Intracellular tension in periosteum/perichondrium cells regulates long bone growth

Abstract

Perichondrium/periosteum is involved in regulating long bone growth. Long bones grow faster after removal or circumferential division of periosteum. This can be countered by culturing them in conditioned medium from perichondrium/periosteum cells. Because both complete removal and circumferential division are effective, we hypothesized that perichondrium/periosteum cells require an intact environment to release the appropriate soluble factors. More specifically, we propose that this release depends on their ability to generate intracellular tension. This hypothesis was explored by modulating the ability of perichondrium/periosteum cells to generate intracellular tension and monitoring the effect thereof on long bone growth. Perichondrium/periosteum cells were cultured on substrates with different stiffness. The medium produced by these cultures was added to embryonic chick tibiotarsi from which perichondrium/periosteum was either stripped or left intact. After 3 culture days, long bone growth was proportionally related to the stiffness of the substrate on which perichondrium/periosteum cells were grown while they produced conditioned medium. A second set of experiments demonstrated that the effect occurred through expression of a growth-inhibiting factor, rather than through the reduction of a stimulatory factor. Finally, evidence for the importance of intracellular tension was obtained by showing that the inhibitory effect was abolished when perichondrium/periosteum cells were treated with cytochalasin D, which disrupts the actin microfilaments. Thus, we concluded that modulation of long bone growth occurs through release of soluble inhibitors by perichondrium/periosteum cells, and that the ability of cells to develop intracellular tension through their actin microfilaments is at the base of this mechano-regulated control pathway.

Elucidating Multiscale Periosteal Mechanobiology: A Key to Unlocking the Smart Properties and Regenerative Capacity of the Periosteum?

“…Characterization of the the periosteum's material and mechanical properties will allow for a better understanding of the periosteum's role as the barrier membrane, 38,[51][52][53] PDCs are commonly used for bone and cartilage tissue engineering applications due to their ability to differentiate into tissues of mesodermal origin, specifically bone and cartilage. [16][17][18][19][54][55][56] Current methods for isolating PDCs from periosteum include enzymatic digestion or explant culture. 38 The choice of isolation protocol has not only practical, but also potentially important mechano-chemo-biological consequences; digestion liberates cells from the entire periosteum and exposes cells to collagenase (with unknown downstream effects) and explant culture favors the isolation of motile cells, which are capable of egressing from the cambium layer.…”

“…The intracellular tension PDCs experience is suggested to regulate long bone growth. 17,19 Surgical release of the inherent tension within the periosteum alters the local mechanical environment of PDCs. Periosteal release has been shown to increase proliferation of cambium layer PDCs as early as 1 h after periosteal release as measured by mRNA expression for BMP-2, 19 a growth factor commonly expressed during bone and cartilage development.…”

“…PDCs were cultured on substrates of varying stiffnesses which allowed cells to generate various magnitudes of intracellular tension. 17 The conditioned medium from these cell cultures was added to cultures of intact or periosteum stripped embryonic chick tibiotarsi to evaluate the growth response. The culture medium from cells grown on low-stiffness substrates (3 kPa) resulted in a greater cartilage growth of periosteum stripped bones compared to a medium from stiffer substrates (80 kPa).…”

“…61 Pluripotent cells, 39 including PDCs, 74,75 have been shown to exhibit mechanical sensitivity as well. Mechanical stimulation of PDCs is thought to stimulate paracrine signaling pathways, [17][18][19] leading to the absence of production of soluble factors that stimulate cell proliferation and differentiation. The specific cells stimulated (PDCs deriving from the cambium versus fibrous layer) remain to be elucidated.…”

“…In addition, these biophysical and chemical effects are likely to interact at multiple length scales, that is, tissue-, cell-, and molecular-length scales. While previous studies have addressed specific aspects of the mechanobiological structure and function within the periosteum, for example, cellular changes in the periosteum subjected to mechanical loading, [16][17][18][19] structural changes in developing 20 and in aging periosteum, 21 as well as mechanical properties of periosteum from different species, 22 and anatomic sampling sites, 23 relatively little is known with regard to periosteum's multiscale mechanobiology.…”