Contribution of PTHrP to mechanical strain-induced fibrochondrogenic differentiation in entheses of Achilles tendon of miniature pigs.

Abstract

Fibrochondrocytes are involved in entheses repair, but their response to mechanical strain (MS) is ill known. 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. 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. 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). Dynamic MS modulate PTHrP expressions. Thus, PTHrP might play an important role in fibrochondrocyte differentiation, indirectly revealing a role in entheses׳ formation and repair.