Knee loading stimulates healing of mouse bone wounds in a femur neck

Mechanical Loading Promotes the Migration of Endogenous Stem Cells and Chondrogenic Differentiation in a Mouse Model of Osteoarthritis

Osteoarthritis (OA) is a major health problem, characterized by progressive cartilage degeneration. Previous works have shown that mechanical loading can alleviate OA symptoms by suppressing catabolic activities. This study evaluated whether mechanical loading can enhance anabolic activities by facilitating the recruitment of stem cells for chondrogenesis. We evaluated cartilage degradation in a mouse model of OA through histology with H&E and safranin O staining. We also evaluated the migration and chondrogenic ability of stem cells using in vitro assays, including immunohistochemistry, immunofluorescence, and Western blot analysis. The result showed that the OA mice that received mechanical loading exhibited resilience to cartilage damage. Compared to the OA group, mechanical loading promoted the expression of Piezo1 and the migration of stem cells was promoted via the SDF-1/CXCR4 axis. Also, the chondrogenic differentiation was enhanced by the upregulation of SOX9, a transcription factor important for chondrogenesis. Collectively, the results revealed that mechanical loading facilitated cartilage repair by promoting the migration and chondrogenic differentiation of endogenous stem cells. This study provided new insights into the loading-driven engagement of endogenous stem cells and the enhancement of anabolic responses for the treatment of OA.

Mechanical loading stimulates bone angiogenesis through enhancing type H vessel formation and downregulating exosomal miR-214-3p from bone marrow-derived mesenchymal stem cells

Exosomes are important transporters of miRNAs, which play varying roles in the healing of the bone fracture. Angiogenesis is one of such critical events in bone healing, and we previously reported the stimulatory effect of mechanical loading in vessel remodeling. Focusing on type H vessels and exosomal miR-214-3p, this study examined the mechanism of loading-driven angiogenesis. MiRNA sequencing and qRT-PCR revealed that miR-214-3p was increased in the exosomes of the bone-losing ovariectomized (OVX) mice, while it was significantly decreased by knee loading. Furthermore, compared to the OVX group, exosomes, derived from the loading group, promoted the angiogenesis of endothelial cells. In contrast, exosomes, which were transfected with miR-214-3p, decreased the angiogenic potential. Notably, knee loading significantly improved the microvascular volume, type H vessel formation, and bone mineral density and contents, as well as BV/TV, Tb.Th, Tb.N, and Tb.Sp. In cell cultures, the overexpression of miR-214-3p in endothelial cells reduced the tube formation and cell migration. Collectively, this study demonstrates that knee loading promotes angiogenesis by enhancing the formation of type H vessels and downregulating exosomal miR-214-3p.

Mechanical stimulations can inhibit local and remote tumor progression by downregulating WISP1

Mechanical stimulations can prevent bone loss, but their effects on the tumor-invaded bone or solid tumors are elusive. Here, we evaluated the effect of knee loading, dynamic loads applied to the knee, on metastasized bone and mammary tumors. In a mouse model, tumor cells were inoculated to the mammary fat pad or the proximal tibia. Daily knee loading was then applied and metabolic changes were monitored mainly through urine. Urine samples were also collected from human subjects before and after step aerobics. The result showed that knee loading inhibited tumor progression in the loaded tibia. Notably, it also reduced remotely the growth of mammary tumors. In the urine, an altered level of cholesterol was observed with an increase in calcitriol, which is synthesized from a cholesterol derivative. In urinary proteins, knee loading in mice and step aerobics in humans markedly reduced WNT1-inducible signaling pathway protein 1, WISP1, which leads to poor survival among patients with breast cancer. In the ex vivo breast cancer tissue assay, WISP1 promoted the growth of cancer fragments and upregulated tumor-promoting genes, such as Runx2, MMP9, and Snail. Collectively, the present preclinical and human study demonstrated that mechanical stimulations, such as knee loading and step aerobics, altered urinary metabolism and downregulated WISP1. The study supports the benefit of mechanical stimulations for locally and remotely suppressing tumor progression. It also indicated the role of WISP1 downregulation as a potential mechanism of loading-driven tumor suppression.

Knee loading repairs osteoporotic osteoarthritis by relieving abnormal remodeling of subchondral bone via Wnt/β-catenin signaling

Osteoporotic osteoarthritis (OPOA) is a common bone disease mostly in the elderly, but the relationship between Osteoporotic (OP) and osteoarthritis (OA) is complex. It has been shown that knee loading can mitigate OA symptoms. However, its effects on OPOA remain unclear. In this study, we characterized pathological linkage of OP to OA, and evaluated the effect of knee loading on OPOA. We employed two mouse models (OA and OPOA), and conducted histology, cytology, and molecular analyses. In the OA and OPOA groups, articular cartilage was degenerated and Osteoarthritis Research Society International score was increased. Subchondral bone underwent abnormal remodeling, the differentiation of bone marrow mesenchymal stem cells (BMSCs) to osteoblasts and chondrocytes was reduced, and migration and adhesion of pre-osteoclasts were enhanced. Compared to the OA group, the pathological changes of OA in the OPOA group were considerably aggravated. After knee loading, however, cartilage degradation was effectively prevented, and the abnormal remodeling of subchondral bone was significantly inhibited. The differentiation of BMSCs was also improved, and the expression of Wnt/β-catenin was elevated. Collectively, this study demonstrates that osteoporosis aggravates OA symptoms. Knee loading restores OPOA by regulating subchondral bone remodeling, and may provide an effective method for repairing OPOA.

Finite-element analysis of the mouse proximal ulna in response to elbow loading

Bone is a mechano-sensitive tissue that alters its structure and properties in response to mechanical loading. We have previously shown that application of lateral dynamic loads to a synovial joint, such as the knee and elbow, suppresses degradation of cartilage and prevents bone loss in arthritis and postmenopausal mouse models, respectively. While loading effects on pathophysiology have been reported, mechanical effects on the loaded joint are not fully understood. Because the direction of joint loading is non-axial, not commonly observed in daily activities, strain distributions in the laterally loaded joint are of great interest. Using elbow loading, we herein characterized mechanical responses in the loaded ulna focusing on the distribution of compressive strain. In response to 1-N peak-to-peak loads, which elevate bone mineral density and bone volume in the proximal ulna in vivo, we conducted finite-element analysis and evaluated strain magnitude in three loading conditions. The results revealed that strain of ~ 1000 μstrain (equivalent to 0.1% compression) or above was observed in the limited region near the loading site, indicating that the minimum effective strain for bone formation is smaller with elbow loading than axial loading. Calcein staining indicated that elbow loading increased bone formation in the regions predicted to undergo higher strain.

Wnt3a involved in the mechanical loading on improvement of bone remodeling and angiogenesis in a postmenopausal osteoporosis mouse model

Osteoporosis is a major health problem, making bones fragile and susceptible to fracture. Previous works showed that mechanical loading stimulated bone formation and accelerated fracture healing. Focusing on the role of Wnt3a (wingless/integrated 3a), this study was aimed to assess effects of mechanical loading to the spine, using ovariectomized (OVX) mice as a model of osteoporosis. Two-week daily application of this novel loading (4 N, 10 Hz, 5 min/d) altered bone remodeling with an increase in Wnt3a. Spinal loading promoted osteoblast differentiation, endothelial progenitor cell migration, and tube formation and inhibited osteoclast formation, migration, and adhesion. A transient silencing of Wnt3a altered the observed loading effects. Spinal loading significantly increased bone mineral density, bone mineral content, and bone area per tissue area. The loaded OVX group showed a significant increase in the number of osteoblasts and reduction in osteoclast surface/bone surface. Though expression of osteoblastic genes was increased, the levels of osteoclastic genes were decreased by loading. Spinal loading elevated a microvascular volume as well as VEGF expression. Collectively, this study supports the notion that Wnt3a-mediated signaling involves in the effect of spinal loading on stimulating bone formation, inhibiting bone resorption, and promoting angiogenesis in OVX mice. It also suggests that Wnt3a might be a potential therapeutic target for osteoporosis treatment.-Li, X., Liu, D., Li, J., Yang, S., Xu, J., Yokota, H., Zhang, P. Wnt3a involved in the mechanical loading on improvement of bone remodeling and angiogenesis in a postmenopausal osteoporosis mouse model.

Mechanical loading mitigates osteoarthritis symptoms by regulating endoplasmic reticulum stress and autophagy

Osteoarthritis (OA) is a disease characterized by cartilage damage and abnormal remodeling of subchondral bone. Our previous study showed that in the early stage of OA, knee loading exerts protective effects by suppressing osteoclastogenesis through Wnt signaling, but little is known about loading effects at the late OA stage. Endoplasmic reticulum (ER) stress and autophagy are known to be involved in the late OA stage. We determined the effects of mechanical loading on ER stress and autophagy in OA mice. One hundred seventy-four mice were used for a surgery-induced OA model. In the first set of experiments, 60 mice were devoted to evaluation of the role of ER stress and autophagy in the development of OA. In the second set, 114 mice were used to assess the effect of knee loading on OA. Histologic, cellular, microcomputed tomography, and electron microscopic analyses were performed to evaluate morphologic changes, ER stress, and autophagy. Mechanical loading increased phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) and regulated expressions of autophagy markers LC3II/I and p62. Osteoarthritic mice also exhibited an elevated ratio of calcified cartilage to total articular cartilage (CC/TAC), and synovial hyperplasia with increased lining cells was found. At the early disease stage, subchondral bone plate thinning and reduced subchondral bone volume fraction (B.Ar/T.Ar) were observed. At the late disease stages, subchondral bone plate thickened concomitant with increased B.Ar/T.Ar. Mice subjected to mechanical loading exhibited resilience to cartilage destruction and a correspondingly reduced Osteoarthritis Research Society International score at 4 and 8 wk, as well as a decrease in synovitis and CC/TAC. While chondrocyte numbers in the OA group was notably decreased, mechanical loading restored chondrogenic differentiation. These results demonstrate that mechanical loading can retard the pathologic progression of OA at its early and late stages. The observed effects of loading are associated with the regulations of ER stress and autophagy.-Zheng, W., Li, X., Liu, D., Li, J., Yang, S., Gao, Z., Wang, Z., Yokota, H., Zhang, P. Mechanical loading mitigates osteoarthritis symptoms by regulating endoplasmic reticulum stress and autophagy.

Effects of knee loading on obesity-related non-alcoholic fatty liver disease in an ovariectomized mouse model with high-fat diet

AIM

Hormonal and nutritional disorders are the main causes of obesity and non-alcoholic fatty liver disease, especially in the elderly and in postmenopausal women. Although physical activity might alleviate these disorders, the elderly may often have difficulty in carrying out physical exercise. The purpose of this study was to investigate the therapeutic effect of knee loading, a new form of physical stimulation, on the symptoms of obesity and fatty liver.

METHODS

Using ovariectomized mice fed a high-fat diet, we evaluated the effect of knee loading that applies gentle cyclic loads to the knee. Female C57BL/6 mice were divided into five groups: control (SCD), high-fat diet (HF), HF with loading (HF + L), HF with ovariectomy (HF + OVX), and HF + OVX with loading (HF + OVX + L). Except for SCD, mice underwent sham operation or ovariectomy and were maintained on HF diet. After 6 weeks, the mice in the HF + L and HF + OVX + L groups were treated with knee loading for 6 weeks.

RESULTS

Compared to the obesity groups (HF and HF + OVX), knee loading significantly decreased a gain in body weight, liver weight, and white adipose tissue (all P < 0.01). It also reduced the lipid level in the serum (P < 0.01) and histological severity of hepatic steatosis (P < 0.01). Furthermore, knee loading downregulated biomarkers related to endoplasmic reticulum (ER) stress (GRP78, p-eIF2α, and ATF4) and altered biomarkers in autophagy (LC3 and p62).

CONCLUSIONS

Knee loading suppressed obesity-associated metabolic alterations and hepatic steatosis. These effects with knee loading might be associated with suppression of ER stress and promotion of autophagy.

Development of an Artificial Finger-Like Knee Loading Device to Promote Bone Health

This study presents the development of an innovative artificial finger-like device that provides position specific mechanical loads at the end of the long bone and induces mechanotransduction in bone. Bone cells such as osteoblasts are the mechanosensitive cells that regulate bone remodelling. When they receive gentle, periodic mechanical loads, new bone formation is promoted. The proposed device is an under-actuated multi-fingered artificial hand with 4 fingers, each having two phalanges. These fingers are connected by mechanical linkages and operated by a worm gearing mechanism. With the help of 3D printing technology, a prototype device was built mostly using plastic materials. The experimental validation results show that the device is capable of generating necessary forces at the desired frequencies, which are suitable for the stimulation of bone cells and the promotion of bone formation. It is recommended that the device be tested in a clinical study for confirming its safety and efficacy with patients.

A Mechatronic Loading Device to Stimulate Bone Growth via a Human Knee

This paper presents the design of an innovative device that applies dynamic mechanical load to human knee joints. Dynamic loading is employed by applying cyclic and periodic force on a target area. The repeated force loading was considered to be an effective modality for repair and rehabilitation of long bones that are subject to ailments like fractures, osteoporosis, osteoarthritis, etc. The proposed device design builds on the knowledge gained in previous animal and mechanical studies. It employs a modified slider-crank linkage mechanism actuated by a brushless Direct Current (DC) motor and provides uniform and cyclic force. The functionality of the device was simulated in a software environment and the structural integrity was analyzed using a finite element method for the prototype construction. The device is controlled by a microcontroller that is programmed to provide the desired loading force at a predetermined frequency and for a specific duration. The device was successfully tested in various experiments for its usability and full functionality. The results reveal that the device works according to the requirements of force magnitude and operational frequency. This device is considered ready to be used for a clinical study to examine whether controlled knee-loading could be an effective regimen for treating the stated bone-related ailments.

Knee loading inhibits osteoclast lineage in a mouse model of osteoarthritis

Osteoarthritis (OA) is a whole joint disorder that involves cartilage degradation and periarticular bone response. Changes of cartilage and subchondral bone are associated with development and activity of osteoclasts from subchondral bone. Knee loading promotes bone formation, but its effects on OA have not been well investigated. Here, we hypothesized that knee loading regulates subchondral bone remodeling by suppressing osteoclast development, and prevents degradation of cartilage through crosstalk of bone-cartilage in osteoarthritic mice. Surgery-induced mouse model of OA was used. Two weeks application of daily dynamic knee loading significantly reduced OARSI scores and CC/TAC (calcified cartilage to total articular cartilage), but increased SBP (subchondral bone plate) and B.Ar/T.Ar (trabecular bone area to total tissue area). Bone resorption of osteoclasts from subchondral bone and the differentiation of osteoclasts from bone marrow-derived cells were completely suppressed by knee loading. The osteoclast activity was positively correlated with OARSI scores and negatively correlated with SBP and B.Ar/T.Ar. Furthermore, knee loading exerted protective effects by suppressing osteoclastogenesis through Wnt signaling. Overall, osteoclast lineage is the hyper responsiveness of knee loading in osteoarthritic mice. Mechanical stimulation prevents OA-induced cartilage degeneration through crosstalk with subchondral bone. Knee loading might be a new potential therapy for osteoarthritis patients.

Knee loading protects against osteonecrosis of the femoral head by enhancing vessel remodeling and bone healing

Osteonecrosis of the femoral head is a serious orthopedic problem. Moderate loads with knee loading promote bone formation, but their effects on osteonecrosis have not been investigated. Using a rat model, we examined a hypothesis that knee loading enhances vessel remodeling and bone healing through the modulation of the fate of bone marrow-derived cells. In this study, osteonecrosis was induced by transecting the ligamentum teres followed by a tight ligature around the femoral neck. For knee loading, 5 N loads were laterally applied to the knee at 15 Hz for 5 min/day for 5 weeks. Changes in bone mineral density (BMD) and bone mineral content (BMC) of the femur were measured by pDEXA, and ink infusion was performed to evaluate vessel remodeling. Femoral heads were harvested for histomorphometry, and bone marrow-derived cells were isolated to examine osteoclast development and osteoblast differentiation. The results showed that osteonecrosis significantly induced bone loss, and knee loading stimulated both vessel remodeling and bone healing. The osteonecrosis group exhibited the lowest trabecular BV/TV (p b 0.001) in the femoral head, and lowest femoral BMD and BMC (both p b 0.01). However, knee loading increased trabecular BV/TV (p b 0.05) as well as BMD (pb 0.05) and BMC (p b 0.01). Osteonecrosis decreased the vessel volume (pb 0.001), vessel number (pb 0.001) and VEGF expression (p b 0.01), and knee loading increased them (pb 0.001, pb 0.001 and p b 0.01). Osteonecrosis activated osteoclast development, and knee loading reduced its formation, migration, adhesion and the level of “pit” formation (pb 0.001, pb 0.01, pb 0.001 and pb 0.001). Furthermore, knee loading significantly increased osteoblast differentiation and CFU-F (both p b 0.001). A significantly positive correlation was observed between vessel remodeling and bone healing (both p b 0.01). These results indicate that knee loading could be effective in repair osteonecrosis of the femoral head in a rat model. This effect might be attributed to promoting vessel remodeling, suppressing osteoclast development, and increasing osteoblast and fibroblast differentiation. In summary, the current study suggests that knee loading might potentially be employed as a non-invasive therapy for osteonecrosis of the femoral head.

Physical weight loading induces expression of tryptophan hydroxylase 2 in the brain stem

Sustaining brain serotonin is essential in mental health. Physical activities can attenuate mental problems by enhancing serotonin signaling. However, such activity is not always possible in disabled individuals or patients with dementia. Knee loading, a form of physical activity, has been found to mimic effects of voluntary exercise. Focusing on serotonergic signaling, we addressed a question: Does local mechanical loading to the skeleton elevate expression of tryptophan hydroxylase 2 (tph2) that is a rate-limiting enzyme for brain serotonin? A 5 min knee loading was applied to mice using 1 N force at 5 Hz for 1,500 cycles. A 5-min treadmill running was used as an exercise (positive) control, and a 90-min tail suspension was used as a stress (negative) control. Expression of tph2 was determined 30 min – 2 h in three brain regions ––frontal cortex (FC), ventromedial hypothalamus (VMH), and brain stem (BS). We demonstrated for the first time that knee loading and treadmill exercise upregulated the mRNA level of tph2 in the BS, while tail suspension downregulated it. The protein level of tph2 in the BS was also upregulated by knee loading and downregulated by tail suspension. Furthermore, the downregulation of tph2 mRNA by tail suspension can be partially suppressed by pre-application of knee loading. The expression of tph2 in the FC and VMH was not significantly altered with knee loading. In this study we provided evidence that peripheral mechanical loading can activate central tph2 expression, suggesting that physical cues may mediate tph2-cathalyzed serotonergic signaling in the brain.

Knee loading reduces MMP13 activity in the mouse cartilage

Background

Moderate loads with knee loading enhance bone formation, but its effects on the maintenance of the knee are not well understood. In this study, we examined the effects of knee loading on the activity of matrix metalloproteinase13 (MMP13) and evaluated the role of p38 MAPK and Rac1 GTPase in the regulation of MMP13.

Methods

Knee loading (0.5–3 N for 5 min) was applied to the right knee of surgically-induced osteoarthritis (OA) mice as well as normal (non-OA) mice, and MMP13 activity in the femoral cartilage was examined. The sham-loaded knee was used as a non-loading control. We also employed primary non-OA and OA human chondrocytes as well as C28/I2 chondrocyte cells, and examined MMP13 activity and molecular signaling in response to shear at 2–20 dyn/cm².

Results

Daily knee loading at 1 N for 2 weeks suppressed cartilage destruction in the knee of OA mice. Induction of OA elevated MMP13 activity and knee loading at 1 N suppressed this elevation. MMP13 activity was also increased in primary OA chondrocytes, and this increase was attenuated by applying shear at 10 dyn/cm². Load-driven reduction in MMP13 was associated with a decrease in the phosphorylation level of p38 MAPK (p-p38) and NFκB (p-NFκB). Molecular imaging using a fluorescence resonance energy transfer (FRET) technique showed that Rac1 activity was reduced by shear at 10 dyn/cm² and elevated by it at 20 dyn/cm². Silencing Rac1 GTPase significantly reduced MMP13 expression and p-p38 but not p-NFκB. Transfection of a constitutively active Rac1 GTPase mutant increased MMP13 activity, while a dominant negative mutant decreased it.

Conclusions

Knee loading reduces MMP13 activity at least in part through Rac1-mediated p38 MAPK signaling. This study suggests the possibility of knee loading as a therapy not only for strengthening bone but also preventing tissue degradation of the femoral cartilage.