Association Between The Expression Of Aggrecan And The Distribution Of Aggrecan Gene VNTR With Symptomatic Lumbar Disc Herniation

ObjectiveThe majority of patients with symptomatic lumbar disc herrniation (LDH) presented with leg and back pain. Despite numerous studies of its etiology and pathogenesis, it is not clear why susceptivity of symptomatic LDH is low in some individuals while high in others.LDH, degeneration, and herrniation of the nucleus pulposus of intervertebral disc in the spine, constitute some of the most common musculoskeletal diseases. LDH occurs when the nucleus pulposus protrudes from the defective disc due to degeneration, a common and important cause of leg and back pain. The traditional etiology of LDH, primarily due to age, occupation, smoking, and exposure to vehicular vibration, dominated much of this past century. The contribution of other factors such as height, weight, and genetics is less certain. In recent years, however, a dramatic advance has been made in our understanding of genetic influences on the risk for disc degeneration, thus changing our traditional views. Genetic factors, in particular, may be largely responsible for the degeneration as well as herniation of intervertebral discs.Aggrecan is the major proteoglycan of hyaline cartilage, and it is present at very high concentrations in the form of aggregates, which create osmotic swelling pressure gradients that draw water into the tissue. The aggrecan has 3 globular domains (G1, G2, and G3), a short interglobular domain (IGD) between domains G1 and G2, and a long glycosaminoglycan (GAG) attachment region between domains G2 and G3 that consists of adjacent domains of keratan sulfate (KS) and chondroitin sulfate (CS). The glycosaminoglycan chain structures vary throughout life as keratan sulfate chains become longer and the CS chains become shorter in the adult.A study showed that reduced aggrecan content may lead to an inability of the discs to resist mechanical load and thus alter the repair processes. Therefore, it is reasonable to consider the possibility that the genes coding for aggrecan could play a role in the genetic predisposition of symptomatic LDH.Analysis of cDNA sequences for human aggrecan revealed that the serine-glycine pairs occurr in patterns of repeating sequences, designated the CS-1 repeat regions. The human aggrecan gene is unique amongst species analyzed to date in possessing variable number of tandem repeat (VNTR) polymorphism. The polymorphism has repeats of 57 nucleotides, encoding each 19-amino acid unit. The described alleles range from 13 to 34 repeats. The most common alleles possess 26,27 or 28 repeats. It is readily apparent that individuals possessing the longer alleles have the potential to produce aggrecan bearing a greater number of CS chains to a proteoglycan core protein, thereby changing functional properties of cartilage.This study aims to ascertain if the distribution of aggrecan VNTR polymorphism and expression of aggrecan are associated with symptomatic LDH.MethodsThe disease group comprised of 70 patients already diagnosed with symptomatic LDH. The control group consisted of 14 patients restricted to spinal trauma and 113 healthy blood donors without symptoms of LDH who were not diagnosed with LDH. Disc tissue samples were obtained from surgical operations and blood samples were donated from all participants. The aggrecan expression in isolated tissues was assessed by western blot using specific antibodies. The aggrecan gene VNTR region was analyzed by PCR.ResultsThe aggrecan expression positive rate of control group was statistically and significantly higher (P<0.001) than that of the disease group. Moreover, there was a statistically significant higher frequency of Allele 25 or Allele 21 in disease group compared to controls (PA25=0.003416; PA21=0.000716). Compared to the participants with 2 Alleles> 25 repeats, subjects with 1 or 2 Alleles≤25 repeats statistically and significantly overrepresented the disease group without the expression of aggrecan (P<0.001). ConclusionThe findings suggest a relation between aggrecan and symptomatic LDH, where symptomatic LDH has a lower tendency of allele repeats. In addition, this study observed an association between the distribution of aggrecan gene VNTR polymorphism and the expression of aggrecan in symptomatic LDH.