Human parvovirus B19 VP1u‑induced osteoclastogenesis is enhanced by RANKL in RAW264.7 macrophage cells

Human parvovirus B19 (B19V) DNA and antigens are frequently detected in synovial tissue; however, the mechanisms linking B19V infection to bone destruction remain unclear. The present study investigated the B19V VP1 unique region (VP1u) and its influence on osteoclast differentiation. RAW264.7 macrophages were cultured with or without receptor activator of NF‑κB ligand (RANKL) and B19V‑VP1u for up to 7 days. Tartrate‑resistant acid phosphatase staining, bone resorption assays and western blotting were used to assess osteoclastogenesis. The involvement of signaling pathways was investigated using an anti‑TNF‑α antibody, and inhibitors of MAPK, ERK, JNK and NF‑κB signaling. B19V‑VP1u alone induced osteoclastogenesis in a dose‑ and time‑dependent manner and, in the presence of RANKL, further increased osteoclast size and number. B19V‑VP1u significantly increased pit resorption, and nuclear factor of activated T cells (NFAT)2 (also known as NFATc1), cathepsin K, c‑FOS, MMP9 and dendritic cell‑specific transmembrane protein expression. The inhibition of ERK, JNK, NF‑κB or TNF‑α did not alter the effects of VP1u, whereas blockade of p38 MAPK nearly abolished VP1u‑induced osteoclastogenesis. These findings indicate that B19V‑VP1u acts as a strong osteoclastogenic factor through a p38‑dependent but TNF‑α‑independent pathway in vitro. The present study supports a dual mechanism of B19V‑induced bone pathology, whereby VP1u directly promotes osteoclastogenesis, whereas inflammation mediates bone resorption via cytokine signaling. Targeting viral protein‑host signaling interactions may offer novel therapeutic approaches for B19V‑associated bone erosion.