Abstract
Hypoxia-inducible factor-1α (HIF-1α) has been reported to have an important role in the metabolism and synthesis of extracellular matrix of the nucleus pulposus cells (NPCs) and was assumed to be involved in the process of intervertebral disc degeneration. The objective of this study was to investigate the role of HIF-1α in disc degeneration in vivo using a conditional HIF-1α knockout (KO) mouse model. ShhCre transgenic mice were mated with HIF-1α fl/fl mice to generate conditional HIF-1α KO mice (HIF-1α fl/fl -ShhCre+). Three mice of each genotype (Wide-type and HIF-1α KO) at the age of 3 days, 6, and 12 weeks were sacrificed after genotyping. Five lumbar disc samples were harvested from each mouse, with a total of 45 disc samples for each genotype. In situ hybridization and immunohistochemical analysis were used to check the efficacy of HIF-1α knockout. Histological grading of the disc degeneration was performed according to the classification system proposed by Boos et al. Picro-sirius red staining, Safranine O/fast green staining and immunohistochemical study were used to evaluate the expression of aggrecan, type-II collagen and vascular endothelial growth factor (VEGF). Histologic analysis revealed more NPC deaths and signs of degeneration in HIF-1α KO mice and the degeneration scores of HIF1-α KO mice were significantly higher than those of the Wide-type mice at the age of 6 weeks and 12 weeks. There were less expressions of aggrecan, type-II collagen and VEGF in the intervertebral discs of HIF1-α KO mice than in those of wild-type mice. Taken together, the results of our study indicated that HIF-1α is a pivotal contributor to NPC survival and the homeotasis of extracellular matrix through the HIF-1α/VEGF signaling pathway, and plays an important role in the development of disc degeneration.