TLR4 inactivation in myeloid cells accelerates bone healing of a calvarial defect model in mice

Dan Wang, James R. Gilbert, Gwen M. Taylor, Chhinder Sodhi, David Hackam, Joseph E. Losee, Timothy R. Billiar, Gregory M. Cooper

Research output: Contribution to journalArticle

Abstract

Background: Toll-like receptor 4 (TLR4) has been implicated in inflammation-induced bone destruction in various chronic bone diseases; however, its direct influence on bone healing is not well understood. The authors' previous study showed accelerated bone healing with higher osteoclastogenesis gene expression in toll-like receptor 4 knockout mice (TLR4-/-). This study aimed to further elucidate the underlying cellular mechanisms during fracture healing by generating a myeloid cell-specific toll-like receptor 4 knockout model (Lyz-TLR4-/- mice). Methods: Calvarial defects, 1.8 mm in diameter, were created in wild-type, TLR4-/-, and Lyz-TLR4-/- mice. Bone healing was investigated using micro-computed tomography and histologic, histomorphometric, and immunohistochemistry analyses. Primary bone marrow-derived cells were also isolated from wild-type, TLR4-/-, and Lyz-TLR4-/- mice to measure their osteoclast differentiation and resorption properties. Results: A similar faster bone healing response, with active intramembranous bone formation, intense osteopontin staining, and more osteoblast infiltration, was observed in TLR4-/- and Lyz-TLR4-/- mice. Tartrate-resistant acid phosphatase staining showed more osteoclast infiltration in Lyz-TLR4-/- mice than in wild-type mice at day 7. Primary bone marrow-derived cells isolated from TLR4-/- and Lyz-TLR4-/- mice presented enhanced osteoclastogenesis and resorption activity compared with those from wild-type mice. Comparable M0, M1, and M2 macrophage infiltration was found among all groups at days 1, 4, and 7. Conclusions: This study revealed that inactivation of toll-like receptor 4 in myeloid cells enhanced osteoclastogenesis and accelerated healing response during skull repair. Together with the role of toll-like receptor 4 in inflammation-mediated bone destruction, it suggests that toll-like receptor 4 might regulate inflammation-induced osteoclastogenesis under different clinical settings.

Original languageEnglish (US)
Pages (from-to)296e-306e
JournalPlastic and Reconstructive Surgery
Volume140
Issue number2
DOIs
StatePublished - Aug 1 2017

ASJC Scopus subject areas

  • Surgery

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