Abstract: BACKGROUND: MicroRNA (miRNA) levels are closely related to cell apoptosis and proliferation, extracellular matrix metabolism and inflammatory response in intervertebral disc cells. However, the specific role of miR-142-3p in lumbar intervertebral disc degeneration remains unclear.
OBJECTIVE: To investigate the correlation between the expression of miRNA-142-3p, mixed lineage kinase 3 and interleukin-1β in nucleus pulposus tissue and degree of human lumbar intervertebral disc degeneration. 
METHODS: A total of 82 patients with lumbar intervertebral disc degenerative diseases in Suzhou Ninth People’s Hospital from January 2020 to March 2022 were collected as the study subjects, all of whom underwent MRI examination before operation. According to the Videman classification, the patients were divided into mild degeneration group (n=36), moderate degeneration group (n=26) and severe degeneration group (n=20). Eighty-two specimens of the nucleus pulposus were obtained. The mRNA expression of miRNA-142-3p as well as the mRNA and protein expression of mixed lineage kinase 3, interleukin-1β, type I collagen, type II collagen in nucleus pulposus tissue were detected by qPCR and western blot assay. The correlation between the degree of human lumbar intervertebral disc degeneration and the expression levels of miRNA-142-3p, mixed lineage kinase 3, and interleukin-1β was also assessed using the Spearman correlation coefficient method. Thirty adult Sprague-Dawley rats were divided into sham-operated group (executed after puncturing skin and muscle only), mild degeneration group (executed 1 week after puncturing Co7/8 segments) and severe degeneration group (executed 2 weeks after puncturing Co7/8 segments), with 10 rats in each group. After that, we detected the protein expression of mixed lineage kinase 3 and interleukin-1β as well as the gene expression of miRNA-142-3p, mixed lineage kinase 3 and interleukin-1β in the nucleus pulposus tissue.
RESULTS AND CONCLUSION: In human nucleus pulposus tissue, the miRNA-142-3p expression ranked from high to low as follows: mild degeneration group > moderate degeneration group > severe degeneration group (P < 0.05); the gene and protein expression of mixed lineage kinase 3 and interleukin-1β from low to high was as follows: mild degeneration group < moderate degeneration group < severe degeneration group (P < 0.05); the gene and protein expression of type I collagen from low to high was as follows: mild degeneration group < moderate degeneration group < severe degeneration group (P < 0.05), and the gene and protein expression of type I collagen from high to low was as follows: mild degeneration group > moderate degeneration group > severe degeneration group (P < 0.05). Spearman correlation analysis showed that the degree of disc degeneration was negatively correlated with miRNA-142-3p expression (P < 0.05) and positively correlated with mixed lineage kinase 3 and interleukin-1β expression (P < 0.05). In rat nucleus pulposus tissue, compared with the sham-operated group, the expression of mixed lineage kinase 3 and interleukin-1β gene and protein was elevated in the mild degeneration group (P < 0.05) while miRNA-142-3p expression was decreased (P < 0.05); compared with the mild degeneration group, the expression of mixed lineage kinase 3 and interleukin-1β gene and protein was increased in the severe degeneration group (P < 0.05) while miRNA-142-3p expression was decreased (P < 0.05). To conclude, the degree of human lumbar intervertebral disc degeneration is negatively correlated with miRNA-142-3p expression and positively correlated with mixed lineage kinase 3 and interleukin-1β expression in nucleus pulposus tissue. 

Key words: lumbar intervertebral disc degeneration, nucleus pulposus tissue, miRNA-142-3p, mixed lineage kinase 3, interleukin-1β, correlation