Mechanics and biology in intervertebral disc degeneration: a vicious circle

FOXO are required for intervertebral disk homeostasis during aging and their deficiency promotes disk degeneration

Intervertebral disk (IVD) degeneration is a prevalent age-associated musculoskeletal disorder and a major cause of chronic low back pain. Aging is the main risk factor for the disease, but the molecular mechanisms regulating IVD homeostasis during aging are unknown. The aim of this study was to investigate the function of FOXO, a family of transcription factors linked to aging and longevity, in IVD aging and age-related degeneration. Conditional deletion of all FOXO isoforms (FOXO1, 3, and 4) in IVD using the Col2a1Cre and AcanCreER mouse resulted in spontaneous development of IVD degeneration that was driven by severe cell loss in the nucleus pulposus (NP) and cartilaginous endplates (EP). Conditional deletion of individual FOXO in mature mice showed that FOXO1 and FOXO3 are the dominant isoforms and have redundant functions in promoting IVD homeostasis. Gene expression analyses indicated impaired autophagy and reduced antioxidant defenses in the NP of FOXO-deficient IVD. In primary human NP cells, FOXO directly regulated autophagy and adaptation to hypoxia and promoted resistance to oxidative and inflammatory stress. Our findings demonstrate that FOXO are critical regulators of IVD homeostasis during aging and suggest that maintaining or restoring FOXO expression can be a therapeutic strategy to promote healthy IVD aging and delay the onset of IVD degeneration.

Early changes in the extracellular matrix of the degenerating intervertebral disc, assessed by Fourier transform infrared imaging

OBJECTIVE

Mechanical overloading induces a degenerative cell response in the intervertebral disc. However, early changes in the extracellular matrix (ECM) are challenging to assess with conventional techniques. Fourier Transform Infrared (FTIR) imaging allows visualization and quantification of the ECM. We aim to identify markers for disc degeneration and apply these to investigate early degenerative changes due to overloading and katabolic cell activity.

DESIGN

Three experiments were conducted; Exp 1.: In vivo, lumbar spines of seven goats were operated: one disc was injected with chondroitinase ABC [cABC (mild degeneration)] and compared to the adjacent disc (control) after 24 weeks. Exp 2a: Ex vivo, caprine discs received physiological loading (n = 10) or overloading (n = 10) in a bioreactor. Exp 2b: Cell activity was diminished prior to testing by freeze-thaw cycles, 18 discs were then tested as in Exp 2a. In all experiments, FTIR images (spectral region: 1000-1300 cm^-1) of mid-sagittal slices were analyzed using multivariate curve resolution.

RESULTS

In vivo, FTIR was more sensitive than biochemical and histological analysis in identifying reduced proteoglycan content (P = 0.046) and increased collagen content in degenerated discs (P < 0.01). Notably, FTIR analysis additionally showed disorganization of the ECM, indicated by increased collagen entropy (P = 0.011). Ex vivo, the proteoglycan/collagen ratio decreased due to overloading (P = 0.047) and collagen entropy increased (P = 0.047). Cell activity affected collagen content only (P = 0.044).

CONCLUSION

FTIR imaging allows a more detailed investigation of early disc degeneration than traditional measures. Changes due to mild overloading could be assessed and quantified. Matrix remodeling is the first detectable step towards intervertebral disc degeneration.

Osteoporosis of the vertebra and osteochondral remodeling of the endplate causes intervertebral disc degeneration in ovariectomized mice

Background

Studies on the relationship between osteoporosis and intervertebral disc degeneration (IVDD) are inconsistent. Therefore, we assessed whether IVDD is affected by vertebral osteoporosis in ovariectomized mice and investigated the underlying pathogenesis of IVDD related to osteoporosis.

Methods

Thirty healthy female C57BL/6 J mice aged 8 weeks were randomly divided into two groups: a control group (sham operation, n = 15) and an ovariectomy group (OVX; bilateral ovariectomy, n = 15). At 12 weeks after surgery, the bone quantity and microstructure in the lumbar vertebra and endplate as well as the volume of the L4/5 disc space were evaluated by microcomputed tomography (micro-CT). The occurrence and characteristic alterations of IVDD were identified via histopathological staining. The osteoclasts were detected using tartrate-resistant acid phosphatase (TRAP) staining. Type II collagen (Col II), osterix (OSX), osteopontin (OPN), and vascular endothelial growth factor (VEGF) expression in the intervertebral disc were detected by immunohistochemical analysis.

Results

OVX significantly increased the body weight and decreased the uterus weight. Micro-CT analysis showed that osteoporosis of the vertebra and osteochondral remodeling of the endplate were accompanied by an increase in the endplate porosity and a decrease in the disc volume in the OVX group. Likewise, histological evaluation revealed that IVDD occurred at 12 weeks after ovariectomy, with features of endochondral ossification of the endplate, loose and broken annulus fibrosus, and degeneration of nucleus pulposus. TRAP staining showed that numerous active osteoclasts appeared in the subchondral bone and cartilaginous endplate of OVX mice, whereas osteoclasts were rarely detected in control mice. Immunohistochemical analysis demonstrated that the expression of osterix was significantly increased, notably in the endplate of OVX mice. In addition, Col II was decreased in the ossification endplate and the degenerative annulus fibrosus, where OPN and VEGF expressions were elevated in OVX mice.

Conclusions

OVX induced vertebral osteoporosis and osteochondral remodeling of the cartilaginous endplate contributing to the angiogenesis and an increase in porosity of the bone-cartilage surface, and also affected the matrix metabolism which consequently had detrimental effects on the intervertebral disc. Our study suggests that preserving the structural integrity and the function of the adjacent structures, including the vertebrae and endplates, may protect the disc against degeneration.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1701-1) contains supplementary material, which is available to authorized users.

Biomaterials for intervertebral disc regeneration: Current status and looming challenges

A biomaterial-based strategy is employed to regenerate the degenerated intervertebral disc, which is considered a major generator of neck and back pain. Although encouraging enhancements in the anatomy and kinematics of the degenerative disc have been gained by biomaterials with various formulations in animals, the number of biomaterials tested in humans is rare. At present, most studies that involve the use of newly developed biomaterials focus on regeneration of the degenerative disc, but not pain relief. In this review, we summarise the current state of the art in the field of biomaterial-based regeneration or repair for the nucleus pulposus, annulus fibrosus, and total disc transplantation in animals and humans, and we then provide essential suggestions for the development and clinical translation of biomaterials for disc regeneration. It is important for researchers to consider the commonly neglected issues instead of concentrating solely on biomaterial development and fabrication.

Asymmetry between the superior and inferior endplates is a risk factor for lumbar disc degeneration

Endplate pathology plays an important role in the development of lumbar disc degeneration. Previous research paid little attention to differences between the superior and inferior endplates as a possible risk factor for disc degeneration. The purpose of this study was to test the hypothesis that asymmetry between the superior and inferior endplates is a risk factor for the development of lumbar disc degeneration. A total of 134 patients with lumbar disc herniation (LDH) and 100 healthy adults ("Controls") underwent magnetic resonance imaging scans. Each disc was categorized as non-degenerated (Pfirrmann grades I-II) or degenerated (Pfirrmann grades III-V) and get the following three groups: "Degenerated LDH" discs (n = 145), "Non-degenerated LDH" discs (n = 525) and "Non-degenerated Control" discs (n = 500). On mid-sagittal image, the lumbar endplate morphology could be categorized into three types: Flat, concave, and irregular. Superior and inferior endplates of a given disc were "symmetric" if both were of the same type, and "asymmetric" if they were of different types. The proportion of asymmetric endplates at L4-5 was higher in the "Degenerated LDH" discs group (47%) than in the "Non-degenerated LDH" discs group (21%) or "Non-degenerated Control" discs group (7%) (p < 0.05). At L5-S1 the proportions were 73%, 55%, and 38% (p < 0.05). Asymmetry of superior and inferior endplates in the mid-sagittal plane is a risk factor for lumbar disc degeneration. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2469-2475, 2018.

Changes in Intervertebral Disk Mechanical Behavior During Early Degeneration

Intervertebral disk (IVD) degeneration is commonly described by loss of height and hydration. However, in the first stage of IVD degeneration, this loss has not yet occurred. In the current study, we use an ex vivo degeneration model to analyze the changes in IVDs mechanical behavior in the first phase of degeneration. We characterize these changes by stretched-exponential fitting, and suggest the fitted parameters as markers for early degeneration. Enzymatic degeneration of healthy lumbar caprine IVDs was induced by injecting 100 μL of Chondroïtinase ABC (Cabc) into the nucleus. A no-intervention and phosphate buffered saline (PBS) injected group were used as controls. IVDs were cultured in a bioreactor for 20 days under diurnal, simulated-physiological loading (SPL) conditions. Disk deformation was continuously monitored. Changes in disk height recovery behavior were quantified using stretched-exponential fitting. Disk height, histological sections, and water- and glycosaminoglycan (GAG)-content measurements were used as gold standards for the degenerative state. Cabc injection caused significant GAG loss from the nucleus and had detrimental effects on poro-elastic mechanical properties of the IVDs. These were progressive over time, with a propensity toward more linear recovery behavior. On histological sections, both PBS and Cabc injected IVDs showed moderate degeneration. A small GAG loss yields changes in IVD recovery behavior, which can be quantified with stretched-exponential fitting. Parameters changed significantly compared to control. Studies on disk degeneration and biomaterial engineering for degenerative disk disease (DDD) could benefit from focusing on IVD biomechanical behavior rather than height and water-content, as a marker for early disk degeneration.

Resveratrol enhances matrix biosynthesis of nucleus pulposus cells through activating autophagy via the PI3K/Akt pathway under oxidative damage

The decrease in nucleus pulposus (NP) matrix production is a classic feature during disc degeneration. Resveratrol (RSV) is reported to play protective effects under many pathological factors.The present study aims to study the effects of RSV on NP matrix homeostasis under oxidative damage and the potential mechanism. Rat NP cells were exposed to H2O2 solution to create an oxidative damage. RSV and the 3-methyladenine (3-MA) were added along with the culture medium to respectively investigate the role of RSV and cellular autophagy. NP matrix synthesis was evaluated by the expression of macromolecules (aggrecan and collagen II) and glycosaminoglycan (GAG) content. Activation of cellular autophagy was assessed by the expression of several molecular markers. Additionally, activity of the PI3K/Akt pathway was also evaluated to study its potential role. Compared with the control group (NP cells treated with H2O2), RSV significantly up-regulated expression of matrix macromolecules (aggrecan and collagen), promoted GAG production, and increased the expression of autophagy-related markers (Beclin-1 and LC-3). Further analysis showed that inhibition of autophagy by 3-MA partly attenuated NP matrix production. Additionally, RSV increased activity of the PI3K/Akt pathway compared with the control NP cells, but it was not affected by the addition of 3-MA. RSV plays a protective role in enhancing NP matrix synthesis under oxidative damage. Mechanistically, activation of the cellular autophagy via the PI3K/Akt pathway may participate in this process. RSV may be an effective drug to attenuate oxidative stress-induced disc degeneration.

Nucleus pulposus cell senescence is alleviated by resveratrol through regulating the ROS/NF-κB pathway under high-magnitude compression

Mechanical overloading is a risk factor of disc degeneration. Studies have demonstrated that resveratrol helps to maintain the disc cell's healthy biology. The present study aims to investigate whether resveratrol can suppress mechanical overloading-induced nucleus pulposus (NP) cell senescence in vitro and the potential mechanism. The isolated rat NP cells were seeded in the decalcified bone matrix (DBM) and cultured under non-compression (control) and compression (20% deformation, 1.0 Hz, 6 h/day) for 5 days using the mechanically active bioreactor. The resveratrol (30 and 60 μM) was added into the culture medium of the compression group to investigate its protective effects against the NP cell senescence. NP cell senescence was evaluated by cell proliferation, cell cycle, senescence-associated β-galactosidase (SA-β-Gal) activity, telomerase (TE) activity, and gene expression of the senescence markers (p16 and p53). Additionally, the reactive oxygen species (ROS) content and activity of the NF-κB pathway were also analyzed. Compared with the non-compression group, the high-magnitude compression significantly promoted NP cell senescence, increased ROS generation and activity of the NF-κB pathway. However, resveratrol partly attenuated NP cell senescence, decreased ROS generation and activity of the NF-κB pathway in a concentration-dependent manner under mechanical compression. Resveratrol can alleviate mechanical overloading-induced NP cell senescence through regulating the ROS/NF-κB pathway. The present study provides that resveratrol may be a potential drug for retarding mechanical overloading-induced NP cell senescence.

[Changes in shape and signal intensity of high intensity zone in lumbar intervertebral discs on magnetic resonance images: a longitudinal study]

OBJECTIVE

To investigate changes over time in the shape and signal intensity of high intensity zone (HIZ) in the lumbar intervertebral discs on magnetic resonance images in patients with low back pain.

METHODS

The imaging data were collected from 27 patients with low back pain, who underwent lumbar magnetic resonance (MR) imaging examinations that identified HIZ lesions and received follow-up MR examinations at least 1.5 years later over the period from January 2009 to January 2017. The initial and follow-up MR T2WI images of the patients were read by two experienced radiologists to categorize the changes in the shape of the HIZ lesions into enlarged, unchanged, shrunk, and disappeared. The volume and signal/cerebrospinal fluid signal intensity (T2/CSF) ratio of the HIZ were measured on sagittal MR images using ImageJ software.

RESULTS

Of the 43 HIZ lesions found in the initial examinations, 22 (51.2%) remained unchanged in the follow-up examinations, 10 (21.3%) were enlarged, 9 (20.9%) shrank, and 2 (23.3%) disappeared. The follow-up examinations revealed 4 new HIZ lesions in the intervertebral discs. The volumes of these lesions did not vary significantly in the follow-up examinations (P=0.653), but the T2/CSF ratio was significantly higher in the follow-up than in the initial examinations (P=0.043).

CONCLUSIONS

After observation for an average of 3 years and 3 months, most of the HIZ lesions in the lumbar intervertebral discs of the patients with low back pain remained stable in shape, but their signal intensity on MR images increased.

Age-related changes in shock absorption capacity of the human spinal column

Background

The spinal column possesses shock absorption properties, mainly provided by the intervertebral discs. However, with the process of senescence, all structures of the spine, including the discs, undergo degenerative changes. It may lead to alteration of the mechanical properties of the spinal motion segment and diminished capacity for vibration attenuation.

Objective

The objective of this study was to investigate the age-related changes in shock absorption properties of the spine.

Patients and methods

A total of 112 individuals divided into three groups according to age (third, fifth, and seventh decades of life) were enrolled in this study. The transmissibility of vibrations through the spine was measured in a standing position on a vibration platform by accelerometers mounted at the levels of S2 and C0. Registered signals were described using four parameters: VMS (variability), peak-to-peak amplitude (PPA), and spectral activity in two bands F2 (0.7–5 Hz) and F20 (15–25 Hz).

Results

In all age groups, signals registered at C0 were characterized by significantly lower values of VMS, PPA, and F20, when compared to level S2. Simultaneously, the parameter F20 significantly differed among all age groups when C0 vibrations were analyzed: 2.43±1.93, 5.02±3.61, and 10.84±5.12 for the third, fifth, and seventh decades of life, respectively.

Conclusion

The human spinal column provides vibration attenuation; however, this property gradually declines with the aging process.

The response of nucleus pulposus cell senescence to static and dynamic compressions in a disc organ culture

Mechanical stimuli obviously affect disc nucleus pulposus (NP) biology. Previous studies have indicated that static compression exhibits detrimental effects on disc biology compared with dynamic compression. To study disc NP cell senescence under static compression and dynamic compression in a disc organ culture, porcine discs were cultured and subjected to compression (static compression: 0.4 MPa for 4 h once per day; dynamic compression: 0.4 MPa at a frequency of 1.0 Hz for 4 h once per day) for 7 days using a self-developed mechanically active bioreactor. The non-compressed discs were used as controls. Compared with the dynamic compression, static compression significantly promoted disc NP cell senescence, reflected by the increased senescence-associated β-galactosidase (SA-β-Gal) activity, senescence-associated heterochromatic foci (SAHF) formation and senescence markers expression, and the decreased telomerase (TE) activity and NP matrix biosynthesis. Static compression accelerates disc NP cell senescence compared with the dynamic compression in a disc organ culture. The present study provides that acceleration of NP cell senescence may be involved in previously reported static compression-mediated disc NP degenerative changes.

Resveratrol attenuates mechanical compression-induced nucleus pulposus cell apoptosis through regulating the ERK1/2 signaling pathway in a disc organ culture

BACKGROUND

Nucleus pulposus (NP) cell apoptosis is a typical feature within the degenerative disc. High magnitude compression significantly promotes NP cell apoptosis. Several studies have indicated that resveratrol has protective effects on disc cell's normal biology.

OBJECTIVE

The present study aims to investigate whether resveratrol can attenuate mechanical overloading-induced NP cell apoptosis in a disc organ culture.

METHODS

Isolated porcine discs were cultured in culture chambers of a mechanically active perfusion bioreactor and subjected to a relatively high magnitude compression (1.3 MPa at a frequency of 1.0 Hz for 2 h once per day) for 7 days. Different concentrations (50 and 100 μM) of resveratrol were added into the culture medium to observe the protective effects of resveratrol against NP cell apoptosis under mechanical compression. The noncompressed discs were used as controls.

RESULTS

Similar with the previous studies, this high magnitude compression significantly promoted NP cell apoptosis, reflected by the increased number of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining-positive NP cells and enzyme (caspase-9 and caspase-3) activity, the up-regulated expression of proapoptotic molecules (Bax and caspase-3/cleaved caspase-3), and down-regulated expression of antiapoptotic molecule (Bcl-2). However, resveratrol partly attenuated NP cell apoptosis under this high magnitude compression in a dose-dependent manner. Additionally, though the ERK1/2 pathway was significantly activated in the mechanical compression group, resveratrol partly attenuated activation of the ERK1/2 pathway under mechanical compression in a dose-dependent manner.

CONCLUSION

Resveratrol attenuates mechanical overloading-induced NP cell apoptosis in a dose-dependent manner, and inhibiting activation of the ERK1/2 pathway may be one potential mechanism behind this regulatory process.

Inflammatory microRNA-194 and -515 attenuate the biosynthesis of chondroitin sulfate during human intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is characterized by dehydration and loss of extracellular matrixes in the nucleus pulposus region. Chondroitin sulfate has been found to be the water-binding molecule that played a key role in IDD. Although investigators have reported that inflammatory cytokines are involved in the reduction of chondroitin sulfate in IDD, but the underlying mechanism is unrevealed. Since chondroitin sulfate synthesis is controlled by chondroitin sulfate glycosyltransferases CHSY-1/2/3 and CSGALNACT-1/2, their functional role and regulatory mechanism in IDD is not fully studied. Here, we set out to investigate the function and regulatory roles of these factors during IDD development. We found that among these chondroitin sulfate glycosyltransferases, CHSY-1/2/3 are significantly down-regulated in severe IDD samples than mild IDD samples. In vitro experiments revealed that Interleukin-1β and Tumor Necrosis Factor-α stimulation led to significant reduction of CHSY-1/2/3 at protein level than mRNA level in NP cells, indicating a post-transcriptional regulatory mechanisms are involved. By computational prediction and analysis, we found that inflammatory cytokines stimulated microRNA-194 and -515 target CHSY-1/2/3 mRNA and significantly interrupt their translation and downstream chondroitin sulfate deposition. Inhibition of microRNA-194 and -515 however, significantly rescued CHSY-1/2/3 expressions and chondroitin sulfate deposition. These findings together demonstrated a vital role of inflammatory stimulated microRNAs in promoting intervertebral disc degeneration by interrupt chondroitin sulfate synthesis, which may provide new insights into the mechanism and therapeutic approaches in IDD.

[Resveratrol regulate the extracellular matrix expression via Wnt/β-catenin pathway in nucleus pulposus cells]

Objective

To investigate the regulatory effect of resveratrol (RES) on the extracellular matrix (ECM) expression of nucleus pulposus cells (NPC), and its relative molecular mechanism.

Methods

Ten patients receiving discectomy were collected, of which 5 patients were young with spinal burst fracture, classified as control group; the rest 5 patients were senile with lumbar disc herniation, classified as degenerative group. The nucleus pulposus tissue of 2 groups were collected, the in situexpression of β-catenin was detected by immunohistochemistry, and the protein expressions of collagen type Ⅱ and Aggrecan were detected by Western blot. The NPC were isolated and cultured from degenerative nucleus pulposus tissues. RES treated the third-passage NPC with (group B) or without IL-1β (group C), to further determine the protein expressions of collagen type Ⅱ and Aggrecan by Western blot, the unstimulated cells were set up as blank control group (group A). Moreover, NPC treated with small interfering RNA (siRNA) targeted silent SIRT1 or β-catenin were used to determine the protein and gene expressions of β-catenin and SIRT1 by Western blot and real-time fluorescence quantitative PCR. In addition, the third-passage NPC treated with complete medium (group 1), IL-1β (group 2), RES+IL-1β (group 3), and SIRT1-siRNA+RES+IL-1β (group 4) for 24 hours were used to detect the nuclear translocation of β-catenin by cell immunofluorescence staining. Finally, the third-passage NPC treated with complete medium (group Ⅰ), IL-1β (group Ⅱ), IL-1β+β-catenin-siRNA (group Ⅲ), IL-1β+RES (group Ⅳ), and IL-1β+RES+SIRT1-siRNA (group Ⅴ) for 24 hours were used to detect the protein expressions of collagen type Ⅱ and Aggrecan by Western blot.

Results

Immunohistochemical staining and Western blot detection showed that when compared with control group, the cell proportion of expression of β-catenin were significantly increased in degenerative group ( t=4.616, P=0.010); the protein expression of β-catenin was also significantly increased and the protein expressions of collagen type Ⅱ and Aggrecan were significantly decreased ( P<0.05). In cytology experiments, the protein expression of β-catenin in group B was significantly higher than that in groups A and C, and the protein expressions of collagen type Ⅱ and Aggrecan in group B were significantly lower than those in groups A and C ( P<0.05). After transfection of siRNA, the protein expressions of SIRT1 and β-catenin significantly decreased ( P<0.05). The results of cell immunofluorescence staining further confirmed that when compared with group 3, after the SIRT1 was silenced by siRNA in group 4, the attenuated nuclear translocation of β-catenin by RES treatment was aggravated. Western blot results showed that the protein expressions of collagen type Ⅱ and Aggrecan in group Ⅱ were significantly lower than those in group Ⅰ( P<0.05); after transfection of β-catenin-siRNA in group Ⅲ, the degradation of ECM by IL-1β was obviously inhibited, the protein expressions of collagen type Ⅱ and Aggrecan were significantly increased when compared with group Ⅱ ( P<0.05); after transfection of SIRT1-siRNA in group Ⅴ, the protective effect of RES on the degradation of ECM was inhibited, the protein expressions of collagen type Ⅱ and Aggrecan were significantly decreased when compared with group Ⅳ ( P<0.05).

Conclusion

RES regulates the ECM expression of NPC via Wnt/β-catenin signaling pathway, which provide a new idea for intervertebral disc degeneration disease treatment.

Identifying subsets of patients with single-level degenerative disc disease for lumbar fusion: the value of prognostic tests in surgical decision making

BACKGROUND CONTEXT

Fusion surgery for degenerative disc disease (DDD) has become a standard of care, albeit not without controversy. Outcomes are inconsistent and a superiority over conservative treatment is debatable. Proper patient selection is key to clinical success, and a comprehensive understanding of prognostic tests does not currently exist.

PURPOSE

This study aimed to investigate the value of prognostic tests and sociodemographic factors in predicting outcomes following lumbar fusion surgery for DDD.

STUDY DESIGN

This is a retrospective analysis of prospectively collected data.

PATIENT SAMPLE

We included patients who underwent fusion surgery for DDD between 2010 and 2016.

OUTCOME MEASURES

The outcome measures included pre- and postoperative visual analog scale and Oswestry Disability Index scores.

MATERIALS AND METHODS

Prospectively collected patient data were reviewed for preoperative tests, perioperative data, and clinical outcomes. Prognostic tests used were discography, pantaloon cast test (PCT), Modic changes, and a summary of physical symptoms, coined "loading factor." By means of multivariate stepwise regression, prognostic factors that were useful in predicting outcomes were identified.

RESULTS

A total of 91 patients fit the inclusion criteria, with a mean follow-up of 33±16 months. Discography, Modic changes, and loading factor were of no value for predicting outcome scores (p>.05). A positive PCT predicted improved outcomes in back pain severity, but only in patients without prior surgery (p=.02). Demographic factors that showed a consistent reduction in back pain were female sex (p=.021) and no prior surgery at index level (p=.009). No other sociodemographic factors were of predictive value (p>.05).

CONCLUSIONS

In patients without prior surgery, the PCT appears to be the most promising prognostic tool. Other prognostic selection tools such as discography and Modic changes yield disappointing results. In this study, female patients and those without prior spine surgery appear to be most likely to benefit from fusion surgery for DDD.

Hydrogen peroxide induces programmed necrosis in rat nucleus pulposus cells through the RIP1/RIP3-PARP-AIF pathway

This study aimed to systematically investigate whether programmed necrosis contributes to H2 O2 -induced nucleus pulposus (NP) cells death and to further explore the underlying mechanism involved. Rat NP cells were subjected to different concentrations of H2 O2 for various time periods. The cell viability was measured using a cell counting kit-8, and the death rate was detected by Hoechst 33258/propidium iodide (PI) staining. The programmed necrosis-related molecules receptor-interacting protein 1 (RIP1), receptor-interacting protein 3 (RIP3), poly (ADP-ribose) polymerase (PARP), and apoptosis inducing factor (AIF) were determined by real-time polymerase chain reaction and Western blotting, respectively. The morphologic and ultrastructural changes were examined by phasecontrast microscopy and transmission electron microscopy (TEM). In addition, the necroptosis inhibitor Necrostatin-1 (Nec-1), the PARP inhibitor diphenyl-benzoquinone (DPQ) and small interfering RNA (siRNA) technology were used to indirectly evaluate programmed necrosis. Our results indicated that H2 O2 induced necrotic morphologic and ultrastructural changes and an elevated PI positive rate in NP cells; these effects were mediated by the upregulation of RIP1 and RIP3, hyperactivation of PARP, and translocation of AIF from mitochondria to nucleus. Additionally, NP cells necrosis was significantly attenuated by Nec-1, DPQ pretreatment and knockdown of RIP3 and AIF, while knockdown of RIP1 produced the opposite effects. In conclusion, these results suggested that under oxidative stress, RIP1/RIP3-mediated programmed necrosis, executed through the PARP-AIF pathway, played an important role in NP cell death. Protective strategies aiming to regulate programmed necrosis may exert a beneficial effect for NP cells survival, and ultimately retard intervertebral disc (IVD) degeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1269-1282, 2018.

Osmotic Pressure Alters Time-dependent Recovery Behavior of the Intervertebral Disc

STUDY DESIGN

Disc recovery behavior under hypo- and hyperosmotic pressure.

OBJECTIVE

To evaluate the effect of osmotic pressure on the unloaded recovery response of healthy discs.

SUMMARY OF BACKGROUND DATA

The intervertebral disc is a poroviscoelastic material that experiences large fluctuations in water composition throughout a diurnal loading cycle. Fluid flow out of the disc occurs through mechanical loading, whereas fluid flow into the disc occurs through passive diffusion because of an imbalance of ions between the disc and its surrounding environment. Osmotic pressure has been used to alter water uptake and tissue hydration.

METHODS

Motion segments were prepared from the caudal spine sections of the skeletally mature bovines. A 300-N compressive load was applied for 2 hours before unloaded recovery for 12 hours. Hypo- and hyperosmotic pressure was used to alter the rate of water uptake and disc height recovery during unloaded recovery. A 5-parameter rheological model was used to describe the disc's time-dependent recovery behavior.

RESULTS

The elastic response was not altered by changes in osmotic pressure; however, viscoelastic recovery was highly dependent on saline osmolarity and recovery time. The fast response of viscoelastic recovery was not dependent on osmotic pressure. The time constant for the slow response decreased whereas the slow response stiffness increased as osmotic pressure increased.

CONCLUSION

The fast response of viscoelastic recovery is governed by flow-independent recovery, whereas the slow response is related to flow-dependent recovery. The rate and magnitude of flow-dependent recovery are highly sensitive to changes in osmotic pressure of the saline bath. There is an osmotic pressure that reduces disc recovery behavior to an elastic response or flow-independent recovery.

LEVEL OF EVIDENCE

N/A.

Collagen IX gene polymorphisms and lumbar disc degeneration: a systematic review and meta-analysis

Background

An increasing number of studies have investigated associations between collagen IX alpha 2 chain (COL9A2) and collagen IX alpha 3 chain (COL9A3) gene polymorphisms and the risk of lumbar disc degeneration (LDD). However, these studies have yielded contradictory results. The purpose of this meta-analysis is to investigate the association between the collagen IX gene polymorphisms (rs12077871, rs12722877, rs7533552 in COL9A2; rs61734651 in COL9A3) and LDD.

Methods

All relevant articles were collected from PubMed, Web of Science, and China National Knowledge Infrastructure (CNKI). The last electronic search was performed on September 1, 2017. The allele/genotype frequencies were extracted from each study. The odds ratio (OR) and 95% confidence interval (CI) were used to assess the strength of associations under the five comparison genetic models. Statistical analysis was performed by Review Manager (RevMan) 5.31 software.

Results

The meta-analysis of 10 case-control studies, including 2102 LDD cases and 2507 controls, indicated that COL9A2 gene (rs12077871, rs12722877, rs7533552) and COL9A3 gene (rs61734651) polymorphisms were not associated with LDD (rs12077871: T vs. C, OR = 1.85, 95% CI = 0.87–3.91, P = 0.11; rs12722877: G vs. C, OR = 0.83, 95% CI = 0.69–1.01, P = 0.06; rs7533552: G vs. A, OR = 1.11, 95% CI = 0.98–1.25, P = 0.09; rs61734651: T vs. C, OR = 1.57, 95% CI = 0.51–4.84, P = 0.43). The Egger text and the Begg funnel plot did not show any evidence of publication bias.

Conclusion

rs12077871, rs12722877, and rs7533552 variants in COL9A2 and rs61734651 variant in COL9A3 were not significantly associated with a predisposition to LDD. Large-scale and well-designed studies are needed to confirm this conclusion.

Cyclic mechanical tension reinforces DNA damage and activates the p53-p21-Rb pathway to induce premature senescence of nucleus pulposus cells

Intervertebral disc (IVD) degeneration (IDD) is a widely recognized contributor to low back pain. Mechanical stress is a crucial etiological factor of IDD. During the process of IDD, a vicious circle is formed between abnormal mechanical stress and the damage of disc structure and function. Notably, the pathological process of IDD is mediated by the phenotypic shift of IVD cells from an extracellular matrix anabolic phenotype to a catabolic and pro-inflammatory phenotype. Therefore, the effects of mechanical stress on the initiation and progression of IDD depend on the mechanobiology of IVD cells. Recently, disc cell senescence was identified as a new hallmark of IDD. However, the senescent response of disc cells to mechanical stress remains unknown. In this study, we found that prolonged exposure of cyclic mechanical tension (CMT) with unphysiological magnitude generated by the Flexercell tension system markedly induced premature senescence of nucleus pulposus (NP) cells. CMT augmented the DNA damage of NP cells, but did not affect the redox homeostasis of NP cells. Moreover, the p53-p21-retinoblastoma protein (Rb) pathway was activated by CMT to mediate the CMT-induced premature senescence of NP cells. The findings are beneficial to understanding the mechanism of disc cell senescence and the mechanobiology of disc cells further. It suggests that prolonged abnormal mechanical stress accelerates the establishment and progression of disc cell senescence and consequently impairs the structural and functional homeostasis of IVDs to cause IDD. Preventing the pro-senescent effect of mechanical stress on IVD cells is a promising approach to delay the process of IDD.

Epoxyeicosanoids prevent intervertebral disc degeneration in vitro and in vivo

Intervertebral disc (IVD) degeneration is considered a common cause of low back pain. In the degenerating IVD, the production of pro-inflammatory cytokines, including IL-1 and TNF-α, progressively increases, contributing to the degenerative process. Epoxyeicosatrienoic acids (EETs), synthesized from arachidonic acid by cytochrome P450 enzymes, act as autocrine and paracrine effectors in regulating inflammation, cardiovascular functions, and angiogenesis. EETs were shown to be especially potent promoters of tissue regeneration. Considering their anti-inflammatory and anti-catabolic potential, we investigated whether EETs can influence IVD degeneration. We found that 14,15-EET protected rat nucleus pulposus (NP) cells against death induced by treatment with H₂O₂and TNF-α in vitro. At the molecular level, 14,15-EET significantly inhibited the NF-κB pathway, which plays essential roles in the degeneration and survival of NP cells. As a result, 14,15-EET efficiently prevented the matrix remodeling response of NP cells to TNF-α. Using a needle-punctured rat tail model, the influence of 14,15-EET on IVD degeneration in vivo was evaluated using radiographs, magnetic resonance images (MRI), and histological analysis. We observed that 14,15-EET prevented IVD degeneration. Our findings demonstrated that 14,15-EET can enhance the survival of NP cells and inhibit IVD degeneration. The EET pathway may be a novel therapeutic target against IVD degeneration.

Osteogenic protein-1 attenuates apoptosis and enhances matrix synthesis of nucleus pulposus cells under high-magnitude compression though inhibiting the p38 MAPK pathway

BACKGROUND

Disc degeneration is correlated with mechanical load. Osteogenic protein-1 (OP-1) is potential to regenerate degenerative disc.

OBJECTIVE

To investigate whether OP-1 can protect against high magitude compression-induced nucleus pulposus (NP) cell apoptosis and NP matrix catabolism, and its potential mechanism.

METHODS

Porcine discs were cultured in a bioreactor and compressed at a relatively high-magnitude mechanical compression (1.3 MPa at a frequency of 1.0 Hz for 2 hours once per day) for 7 days. OP-1 was added along with the culture medium to investigate the protective effects of OP-1. NP cell apoptosis and matrix biosynthesis were evaluated. Additionally, activity of the p38 MAPK pathway is also analyzed.

RESULTS

Compared with the control group, high magnitude compression significantly promoted NP cell apoptosis and decreased NP matrix biosynthesis, reflected by the increase in the number of TUNEL-positive cells and caspase-3 activity, the up-regulated expression of Bax and caspase-3 mRNA and down-regulated expression of Bcl-2 mRNA, and the decreased alcian blue staining intensity and expression of matrix proteins (aggrecan and collagen II). However, OP-1 addition partly attenuated the effects of high magnitude compression on NP cell apoptosis and NP matrix biosynthesis. Further analysis showed that inhibition of the p38 MAPK pathway partly participated in this process.

CONCLUSION

OP-1 can attenuate high magnitude compression-induced NP cell apoptosis and promoted NP matrix biosynthesis, and inhibition of the p38 MAPK pathway may participate in this regulatory process. This study provides that OP-1 may be efficacy in retarding mechanical overloading-exacerbated disc degeneration.

Intermittent cyclic mechanical tension altered the microRNA expression profile of human cartilage endplate chondrocytes

Previous studies have identified the association between cartilage endplate (CEP) degeneration and abnormal mechanical loading. Several studies have reported that intermittent cyclic mechanical tension (ICMT) regulates CEP degeneration via various biological processes and signaling pathways. However, the functions of microRNAs in regulating the cellular responses of CEP chondrocytes to ICMT remain to be elucidated. The current study determined the differentially expressed microRNAs in human CEP chondrocytes exposed to ICMT using microarray analysis. A total 21 significantly upregulated and 62 downregulated miRNAs were identified compared with the control. The findings were subsequently partially validated by reverse transcription-quantitative polymerase chain reaction. Potential target genes of the significantly differentially expressed miRNAs were predicted using bioinformatics analysis and were used for Gene Ontology analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis. The present study revealed that the significantly differentially expressed microRNAs were involved in various signaling pathways and biological processes that are crucial to regulating the responses of CEP chondrocytes to ICMT. The current study provided a global view of microRNA expression in CEP chondrocytes under mechanical stimulation, suggesting that microRNAs are important for regulating the mechanical response of CEP chondrocytes. Additionally, it provided a novel insight into the association between mechanical stress and the establishment and progression of intervertebral disc degeneration.

Prolactin inhibits the progression of intervertebral disc degeneration through inactivation of the NF-κB pathway in rats

Intervertebral disc degeneration (IVDD) is one of the key predisposing factors for low back pain. Although the exact mechanism remains unclear, inflammatory response and nucleus pulposus (NP) apoptosis are known to play important roles in this process. Prolactin protects against inflammation-associated chondrocyte apoptosis in arthritis. Based on prior studies, we hypothesized that prolactin might have therapeutic effects on IVDD by inhibiting the apoptosis of degenerative human disc NP cells. An experimental model of IVDD was established in 3-month-old Sprague-Dawley rats by submitting them to percutaneous disc puncture with a 20-gauge needle on levels 7–8 and 8–9 of the coccygeal vertebrae. Then the rats were injected with 20 or 200 ng prolactin on a weekly basis. Radiologic and histologic analyses were performed on days 4, 7, 14, and 28. The expression of prolactin and its receptor was analyzed in human tissue obtained from symptomatic patients undergoing microencoscopy discectomy, or from scoliosis patients undergoing deformity correction surgery. The results showed that intradiscal injection of prolactin maintained disc height and the mean signal intensity of the punctured disc. Histological analysis indicated that prolactin treatment significantly retained the complete structure of the NP and annulus fibrosus compared with the vehicle group. In addition, more collagen II, but fewer collagen I-containing tissues were detected in the prolactin treatment groups compared to the vehicle group. Moreover, low levels of tumor necrosis factor-α, interleukin-1β, cleaved-caspase 3, and TUNEL staining were observed in the prolactin treatment groups. We also demonstrated that prolactin impaired puncture-induced inflammation and cell apoptosis by downregulating activation of the NF-κB pathway. The degenerated NP tissues from patients had decreased expression of prolactin and its receptor, whereas expression was increased in the NP tissues removed from scoliosis patients. These results suggest that prolactin may be a novel therapeutic target for the treatment of IVDD.

Biologic therapies to enhance intervertebral disc repair

Degenerative disc disease is a progressive, chronic disorder with strong association to pain, where the dysregulated tissue environment signals disc cells, thereby leading to a low inflammatory process and slow extracellular matrix degradation and fibrosis in a perpetual vicious cycle, generating a structural and functional failure of intervertebral disc joint (IVDJ). Among current biologic therapies, there is an emerging minimally invasive strategy that consists of infiltrating plasma rich in growth factors, a safe and efficacious therapeutic approach for other musculoskeletal degenerative conditions. This review summarizes the homeostasis and degeneration of IVDJ, discusses some results on basic science and therapeutic use of platelet-rich plasma products and advances an alternative minimally invasive biologic therapy in IVDJ degeneration and chronic back pain.

Degree of endplate chondrocyte degeneration in different tension regions during mechanical stimulation

The aim of this study was to explore the degree of degeneration of endplate chondrocytes in different tension regions induced by intermittent cyclic mechanical tension (ICMT) in vitro. Rat endplate chondrocytes were harvested and treated with 10% ICMT for 8 h/day with a frequency of 0.5 Hz. A cartilage degeneration model was induced using an FX‑5000T cell strain‑loading system. The experiment was divided into the central region and the peripheral region, according to the contact area between the loading post and the six‑well flexible silicone rubber BioFlex plates. Toluidine blue and phalloidin staining were used to observe the morphological changes of cells following mechanical stimulation. Apoptosis was detected by flow cytometry and the mRNA and protein expression levels of collagen type II α1, aggrecan, SRY‑box 9 and matrix metalloproteinase 13 were detected by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blotting, respectively. Endplate chondrocytes exhibited degenerative alterations under mechanical conditions of 10% ICMT and 0.5 Hz at 8 h/day. Toluidine blue and phalloidin staining demonstrated that the cells in the peripheral region were more slender compared with cells in the central region, but RT‑qPCR and western blotting results demonstrated that the degree of cell degeneration between the two groups was not statistically differences. So that cell morphological alteration does not imply that cells have undergone degeneration.

Effects of Training and Overtraining on Intervertebral Disc Proteoglycans

STUDY DESIGN

Animal experimental study.

OBJECTIVE

Evaluate the effect of physical activity and overtraining condition on glycosaminoglycan concentration on the intervertebral disc (IVD) using a rat running model.

SUMMARY OF BACKGROUND DATA

Some guidelines recommend the implementation of a physical exercise program as treatment for low back pain; however, cyclic loading impact on the health of the IVD and whether there is a dose-response relationship is still incompletely understood.

METHODS

Thirty-two rats ages 8 weeks were divided into four groups with eight animals each. The first 8 weeks were the adaptive phase, the overtraining phase was from the ninth to the eleventh week, which consisted of increasing the number of daily training sessions from 1 to 4 and the recovery phase was represented by the 12th and 13th weeks without training. Control group 1 (CG1) did not undergo any kind of training. Control group 2 (CG2) completed just the adaptive phase. Overtraining group 1 (OT1) completed the overtraining phase. Overtraining group 2 (OT2) completed the recovery phase. Running performance tests were used to assess the "overtraining" status of the animals. IVD glycosaminoglycans were extracted and quantified, and identified by electrophoresis.

RESULTS

Glycosaminoglycans showed a distribution between chondroitin sulfate and dermatan sulfate. Glycosaminoglycans quantification showed decreasing concentration at the following order: OT1 > CG2 > OT2 > CG1. Increased expression of dermatan sulfate was verified at the groups submitted to any training.

CONCLUSION

Overtraining condition, as assessed by muscle and cardiovascular endurance did not lessen glycosaminoglycan concentration in the IVD. In fact, physical exercise increased glycosaminoglycan concentration in the IVD in proportion to the training load, even at overtraining condition, returning to normal levels after the recovery phase and glycosaminoglycan production is a reversible acute positive response for mechanical stimulation of the IVD.

LEVEL OF EVIDENCE

N/A.

Age-related reduction in the expression of FOXO transcription factors and correlations with intervertebral disc degeneration

Aging is a main risk factor for intervertebral disc (IVD) degeneration, the main cause of low back pain. FOXO transcription factors are important regulators of tissue homeostasis and longevity. Here, we determined the expression pattern of FOXO in healthy and degenerated human IVD and the associations with IVD degeneration during mouse aging. FOXO expression was assessed by immunohistochemistry in normal and degenerated human IVD samples and in cervical and lumbar IVD from 6-, 12-, 24-, and 36-month-old C57BL/6J mice. Mouse spines were graded for key histological features of disc degeneration in all the time points and expression of two key FOXO downstream targets, sestrin 3 (SESN3) and superoxide dismutase (SOD2), was assessed by immunohistochemistry. Histological analysis revealed that FOXO proteins are expressed in all compartments of human and mouse IVD. Expression of FOXO1 and FOXO3, but not FOXO4, was significantly deceased in human degenerated discs. In mice, degenerative changes in the lumbar spine were seen at 24 and 36 months of age whereas cervical IVD showed increased histopathological scores at 36 months. FOXO expression was significantly reduced in lumbar IVD at 12-, 24-, and 36-month-old mice and in cervical IVD at 36-month-old mice when compared with the 6-month-old group. The reduction of FOXO expression in lumbar IVD was concomitant with a decrease in the expression of SESN3 and SOD2. These findings suggest that reduced FOXO expression occurs in lumbar IVD during aging and precedes the major histopathological changes associated with lumbar IVD degeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2682-2691, 2017.

Is it appropriate to measure age-related lumbar disc degeneration on the mid-sagittal MR image? A quantitative image study

PURPOSE

Even though phenotypes of disc degeneration vary on different sagittal magnetic resonance images (MRI), measurements typically are acquired on the mid-sagittal MRI. This study investigated the appropriateness of using the mid-sagittal MRI to measure various phenotypes of age-related disc degeneration.

METHODS

Lumbar spine MRIs of 66 subjects (mean age 50.3 years, standard deviation 16.5 years, range 22-84 years) were studied. An image analysis program Spine Explorer was used to obtain quantitative measurements for disc height, bulging, and signal on para- and mid-sagittal T2-weighted MRIs. Measurements on para- and mid-sagittal MRIs and their associations with age were compared.

RESULTS

Measurements of disc height, signal, and posterior disc bulging acquired on the mid-sagittal MRI were greater than those on the para-sagittal MRIs. Disc height measurements were not linearly associated with age. Greater age was correlated with greater anterior (r = 0.45, P < 0.001) and posterior (r = 0.33, P < 0.01) bulging on para-sagittal MRIs, but not posterior disc bulging on the mid-sagittal MRI (r = - 0.10, P > 0.05). Disc signal intensity measurements on the mid-sagittal MRI had stronger correlations with age than those on para-sagittal MRIs. Mean and standard deviation of disc signal intensity acquired on the mid-sagittal MRI had the strongest correlations with age among all measures of disc degeneration studied (r = - 0.50, - 0.67, respectively, P < 0.001 for both).

CONCLUSIONS

Disc signal measurements acquired on the mid-sagittal MRI were reliable and had strong correlations with age and thus can be used as an appropriate measure of disc degeneration. Disc bulging had better be measured on para-sagittal MRIs. Although severe disc narrowing clearly is a sign of severe disc degeneration, disc height was not linearly associated with age.

Current strategies for treatment of intervertebral disc degeneration: substitution and regeneration possibilities

Background

Intervertebral disc degeneration has an annual worldwide socioeconomic impact masked as low back pain of over 70 billion euros. This disease has a high prevalence over the working age class, which raises the socioeconomic impact over the years. Acute physical trauma or prolonged intervertebral disc mistreatment triggers a biochemical negative tendency of catabolic-anabolic balance that progress to a chronic degeneration disease. Current biomedical treatments are not only ineffective in the long-run, but can also cause degeneration to spread to adjacent intervertebral discs. Regenerative strategies are desperately needed in the clinics, such as: minimal invasive nucleus pulposus or annulus fibrosus treatments, total disc replacement, and cartilaginous endplates decalcification.

Main body

Herein, it is reviewed the state-of-the-art of intervertebral disc regeneration strategies from the perspective of cells, scaffolds, or constructs, including both popular and unique tissue engineering approaches. The premises for cell type and origin selection or even absence of cells is being explored. Choice of several raw materials and scaffold fabrication methods are evaluated. Extensive studies have been developed for fully regeneration of the annulus fibrosus and nucleus pulposus, together or separately, with a long set of different rationales already reported. Recent works show promising biomaterials and processing methods applied to intervertebral disc substitutive or regenerative strategies. Facing the abundance of studies presented in the literature aiming intervertebral disc regeneration it is interesting to observe how cartilaginous endplates have been extensively neglected, being this a major source of nutrients and water supply for the whole disc.

Conclusion

Several innovative avenues for tackling intervertebral disc degeneration are being reported – from acellular to cellular approaches, but the cartilaginous endplates regeneration strategies remain unaddressed. Interestingly, patient-specific approaches show great promise in respecting patient anatomy and thus allow quicker translation to the clinics in the near future.

Autologous bone marrow concentrate intradiscal injection for the treatment of degenerative disc disease with three-year follow-up

PURPOSE

The purpose of this study is to assess safety and feasibility of intradiscal bone marrow concentrate (BMC) injections to treat low back discogenic pain as an alternative to surgery with three year minimum follow-up.

METHODS

A total of 26 patients suffering from degenerative disc disease and candidates for spinal fusion or total disc replacement surgery were injected with 2 ml autologous BMC into the nucleus pulposus of treated lumbar discs. A sample aliquot of BMC was characterized by flow cytometry and CFU-F assay to determine progenitor cell content. Improvement in pain and disability scores and 12 month post-injection MRI were compared to patient demographics and BMC cellularity.

RESULTS

After 36 months, only six patients progressed to surgery. The remaining 20 patients reported average ODI and VAS improvements from 56.7 ± 3.6 and 82.1 ± 2.6 at baseline to 17.5 ± 3.2 and 21.9 ± 4.4 after 36 months, respectively. One year MRI indicated 40% of patients improved one modified Pfirrmann grade and no patient worsened radiographically. Cellular analysis showed an average of 121 million total nucleated cells per ml, average CFU-F of 2713 per ml, and average CD34+ of 1.82 million per ml in the BMC. Patients with greater concentrations of CFU-F (>2000 per ml) and CD34+ cells (>2 million per ml) in BMC tended to have significantly better clinical improvement.

CONCLUSIONS

There were no adverse events related to marrow aspiration or injection, and this study provides evidence of safety and feasibility of intradiscal BMC therapy. Patient improvement and satisfaction with this surgical alternative supports further study of the therapy.

Are axial intervertebral disc biomechanics determined by osmosis?

The intervertebral disc faces high compressive forces during daily activities. Axial compression induces creeping fluid loss and reduction in disc height. With degeneration, disc fluids and height are progressively lost, altering biomechanics. It is assumed that this reduction of fluids is caused by a decline of osmolality within the disc due to proteoglycan depletion. Here we investigate the isolated effect of a reduction in osmosis on the biomechanical properties of the intervertebral disc. Continuous diurnal loading was applied to healthy caprine intervertebral discs in a loaded disc culture system for a total of 6days. We increased testing bath osmolality with two doses of polyethylene-glycol (PEG), thereby reducing the osmotic gradient between the disc and the surrounding fluid. This way we could study the isolated effect of reduced osmosis on axial creep, without damaging the disc. We evaluated: daily creep and recovery, recovery time-constants and compressive stiffness. Additionally, we investigated water content. There was a strong dose-dependent effect of PEG concentration on water content and axial creep behaviour: disc height, amplitude and rate of creep and recovery were all significantly reduced. Axial compressive stiffness of the disc was not affected. Reduction of water content and amplitude of creep and recovery showed similarity to degenerative disc biomechanics. However, the time-constants increased, indicating that the hydraulic permeability was reduced, in contrast to what happens with degeneration. This suggests that besides the osmotic gradient, the permeability of the tissues determines healthy intervertebral disc biomechanics.

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.

Bedside to bench and back to bedside: Translational implications of targeted intervertebral disc therapeutics

Spinal pain and associated disability is a leading cause of morbidity worldwide that has a strong association with degenerative disc disease (DDD). DDD can begin in early–late adolescence and has a variable course. Biologically based therapies to treat DDD face significant challenges posed by the unique milieu of the environment within the intervertebral discs. Many potential promising therapies are still in the early stages of development with a hostile microenvironment within the disc presenting unique challenges.

The translational potential of this article: Patient selection, reasonable therapeutic goals, approach, and timing will need to be discerned in order to successfully translate potential therapeutics.

Static axial overloading primes lumbar caprine intervertebral discs for posterior herniation

Introduction

Lumbar hernias occur mostly in the posterolateral region of IVDs and mechanical loading is an important risk factor. Studies show that dynamic and static overloading affect the nucleus and annulus of the IVD differently. We hypothesize there is also variance in the effect of overloading on the IVD’s anterior, lateral and posterior annulus, which could explain the predilection of herniations in the posterolateral region. We assessed the regional mechanical and cellular responses of lumbar caprine discs to dynamic and static overloading.

Material and methods

IVDs (n = 125) were cultured in a bioreactor and subjected to simulated-physiological loading (SPL), high dynamic (HD), or high static (HS) overloading. The effect of loading was determined in five disc regions: nucleus, inner-annulus and anterior, lateral and posterior outer-annulus. IVD height loss and external pressure transfer during loading were measured, cell viability was mapped and quantified, and matrix integrity was assessed.

Results

During culture, overloaded IVDs lost a significant amount of height, yet the distribution of axial pressure remained unchanged. HD loading caused cell death and disruption of matrix in all IVD regions, whereas HS loading particularly affected cell viability and matrix integrity in the posterior region of the outer annulus.

Conclusion

Axial overloading is detrimental to the lumbar IVD. Static overloading affects the posterior annulus more strongly, while the nucleus is relatively spared. Hence, static overloading predisposes the disc for posterior herniation. These findings could have implications for working conditions, in particular of sedentary occupations, and the design of interventions aimed at prevention and treatment of early intervertebral disc degeneration.

The role of miR-320a and IL-1β in human chondrocyte degradation

Objectives

This study aimed to explore the role of miR-320a in the pathogenesis of osteoarthritis (OA).

Methods

Human cartilage cells (C28/I2) were transfected with miR-320a or antisense oligonucleotides (ASO)-miR-320a, and treated with IL-1β. Subsequently the expression of collagen type II alpha 1 (Col2α1) and aggrecan (ACAN), and the concentrations of sulfated glycosaminoglycans (sGAG) and matrix metallopeptidase 13 (MMP-13), were assessed. Luciferase reporter assay, qRT-PCR, and Western blot were performed to explore whether pre-B-cell leukemia Homeobox 3 (PBX3) was a target of miR-320a. Furthermore, cells were co-transfected with miR-320a and PBX3 expressing vector, or cells were transfected with miR-320a and treated with a nuclear factor kappa B (NF-κB) antagonist MG132. The changes in Col2α1 and ACAN expression, and in sGAG and MMP-13 concentrations, were measured again. Statistical comparisons were made between two groups by using the two-tailed paired t-test.

Results

Expression of miR-320a was elevated in OA cartilage tissues and chondrocytes, and in IL-1β-stimulated C28/I2 cells (p < 0.05 or p < 0.01). MiR-320a overexpression enhanced IL-1β-induced down-regulation of Col2α1 and ACAN and sGAG, and increased the IL-1β-induced overexpression of MMP-13 (p < 0.01). PBX3 was a direct target of miR-320a. PBX3 and MG132 co-transfection attenuated the effects of miR-320a on the expression of Col2α1, ACAN, sGAG and MMP-13(p < 0.01).

Conclusion

Overexpression of miR-320a might enhance IL-1β-induced cartilage degradation factors. These effects might be via targeting PBX3 and regulating NF-κB.

Cite this article: Y. Jin, X. Chen, Z. Y. Gao, K. Liu, Y. Hou, J. Zheng. The role of miR-320a and IL-1β in human chondrocyte degradation. Bone Joint Res 2017;6:–203. DOI: 10.1302/2046-3758.64.BJR-2016-0224.R1.

In vitro and biomechanical screening of polyethylene glycol and poly(trimethylene carbonate) block copolymers for annulus fibrosus repair

Herniated intervertebral discs (IVDs) are a common cause of back and neck pain. There is an unmet clinical need to seal annulus fibrosus (AF) defects, as discectomy surgeries address acute pain but are complicated by reherniation and recurrent pain. Copolymers of polyethylene glycol with trimethylene carbonate (TMC) and hexamethylene diisocyanate (HDI) end-groups were formulated as AF sealants as the HDI form covalent bonds with native AF tissue. TMC adhesives were evaluated and optimized using the design criteria: stable size, strong adherence to AF tissue, high cytocompatibility, restoration of IVD biomechanics to intact levels following in situ repair, and low extrusion risk. TMC adhesives had high adhesion strength as assessed with a pushout test (150 kPa), and low degradation rates over 3 weeks in vitro. Both TMC adhesives had shear moduli (220 and 490 kPa) similar to, but somewhat higher than, AF tissue. The adhesive with three TMC moieties per branch (TMC3) was selected for additional in situ testing because it best matched AF shear properties. TMC3 restored torsional stiffness, torsional hysteresis area and axial range of motion to intact states. However, in a failure test of compressive deformation under fixed 5 ° flexion, some herniation risk was observed with failure strength of 5.9 MPa compared with 13.5 MPa for intact samples; TMC3 herniated under cyclic organ culture testing. These TMC adhesives performed well during in vitro and in situ testing, but additional optimization to enhance failure strength is required to further this material to advanced screening tests, such as long-term degradation. Copyright © 2016 John Wiley & Sons, Ltd.

Sirtuin 6 prevents matrix degradation through inhibition of the NF-κB pathway in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is marked by imbalanced metabolism of the extracellular matrix (ECM) in the nucleus pulposus (NP) of intervertebral discs. This study aimed to determine whether sirtuin 6 (SIRT6), a member of the sirtuin family of nicotinamide adenine dinucleotide-dependent deacetylases, protects the NP from ECM degradation in IDD. Our study showed that expression of SIRT6 markedly decreased during IDD progression. Overexpression of wild-type SIRT6, but not a catalytically inactive mutant, prevented IL-1β-induced NP ECM degradation. SIRT6 depletion by RNA interference in NP cells caused ECM degradation. Moreover, SIRT6 physically interacted with nuclear factor-κB (NF-κB) catalytic subunit p65, transcriptional activity of which was significantly suppressed by SIRT6 overexpression. These results suggest that SIRT6 prevented NP ECM degradation in vitro via inhibiting NF-κB-dependent transcriptional activity and that this effect depended on its deacetylase activity.