circSKIL promotes the ossification of cervical posterior longitudinal ligament by activating the JNK/STAT3 pathway

Ossification of the posterior longitudinal ligament (OPLL) is a hyperostotic spinal condition that involves genetic factors as well as non-genetic factors, and its underlying molecular mechanism is largely unknown. Recently, circular RNAs (circRNAs) have been attracting the attention of researchers since they have important regulatory roles in many diseases, including bone metabolism disorders. The present study aimed to investigate the role of circRNA SKI-like proto-oncogene (circSKIL) in OPLL disease progression. First, primary posterior longitudinal ligament cells from patients with cervical spondylotic myelopathy (CSM) without OPLL (control group) and CSM patients with OPLL (OPLL group) were isolated, and the expression levels of circSKIL in ligament cells was found to be significantly increased in the OPLL group compared with control. This result was also confirmed in OPLL tissues. Next, circSKIL was overexpressed in control ligament cells, and the proliferation, mineralization, and osteogenic differentiation of ligament cells were found to be significantly enhanced; the phosphorylation levels of both JNK and STAT3 were upregulated. By contrast, the knockdown of circSKIL in OPLL ligament cells inhibited proliferation, mineralization, and osteogenic differentiation and inactivated the JNK/STAT3 pathway. Therefore, circSKIL may have a significant role in osteogenic differentiation and could serve as a potential target to prevent OPLL progression.