Sensory Neuron-Specific Deletion of Tropomyosin Receptor Kinase A (TrkA) in Mice Abolishes Osteoarthritis (OA) Pain via NGF/TrkA Intervention of Peripheral Sensitization.

Tropomyosin receptor kinase A (TrkA/NTRK1) is a high-affinity receptor for nerve growth factor (NGF), a potent pain mediator. NGF/TrkA signaling elevates synovial sensory neuronal distributions in the joints and causes osteoarthritis (OA) pain. We investigated the mechanisms of pain transmission as to whether peripheral sensory neurons are linked to the cellular plasticity in the dorsal root ganglia (DRG) and are critical for OA hyperalgesia. Sensory neuron-specific deletion of TrkA was achieved by tamoxifen injection in 4-week-old TrkAfl/fl;NaV1.8CreERT2 (Ntrk1 fl/fl;Scn10aCreERT2) mice. OA was induced by partial medial meniscectomy (PMM) in 12-week-old mice, and OA-pain-related behavior was analyzed for 12 weeks followed by comprehensive histopathological examinations. OA-associated joint pain was markedly improved without cartilage protection in sensory-neuron-specific conditional TrkA knock-out (cKO) mice. Alleviated hyperalgesia was associated with suppression of the NGF/TrkA pathway and reduced angiogenesis in fibroblast-like synovial cells. Elevated pain transmitters in the DRG of OA-induced mice were significantly diminished in sensory-neuron-specific TrkA cKO and global TrkA cKO mice. Spinal glial activity and brain-derived neurotropic factor (BDNF) were significantly increased in OA-induced mice but were substantially eliminated by sensory-neuron-specific deletion. Our results suggest that augmentation of NGF/TrkA signaling in the joint synovium and the peripheral sensory neurons facilitate pro-nociception and centralized pain sensitization.

Absence of VEGFR-1/Flt-1 signaling pathway in mice results in insensitivity to discogenic low back pain in an established disc injury mouse model.

Although degenerative disc disease (DDD) and related low back pain (LBP) are growing public health problems, the underlying disease mechanisms remain unclear. An increase in the vascular endothelial growth factor (VEGF) levels in DDD has been reported. This study aimed to examine the role of VEGF receptors (VEGFRs) in DDD, using a mouse model of DDD. Progressive DDD was induced by anterior stabbing of lumbar intervertebral discs in wild type (WT) and VEGFR-1 tyrosine-kinase deficient mice (vegfr-1TK-/- ). Pain assessments were performed weekly for 12 weeks. Histological and immunohistochemical assessments were made for discs, dorsal root ganglions, and spinal cord. Both vegfr-1TK-/- and WT mice presented with similar pathological changes in discs with an increased expression of inflammatory cytokines and matrix-degrading enzymes. Despite the similar pathological patterns, vegfr-1TK-/- mice showed insensitivity to pain compared with WT mice. This insensitivity to discogenic pain was related to lower levels of pain factors in the discs and peripheral sensory neurons and lower spinal glial activation in the vegfr-1TK- /- mice than in the WT mice. Exogenous stimulation of bovine disc cells with VEGF increased inflammatory and cartilage degrading enzyme. Silencing vegfr-1 by small-interfering-RNA decreased VEGF-induced expression of pain markers, while silencing vegfr-2 decreased VEGF-induced expression of inflammatory and metabolic markers without changing pain markers. This suggests the involvement of VEGFR-1 signaling specifically in pain transmission. Collectively, our results indicate that the VEGF signaling is involved in DDD. Particularly, VEGFR-1 is critical for discogenic LBP transmission independent of the degree of disc pathology.

Development of an in vivo mouse model of discogenic low back pain.

Discogenic low back pain (DLBP) is extremely common and costly. Effective treatments are lacking due to DLBP's unknown pathogenesis. Currently, there are no in vivo mouse models of DLBP, which restricts research in this field. The aim of this study was to establish a reliable DLBP model in mouse that captures the pathological changes in the disc and allows longitudinal pain testing. The model was generated by puncturing the mouse lumbar discs (L4/5, L5/6, and L6/S1) and removing the nucleus pulposus using a microscalpel under the microscope. Histology, molecular pathways, and pain-related behaviors were examined. Over 12 weeks post-surgery, animals displayed the mechanical, heat, and cold hyperalgesia along with decreased burrowing and rearing. Histology showed progressive disc degeneration with loss of disc height, nucleus pulposus reduction, proteoglycan depletion, and annular fibrotic disorganization. Immunohistochemistry revealed a substantial increase in inflammatory mediators at 2 and 4 weeks. Nerve growth factor was upregulated from 2 weeks to the end of the experiment. Nerve fiber ingrowth was induced in the injured discs after 4 weeks. Disc-puncture also produced an upregulation of neuropeptides in dorsal root ganglia neurons and an activation of glial cells in the spinal cord dorsal horn. These findings indicate that the cellular and structural changes in discs, as well as peripheral and central nervous system plasticity, paralleled persistent, and robust behavioral pain responses. Therefore, this mouse DLBP model could be used to investigate mechanisms underlying discogenic pain, thereby facilitating effective drug screening and development of treatments for DLBP.

Syndecan 4 signaling and intervertebral disc degeneration.

This commentary highlights the article by Wang et al, exploring the regulatory relationship between matrix metalloproteinase-3 and syndecan 4 in disc degeneration.

Enhancing Bone Healing through Localized Cold Therapy in a Murine Femoral Fracture Model.

Fracture healing, a critical and complex biological process, often presents challenges in clinical practice with the current standards failing to fully address the medical needs for rapid and effective recovery. In this work, a localized cold therapy is investigated as an alternative approach to expedite bone healing. We hypothesized that optimized cold application can enhance bone healing within a fracture model by inducing hypoxia, leading to accelerated angiogenesis along with improved osteogenesis. A short, localized cold exposure is directly applied to the fracture site over a four-week period in a mouse fracture model, aiming to assess its impact on bone formation through mechanisms of angiogenesis and osteogenesis. Our results revealed a significantly greater volume of new bone tissue and enhanced vascularity at the fracture site in the cold-treated group compared to controls. Calcified tissue histology analysis showed that the accelerated callus maturation and development of the vascular network following cold exposure were associated with an activity increase of alkaline phosphatase (ALP) and transient receptor potential vanilloid 1 (TRPV1). These biological changes were accompanied by a hypoxic environment induced during cold therapy. The study provides compelling evidence supporting the efficacy of intermittent cold therapy in accelerating fracture healing. These promising results highlight the need for further research in larger-scale studies and diverse fracture models, underlining the potential of cold therapy as a novel, non-invasive treatment strategy in orthopedic care.

Cobalt ions induce a cellular senescence secretory phenotype in human synovial fibroblast-like cells that may be an early event in the development of adverse local tissue reactions to hip implants.

Objectives: Total hip arthroplasty is a successful procedure for treating advanced osteoarthritis (OA). Metal bearing surfaces remain one of the most widely implanted prosthesis, however approximately 10% of patients develop adverse local tissue reactions (ALTRs), namely lymphocytic predominant soft tissue reaction with or without necrosis and osteolysis resulting in high revision rates. The mechanism(s) for these reactions remains unclear although T lymphocyte mediated type IV hypersensitivity to cobalt (Co) and chromium (Cr) ions have been described. The purpose of this study was to determine the prolonged effects of Co and Cr metal ions on synovial fibroblasts to better understand the impact of the synovial membrane in the development of ALTRs. Methods: Human synovial fibroblast-like cells were isolated from donors undergoing arthroplasty. DNA content and Alamar blue assay were used to determine cellular viability against exposure to Co and Cr. A beta-galactosidase assay was used to determine the development of cellular senescence. Western blotting and RT-qPCR were employed to determine changes in senescent associated secretory factors, signaling and anti-oxidant enzyme expression. A fluorescent assay was used to measure accumulation of hydrogen peroxide. Results: We demonstrate that prolonged cobalt exposure results in a downregulation of the enzyme catalase resulting in cytosolic accumulation of hydrogen peroxide, decreased Akt activity and cellular senescence. Senescent fibroblasts demonstrated upregulation of proinflammatory cytokines IL-1ß and TNFα in addition to the neurotrophic factor NGF. Conclusion: Our results provide evidence that metal ions induce a senescent associated secretory phenotype in synovial fibroblasts that could contribute to the development of adverse local tissue reactions.

Nanoparticle-based inhibition of vascular endothelial growth factor receptors alleviates osteoarthritis pain and cartilage damage.

Osteoarthritis (OA) is characterized by cartilage damage, inflammation, and pain. Vascular endothelial growth factor receptors (VEGFRs) have been associated with OA severity, suggesting that inhibitors targeting these receptors alleviate pain (via VEGFR1) or cartilage degeneration (via VEGFR2). We have developed a nanoparticle-based formulation of pazopanib (Votrient), an FDA-approved anticancer drug that targets both VEGFR1 and VEGFR2 (Nano-PAZII). We demonstrate that a single intraarticular injection of Nano-PAZII can effectively reduce joint pain for a prolonged time without substantial side effects in two different preclinical OA rodent models involving either surgical (upon partial medial meniscectomy) or nonsurgical induction (with monoiodoacetate). The injection of Nano-PAZII blocks VEGFR1 and relieves OA pain by suppressing sensory neuronal ingrowth into the knee synovium and neuronal plasticity in the dorsal root ganglia and spinal cord. Simultaneously, the inhibition of VEGFR2 reduces cartilage degeneration. These findings provide a mechanism-based disease-modifying drug strategy that addresses both pain symptoms and cartilage loss in OA.

Loss of PKCδ/Prkcd prevents cartilage degeneration in joints but exacerbates hyperalgesia in an experimental osteoarthritis mouse model.

Pain is the prime symptom of osteoarthritis (OA) that directly affects the quality of life. Protein kinase Cδ (PKCδ/Prkcd) plays a critical role in OA pathogenesis; however, its significance in OA-related pain is not entirely understood. The present study investigated the functional role of PKCδ in OA pain sensation. OA was surgically induced in control (Prkcdfl/fl), global- (Prkcdfl/fl; ROSACreERT2), and sensory neuron-specific conditional knockout (cKO) mice (Prkcdfl/fl; NaV1.8/Scn10aCreERT2) followed by comprehensive analysis of longitudinal behavioral pain, histopathology and immunofluorescence studies. GlobalPrkcd cKO mice prevented cartilage deterioration by inhibiting matrix metalloproteinase-13 (MMP13) in joint tissues but significantly increased OA pain. Sensory neuron-specificdeletion of Prkcd in mice did not protect cartilage from degeneration but worsened OA-associated pain. Exacerbated pain sensitivity observed in global- and sensory neuron-specific cKO of Prkcd was corroborated with markedly increased specific pain mediators in knee synovium and dorsal root ganglia (DRG). These specific pain markers include nerve growth factor (NGF) and vascular endothelial growth factor (VEGF), and their cognate receptors, including tropomyosin receptor kinase A (TrkA) and vascular endothelial growth factor receptor-1 (VEGFR1). The increased levels of NGF/TrkA and VEGF/VEGFR1 were comparable in both global- and sensory neuron-specific cKO groups. These data suggest that the absence of Prkcd gene expression in the sensory neurons is strongly associated with OA hyperalgesia independent of cartilage protection. Thus, inhibition of PKCδ may be beneficial for cartilage homeostasis but could aggravate OA-related pain symptoms.

Analysis of quantitative magnetic resonance imaging and biomechanical parameters on human discs with different grades of degeneration.

PURPOSE: To establish relationships between quantitative MRI (qMRI) and biomechanical parameters in order to help inform and interpret alterations of human intervertebral discs (IVD) with different grades of degeneration. MATERIALS AND METHODS: The properties of the nucleus pulposus (NP) and annulus fibrosus (AF) of each IVD of 10 lumbar spines (range, 32-77 years) were analyzed by qMRI (relaxation times T1 and T2, magnetization transfer ratio [MTR], and apparent diffusion coefficient [ADC]), and tested in confined compression and dynamic shear. RESULTS: T1 and T2 significantly decreased in both the NP and AF with increasing degeneration grades while the MTR increased significantly with grade 4. In contrast to the other qMRI parameters, the ADC had a tendency to decrease with increasing grade. Disc degeneration caused a decrease in the aggregate modulus, hydraulic permeability and shear modulus magnitude along with an increase in phase angle in the AF. In contrast, disc degeneration of NPs demonstrated decreases in shear modulus and phase angle. CONCLUSION: Our studies indicate that qMRI can be used as a noninvasive diagnostic tool in the detection of IVD properties with the potential to help interpret and detect early, middle, and late stages of degeneration. QMRI of human IVD can therefore become a very important diagnostic assessment tool in determining the functional state of the disc.

Best paper NASS 2013: link-N can stimulate proteoglycan synthesis in the degenerated human intervertebral discs.

Intervertebral disc (IVD) degeneration is the most common cause of back pain. Presently there is no medical treatment, leaving surgery as the only offered option. Here we evaluate the potential of Link-N to promote extracellular matrix regeneration in human IVDs. Human disc cells cultured in alginate and intact human discs were exposed to a combination of Link-N and ³5SO4 in the presence or absence of interleukin (IL)-1, and the effect on proteoglycan synthesis was evaluated. In addition, message levels of aggrecan, matrix metalloproteinase (MMP)-3, MMP-13, a Disintegrin And Metalloproteinase with Thrombospondin Motifs (ADAMTS)-4 and ADAMTS-5 were evaluated in alginate cultures. Human disc cells responded in a dose dependent manner with maximal proteoglycan synthesis at 1 µg/mL Link-N. Link-N treatment also induced proteoglycan synthesis in intact human discs, and a prolonged effect was found up to one week after Link-N treatment. Message levels of proteinases were decreased by Link-N in the presence of IL-1. Thus, Link-N can promote proteoglycan synthesis and deplete proteinase expression in adult human discs. Link-N could therefore be a promising candidate for biologically-induced disc repair, and could provide an alternative to surgical intervention for early stage disc degeneration.

Opiate Antagonists for Chronic Pain: A Review on the Benefits of Low-Dose Naltrexone in Arthritis versus Non-Arthritic Diseases.

Chronic pain conditions create major financial and emotional burdens that can be devastating for individuals and society. One primary source of pain is arthritis, a common inflammatory disease of the joints that causes persistent pain in affected people. The main objective of pharmacological treatments for either rheumatoid arthritis (RA) or osteoarthritis (OA) is to reduce pain. Non-steroidal anti-inflammatory drugs, opioids, and opioid antagonists have each been considered in the management of chronic pain in arthritis patients. Naltrexone is an oral-activated opioid antagonist with biphasic dose-dependent pharmacodynamic effects. The molecule acts as a competitive inhibitor of opioid receptors at high doses. However, naltrexone at low doses has been shown to have hormetic effects and provides relief for chronic pain conditions such as fibromyalgia, multiple sclerosis (MS), and inflammatory bowel disorders. Current knowledge of naltrexone suggests that low-dose treatments may be effective in the treatment of pain perception in chronic inflammatory conditions observed in patients with either RA or OA. In this review, we evaluated the therapeutic benefits of low-dose naltrexone (LDN) on arthritis-related pain conditions.

Mechanisms and clinical implications of intervertebral disc calcification.

Low back pain is a leading cause of disability worldwide. Intervertebral disc (IVD) degeneration is often associated with low back pain but is sometimes asymptomatic. IVD calcification is an often overlooked disc phenotype that might have considerable clinical impact. IVD calcification is not a rare finding in ageing or in degenerative and scoliotic spinal conditions, but is often ignored and under-reported. IVD calcification may lead to stiffer IVDs and altered segmental biomechanics, more severe IVD degeneration, inflammation and low back pain. Calcification is not restricted to the IVD but is also observed in the degeneration of other cartilaginous tissues, such as joint cartilage, and is involved in the tissue inflammatory process. Furthermore, IVD calcification may also affect the vertebral endplate, leading to Modic changes (non-neoplastic subchondral vertebral bone marrow lesions) and the generation of pain. Such effects in the spine might develop in similar ways to the development of subchondral marrow lesions of the knee, which are associated with osteoarthritis-related pain. We propose that IVD calcification is a phenotypic biomarker of clinically relevant disc degeneration and endplate changes. As IVD calcification has implications for the management and prognosis of degenerative spinal changes and could affect targeted therapeutics and regenerative approaches for the spine, awareness of IVD calcification should be raised in the spine community.

Effect of nitrogen-rich cell culture surfaces on type X collagen expression by bovine growth plate chondrocytes.

BACKGROUND: Recent evidence indicates that osteoarthritis (OA) may be a systemic disease since mesenchymal stem cells (MSCs) from OA patients express type X collagen, a marker of late stage chondrocyte hypertrophy (associated with endochondral ossification). We recently showed that the expression of type X collagen was suppressed when MSCs from OA patients were cultured on nitrogen (N)-rich plasma polymer layers, which we call "PPE:N" (N-doped plasma-polymerized ethylene, containing up to 36 atomic percentage (at.% ) of N. METHODS: In the present study, we examined the expression of type X collagen in fetal bovine growth plate chondrocytes (containing hypertrophic chondrocytes) cultured on PPE:N. We also studied the effect of PPE:N on the expression of matrix molecules such as type II collagen and aggrecan, as well as on proteases (matrix metalloproteinase-13 (MMP-13) and molecules implicated in cell division (cyclin B2). Two other culture surfaces, "hydrophilic" polystyrene (PS, regular culture dishes) and nitrogen-containing cation polystyrene (Primaria®), were also investigated for comparison. RESULTS: Results showed that type X collagen mRNA levels were suppressed when cultured for 4 days on PPE:N, suggesting that type X collagen is regulated similarly in hypertrophic chondrocytes and in human MSCs from OA patients. However, the levels of type X collagen mRNA almost returned to control value after 20 days in culture on these surfaces. Culture on the various surfaces had no significant effects on type II collagen, aggrecan, MMP-13, and cyclin B2 mRNA levels. CONCLUSION: Hypertrophy is diminished by culturing growth plate chondrocytes on nitrogen-rich surfaces, a mechanism that is beneficial for MSC chondrogenesis. Furthermore, one major advantage of such "intelligent surfaces" over recombinant growth factors for tissue engineering and cartilage repair is potentially large cost-saving.

Tungsten Increases Sex-Specific Osteoclast Differentiation in Murine Bone.

Tungsten is a naturally occurring metal that is increasingly used in industry and medical devices, and is labeled as an emerging environmental contaminant. Like many metals, tungsten accumulates in bone. Our previous data indicate that tungsten decreases differentiation of osteoblasts, bone-forming cells. Herein, we explored the impact of tungsten on osteoclast differentiation, which function in bone resorption. We observed significantly elevated osteoclast numbers in the trabecular bone of femurs following oral exposure to tungsten in male, but not female mice. In order to explore the mechanism(s) by which tungsten increases osteoclast number, we utilized in vitro murine primary and cell line pre-osteoclast models. Although tungsten did not alter the adhesion of osteoclasts to the extracellular matrix protein, vitronectin, we did observe that tungsten enhanced RANKL-induced differentiation into tartrate-resistant acid phosphatase (TRAP)-positive mononucleated osteoclasts. Importantly, tungsten alone had no effect on differentiation or on the number of multinucleated TRAP-positive osteoclasts. Enhanced RANKL-induced differentiation correlated with increased gene expression of differentiated osteoclast markers Nfatc1, Acp5, and Ctsk. Although tungsten did not alter the RANK surface receptor expression, it did modulate its downstream signaling. Co-exposure of tungsten and RANKL resulted in sustained positive p38 signaling. These findings demonstrate that tungsten enhances sex-specific osteoclast differentiation, and together with previous findings of decreased osteoblastogenesis, implicate tungsten as a modulator of bone homeostasis.

Patient-Specific Functional Analysis: The Key to the Next Revolution Towards the Treatment of Hip and Knee Osteoarthritis.

Lower extremity joint arthroplasty surgery remains one of the most successful interventions in orthopaedics. While improvements in patient mobility and physical functioning following surgery are well-documented, there remains significant post-operative functional deficits in many patients. This highlights a need and an opportunity towards improving functional and patient-reported outcomes of arthroplasty surgery. This review summarizes key opportunities arising from the recent 2018 Orthopaedic Research Society Meeting in New Orleans, USA. In this review, the Canadian Orthopaedic Research Society (i.e., CORS) highlights key research advances, case examples, scientific messages, and personalized medical care approaches toward improving physical functioning in our knee and hip joint arthroplasty patients. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1754-1759, 2019.

Injectable Chitosan Hydrogels with Enhanced Mechanical Properties for Nucleus Pulposus Regeneration.

IMPACT STATEMENT: A thermosensitive chitosan-based hydrogel was developed, which mimics the mechanical properties of the human nucleus pulposus (NP) tissue and provides a suitable environment for seeded NP cells to live and produce glycosaminoglycans. This scaffold is injectable through 25G needle and rapidly gels in vivo at body temperature. It has the potential to restore mechanical properties and stimulate biological repair of the degenerated intervertebral disc (IVD). It could therefore be used for the minimally invasive treatment of degenerated IVD, which affects more than one person out of five in the world.

Quantitative MRI as a diagnostic tool of intervertebral disc matrix composition and integrity.

Degenerative disc disease has been implicated as a major component of spine pathology. The current major clinical procedures for treating disc degeneration have been disappointing, because of altered spinal mechanics leading to subsequent degeneration at adjacent disc levels. Disc pathology treatment is shifting toward prevention and treatment of underlying etiologic processes at the level of the disc matrix composition and integrity and the biomechanics of the disc. The ability to perform such treatment relies on one's ability to accurately and objectively assess the state of the matrix and the effectiveness of treatment by a non-invasive technique. In this review, we will summarize our advances in efforts to develop an objective, accurate, non-invasive diagnostic tool (quantitative MRI) in the detection and quantification of matrix composition and integrity and of biomechanical changes in early intervertebral disc degeneration.

Link N as a therapeutic agent for discogenic pain.

Neurotrophins (NTs) are the major contributors of sensory axonal sprouting, neural survival, regulation of nociceptive sensory neurons, inflammatory hyperalgesia, and neuropathic pain. Intervertebral disc (IVD) cells constitutively express NTs. Their expression is upregulated by proinflammatory cytokines present in the IVD during degeneration, which can promote peripheral nerve ingrowth and hyperinnervation, leading to discogenic pain. Currently, there are no targeted therapies that decrease hyperinnervation in degenerative disc disease. Link N is a naturally occurring peptide with a high regenerative potential in the IVD. Therefore, the suitability of Link N as a therapeutic peptide for suppressing NTs, which are known modulators and mediators of pain, was investigated. The aim of the present study is to determine the effect of Link N on NTs expression, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and their cognate receptors TrkA and TrkB as they are directly correlated with symptomatic back pain. Furthermore, the neurotransmitter (substance P) was also evaluated in human annulus fibrosus (AF) cells stimulated with cytokines. Human AF cells isolated from normal IVDs were stimulated with interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) in the presence or absence of Link N. NGF release in the media was evaluated by Western blotting. Total RNA was isolated and gene expression was measured using real-time PCR. Gene expression of NGF, BDNF, TrkA, and TrkB significantly decreased in human disc cells stimulated with either IL-1ß or TNF-α supplemented with Link N when compared to the cells stimulated only with IL-1ß or TNF-α. NGF protein expression was also suppressed in AF cells coincubated with Link N and IL-1ß when compared to the cells stimulated only with IL-1ß. Link N can suppress the stimulation of NGF, BDNF, and their receptors TrkA and TrkB in AF cells in an inflammatory milieu. Thus, coupled with previous observations, this suggests that administration of Link N has the potential to not only repair the discs in early stages of the disease but also suppress pain.

Leaping the hurdles in developing regenerative treatments for the intervertebral disc from preclinical to clinical.

Chronic back and neck pain is a prevalent disability, often caused by degeneration of the intervertebral disc. Because current treatments for this condition are less than satisfactory, a great deal of effort is being applied to develop new solutions, including regenerative strategies. However, the path from initial promising idea to clinical use is fraught with many hurdles to overcome. Many of the keys to success are not necessarily linked to science or innovation. Successful translation to clinic will also rely on planning and awareness of the hurdles. It will be essential to plan your entire path to clinic from the outset and to do this with a multidisciplinary team. Take advice early on regulatory aspects and focus on generating the proof required to satisfy regulatory approval. Scientific demonstration and societal benefits are important, but translation cannot occur without involving commercial parties, which are instrumental to support expensive clinical trials. This will only be possible when intellectual property can be protected sufficiently to support a business model. In this manner, commercial, societal, medical, and scientific partners can work together to ultimately improve patient health. Based on literature surveys and experiences of the co-authors, this opinion paper presents this pathway, highlights the most prominent issues and hopefully will aid in your own translational endeavors.

Short Link N promotes disc repair in a rabbit model of disc degeneration.

BACKGROUND: The degeneration of the intervertebral disc (IVD) is characterized by proteolytic degradation of the extracellular matrix, and its repair requires the production of an extracellular matrix with a high proteoglycan-to-collagen ratio characteristic of a nucleus pulposus (NP)-like phenotype in vivo. At the moment, there is no medical treatment to reverse or even retard disc degeneration. The purpose of the present study was to determine if a low dose of short link N (sLN), a recently discovered fragment of the link N peptide, could behave in a manner similar to that of link N in restoring the proteoglycan content and proteoglycan-to-collagen ratio of the disc in a rabbit model of IVD degeneration, as an indication of its potential therapeutic benefit in reversing disc degeneration. METHODS: Adolescent New Zealand white rabbits received an annular puncture with an 18-gauge needle into two noncontiguous discs to induce disc degeneration. Two weeks later, either saline (10 µL) or sLN (25 µg in 10 µL saline) was injected into the center of the NP. The sLN concentration was empirically chosen at a lower molar concentration equivalent to half that of link N (100 µg in 10 µL). The effect on radiographic, biochemical and histologic changes were evaluated. RESULTS: Following needle puncture, disc height decreased by about 25-30% within 2 weeks and maintained this loss for the duration of the 12-week study; a single 25-µg sLN injection at 2 weeks partially restored this loss in disc height. sLN injection led to an increase in glycosaminoglycans (GAG) content 12 weeks post-injection in both the NP and annulus fibrosus (AF). There was a trend towards maintaining control disc collagen-content with sLN supplementation and the GAG-to-collagen ratio in the NP was increased when compared to the saline group. CONCLUSIONS: When administered to the degenerative disc in vivo, sLN injection leads to an increase in proteoglycan content and a trend towards maintaining control disc collagen content in both the NP and AF. This is similar to link N when it is administered to the degenerative disc. Thus, pharmacologically, sLN supplementation could be a novel therapeutic approach for treating disc degeneration.