Variation in hemolysin A expression between uropathogenic Escherichia coli isolates determines NLRP3‐dependent vs . ‐independent macrophage cell death and host colonization

Abstract

Uropathogenic Escherichia coli (UPEC) is the major cause of urinary tract infections (UTIs). The multidrug‐resistant E. coli sequence type 131 (ST131) clone is a serious threat to human health, yet its effects on immune responses are not well understood. Here we screened a panel of ST131 isolates, finding that only strains expressing the toxin hemolysin A (HlyA) killed primary human macrophages and triggered maturation of the inflammasome‐dependent cytokine IL‐1β. Using a representative strain, the requirement for the hlyA gene in these responses was confirmed. We also observed considerable heterogeneity in levels of cell death initiated by different HlyA+ve ST131 isolates, and this correlated with secreted HlyA levels. Investigation into the biological significance of this variation revealed that an ST131 strain producing low levels of HlyA initiated cell death that was partly dependent on the nod‐like receptor family pyrin domain–containing 3 (NLRP3) inflammasome, with this response being associated with a host‐protective role in a mouse UTI model. When the same ST131 strain was engineered to overexpress high HlyA levels, macrophage cell death occurred even when NLRP3 function was abrogated, and bladder colonization was significantly increased. Thus, variation in HlyA expression in UPEC affects mechanisms by which macrophages die, as well as host susceptibility vs. resistance to colonization.—Murthy, A. M. V., Sullivan, M. J., Nhu, N. T. K., Lo, A. W., Phan, M.‐D., Peters, K. M., Boucher, D., Schroder, K., Beatson, S. A., Ulett, G. C., Schembri, M. A., Sweet, M. J. Variation in hemolysin A expression between uropathogenic Escherichia coli isolates determines NLRP3‐dependent vs. ‐independent macrophage cell death and host colonization. FASEB J. 33, 7437–7450 (2019). http://www.fasebj.org

Complex Multilevel Control of Hemolysin Production by Uropathogenic Escherichia coli

“…We previously characterized the clade B strain HVM277 as a low-level hemolysin producer (32). Intriguingly, while this strain possessed an identical 1.616-kb leader sequence and similar hlyC/hlyA transcript levels to the other clade B strains HVM2044 and HVM52, their hemolytic activities differed significantly (Fig.…”

“…UPEC strains that possess either strong or weak hemolytic activity have been described, as well as different effects of hemolysin on host cells at lytic and sublytic doses (27–32). While these observations have been linked to differential expression of hemolysin (32–34), the precise genetic basis for such differences remains to be properly elucidated. Hemolysin expression is regulated by several environmental stimuli, including temperature, oxygen, and osmolarity (35, 36).…”

“…In the context of UTI, the function of hemolysin has been associated with exfoliation of uroepithelial cells in mice (47) and human bladder organoids (48), as well as inhibition of the proinflammatory cytokine interleukin-6 (IL-6) from human bladder epithelial cells (49) and peritoneal macrophages (50). We recently showed that hemolysin activates the NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome and triggers macrophage cell death (30, 32, 51). We also found that variation in hemolysin expression by UPEC can have profound effects on biological outcomes; low-level hemolysin expression triggers NLRP3-mediated macrophage cell death that is associated with host protection in a mouse model of experimental UTI, whereas high-level hemolysin expression triggers NLRP3-independent macrophage cell death and increased bladder colonization (32).…”

“…We recently showed that hemolysin activates the NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome and triggers macrophage cell death (30, 32, 51). We also found that variation in hemolysin expression by UPEC can have profound effects on biological outcomes; low-level hemolysin expression triggers NLRP3-mediated macrophage cell death that is associated with host protection in a mouse model of experimental UTI, whereas high-level hemolysin expression triggers NLRP3-independent macrophage cell death and increased bladder colonization (32).…”

Activation of NLRP3 by uropathogenic Escherichia coli is associated with IL-1β release and regulation of antimicrobial properties in human neutrophils

“…In vivo studies have shown that IL-1β is part of the innate immune response that protects the urinary tract and counteracts UPEC colonization 16 , 27 . On the other hand, studies demonstrating a correlation between increased levels of IL-1β and bacterial loads in the mouse bladder 58 , and that IL-1β deficient mice are protected from UTI 20 rather suggest that IL-1β favors bacterial colonization. Thus, the role of IL-1β in the pathogenesis of UTI is presently unclear.…”