Purpose: Transforming growth factor-beta (TGF-beta) superfamily consists of many multifunctional cytokines including TGF-beta, activins, and bone morphogenetic proteins (BMPs). Previous reports show that these factors are expressed in ocular tissue, and exert their effects through type I and type II serine/threonine type receptors. The purpose of this study is to observe the expression of these receptor families in normal rat eyes as the first step in investigating the functions of TGF-beta superfamily members in ocular tissue.
Methods: The expression of receptors was examined immunohistochemically in one eye each of 6 Lewis rats. The type I receptors examined were the TGF-beta type I receptor (TbetaR-I), activin type I receptor (ActR-I), activin type IB receptor (ActR-IB), bone BMP type IA receptor (BMPR-IA), BMP type IB receptor (BMPR-IB), and activin receptor-like kinase-1 (ALK-1). The type II receptors examined were TGF-beta type II receptor (TbetaR-II), activin type II receptor (ActR-II), and BMP type II receptor (BMPR-II).
Results: All 6 type I receptors, ActR-II and the alternative spliced long version of BMPR-II were expressed in the following cells: corneal and conjunctival epithelium, corneal keratocytes, corneal endothelium, epithelium of iris and ciliary body, epithelium of lens, sensory retina excluding the outer segments of photoreceptors, retinal pigment epithelium (RPE), and vascular cells. TbetaR-II and the short version of BMPR-II (truncated form) were expressed in the outer segments of the photoreceptors in addition to the above. The results of staining were similar in all the sections examined.
Conclusions: The cornea, ciliary body, iris, lens, retinal cells, RPE and vascular cells expressed the receptors for TGF-beta superfamily at protein level.