (IL-1beta), and interferon- gamma (IFN-gamma)].


RESULTS
The anti-Muc2 (C4) and anti-MUC5AC (45M1) monoclonal antibodies specifically recognized proteins located in Muc2-dominant small intestinal and Muc5ac-dominant stomach mucosae, respectively, in both Western and ELISA experimental protocols. IHC protocols confirmed that C4 recognizes murine small intestine mucosal proteins while 45M1 does not react. C4 and 45M1 also stained specific epithelial cells in guinea pig lung sections. In the resting state, Muc2 was recognized as a highly expressed intracellular mucin in GPTE cells in vitro. Following cytokine exposure, secretion of Muc2, but not the mucin recognized by the 45M1 antibody (likely Muc5ac), was increased from the GPTE cells, with a concomitant increase in intracellular expression of both mucins.


CONCLUSIONS
Given the tissue specificity in IHC and the differential hybridization to high molecular weight proteins by Western blot, we conclude that the antibodies used in this study can recognize specific mucin subtypes in guinea pig airway epithelium and in proteins from GPTE cells. In addition, Muc2 is highly expressed constitutively, modulated by inflammation, and secreted differentially (as compared to Muc5ac) in GPTE cells. This finding contrasts with expression patterns in the airway epithelium of a variety of mammalian species in which only Muc5ac predominates.
Chorley
Brian N
BN
North Carolina State University, College of Veterinary Medicine, Raleigh, NC, USA. chorleyb@niehs.nih.gov
Crews
Anne L
AL
Li
Yuehua
Y
Adler
Kenneth B
KB
Minnicozzi
Michael
M
Martin
Linda D
LD
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002478:Cells, Cultured; D016207:Cytokines; D004797:Enzyme-Linked Immunosorbent Assay; D004847:Epithelial Cells / Q000378:metabolism*; D005786:Gene Expression Regulation; D006168:Guinea Pigs; D007150:Immunohistochemistry; D055271:Mucin 5AC; D055262:Mucin-2; D009077:Mucins / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D020545:Respiratory Mucosa / Q000187:drug effects / Q000378:metabolism; D014132:Trachea / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D016207:Cytokines; C524625:MUC2 protein, human; C524678:MUC5AC protein, human; D055271:Mucin 5AC; D055262:Mucin-2; D009077:Mucins; D012333:RNA, Messenger