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

Hypertrophic Ligamentum Flavum in Lumbar Spine Stenosis Is Associated With the Increased Expression of Secreted Protein Acidic and Rich in Cysteine

STUDY DESIGN

Basic research.

OBJECTIVES

Secreted protein acidic and rich in cysteine (SPARC) is a critical pro-fibrotic mediator. This study aims to characterize the role of SPARC in hypertrophic ligamentum flavum (LF) and fibrosis.

METHODS

Hypertrophic LF samples were obtained from 8 patients with L4/5 lumbar spinal stenosis (LSS) during the decompressive laminectomy. Non-hypertrophic LF from age- and sex-matched 8 patients with L4/5 lumbar disc herniation was selected as control. An in vitro model of fibrosis in human LF cells was established by interleukin 6 (IL-6) to assess SPARC expression.

RESULTS

Hypertrophic LF samples had higher fibrosis scores than control samples by Masson's trichrome staining (3.6 vs. 1.3, P < .001). Hypertrophic LF samples had significantly more positive staining for collagen and SPARC. Collagen III (Col3), α smooth muscle actin (α-SMA), and SPARC mRNA expression levels were significantly higher in hypertrophic LF samples than in control samples by qPCR. SPARC expression and fibrotic and inflammatory makers (collagen I, Col3, IL-6, interleukin 1β) were significantly upregulated in IL-6 stimulation of normal LF in vitro.

CONCLUSION

SPARC was detected in human LF and significantly upregulated in the clinical samples of hypertrophic LF compared to their normal counterparts. We also demonstrated an increased level of SPARC in an in vitro fibrosis model of LF. Thus, SPARC could be a crucial biomarker for the pathogenesis of hypertrophic LF and a therapeutic target for LSS.

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.

Mechanisms of tissue degeneration mediated by periostin in spinal degenerative diseases and their implications for pathology and diagnosis: a review

Periostin (POSTN) serves a dual role as both a matricellular protein and an extracellular matrix (ECM) protein and is widely expressed in various tissues and cells. As an ECM protein, POSTN binds to integrin receptors, transduces signals to cells, enabling cell activation. POSTN has been linked with various diseases, including atopic dermatitis, asthma, and the progression of multiple cancers. Recently, its association with orthopedic diseases, such as osteoporosis, osteoarthritis resulting from cartilage destruction, degenerative diseases of the intervertebral disks, and ligament degenerative diseases, has also become apparent. Furthermore, POSTN has been shown to be a valuable biomarker for understanding the pathophysiology of orthopedic diseases. In addition to serum POSTN, synovial fluid POSTN in joints has been reported to be useful as a biomarker. Risk factors for spinal degenerative diseases include aging, mechanical stress, trauma, genetic predisposition, obesity, and metabolic syndrome, but the cause of spinal degenerative diseases (SDDs) remains unclear. Studies on the pathophysiological effects of POSTN may significantly contribute toward the diagnosis and treatment of spinal degenerative diseases. Therefore, in this review, we aim to examine the mechanisms of tissue degeneration caused by mechanical and inflammatory stresses in the bones, cartilage, intervertebral disks, and ligaments, which are crucial components of the spine, with a focus on POSTN.

Transcriptomic alterations in hypertrophy of the ligamentum flavum: interactions of Rho GTPases, RTK, PIK3, and FGF

PURPOSE

To analyze the differential transcriptome expression in hypertrophic ligaments flavum (HLF) compared to normal ligaments.

METHODS

A case-control study was conducted that included 15 patients with hypertrophy of LF and 15 controls. Samples of LF were obtained through a lumbar laminectomy and analyzed by DNA microarrays and histology. The dysregulated biological processes, signaling pathways, and pathological markers in the HLF were identified using bioinformatics tools.

RESULTS

The HLF had notable histological alterations, including hyalinosis, leukocyte infiltration, and disarrangement of collagen fibers. Transcriptomic analysis showed that up-regulated genes were associated with the signaling pathways of Rho GTPases, receptor tyrosine kinases (RTK), fibroblast growth factors (FGF), WNT, vascular endothelial growth factor, phosphoinositide 3-kinase (PIK3), mitogen-activated protein kinases, and immune system. The genes PIK3R1, RHOA, RPS27A, CDC42, VAV1, and FGF5, 9, 18, and 19 were highlighted as crucial markers in HLF. The down-expressed genes in the HLF had associations with the metabolism of RNA and proteins.

CONCLUSION

Our results suggest that abnormal processes in hypertrophied LF are mediated by the interaction of the Rho GTPase, RTK, and PI3K pathways, which have not been previously described in the HLF, but for which there are currently therapeutic proposals. More studies are required to confirm the therapeutic potential of the pathways and mediators described in our results.

Periostin increased by mechanical stress upregulates interleukin-6 expression in the ligamentum flavum

Ligamentum flavum (LF) hypertrophy is a major cause of lumbar spinal canal stenosis. Although mechanical stress is thought to be a major factor involved in LF hypertrophy, the exact mechanism by which it causes hypertrophy has not yet been fully elucidated. Here, changes in gene expression due to long-term mechanical stress were analyzed using RNA-seq in a rabbit LF hypertrophy model. In combination with previously reported analysis results, periostin was identified as a molecule whose expression fluctuates due to mechanical stress. The expression and function of periostin were further investigated using human LF tissues and primary LF cell cultures. Periostin was abundantly expressed in human hypertrophied LF tissues, and periostin gene expression was significantly correlated with LF thickness. In vitro, mechanical stress increased gene expressions of periostin, transforming growth factor-β1, α-smooth muscle actin, collagen type 1 alpha 1, and interleukin-6 (IL-6) in LF cells. Periostin blockade suppressed the mechanical stress-induced gene expression of IL-6 while periostin treatment increased IL-6 gene expression. Our results suggest that periostin is upregulated by mechanical stress and promotes inflammation by upregulating IL-6 expression, which leads to LF degeneration and hypertrophy. Periostin may be a pivotal molecule for LF hypertrophy and a promising therapeutic target for lumbar spinal stenosis.

Angiopoietin-like 2 is essential to aortic valve development in mice

Aortic valve (AoV) abnormalities during embryogenesis are a major risk for the development of aortic valve stenosis (AVS) and cardiac events later in life. Here, we identify an unexpected role for Angiopoietin-like 2 (ANGPTL2), a pro-inflammatory protein secreted by senescent cells, in valvulogenesis. At late embryonic stage, mice knocked-down for Angptl2 (Angptl2-KD) exhibit a premature thickening of AoV leaflets associated with a dysregulation of the fine balance between cell apoptosis, senescence and proliferation during AoV remodeling and a decrease in the crucial Notch signalling. These structural and molecular abnormalities lead toward spontaneous AVS with elevated trans-aortic gradient in adult mice of both sexes. Consistently, ANGPTL2 expression is detected in human fetal semilunar valves and associated with pathways involved in cell cycle and senescence. Altogether, these findings suggest that Angptl2 is essential for valvulogenesis, and identify Angptl2-KD mice as an animal model to study spontaneous AVS, a disease with unmet medical need.

Elucidating the effect of mechanical stretch stress on the mechanism of ligamentum flavum hypertrophy: Development of a novel in vitro multi-torsional stretch loading device

Objective

We developed a novel multi-torsional mechanical stretch stress loading device for ligamentum flavum cells and evaluated its influence on the development of ligamentum flavum hypertrophy, a common cause of lumbar spinal canal stenosis.

Materials and methods

Stretch strength of the device was optimized by applying 5% and 15% MSS loads for 24, 48, and 72 h. A cytotoxicity assay of human ligamentum flavum cells was performed and the results were compared to control (0% stress). Inflammatory markers (interleukin [IL]-6, IL-8), vascular endothelial growth factor [VEGF], and extracellular matrix (ECM)-regulating cytokines (matrix metalloproteinase [MMP]-1, MMP-3 and MMP-9, and tissue inhibitor of metalloproteinase [TIMP]-1 and TIMP-2) were quantified via enzyme-linked immunosorbent assay.

Results

Using our multi-torsional mechanical stretch stress loading device, 5% stress for 24 hour was optimal for ligamentum flavum cells. Under this condition, the IL-6 and IL-8 levels, VEGF level, and MMP-1, MMP-3, and TIMP-2 were significantly increased, compared to the control.

Conclusion

Using the novel multi-torsional mechanical stretch stress loading device we confirmed that, mechanical stress enhances the production of inflammatory cytokines and angiogenic factors, and altered the expression of ECM-regulating enzymes, possibly triggering ligamentum flavum hypertrophy.

Expression and function of fibroblast growth factor 1 in the hypertrophied ligamentum flavum of lumbar spinal stenosis

BACKGROUND

Fibrosis is one of the main pathologies caused by hypertrophy of the ligamentum flavum (LF), which leads to lumbar spinal stenosis (LSS). The fibroblast growth factor (FGF) family is a key mediator of fibrosis. However, acidic fibroblast growth factor (FGF-1) expression and function are not well understood in LF. This study sought to evaluate FGF-1 expression in the hypertrophied and non-hypertrophied human LF, and to investigate its function using primary human LF cell cultures.

METHODS

We obtained hypertrophied lumbar LF from LSS patients and non-hypertrophied lumbar LF from control patients during surgery. Immunohistochemistry and qPCR were performed to evaluate FGF-1 expression in LF tissue. The function of FGF-1 and transforming growth factor beta 1 (TGF-β1) was also investigated using primary LF cell culture. The effects on cell morphology and cell proliferation were examined using a crystal violet staining assay and MTT assay, respectively. Immunocytochemistry, western blotting, and qPCR were performed to evaluate the effect of FGF-1 on TGF-β1-induced myofibroblast differentiation and fibrosis.

RESULTS

Immunohistochemistry and qPCR showed higher FGF-1 expression in hypertrophied LF compared to control LF. Crystal violet staining and MTT assay revealed that FGF-1 decreases LF cell size and inhibits their proliferation in a dose-dependent manner, whereas TGF-β1 increases cell size and promotes proliferation. Immunocytochemistry and western blotting further demonstrated that TGF-β1 increases, while FGF-1 decreases, α-SMA expression in LF cells. Moreover, FGF-1 also caused downregulation of collagen type 1 and type 3 expression in LF cells.

CONCLUSION

FGF-1 is highly upregulated in the LF of LSS patients. Meanwhile, in vitro, FGF-1 exhibits antagonistic effects to TGF-β1 by inhibiting cell proliferation and decreasing LF cell size as well as the expression of fibrosis markers. These results suggest that FGF-1 has an anti-fibrotic role in the pathophysiology of LF hypertrophy.

ANGPTL2 Promotes Inflammation via Integrin α5β1 in Chondrocytes

BACKGROUND

Angiopoietin-like protein 2 (ANGPTL2) is a secreted molecule with numerous physiologic and pathologic functions, for example, in angiogenesis, hematopoiesis, and tumorigenesis. Although recent studies implicated ANGPTL2 in chronic inflammation in mouse peritoneal macrophages, human ligamentum flavum fibroblasts, and human retinal microvascular endothelial cells, the mechanism underlying ANGPTL2-associated inflammation in chondrocytes remains unclear. Therefore, it was investigated whether ANGPTL2 is expressed in or functions in chondrocytes.

METHODS

Expression of ANGPTL2 and its receptor, integrin α5β1 were examined over time in ATDC5 cells using real-time RT-PCR (reverse transcription-polymerase chain reaction) analysis. ATDC5 cells were then incubated with or without ANGPTL2 for 3 hours, and expression of the IL-1β, TNF-α, COX-2, aggrecanase (ADAMTS)-5, matrix metalloproteinase (MMP)-3, and MMP-13 genes were examined using real-time RT-PCR. Additionally, phosphorylation of ERK, JNK, p38, Akt, and NF-κB was examined by western blotting. Furthermore, it was also investigated for the effect of anti-integrin α₅β₁ antibody on the expression of inflammatory markers and intracellular signaling pathways.

RESULTS

ANGPTL2 induced the phosphorylation of all 3 MAPKs, Akt, and NF-κB and dramatically upregulated the expression of inflammation-related factor genes. Inhibiting the activation of integrin α5β1 suppressed these reactions.

CONCLUSION

ANGPTL2 may induce inflammatory factors by stimulating the integrin α5β1/MAPKs, Akt, and NF-κB signaling pathway.

Angptl2 is a Marker of Cellular Senescence: The Physiological and Pathophysiological Impact of Angptl2-Related Senescence

Cellular senescence is a cell fate primarily induced by DNA damage, characterized by irreversible growth arrest in an attempt to stop the damage. Senescence is a cellular response to a stressor and is observed with aging, but also during wound healing and in embryogenic developmental processes. Senescent cells are metabolically active and secrete a multitude of molecules gathered in the senescence-associated secretory phenotype (SASP). The SASP includes inflammatory cytokines, chemokines, growth factors and metalloproteinases, with autocrine and paracrine activities. Among hundreds of molecules, angiopoietin-like 2 (angptl2) is an interesting, although understudied, SASP member identified in various types of senescent cells. Angptl2 is a circulatory protein, and plasma angptl2 levels increase with age and with various chronic inflammatory diseases such as cancer, atherosclerosis, diabetes, heart failure and a multitude of age-related diseases. In this review, we will examine in which context angptl2 was identified as a SASP factor, describe the experimental evidence showing that angptl2 is a marker of senescence in vitro and in vivo, and discuss the impact of angptl2-related senescence in both physiological and pathological conditions. Future work is needed to demonstrate whether the senescence marker angptl2 is a potential clinical biomarker of age-related diseases.

miR-10396b-3p inhibits mechanical stress-induced ligamentum flavum hypertrophy by targeting IL-11

Ligamentum flavum hypertrophy (LFH) leads to lumbar spinal stenosis (LSS) caused by LF tissue inflammation and fibrosis. Emerging evidence has indicated that dysregulated microRNAs (miRNAs) have an important role in inflammation and fibrosis. Mechanical stress (MS) has been explored as an initiating step in LFH pathology progression; the inflammation-related miRNAs induced after mechanical stress have been implicated in fibrosis pathology. However, the pathophysiological mechanism of MS-miRNAs-LFH remains to be elucidated. Using miRNAs sequencing analysis and subsequent confirmation with qRT-PCR assays, we identified the decreased expression of miR-10396b-3p and increased expression of IL-11 (interleukin-11) as responses to the development of LSS in hypertrophied LF tissues. We also found that IL-11 is positively correlated with fibrosis indicators of collagen I and collagen III. The up-regulation of miR-10396b-3p significantly decreased the level of IL-11 expression, whereas miR-10396b-3p down-regulation increased IL-11 expression in vitro. Luciferase reporter assay indicates that IL-11 is a direct target of miR-10396b-3p. Furthermore, cyclic mechanical stress inhibits miR-10396b-3p and induces IL-11, collagen I, and collagen III in vitro. Our results showed that overexpression of miR-10396b-3p suppresses MS-induced LFH by inhibiting collagen I and III via the inhibition of IL-11. These data suggest that the MS-miR-10396b-3p-IL-11 axis plays a key role in the pathological progression of LFH.

Long-term, Time-course Evaluation of Ligamentum Flavum Hypertrophy Induced by Mechanical Stress: An Experimental Animal Study

STUDY DESIGN

Experimental animal study.

OBJECTIVE

The aim of this study was to clarify chronological effects of mechanical stress on ligamentum flavum (LF) using a long-term fusion rabbit model.

SUMMARY OF BACKGROUND DATA

LF hypertrophy is a major pathology of lumbar spinal stenosis (LSS), but its mechanism remains unclear. We previously demonstrated mechanical-stress-induced LF hypertrophy with a rabbit model. However, we only investigated LFs at a single time point in the short-term; the effects of long-term mechanical stress have not been elucidated.

METHODS

Eighteen-week-old male New Zealand White rabbits were randomly divided into two groups: the mechanical stress group underwent L2-3 and L4-5 posterolateral fusion and resection of the L3-4 supraspinal muscle, whereas the control group underwent only surgical exposure. Rabbits were sacrificed 16 and 52 weeks after the procedure. Axial specimens of LFs at L3-4 were evaluated histologically. Immunohistochemistry for alpha-smooth muscle actin (α-SMA) was performed to assess the numbers of vessels and myofibroblasts.

RESULTS

In the mechanical stress group, LFs at the L3-4 level exhibited hypertrophy with elastic fiber disruption and cartilage matrix production at 16 and 52 weeks. A trend test indicated that mechanical stress induced LF hypertrophy, elastic fiber disruption, and cartilage matrix production in a time-dependent manner, with the lowest levels before treatment and the highest at 52 weeks. Immunostaining for α-SMA showed similar numbers of vessels in both groups, whereas the percentage of myofibroblasts was significantly larger at 16 and 52 weeks in the mechanical stress group than in the control group.

CONCLUSION

We demonstrated that long-term mechanical stress caused LF hypertrophy with progressive elastic fiber disruption and cartilage matrix production accompanied by enhanced myofibroblasts. In addition, the reported rabbit model could be extended to elucidate the mechanism of LF hypertrophy and to develop new therapeutic strategies for LSS by preventing LF hypertrophy.Level of Evidence: SSSSS.

The Role of Smad2 in Transforming Growth Factor β1-Induced Hypertrophy of Ligamentum Flavum

BACKGROUND

Hypertrophy of the ligamentum flavum (LF) contributes to the development of spinal stenosis. Smad proteins can mediate the fibrogenesis activity through the transforming growth factor β₁ (TGF-β₁) pathway, but which Smad protein plays a more important role in the hypertrophy process of LF is unclear.

METHODS

The LF samples were obtained from 50 patients. After the LF cells (LFCs) were cultured, small interfering ribonucleic acid (siRNA) that target human phosphorylated-Smad2, 3, or 4 (p-Smad2,3,4) genes was transfected into LFCs. Next, proteins from cells were extracted and the protein levels of Smad2, Smad3, and Smad4 were detected by Western blot. The messenger ribonucleic acid level of TGF-β₁ was measured by real-time polymerase chain reaction (PCR). Furthermore, an enzyme-linked immunosorbent assay was performed to test the impact of Smad2 downstream of the TGF-β₁ signaling pathway.

RESULTS

Degeneration of the LF was characterized by an increase in disorganized elastic fibers and fibrotic transformation by extracellular collagen deposition. The gene expression analysis of fibrotic genes in LFCs showed that knockdown of phosphorylated-Smad2 by siRNA significantly reduced the protein expression level of TGF-β₁ compared with other groups. The enzyme-linked immunosorbent assay suggested that the protein expression level of Smad2 can influence the downstream events of TGF-β₁ signaling pathway in the LFCs.

CONCLUSIONS

Our findings suggest that Smad2 plays a potential role in the pathologic development of hypertrophy of LF. We also found that Smad2 knockdown by Smad-siRNA can influence the TGF-β₁ signaling pathway through decreasing expression of TGF-β₁, tumor necrosis factor α, and nuclear factor κb.

Fetal cervical zygapophysial joint with special reference to the associated synovial tissue: a histological study using near-term human fetuses

Human fetal cervical vertebrae are characterized by the large zygapophysial joint (ZJ) extending posteriorly. During our recent studies on regional differences in the shape, extent, and surrounding tissue of the fetal ZJ, we incidentally found a cervical-specific structure of synovial tissues. This study aimed to provide a detailed evaluation of the synovial structure using sagittal and horizontal sections of 20 near-term fetuses. The cervical ZJ consistently had a large cavity with multiple recesses at the margins and, especially at the anterior end, the recess interdigitated with or were located close to tree-like tributaries of the veins of the external vertebral plexus. In contrast to the flat and thin synovial cell lining of the recess, the venous tributary had cuboidal endothelial cells. No or few elastic fibers were identified around the ZJ. The venous-synovial complex seems to be a transient morphology at and around birth, and it may play a role in the stabilization of the growing cervical ZJ against frequent spontaneous dislocation reported radiologically in infants. The venous-synovial complex in the cervical region should be lost and replaced by elastic fibers in childhood or adolescence. However, the delayed development of the ligament flavum is also likely to occur in the lumbar ZJ in spite of no evidence of a transient venous-synovial structure. The cuboidal venous endothelium may simply represent the high proliferation rate for the growing complex.

Circulating angiopoietin-like protein 2 levels and arterial stiffness in patients receiving maintenance hemodialysis: A cross-sectional study

BACKGROUND AND AIMS

Chronic low-grade inflammation is receiving much attention as a critical pathology that induces various aging phenotypes, a concept known as "inflammaging". Uremic patients undergoing hemodialysis therapy show vascular aging phenotypes characterized by greater arterial stiffness and calcification compared to healthy controls of the same generation. In the current study, we investigated whether levels of inflammaging markers in the circulation were associated with vascular aging phenotypes in hemodialysis patients, as estimated by the cardio-ankle vascular index (CAVI).

METHODS

We conducted a multicenter cross-sectional study of 412 patients receiving hemodialysis and evaluated the relationship between circulating hs-CRP or ANGPTL2 levels, as markers of inflammaging, and CAVI.

RESULTS

Of 412 patients, 376 were analyzed statistically. While circulating hs-CRP levels had no significant association with CAVI, generalized linear models revealed that high circulating ANGPTL2 levels were significantly associated with increasing CAVI after adjustment for classical metabolic factors and hemodialysis-related parameters [β 0.63 (95%CI 0.07-1.18)]. Exploratory analysis revealed that high circulating ANGPTL2 levels were also strongly associated with increased CAVI, particularly in patients with conditions of increased vascular mechanical stress, such elevated blood pressure [β 1.00 (95%CI 0.23-1.76)], elevated pulse pressure [β 0.75 (95%CI 0.52-0.98)], or excess body fluid [β 1.25 (95%CI 0.65-1.84)].

CONCLUSIONS

We conclude that circulating levels of ANGPTL2 rather than hs-CRP are positively associated with CAVI in the uremic population and that ANGPTL2 could be a unique marker of progression of vascular aging in patients receiving hemodialysis.

Development of an In Vitro 3D Model for Investigating Ligamentum Flavum Hypertrophy

Background

Ligamentum flavum hypertrophy (LFH) is among the most crucial factors in degenerative lumbar spinal stenosis, which can cause back pain, lower extremity pain, cauda equina syndrome and neurogenic claudication. The exact pathogenesis of LFH remains elusive despite extensive research. Most in vitro studies investigating LFH have been carried out using conventional two-dimensional (2D) cell cultures, which do not resemble in vivo conditions, as they lack crucial pathophysiological factors found in three-dimensional (3D) LFH tissue, such as enhanced cell proliferation and cell cluster formation. In this study, we generated ligamentum flavum (LF) clusters using spheroid cultures derived from primary LFH tissue.

Results

The cultured LF spheroids exhibited good viability and growth on an ultra-low attachment 96-well plate (ULA 96-plate) platform according to live/dead staining. Our results showed that the 100-cell culture continued to grow in size, while the 1000-cell culture maintained its size, and the 5000-cell culture exhibited a decreasing trend in size as the culture time increased; long-term culture was validated for at least 28 days. The LF spheroids also maintained the extracellular matrix (ECM) phenotype, i.e., fibronectin, elastin, and collagen I and III. The 2D culture and 3D culture were further compared by cell cycle and Western blot analyses. Finally, we utilized hematoxylin and eosin (H&E) staining to demonstrate that the 3D spheroids resembled part of the cell arrangement in LF hypertrophic tissue.

Conclusions

The developed LF spheroid model has great potential, as it provides a stable culture platform in a 3D model that can further improve our understanding of the pathogenesis of LFH and has applications in future studies.

Ligamentum flavum fibrosis and hypertrophy: Molecular pathways, cellular mechanisms, and future directions

Hypertrophy of ligamentum flavum (LF), along with disk protrusion and facet joints degeneration, is associated with the development of lumbar spinal canal stenosis (LSCS). Of note, LF hypertrophy is deemed as an important cause of LSCS. Histologically, fibrosis is proved to be the main pathology of LF hypertrophy. Despite the numerous studies explored the mechanisms of LF fibrosis at the molecular and cellular levels, the exact mechanism remains unknown. It is suggested that pathophysiologic stimuli such as mechanical stress, aging, obesity, and some diseases are the causative factors. Then, many cytokines and growth factors secreted by LF cells and its surrounding tissues play different roles in activating the fibrotic response. Here, we summarize the current status of detailed knowledge available regarding the causative factors, pathology, molecular and cellular mechanisms implicated in LF fibrosis and hypertrophy, also focusing on the possible avenues for anti-fibrotic strategies.

Angiopoietin-like protein 2 as a novel marker for patients with primary Sjogren's syndrome-related interstitial lung disease

Angiopoietin-like protein 2 (Angptl2) plays a key role in chronic inflammation and tissue remodeling. We evaluated whether serum Angptl2 is associated with interstitial lung disease (ILD) in primary Sjogren's syndrome (pSS) patients. A total of 158 consecutive pSS patients and 25 normal healthy controls, which completed lung HRCT, were enrolled in our research. The levels of serum Angptl2 and TGF-β1 were measured by enzyme-linked immunosorbent assay. We investigated the correlation between the activity indexes of pSS-ILD patients and the serum Angptl2 levels. There were 71 of 158 (44.94%) patients interpreted pSS-ILD by radiologists at the initial presentation. The median interquartile range for serum Angptl2 was 16.55 ng/mL (range 10.82-41.07) in pSS patients, compared with 6.05 ng/mL (range 3.53-9.91) in normal healthy controls (P < 0.001). Importantly, differences between Angptl2 levels in pSS-ILD patients and pSS-N-ILD patients were also statistically significant [29.80 ng/mL (range 15.42-54.40), 14.75 ng/mL (range 9.85-40.48), P < 0.001]. A logistic regression analysis suggested that anti-Ro52, serum Angptl2 and DLCO were associated with pSS patients with interstitial lung disease, with aORs and 95% CIs of 2.06 (1.14-7.65), 4.13 (1.25-15.89) and 9.51 (2.10-37.74), respectively. Moreover, anti-Ro52 (r_s = 0.48, P = 0.016) and TGF-β1 (r_s = 0.64, P = 0.003) were significantly correlated with the serum Angptl2 in pSS-ILD patients. And, in pulmonary function tests, the serum Angptl2 was significantly correlated with DLCO (r_s = - 0.40, P = 0.009) and FVC (r_s = -0.37, P = 0.020). Serum Angptl2 may display a peculiar role in the pathogenesis of pSS-ILD and might be a potential biomarker.

Indirect Decompression on MRI Chronologically Progresses After Immediate Postlateral Lumbar Interbody Fusion: The Results From a Minimum of 2 Years Follow-Up

MINI: On magnetic resonance imaging, indirect decompression using lateral lumbar interbody fusion and posterior fixation was confirmed immediately after surgery and also continuously progressed after surgery, particularly during the first 6 months. Thecal sac enlargement was also confirmed, and is suspected to be caused by the atrophy of the ligamentum flavum and the disc.

STUDY DESIGN

A prospective cohort study.

OBJECTIVE

The aim of this study was to investigate radiographical changes related to indirect decompression using lateral lumbar interbody fusion (LLIF) with posterior fixation.

SUMMARY OF BACKGROUND DATA

Indirect lumbar decompression via LLIF is used to treat degenerative lumbar diseases requiring neural decompression. Although evidence suggests that thecal sac enlargement follows shortly after surgery, few studies have described the postoperative changes on MRIs.

METHODS

This study involved 102 patients who underwent indirect decompression at 136 levels, with LLIF and posterior fixation. Magnetic resonance imaging (MRIs) were collected preoperatively and several times postoperatively (over a 2-year period starting immediately after surgery). We then quantified the cross-sectional areas of the thecal sac and ligamentum flavum, as well as the anteroposterior diameter of disc bulging, and qualitatively assessed lumbar spinal stenosis according to a modified version of Schizas' classification [Grades A (mild) to C (severe)]. The Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) was used for the assessment of the clinical symptoms.

RESULTS

All changes were observable immediately after surgery, progressed over time, and were significantly different statistically at 2 years after surgery. The thecal sac was significantly larger (189% of preoperative; P < 0.0001), while the ligamentum flavum and disc bulge were significantly smaller [58.9% and 67.3% of preoperative (P < 0.001), respectively]. The number of patients with grade C (severe) lumbar stenosis also dropped significantly (preoperative, 17.6%; 2 years postoperative, 0%). There were no significant differences in JOABPEQ results at 6 months, 1 year, and 2 years postsurgery.

CONCLUSION

Indirect decompression produces immediate positive results that continue to improve over time. The cross-sectional area of the thecal sac doubled by 2 years after surgery, and the ligamentum flavum cross-sectional area and disc bulging both shrank significantly. At the same time, however, postoperative radiographical improvements do not appear to correlate with clinical symptoms.

LEVEL OF EVIDENCE

3.

Numerical simulations of bone remodelling and formation following nucleotomy

Nucleotomy is the gold standard treatment for disc herniation and has proven ability to restore stability by creating a bony bridge without any additional fixation. However, the evolution of mineral density in the extant and new bone after nucleotomy and fixation techniques has to date not been investigated in detail. The main goal of this study is to determine possible mechanisms that may trigger the bone remodelling and formation processes. With that purpose, a finite element model of the L4-L5 spinal segment was used. Bone mineral density (BMD), new tissue composition, and endplate deflection were determined as indicators of lumbar fusion. A bone-remodelling algorithm and a tissue-healing algorithm, both mechanically driven, were implemented to predict vertebral bone alterations and fusion patterns after nucleotomy, internal fixation, and anterior plate placement. When considering an intact disc height, neither nucleotomy nor internal fixation were able to provide the necessary stability to promote bony fusion. However, when 75% of the disc height was considered, bone fusion was predicted for both techniques. By contrast, an anterior plate allowed bone fusion at all disc heights. A 50% disc-height reduction led to osteophyte formation in all cases. Changes in the intervertebral disc tissue caused BMD alterations in the endplates. From this observations it can be drawn that fusion may be self-induced by controlling the mechanical stabilisation without the need of additional fixation. The amount of tissue to be removed to achieve this stabilisation remains to be determined.

Increased pain and sensory hyperinnervation of the ligamentum flavum in patients with lumbar spinal stenosis

Nociceptive sensory nerve fibers have never been investigated in the ligamentum flavum (LF) of patients with LSS. The aim was to analyze nociceptive sensory nerve fibers in the ligamentum flavum (LF) of patients with LSS. A prospective study in patients with lumbar spinal stenosis (LSS) undergoing invasive surgical treatment for lumbar spinal stenosis (LSS) with flavectomy was performed. Patients with LSS were subjected to flavectomy and density of sensory and sympathetic nerve fibers, macrophages, vessels, activated fibroblasts, and cells were investigated by immunostaining techniques. A group of patients with acute disc herniation served as control group. We found a higher density of sensory nerve fibers in LSS patients versus controls. These findings support the role of LF in associated low back pain. Density of sensory nerve fibers in LSS, was positively correlated with typical markers of clinical pain and functional disability, but not with LF density of activated fibroblasts. Inflammation as estimated by macrophage infiltration and higher vascularity does not play a marked role in LF in our LSS patients. In the present study, compared to men with LSS, women with LSS demonstrate more pain and depression, and show a higher density of sensory nerve fibers in LF. This study shed new light on nociceptive nerve fibers, which are increased in LSS compared to controls. The findings speak against a strong inflammatory component in LSS. A higher pain levels in women compared to men can be explained by a higher density of nociceptive nerve fibers. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-7, 2019.

Angiopoietin-Like Protein 2 Induces Synovial Inflammation in the Facet Joint Leading to Degenerative Changes via Interleukin-6 Secretion

Study Design

Experimental human study.

Purpose

To determine whether angiopoietin-like protein 2 (ANGPTL2) is highly expressed in the hyperplastic facet joint (FJ) synovium and whether it activates interleukin-6 (IL-6) secretion in FJ synoviocytes.

Overview of Literature

Mechanical stress-induced synovitis is partially, but significantly, responsible for degenerative and subsequently osteoarthritic changes in the FJ tissues in patients with lumbar spinal stenosis (LSS). However, the underlying molecular mechanism remains unclear. IL-6 is highly expressed in degenerative FJ synovial tissue and is responsible for local chronic inflammation. ANGPTL2, an inflammatory and mechanically induced mediator, promotes the expression of IL-6 in many cells.

Methods

FJ tissues were harvested from five patients who had undergone lumbar surgery. Immunohistochemistry for ANGPTL2, IL-6, and cell markers was performed in the FJ tissue samples. After cultured synoviocytes from the FJ tissues were subjected to mechanical stress, ANGPTL2 expression and secretion were measured quantitatively using real-time quantitative reverse-transcription–polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA), respectively. Following ANGPTL2 administration in the FJ synoviocytes, anti-nuclear factor-κB (NF-κB) activation was investigated using immunocytochemistry, and IL-6 expression and secretion were assayed quantitatively with or without NF-κB inhibitor. Moreover, we assessed whether ANGPTL2-induced IL-6 modulates leucocyte recruitment in the degenerative process by focusing on the monocyte chemoattractant protein-1 (MCP-1) expression.

Results

ANGPTL2 and IL-6 were highly expressed in the hyperplastic FJ synovium samples. ANGPTL2 was co-expressed in both, fibroblast-like and macrophage-like synoviocytes. Further, the expression and secretion of ANGPTL2 in the FJ synoviocytes increased in response to stimulation by mechanical stretching. ANGPTL2 protein promoted the nuclear translocation of NF-κB and induced IL-6 expression and secretion in the FJ synoviocytes. This effect was reversed following treatment with NF-κB inhibitor. Furthermore, ANGPTL2-induced IL-6 upregulated the MCP-1 expression in the FJ synoviocytes.

Conclusions

Mechanical stress-induced ANGPTL2 promotes chronic inflammation in the FJ synovium by activating IL-6 secretion, leading to FJ degeneration and subsequent LSS.

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.

Matrix metalloproteinase promotes elastic fiber degradation in ligamentum flavum degeneration

Ligamentum flavum (LF) hypertrophy in lumbar spinal canal stenosis (LSCS) is characterized by a loss of elastic fibers and fibrosis. Chronic inflammation is thought to be responsible for the histological change but the mechanism underlying elastic fiber degradation remains unclear. Given that matrix metalloproteinase (MMP)-2 and -9 have elastolytic activity and are partly regulated by inflammatory cytokines such as interleukin (IL)-6, in this study, we investigated whether MMPs mediate LF degeneration using 52 LF samples obtained during lumbar surgery, including 31 LSCS and 21 control specimens. We confirmed by histological analysis that the LSCS samples exhibited severe degenerative changes compared with the controls. We found that MMP-2 was upregulated in LF tissue from patients with LSCS at the mRNA and protein levels, whereas MMP-9 expression did not differ between the two groups. The MMP-2 level was positively correlated with LF thickness and negatively correlated with the area occupied by elastic fibers. IL-6 mRNA expression was also increased in LF tissue from patients with LSCS and positively correlated with that of MMP-2. Signal transducer and activator of transcription (STAT)3, a component of the IL-6 signaling pathway, was activated in hypertrophied LF tissues. Our in vitro experiments using fibroblasts from LF tissue revealed that IL-6 increased MMP-2 expression, secretion, and activation via induction of STAT3 signaling, and this effect was reversed by STAT3 inhibitor treatment. Moreover, elastin degradation was promoted by IL-6 stimulation in LF fibroblast culture medium. These results indicate that MMP-2 induction by IL-6/STAT3 signaling in LF fibroblasts can degrade elastic fibers, leading to LF degeneration in LSCS.

Angiopoietin-like protein 2 promotes chondrogenic differentiation during bone growth as a cartilage matrix factor

OBJECTIVE

Chondrocyte differentiation is crucial for long bone growth. Many cartilage extracellular matrix (ECM) proteins reportedly contribute to chondrocyte differentiation, indicating that mechanisms underlying chondrocyte differentiation are likely more complex than previously appreciated. Angiopoietin-like protein 2 (ANGPTL2) is a secreted factor normally abundantly produced in mesenchymal lineage cells such as adipocytes and fibroblasts, but its loss contributes to the pathogenesis of lifestyle- or aging-related diseases. However, the function of ANGPTL2 in chondrocytes, which are also differentiated from mesenchymal stem cells, remains unclear. Here, we investigate whether ANGPTL2 is expressed in or functions in chondrocytes.

METHODS

First, we evaluated Angptl2 expression during chondrocyte differentiation using chondrogenic ATDC5 cells and wild-type epiphyseal cartilage of newborn mice. We next assessed ANGPTL2 function in chondrogenic differentiation and associated signaling using Angptl2 knockdown ATDC5 cells and Angptl2 knockout mice.

RESULTS

ANGPTL2 is expressed in chondrocytes, particularly those located in resting and proliferative zones, and accumulates in ECM surrounding chondrocytes. Interestingly, long bone growth was retarded in Angptl2 knockout mice from neonatal to adult stages via attenuation of chondrocyte differentiation. Both in vivo and in vitro experiments show that changes in ANGPTL2 expression can also alter p38 mitogen-activated protein kinase (MAPK) activity mediated by integrin α5β1.

CONCLUSION

ANGPTL2 contributes to chondrocyte differentiation and subsequent endochondral ossification through α5β1 integrin and p38 MAPK signaling during bone growth. Our findings provide insight into molecular mechanisms governing communication between chondrocytes and surrounding ECM components in bone growth activities.

MicroRNA transcriptome analysis on hypertrophy of ligamentum flavum in patients with lumbar spinal stenosis

Introduction

Molecular pathways involved in ligamentum flavum (LF) hypertrophy are still unclarified. The purpose of this study was to characterize LF hypertrophy by microRNA (miRNA) profiling according to the classification of lumbar spinal stenosis (LSS).

Methods

Classification of patients with LSS into ligamentous and non-ligamentous cases was conducted by clinical observation and the morphometric parameter adopting the LF/spinal canal area ratio (LSAR) from measurements of magnetic resonance imaging (MRI) T2 weighed images. LF from patients with ligamentous stenosis (n=10) were considered as the degenerative hypertrophied samples, and those from patients with non-ligamentous LSS (n=7) and lumbar disc herniation (LDH, n=3) were used as non-hypertrophied controls. Profiling of miRNA from all samples was conducted by Agilent microarray. Microarray data analysis was performed with GeneSpring GX, and pathway analysis was performed using Ingenuity Pathway Analysis.

Results

The mean LSAR in the ligamentous group was significantly higher than that in the control group (0.662±0.154 vs 0.301±0.068, p=0.0000171). Ten significantly differentially expressed miRNA were identified and taken as a signature of LF hypertrophy: nine miRNA showed down-regulated expression, and one showed up-regulated expression in the ligamentous LF. Among those, miR-423-5p (r_s=-0.473, p<0.05), miR-4306 (r_s=-0.628, p<0.01), miR-516b-5p (r_s=-0.629, p<0.01), and miR-497-5p (r_s=0.461, p<0.05) were correlated to the LSAR. Pathway analysis predicted aryl hydrocarbon receptor signaling (p<0.01), Wnt/β-catenin signaling (p<0.01), and insulin receptor signaling (p<0.05) as canonical pathways associated with the miRNA signature.

Conclusions

Classification based on quantification of the MRI axial image is useful for studying hypertrophy of the LF. Aryl hydrocarbon receptor and Wnt/β-catenin signaling may be involved in LF hypertrophy.

Mechanical stress induces elastic fibre disruption and cartilage matrix increase in ligamentum flavum

Lumbar spinal stenosis (LSS) is one of the most frequent causes of low back pain and gait disturbance in the elderly. Ligamentum flavum (LF) hypertrophy is the main pathomechanism of LSS, but the reason for its occurrence is not clearly elucidated. In this study, we established a novel animal model of intervertebral mechanical stress concentration and investigated the biological property of the LF. The LF with mechanical stress concentration showed degeneration with elastic fibres disruption and cartilage matrix increase, which are similar to the findings in hypertrophied LF from patients with LSS. By contrast, decreased Col2a1 expression was found in the LF at fixed levels, in which mechanical stress was strongly reduced. These findings indicate that mechanical stress plays a crucial role in LF hypertrophy through cartilage matrix increase. The findings also suggest that fusion surgery, which eliminates intervertebral instability, may change the property of the LF and lead to the relief of patients' symptoms.

Diabetes mellitus is associated with increased elastin fiber loss in ligamentum flavum of patients with lumbar spinal canal stenosis: results of a pilot histological study

PURPOSE

Lumbar spinal canal stenosis (LSCS) is associated with fibrosis, decreased elastin-to-collagen ratio, and hypertrophy of the ligamentum flavum (LF). Diabetes mellitus (DM) is known to cause metabolic disturbances within the extracellular matrix in multiple tissues. These alterations may play a major role in the severity of clinical symptoms of LSCS affecting diabetic patients. We aimed to examine the hypothesis that DM may contribute to the LF changes seen in patients with LSCS.

METHODS

The study cohort included 29 patients: 23 with LSCS (10 with DM vs. 13 without DM) as well as six patients with lumbar disc herniation (LDH). Surgical LF specimens were retrieved for histological assessment. Morphologic quantification of confocal microscopy images using fast Fourier transform analysis allowed us to compare anisotropy and elastin fiber orientation between groups.

RESULTS

There was a significant positive correlation between fasting plasma glucose values and degree of elastin degradation (r = 0.36, p = 0.043). The diabetic patients with LSCS showed a significantly greater loss of elastic fibers (2.3 ± 0.9 vs. 1.5 ± 0.55, p = 0.009), although fibrosis was shown to be similar (1.44 ± 0.7 vs. 1.43 ± 0.88, p = 0.98). There was no significant difference in the degree of calcification in the LSCS group between patients with and without diabetes (1.71 vs. 2.05%, p = 0.653). Fiber orientation was found to be less homogenous in the LSCS compared with the LDH group, although not significantly affected by DM.

CONCLUSIONS

The present study points to a significant contribution of DM to the loss of elastin fibers that occurs in the LF of patients with LSCS.

Angiopoietin-like protein as a novel marker for liver fibrosis in chronic hepatitis B patients with normal to minimally raised ALT

Background

For hepatitis B patients who do not meet the treatment criteria recommended by guidelines, therapy decisions depend on hepatic histology. Angiopoietin-like protein 2 (Angptl2) is a mediator of chronic inflammation that contributes to extracellular matrix remodeling. The aim of this study was to explore the predictive value of Angptl2 as a novel biomarker of liver histology.

Methods

Hepatitis B patients with normal to minimally raised ALT were recruited. Serum Angptl2 concentrations were detected using commercial ELISA kit. The fibrosis score were assessed according to Ishak criteria. Significant fibrosis was defined as ISHAK score ≥ 3.

Results

Of 460 patients, 223 cases served as training cohort and 237 ones as validation cohort. Serum Angptl2 concentration was significantly associated with fibrosis scores in both training and validation group. Angptl2 combined index (ACI) for assessing significant fibrosis was developed from training cohort, based on Angptl2 and conventional variables. ACI showed areas under receiver-operating characteristic curve (AUC) of 0.835 for predicting significant fibrosis, which was superior to APRI (AUC = 0.776, P = 0.049), FIB-4 (AUC = 0.750, P = 0.010), Hui model (AUC = 0.756, P = 0.028), and had a better trend than Forn’s index (AUC = 0.796, P = 0.083) in training cohort. Finally, validation cohort revealed its robustness and reliability.

Conclusion

Higher Angptl2 level represents as a potential biomarker independently associated with fibrosis stages. Compared with APRI, Hui model, FIB-4, Forn’s index, ACI did better in diagnosing significant fibrosis in hepatitis B patients.

Trial registration

The complete clinical trials protocol is available by request at clinicaltrials.gov (NCT01962155) and chictr.org (ChiCTR-DDT-13003724).

Electronic supplementary material

The online version of this article (10.1186/s12879-017-2728-7) contains supplementary material, which is available to authorized users.

Spinal fusion without instrumentation - Experimental animal study

BACKGROUND

The number and cost of instrumented spinal fusion surgeries have increased rapidly, primarily for the treatment of lumbar segmental instabilities. However, what if the organism itself is able to restore segmental stability over time? This large-animal study using sheep aimed to investigate whether the reparative response after destabilization via facetectomy and nucleotomy without instrumentation can effectively fuse the spinal segment comparable to instrumented standard fusion surgery.

METHODS

The following four surgical interventions were investigated: dorsal fixation via internal fixator, ventral fixation via cage as well as facetectomy and nucleotomy without additional instrumentation. Six months postoperatively, the animals were sacrificed, and the lumbar spines were used for biomechanical tests.

FINDINGS

Spinal stability was restored to the destabilized spinal segments at six months postoperatively and was comparable to the results of conventional surgery via screws and cages. Iatrogenic hypomobilization caused significant reductions in facet joint space and intervertebral disc height of segments at index and adjacent level. Restabilized segments after iatrogenic hypermobilzation also significantly decreased facet joint space and disc height at index level, but revealed no influence on adjacent segments.

INTERPRETATION

These findings in the sheep model question the necessity of costly instrumentation and suggest the alternative possibility of stimulating the reparative capacity of the body in human lumbar spine fusion surgery.

MiR-21 promotes fibrosis and hypertrophy of ligamentum flavum in lumbar spinal canal stenosis by activating IL-6 expression

The molecular mechanism underlying the fibrosis of ligamentum flavum(LF) in patients with lumbar spinal canal stenosis(LSCS) remains unknown. MicroRNAs are reported to play important roles in regulating fibrosis in different organs. The present study aimed to identify fibrosis related miR-21 expression profile and investigate the pathological process of miR-21 in the fibrosis of LF hypertrophy and associated regulatory mechanisms. 15 patients with LSCS underwent surgical treatment were enrolled in this study. For the control group, 11 patients with lumbar disc herniation(LDH) was included. The LF thickness was measured on MRI. LF samples were obtained during the surgery. Fibrosis score was assessed by Masson's trichrome staining. The expression of miR-21 in LF tissues were determined by RT-PCR. Correlation among LF thickness, fibrosis score, and miR-21 expression was analyzed. In addition, Lentiviral vectors for miR-21 mimic were constructed and transfected into LF cells to examine the role of miR-21 in LF fibrosis. Types I and III collagen were used as indicators of fibrosis. IL-6 expression in LF cells after transfection was investigated by RT-PCR and ELISA. Patients in two groups showed similar outcomes regarding age, gender, level of LF tissue. The thickness and fibrosis score of LF in the LSCS group were significantly greater than those in LDH group (all P < 0.05). Similarly, the expression of miR-21 in LSCS group was substantially higher than that in LDH group(P < 0.05). Furthermore, the miR-21 expression exhibited positive correlations with the LF thickness (r = 0.595, P < 0.05) and fibrosis score (r = 0.608, P < 0.05). Of note, miR-21 over-expression increased the expression levels of collagen I and III (P < 0.05). Also, IL-6 expression and secretion in LF cells was elevated after transfection of miR-21 mimic. MiR-21 is a fibrosis-associated miRNA and promotes inflammation in LF tissue by activating IL-6 expression, leading to LF fibrosis and hypertrophy.

Interstitial pneumonia induced by bleomycin treatment is exacerbated in Angptl2-deficient mice

Angiopoietin-like protein 2 (ANGPTL2) is a chronic inflammatory mediator that, when deregulated, is associated with various pathologies. However, little is known about its activity in lung. To assess a possible lung function, we generated a rabbit monoclonal antibody that specifically recognizes mouse ANGPTL2 and then evaluated protein expression in mouse lung tissue. We observed abundant ANGPTL2 expression in both alveolar epithelial type I and type II cells and in resident alveolar macrophages under normal conditions. To assess ANGPTL2 function, we compared lung phenotypes in Angptl2 knockout (KO) and wild-type mice but observed no overt changes. We then generated a bleomycin-induced interstitial pneumonia model using wild-type and Angptl2 KO mice. Bleomycin-treated wild-type mice showed specifically upregulated ANGPTL2 expression in areas of severe fibrosing interstitial pneumonia, while Angptl2 KO mice developed more severe lung fibrosis than did comparably treated wild-type mice. Lung fibrosis seen following bone marrow transplant was comparable in wild-type or Angptl2 KO mice treated with bleomycin, suggesting that Angptl2 loss in myeloid cells does not underlie fibrotic phenotypes. We conclude that Angptl2 deficiency in lung epithelial cells and resident alveolar macrophages causes severe lung fibrosis seen following bleomycin treatment, suggesting that ANGPTL2 derived from these cell types plays a protective role against fibrosis in lung.

Angiopoietin-like protein 2 and kidney fibrosis: lessons from knockout mice

The angiopoietin-like protein (ANGPTL) family is homologous to angiopoietins but does not bind to the Tie2 receptor. The function of ANGPTLs has been elucidated largely in the context of angiogenesis and lipid metabolism. Morinaga et al. demonstrated that genetic depletion of Angptl2 confers amelioration of the mouse kidney fibrosis induced by a unilateral ureteral obstruction, implicating that ANGPTL2, predominantly in the renal tubular compartments, activates the transforming growth factor-β signaling and vice versa through miR-221.

Tissue transglutaminase is involved in mechanical load-induced osteogenic differentiation of human ligamentum flavum cells

Mechanical load-induced osteogenic differentiation might be the key cellular event in the calcification and ossification of ligamentum flavum. The aim of this study was to investigate the influence of tissue transglutaminase (TGM2) on mechanical load-induced osteogenesis of ligamentum flavum cells. Human ligamentum flavum cells were obtained from 12 patients undergoing lumbar spine surgery. Osteogenic phenotypes of ligamentum flavum cells, such as alkaline phosphatase (ALP), Alizarin red-S stain, and gene expression of osteogenic makers were evaluated following the administration of mechanical load and BMP-2 treatment. The expression of TGM2 was evaluated by real-time PCR, Western blotting, and enzyme-linked immunosorbent assay (ELISA) analysis. Our results showed that mechanical load in combination with BMP-2 enhanced calcium deposition and ALP activity. Mechanical load significantly increased ALP and OC gene expression on day 3, whereas BMP-2 significantly increased ALP, OPN, and Runx2 on day 7. Mechanical load significantly induced TGM2 gene expression and enzyme activity in human ligamentum flavum cells. Exogenous TGM2 increased ALP and OC gene expression; while, inhibited TG activity significantly attenuated mechanical load-induced and TGM2-induced ALP activity. In summary, mechanical load-induced TGM2 expression and enzyme activity is involved in the progression of the calcification of ligamentum flavum.

TGF-β1, in association with the increased expression of connective tissue growth factor, induce the hypertrophy of the ligamentum flavum through the p38 MAPK pathway

Hypertrophy of the ligamentum flavum (LF) is one of the key pathomechanisms of lumbar spinal stenosis (LSS). Transforming growth factor (TGF)-β1 is abundantly expressed in hypertrophied degenerative LF tissues from LSS. However, the molecular mechanisms underling the association between TGF-β1 and LF hypertrophy have not yet been fully elucidated. In this study, we investigated the important role of the mitogen-activated protein kinase (MAPK) pathway in the pathogenesis of LSS by analyzing the expression of connective tissue growth factor (CTGF) and extracellular matrix (ECM) components (collagen I and collagen III) in TGF-β1-treated LF cells. Cell growth assay revealed that TGF-β1, in association with CTGF, enhanced the the proliferation of LF cells, and we found that TGF-β1 also elevated CTGF expression and subsequently enhanced the mRNA expression of collagen I and collagen III. The increased mRNA expression levels of CTGF, collagen I and collagen III were abolished by p38 inhibitors. Both immunofluorescence imaging and western blot analysis of p38 and p-p38 revealed the increased expression and phosphorylation of p38. Silencing the expression of p38 by siRNA in LF cells decreased the protein expression of p38, p-p38 and CTGF, as well as the mRNA expression of CTGF, collagen I and collagen III. Taken together, our findings indicate that TGF-β1, in association with the increased expression of CTGF, contribute to the homeostasis of the ECM and to the hypertrophy of LF through the p38 MAPK pathway.

The Mechanism of Ligamentum Flavum Hypertrophy: Introducing Angiogenesis as a Critical Link That Couples Mechanical Stress and Hypertrophy

BACKGROUND

Biochemical alterations associated with mechanical stress have been explored as an initiating step in the pathological progression of ligamentum flavum hypertrophy (LFH); however, this mechanism remains poorly understood. Recently, the inflammation induced after mechanical stress and the subsequent response of ligamentum flavum (LF) cells have been implicated in LFH pathology.

OBJECTIVE

To investigate the hypothesis that angiogenesis may be a critical link between hypertrophy and a series of stimulating events, including mechanical stress.

METHODS

LF from 20 lumbar spinal canal stenosis (LSCS) patients and 16 non-LSCS patients (control group) were collected during surgery. Patient demographic and radiographic data were obtained. The levels of angiogenic factors (vascular endothelial growth factor [VEGF], angiopoietin-1, vascular cell adhesion molecule, and basic fibroblast growth factor) in the LF were investigated by using an enzyme-linked immunosorbent assay. Angiogenesis was also quantified by immunohistochemical detection of CD34-positive capillaries. The correlations among clinical factors, including radiographic factors, angiogenic factors, and angiogenesis, were statistically analyzed.

RESULTS

The LSCS group was older and exhibited a longer symptom duration, wider segmental motion, and thicker LF than the control group. The LSCS group showed significantly higher tissue concentrations of VEGF (P < .001) that positively correlated with LF thickness (r = 0.557, P < .001) and segmental motion (r = 0.586, P < .001). The LSCS group showed significantly more CD34-positive capillaries than the control group (P = .004).

CONCLUSION

The LSCS group showed greater segmental motion, higher VEGF concentrations, and more CD34-positive capillaries than the control group. These data indicate that VEGF-mediated angiogenesis following mechanical stress may be a critical step within the series of pathological events in LFH.

Morphogens and blood-brain barrier function in health and disease

The microvasculature of the brain forms a protective blood-brain barrier (BBB) that ensures a homeostatic environment for the central nervous system (CNS), which is essential for optimal brain functioning. The barrier properties of the brain endothelial cells are maintained by cells surrounding the capillaries, such as astrocytes and pericytes. Together with the endothelium and a basement membrane, these supporting cells form the neurovascular unit (NVU). Accumulating evidence indicates that the supporting cells of the NVU release a wide variety of soluble factors that induce and control barrier properties in a concentration-dependent manner. The current review provides a comprehensive overview of how such factors, called morphogens, influence BBB integrity and functioning. Since impaired BBB function is apparent in numerous CNS disorders and is often associated with disease severity, we also discuss the potential therapeutic value of these morphogens, as they may represent promising therapies for a wide variety of CNS disorders.

Bioinformatics analysis of potential essential genes that response to the high intraocular pressure on astrocyte due to glaucoma

AIM

To study the gene expression response and predict the network in cell due to pressure effects on optic nerve injury of glaucoma.

METHODS

We used glaucoma related microarray data in public database [Gene Expression Omnibus (GEO)] to explore the potential gene expression changes as well as correspondent biological process alterations due to increased pressure in astrocytes during glaucoma development.

RESULTS

A total of six genes were identified to be related with pressure increasing. Through the annotation and network analysis, we found these genes might be involved in cell morphological remodeling, angiogenesis, mismatch repair.

CONCLUSION

Increasing pressure in glaucoma on astrocytes might cause gene expression alterations, which might induce some cellular responses changes.

Angiopoietin-like protein 2 promotes inflammatory conditions in the ligamentum flavum in the pathogenesis of lumbar spinal canal stenosis by activating interleukin-6 expression

PURPOSE

Chronic inflammation is thought to cause ligamentum flavum (LF) degeneration and hypertrophy in lumbar spinal canal stenosis (LSCS). Angiopoietin-like protein 2 (Angptl2) is highly expressed in hypertrophied LF. Because Angptl2 regulates interleukin-6 (IL-6) expression in various tissues, we investigated whether IL-6 is expressed in hypertrophied LF and, if so, does Angptl2 induce IL-6 expression in LF fibroblasts.

METHODS

LF tissue was obtained from LSCS patients and non-LSCS patients. Polymerase chain reaction (PCR) for Angptl2 and IL-6 genes and immunohistochemistry for IL-6 protein were performed in LF tissue. Fibroblasts from LF tissue were used for in vitro experiments. Expression of integrin α5β1 (an Angptl2 receptor) and Angptl2 binding to receptors on LF fibroblasts were examined by fluorescence-activated cell sorter analysis and cell adhesion assays. After Angptl2 recombinant protein treatment, NF-κB activation and IL-6 expression in LF fibroblasts were investigated by immunocytochemistry, PCR, and enzyme-linked immunosorbent assay.

RESULTS

IL-6 mRNA expression was increased in hypertrophied LF tissue from LSCS patients and positively correlated with LF thickness and Angptl2 mRNA expression. IL-6 protein was highly expressed in LF fibroblasts in hypertrophied LF tissue. In vitro experiments demonstrated integrin α5β1 expression on LF fibroblasts and Angptl2 binding to cells via receptors. Angptl2 stimulation promoted NF-κB nuclear translocation and induced IL-6 expression and secretion in LF fibroblasts.

CONCLUSIONS

Angptl2 promotes inflammation in LF tissue by activating IL-6 expression, leading to LF degeneration and hypertrophy.

Angiopoietin-like-2: a multifaceted protein with physiological and pathophysiological properties

Angptl2 is a multifaceted protein, displaying both physiological and pathological functions, in which scientific and clinical interest is growing exponentially within the past few years. Its physiological functions are not well understood, but angptl2 was first acknowledged for its pro-angiogenic and antiapoptotic capacities. In addition, angptl2 can be considered a growth factor, since it increases survival and expansion of hematopoietic stem cells and may promote vasculogenesis. Finally, angptl2 has an important, but largely unrecognised, physiological role: in the cytosol, angptl2 binds to type 1A angiotensin II receptors and induces their recycling, with recovery of the receptor signal functions. Despite these important physiological properties, angptl2 is better acknowledged for its deleterious pro-inflammatory properties and its contribution in multiple chronic diseases such as cancer, diabetes, atherosclerosis, metabolic disorders and many other chronic diseases. This review aims at presenting an updated description of both the beneficial and deleterious biological properties of angptl2, in addition to its molecular signalling pathways and transcriptional regulation. The multiplicity of diseases in which angptl2 contributes makes it a new highly relevant clinical therapeutic target.