Snapshot of degenerative aging of porcine intervertebral disc: a model to unravel the molecular mechanisms

Minimally Invasive Intradiscal Delivery of BM-MSCs via Fibrous Microscaffold Carriers

Current treatments of degenerated intervertebral discs often provide only temporary relief or address specific causes, necessitating the exploration of alternative therapies. Cell-based regenerative approaches showed promise in many clinical trials, but limitations such as cell death during injection and a harsh disk environment hinder their effectiveness. Injectable microscaffolds offer a solution by providing a supportive microenvironment for cell delivery and enhancing bioactivity. This study evaluated the safety and feasibility of electrospun nanofibrous microscaffolds modified with chitosan (CH) and chondroitin sulfate (CS) for treating degenerated NP tissue in a large animal model. The microscaffolds facilitated cell attachment and acted as an effective delivery system, preventing cell leakage under a high disc pressure. Combining microscaffolds with bone marrow-derived mesenchymal stromal cells demonstrated no cytotoxic effects and proliferation over the entire microscaffolds. The administration of cells attached to microscaffolds into the NP positively influenced the regeneration process of the intervertebral disc. Injectable poly(l-lactide-co-glycolide) and poly(l-lactide) microscaffolds enriched with CH or CS, having a fibrous structure, showed the potential to promote intervertebral disc regeneration. These features collectively address critical challenges in the fields of tissue engineering and regenerative medicine, particularly in the context of intervertebral disc degeneration.

Characterization of the Age-Related Differences in Porcine Acetabulum and Femoral Head Articular Cartilage

OBJECTIVE

The use of porcine animal models for cartilage injury has increased recently due to their similarity with humans with regard to cartilage thickness, limited intrinsic healing of chondral defects, and joint loading biomechanics. However, variations in the mechanical and biochemical properties of porcine hip articular cartilage among various tissue ages and weightbearing (WB) regions are still unknown. This study's aim was to characterize the mechanical and biochemical properties of porcine hip articular cartilage across various ages and WB regions.

METHODS

Articular cartilage explants were harvested from WB and non-weightbearing (NWB) surfaces of the femoral head and acetabulum of domesticated pigs (Sus scrofa domesticus) at fetal (gestational age: 80 days), juvenile (6 months), and adult (2 years) ages. Explants underwent compressive stress-relaxation mechanical testing, biochemical analysis for total collagen and glycosaminoglycan (GAG) content, and histological staining.

RESULTS

Juvenile animals consistently had the highest mechanical properties, with 2.2- to 7.6-time increases in relaxation modulus, 1.3- to 2.3-time increases in instantaneous modulus, and 4.1- to 14.2-time increases in viscosity compared with fetal cartilage. Mechanical properties did not significantly differ between the WB and NWB regions. Collagen content was highest in the NWB regions of the juvenile acetabulum (65.3%/dry weight [DW]) and femoral head (75.4%/DW) cartilages. GAG content was highest in the WB region of the juvenile acetabulum (23.7%/DW) and the WB region of the fetal femoral head (27.5%/DW) cartilages. Histological staining for GAG and total collagen content followed the trends from the quantitative biochemical assays.

CONCLUSION

This study provides a benchmark for the development and validation of preclinical porcine models for hip cartilage pathologies.

The clock transcription factor BMAL1 is a key regulator of extracellular matrix homeostasis and cell fate in the intervertebral disc

The circadian clock in mammals temporally coordinates physiological and behavioural processes to anticipate daily rhythmic changes in their environment. Chronic disruption to circadian rhythms (e.g., through ageing or shift work) is thought to contribute to a multitude of diseases, including degeneration of the musculoskeletal system. The intervertebral disc (IVD) in the spine contains circadian clocks which control ∼6% of the transcriptome in a rhythmic manner, including key genes involved in extracellular matrix (ECM) homeostasis. However, it remains largely unknown to what extent the local IVD molecular clock is required to drive rhythmic gene transcription and IVD physiology. In this work, we identified profound age-related changes of ECM microarchitecture and an endochondral ossification-like phenotype in the annulus fibrosus (AF) region of the IVD in the Col2a1-Bmal1 knockout mice. Circadian time series RNA-Seq of the whole IVD in Bmal1 knockout revealed loss of circadian patterns in gene expression, with an unexpected emergence of 12 h ultradian rhythms, including FOXO transcription factors. Further RNA sequencing of the AF tissue identified region-specific changes in gene expression, evidencing a loss of AF phenotype markers and a dysregulation of ECM and FOXO pathways in Bmal1 knockout mice. Consistent with an up-regulation of FOXO1 mRNA and protein levels in Bmal1 knockout IVDs, inhibition of FOXO1 in AF cells suppressed their osteogenic differentiation. Collectively, these data highlight the importance of the local molecular clock mechanism in the maintenance of the cell fate and ECM homeostasis of the IVD. Further studies may identify potential new molecular targets for alleviating IVD degeneration.

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.

PRIMUS: Comprehensive proteomics of mouse intervertebral discs that inform novel biology and relevance to human disease modelling

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Proteomics of healthy mouse IVDs differentiating compartments and spine levels.

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NP cells feature vacuoles with lysosomal, transport and cell–cell communication functions.

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Collagen XII, decorin and other ECM proteins contribute to function of the AF.

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Distinct proteomics between lumbar and tail discs.

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Mouse is a relevant model for human disc biology but care is needed in its use.

Mice are commonly used to study intervertebral disc (IVD) biology and related diseases such as IVD degeneration. Discs from both the lumbar and tail regions are used. However, little is known about compartmental characteristics in the different regions, nor their relevance to the human setting, where a functional IVD unit depends on a homeostatic proteome. Here, we address these major gaps through comprehensive proteomic profiling and in-depth analyses of 8-week-old healthy murine discs, followed by comparisons with human. Leveraging on a dataset of over 2,700 proteins from 31 proteomic profiles, we identified key molecular and cellular differences between disc compartments and spine levels, but not gender. The nucleus pulposus (NP) and annulus fibrosus (AF) compartments differ the most, both in matrisome and cellularity contents. Differences in the matrisome are consistent with the fibrous nature required for tensile strength in the AF and hydration property in the NP. Novel findings for the NP cells included an enrichment in cell junction proteins for cell–cell communication (Cdh2, Dsp and Gja1) and osmoregulation (Slc12a2 and Wnk1). In NP cells, we detected heterogeneity of vacuolar organelles; where about half have potential lysosomal function (Vamp3, Copb2, Lamp1/2, Lamtor1), some contain lipid droplets and others with undefined contents. The AF is enriched in proteins for the oxidative stress responses (Sod3 and Clu). Interestingly, mitochondrial proteins are elevated in the lumbar than tail IVDs that may reflect differences in metabolic requirement. Relative to the human, cellular and structural information are conserved for the AF. Even though the NP is more divergent between mouse and human, there are similarities at the level of cell biology. Further, common cross-species markers were identified for both NP (KRT8/19, CD109) and AF (COL12A1). Overall, mouse is a relevant model to study IVD biology, and an understanding of the limitation will facilitate research planning and data interpretation, maximizing the translation of research findings to human IVDs.

Proper animal experimental designs for preclinical research of biomaterials for intervertebral disc regeneration

Low back pain is a vital musculoskeletal disease that impairs life quality, leads to disability and imposes heavy economic burden on the society, while it is greatly attributed to intervertebral disc degeneration (IDD). However, the existing treatments, such as medicines, chiropractic adjustments and surgery, cannot achieve ideal disc regeneration. Therefore, advanced bioactive therapies are implemented, including stem cells delivery, bioreagents administration, and implantation of biomaterials etc. Among these researches, few reported unsatisfying regenerative outcomes. However, these advanced therapies have barely achieved successful clinical translation. The main reason for the inconsistency between satisfying preclinical results and poor clinical translation may largely rely on the animal models that cannot actually simulate the human disc degeneration. The inappropriate animal model also leads to difficulties in comparing the efficacies among biomaterials in different reaches. Therefore, animal models that better simulate the clinical charateristics of human IDD should be acknowledged. In addition, in vivo regenerative outcomes should be carefully evaluated to obtain robust results. Nevertheless, many researches neglect certain critical characteristics, such as adhesive properties for biomaterials blocking annulus fibrosus defects and hyperalgesia that is closely related to the clinical manifestations, e.g., low back pain. Herein, in this review, we summarized the animal models established for IDD, and highlighted the proper models and parameters that may result in acknowledged IDD models. Then, we discussed the existing biomaterials for disc regeneration and the characteristics that should be considered for regenerating different parts of discs. Finally, well-established assays and parameters for in vivo disc regeneration are explored.

Painful intervertebral disc degeneration and inflammation: from laboratory evidence to clinical interventions

Low back pain (LBP), as a leading cause of disability, is a common musculoskeletal disorder that results in major social and economic burdens. Recent research has identified inflammation and related signaling pathways as important factors in the onset and progression of disc degeneration, a significant contributor to LBP. Inflammatory mediators also play an indispensable role in discogenic LBP. The suppression of LBP is a primary goal of clinical practice but has not received enough attention in disc research studies. Here, an overview of the advances in inflammation-related pain in disc degeneration is provided, with a discussion on the role of inflammation in IVD degeneration and pain induction. Puncture models, mechanical models, and spontaneous models as the main animal models to study painful disc degeneration are discussed, and the underlying signaling pathways are summarized. Furthermore, potential drug candidates, either under laboratory investigation or undergoing clinical trials, to suppress discogenic LBP by eliminating inflammation are explored. We hope to attract more research interest to address inflammation and pain in IDD and contribute to promoting more translational research.

Tissue physiology revolving around the clock: circadian rhythms as exemplified by the intervertebral disc

Circadian clocks in the brain and peripheral tissues temporally coordinate local physiology to align with the 24 hours rhythmic environment through light/darkness, rest/activity and feeding/fasting cycles. Circadian disruptions (during ageing, shift work and jet-lag) have been proposed as a risk factor for degeneration and disease of tissues, including the musculoskeletal system. The intervertebral disc (IVD) in the spine separates the bony vertebrae and permits movement of the spinal column. IVD degeneration is highly prevalent among the ageing population and is a leading cause of lower back pain. The IVD is known to experience diurnal changes in loading patterns driven by the circadian rhythm in rest/activity cycles. In recent years, emerging evidence indicates the existence of molecular circadian clocks within the IVD, disruption to which accelerates tissue ageing and predispose animals to IVD degeneration. The cell-intrinsic circadian clocks in the IVD control key aspects of physiology and pathophysiology by rhythmically regulating the expression of ~3.5% of the IVD transcriptome, allowing cells to cope with the drastic biomechanical and chemical changes that occur throughout the day. Indeed, epidemiological studies on long-term shift workers have shown an increased incidence of lower back pain. In this review, we summarise recent findings of circadian rhythms in health and disease, with the IVD as an exemplar tissue system. We focus on rhythmic IVD functions and discuss implications of utilising biological timing mechanisms to improve tissue health and mitigate degeneration. These findings may have broader implications in chronic rheumatic conditions, given the recent findings of musculoskeletal circadian clocks.

Animal models of spinal injury for studying back pain and SCI

INTRODUCTION

Back pain is a common ailment affecting individuals around the globe. Animal models to understand the back pain mechanism, treatment modalities, and spinal cord injury are widely researched topics worldwide. Despite the presence of several animal models on disc degeneration and Spinal Cord Injury, there is a lack of a comprehensive review.

MATERIAL AND METHOD

A methodological narrative literature review was carried out for the study. A total of 1273 publications were found, out of which 763 were related to spine surgery in animals. The literature with full-text availability was selected for the review. Scale for the Assessment of Narrative Review Articles (SANRA) guidelines was used to assess the studies. Only English language publications were included which were listed on PubMed. A total of 113 studies were shortlisted (1976-2019) after internal validation scoring.

RESULT

The animal models for spine surgery ranged from rodents to primates. These are used to study the mechanisms of back pain as well as spinal cord injuries. The models could either be created surgically or through various means like use of electric cautery, chemicals or trauma. Genetic spine models have also been documented in which the injuries are created by genetic alterations and knock outs. Though the dorsal approach is the most common, the literature also mentions the anterior and lateral approach for spine surgery animal experiments.

CONCLUSION

There are no single perfect animal models to represent and study human models. The selection is based on the application and the methodology. Careful selection is needed to give optimum and appropriate results.

In vitro modulation of extracellular matrix genes by stingless bee honey in cellular aging of human dermal fibroblast cells

This study determined the antiaging effect of stingless bee honey on the expression of extracellular matrix genes. MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt) assay was performed for determination of optimum concentration and incubation time of stingless bee honey. Gene expression of matrix metalloproteinase-1 (MMP-1) and collagen type Ⅰ (COL1A1) were analyzed using real time reverse transcriptase polymerase chain reaction technique. Incubation with stingless bee honey at concentration of 0.02% for 72 hr showed significant increase in the viability of human fibroblast cells. Stingless bee honey significantly downregulates metalloproteinase-1 gene expression in both pre-senescence and senescence fibroblast cells and upregulates collagen type Ⅰ gene expression in senescence fibroblast cells. In conclusion, stingless bee honey potentially delayed skin aging through modulation of extracellular matrix genes. PRACTICAL APPLICATIONS: Changes of the extracellular matrix regulation promote skin aging. Stingless bee honey is a good source of natural antioxidant which potentially delays skin aging. This study demonstrated that stingless bee honey beneficially increases collagen type Ⅰ expression and decreases MMP-1 expression during cellular aging of human dermal fibroblast cells.

Resveratrol increases nucleus pulposus matrix synthesis through activating the PI3K/Akt signaling pathway under mechanical compression in a disc organ culture

Disc nucleus pulposus (NP) matrix homeostasis is important for normal disc function. Mechanical overloading seriously decreases matrix synthesis and increases matrix degradation. The present study aims to investigate the effects of resveratrol on disc NP matrix homeostasis under a relatively high-magnitude mechanical compression and the potential mechanism underlying this process. Porcine discs were perfusion-cultured and subjected to a relatively high-magnitude mechanical compression (1.3 MPa at a frequency of 1.0 Hz for 2 h once per day) for 7 days in a mechanically active bioreactor. The non-compressed discs were used as controls. Resveratrol was added along with culture medium to observe the effects of resveratrol on NP matrix synthesis under mechanical load respectively. NP matrix synthesis was evaluated by histology, biochemical content (glycosaminoglycan (GAG) and hydroxyproline (HYP)), and expression of matrix macromolecules (aggrecan and collagen II). Results showed that this high-magnitude mechanical compression significantly decreased NP matrix content, indicated by the decreased staining intensity of Alcian Blue and biochemical content (GAG and HYP), and the down-regulated expression of NP matrix macromolecules (aggrecan and collagen II). Further analysis indicated that resveratrol partly stimulated NP matrix synthesis and increased activity of the PI3K/Akt pathway in a dose-dependent manner under mechanical compression. Together, resveratrol is beneficial for disc NP matrix synthesis under mechanical overloading, and the activation of the PI3K/Akt pathway may participate in this regulatory process. Resveratrol may be promising to regenerate mechanical overloading-induced disc degeneration.

Role of p38-MAPK pathway in the effects of high-magnitude compression on nucleus pulposus cell senescence in a disc perfusion culture

Nucleus pulposus (NP) cell senescence is a typical pathological feature within the degenerative intervertebral disc. As a potential inducing and aggregating factor of disc degeneration, mechanical overloading affects disc biology in multiple ways. The present study was to investigate the NP cell senescence-associated phenotype under intermittent high compression in an ex vivo disc bioreactor culture, and the role of the p38-MAPK pathway in this regulatory process. Porcine discs were cultured in culture chambers of a self-developed mechanically active bioreactor and subjected to different magnitudes of dynamic compression (low-magnitude and high-magnitude: 0.1 and 1.3 MPa at a frequency of 1.0 Hz for 2 h per day respectively) for 7 days. Non-compressed discs were used as controls. The inhibitor SB203580 was used to study the role of the p38-MAPK pathway in this process. Results showed that intermittent high-magnitude compression clearly induced senescence-associated changes in NP cells, such as increasing β-galactosidase-positive NP cells, decreasing PCNA-positive NP cells, promoting the formation of senescence-associated heterochromatic foci (SAHF), up-regulating the expression of senescence markers (p16 and p53), and attenuating matrix production. However, inhibition of the p38-MAPK pathway partly attenuated the effects of intermittent high-magnitude (1.3 MPa) compression on those described NP cell senescence-associated parameters. In conclusion, intermittent high-magnitude compression can induce NP cell senescence-associated changes in an ex vivo disc bioreactor culture, and the p38-MAPK pathway is involved in this process.

Animal models for disc degeneration-an update

Intervertebral disc degeneration is considered a major cause of back pain that places a heavy burden on society, both because of its effect on the physiology of individuals and its consequences on the world economy. During the past few decades, research findings in the pre-clinical setting have led to a significant increase in the understanding of intervertebral disc degeneration, although many aspects of the disease remain unclear. The goal of this review is to summarize existing animal models for disc degeneration studies and the difficulties that are associated with the use of such models. A firm understanding of the cellular and molecular events that ensue as a result of injuries, as well as environmental factors, could be instrumental in the development of targeted therapies for the treatment of intervertebral disc degeneration.

Long-term load duration induces N-cadherin down-regulation and loss of cell phenotype of nucleus pulposus cells in a disc bioreactor culture

Long-term exposure to a mechanical load causes degenerative changes in the disc nucleus pulposus (NP) tissue. A previous study demonstrated that N-cadherin (N-CDH)-mediated signalling can preserve the NP cell phenotype. However, N-CDH expression and the resulting phenotype alteration in NP cells under mechanical compression remain unclear. The present study investigated the effects of the compressive duration on N-CDH expression and on the phenotype of NP cells in an ex vivo disc organ culture. Porcine discs were organ cultured in a self-developed mechanically active bioreactor for 7 days. The discs were subjected to different dynamic compression durations (1 and 8 h at a magnitude of 0.4 MPa and frequency of 1.0 Hz) once per day. Discs that were not compressed were used as controls. The results showed that long-term compression duration (8 h) significantly down-regulated the expression of N-CDH and NP-specific molecule markers (Brachyury, Laminin, Glypican-3 and Keratin 19), attenuated Alcian Blue staining intensity, decreased glycosaminoglycan (GAG) and hydroxyproline (HYP) contents and decreased matrix macromolecule (aggrecan and collagen II) expression compared with the short-term compression duration (1 h). Taken together, these findings demonstrate that long-term load duration can induce N-CDH down-regulation, loss of normal cell phenotype and result in attenuation of NP-related matrix synthesis in NP cells.

Matrix homeostasis within the immature annulus fibrosus depends on the frequency of dynamic compression: a study based on the self-developed mechanically active bioreactor

Evidence suggests that mechanical load is related to structural destruction of disk annulus fibrosus (AF) either in adult disk degeneration or in child disk acute injury. Both biochemical and biomechanical properties are different between immature and mature disks. However, the effects of mechanical compression on immature AF are not fully clear. This study was to investigate the effects of a relatively wide range of dynamic compressive frequency on matrix homeostasis within the immature AF. Immature disks from pig (3-4 months) were randomly assigned into the control group (non-compression) and compression groups (0.1, 0.5, 1.0, 3.0 and 5.0 Hz). All disks were bioreactor-cultured for 7 days. AF matrix production was evaluated by histology, gene expression, glycosaminoglycan (GAG) content, hydroxyproline (HYP) content and immunohistochemistry. Generally, no obvious difference was found in HE staining between control group and compression groups. However, alcian blue staining indicated proteoglycan content in the 5.0-Hz group was decreased compared with the control group and other compression groups. Similarly, a catabolic remodeling gene expression profile with the down-regulated matrix genes (aggrecan, collagen I and collagen II) and tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-3) and the up-regulated matrix catabolic enzymes (ADAMTS-4 and MMP-3) was found in the 5.0-Hz group. Further analysis indicated that GAG content, HYP content and aggrecan protein deposition were also decreased in the 5.0-Hz group. Hence, we concluded that matrix homeostasis within the immature AF was compressive frequency dependent, and the relatively higher frequency (5.0 Hz) is unfavorable for matrix production within the immature AF. These findings will contribute to further understanding of the relationship between mechanical compression and immature AF biosynthesis.

Genetic aspects of intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is one of the common causes of low back pain. Similar to many other multifactorial diseases, it is affected by environmental and genetic factors. Although not completely understood, genetic factors include a wide spectrum of variations, such as single nucleotide polymorphisms, which could play a significant role in the etiology of this disease. Besides, the interactions with environmental factors could make the role of genetic factors more complicated. Genetic variations in disc components could participate in developing degenerative disc disease through altering the normal homeostasis of discs. Gene polymorphisms in disc proteins (collagens I, II, III, IX, and XI), proteoglycans (aggrecan), cytokines (interleukins I, VI, and X), enzymes (matrix metalloproteinases II, III, and IX), and vitamin D receptor seem to play considerable roles in the pathology of this disease. There are also many other investigated genes that could somehow take part in the process. However, it seems that more studies are needed to clarify the exact role of genetics in IVDD.

Molecular mechanisms of biological aging in intervertebral discs

Advanced age is the greatest risk factor for the majority of human ailments, including spine-related chronic disability and back pain, which stem from age-associated intervertebral disc degeneration (IDD). Given the rapid global rise in the aging population, understanding the biology of intervertebral disc aging in order to develop effective therapeutic interventions to combat the adverse effects of aging on disc health is now imperative. Fortunately, recent advances in aging research have begun to shed light on the basic biological process of aging. Here we review some of these insights and organize the complex process of disc aging into three different phases to guide research efforts to understand the biology of disc aging. The objective of this review is to provide an overview of the current knowledge and the recent progress made to elucidate specific molecular mechanisms underlying disc aging. In particular, studies over the last few years have uncovered cellular senescence and genomic instability as important drivers of disc aging. Supporting evidence comes from DNA repair-deficient animal models that show increased disc cellular senescence and accelerated disc aging. Additionally, stress-induced senescent cells have now been well documented to secrete catabolic factors, which can negatively impact the physiology of neighboring cells and ECM. These along with other molecular drivers of aging are reviewed in depth to shed crucial insights into the underlying mechanisms of age-related disc degeneration. We also highlight molecular targets for novel therapies and emerging candidate therapeutics that may mitigate age-associated IDD. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1289-1306, 2016.

Biological Responses of the Immature Annulus Fibrosus to Dynamic Compression in a Disc Perfusion Culture

Mechanical stimuli participate in disc development and remodelling. However, the effects of mechanical load on the immature annulus fibrosus (AF) are largely unclear. This study aimed to investigate how the immature AF responded to dynamic compressive magnitude and duration. Immature porcine discs were bioreactor-cultured for 7 days and then dynamically compressed at various magnitudes (0.1, 0.2, 0.4, 0.8 and 1.3 MPa at a frequency of 1.0 Hz for 2 h/day) and durations (1, 2, 4 and 8 h/day at a magnitude of 0.4 MPa and a frequency of 1.0 Hz). Non-compressed discs were used as controls. The immature AF tissue was analysed for histology, gene expression (aggrecan, collagen I, ADAMTS-4, MMP-3, TIMP-1 and TIMP-3), biochemical content of glycosaminoglycans (GAG) and hydroxyproline (HYP) and aggrecan immunohistochemical staining. In the lower-compressive-magnitude groups (0.1, 0.2 and 0.4 MPa), the immature AF showed an up-regulation in the expression of matrix genes, GAG and HYP content and aggrecan deposition. In the compression duration groups, the GAG and HYP content and aggrecan deposition declined to a minimum in the 8-hour group, in which a catabolic gene expression profile was found. In conclusion, this study indicated that the effects of dynamic compression on the immature AF are magnitude and duration dependent and that catabolic remodelling within the immature AF can be induced by high compressive magnitudes and long compressive durations.

Osmolarity affects matrix synthesis in the nucleus pulposus associated with the involvement of MAPK pathways: A study of ex vivo disc organ culture system

Matrix homeostasis within the nucleus pulposus (NP) is important for disc function. Unfortunately, the effects of osmolarity on NP matrix synthesis in a disc organ culture system and the underlying mechanisms are largely unknown. The present study was to investigate the effects of different osmolarity modes (constant and cyclic) and osmolarity levels (hypo-, iso-, and hyper-) on NP matrix synthesis using a disc organ culture system and determine whether ERK1/2 or p38MAPK pathway has a role in this process. Porcine discs were cultured for 7 days in various osmotic media, including constant hypo-, iso-, hyper-osmolarity (330, 430, and 550 mOsm/kg, respectively) and cyclic-osmolarity (430 mOsm/kg for 8 h, followed by 550 mOsm/kg for 16 h). The role of ERK1/2 and p38MAPK pathways were determined by their inhibitors U0126 and SB202190 respectively. The expression of SOX9 and downstream aggrecan and collagen II, biochemical content, and histology were used to assess NP matrix synthesis. The findings revealed that NP matrix synthesis was promoted in iso- and cyclic-osmolarity cultures compared to hypo- or hyper-osmolarity culture although the level of matrix synthesis in cyclic-osmolarity culture did not reach that in iso-osmolarity culture. Further analysis suggested that inhibition of the ERK1/2 or p38MAPK pathway in iso- and cyclic-osmolarity cultures reduced NP matrix production. Therefore, we concluded that the effects of osmolarity on NP matrix synthesis depend on osmolarity level (hypo-, iso-, or hyper-) and osmolarity mode (constant or cyclic), and the ERK1/2 and p38MAPK pathways may participate in this process. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1092-1100, 2016.

Chitosan functionalized thermosponge nano-carriers for prolonged retention and local delivery of chymopapain at the nucleus pulposus in porcine discs ex vivo

Chitosan functionalized nano-carriers could function as an efficient delivery carrier for local administration of chymopapain to reduce the side effect associated with chemonucleolysis.

MMPs and ADAMTSs in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the most common diagnosis in patients with low back pain, a leading cause of musculoskeletal disability worldwide. The major components of extracellular matrix (ECM) within the discs are type II collagen (Col II) and aggrecan. Excessive destruction of ECM, especially loss of Col II and aggrecan, plays a critical role in promoting the occurrence and development of IDD. Matrix metalloproteinases (MMPs) and a disintegrin and metalloprotease with thrombospondin motifs (ADAMTSs) are primary enzymes that degrade collagens and aggrecan. There is a large and growing body of evidence that many members of MMPs and ADAMTSs are highly expressed in degenerative IVD tissue and cells, and are closely involved in ECM breakdown and the process of disc degeneration. In contrast, targeting these enzymes has shown promise for promoting ECM repair and mitigating disc regeneration. In the current review, after a brief description regarding the biology of MMPs and ADAMTSs, we mainly focus on their expression profiles, roles and therapeutic potential in IDD. A greater understanding of the catabolic pathways involved in IDD will help to develop potential prophylactic or regenerative biological treatment for degenerative disc disease in the future.

The effect of gamma irradiation on the biological properties of intervertebral disc allografts: in vitro and in vivo studies in a beagle model

Study Design

An animal experiment about intervertebral disc allograft.

Objective

To explore the feasibility to decellularize disc allografts treated by ⁶°Co Gamma Irradiation, and simultaneously, to assess the possibility to make use of the decellularized natural disc scaffold for disc degeneration biotherapy.

Summary of Background Data

Studies of both animal and human disc allograft transplantation indicated that the disc allograft may serve as a scaffold to undertake the physiological responsibility of the segment.

Methods

Experiment in vitro: 48 discs of beagles were harvested and divided randomly into four groups including a control group and three irradiated groups. Immediate cell viability and biomechanical properties of the discs were checked and comparisons were made among these groups. Experiment in vivo: 24 beagles accepted single-level allografted disc treated with different doses of gamma irradiation. Plain X-rays and MRIs were taken before and after surgery. Then, the spinal columns were harvested en bloc from the sacrificed beagles and were examined morphologically.

Results

There were significant differences of both the annulus fibrosus and nucleus pulposus immediate cell viabilities among the various groups. There were no obvious differences of the biomechanical properties among the four groups. The disc height and range of motion decreased significantly in all groups as time went on. The observed indexes in irradiated groups were much smaller than those in the control group, but the indexes in 18-kGy group were larger than those in 25-kGy and 50-kGy groups. Both MRI and macroscopic findings showed that the segmental degeneration in the control and 18-kGy group was less severe than that in 25-kGy and 50-kGy groups.

Conclusion

Gamma Irradiation can decellularize disc allograft successfully to provide natural scaffold for the study of degenerative disc disease therapy, and also can be used as an effective method to produce adjustable animal models.

Spinal traction promotes molecular transportation in a simulated degenerative intervertebral disc model

STUDY DESIGN

Biomechanical experiment using an in situ porcine model.

OBJECTIVE

To find the effect of traction treatment on annulus microstructure, molecular convection, and cell viability of degraded discs.

SUMMARY OF BACKGROUND DATA

Spinal traction is a conservative treatment for disc disorders. The recognized biomechanical benefits include disc height recovery, foramen enlargement, and intradiscal pressure reduction. However, the influence of traction treatment on annulus microstructure, molecular transportation, and cell viability of degraded discs has not been fully investigated.

METHODS

A total of 48 thoracic discs were dissected from 8 porcine spines (140 kg, 6-month old) within 4 hours after killing them and then divided into 3 groups: intact, degraded without traction, and degraded with traction. Each disc was incubated in a whole-organ culture system and subjected to diurnal loadings for 7 days. Except for the intact group, discs were degraded with 0.5 mL of trypsin on day 1 and a 5-hour fatigue loading on day 2. From day 4 to day 6, half of the degraded discs received a 30-minute traction treatment per day (traction force: 20 kg; loading: unloading = 30 s: 10 s). By the end of the incubation, the discs were inspected for disc height loss, annulus microstructure, molecular (fluorescein sodium) intensity, and cell viability.

RESULTS

Collagen fibers were crimped and delaminated, whereas the pores were occluded in the annulus fibrosus of the degraded discs. Molecular transportation and cell viability of the discs decreased after matrix degradation. With traction treatment, straightened collagen fibers increased within the degraded annulus fibrosus, and the annulus pores were less occluded. Both molecular transportation and cell viability increased, but not to the intact level.

CONCLUSION

Traction treatment is effective in enhancing nutrition supply and promoting disc cell proliferation of the degraded discs.

LEVEL OF EVIDENCE

N/A.

Rheological and dynamic integrity of simulated degenerated disc and consequences after cross-linker augmentation

STUDY DESIGN

An in situ study using whole-organ culture system.

OBJECTIVE

To study the effect of disc degeneration at different stages on its rheological and dynamic properties and to investigate the efficacy of exogenous cross-linking therapy.

SUMMARY OF BACKGROUND DATA

Disc degeneration can involve protein denaturation or microdefects to the disc's collagen fiber network. A disc degeneration model using whole-organ culture technique can be effectively used for the screening of treatments of degenerated discs. Exogenous cross-linking therapy has been shown to enhance the mechanical properties of the disc by cross-linking collagen. However, the efficacy of this therapy on the degenerated disc is unclear.

METHODS

A total of 40 porcine thoracic discs were assigned to 5 groups: intact discs, moderately degenerated discs, moderately degenerated discs with cross-linker augmentation, severely degenerated discs, and severely degenerated discs with cross-linker augmentation. The disc degeneration was simulated by trypsin digestion and mechanical fatigue loading. Rheological properties, dynamic properties, water content, and histological analysis were conducted after a 7-day incubation.

RESULTS

The mechanical properties of moderate degenerated discs significantly decrease both in rheological and dynamic properties, and laminate structure disorganization was observed. Mechanical defects of severely degenerated discs resulted in disc height loss, an increase in the aggregate modulus and stiffness modulus, and a decrease in the damping coefficient, hydraulic permeability, and water content. Cross-linker augmentation significantly recovered mechanical properties of moderately degenerated discs and restored the water content compared with the intact disc. However, the augmentation did not fully repair the severely degenerated discs.

CONCLUSION

Trypsin-induced extracellular matrix damage resulted in a change of the disc's biomechanics. Cross-linker augmentation recovers the rheological and dynamic properties of moderately degenerated discs but not of the severely degenerated discs. The genipin cross-linker may be able to improve the proteoglycan depletion effect in the nucleus pulposus but may not be effective to restore the structural damage in the collagen molecule of the anulus fibrosus.

Expression and function of vascular endothelial growth inhibitor in aged porcine bladder detrusor muscle cells

Aging of the bladder detrusor muscle plays an important role in lower urinary tract symptoms in elderly people. Our previous work demonstrated that elderly patients have increased levels of vascular endothelial growth inhibitor (VEGI) in bladder tissue. Therefore, we hypothesized that VEGI may play a role in aging of the bladder detrusor muscle cells. This study aims to develop and characterize primary cultures of aged porcine bladder detrusor muscle cells in order to explore the expression and function of VEGI. Bladder samples from female pigs were divided into two groups: the aged group (Model) and the young group (Control). We confirmed β-galactosidase expression, a marker for senescence, in aged muscle cells (identified by α-smooth muscle actin (α-SMA) staining), but not in the young group. mRNA levels of VEGI-251 and death receptor 3 (DR3) were up-regulated (P < 0.05) and total cell protein levels of VEGI-251, DR3 and nuclear factor-kappa B [NF-κB (p65)], membrane protein levels of DR3, and nuclear protein levels of NF-κB (p65) were significantly higher (P < 0.01) in the Model cells compared to Control cells. In conclusion, we have established a method to culture aged detrusor muscle cells derived from porcine bladder. Higher levels of VEGI-251, DR3 and NF-κB (p65) were observed in the aged cells. VEGI-251 may function by increasing DR3 on cellular membranes and promoting the transfer of NF-κB into the nucleus. This suggests that VEGI may be a target for reversing the aging process of bladder detrusor muscle cells.

Construction of a tissue-engineered annulus fibrosus

The intervertebral disc is composed of load-bearing fibrocartilage that may be subjected to compressive forces up to 10 times the body weight. The multilaminated outer layer, the annulus fibrosus (AF), is vulnerable to damage and its regenerative potential is limited, sometimes leading to nuclear herniation. Scaffold-based tissue engineering of AF using stem cell technology has enabled the development of bi-laminate constructs after 10 weeks of culture. It is difficult to know if these constructs are limited by the differentiation state of the stem cells or the culture system. In this study, we have characterized an expandable scaffold-free neoconstruct using autologous AF cells. The construct was prepared from pellet cultures derived from monolayer cultures of AF cells from mature pigs that became embedded in their own extracellular matrix. The pellet cultures were incubated for 24 h in a standardized conical tube and then carefully transferred intact to a culture flask and incubated for 21 days to allow continued matrix synthesis. Cell viability was maintained above 90% throughout the culture period. The engineered scaffold-free construct was compared with the native AF tissue by characterization of gene expression of representative markers, histological architecture, and biochemical composition. The morphological and biochemical characteristics of the cultured disc construct are very similar to that of native AF. The cell number per gram of construct was equal to that of native AF. Expression of aggrecan was elevated in the engineered construct compared with RNA extracted from the AF. The glycosaminoglycan content in the engineered construct showed no significant difference to that from native construct. These data indicate that scaffold-free tissue constructs prepared from AF cells using a pellet-culture format may be useful for in vitro expansion for transplantation into damaged discs.

Synergistic effect of combined growth factors in porcine intervertebral disc degeneration

Although intervertebral disc (IVD) degeneration is one of most common causes of morbidity, its etiology remains unclear. In healthy discs, the rates of synthesis and breakdown of the extracelluar matrix (ECM) are in equilibrium because of intricate regulation by growth factors and catabolic cytokines. Important among these physiologic growth factors are transforming growth factor-β (TGF-β1) and bone morphogenetic protein-2 (BMP-2). Disc degeneration is thought to be associated with a loss of this homeostasis between proteoglycan (PG) synthesis and cytokine-induced degradation leading to up-regulation of matrix metalloproteinases (MMP) families and down-regulation of extracelluar matrix production. Several strategies using biological agents have been attempted to manage IVD degeneration, improving the function and anabolic capabilities of IVD cells and inhibiting matrix degradation. The purpose of this study is to compare the effects of the anabolic cytokines BMP-2 and TGF-β1 with those of the catabolic cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) on porcine annulus fibrosus (AF). The results of this study show that the application of pro-inflammatory cytokines like tumor necrosis factor-α and interleukin-1β to normal annulus fibrosus cells leads to a significant increase in tissue levels of the degradative protease MMP-1. Treatment with a combination of minimum doses of both BMP-2 and TGF-β1 caused a greater decrease in MMP-1 and increase in aggrecan than either cytokine alone, suggesting a synergistic effect of the combined cytokines.

The correlation between microvessel pathological changes of the endplate and degeneration of the intervertebral disc in diabetic rats

In this study, the pathological microvessel changes to the endplate and the degeneration of the intervertebral disc of diabetic rats were examined in order to identify the possible mechanism by which diabetes mellitus (DM) induces degeneration of the intervertebral disc. A total of 30 Sprague-Dawley rats were randomly divided into two groups. DM was induced in one of the groups by streptozotocin (STZ) administration. The rats were sacrificed 4, 8 and 12 weeks later. Five rats from each group were sacrificed at each time interval and lumbar disc and endplate tissue were obtained from each rat. The histological changes, collagen expression, microvessel density (MVD) and apoptosis of the disc were investigated by different methods. The expression of collagen I in the diabetic DM group was higher compared to the control group at the three time points (P<0.01), in contrast to the expression of collagen II. The factor VIII-related antigen (FVIII RAg) was expressed in the control and DM groups, while its expression was relatively low in the DM group. The MVD of the DM group was smaller compared to that of the control group at the three time points (P<0.01). The apoptotic index (AI) in the diabetic group was significantly higher compared to that of the control group at the three time points (P<0.01). A negative correlation was observed between the MVD of the endplates and the notochordal cell AI in the two groups. Compared to the control group, the endplate MVD decreased and the cavity became smaller or disappeared in the diabetic rats. In conclusion, there was a negative correlation between MVD and degenerative changes of the intervertebral disc in diabetic rats.

Intervertebral disk tissue engineering using biphasic silk composite scaffolds

Scaffolds composed of synthetic, natural, and hybrid materials have been investigated as options to restore intervertebral disk (IVD) tissue function. These systems fall short of the lamellar features of the native annulus fibrosus (AF) tissue or focus only on the nucleus pulposus (NP) tissue. However, successful regeneration of the entire IVD requires a combination approach to restore functions of both the AF and NP. To address this need, a biphasic biomaterial structure was generated by using silk protein for the AF and fibrin/hyaluronic acid (HA) gels for the NP. Two cell types, porcine AF cells and chondrocytes, were utilized. For the AF tissue, two types of scaffold morphologies, lamellar and porous, were studied with the porous system serving as a control. Toroidal scaffolds formed out of the lamellar, and porous silk materials were used to generate structures with an outer diameter of 8 mm, inner diameter of 3.5 mm, and a height of 3 mm (the interlamellar distance in the lamellar scaffold was 150-250 μm, and the average pore sizes in the porous scaffolds were 100-250 μm). The scaffolds were seeded with porcine AF cells to form AF tissue, whereas porcine chondrocytes were encapsulated in fibrin/HA hydrogels for the NP tissue and embedded in the center of the toroidal disk. Histology, biochemical assays, and gene expression indicated that the lamellar scaffolds supported AF-like tissue over 2 weeks. Porcine chondrocytes formed the NP phenotype within the hydrogel after 4 weeks of culture with the AF tissue that had been previously cultured for 2 weeks, for a total of 6 weeks of cultivation. This biphasic scaffold simulating in combination of both AF and NP tissues was effective in the formation of the total IVD in vitro.