Elsevier

Bone

Volume 110, May 2018, Pages 267-283
Bone

Prolonged high force high repetition pulling induces osteocyte apoptosis and trabecular bone loss in distal radius, while low force high repetition pulling induces bone anabolism

https://doi.org/10.1016/j.bone.2018.02.014Get rights and content

Highlights

  • 18 weeks of high force high repetition reaching and grasping induced bone loss, microcracks and increased catabolism in radial bone trabeculae.

  • 18 weeks of a low force high repetition task induced adaptive bone remodeling in radial bone trabeculae.

  • Fewer changes were induced in the ulnar bone by either task.

  • Prolonged performance of a high force high repetition task may increase fracture risk.

Abstract

We have an operant rat model of upper extremity reaching and grasping in which we examined the impact of performing a high force high repetition (High-ForceHR) versus a low force low repetition (Low-ForceHR) task for 18 weeks on the radius and ulna, compared to age-matched controls. High-ForceHR rats performed at 4 reaches/min and 50% of their maximum voluntary pulling force for 2 h/day, 3 days/week. Low-ForceHR rats performed at 6% maximum voluntary pulling force. High-ForceHR rats showed decreased trabecular bone volume in the distal metaphyseal radius, decreased anabolic indices in this same bone region (e.g., decreased osteoblasts and bone formation rate), and increased catabolic indices (e.g., microcracks, increased osteocyte apoptosis, secreted sclerostin, RANKL, and osteoclast numbers), compared to controls. Distal metaphyseal trabeculae in the ulna of High-ForceHR rats showed a non-significant decrease in bone volume, some catabolic indices (e.g., decreased trabecular numbers) yet also some anabolic indices (e.g., increased osteoblasts and trabecular thickness). In contrast, the mid-diaphyseal region of High-ForceHR rats' radial and ulnar bones showed few to no microarchitecture differences and no changes in apoptosis, sclerostin or RANKL levels, compared to controls. In further contrast, Low-ForceHR rats showed increased trabecular bone volume in the radius in the distal metaphysis and increased cortical bone area its mid-diaphysis. These changes were accompanied by increased anabolic indices, no microcracks or osteocyte apoptosis, and decreased RANKL in each region, compared to controls. Ulnar bones of Low-ForceHR rats also showed increased anabolic indices, although fewer than in the adjacent radius. Thus, prolonged performance of an upper extremity reaching and grasping task is loading-, region-, and bone-dependent, with high force loads at high repetition rates inducing region-specific increases in bone degradative changes that were most prominent in distal radial trabeculae, while low force task loads at high repetition rates induced adaptive bone responses.

Introduction

Most types of physical activity are considered beneficial, whether sports, planned exercise, household work or occupational tasks [1,2]. Yet, work activities are not considered exercise; the former typically lacking any cardiovascular benefits [3]. Involvement in heavy manual occupations is linked to higher incidence of musculoskeletal injuries than nonmanual and light manual occupations [4,5]. The negative effects of repetitive and high compressive forces on lumbar spine structures when performing occupational jobs are well established [[6], [7], [8]]. A small number of studies showing increased incidence of hand/wrist osteoarthritis and reduced bone mass in the hand and wrist in individuals with heavy or one-sided hand workloads [[9], [10], [11], [12]]. This is a concern because incidence of distal radial bone fractures is increasing in the U.S. and worldwide [13,14]. There is also a need for etiologic research examining mechanisms underlying tissue degradative changes occurring with high demand upper extremity occupational tasks [15].

Although not yet investigated with overuse injuries occurring as a consequence of occupational tasks, RANKL (Receptor activator of nuclear factor kappa-B ligand) is expressed by osteoblasts and osteocytes [16], and stimulates differentiation and activation of osteoclasts by binding to its receptor, RANK [17,18]. Osteocytes show metabolic responsiveness to bone loading or unloading [19,20], and RANKL is one protein released by apoptotic osteocytes following loading-induced microdamage [17,21]. Such microdamage has a catabolic effect on bones by promoting osteoclast activity in a RANKL-dependent manner [22]. Osteoprotegerin (OPG) is a RANK decoy receptor that binds RANKL, segregating the ligand and preventing activation of the RANKL/RANK pathway [23]. While osteocyte apoptosis and their subsequent release of RANKL is essential for bone remodeling, a prolonged shift in the RANKL and OPG ratio towards more RANKL enhances osteoclastogenesis and net bone resorption [17].

Sclerostin is another protein expressed by osteocytes [24] that has yet to be examined with overuse occupational injuries. It is the product of the SOST gene and a negative regulator of osteoblast differentiation and function, making it a potent inhibitor of bone formation [25,26]. Although the exact mechanisms by which sclerostin inhibits bone formation are still unclear, it is known that sclerostin selectively inhibits Wnt proteins from binding to low-density lipoprotein receptor-related protein 5/6 (LPR5/6) receptors, a change that antagonizes Wnt signaling [27]. The Wnt pathway is essential for loading-induced osteogenesis [28], and its inhibition suppresses osteoblast activity and reduces osteoblast and osteocyte viability [27]. Applied mechanical loads typically suppress sclerostin production, a change that releases the break on Wnt signaling and allows for bone formation [19]. However, loading-induced matrix microdamage in which osteocyte apoptosis occurs is associated with an enhanced release of both sclerostin and RANKL [26], changes that promote bone catabolism.

We have developed an operant and clinically relevant rat model of upper extremity WMSDs in which rats learn a reaching and lever bar pulling task for a food reward [29]. Rats reach forward using their whole forearm to pull on a lever bar located outside of the chamber (which is attached to a force transducer) at learned and defined reach rates and target forces for a food reward. Young adult rats performing the task at low force loads and high repetition rates (Low-ForceHR) for 12 weeks show adaptive bone changes, including increased trabecular bone volume in the distal metaphysis of the radius [29,30]. This is consistent with studies reporting bone anabolism in response to loading [31]. In contrast, rats performing a high force high repetition (High-ForceHR) task for 12 weeks show significant trabecular bone loss in the distal metaphysis [29,32]. Initially, an underlying inflammatory mechanism contributed to this overuse-induced trabecular bone loss, a mechanism confirmed with findings that anti-inflammatory treatments reduced this loss when provided in task weeks 4 through 12 since the inflammatory changes peaked in task week 6 [32,33]. These inflammatory responses were resolved in serum and muscles in 18 week High-ForceHR task rats [34]. However, we hypothesized that trabecular bone catabolism would persist in distal radial metaphysis of 18 week High-ForceHR rats in association with increased microdamage, osteocyte apoptosis, sclerostin and RANKL. These findings would be consistent with a Damage-Repair Theory for bone in which persistent high loading causes an accumulation of damage in bone if the loading is so high that self-repair mechanisms cannot keep pace with the level of damage or overload-induced resorption [[35], [36], [37], [38]]. That said, as stated in a recent review: “the contributions of varied, but unique, stimuli generated by muscle to bone remains to be established” [39].

To explore this hypothesis, we compared radial and ulnar bone microarchitecture changes in rats performing a High-ForceHR reaching and lever pulling task for 18 weeks to those occurring in rats performing a Low-ForceHR task for 18 weeks (extending our past 12 week studies), versus resting control (C) rats. We examined for indices of bone microdamage and changes in proteins known to modulate loading-induced bone resorption versus formation (e.g., RANKL, RANK, OPG and sclerostin), proteins not yet examined in our operant repetitive loading model or in other models of chronic muscle-contraction loading of bone.

Section snippets

Animals and overview

The Temple University Institutional Animal Care and Use Committee approved all experiments in compliance with NIH guidelines for the care and use of laboratory animals. A total of 70 young (2.5 months of age at onset) female Sprague-Dawley rats were used (one rat was excluded after onset of experiments reducing the total number of rats used to 69; Fig. 1A). All rats were housed in a central animal facility in separate cages with a 12 hour light:dark cycle, with free access to water and

Reach performance across the 18 weeks

We first investigated the consistency of performance of the operant High-ForceHR and Low-ForceHR tasks by the task rats. Each group learned to perform their respective task appropriately by task week 3 (Fig. 2A–D). The High-ForceHR rats performed the task at or near 4 reaches/min in task weeks 3 through 12, although below target levels in weeks 1 and 18 (Fig. 2A), matching past findings of symptoms of forepaw discomfort in High-ForceHR 18 week rats [34]. The Low-ForceHR rats had a tendency to

Discussion

This is the first study, to our knowledge, to show clear support of the Damage Repair Theory response in trabecular bone when loaded at high force levels, rather than just positive adaptive changes in response to prolonged muscle contraction-induced loading. Prolonged high force loading was a key factor driving radial bone microarchitecture and cellular responses. Rats performing a High-ForceHR task for 18 weeks showed several catabolic indices trabeculae in their distal radial metaphyses,

Conclusion

It is commonly assumed that bone mass increases with vigorous exercise and decreases as a result of unloading or reduced mechanical stimulation. We observed different remodeling responses when using a similar repetition rate yet two different stress magnitudes (Low-Force versus High-Force). Performance of a Low-ForceHR task for 18 weeks was matched by positive bone adaptation in both distal trabecular and mid-diaphyseal cortical bone of the radius (and somewhat in the ulna of these rats),

Acknowledgements

Research reported in this publication was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award Number AR056019 to MFB. This study utilized services offered by core facilities of the Center for Substance Abuse Research (Grant Number DA013429), the MicroCT and Imaging Core at Temple University School of Medicine, and Bioquant Image Analysis Corporation. We would also like to thank Vicki Kalscheur at the School of

Competing interests

None of the authors have any competing interests to declare.

References (108)

  • S.A. Colopy et al.

    Response of the osteocyte syncytium adjacent to and distant from linear microcracks during adaptation to cyclic fatigue loading

    Bone

    (2004)
  • P. Muir et al.

    Effect of fatigue loading and associated matrix microdamage on bone blood flow and interstitial fluid flow

    Bone

    (2007)
  • T.E. Wenzel et al.

    In vivo trabecular microcracks in human vertebral bone

    Bone

    (1996)
  • G.M. Bove et al.

    Manual therapy as an effective treatment for fibrosis in a rat model of upper extremity overuse injury

    J. Neurol. Sci.

    (2016)
  • C. Tagliaferri et al.

    Muscle and bone, two interconnected tissues

    Ageing Res. Rev.

    (2015)
  • R. Guo et al.

    Ubiquitin ligase Smurf1 mediates tumor necrosis factor-induced systemic bone loss by promoting proteasomal degradation of bone morphogenetic signaling proteins

    J. Biol. Chem.

    (2008)
  • B.J. Kim et al.

    TNF-alpha mediates the stimulation of sclerostin expression in an estrogen-deficient condition

    Biochem. Biophys. Res. Commun.

    (2012)
  • J.R. Potvin et al.

    Maximal acceptable forces for manual insertions using a pulp pinch, oblique grasp and finger press

    Int. J. Ind. Ergon.

    (2006)
  • W. Rohmert

    Problems in determining rest allowances part 1: use of modern methods to evaluate stress and strain in static muscular work

    Appl. Ergon.

    (1973)
  • X. Tu et al.

    Sost downregulation and local Wnt signaling are required for the osteogenic response to mechanical loading

    Bone

    (2012)
  • Y.F. Hsieh et al.

    In vivo fatigue loading of the rat ulna induces both bone formation and resorption and leads to time-related changes in bone mechanical properties and density

    J. Orthop. Res.

    (2002)
  • S.P. Kotha et al.

    Experimental and finite element analysis of the rat ulnar loading model-correlations between strain and bone formation following fatigue loading

    J. Biomech.

    (2004)
  • M.R. Laurent et al.

    Muscle-bone interactions: from experimental models to the clinic? A critical update

    Mol. Cell. Endocrinol.

    (2016)
  • S. Erhart et al.

    The biomechanical effects of a deepened articular cavity during dynamic motion of the wrist joint

    Clin. Biomech. (Bristol, Avon)

    (2012)
  • T. Hara et al.

    Force distribution across wrist joint: application of pressure-sensitive conductive rubber

    J. Hand. Surg. [Am.]

    (1992)
  • K. Marquez-Florez et al.

    Theoretical distribution of load in the radius and ulna carpal joint

    Comput. Biol. Med.

    (2015)
  • D.A. Rikli et al.

    Intra-articular pressure measurement in the radioulnocarpal joint using a novel sensor: in vitro and in vivo results

    J. Hand. Surg. [Am.]

    (2007)
  • O.D. Kennedy et al.

    Activation of resorption in fatigue-loaded bone involves both apoptosis and active pro-osteoclastogenic signaling by distinct osteocyte populations

    Bone

    (2012)
  • A.G. Robling et al.

    Sost, independent of the non-coding enhancer ECR5, is required for bone mechanoadaptation

    Bone

    (2016)
  • J. Delgado-Calle et al.

    Role and mechanism of action of sclerostin in bone

    Bone

    (2017)
  • L.E. Mulcahy et al.

    RANKL and OPG activity is regulated by injury size in networks of osteocyte-like cells

    Bone

    (2011)
  • C.A. O'Brien et al.

    Osteocyte control of osteoclastogenesis

    Bone

    (2013)
  • S.N. Blair et al.

    How much physical activity is good for health?

    Annu. Rev. Public Health

    (1992)
  • E.A. Clark et al.

    Locomotor bone strain as the stimulus for bone's mechanical adaptability

    J. Physiol.

    (1975)
  • Bureau of Labor Statistics (2016). Nonfatal Occupational Injuries and Illnesses Requiring Days Away From Work, 2015....
  • S. Villotte et al.

    Enthesopathies as occupational stress markers: evidence from the upper limb

    Am. J. Phys. Anthropol.

    (2010)
  • J. Hlavkova et al.

    Evaluation of lumbar spine load by computational method in order to acknowledge low-back disorders as occupational diseases

    Cent. Eur. J. Public Health

    (2016)
  • A. Seidler et al.

    Cumulative occupational lumbar load and lumbar disc disease—results of a German multi-center case-control study (EPILIFT)

    BMC Musculoskelet. Disord.

    (2009)
  • H. Vanharanta et al.

    Occupation, work load and the size and shape of lumbar vertebral canals

    Scand. J. Work Environ. Health

    (1987)
  • A.M. Dale et al.

    Comparison of musculoskeletal disorder health claims between construction floor layers and a general working population

    Occup. Environ. Med.

    (2015)
  • H. Ding et al.

    Hand osteoarthritis and pinch grip strength among middle-aged female dentists and teachers

    Scand. J. Rheumatol.

    (2010)
  • S. Solovieva et al.

    Hand use and patterns of joint involvement in osteoarthritis. A comparison of female dentists and teachers

    Rheumatology (Oxford)

    (2005)
  • T. Vehmas et al.

    Hand workload and the metacarpal cortical index. A study of middle-aged teachers and dentists

    Osteoporos. Int.

    (2005)
  • J.W. Karl et al.

    The epidemiology of upper extremity fractures in the United States, 2009

    J. Orthop. Trauma

    (2015)
  • NIOSH

    National Manufacturing Agenda - June 2010

  • D.M. Findlay et al.

    Relationship between serum RANKL and RANKL in bone

    Osteoporos. Int.

    (2011)
  • K. Matsuo

    Osteocytes Communicate with Osteoclast Lineage Cells Via RANKL IBMS BoneKEy 9(February 2012)

    (2012)
  • T.M. Skerry et al.

    Early strain-related changes in enzyme activity in osteocytes following bone loading in vivo

    J. Bone Miner. Res.

    (1989)
  • S.A. Al-Dujaili et al.

    Apoptotic osteocytes regulate osteoclast precursor recruitment and differentiation in vitro

    J. Cell. Biochem.

    (2011)
  • A.R. Wijenayaka et al.

    Sclerostin stimulates osteocyte support of osteoclast activity by a RANKL-dependent pathway

    PLoS One

    (2011)
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