Do Angiotensin II receptors play a role in cerebellar development and neuronal migration?

Abstract

Angiotensin II (Ang II), the active peptide of the renin–angiotensin system, binds and activates two major receptor subtypes, namely AT1 and AT2. The classical effects of Ang II in the control of blood pressure and fluid homeostasis are mediated by AT1 receptors. The AT2 receptor is involved in vasodilatation, inhibition of the cell proliferation, induction of programmed cell death and cellular differentiation. Ang II AT2 receptor expression is highly modulated during development. In the fetus, AT2 receptors predominate in all tissues and decline shortly after birth, being restricted to a few organs including brain. Interpretation of the function of Ang II in cerebellum necessitates a thorough understanding about the localization and signal transduction of Ang II receptors. A clear complementary pattern of AT1 and AT2 binding labeled by [125I] Ang II was observed on adjacent layers in young rats within the cerebellar cortex. By using specific markers of the Purkinje cells (PCs) (Zebrin II and calbindin28K), we demonstrated that Ang II AT2 receptors co-localized with the PCs as a monolayer, in correspondence with the well- defined layer observed by binding autoradiography at differential developmental stages (P0 to P60). Blockade of AT2 receptors with PD12319 during late pregnancy caused a lost of AT2 binding in the external granular layer (EGL) in P0 pups. A detailed histological analysis evidenced an enlarged EGL in the cerebellar cortex. It is well known that PCs migrate early during fetal stage (E14) toward the cerebellar cortex. Aiming to elucidate the non-classical signaling pathway of Ang II AT2 receptors in rat hindbrain we selected PND15, a critical developmental stage. Following Ang II stimulation, SHP-1 associates to AT2 receptors but not to AT1 subtype. Immunocomplexes obtained with anti-AT2 or anti-SHP-1 exhibited PTPase activity, blocked by PD123319 (AT2 antagonist) or PP2. SHP-1 activation was correlated with tyr-phosphorylation level of SHP-1 in immunocomplexes. Both immunocomplexes contained c-Src and PP2 blocked SHP-1 tyr-phosphorylation as well as activation and association SHP-1 to c-Src. Taken together, the localization of AT2 receptors in the Purkinje cells, the effect of blockade during late pregnancy on the development of the cerebellar cortex and the signal transduction mechanisms, a potential role for AT2 receptors can be assigned on neuronal migration and cerebellar cortex organization.