Expression of the Trp2 allele of COL9A2 is associated with alterations in the mechanical properties of human intervertebral discs

Patient-related risk factors and lifestyle factors for lumbar degenerative disc disease: a systematic review

OBJECTIVE

Back pain is a very widespread disease pattern and is one of the most frequent causes for consultation of a physician in general. In most cases, discogenic changes are the pathomorphological correlate of back pain. Numerous risk factors have been identified for these degenerative changes, but the influence and significance of the risk factors remain unclear, which was the aim of this systematic review.

METHODS

A systematic literature search of the commonly used Pubmed database was performed using specific MESH terms. Further selection of the included studies was performed according to the PRISMA scheme, taking into account scientific merit as well as the relation to the research question.

RESULTS

A total of 111 studies out of 1035 found were finally included in the literature search. 134 risk factors for disc degeneration and disc herniation were identified. These were divided into (1) patient-specific risk factors (n░=░34), (2) radiological risk factors (n░=░31), (3) lifestyle risk factors (n░=░6), (4) workplace-related risk factors (n░=░12), (5) genetic risk factors (n░=░50), and (6) other risk factors (n░=░1). Non-adjustable risk factors were age >50 years (OR 1.7/year), female gender (OR 1.41), family disposition (OR 4.0), comorbidities like atherosclerosis (OR 2.24), arthritic changes in other joints (OR 3.1) and history of injuries of the back (OR 3.1). Adjustable factors were elevated BMI (OR 2.77), comorbidities like hypertension (OR 1.25), dyslipidemia (OR 1.26) and diabetes mellitus (OR 6.8), as well as lifestyle habits like smoking (OR 3.8).

DISCUSSION

In summary, intervertebral disc degenerations and herniations represent multifactorial events whose risk factors can be partly influenced and partly not influenced. This systematic review highlights the current state of knowledge as a basis for creating patient-specific algorithms to calculate risk for the development or progression of degenerative disc changes and disc herniations.

Disruption of Col9a2 expression leads to defects in osteochondral homeostasis and osteoarthritis-like phenotype in mice

Background/Objective

As one of the branched chains of Type IX collagen (Col9), Collagen IX alpha2 (Col9a2) has been reported to be associated with several orthopedic conditions. However, the relationship between Col9a2 and knee osteoarthritis (KOA) remains to be elucidated.

Methods

To probe the relationship between Col9a2 and KOA, we performed a systematic analysis of Col9a2-deficient (Col9a2-/-) mice using whole-mount skeletal staining, Micro-CT (μCT), biomechanics, histomorphometry, immunohistochemistry (IHC), immunofluorescence (IF) and Elisa.

Results

We found that the subchondral bone (SCB) in the knee joint of Col9a2-/- mice became sparse and deformed in the early stage, with altered bone morphometric parameters, reduced load-bearing capacity, dysfunctional bone homeostasis (decreased osteogenesis capacity and elevated bone resorption capacity), diminished cartilage proteoglycans and disrupted cartilage extracellular matrix (ECM) anabolism and catabolism compared with the Col9a2+/+ mice. In the late stage, the cartilage degeneration in Col9a2-/- mice were particularly pronounced compared to Col9a2+/+ mice, as evidenced by severe cartilage destruction and a marked reduction in cartilage thickness and area.

Conclusion

Overall, Col9a2 is essential for maintaining osteochondral homeostasis in the knee joint of mice, and the absence of this gene is accompanied by distinct sclerosis of the SCB and a reduction in load-bearing capacity; in the late stage, in the lack of SCB stress inhibition, excessive load is consistently exerted on the cartilage, ultimately leading to osteoarthritic-like articular cartilage damage.

Mechanobiology of the Human Intervertebral Disc: Systematic Review of the Literature and Future Perspectives

Low back pain is an extremely common condition with severe consequences. Among its potential specific causes, degenerative disc disease (DDD) is one of the most frequently observed. Mechanobiology is an emerging science studying the interplay between mechanical stimuli and the biological behavior of cells and tissues. The aim of the presented study is to review, with a systematic approach, the existing literature regarding the mechanobiology of the human intervertebral disc (IVD), define the main pathways involved in DDD and identify novel potential therapeutic targets. The review was carried out in accordance with the Preferential Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Studies were included if they described biological responses of human IVD cells under mechanical stimulation or alterations of mechanical properties of the IVD determined by different gene expression. Fifteen studies were included and showed promising results confirming the mechanobiology of the human IVD as a key element in DDD. The technical advances of the last decade have allowed us to increase our understanding of this topic, enabling us to identify possible therapeutic targets to treat and to prevent DDD. Further research and technological innovations will shed light on the interactions between the mechanics and biology of the human IVD.

Association between polymorphisms of collagen genes and susceptibility to intervertebral disc degeneration: a meta-analysis

Background

Collagens are important structural components of intervertebral disc. A number of studies have been performed for association between polymorphisms of collagen genes and risk of intervertebral disc degeneration (IVDD) but yielded inconsistent results. Here, we performed a meta-analysis to investigate the association of collagen IX alpha 2 (COL9A2) Trp2, collagen IX alpha 3 (COL9A3) Trp3, collagen I alpha 1 (COL1A1) Sp1 and collagen XI alpha 1 (COL11A1) C4603T polymorphisms with susceptibility to IVDD.

Method

Eligible studies were retrieved by searching MEDLINE, EMBASE, Web of Science prior to 31 March, 2021. Odds ratio (OR) and corresponding 95% confidence interval (CI) were calculated for association strength.

Results

A total of 28 eligible studies (31 datasets comprising 5497 cases and 5335 controls) were included. COL9A2 Trp2 carriers had an increased risk of IVDD than non-carriers in overall population (OR = 1.43, 95% CI 0.99–2.06, P = 0.058), which did not reach statistical significance. However, Trp2 carriers had 2.62-fold (95% CI 1.15–6.01, P = 0.022) risk than non-carriers in Caucasians. COL9A3 Trp3 was not associated with IVDD risk (OR = 1.28, 95% CI 0.81–2.02, P = 0.299). T allele and TT genotype of COL1A1 Sp1 (+ 1245G > T) were correlated with increased risk of IVDD. Significant associations were found between COL11A1 C4603T and IVDD risk under allelic (OR = 1.33, 95% CI 1.20–1.48), dominant (OR = 1.45, 95% CI 1.26–1.67), recessive (OR = 1.55, 95% CI 1.21–1.98) and homozygote model (OR = 1.81, 95% CI 1.40–2.34).

Conclusions

COL1A1 Sp1 and COL11A1 C4603T polymorphism are associated with IVDD risk while the predictive roles of collagen IX gene Trp2/3 need verification in more large-scale studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02724-8.

Actions of Prostaglandins on Human Nucleus Pulposus Metabolism Inferred by Cyclooxygenase 2 Inhibition of Cytokine Activated Cells

OBJECTIVE

Low back pain is frequently treated with nonsteroidal anti-inflammatory drugs (NSAIDs), but little is known about intervertebral disc metabolism of the prostaglandins that are diminished by these drugs. Hence, this study aimed at delineating prostaglandin actions in cytokine activated disc cells by comparing the response of nucleus pulposus (NP) cells to the pro-inflammatory cytokine interleukin (IL)-1β with and without cyclooxygenase 2 (COX-2) inhibition.

METHODS

NP cells cultured in alginate beads were activated with IL-1β ± the COX-2 inhibitor Sc-58125. Media harvested from cultured cells were analyzed for prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2α), IL-6, and matrix metalloproteinase (MMP)-3 by enzymelinked immunosorbent assay and nitric oxide by Griess Reaction. Gene expression along with proteoglycan, collagen, and total protein synthesis were also measured.

RESULTS

IL-1β increased culture media PGE2 and PGF2α, but decreased proteoglycan and collagen syntheses as well as mRNA expression of the matrix genes aggrecan, versican, collagen I, and collagen II. COX-2 inhibition partially rescued proteoglycan and collagen syntheses and collagen I mRNA, but decreased collagen II mRNA IL-1β activated NP cells. COX-2 inhibition initially enhanced and subsequently reduced IL-1β induced inducible nitric oxide synthase, without altering medium nitrite. IL-1β induction of MMP-3 mRNA was increased by COX-2 inhibition at 24 and 48 hours.

CONCLUSION

COX-2 inhibition alters the response of NP cells to IL-1β, suggesting IL-1β action on disc cells is mediated at least in part through COX-2 and its prostaglandins. COX-2 inhibition produces minimal effects on several key catabolic mediators, with the exception of MMP-3. Blocking COX-2 might be beneficial for maintaining disc matrix since it provides an overall rescue of IL-1 induced loss of matrix protein synthesis.

Etiology of developmental spinal stenosis: A genome-wide association study

Our study aimed to identify possible single nucleotide polymorphisms (SNPs) via a genome-wide association study (GWAS) approach and a candidate gene platform that were associated with lumbar developmental spinal stenosis (DSS). Southern Chinese population-based study volunteers were assessed (age range: 18-55 years). DSS was defined as the anteroposterior bony spinal canal diameter on T1-weighted axial MRI of L1 to S1. Genotyping was performed using the Illumina HumanOmniZhongHua-8 BeadChip. Using the canal diameter as the quantitative trait, genomic statistical analyses was performed. A total of 469 subjects were recruited. The mean axial AP measurements noted were: L1: 21.8 mm, L2: 21.9 mm, L3: 22.4 mm, L4: 20.2 mm, L5: 19.6 mm, and S1: 17.3 mm. Q-Q plots of genome-wide associations found significant differences in L4 and L5 measurements. More significant SNPs were found on chromosomes 8, 11, and 18. Low-density lipoprotein receptor-related protein 5 on chromosome 11 was found to be an important functional gene in canal bony development via candidate gene approach. We found two clusters in the findings with one including the upper levels (L1-L4) and the other the lower levels (L5 and S1). This is the first GWAS addressing DSS. The presence of multiple SNPs suggests a multi-factorial origin of DSS. Further analyses noted region-specific genetic predisposition, delineating distinct upper to lower lumbar regions of DSS. With better understanding of the DSS phenotype and genetic markers, the at-risk population can be identified early, preventative measures can be initiated, lifestyle/activity modification can be implemented, and more novel and precision-based therapeutics can be developed. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1262-1268, 2018.

PARAMETERS OF NUCLEAR MAGNETIC RESONANCE IN PATIENTS WITH CONGENITAL NARROWING OF THE LUMBAR SPINAL CANAL

ABSTRACT Objective: To compare the morphological parameters of magnetic resonance in patients with congenital narrowing of the lumbar spinal canal with patients with low back pain. Methods: A descriptive, retrospective, observational study was conducted with measurements in the axial and sagittal magnetic resonance sections of the vertebral body and canal of the lumbar spine of 64 patients with diagnosis of low back pain, which were compared with resonance images taken from 31 Mexican patients with congenital narrowing of the lumbar spinal canal. Results: The results show that patients with congenital narrowing of the lumbar spinal canal in the axial sections have a difference in diameters, being L2<13.9 mm, L3<13.3 mm, L4<12.9 mm, L5<13.1 mm, compared with controls L2<20.5 mm, L3<20.5 mm, L4<19.3 mm, L5<18.1 mm with p = 0.000. Conclusions: We found different measurements in the Mexican population compared to those found by similar studies. With the parameters obtained, it would be possible to make the proper diagnosis, surgical planning, and treatment.

Modic changes of the lumbar spine: prevalence, risk factors, and association with disc degeneration and low back pain in a large-scale population-based cohort

BACKGROUND CONTEXT

Modic changes (MC) are bone marrow lesions on magnetic resonance imaging (MRI), suggestive of being associated with low back pain (LBP). Data on determinants of MC and their association with disc degeneration and other spinal phenotypes, as well as that of LBP, rely mostly on small-scale patient populations and remain controversial.

PURPOSE

This study addressed the potential determinants of MC and their association with disc degeneration and LBP among Southern Chinese.

STUDY DESIGN/SETTING

A cross-sectional, population-based study was carried out.

PATIENT SAMPLE

This study consisted of 2,449 Southern Chinese volunteers.

METHODS

Sagittal T2-weighted MRIs of the lumbar spine were assessed for the presence of MC and other spinal phenotypes (eg, disc degeneration, disc displacement, Schmorl nodes) in all individuals. Subjects' demographics, occupation, lifestyle, and clinical profiles were assessed.

RESULTS

The overall prevalence of MC was 5.8% (n=141), which increased with advancing age. Modic changes predominantly occurred at the lowest two lumbar levels (83%). In the multivariate analyses, only the presence of disc displacement and a higher disc degeneration score were associated with MC at the upper lumbar levels (L1/L2-L3/L4) (p<.01). The presence of MC at the lowest two lumbar levels (L4/L5-L5/S1) were associated with age, the presence of Schmorl nodes, disc degeneration or displacement, and historical lumbar injury (p<.01). Subjects who were both smokers and overweight or obese had increased likelihood of MC in the lower spine (OR: 2.18; 95% CI: 1.10-4.30). The presence of MC at the lower lumbar levels were associated with historical LBP (OR: 1.93; 95% CI: 1.05-3.54) and with severity and duration of symptoms (p<.05).

CONCLUSIONS

Based on one of the largest MRI studies to assess lumbar MC, we noted that MC were associated with both disc degeneration and the presence and severity of LBP. Determinants and association of MC with disc degeneration and clinical symptoms in the upper versus the lower lumbar spine were different. Our study further stresses the significance of MC as important imaging phenotypes associated with LBP.

Presence and function of microRNA-92a in chondrogenic ATDC5 and adipose-derived mesenchymal stem cells

The aim of the present study was to investigate the presence and biological function of microRNA-92a (miR-92a) in chondrogenesis and cartilage degeneration. Human adipose-derived mesenchymal stem cells (hADSCs) in micromass and chondrocyte-like ATDC5 cells were induced to chondrogenesis, and primary human/mouse chondrocytes (PHCs/PMCs) and chondrogenic ATDC5 cells were stimulated with interleukin-1β (IL-1β). An miR-92a mimic/inhibitor was transfected into the ATDC5 cells using lipofectamine 2000. Gene expression was analyzed using reverse transcription-quantitative polymerase chain reaction. Alcian blue was used to stain the cartilage nodules and chondrogenic micromass. The potential target genes, signaling pathways and functions of miR-92a were examined using miRanda, miRDB, CLIP-Seq, TargetScan and Kyoto Encyclopedia of Genes and Genomes. The expression of miR-92a was elevated in the chondrogenic ATDC5 cells and hADSCs, and also in the IL-1β-induced ATDC5 cells, PMCs and PHCs. Forced expression of miR-92a enhanced the expression levels of col9a2 and aggrecan. A total of 279 genes were predicted as potential target genes of miR-92a. The phosphoinositide 3-kinase/PI3K)-Akt, ErbB and focal adhesion kinase pathways, extracellular matrix (ECM)-receptor interaction and the mammalian target of rapamycin (mTOR) signaling pathway were suggested to mediate the effects of miR-92a on chondrogenesis and cartilage degeneration. These results demonstrated that miR-92a was involved in chondrogenesis and the chondrocyte response induced by IL-1β. miR-92a positively contributed to the expression of col9a2 and of aggrecan.

MiR-34a promotes Fas-mediated cartilage endplate chondrocyte apoptosis by targeting Bcl-2

Apoptosis of cartilage endplate (CEP) chondrocytes is associated with the pathogenesis of intervertebral disk degeneration (IDD). Recent studies have shown that miR-34a is crucially involved in chondrocyte apoptosis during osteoarthritic cartilage. Here, we investigated the involvement of miR-34a in CEP chondrocyte apoptosis in IDD. In human degenerated CEP chondrocytes, miRNA (miR)-34a was markedly elevated in association with increased apoptosis. Bioinformatics target prediction identified Bcl-2 as a putative target of miR-34a. Furthermore, miR-34a inhibited Bcl-2 expression by directly targeting their 3'-untranslated regions, and this inhibition was abolished by mutation of the miR-34a binding sites. In vitro, knockdown of miR-34a in human endplate chondrocytes resulted in overexpression of Bcl-2, whereas upregulation of miR-34a led to repression of Bcl-2. Fas-mediated apoptosis was decreased when antagonizing miR-34a with locked nucleotide analog-miR-34a in human endplate chondrocytes. Taken together, our results demonstrate that upregulated miR-34a potentiates Fas-mediated endplate chondrocyte apoptosis, which is associated with IDD.

Electroacupuncture stimulates remodeling of extracellular matrix by inhibiting apoptosis in a rabbit model of disc degeneration

The present study was designed to determine whether EA stimulates remodeling of extracellular matrix by inhibiting apoptosis in degenerated disc. 40 rabbits were randomly assigned to one of the four groups. Animal model was established by a loading device. Magnetic resonance imaging and Pfirrmann's classification were obtained to evaluate both the model and the EA treatment on disc degeneration. The ultrastructure of discs was observed by TEM. Apoptosis involvement was determined with TUNEL staining and western blot for the protein expression of Bax and Bcl-2. The results indicated that EA intervention decreased the MRI grades. TEM analysis showed an apparent remodeling and rearrangement of disc ECM after EA intervention for 28 days. The number of TUNEL-positive cells in the EA group was significantly lower than that in the compression group. The protein expression demonstrated an antiapoptosis effect mediated by EA. Increased expression of Bcl-2 proteins and reduced Bax protein expression were detected after 28 days treatment. It was concluded that antiapoptosis pathway probably participates in the mechanism of EA stimulating the remodeling of ECM in disc degeneration.

Defining clinically relevant values for developmental spinal stenosis: a large-scale magnetic resonance imaging study

STUDY DESIGN

Case-control study.

OBJECTIVE

The aim of this study was to define clinically relevant relative and critical (absolute) magnetic resonance imaging values of lumbar spinal stenosis in a cohort of 100 surgical cases and 100 asymptomatic controls.

SUMMARY OF BACKGROUND DATA

Developmental spinal stenosis is a precipitating factor in patients presenting with lumbar canal stenosis. Yet, due to a lack of agreement on definitions and methods of assessment, as well as ethnic-specific normative values, its prevalence and significance is not known.

METHODS

This was a case-control study comparing 100 age and sex-matched asymptomatic, volunteers with that of 100 patients who underwent surgery for spinal stenosis. All patients were of Chinese ethnicity and their details were blinded to 2 observers. Spinal stenosis parameters were measured on the basis of axial (pedicle level) and sagittal (midsagittal) magnetic resonance images.

RESULTS

Anteroposterior spinal canal diameters change with levels. At each level, patients were found to have significantly narrower anteroposterior canal diameters than controls. By use of receiver operating characteristic curve, we defined developmental spinal stenosis if the anteroposterior canal diameter was at L1 <20 mm, L2 <19 mm, L3 <19 mm, L4 <17 mm, L5 <16 mm, and at S1 <16 mm on the basis of a value including 50% of controls and demonstrated best sensitivity and specificity. Furthermore, for L4, L5, and S1, critical stenosis values could be defined, below which almost all subjects needed surgery, these were L4 <14 mm, L5 <14 mm, and S1 <12 mm.

CONCLUSION

This is the largest magnetic resonance imaging-based study with standardized measurements and comparable groups to determine clinically relevant magnetic resonance imaging criteria for lumbar spinal stenosis. The findings strongly suggest that developmental stenosis plays an important role in the pathogenesis of symptomatic spinal stenosis. Critical values of stenosis below which symptoms were highly likely were defined. These will need to be validated by longitudinal studies in future. However, they may possess clinical utility in determining the appropriate levels requiring canal-widening surgery.

LEVEL OF EVIDENCE

3.

Intervertebral discs from spinal nondeformity and deformity patients have different mechanical and matrix properties

BACKGROUND CONTEXT

It is well-established that disc mechanical properties degrade with degeneration. However, prior studies utilized cadaveric tissues from donors with undefined back pain history. Disc degeneration may present with pain at the affected motion segment, or it may be present in the absence of back pain. The mechanical properties and matrix quantity of discs removed and diagnosed for degeneration with patient chronic pain may be distinct from those with other diagnoses, such as spinal deformity.

PURPOSE

To test the hypothesis that discs from nondeformity segments have inferior mechanical properties than deformity discs owing to differences in matrix quality.

STUDY DESIGN/SETTING

In vitro study comparing the mechanical and matrix properties of discs from surgery patients with spinal nondeformity and deformity.

METHODS

We analyzed nucleus and annulus samples (8-11 specimens per group) from surgical discectomy patients as part of a fusion or disc replacement procedure. Tissues were divided into two cohorts: nondeformity and deformity. Dynamic indentation tests were used to determine energy dissipation, indentation modulus, and viscoelasticity. Tissue hydration at a physiologic pressure was assessed by equilibrium dialysis. Proteoglycan, collagen, and collagen cross-link content were quantified. Matrix structure was assessed by histology.

RESULTS

We observed that energy dissipation was significantly higher in the nondeformity nucleus than in the deformity nucleus. Equilibrium dialysis experiments showed that annulus swelling was significantly lower in the nondeformity group. Consistent with this, we observed that the nondeformity annulus had lower proteoglycan and higher collagen contents.

CONCLUSIONS

Our data suggest that discs from nondeformity discs have subtle differences in mechanical properties compared with deformity discs. These differences were partially explained by matrix biochemical composition for the annulus, but not for the nucleus. The results of this study suggest that compromised matrix quality and diminished mechanical properties are features that potentially accompany discs of patients undergoing segmental fusion or disc replacement for disc degeneration and chronic back pain. These features have previously been implicated in pain via instability or reduced motion segment stiffness.

Characterization of microRNA expression profiles in patients with intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is associated with lower back pain and is a global burden with severe healthcare and socioeconomic consequences. However, the underlying mechanisms of IDD remain largely unelucidated. Accumulating evidence has indicasted that newly defined gene regulators, microRNAs (miRNAs), play a vital role in neurodegenerative, pathophysiological and certain reproductive disorders. To characterize the differential miRNA expression profiles between IDD and spinal cord injury, specimens from 3 patients with IDD and 3 with spinal cord injury were selected for microarray analysis. Total RNA from these 6 specimens was extracted and subjected to global miRNA expression analysis using the Exiqon miRCURY™ LNA Array (v.16.0). The microarray data were then validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). In addition, bioinformatics analysis was performed to investigate the dysregulated miRNA target genes and signaling pathways involved. Among the miRNAs analyzed, 25 miRNAs were found to be upregulated and 26 were found to be downregulated in the IDD group compared with the spinal cord injury group. The qRT-PCR results validated the microarray data. Bioinformatics analysis indicated that the signaling pathways most likely to be controlled by these miRNAs were the phosphoinositide 3-kinase (PI3K)-Akt, mitogen-activated protein kinase (MAPK), epidermal growth factor receptor (EGFR; ErbB) and Wnt pathways. Our results demonstrated that the miRNA expression in patients with IDD differed significantly from that in patients who sustained injury to the intervertebral disc. Our data indicate that the dysregulated miRNAs control the signaling pathways important for the maintenance of IDD. Further studies on miRNA target gene identification and biological functions may address the specific regulatory mechanisms of miRNAs in IDD, and may provide valuable insight into the diagnosis and treatment of IDD.

MiR-27a regulates apoptosis in nucleus pulposus cells by targeting PI3K

The precise role of apoptosis in the pathogenesis of intervertebral disc degeneration (IDD) remains to be elucidated. We analyzed degenerative nucleus pulposus (NP) cells and found that the expression of miR-27a was increased. The overexpression of miR-27a was further verified using real-time RT-PCR. Bioinformatics target prediction identified phosphoinositide-3 kinases (PI3K) as putative targets of miR-27a. Furthermore, miR-27a inhibited PI3K expression by directly targeting their 3’-UTRs, and this inhibition was abolished by mutation of the miR-27a binding sites. Various cellular processes including cell growth, proliferation, migration and adhesion are regulated by activation of the PI3K/AKT signaling pathway, and nucleus pulposus cells are known to strongly express the phosphorylated survival protein AKT. Our results identify PI3K as a novel target of miR-27a. Upregulation of miR-27a thus targets PI3K, initiating apoptosis of nucleus pulposus cells. This present study revealed that downregulated miR-27a might develop a novel intervention for IDD treatment through the prevention of apoptosis in Nucleus pulposus Cells.

Global identification of genes related to nutrient deficiency in intervertebral disc cells in an experimental nutrient deprivation model

Background

Intervertebral disc degeneration is a significant cause of degenerative spinal diseases. Nucleus pulposus (NP) cells reportedly fail to survive in large degenerated discs with limited nutrient availability. Therefore, understanding the regulatory mechanism of the molecular response of NP cells to nutrient deprivation may reveal a new strategy to treat disc degeneration. This study aimed to identify genes related to nutrient deprivation in NP cells on a global scale in an experimental nutrient deprivation model.

Methodology/Principal Findings

Rat NP cells were subjected to serum starvation. Global gene expression was profiled by microarray analysis. Confirmation of the selected genes was obtained by real-time polymerase chain reaction array analysis. Western blotting was used to confirm the expression of selected genes. Functional interactions between p21^Cip1 and caspase 3 were examined. Finally, flow cytometric analyses of NP cells were performed. Microarray analysis revealed 2922 differentially expressed probe sets with ≥1.5-fold changes in expression. Serum starvation of NP cells significantly affected the expression of several genes involved in DNA damage checkpoints of the cell cycle, including Atm, Brca1, Cdc25, Gadd45, Hus1, Ppm1D, Rad 9, Tp53, and Cyclin D1. Both p27^Kip1 and p53 protein expression was upregulated in serum-starved cells. p21^Cip1 expression remained in NP cells transfected with short interfering RNA targeting caspase 3 (caspase 3 siRNA). Both G1 arrest and apoptosis induced by serum starvation were inhibited in cells transfected with caspase 3 siRNA.

Conclusions/Significance

Nutrient deprivation in NP cells results in the activation of a signaling response including DNA damage checkpoint genes regulating the cell cycle. These results provide novel possibilities to improve the success of intervertebral disc regenerative techniques.

Genetic polymorphisms associated with intervertebral disc degeneration

BACKGROUND CONTEXT

Disc degeneration (DD) is a multifaceted chronic process that alters the structure and function of the intervertebral discs and can lead to painful conditions. The pathophysiology of degeneration is not well understood, but previous studies suggest that certain genetic polymorphisms may be important contributing factors leading to an increased risk of DD.

PURPOSE

To review the genetic factors in DD with a focus on polymorphisms and their putative role in the pathophysiology of degeneration. Elucidating the genetic components that are associated with degeneration could provide insights into the mechanism of the process. Furthermore, defining these relationships and eventually using them in a clinical setting may allow an identification and early intervention for those who are at a high risk for painful DD.

STUDY DESIGN

Literature review.

METHODS

This literature review focused on the studies concerning genetic polymorphisms and their associations with DD.

RESULTS

Genetic polymorphisms in 20 genes have been analyzed in association with DD, including vitamin D receptor, growth differentiation factor 5 (GDF5), aggrecan, collagen Types I, IX, and XI, fibronectin, hyaluronan and proteoglycan link protein 1 (HAPLN1), thrombospondin, cartilage intermediate layer protein (CILP), asporin, MMP1, 2, and 3, parkinson protein 2, E3 ubiquitin protein ligase (PARK2), proteosome subunit β type 9 (PSMB9), tissue inhibitor of metalloproteinase (TIMP), cyclooxygenase-2 (COX2), and IL1α, IL1β, and IL6. Each genetic polymorphism codes for a protein that has a functional role in the pathogenesis of DD.

CONCLUSIONS

There are known associations between several genetic polymorphisms and DD. Of the 20 genes analyzed, polymorphisms in vitamin D receptor, aggrecan, Type IX collagen, asporin, MMP3, IL1, and IL6 show the most promise as functional variants. Genetic studies are crucial for understanding the mechanism of the degeneration. This genetic information could eventually be used as a predictive model for determining a patient's risk for symptomatic DD.

FasL expression on human nucleus pulposus cells contributes to the immune privilege of intervertebral disc by interacting with immunocytes

The mechanisms of immune privilege in human nucleus pulposus (NP) remain unclear. Accumulating evidence indicates that Fas ligand (FasL) might play an important role in the immune privilege of the disc. We aimed for addressing the role of FasL expression in human intervertebral disc degeneration (IDD) and immune privilege in terms of the interaction between NP cells and immunocytes via the FasL-Fas machinery. We collected NP specimens from 20 patients with IDD as degenerative group and 8 normal cadaveric donors as control. FasL expression was detected by qRT-PCR, western blotting and flow cytometry (FCM). We also collected macrophages and CD8(+) T cells from the peripheral blood of patients with IDD for co-cultures with NP cells. And macrophages and CD8(+) T cells were harvested for apoptosis analysis by FCM after 2 days of co-cultures. We found that FasL expression in mRNA, protein and cellular resolutions demonstrated a significant decrease in degenerative group compared with normal control (p<0.05). FCM analysis found that human NP cells with increased FasL expression resulted in significantly increased apoptosis ratio of macrophages and CD8(+) T cells. Our study demonstrated that FasL expression tends to decrease in degenerated discs and FasL plays an important role in human disc immune privilege, which might provide a novel target for the treatment strategies for IDD.

Down-regulated CK8 expression in human intervertebral disc degeneration

As an intermediate filament protein, cytokeratin 8 (CK8) exerts multiple cellular functions. Moreover, it has been identified as a marker of notochord cells, which play essential roles in human nucleus pulposus (NP). However, the distribution of CK8 positive cells in human NP and their relationship with intervertebral disc degeneration (IDD) have not been clarified until now. Here, we found the percentage of CK8 positive cells in IDD (25.7±4.14%) was significantly lower than that in normal and scoliosis NP (51.9±9.73% and 47.8±5.51%, respectively, p<0.05). Western blotting and qRT-PCR results confirmed the down-regulation of CK8 expression in IDD on both of protein and mRNA levels. Furthermore, approximately 37.4% of cell clusters were CK8 positive in IDD. Taken together, this is the first study to show a down-regulated CK8 expression and the percentage of CK8 positive cell clusters in IDD based upon multiple lines of evidence. Consequently, CK8 positive cells might be considered as a potential option in the development of cellular treatment strategies for NP repair.

The association of lumbar intervertebral disc degeneration on magnetic resonance imaging with body mass index in overweight and obese adults: a population-based study

OBJECTIVE

To investigate the association of being overweight or obese with the presence, extent, and severity of lumbar disc degeneration on magnetic resonance imaging (MRI) in adults.

METHODS

A population-based cross-sectional study of 2,599 southern Chinese volunteers was conducted. Subjects underwent radiographic and clinical assessment, and weight and height were measured. Sagittal T2-weighted MRIs of the lumbar spine were obtained. The presence, extent, and severity of disc degeneration and additional radiographic and clinical parameters were assessed. Asian-modified body mass index (BMI) (kg/m(2) ) categories were used. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated.

RESULTS

The study included 1,040 men and 1,559 women (mean age 41.9 years). Disc degeneration was noted in 1,890 subjects (72.7%). BMI was significantly higher in subjects with disc degeneration (mean 23.3 kg/m(2) ) than in subjects without degeneration (mean 21.7 kg/m(2) ) (P < 0.001). A significant increase in the number of degenerated levels (P < 0.001), global severity of disc degeneration (P < 0.001), and end-stage disc degeneration with disc space narrowing (P < 0.001) was noted with elevated BMI, in particular in overweight and obese subjects. In the adjusted multivariate logistic regression model, there was a positive linear trend (r(2) = 0.99) between BMI and the overall presence of disc degeneration in overweight (OR 1.30 [95% CI 1.03-1.62]) and obese (OR 1.79 [95% CI 1.17-2.74]) subjects. End-stage disc degeneration with disc space narrowing was significantly more pronounced in obese subjects (adjusted OR 1.72 [95% CI 1.23-2.41] [reference normal weight]).

CONCLUSION

Our findings, in one of the largest studies to systematically assess lumbar disc degeneration on MRI, indicated a significant association between the presence, extent, and global severity of disc degeneration with weight in overweight and obese adults.

Type IX collagen neo-deposition in degenerative discs of surgical patients whether genotyped plus or minus for COL9 risk alleles

STUDY DESIGN

Immunohistochemical analysis of type IX collagen in disc tissue from spinal fusion patients.

OBJECTIVE

To determine if collagen IX can be detected in adult disc tissue removed at spinal fusion surgery from patients either with or without degeneration-associated tryptophan single nucleotide polymorphisms (SNPs) and whether the distribution is associated either with severity of degeneration or incidence of a collagen IX SNP genotype.

SUMMARY OF BACKGROUND DATA

Genetic factors are strongly associated with risk of development and/or progression of disc degeneration. Two SNPs that introduce tryptophan polymorphisms in COL9A2 and COL9A3 are independently linked to an increased risk of lumbar disc disease. Although tryptophan variants are associated with accelerated degeneration, it is not known if collagen IX can be detected in adult disc tissue.

METHODS

We selected age-matched disc samples from five clinical groups: fracture with Trp(-) (six cases), herniation (six cases), degeneration (five cases), spondylolisthesis with Trp(-) (eight cases), and spondylolisthesis/herniation/fracture with Trp(+) (six cases of Trp3 allele and one case of Trp2 allele). Using hematoxylin and eosin staining and immunohistochemical staining (collagens IX and IIA), 78 sections from 32 patients were analyzed. Selected disc tissues were assayed biochemically for collagen IX.

RESULTS

Focal deposition of collagen IX was observed in regions of adult human disc tissue from spines showing degenerative changes in patients whether or not they were positive for a tryptophan SNP. However, in nondegenerative control disc tissue from fracture cases, little or no collagen IX was detected. The latter finding was confirmed by direct biochemical analyses for collagen IX in pooled samples of normal adult human annulus fibrosus or nucleus pulposus.

CONCLUSION

During growth and maturation of the disc, collagen IX is presumably removed completely during matrix remodeling so that the protein is absent from normal adult annulus and nucleus but can reappear at sites of degeneration presumably as part of a repair response to mechanical injury.

Does hormone replacement therapy prevent lateral rotatory spondylolisthesis in postmenopausal women?

PURPOSE

Degenerative scoliosis usually begins at menopause and lateral rotatory olisthesis (LRO) might be a triggering factor in the onset of degenerative scoliosis in postmenopausal women. We set out to evaluate the influence of hormone replacement therapy (HRT) on degenerative scoliosis and on LRO.

METHODS

A cross-sectional study was conducted in 146 postmenopausal women: 75 women had received HRT for more than 1 year (HRT > 1) and 71 women had never received HRT or less than 1 year (HRT < 1). Scoliotic curve, LRO, sacral slope, lordosis, kyphosis were measured. The excess risk of LRO associated with age, BMI, isometric strength of brachial biceps, bone mineral density, lean mass and HRT was evaluated using a multiple logistic regression model.

RESULTS

No difference was found in sacral slope, lumbar lordosis or thoracic kyphosis between both groups or in the presence of scoliosis. The prevalence of LRO was significantly lower in HRT >1 than HRT <1 (8 vs. 30%) while the risk was dependent on age, HRT and their interaction. LRO increased with age only in HRT <1 (11% when aged ≤66 years vs. 39% when aged >66 years, p = 0.013), whereas the prevalence of LRO remained stable in HRT >1.

CONCLUSIONS

LRO was significantly lower in women who received HRT. The excess risk of LRO was dependent on both age and HRT status. These findings suggest that HRT might prevent the onset of LRO, and therefore might contribute to the prevention of low back pain.

Structure and biology of the intervertebral disk in health and disease

The intervertebral disks along the spine provide motion and protection against mechanical loading. The 3 structural components, nucleus pulposus, annulus fibrosus, and cartilage endplate, function as a synergistic unit, though each has its own role. The cells within each of these components have distinct origins in development and morphology, producing specific extracellular matrix proteins that are organized into unique architectures fit for intervertebral disk function. This article focuses on various aspects of intervertebral disk biology and disruptions that could lead to diseases such as intervertebral disk degeneration.

Deregulated miR-155 promotes Fas-mediated apoptosis in human intervertebral disc degeneration by targeting FADD and caspase-3

The role of apoptosis in the pathogenesis of intervertebral disc degeneration (IDD) remains enigmatic. Accumulating evidence has shown that the apoptotic machinery is regulated by miRNAs. We hypothesized that miRNAs might contribute to apoptosis in IDD. We have found that 29 miRNAs were differentially expressed and miR-155 was down-regulated in degenerative nucleus pulposus (NP). The deregulation of miR-155 was further verified using real-time PCR (0.56 fold, p < 0.05). Bioinformatics target prediction identified FADD and caspase-3 as putative targets of miR-155. Furthermore, miR-155 inhibited FADD and caspase-3 expression by directly targeting their 3'-UTRs, which was abolished by mutation of the miR-155 binding sites. In vitro up-regulation of miR-155 in human NP cells by transfection with lentiviral pre-miR-155 resulted in repression of FADD and caspase-3; whereas knockdown of miR-155 with lentiviral antigomiR-155 led to over-expression of FADD and caspase-3. Also, Fas-mediated apoptosis was increased when antagonizing miR-155 and decreased when using pre-miR-155 in human NP cells. In addition, we presented direct evidence of NP cells undergoing apoptosis in IDD tissues using transmission electron microscopy analysis. Moreover, a combination of in situ hybridization (ISH) and immunohistochemistry (IHC) revealed that miR-155 expressed in the cytoplasm of human NP cells with reverse correlation with FADD and caspase-3. In summary, this is the first study addressing the underlying mechanisms of IDD in terms of apoptosis and miRNAs. Furthermore, caspase-3 is identified as a novel target of miR-155. Our results suggest that deregulated miR-155 promotes Fas-mediated apoptosis in human IDD by targeting FADD and caspase-3, implicating an aetiological and therapeutic role of miR-155 in IDD.

The relationship between disc degeneration, low back pain, and human pain genetics

Dai F, Belfer I, Schwartz C, et al. Association of catechol-O-methyltransferase genetic variants with outcome in patients undergoing surgical treatment for lumbar degenerative disc disease. Spine J 2010:10:949-957 (in this issue).

ISSLS prize winner: prevalence, determinants, and association of Schmorl nodes of the lumbar spine with disc degeneration: a population-based study of 2449 individuals

STUDY DESIGN

A cross-sectional population-based magnetic resonance imaging study of Schmorl nodes (SN) in the lumbar spine.

OBJECTIVE

To determine the prevalence and potential determinants of SN, and their association with intervertebral disc degeneration.

SUMMARY OF BACKGROUND DATA

SN represent intravertebral disc herniation and are commonly seen in the spine. Their reported prevalence and determinants vary, and their association with disc degeneration remains uncertain. Data based on this large scale population-based study of intervertebral disc degeneration would provide important information for understanding SN and their pathomechanism.

METHODS

Sagittal T2-weighted magnetic resonance imagings of the lumbar spine were analyzed in 2449 volunteers. Two independent observers assessed the images for the presence of SN, and scored for additional radiologic features (e.g., severity of degeneration, presence of disc bulge/extrusion). Subject demographics were assessed by standardized questionnaire.

RESULTS

SN were found in 16.4% (n = 401; 219 males, 182 females; mean age = 42.3) of our study population (981 males, 1468 females; mean age = 40.4), being most common at L1/2 and L2/3 (54.1%). Multivariate logistic regression revealed that males, taller and heavier individuals had an increased likelihood of SN (P < 0.005), but association between SN and age were not discerned. Overall presence of SN was associated with disc degeneration (P < 0.001), and linearly correlated (R = 0.97) with increase in severity of degeneration. SN were particularly associated with severe disc degeneration at L1/2 and L2/3 with 22- to 15-fold increased odds, respectively (P < 0.0001), but less than 5-fold increased odds (P < 0.001) were noted in the lower lumbar spine.

CONCLUSION

In a population-based cohort, 16.4% of Southern Chinese subjects had SN at 1 or more lumbar levels. Males, taller and heavier individuals had increased likelihood of SN. Interestingly, SN were highly associated with severity of disc degeneration.

Localized Intervertebral Disc Injury Leads to Organ Level Changes in Structure, Cellularity, and Biosynthesis

A literature review and new data are presented to evaluate the influence of intervertebral disc (IVD) injury on biomechanics, cellularity, inflammation, and biosynthesis. Literature and new experimental evidence support the hypothesis that localized injury in the disc can lead to immediate and long-term organ level changes in biomechanics and biology of the IVD. Biomechanical properties defining motion segment bending behaviors sensitive to injuries that affect anulus fibrosus (AF) integrity and nucleus pulposus (NP) pressurization. Axial mechanics and IVD height measurements show sensitivity to puncture and other injuries that reduce NP pressurization. Torsional biomechanics are strongly affected by the extent and location of AF lesions but are less sensitive to reduced NP pressurization. IVD injuries such as puncture and stab incisions may also lead to a cascade of biological changes consistent with degeneration, including loss of cellularity, altered biosynthesis and inflammation. New results on effects of 25G needle injection of saline into a bovine IVD organ culture model demonstrated a loss of cellularity and down-regulation of matrix gene expression, providing a specific example of how a minor injury affects the IVD organ response. We conclude that localized injuries in the IVD can induce an organ level degenerative cascade through biomechanical and biological mechanisms, and their interactions. Attempts at IVD repair should target the dual biomechanical roles of the anulus of maintaining nucleus pressurization and transmitting loads across the vertebrae. Biologically, it remains important to maintain IVD cellularity and biosynthesis rates following injury to prevent downstream degenerative changes.

Current evidence for a modulation of low back pain by human genetic variants

The manifestation of chronic back pain depends on structural, psychosocial, occupational and genetic influences. Heritability estimates for back pain range from 30% to 45%. Genetic influences are caused by genes affecting intervertebral disc degeneration or the immune response and genes involved in pain perception, signalling and psychological processing. This inter-individual variability which is partly due to genetic differences would require an individualized pain management to prevent the transition from acute to chronic back pain or improve the outcome. The genetic profile may help to define patients at high risk for chronic pain. We summarize genetic factors that (i) impact on intervertebral disc stability, namely Collagen IX, COL9A3, COL11A1, COL11A2, COL1A1, aggrecan (AGAN), cartilage intermediate layer protein, vitamin D receptor, metalloproteinsase-3 (MMP3), MMP9, and thrombospondin-2, (ii) modify inflammation, namely interleukin-1 (IL-1) locus genes and IL-6 and (iii) and pain signalling namely guanine triphosphate (GTP) cyclohydrolase 1, catechol-O-methyltransferase, mu opioid receptor (OPMR1), melanocortin 1 receptor (MC1R), transient receptor potential channel A1 and fatty acid amide hydrolase and analgesic drug metabolism (cytochrome P450 [CYP]2D6, CYP2C9).