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.
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan ; Department of Molecular Genetics, Graduate School of Medical Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Takayuki
T
Nakamura
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Tatsuya
T
Okada
Department of Molecular Genetics, Graduate School of Medical Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Motoyoshi
M
Endo
Department of Molecular Genetics, Graduate School of Medical Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Tsuyoshi
T
Kadomatsu
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Takuya
T
Taniwaki
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Akira
A
Sei
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan ; Department of Molecular Genetics, Graduate School of Medical Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Haruki
H
Odagiri
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan ; Department of Molecular Genetics, Graduate School of Medical Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Tetsuro
T
Masuda
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Toru
T
Fujimoto
Nakamura Orthopaedic Clinic, Ikeda-machi, Kita-ku, Kumamoto, Japan.
Takafumi
T
Nakamura
Department of Molecular Genetics, Graduate School of Medical Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan ; CREST, Japan Science and Technology Agency, Honcho, Kawaguchi, Saitama, Japan.
Yuichi
Y
Oike
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto, Japan.
Hiroshi
H
Mizuta
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000091302:Angiopoietin-Like Protein 2; D000075802:Angiopoietin-like Proteins; D042682:Angiopoietins / Q000378:metabolism*; D003251:Constriction, Pathologic; D005260:Female; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006801:Humans; D006984:Hypertrophy; D017843:Ligamentum Flavum / Q000378:metabolism* / Q000473:pathology*; D008159:Lumbar Vertebrae / Q000378:metabolism* / Q000473:pathology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D015398:Signal Transduction; D051785:Smad Proteins / Q000378:metabolism; D013314:Stress, Mechanical; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
C485792:ANGPTL2 protein, human; D000091302:Angiopoietin-Like Protein 2; D000075802:Angiopoietin-like Proteins; D042682:Angiopoietins; D051785:Smad Proteins; D053773:Transforming Growth Factor beta1