Ho Kim

Ho Kim. Microbiol. Biotechnol. Lett. 2023;51:243-9. https://doi.org/10.48022/mbl.2305.05008

Ho Kim. Microbiol. Biotechnol. Lett. 2022;50:157-63. https://doi.org/10.48022/mbl.2108.08004

Clostridium difficile toxin A is known to cause colonic epithelial cell apoptosis, which is considered the main causative event that triggers inflammatory responses in the colon, reflecting the concept that the essential role of epithelial cells in the colon is to form a physical barrier in the gut. We previously showed that toxin A-induced colonocyte apoptosis and subsequent inflammation were dependent on prostaglandin E2 (PGE(2)) produced in response to toxin A stimulation. However, the molecular mechanism by which PGE(2) mediates cell apoptosis in toxin A-exposed colonocytes has remained unclear. Here, we sought to identify the signaling pathway involved in toxin A-induced, PGE(2)-mediated colonocyte apoptosis. In non-transformed NCM460 human colonocytes, toxin A exposure strongly upregulated expression of Bak, which is known to form mitochondrial outer membrane pores, resulting in apoptosis. RT-PCR analyses revealed that this increase in Bak expression was attributable to toxin A-induced transcriptional upregulation. We also found that toxin A upregulation of Bak expression was dependent on PGE(2) production, and further showed that this effect was recapitulated by an Prostaglandin E2(PGE(2)) receptor-1 receptor agonist, but not by agonists of other EP receptors. Collectively, these results suggest that toxin A-induced cell apoptosis involves PGE(2)-upregulation of Bak through the EP1 receptor.

Many reports have shown that crude extracts of the American cockroach have therapeutic effects on inflammation. In a previous study, our research group showed that an antimicrobial peptide (Periplanetasin‐2) derived from the American cockroach via de novo transcriptome analysis inhibited apoptosis of human colonocytes and inflammatory responses of the mouse gut caused by Clostridium difficile toxin A. Here, we examined whether Periplanetasin‐4 (Peri‐4), another antimicrobial peptide identified via de novo transcriptome analysis of the American cockroach, could also inhibit the various toxicities induced by C. difficile toxin A. We found that Peri‐4 significantly reduced the cell viability loss and cell apoptosis caused by toxin A in vitro. Peri‐4 also ameliorated the severe inflammatory responses seen in the toxin A‐induced mouse enteritis model, rescuing the villus disruption and interleukin‐6 production induced by luminal injection of toxin A into the mouse gut. Mechanistically, we found that Peri‐4 could reduce toxin A‐induced reactive oxygen species production to inhibit the activations of p38MAPK and p21^Cip1/Waf1, which are critical for the cell damages induced by toxin A. These results collectively suggest that the Peri‐4 may be a potential therapeutic agent for treating toxin A‐induced pseudomembranous colitis. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

NADH:quinone oxidoreductase 1 (NQO1) is known to be involved in the regulation of energy synthesis and metabolism, and the functional studies of NQO1 have largely focused on metabolic disorders. Here, we show for the first time that compared to NQO1-WT mice, NQO1-KO mice exhibited a marked increase of permeability and spontaneous inflammation in the gut. In the DSS-induced colitis model, NQO1-KO mice showed more severe inflammatory responses than NQO1-WT mice. Interestingly, the transcript levels of claudin and occludin, the major tight junction molecules of gut epithelial cells, were significantly decreased in NQO1-KO mice. The colons of NQO1-KO mice also showed high levels of reactive oxygen species (ROS) and histone deacetylase (HDAC) activity, which are known to affect transcriptional regulation. Taken together, these novel findings indicate that NQO1 contributes to the barrier function of gut epithelial cells by regulating the transcription of tight junction molecules.

We recently demonstrated that the insect peptide CopA3 (LLCIALRKK), a disulfide-linked dimeric peptide, exerts antimicrobial and anti-inflammatory activities in a mouse colitis model. Here, we examined whether CopA3 inhibited activation of macrophages by LPS. Exposure of an unseparated mouse peritoneal cell population or isolated peritoneal macrophages to LPS markedly increased secretion of IL-6 and TNF-α; these effects were significantly inhibited by CopA3 treatment. The inhibitory effect of CopA3 was also evident in murine macrophage cell line, RAW 264.7. Western blotting revealed that LPS-induced activation of STAT1 and STAT5 in macrophages was significantly inhibited by CopA3. Inhibition of JAK (STAT1/STAT5 kinase) with AG490 markedly reduced the production of IL-6 and TNF-α in macrophages. Collectively, these observations suggest that CopA3 inhibits macrophage activation by inhibiting activating phosphorylations of the transcription factors, STAT1 and STAT5, and blocking subsequent production of IL-6 and TNF-α and indicate that CopA3 may be useful as an immune-modulating agent. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.