Strain- and host species-specific inflammasome activation, IL-1β release, and cell death in macrophages infected with uropathogenic Escherichia coli

Abstract

Uropathogenic Escherichia coli (UPEC) is the main etiological agent of urinary tract infections (UTIs). Little is known about interactions between UPEC and the inflammasome, a key innate immune pathway. Here we show that UPEC strains CFT073 and UTI89 trigger inflammasome activation and lytic cell death in human macrophages. Several other UPEC strains, including two multidrug-resistant ST131 isolates, did not kill macrophages. In mouse macrophages, UTI89 triggered cell death only at a high multiplicity of infection, and CFT073-mediated inflammasome responses were completely NLRP3-dependent. Surprisingly, CFT073- and UTI89-mediated responses only partially depended on NLRP3 in human macrophages. In these cells, NLRP3 was required for interleukin-1β (IL-1β) maturation, but contributed only marginally to cell death. Similarly, caspase-1 inhibition did not block cell death in human macrophages. In keeping with such differences, the pore-forming toxin α-hemolysin mediated a substantial proportion of CFT073-triggered IL-1β secretion in mouse but not human macrophages. There was also a more substantial α-hemolysin-independent cell death response in human vs. mouse macrophages. Thus, in mouse macrophages, CFT073-triggered inflammasome responses are completely NLRP3-dependent, and largely α-hemolysin-dependent. In contrast, UPEC activates an NLRP3-independent cell death pathway and an α-hemolysin-independent IL-1β secretion pathway in human macrophages. This has important implications for understanding UTI in humans.

Inhibition of P2X Receptors Protects Human Monocytes against Damage by Leukotoxin from Aggregatibacter actinomycetemcomitans and α-Hemolysin from Escherichia coli

“…The conventional view is that ATP causes massive K ϩ loss through the P2X 7 receptor that leads to activation of NOD-like receptor family, pyrin domain containing 3 (NRPD3) inflammasome activation, caspase 1 activation, and subsequent IL-1␤ release (for a review, see references 19 and 20). Interestingly, this pathway is essential for both LtxA-and HlyA-induced caspase 1 activation and IL-1␤ release from macrophages (17,18,74), underscoring the importance of P2X receptors in the cellular effects of the two toxins. Moreover, we found that desensitization of P2X receptors by preincubation with ATP at high concentrations reduced LtxAinduced lysis, whereas HlyA-induced lysis declined marginally at low concentrations.…”

CRIg-expressing peritoneal macrophages are associated with disease severity in patients with cirrhosis and ascites

“…Culture supernatants were collected to assess cell death through the release of the metabolic enzyme, LDH, from dying cells into culture supernatants. LDH release was quantified by measuring LDH in culture supernatants in comparison to total LDH (LDH present in supernatants from untreated cells following cell lysis with 0.1% Triton X-100), as previously described (56).…”

Histone Deacetylase Inhibitors Promote Mitochondrial Reactive Oxygen Species Production and Bacterial Clearance by Human Macrophages

“…On day 6, HMDM were harvested and replated in the presence of CSF-1 for experimentation. THP-1 cells were cultured as previously described (25), differentiated for 48 h with 30 ng/ml phorbol 12-myristate 13-acetate (PMA; Sigma-Aldrich), and rested for 4 h before experimentation. All cells were cultured in an incubator at 37°C with 5% CO 2 .…”

“…In some experiments, supernatants were harvested at the indicated time points to assess cell death through the release of the metabolic enzyme lactate dehydrogenase (LDH) from dying cells into culture supernatants. LDH release was quantified by measuring LDH in culture supernatants compared to total LDH (LDH present in supernatants from untreated cells following cell lysis with 0.1% Triton X-100), as previously described (25).…”