There is a general lack of a detailed understanding of the mechanistic pathway, cellular events and expression of markers at different phases of bone healing.

The purpose of a recent study published in the Journal of Orthopaedic Translation was to describe the role of osteocytes in fracture healing from the early to late phase.

This systematic review entailed a literature search from PubMed and Embase, wherefrom 23 articles were included. Most studies investigated changes of various genes and proteins expression patterns related to osteocytes. Several studies also described a constant expression of osteocyte-specific marker genes throughout the fracture healing cascade, followed by a decline phase with the progress of healing—denoting the important physiological role of osteocytes and the osteocyte lacuno-canalicular network in fracture healing.

The findings revealed that:

• Osteocytes could trigger coordinated bone healing responses from cell death and expression of proinflammatory markers cyclooxygenase-2 and interleukin-6, at an early phase of fracture integration.
• This is followed by the expression of growth factors bone morphogenetic protein-2 and cysteine-rich angiogenic inducer 61—that matched with the neo-angiogenesis, chondrogenesis and callus formation during the intermediate phase.
• Tightly controlled regulation of osteocyte-specific markers—E11/Podoplanin (E11), dentin matrix protein 1 and sclerostin—modulate and promote osteogenesis, mineralization and remodeling across different phases of fracture healing.
• Stabilized fixation is associated with a higher number of osteocytes with little detectable bone morphogenetic proteins expressions in osteocytes.
• While sclerostin-antibody treatment can confer improvements in the bone mass, bone strength and mineralization.

Thus, the results further illustrated the function of osteocytes. The findings provided an up-to-date chronological overview and highlighted the osteocyte-regulated events at gene, protein, cellular and tissue levels throughout the fracture healing cascade.

Source: Journal of Orthopaedic Translation. 2019 Aug 8;21:111-121. doi: 10.1016/j.jot.2019.07.005.