Function and Regulation of SPLUNC1 Protein in Mycoplasma Infection and Allergic Inflammation

Abstract

Respiratory infections, including Mycoplasma pneumoniae (Mp), contribute to asthma pathobiology. To date, the mechanisms underlying the increased susceptibility of asthmatics to airway Mp infection remain unclear. Short palate, lung, and nasal epithelium clone 1 (SPLUNC1) protein is a recently described large airway epithelial cell-derived molecule that was predicted to exert host defense activities. However, SPLUNC1 function and regulation in an infectious or allergic milieu are still unknown. We determined host defense and anti-inflammatory functions of SPLUNC1 protein in Mp infection and the regulation of SPLUNC1 by Mp and allergic inflammation (e.g., IL-13). SPLUNC1 function was examined in Mp or human airway epithelial cell cultures by using SPLUNC1 recombinant protein, overexpression and RNA interference. Human and mouse bronchial epithelial SPLUNC1 was examined using immunostaining, Western blotting, ELISA, laser capture microdissection, and real-time PCR. Mouse models of Mp infection and allergic inflammation and air-liquid interface cultures of normal human primary bronchial epithelial cells were used to study SPLUNC1 regulation by Mp and IL-13. We found that: 1) SPLUNC1 protein decreased Mp levels and inhibited epithelial IL-8 production induced by Mp-derived lipoproteins; 2) normal human and mouse large airway epithelial cells expressed high levels of SPLUNC1; and 3) although Mp infection increased SPLUNC1, IL-13 significantly decreased SPLUNC1 expression and Mp clearance. Our results suggest that SPLUNC1 serves as a novel host defense protein against Mp and that an allergic setting markedly reduces SPLUNC1 expression, which may in part contribute to the persistent nature of bacterial infections in allergic airways.

An innate defense peptide BPIFA1/SPLUNC1 restricts influenza A virus infection

“…7B, C). Thus, our data show that IAV bound 178 predominantly to ciliated cells that were BPIFA1-negative, 2, 3 post infection but this is followed by a decrease over 2 -7 days 15,18,40 . Our results in 252 vivo extend these observations using IAV (Figs.…”

“…It has also been shown to have anti-10 bacterial roles. For example, Bpifa1 expression is induced after Mycoplasma 11 infection, enhancing IL-8 production and bacterial clearance 15 . BPIFA1 also has a 12 role in defense against Klebsiella pneumoniae 16 , possibly acting through modulation 13 of macrophage function 17 .…”

SPLUNC1 regulates airway surface liquid volume by protecting ENaC from proteolytic cleavage

“…However, this hypothesis is controversial, and some investigators have found that SPLUNC1 appears to have little antimicrobial activity against Escherichia coli, Listeria monocytogenes, or Pseudomonas aeruginosa (17), and does not appear to bind lipopolysaccharide (15). However, SPLUNC1 has recently been shown to inhibit Mycoplasma pneumoniae in airway cultures (28), and bind to lipopolysaccharide and disrupt Epstein-Barr virus proliferation (29). Although there is no current explanation for these discrepancies, we do not know whether SPLUNC1 is posttranslationally modified and/or how labile SPLUNC1 is once purified, and it is possible that the purification and storing of SPLUNC1 may alter its biological activity, leading to differing results.…”

“…Because SPLUNC1 is secreted by proximal airways, we propose that this regulation primarily occurs in the proximal airways, with little effect in the distal airways. However, if SPLUNC1 secretion is indeed up-regulated by inflammation (28), this secretion may serve to decrease ENaC activity and increase mucus clearance in the distal airways during these times. In conclusion, ENaC is a soluble regulator of ENaC that is expressed in multiple organs.…”

“…SPLUNC1 is up-regulated by inflammation (28), which may decrease ENaC activity and shift the fluid balance toward secretion in inflamed regions of the airways, colon and/or kidneys. In times of infection, this action may help to ''flush out'' the afflicted organ.…”