Osteoarthritis is one of the leading causes of chronic pain, but almost nothing is known about the mechanisms and molecules that mediate osteoarthritis-associated joint pain. Consequently, treatment options remain inadequate and joint replacement is often inevitable. Here, we use a surgical mouse model that captures the long-term progression of knee osteoarthritis to longitudinally assess pain-related behaviors and concomitant changes in the innervating dorsal root ganglia (DRG). We demonstrate that monocyte chemoattractant protein (MCP)-1 (CCL2) and its high-affinity receptor, chemokine (C-C motif) receptor 2 (CCR2), are central to the development of pain associated with knee osteoarthritis. After destabilization of the medial meniscus, mice developed early-onset secondary mechanical allodynia that was maintained for 16 wk. MCP-1 and CCR2 mRNA, protein, and signaling activity were temporarily up-regulated in the innervating DRG at 8 wk after surgery. This result correlated with the presentation of movement-provoked pain behaviors, which were maintained up to 16 wk. Mice that lack Ccr2 also developed mechanical allodynia, but this started to resolve from 8 wk onwards. Despite severe allodynia and structural knee joint damage equal to wild-type mice, Ccr2-null mice did not develop movement-provoked pain behaviors at 8 wk. In wild-type mice, macrophages infiltrated the DRG by 8 wk and this was maintained through 16 wk after surgery. In contrast, macrophage infiltration was not observed in Ccr2-null mice. These observations suggest a key role for the MCP-1/CCR2 pathway in establishing osteoarthritis pain.O steoarthritis is the most common joint disorder and is one of the leading causes of chronic pain (1, 2). Osteoarthritis commonly affects knees, hips, and hands and is characterized by radiographic changes (primarily joint space narrowing, subchondral bone sclerosis, and osteophytes) accompanied by clinical symptoms, most prominently pain. Treatments that alter the progression of the structural damage in the joint are not yet available. Options for treating the pain include nonsteroidal anti-inflammatory drugs, steroids, and viscosupplementation, but analgesia is often inadequate, and uncontrolled pain is the number one reason why people with osteoarthritis undergo joint-replacement surgery (3). Despite the enormous health and economic burden of osteoarthritis and associated pain (4), very few studies have examined the molecular pathways that mediate osteoarthritis pain. As in all types of chronic pain, osteoarthritis pain is the dynamic result of a complex interaction between local tissue damage and inflammation, peripheral and central sensitization, and the brain (5-7). Joint pain associated with osteoarthritis, however, has unique clinical features that provide insight into the mechanisms that cause it. First, joint pain has a strong mechanical component: it is typically triggered by specific activities (for example, climbing stairs elicits knee pain) and is relieved by rest. As structural joint disease advance...

Rotator cuff repair is known to have a high failure rate. Little is known about the natural healing process of the rotator cuff repair site, hence little can be done to improve the tendon's ability to heal. The purpose of this study was to investigate the collagen formation at the early repair site and to localize TGFb-1 and 3 during early healing and compare their levels to cell proliferation and histological changes. Bilateral supraspinatus tendons were transected and repaired in 60 rats. Specimens were harvested and evaluated at 0, 1, 3, 7, 10, 28, and 56 days. Histological sections were evaluated for cell morphology. Immunohistochemistry and in situ hybridization was performed to localize protein and mRNA for collagen types I and III and TGFb-1 and 3. Proliferating cell nuclear antigen (PCNA) assay was performed to measure cell proliferation, and cells were counted to determine cell density. Biomechanical properties were evaluated. Repair tissue demonstrated an initial inflammatory response with multinucleated cells present at 1 and 3 days, and lymphocytes and plasma cells presents at 7 and 10 days. Capillary proliferation began at 3 days and peaked at 10 days. Ultimate force increased significantly over the time period studied. Collagen I protein and mRNA significantly increased at 10 days, and reached a plateau by 28 and 56 days. Collagen III showed a similar trend, with an early increase, and remained high until 56 days. TGFb-1 was localized to the forming scar tissue and showed a distinct peak at 10 days. TGFb-3 was not seen at the healing insertion site. Cell proliferation and density followed the same trend as TGFb-1. A wound healing response does occur at the healing rotator cuff insertion site, however, the characteristics of the tendon after healing differ significantly from the uninjured tendon insertion site at the longest time-point studied. A distinctive collagen remodeling process occurred with an initial increase in the formation of collagen types I and III followed by a decrease toward baseline levels seen at time 0. Growth factor TGFb-1 was localized to repair tissue and coincided with a peak in cell proliferation and cellularity. Repair sites remained unorganized histologically and biomechanically inferior in comparison to previously described uninjured insertion sites. ß

Physical environment influences the development and maintenance of musculoskeletal tissues. The current study uses an animal model to explore the role of the physical environment on the postnatal development of the supraspinatus tendon enthesis. A supraspinatus intramuscular injection of botulinum toxin A was used to paralyze the left shoulders of mice at birth. The supraspinatus muscles of right shoulders were injected with saline to serve as contralateral controls. The supraspinatus enthesis was examined after 14, 21, 28, and 56 days of postnatal development. Histologic assays were used to examine fibrocartilage morphology and percentage osteoclast surface. Micro-computed tomography was used to examine muscle geometry and bone architecture. At 14 days there were no differences between groups in fibrocartilage formation, muscle geometry, bone architecture, or osteoclast surface. When comparing groups at 21, 28, and 56 days, muscle volume was decreased, fibrocartilage development was delayed, mineralized bone was decreased, and osteoclast surface was higher at each timepoint in the botulinum group compared to the contralateral saline control group. Our results indicate that the development of the tendon enthesis is sensitive to its mechanical environment. A reduction in muscle loading delayed the development of the tendonto-bone insertion site by impeding the accumulation of mineralized bone. Physical factors did not play a significant role in enthesis maturation in the first 14 days postnatally, implying that biologic factors may drive early postnatal development. ß

The purpose of this study was to promote fibroblast proliferation and collagen remodeling in flexor tendon repair through sustained delivery of platelet derived growth factor (PDGF-BB). The release kinetics of PDGF-BB from a novel fibrin matrix delivery system was initially evaluated in vitro. After the in vivo degradation rate of the fibrin matrix was determined using fluorescently tagged fibrin, PDGF-BB was delivered to the site of flexor tendon repair in vivo in a canine model. The effect of PDGF-BB on intrasynovial tendon healing was studied using histology-based assays (cell density, proliferation, and type I collagen expression) and by measuring total DNA levels and reducible collagen crosslink levels. The fibrin matrix delivery system provided sustained release of PDGF-BB in vitro at a rate modulated by the ratio of heparin to growth factor. In vivo, the fibrin matrix remained at the repair site for more than 10 days. Delivery of PDGF-BB led to a qualitative increase in cell density, cell proliferation, and type I collagen mRNA expression. PDGF-BB also led to statistically significant increases in total DNA (20% increase at 7 days, 18% increase at 14 days) and reducible collagen crosslinks (30% increase at 7 days). Sustained delivery of growth factors may be achieved using a novel fibrin-based delivery system. PDGF-BB delivery increased cell proliferation and matrix remodeling and thus may accelerate flexor tendon healing. ß

No abstract

A fibrin/heparin-based delivery system was used to provide controlled delivery of platelet derived growth factor BB (PDGF-BB) in an animal model of intrasynovial flexor tendon repair. We hypothesized that PDGF-BB, administered in this manner, would stimulate cell proliferation and matrix remodeling, leading to improvements in the sutured tendon's functional and structural properties. Fifty-six flexor digitorum profundus tendons were injured and repaired in 28 dogs. Three groups were compared: (1) controlled delivery of PDGF-BB using a fibrin/heparin-based delivery system; (2) delivery system carrier control; and (3) repair-only control. The operated forelimbs were treated with controlled passive motion rehabilitation. The animals were euthanized at 7, 14, and 42 days, at which time the tendons were assessed using histologic (hyaluronic acid content, cellularity, and inflammation), biochemical (total DNA and reducible collagen crosslink levels), and biomechanical (gliding and tensile properties) assays. We found that cell activity (as determined by total DNA, collagen crosslink analyses, and hyaluronic acid content) was accelerated due to PDGF-BB at 14 days. Proximal interphalangeal joint rotation and tendon excursion (i.e., tendon gliding properties) were significantly higher for the PDGF-BB-treated tendons compared to the repair-alone tendons at 42 days. Improvements in tensile properties were not achieved, possibly due to suboptimal release kinetics or other factors. In conclusion, PDGF-BB treatment consistently improved the functional but not the structural properties of sutured intrasynovial tendons through 42 days following repair. ß

No abstract

Although basic fibroblast growth factor accelerated the cell-proliferation phase of tendon healing, it also promoted neovascularization and inflammation in the earliest stages following the suturing of the tendon. Despite a substantial biologic response, the administration of basic fibroblast growth factor failed to produce improvements in either the mechanical or functional properties of the repair. Rather, increased cellular activity resulted in peritendinous scar formation and diminished range of motion.