The Significance And Relevance Between The Expressions Of Hypoxia-inducible Factor-1α (HIF-1α) And Cylooxygenase-2 (COX-2) In Lumbar Disc Herniation

BackgroundThe local pathological anatomy and pathological physiology changes caused by lumbar degenerative changes not only can lead to disc dysfunction and lumbar spinal canal stenosis, but also may affect the stability of the motion segment and abnormal activity which can also further exacerbate the intervertebral disc degeneration. Many studies had confirmed that intervertebral disc degeneration be the first step of the spinal degeneration. Therefore, degeneration of lumbar intervertebral disc is the premise and basis pathological process of a series of lumbar degenerative disease. There are many clinical manifestations of lumbar degenerative disease such as lumbar spinal stenosis, lumbar segmental instability and lumbar disc herniation. Recently, the exact mechanism attracted lumbar intervertebral disc degeneration is still inconclusive. The occurrence of lumbar disc degeneration in addition to the traditional mechanical factors, neuro-psychological factors and biochemical factors, but also closely related to immune response. In recent years, with the rapid development of molecular biology and molecular immunology, the cytokines and inflammatory mediators had played an increasingly important role in intervertebral disc degeneration. A large number of studies have shown that degenerated intervertebral disc tissue could produce inflammatory mediators, which has been considered to be one of the main factors leading to intervertebral disc degeneration. With the in-depth study, the important role of neovascularization in intervertebral disc degeneration has increasingly attracted the researchers. In early days, some scholars abroad found some vascular structures in the degenerated lumbar intervertebral disc and they also confirmed that vascular structure was found to be more prevalent in intervertebral disc herniation. Therefore, they believed that the angiogenesis play an important role in the intervertebral disc degeneration process. However, there are two different views about the role of the angiogenesis in the intervertebral disc degeneration process. Some scholars believed that the angiogenesis was the body trying to repair tissue damage and the spontaneous reaction to delaying the process. Thus it was considered to be useful for the body. While others believed that the disc vascularization caused disc degeneration occurs and it was the pathological basis of disc degeneration, so it was harmful to the body.Cyclooxygenase-2 (COX-2) factor is a multifunctional protein highly expressed in many malignant tissues, which closely related to tumor cell proliferation, apoptosis and angiogenesis. And this correlation is manifested mainly about the regulation COX-2 does to tumor angiogenesis process. The study has already been confirmed that neovascularization is very in common in degenerative disc, so whether the role of COX-2 factor played in the vascularization of intervertebral disc degeneration as well as in the formation of vascular structure in tumor tissue? And COX-2 factors is a rate-limiting enzyme to catalysts arachidonic acid into prostaglandins material. The researchers first discovered that the concentration of prostagland materials in the degenerative disc was significantly higher than the normal disc. Prostaglandins substances can inhibited disc cells proteoglycan synthesis, while the reduce of nucleus pulposus proteoglycan content is an important reason leading to disc degeneration occurs. Some studies have shown that factor COX-2 expression was significantly higher in degeneration of human intervertebral disc tissue than normal levels, and related clinical studies have shown that selective COX-2 inhibitors can significantly reduce the inflammatory response in patients with disc herniation.Hypoxia-inducible factor-1 (HIF-1α) was initially discovered in 1992. It is an oxygen-dependent transcriptional activator and can trigger the transcription of downstream genes through a hypoxia response element (HRE) binding. HIF-la is an important molecule for cells to adapt to the hypoxia and can increase the expression of erythropoietin, glucose receptors, glycolytic enzymes andvascular endothelial growth factor and regulate the cells apoptosis. When the tumor grows rapidly, it will definitely lead to serious local tissue hypoxia and induce the expression of HIF-la. Previous studies suggested that insufficient supply of nutrients in intervertebral disc degeneration could result in a relatively hypoxic environment of local disc. Therefore, some scholars have proposed that whether there are any expressions of HIF-la in the human lumbar intervertebral disc. And then they confirmed that the expression of HIF-la was significantly higher than the normal disc by the method of the immunohistochemistry.ObjectivePrevious studies had shown that cyclooxygenase-2 (COX-2) and hypoxia-inducible factor-1 (HIF-la) were important factors in the angiogenesis in tumor tissue and the expression of COX-2 and HIF-la have even been confirmed in the human intervertebral disc. However, researches were limited to the role and the mechanism of these two factors in the process of disc degeneration, respectively. Therefore, exploring the expression correlation of these two factors in degenerative intervertebral disc tissue and the correlation with the neovascularization in degenerative intervertebral disc will be very significant. So in this study, on one hand, we are trying to further reveal and improve the mechanism of disc degeneration; On the other hand, it will be great importance to development of the assay for the early prevention and treatment of intervertebral disc degeneration.MethodsAfter information consent, we collected the degenerated and normal intervertebral disc tissue of the patients which removed during the surgical operation. And then the selected tissue was made for pathological slices. Immunohistochemical techniques were used to indicate the expression of COX-2 factor and HIF-la factor in degenerated and normal intervertebral disc and count the density of microvessels in degenerated intervertebral disc. Finally, describe the relationship between the COX-2 factor and HIF-la factor and the expression of micro vessel density (MVD) respectively in and COX-2 group and HIF-1αgroup through statistical methods.Result1. Optical microscopy resultsAfter the normal nucleus pulposus tissue sections stained by HE dyed, we can see that the thickness of collagen fibers are uniform and arranged parallel to each other. And we could even see a small amount types of chondrocytes under the optical microscopy. But in the degenerated intervertebral disc, the collagen fibers were disarrangement with significant hyperplasia. Hyaline degeneration and large number of honeycomb-like, vesicle-like cavities and cracks can be seen in nucleus pulposus matrix.2. Immunohistochemical resultsThe immunohistochemical dyed revealed that the expression of COX-2 and HIF-la in the normal disc were both too weak to be observed, but they significantly increased in the degenerated nucleus pulposus. The positive expression of COX-2 in degenerative intervertebral disc was at a rate of 42.5%. Positive particles can be observed in most of the cytoplasm ormembrane. However, the positive expression of HIF-la in degenerated intervertebral disc was at a rate of 45%. Positive particles can be observed in most of the cytoplasm or nucleus.3. Statistical resultsThe expression of COX-2 and HIF-lain degenerative intervertebral disc tissue had a significant positive correlation by the Spearman rank correlation analysis (P <0.01, r= 0.406). By the independent samples t test, MVD in the HIF-la-positive group was higher than negative group in degenerative intervertebral disc (t=-4.052, P= 0.000), as well as in COX-2 group (t=-5.103, P= 0.000).Conclusions1. The expression of COX-2 factor and HIF-1αfactor in the degenerated nucleus pulposus tissue significantly increased.2. There was a positive correlation between the expression of COX-2 factor and HIF-1αfactor in degenerated nucleus pulposus tissue.3. MVD in HIF-1α-positive group was higher than HIF-1α-negative group in degenerated intervertebral disc tissue.4. MVD in COX-2-positive group was higher than COX-2-negative group in degenerated intervertebral disc tissue.