Contribution of PTHrP to mechanical strain-induced fibrochondrogenic differentiation in entheses of Achilles tendon of miniature pigs.
BACKGROUND
Fibrochondrocytes are involved in entheses repair, but their response to mechanical strain (MS) is ill known.


OBJECTIVE
To determine if parathyroid hormone-related protein (PTHrP) expression in fibrochondrocytes from fibrocartilaginous entheses is modulated by MS, and to further observe the regulatory effects of human (h) PTHrP on fibrochondrocyte differentiation.


METHODS
Fibrochondrocytes from fibrocartilaginous entheses of Guizhou miniature pig׳s Achilles tendon were submitted or not to MS (4%, 8% or 12% cyclic tensile strain; 1 Hz). Fibrochondrocytes were also exposed to: cyclopamine (Indian hedgehog (Ihh) inhibitor) (10 μM), hPTHrP (10 nM) or cyclopamine/hPTHrP (cyclopamine 10 uM+hPTHrP 10 nM). Types I, II and X collagen and PTHrP expressions were measured by real-time RT-PCR and Western blot.


RESULTS
Under 4% strain load for 12 h, types I and II collagen mRNA expressions were increased (+324% and +659%, P<0.001), while type X collagen was decreased (-89%, P<0.001). At 12%, types I and II collagen mRNA expressions were decreased (-62% and -62%, P<0.001), while type X collagen was increased (+375%, P<0.05). Under 4% strain load, PTHrP mRNA expression was increased in relation with strain duration (from 3 to 12 h: +168%, P<0.001), while at 12%, PTHrP expression decreased with time (from 3 to 12 h: -81%, P<0.001). Using cyclopamine for 24 h, PTHrP mRNA expression was significantly decreased (-88%, P<0.05), types I and II collagen were decreased (-90% and -82%, P<0.001), and type X collagen was increased (+261%, P<0.001).


CONCLUSIONS
Dynamic MS modulate PTHrP expressions. Thus, PTHrP might play an important role in fibrochondrocyte differentiation, indirectly revealing a role in entheses׳ formation and repair.
Department of Orthopaedics, Xijing Hospital, The Fourth Military Medical University, Xi׳an 710032, China; Department of Orthopedics, Fuzhou General Hospital of Nanjing, Command, PLA, Fuzhou 350025, China.
Xuesong
X
Han
Center of Joint Surgery, Southwest Hospital, The Third Military Medical University, Chongqing 400038, China. Electronic address: guolin6212@163.com.
Lin
L
Guo
Center of Joint Surgery, Southwest Hospital, The Third Military Medical University, Chongqing 400038, China.
Fuyou
F
Wang
Department of Orthopaedics, Xijing Hospital, The Fourth Military Medical University, Xi׳an 710032, China. Electronic address: zhuqsh@fmmu.edu.cn.
Qingsheng
Q
Zhu
Center of Joint Surgery, Southwest Hospital, The Third Military Medical University, Chongqing 400038, China.
Liu
L
Yang
D000125:Achilles Tendon / Q000378:metabolism* / Q000502:physiology*; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism; D003094:Collagen / Q000378:metabolism; D006801:Humans; D044162:Parathyroid Hormone-Related Protein / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D013314:Stress, Mechanical; D013552:Swine; D013556:Swine, Miniature; D013718:Tensile Strength; D014704:Veratrum Alkaloids / Q000737:chemistry
D044162:Parathyroid Hormone-Related Protein; D014704:Veratrum Alkaloids; D003094:Collagen; C000541:cyclopamine
Cyclic tensile strain; Entheses; Fibrochondrocytes; Ihh; Mechanical strain; PTHrP