The Expression Of Netrin-1in Lumbar Degenerative Disc Diseases

BackgroundChronic low back pain is a common symptom in daily life and work,and is an most frequently disease in orthopedic clinic activity. Accordingto literatures, up to50%-80%people suffer from chronic low back painin different stage of their whole lifetime. Further,24%-87%patientswith chronic low back pain would reoccur within one year after initialpain disappearing. Low back pain costs billions of dollars in Americaevery year. Therefore, low back pain is a general healthy problem inpeople influencing people’s work and study severely, and it developssocial-economic problem increasingly. A variety of causes can lead tolow back pain, and lumbar discogenic pain accounts for approximately39%cases. Differentiating from the aging intervertebral discs (IVDs), thedegenerated IVDs develop tears and/or clefts in the posterior anulus fibrosus during degenerating into which nerve fiber accompanied byvascular granulation tissue grow, which is an important pathology of painbelieved by many authors. Thus, studies on the mechanisms of theneurovascular ingrowth might interpret the mechanisms of discogenicpain depending on which new methods or ideas might be found fortreatment of low back pain.Degenerative cascade is the widely accepted pathophysiologic modeldescribing the lumbar disc degenerative process as it affects the lumbarspine. This process occurs in3phases that comprise a continuum withgradual transition. Phase I is the dysfunctional phase, which ischaracterized histologically by tears or fissures in the outer annulus.Tears can be accompanied by endplate separation or failure, interruptingblood supply to the disk and impairing nutritional supply and wasteremoval. Since the outer one third of the annular wall is innervated, tearsor fissures in this area may be painful. Circumferential tears may coalesce to form radial tears. The nucleus pulposus may lose its normalwater-imbibing abilities. MRI at this stage may reveal desiccation, diskbulging without herniation, or a high-intensity zone (HIZ) in the annulus.The phase II is the unstable phase. The trijoint complex including IVDsand facet joint loses its mechanical integrity progressively as a result oflosing water and height. Disk-related changes include multiple annulartears, internal disk disruption (IDD) and resorption, or loss of disk-spaceheight. Phase III is the final stage, stabilization. The characteristics arefurther disk resorption, disk-space narrowing, endplate destruction, diskfibrosis, and osteophyte formation. Discogenic pain from such IVDs mayhave a higher incidence than that of the pain from the discs in phases Iand II; however, great variation of phases can be expected in differentdiscs in any given individual and individuals of similar ages vary greatly.At present, no report has described the factors which direct theneurovascular pathfinding into the inner part of IVDs during the progress of IVDs degeneration. Netrins are important chemoattractive factorsdirecting axonal pathfinding in the development of central nerve system.Netrins guide or repulse axonal growth and induce cells migration,adhesion and survival via different receptor. Recent studies have shownNetrins as angiogenic factors playing similar role in vascularization.Netrin-1is the most studied factors in the family of Netrins. Indeveloping, netrin-1is not only involved in the development of nervesystem but in the development of vascularity and other organs formation;in adult, netrin-1is involved in other pathophysiologies such asinflammatory diseases, tumor formation, regeneration of nerve injury,degenerative osteoarthritis, myocardial ischemia, acute kidney injurypostcardiac surgery.ObjectiveTo evaluate the histological scores and imaging grades of human IVDs specimens; to explore the expression of Netrin-1and deleted incolorectal carcinoma gene receptor in the specimens; to explore themRNA of Netrin-1in the specimens; to score the neurovascular ingrowth.The correlation between the expression of netrin-1and the scores of theneurovascular are analyzed. To provide new ideas and theoretical basisfor the further studies on the mechanisms of low back pain animally andclinically and for developing new treatment for the pain.Materials and methodsSurgical specimens of IVDs were collected from patients with lowback pain undergoing posterior lumbar intervetebral fusion, and normallumbar IVDs were collected at autopsy. The magnetic resonanceimagings grades were evaluated. Histological scores of IVDs wereevaluated by H&E staining and Alcian blue-PAS staining. Netrin-1, DCC,NF and CD34were stained immunohistochemically to evaluate the scores respectively. The mRNA of Netrin-1was studied by RT-PCR inthe two groups of specimens.Results35surgical specimens presents moderate to sever degenerationhistologically, graded II-IV on MR imagings, while the specimens fromcadavers appeared normal to mild dengeneration; Netrin-1and DCCwere expressed substaintially in34from35specimens, and Netrin-1localized in the cell membrane and in the extracellar matrix, while DCCin the membrane only. Netrin-1and DCC were expressed slightly in7of8normal discs, the localization of Netrin-1and DCC were similar tothose in surgical specimens, but not in the extracellar matrix. TheNetrin-1and DCC immunopositive cells included fibroblast-like cells,chondrocyte-like cells, vascular endothelial cells and other cells in thegranulation tissue in the surgical specimens. Netrin-1immunopositive cells in the nucleus pulposus were more than that in the annulus fibrous(inmmunopositivity in endothelia cells and granulation cells were notcounted). In contrast, Netrin-1and DCC immuonpositive cells in theautopsy specimens included fibroblast-like cells, chondrocyte-like cells.And DCC immunopositive cells were more in the surgical specimens(70%) than that in the controls (33%). Neurovascular ingrowth was foundin33surgical specimens while nerve and vessels were found in the outerpart of annulus fibrous in2and3normal specimens respectively. Therewas positive correlation between Netrin-1positivity, socres ofneurovascular ingrowth (0.59and0.67respectively). Nonsignificantnegative correlation between age and Netrin-1positivity was found. Nocorrelation was found in between the Netrin-1positivity and grade onMR imagings. The mRNA of Netrin-1has not been detected in onespecimen in each group respectively. The mRNA of Netrin-1is higher insurgical specimens than that in the controls. ConculsionNetrin-1and its DCC receptor in the chronic low back pain resultedfrom disc degeneration were expressed more than those in the normalintervertebral discs. The increased expression and the distribution ofNetrin-1and DCC indicated they might be involved in the process of theneurovascular ingrowth with the mechanisms being studied further. Theimplication of Netrin-1and DCC in the normal discs needs to be studiedfurther.