Proinflammatory Microenvironment During Kingella kingae Infection Modulates Osteoclastogenesis

Abstract

Kingella kingae is an emerging pathogen that causes septic arthritis, osteomyelitis, and bacteremia in children from 6 to 48 months of age. The presence of bacteria within or near the bone is associated with an inflammatory process that results in osteolysis, but the underlying pathogenic mechanisms involved are largely unknown. To determine the link between K. kingae and bone loss, we have assessed whether infection per se or through the genesis of a pro-inflammatory microenvironment can promote osteoclastogenesis. For that purpose, we examined both the direct effect of K. kingae and the immune-mediated mechanism involved in K. kingae-infected macrophage-induced osteoclastogenesis. Our results indicate that osteoclastogenesis is stimulated by K. kingae infection directly and indirectly by fueling a potent pro-inflammatory response that drives macrophages to undergo functional osteoclasts via TNF-α and IL-1β induction. Such osteoclastogenic capability of K. kingae is counteracted by their outer membrane vesicles (OMV) in a concentration-dependent manner. In conclusion, this model allowed elucidating the interplay between the K. kingae and their OMV to modulate osteoclastogenesis from exposed macrophages, thus contributing to the modulation in joint and bone damage.

Roles of bacterial extracellular vesicles in systemic diseases

“…Intriguingly, BEVs counteracted bacteria-mediated osteoclastogenic pathways. For example, K. kingae OMVs decreased osteoclastogenesis in a dose-dependent manner and inhibited proinflammatory cytokine production by infected macrophages ( Pesce Viglietti et al, 2021 ). Therefore, BEVs exhibit advantages in bone health, and these studies offer a mechanistic basis for BEV-mediated osteoprotective functions.…”

Fibulin2: a negative regulator of BMSC osteogenic differentiation in infected bone fracture healing

“…Infection disrupts this reciprocal balance, enhancing bone resorption and slowing bone formation, but the underlying mechanisms are unclear 15 . For instance, James et al demonstrated that infection triggered osteoblast death, and Ayelén et al showed that infection modulated osteoclastogenesis; both of these outcomes are detrimental to bone healing 11,16 .…”

Pathogenic determinants of Kingella kingae disease

“…The rtxA gene is absent in other Kingella species except K. negevensis ( 26 – 30 ). RtxA is cytotoxic against a broad range of eukaryotic cells in vitro , including red blood cells, epithelial cells (HeLa, A549, FaDu, HLac-78), endothelial cells, synovial cells (SW-982, Hig-82), osteoblasts (U-2), and monocytes (THP-1, RAW264.7) ( 18 , 24 , 31 – 33 ). Mutants that lack RtxA are non-hemolytic and non-cytotoxic in vitro and are avirulent in an infant rat model of invasive disease, underscoring the role of this toxin as a major contributor to K. kingae virulence ( 10 , 33 ).…”

“…Beyond secretion via the TISS, RtxA is released from the organism in outer membrane vesicles (OMV). OMV production is highly variable among clinical isolates ( 31 , 32 ). Along with RtxA, K. kingae OMVs contain a host of other proteins in the outer membrane.…”

“…OMVs are rapidly phagocytosed by eukaryotic cells and are cytotoxic against red blood cells and monocytes but not epithelial cells ( 32 ). Exposure to OMVs results in increased production of granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-α (TNF-α) from SW982 (synovial) cells and hFOB 1.19 (osteoblast) cells in vitro ( 31 , 32 ). Currently, it is unclear if stimulation of these inflammatory molecules is due to RtxA or to other factors found in OMVs, such as lipopolysaccharide (LPS).…”