Thrombospondin-1 promotes mechanical stress-mediated ligamentum flavum hypertrophy through the TGFβ1/Smad3 signaling pathway

Lumbar spinal canal stenosis is primarily caused by ligamentum flavum hypertrophy (LFH), which is a significant pathological factor. Nevertheless, the precise molecular basis for the development of LFH remains uncertain. The current investigation observed a notable increase in thrombospondin-1 (THBS1) expression in LFH through proteomics analysis and single-cell RNA-sequencing analysis of clinical ligamentum flavum specimens. In laboratory experiments, it was demonstrated that THBS1 triggered the activation of Smad3 signaling induced by transforming growth factor β1 (TGFβ1), leading to the subsequent enhancement of COL1A2 and α-SMA, which are fibrosis markers. Furthermore, experiments conducted on a bipedal standing mouse model revealed that THBS1 played a crucial role in the development of LFH. Sestrin2 (SESN2) acted as a stress-responsive protein that suppressed the expression of THBS1, thus averting the progression of fibrosis in ligamentum flavum (LF) cells. To summarize, these results indicate that mechanical overloading causes an increase in THBS1 production, which triggers the TGFβ1/Smad3 signaling pathway and ultimately results in the development of LFH. Targeting the suppression of THBS1 expression may present a novel approach for the treatment of LFH.

Transthyretin amyloid deposition in ligamentum flavum (LF) is significantly correlated with LF and epidural fat hypertrophy in patients with lumbar spinal stenosis

Lumbar spinal stenosis (LSS) is a degenerative disease characterized by intermittent claudication and numbness in the lower extremities. These symptoms are caused by the compression of nerve tissue in the lumbar spinal canal. Ligamentum flavum (LF) hypertrophy and spinal epidural lipomatosis in the spinal canal are known to contribute to stenosis of the spinal canal: however, detailed mechanisms underlying LSS are still not fully understood. Here, we show that surgically harvested LFs from LSS patients exhibited significantly increased thickness when transthyretin (TTR), the protein responsible for amyloidosis, was deposited in LFs, compared to those without TTR deposition. Multiple regression analysis, which considered age and BMI, revealed a significant association between LF hypertrophy and TTR deposition in LFs. Moreover, TTR deposition in LF was also significantly correlated with epidural fat (EF) thickness based on multiple regression analyses. Mesenchymal cell differentiation into adipocytes was significantly stimulated by TTR in vitro. These results suggest that TTR deposition in LFs is significantly associated with increased LF hypertrophy and EF thickness, and that TTR promotes adipogenesis of mesenchymal cells. Therapeutic agents to prevent TTR deposition in tissues are currently available or under development, and targeting TTR could be a potential therapeutic approach to inhibit LSS development and progression.

ACSM5 inhibits ligamentum flavum hypertrophy by regulating lipid accumulation mediated by FABP4/PPAR signaling pathway

BACKGROUND

Ligamentum flavum (LF) hypertrophy is the main cause of lumbar spinal canal stenosis (LSCS). Previous studies have shown that LF hypertrophy tissue exhibits abnormal lipid accumulation, but the regulatory mechanism remains unclear. The objective of this study was to explore the function and potential mechanism of ACSM5 in LF lipid accumulation.

METHODS

To assess the ACSM5 expression levels, lipid accumulation and triglyceride (TG) level in LF hypertrophy and normal tissue, we utilized RT-qPCR, western blot, oil red O staining, and TG assay kit. The pearson correlation coefficient assay was used to analyze the correlation between ACSM5 levels and lipid accumulation or TG levels in LF hypertrophy tissue. The role of ACSM5 in free fatty acids (FFA)-induced lipid accumulation in LF cells was assessed in vitro, and the role of ACSM5 in LF hypertrophy in mice was verified in vivo. To investigate the underlying mechanisms of ACSM5 regulating lipid accumulation in LF, we conducted the mRNA sequencing, bioinformatics analysis, and rescue experiments.

RESULTS

In this study, we found that ACSM5, which was significantly down-regulated in LF tissues, correlated with lipid accumulation. In vitro cell experiments demonstrated that overexpression of ACSM5 significantly inhibited FFA-induced lipid accumulation and fibrosis in LF cells. In vivo animal experiments further confirmed that overexpression of ACSM5 inhibited LF thickening, lipid accumulation, and fibrosis. Mechanistically, ACSM5 inhibited lipid accumulation of LF cells by inhibiting FABP4-mediated PPARγ signaling pathway, thereby improving hypertrophy and fibrosis of LF.

CONCLUSIONS

our findings elucidated the important role of ACSM5 in the regulation of LF lipid accumulation and provide insight into potential therapeutic interventions for the treatment of LF hypertrophy. This study further suggested that therapeutic strategies targeting lipid deposition may be an effective potential approach to treat LF hypertrophy-induced LSCS.

Interleukin-17A Promotes Proliferation and Osteogenic Differentiation of Human Ligamentum Flavum Cells Through Regulation of β-Catenin Signaling

STUDY DESIGN

A basic experimental study.

OBJECTIVE

To elucidate the role and mechanism of interleukin (IL)-17A in thoracic ossification of the ligamentum flavum (TOLF).

SUMMARY OF BACKGROUND DATA

TOLF is characterized by the replacement of the thoracic ligamentum flavum with ossified tissue and is one of the leading causes of thoracic spinal stenosis. IL-17A is an important member of the IL-17 family that has received widespread attention for its key contributions to the regulation of bone metabolism and heterotopic ossification. However, it is unclear whether IL-17A is involved in TOLF.

MATERIALS AND METHODS

Cell counting kit-8 assay and 5-ethynyl-2'-deoxyuridine staining were performed to assess the proliferation of ligamentum flavum cells (LFCs). Alkaline phosphatase activity assay, Alizarin red staining, and protein level expression of osteogenic-related genes were used to evaluate the osteogenic differentiation potential of LFCs. The effect of IL-17A on the proliferation and osteogenic differentiation of LFCs was further assessed after silencing β-catenin by transfection with small interfering RNA. In addition, the possible source of IL-17A was further demonstrated by coculture assays of T helper 17 (Th17) cells with LFCs. Student t test was used for comparisons between groups, and the one-way analysis of variance, followed by the Tukey post hoc test, was used for comparison of more than two groups.

RESULTS

IL-17A was elevated in TOLF tissue compared with normal ligamentum flavum. IL-17A stimulation promoted the proliferation and osteogenic differentiation of LFCs derived from patients with TOLF. We found that IL-17A promoted the proliferation and osteogenic differentiation of LFCs by regulating the β-catenin signaling. Coculture of Th17 cells with LFCs enhanced β-catenin signaling-mediated proliferation and osteogenic differentiation of LFCs. However, these effects were markedly attenuated after the neutralization of IL-17A.

CONCLUSIONS

This is the first work we are aware of to highlight the importance of IL-17A in TOLF. IL-17A secreted by Th17 cells in the ligamentum flavum may be involved in the ossification of the microenvironment by regulating β-catenin signaling to promote the proliferation and osteogenic differentiation of LFCs.

PTGR1 is involved in cell proliferation in thoracic ossification of the ligamentum flavum

Thoracic ossification of the ligamentum flavum (TOLF) is a heterotopic ossification of spinal ligaments, leading to serious myelopathy. TOLF underlying mechanisms are not well understood. Our iTRAQ analysis have identified ten inflammatory factors related to TOLF, including l. We found that PTGR1 expressions increased in TOLF by RT-PCR and western blot in this study. Both cell proliferation and differentiation are important for the process of bone formation. In our previous study, we demonstrated that TOLF primary cells grew faster than control cells. It was reported that knockdown of PTGR1 inhibited cell proliferation. We hypothesize that PTGR1 may participate in cell proliferation in TOLF. To test this hypothesis, TOLF primary cells were treated for 24h with PTGR1. We observed that PTGR1 increased cell proliferation. The effect of PTGR1 on cell proliferation related genes was examined in TOLF primary cells. Our results showed that PTGR1 was able to activate expressions of c-Myc and CyclinD1. Moreover, blocking JNK pathway by selective JNK inhibitor SP600125 eliminated the positive effect of PTGR1 on c-Myc expression, indicating that PTGR1 activated the expression of c-Myc via JNK pathway. Our new findings suggest that PTGR1 is involved in cell proliferation of TOLF.

Relationship between Severity of Lumbar Spinal Stenosis and Ligamentum Flavum Hypertrophy and Serum Inflammatory Factors

Objective

This study is aimed at investigating the correlation between lumbar spinal stenosis (LSS) severity, ligamentum flavum hypertrophy, and the upregulation of inflammatory markers.

Methods

From March 2019 and May 2022, eighty-five inpatients with LSS were enlisted as the study's research group, while sixty-five patients hospitalized for lumbar intervertebral disc herniation over the same time period served as the study's control group. Moreover, mild, moderate, and severe subgroups of patients were created within the research population based on their LSS severity. The ligamentum flavum thickness and the positive expression rates of TNF-α, TGF-β1, and IL-1α were compared between the study group and the control group. The levels of TNF-α, TGF-β1, and IL-1α that were found to be positively expressed were compared between the mild, moderate, and severe groups. Patients with LSS had their ligamentum flavum thickness and their positive expression rates of TNF-α, TGF-β1, and IL-1α analyzed using Spearman correlation analysis. We evaluated the diagnostic utility of the positive expression rates of IL-α1, TGF-β1, and TNF-α and ligamentum flavum thickness in distinguishing the severity of LSS using a receiver operating characteristic (ROC) curve.

Results

The rates of both lower limb pain (40.00%) and intermittent claudication (80.00%) in the LSS group were higher than those in the lumbar disc herniation group (15.38%, 12.31%), with statistical significance (P < 0.05). However, no substantial disparity was observed in left lower limb pain, right lower limb pain, low back pain, lower limb sensation, muscle strength, and reflex abnormalities between the two groups (P > 0.05). Positive expressions of TGF-β1, TNF-α, and IL-1α and thicker ligamentum flavum were more prevalent in the LSS group than in the lumbar intervertebral disc herniation group. All indexes were significantly (P < 0.05) higher in the moderate stenosis group than in the severe stenosis group. Additionally, the thickness of the ligamentum flavum and the positive expression rates of TNF-α, TGF-β1, and IL-1α were higher in the mild and moderate stenosis groups than in the severe stenosis group. The expression levels of TNF-α, TGF-β1, and IL-1α were favorably linked with ligamentum flavum thickness (P < 0.05). ROC curve analysis showed that the thickness of ligamentum flavum, the expression of IL-1α, the expression of TGF-β1, and the expression of TNF-α could effectively diagnose mild, moderate, and severe LSS (P < 0.05).

Conclusion

Ligamentum flavum hypertrophy and positive expression rates of IL-1α, TGF-β1, and TNF-α are closely linked to LSS, which can effectively identify mild, moderate, and severe LSS.

Revealing the novel autophagy-related genes for ligamentum flavum hypertrophy in patients and mice model

Background

Fibrosis is a core pathological factor of ligamentum flavum hypertrophy (LFH) resulting in degenerative lumbar spinal stenosis. Autophagy plays a vital role in multi-organ fibrosis. However, autophagy has not been reported to be involved in the pathogenesis of LFH.

Methods

The LFH microarray data set GSE113212, derived from Gene Expression Omnibus, was analyzed to obtain differentially expressed genes (DEGs). Potential autophagy-related genes (ARGs) were obtained with the human autophagy regulator database. Functional analyses including Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, Gene Set Enrichment Analysis (GSEA), and Gene Set Variation Analysis (GSVA) were conducted to elucidate the underlying biological pathways of autophagy regulating LFH. Protein-protein interaction (PPI) network analyses was used to obtain hub ARGs. Using transmission electron microscopy, quantitative RT-PCR, Western blotting, and immunohistochemistry, we identified six hub ARGs in clinical specimens and bipedal standing (BS) mouse model.

Results

A total of 70 potential differentially expressed ARGs were screened, including 50 up-regulated and 20 down-regulated genes. According to GO enrichment and KEGG analyses, differentially expressed ARGs were mainly enriched in autophagy-related enrichment terms and signaling pathways related to autophagy. GSEA and GSVA results revealed the potential mechanisms by demonstrating the signaling pathways and biological processes closely related to LFH. Based on PPI network analysis, 14 hub ARGs were identified. Using transmission electron microscopy, we observed the autophagy process in LF tissues for the first time. Quantitative RT-PCR, Western blotting, and immunohistochemistry results indicated that the mRNA and protein expression levels of FN1, TGFβ1, NGF, and HMOX1 significantly higher both in human and mouse with LFH, while the mRNA and protein expression levels of CAT and SIRT1 were significantly decreased.

Conclusion

Based on bioinformatics analysis and further experimental validation in clinical specimens and the BS mouse model, six potential ARGs including FN1, TGFβ1, NGF, HMOX1, CAT, and SIRT1 were found to participate in the fibrosis process of LFH through autophagy and play an essential role in its molecular mechanism. These potential genes may serve as specific therapeutic molecular targets in the treatment of LFH.

M1 Macrophage-Derived Interleukin-6 Promotes the Osteogenic Differentiation of Ligamentum Flavum Cells

STUDY DESIGN

Basic experimental study.

OBJECTIVE

The aim of this study was to clarify the role of macrophages (Mφs) in the osteogenic differentiation of ligamentum flavum (LF) cells.

SUMMARY OF BACKGROUND DATA

Mφs and secreted factors are involved in the regulation of cell osteogenic differentiation, and play an important role in the process of heterotopic ossification. Whether Mφs are involved in the development of ossification of the ligamentum flavum (OLF) have not been reported.

METHODS

The expression of CD68+ Mφs in ossified LF tissue was identified by immunohistochemical staining. THP-1 cells were polarized to M1 and M2, and identified by flow cytometry and immunofluorescence. The alkaline phosphatase activity and osteogenic differentiation-related gene expression in LF cells were evaluated following incubation with each Mφs conditioned medium (CM). Enzyme-linked immunosorbent assay was used to detect the pro-inflammatory cytokines in the supernatants, and qPCR was used to detect the expression of the corresponding receptors in the LF cells after incubation with the CM. LF cells were induced with CM-M1 in the presence of neutralizing antibodies to further test whether cytokines secreted by M1 Mφs impacted their osteogenic differentiation.

RESULTS

CD68+ Mφs were found on the OLF samples. THP-1 cells were polarized into M1 and M2, and both M1 and M2 Mφs promoted the osteogenic differentiation of LF cells. The concentrations of tumor necrosis factor (TNF)-α, interleukin (IL)-1 β, and IL-6 in M1 Mφ supernatants were greater than those in M2, and greater levels of these cytokine receptors were observed in LF cells induced with CM-M1 than those with CM-M2. Osteogenic differentiation of LF cells induced by CM-M1 decreased after IL-6 was neutralized; however, not after IL-1β and TNF-α were neutralized.

CONCLUSION

M1 Mφ-derived IL-6 promotes the osteogenic differentiation of LF cells, which may be a pathway in which Mφs regulate the osteogenic differentiation of LF cells.

Deciphering Obesity-Related Gene Clusters Unearths SOCS3 Immune Infiltrates and 5mC/m6A Modifiers in Ossification of Ligamentum Flavum Pathogenesis

BACKGROUND

Ossification of ligamentum flavum (OLF) is an insidious and debilitating heterotopic ossifying disease with etiological heterogeneity and undefined pathogenesis. Obese individuals predispose to OLF, whereas the underlying connections between obesity phenotype and OLF pathomechanism are not fully understood. Therefore, this study aims to explore distinct obesity-related genes and their functional signatures in OLF.

METHODS

The transcriptome sequencing data related to OLF were downloaded from the GSE106253 in the Gene Expression Omnibus (GEO) database. The obesity-related differentially expressed genes (ORDEGs) in OLF were screened, and functional and pathway enrichment analysis were applied for these genes. Furthermore, protein-protein interactions (PPI), module analysis, transcription factor enrichment analysis (TFEA), and experiment validation were used to identify hub ORDEGs. The immune infiltration landscape in OLF was depicted, and correlation analysis between core gene SOCS3 and OLF-related infiltrating immune cells (OIICs) as well as 5mC/m6A modifiers in OLF was constructed.

RESULTS

Ninety-nine ORDEGs were preliminarily identified, and functional annotations showed these genes were mainly involved in metabolism, inflammation, and immune-related biological functions and pathways. Integrative bioinformatic algorithms determined a crucial gene cluster associated with inflammatory/immune responses, such as TNF signaling pathway, JAK-STAT signaling pathway, and regulation of interferon-gamma-mediated signaling. Eight hub ORDEGs were validated, including 6 down-regulated genes (SOCS3, PPARG, ICAM-1, CCL2, MYC, and NT5E) and 2 up-regulated genes (PTGS2 and VEGFA). Furthermore, 14 differential OIICs were identified by ssGSEA and xCell, and SOCS3 was overlapped to be the core gene, which was associated with multiple immune infiltrates (dendritic cells, macrophage, and T cells) and six m6A modifiers as well as four 5mC regulators in OLF. Reduced SOCS3 and FTO expression and up-regulated DNMT1 level in OLF were validated by Western blotting.

CONCLUSION

This study deciphered immune/inflammatory signatures of obesity-related gene clusters for the first time, and defined SOCS3 as one core gene. The crosstalk between 5mC/m6A methylation may be a key mediator of SOCS3 expression and immune infiltration. These findings will provide more insights into molecular mechanisms and therapeutic targets of obesity-related OLF.

WISP-1 induced by mechanical stress contributes to fibrosis and hypertrophy of the ligamentum flavum through Hedgehog-Gli1 signaling

Ongoing chronic fibrosis and hypertrophy of the ligamentum flavum (LF) is an important cause of lumbar spinal canal stenosis (LSCS). Our previous work showed that WNT1-inducible signaling pathway protein 1 (WISP-1) is a critical driver of LF fibrosis. However, the potential mechanism has not been explored. Here, we found that Gli1 was upregulated in hypertrophic LF tissues and required for fibrogenesis in fibroblasts. Moreover, mechanical stretching increased the expression of WISP-1 in LF fibroblasts. Furthermore, WISP-1 induced fibrogenesis in vitro through the Hedgehog-Gli1 pathway. This conclusion was supported by the fact that WISP-1 activated the Hedgehog-Gli1 pathway in LF fibroblasts and that cyclopamine attenuated the effect of WISP-1-induced fibrogenesis. WISP-1 also promoted the transition of fibroblasts into myofibroblasts via the Hedgehog pathway. Importantly, a hypertrophic LF rabbit model induced by mechanical stress also showed pathological changes in fibrosis and elevated expression of WISP-1, Gli1, and α-SMA. Therapeutic administration of cyclopamine reduced collagen expression, fibroblast proliferation, and myofibroblast differentiation and ameliorated fibrosis in the mechanical stress-induced rabbit model. Collectively, our findings show mechanical stress/WISP-1/Hedgehog signaling as a new fibrotic axis contributing to LF hypertrophy and identify Hedgehog signaling as a therapeutic target for the prevention and treatment of LF fibrosis.

Cyclic stretch promotes the ossification of ligamentum flavum by modulating the Indian hedgehog signaling pathway

The Indian hedgehog (IHH) signaling pathway is an important pathway for bone growth and development. The aim of the present study was to examine the role of the IHH signaling pathway in the development of the ossification of ligamentum flavum (OLF) at the cellular and tissue levels. The expression levels and localization of the osteogenic genes Runt-related transcription factor 2 (RUNX2), Osterix, alkaline phosphatase (ALP), osteocalcin (OCN) and IHH were evaluated in OLF tissues by reverse transcription-quantitative PCR (RT-qPCR) and immunohistochemistry. Non-ossified ligamentum flavum (LF) sections were used as control samples. The tissue explant method was used to obtain cultured LF cells. In addition, OLF cells were subjected to cyclic stretch application for 0, 6, 12 or 24 h. The expression levels of osteogenic genes, and the IHH signaling pathway genes IHH, Smoothened (SMO), GLI family zinc finger 1 (GLI1), GLI2 and GLI3 were evaluated with RT-qPCR and western blotting. Osteogenic differentiation was further evaluated by assessing ALP activity and staining. Moreover, the effect of cyclopamine (Cpn), an IHH signaling inhibitor, on osteogenic differentiation was examined. The RT-qPCR and immunohistochemical results indicated that the mRNA and protein expression levels of RUNX2, Osterix, ALP, OCN and IHH were significantly higher in the OLF group compared with the LF group. Furthermore, application of cyclic stretch to OLF cells resulted in greater ALP activity, and significant increases in mRNA and protein expression levels of RUNX2, Osterix, ALP and OCN in a time-d00ependent manner. Cyclic stretch application also led to significant increases in IHH signaling pathway genes, including IHH, SMO, GLI1 and GLI2, while no significant effect was found on GLI3 expression level. In addition, it was found that Cpn significantly reversed the effect of cyclic stretch on the ALP activity, and the expression levels of RUNX2, Osterix, ALP, OCN, GLI1 and GLI2. Collectively, the present results suggested that the IHH signaling pathway may mediate the effect of cyclic stretch on the OLF cells.

BMP2 Modified by the m6A Demethylation Enzyme ALKBH5 in the Ossification of the Ligamentum Flavum Through the AKT Signaling Pathway

Ossification of the ligamentum flavum (OLF) is characterized by a process of ectopic bone formation in the ligamentum flavum. The definitive pathophysiology of OLF still remains unclear, but the epigenetic m6A modification plays an important role in OLF. In addition, no studies have reported the function of ALKBH5 in OLF development. In this study, we investigated the function of the m6A demethylation enzyme ALKBH5 in OLF. To evaluate the function of ALKBH5, OLF tissues and normal ligamentum flavum tissues were collected. In vitro methods, including HE, IHC and western blotting assays, were used to evaluate the association of ALKBH5 with OLF. In addition, we verified the effects of ALKBH5 on osteogenesis using alizarin red and ALP staining. MeRIP q-PCR was performed to investigate the methylation level of BMP2. Moreover, the mechanism of ALKBH5-mediated regulation of the ossification of the ligamentum flavum cells through the AKT signaling pathway was also verified. The present study showed that the expression of ALKBH5 increased in OLF tissues. The overexpression of ALKBH5 increased the expression of osteogenic genes and promoted the ossification of ligamentum flavum cells. Furthermore, BMP2 was significantly enriched in the ligamentum flavum cells of the anti-m6A group compared with those of the IgG group. The overexpression of ALKBH5 led to the activation of p-AKT, and BMP2 was regulated by ALKBH5 through the AKT signaling pathway. ALKBH5 promoted the osteogenesis of the ligamentum flavum cells through BMP2 demethylation and AKT activation. ALKBH5 was shown to be an important demethylation enzyme in OLF development.

The Role of JAK-STAT Signaling Activation in Hypertrophied Ligamentum Flavum

BACKGROUND

Although previous studies have reported the expression of JAK1, STAT3, and phosphorylated STAT3 in hypertrophied ligamentum flavum (LF), the role of the Janus kinase-signal transducer and activator of transcription (JAK/STAT) signaling pathway in hypertrophied LF has not been fully elucidated. The aim of this study was to identify the important JAK/STAT gene expression patterns of the 3 main receptors involved in this pathway: interferon (IFN)-γ receptor (IFN-γR), IFN-α receptor (IFNAR), and interleukin (IL)-6 receptor (IL-6R).

METHODS

The human LF specimens were obtained from 28 patients who underwent lumbar spine surgery for either degenerative lumbar canal stenosis (DLCS) (n = 28) or lumbar disc herniation (LDH) (n = 20). In this design, patients with LDH served as the control group. The degree of fibrosis was demonstrated by Masson's trichrome staining. The location and expression profiling of the JAK/STAT pathway were analyzed by quantitative real-time polymerase chain reaction and Western blotting. The thickness of the LF was measured with axial T1-weighted magnetic resonance imaging.

RESULTS

The most severe fibrotic changes were on the dorsal side of the LF. IL-6 and IFN-I expression levels were significantly increased on the dorsal side of the LF. While expression levels of IL-6R and IFNAR on the dural and dorsal side were significantly higher in the DLCS samples, IFN-γR and endothelial epidermal growth factor receptor in LF samples showed a significant increase only on the dorsal side. JAK/STAT genes were significantly expressed, especially on the dorsal side.

CONCLUSIONS

Our data suggest that IFNAR- and IL-6R-dependent JAK/STAT signaling pathways may be significant targets in drug development strategies for the treatment of LF hypertrophy.

Angiopoietin-2 promotes osteogenic differentiation of thoracic ligamentum flavum cells via modulating the Notch signaling pathway

Thoracic ossification of the ligamentum flavum (TOLF) is heterotopic ossification of spinal ligaments, which may cause serious thoracic spinal canal stenosis and myelopathy. However, the underlying etiology remains inadequately understood. In this study, the ossification patterns of TOLF were analyzed by micro-computer tomography (micro-CT). The expression profile of genes associated with angiogenesis was analyzed in thoracic ligamentum flavum cells at sites of different patterns of ossification using RNA sequencing. Significant differences in the expression profile of several genes were identified from Gene Ontology (GO) analysis. Angiopoietin-2 (ANGPT2) was significantly up-regulated in primary thoracic ligamentum flavum cells during osteogenic differentiation. To address the effect of ANGPT2 on Notch signaling and osteogenesis, ANGPT2 stimulation increased the expression of Notch2 and osteogenic markers of primary thoracic ligamentum flavum cells of immature ossification, while inhibition of ANGPT2 exhibited opposite effect on Notch pathway and osteogenesis of cells of mature ossification. These findings provide the first evidence for positive regulation of ANGPT2 on osteogenic differentiation in human thoracic ligamentum flavum cells via modulating the Notch signaling pathway.

iTRAQ quantitative proteomic study in patients with thoracic ossification of the ligamentum flavum

Thoracic ossification of the ligamentum flavum (TOLF) is a unique disease with ectopic ossification, and is a major cause of thoracic spinal stenosis and myelopathy. However, the underlying etiology remains largely unknown. In this study, the ligamentum flavum was systematically analyzed in TOLF patients by using comprehensive iTRAQ labeled quantitative proteomics. Among 1285 detected proteins, there were 282 proteins identified to be differentially expressed. The Gene Ontology (GO) analysis regarding functional annotation of proteins consists of the following three aspects: the biological process, the molecular function, and the cellular components. The function clustering analysis revealed that ten of the above proteins are related to inflammation, such as tumor necrosis factor (TNF). This finding was subsequently validated by ELISA, which indicated that serum TNF-α of TOLF patients was significantly higher compared with the control group. To address the effect of TNF-α on ossification-related gene expression, we purified and cultured primary cells from thoracic ligamentum flavum of patients with TOLF. TNF-α was then used to stimulate cells. RNA was isolated and analyzed by RT-PCR. Our results showed that TNF-α was able to induce the expressions of osteoblast-specific transcription factor Osterix (Osx) in ligamentum flavum cells, suggesting that it can promote osteoblast differentiation. In addition, as the Osx downstream osteoblast genes OCN and ALP were also activated by TNF-α. This is the first proteomic study to identify inflammation factors such as TNF-α involved in ossified ligamentum flavum in TOLF, which may contribute to a better understanding of the cause of TOLF.

Expression of the JAK/STAT signaling pathway in the ligamentum flavum of patients with lumbar spinal canal stenosis

BACKGROUND

Ligamentum flavum (LF) hypertrophy is an important cause of lumbar spinal canal stenosis (LSS), one of the most common spinal disorders in the elderly. Although many cytokines are reported to be associated with LF hypertrophy, the intracellular signaling system is rarely discussed. The purpose of this study was to identify the JAK/STAT signaling pathway and to examine the role of the JAK/STAT systems in the hypertrophied LF.

METHODS

The LF of 10 LSS patients was analyzed and the expression of JAK1, STAT3, phosphorylated (p)-STAT3, and actin was examined by Western blot analysis. The expression of p-STAT3 was also examined by immunostaining and its positive cell ratio was compared between LSS and non-LSS samples. We measured the thickness of the LF on magnetic resonance images and studied the relationship between its thickness and the expression of p-STAT3.

RESULTS

JAK1, STAT3, and p-STAT3 were detected in almost all samples by Western blot analysis. Immunoreactivity against p-STAT3 was observed mainly in endothelial- and fibroblast-like cells. The expression of p-STAT3 was significantly higher in LSS than non-LSS samples; it was significantly stronger on the dorsal than the dural side of the LF and positively correlated with the thickness of the LF on the dorsal side.

CONCLUSIONS

The JAK/STAT signaling pathway is positively correlated with the thickness of the LF. Our findings suggest that JAK1 and STAT3 molecules are involved in and regulate LF hypertrophy.

Experimental Mouse Model of Lumbar Ligamentum Flavum Hypertrophy

Lumbar spinal canal stenosis (LSCS) is one of the most common spinal disorders in elderly people, with the number of LSCS patients increasing due to the aging of the population. The ligamentum flavum (LF) is a spinal ligament located in the interior of the vertebral canal, and hypertrophy of the LF, which causes the direct compression of the nerve roots and/or cauda equine, is a major cause of LSCS. Although there have been previous studies on LF hypertrophy, its pathomechanism remains unclear. The purpose of this study is to establish a relevant mouse model of LF hypertrophy and to examine disease-related factors. First, we focused on mechanical stress and developed a loading device for applying consecutive mechanical flexion-extension stress to the mouse LF. After 12 weeks of mechanical stress loading, we found that the LF thickness in the stress group was significantly increased in comparison to the control group. In addition, there were significant increases in the area of collagen fibers, the number of LF cells, and the gene expression of several fibrosis-related factors. However, in this mecnanical stress model, there was no macrophage infiltration, angiogenesis, or increase in the expression of transforming growth factor-β1 (TGF-β1), which are characteristic features of LF hypertrophy in LSCS patients. We therefore examined the influence of infiltrating macrophages on LF hypertrophy. After inducing macrophage infiltration by micro-injury to the mouse LF, we found excessive collagen synthesis in the injured site with the increased TGF-β1 expression at 2 weeks after injury, and further confirmed LF hypertrophy at 6 weeks after injury. Our findings demonstrate that mechanical stress is a causative factor for LF hypertrophy and strongly suggest the importance of macrophage infiltration in the progression of LF hypertrophy via the stimulation of collagen production.

MiR-132-3p Regulates the Osteogenic Differentiation of Thoracic Ligamentum Flavum Cells by Inhibiting Multiple Osteogenesis-Related Genes

Ossification of the ligamentum flavum (OLF) is a disorder of heterotopic ossification of spinal ligaments and is the main cause of thoracic spinal canal stenosis. Previous studies suggested that miR-132-3p negatively regulates osteoblast differentiation. However, whether miR-132-3p is involved in the process of OLF has not been investigated. In this study, we investigated the effect of miR-132-3p and its target genes forkhead box O1 (FOXO1), growth differentiation factor 5 (GDF5) and SRY-box 6 (SOX6) on the osteogenic differentiation of ligamentum flavum (LF) cells. We demonstrated that miR-132-3p was down-regulated during the osteogenic differentiation of LF cells and negatively regulated the osteoblast differentiation. Further, miR-132-3p targeted FOXO1, GDF5 and SOX6 and down-regulated the protein expression of these genes. Meanwhile, FOXO1, GDF5 and SOX6 were up-regulated after osteogenic differentiation and the down-regulation of endogenous FOXO1, GDF5 or SOX6 suppressed the osteogenic differentiation of LF cells. In addition, we also found FOXO1, GDF5 and SOX6 expression in the ossification front of OLF samples. Overall, these results suggest that miR-132-3p inhibits the osteogenic differentiation of LF cells by targeting FOXO1, GDF5 and SOX6.

Angiopoietin-like protein 2 induced by mechanical stress accelerates degeneration and hypertrophy of the ligamentum flavum in lumbar spinal canal stenosis

Chronic inflammation and subsequent fibrosis induced by mechanical stress play an important role in ligamentum flavum (LF) hypertrophy and degeneration in patients with lumbar spinal canal stenosis (LSCS). Angiopoietin-like protein 2 (Angptl2) is a chronic inflammatory mediator induced under various pathological conditions and increases the expression of TGF-β1, which is a well-characterized mediator in LF hypertrophy. We investigated whether Angptl2 is induced by mechanical stress, and whether it contributes to LF hypertrophy and degeneration by activating the TGF-β1 signaling cascade. In this study, we investigated human LF tissue and LF fibroblasts isolated from patients who underwent lumbar surgery. We found that Angptl2 was abundantly expressed in fibroblasts of hypertrophied LF tissues at both the mRNA and protein levels. This expression was not only positively correlated with LF thickness and degeneration but also positively correlated with lumbar segmental motion. Our in vitro experiments with fibroblasts from hypertrophied LF tissue revealed that mechanical stretching stress increases the expression and secretion of Angptl2 via activation of calcineurin/NFAT pathways. In hypertrophied LF tissue, expression of TGF-β1 mRNA was also increased and TGF-β1/Smad signaling was activated. Angptl2 expression in LF tissue was positively correlated with the expression of TGF-β1 mRNA, suggesting cooperation between Angptl2 and TGF-β1 in the pathogenesis of LF hypertrophy. In vitro experiments revealed that Angptl2 increased levels of TGF-β1 and its receptors, and also activated TGF-β1/Smad signaling. Mechanical stretching stress increased TGF-β1 mRNA expression, which was partially attenuated by treatment with a calcineurin/NFAT inhibitor or Angptl2 siRNA, indicating that induction of TGF-β1 expression by mechanical stretching stress is partially mediated by Angptl2. We conclude that expression of Angptl2 induced by mechanical stress in LF fibroblasts promotes LF tissue degeneration by activation of TGF-β1/Smad signaling, which results in LF hypertrophy in patients with LSCS.

Increased expression of CD44 in hypertrophied ligamentum flavum and relevance of splice variants CD44v5 and CD44v6

BACKGROUND

The most common spinal disorder in the elderly is lumbar spinal stenosis (LSS), which results in part from ligamentum flavum (LF) hypertrophy. Although prior histologic and immunochemical studies have been performed in this area, the pathophysiology of loss of elasticity and hypertrophy is not completely understood. The purpose of this immunohistological study is to elucidate the role of CD44 and its splice variants CD44v5 and CD44v6 in the hypertrophied LF obtained from patients with lumbar spinal stenosis (LSS).

MATERIALS AND METHODS

LF samples of 38 patients with LSS were harvested during spinal decompression. Twelve LF samples obtained from patients with disc herniation and no visible degeneration on preoperative MRI were obtained as controls. Samples were dehydrated and embedded in paraffin. For immunohistochemical determination, slices were stained with antibodies against CD44, Cd44v4, and CD44v6 stained with DAB. LF hypertrophy and cross-sectional area (CSA) were measured with T1-weighted MRI.

RESULTS

CD44 and CD44v5 expression were significantly increased in the hypertrophy group (p < 0.05). CD44v6 expression was not significantly increased. The number of elastic fibers was significantly higher in the hypertrophy group. In the hypertrophy group, LF thickness was significantly increased while CSA was significantly decreased. There was a statistical correlation between LF thickness, CSA, CD44, and CD44v5 expression in the hypertrophy group (p < 0.05).

CONCLUSIONS

LF hypertrophy is accompanied by increased CD44 and CD44v5 expression. CD44v6 expression is not enhanced in LF hypertrophy.

[Over-expression of platelet-derived growth factor-BB in degenerative hypertrophied ligamentum flavum]

OBJECTIVE

To investigate the role of platelet-derived growth factor-BB (PDGF-BB) in the degeneration of the hypertrophied ligamentum flavum (LF) in the lumbar spine.

METHODS

Surgical specimens of degenerative hypertrophied LF were obtained from 11 patients with lumbar spinal stenosis (LSS, mean age 57.8 years), with those from 10 age-matched patients with lumbar disc herniation (LDH, mean age 53.5 years) as the normal controls. The thickness of the LF was measured preoperatively by axial T1-weighted magnetic resonance imaging (MRI) at the facet joint level. Immunohistochemistry was employed to determine the expression of PDGF β and PDGF-BB in the LF. The mRNA and protein expressions of PDGF-BB in the LF were detected using real-time PCR and Western blotting, respectively.

RESULTS

The thickness of the LF was 5.30±1.12 mm in the degenerative group and 2.80±1.53 mm in the control group, showing a significant difference between the two groups (P<0.001). PDGF-β and PDGF-BB were positive in the fibroblasts in hypertrophied LF. The mRNA and protein expressions of PDGF-BB were significantly higher in the degenerative group than in the control group (P=0.013 and 0.023, respectively).

CONCLUSION

The high expression of PDGF-BB in the hypertrophied LF suggests its important role in the development of hypertrophy of LF in lumbar spinal canal stenosis.

Phenotypic characterization of ligamentum flavum cells from patients with ossification of ligamentum flavum

PURPOSE

The objective of this study was to determine the phenotypic characterization of ligamentum flavum cells from patients with ossification of the ligamentum flavum (OLF).

MATERIALS AND METHODS

Ligamentum flavum tissues were harvested from OLF and non-OLF patients during surgery. OLF and non-OLF cells were isolated from explant cultures. Cultured cells were analyzed using immunofluorescence staining and reverse transcription-polymerase chain reaction.

RESULTS

OLF cells exhibited various appearances compared with the typical fibroblast-like morphology of non-OLF cells. Expressions of collagen type I and collagen type III were observed in OLF and non-OLF cells. OLF cells uniquely expressed osteocalcin, which is a marker for osteoblasts, and collagen type II which is a marker for chondrocytes, whereas they were negative in non-OLF cells.

CONCLUSION

These findings indicate that OLF cells have phenotypic characterization of osteoblasts and chondrocytes which could play a role in the pathophysiology of OLF.

Calcium pyrophosphate dehydrate crystal deposition in the ligamentum flavum of the cervical spine: histopathological and immunohistochemical findings

OBJECTIVE

To investigate the histopathological and immunohistochemical properties of degenerative changes in the ligamentum flavum of the cervical spine with calcium crystal deposition.

METHODS

Sections of the calcified ligamentum flavum harvested from 26 patients who required cervical decompression were examined by scanning electron microscopy (SEM), energy dispersive X-ray microanalysis, immunohistochemical staining [for transforming growth factor (TGF)-Beta, vascular endothelial growth factor (VEGF), Sox9, and Msx2] and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labelling (TUNEL) method (for cell apoptosis).

RESULTS

Energy dispersive x-ray microanalysis and SEM confirmed the deposited calcium to be calcium pyrophosphate dihydrate (CPPD) crystals. The calcified ligamentum flavum showed disorganisation of the elastic fibre bundles together with increased collagen fibrils in the matrix. Abundant hypertrophic chondrocytes were noted around the calcified lesions, which were strongly immunoreactive to TGF-Beta and VEGF. Staining for Sox9 was positive in metaplastic chondrocytes but negative in hypertrophic chondrocytes. Both chondrocytes and mesenchymal cells were positive for Msx2. TUNEL-positive hypertrophic chondrocytes were significantly more noticeable in nodular than diffusely scattered type of CPPD deposition.

CONCLUSIONS

Calcium crystal deposition in the cervical ligamentum flavum seems to progress with reduction in elastic fibres, increase in collagen fibrils in the matrix, and migration of metaplastic hypertrophic chondrocytes, whose differentiation is controlled by cytokines and transcriptional factors, and potentially regulate crystal formation. The presence of abundant TUNEL-positive hypertrophic chondrocytes around CPPD deposition suggests that materials from apoptotic cells play some role in crystal deposition.

[Overexpression of transforming growth factor-beta1 in degenerative ligamentum flavum]

OBJECTIVE

To investigate the role of transforming growth factor (TGF)-beta1 in degeneration of the ligamentum flavum in the lumbar spine.

METHODS

The degenerative ligamentum flavum was obtained during surgery from 8 patients with lumbar spinal stenosis (mean age 58.6 years), and 8 young patients (mean age 24.2 years) with acute lumbar disc herniation were included as normal controls. The thickness of the ligamentum flavum was measured on preoperative magnetic resonance images, and the mRNA expressions of type-I collagen and TGF-beta1 in the ligamentum flavum were detected using reverse transcriptase-polymerase chain reaction. The protein expression and localization of TGF-beta1 were investigated by Western blotting and immunohistochemical staining, respectively.

RESULTS

The thickness of the ligamentum flavum were 4.70-/+0.40 mm in the degenerative group and 2.50-/+0.36 mm in the control group, showing significant difference between the two groups (P<0.001). The type-I collagen mRNA expression in the degenerative group was significantly higher than that in the control group (P=0.007). The mRNA and protein expressions of TGF-beta1 were significantly higher in the degenerative group than in the control group (P=0.008 and 0.004, respectively). Immunohistochemistry showed that TGF protein was localized in the fibroblasts within the ligamentum flavum.

CONCLUSION

Degenerative ligamentum flavum shows hypertrophy and fibrosis, and TGF-beta1 overexpression may be associated with in the development and progression of ligamentum flavum degeneration in the lumbar spine.

Changes in basic metabolic elements associated with the degeneration and ossification of ligamenta flava

OBJECTIVE

To determine the association between levels of basic metabolic elements and degeneration and ossification of the ligamentum flavum (LF).

SUBJECTS

Fourteen consecutive patients with degenerative lumbar stenosis, 11 with ossification of the thoracic ligamenta flava, and 11 control subjects.

METHODS

The basic elements of calcium (Ca), phosphorus (P), magnesium (Mg), zinc (Zn), copper (Cu), manganese (Mn), molybdenum (Mo), and fluoride (F) in the specimens were measured using atomic absorption spectrometry, the phosphomolybdic blue method, and a fluoride-selected electrode.

RESULTS

Ca content and the ratio of Ca/Mg in the LF specimens increased significantly in the sequence of control, degeneration, and ossification groups. Compared with values for the control group, the Zn, Mn, and Mo contents in the ossification and degeneration groups were significantly lower (P < 0.01); in contrast, Cu content was significantly higher (P < 0.01). As to F, its content in the specimens of the ossification group was much higher than those in the degeneration and control groups (P < 0.01); the F content in the ligamenta flava and sera from patients with fluorosis was also significantly higher than in those from patients without fluorosis (P < 0.01). Compared with the control group, there were no differences in the F content in serum from patients without fluorosis; however, the F content in ligamenta flava specimens from patients without fluorosis was significantly higher (P < 0.01).

CONCLUSIONS

There are trends in the contents of basic metabolic elements in the degeneration and ossification of ligamenta flava. These basic metabolic elements may play an important role in this process.

[The research of bone morphogenetic protein expression, CT value and mature degree of ossification in the thoracic ossification of ligamentum flavum]

OBJECTIVE

To investigate the correlation of pathology, bone morphogentic protein (BMP) expression, CT value with the ossification of thoracic ligamentum flavum (TOLF) to afford the evidence to choose appropriate treatment methods.

METHODS

Twenty-three patients aged 35 - 65 years old had TOLF in my hospital as case. Their courses of disease were 2 months to 9 years. The values of blood calcium, blood phosphorus and AKP in them were normal. The 5 peoples aged 21 - 35 years old who presented fracture of thoracic but not the ligamentum flavum ossification were selected as control. We excluded those who have DISH, ankylosing spondylitis, fluorosis and other disease related with TOLF. The lesion locus were scanned and mensurated by CT. The pathology characteristics were classified into immature ossification and mature ossification by general observation, histology examination. BMP were measured by the immunohistochemical (IHC) staining techniques.

RESULTS

The CT value was significantly higher in the case group (547.2 +/- 131.4) than controlled group (137.7 +/- 10.6) (t = 6.922, P = 0.000). Further, the CT value in the mature ossification (702.9 +/- 17.7) was significantly higher than the immature (480.5 +/- 180.2) (t = 5.623, P = 0.000). In addition, BMP both expressed negative in the mature ossification and the controlled group, but positive in the immature ossification. BMP expression was significantly different between the immature ossification and the mature (chi2 = 70.000, P = 0.000).

CONCLUSIONS

The CT values, pathological types and BMP expression results are similar to evaluate the ossification degrees of ligamentum flavum, and then could be indirectly judged the maturation degrees of TOLF by CT to confirm the treatment methods before operation.

De novo osteogenesis from human ligamentum flavum by adenovirus-mediated bone morphogenetic protein-2 gene transfer

STUDY DESIGN

In vitro and in vivo experiment using degenerated human ligamentum flavum (LF) and Type 5 adenovirus construct with bone morphogenetic protein-2 (BMP-2) cDNA.

OBJECTIVES

To demonstrate in vitro and in vivo osteogenic effect of BMP-2 gene transfer to human LF and to propose genetically modified LF as a substitute for autogenous bone graft in spinal fusion.

SUMMARY OF BACKGROUND DATA

Spinal fusion is still considered to be an important option for treating various spinal disorders. To induce solid spinal fusion, osteoinductive and/or osteoconductive agents have been widely adopted. Autogenous LF, however, has never been seriously considered as a carrier for ex vivo osteoinductive gene therapy for spinal fusion.

METHODS

In vitro experiment: Degenerated human LF was harvested and cultured. Type 5 adenovirus lacZ (Ad/lacZ) and BMP-2 construct (Ad/BMP-2) were produced. LF cell cultures were then exposed to Ad/BMP-2. Expressions of osteocalcin and BMP-2 mRNA were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). Western blot analysis was performed to detect osteocalcin protein. Alkaline phosphatase and von Kossa stains were used to detect osteogenic markers and bone nodule formation, respectively. In vivo experiment: Human LF tissues treated with Ad/lacZ, Ad/BMP-2, and saline were implanted into the subcutaneous tissue of nude mice. After 4 weeks, nude mice were radiographed and killed. Implanted LF tissues were harvested and histologically stained.

RESULTS

LF cell cultures with Ad/BMP-2 revealed strong expression of BMP-2 and osteocalcin mRNA in RT-PCR and osteocalcin protein in western blot analysis. LF cell culture with saline showed baseline expression of BMP-2, osteocalcin mRNA, and osteocalcin protein, respectively. Furthermore, LF cell culture with Ad/BMP-2 demonstrated the expression of alkaline phosphatase and bone nodule formation in the aforementioned histochemical stain. LF tissues with Ad/BMP-2 revealed de novo osteogenesis in nude mice, whereas LF with Ad/lacZ or saline showed only remaining LF tissue without sign of bone formation.

CONCLUSION

Human LF cells transduced with Ad/BMP-2 exhibited the expression of osteogenic phenotype and bone nodule formation. Additionally, genetically modified human LF with BMP-2 cDNA clearly demonstrated de novo osteogenesis, which supports the concept that biologically modified LF can be a substitute for autogenous bone graft in spinal fusion surgery.

Histological analysis of the ligamentum flavum of patients with dialysis-related spondyloarthropathy

Dialysis-related spondyloarthropathy (DRS) is a severe complication of long-term hemodialysis that ultimately leads to functional disability of the upper and lower extremities. Although the cause of this disease is still unknown, it is thought that amyloid deposits are involved. beta2-Microglobulin (beta2M) is a major component of amyloid fibrils, some of which are modified with the advanced glycation end-product (AGE). To clarify the pathophysiology of DRS we histologically examined the ligamentum flavum of the cervical spine in 15 patients with DRS. The mean duration of hemodialysis was 20 years (12-27 years). In addition to the congo red stain for amyloid, beta2M and AGE were detected by immunohistochemical methods. Macrophages were stained with CD68 antibody. Amyloid deposits were found in tissues, although the extent of the stained area differed among the patients. Part of the amyloid deposit area was positively immunostained for beta2M and AGE. In 10 cases macrophages positive for CD68 infiltrated around the amyloid deposits. Comparing these histological findings with the dialysis duration, more positive staining areas for beta2M and AGE were found in the tissue from patients with long-term dialysis. These findings suggest that both beta2M and AGE play roles in the pathogenesis of DRS.

Biologic modification of ligamentum flavum cells by marker gene transfer and recombinant human bone morphogenetic protein-2

STUDY DESIGN

The study involves an in vitro experiment using human ligamentum flavum (LF), adenovirus lacZ construct (Ad/lacZ), and recombinant human bone morphogenetic protein-2 (BMP-2).

OBJECTIVES

To demonstrate the feasibility of marker gene transfer to human LF cells and the effect of BMP-2 on the osteogenic differentiation of human LF cells.

SUMMARY OF BACKGROUND DATA

BMP-2 is a widely known pivotal osteoinductive agent. Clinically and experimentally, BMP-2 has proven to be an effective in spinal fusion. Degenerated LF has only been implicated to be of pathophysiological significance in spinal stenosis. However, biologic modifications of LF to enhance osteogenesis have not been attempted previously.

MATERIALS AND METHODS

Human LF and cancellous bone from the ilium were harvested from patients with lumbar spinal stenosis. LF cells and osteoblasts were isolated and cultured, and adenovirus lacZ construct (Ad/ lacZ), luciferase construct (Ad/luciferase), and BMP-2 were designed and produced. LF cell cultures were then exposed to various concentrations of Ad/lacZ (25, 50, 75, 100, 150 multiplicity of infection) and BMP-2 (50, 100, 500, 1,000, and 1,500 ng/mL). Osteoblast cultures were used as a positive control for LF culture. LF cell cultures with Ad/luciferase served as viral controls for culture with Ad/ lacZ. The transgene expression of lacZ was assessed by X-gal stain and beta-galactosidase assay. Alkaline phosphatase, Von Kossa, and Alizarin red-S stains were used to confirm osteogenic differentiation and bone nodule formation. Immunocytochemical staining was also performed to detect osteocalcin expression.

RESULTS

LF cell cultures transduced with Ad/lacZ showed extensive X-gal expression and increased beta-galactosidase activity compared to viral (Ad/luciferase) and saline controls. In LF cultures treated with BMP-2, robust alkaline phosphatase expression, and bone nodule formations were observed as evidenced by positive Von Kossa and Alizarin red-S staining, and the strong expression of osteocalcin. The osteogenic response of LF cells to BMP-2 was dose dependent.

CONCLUSIONS

Human LF cells were found to be susceptible to adenovirus-mediated marker gene transfer, which offers the possibility of a new range of possible genetic modifications. In human LF cells, BMP-2 was found to markedly up-regulate the expression of osteogenic phenotypes and to induce bone nodule formation. The results of this study support the notion that biologically modified LF cells, i.e., LF cells treated with BMP-2, or with adenovirus-mediated BMP-2 cDNA gene transfer, may facilitate spinal fusion.

Calcium pyrophosphate dihydrate crystal deposition disease in cervical radiculomyelopathy

One patient had cervical spinal canal stenosis with radiculomyelopathy due to deposition of calcium pyrophosphate dihydrate within the ligamentum flavum. The MRI of cervical spine showed a calcified nodule over C5-6 level ligamentum flavum with obvious cord compression. After posterior decompressive laminectomy with removal of the calcified nodule, the symptom and sign relieved remarkedly and the pathology showed calcium pyrophosphate dihydrate deposition within the ligamentum flavum. We presented this case and reviewed the literature to acknowledge so-call "pseudogout syndrome."

Mechanical stretching force promotes collagen synthesis by cultured cells from human ligamentum flavum via transforming growth factor-beta1

Although mechanical stress as a result of spinal instability is known to cause hypertrophy of the ligamentum flavum resulting in degenerative spinal canal stenosis, the mechanism of the ligament hypertrophy is not well understood. In the present study, we investigated the effect of mechanical stretching force on collagen synthesis and transforming growth factor-beta1 (TGF-beta1) production using ligament cells isolated from human ligamentum flavum in vitro. Ligamentum flavum cells (LFCs) were isolated from human ligamentum flavum obtained from patients who underwent lumbar spine surgery. The LFCs were subjected to a mechanical stretching force using a commercially available stretching device that physically deformed the cells. Collagen synthesis and TGF-beta1 production levels in the LFCs were then examined. Notable increases were observed in the gene expressions of collagen types I, III, and V in LFCs subjected to mechanical stretching force. The increase in collagen gene expression of LFCs was inhibited in the presence of anti-TGF-beta1 antibodies. Production of TGF-beta1 by the LFCs also increased significantly by the mechanical stretching force. Exogenous application of TGF-beta1 was confirmed to increase collagen synthesis of the LFCs. This data indicated that mechanical stretching force can promote TGF-beta1 production by LFCs, resulting in hypertrophy of the ligament.

Quantitative analysis of transforming growth factor-beta 1 in ligamentum flavum of lumbar spinal stenosis and disc herniation

STUDY DESIGN

The concentration of transforming growth factor-beta 1 (TGF-beta1) was examined in the ligamentum flavum of lumbar spinal stenosis and disc herniation.

OBJECTIVE

To investigate the role of TGF-beta1 on hypertrophy of the ligamentum flavum in lumbar spinal stenosis compared with that of lumbar disc herniation.

SUMMARY OF BACKGROUND DATA

The hypertrophy of the ligamentum flavum is known to be related to degenerative changes that are secondary to the aging process or mechanical instability. However, there has been no study to investigate the effect of biochemical factors, such as growth factors, associated with hypertrophy of the ligamentum flavum.

METHODS

The concentrations of TGF-beta1 were analyzed in the surgically obtained ligamentum flavum specimens from lumbar spinal stenosis (n = 10; mean age 62.8 years) and disc herniation (n = 10; mean age 35.6 years) by enzyme-linked immunosorbent assay. The localization of TGF-beta1 within the ligamentum flavum was determined using immunohistochemical study. The thickness of the ligamentum flavum was measured with axial T1-weighted magnetic resonance imaging. The biochemical and radiologic results were compared for these two conditions.

RESULTS

The mean concentration of TGF-beta1 was 123.78 pg/100 microg protein (range 11-374 pg/100 microg protein) in lumbar spinal stenosis and 38.56 pg/100 microg protein (range 0-155 pg/100 microg protein) in lumbar disc herniation; the difference between lumbar spinal stenosis and disc herniation was statistically significant (P = 0.029). The mean thickness of the ligamentum flavum was 4.44 mm (range 3.4-5.4 mm) in lumbar spinal stenosis and 2.44 mm (range 1.8-4.0 mm) in lumbar disc herniation; the difference between lumbar spinal stenosis and disc herniation was statistically significant (P = 0.001). On immunohistochemical study TGF-beta1 was positively stained on the fibroblasts within the ligamentum flavum specimens.

CONCLUSION

The current results suggest that higher expression of TGF-beta1 by fibroblasts might be related to the development of hypertrophy of the ligamentum flavum in lumbar spinal stenosis.

Activation and localization of cartilage-derived morphogenetic protein-1 at the site of ossification of the ligamentum flavum

Localization and expression of cartilage-derived morphogenetic protein (CDMP)-1 in tissues at the site of ossification of the ligamentum flavum (OLF) were examined by immunohistochemistry and in situ hybridization. The CDMP-1 protein and messenger ribonucleic acid (mRNA) were localized in spindle-shaped cells and chondrocytes in the OLF tissues. CDMP-1 was not detected in cells in non-ossified sites. These data indicate that CDMP-1 is locally activated and localized in spindle-shaped cells and chondrocytes at the site of OLE. Given the previously reported promoting action of CDMP-1 for chondrogenesis, the current results suggest that CDMP-1 may be involved in the progression of OLF, leading to the narrowing of spinal canal and thus causing severe clinical manifestations.

Characterization of cultured human ligamentum flavum cells in lumbar spine stenosis

To investigate the pathogenesis of the degenerative changes of the ligamentum flavum occurring in lumbar spine stenosis, yellow ligament cells from patients with lumbar spine stenosis were cultured for the first time and subjected to biochemical, histochemical and immunohistochemical study. Stenotic ligamentum flavum (SLF) cells were seen to express high levels of alkaline phosphatase (ALP) activity and to produce a matrix rich in type I and III collagen, fibronectin and osteonectin. The matrix mineralized only following beta-glycerophosphate (betaGP) and ascorbic acid supplementation. Stimulation with human parathyroid hormone (PTH) increased intracellular cAMP concentration. These findings indicate that there was significant evidence of osteoblast-like activity in these cells. SLF cells also stained for S100 protein, type II and type X collagen, and co-localized type II collagen and ALP labelling, reflecting the presence of hypertrophic chondrocyte-like cells. Cultures from control patients showed neither osteoblastic nor chondrocytic features: they expressed type I and type III collagen and fibronectin, but did not stain for osteonectin, nor were bone-like calcifications observed in presence or absence of betaGP. Normal ligamentum flavum (NLF) cells did not synthesized S100 protein or type II or type X collagen, and showed a weaker response to PTH stimulation. Our data demonstrated the presence of hypertrophic chondrocytes with an osteoblast-like activity in the ligamentum flavum of patients with spinal stenosis suggesting that they could have a role in the pathophysiology of the heterotopic ossification of ligamentum flavum (OLF) in lumbar spine stenosis.

Membranocystic lesion in lumbar yellow ligament

STUDY DESIGN

An examination of surgical cases of membranocystic lesions in the lumbar yellow ligament between the fourth and fifth lumbar vertebrae.

OBJECTIVES

To report the incidence and pathogenesis of membranocystic lesions of the yellow ligament in surgical specimens.

SUMMARY OF BACKGROUND DATA

The membranocystic lesion has been observed not only in membranous lipodystrophy, but also in other conditions. However, there has been no report concerning this lesion in the yellow ligament.

METHODS

Forty-four yellow ligaments excised in surgery were histologically reviewed. In eight cases, S-100 expression was investigated. In two cases, ultrastructural findings were examined.

RESULTS

Membranocystic lesions were present in 8 (18%) of the 44 cases. The cases with the lesions had undergone surgery for spondylolisthesis (4 cases), sequestration-type disc herniation (2 cases), postradiation status (1 case), and spinal stenosis (1 case). Histologically, in all 8 cases, fibrosis was present around the lesion. In 5 of the 8 cases, chondrocytes were observed adjacent to the lesion, and nuclei positive for S-100 protein were observed in 4 cases. Nuclei of chondrocytes adjacent to the lesion also were positive for S-100 protein. Ultrastructurally, irregularly shaped cystic spaces surrounded by an electron-dense membranous structure, which were identical to those of membranous lipodystrophy, were observed.

CONCLUSIONS

These results suggest that degeneration of the chondrocytes has a causal relationship to the formation of membranocystic lesions in the yellow ligament.

Fibroblasts of spinal ligaments pathologically differentiate into chondrocytes induced by recombinant human bone morphogenetic protein-2: morphological examinations for ossification of spinal ligaments

To elucidate the process of ossification in spinal ligaments, an aqueous solution containing recombinant human bone morphogenetic protein (BMP)-2 (40 micrograms/100 microL) was injected into murine ligamenta flava, and the ossification process was analyzed morphologically. In the control group, the solution administered lacked the protein; these flattened ligamentous fibroblasts possessing BMP receptors type IA and type II existed among type I collagen bundles. In the week immediately following the injection of BMP-2, ligamentous fibroblasts began to proliferate, differentiating into alkaline phosphatase-positive chondrocytes surrounded by an extracellular matrix composed of type I and II collagen. By the second week, differentiated chondrocytes of various stages were observed in type II collagen-rich matrix. These chondrocytes showed an abundance of BMP receptors type IA and II. The pathologically induced cartilage was resorbed by chondroclasts, permitting migration of blood vessels and osteogenic cells, as well as providing a site for endochondral ossification. By the third week, BMP-induced ossification had compressed the spinal cord, and by the sixth week, the ligamentous tissue had been almost completely replaced by bone. Ligamentous fibroblasts appeared to possess BMP receptors, as well as the potentiality to differentiate into chondrocytes. BMP receptors were upregulated during chondrification of ligamentous fibroblasts induced by exogenous BMP-2, suggesting that BMPs may play an important role in ossification of spinal ligaments.

Expression and localization of bone morphogenetic proteins (BMPs) and BMP receptors in ossification of the ligamentum flavum

To clarify the pathogenesis of ossification of the ligamentum flavum (OLF), we examined the expression and localization of bone morphogenetic proteins (BMPs) and their receptors (BMPRs) in the ligamentum flavum of the patients with OLF by immunohistochemical staining and compared them with staining patterns in control patients. The BMPRs appeared extensively in mature and immature chondrocytes around the calcified zone and in spindle-shaped cells and round cells in the remote part from ossified foci in examined tissue of OLF. The ligands for BMPRs, BMP-2/-4 and osteogenic protein-1 (OP-1)/BMP-7, colocalized in OLF patients. In the control cases, expression of BMPs and BMPRs was observed around the calcified zone at the insertion of the ligamentum flavum to the bone, and limited expression was found in the smaller range. Thus, the expression profile of BMPs and BMPRs in OLF patients was entirely different from the control patients, suggesting that BMPs may be involved in promoting endochondral ossification at ectopic ossification sites in OLF, and that ossification activity is continuous in these patients.

Amyloid deposits of immunohistochemically different classes in the ligamentum flavum in biopsies from patients with herniated discs or lumbar spinal stenosis

Ligamenta flava of 100 patients (n = 107 tissue blocks) were examined for the presence of amyloid by means of polarization microscopy after staining with Congo red. Ninety-three ligamenta flava were resected due to operation of herniated discs while 14 ligamenta flava were obtained after surgical treatment of lumbar spinal stenosis. Amyloid of various amounts (score I-III) and 4 morphologically different appearances were detected in the ligamenta flava of 12 patients. In 6 patients small amyloid deposits were seen along elastic fibres (pattern 1) and/or minute, comma-like deposits in certain areas (pattern 2). In 5 other patients amyloid deposits in form of large lumps were present (pattern 3) intermingled with deposits of pattern 1 and/or 2. Only 1 patient could be detected with amyloid deposits partly associated with blood vessels (pattern 4). The amyloid-containing tissue samples (n = 13) were immunohistochemically analyzed using anti-AA-, anti-A lambda-, anti-A kappa-, anti-ATTR- and anti-A beta 2m-antibodies which are able to identify the major known amyloid classes of tissue sections. Tissues with pattern 1 and 2 amyloid deposits did not react above background with any of the antibodies. In contrast, the 5 patients with pattern 3 amyloid stained strongly with anti-ATTR but not with the other antisera. In this group, therefore, senile systemic amyloid (sporadic ATTR) was also identified which had not been detected at this site before. Consistent with this finding is the advanced age of these patients which was seen to be significantly higher than the average age of the entire group of patients examined.

The potential role of the elastic fiber system in adolescent idiopathic scoliosis

To assess its possible role in the etiology of adolescent idiopathic scoliosis, the elastic fiber system of the ligamentum flavum was examined in twenty-three patients who had scoliosis and in five age-matched individuals who did not. Elastic fibers are composed of two components: the amorphous core of elastin and microfibrils, of which fibrillin is the primary element. Fresh-frozen histological specimens of ligamentum flavum removed at the time of an operation were examined by Verhoeff staining for elastic fibers and by immunohistochemical staining with use of a monoclonal antibody to fibrillin. Additionally, cultures of fibroblast cells from the ligamentum flavum were used to study the biosynthesis and secretion of fibrillin and its incorporation into the extracellular matrix in vitro. The specimens from one patient did not provide sufficient material for the histological studies; however, fibroblasts were harvested from this specimen. In five (23 percent) of the remaining twenty-two specimens from patients who had adolescent idiopathic scoliosis, Verhoeff staining of elastic fibers showed a marked decrease in fiber density (the number of fibers per unit area) and a non-uniform distribution of fibers throughout the ligament. Eighteen specimens (82 percent) exhibited abnormalities on immunohistochemical staining, including a marked disarrangement of the fibers and a difference in the density of staining, when compared with the control specimens from individuals who did not have adolescent idiopathic scoliosis. Studies of the biosynthesis and secretion of fibrillin and its incorporation into the extracellular matrix in vitro demonstrated that fibroblasts from four (17 percent) of the twenty-three specimens produced normal amounts of fibrillin and secreted it from the cell, but the fibrillin failed to bind to other macromolecules, to form a sedimentable complex, and to incorporate into the extracellular matrix. Collectively, the results suggest the potential role of the elastic fiber system as a component in the pathogenesis of adolescent idiopathic scoliosis in some individuals.