Rapid baso-apical translocation of Mycobacterium avium ssp. paratuberculosis in mammary epithelial cells in the presence of Escherichia coli

Infection of mammary gland cells with bacterial pathogens begins with adhesion, invasion, and persistence within the cells or systemic distribution. Some bacteria, such as Escherichia coli, are known to causes bovine mastitis, resulting in acute proinflammatory responses in the mammary tissue. Mycobacterium avium ssp. paratuberculosis (MAP), the etiological agent of paratuberculosis, is able to spread to distant organs after crossing intestinal cells, reaching the mammary gland and potentially being released in milk, infecting calves during suckling. Its exit from systemic sites may be influenced by preexisting inflammation such as that caused by E. coli mastitis. Interactions between E. coli and MAP in mammary epithelial cells have not yet been described. In this study, we posited that E. coli-infected bovine mammary epithelial cells would facilitate baso-apical translocation of MAP in an ex vivo model. We showed that the presence of E. coli in a bovine mammary epithelial cell line (MAC-T) increased baso-apical translocation of MAP to the apical side of the cells. Levels were significantly higher 30 min post-infection and decreased at 120 min post-infection. Cells previously infected with E. coli and MAP or with E. coli alone showed a significant increase in IL1B mRNA expression at 120 min. We detected no significant expression of p38 mitogen-activated protein kinase (mapkp38) or IL10, regardless of treatment. Thereby, the presence of E. coli in MAC-T cells alters the translocation of MAP through epithelial cells, enabling its rapid translocation to the cellular surface. Expression of IL1B was shown to influence the apical-basal translocation of MAP at 120 min. Findings from the current study suggest that MAP translocation into milk is likely enhanced by inflammatory states such as those induced during E. coli mastitis. This is the first report demonstrating the effect of E. coli under MAP coinfection in bovine mammary epithelial cells under experimental conditions.

A Mycobacterium avium subsp. paratuberculosis Predicted Serine Protease Is Associated with Acid Stress and Intraphagosomal Survival

The ability to maintain intra-cellular pH is crucial for bacteria and other microbes to survive in diverse environments, particularly those that undergo fluctuations in pH. Mechanisms of acid resistance remain poorly understood in mycobacteria. Although, studies investigating acid stress in M. tuberculosis are gaining traction, few center on Mycobacterium avium subsp. paratuberculosis (MAP), the etiological agent of chronic enteritis in ruminants. We identified a MAP acid stress response network involved in macrophage infection. The central node of this network was MAP0403, a predicted serine protease that shared an 86% amino acid identity with MarP in M. tuberculosis. Previous studies confirmed MarP as a serine protease integral to maintaining intra-bacterial pH and survival in acid in vitro and in vivo. We show that MAP0403 is upregulated in infected macrophages and MAC-T cells that coincided with phagosome acidification. Treatment of mammalian cells with bafilomcyin A1, a potent inhibitor of phagosomal vATPases, diminished MAP0403 transcription. MAP0403 expression was also noted in acidic medium. A surrogate host, M. smegmatis mc² 155, was designed to express MAP0403 and when exposed to either macrophages or in vitro acid stress had increased bacterial cell viability, which corresponds to maintenance of intra-bacterial pH in acidic (pH = 5) conditions, compared to the parent strain. These data suggest that MAP0403 may be the equivalent of MarP in MAP. Future studies confirming MAP0403 as a serine protease and exploring its structure and possible substrates are warranted.

The autoimmunity-associated gene PTPN22 potentiates toll-like receptor-driven, type 1 interferon-dependent immunity

Immune cells sense microbial products through Toll-like receptors (TLR), which trigger host defense responses including type 1 interferons (IFNs) secretion. A coding polymorphism in the protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene is a susceptibility allele for human autoimmune and infectious disease. We report that Ptpn22 selectively regulated type 1 IFN production after TLR engagement in myeloid cells. Ptpn22 promoted host antiviral responses and was critical for TLR agonist-induced, type 1 IFN-dependent suppression of inflammation in colitis and arthritis. PTPN22 directly associated with TNF receptor-associated factor 3 (TRAF3) and promotes TRAF3 lysine 63-linked ubiquitination. The disease-associated PTPN22W variant failed to promote TRAF3 ubiquitination, type 1 IFN upregulation, and type 1 IFN-dependent suppression of arthritis. The findings establish a candidate innate immune mechanism of action for a human autoimmunity "risk" gene in the regulation of host defense and inflammation.