Osteoporosis therapies might lead to intervertebral disc degeneration via affecting cartilage endplate

Causal relationship between bone mineral density and intervertebral disc degeneration: a univariate and multivariable mendelian randomization study

BACKGROUND

Although previous studies have suggested a possible association between bone mineral density (BMD) and intervertebral disc degeneration (IDD), the causal relationship between them remains unclear. Evidence from accumulating studies indicates that they might mutually influence one another. However, observational studies may be affected by potential confounders. Meanwhile, Mendelian randomization (MR) study can overcome these confounders to assess causality.

OBJECTIVES

This Mendelian randomization (MR) study aimed to explore the causal effect of bone mineral density (BMD) on intervertebral disc degeneration (IDD).

METHODS

Summary data from genome-wide association studies of bone mineral density (BMD) and IDD (the FinnGen biobank) have been acquired. The inverse variance weighted (IVW) method was utilized as the primary MR analysis approach. Weighted median, MR-Egger regression, weighted mode, and simple mode were used as supplements. The Mendelian randomization pleiotropy residual sum and outlier (MR-PRESSO) and MR-Egger regression were performed to assess horizontal pleiotropy. Cochran's Q test evaluated heterogeneity. Leave-one-out sensitivity analysis was further conducted to determine the reliability of the causal relationship. Multivariate MR (MVMR) analyses used multivariable inverse variance-weighted methods to individually and jointly adjust for four potential confounders, body mass index (BMI), Type2 diabetes, hyperthyroidism and smoking. A reverse MR analysis was conducted to assess potential reverse causation.

RESULTS

In the univariate MR analysis, femoral neck bone mineral density (FNBMD), heel bone mineral density (eBMD), lumbar spine bone mineral density (LSBMD), and total body bone mineral density (TB BMD) had a direct causal effect on intervertebral disc degeneration (IDD) [FNBMD-related analysis: OR(95%CI) = 1.17 (1.04 to 1.31), p = 0.008, eBMD-related analysis: OR(95%CI) = 1.06 (1.01 to 1.12), p = 0.028, LSBMD-related analysis: OR(95%CI) = 1.20 (1.10 to 1.31), p = 3.38E-7,TB BMD-related analysis: OR(95%CI) = 1.20 (1.12 to 1.29), p = 1.0E-8]. In the MVMR analysis, it was revealed that, even after controlling for confounding factors, heel bone mineral density (eBMD), lumbar spine bone mineral density (LSBMD), and total body bone mineral density (TB BMD) still maintained an independent and significant causal association with IDD(Adjusting for heel bone mineral density: beta = 0.073, OR95% CI = 1.08(1.02 to 1.14), P = 0.013; Adjusting for lumbar spine bone mineral density: beta = 0.11, OR(95%CI) = 1.12(1.02 to 1.23), P = 0.03; Adjusting for total body bone mineral density: beta = 0.139, OR95% CI = 1.15(1.06 to 1.24), P = 5.53E - 5). In the reverse analysis, no evidence was found to suggest that IDD has an impact on BMD.

CONCLUSIONS

The findings from our univariate and multivariable Mendelian randomization analysis establish a substantial positive causal association between BMD and IDD, indicating that higher bone mineral density may be a significant risk factor for intervertebral disc degeneration. Notably, no causal effect of IDD on these four measures of bone mineral density was observed. Further research is required to elucidate the underlying mechanisms governing this causal relationship.

Effect of patient-specific factors on regeneration in lumbar spine at healthy disc and total disc replacement. Computer simulation

BACKGROUND AND OBJECTIVE

Degenerative diseases of the spine have a negative impact on the quality of life of patients. This study presents the results of numerical modelling of the mechanical behaviour of the lumbar spine with patient-specific conditions at physiological loads. This paper aims to numerically study the influence of degenerative changes in the spine and the presence of an endoprosthesis on the creation of conditions for tissue regeneration.

METHODS

A numerical model of the mechanical behaviour of lumbar spine at healthy and after total disc replacement under low-energy impacts equivalent to physiological loads is presented. The model is based on the movable cellular automaton method (discrete elements), where the mechanical behaviour of bone tissue is described using the Biot poroelasticity accounting for the presence and transfer of interstitial biological fluid. The nutritional pathways of the intervertebral disc in cases of healthy and osteoporotic bone tissues were predicted based on the analysis of the simulation results according to the mechanobiological principles.

RESULTS

Simulation of total disc replacement showed that osseointegration of the artificial disc plates occurs only in healthy bone tissue. With total disc replacement in a patient with osteoporosis, there is an area of increased risk of bone resorption in the near-contact area, approximately 1 mm wide, around the fixators. Dynamic loads may improve the osseointegration of the implant in pathological conditions of the bone tissue.

CONCLUSIONS

The results obtained in the case of healthy spine and osteoporotic bone tissues correspond to the experimental data on biomechanics and possible methods of IVD regeneration from the position of mechanobiological principles. The results obtained with an artificial disc (with keel-type fixation) showed that the use of this type of endoprosthesis in healthy bone tissues allows to reproduce the function of the natural intervertebral disc and does not contribute to the development of neoplastic processes. In the case of an artificial disc with osteoporosis of bone tissues, there is a zone with increased risk of tissue resorption and development of neoplastic processes in the area near the contact of the implant attachment. This circumstance can be compensated by increasing the loading level.

Stepwise reduction of bony density in patients induces a higher risk of annular tears by deteriorating the local biomechanical environment

BACKGROUND CONTEXT

The relationship between osteoporosis and intervertebral disc degeneration (IDD) remains unclear. Considering that annular tear is the primary phenotype of IDD in the lumbar spine, the deteriorating local biomechanical environment may be the main trigger for annular tears.

PURPOSE

To investigate whether poor bone mineral density (BMD) in the vertebral bodies may increase the risk of annular tears via the degradation of the local biomechanical environment.

STUDY DESIGN

This study was a retrospective investigation with relevant numerical mechanical simulations.

PATIENT SAMPLE

A total of 64 patients with low back pain (LBP) and the most severe IDD in the L4-L5 motion segment were enrolled.

OUTCOME MEASURES

Annulus integration status was assessed using diffusion tensor fibre tractography (DTT). Hounsfield unit (HU) values of adjacent vertebral bodies were employed to determine BMD. Numerical simulations were conducted to compute stress values in the annulus of models with different BMDs and body positions.

METHODS

The clinical data of the 64 patients with low back pain were collected retrospectively. The BMD of the vertebral bodies was measured using the HU values, and the annulus integration status was determined according to DTT. The data of the patients with and without annular tears were compared, and regression analysis was used to identify the independent risk factors for annular tears. Furthermore, finite element models of the L4-L5 motion segment were constructed and validated, followed by estimating the maximum stress on the post and postlateral interfaces between the superior and inferior bony endplates (BEPs) and the annulus.

RESULTS

Patients with lower HU values in their vertebral bodies had significantly higher incidence rates of annular tears, with decreased HU values being an independent risk factor for annular tears. Moreover, increased stress on the BEP-annulus interfaces was associated with a stepwise reduction of bony density (ie, elastic modulus) in the numerical models.

CONCLUSIONS

The stepwise reduction of bony density in patients results in a higher risk of annular tears by deteriorating the local biomechanical environment. Thus, osteoporosis should be considered to be a potential risk factor for IDD biomechanically.

EGR1 knockdown confers protection against ferroptosis and ameliorates intervertebral disc cartilage degeneration by inactivating the MAP3K14/NF-κB axis

This study explored whether EGR1-MAP3K14-NF-κB axis regulated ferroptosis and IVD cartilage generation. EGR1 and MAP3K14 expression levels were determined in CEP tissues of IVDD patients and intermittent cyclic mechanical tension (ICMT)-treated CEP cells. After EGR1 and MAP3K14 were altered in ICMT-treated CEP cells, the expression levels of degeneration- and ferroptosis-related proteins were measured. Binding relationship between EGR1 and MAP3K14 was evaluated. Additionally, the impacts of EFR1 knockdown on ferroptosis and cartilage degeneration in vivo were analyzed. EGR1 and MAP3K14 were overexpressed in clinical samples and cell models of IVDD. In IVDD cell models, EGR1 knockdown reduced ferroptosis and cartilage degeneration, which was reversed by MAP3K14 overexpression or Erastin treatment. NF-κB pathway inhibition nullified these effects of sh-EGR1 + oe-MAP3K14 treatment. EGR1 knockdown inhibited ferroptosis and relieved CEP degeneration via MAP3K14-NF-κB axis inactivation in vivo. Collectively, our findings highlighted that EGR1 promoted ferroptosis and IVD cartilage degeneration through MAP3K14-NF-κB axis.

EGR1 mediates METTL3/m6A/CHI3L1 to promote osteoclastogenesis in osteoporosis

OBJECTIVE

To investigate EGR1-mediated METTL3/m6A/CHI3L1 axis in osteoporosis.

METHODS

Ovariectomy (OVX) was performed on mice to induce osteoporosis, followed by μ-CT scanning of femurs, histological staining, immunohistochemistry analysis of MMP9 and NFATc1, and ELISA of serum BGP, ALP, Ca, and CTXI. The isolated mouse bone marrow mononuclear macrophages (BMMs) were differentiated into osteoclasts under cytokine stimulation. TRAP staining was performed to quantify osteoclasts. The levels of Nfatc1, c-Fos, Acp5, and Ctsk in osteoclasts, m6A level, and the relationships among EGR1, METTL3, and CHI3L1 were analyzed.

RESULTS

The EGR1/METTL3/CHI3L1 levels and m6A level were upregulated in osteoporotic mice and the derived BMMs. EGR1 was a transcription factor of METTL3. METTL3 promoted the post-transcriptional regulation of CHI3L1 by increasing m6A methylation. EGR1 downregulation reduced BMMs-differentiated osteoclasts and alleviated OVX-induced osteoporosis by regulating the METTL3/m6A/CHI3L1 axis.

CONCLUSION

EGR1 promotes METTL3 transcription and increases m6A-modified CHI3L1 level, thereby stimulating osteoclast differentiation and osteoporosis development.

A systematic morphology study on the effect of high glucose on intervertebral disc endplate degeneration in mice

To explore the relationship between diabetes and intervertebral disc degeneration in mice and the associated underlying mechanism. Four-week-old male Kunming mice were used to model diabetes using a high-fat diet combined with streptozotocin injection. After 6 months, morphological and pathological changes in L4-L6 intervertebral discs were detected by magnetic resonance imaging, micro-CT and histological staining. Immunostaining of CD31, F4/80 and CD16/32 receptors was used to detect vascular invasion and inflammatory infiltration in endplates; the exact changes were then explored by the transmission electron microscopy. The nucleus pulposus of the control and the diabetic group had a clear boundary and regular shape without collapse, while endplate calcification and chondrocyte abnormality in the diabetic group were more obvious. Immunofluorescence confirmed that compared to control, expression levels of CD31 (vascular endothelial marker) and F4/80 (monocyte/macrophage marker) in the diabetic group were significantly increased (P < 0.05), with an elevated number of F4/80 (+)/CD16/32 (+) cells (P < 0.05). The morphology of endplates was observed by transmission electron microscopy, which showed monocytes/macrophage accumulation in the endplate of the diabetic group, accompanied by increased vascular density, collagen fiber distortion and chondrocyte abnormality. In a conclusion, diabetes promotes endplate degeneration with vascular invasion, monocyte/macrophage infiltration and inflammation in mice.

Endplate role in the degenerative disc disease: A brief review

The degenerative disease of the intervertebral disc is nowadays an important health problem, which has still not been understood and solved adequately. The vertebral endplate is regarded as one of the vital elements in the structure of the intervertebral disc. Its constituent cells, the chondrocytes in the endplate, may also be involved in the process of the intervertebral disc degeneration and their role is central both under physiological and pathological conditions. They main functions include a role in homeostasis of the extracellular environment of the intervertebral disc, metabolic support and nutrition of the discal nucleus and annulus beneath and the preservation of the extracellular matrix. Therefore, it is understandable that the cells in the endplate have been in the centre of research from several viewpoints, such as development, degeneration and growth, reparation and remodelling, as well as treatment strategies. In this article, we briefly review the importance of vertebral endplate, which are often overlooked, in the intervertebral disc degeneration.

Immune exposure: how macrophages interact with the nucleus pulposus

Intervertebral disc degeneration (IDD) is a primary contributor to low back pain. Immune cells play an extremely important role in modulating the progression of IDD by interacting with disc nucleus pulposus (NP) cells and extracellular matrix (ECM). Encased within the annulus fibrosus, healthy NP is an avascular and immune-privileged tissue that does not normally interact with macrophages. However, under pathological conditions in which neovascularization is established in the damaged disc, NP establishes extensive crosstalk with macrophages, leading to different outcomes depending on the different microenvironmental stimuli. M1 macrophages are a class of immune cells that are predominantly pro-inflammatory and promote inflammation and ECM degradation in the NP, creating a vicious cycle of matrix catabolism that drives IDD. In contrast, NP cells interacting with M2 macrophages promote disc tissue ECM remodeling and repair as M2 macrophages are primarily involved in anti-inflammatory cellular responses. Hence, depending on the crosstalk between NP and the type of immune cells (M1 vs. M2), the overall effects on IDD could be detrimental or regenerative. Drug or surgical treatment of IDD can modulate this crosstalk and hence the different treatment outcomes. This review comprehensively summarizes the interaction between macrophages and NP, aiming to highlight the important role of immunology in disc degeneration.

Effects of whole-body vibration at different periods on lumbar vertebrae in female rats

The current study aimed to investigate the effects of whole-body vibration (WBV) before and after ovariectomy on lumbar vertebrae, and to observe whether the positive effects of WBV before and after ovariectomy on lumbar vertebrae in rats could be maintained after vibration stopped. Three-month-old female rats were divided into four groups (n = 45/group): control (CON), ovariectomy (OVA), WBV before ovariectomy (WBV-BO), and WBV after ovariectomy (WBV-AO) groups. For 1-8 weeks, WBV-BO group was subjected to vertical WBV. At the 9th week, the rats in WBV-BO, WBV-AO, and OVA groups were ovariectomized. During 11-18 weeks, WBV-AO group was subjected to vibration. For 19-26 weeks, no intervention was done for rats. The lumbar vertebrae were examined by Micro-CT, compressive test, creep test, and microindentation test. At the 8th week, the displacement of the L1-L2 annulus fibrosus in WBV-BO group was 18% smaller compared with CON group (p<0.05). At the 18th week, the elastic modulus of the L5 vertebral body in WBV-BO and WBV-AO groups was 53% and 57% higher than that in CON group, respectively (p<0.05); the displacement of the L1-L2 annulus fibrosus in WBV-BO group was 25% smaller than those in the other groups (p<0.05). At the 26th week, there was no significant difference in the displacement of the L1-L2 annulus fibrosus between WBV-BO group and other groups (p>0.05); the elastic modulus of the L5 vertebral body had no significant difference between WBV-AO group and CON group (p>0.05). Our results demonstrated that WBV before ovariectomy effectively prevented disc degeneration with significant effects up to 8 weeks after ovariectomy. The vertebral mechanical properties could be significantly improved by WBV after ovariectomy, but the residual effect did not maintain after WBV stopped.

Vertebral endplate defects are associated with bone mineral density in lumbar degenerative disc disease

PURPOSE

Evidence has shown that lumbar vertebral endplate defects are clinically relevant and closely related to disc degeneration, but the relationship between endplate defects and bone mineral density (BMD) remains unclear. This study aimed to explore the association between endplate defects and BMD-related values in patients with lumbar degenerative disc disease (LDD).

METHODS

Three hundred and twenty-five Chinese adult subjects diagnosed with LDD underwent dual energy X-ray absorptiometry. Endplate defects were classified using lumbar MRI. Groups were subdivided based on the occurrence rates of defect endplates. BMD at the lumbar vertebral and bilateral femur necks was compared between groups, and the association between endplate defects and lumbar BMD-related values was analyzed and adjusted for confounders including age, sex, serum levels of 25-hydroxy vitamin D (25(OH)D), calcium (Ca) and phosphorus (P).

RESULTS

Of 325 patients and 3250 endplates, 59.72% had defects, and 188 patients were divided into the higher defect rate group (occurrence rate > 50%). The higher defect rate group was associated with older age, more common postmenopausal females, higher osteoporosis rates and lower serum Ca and P levels. Lumbar BMD was greater than that at bilateral femur necks and was not equal to osteoporosis diagnosis. Endplate defects were more prevalent in lower segments. The occurrence of endplate defects was positively associated with lumbar BMD-related values in the partial correlation analysis. The association between endplate defects and lumbar BMD varies for subtypes and segments, with a trend of positive association in rim and erosive subtypes after adjusting for confounders.

CONCLUSIONS

The present study demonstrated that the occurrence of endplate defects was associated with greater lumbar BMD values in patients with LDD. This association varies for different defect subtypes and segments. The results indicated that endplate defects should be taken into consideration in osteoporosis treatment to alleviate disc degeneration.

The Endplate Role in Degenerative Disc Disease Research: The Isolation of Human Chondrocytes from Vertebral Endplate—An Optimised Protocol

Background: Degenerative disc disease is a progressive and chronic disorder with many open questions regarding its pathomorphological mechanisms. In related studies, in vitro organ culture systems are becoming increasingly essential as a replacement option for laboratory animals. Live disc cells are highly appealing to study the possible mechanisms of intervertebral disc (IVD) degeneration. To study the degenerative processes of the endplate chondrocytes in vitro, we established a relatively quick and easy protocol for isolating human chondrocytes from the vertebral endplates. Methods: The fragments of human lumbar endplates following lumbar fusion were collected, cut, ground and partially digested with collagenase I in Advanced DMEM/F12 with 5% foetal bovine serum. The sediment was harvested, and cells were seeded in suspension, supplemented with special media containing high nutrient levels. Morphology was determined with phalloidin staining and the characterisation for collagen I, collagen II and aggrecan with immunostaining. Results: The isolated cells retained viability in appropriate laboratory conditions and proliferated quickly. The confluent culture was obtained after 14 days. Six to 8 h after seeding, attachments were observed, and proliferation of the isolated cells followed after 12 h. The cartilaginous endplate chondrocytes were stable with a viability of up to 95%. Pheno- and geno-typic analysis showed chondrocyte-specific expression, which decreased with passages. Conclusions: The reported cell isolation process is simple, economical and quick, allowing establishment of a viable long-term cell culture. The availability of a vertebral endplate cell model will permit the study of cell properties, biochemical aspects, the potential of therapeutic candidates for the treatment of disc degeneration, and toxicology studies in a well-controlled environment.

High-Throughput Gene and Protein Analysis Revealed the Response of Disc Cells to Vitamin D, Depending on the VDR FokI Variants

Vitamin D showed a protective effect on intervertebral disc degeneration (IDD) although conflicting evidence is reported. An explanation could be due to the presence of the FokI functional variant in the vitamin D receptor (VDR), observed as associated with spine pathologies. The present study was aimed at investigating—through high-throughput gene and protein analysis—the response of human disc cells to vitamin D, depending on the VDR FokI variants. The presence of FokI VDR polymorphism was determined in disc cells from patients with discopathy. 1,25(OH)₂D₃ was administered to the cells with or without interleukin 1 beta (IL-1β). Microarray, protein arrays, and multiplex protein analysis were performed. In both FokI genotypes (FF and Ff), vitamin D upregulated metabolic genes of collagen. In FF cells, the hormone promoted the matrix proteins synthesis and a downregulation of enzymes involved in matrix catabolism, whereas Ff cells behaved oppositely. In FF cells, inflammation seems to hamper the synthetic activity mediated by vitamin D. Angiogenic markers were upregulated in FF cells, along with hypertrophic markers, some of them upregulated also in Ff cells after vitamin D treatment. Higher inflammatory protein modulation after vitamin D treatment was observed in inflammatory condition. These findings would help to clarify the clinical potential of vitamin D supplementation in patients affected by IDD.

Carbohydrate sulfotransferase 3 (CHST3) overexpression promotes cartilage endplate-derived stem cells (CESCs) to regulate molecular mechanisms related to repair of intervertebral disc degeneration by rat nucleus pulposus

To investigate the regulatory effect of carbohydrate sulfotransferase 3 (CHST3) in cartilage endplate-derived stem cells (CESCs) on the molecular mechanism of intervertebral disc degeneration after nucleus pulposus repair in rats. We performed GO and KEGG analysis of GSE15227 database to select the differential genes CHST3 and CSPG4 in grade Ⅱ, Ⅲ and Ⅳ intervertebral disc degeneration, IHC and WB to detect the protein profile of CHST3 and CSPG4, Co-IP for the interaction between CHST3 and CSPG4. Then, immunofluorescence was applied to measure the level of CD90 and CD105, and flow cytometry indicated the level of CD73, CD90 and CD105 in CESCs. Next, Alizarin red staining, Alcian blue staining and TEM were performed to evaluate the effects of CESCs into osteoblasts and chondroblasts, respectively, CCK8 for the cell proliferation of osteoblasts and chondroblasts after induction for different times; cell cycle of osteoblasts or chondroblasts was measured by flow cytometry after induction, and WB for the measurement of specific biomarkers of OC and RUNX in osteoblasts and aggrecan, collagen II in chondroblasts. Finally, colony formation was applied to measure the cell proliferation of CESCs transfected with ov-CHST3 or sh-CHST3 when cocultured with bone marrow cells, WB for the protein expression of CHST3, CSPG4 and ELAVL1 in CSECs, transwell assay for the migration of CESCs to bone marrow cells, TEM image for the cellular characteristics of bone marrow cells, and WB for the protein profile of VCAN, VASP, NCAN and OFD1 in bone marrow cells. CHST3 and CSPG4 were differentially expressed and interacted in grade Ⅱ, Ⅲ and Ⅳ intervertebral disc degeneration; CD73, CD90 and CD105 were lowly expressed in CESCs, osteogenic or chondroblastic induction changed the characteristics, proliferation, cell cycle and specific biomarkers of osteoblasts and chondroblasts after 14 or 21 days,; CHST3 affected the cell proliferation, protein profile, migration and cellular features of cocultured CESCs or bone marrow cells. CHST3 overexpression promoted CESCs to regulate bone marrow cells through interaction with CSPG4 to repair the grade Ⅱ, Ⅲ and Ⅳ intervertebral disc degeneration.

Melatonin Attenuates Intervertebral Disk Degeneration via Maintaining Cartilaginous Endplate Integrity in Rats

Objective

The aim of this study is to verify whether melatonin (Mel) could mitigate intervertebral disk degeneration (IVDD) in rats and to investigate the potential mechanism of it.

Method

A rat acupuncture model of IVDD was established with intraperitoneal injection of Mel. The effect of Mel on IVDD was analyzed via radiologic and histological evaluations. The specific Mel receptors were investigated in both the nucleus pulposus (NP) and cartilaginous endplates (EPs). In vitro, EP cartilaginous cells (EPCs) were treated by different concentrations of Mel under lipopolysaccharide (LPS) and Luzindole conditions. In addition, LPS-induced inflammatory response and matrix degradation following nuclear factor kappa-B (NF-κB) pathway activation were investigated to confirm the potential mechanism of Mel on EPCs.

Results

The percent disk height index (%DHI) and MRI signal decreased after initial puncture in the degeneration group compared with the control group, while Mel treatment protected disk height from decline and prevented the loss of water during the degeneration process. In the meantime, the histological staining of the Mel groups showed more integrity and well-ordered construction of the NP and EPs in both low and high concentration than that of the degeneration group. In addition, more deep-brown staining of type II collagen (Coll-II) was shown in the Mel groups compared with the degeneration group. Furthermore, in rat samples, immunohistochemical staining showed more positive cells of Mel receptors 1a and 1b in the EPs, instead of in the NP. Moreover, evident osteochondral lacuna formation was observed in rat EPs in the degeneration group; after Mel treatment, the osteochondral destruction alleviated accompanying fewer receptor activator for nuclear factor-κB ligand (RANKL) and tartrate-resistant acid phosphatase (TRAP)-stained positive cells expressed in the EPs. In vitro, Mel could promote the proliferation of EPCs, which protected EPCs from degeneration under LPS treatment. What is more, Mel downregulated the inflammatory response and matrix degradation of EPCs activated by NF-κB pathway through binding to its specific receptors.

Conclusion

These results indicate that Mel protects the integrity of the EPs and attenuates IVDD by binding to the Mel receptors in the EPs. It may alleviate the inflammatory response and matrix degradation of EPCs activated by NF-κB pathway.

Mechanics and Biology Interact in Intervertebral Disc Degeneration: A Novel Composite Mouse Model

The aim of this study was to distinguish the characteristics of intervertebral disc degeneration (IVDD) originating from mechanics imbalance, biology disruption, and their communion, and to develop a composite IVDD model by ovariectomy combined with lumbar facetectomy for mimicking elderly IVDD with osteoporosis and lumbar spinal instability. Mice were randomly divided into four groups and subjected to sham surgery (CON), ovariectomy (OVX), facetectomy (mechanical instability, INS) or their combination (COM), respectively. Radiographical (n = 4) and histological changes (n = 8) of L4/5 spinal segments were analyzed. Tartrate-resistant acid phosphatase (TRAP) staining was conducted to detect osteoclasts, and expression of osterix (OSX), type I collagen (Col I), type II collagen (Col II) and vascular endothelial growth factor (VEGF) were evaluated by immunochemistry. OVX affected the body's metabolism but INS did not, as the body weight increased and uterus weight decreased in OVX and COM mice compared to CON and INS mice. OVX, INS, and COM caused IVDD in various degrees at 12 weeks after surgery. However, the major pathogeneses of OVX- and INS-induced IVDD were different, which focused on endplate (EP) remodeling and annulus fibrosus (AF) collapse, respectively. OVX induced osteopenia of vertebra. In contrast, INS promoted the stress-adaptive increase of subchondral bone trabeculae. The COM produced a reproducible severe IVDD model with characteristics of sparse vertebral trabeculae, cartilaginous EP ossification, subchondral bone sclerosis, fibrous matrix disorder, angiogenesis, disc stiffness, as well as space fusion. Additionally, all groups had elevated bone and cartilage turnover compared with CON group, as the quantity of trap + osteoclasts and the osteogenic OSX expression increased in these groups. Likewise, the VEGF expression levels were similar, accompanied by the altered matrix expression of disc, including the changed distribution and contents of Col II and Col I. The findings suggested that the composite mouse model to some extent could effectively mimic the interactions of biology and mechanics engaged in the onset and natural course of IVDD, which would be more compatible with the IVDD of elderly with vertebral osteoporosis and spinal instability and benefit to further clarify the complicated mechanobiological environment of elderly IVDD progression.

Melatonin modulates IL-1β-induced extracellular matrix remodeling in human nucleus pulposus cells and attenuates rat intervertebral disc degeneration and inflammation

The inflammatory-associated factors interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) are widely reported to be associated with intervertebral disc (IVD) degeneration (IVDD). N-acetyl-5-methoxytryptamine (melatonin) is a natural hormone secreted by the pineal gland which has been shown to participate in several physiological and pathological progresses, such as aging, anti-inflammation, anti-apoptosis and autophagy regulation. However, the effects of melatonin on IVD remain unclear. In the present study, we treated human nucleus pulposus cells (NPCs) with melatonin and discovered that melatonin could modulate extracellular matrix (ECM) remodeling induced by IL-1β by enhancing collagen II and aggrecan expression levels and by downregulating matrix metalloproteinase-3 (MMP-3) levels. These findings were verified by western blot and immunofluorescence assays. Intraperitoneal injection of melatonin mitigated IVDD in the rat tail puncture model. X-ray and magnetic resonance imaging (MRI), as well as hematoxylin-eosin (H&E), Safranine O-Green, Alcian blue and Celium red staining methods were adopted to evaluate IVDD grades, the structural integrity of nucleus pulposus (NP) and annulus fibrosus (AF) and the damage and calcification of the cartilage endplate. Melatonin reduced inflammatory cell aggregation and the release of the inflammatory factors IL-1β, IL-6, TNF-α as determined by immunohistochemistry. In conclusion, the present study demonstrated that melatonin could modulate ECM remodeling by IL-1β in vitro and attenuate the IVDD and induction of inflammation in a rat tail puncture model in vivo. The data demonstrated that melatonin may contribute to the restoration processs of IVD following damage and may be used as a potential novel therapy for IVDD.

Moderate osteoporosis itself is beneficial for bones

There have been increasing numbers of reports that anti-osteoporosis drugs cause osteonecrosis. A typical example is medication-related osteonecrosis of the jaws (MRONJ) which can cause massive necrosis and defects of the jaws. Thus, the dosage and effects of anti-osteoporosis drugs should be re-examined. Our hypothesis is that primary moderate osteoporosis itself is beneficial for bones and should not be excessively treated other than vitamin D, calcium supplementation and functional exercises. The self-repair and anti-infection abilities of bone depend on its organic tissues including stem cells, blood vessels, osteoclastic and osteogenic factors in bone, which jointly fight against invading pathogens and repair bone damage. Recent evidence supports age-related changes in mesenchymal stem cell including loss of self-renewal and increases in senescent cell numbers. Thus, the number of MSCs and vessels need to be increased to achieve functions similar to those in young people. This requires dissolving a portion of inorganic materials and providing extra space to hold more cells and blood vessels. In contrast, anti-osteoporosis drugs prevent bone destruction, and increase mineralization that occupies the space of organic materials, reduces bone immunity and self-repair. Moreover, long term use of anti-osteoporosis drugs also have negative effects on long bones and cartilages. Therefore, moderate age-related osteoporosis is natural in humans to protect bones. Excessive treatment of osteoporosis weakens immunity and self-repair.