A Continuous Observation of the Degenerative Process in the Intervertebral Disc of Smad3 Gene Knock-Out Mice

Study Design. Pathologic changes were observed in the spine of small mother against decapentaplegic (Smad) 3(-/-) mice at different time points. Objective. To observe the degeneration of the intervertebral disc (IVD) in Smad3 gene knock-out mice with growth. Summary of Background Data. Smad3 gene knock-out (Smad3(-/-)) mice displays phenotypes similar to human osteoarthritis. Despite the similarities between IVD cartilage endplate and the articular cartilage, there has been relatively little interest in exploring the possibility that IVD degeneration might be driven by the deficiency of Smad3. Methods. The Smad3(-/-) mice were killed at the 10th, 30th, and 60th day after their birth and the IVD samples of spine were harvested for histologic and immunohistochemical studies. Total RNA isolated from these samples were used for real-time PCR analysis of type II collagen (Col2 alpha 1), type X collagen (Col10 alpha 1), aggrecan, and transforming growth factor-beta 1 (TGF-beta 1). Results. Compared with the wild-type mice, Smad3(-/-) mice appeared significantly smaller in size. Radiograph showed that the spine of Smad3(-/-) mice is malformation and kyphosis. Histologic analysis revealed the declined height of cartilage endplate, decreased proteoglycan and collagen content in disc of Smad3(-/-) mice. With growth, especially of the 30- and 60-day old Smad3(-/-) mice, the protein positive staining of type II collagen, aggrecan, and TGF-beta 1 in the disc decreased, while that of type X collagen increased. And the analysis of real-time PCR showed that the mRNA expression of Col2 alpha 1, aggrecan, and TGF-beta 1 decreased, while that of Col10 alpha 1 increased. Conclusion. Smad3 gene knock-out mice develop IVD degeneration with growth.