The Effect of Age on Bone and Its Response to Mechanical Stimulation

Bone is a specialized connective tissue system which is able to regulate its own bone mass and architecture to meet the daily demands of its external environment. Mechanical loading directly or indirectly influences the activity of cell populations to deposit, maintain, or remove bone tissue as appropriate, which is integral to skeletal adaptation to load. With advancing age there are alterations in bone structure and mineralization which are often associated with an increase in osteoporotic fracture risk. The transduction of mechanical cues affects bone structure and mineralization and could be altered with advancing age. Current in vivo and in vitro data suggest age may affect the capacity of bone cells to respond to mechanical stimulation; however the effect of age on this response to mechanical stimulation in the regenerative skeleton and on osteocytes, which are thought to be the primary mechanical sensors, is unknown.

It was hypothesized that the influence of mechanical factors on the maintenance or repair of bone is influenced by age. In this study regenerative specimens primarily composed of osteocytes were produced in young and old animals. Their response to mechanical loading via nitric oxide (NO), prostaglandin E2 (PGE2), connexin 43 (Cx43), MAP Kinase, and c-fos signaling was assessed via ELISA and western blot and compared to the response of age matched mature bone. Regenerative specimens from young animals had a higher net increase in NO, PGE2, Cx43 and c-fos after mechanical stimulation than regenerative specimens from old animals. The mechanical stimulation of regenerative tissue resulted in a higher net increase of mechanical response molecules than mature bone in both age groups. This was observed at an earlier time point of regeneration in specimens produced in young animals which could initiate earlier remodeling and thus maintaof regenerative tissue resulted in a higher net increase of mechanical response molecules than mature bone in both age groups. This was observed at an earlier time point of regeneration in specimens produced in young animals which could initiate earlier remodeling and thus maintain a mean tissue age that is fairly constant and less susceptible to brittle fracture. Progenitor cells from old animals exhibited delayed mineralization and a decrease response to mechanical stimulation throughout differentiation. The data from this study suggests primary cells from old donors with appropriate differentiation time and mechanical stimulus may promote bone formation, which could make them useful for tissue engineering applications. In addition, key differences in mechanical response were highlighted which have the potential for further investigation to develop therapeutics for bone loss in aging populations. in a mean tissue age that is fairly constant and less susceptible to brittle fracture.

Progenitor cells from old animals exhibited delayed mineralization and a decrease response to mechanical stimulation throughout differentiation. The data from this study suggests primary cells from old donors with appropriate differentiation time and mechanical stimulus may promote bone formation, which could make them useful for tissue engineering applications. In addition, key differences in mechanical response were highlighted which have the potential for further investigation to develop therapeutics for bone loss in aging populations.

Year	Entry
1983	Bonar LC, Roufosse AH, Sabine WK, Grynpas MD, Glimcher MJ. X-ray diffraction studies of the crystallinity of bone mineral in newly synthesized and density fractionated bone. Calcif Tiss Int. December 1983;35(2):202-209.
2003	Simmons CA, Matlis S, Thornton AJ, Chen S, Wang C-Y, Mooney DJ. Cyclic strain enhances matrix mineralization by adult human mesenchymal stem cells via the extracellular signal-regulated kinase (ERK1/2) signaling pathway. J Biomech. August 2003;36(8):1087-1096.
2006	Sawakami K, Robling AG, Ai M, Pitner ND, Liu D, Warden SJ, Li J, Maye P, Rowe DW, Duncan RL, Warman ML, Turner CH. The Wnt co-receptor LRP5 is essential for skeletal mechanotransduction but not for the anabolic bone response to parathyroid hormone treatment. J Biol Chem. August 18, 2006;281(33):23698-23711.
2006	Rubin J, Rubin C, Jacobs CR. Molecular pathways mediating mechanical signaling in bone. Gene. February 15, 2006;367:1-16.
1987	Frost HM. The mechanostat: a proposed pathogenic mechanism of osteoporoses and the bone mass effects of mechanical and nonmechanical agents. Bone Miner. April 1987;2(2):73-85.
1997	Smalt R, Mitchell FT, Howard RL, Chambers TJ. Induction of NO and prostaglandin E₂ in osteoblasts by wall-shear stress but not mechanical strain. Am J Physiol Endocrinol Metab. October 1997;273(4):E751-E758.
2007	Ponik SM, Triplett JW, Pavalko FM. Osteoblasts and osteocytes respond differently to oscillatory and unidirectional fluid flow profiles. J Cell Biochem. February 15, 2007;100(3):794-807.
1994	Rubin CT, McLeod KJ. Promotion of bony ingrowth by frequency-specific, low-amplitude mechanical strain. Clin Orthop Relat Res. January 1994;298:165-174.
2001	Turner CH, Burr DB. Experimental techniques for bone mechanics. In: Cowin SC, ed. Bone Mechanics Handbook. 2nd ed. Boca Raton, FL: CRC Press; 2001:chap 7.
2005	Nyman JS, Reyes M, Wang X. Effect of ultrastructural changes on the toughness of bone. Micron. October–December 2005;36(7-8):566-582.
2005	Sugawara Y, Kamioka H, Honjo T, Tezuka K-i, Takano-Yamamoto T. Three-dimensional reconstruction of chick calvarial osteocytes and their cell processes using confocal microscopy. Bone. May 2005;36(5):877-883.
1997	Owan I, Burr DB, Turner CH, Qiu J, Tu Y, Onyia JE, Duncan RL. Mechanotransduction in bone: osteoblasts are more responsive to fluid forces than mechanical strain. Am J Physiol Cell Physiol. September 1997;273(3):C810-C815.
1995	Turner CH, Takano Y, Owan I. Aging changes mechanical loading thresholds for bone formation in rats. J Bone Miner Res. October 1995;10(10):1544-1549.
1985	Frangos JA, Eskin SG, McIntire LV, Ives CL. Flow effects on prostacyclin production by cultured human endothelial cells. Science. March 22, 1985;227(4693):1477-1479.
2004	Li YJ, Batra NN, You L, Meier SC, Coe IA, Yellowley CE, Jacobs CR. Oscillatory fluid flow affects human marrow stromal cell proliferation and differentiation. J Orthop Res. November 2004;22(6):1283-1289.
2003	Lee K, Jessop H, Suswillo R, Zaman G, Lanyon L. Bone adaptation requires oestrogen receptor-α. Nature. July 24, 2003;424(6947):389.
1996	Johnson DL, McAllister TN, Frangos JA. Fluid flow stimulates rapid and continuous release of nitric oxide in osteoblasts. Am J Physiol Endocrinol Metab. July 1996;271(1):E205-E208.
2004	Hoffler CE II. In Pursuit of Accurate Structural and Mechanical Osteocyte Mechanotransduction Models [PhD thesis]. University of Michigan; 2004.
1994	Aarden EM, Burger EH, Nijweide PJ. Function of osteocytes in bone. J Cell Biochem. July 1994;55(3):287-299.
2007	Tatsumi S, Ishii K, Amizuka N, Li M, Kobayashi T, Kohno K, Ito M, Takeshita S, Ikeda K. Targeted ablation of osteocytes induces osteoporosis with defective mechanotransduction. Cell Metab. June 2007;5(6):464-475.
1999	Jepsen KJ, Davy DT, Krzypow DJ. The role of the lamellar interface during torsional yielding of human cortical bone. J Biomech. March 1999;32(3):303-310.
1997	Burr DB. Muscle strength, bone mass, and age‐related bone loss. J Bone Miner Res. 1997;12(10):1547-1551.
2003	Haut Donahue TL, Haut TR, Yellowley CE, Donahue HJ, Jacobs CR. Mechanosensitivity of bone cells to oscillating fluid flow induced shear stress may be modulated by chemotransport. J Biomech. September 2003;36(9):1363-1371.
1995	Duncan RL, Turner CH. Mechanotransduction and the functional response of bone to mechanical strain. Calcif Tiss Int. December 1995;57(5):344-358.
1999	McAllister TN, Frangos JA. Steady and transient fluid shear stress stimulate NO release in osteoblasts through distinct biochemical pathways. J Bone Miner Res. June 1999;14(6):930-936.
1998	Pavalko FM, Chen NX, Turner CH, Burr DB, Atkinson S, Hsieh Y-F, Qiu J, Duncan RL. Fluid shear-induced mechanical signaling in MC3T3-E1 osteoblasts requires cytoskeleton-integrin interactions. Am J Physiol. December 1998;275(6):C1591-C1601.
2003	Ominsky MS. Effects of Hydrostatic Pressure, Biaxial Strain, and Fluid Shear on Osteoblastic Cells: Mechanotransduction Via NF-ΚB, MAP Kinase, and AP-1 Pathways [PhD thesis]. University of Michigan; 2003.
1994	Turner CH, Forwood MR, Rho J, Yoshikawa T. Mechanical loading thresholds for lamellar and woven bone formation. J Bone Miner Res. January 1994;9(1):87-97.
2000	Wallace BA, Cumming RG. Systematic review of randomized trials of the effect of exercise on bone mass in pre- and postmenopausal women. Calcif Tiss Int. July 2000;67(1):10-18.
2001	Cheng B, Zhao S, Luo J, Sprague E, Bonewald LF, Jiang JX. Expression of functional gap junctions and regulation by fluid flow in osteocyte-like MLO-Y4 cells. J Bone Miner Res. February 2001;16(2):249-259.
1996	Oxlund H, Mosekilde L, Ørtoft G. Reduced concentration of collagen reducible cross links in human trabecular bone with respect to age and osteoporosis. Bone. November 1996;19(5):479-484.
1984	Rubin CT, Lanyon LE. Regulation of bone formation by applied dynamic loads. J Bone Joint Surg. March 1984;66A(3):397-402.
2000	McCreadie BR, Goldstein SA. Biomechanics of fracture: is bone mineral density sufficient to assess risk? J Bone Miner Res. December 2000;15(12):2305-2308.
2008	Yerramshetty JS, Akkus O. The associations between mineral crystallinity and the mechanical properties of human cortical bone. Bone. March 2008;42(3):476-482.
2004	McCreadie BR, Hollister SJ, Schaffler MB, Goldstein SA. Osteocyte lacuna size and shape in women with and without osteoporotic fracture. J Biomech. April 2004;37(4):563-572.
1994	Weinbaum S, Cowin SC, Zeng Y. A model for the excitation of osteocytes by mechanical loading-induced bone fluid shear stresses. J Biomech. March 1994;27(3):339-360.
1997	Majumdar S, Genant HK, Grampp S, Newitt DC, Truong V-H, Lin JC, Mathur A. Correlation of trabecular bone structure with age, bone mineral density, and osteoporotic status: in vivo studies in the distal radius using high resolution magnetic resonance imaging. J Bone Miner Res. January 1997;12(1):111-118.
2001	Donahue SW, Jacobs CR, Donahue HJ. Flow-induced calcium oscillations in rat osteoblasts are age, loading frequency, and shear stress dependent. Am J Physiol Cell Physiol. November 2001;281(5):C1635-C1641.
1996	Lean JM, Mackay AG, Chow JW, Chambers TJ. Osteocytic expression of mRNA for c-fos and IGF-I: an immediate early gene response to an osteogenic stimulus. Am J Physiol Endocrinol Metab. June 1996;270(6):E937-E945.
2001	You J, Reilly GC, Zhen X, Yellowley CE, Chen Q, Donahue HJ, Jacobs CR. Osteopontin gene regulation by oscillatory fluid flow via intracellular calcium mobilization and activation of mitogen-activated protein kinase in MC3T3–E1 osteoblasts. J Biol Chem. April 20, 2001;276(16):13365-13371.
2002	Halloran BP, Ferguson VL, Simske SJ, Burghardt A, Venton LL, Majumdar S. Changes in bone structure and mass with advancing age in the male C57BL/6J mouse. J Bone Miner Res. June 2002;17(6):1044-1050.
2003	Kim CH, Takai E, Zhou H, Von Stechow D, Müller R, Dempster DW, Guo XE. Trabecular bone response to mechanical and parathyroid hormone stimulation: the role of mechanical microenvironment. J Bone Miner Res. December 2003;18(12):2116-2125.
1991	Caplan AI. Mesenchymal stem cells. J Orthop Res. September 1991;9(5):641-650.
2009	Riddle RC, Donahue HJ. From streaming-potentials to shear stress: 25 years of bone cell mechanotransduction. J Orthop Res. February 2009;27(2):143-149.
2000	You J, Yellowley CE, Donahue HJ, Zhang Y, Chen Q, Jacobs CR. Substrate deformation levels associated with routine physical activity are less stimulatory to bone cells relative to loading-induced oscillatory fluid flow. J Biomech Eng. August 2000;122(4):387-393.
2003	Akkus O, Polyakova‐Akkus A, Adar F, Schaffler MB. Aging of microstructural compartments in human compact bone. J Bone Miner Res. June 2003;18(6):1012-1019.
1990	Brear K, Currey JD, Pond CM. Ontogenetic changes in the mechanical properties of the femur of the polar bear Ursus maritimus. J Zool. 1990;222(1):49-58.
1997	Paschalis EP, Betts F, DiCarlo E, Mendelsohn R, Boskey AL. FTIR microspectroscopic analysis of human iliac crest biopsies from untreated osteoporotic bone. Calcif Tiss Int. December 1997;61(6):487-492.
2006	Robling AG, Castillo AB, Turner CH. Biomechanical and molecular regulation of bone remodeling. Annu Rev Biomed Eng. 2006;8:455-498.

Year

Entry

1983

Bonar LC, Roufosse AH, Sabine WK, Grynpas MD, Glimcher MJ. X-ray diffraction studies of the crystallinity of bone mineral in newly synthesized and density fractionated bone. Calcif Tiss Int. December 1983;35(2):202-209.

2003

Simmons CA, Matlis S, Thornton AJ, Chen S, Wang C-Y, Mooney DJ. Cyclic strain enhances matrix mineralization by adult human mesenchymal stem cells via the extracellular signal-regulated kinase (ERK1/2) signaling pathway. J Biomech. August 2003;36(8):1087-1096.

2006

Sawakami K, Robling AG, Ai M, Pitner ND, Liu D, Warden SJ, Li J, Maye P, Rowe DW, Duncan RL, Warman ML, Turner CH. The Wnt co-receptor LRP5 is essential for skeletal mechanotransduction but not for the anabolic bone response to parathyroid hormone treatment. J Biol Chem. August 18, 2006;281(33):23698-23711.

2006

Rubin J, Rubin C, Jacobs CR. Molecular pathways mediating mechanical signaling in bone. Gene. February 15, 2006;367:1-16.

1987

Frost HM. The mechanostat: a proposed pathogenic mechanism of osteoporoses and the bone mass effects of mechanical and nonmechanical agents. Bone Miner. April 1987;2(2):73-85.