Smad7 Is Highly Expressed in Human Degenerative Discs and Participates in IL-1 β-Induced Apoptosis of Rat AF Cells via the Mitochondria Pathway

by Selleckchem | Jun 03 2023

Background: Abnormal Smad7 expression can lead to apoptosis in different cell types. Previously, we found high expression of Smad7 in rat degenerative discs. However, the exact role of Smad7 in the apoptosis of disc cells and the possible underlying mechanism remain unclear.

Methods: Degenerative and nondegenerative human lumbar intervertebral discs were collected from patients during operation. The expressions of SMAD7 mRNA and protein in the different components of these discs were measured with real-time PCR and Western blotting, respectively. Annulus fibrosus (AF) cells were isolated and cultivated from the discs of young healthy rats. Smad7 in the AF cells was overexpressed with adenovirus and knocked down with siRNA. IL-1β was used to induce apoptosis in the AF cells. Loss-and-gain cell function experiments were performed to show the effect of Smad7 on the apoptosis of AF cells. The function recovery experiments were performed to verify whether Smad7 regulates the apoptosis of AF cells through the mitochondria-mediated pathway.

Results: Both the mRNA and protein expressions of Smad7 were significantly higher in the different components of human degenerative discs than in those of the nondegenerative discs. IL-1β stimulated apoptosis while upregulating the Smad7 expression in the AF cells in vitro. Overexpression of Smad7 in AF cells exaggerated the IL-1β-induced apoptosis in the cells while knockdown of Smad7 expression suppressed this apoptosis. With the exaggerated apoptosis in the AF cells with Smad7 overexpression, both active cleaved caspase-3 and cleaved caspase-9, the ratio of Bax/Bcl-2, and Cyt-c increased significantly. However, the inhibitor of caspase-9, Z-LEHD-FMK, significantly diminished the apoptosis in these cells.

Conclusion: Smad7 is highly expressed in human degenerative discs and participates in IL-1β-induced apoptosis of rat AF cells via the mitochondria pathway. Smad7 may be a potential target for the prevention and treatment of degenerative disc disease.

Comments：

In summary, this study investigated the role of Smad7 in the apoptosis of disc cells in degenerative discs and the underlying mechanism. The researchers found that the expression of Smad7 was significantly higher in the different components of human degenerative discs compared to nondegenerative discs. In vitro experiments using rat AF cells showed that IL-1β induced apoptosis and upregulated the expression of Smad7. Overexpression of Smad7 in AF cells exaggerated the IL-1β-induced apoptosis, while knockdown of Smad7 expression suppressed apoptosis. The study also showed that Smad7 regulates apoptosis through the mitochondria-mediated pathway, as evidenced by changes in the expression of active cleaved caspase-3 and cleaved caspase-9, the ratio of Bax/Bcl-2, and Cyt-c. The inhibitor of caspase-9, Z-LEHD-FMK, significantly diminished the apoptosis in cells with Smad7 overexpression. These findings suggest that Smad7 may be a potential target for the prevention and treatment of degenerative disc disease.