Objectives. Many in vitro studies have investigated the mechanism by which mechanical signals are transduced into biological signals that regulate bone homeostasis via periodontal ligament fibroblasts during orthodontic treatment, but the results have not been systematically reviewed. This review aims to do this, considering the parameters of various in vitro mechanical loading approaches and their effects on osteogenic and osteoclastogenic properties of periodontal ligament fibroblasts. Methods. Specific keywords were used to search electronic databases (EMBASE, PubMed, and Web of Science) for English-language literature published between 1995 and 2017. Results. A total of 26 studies from the 555 articles obtained via the database search were ultimately included, and four main types of biomechanical approach were identified. Compressive force is characterized by static and continuous application, whereas tensile force is mainly cyclic. Only nine studies investigated the mechanisms by which periodontal ligament fibroblasts transduce mechanical stimulus. The studies provided evidence from in vitro mechanical loading regimens that periodontal ligament fibroblasts play a unique and dominant role in the regulation of bone remodelling during orthodontic tooth movement. Conclusion. Evidence from the reviewed studies described the characteristics of periodontal ligament fibroblasts exposed to mechanical force. This is expected to benefit subsequent research into periodontal ligament fibroblasts and to provide indirectly evidence-based insights regarding orthodontic treatment. Further studies should be performed to explore the effects of static tension on cytomechanical properties, better techniques for static compressive force loading, and deeper analysis of underlying regulatory systems. Cite this article: M. Li, C. Zhang, Y. Yang. Effects of mechanical forces on osteogenesis and osteoclastogenesis in human periodontal ligament fibroblasts: A systematic review of in vitro studies. Bone Joint Res 2019;8:19–31. DOI: 10.1302/2046-3758.81.BJR-2018-0060.R1

Cells typically respond to a variety of geometrical cues in their environment, ranging from nanoscale surface topography to mesoscale surface curvature. The ability to control cellular organisation and fate by engineering the shape of the extracellular milieu offers exciting opportunities within tissue engineering. Despite great progress, however, many questions regarding geometry-driven tissue growth remain unanswered. Here, we combine mathematical surface design, high-resolution microfabrication, in vitro cell culture, and image-based characterization to study spatiotemporal cell patterning and bone tissue formation in geometrically complex environments. Using concepts from differential geometry, we rationally designed a library of complex mesostructured substrates (10. 1. -10. 3. µm). These substrates were accurately fabricated using a combination of two-photon polymerisation and replica moulding, followed by surface functionalisation. Subsequently, different cell types (preosteoblasts, fibroblasts, mesenchymal stromal cells) were cultured on the substrates for varying times and under varying osteogenic conditions. Using imaging-based methods, such as fluorescent confocal microscopy and second harmonic generation imaging, as well as quantitative image processing, we were able to study early-stage spatiotemporal cell patterning and late-stage extracellular matrix organisation. Our results demonstrate clear geometry-dependent cell patterning, with cells generally avoiding convex regions in favour of concave domains. Moreover, the formation of multicellular bridges and collective curvature-dependent cell orientation could be observed. At longer time points, we found clear and robust geometry-driven orientation of the collagenous extracellular matrix, which became apparent with second harmonic generation imaging after ∼2 weeks of culture. Our results highlight a key role for geometry as a cue to guide spatiotemporal cell and tissue organisation, which is relevant for scaffold design in tissue engineering applications. Our ongoing work aims at understanding the underlying principles of geometry-driven tissue growth, with a focus on the interactions between substrate geometry and mechanical forces

Bone is a dynamic tissue that undergoes continuous mechanical forces. Mechanical stimuli applied on scaffolds resembling a part of the human bone tissue affects the osteogenesis [1]. Poly(3,4-ethylenedioxythiophene) (PEDOT) is a piezoelectric material that responds to mechanical stimulation producing an electrical signal, which in turn promotes the osteogenic differentiation of bone-forming cells by opening voltage-gated calcium channels [2]. In this study we examined the biological behavior of pre-osteoblastic cells seeded onto lyophilized piezoelectric PEDOT-containing scaffolds applying uniaxial compression. Two different concentrations of PEDOT (0.10 and 0.15% w/v) were combined with a 5% w/v poly(vinyl alcohol) (PVA) and 5% w/v gelatin, casted into wells, freeze dried and crosslinked with 2% v/v (3-glycidyloxypropyl)trimethoxysilane and 0.025% w/v glutaraldehyde. The scaffolds were physicochemically characterized by FTIR, measurement of the elastic modulus, swelling ratio and degradation rate. The cell-loaded scaffolds were subjected to uniaxial compression with a frequency of 1 Hz and a strain of 10% for 1 h every second day for 21 days. The loading parameters were selected to resemble the in vivo loading situation [3]. Cell viability and morphology on the PEDOT/PVA/gelatin scaffolds was determined. The alkaline phosphatase (ALP) activity, the collagen and calcium production were determined. The elastic modulus of PEDOT/PVA/gelatin scaffolds ranged between 1 and 5 MPa. The degradation rate indicates a mass loss of 15% after 21 days. The cell viability assessment displays excellent biocompatibility, while SEM images display well-spread cells. The ALP activity at days 3, 7 and 18 as well as the calcium production are higher in the dynamic culture compared to the static one. Moreover, energy dispersive spectroscopy analysis revealed the presence of calcium phosphate in the extracellular matrix after 14 days. The results demonstrate that PEDOT/PVA/gelatin scaffolds promote the adhesion, proliferation, and osteogenic differentiation of pre-osteoblastic cells under mechanical stimulation, thus favoring bone regeneration

Intraosseous Transcutaneous Amputation Prosthesis (ITAP) is a new generation of limb replacements that can provide to amputees, an alternative solution to the main problems caused by the most common used external prosthesis such as pressure sores, infections and unnatural gait. ITAP is designed as one pylon osteointegrated into the bone and protruding through the skin, allowing both the mechanical forces to be directly transferred to the skeleton and the external skin being free from frictions and infections. The skin attachment to the implant is fundamental for the success of the ITAP, as it prevents the implant to move and consequently fail. In this study we wanted to test if cell viability and attachment was improved using TiO2 nanotubes. Human keratinocytes and human dermal fibroblasts were seeded for three days on TiO2 nanotubes with different sizes (18–30nm, 40–60nm and 60–110nm), compared with controls (smooth titanium) and tested for viability and attachment. A Mann-Whitney U test was used to compare groups where p values < 0.05 were considered significant. The results showed that the viability and cell attachment for keratinocytes were significantly higher after three days on controls comparing with all nanotubes (p=0.02), while attachment was higher on bigger nanotubes and controls. Cell viability for fibroblasts was significantly higher on nanotubes between 40 and 110nm comparing with smaller size and controls (p=0.03), while investigation of cell attachment is ongoing. From these early results, we can say that TiO2 nanotubes can improve the soft tissue attachment on ITAP. Further in-vitro and ex-vivo experiments on cell attachment will be carried out

Scoliosis is a disease characterised by vertebral rotation, lateral curvature and changes in sagittal profile. The role of mechanical forces in producing this deformity is not clear. It is thought that abnormal loading deforms the disc, which becomes permanently wedged. Modelling and in vitro studies suggest that such deformations should increase intradiscal pressure. Intradiscal pressure has been measured previously in a variety of clinical environments. The aim of this study is to measure pressure profiles across scoliotic discs to provide further information on the role of mechanical forces in scoliosis. Pressure readings were obtained in consented patients with ethical approval using a needle-mounted sterilised pressure transducer (Gaeltec, Dunvegan, Isle of Skye) calibrated as described previously. The transducer needle was introduced into the disc of an anaesthetised patient during routine anterior scoliosis surgery and pressure profiles measured. Signals were collected, amplified and analysed using Power-lab and a laptop computer. Pressure profiles across 10 human scoliotic discs from 3 patients have been measured to date. Pressures varied from 0.1 to 1.2 MPa. Annular pressures showed high pressure, non-isotropic regions on the concave but not convex side of these discs. Nuclear pressures recorded from the discs of these scoliotic patients were higher than those recorded previously in non-scoliotic recumbent individuals

Background. To investigate the new theory of hydroneurolysis and hydrodissection in the treatment of carpal tunnel syndrome (CTS). Independently of the fluid hydrodissolution works due to mechanical forces and it may have some positive effects in patients with ischemic damage caused by scar tissue pressure at the nerve's surface. Methods. A prospective blind clinical study of 31 patients suffering from carpal tunnel syndrome, established by nerve conduction studies and clinical tests. 14 patients (out of 29), who refused to undergo an open operation as a treatment to their disease at this point of time, were treated with a simple ultrasound-guided injection at the proximal carpal tunnel. In order to exclude the biochemical influence of the fluid in the treating disease we choosed to infiltrate 3 cc. of normal saline 0,9%. In the follow-up period our group was asked to answer to a new Q-DASH score and visual analogue scale (VAS) 100/100 in 2, 4 and 8 weeks. Results. At the end of the second month we found only 2 out of 14 patients of the infiltration's group with clinical improvement. As far as the control group (17 patients), there was just one patient with recovery of the symptoms at the end of the second month who avoided operation. The rest 16 patients experienced insistence or worsening of CTS while they were waiting to be operated (mean time till operation in our department's waiting list: 2 months) and underwent a surgical decompression of the median nerve. Comparing the two groups in Q-DASH score, VAS 100/100 and ultrasound cross sectional area measurements we found no statistical difference between the two groups at the endpoint of our follow-up period. Conclusion. As far as nerve entrapment syndromes we proved that normal saline hydrodissolution appears to be non effective as a conservative treatment. The mechanical way of action seems to have only very short term effects. Level of Evidence. II

PURPOSE. Recently, in tissue engineering several methods using stem cells have been developed to repair chondral and osteochondral defects. Most of these methods rely on the use of scaffolds. Studies in the literature have demonstrated, first in animals and then in humans, that the use of mesenchymal stem cells withdrawn by several methods from adipose tissue allows to regenerate hyaline articular cartilage. In fact, it has been cleared that adipose-derived cells have multipotentiality equivalent to bone marrow-derived stem cells and that they can very easily and very quickly be isolated in large amounts enabling their immediate use in operating room for one-step cartilage repair techniques. The purpose of this study is to evaluate the therapeutic effect of adipose-derived stem cells on cartilage repair and present our experience in the treatment of knee cartilage defects by the novel AMIC REPAIR TECHNIQUE AUGMENTED by immersing the collagen scaffold with mesenchymal stem cells withdrawn from adipose tissue of the abdomen. MATERIALS AND METHODS. Fat tissue processing involves mechanical forces and does not mandatorily require any enzymatic or chemical treatment in order to obtain the regenerative cells from the lipoaspirate. In our study, mesenchymal adipose stem cells were obtained by non-enzymatic filtration or microfragmentation of lipoaspirates of the abdomen adipose tissue that enabled the separation of the stromal vascular fraction and were used in one-step reconstruction of knee cartilage defects by means of this new AUGMENTED AMIC TECHNIQUE. The focal defects underwent bone marrow stimulation microfractures, followed by coverage with collagen double layer resorbable membrane (Chondro-gide. TM. -Geistlich Pharma AG, Wolhusen, Switzerland) soaked in the cells obtained from fat in 18 patients, aged between 31 and 58 years, at the level of the left knee in 10 cases and in the right in eight, with follow-up ranging between 12 and 36 months. RESULTS: Surgical procedures have been completed without technical problems neither intraoperative or early postoperative complications. The evaluation scores (IKDC, KOOS and VAS) showed a significant improvement, more than 30%, at the initial 6 months follow-up and furtherly improved in the subsequent follow-ups. Also the control MRIs showed a progressive filling and maturation of the repair tissue of the defects. CONCLUSIONS. Since we are reporting a short and medium-term experience, it is not, of course, possible to provide conclusive assessment considerations on this technique, as the experience has to mature along with the progression of follow-ups. The simplicity together with the absence of intraoperative difficulties or immediate complications and the experience gained by other authors, first in animals and then in early clinical cases, makes it, however, possible to say that this can be considered one of the techniques to which resort for one-step treatment of cartilage defects in the knee because it improves patient's conditions and has the potential to regenerate hyaline-like cartilage. Future follow-up works will confirm the results

Rotating Hinge total knee replacement designs are currently more frequently used for revision total knee replacement. As the designs of these implants have improved over time, the threshold for using them has been lowered. Cases of global instability and severe bone loss have not been adequately addressed by the standard use of unlinked constrained designs. Recurrent dislocation and polyethylene post failure due to cold flow and wear make the use of the unlinked designs insufficient to address the mechanical forces developed in a grossly unstable knee. The linked rotating hinge designs have been able to address global ligamentous instability in four planes. Medial-lateral instability is well addressed by these implants. In cases of severe ankylosis with large flexion contractures, it is often necessary to resect the distal femur above the femoral insertions of the medial and lateral collateral ligaments. The absence of the tethering effect of severely contracted collateral ligaments demand the need for linked designs, although there has been reported success with the use of unlinked designs. Rotating hinges are particularly important for use in cases of recurvatum where an extension stop is incorporated in the design. The design permits slight hyperextension which permits application to clinical situations with incompetent quadriceps strength or paralysis. The clinical results are quite acceptable even though most reports present 65–75% success rates. However, it should also be stated that these patient cohorts represent the most severe cases of revision surgery. Current hinged designs should continue to lower the threshold for use

Aims

To systematically evaluate whether bracing can effectively achieve curve regression in patients with adolescent idiopathic scoliosis (AIS), and to identify any predictors of curve regression after bracing.

Aims

This study investigated vancomycin-microbubbles (Vm-MBs) and meropenem (Mp)-MBs with ultrasound-targeted microbubble destruction (UTMD) to disrupt biofilms and improve bactericidal efficiency, providing a new and promising strategy for the treatment of device-related infections (DRIs).

Aims

The aim of this study is to report the implant survival and factors associated with revision of total elbow arthroplasty (TEA) using data from the Dutch national registry.

Failure of a TKA is caused many times from the polyethylene debris or the mechanical forces which lead to loosening mostly to tibial component. The mobile meniscal knee prosthesis could provide solution as it simulates better normal knee function. The aim of our study is to present the midterm results of TKA using mobile bearing platform Rotaglide. During the period 2000–2004 we performed 261 TKA with the Rotaglide mobile polyethylene prosthesis (Corin Medical, UK). They are 235 women and 26 men, mean age 76.33 years, and the 93.7% of them (N=245) with primary osteoarthritis. The tibial component was cemented for all them, and for the femur was cementless for 146 cases (hybrid) and cemented for 115. None of them had patella replacement. One hundred five patients (59 hybrid and 46 cemented) were examined clinically and radiologically and the minimum follow-up time was 5 years (mean 6,6 /range 5–8 years). We use the Knee injury and Osteoarthritis Outcome Score (KOOS- range of scale for each subscore 0–100). There was significant improvement of knee function and the majority of our patients were satisfied from the result. Specifically, the score for general symptoms and joint stiffness was 89.1, for pain was 83.3, for daily activities was 75.6 and for the quality of life was 72.5. One patient had revision TKA for femur component aseptic loosening. Our results indicate that the Rotaglide total knee arthroplasty is a great choice for primary knee OA with excellent functional result

Objective: To measure intradiscal pressures in scoliotic spines to further understand the role of mechanical forces in the development of scoliosis. Design: Pressure readings were obtained in consented patients with ethical approval. A needle mounted pressure transducer was introduced into the disc during routine anterior scoliosis surgery. Subjects: Ten human scoliotic discs from three patients. Outcome measures: Intradiscal pressure profiles. Results: Nuclear hydrostatic pressures varied from 0.2 to 0.6 MPa. The mean nuclear pressures for the three spines were 0.27+0.12, 0.35+0.06 and 0.47+0.12 MPa. High stress, non- hydrostatic regions were consistently recorded in the concave annulus. Conclusions: Nuclear pressures in these scoliotic patients were significantly higher than the 0.12 and 0.15 MPa recorded previously in non-scoliotic recumbent individuals. 1;. 2. suggesting that spinal loading is abnormal in scoliosis

Bone fixation plates are routinely used in corrective and reconstructive interventions. Design of such implants must take into consideration not only good surface fit, but also reduced intra-operative bending and twisting of the implant itself. This process increases mechanical stresses within the implant and affects its durability and the functional outcome of the surgery. Wound exposure and anaesthesia times are also reduced. Current population-based designs consider the average shape of a target bone as a template to pre-shape the implant. Other studies try to enhance the average design by optimising surface metrics in a statistical shape space. This could ensure a low mean distance between the implant and any bone in the population, but does not reduce neither the maximum possible distances nor directly the mechanical forces needed to fit the implant to the specific patient. We propose a population-based study that considers the bending and torsion forces as metrics to be minimised for the design of enhanced fixation plates. Our aim is to minimise the necessary intra-operative deformations of the plates. In our approach, we first propose to represent a fixation plate by dividing it into discrete sections lengthwise and fitting a plane to each section. The number of sections depends on the size of the implant and anatomical location. It should be small enough to capture the anatomical curvatures, but large enough not to be affected by local noise in the surface. Surface patches corresponding to common locations for plate fixations are extracted from 200 segmented computed tomography (CT) images. In this work, distal lateral femoral patches are considered. A statistical shape model of the patches is then computed and a large population of 2,197 instances is generated, evenly covering the natural statistical variation within the initial population. These instances are considered as both bone surfaces and potential new designs of the contact surface of the fixation plate. The key formulation of our solution is to examine the effect of deforming each section of the implant on the rest of the sections and compute the amount of bending and torsion needed to shape one patch to another. Each instance of the population is fitted to all others and the maximum bending and torsion angles are recorded. A similar process was applied for the mean of the population. The goal is to pick from the population the shape that simultaneously minimises the bending and torsion angles. The maximum required bending was reduced from 25.3® to 19.3® (24.72% reduction), whereas the torsion component was reduced from 12.4® to 6.2® (50% reduction). The method proposed in this abstract enhances the current state-of-the-art in orthopaedic implant design by considering the mechanical deformations applied to the implant during the surgery. The obtained results are promising and indicate a noticeable improvement over the standard pre-contouring to the population mean. We plan to further validate the method and as a future outlook, we intend to test the approach in real surgical scenarios

The skeleton is tuned for sensing and responding to mechanical forces: a global bone strain moves the extra-cellular fluid through the lacunocanalicular network of compact bone, so gene expression of osteocytes is mechanically modulated by extra cellular fluid flow shear stress. Several studies showed that shear stress modulates bone cells gene expression: in vitro mechanical stimulation impacts the levels of alkaline phosphatase, cAMP, intracellular calcium, NO, prostaglandin E2, c-fos, COX-2, osteopontin and osteocalcin. Aim of this study is to investigate the effect of shear stress on SAOS-2 human osteoblasts proliferation, bone matrix production and mineralization, using a biostable polyurethane as scaffold and a perfusion bioreactor. Polyurethane scaffolds with an average porediameter of 624 micron were utilized. Scaffolds were sterilized and placed in to standard well-plates (condition A) and into a bioreactor with forced perfusion at a rate of 3 ml/min (condition B). Human osteosarcoma cell lineSAOS-2 was obtained from the ATCC and cultured in McCoy’s 5A modified medium. A suspension of 7′105 osteoblasts was added onto the top of each scaffold. Medium was changed every 3 days and sampled for osteopontin and-osteocalcin ELISA kits. After 16 days culture DNA and calcium contents were measured, light microscopy and SEM analysis were performed. In condition B, in comparison to A, we observed 33% higher cells proliferation, 12.6-fold higher osteopontin secretion, 99.6-foldhigher osteocalcin secretion and 8-fold higher calcium deposition. Microscopy observations revealed that in condition A osteoblasts were few with thin discontinuous extracellular matrix; in contrast shear stress induced 3D modeling of cells and matrix organization, so several cells were in multilayer with highly developed matrix and no surfaces were cell free. Statically cultured osteoblasts showed normal proliferation, but a very low matrix synthesis. Into bioreactor, which provides physiological levels of shear stress, the osteoblasts proliferated and showed increased metabolic activity

Background: Reverse obliquity and transverse fractures of the proximal femur represent a distinct fracture pattern in which the mechanical forces displace the femur medially thus increasing the risk of fixation failure. There is a paucity of published literature in this area of trauma. This study constitutes the largest series of such fractures. Methods: Using the hip fracture registry at this institution 101 reverse obliquity and transverse fracture patterns were identified from 3336 consecutive hip fractures. All surviving patients were followed up for 1 year. Results: Of 100 patients treated operatively, 59 were treated with 1350 sliding hip screws (SHS), 22 were treated with 1350 sliding hip screw devices designed to resist medialization (3 sliding hip screws with trochanteric plate and 19 Medoff plates), and 19 were treated with intramedullary sliding hip screw devices (1 short Gamma nail, 9 long Gamma nails, 6 Reconstruction nails, 6 long Targon nails, 1 short Targon nail). The SHS had 4 failures (6.8%), and the intramedullary devices one failure (5.3%). Those extramedullary devices augmented to prevent medialization had higher failure rates (1 of 3 SHS with trochanteric plate and 3 of 19 Medoff plates), with combined failure rate of 15.8%. Conclusion: The 1350 SHS and the intramedullary devices had similar failure rates of 6.8% and 5.2% respectively. Those extramedullary devices designed to prevent medialization had higher failure rates (combined failure rate of 4/22 or 18%). This is similar to the high failure rate in 950 devices reported elsewhere. This suggests that extramedullary devices attempting to combat the difficult biomechanics of these fractures are unsuccessful. Better results can be obtained by using the standard 1350 SHS or with intramedullary sliding hip screw devices

Aims

Hydroxyapatite (HA)-coated collars have been shown to reduce aseptic loosening of massive endoprostheses following primary surgery. Limited information exists about their effectiveness in revision surgery. The aim of this study was to radiologically assess osteointegration to HA-coated collars of cemented massive endoprostheses following revision surgery.

One of the mechanisms which controls bone growth, repair remodeling and absorption is mechanical loading. There exists no long-term in vitro model to study bone cells together with their matrix, nor a model that can apply quantitative mechanical forces of physiological amplitudes and frequencies. The analysis of the mechanical properties of bone (Young’s modulus and visco-elastic moduli) on small pieces of bone is also difficult with present devices. We have built a device that can maintain full viability and physiological response of bone for a period of several weeks and integrates all three functions. 10mm diameter bone cores 5 mm thick were obtained from the trabecular bone of the distal ulna of a 24 months old cow by precision cutting with diamond saws and keyhole cutters (our pattern) in sterile 7–10°C phosphate buffered saline (PBS) and cultured in a variation of DMEM containing fructose HI GEM. Results: The results of these studies have shown that perfusion of trabecular bone can maintain all cells and maintain bone structure for at least 72 days. In conventional methods for bone organ cultures, small bones, such as rat calvaria, quickly start to resorb bone and degenerate. In our perfusion system we see no evidence of change.. Initial experiments have indicated that there are 2 visco-elastic moduli of bone with different time constants, that the elastic modulus of trabecular bone varies is site dependant and that loading to 0.4% compression raises prostaglandin E2 and insulin-like growth factor 1 within a few hours. Mechanical stiffness of bone is increased by 35% when loaded for 20 days at 4,000μ, and decreases by 25% when not loaded. PTH at 10-10M increases stiffness over the load effect and 10-6M PTH decreases stiffness even in the presence of loading. Active osteoclasts are seen during the whole culture period indicating that the stem cells are present and functional. We gratefully acknowledge support by the German Arthrose Foundation (DAH) and the AO in Davos, CH

Aims

To investigate whether idiopathic osteonecrosis of the femoral head (ONFH) is related to impaired osteoblast activities.

Osteoblastic cells response to mechanical forces by activating signal transduction cascades and altering gene expression patterns. We examined the responses of MC3T3E1 mouse osteoblasts to short term, low level (1000 microstrain, 1Hz) loads applied by cyclic deformation of the growth surface. At these load levels, daily short-term loading significantly retards the ascorbate induced differentiation of the cells as measured by alkaline phosphatase and osteopontin expression. This effect peaked at 5 minutes of loading per day; loads of 1 or more hours per day accelerated the differentiation process slightly as measured by the same criteria. C-fos is known to respond to mechanical loading of bones in vivo, we therefore examined the effect of brief loading bouts on c-fos promoter activity. Stable lines of MC3T3E1 cells carrying the fos promoter driving a luciferase reporter gene were loaded for 0, 5 or 60 minutes. For these experiments cells were grown in MEM without ascorbate and were then either supplemented or not with 37.5mM ascorbate-2-phosphate at confluence. In cells which had not been pre-treated with ascorbate the c-fos promoter was essentially unresponsive to loads. Following 24 hours of ascorbate treatment (placing these cells at the earliest stages differentiation) a 5 minute loading bout resulted in a marked (~ 50%) decrease in luciferase activity with a trough at 6–8 hours. Loading for 60 minutes caused a similar, but accelerated inhibition of luciferase activity with a trough at 2–4 hours after loading. 24 hours after loading, fos promoter activity had returned to baseline in cells loaded for 60 minutes but remained depressed at 75% of baseline in cells loaded for 5 minutes. Ets family transcription factors have been implicated in gene regulation in response to mechanical stimulation in several systems. The c-fos promoter contains a Serum Response Element which contains both a CarG motif responsible for binding the Serum Response Factor and an ets core motif CAGGT which can bind ets factors. We therefore repeated these experiments using a mutant c-fos promoter in which the ets binding site is destroyed. The response of this mutant to loading for 60 minutes was indistinguishable from that of the wt-promoter. However, in contrast to the wt-promoter, the ets-mutated promoter responded to a 5 minute loading with a rapid increase in activity (~150%) which peaked at 10 hours before returning to baseline at 24 hours. These results suggest that although similar in magnitude, the inhibition of the c-fos promoter by 5 and 60 minute loading bouts are regulated by different mechanisms, and implicate the ets family of transcription factors in the response to the briefer loading events