Propolis Flavonoids Ameliorate Chronic Osteomyelitis in a Rat Model by Modulating TAZ-Regulated Treg/Th17 Balance

To investigate the therapeutic mechanism of propolis flavonoids (PF) in chronic osteomyelitis (COM) through transcriptional coactivator with PDZ-binding motif (TAZ)-mediated regulation of regulatory T cell (Treg)/T helper 17 (Th17) cell homeostasis.

Sixty 3-month-old Wistar rats were randomly divided into control, model, and PF-treated groups. In vitro, human peripheral blood mononuclear cells (PBMCs) and rat PBMCs were stratified into five treatment groups: control (10% healthy control (HC) serum), osteomyelitis model (15 ng/mL transforming growth factor-β1 $\mathrm{TGF}-\beta 1$  + 10% HC serum), model+PF $15\mathrm{ng}/\mathrm{mLTGF}-\beta 1+10\mu g/\mathrm{mLPF}$ , TEA domain transcription factor 1 (TEAD1)+model $\mathrm{TGF}-\beta 1+25\mathrm{nMTEAD}1$ , and TEAD1+model+PF. TAZ signaling components (TAZ, RAR-related orphan receptor gamma t (RORγt), Forkhead box P3 (FOXP3)), inflammatory cytokines (interleukin (IL)-17, IL-21, IL-2, IL-10), and T cell subsets (Th17/Treg ratios) were analyzed via Western blot, enzyme-linked immunosorbent assay (ELISA), and flow cytometry. Periosteal cell proliferation was quantified using 5-ethynyl-2'-deoxyuridine (EdU) assay. Bacterial load in bone tissue was quantified using colony-forming unit (CFU) counts.

PF administration significantly upregulated TAZ protein expression compared to untreated osteomyelitis models (p < 0.05). PF treatment significantly reduced bacterial burden in bone tissue (p < 0.001). In the PF group, Th17 cell proportions increased (2.28 ± 0.35%) compared to the osteomyelitis model group (1.58 ± 0.31%) and RORγt expression was elevated, coupled with reduced Treg populations (1.66 ± 0.27%) compared to the osteomyelitis model group (11.5 ± 0.29%) and reduced FOXP3 levels. Notably, pro-inflammatory cytokines IL-17 and IL-21 decreased in PF-treated groups, while anti-inflammatory IL-10 and IL-2 increased. Periosteal cell proliferation rates improved significantly with PF intervention. TEAD1 overexpression attenuated PF-mediated effects in both human and rat PBMCs, confirming TAZ's central regulatory role across species.

Propolis flavonoids ameliorate chronic osteomyelitis through TAZ-dependent mechanisms that rebalance Treg/Th17 polarization and promote bacterial clearance. This involves restoring Th17 cell populations while concurrently suppressing their key effector cytokines, ultimately reducing inflammatory pathology and promoting bone repair.