The Mechanotransduction In Tntervertebral Disc Degeneration Induced By Over-loading

Objective To verify the mechanical properties of lumbar degenerativedisc and adjacent levels under various loading. To investigate the role of cellsurface mechanoreceptors (mainly β1integrin subunit) in the cell apoptosisinduced by the mechanical forces in vivo. To explore the correlationbetween β1integrin expression and annulus fibrosus (AF) cell apoptosis invitro and the possibility of apoptosis inhibition in AF cells by β1integrinlentiviral transduction.Methods A3-D fnite element model of the lumbar spine withdegeneration at the L4–L5disc level was used to analysis the mechanicalproperties of degenerative and adjacent levels under various loading. Ratlumbar IVDD induced by unbalanced dynamic and static forces wasperformed to assess disc apoptosis and examine the involvement ofmechanoreceptors (integrin, DDR2, BK channel, and TRPV4). Cyclictension of20%deformation at0.5Hz was applied on cultured AF cells andAF cells with ITGB1gene over-expression using a Flexercell Tension Plussystem. Apoptosis was detected by flow cytometry and Hoechst33258staining and Caspase activity assay. Furthemore, expression of β1integrinand activation of the intracellular signaling pathway were assessed byWestern blotting.Results Disc degeneration affected intradiscal pressure and motionpatterns of degenerative and adjacent disc levels. In the rat IVDD model,unbalanced dynamic and static forces induced apoptosis of disc cells, whichcorresponded to decreased expression of β1integrin. Cyclic stretch-inducedapoptosis in rat AF cells correlated with the activation of caspase-9and caspase-3and decreased levels of β1integrin. We showed that ERK1/2phosphorylation decreased and the phosphorylation of JNK, p38increasedduring applied cyclic tension and that these changes correlated partly withthe onset of AF cells apoptosis. However, the overexpression of β1integrinin lentivirus-transducted AF cells ameliorated cyclic elongation-inducedapoptosis and decreased caspase-3activation.Conclusions IVDD changed the loading and the motion patterns at thediseased and adjacent disc levels. Our results identify a novel role for beta1integrin in regulating AF cells apoptosis through a FAK/src-MAPKsignaling pathway in response to mechanical overload. Further studies arenecessary to identify the mechanisms underlying IVD pathology induced bymechnical stimulus.