Angiopoietin-like protein 2 promotes inflammatory conditions in the ligamentum flavum in the pathogenesis of lumbar spinal canal stenosis by activating interleukin-6 expression.
OBJECTIVE
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.
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, 1-1-1 Honjo, Chuo-ku, Kumamoto, 860-8556, Japan, 110r5135@st.kumamoto-u.ac.jp.
Takayuki
T
Nakamura
Tatsuya
T
Okada
Motoyoshi
M
Endo
Takafumi
T
Nakamura
Yuichi
Y
Oike
Hiroshi
H
Mizuta
D000368:Aged; D000369:Aged, 80 and over; D000091302:Angiopoietin-Like Protein 2; D000075802:Angiopoietin-like Proteins; D042682:Angiopoietins / Q000235:genetics / Q000276:immunology*; D016022:Case-Control Studies; D002448:Cell Adhesion; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005347:Fibroblasts / Q000276:immunology*; D005434:Flow Cytometry; D006801:Humans; D006984:Hypertrophy; D007150:Immunohistochemistry; D007249:Inflammation / Q000473:pathology; D039081:Integrin alpha5beta1 / Q000276:immunology; D015850:Interleukin-6 / Q000235:genetics / Q000276:immunology*; D017843:Ligamentum Flavum / Q000276:immunology* / Q000473:pathology; D008159:Lumbar Vertebrae; D008297:Male; D008875:Middle Aged; D016328:NF-kappa B / Q000276:immunology*; D012333:RNA, Messenger / Q000378:metabolism*; D015398:Signal Transduction; D013130:Spinal Stenosis / Q000276:immunology* / Q000473:pathology
C485792:ANGPTL2 protein, human; D000091302:Angiopoietin-Like Protein 2; D000075802:Angiopoietin-like Proteins; D042682:Angiopoietins; C508600:IL6 protein, human; D039081:Integrin alpha5beta1; D015850:Interleukin-6; D016328:NF-kappa B; D012333:RNA, Messenger