Loss of Vhl alters trabecular bone loss during S. aureus osteomyelitis in a cell-specific manner

Abstract

Osteomyelitis, or bone infection, is a major complication of accidental trauma or surgical procedures involving the musculoskeletal system. Staphylococcus aureus is the most frequently isolated pathogen in osteomyelitis and triggers significant bone loss. Hypoxia-inducible factor (HIF) signaling has been implicated in antibacterial immune responses as well as bone development and repair. In this study, the impact of bone cell HIF signaling on antibacterial responses and pathologic changes in bone architecture was explored using genetic models with knockout of either Hif1a or a negative regulator of HIF-1α, Vhl. Deletion of Hif1a in osteoblast-lineage cells via Osx-Cre (Hif1aΔOB) had no impact on bacterial clearance or pathologic changes in bone architecture in a model of post-traumatic osteomyelitis. Knockout of Vhl in osteoblast-lineage cells via Osx-Cre (VhlΔOB) caused expected increases in trabecular bone volume per total volume (BV/TV) at baseline and, intriguingly, did not exhibit an infection-mediated decline in trabecular BV/TV, unlike control mice. Despite this phenotype, bacterial burdens were not affected by loss of Vhl. In vitro studies demonstrated that transcriptional regulation of the osteoclastogenic cytokine receptor activator of NF-κB ligand (RANKL) and its inhibitor osteoprotegerin (OPG) is altered in osteoblast-lineage cells with knockout of Vhl. After observing no impact on bacterial clearance with osteoblast-lineage conditional knockouts, a LysM-Cre model was used to generate Hif1aΔMyeloid and VhlΔMyeloid mouse models to explore the impact of myeloid cell HIF signaling. In both Hif1aΔMyeloid and VhlΔMyeloid models, bacterial clearance was not impacted. Moreover, minimal impacts on bone architecture were observed. Thus, skeletal HIF signaling was not found to impact bacterial clearance in our mouse model of post-traumatic osteomyelitis, but Vhl deletion in the osteoblast lineage was found to limit infection-mediated trabecular bone loss, possibly via altered regulation of RANKL-OPG gene transcription.

SPA inhibits hBMSC osteogenic differentiation and M1 macrophage polarization by suppressing SETD2 in acute suppurative osteomyelitis

“…HIF-1α is known to regulate glycolysis in various diseases, including osteomyelitis 25 . Likewise, our findings demonstrated the activation of HIF-1α in TPH-1 cells upon stimulation with SPA.…”

Choosing the right animal model for osteomyelitis research: Considerations and challenges

“…The defect was observed for 2 weeks before complete debridement and antibiotic therapy, followed by monitoring for another 1 or 2 weeks. Another osteomyelitis model, following femoral defect, utilized 6-8 week-old C57BL/6 mice [ 70 , 71 , 72 ]. 10 6 CFU of S. aureus , an erythromycin-sensitive derivative of the USA300 strain LAC, in 2 μL PBS was delivered to a 1 mm-diameter unicortical bone defect at midshaft of femur, and the infection was allowed to proceed for 2 weeks.…”

“…Although Gram-negative bacterial osteomyelitis is less prevalent, a P. aeruginosa osteomyelitis model was induced in C57BL/6 mice radius [ 22 ], in which contamination of P. aeruginosa PsAer-9 was induced to the radius segmental bone defect with bacteria-encapsulating gels containing 3.0 × 10 4 CFU. Despite the surgical difficulty due to small size, mice allow genetic modification [ 72 ], relevant biomarker and in-depth research into immune-responses [ 73 ] toward osteomyelitis.…”