Poster 130: Tendon-to-bone Healing in a CCR2 Knockout Mouse Model of Delayed Rotator Cuff Repair

Objectives:

Rotator cuff tears are one of the most prevalent musculoskeletal injuries with over 250,000 rotator cuff repairs performed annually in the Unites States. While surgical techniques have advanced, incomplete/failed healing after rotator cuff repair is still relatively common with rates ranging from 11-95%. Extrinsic factors such as excessive early activity and patient comorbidities such as smoking and diabetes have been previously identified as factors which may contribute to decreased rates of rotator cuff repair healing. However, there has been a recent focus on the intrinsic biologic factors which affect repair healing at the tendon-bone interface. CCR2 is a chemokine receptor that has been linked to the recruitment of monocytes into wound sites in early inflammatory stages and is associated with an increase in “pro-inflammatory” macrophages. The purpose of this study was to evaluate the role of CCR2 on rotator cuff tendon healing by evaluating relative gene expression and biomechanics following rotator cuff repair in wildtype (WT) and CCR2-/- knockout (KO) mice in a chronic rotator cuff injury model. We hypothesized that CCR2 KO would lead to decreased inflammatory cell recruitment and increased biomechanical properties after rotator cuff repair compared to WT mice.

Methods:

All procedures were approved by our Institutional Animal Care and Use Committee (Protocol# 2019-0021). A total of 28 12-week-old male mice were utilized for this study and divided into 2 groups (wildtype C57BL/6J and CCR2 KO). All mice underwent unilateral supraspinatus tendon detachment at the initial surgery, followed by delayed supraspinatus repair 2 weeks following the initial procedure. They were sacrificed at the 4-week time point following the second procedure (Fig 1). The primary outcome measures included biomechanical testing and gene expression analysis. Biomechanical testing was performed on the repaired rotator cuff tendons on a custom-designed materials testing system. Contralateral intact tendons were also tested as controls. Specimens were prepared and loaded to failure at a rate of 1mm/min. Load-to-failure data were recorded and stiffness was calculated from the load-deformation curves. Following total RNA isolation from both the control and repaired tendons (50ng) and muscles (100ng), gene expression was measured using the NanoString nCounter® Fibrosis Panel. Genes were assessed based on fold change and significance level, determined by adjusted p-values using the Benjamini-Yekutieli procedure. The significance level was set at p=0.05 for all statistical analyses.

Results:

All repaired tendons remained intact at the time of sacrifice 4 weeks following repair. The CCR2 KO group had thicker, more robust tendons on gross inspection than the WT controls. Biomechanical analysis demonstrated a significantly increased load-to-failure and stiffness of the supraspinatus tendon repair in the CCR2 KO group compared to the WT group. Mean load-to-failure in the WT group was 1.64 N ± 0.41 N versus 2.50 N ± 0.42 N in the CCR2 KO group (p<0.001) (Fig 2A). Mean stiffness in the WT group was 1.43 ± 0.66 N/mm versus 3.00 ± 0.95 N/mm in the CCR2 KO group (p=0.001) (Fig 2B). There were significant differences in both load-to-failure and stiffness between the repaired tendons and the intact contralateral tendons in both the WT and CCR2 KO groups (p<0.001). There were no significant differences in load-to-failure or stiffness between the WT and CCR2 KO controls. The site of failure was in the tendon midsubstance for all of the rotator cuff repair samples in both groups. NanoString analysis comparing WT repaired tendons with WT controls revealed 42 differentially expressed genes (see Fig 3 for relative pathway scores). There was significantly increased expression of Ccr2 in the WT repair group compared to the WT control group (log2 fold ratio: 3.28, 95% CI 2.63 to 3.94, p=0.003). NanoString analysis of the repaired tendon samples confirmed lower expression of Ccr2 in the repaired tendons of the CCR2 KO mice compared to WT tendons. There were no significant differences in expression ratios of the supraspinatus muscle samples between the CCR2 KO repair group and the WT repair group. There were also no significant differences in gene expression between the CCR2 KO repair group and the CCR2 KO control group muscles.

Conclusions:

In this study, we utilized a delayed rotator cuff repair model, which is more clinically relevant than previously established models of acute tendon transection and repair. Utilizing CCR2 KO mice, we found that there were significant differences in biomechanical properties – both load-to-failure and stiffness – between the WT mice and the CCR2 KO mice. Given the role of CCR2 in recruitment and accumulation of pro-inflammatory macrophages, these data suggest that excessive or unresolved inflammation may hinder tendon healing. Our results suggest that CCR2 KO leads to improved biomechanical properties in a mouse model of delayed rotator cuff repair. Additional studies are necessary to further elucidate the role of CCR2 in inflammation in the setting of chronic rotator cuff disease; however, CCR2 may be a promising target for novel therapeutics which aim to improve tendon healing and decrease re-tear rates following rotator cuff repair.

Distinct inflammatory macrophage populations sequentially infiltrate bone‐to‐tendon interface tissue after ACL reconstruction surgery in mice

Macrophages are important for repair of injured tissues, but their role in healing after surgical repair of musculoskeletal tissues is not well understood. We used single‐cell RNA sequencing (RNA‐seq), flow cytometry, and transcriptomics to characterize functional phenotypes of macrophages in a mouse anterior cruciate ligament reconstruction (ACLR) model that involves bone injury followed by a healing phase of bone and fibrovascular interface tissue formation that results in bone‐to‐tendon attachment. We identified a novel “surgery‐induced” highly inflammatory CD9+ IL1+ macrophage population that expresses neutrophil‐related genes, peaks 1 day after surgery, and slowly resolves while transitioning to a more homeostatic phenotype. In contrast, CX3CR1+ CCR2+ macrophages accumulated more slowly and unexpectedly expressed an interferon signature, which can suppress bone formation. Deletion of Ccr2 resulted in an increased amount of bone in the surgical bone tunnel at the tendon interface, suggestive of improved healing. The “surgery‐induced macrophages” identify a new cell type in the early phase of inflammation related to bone injury, which in other tissues is dominated by blood‐derived neutrophils. The complex patterns of macrophage and inflammatory pathway activation after ACLR set the stage for developing therapeutic strategies to target specific cell populations and inflammatory pathways to improve surgical outcomes. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

A reply to "Relevant factors in the eutrophication of the Uruguay River and the Río Negro"

A recent paper by Beretta-Blanco and Carrasco-Letelier (2021) claims that agricultural eutrophication is not one of the main causes for cyanobacterial blooms in rivers and artificial reservoirs. By combining rivers of markedly different hydrological characteristics e.g., presence/absence and number of dams, river discharge and geological setting, the study speculates about the role of nutrients for modulating phytoplankton chlorophyll-a. Here, we identified serious flaws, from erratic and inaccurate data manipulation. The study did not define how erroneous original dataset values were treated, how the variables below the detection/quantification limit were numerically introduced, lack of mandatory variables for river studies such as flow and rainfall, arbitrary removal of pH > 7.5 values (which were not outliers), and finally how extreme values of other environmental variables were included. In addition, we identified conceptual and procedural mistakes such as biased construction/evaluation of model prediction capability. The study trained the model using pooled data from a short restricted lotic section of the (large) Uruguay River and from both lotic and reservoir domains of the Negro River, but then tested predictability within the (small) Cuareim River. Besides these methodological considerations, the article shows misinterpretations of the statistical correlation of cause and effect neglecting basic limnological knowledge of the ecology of harmful algal blooms (HABs) and international research on land use effects on freshwater quality. The argument that pH is a predictor variable for HABs neglects overwhelming basic paradigms of carbon fluxes and change in pH because of primary productivity. As a result, the article introduces the notion that HABs formation are not related to agricultural land use and water residence time and generate a great risk for the management of surface waterbodies. This reply also emphasizes the need for good practices of open data management, especially for public databases in view of external reproducibility.

Effect of Lubricin Mimetics on the Inhibition of Osteoarthritis in a Rat Anterior Cruciate Ligament Transection Model

BACKGROUND

Lubricin, a mucinous glycoprotein, plays a chondroprotective role as a constituent of synovial fluid. Structural analogs have been synthesized to mimic the structure and function of native lubricin in an effort to recapitulate this effect with the goal of delaying progression of osteoarthritis (OA).

PURPOSE

To investigate the efficacy of intra-articular injections of lubricin mimetics in slowing or preventing the progression of posttraumatic OA by using a rat anterior cruciate ligament transection model.

STUDY DESIGN

Controlled laboratory design.

METHODS

Four lubricin mimetics were investigated, differing from one another in their binding orientations and steric interactions. Eighty skeletally mature Sprague-Dawley rats underwent bilateral anterior cruciate ligament transections and were randomly allocated to receive intra-articular injections (50 µL/injection) of 1 of the 4 mimetics in the right knee and equal volumes of saline injection in the contralateral knee (control). All rats were euthanized 8 weeks postoperatively and assessed via biomechanical analysis, which evaluated comparative friction coefficients across the 4 groups, and histological evaluation of articular cartilage, osteophytes, and synovitis. The Osteoarthritis Research Society International (OARSI) histopathological assessment system was used to evaluate the degree of articular cartilage degeneration and osteophytes, while synovitis was assessed through a semiquantitative scoring system. Binding efficacy of the 4 mimetics was assessed in vitro and in vivo through the immunohistochemical localization of polyethylene glycol. Articular cartilage degeneration and synovitis scoring data analyses were performed with generalized estimating equation modeling.

RESULTS

Injection of the group 3 mimetic (random 24 + 400 + 30) directly correlated with improved OARSI scores for femoral articular cartilage degeneration when compared with saline-injected contralateral control knees (P = .0410). No lubricin mimetic group demonstrated statistically significant differences in OARSI scores for tibial articular cartilage degeneration. Injection of the group 4 mimetic (AB 24 + 400 + 30) led to a statistically significant difference in osteophyte OARSI score (P = .0019). None of the 4 lubricin mimetics injections incited an additive synovial inflammatory response. Immunohistochemical staining substantiated the binding capacity of all 4 mimetics, while in vivo experimentation revealed that the group 1 and 3 mimetics were still retained within the joint 4 weeks after injection. There were no differences in friction coefficients between any pair of groups and no significant trends based on lubricin mimetic structure.

CONCLUSION

We demonstrated that the tribosupplementation of a traumatically injured knee with a specific lubricin structural analog may attenuate the natural progression of OA.

CLINICAL RELEVANCE

The current lack of efficacious clinical options to counter the onset and subsequent development of OA suggests that further investigation into the synthesis and behavior of lubricin analogs could yield novel translational applications.

Blood-induced bone loss in murine hemophilic arthropathy is prevented by blocking the iRhom2/ADAM17/TNF-α pathway

Hemophilic arthropathy (HA) is a debilitating degenerative joint disease that is a major manifestation of the bleeding disorder hemophilia A. HA typically begins with hemophilic synovitis that resembles inflammatory arthritides, such as rheumatoid arthritis, and frequently results in bone loss in patients. A major cause of rheumatoid arthritis is inappropriate release of the proinflammatory cytokine tumor necrosis factor-α (TNF-α) by the TNF-α convertase (TACE; also referred to as ADAM17) and its regulator, iRhom2. Therefore, we hypothesized that iRhom2/ADAM17-dependent shedding of TNF-α also has a pivotal role in mediating HA. Here, we show that addition of blood or its components to macrophages activates iRhom2/ADAM17-dependent TNF-α shedding, providing the premise to study the activation of this pathway by blood in the joint in vivo. For this, we turned to hemophilic FVIII-deficient mice (F8-/- mice), which develop a hemarthrosis following needle puncture injury with synovial inflammation and significant osteopenia adjacent to the affected joint. We found that needle puncture-induced bleeding leads to increased TNF-α levels in the affected joint of F8-/- mice. Moreover, inactivation of TNF-α or iRhom2 in F8-/- mice reduced the osteopenia and synovial inflammation that develops in this mouse model for HA. Taken together, our results suggest that blood entering the joint activates the iRhom2/ADAM17/TNF-α pathway, thereby contributing to osteopenia and synovitis in mice. Therefore, this proinflammatory signaling pathway could emerge as an attractive new target to prevent osteoporosis and joint damage in HA patients.

Timing of Postoperative Mechanical Loading Affects Healing Following Anterior Cruciate Ligament Reconstruction: Analysis in a Murine Model

BACKGROUND

Following anterior cruciate ligament (ACL) reconstruction, the mechanical loading of the tissues has a significant impact on tendon-to-bone healing. The purpose of this study was to determine the effect of the timing of the initiation of mechanical loading on healing of a tendon graft in a bone tunnel.

METHODS

ACL reconstruction using a flexor tendon autograft was performed in 56 mice randomized to 4 groups with differing times to initiation of postoperative mechanical loading: (1) immediate, (2) 5 days, (3) 10 days, or (4) 21 days following surgery. An external fixator was placed across the knee at the time of surgery and removed when mechanical loading was scheduled to commence. Following removal of the external fixator, animals were permitted free, unrestricted cage activity. All mice were killed on postoperative day 28, and tendon-to-bone healing was assessed by biomechanical testing, microcomputed tomography (micro-CT), and histological analysis.

RESULTS

The mean failure force (and standard deviation) of the reconstructed ACL at the time of sacrifice was highest for Group 2 (3.29 ± 0.68 N) compared with Groups 1, 3, and 4 (p = 0.008). Micro-CT bone volume fraction was greatest for Group 2 in the femoral tunnel (p = 0.001), tibial tunnel (p = 0.063), and both bones (p < 0.001). Similarly, histological analysis demonstrated a narrower scar tissue interface and increased direct contact at the tendon-bone interface (p = 0.012) for Group 2.

CONCLUSIONS

Following ACL reconstruction, a defined period of immobilization without weight-bearing appears to improve biomechanical strength of the healing tendon-bone interface, while prolonged periods without mechanical load and motion decrease the ultimate load to failure in this murine model.

CLINICAL RELEVANCE

The ideal period of restricted weight-bearing and motion following ACL reconstruction remains undefined. In a murine model, improved healing was noted for animals immobilized for a brief period of 5 days. This work may serve as an initial step in determining the ideal time period in a clinical population.

Involvement of Indian hedgehog signaling in mesenchymal stem cell-augmented rotator cuff tendon repair in an athymic rat model

BACKGROUND

Bone marrow aspirate has been used in recent years to augment tendon-to-bone healing, including in rotator cuff repair. However, the healing mechanism in cell-based therapy has not been elucidated in detail.

METHODS

Sixteen athymic nude rats were randomly allocated to 2 groups: experimental (human mesenchymal stem cells in fibrin glue carrier) and control (fibrin glue only). Animals were sacrificed at 2 and 4 weeks. Immunohistochemical staining was performed to evaluate Indian hedgehog (Ihh) signaling and SOX9 signaling in the healing enthesis. Macrophages were identified using CD68 and CD163 staining, and proliferating cells were identified using proliferating cell nuclear antigen staining.

RESULTS

More organized and stronger staining for collagen II and a higher abundance of SOX9⁺ cells were observed at the enthesis in the experimental group at 2 weeks. There was significantly higher Gli1 and Patched1 expression in the experimental group at the enthesis at 2 weeks and higher numbers of Ihh⁺ cells in the enthesis of the experimental group vs control at both 2 weeks and 4 weeks postoperatively. There were more CD68⁺ cells localized to the tendon midsubstance at 2 weeks compared with 4 weeks, and there was a higher level of CD163 staining in the tendon midsubstance in the experimental group than in the control group at 4 weeks.

CONCLUSION

Stem cell application had a positive effect on fibrocartilage formation at the healing rotator cuff repair site. Both SOX9 and Ihh signaling appear to play an important role in the healing process.

The Effect of Purified Human Bone Marrow-Derived Mesenchymal Stem Cells on Rotator Cuff Tendon Healing in an Athymic Rat

PURPOSE

To evaluate the ability of purified human bone marrow-derived mesenchymal stem cells (MSCs) to augment healing of an acute small- to medium-sized rotator cuff repair in a small-animal model, evaluating the structure and composition of the healing tendon-bone interface with histologic and biomechanical analyses.

METHODS

Fifty-two athymic rats underwent unilateral detachment and transosseous repair of the supraspinatus tendon augmented with either fibrin glue (control group) or fibrin glue with 10⁶ human MSCs (experimental group) applied at the repair site. Flow cytometry verified the stem cell phenotype of the cells as CD73⁺, CD90⁺, CD105⁺, CD14^-, CD34^-, and CD45^-. Rats were killed at 2 and 4 weeks, with 10 from each group used for biomechanical testing and 3 for histologic analysis.

RESULTS

Safranin O staining identified increased fibrocartilage formation at the repair site at 2 weeks in the human MSC group (18.6% ± 2.9% vs 9.1% ± 1.6%, P = .026). Picrosirius staining identified decreased energy (36.88 ± 4.99 J vs 54.97 ± 8.33 J, P = .04) and increased coherence in the human MSC group (26.96% ± 15.32% vs 14.53% ± 4.10%, P = .05), indicating improved collagen orientation. Biomechanical testing showed a significant increase in failure load (11.5 ± 2.4 N vs 8.5 ± 2.4 N, P = .002) and stiffness (7.1 ± 1.2 N/mm vs 5.7 ± 2.1 N/mm, P < .001) in the experimental group compared with the control group at 2 weeks. These effects dissipated by 4 weeks, with no significant differences in fibrocartilage formation (35% ± 5.0% vs 26.6% ± 0.6%, P = .172) or biomechanical load to failure (24.6 ± 7.1 N vs 21.5 ± 4.1 N, P = .361) or stiffness (13.5 ± 3.1 N/mm vs 16.1 ± 5.6 N/mm, P = .384). All failures occurred at the bone-tendon interface.

CONCLUSIONS

Rotator cuff repair augmentation with purified human MSCs improved early histologic appearance and biomechanical strength of the repair at 2 weeks, although the effects dissipated by 4 weeks with no significant differences between groups.

CLINICAL RELEVANCE

Human MSCs may improve early rotator cuff healing during the first 2 weeks after repair.

Dendritic cells maintain dermal adipose-derived stromal cells in skin fibrosis

Scleroderma is a group of skin-fibrosing diseases for which there are no effective treatments. A feature of the skin fibrosis typical of scleroderma is atrophy of the dermal white adipose tissue (DWAT). Adipose tissue contains adipose-derived mesenchymal stromal cells (ADSCs) that have regenerative and reparative functions; however, whether DWAT atrophy in fibrosis is accompanied by ADSC loss is poorly understood, as are the mechanisms that might maintain ADSC survival in fibrotic skin. Here, we have shown that DWAT ADSC numbers were reduced, likely because of cell death, in 2 murine models of scleroderma skin fibrosis. The remaining ADSCs showed a partial dependence on dendritic cells (DCs) for survival. Lymphotoxin β (LTβ) expression in DCs maintained ADSC survival in fibrotic skin by activating an LTβ receptor/β1 integrin (LTβR/β1 integrin) pathway on ADSCs. Stimulation of LTβR augmented the engraftment of therapeutically injected ADSCs, which was associated with reductions in skin fibrosis and improved skin function. These findings provide insight into the effects of skin fibrosis on DWAT ADSCs, identify a DC-ADSC survival axis in fibrotic skin, and suggest an approach for improving mesenchymal stromal cell therapy in scleroderma and other diseases.

Indian hedgehog signaling and the role of graft tension in tendon-to-bone healing: Evaluation in a rat ACL reconstruction model

The structure and composition of the native enthesis is not recapitulated following tendon-to-bone repair. Indian Hedgehog (IHH) signaling has recently been shown to be important in enthesis development in a mouse model but no studies have evaluated IHH signaling in a healing model. Fourteen adult male rats underwent ACL reconstruction using a flexor tendon graft. Rats were assigned to two groups based on whether or not they received 0N or 10N of pre-tension of the graft. Specimens were evaluated at 3 and 6 weeks post-operatively using immunohistochemistry for three different protein markers of IHH signaling. Quantitative analysis of staining area and intensity using custom software demonstrated that IHH signaling was active in interface tissue formed at the healing tendon-bone interface. We also found increased staining area and intensity of IHH signaling proteins at 3 weeks in animals that received a pre-tensioned tendon graft. No significant differences were seen between the 3-week and 6-week time points. Our data suggests that the IHH signaling pathway is active during the tendon-bone healing process and appears to be mechanosensitive, as pre-tensioning of the graft at the time of surgery resulted in increased IHH signaling at three weeks.

[Ocular paraneoplastic syndrome: cancer-associated retinopathy]

CASE REPORT

We review a patient with ocular manifestations of a paraneoplastic syndrome. It was a cancer-associated retinopathy (CAR) in a woman with visual loss, and attenuated and sheathed retinal arterioles. The electroretinography (ERG) showed severe abnormalities of the a and b-waves. The tumour process was not discovered until 6 months later, when a squamous neoplasia that invaded the uterus and vagina was observed.

DISCUSSION

Paraneoplastic syndromes are a group of manifestations produced as a remote effect of cancer cells. CAR syndrome is caused by autoimmune reactions to retinal antigens induced by aberrant expression of recoverin in cancer tissues. Ophthalmologists must be aware of ocular paraneoplastic signs as they can be the first manifestations of a malignant tumour.

Nifedipine in rat liver cirrhosis

Rat liver cirrhosis induced by CCl4+ethanol was employed to assess the effectiveness of nifedipine in reducing liver injury. Nifedipine reduced the severity of hepatocellular necrosis, significantly decreased Mallory bodies (p < 0.01), decreased polymorphonuclear inflammatory infiltrate (p < 0.05) and reduced perivenular fibrosis. Plasma lactic acid levels were significantly increased in the CCl4+ethanol group (p < 0.01). Lactacidaemia remained at normal values when the calcium antagonist blocker was employed. Nifedipine did not significantly alter the incidence of cirrhosis in this experimental model.

[Ultrastructural study of the liver from rats treated with ethanol and/or carbon tetrachloride]

The cellular ultrastructure of isolated hepatocytes and hepatic tissue in ethanol and/or carbon tetrachloride treated rats at different times. The ultrastructural modifications induced by ethanol and carbon tetrachloride, isolated administrations, are similar: Many lipidic vacuoles, several graded-injury mitochondria and R. E. R. degeneration. These effects are also induced by ethanol and carbon tetrachloride association and furthermore nuclei indentations. Some mitochondrial autophagocytosis affecting to the less electrodense hepatocytes are noted.