Protective effects of cannabinoid receptor 2 on annulus fibrosus degeneration by upregulating autophagy via AKT-mTOR-p70S6K signal pathway

As an important pathological process, annulus fibrosus (AF) degeneration contributes greatly to intervertebral disc degeneration (IVDD). Moreover, extracellular matrix (ECM) degradation and AF cell (AFC) autophagy are of utmost importance. The involvement of cannabinoid receptor type 2 (CB2) in the pathological mechanisms underlying different diseases has been demonstrated due to its capacity to regulate autophagy. The objective of this study was to explore the impact of CB2-induced autophagy on AF degeneration and its underlying mechanism. First, the expression of CB2 in human degenerative AF tissues decreased with increasing degeneration degree, whereas its expression in rat AFCs increased in a concentration- and time-dependent manner following H2O2 intervention. Activation of CB2 increased collagen I and II expression while decreasing MMP3 and MMP13 expression. In addition, p62 expression decreased, whereas beclin-1 and LC3-II/LC3-I expression increased after JWH133 intervention. After CB2 activation, the addition of 3-MA impeded the synthesis of collagen I and II while preserving the elevated levels of MMP3 and MMP13. The activation of CB2 greatly suppressed the protein levels of the AKT/mTOR/p70S6K signaling pathway. In vivo, the JWH133 group exhibited elevated disk height index (DHI) and MRI signals, along with a comparatively intact structure of the intervertebral disc in contrast to the vehicle group. In general, CB2 activation could modulate apoptosis and autophagy in rat AFCs, thereby mitigating the advancement of IVDD. Moreover, the AKT/mTOR/p70S6K signaling pathway plays a role in the development of AF degeneration through the regulation of autophagy. The findings suggest that CB2 is a potentially effective therapeutic target for IVDD.