A continuous model of osteocyte generation in bone matrix
Author: P R Buenzli
Abstract:
Abstract:
The formation of new bone involves both the deposition of bone matrix by cells called osteoblasts,
and the formation of a network of cells embedded within the bone matrix, called osteocytes. Osteocytes derive from
osteoblasts that become buried in bone matrix during bone deposition. There has been a growing interest in osteocytes
in recent years with the realisation that these cells are essential to the detection of micro-damage in bone, and that
they participate in the orchestration of local bone renewal. However, the generation of osteocytes is a complex
process that remains incompletely understood. Whilst osteoblast burial determines the density of osteocytes, the
expanding network of osteocytes regulates in turn osteoblast activity and osteoblast burial through their interconnected
cell processes. In this contribution, a spatiotemporal continuous model is proposed to investigate the osteoblast-to-
osteocyte transition. The model elucidates the interplays between matrix secretory rate, rate of entrapment, and
curvature of the bone substrate in determining the density of osteocytes in the new bone matrix. We find that the
density of osteocytes generated at the moving deposition front depends solely on the ratio of the instantaneous burial
rate and matrix secretory rate. It is remarkably independent of osteoblast density and substrate curvature. This
mathematical result is used with experimental measurements of osteocyte lacuna distributions in a human cortical
bone sample to determine for the first time the rate of burial of osteoblasts in bone matrix. Our results suggest that
in the bone specimen analysed: (i) burial rate decreases during osteonal infilling, and (ii) the control of osteoblast
burial by osteocytes is likely to emanate as a collective signal from a large group of osteocytes, rather than from the
osteocytes closest to the bone deposition front.
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