Proinflammatory Caspase-2-Mediated Macrophage Cell Death Induced by a Rough Attenuated Brucella suis Strain

Abstract

Brucella spp. are intracellular bacteria that cause an infectious disease called brucellosis in humans and many domestic and wildlife animals. B. suis primarily infects pigs and is pathogenic to humans. The macrophage-Brucella interaction is critical for the establishment of a chronic Brucella infection. Our studies showed that smooth virulent B. suis strain 1330 (S1330) prevented programmed cell death of infected macrophages and rough attenuated B. suis strain VTRS1 (a vaccine candidate) induced strong macrophage cell death. To further investigate the mechanism of VTRS1-induced macrophage cell death, microarrays were used to analyze temporal transcriptional responses of murine macrophage-like J774.A1 cells infected with S1330 or VTRS1. In total 17,685 probe sets were significantly regulated based on the effects of strain, time and their interactions. A miniTUBA dynamic Bayesian network analysis predicted that VTRS1-induced macrophage cell death was mediated by a proinflammatory gene (the tumor necrosis factor alpha [TNF-␣] gene), an NF-B pathway gene (the IB-␣ gene), the caspase-2 gene, and several other genes. VTRS1 induced significantly higher levels of transcription of 40 proinflammatory genes than S1330. A Mann-Whitney U test confirmed the proinflammatory response in VTRS1-infected macrophages. Increased production of TNF-␣ and interleukin 1␤ (IL-1␤) were also detected in the supernatants in VTRS1-infected macrophage cell culture. Hyperphosphorylation of IB-␣ was observed in macrophages infected with VTRS1 but not S1330. The important roles of TNF-␣ and IB-␣ in VTRS1-induced macrophage cell death were further confirmed by individual inhibition studies. VTRS1-induced macrophage cell death was significantly inhibited by a caspase-2 inhibitor but not a caspase-1 inhibitor. The role of caspase-2 in regulating the programmed cell death of VTRS1-infected macrophages was confirmed in another study using caspase-2-knockout mice. In summary, VTRS1 induces a proinflammatory, caspase-2-and NF-B-mediated macrophage cell death. This unique cell death differs from apoptosis, which is not proinflammatory. It is also different from classical pyroptosis, which is caspase-1 mediated.Brucella spp. are facultative, intracellular, Gram-negative bacteria that cause a zoonotic disease called brucellosis in swine, cattle, other animals, and humans. Human brucellosis remains the most common zoonotic disease worldwide, with more than 500,000 new cases reported annually (28). B. suis is the main causative agent of brucellosis in swine and humans (28). Brucella enters and replicates efficiently in a variety of cells, including macrophages, epithelial cells, dendritic cells, and trophoblasts (34). Interaction between Brucella and macrophages is critical for the establishment of a chronic infection. The virulence of Brucella relies on its ability to survive and replicate in the vacuolar compartments of macrophages (18). In contrast, many rough derivatives of B. suis, B. abortus, and B. melitensis, which are deficient in the O antigen (o...

Critical Role of ASC Inflammasomes and Bacterial Type IV Secretion System in Caspase-1 Activation and Host Innate Resistance to Brucella abortus Infection

“…In this study, we demonstrated that caspase-1 activation induced by B. abortus does not lead to pyroptosis. Chen et al (57) demonstrated that rough attenuated Brucella suis induces caspase-2-mediated cell death, but not caspase-1-mediated cell death, in infected macrophages. It is tempting to suggest that Brucella has developed a strategy to avoid pyroptosis, therefore limiting inflammation and allowing continued intracellular replication of the bacteria.…”

Comparative Gene Expression Analysis within Mouse Macrophage for Identifying Critical Pathways in Macrophage and Brucella suis Interaction

“…Rough Brucella organisms induce caspase2-mediated macrophage death (1,4), whereas smooth Brucella organisms inhibit macrophage apoptosis by inhibiting mitochondrial cell death pathway and caspase activation (4,5). These results suggest that inhibition of macrophage death provide a hospitable intracellular niche for Brucella survival, while death induction promote Brucella release and dissemination (6)(7)(8).…”

“…Brucella spp., a Gram-negative and facultative intracellular bacteria, causes a zoonotic disease called brucellosis in humans and many animals including domestic pigs, cattle, wildlife camels, and so on by chronic macrophage infection (1). In 10 species reported (2), Brucella suis is one of 3 pathogenic bacteria (B. melitensis, B. suis and B. abortus) that are the biggest threat to human health and food safety.…”

The PIDDosome, DNA-damage-induced apoptosis and beyond

“…[16][17][18][19][20][21][22] It is currently unknown whether these are true biological triggers for caspase-2 and/or whether PIDD and RAIDD are involved in these processes as well.…”