Characterization of a new animal model for evaluation and treatment of back pain due to lumbar facet joint osteoarthritis

Mechanical crosstalk between the intervertebral disc, facet joints, and vertebral endplate following acute disc injury in a rabbit model

Background

Vertebral endplate sclerosis and facet osteoarthritis have been documented in animals and humans. However, it is unclear how these adjacent pathologies engage in crosstalk with the intervertebral disc. This study sought to elucidate this crosstalk by assessing each compartment individually in response to acute disc injury.

Methods

Eleven New Zealand White rabbits underwent annular disc puncture using a 16G or 21G needle. At 4 and 10 weeks, individual compartments of the motion segment were analyzed. Discs underwent T 1 relaxation mapping with MRI contrast agent gadodiamide as well T 2 mapping. Both discs and facets underwent mechanical testing via vertebra-disc-vertebra tension-compression creep testing and indentation testing, respectively. Endplate bone density was quantified via μCT. Discs and facets were sectioned and stained for histology scoring.

Results

Intervertebral discs became more degenerative with increasing needle diameter and time post-puncture. Bone density also increased in endplates adjacent to both 21G and 16G punctured discs leading to reduced gadodiamide transport at 10 weeks. The facet joints, however, did not follow this same trend. Facets adjacent to 16G punctured discs were less degenerative than facets adjacent to 21G punctured discs at 10 weeks. 16G facets were more degenerative at 4 weeks than at 10, suggesting the cartilage had recovered. The formation of severe disc osteophytes in 16G punctured discs between 4 and 10 weeks likely offloaded the facet cartilage, leading to the recovery observed.

Conclusions

Overall, this study supports that degeneration spans the whole spinal motion segment following disc injury. Vertebral endplate thickening occurred in response to disc injury, which limited the diffusion of small molecules into the disc. This work also suggests that altered disc mechanics can induce facet degeneration, and that extreme bony remodeling adjacent to the disc may promote facet cartilage recovery through offloading of the articular cartilage.

Lumbar endplate microfracture injury induces Modic-like changes, intervertebral disc degeneration and spinal cord sensitization - an in vivo rat model

BACKGROUND CONTEXT

Endplate (EP) injury plays critical roles in painful IVD degeneration since Modic changes (MCs) are highly associated with pain. Models of EP microfracture that progress to painful conditions are needed to better understand pathophysiological mechanisms and screen therapeutics.

PURPOSE

Establish in vivo rat lumbar EP microfracture model and assess crosstalk between IVD, vertebra and spinal cord.

STUDY DESIGN/SETTING

In vivo rat EP microfracture injury model with characterization of IVD degeneration, vertebral remodeling, spinal cord substance P (SubP), and pain-related behaviors.

METHODS

EP-injury was induced in 5 month-old male Sprague-Dawley rats L4-5 and L5-6 IVDs by puncturing through the cephalad vertebral body and EP into the NP of the IVDs followed by intradiscal injections of TNFα (n=7) or PBS (n=6), compared with Sham (surgery without EP-injury, n=6). The EP-injury model was assessed for IVD height, histological degeneration, pain-like behaviors (hindpaw von Frey and forepaw grip test), lumbar spine MRI and μCT, and spinal cord SubP.

RESULTS

Surgically-induced EP microfracture with PBS and TNFα injection induced IVD degeneration with decreased IVD height and MRI T2 signal, vertebral remodeling, and secondary damage to cartilage EP adjacent to the injury. Both EP injury groups showed MC-like changes around defects with hypointensity on T1-weighted and hyperintensity on T2-weighted MRI, suggestive of MC type 1. EP injuries caused significantly decreased paw withdrawal threshold, reduced axial grip, and increased spinal cord SubP, suggesting axial spinal discomfort and mechanical hypersensitivity and with spinal cord sensitization.

CONCLUSIONS

Surgically-induced EP microfracture can cause crosstalk between IVD, vertebra, and spinal cord with chronic pain-like conditions.

CLINICAL SIGNIFICANCE

This rat EP microfracture model was validated to induce broad spinal degenerative changes that may be useful to improve understanding of MC-like changes and for therapeutic screening.

Level dependent alterations in human facet cartilage mechanics and bone morphometry with spine degeneration

The zygapophyseal joints of the spine, also known as the facet joints, are paired diarthrodial joints posterior to the intervertebral disc and neural elements. The pathophysiology of facet osteoarthritis (OA), as well as crosstalk between the disc and facets, remains largely understudied compared to disc degeneration. The purpose of this study was to characterize alterations to human facet cartilage and subchondral bone across a spectrum of degeneration and to investigate correlations between disc and facet degeneration. Human lumbar facet articular surfaces from six independent donors were subject to creep indentation mechanical testing to quantify cartilage mechanical properties, followed by microcomputed tomography (µCT) analyses for subchondral bone morphometry. The degenerative state of each articular surface was assessed via macroscopic scoring and via Osteoarthritis Research Society International histopathology scoring. Our data suggest reduced facet cartilage compressive and tensile moduli and increased permeability with increasing degenerative grade, particularly at the lower levels of the spine. µCT analyses revealed spinal level-dependent alterations to the subchondral bone, with an increase in trabecular bone at the L4-L5 level, but a decrease at the upper levels of the lumbar spine with increasing degenerative grade. Cortical bone volume fraction was generally decreased with increasing degenerative grade across spinal levels. Correlation analysis revealed several associations between quantitative measures of disc degeneration and facet OA. This study showed that alterations in the mechanical properties of facet cartilage and in the structural properties of facet subchondral bone correlated with aspects of disc degeneration and were highly dependent on spinal level.

Lumbar endplate microfracture injury induces Modic-like changes, intervertebral disc degeneration and spinal cord sensitization - An In Vivo Rat Model

BACKGROUND CONTEXT : Endplate (EP) injury plays critical roles in painful IVD degeneration since Modic changes (MCs) are highly associated with pain. Models of EP microfracture that progress to painful conditions are needed to better understand pathophysiological mechanisms and screen therapeutics. PURPOSE : Establish in vivo rat lumbar EP microfracture model with painful phenotype. STUDY DESIGN/SETTING : In vivo rat study to characterize EP-injury model with characterization of IVD degeneration, vertebral bone marrow remodeling, spinal cord sensitization, and pain-related behaviors. METHODS : EP-driven degeneration was induced in 5-month-old male Sprague-Dawley rats L4-5 and L5-6 IVDs through the proximal vertebral body injury with intradiscal injections of TNFα (n=7) or PBS (n=6), compared to Sham (surgery without EP-injury, n=6). The EP-driven model was assessed for IVD height, histological degeneration, pain-like behaviors (hindpaw von Frey and forepaw grip test), lumbar spine MRI and μCT analyses, and spinal cord substance P (SubP). RESULTS : EP injuries induced IVD degeneration with decreased IVD height and MRI T2 values. EP injury with PBS and TNFα both showed MC type1-like changes on T1 and T2-weighted MRI, trabecular bone remodeling on μCT, and damage in cartilage EP adjacent to the injury. EP injuries caused significantly decreased paw withdrawal threshold and reduced grip forces, suggesting increased pain sensitivity and axial spinal discomfort. Spinal cord dorsal horn SubP was significantly increased, indicating spinal cord sensitization. CONCLUSIONS : EP microfracture can induce crosstalk between vertebral bone marrow, IVD and spinal cord with chronic pain-like conditions. CLINICAL SIGNIFICANCE : This rat EP microfracture model of IVD degeneration was validated to induce MC-like changes and pain-like behaviors that we hope will be useful to screen therapies and improve treatment for EP-drive pain.

Establishment of a bipedal rat model of lumbar facet joint osteoarthritis using intraarticular injection of urinary plasminogen activator

Background

Previous studies have demonstrated that by injecting uPA into the lumbar facet joints (LFJ) of normal rats, a rat LFJOA animal model can be successfully established. However, there is no evidence that intraarticular injection of uPA can induce or much serious osteoarthritis in bipedal rats, which biomechanics is much more similar to human than normal rats. To investigate whether intraarticular injection of urinary plasminogen activator (uPA) can induce LFJOA and low back pain symptoms in bipedal rats.

Methods

An experimental study on the construction of a modified animal model of lumbar facet joints osteoarthritis (LFJOA) which biomechanics is similar to human. Sprague–Dawley rats were treated with intraarticular injection of uPA in the L5–L6 facet joints (uPA group, n = 15) or saline (saline group, n = 15). The forelimbs of both two group rats were amputated. Mechanical and thermal hyperalgesia in the ipsilateral hind paws were evaluated using von Frey hairs and a thermoalgesia instrument, respectively. Toluidine blue staining, hematoxylin–eosin staining, and immunohistochemical examination of the LFJ was performed.

Results

The saline group rats have not demonstrated significant osteoarthritis in rats LFJ after surgery. The uPA group has not been induced significantly higher mechanical and thermal hyperalgesia in comparison with the saline group. But intraarticular injection of uPA in biped rats induced significantly stronger articular cartilage damage, synovitis, and proliferation of synovial cells in the LFJ. Inflammatory factors such as iNOS, IL-1β, and TNF-a were more significantly expressed in bipedal rat injected with uPA (p < 0.05).

Conclusions

Intraarticular injection of uPA can induce LFJOA in bipedal rats, while upright posture does not induce osteoarthritis in rats LFJ in the short term.

Spontaneous Facet Joint Osteoarthritis in NFAT1-Mutant Mice: Age-Dependent Histopathologic Characteristics and Molecular Mechanisms

BACKGROUND

Facet joint (FJ) osteoarthritis (FJOA) is a widely prevalent spinal disorder but its pathogenesis remains unclear, largely due to the difficulties in conducting longitudinal human studies and lack of spontaneous-FJOA animal models for mechanistic investigations. This study aimed to investigate whether spontaneous FJOA occurs in mice bearing mutant NFAT1 (nuclear factor of activated T cells 1) transcription factor.

METHODS

The lumbar FJs of 50 NFAT1-mutant mice and of 50 wild-type control mice, of both sexes, were examined by histopathology, quantitative gene expression analysis, semiquantitative immunohistochemistry, and a novel FJOA scoring system for semiquantitative assessment of the histopathologic changes at 2, 6, 12, and 18 months of age. Age-dependent and tissue-specific histopathologic and gene or protein expression changes were analyzed statistically.

RESULTS

FJs in NFAT1-mutant mice displayed significantly increased expression of specific catabolic genes (p < 0.05) and proteins (p < 0.001) in cartilage and synovium as early as 2 months of age, followed by early osteoarthritic structural changes such as articular surface fissuring and chondro-osteophyte formation at 6 months. More severe cartilage lesions, osteophytes, subchondral bone changes, synovitis, and tissue-specific molecular alterations in FJs of NFAT1-mutant mice were observed at 12 and 18 months. Osteoarthritic structural changes were not detected in FJs of wild-type mice at any ages, although age-related cartilage degeneration was observed at 18 months. The novel FJOA scoring system had high intraobserver and interobserver reproducibility (correlation coefficients: r > 0.97). Whole-joint FJOA scoring showed significantly higher OA scores in FJs of NFAT1-mutant mice compared with wild-type mice at all time points (p = 0.0033 at 2 months, p = 0.0001 at 6 months, p < 0.0001 at 12 and 18 months).

CONCLUSIONS

This study has identified the NFAT1-mutant mouse as a novel animal model of spontaneous FJOA with age-dependent and slowly progressing osteoarthritic features, developed the first FJOA scoring system, and elucidated the molecular mechanisms of NFAT1 mutation-induced FJOA.

CLINICAL RELEVANCE

This murine FJOA model resembles the features of human FJOA and may provide new insights into the pathogenesis of and therapeutic strategies for FJOA in humans.

MMPs in tissues retrieved during surgery from patients with TMJ disorders relate to pain more than to radiological damage score

Orofacial pain is among the most common chronic pain conditions and can result from temporomandibular disorders (TMDs) of the temporomandibular joint (TMJ). Matrix metalloproteinases (MMPs) drive degeneration of TMJ tissues and likely mediate pain in TMJ disorders given their role in nociception. However, few studies have assessed MMPs in the TMJ innervated tissues nor in the context of pain. This study defined the extent of MMP-1, MMP-9, and MMP-2 in TMJ tissues from patients undergoing total joint replacement (TJR) or arthroplasty discectomy for painful TMJ disorders. Protein expression was probed by Western blot in TMJ disc and capsular ligaments taken during TJR (n = 6) or discectomy (n = 3) for osteoarthritis or internal derangement in an IRB-approved study. Pro- and active MMP-1, active MMP-9, and pro- and active MMP-2 are detectable. MMP-1 and MMP-9 correlate positively to each other (Kendall's τ = 0.63; p = 0.01), strengthening the hypothesis that they are mechanistically related in regulatory cascades. Active MMP-1 and active MMP-9 correlate positively with self-reported pain scores (τ ≥ 0.51; p ≤ 0.04), suggesting their involvement in peripheral nociception. Overall, neither MMPs nor pain correlate with the functional vertical opening of the jaw. MMP-1 varies with the observed stage of degeneration during surgery (p = 0.04). Neither overall MMPs nor pain correlate with the overall magnetic resonance imaging scores, corroborating the longstanding, but confounding, clinical observation that pain and radiological evidence of joint damage are not always related. Clinical significance: These findings suggest that MMPs mediate pain in innervated soft tissues and may be targets for diagnosing disease stage and treatments in painful TMJ disorders.

Experimentally induced spine osteoarthritis in rats leads to neurogenic inflammation within neurosegmentally linked myotomes

Naturally occurring spine osteoarthritis is clinically associated with the manifestation of chronic inflammatory muscle (myofascial) disease. The purpose of this study was to investigate the causal association between experimentally induced spine osteoarthritis and neurogenic inflammatory responses within neurosegmentally linked myotomes. Wistar Kyoto rats were randomly assigned to spine facet compression surgery (L4-L6) or sham surgery. Animals exposed to facet compression surgery demonstrated radiographic signs of facet-osteoarthritis (L4-L6 spinal levels) and sensory changes (allodynia, thermal hyperalgesia) at 7, 14 and 21 days post-intervention, consistent with the induction of central sensitization; no radiologic or sensory changes were observed after sham surgery. Increased levels of proinflammatory biomarkers including substance P (SP), calcitonin gene related peptide (CGRP), protease-activated receptor-2 (PAR2) and calcium/calmodulin dependent protein kinase II (CaMKII) were observed post-surgery within neurosegmentally-linked rectus femoris (L2-L5) muscle when compared to the non-segmentally linked biceps brachii (C4-C7) muscle; no differences were observed between muscles in the sham surgery group. These findings offer novel insight into the potential role of spine osteoarthritis and neurogenic inflammatory mechanisms in the pathophysiology of chronic inflammatory muscle (myofascial) disease.

Development of a novel rat model of lumbar facet joint osteoarthritis induced by persistent compressive injury

The aim of the present study was to develop a novel animal model of lumbar facet joint osteoarthritis induced by persistent compressive injury. An intraspinal compression spring was randomly implanted into either the L4/5 or the L5/6 spinal segments of 40 Sprague Dawley (SD) rats to induce compression. Sham-operations were used in the other segment of the same rats as the control levels. The animals were sacrificed at 7, 14, 28, 42 and 56 days after surgery, prior to the radiological confirmation of the spring location. Degeneration of the lumbar facet joints was evaluated by macroscopic observation in addition to histological and immunohistological analyses. The results of this present study revealed the absence of spring dislocation during the entire observation period. Macroscopic and Osteoarthritis Research Society International scores of the compression levels were found to be higher in the compression levels compared with those noted in the control levels (P<0.05). In addition, interleukin-1β and tumor necrosis factor-α expression in the compression levels were increased over time compared with those recorded in the control levels. In conclusion, persistent compressive injury may induce degeneration of the lumbar facet joint. This novel animal model could serve as a useful tool for further studies into the mechanisms of action and potential treatment of lumbar facet joint osteoarthritis.

BMSCs-Derived Exosomes Ameliorate Pain Via Abrogation of Aberrant Nerve Invasion in Subchondral Bone in Lumbar Facet Joint Osteoarthritis

Lumbar facet joint osteoarthritis (LFJ OA) is regarded as one of the common causes of low back pain (LBP). The pathogenesis and underlying mechanism of this disease are largely unknown, there is still no effective disease-modifying therapy. This study aims to investigate the efficacy of exosomes derived from bone marrow mesenchymal stem cells (BMSCs) on the pathogenesis and behavioral signs of LBP in the LFJ OA mouse model. The pathogenetic change in cartilage and aberrant nerve invasion in the subchondral bone of LFJ in a mouse model after treatment with BMSC-exosomes was evaluated. BMSC-exosomes could relieve pain via abrogation of aberrant CGRP-positive nerve and abnormal H-type vessel formation in the subchondral bone of LFJ. Moreover, BMSC-exosomes attenuated cartilage degeneration and inhibited tartrate-resistant acid phosphatase expression and RANKL-RANK-TRAF6 signaling activation to facilitate subchondral bone remodeling. These results indicated that BMSC-exosomes could relive behavioral signs of LBP and pathological processes in LFJ OA. BMSC-exosomes have a prominent protective effect and might be a potential therapeutic option for the treatment of LFJ OA causing LBP. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:670-679, 2020.

Salmon calcitonin exerts better preventive effects than celecoxib on lumbar facet joint degeneration and long-term tactile allodynia in rats

OBJECTIVE

To evaluate and compare the effects of salmon calcitonin (sCT) and celecoxib (CLX) on cartilage, subchondral bone and tactile allodynia in a rat model of lumbar facet joint (FJ) osteoarthritis (OA).

METHOD

Forty 3-month-old male Sprague-Dawley rats were randomly divided into four groups: 30 received surgical collagenase (type II) injections in the right L3-L6 facet joints followed by 8 weeks of treatment with normal saline, CLX or sCT, and the other 10 received sham surgery. Tactile allodynia, changes of cartilage and subchondral bone of the L4-L5 FJs, and serum biomarkers were analyzed for all rats.

RESULTS

Both sCT and CLX ameliorated cartilage lesions, significantly increased aggrecan expression and decreased caspase-3 expression. sCT also decreased the expression of a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4). According to the micro-computed tomography (micro-CT) analysis, sCT significantly improved microarchitecture parameters of subchondral bone and micro-CT score; and inhibited articular process hypertrophy. CLX showed better antihyperalgesic effects than sCT on days 3 and 7 postoperatively despite no statistical differences, whereas sCT possessed better analgesic effects than CLX on days 42 and 56. Besides, the sCT treatment reduced the elevated cartilage oligomeric matrix protein (COMP) concentration in rats injected with collagenase (type II).

CONCLUSIONS

Both sCT and CLX exerted preventive effects on FJ OA caused by collagenase (type II), but sCT showed more protective effects, particularly on maintaining cartilage metabolism, restraining the deterioration of the subchondral bone microarchitecture and tactile allodynia, and reducing serum COMP concentrations.

Unilateral Osteotomy of Lumbar Facet Joint Induces a Mouse Model of Lumbar Facet Joint Osteoarthritis

STUDY DESIGN

The lumbar facet joint (LFJ) osteoarthritis (OA) model that highly mimics the clinical conditions was established and evaluated.

OBJECTIVE

Here, we innovatively constructed and evaluated the aberrant mechanical loading-related LFJ OA model.

SUMMARY OF BACKGROUND DATA

LFJ is the only true synovial joint in a functional spinal unit in mammals. The LFJ osteoarthritis is considered to contribute 15% to 45% of low back pain. The establish of animal models highly mimicking the clinical conditions is a useful tool for the investigation of LFJ OA. However, the previously established animal models damaged the LFJ structure directly, which did not demonstrate the effect of aberrant mechanical loading on the development of LFJ osteoarthritis.

METHODS

In the present study, an animal model for LFJ degeneration was established by the unilateral osteotomy of LFJ (OLFJ) in L4/5 unit to induce the spine instability. Then, the change of contralateral LFJ was evaluated by morphological and molecular biological techniques.

RESULTS

We showed that the OLFJ induced instability accelerated the cartilage degeneration of the contralateral LFJ. Importantly, the SRμCT elucidated that the three-dimensional structure of the subchondral bone changed in contralateral LFJ, indicated as the abnormity of bone volume/total volume ratio (BV/TV), trabecular pattern factor (Tb. Pf), and the trabecular thickness (Tb. Th). Immunostaining further demonstrated the uncoupled osteoclastic bone resorption, and bone formation in the subchondral bone of contralateral LFJ, indicated as increased activity of osteoclast, osteoblast, and Type H vessels.

CONCLUSION

We develop a novel LFJ OA model demonstrating the effect of abnormal mechanical instability on the degeneration of LFJ. This LFJ degeneration model that highly mimics the clinical conditions is a valuable tool to investigate the LFJ osteoarthritis.

LEVEL OF EVIDENCE

N/A.

Velvet antler polypeptide partially rescue facet joint osteoarthritis-like phenotype in adult β-catenin conditional activation mice

BACKGROUND

Wnt/β-catenin signaling pathway is closely related to osteoarthritis. In our preliminary study, β-catenin conditional activation (cAct) mice that specifically over-express β-catenin gene in cartilage chondrocyte exhibits osteoarthritis-like phenotype in the lumbar disc and knee joint. Therefore, we used the mice to model FJ-OA and test the potential curative effect of Velvet Antler Polypeptide (VAP) on this mice model.

METHODS

We tested the effect of VAP on β-catenin conditional activation mice, and used Cre negative littermates as controls. Micro-CT, histology and histomorphometry analysis were performed to evaluate the curative effect of VAP on mice facet joint-like phenotype. Expression of β-catenin and collagen II was detected by immunohistochemistry (IHC) and western-blot., MMP13, ADAMTS4 and ADAMTS5 was detected by immunofluorescence (IF). RT-PCR analysis was preformed to detect mRNA expression of cartilage degrading enzymes, such as MMP13, ADAMTS4 and ADAMTS5.

RESULTS

Results of micro-CT (μCT) analysis showed that VAP could partially reverse lumbar disc osteophyte formation observed in β-catenin(ex3)^Col2ER mice. Histology data revealed VAP partially improved facet joint cartilage tissue invades. Histomorphometry analysis showed an increase in total cartilage area after VAP treatment. IHC show that VAP reduced β-catenin protein levels and moderately up-regulated collagen II protein levels. RT-PCR and IF data showed that VAP down-regulated the expression of extracellular matrix synthesis (ECM) degradation enzymes MMP13, ADAMTS4 and ADAMTS5.

CONCLUSION

Taken together, VAP may modulate ECM by inhibits MMP13, ADAMTS4 and ADAMTS5 via Wnt /β-catenin signaling pathway. Velvet Antler Polypeptide may be a potential medicine for FJ-OA.

The Effect of Mesenchymal Stem Cell Wharton's Jelly on Matrix Metalloproteinase-1 and Interleukin-4 Levels in Osteoarthritis Rat Model

BACKGROUND:

Osteoarthritis (OA) is generally considered a degenerative joint disease caused by biomechanical changes and the ageing process. In OA pathogenesis, the development of OA is thought to be regulated largely by excess matrix metalloproteinase (MMP), which contributes to the degradation of extracellular matrices such as MMP-1 and Interleukin-4.

AIM:

This study aims to prove the influence of Mesenchymal Stem Cell Wharton Jelly on decreasing MMP-1 levels and increasing IL-4 which is a specific target as a target component in cases of osteoarthritis in vivo.

MATERIAL AND METHODS:

This research is an experimental study with the design of Post-Test-Only Control Group Design. The sample consisted of 16 OA rats as a control group and 16 OA rats treated with MSC-WJ as a treatment group. OA induction is done by injection of monosodium iodoacetate (MIA) into the intra-articular right knee. Giving MSC-WJ is done in the third week after MIA induction. The serum MMP-1 and IL-4 levels were measured after 3 weeks treated with MSC-WJ using the ELISA method. The statistical test used is an independent t-test. The value of p < 0.05 was said to be statistically significant.

RESULTS:

The result showed that serum MMP-1 levels were higher in the group treated with MSC-WJ than in the control group (p < 0.05). Serum IL-4 levels were higher in the group treated with MSC-WJ than in the control group (p < 0.05).

CONCLUSION:

This study concluded that MSC-WJ increased MMP-1 levels and IL-4 levels in serum OA rats. MSC-WJ showed a negative effect on MMP-1 in the serum of OA rats.

Animal models for studying the etiology and treatment of low back pain

Chronic low back pain is a major cause of disability and health care costs. Effective treatments are inadequate for many patients. Animal models are essential to further understanding of the pain mechanism and testing potential therapies. Currently, a number of preclinical models have been developed attempting to mimic aspects of clinical conditions that contribute to low back pain (LBP). This review focused on describing these animal models and the main behavioral tests for assessing pain in each model. Animal models of LBP can be divided into the following five categories: Discogenic LBP, radicular back pain, facet joint osteoarthritis back pain, muscle-induced LBP, and spontaneous occurring LBP models. These models are important not only for enhancing our knowledge of how LBP is generated, but also for the development of novel therapeutic regimens to treat LBP in patients. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1305-1312, 2018.

Three-dimensional visualization and pathologic characteristics of cartilage and subchondral bone changes in the lumbar facet joint of an ovariectomized mouse model

BACKGROUND CONTEXT

Low back pain (LBP) is more prevalent among postmenopausal women than men. Ovariectomy (OVX) is an established animal model that mimics the estrogen deficiency of postmenopausal women. Little is known about the three-dimensional (3D) morphologic properties of cartilage and subchondral bone changes in the lumbar facet joint (LFJ) of an OVX mouse model.

PURPOSE

The purpose of this study was to characterize the 3D morphologic change of cartilage and subchondral bone in the LFJ of an OVX mouse model.

STUDY DESIGN

Three-dimensional visualization and a histologic study on degenerative changes in cartilage and subchondral bone in the LFJ of an OVX mouse model were conducted.

MATERIALS AND METHODS

Ovariectomy is performed to mimic postmenopausal changes in adult female mice. We present an imaging tool for 3D visualization of the pathologic characteristics of cartilage and subchondral bone changes LFJ degradation using propagation-based phase-contrast computed tomography (PPCT). The samples were further dissected, fixed, and stained for histologic examination.

RESULTS

Propagation-based phase-contrast computed tomography imaging provides a 3D visualization of altered cartilage with a simultaneous high detail of the subchondral bone abnormalities in an OVX LFJ model. A quantitative analysis demonstrated that the cartilage volume, the surface area, and thickness were decreased in the OVX group compared with the control group (p<.05). Meanwhile, these decreases were accompanied by an obvious destruction of the subchondral bone surface and a loss of trabecular bone in the OVX group (p<.05). The delineation of the 3D pathologic changes in the PPCT imaging was confirmed by a histopathologic method with Safranin-O staining. Tartrate-resistant acid phosphatase staining revealed an increased number of osteoclasts in the subchondral bone of the OVX mice compared with that of the control group.

CONCLUSIONS

These results demonstrated that a mouse model of OVX-induced LFJ osteoarthritis (OA)-like changes was successfully established and showed a good resemblance to the human OA pathology. Propagation-based phase-contrast computed tomography has great potential to becomea powerful 3D imaging method to comprehensively characterize LFJ OA and to effectively monitor therapeutics. Moreover, degenerative LFJ possesses a severe morphologic change in the subchondral bone, may be the source of postmenopausal LBP, and has the potential to be a novel therapeutic target for LBP treatment.

Transcriptional analysis of long non-coding RNAs in facet joint osteoarthritis

It is recognized that facet joint osteoarthritis (FJOA) is commonly induced by the degeneration of articular cartilage of the facet joint.

WITHDRAWN: 3D visualization and pathological characteristics of cartilage and subchondral bone changes in the lumbar facet joint of an Ovariectomized mouse model

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.spinee.2017.11.009. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Hyperlordosis is Associated With Facet Joint Pathology at the Lower Lumbar Spine

STUDY DESIGN

A retrospective study.

OBJECTIVE

Our study opted to clarify the remaining issues of lumbar lordosis (LL) with regard to (1) its physiological values, (2) age, (3) sex, and (4) facet joint (FJ) arthritis and orientation using computed tomography (CT) scans.

SUMMARY OF BACKGROUND DATA

Recent studies have questioned whether LL really decreases with age, but study sample sizes have been rather small and mostly been based on x-rays. As hyperlordosis increases the load transferred through the FJs, it seems plausible that hyperlordosis may lead to FJ arthritis at the lower lumbar spine.

METHODS

We retrospectively analyzed the CT scans of 620 individuals, with a mean age of 42.5 (range, 14-94) years, who presented to our traumatology department and underwent a whole-body CT scan, between 2008 and 2010. LL was evaluated between the superior endplates of L1 and S1. FJs of the lumbar spine were evaluated for arthritis and orientation between L2 and S1.

RESULTS

(1) The mean LL was 49.0 degrees (SD 11.1 degrees; range, 11.4-80.1 degrees). (2) LL increased with age and there was a significant difference in LL in our age groups (30 y and below, 31-50, 51-70, and ≥71 y and above) (P=0.02). (3) There was no significant difference in LL between females and males (50 and 49 degrees) (P=0.17). (4) LL showed a significant linear association with FJ arthritis [P=0.0026, OR=1.022 (1.008-1.036)] and sagittal FJ orientation at L5/S1 (P=0.001). In a logistic regression analysis, the cutoff point for LL was 49.4 degrees.

CONCLUSIONS

This is the largest CT-based study on LL and FJs. LL significantly increases with age. As a novelty finding, hyperlordosis is significantly associated with FJ arthritis and sagittal FJ orientation at the lower lumbar spine. Thus, hyperlordosis may present with back pain and patients may benefit from surgical correction, for example, in the setting of trauma.

Animal models of chronic pain: Advances and challenges for clinical translation

Chronic pain is a global problem that has reached epidemic proportions. An estimated 20% of adults suffer from pain, and another 10% are diagnosed with chronic pain each year (Goldberg and McGee, ). Despite the high prevalence of chronic pain (an estimated 1.5 billion people are afflicted worldwide), much remains to be understood about the underlying causes of this condition, and there is an urgent requirement for better pain therapies. The discovery of novel targets and the development of better analgesics rely on an assortment of preclinical animal models; however, there are major challenges to translating discoveries made in animal models to realized pain therapies in humans. This review discusses common animal models used to recapitulate clinical chronic pain conditions (such as neuropathic, inflammatory, and visceral pain) and the methods for assessing the sensory and affective components of pain in animals. We also discuss the advantages and limitations of modeling chronic pain in animals as well as highlighting strategies for improving the predictive validity of preclinical pain studies. © 2016 Wiley Periodicals, Inc.

Effects of intra-articular SHINBARO treatment on monosodium iodoacetate-induced osteoarthritis in rats

BACKGROUND

SHINBARO is a refined herbal formulation used to treat inflamed lesions and bone diseases. This study aimed to investigate the anti-osteoarthritic activities of intra-articular administration of SHINBARO and determine its underlying molecular mechanism in a monosodium iodoacetate (MIA)-induced osteoarthritis rat model.

METHODS

Male Sprague-Dawley rats received a single intra-articular injection of MIA into the infrapatellar ligament of the right knee. Subsequently, the rats were treated with normal saline, SHINBARO, and diclofenac once daily for 21 days. Rats treated with normal saline, but not MIA, comprised the control group. Histological changes in the femur of the MIA-induced osteoarthritis rat model were observed by micro-computed tomography scanning and staining with hematoxylin and eosin, and safranin-O fast green. Serum levels of PGE2 and anti-type II collagen antibodies in the MIA-induced osteoarthritis rat model were measured using commercial kits. Protein levels of inflammatory enzymes (iNOS, COX-2), pro-inflammatory cytokines (TNF-α, IL-1β), and inflammatory mediators (NF-κB, IκB) in cartilaginous tissues were determined by western blot analysis.

RESULTS

Intra-articular administration of SHINBARO (IAS) at 20 mg/kg remarkably restrained the decrease in bone volume/total volume, being 28 % (P = 0.0001) higher than that in the vehicle-treated MIA group. IAS (2, 10, and 20 mg/kg) treatment significantly recovered the mean number of objects values with increased percentage changes of 13.5 % (P = 0.147), 27.5 % (P = 0.028), and 44.5 % (P = 0.031), respectively, compared with the vehicle-treated MIA group. The serum level of PGE2 in the IAS group at 20 mg/kg was markedly inhibited by 60.6 % (P = 0.0007) compared with the vehicle-treated MIA group, and the anti-collagen type II antibody level in the IAS group was reduced in a dose-dependent manner. IAS (20 mg/kg) effectively suppressed the induction of inflammation-mediated enzymes (iNOS and COX-2) and pro-inflammatory cytokines (TNF-α and IL-1β). IAS treatment also downregulated the NF-κB level and increased the IκB-α level in the MIA- induced osteoarthritis rat model.

CONCLUSION

SHINBARO inhibited PGE2 and anti-type II collagen antibody production and modulated the balance of inflammatory enzymes, mediators, and cytokines in the MIA-induced osteoarthritis rat model.

3D visualization of the lumbar facet joint after degeneration using propagation phase contrast micro-tomography

Lumbar facet joint (LFJ) degeneration is believed to be an important cause of low back pain (LBP). Identifying the morphological changes of the LFJ in the degeneration process at a high-resolution level could be meaningful for our better understanding of the possible mechanisms underlying this process. In the present study, we determined the 3D morphology of the LFJ using propagation phase contrast micro-tomography (PPCT) in rats to assess the subtle changes that occur during the degeneration process. PPCT provides vivid 3D images of micromorphological changes in the LFJ during its degeneration process, and the changes in the subchondral bone occurred earlier than in the cartilage during the early stage of degeneration of the LFJ. The delineation of this alteration was similar to that with the histological method. Our findings demonstrated that PPCT could serve as a valuable tool for 3D visualization of the morphology of the LFJ by providing comprehensive information about the cartilage and the underlying subchondral bone and their changes during degeneration processes. It might also have great potential for providing effective diagnostic tools to track changes in the cartilage and to evaluate the effects of therapeutic interventions for LFJ degeneration in preclinical studies.

A review of percutaneous techniques for low back pain and neuralgia: current trends in epidural infiltrations, intervertebral disk and facet joint therapies

Low back pain and neuralgia due to spinal pathology are very common symptoms debilitating numerous patients with peak prevalence at ages between 45 and 60 years. Intervertebral discs and facet joints act as pain sources in the vast majority of the cases. Diagnosis is based on the combination of clinical examination and imaging studies. Therapeutic armamentarium for low back pain and neuralgia due to intervertebral discs and/or facet joints includes conservative therapy, injections, percutaneous therapeutic techniques and surgical options. Percutaneous, therapeutic techniques are imaging-guided, minimally invasive treatments which can be performed as outpatient procedures. In cases of facet joint syndrome, they include, apart from injections, neurolysis with radiofrequency/cryoablation, MR-guided high-intensity focused ultrasound and percutaneous fixation techniques. In case of discogenic pain, apart from infiltrations, therapeutic techniques can be classified in to two main categories: decompression (mechanical, thermal, chemical) techniques and biomaterials implantation/disc cell therapies. Strict sterility measures are a prerequisite and should include extensive local sterility and antibiotic prophylaxis. This article will report clinical and imaging findings for each pathology type and the association with treatment decision. In addition, we will describe in detail all possible treatment techniques for low back pain and neuralgia, and we will report recently published results of these techniques summarizing the data concerning safety and effectiveness as well as the level of evidence. Finally, we will try to provide a rational approach for the therapy of low back pain and neuralgia by means of minimally invasive imaging-guided percutaneous techniques.

Development of an Experimental Animal Model for Lower Back Pain by Percutaneous Injury-Induced Lumbar Facet Joint Osteoarthritis

We report generation and characterization of pain-related behavior in a minimally invasive facet joint degeneration (FJD) animal model in rats. FJD was produced by a non-open percutaneous puncture-induced injury on the right lumbar FJs at three consecutive levels. Pressure hyperalgesia in the lower back was assessed by measuring the vocalization response to pressure from a force transducer. After hyperalgesia was established, pathological changes in lumbar FJs and alterations of intervertebral foramen size were assessed by histological and imaging analyses. To investigate treatment options for lumber FJ osteoarthritis-induced pain, animals with established hyperalgesia were administered with analgesic drugs, such as morphine, a selective COX-2 inhibitor, a non-steroidal anti-inflammatory drug (NSAID) (ketorolac), or pregabalin. Effects were assessed by behavioral pain responses. One week after percutaneous puncture-induced injury of the lumbar FJs, ipsilateral primary pressure hyperalgesia developed and was maintained for at least 12 weeks without foraminal stenosis. Animals showed decreased spontaneous activity, but no secondary hyperalgesia in the hind paws. Histopathological and microfocus X-ray computed tomography analyses demonstrated that the percutaneous puncture injury resulted in osteoarthritis-like structural changes in the FJs cartilage and subchondral bone. Pressure hyperalgesia was completely reversed by morphine. The administration of celecoxib produced moderate pain reduction with no statistical significance while the administration of ketorolac and pregabalin produced no analgesic effect on FJ osteoarthritis-induced back pain. Our animal model of non-open percutanous puncture-induced injury of the lumbar FJs in rats shows similar characteristics of low back pain produced by human facet arthropathy.

Establishment of a new animal model for ischemic lumbar vertebrae

Degeneration and ischemia of lumbar intervertebral disc has become a more and more important issue for elder people. However the mechanism for this is still known, largely due to a lack of a suitable animal model. In this study, we constructed a new animal model for the study of ischemic lumbar vertebrae. 42 New Zealand white rabbits were chosen for the study. For each rabbit, two vertebrae were used. L5 was set as the experimental group and L4 was set as the control group. Percutaneous lumbar puncture needles were applied in vertebrae adjacent to endplate for L5 and L4. For L4 1 ml saline was injected and for L5 1 ml pingyangmycin (2 mg/mL) was used. 1, 2, 3, 4, 5 weeks; 2 and 3 months after surgery, 6 rabbits at each time point were randomly chosen and underwent MRI, pathological test. The results in L5 and L4 were compared. Another 6 rabbits were used for DSA (Digital Subtraction Angiography) and vascular cast to study the length and diameters of the branches of lumbar artery. It was identified that since the third week, slightly hyperintense signal on T2-weighted image (T2WI) and fat-suppression T2-weighted image (FS T2WI) were detected. Lumbar vertebrae damage could be identified since the fourth week. Results of MRI and the size of pathological area were positively related (r=0.965, P<0.05). DSA and vascular cast could both clearly show the third level branches of lumbar artery. Our study suggested that injection of pingyangmycin via percutaneous lumbar needle could successfully induce ischemia in lumbar endplate. This method had little trauma, required a simple operation process and is highly repetitive. Besides, by vascular cast, the most important source of blood supply is the media branch of the lumbar artery. This branch could be a new therapy pathway for the degeneration of lumbar vertebrae.

Establishment of a rat model of adjuvant-induced osteoarthritis of the lumbar facet joint

To study the establishment of adjuvant-induced osteoarthritis of the lumbar facet joint in a rat model. Complete Freund's adjuvant (experimental group) and saline (control group) were randomly injected into the right and left side of rat, respectively. The rats were killed, and degeneration of lumbar facet joint was evaluated at macroscopic level and scored based on OARSI scores system. Moreover, Interleukin-1β and tumor necrosis factor-α levels in the synovium were measured. The macroscopic scores and OARSI scores of experimental group were higher than the control group (P < 0.05). The concentration of tumor necrosis factor-α was significantly increased only on 3- and 7-day post-surgery when compared with controls, and interleukin-1β was increased on days 3,7 and 14 post-surgery (P < 0.05). The rat model of adjuvant can induce degeneration of the lumbar facet joint. It can be useful for studies on mechanisms and treatment of lumbar facet joint osteoarthritis.

Grading Osteoarthritic Changes of the Zygapophyseal Joints from Radiographs: A Reliability Study

OBJECTIVE

This study tested the reliability of a 5-point ordinal scale used to grade the severity of degenerative changes of zygapophyseal (Z) joints on standard radiographs.

METHODS

Modifications were made to a Kellgren grading system to improve agreement for grading the severity of osteoarthritic changes in lumbar Z joints. These included adding 1 grade of no degeneration, multiple radiographic views, and structured examiner training. Thirty packets of radiographic files were obtained, which included representation of all 5 grades including no degeneration (0) and Kellgren's 4-point (1-4) joint degeneration classification criteria. Radiographs were digitized to create a radiographic atlas that was given to examiners for individual study and blinded evaluation sessions. Intrarater and interrater agreement was determined by weighted κ (κw) from the examination of 79 Z joints (25 packets).

RESULTS

Using the modified scale and after training, examiners demonstrated a moderate-to-substantial level of interrater agreement (κw = 0.57, 0.60, and 0.68). Intrarater agreement was moderate (κw = 0.42 and 0.54).

CONCLUSIONS

The modified Kellgren 5-point grading system provides acceptable intrarater and interrater reliability when examiners are adequately trained. This grading system may be a useful method for future investigations assessing radiographic osteoarthritis of the Z joints.

Establishment of a rat model of lumbar facet joint osteoarthritis using intraarticular injection of urinary plasminogen activator

Lumbar facet joint (LFJ) osteoarthritis (OA) is an important etiology of low back pain. Several animal models of LFJ OA have been established using intraarticular injection of various chemicals. This study aimed to establish a rat model of LFJ OA using urinary plasminogen activator (uPA). Sprague-Dawley rats were treated with intraarticular injection in the L5-L6 facet joints with uPA (OA group, n = 40) or normal saline (vehicle group, n = 40). Mechanical and thermal hyperalgesia in the ipsilateral hind paws were evaluated using von Frey hairs and a thermoalgesia instrument, respectively. Toluidine blue staining, hematoxylin-eosin staining, and immunohistochemical examination of the LFJ was performed. Treatment with uPA induced cartilage damage, synovitis, and proliferation of synovial cells in the fact joints. The OA group showed significantly higher hyperalgesia in the hind paws in comparison with the vehicle group and normal controls (P < 0.05). Expression of IL-1β, TNF-α, and iNOS in the LFJ cartilage in the OA group was significantly increased (P < 0.05). A rat model of LFJ OA was successfully established using intraarticular injection of uPA. This animal model is convenient and shows good resemblance to human OA pathology.

The role of imaging in osteoarthritis

Osteoarthritis (OA) is the most prevalent joint disorder with no approved disease-modifying treatment available. The importance of imaging in assessing all joint structures involved in the disease process, including articular cartilage, meniscus, subarticular bone marrow, and synovium for diagnosis, prognostication, and follow-up, has been well recognized. In daily clinical practice, conventional radiography is still the most commonly used imaging technique for the evaluation of a patient with known or suspected OA and radiographic outcome measures are still the only approved end point by regulatory authorities in clinical trials. The ability of magnetic resonance imaging (MRI) to visualize all joint structures in three-dimensional fashion including tissue ultrastructure has markedly deepened our understanding of the natural history of the disease. This article describes the roles and limitations of different imaging modalities for clinical practice and research in OA, with a focus on radiography and MRI and an emphasis on the knee joint.

Increased pelvic incidence may lead to arthritis and sagittal orientation of the facet joints at the lower lumbar spine

BACKGROUND

Correct sagittal alignment with a balanced pelvis and spine is crucial in the management of spinal disorders. The pelvic incidence (PI) describes the sagittal pelvic alignment and is position-independent. It has barely been investigated on CT scans. Furthermore, no studies have focused on the association between PI and facet joint (FJ) arthritis and orientation. Therefore, our goal was to clarify the remaining issues about PI in regard to (1) physiologic values, (2) age, (3) gender, (4) lumbar lordosis (LL) and (5) FJ arthritis and orientation using CT scans.

METHODS

We retrospectively analyzed CT scans of 620 individuals, with a mean age of 43 years, who presented to our traumatology department and underwent a whole body CT scan, between 2008 and 2010. The PI was determined on sagittal CT planes of the pelvis by measuring the angle between the hip axis to an orthogonal line originating at the center of the superior end plate axis of the first sacral vertebra. We also evaluated LL, FJ arthritis and orientation of the lumbar spine.

RESULTS

596 individuals yielded results for (1) PI with a mean of 50.8°. There was no significant difference for PI and (2) age, nor (3) gender. PI was significantly and linearly correlated with (4) LL (p = < 0.0001). Interestingly, PI and (5) FJ arthritis displayed a significant and linear correlation (p = 0.0062) with a cut-off point at 50°. An increased PI was also significantly associated with more sagitally oriented FJs at L5/S1 (p = 0.01).

CONCLUSION

PI is not correlated with age nor gender. However, this is the first report showing that PI is significantly and linearly associated with LL, FJ arthritis and more sagittal FJ orientation at the lower lumbar spine. This may be caused by a higher contact force on the lower lumbar FJs by an increased PI. Once symptomatic or in the event of spinal trauma, patients with increased PI and LL could benefit from corrective surgery and spondylodesis.

Lactoferricin mediates anti-inflammatory and anti-catabolic effects via inhibition of IL-1 and LPS activity in the intervertebral disc

The catabolic cytokine interleukin-1 (IL-1) and endotoxin lipopolysaccharide (LPS) are well-known inflammatory mediators involved in degenerative disc disease, and inhibitors of IL-1 and LPS may potentially be used to slow or prevent disc degeneration in vivo. Here, we elucidate the striking anti-catabolic and anti-inflammatory effects of bovine lactoferricin (LfcinB) in the intervertebral disc (IVD) via antagonism of both IL-1 and LPS-mediated catabolic activity using in vitro and ex vivo analyses. Specifically, we demonstrate the biological counteraction of LfcinB against IL-1 and LPS-mediated proteoglycan (PG) depletion, matrix-degrading enzyme production, and enzyme activity in long-term (alginate beads) and short-term (monolayer) culture models using bovine and human nucleus pulposus (NP) cells. LfcinB significantly attenuates the IL-1 and LPS-mediated suppression of PG production and synthesis, and thus restores PG accumulation and pericellular matrix formation. Simultaneously, LfcinB antagonizes catabolic factor mediated induction of multiple cartilage-degrading enzymes, including MMP-1, MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5, in bovine NP cells at both mRNA and protein levels. LfcinB also suppresses the catabolic factor-induced stimulation of oxidative and inflammatory factors such as iNOS, IL-6, and toll-like receptor-2 (TLR-2) and TLR-4. Finally, the ability of LfcinB to antagonize IL-1 and LPS-mediated suppression of PG is upheld in an en bloc intradiscal microinjection model followed by ex vivo organ culture using both mouse and rabbit IVD tissue, suggesting a potential therapeutic benefit of LfcinB on degenerative disc disease in the future.

Osteoarthritis: a review of strengths and weaknesses of different imaging options

Slowing of radiographic joint space narrowing represents the only recommended imaging-based outcome measure to assess structural disease progression in osteoarthritis (OA) clinical trials. There are no effective disease-modifying OA drugs. The ability of magnetic resonance (MR) to image structures within the knee and to visualize cartilage morphology and composition gives MR imaging a critical role in understanding the natural history of the disease and in the search for therapies. In this article, the roles and limitations of conventional radiography and MR imaging, focusing on knee OA, and the use of other modalities in clinical practice and OA research are described.

Lumbar facet joint compressive injury induces lasting changes in local structure, nociceptive scores, and inflammatory mediators in a novel rat model

Objective. To develop a novel animal model of persisting lumbar facet joint pain. Methods. Sprague Dawley rats were anaesthetized and the right lumbar (L5/L6) facet joint was exposed and compressed to ~1 mm with modified clamps applied for three minutes; sham-operated and naïve animals were used as control groups. After five days, animals were tested for hind-paw sensitivity using von Frey filaments and axial deep tissue sensitivity by algometer on assigned days up to 28 days. Animals were sacrificed at selected times for histological and biochemical analysis. Results. Histological sections revealed site-specific loss of cartilage in model animals only. Tactile hypersensitivity was observed for the ipsi- and contralateral paws lasting 28 days. The threshold at which deep tissue pressure just elicited vocalization was obtained at three lumbar levels; sensitivity at L1 > L3/4 > L6. Biochemical analyses revealed increases in proinflammatory cytokines, especially TNF-α, IL-1α, and IL-1β. Conclusions. These data suggest that compression of a facet joint induces a novel model of local cartilage loss accompanied by increased sensitivity to mechanical stimuli and by increases in inflammatory mediators. This new model may be useful for studies on mechanisms and treatment of lumbar facet joint pain and osteoarthritis.

The pathophysiologic role of the protein kinase Cδ pathway in the intervertebral discs of rabbits and mice: in vitro, ex vivo, and in vivo studies

OBJECTIVE

Protein kinase Cδ (PKCδ) activation has been shown to be a principal rate-limiting step in matrix-degrading enzyme production in human articular chondrocytes. The aim of this study was to assess the role of the PKC pathways, specifically PKCδ, in intervertebral disc tissue homeostasis.

METHODS

Using in vitro, ex vivo, and in vivo techniques, we evaluated the pathophysiologic role of the PKCδ pathway by examining 1) proteoglycan deposition, 2) matrix-degrading enzyme production and activity, 3) downstream signaling pathways regulated by PKCδ, and 4) the effect on in vivo models of disc degeneration in genetically engineered PKCδ-knockout mice.

RESULTS

Studies of pathway-specific inhibitors revealed a vital role of the PKCδ/MAPK (ERK, p38, JNK) axis and NF-κB in disc homeostasis. Accordingly, in an in vivo model of disc injury, PKCδ-knockout mice were markedly resistant to disc degeneration.

CONCLUSION

Suppression of the PKCδ pathway may be beneficial in the prevention and/or treatment of disc degeneration. The results of this study provide evidence for a potential therapeutic role of pathway-specific inhibitors of the PKCδ cascade in the future.