Discovery of a novel role of vasopressin in astrocytes: Vasopressin-induced cytoplasmic and nuclear calcium and kinases signaling cascade and modulation of astrocytes immune function

We sought to determine whether vasopressin V_1a receptor (V _1aR) mRNA detected in cortical astrocytes was translated into functional receptors by investigating the effector signaling cascade and gene expression associated with V_1aR. Analysis of intracellular Ca2+ ([Ca2+]_i) dynamics using the Ca2+ sensitive dyes fura-2 AM and/or fluo-3 AM indicated that exposure of astrocytes to V₁ vasopressin receptor agonist (V₁ agonist), [Phe 2, Orn8]-oxytocin, induced a marked increase in [Ca 2+]_i which was the result of influx of extracellular Ca 2+ and activation of the phosphatidylinositol signaling cascade which releases Ca2+ from endoplasmic reticulum stores. Furthermore, a rapid dynamic translocation of Ca2+ from the cytoplasm to the nucleus occurred in response to V₁ agonist. In the pursuit of the downstream consequences of V_1aR activation of Ca 2+ signaling, we demonstrated that V1aR activation led to a significant rise in PKC, CaMKII and ERK1/2 activation with CaMKII and ERK1/2 demonstrating dynamic transport between cytoplasmic and nuclear compartments. While no evidence of PKC translocation was apparent, PKC and CaM kinases were required for activation and nuclear translocation of ERK1/2. Subsequent to CaMKII and ERK1/2 translocation to the nucleus, CREB activation occurred and was found to be dependent upon upstream activation of ERK1/2 and CaM kinases. Because astrocytes can exert immune effects analogous to immune cells in the periphery, we further investigated vasopressin regulation of cytokine gene expression in astrocytes. Results from gene array, RT-PCR and ELISA studies indicated that vasopressin dramatically decreased the mRNA and peptide levels of two important pro-inflammatory cytokines, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), suggesting an immunomodulatory function of vasopressin in astrocytes in vitro. This cytokine suppression was dependent on the upstream CREB activation and was demonstrated to be neuroprotective. To our knowledge, this is the first documentation of a vasopressin receptor-induced nuclear Ca2+ signaling and modulation of cytokine gene expression in any cell type. Implications for vasopressin's role in fever, neurodegeneration, autoimmune diseases, stress and neuropsychiatric behaviors are discussed.