INTRODUCTION: Angiotensin II (Ang II), the primary effector of the renin‐angiotensin system (RAS), is classically known as an endocrine regulator of blood pressure. However, recent studies have shown that locally produced Ang II that is called the “tissue renin‐angiotensin system (tRAS), contributed to the process of inflammatory diseases in several types of tissues. The expression of tRAS in intervertebral disc (IVD) is unknown. The purpose of this study was (1) to determine if rat IVD cells express the tRAS, and (2) to examine the effect of tRAS activation on the matrix metabolism, and (3) to examine the effects of a pro‐inflammatory cytokine on the expression of tRAS by rat IVD cells.
METHODS: Expression analysis: Lumbar IVDs were harvested from rat spines. The IVD cells were isolated by enzyme digestion and were cultured in monolayer. The expression of the tRAS components (angiotensinogen [AGT], angiotensin‐converting enzyme [ACE], Ang II type I receptor [AT1] and Ang II type II receptor [AT2]) in IVD cells was analyzed by real‐time PCR and immunohistochemistry. Functional analysis: IVD cells were cultured in the presence of Ang II peptide, and the effect of Ang II on matrix synthesis was analyzed by real‐time PCR. The expression of tRAS components with/without rhIL‐1β stimulation was analyzed by real‐time PCR.
RESULTS: In rat IVD cells, the expression of each tRAS component (AGT, ACE, AT1 or AT2) was confirmed at the mRNA level by quantitative‐PCR and at the protein level by immunohistochemistry. Stimulation of the rat IVD cells with Ang II peptide significantly increased mRNA expression of Type1 and Type2 collagen and Aggrecan. The mRNA expression of each tRAS components was significantly down‐regulated by stimulation with rhIL‐1β.
DISCUSSION: The results of our study suggest that the expression of tRAS, which is controlled by pro‐inflammatory cytokines, may contribute to the process of IVD degeneration.