Fang He

Pasteurella multocida (P. multocida) causes a broad spectrum of zoonotic diseases through various virulence factors, imposing substantial economic burdens on global livestock industry. The hvfB is a component of the hvf operon encoding multinuclear non-heme iron oxidases (MNIO). However, the precise mechanistic by which hvfB regulates virulence of P. multocida remains largely unknown. In this study, an hvfB deletion strain was generated using homologous recombination. The resulting mutant was characterized in terms of growth, pathogenicity, transcriptional profiles, immune and inflammatory responses. The results showed that hvfB promotes bacterial growth, modulates capsule synthesis, enhances stress resistance in the PmCQ2 strain, and facilitates resistance to macrophage phagocytosis. Consequently, loss of hvfB markedly attenuated P. multocida pathogenicity, as evidenced by reduced bacterial loads in tissues and decreased levels of inflammatory factors. Transcriptomic analysis further revealed that hvfB influences stress resistance and virulence by affecting pathways associated with carbon metabolism, capsule synthesis, biofilm formation, and adhesion. Notably, the hvfB deletion strain conferred robust cross-protective immunity against P. multocida serotypes A and B. Collectively, these findings elucidate the pathogenic role of hvfB in P. multocida and support the potential of the hvfB deletion strain as an attenuated vaccine candidate against serotypes A and B.

P. multocida is notorious for inducing excessive inflammation with high lethality in multiple animals, such as cattle, pigs, and chickens. Our previous study revealed that L-serine was decreased in the lungs of mice infected with P. multocida capsular type A strain CQ2 (PmCQ2), and 2 mg/kg of L-serine could alleviate PmCQ2-induced lung inflammation in vivo, which may largely depend on macrophages. However, the underlying intrinsic alterations remain unknown. Here, we demonstrated that 10 mM of L-serine significantly inhibited the release of inflammatory cytokines (e.g., IL-1β and TNF-α) by blocking inflammasome activation (including NALP1, NLRP3, NLRC4, AIM2, and Caspase-1) in PmCQ2-infected macrophages. Furthermore, the results of RNA-seq and metabonomics revealed that exogenous L-serine supplementation substantially reprogrammed macrophage transcription and metabolism. Mechanically, L-serine reduced inflammatory responses via the inhibition of glycolysis in macrophages based on a seahorse assay. Together, these findings characterize the intrinsic molecular alterations in activated macrophages and provide new targets for modulating P. multocida infection-induced macrophage inflammation.

Pasteurella multocida is an opportunistic zoonotic pathogen that primarily causes fatal respiratory diseases, such as pneumonia and respiratory syndromes. However, the precise mechanistic understanding of how P. multocida disrupts the epithelial barrier in mammalian lung remains largely unknown. In this study, using unbiased RNA-seq analysis, we found that the evolutionarily conserved Hippo-Yap pathway was dysregulated after P. multocida infection. Given the complexity of P. multocida infection associated with lung injury and systemic inflammatory processes, we employed a combination of cell culture models, mouse models, and rabbit models to investigate the dynamics of the Hippo-Yap pathway during P. multocida infection. Our findings reveal that P. multocida infection activates the Hippo-Yap pathway both in vitro and in vivo, by upregulating the upstream factors p-Mst1/2, p-Lats1, and p-Yap, and downregulating the downstream effectors Birc5, Cyr61, and Slug. Conversely, pharmacological inhibition of the Hippo pathway by XMU-MP-1 significantly rescued pulmonary epithelial cell apoptosis in vitro and reduced lung injury, systemic inflammation, and mouse mortality in vivo. Mechanistic studies revealed that P. multocida induced up-regulation of Rassf1 expression, and Rassf1 enhanced Hippo-Yap pathway through phosphorylation. Accordingly, in vitro knockdown of Rassf1 significantly enhanced Yap activity and expression of Yap downstream factors and reduced apoptosis during P. multocida infection. P. multocida-infected rabbit samples also showed overexpression of Rassf1, p-Lats1, and p-Yap, suggesting that P. multocida activates the Rassf1-Hippo-Yap pathway. These results elucidate the pathogenic role of the Rassf1-Hippo-Yap pathway in P. multocida infection and suggest that this pathway has the potential to be a drug target for the treatment of pasteurellosis.

Bovine Pasteurella multocida (P. multocida) serotype A is one of the major causes of bovine respiratory disease (BRD). We used data-independent acquisition (DIA) LC-MS/MS combined with bioinformatics analysis to identify proteins secreted by P. multocida. A total of 154 proteins were obtained from the supernatants of two isolates of bovine P. multocida serotype A (high virulent PmCQ2 and low virulent PmCQ6) cultured in Martin or BHI media, of which 50 were identified as putative secreted proteins. Further studies showed that Tuf, an elongation factor Tu, was highly expressed in P. multocida and secreted into infected tissues. Tuf stimulated strong innate immune responses of macrophages and had protective efficacy against P. multocida infection in a mouse model. The results provide insight into the secreted proteins of P. multocida and suggest new targets for vaccine development against P. multocida.

GAT2 links metabolism to DNA methylation to orchestrate macrophage-dependent inflammation.

Innate immunity forms a protective line of defense in the early stages of pulmonary infection. The primary cellular players of the innate immunity against respiratory infections are alveolar macrophages (AMs), dendritic cells (DCs), neutrophils, natural killer (NK) cells, and innate lymphoid cells (ILCs). They recognize conserved structures of microorganisms through membrane‐bound and intracellular receptors to initiate appropriate responses. In this review, we focus on the prominent roles of innate immune cells and summarize transmembrane and cytosolic pattern recognition receptor (PRR) signaling recognition mechanisms during pulmonary microbial infections. Understanding the mechanisms of PRR signal recognition during pulmonary pathogen infections will help us to understand pulmonary immunopathology and lay a foundation for the development of effective therapies to treat and/or prevent pulmonary infections.

Pasteurella multocidacauses a variety of infectious diseases in various species of mammals and birds, resulting in enormous economic loss to the modern livestock and poultry industry. However, the mechanism of host-pathogen interaction is unclear. Here, we found thatl-serine levels were significantly decreased in murine lungs infected withP. multocida.

Betaine is known as trimethylglycine and is widely distributed in animals, plants, and microorganisms. Betaine is known to function physiologically as an important osmoprotectant and methyl group donor. Accumulating evidence has shown that betaine has anti-inflammatory functions in numerous diseases. Mechanistically, betaine ameliorates sulfur amino acid metabolism against oxidative stress, inhibits nuclear factor-κB activity and NLRP3 inflammasome activation, regulates energy metabolism, and mitigates endoplasmic reticulum stress and apoptosis. Consequently, betaine has beneficial actions in several human diseases, such as obesity, diabetes, cancer, and Alzheimer’s disease.