RNase 7 but not psoriasin nor sPLA2-IIA associates with Mycobacterium tuberculosis during airway epithelial cell infection

Abstract

Tuberculosis is a disease caused by Mycobacterium tuberculosis (Mtb). Innate immunity is the first line of defense against Mtb and malfunctions in any of its components are associated with the susceptibility to the disease. Epithelial products such as host defense peptides (HDPs) are the first molecules produced to counteract the infection. Although a wide variety of HDPs are produced by epithelial cells only a few of them have been studied during Mtb infection. Here, we assessed the expression and production of the HDPs psoriasin, secreted phospholipases A2 (sPLA2-IIA) and Ribonuclease (RNase) 7 in airway epithelial cells (NCI-H292), type II pneumocytes (A549 cells) and monocyte-derived macrophages from human peripheral blood mononuclear cells and from the human cell line THP1 after Mtb in vitro infection. Results show that psoriasin and sPLA2-IIA were not induced by Mtb in any of the evaluated cells, while RNase 7 was overexpressed in infected airway epithelial cells. Intracellular analysis by flow cytometry demonstrated that the highest levels of RNase 7 were observed 6 h post-infection and the induction was dependent on direct interaction between airway epithelial cells and Mtb. In addition, analysis by electron microscopy showed that RNase 7 was capable of attaching to the cell wall of intracellular mycobacteria. Our studies suggest that the induction of RNase 7 in response to Mtb could have a role in anti-mycobacterial immunity, which needs to be studied as an innate immune mechanism.

Human Antimicrobial RNases Inhibit Intracellular Bacterial Growth and Induce Autophagy in Mycobacteria-Infected Macrophages

“…The present time-course expression profiles in M. aurum infected THP1 macrophages indicates a downregulation of RNase3 and RNase6 after a short infection period followed by a significant upregulation at longer incubation times. Modulation of antimicrobial RNases following M. aurum infection are in agreement with previously reported results using M. tuberculosis (18, 24). In the literature there are other examples of AMPs downregulated upon mycobacteria infection, a process induced by the Mtb bacilli as a protection mechanism against the host innate armory (12, 30).…”

“…Interestingly, the researchers observed the specific recruitment and induction of eosinophils by lipomannan, a unique mycobacterial cell-wall component. Very recently, Rivas-Santiago and coworkers reported the overexpression of RNase7 in airway epithelial cells infected by M. tuberculosis (24). In our laboratory we have confirmed the antimycobacterial activity of recombinant RNase3 and RNase7 on M. vaccae in vitro and characterized the protein mechanism of action at the bacterial cell-wall (25).…”

“…In particular, human RNase3, RNase6, and RNase7 are highly cationic proteins with reported antimicrobial activity against a variety of microbes (20–23). Interestingly, secretion of RNases 3 and 7 was associated to Mycobacterium bovis ( M. bovis) BCG and M. tuberculosis infection, respectively (14, 24). Indeed, both RNases displayed antimycobacterial activity in vitro (25).…”

The Antimicrobial and Immunomodulatory Function of RNase 7 in Skin

“…In vitro studies showed that RNase 7 is highly antimicrobial effective in low micromolar concentrations against Gram-positive and Gram-negative bacteria like S. aureus, P. aeruginosa, C. amycolatum, E. faecium, Mycobacterium vaccae , the yeast Candida (C.) albicans and Pichia pastoris and the dermatophyte T. rubrum (12, 16, 30, 37–41). The known microorganisms susceptible to RNase 7 are listed in Table 1 (6, 7, 12, 14–16, 25, 29–31, 37–50). The functional relevance of the antimicrobial activity of RNase 7 and its contribution to the antimicrobial capacity of stratum corneum was demonstrated by the use of antibodies that neutralized the antimicrobial activity of RNase 7.…”

“…It has been reported that RNase 7 exhibits antimicrobial activity against Mycobacterium vaccae at low micromolar concentrations (40). Furthermore, infection of airway epithelial cells with Mycobacterium tuberculosis led to induction of RNase 7 expression and an intracellular association of RNase 7 with Mycobacterium tuberculosis (50). This may suggest a direct antimicrobial effect of RNase 7 on Mycobacterium tuberculosis , but this has to be confirmed in further studies.…”