Effect of cyclic tensile load on the regulation of the expression of matrix metalloproteases (MMPs -1, -3) and structural components in synovial cells

The cellular responses of corneal fibroblasts to cyclic stretching loads

Mechanical signaling plays a crucial role in maintaining extracellular matrix (ECM) homeostasis in various structures. In this study, we investigated the responses of corneal fibroblasts to cyclic stretching loads using an in vitro cell culture system. Bovine corneal fibroblasts were cultured and subjected to equibiaxial cyclic strain of 15% for 72 h at a frequency of 0.25 Hz, with bovine skin fibroblasts used as a comparison. We explored various cellular behaviors, including morphological changes, cell proliferation, and metabolism in response to mechanical stretching loads. The expression of genes, protein secretion, and enzymatic activity for several major metalloproteinases was also determined through Q-PCR, Western blot, and gel zymography. Additionally, we investigated the involvement of mitogen-activated protein kinases (MAPKs) signaling pathways in the corneal fibroblasts when subjected to mechanical stimuli. Our findings revealed that, compared to skin fibroblasts, corneal fibroblasts were reluctant to morphological changes in response to a prolonged (72 h) and high-amplitude (15% of strain) cyclic stretching load. However, cyclic stretching loads stimulated the upregulation of MMP-2 expression in corneal fibroblasts via the MAPK signaling pathways involving extracellular signal-regulated kinase and p38. Together with a lack of upregulation in type I collagen expression, our results indicate the induction of the ECM degradation process in corneal fibroblasts in response to cyclic stretching. These findings emphasize the mechanoresponsive nature of corneal fibroblasts and shed light on the potential impact of intense mechanical stress on the cornea in both normal and pathological conditions such as keratoconus, providing valuable insights for understanding corneal mechanobiology.

The Effects of Tensioning of the Anterior Cruciate Ligament Graft on Healing after Soft Tissue Reconstruction

The purpose of this study is to determine the effect of the magnitude of static mechanical tension on the anterior cruciate ligament (ACL) graft at the time of surgery on healing within the graft tunnels. Ninety male rats underwent unilateral ACL resection followed by reconstruction with a soft tissue tendon autograft. The ACL graft mechanical environment was modulated by different ACL graft pretension levels at the time of surgery (no pretension: 0N; moderate tension: 5N; over tension: 10N). External fixators were used to eliminate graft and joint motion during cage activity. Graft-tunnel healing was assessed at 3- and 6-week postoperatively, and articular joint surfaces were assessed at 9 weeks. Our results demonstrate that the ACL graft-tunnel healing was sensitive to different static graft pretension levels as demonstrated by different load-to-failure and stiffness properties among the different pretension levels. Pretensioning the graft to 5N (7-8% of the rat ACL ultimate load to failure) resulted in the best graft-tunnel healing as shown by higher graft-tunnel failure load and stiffness. Higher bone volume fraction was also seen in the 5N group relative to other pretension levels. Histological analysis of the graft-tunnel interface revealed differences in cellularity of the ACL graft between the 5N group and the other two groups. Furthermore, the highest graft pretension level (10N) resulted in loss of proteoglycan content among articular joint surfaces. In conclusion, we found that ACL graft-tunnel healing is sensitive to the magnitude of graft pretension at the time of surgery in a preclinical model of ACL reconstruction with joint immobilization. The combination of high-graft tension and immobilization is also deleterious for the articular surface. Further study is necessary to understand the interaction between the magnitude of graft tensioning and joint motion.

Effect of Dynamic Changes in Anterior Cruciate Ligament In Situ Graft Force on the Biological Healing Response of the Graft-Tunnel Interface

BACKGROUND

Anterior cruciate ligament (ACL) grafts that are placed for reconstruction are subject to complex forces. Current "anatomic" ACL reconstruction techniques may result in greater in situ graft forces. The biological effect of changing magnitudes of ACL graft force on graft-tunnel osseointegration is not well understood.

PURPOSE

The research objective is to determine how mechanical force on the ACL graft during knee motion affects tendon healing in the tunnel.

STUDY DESIGN

Controlled laboratory study.

METHODS

Male rats (N = 120) underwent unilateral ACL reconstruction with a soft tissue flexor tendon autograft. ACL graft force was modulated by different femoral tunnel positions at the time of surgery to create different graft force patterns with knee motion. External fixators were used to eliminate graft load during cage activity. A custom knee flexion device was used to deliver graft load through controlled daily knee motion. Graft-tunnel healing was then assessed via biomechanical, micro-computed tomography, and histological analyses.

RESULTS

ACL graft-tunnel healing was sensitive to dynamic changes in graft forces with postoperative knee motion. High ACL graft force with joint motion resulted in early inferior ACL graft load to failure as compared with knees that had low-force ACL grafts and joint motion and knees that were immobilized (mean ± SD: 5.50 ± 2.30 N vs 9.91 ± 3.54 N [ P = .013] and 10.90 ± 2.8 N [ P = .001], respectively). Greater femoral bone volume fraction was seen in immobilized knees and knees with low-force ACL grafts when compared with high-force ACL grafts at 3 and 6 weeks.

CONCLUSION

The authors were able to demonstrate that ACL graft-tunnel incorporation is sensitive to dynamic changes in ACL graft force with joint motion. Early high forces on the ACL graft appear to impair graft-tunnel osseointegration.

CLINICAL RELEVANCE

Current "anatomic" techniques of ACL reconstruction may result in greater graft excursion and force with knee motion. Our results suggest that the postoperative rehabilitation regimen may need to be modified during the early phase of healing to protect the reconstruction.

The role of elastic fibers in pathogenesis of conjunctivochalasis

The PubMed, MEDLINE databases and China National Knowledge Infrastructure (CNKI) were searched for information regarding the etiology and pathogenesis of conjunctivochalasis (CCh) and the synthesis and degradation of elastic fibers. After analysis of the literature, we found elastic fibers was a complex protein molecule from the structure and composition; the degradation of elastic fibers was one of the histopathological features of the disease; the vast majority of the factors related to the pathogenesis of CCh ultimately pointed to abnormal elastic fibers. By reasonably speculating, we considered that abnormal elastic fibers cause the conjunctival relaxation. In conclusion, we hypothesize that elastic fibers play an important role in the pathogenesis of CCh. Studies on the mechanism of synthesis, degradation of elastic fibers are helpful to clarify the pathogenesis of the disease and to find effective treatment methods.

A comparative study of effect of autograft compared with allograft anterior cruciate ligament reconstruction on expressions of LOXs and MMPs

The present study aimed to compare the effect of autograft or allograft anterior cruciate ligament (ACL) reconstruction on the expressions of lipoxygenases (LOXs) and matrix metalloproteinases (MMPs) in a New Zealand white rabbit model. New Zealand white rabbits were divided randomly into control, sham, autograft and allograft groups. At the 4th and 8th week after operation, biomechanical testing was performed to measure the primary length, cross-sectional area, maximum tensile load and stiffness of ACL, and HE staining was used to observe cell morphology and fibre alignment of ACL. At the 2nd, 4th and 8th week after operation, quantitative real-time PCR (qRT-PCR), Western blotting and immunohistochemistry were applied to detect LOXs and MMPs expressions, and expressions of adenomatous polyposis coli (APC)/Wnt signalling pathway-related proteins. At the 4th and 8th week after operation, the maximum tensile load and stiffness were higher in the autograft group than in the allograft group, and the values at the 8th week were higher than those at the 4th week after operation. The fibroblast proliferation in the allograft group was more significant than that in the autograft group. Compared with the control group, LOXs and MMPs expressions and the positive expression rates of LOXs and MMPs proteins were elevated, and the values in the allograft group were higher than those in the autograft group at all time points. At 8th week after operation, compared with the autograft group, Wnt expression was higher and APC expression was lower in the allograft group. Autograft and allograft ACL reconstruction can promote LOXs and MMPs expressions by activating the APC/Wnt signalling pathway.

Local mechanical response in semiflexible polymer networks subjected to an axisymmetric prestress

Analytical and numerical calculations are presented for the mechanical response of fiber networks in a state of axisymmetric prestress, in the limit where geometric nonlinearities such as fiber rotation are negligible. This allows us to focus on the anisotropy deriving purely from the nonlinear force-extension curves of individual fibers. The number of independent elastic coefficients for isotropic, axisymmetric, and fully anisotropic networks are enumerated before deriving expressions for the response to a locally applied force that can be tested against, e.g., microrheology experiments. Localized forces can generate anisotropy away from the point of application, so numerical integration of nonlinear continuum equations is employed to determine the stress field, and induced mechanical anisotropy, at points located directly behind and in front of a force monopole. Results are presented for the wormlike chain model in normalized forms, allowing them to be easily mapped to a range of systems. Finally, the relevance of these findings to naturally occurring systems and directions for future investigation are discussed.

Spontaneous osteoarthritis in Str/ort mice is unlikely due to greater vulnerability to mechanical trauma

OBJECTIVE

Relative contributions of genetic and mechanical factors to osteoarthritis (OA) remain ill-defined. We have used a joint loading model found to produce focal articular cartilage (AC) lesions, to address whether genetic susceptibility to OA in Str/ort mice is related to AC vulnerability to mechanical trauma and whether joint loading influences spontaneous OA development. We also develop finite element (FE) models to examine whether AC thickness may explain any differential vulnerability to load-induced lesions.

METHODS

Right knees of 8-week-old Str/ort mice were loaded, AC integrity scored and thickness compared to CBA mice. Mechanical forces engendered in this model and the impact of AC thickness were simulated in C57Bl/6 mice using quasi-static FE modelling.

RESULTS

Unlike joints in non-OA prone CBA mice, Str/ort knees did not exhibit lateral femur (LF) lesions in response to applied loading; but exhibited thicker AC. FE modeling showed increased contact pressure and shear on the lateral femoral surface in loaded joints, and these diminished in joints containing thicker AC. Histological analysis of natural lesions in the tibia of Str/ort joints revealed that applied loading increased OA severity, proteoglycan loss and collagen type II degradation.

CONCLUSION

Genetic OA susceptibility in Str/ort mice is not apparently related to greater AC vulnerability to trauma, but joint loading modifies severity of natural OA lesions in the medial tibia. FE modelling suggests that thicker AC in Str/ort mice diminishes tissue stresses and protects against load-induced AC lesions in the LF but that this is unrelated to their genetic susceptibility to OA.

Sterilization of tendon allografts: a method to improve strength and stability after exposure to 50 kGy gamma radiation

Terminal sterilization of tendon allografts with high dose gamma irradiation has deleterious effects on tendon mechanical properties and stability after implantation. Our goal is to minimize these effects with radio protective methods. We previously showed that radio protection via combined crosslinking and free radical scavenging maintained initial mechanical properties of tendon allografts after irradiation at 50 kGy. This study further evaluates the tissue response and simulated mechanical degradation of tendons processed with radio protective treatment, which involves crosslinking in 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide followed by soaking in an ascorbate/riboflavin-5-phosphate solution. Control untreated and treated tendons were irradiated at 50 kGy and implanted in New Zealand White rabbit knees within the joint capsule for four and 8 weeks. Tendons were also exposed to cyclic loading to 20 N at one cycle per 12 s in a collagenase solution for 150 cycles, followed by tension to failure. Control irradiated tendons displayed increased degradation in vivo, and failed prematurely during cyclic processing at an average of 25 cycles. In contrast, radio protected irradiated tendons displayed greater stability following implantation over 8 weeks, and possessed strength at 59 % of native tendons and modulus equivalent to that of native tendons after cyclic loading in collagenase. These results suggest that radio protective treatment improves the strength and the stability of tendon allografts.

Involvement of matrix metalloproteinases in the growth plate response to physiological mechanical load

Enzymes from the matrix metalloproteinase (MMP) family play a crucial role in growth-plate vascularization and ossification via proteolytic cleavage and remodeling of the extracellular matrix. Their regulation in the growth plate is crucial for normal matrix assembly. Endochondral ossification, which takes place at the growth plates, is influenced by mechanical loading. Using an in vivo avian model for mechanical loading, we have found increased blood penetration into the growth plates of loaded chicks. The purpose of this work was to study the involvement of MMP-2, -3, -9, -13, and -16 in the growth plate's response to loading and in the catch-up growth resulting from load release. We found that mechanical loading, as well as release from load, upregulated MMP-2, -9, and -13 expressions. In contrast, MMP-3, associated with cartilage injuries, and its associated protein connective tissue growth factor (CTGF), were downregulated by the load. However, after release from load, MMP-3 was upregulated and CTGF levels were elevated and caught up with the control. MMP-3 and CTGF were also downregulated after 60 min of mechanical stretching in vitro. These results demonstrate the central role of MMPs in the growth plate's response to mechanical loading, as well as in the catch-up growth followed load release.