Inducible expression of green fluorescent protein in porcine tracheal epithelial cells by the bovine tracheal antimicrobial peptide promoter

Bacteria-induced expression of the pig-derived protegrin-1 transgene specifically in the respiratory tract of mice enhances resistance to airway bacterial infection

About 70% of all antibiotics produced in the world are used in the farm animal industry. The massive usage of antibiotics during farm animal production has caused rapid development of antibiotic resistance in bacteria, which poses a serious risk to human and livestock health when treating bacterial infections. Protegrin-1 (PG-1) is a potent antimicrobial peptide (AMP). It was initially identified in pig leukocytes with a broad-spectrum antibacterial and antiviral activity, and a low rate of inducing bacterial resistance. To develop a genetic approach for reducing the use of antibiotics in farm animal production, we produced transgenic mice carrying a bovine tracheal AMP gene promoter-controlled PG-1 transgene. The PG-1 transgene was specifically expressed in the respiratory tract of transgenic mice upon induction by bacterial infection. These PG-1 transgenic mice exhibited enhanced resistance to nasal bacterial infection as the transgenic mice showed a higher survival rate (79.17% VS. 34.78%), lower bacterial load and milder histological severity than their wild-type control littermates. The improved resistance to bacterial infection in the PG-1 transgenic mice could be resulted from the direct bacteria-killing activities of PG-1, and the immunomodulatory effects of PG-1 via stimulating interleukin 1 beta secretion. The present study provides a promising genetic strategy to prevent airway bacterial infections in farm animals by bacteria-inducible tissue-specific expression of PG-1 transgene. This approach may also be helpful for decreasing the possibility of inducing bacterial resistance during farm animal production.

Primary in vitro culture of porcine tracheal epithelial cells in an air-liquid interface as a model to study airway epithelium and Aspergillus fumigatus interactions

Since the airway epithelium is the first tissue encountered by airborne fungal spores, specific models are needed to study this interaction. We developed such a model using primary porcine tracheal epithelial cells (PTEC) as a possible alternative to the use of primary human cells. PTEC were obtained from pigs and were cultivated in an air-liquid interface. Fluorescent brightener was employed to quantify the internalization of Aspergillus fumigatus conidia. Potential differences (Vt) and transepithelial resistances (Rt) after challenge with the mycotoxin, verruculogen, were studied. Primers for porcine inflammatory mediator genes IL-8, TNF-alpha, and GM-CSF were designed for a quantitative real-time PCR procedure to study cellular responses to challenges with A. fumigatus conidia. TEM showed the differentiation of ciliated cells and the PTEC ability to internalize conidia. The internalization rate was 21.9 ± 1.4% after 8 h of incubation. Verruculogen (10(-6) M) significantly increased Vt without having an effect on the Rt. Exposure of PTEC to live A. fumigatus conidia for 24 h induced a 10- to 40-fold increase in the mRNA levels of inflammatory mediator genes. PTEC behave similarly to human cells and are therefore a suitable alternative to human cells for studying interaction between airway epithelium and A. fumigatus.

Enhanced resistance to bacterial infection in protegrin-1 transgenic mice

Antibiotic-resistant bacteria have become a public health concern. It was suggested that one source of resistant pathogens may be food-producing animals. Alternative approaches are therefore needed to enhance the resistance of farm animals to bacterial infection. Protegrin-1 (PG-1) is a neutrophil-derived antimicrobial peptide that possesses activity against a wide range of bacteria and enveloped viruses. Here we report on the production of transgenic mice that ectopically expressed PG-1 and compare their susceptibilities to Actinobacillus suis infection with those of their wild-type (WT) littermates. Of the 126 mice that were challenged with A. suis, 87% of the transgenic mice survived, whereas 31% of their WT littermates survived. The PG-1 transgenic mice had significantly lower bacterial loads in their lungs and reduced numbers of pulmonary pathological lesions. The antimicrobial function of PG-1 was confirmed in vitro by using fibroblast cells isolated from the transgenic mice but not the WT mice. Moreover, differential blood cell counts in bronchoalveolar lavage fluid indicated greater number of neutrophils in PG-1 transgenic mice than in their WT littermates after bacterial challenge. Our data suggest that the ectopic expression of PG-1 in mice confers enhanced resistance to bacterial infection, laying the foundation for the development of livestock with improved resistance to infection.