MicroRNA-199 has been reported to play a potential role in the apoptosis of Human nucleus pulposus cells. However, the effect of miR-199 in regulating Human nucleus pulposus cell injury induced by TNF-alpha has not been previously illustrated. This study searched to probe the effect and the molecular mechanism of miR-199 on Human nucleus pulposus cell injury induced by TNF-alpha. Using the TNF-alpha. model of Human nucleus pulposus cell in vitro, we found that miR-199 was extremely decreased in Human nucleus pulposus cells after TNF-alpha. treatment. Knockdown the expression of miR-199 by recombinant adeno-associated viral vector infection markedly promoted the apoptosis of Human nucleus pulposus cells induced by TNF-alpha treatment, whereas miR-199 overexpression significantly decreased Human nucleus pulposus cell apoptosis. Both Dual-luciferase reporter and western blot assay proved that MAP3K5 was a direct target gene of miR-199, and miR-199 inhibited the expression of MAP3K5 via binding to its 3'-UTR. Furthermore, we proved that overexpression of miR-199 could inhibit the expression of MAP3K5 at the transcription and translation levels, whereas the inhibition of miR-199 could upregulate the expression of MAP3K5. Moreover, MAP3K5 was highly expressed in TNF-alpha. treated Human nucleus pulposus cells and the apoptosis rate induced by TNF-alpha was associated with the increase in MAP3K5 expression. Importantly, knockdown the expression of MAP3K5 apparently abrogated the inhibitory effect of miR-199 mimics on TNF-alpha. induced Human nucleus pulposus cell apoptosis. In conclusion, these results indicate that upregulation of miR-199 could inhibit Human nucleus pulposus cells injury through downregulation of MAP3K5 expression, providing an important molecular target mechanism for Human nucleus pulposus cells injury. (C) 2018 Elsevier Inc. All rights reserved.