The Role of Panx3 in Age-Associated and Injury-Induced Intervertebral Disc Degeneration

Finite element models of intervertebral disc: recent advances and prospects

OBJECTIVES

The incidence rate of intervertebral disc degeneration (IVDD) is increasing year by year, which brings great harm to our health. The change of biomechanical factors is an important reason for IVDD. Therefore, more and more studies use finite element (FE) models to analyze the biomechanics of spine.

METHODS

In this review, literatures which reported the FE model of intervertebral disc (IVD) were reviewed. We summarized the types and constructional methods of the FE models and analyzed the applications of some representative FE models.

RESULTS

The most widely used model was the nonlinear model which considers the behavior of porous elastic materials. As more advanced methods, More and more models which involve penetration parameters were used to simulate the biological behavior and biomechanical properties of IVD.

CONCLUSIONS

Personalized modeling should be carried out in order to better provide accurate basis for the diagnosis and treatment of the disease. In addition, microstructure, cell behavior and complex load should be considered in the process of model construction to build a more realistic model.

Pannexin 3 deletion in mice results in knee osteoarthritis and intervertebral disc degeneration after forced treadmill running

Pannexin 3 (Panx3) is a glycoprotein that forms mechanosensitive channels expressed in chondrocytes and annulus fibrosus cells of the intervertebral disc (IVD). Evidence suggests Panx3 plays contrasting roles in traumatic versus aging osteoarthritis (OA) and intervertebral disc degeneration (IDD). However, whether its deletion influences the response of joint tissue to forced use is unknown. The purpose of this study was to determine if Panx3 deletion in mice causes increased knee joint OA and IDD after forced treadmill running. Male and female wildtype (WT) and Panx3 knockout (KO) mice were randomized to either a no-exercise group (sedentary; SED) or daily forced treadmill running (forced exercise; FEX) from 24 to 30 weeks of age. Knee cartilage and IVD histopathology were evaluated by histology, while tibial secondary ossification centers were analyzed using microcomputed tomography (µCT). Both male and female Panx3 KO mice developed larger superficial defects of the tibial cartilage after forced treadmill running compared with SED WT mice. Additionally, Panx3 KO mice developed reduced bone volume, and female PANX3 KO mice had lengthening of the lateral tubercle at the intercondylar eminence. In the lower lumbar spine, both male and female Panx3 KO mice developed histopathological features of IDD after running compared to SED WT mice. These findings suggest that the combination of deleting Panx3 and forced treadmill running induces OA and causes histopathological changes associated with the degeneration of the IVDs in mice.

Transient receptor potential vanilloid 4 regulates extracellular matrix composition and mediates load-induced intervertebral disc degeneration in a mouse model

OBJECTIVE

Transient receptor potential vanilloid 4 (TRPV4) is a multi-modally activated cation channel that mediates mechanotransduction pathways by which musculoskeletal tissues respond to mechanical load and regulate tissue health. Using conditional Trpv4 knockout mice, we investigated the role of Trpv4 in regulating intervertebral disc (IVD) health and injury-induced IVD degeneration.

METHODS

Col2-Cre;Trpv4fl/f (Trpv4 KO) mice were used to knockout Trpv4 in all type 2 collagen-expressing cells. Effects of gene targeting alone was assessed in lumbar spines, using vertebral bone length measurement, histological, immunohistochemistry and gene expression analyses, and mechanical testing. Disc puncture was performed on caudal IVDs of wild-type (WT) and Trpv4 KO mice at 2.5- and 6.5-months-of-age. Six weeks after puncture (4- and 8-months-of-age at sacrifice), caudal spines were assessed using histological analyses.

RESULTS

While loss of Trpv4 did not significantly alter vertebral bone length and tissue histomorphology compared to age-matched WT mice, Trpv4 KO mice showed decreased proteoglycan and PRG4 staining in the annulus fibrosus compared to WT. At the gene level, Trpv4 KO mice showed significantly increased expression of Acan, Bgn, and Prg4 compared to WT. Functionally, loss of Trpv4 was associated with significantly increased neutral zone length in lumbar IVDs. Following puncture, both Trpv4 KO and WT mice showed similar signs of degeneration at the site of injury. Interestingly, loss of Trpv4 prevented mechanically-induced degeneration in IVDs adjacent to sites of injury.

CONCLUSION

These studies suggest a role for Trpv4 in regulating extracellular matrix synthesis and mediating the response of IVD tissues to mechanical stress.

Pannexins in the musculoskeletal system: new targets for development and disease progression

During cell differentiation, growth, and development, cells can respond to extracellular stimuli through communication channels. Pannexin (Panx) family and connexin (Cx) family are two important types of channel-forming proteins. Panx family contains three members (Panx1-3) and is expressed widely in bone, cartilage and muscle. Although there is no sequence homology between Panx family and Cx family, they exhibit similar configurations and functions. Similar to Cxs, the key roles of Panxs in the maintenance of physiological functions of the musculoskeletal system and disease progression were gradually revealed later. Here, we seek to elucidate the structure of Panxs and their roles in regulating processes such as osteogenesis, chondrogenesis, and muscle growth. We also focus on the comparison between Cx and Panx. As a new key target, Panxs expression imbalance and dysfunction in muscle and the therapeutic potentials of Panxs in joint diseases are also discussed.

Comparative histopathological analysis of age-associated intervertebral disc degeneration in CD-1 and C57BL/6 mice: Anatomical and sex-based differences

Background

Intervertebral disc (IVD) degeneration is a major contributor to back pain and disability. The cause of IVD degeneration is multifactorial, with no disease-modifying treatments. Mouse models are commonly used to study IVD degeneration; however, the effects of anatomical location, strain, and sex on the progression of age-associated degeneration are poorly understood.

Methods

A longitudinal study was conducted to characterize age-, anatomical-, and sex-specific differences in IVD degeneration in two commonly used strains of mice, C57BL/6 and CD-1. Histopathological evaluation of the cervical, thoracic, lumbar, and caudal regions of mice at 6, 12, 20, and 24 months of age was conducted by two blinded observers at each IVD for the nucleus pulposus (NP), annulus fibrosus (AF), and the NP/AF boundary compartments, enabling analysis of scores by tissue compartment, summed scores for each IVD, or averaged scores for each anatomical region.

Results

C57BL/6 mice displayed mild IVD degeneration until 24 months of age; at this point, the lumbar spine demonstrated the most degeneration compared to other regions. Degeneration was detected earlier in the CD-1 mice (20 months of age) in both the thoracic and lumbar spine. In CD-1 mice, moderate to severe degeneration was noted in the cervical spine at all time points assessed. In both strains, age-associated IVD degeneration in the thoracic and lumbar spine was associated with increased histopathological scores in all IVD compartments. In both strains, minimal degeneration was detected in caudal IVDs out to 24 months of age. Both C57BL/6 and CD-1 mice displayed sex-specific differences in the presentation and progression of age-associated IVD degeneration.

Conclusions

These results showed that the progression and severity of age-associated degeneration in mouse models is associated with marked differences based on anatomical region, sex, and strain. This information provides a fundamental baseline characterization for users of mouse models to enable effective and appropriate experimental design, interpretation, and comparison between studies.

Noncoding rare variants in PANX3 are associated with chronic back pain

ABSTRACT

Back pain is the leading cause of years lived with disability worldwide, yet surprisingly, little is known regarding the biology underlying this condition. The impact of genetics is known for chronic back pain: its heritability is estimated to be at least 40%. Large genome-wide association studies have shown that common variation may account for up to 35% of chronic back pain heritability; rare variants may explain a portion of the heritability not explained by common variants. In this study, we performed the first gene-based association analysis of chronic back pain using UK Biobank imputed data including rare variants with moderate imputation quality. We discovered 2 genes, SOX5 and PANX3 , influencing chronic back pain. The SOX5 gene is a well-known back pain gene. The PANX3 gene has not previously been described as having a role in chronic back pain. We showed that the association of PANX3 with chronic back pain is driven by rare noncoding intronic polymorphisms. This result was replicated in an independent sample from UK Biobank and validated using a similar phenotype, dorsalgia, from FinnGen Biobank. We also found that the PANX3 gene is associated with intervertebral disk disorders. We can speculate that a possible mechanism of action of PANX3 on back pain is due to its effect on the intervertebral disks.

Preclinical in vivo animal models of intervertebral disc degeneration. Part 1: A systematic review

Intervertebral disc degeneration (IVDD), a widely recognized cause of lower back pain, is the leading cause of disability worldwide. A myriad of preclinical in vivo animal models of IVDD have been described in the literature. There is a need for critical evaluation of these models to better inform researchers and clinicians to optimize study design and ultimately, enhance experimental outcomes. The purpose of this study was to conduct an extensive systematic literature review to report the variability of animal species, IVDD induction method, and experimental timepoints and endpoints used in in vivo IVDD preclinical research. A systematic literature review of peer-reviewed manuscripts featured on PubMed and EMBASE databases was conducted in accordance with PRISMA guidelines. Studies were included if they reported an in vivo animal model of IVDD and included details of the species used, how disc degeneration was induced, and the experimental endpoints used for analysis. Two-hundred and fifty-nine (259) studies were reviewed. The most common species, IVDD induction method and experimental endpoint used was rodents(140/259, 54.05%), surgery (168/259, 64.86%) and histology (217/259, 83.78%), respectively. Experimental timepoint varied greatly between studies, ranging from 1 week (dog and rodent models), to >104 weeks in dog, horse, monkey, rabbit, and sheep models. The two most common timepoints used across all species were 4 weeks (49 manuscripts) and 12 weeks (44 manuscripts). A comprehensive discussion of the species, methods of IVDD induction and experimental endpoints is presented. There was great variability across all categories: animal species, method of IVDD induction, timepoints and experimental endpoints. While no animal model can replicate the human scenario, the most appropriate model should be selected in line with the study objectives to optimize experimental design, outcomes and improve comparisons between studies.

Constitutive and conditional gene knockout mice for the study of intervertebral disc degeneration: Current status, decision considerations, and future possibilities

There have been an increasing number of patients with degenerative disc diseases due to the aging population. In light of this, studies on the pathogenesis of intervertebral disc degeneration have become a hot topic, and gene knockout mice have become a valuable tool in this field of research. With the development of science and technology, constitutive gene knockout mice can be constructed using homologous recombination, zinc finger nuclease, transcription activator-like effector nuclease technology and clustered regularly interspaced short palindromic repeats/Cas9 (CRISPR/Cas9) system, and conditional gene knockout mice can be constructed using the Cre/LoxP system. The gene-edited mice using these techniques have been widely used in the studies on disc degeneration. This paper reviews the development process and principles of these technologies, functions of the edited genes in disc degeneration, advantages, and disadvantages of different methods and possible targets of the specific Cre recombinase in intervertebral discs. Recommendations for the choice of suitable gene-edited model mice are presented. At the same time, possible technological improvements in the future are also discussed.

Pannexin biology and emerging linkages to cancer

Pannexins are a family of glycoproteins that comprises three members, PANX1, PANX2, and PANX3. The widely expressed and interrogated PANX1 forms heptameric membrane channels that primarily serve to connect the cytoplasm to the extracellular milieu by being selectively permeable to small signaling molecules when activated. Apart from notable exceptions, PANX1 in many tumor cells appears to facilitate tumor growth and metastasis, suggesting that pannexin-blocking therapeutics may have utility in cancer. Attenuation of PANX1 function must also consider the fact that PANX1 is found in stromal cells of the tumor microenvironment (TME), including immune cells. This review highlights the key discoveries of the past 5 years that suggest pannexins facilitate, or in some cases inhibit, tumor cell growth and metastasis via direct protein interactions and through the regulated efflux of signaling molecules.

Pannexin 3 channels in health and disease

Pannexin 3 (PANX3) is a member of the pannexin family of single membrane channel-forming glycoproteins. Originally thought to have a limited localization in cartilage, bone, and skin, PANX3 has now been detected in a variety of other tissues including skeletal muscle, mammary glands, the male reproductive tract, the cochlea, blood vessels, small intestines, teeth, and the vomeronasal organ. In many cell types of the musculoskeletal system, such as osteoblasts, chondrocytes, and odontoblasts, PANX3 has been shown to regulate the balance of proliferation and differentiation. PANX3 can be induced during progenitor cell differentiation, functioning at the cell surface as a conduit for ATP and/or in the endoplasmic reticulum as a calcium leak channel. Evidence in osteoblasts and monocytes also highlight a role for PANX3 in purinergic signalling through its function as an ATP release channel. PANX3 is critical in the development and ageing of bone and cartilage, with its levels temporally regulated in other tissues such as skeletal muscle, skin, and the cochlea. In diseases such as osteoarthritis and intervertebral disc degeneration, PANX3 can have either protective or detrimental roles depending on if the disease is age-related or injury-induced. This review will discuss PANX3 function in tissue growth and regeneration, its role in cellular differentiation, and how it becomes dysregulated in disease conditions such as obesity, Duchenne's muscular dystrophy, osteosarcoma, and non-melanoma skin cancer, where most of the findings on PANX3 function can be attributed to the characterization of Panx3 KO mouse models.

Development of a standardized histopathology scoring system using machine learning algorithms for intervertebral disc degeneration in the mouse model-An ORS spine section initiative

Mice have been increasingly used as preclinical model to elucidate mechanisms and test therapeutics for treating intervertebral disc degeneration (IDD). Several intervertebral disc (IVD) histological scoring systems have been proposed, but none exists that reliably quantitate mouse disc pathologies. Here, we report a new robust quantitative mouse IVD histopathological scoring system developed by building consensus from the spine community analyses of previous scoring systems and features noted on different mouse models of IDD. The new scoring system analyzes 14 key histopathological features from nucleus pulposus (NP), annulus fibrosus (AF), endplate (EP), and AF/NP/EP interface regions. Each feature is categorized and scored; hence, the weight for quantifying the disc histopathology is equally distributed and not driven by only a few features. We tested the new histopathological scoring criteria using images of lumbar and coccygeal discs from different IDD models of both sexes, including genetic, needle-punctured, static compressive models, and natural aging mice spanning neonatal to old age stages. Moreover, disc sections from common histological preparation techniques and stains including H&E, SafraninO/Fast green, and FAST were analyzed to enable better cross-study comparisons. Fleiss's multi-rater agreement test shows significant agreement by both experienced and novice multiple raters for all 14 features on several mouse models and sections prepared using various histological techniques. The sensitivity and specificity of the new scoring system was validated using artificial intelligence and supervised and unsupervised machine learning algorithms, including artificial neural networks, k-means clustering, and principal component analysis. Finally, we applied the new scoring system on established disc degeneration models and demonstrated high sensitivity and specificity of histopathological scoring changes. Overall, the new histopathological scoring system offers the ability to quantify histological changes in mouse models of disc degeneration and regeneration with high sensitivity and specificity.