Contrast enhanced μCT imaging of early articular changes in a pre-clinical model of osteoarthritis

Temporal progression of subchondral bone alterations in OA models involving induction of compromised meniscus integrity in mice and rats: A scoping review

OBJECTIVE

To categorize the temporal progression of subchondral bone alterations induced by compromising meniscus integrity in mouse and rat models of knee osteoarthritis (OA).

METHOD

Scoping review of investigations reporting subchondral bone changes with appropriate negative controls in the different mouse and rat models of OA induced by compromising meniscus integrity.

RESULTS

The available literature provides appropriate temporal detail on subchondral changes in these models, covering the entire spectrum of OA with an emphasis on early and mid-term time points. Microstructural changes of the subarticular spongiosa are comprehensively described; those of the subchondral bone plate are not. In mouse models, global subchondral bone alterations are unidirectional, involving an advancing sclerosis of the trabecular structure over time. In rats, biphasic subchondral bone alterations begin with an osteopenic degeneration and loss of subchondral trabeculae, progressing to a late sclerosis of the entire subchondral bone. Rat models, independently from the applied technique, relatively faithfully mirror the early bone loss detected in larger animals, and the late subchondral bone sclerosis observed in human advanced OA.

CONCLUSION

Mice and rats allow us to study the microstructural consequences of compromising meniscus integrity at high temporal detail. Thickening of the subchondral bone plate, an early loss of thinner subarticular trabecular elements, followed by a subsequent sclerosis of the entire subchondral bone are all important and reliable hallmarks that occur in parallel with the advancing articular cartilage degeneration. Thoughtful decisions on the study design, laterality, selection of controls and volumes of interest are crucial to obtain meaningful data.

Mild exercise expedites joint clearance and slows joint degradation in a joint instability model of osteoarthritis in male rats

OBJECTIVE

Exercise remains a hallmark treatment for post-traumatic osteoarthritis (PTOA) and may maintain joint homeostasis in part by clearing inflammatory cytokines, cells, and particles. It remains largely unknown whether exercise-induced joint clearance can provide therapeutic relief of PTOA. In this study, we hypothesized that exercise could slow the progression of preclinical PTOA in part by enhancing knee joint clearance.

DESIGN

Surgical medial meniscal transection was used to induce PTOA in 3-month-old male Lewis rats. A sham surgery was used as a control. Mild treadmill walking was introduced 3 weeks post-surgery and maintained to 6 weeks post-surgery. Gait and isometric muscle torque were measured at the study endpoint. Near-infrared imaging tracked how exercise altered lymphatic and venous knee joint clearance during discrete time points of PTOA progression.

RESULTS

Exercise mitigated joint degradation associated with PTOA by preserving glycosaminoglycan content and reducing osteophyte volume (effect size (95% Confidence Interval (CI)); 1.74 (0.71-2.26)). PTOA increased hind step widths (0.57 (0.18-0.95) cm), but exercise corrected this gait dysfunction (0.54 (0.16-0.93) cm), potentially indicating pain relief. Venous, but not lymphatic, clearance was quicker 1-, 3-, and 6-weeks post-surgery compared to baseline. The mild treadmill walking protocol expedited lymphatic clearance rate in moderate PTOA (3.39 (0.20-6.59) hrs), suggesting exercise may play a critical role in restoring joint homeostasis.

CONCLUSIONS

We conclude that mild exercise has the potential to slow disease progression in part by expediting joint clearance in moderate PTOA.

Intra-articular delivery of micronized dehydrated human amnion/chorion membrane reduces degenerative changes after onset of post-traumatic osteoarthritis

Background: Micronized dehydrated human amnion/chorion membrane (mdHACM) has reduced short term post-traumatic osteoarthritis (PTOA) progression in rats when delivered 24 h after medial meniscal transection (MMT) and is being investigated for clinical use as a disease modifying therapy. Much remains to be assessed, including its potential for longer-term therapeutic benefit and treatment effects after onset of joint degeneration. Objectives: Characterize longer-term effects of acute treatment with mdHACM and determine whether treatment administered to joints with established PTOA could slow or reverse degeneration. Hypotheses: Acute treatment effects will be sustained for 6 weeks, and delivery of mdHACM after onset of joint degeneration will attenuate structural osteoarthritic changes. Methods: Rats underwent MMT or sham surgery (left leg). mdHACM was delivered intra-articularly 24 h or 3 weeks post-surgery (n = 5-7 per group). Six weeks post-surgery, animals were euthanized and left tibiae scanned using equilibrium partitioning of an ionic contrast agent microcomputed tomography (EPIC-µCT) to structurally quantify joint degeneration. Histology was performed to examine tibial plateau cartilage. Results: Quantitative 3D µCT showed that cartilage structural metrics (thickness, X-ray attenuation, surface roughness, exposed bone area) for delayed mdHACM treatment limbs were significantly improved over saline treatment and not significantly different from shams. Subchondral bone mineral density and thickness for the delayed treatment group were significantly improved over acute treated, and subchondral bone thickness was not significantly different from sham. Marginal osteophyte degenerative changes were decreased with delayed mdHACM treatment compared to saline. Acute treatment (24 h post-surgery) did not reduce longer-term joint tissue degeneration compared to saline. Histology supported µCT findings and further revealed that while delayed treatment reduced cartilage damage, chondrocytes displayed qualitatively different morphologies and density compared to sham. Conclusion: This study provides insight into effects of intra-articular delivery timing relative to PTOA progression and the duration of therapeutic benefit of mdHACM. Results suggest that mdHACM injection into already osteoarthritic joints can improve joint health, but a single, acute mdHACM injection post-injury does not prevent long term osteoarthritis associated with meniscal instability. Further work is needed to fully characterize the durability of therapeutic benefit in stable osteoarthritic joints and the effects of repeated injections.

Quantitative evaluation of very early cartilage damage in experimental osteoarthritis using scanning electron microscopy

OBJECTIVE

To describe parametric changes observed using scanning electron microscopy (SEM) in very early stages in posttraumatic osteoarthritis (OA) models in mice.

METHODS

Mice (5/group) had their knees subjected to anterior cruciate ligament transection (ACLT), ACLT plus meniscectomy (MNCT) or sham surgery, sacrificed after 3, 7 or 14 days, had the articular cartilage evaluated under optical microscopy using Osteoarthritis Research Society International (OARSI) parameters as well as cartilage thickness, roughness, and a damage index using SEM.

RESULTS

Alterations of the cartilage under optical microscopy were not significantly relevant among groups. SEM analysis revealed reduction of femoral and tibial cartilage thickness in ACLT and MNCT groups at 7 and 14 days, with increased cartilage roughness in MNCT group as early as 3 days postsurgery, being sustained up to 14 days. Articular damage index was significantly higher at 14 days post surgery in ACLT and MNCT vs control groups.

CONCLUSION

This is the first demonstration of very early quantitative changes in the cartilage of mice subjected to posttraumatic experimental OA using SEM, revealing increased roughness and thickness as early as 3 days post surgery. These changes may be used as early surrogates for later joint damage in experimental OA.

NSAIDs Reduce Therapeutic Efficacy of Mesenchymal Stromal Cell Therapy in a Rodent Model of Posttraumatic Osteoarthritis

BACKGROUND

Intra-articular injections of human mesenchymal stromal cells (hMSCs) have shown promise in slowing cartilage degradation in posttraumatic osteoarthritis (PTOA). Clinical use of cell therapies for osteoarthritis has accelerated in recent years without sufficient scientific evidence defining best-use practices. Common recommendations advise patients to avoid nonsteroidal anti-inflammatory drug (NSAID) use before and after cell injection over concerns that NSAIDs may affect therapeutic efficacy. Recommendations to restrict NSAID use are challenging for patients, and it is unclear if patients are compliant.

HYPOTHESIS

NSAIDs will reduce the efficacy of hMSC therapy in treating a preclinical model of PTOA.

STUDY DESIGN

Controlled laboratory study.

METHODS

Lewis rats underwent medial meniscal transection (MMT) surgery to induce PTOA or a sham (sham group) surgery that did not progress to PTOA. Rats received naproxen solution orally daily before (Pre-NSAID group) or after (Post-NSAID group) hMSC treatment, throughout the course of the experiment (Full-NSAID group), or received hMSCs without NSAIDs (No NSAID). Cartilage morphology and composition were quantified using contrast-enhanced micro-computed tomography and histology. Pain (secondary allodynia) was measured using a von Frey filament.

RESULTS

Injection of hMSCs attenuated cartilage degeneration associated with MMT. hMSCs prevented proteoglycan loss, maintained smooth cartilage surfaces, reduced cartilage lesions, reduced mineralized osteophyte formation, and reduced pain by week 7. The Pre-NSAID group had decreased proteoglycan levels compared with the hMSC group, although there were no other significant differences. Thus, pretreatment with NSAIDs had minimal effects on the therapeutic benefits of hMSC injections. The Post-NSAID and Full-NSAID groups, however, exhibited significantly worse osteoarthritis than the hMSC-only group, with greater proteoglycan loss, surface roughness, osteophyte volume, and pain.

CONCLUSION

Use of NSAIDs before hMSC injection minimally reduced the therapeutic benefits for PTOA, which included preservation of cartilage surface integrity as well as a reduction in osteophytes. Use of NSAIDs after injections, however, substantially reduced the therapeutic efficacy of cellular treatment.

CLINICAL RELEVANCE

Our data support the clinical recommendation of avoiding NSAID use after hMSC injection but suggest that using NSAIDs before treatment may not substantially diminish the therapeutic efficacy of cell treatment.

Sodium alginate microencapsulation of human mesenchymal stromal cells modulates paracrine signaling response and enhances efficacy for treatment of established osteoarthritis

Mesenchymal stromal cells (MSCs) have shown promise as osteoarthritis (OA) treatments; however, effective translation has been limited by high variability and heterogeneity of MSCs, suboptimal delivery strategies, and poor understanding of critical quality and potency attributes. Furthermore, most pre-clinical studies of MSC therapeutics for OA have focused on delaying OA development and not on treating established OA, which brings added clinical relevance. Thus, the objective of the current study was to assess the effects of sodium alginate microencapsulation on human MSC (hMSC) secretion of immunomodulatory cytokines in an OA microenvironment and therapeutic efficacy in treating established OA. A Medial Meniscal Transection (MMT) pre-clinical model of OA was implemented. Three weeks post-surgery, after OA was established, intra-articular injections of encapsulated hMSCs or nonencapsulated hMSCs were administered. Six weeks post-surgery, microstructural changes in the knee joint were quantified using microCT. Encapsulated hMSCs reduced articular cartilage degeneration and subchondral bone remodeling. A multiplexed immunoassay panel was used to profile the in vitro secretome of hMSCs in response to IL-1β. Nonencapsulated hMSCs showed an indiscriminate increase in all cytokines in response to IL-1β while encapsulated hMSCs showed a targeted secretory response with increased expression of pro-inflammatory (IL-1β, IL-6, IL-7, IL-8), anti-inflammatory (IL-1RA), and chemotactic (G-CSF, MDC, IP10) cytokines. These data show that sodium alginate microencapsulation can modulate hMSC paracrine signaling and enhance the therapeutic efficacy of the hMSCs in treating established OA. This cytokine profile provides a foundation for the identification of key factors affecting the overall potency of hMSC therapeutics for OA. STATEMENT OF SIGNIFICANCE: While there has been considerable interest in material based MSC encapsulation for treatment of OA, there are critical gaps in our translational understanding of these biomaterial-based technologies for OA. More specifically, previous studies have several important limitations: (1) they have been largely focused on preventing OA development, which limits their translational utility and (2) little prior work has been done to delineate potential routes/mechanisms by which material encapsulation alters MSC therapeutic action. In our manuscript, we aimed to fill these gaps in knowledge by testing the hypotheses that: (1) hMSC encapsulation can attenuate established disease progression, which is a more clinically relevant scenario and (2) hMSC encapsulation significantly changes the secreted paracrine factors from hMSCs.

Anionic Contrast-Enhanced MicroCT Imaging Correlates with Biochemical and Histological Evaluations of Osteoarthritic Articular Cartilage

This study addressed difficulties in evaluating osteoarthritis (OA) progression in species with thin cartilage. Feasibility of using short, nonequilibrium contrast-enhanced micro-computed tomography (CE-μCT) to evaluate the physical and biochemical properties of cartilage was investigated. A preliminary in vitro study using CE-μCT study was performed using bovine osteochondral blocks with intact, mildly damaged (fibrillated), or severely damaged (delaminated) cartilage. Delamination of the superficial zone resulted in elevated apparent density compared with intact cartilage after 10 minutes of anionic contrast exposure (P < 0.01). OA was induced by unilateral meniscal destabilization in n = 20 sheep divided into: early phase OA (n = 9) and late phase OA (n = 11), while n = 4 remained as naive controls. In vivo anionic nonequilibrium contrast CT of the operated stifle was conducted in the early phase sheep 13 weeks postoperatively using clinical resolution CT. Cartilage visibility in the contrasted leg was significantly improved compared with the noncontrasted contralateral stifle (P < 0.05). Animals were sacrificed at 3 months (early phase) or 12 months (late phase) for additional ex vivo CE-μCT, and correlative tests with biochemical and histological measures. Concentration of sulfated glycosaminoglycan (sGAG) significantly varied between control, early, and late phase OA (P < 0.005) and showed a negative (r = -0.56) relationship with apparent density in the medial tibial plateau (R2 = 0.28, P < 0.001). Histologically, parameters in proteoglycan and cartilage surface structure correlated with increasing attenuation. While previous studies have shown that CE-CT increases the apparent density of proteoglycan-depleted cartilage, we concluded that superficial zone disruption also contributes to this phenomenon.

Chondroprotective Effects of a Histone Deacetylase Inhibitor, Panobinostat, on Pain Behavior and Cartilage Degradation in Anterior Cruciate Ligament Transection-Induced Experimental Osteoarthritic Rats

Osteoarthritis (OA) is the most common articular degenerative disease characterized by chronic pain, joint inflammation, and movement limitations, which are significantly influenced by aberrant epigenetic modifications of numerous OA-susceptible genes. Recent studies revealed that both the abnormal activation and differential expression of histone deacetylases (HDACs) might contribute to OA pathogenesis. In this study, we investigated the chondroprotective effects of a marine-derived HDAC inhibitor, panobinostat, on anterior cruciate ligament transection (ACLT)-induced experimental OA rats. The intra-articular administration of 2 or 10 µg of panobinostat (each group, n = 7) per week from the 6th to 17th week attenuates ACLT-induced nociceptive behaviors, including secondary mechanical allodynia and weight-bearing distribution. Histopathological and microcomputed tomography analysis showed that panobinostat significantly prevents cartilage degeneration after ACLT. Moreover, intra-articular panobinostat exerts hypertrophic effects in the chondrocytes of articular cartilage by regulating the protein expressions of HDAC4, HDAC6, HDAC7, runt-domain transcription factor-2, and matrix metalloproteinase-13. The study indicated that HDACs might have different modulations on the chondrocyte phenotype in the early stages of OA development. These results provide new evidence that panobinostat may be a potential therapeutic drug for OA.

Spectral CT imaging of human osteoarthritic cartilage via quantitative assessment of glycosaminoglycan content using multiple contrast agents

Detection of early osteoarthritis to stabilize or reverse the damage to articular cartilage would improve patient function, reduce disability, and limit the need for joint replacement. In this study, we investigated nondestructive photon-processing spectral computed tomography (CT) for the quantitative measurement of the glycosaminoglycan (GAG) content compared to destructive histological and biochemical assay techniques in normal and osteoarthritic tissues. Cartilage-bone cores from healthy bovine stifles were incubated in 50% ioxaglate (Hexabrix^®) or 100% gadobenate dimeglumine (MultiHance^®). A photon-processing spectral CT (MARS) scanner with a CdTe-Medipix3RX detector imaged samples. Calibration phantoms of ioxaglate and gadobenate dimeglumine were used to determine iodine and gadolinium concentrations from photon-processing spectral CT images to correlate with the GAG content measured using a dimethylmethylene blue assay. The zonal distribution of GAG was compared between photon-processing spectral CT images and histological sections. Furthermore, discrimination and quantification of GAG in osteoarthritic human tibial plateau tissue using the same contrast agents were demonstrated. Contrast agent concentrations were inversely related to the GAG content. The GAG concentration increased from 25 μg/ml (85 mg/ml iodine or 43 mg/ml gadolinium) in the superficial layer to 75 μg/ml (65 mg/ml iodine or 37 mg/ml gadolinium) in the deep layer of healthy bovine cartilage. Deep zone articular cartilage could be distinguished from subchondral bone by utilizing the material decomposition technique. Photon-processing spectral CT images correlated with histological sections in healthy and osteoarthritic tissues. Post-imaging material decomposition was able to quantify the GAG content and distribution throughout healthy and osteoarthritic cartilage using Hexabrix^® and MultiHance^® while differentiating the underlying subchondral bone.

Anatomy, variation, and asymmetry of the bronchial tree in the African grey parrot (Psittacus erithacus)

The avian bronchial tree has a unique and elaborate architecture for the maintenance of unidirectional airflow. Gross descriptions of this bronchial arrangement have traditionally relied upon dissection and casts of the negative (air-filled) spaces. In this study, the bronchial trees of five deceased African grey parrots (Psittacus erithacus) were segmented from micro-computed tomography (μCT) scans into three-dimensional (3D) surface models, and then compared. Select metrics of the primary bronchi and major secondary branches in the μCT scans of 11 specimens were taken to assess left-right asymmetry and quantify gross lung structure. Analysis of the 3D surface models demonstrates variation in the number and distribution of secondary bronchi with consistent direct connections to specific respiratory air sacs. A single model of the parabronchi further reveals indirect connections to all but two of the nine total air sacs. Statistical analysis of the metrics show significant left-right asymmetry between the primary bronchi and the origins of the first four secondary bronchi (the ventrobronchi), consistently greater mean values for all right primary bronchus length metrics, and relatively high coefficients of variation for cross-sectional area metrics of the primary bronchi and secondary bronchi ostia. These findings suggest that the lengths of the primary bronchi distal to the ventrobronchi do not preserve lung symmetry, and that aerodynamic valving can functionally accommodate a wide range of bronchial proportions.

Articular Cartilage- and Synoviocyte-Binding Poly(ethylene glycol) Nanocomposite Microgels as Intra-Articular Drug Delivery Vehicles for the Treatment of Osteoarthritis

Intra-articular (IA) injection is an attractive route of administration for the treatment of osteoarthritis (OA). However, free drugs injected into the joint space are rapidly cleared and many of them can induce adverse off-target effects on different IA tissues. To overcome these limitations, we designed nanocomposite 4-arm-poly(ethylene glycol)-maleimide (PEG-4MAL) microgels, presenting cartilage- or synoviocyte-binding peptides, containing poly(lactic-co-glycolic) acid (PLGA) nanoparticles (NPs) as an IA small molecule drug delivery system. Microgels containing rhodamine B (model drug)-loaded PLGA NPs were synthesized using microfluidics technology and exhibited a sustained, near zero-order release of the fluorophore over 16 days in vitro. PEG-4MAL microgels presenting synoviocyte- or cartilage-targeting peptides specifically bound to rabbit and human synoviocytes or to bovine articular cartilage in vitro, respectively. Finally, using a rat model of post-traumatic knee OA, PEG-4MAL microgels were shown to be retained in the joint space for at least 3 weeks without inducing any joint degenerative changes as measured by EPIC-μCT and histology. Additionally, all microgel formulations were found trapped in the synovial membrane and significantly increased the IA retention time of a model small molecule near-infrared (NIR) dye compared to that of the free dye. These results suggest that peptide-functionalized nanocomposite PEG-4MAL microgels represent a promising intra-articular vehicle for tissue-localized drug delivery and prolonged IA drug retention for the treatment of OA.

Effects of treadmill running and limb immobilization on knee cartilage degeneration and locomotor joint kinematics in rats following knee meniscal transection

OBJECTIVE

This study examined the effects of reduced and elevated weight bearing on post-traumatic osteoarthritis (PTOA) development, locomotor joint kinematics, and degree of voluntary activity in rats following medial meniscal transection (MMT).

DESIGN

Twenty-one adult rats were subjected to MMT surgery of the left hindlimb and then assigned to one of three groups: (1) regular (i.e., no intervention), (2) hindlimb immobilization, or (3) treadmill running. Sham surgery was performed in four additional rats. Voluntary wheel run time/distance was measured, and 3D hindlimb kinematics were quantified during treadmill locomotion using biplanar radiography. Rats were euthanized 8 weeks after MMT or sham surgery, and the microstructure of the tibial cartilage and subchondral bone was quantified using contrast enhanced micro-CT.

RESULTS

All three MMT groups showed signs of PTOA (full-thickness lesions and/or increased cartilage volume) compared to the sham group, however the regular and treadmill-running groups had greater osteophyte formation than the immobilization group. For the immobilization group, increased volume was only observed in the anterior region of the cartilage. The treadmill-running group demonstrated a greater knee varus angle at mid-stance than the sham group, while the immobilization group demonstrated greater reduction in voluntary running than all the other groups at 2 weeks post-surgery.

CONCLUSIONS

Elevated weight-bearing via treadmill running at a slow/moderate speed did not accelerate PTOA in MMT rats when compared to regular weight-bearing. Reduced weight-bearing via immobilization may attenuate overall PTOA but still resulted in regional cartilage degeneration. Overall, there were minimal differences in hindlimb kinematics and voluntary running between MMT and sham rats.

Reduced Size Profile of Amniotic Membrane Particles Decreases Osteoarthritis Therapeutic Efficacy

Osteoarthritis (OA) is a widespread disease that continues to lack approved and efficacious treatments that modify disease progression. Micronized dehydrated human amnion/chorion membrane (μ-dHACM) has been shown to be effective in reducing OA progression, but many of the engineering design parameters have not been explored. The objectives of this study were to characterize the particle size distributions of two μ-dHACM formulations and to investigate the influence of these distributions on the in vivo therapeutic efficacy of μ-dHACM. Male Lewis rats underwent medial meniscus transection (MMT) or sham surgery, and intra-articular injections of saline, μ-dHACM, or reduced particle size μ-dHACM (RPS μ-dHACM) were administered at 24 hours postsurgery (n = 9 per treatment group). After 3 weeks, the animals were euthanized, and left legs harvested for equilibrium partitioning of an ionic contrast agent microcomputed tomography and histological analysis. μ-dHACM and RPS μ-dHACM particles were fluorescently tagged and particle clearance was tracked in vivo for up to 42 days postsurgery. Protein elution from both formulations was quantified in vitro. Treatment with μ-HACM, but not RPS μ-dHACM, reduced lesion volume in the MMT model 3 weeks postsurgery. In contrast, RPS μ-dHACM increased cartilage surface roughness and osteophyte cartilage thickness and volume compared to saline treatment. There was no difference of in vivo fluorescently tagged particle clearance between the two μ-dHACM sizes. RPS μ-dHACM showed significantly greater protein elution in vitro over 21 days. Overall, delivery of RPS μ-dHACM did result in an increase of in vivo joint degeneration and in vitro protein elution compared to μ-dHACM, but did not result in differences in joint clearance in vivo. These results suggest that particle size and factor elution may be tailorable factors that are important to optimize for particulate amniotic membrane treatment to be an effective therapy for OA. Impact Statement Osteoarthritis (OA) is a widespread disease that continues to lack treatments that modify the progression of the disease. Micronized dehydrated human amnion/chorion membrane (μ-dHACM) has been shown to be effective in reducing OA progression, but many of the engineering design parameters have not been explored. This work investigates the effects of particle size profile of the μ-dHACM particles and lays out the methods used in these studies. The results of this work will guide engineers in designing μ-dHACM treatments specifically and disease-modifying OA therapeutics generally, and it demonstrates the utility of novel therapeutic evaluation methods such as contrast-enhanced microcomputed tomography.

Activation of mTORC1 in subchondral bone preosteoblasts promotes osteoarthritis by stimulating bone sclerosis and secretion of CXCL12

Increasing evidences show that aberrant subchondral bone remodeling plays an important role in the development of osteoarthritis (OA). However, how subchondral bone formation is activated and the mechanism by which increased subchondral bone turnover promotes cartilage degeneration during OA remains unclear. Here, we show that the mechanistic target of rapamycin complex 1 (mTORC1) pathway is activated in subchondral bone preosteoblasts (Osterix+) from OA patients and mice. Constitutive activation of mTORC1 in preosteoblasts by deletion of the mTORC1 upstream inhibitor, tuberous sclerosis 1, induced aberrant subchondral bone formation, and sclerosis with little-to-no effects on articular cartilage integrity, but accelerated post-traumatic OA development in mice. In contrast, inhibition of mTORC1 in preosteoblasts by disruption of Raptor (mTORC1-specific component) reduced subchondral bone formation and cartilage degeneration, and attenuated post-traumatic OA in mice. Mechanistically, mTORC1 activation promoted preosteoblast expansion and Cxcl12 secretion, which induced subchondral bone remodeling and cartilage degeneration during OA. A Cxcl12-neutralizing antibody reduced cartilage degeneration and alleviated OA in mice. Altogether, these findings demonstrate that mTORC1 activation in subchondral preosteoblasts is not sufficient to induce OA, but can induce aberrant subchondral bone formation and secrete of Cxcl12 to accelerate disease progression following surgical destabilization of the joint. Pharmaceutical inhibition of the pathway presents a promising therapeutic approach for OA treatment.

Full-thickness rotator cuff tear in rat results in distinct temporal expression of multiple proteases in tendon, muscle, and cartilage

The etiology of joint tissue degeneration following rotator cuff tear remains unclear. Thus, the purpose of this study was to understand the timeline of protease activity in the soft tissues of the shoulder (tendon, muscle, and cartilage) that may lead to down-stream degeneration following rotator cuff tear. A well-established rat model involving suprascapular nerve denervation and supraspinatus/infraspinatus tendon transection was employed. Histological staining and/or micro-computed tomography (µCT) were used to observe structural damage in the supraspinatus tendon and muscle, humeral head cartilage, and subchondral bone. Multiplex gelatin zymography was utilized to assess protease activity in the supraspinatus tendon and muscle, and humeral head cartilage. Zymography analysis demonstrated that cathepsins were upregulated in the first week in all tissues, while MMP-2 maintained prolonged activity in supraspinatus tendon between 1 and 3 weeks and increased only at 3 weeks in supraspinatus muscle. In supraspinatus tendon, increased cathepsin L and MMP-2 activity in the first week was concurrent with matrix disorganization and infiltration of inflammatory cells. In contrast, significant upregulation of cathepsin L and K activity in supraspinatus muscle and humeral head cartilage did not correspond to any visible tissue damage at 1 week. However, focal defects developed in half of all animals' humeral head cartilage by 12 weeks (volume: 0.12 ± 0.09 mm³ ). This work provides a more comprehensive understanding of biochemical changes to joint tissue over time following rotator cuff tear. Overall, this provides insight into potential therapeutic targets and will better inform ideal intervention times and treatments for each tissue. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:490-502, 2019.

Therapeutic efficacy of intra-articular delivery of encapsulated human mesenchymal stem cells on early stage osteoarthritis

Mesenchymal stem cells (MSCs) represent a great therapeutic promise in pre-clinical models of osteoarthritis (OA), but many questions remain as to their therapeutic mechanism of action: engraftment versus paracrine action. Encapsulation of human MSCs (hMSCs) in sodium alginate microspheres allowed for the paracrine signaling properties of these cells to be isolated and studied independently of direct cellular engraftment. The objective of the present study was to quantitatively assess the efficacy of encapsulated hMSCs as a disease-modifying therapeutic for OA, using a medial meniscal tear (MMT) rat model. It was hypothesized that encapsulated hMSCs would have a therapeutic effect, through paracrine-mediated action, on early OA development. Lewis rats underwent MMT surgery to induce OA. 1 d post-surgery, rats received intra-articular injections of encapsulated hMSCs or controls (i.e., saline, empty capsules, non-encapsulated hMSCs). Microstructural changes in the knee joint were quantified using equilibrium partitioning of a ionic contrast agent based micro-computed tomography (EPIC-μCT) at 3 weeks post-surgery, an established time point for early OA. Encapsulated hMSCs significantly attenuated MMT-induced increases in articular cartilage swelling and surface roughness and augmented cartilaginous and mineralized osteophyte volumes. Cellular encapsulation allowed to isolate the hMSC paracrine signaling effects and demonstrated that hMSCs could exert a chondroprotective therapeutic role on early stage OA through paracrine signaling alone. In addition to this chondroprotective role, encapsulated hMSCs augmented the compensatory increases in osteophyte formation. The latter should be taken into strong consideration as many clinical trials using MSCs for OA are currently ongoing.