Expression of fibronectin and TGF-ß1 mRNA and protein suggest altered regulation of extracellular matrix in degenerated disc tissue

We studied the distribution of fibronectin (a marker for “active” reparative connective tissue processes) and TGF-β1 (a cytokine controlling the connective tissue metabolism) in intervertebral disc tissue from individuals of different age and various histomorphological evidence for tissue degeneration. The protein deposition was determined by immunohistochemistry on 30 complete cross-sections of lumbar spine obtained at autopsy (0–86 years) and 12 surgically removed disc samples. The mRNA expression was detected by non-radioactive in situ hybridization in the surgical material. All control experiments (blank and isotype controls in immunohistochemistry/sense controls in in situ hybridization) were negative. Immunohistochemically, we detected enhanced staining for fibronectin in both nuclear and anular tissues in areas with histological signs of mild-to-severe tissue degeneration (e.g., cleft formation and cell clustering) beginning with 16 years of age. Anular tissue showed less fibronectin staining than did nuclear areas. Fibronectin mRNA was detected mainly in nuclear cells by in situ hybridization corresponding to the protein staining indicating de novo synthesis. In parallel, TGF-β1 was expressed by nuclear and occasional anular cells spatially associated with the fibronectin synthesizing cells. This was seen by both immunohistochemistry and in situ hybridization. This preliminary study provides evidence for a significant ongoing rearrangement of the extracellular matrix during disc degeneration, as monitored by enhanced fibronectin deposition that is produced by local disc cells. These cells also synthesize TGF-β1, as shown by protein and mRNA expression. Since it is known that TGF-β1 induces matrix alterations (by auto and paracrine stimulation of matrix synthesis), these observations suggest that the recently described disturbance of the matrix during disc degeneration may be induced by TGF-β. This may offer new approaches to interfere with disc matrix alterations.