Functional expression of corticotropin-releasing hormone (CRH) receptor 1 in cultured rat microglia

Corticotropin-releasing hormone (CRH), known as a key regulator of the hypothalamic-pituitary-adrenal axis response to stress, elicits its biological effects by binding to two membrane receptors (CRH-R1 and CRH-R2). The present studies examined the presence of functional expression of CRH receptors in cultured microglia of rat. CRH-R1 mRNA and protein were detected by reverse transcriptase polymerase chain reaction (RT-PCR), western blotting and receptor chemical cross-linking assay in cultured microglia. CRH-R2 mRNA was undetectable by RT-PCR. The radioligand binding analysis using [125I]Tyr-rat/human CRH revealed a high affinity binding site (Kd of 1.2 nm and Bmax of 84 fmol/mg of protein). Competition studies using CRH and related peptides indicated kinetic and pharmacological characteristics consistent with the CRH-R1 receptor subtype. Receptor chemical cross-linking assay demonstrated a single band of CRH receptor with a molecular weight of -77 kDa, which was inhibited in the presence of excess unlabeled rat/human CRH in a dose-dependent manner and inhibited by a CRH receptor antagonist astressin. Functional coupled cAMP production in cultured microglia was stimulated by exogenous addition of CRH and related peptides in a dose-dependent manner and blocked by astressin. Our findings suggest the functional expression of CRH-R1 receptor in rat microglia, indicating an important mechanism of interaction between immune and neuroendocrine systems in brain physiological and pathological conditions.