engleski

Increased expression of PTX3 in non-hematopoietic periosteal cells during fracture healing

Pentraxin 3 (PTX3) is a highly conserved member of the long pentraxins subfamily produced in response to proinflammatory stimuli. Its biological roles have been associated to infection, female fertility and angiogenesis. We aimed to elucidate the role of PTX3 in the process of fracture healing. WT mice and mice deficient for the PTX3 gene (PTX3-KO) were used, after obtaining the approval from the Ethical committee. Cells from bone marrow and endosteal/periosteal compartments were cultured to stimulate differentiation into osteoblast or osteoclast lineage. Same populations were analyzed by flow-cytometry to assess the proportion of putative osteoclast and osteoblast progenitor cells. Bone metabolism in vivo was determined by histomorphometry and micro- computerized tomography (μCT). The method of Bonnarens and Einhorn was modified to produce standardized closed tibial fracture. Bones were analyzed at early (2 and 6 days) and late stage (3 weeks) of fracture healing. PTX3-KO mice had lower bone mass (BV/TV 2.72±1.23 for females and 5.39±1.73 for males) than their WT littermates (BV/TV 5.03±0.87 for females and 7.04±0.87 for males, P<0.05). Although, we found increased PTX3 expression with the maturation of osteoblast and osteoclast in vitro, no differences were observed in the osteoblastogenic and osteoclastogenic ex vivo potential between WT and PTX3-KO mice. Nevertheless, we found lower bone formation rate in PTX3-KO mice. Non-hematopoietic periosteal cells highly up-regulate PTX3 expression during initial phase of fracture healing. Moreover, PTX3- KO mice formed significantly less mineralized callus following bone fracture (BV/TV 15.33±2.32 vs 19.66±4.32, P<0.05). Our results confirmed that PTX3 has a positive impact on bone mass. Particularly, we showed that bone regeneration requires PTX3 for the induction of periosteal reaction, supporting previous studies that indicate important role of various inflammatory molecules in the initial phase of fracture repair.

pentraxin; osteoblasts; frature repair

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