Differential expression of matrix metalloproteinases and tissue inhibitors of metalloproteinases in anterior cruciate ligament and medial collateral ligament fibroblasts after a mechanical injury: involvement of the p65 subunit of NF-kappaB

A Diagnosis of Vitamin D Deficiency Is Associated With Increased Rates of Primary Patellar Instability and Need for Recurrent Surgical Stabilization

BACKGROUND

Vitamin D has been proven experimentally to affect musculoskeletal health. The purpose of this study was to identify the relationship between vitamin D deficiency and patellar instability.

HYPOTHESIS

Vitamin D deficiency is associated with an increased risk of experiencing primary patellar instability and recurrent patellar dislocation after primary surgical stabilization.

STUDY DESIGN

Retrospective comparative study.

LEVEL OF EVIDENCE

Level 3.

METHODS

A 1:1 matched retrospective study of 328,011 patients diagnosed with vitamin D deficiency was performed using the PearlDiver database. Incidence of primary patellar instability was calculated according to sex and age. Rates of primary patellar instability and surgical stabilization for recurrent dislocation were calculated with sex- and age-specific stratifications. Multivariable logistic regression was used to compare the rates of primary injury and recurrent stabilization while controlling for demographics and medical comorbidities.

RESULTS

A total of 656,022 patients were analyzed. The overall 1-year incidence rate of patellar instability in patients with vitamin D deficiency was 82.6 per 100,000 person-years (95% CI, 73.2-92.9), compared with 48.5 (95% CI, 41.4-56.5) in the matched control. Women were significantly more likely to experience primary patellar instability within 1 (adjusted odds ratio [aOR] = 1.45; 95% CI, 1.12-1.88) and 2 years (aOR, 1.31; 95% CI, 1.07-1.59) of hypovitaminosis D diagnosis. Patients aged 10 to 25 years with hypovitaminosis D were at greater risk of requiring recurrent patellar stabilization for both men (aOR, 2.48; 95% CI, 1.06-5.80) and women (aOR, 1.77; 95% CI, 1.04-3.02).

CONCLUSION

Patients diagnosed with vitamin D deficiency experienced higher rates of primary patellar instability and have greater risk of requiring recurrent surgical stabilization for subsequent dislocations.

CLINICAL RELEVANCE

These results suggest that monitoring and proactively treating vitamin D deficiency in the physically active patient may lower the risk of suffering primary patellar instability or recurrence after surgical stabilization.

Advanced Gene Therapy Strategies for the Repair of ACL Injuries

The anterior cruciate ligament (ACL), the principal ligament for stabilization of the knee, is highly predisposed to injury in the human population. As a result of its poor intrinsic healing capacities, surgical intervention is generally necessary to repair ACL lesions, yet the outcomes are never fully satisfactory in terms of long-lasting, complete, and safe repair. Gene therapy, based on the transfer of therapeutic genetic sequences via a gene vector, is a potent tool to durably and adeptly enhance the processes of ACL repair and has been reported for its workability in various experimental models relevant to ACL injuries in vitro, in situ, and in vivo. As critical hurdles to the effective and safe translation of gene therapy for clinical applications still remain, including physiological barriers and host immune responses, biomaterial-guided gene therapy inspired by drug delivery systems has been further developed to protect and improve the classical procedures of gene transfer in the future treatment of ACL injuries in patients, as critically presented here.

TGF-β1 and Mechanical-Stretch Induction of Lysyl-Oxidase and Matrix-Metalloproteinase Expression in Synovial Fibroblasts Requires NF-κB Pathways

The imbalance in the expression of matrix metalloproteinases (MMPs) and lysyl oxidases (LOXs) in synovial fibroblasts (SFs) caused by mechanical injury and inflammatory response prevents injured anterior cruciate ligaments (ACLs) from self-healing. However, research on the effect of growth factors on SFs on regulating the microenvironment is limited. In this study, mechanical injury and exogenous transform growth factor-β1 (TGF-β1) were employed to mimic a joint-cavity microenvironment with ACL trauma. The function of the NF-κB transcription factor was further studied. The study found that the gene expression of LOXs (except LOXL-1), MMP-1, -2, and -3 in SFs was promoted by the combination of injurious mechanical stretching and TGF-β1 and that the upregulation of MMPs was higher than that of LOXs. In addition, MMP-2 activity induced by the combination of injurious stretch and TGF-β1 was inhibited by NF-κB inhibitors such as Bay11-7082 and Bay11-7085. The findings concluded that the synovium was an important regulator of the knee joint-cavity microenvironment after ACL injury and that the NF-κB pathway mediated the regulation of MMP-2 in SFs via mechanical factors and TGF-β1.

The novel epiligament theory: differences in healing failure between the medial collateral and anterior cruciate ligaments

According to current literature, 90% of knee ligament injuries involve the medial collateral ligament or the anterior cruciate ligament. In contrast to the medial collateral ligament, which regenerates relatively well, the anterior cruciate ligament demonstrates compromised healing. In the past, there were numerous studies in animal models that examined the healing process of these ligaments, and different explanations were established. Although the healing of these ligaments has been largely investigated and different theories exist, unanswered questions persist.

Therefore, the aim of this article is 1) to review the different historical aspects of healing of the medial collateral ligament and present the theories for healing failure of the anterior cruciate ligament; 2) to examine the novel epiligament theory explaining the medial collateral ligament healing process and failure of anterior cruciate ligament healing; and 3) to discuss why the enveloping tissue microstructure of the aforementioned ligaments needs to be examined in future studies.

We believe that knowledge of the novel epiligament theory will lead to a better understanding of the normal healing process for implementing optimal treatments, as well as a more holistic explanation for anterior cruciate ligament healing failure.

Matrix Metalloproteinase-2 and -9 Expression in the Epiligament of the Medial Collateral and Anterior Cruciate Ligament in Human Knees: A Comparative Study

Aim

Ninety percent of knee ligament injuries involve the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) of the knee joint. Matrix metalloproteinases (MMPs) are a large group of calcium- and zinc-dependent endopeptidases responsible for cleaving and rebuilding various connective tissue components. Previous studies showed that MMP-2 and 9 have a significant effect on the healing process of injured ligaments. Therefore, the aim of this study was to evaluate for the first time in literature the expression and localization of MMP-2 and 9 in the epiligament (EL) and the ligament tissue of the MCL and the ACL of the human knee joint in order to assess their role in ligament healing.

Materials and methods

For the present study, we used histological material from the mid-portion of the MCL and the ACL of 14 knee joints from fresh cadavers. For the purpose of the immunohistochemical analysis, we used primary polyclonal antibodies against MMP-2 and 9. The obtained results were evaluated semi-quantitatively through ImageJ.

Results

Immunoreactivity for MMP-2 was predominantly positive (2+) in the EL of the MCL and remained mostly negative (0) in the ligament tissue. The expression of MMP-9 was mostly low-positive (1+) in the EL of the MCL and almost entirely negative (0) in the ligament tissue. In the EL of the ACL, the immunohistochemical expression of MMP-2 was predominantly low-positive (1+) and that of the MMP-9 was read as mostly low-positive (1+). Expression of the two enzymes in the ligament tissue was similar to the MCL.

Conclusion

The present study is the first comparison of the expression of the aforementioned MMPs in the EL tissue of the MCL and the ACL in human knees, which may play a key role in physiological and pathophysiological processes such as tissue healing and repair and basement membrane degradation.

Presence of meniscus tear alters gene expression profile of anterior cruciate ligament tears

Anterior cruciate ligament (ACL) tears occur in isolation or in tandem with other intra-articular injuries such as meniscus tears. The impact of injury pattern on the molecular biology of the injured ACL is unknown. Here, we tested the hypothesis that the biological response of the ACL to injury varies based on the presence or absence of concomitant meniscus tear. We performed RNA-seq on 28 ACL tears remnants (12 isolated, 16 combined). In total, 16,654 transcripts were differentially expressed between isolated and combined injury groups at false discovery rate of 0.05. Due to the large number of differentially expressed transcripts, we undertook an Ensembl approach to discover features that acted as hub genes that did not necessarily have large fold changes or high statistical significance, but instead had high biological significance. Our data revealed a negatively correlated module containing 5,960 transcripts (down-regulated in combined injury) and a positively correlated module containing 2,260 transcripts (up-regulated in combined injury). TNS1, MEF2D, NOTCH3, SOGA1, and MLXIP were highly-connected hub genes in the negatively correlated module and SCN2A, CSMD3, LRC44, USH2A, and LRP1B were critical hub genes in the positively correlated module. Transcripts in the negatively correlated module were associated with biological adhesion, actin-filament organization, cell junction assembly, and cell matrix adhesion. The positively correlated module transcripts were enriched for neuron migration and exocytosis regulation. These findings indicate genes and pathways reflective of healing deficiency and gain of neurogenic signaling in combined ACL and meniscus tears, suggesting their diminished repair potential. The biological response of ACL to injury could have implications for healing potential of the ligament and the long term health of the knee. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2612-2621, 2018.

Effects of controlled abnormal joint movement on the molecular biological response in intra-articular tissues during the acute phase of anterior cruciate ligament injury in a rat model

Background

The anterior cruciate ligament (ACL) is responsible for braking forward movement of the tibia relative to the femur and for tibial rotation. After ACL injury, this braking performance deteriorates, inducing abnormal joint movement. The purpose of this study was to clarify the effects of controlled abnormal joint movement on the molecular biological response in intra-articular tissues during the acute phase of ACL injury.

Methods

Eighty-four mature Wistar male rats were randomly assigned to a controlled abnormal movement (CAM) group, an ACL-transection (ACL-T) group, a sham-operated group, or an intact group. The ACL was completely transected at its midportion in the ACL-T and CAM groups, and a nylon suture was used to control abnormal tibial translation in the CAM group. The sham-operated group underwent skin and joint capsule incisions and tibial drilling without ACL transection. Animals were not restricted activity until sacrifice 1, 3, or 5 days after surgery for histological and gene expression assessments. Acute-phase inflammation requires an important balance between degenerative and biosynthetic processes and is controlled by the activities of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Both types of gene were analyzed in this study.

Results

The ACL-T and CAM groups exhibited cleavage of the ACL at all time points. However, for the CAM group, the gap in the ligament stump was extremely small, and fibroblast proliferation was observed around the stump. Relative to the ACL-T group, the CAM group demonstrated significantly lower expression of MMP-13 mRNA and a lower MMP-13/TIMP-1 ratio on days 1 and 5 in the ACL, the medial meniscus and the lateral meniscus. The expression of TIMP-1 mRNA was not significantly different between the ACL-T and CAM groups.

Conclusions

The study results suggested that controlling abnormal movement inhibited the inflammatory reaction in intra-articular tissues after ACL injury. This reaction was down-regulated in intra-articular tissues in the CAM group. Abnormal joint control caused prolonged inflammation and inhibited remodeling during the acute phase of ACL rupture.

Human placenta mesenchymal stem cells promote axon survival following optic nerve compression through activation of NF-κB pathway

Different damage factors are known to trigger cell death in the optic nerves. Use of mesenchymal stem cells is a possible treatments option for traumatic optic nerve injury due to their ability to secrete protective cytokines and recovery factors. In this study, we investigated the neuroprotective effects of human placenta-derived mesenchymal stem cells (hPMSCs) using an established optic nerve compression model and model of R28 cells that were exposed to hypoxia. Forty percent of axon death was seen in induced in vivo optic nerve injury model (p < .05), and 70% of R28 cells exposed to cobalt chloride (CoCl₂ ), leading to hypoxia, underwent apoptosis (p < .05). After intravenous injection of hPMSCs into tail vein, there was 25% improvement of axon survival in vivo (p < .05). R28 cells incubated with hPMSCs after exposure to hypoxic condition resulted in 50% increased cell survival compared with R28 cells without hPMSC exposure (p < .05), suggesting the active release of multiple factors related to cell survival. In addition, we found that Nf-κb protein mediates neuroprotection pathway via up-regulation of target proteins regulated by hPMSCs. Therefore, we assert that Nf-κb was one of the mediator proteins in a recovery pathway induced by hPMSCs. In conclusion, these indicate that transactivation of Nf-κb protein has a critical role in recovery mechanism by hPMSCs. We suggest that hPMSCs have abilities to recover neuronal damages by up-regulating the expression of genes associated with axon survival and can a better understanding of the possible role of hPMSCs in the treatment modalities of optic nerve injury.

Combined effects of tumor necrosis factor-α and interleukin-1β on lysyl oxidase and matrix metalloproteinase expression in human knee synovial fibroblasts in vitro

Previous studies have demonstrated that inflammatory cytokines are associated with matrix metalloproteinases (MMPs) and/or lysyl oxidases (LOXs) produced by anterior cruciate ligament (ACL) fibroblasts, which may contribute to the poor healing ability of the ACL. To evaluate whether the synovium also participates in ACL healing, the inflammatory microenvironment of the knee joint cavity was mimicked following ACL injury, and the combined effects of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) on the expression of MMPs and LOXs in synovial fibroblasts were studied. Cell viability was evaluated using trypan blue staining in the presence of TNF-α and IL-1β, and the expression of LOXs and MMPs was measured by reverse transcription-quantitative polymerase chain reaction. MMP-2 activity was also measured by zymography. The results indicated that the combined effects of TNF-α and IL-1β inhibited LOX expression, while promoting MMP-1, −2 and −3 expression and MMP-2 activity in synovial fibroblasts. These changes may impede healing by altering the balance between the degradative and biosynthetic arms of the ligament tissue remodeling process. Collectively, the present results suggest that the poor healing ability of cruciate ligaments may be due to the sensitivity of the synovium to inflammatory factors. Therefore, the synovium potentially serves a key regulatory role in the joint cavity microenvironment and in the healing process of the ACL, and thus should be considered as a therapeutic target to aid in the treatment of patients with ACL trauma.

Mechanical stretch and hypoxia inducible factor-1 alpha affect the vascular endothelial growth factor and the connective tissue growth factor in cultured ACL fibroblasts

PURPOSES

The adult human anterior cruciate ligament (ACL) has poor functional healing response. Hypoxia plays an important role in regulating the microenvironment of the joint cavity after ACL injury, however, its role in mechanical injury is yet to be examined fully in ACL fibroblasts. In this study, we used CoCl₂ to induce Hypoxia-inducible factor-1α (HIF-1α) in our experimental model to study its affect on matrix metalloproteinase-2 (MMP-2), vascular endothelial growth factor (VEGF), and connective tissue growth factor (CTGF) expression in ACL fibroblasts after mechanical stretch.

MATERIALS AND METHODS

Cell treatments were performed in the stretch chamber in all experimental groups. Quantitative real-time PCR was used to check mRNA expression levels of MMP-2, CTGF, VEGF, and HIF-1α. Western blot was used to detect the HIF-1α production. Enzyme-Linked immunosorbent assay was performed to check the VEGF and CTGF protein contents in supernatant. MMP-2 activity was assayed by gelatin zymography.

RESULTS

The real-time PCR results show that mechanical stretch or CoCl₂ treatment increases the expression of MMP-2, VEGF, CTGF, and HIF-1α; however, the combined effects of mechanical stretch and CoCl₂-induced HIF-1α increased MMP-2 production but decreased the VEGF and CTGF expression, compared to the CoCl₂ treatment group alone. Western blot analysis and ELISA also confirmed these results.

CONCLUSIONS

Our results demonstrated that mechanical stretch and CoCl₂-induced HIF-1α together increased the level of MMP-2 and decreased the levels of VEGF and CTGF in cultured ACL fibroblasts. The differential expression and production of HIF-1α, VEGF, MMP-2, and CTGF might help to explain the poor healing ability of ACL.

MGF E peptide pretreatment improves collagen synthesis and cell proliferation of injured human ACL fibroblasts via MEK-ERK1/2 signaling pathway

Injured anterior cruciate ligament (ACL) is hard to heal due to the poor proliferative potential of ACL fibroblasts. To verify whether mechano-growth factor (MGF) E peptide can restore the cell proliferation of injured ACL fibroblasts, ACL fibroblasts pretreated with MGF E peptide were subjected to injurious stretch and the outcomes were evaluated at 0 and 24 h. After injured, the type III collagen synthesis was increased at 0 h while inhibited at 24 h. The matrix metalloproteinase-2 (MMP-2) activity/expression was up-regulated, but the cell proliferation was inhibited. Fortunately, exogenous MGF E peptide decreased the type I/III collagen synthesis at 0 h but improved the type III collagen synthesis at 24 h. It decreased the MMP-2 activity/expression of injured ACL fibroblasts. Besides, MGF E peptide accelerated the cell proliferation via MEK-ERK1/2 signaling pathway. Our results implied that MGF E peptide pretreatment could provide a new efficient approach for ACL regeneration.

The Role of the Lysyl Oxidases in Tissue Repair and Remodeling: A Concise Review

Tissue injury provokes a series of events containing inflammation, new tissue formation and tissue remodeling which are regulated by the spatially and temporally coordinated organization. It is an evolutionarily conserved, multi-cellular, multi-molecular process via complex signalling network. Tissue injury disorders present grievous clinical problems and are likely to increase since they are generally associated with the prevailing diseases such as diabetes, hypertension and obesity. Although these dynamic responses vary not only for the different types of trauma but also for the different organs, a balancing act between the tissue degradation and tissue synthesis is the same. In this process, the degradation of old extracellular matrix (ECM) elements and new ones' synthesis and deposition play an essential role, especially collagens. Lysyl oxidase (LOX) and four lysyl oxidase-like proteins are a group of enzymes capable of catalyzing cross-linking reaction of collagen and elastin, thus initiating the formation of covalent cross-links that insolubilize ECM proteins. In this way, LOX facilitates ECM stabilization through ECM formation, development, maturation and remodeling. This ability determines its potential role in tissue repair and regeneration. In this review, based on the current in vitro, animal and human in vivo studies which have shown the significant role of the LOXs in tissue repair, e.g., tendon regeneration, ligament healing, cutaneous wound healing, and cartilage remodeling, we focused on the role of the LOXs in inflammation phase, proliferation phase, and tissue remodeling phase of the repair process. By summarizing its healing role, we hope to shed light on the understanding of its potential in tissue repair and provide up to date therapeutic strategies towards related injuries.

Matrix Metalloproteinase Expression in the Rat Myometrium During Pregnancy, Term Labor, and Postpartum

Pregnancy, spontaneous term labor (TL), and postpartum (PP) involution are associated with changes in the cellular and extracellular matrix composition of the uterus. Both the uterine smooth muscle (myometrium) and the infiltrating peripheral blood leukocytes involved in the activation of labor secrete extracellular matrix-degrading enzymes (matrix metalloproteinases, MMPs) that can modulate cellular behavior and barrier function. MMP expression is induced by mechanical stretch in several tissues. We hypothesized that the expression and activity of myometrial MMPs and their tissue inhibitors (TIMPs) are modulated in preparation for TL and PP involution and are regulated by mechanical stretch of uterine walls imposed by the growing fetus. Myometrial tissues were collected from bilaterally and unilaterally pregnant rats across gestation, TL, and PP. Total RNA and proteins were subjected to real-time PCR and immunoblotting, respectively, and tissue localization and activity was examined by immunohistochemistry and in situ zymography. We found that Mmp7, Mmp11, and Mmp12 mRNA levels were upregulated during TL and PP, while Mmp2, Mmp3, Mmp8, Mmp9, Mmp10, and Mmp13 mRNAs were only upregulated during PP. Timp1–Timp4 were stably expressed throughout gestation with some fluctuations PP. Active MMP2 was induced in the empty uterine horn during gestation and in the gravid PP uterus, suggesting negative regulation by biological mechanical stretch. We conclude that specific subsets of uterine MMPs are differentially regulated in the rat myometrium in preparation for two major events: TL and PP uterine involution.

Inflammation in joint injury and post-traumatic osteoarthritis

Inflammation is a variable feature of osteoarthritis (OA), associated with joint symptoms and progression of disease. Signs of inflammation can be observed in joint fluids and tissues from patients with joint injuries at risk for development of post-traumatic osteoarthritis (PTOA). Furthermore, inflammatory mechanisms are hypothesized to contribute to the risk of OA development and progression after injury. Animal models of PTOA have been instrumental in understanding factors and mechanisms involved in chronic progressive cartilage degradation observed after a predisposing injury. Specific aspects of inflammation observed in humans, including cytokine and chemokine production, synovial reaction, cellular infiltration and inflammatory pathway activation, are also observed in models of PTOA. Many of these models are now being utilized to understand the impact of post-injury inflammatory response on PTOA development and progression, including risk of progressive cartilage degeneration and development of chronic symptoms post-injury. As evidenced from these models, a vigorous inflammatory response occurs very early after joint injury but is then sustained at a lower level at the later phases. This early inflammatory response contributes to the development of PTOA features including cartilage erosion and is potentially modifiable, but specific mediators may also play a role in tissue repair. Although the optimal approach and timing of anti-inflammatory interventions after joint injury are yet to be determined, this body of work should provide hope for the future of disease modification tin PTOA.

Expression of modulators of extracellular matrix structure after anterior cruciate ligament injury

The ability of the anterior cruciate ligament (ACL) to heal after injury declines within the first 2 weeks after ACL rupture. To begin to explore the mechanism behind this finding, we quantified the expression of genes for collagen I and III, decorin, tenascin-C, and alpha smooth muscle actin, as well as matrix metalloproteinase (MMP)-1 and -13 gene expression within multiple tissues of the knee joint after ACL injury in a large animal model over a 2-week postinjury period. Gene expression of collagen I and III, decorin, and MMP-1 was highest in the synovium, whereas the highest MMP-13 gene expression levels were found in the ACL. The gene expression for collagen and decorin increased over the 2 weeks to levels approaching that in the ligament and synovium; however, no significant increase in either of the MMPs was found in the provisional scaffold. This suggests that although the ACL and synovium up-regulate both anabolic and catabolic factors, the provisional scaffold is primarily anabolic in function. The relative lack of provisional scaffold formation within the joint environment may thus be one of the key reasons for ACL degradation after injury.

Basic science of anterior cruciate ligament injury and repair

Injury to the anterior cruciate ligament (ACL) is one of the most devastating and frequent injuries of the knee. Surgical reconstruction is the current standard of care for treatment of ACL injuries in active patients. The widespread adoption of ACL reconstruction over primary repair was based on early perception of the limited healing capacity of the ACL. Although the majority of ACL reconstruction surgeries successfully restore gross joint stability, post-traumatic osteoarthritis is commonplace following these injuries, even with ACL reconstruction. The development of new techniques to limit the long-term clinical sequelae associated with ACL reconstruction has been the main focus of research over the past decades. The improved knowledge of healing, along with recent advances in tissue engineering and regenerative medicine, has resulted in the discovery of novel biologically augmented ACL-repair techniques that have satisfactory outcomes in preclinical studies. This instructional review provides a summary of the latest advances made in ACL repair. Cite this article: Bone Joint Res 2014;3:20-31.

Small-molecule based musculoskeletal regenerative engineering

Clinicians and scientists working in the field of regenerative engineering are actively investigating a wide range of methods to promote musculoskeletal tissue regeneration. Small-molecule-mediated tissue regeneration is emerging as a promising strategy for regenerating various musculoskeletal tissues and a large number of small-molecule compounds have been recently discovered as potential bioactive molecules for musculoskeletal tissue repair and regeneration. In this review, we summarize the recent literature encompassing the past 4 years in the area of small bioactive molecules for promoting repair and regeneration of various musculoskeletal tissues including bone, muscle, cartilage, tendon, and nerve.

TNF-α induced down-regulation of lysyl oxidase family in anterior cruciate ligament and medial collateral ligament fibroblasts

BACKGROUND

The lysyl oxidase (LOX) family has the capacity to catalyze the cross-linking of collagen and elastin, implicating its important fundamental role in injury healing. Tumor necrosis factor alpha (TNF-α) is considered to be an important chemical mediator in the acute inflammatory phase of the ligament injury. The role of the lysyl oxidase family induced by TNF-α in the knee ligaments' wound healing process is poorly understood. Our purpose was to determine the different expressions of the LOXs in poorly self-healing anterior cruciate ligament (ACL) and well functionally self-healing medial collateral ligament (MCL) induced by TNF-α.

METHODS

Semi-quantitative PCR, quantitative real-time PCR and western blot were performed for original research.

RESULTS

The results showed that all LOX family members were expressed at higher levels in MCL than those in ACL fibroblasts; the significant differences existed in the down-regulations of the LOXs induced by TNF-α; and the TNF-α-mediated down-regulations of the LOXs were more prominent in ACL than those in MCL fibroblasts. 1-20 ng/ml TNF-α down-regulated mRNA levels in ACL and MCL fibroblasts by up to 76% and 58% in LOX; 90% and 45% in LOXL-1; 97.5% and 90% in LOXL-2; 89% and 68% in LOXL-3; 52% and 25% in LOXL-4, respectively. Protein assay also showed LOXs had lower expressions in ACL than those in MCL.

CLINICAL RELEVANCE

Based on these results, the differential expressions of the LOXs might help to explain the intrinsic differences between the poorly self-healing ACL and well functionally self-healing MCL.

Titanium particles up-regulate the activity of matrix metalloproteinase-2 in human synovial cells

PURPOSE

Wear debris particle-induced osteolysis and subsequent aseptic loosening is one of the major causes of failure of total joint replacement. The purpose of this study was to investigate the effect of titanium implant material and inflammatory cytokines on human synovial cells and the development to osteolysis and aseptic loosening.

METHODS

This study investigated the effect of titanium implant material on the ECM-degraded MMP-2 in human synovial cells and analyzed the contribution of synovial cells in osteolysis and aseptic loosening.

RESULTS

When human synovial cells are exposed to titanium materials, MMP-2 activity is induced by 1.72 ± 0.14-fold with Ti disc and 3.95 ± 0.10-fold with Ti particles, compared with that of the controls, respectively. Inflammatory cytokines TNFα and IL-1β are also shown to induce MMP-2 activity by 3.65 ± 0.28-fold and 6.76 ± 0.28-fold, respectively. A combination of Ti particles and cytokines induces MMP-2 activities to a higher level (10.54 ± 0.45-fold). Inhibitors of various signal pathways involved in MMP-2 reverse Ti particle-induced MMP-2 activities.

CONCLUSIONS

Synovial cells surrounding the bone-prosthesis interface may contribute to production of MMP-2, and NFκB inhibitors may be explored as potential therapeutics to alleviate wear debris-induced osteolysis and aseptic loosening.

Characterization of total and active matrix metalloproteinases-1, -3, and -13 synthesized and secreted by anterior cruciate ligament fibroblasts in three-dimensional collagen gels

Anterior cruciate ligament (ACL) injury and subsequent reconstructive surgery is increasing with an estimated 200,000 reconstructions performed yearly in the United States. Current treatment requires reconstruction with autograft or allograft tissue with inherent disadvantages. The development of tissue-engineered ligament replacements or scaffolds may provide an alternative treatment method minimizing these issues. The study of ligament fibroblast catabolic and anabolic responses to mechanical and biologic stimuli in three-dimensional (3D) cell culture systems is critical to the development of such therapies. A 3D cell culture system was used to measure the total content and active forms of matrix metalloproteinases (MMPs)-1, -3, and -13 to assess the potential role of the mechanical environment in regulation of matrix turnover by ligament fibroblasts. The production, retention, and secretion of MMPs by ACL fibroblasts in 3D culture were measured over a 14-day period. The total MMP content and MMP activity were determined. The level of all MMPs studied increased over 7-10 days and then reached a steady state or decreased slightly in both the collagen gels and the media. This system will now permit the study of externally applied cyclic and static strains, strain deprivation, and the potential combined role of the cytoskeleton and MMPs in matrix turnover in ligaments.

Interleukin-1 beta influences on lysyl oxidases and matrix metalloproteinases profile of injured anterior cruciate ligament and medial collateral ligament fibroblasts

PURPOSE

The anterior cruciate ligament (ACL) is known to have a poor healing ability, especially in comparison with the medial collateral ligament (MCL) which can heal relatively well. Interleukin-1beta (IL-1β) is considered to be an important chemical mediator in the acute inflammatory phase of ligament injury. The role of IL-1β-induced expressions of lysyl oxidases (LOXs) and matrix metalloproteinases (MMPs), which respectively facilitate extracellular matrix (ECM) repair and degradation, is poorly understood. In this study, we aim to determine the intrinsic differences between ACL and MCL by characterising the differential expressions of LOXs and MMPs in response to IL-1β in the injury process.

METHODS

Semi-quantitative polymerase chain reaction (PCR), quantitative real-time PCR, Western blot, and zymography were performed.

RESULTS

We detected high expressions of IL-1β-induced LOXs in normal ACL and MCL. Then, we found IL-1β induced injured MCL to express more LOXs than injured ACL (up to 2.85-fold in LOX, 2.58-fold in LOXL-1, 1.89-fold in LOXL-2, 2.46-fold in LOXL-3 and 2.18-fold in LOXL-4). Meanwhile, we found IL-1β induced injured ACL to express more MMPs than injured MCL (up to 1.72-fold in MMP-1, 1.95-fold in MMP-2, 2.05-fold in MMP-3 and 2.3-fold in MMP-12). The further protein results coincided with gene expressions above.

CONCLUSIONS

Lower expressions of LOXs and higher expressions of MMPs might help to explain the poor healing ability of ACL.

Differential response to CoCl2-stimulated hypoxia on HIF-1α, VEGF, and MMP-2 expression in ligament cells

The adult human anterior cruciate ligament (ACL) has a poor functional healing response, whereas the medial collateral ligament (MCL) does not. The difference in intrinsic properties of these ligament cells can be due to their different response to their located microenvironment. Hypoxia is a key environmental regulator after ligament injury. In this study, we investigated the differential response of ACL and MCL fibroblasts to hypoxia on hypoxia-inducible factor-1α, vascular endothelial growth factor, and matrix metalloproteinase-2 (MMP-2) expression. Our results show that ACL cells responded to hypoxia by up-regulating the HIF-1α expression significantly as compared to MCL cells. We also observed that in MCL fibroblasts response to hypoxia resulted in increase in expression of VEGF as compared to ACL fibroblasts. After hypoxia treatment, mRNA and protein levels of MMP-2 increased in both ACL and MCL. Furthermore we found in ACL pro-MMP-2 was converted more into active form. However, hypoxia decreased the percentage of wound closure for both ligament cells and had a greater effect on ACL fibroblasts. These results demonstrate that ACL and MCL fibroblasts respond differently under the hypoxic conditions suggesting that these differences in intrinsic properties may contribute to their different healing responses and abilities.

Combined effects of TNF-α, IL-1β, and HIF-1α on MMP-2 production in ACL fibroblasts under mechanical stretch: an in vitro study

The dynamics between inflammatory factors, mechanical stress, and healing factors, in an intra-articular joint, are very complex after injury. Injury to intra-articular tissue [anterior cruciate ligament (ACL), synovium] results in hypoxia, accumulation of various pro-inflammatory factors, cytokines, and metalloproteases. Although the presence of increased amounts of matrix-metalloproteinases (MMP) in the joint fluid after knee injury is considered the key factor for ACL poor healing ability; however, the exact role of collective participants of the joint fluid on MMP-2 activity and production has not been fully studied yet. To investigate the combined effects of mechanical injury, inflammation and hypoxia induced factor-1α (HIF-1α) on induction of MMP-2; we mimicked the microenvironment of joint cavity after ACL injury. The results show that TNF-α and IL-1β elevate the activity of MMP-2 in a dose- and time-dependent manner. In addition, mechanical stretch further enhances the MMP-2 protein levels with TNF-α, IL-1β, and their mixture. CoCl(2) -induced HIF-1α (100 and 500 µM) also increases the levels and activity of MMP-2. Mechanical stretch has a strong additional effect on MMP-2 production with HIF-1α. Our results conclude that mechanical injury, HIF-1α and inflammatory factors collectively induce increased MMP-2 production in ACL fibroblasts, which was inhibited by NF-κB pathway inhibitor (Bay-11-7082).

Up-regulation expressions of lysyl oxidase family in Anterior Cruciate Ligament and Medial Collateral Ligament fibroblasts induced by Transforming Growth Factor-Beta 1

PURPOSE

The lysyl oxidase (LOX) family plays a crucial role in the formation and stabilisation of extracellular matrix (ECM) by catalysing the cross-linking of collagen and elastin, implicating its important fundamental roles in injury healing. A high level of transforming growth factor-β(1) (TGF-β(1)) accompanies the inflammatory phase of an injury of the knee joint. Our purpose was to detect the expressions of the LOX family in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) response to TGF-β(1).

METHODS

This study used reversed transcript PCR, real time quantitative PCR and Western blot for analyses.

RESULTS

The results showed significant increases in mRNA levels of LOX family members. At 5 ng/ml concentration of TGF-β(1,) the gene profiles of LOXs showed most active, and LOX and LOXL-3 showed increasing peaks at 12 hours after TGF-β(1) treatment (LOX: 7.2, 8.8-fold and LOXL-3: 3.8, 5.4-fold compared with normal controls in ACL and MCL, respectively); LOXL-1, LOXL-2 and LOXL-4 reached their highest amounts at six hours (LOXL-1: 1.9, 2.4-fold; LOXL-2: 14.8, 16.2-fold; LOXL-4: 2.5, 4.4-fold in ACL and MCL, respectively). Protein assays revealed that LOXs in ACL cells had relatively lower response to TGF-β(1) compared with those in MCL cells.

CONCLUSIONS

The differential expression and activities of LOXs might help to explain the intrinsic difference between ACL and MCL, and LOXs could imply a potential capability for ACL healing.

TGF-β1 promoted MMP-2 mediated wound healing of anterior cruciate ligament fibroblasts through NF-κB

The adult human anterior cruciate ligament (ACL) has poor functional healing response. Transforming growth factor (TGF)-β1 enhances the wound repair by stimulating matrix proteins deposition as well as the proliferation and migration of cells. However, the function of the TGF-β1-induced matrix metalloproteinases' (MMPs) activities in the wound healing process is poorly understood. In this study, exogenous MMP-2 is added to mimic the TGF-β1-induced MMP-2 expression. Role of NF-κB pathway is further examined. Our results show that TGF-β1 induces dramatic elevation of MMP-2 activities and the MMP-2/tissue inhibitors of metalloproteinases ratio. Furthermore, the exogenous MMP-2 significantly promoted in vitro wound healing abilities of ACL fibroblasts that are significantly blocked with the addition of its inhibitors. TGF-β1 also increases the proliferation of ACL fibroblasts whereas MMP-2 alone does not, indicating that MMP-2 activities are not involved in the proliferation. TGF-β1-induced MMP-2 activity is inhibited by Bay11-7082 and Bay11-7085 (NF-κB inhibitors). Our results demonstrate that increased TGF-β1 facilitates the ACL healing process by promoting the fibroblasts migration and proliferation. The migration process is mediated by MMP-2 and NF-κB pathway is involved in TGF-β1-mediated MMP-2 release.

Rehabilitation following a minimally invasive procedure for the repair of a combined anterior cruciate and posterior cruciate ligament partial rupture in a 15-year-old athlete

STUDY DESIGN

Case report.

BACKGROUND

The healing response procedure is a minimally invasive arthroscopic surgical technique used to stimulate healing in the treatment of partial cruciate ligament tears. The purpose of this report is to provide information on the surgical procedure, the postoperative rehabilitation, and the overall functional results in a patient who underwent such a procedure.

CASE DESCRIPTION

A 15-year-old male, who sustained a partial tear of both the anterior cruciate and posterior cruciate ligament while playing football, underwent arthroscopic surgical management utilizing a healing response technique. Precautions concerning range of motion and resisted activities were followed postoperatively to protect the healing cruciate ligaments. The postoperative protocol consisted of 3 phases, culminating in return-to-sport training. Treatment incorporated cardiovascular, proprioceptive, strength, power, plyometric, and sport-specific activities. Treatment was progressed based on specific criteria emphasizing proper movement patterns and eccentric control during functional activities.

OUTCOMES

The patient attended 31 physical therapy sessions over 17 weeks. Strength improved from 3/5 to 5/5, knee range of motion returned to normal, Lower Extremity Functional Scale scores improved from 21/80 to 80/80, and successful outcomes on functional return-to-sport testing allowed the patient to return to competitive athletics.

DISCUSSION

Primary repair of cruciate ligament tears has yielded poor results, and partial cruciate ligament tears may not require complete surgical reconstruction. The healing response technique offers a possible solution for the treatment of partial cruciate ligament tears. A criterion-based postoperative protocol was derived based on current evidence regarding rehabilitation following cruciate ligament reconstruction and evidence regarding lower extremity rehabilitation principles and injury prevention.

LEVEL OF EVIDENCE

Therapy, level 4.