Effect of Corticosteroids and Neuropeptides on the Expression of Defensins in Bovine Tracheal Epithelial Cells

Abstract

Susceptibility to bacterial pneumonia in cattle is enhanced by stressors such as transportation, weaning, and commingling, which trigger a physiologic stress response resulting in elevated levels of endogenous corticosteroids and catecholamines. To determine the effect of neuroendocrine mediators on the expression of innate defense peptides in the lung, bovine tracheal epithelial cells were exposed to dexamethasone, catecholamines, acetylcholine, or substance P, and then ␤-defensin expression was quantified using real-time reverse transcription-PCR. Basal expression of tracheal antimicrobial peptide (TAP) mRNA was not affected by any of the mediators tested. However, induction of TAP expression by lipopolysaccharide was significantly inhibited by pretreatment with dexamethasone. Bronchial biopsy specimens from dexamethasone-treated calves had significantly lower expression of TAP and lingual antimicrobial peptide (LAP) mRNA than saline-treated controls following 48 h of treatment. Lipopolysaccharide-elicited neutrophil recruitment was enhanced in the lungs of dexamethasone-treated calves compared to saline-treated controls. These findings indicate that modulation of epithelial antimicrobial peptide expression is one mechanism through which corticosteroids and stress may impair innate pulmonary defenses.

Failure of Respiratory Defenses in the Pathogenesis of Bacterial Pneumonia of Cattle

“…121 Despite these effects, dexamethasone-treated cattle had greater numbers of neutrophils after administration of IL-8 into the lung or uterus, 103,134 with similar findings in the mammary gland of cows experiencing transport stress. 222 These findings surprisingly suggest that either recruitment or survival of neutrophils is increased by glucocorticoid.…”

“…Corticosteroids impair the lipopolysaccharide (LPS)-inducible expression of tracheal antimicrobial peptide expression in cattle 134 and of HBD-2 201 and HBD-3 in humans, 51 perhaps by interfering with TLR4/NF-kB signaling. Inhalation of corticosteroid presents little risk to otherwise healthy human asthmatics as they have few bacteria reaching the lung, but this is a risk factor for patients with chronic obstructive pulmonary disease (COPD) or community-acquired pneumonia, in which bacterial challenge of the lung is greater.…”

“…In contrast, lactotransferrin is constitutively present but induced to higher levels by inflammation. 3,116,134,154,171 Factors that reduce the baseline or induce levels of these innate defense molecules are one mechanism by which predisposing factors lead to bacterial pneumonia.…”

Comparison of innate immune agonists for induction of tracheal antimicrobial peptide gene expression in tracheal epithelial cells of cattle

“…The GAPDH Ct values remained within 1 threshold cycle across various treatments, confirming constant gene expression under the conditions tested. The primer sequences and product sizes for TAP and GAPH were as follows: TAP forward 5'-TCTTCCTGGTCTGTCTGCT-3' , reverse 5'-GCTGTGTCTTGGCCTTCTTT-3' , 183 bp product size; GAPDH forward 5'-GGCGTGAACCACG AGAAGTAT AA-3' , reverse 5'-CCCTCCACGATGCCAAAGT-3' , 120 bp product size [10]. Amplification efficiencies of 1.91 for TAP and 1.88 for GAP were determined from the slope of a standard curve constructed from a series of 1:5 serial dilutions of cDNA synthesized from LPSstimulated bTEC.…”

“…TAP expression is induced by several pro-inflammatory cytokines as well as bacterial components such as lipopolysaccharide (LPS) [4][5][6][7]. However, infection with certain viruses and bacteria, or exposure to glucocorticoids, inhibits this response to LPS, implying that this may be one mechanism by which stress and viral infection increase the risk of bacterial pneumonia in cattle [8][9][10][11]. Importantly, the susceptibility of bovine bacterial pathogens to TAP suggests that restoring this suppressed response may be a viable method to prevent disease in stressed or virus-infected cattle [11].…”