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Hypothesis: Coupling between Resorption and Formation in Cancellous bone Remodeling is a Mechanically Controlled Event.

Erben RG - Front Endocrinol (Lausanne) (2015)

Bottom Line: Although a number of different explanatory models have been developed, the mechanisms that couple bone resorption and formation in bone remodeling are still a matter of controversy.Subsequent bone formation is initiated by strain-sensitive osteocytes in the underlying bone matrix.In this biomechanical strain-driven model, osteoblasts do not need to "know" how much bone was previously resorbed in a given site.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physiology, Pathophysiology and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine Vienna , Vienna , Austria.

ABSTRACT
Coupling is the process that links bone resorption to formation in a temporally and spatially coordinated manner within the remodeling cycle. In order to maintain skeletal integrity, it is of crucial importance that the amount of bone resorbed matches the amount of newly formed bone in each remodeling site. Although a number of different explanatory models have been developed, the mechanisms that couple bone resorption and formation in bone remodeling are still a matter of controversy. Here, I propose a model in which coupling is achieved by biomechanical strain sensed by osteocytes within the newly built bone package. In this model, the resorption cavity created by osteoclasts results in mechanical weakening of the structural element, and, thus, in increased strain under constant loading conditions. Subsequent bone formation is initiated by strain-sensitive osteocytes in the underlying bone matrix. After osteoblastic bone formation has started, the newly built osteocyte-osteoblast network detects strain. Once the mechanical strain within the newly built bone structural unit falls below a certain threshold, bone formation stops. In this biomechanical strain-driven model, osteoblasts do not need to "know" how much bone was previously resorbed in a given site. In addition, this model does not require the transfer of any information from bone-resorbing osteoclasts to bone-forming osteoblasts, because biomechanical strain "guides" osteoblasts through their job of re-filling the resorption cavity.

No MeSH data available.


Related in: MedlinePlus

Unloading reduces bone formation and wall width in the presence of unchanged osteoclast numbers. Mineral apposition rate, bone formation rate (BFR/B.Pm), wall width of completed remodeling units, and osteoclast numbers measured by histomorphometry in the cancellous bone of the proximal tibial metaphysis in 4-month-old non-immobilized control rats and immobilized female Sprague-Dawley rats after 4 weeks of partial unloading by a bandaging technique (Erben et al., unpublished data). Data represent mean ± SEM of 12 animals each. *p < 0.05 byt-test.
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Figure 2: Unloading reduces bone formation and wall width in the presence of unchanged osteoclast numbers. Mineral apposition rate, bone formation rate (BFR/B.Pm), wall width of completed remodeling units, and osteoclast numbers measured by histomorphometry in the cancellous bone of the proximal tibial metaphysis in 4-month-old non-immobilized control rats and immobilized female Sprague-Dawley rats after 4 weeks of partial unloading by a bandaging technique (Erben et al., unpublished data). Data represent mean ± SEM of 12 animals each. *p < 0.05 byt-test.

Mentions: Is there any evidence for the validity of this model? In fact, there is. In a scanning electron microscopic study in lumbar vertebrae of normal subjects of different ages, Mosekilde (13) observed that resorption cavities were not filled with new bone on trabecule which lost 3D connection, i.e., unloaded trabecule. Moreover, partial unloading decreased mineral apposition rate, bone formation rate, and wall thickness in the presence of unchanged osteoclast numbers in a rat hindlimb immobilization model (Figure 2). All these experimental findings are predicted by the proposed model.


Hypothesis: Coupling between Resorption and Formation in Cancellous bone Remodeling is a Mechanically Controlled Event.

Erben RG - Front Endocrinol (Lausanne) (2015)

Unloading reduces bone formation and wall width in the presence of unchanged osteoclast numbers. Mineral apposition rate, bone formation rate (BFR/B.Pm), wall width of completed remodeling units, and osteoclast numbers measured by histomorphometry in the cancellous bone of the proximal tibial metaphysis in 4-month-old non-immobilized control rats and immobilized female Sprague-Dawley rats after 4 weeks of partial unloading by a bandaging technique (Erben et al., unpublished data). Data represent mean ± SEM of 12 animals each. *p < 0.05 byt-test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4440405&req=5

Figure 2: Unloading reduces bone formation and wall width in the presence of unchanged osteoclast numbers. Mineral apposition rate, bone formation rate (BFR/B.Pm), wall width of completed remodeling units, and osteoclast numbers measured by histomorphometry in the cancellous bone of the proximal tibial metaphysis in 4-month-old non-immobilized control rats and immobilized female Sprague-Dawley rats after 4 weeks of partial unloading by a bandaging technique (Erben et al., unpublished data). Data represent mean ± SEM of 12 animals each. *p < 0.05 byt-test.
Mentions: Is there any evidence for the validity of this model? In fact, there is. In a scanning electron microscopic study in lumbar vertebrae of normal subjects of different ages, Mosekilde (13) observed that resorption cavities were not filled with new bone on trabecule which lost 3D connection, i.e., unloaded trabecule. Moreover, partial unloading decreased mineral apposition rate, bone formation rate, and wall thickness in the presence of unchanged osteoclast numbers in a rat hindlimb immobilization model (Figure 2). All these experimental findings are predicted by the proposed model.

Bottom Line: Although a number of different explanatory models have been developed, the mechanisms that couple bone resorption and formation in bone remodeling are still a matter of controversy.Subsequent bone formation is initiated by strain-sensitive osteocytes in the underlying bone matrix.In this biomechanical strain-driven model, osteoblasts do not need to "know" how much bone was previously resorbed in a given site.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physiology, Pathophysiology and Biophysics, Department of Biomedical Sciences, University of Veterinary Medicine Vienna , Vienna , Austria.

ABSTRACT
Coupling is the process that links bone resorption to formation in a temporally and spatially coordinated manner within the remodeling cycle. In order to maintain skeletal integrity, it is of crucial importance that the amount of bone resorbed matches the amount of newly formed bone in each remodeling site. Although a number of different explanatory models have been developed, the mechanisms that couple bone resorption and formation in bone remodeling are still a matter of controversy. Here, I propose a model in which coupling is achieved by biomechanical strain sensed by osteocytes within the newly built bone package. In this model, the resorption cavity created by osteoclasts results in mechanical weakening of the structural element, and, thus, in increased strain under constant loading conditions. Subsequent bone formation is initiated by strain-sensitive osteocytes in the underlying bone matrix. After osteoblastic bone formation has started, the newly built osteocyte-osteoblast network detects strain. Once the mechanical strain within the newly built bone structural unit falls below a certain threshold, bone formation stops. In this biomechanical strain-driven model, osteoblasts do not need to "know" how much bone was previously resorbed in a given site. In addition, this model does not require the transfer of any information from bone-resorbing osteoclasts to bone-forming osteoblasts, because biomechanical strain "guides" osteoblasts through their job of re-filling the resorption cavity.

No MeSH data available.


Related in: MedlinePlus