P2Y2 Nucleotide Receptor-Mediated Responses in Brain Cells

Acute inflammation is important for tissue repair; however, chronic inflammation contributes to neurodegeneration in Alzheimer's disease (AD) and occurs when glial cells undergo prolonged activation. In the brain, stress or damage causes the release of nucleotides and activation of the Gq protein-coupled P2Y2 nucleotide receptor subtype (P2Y2R) leading to pro-inflammatory responses that can protect neurons from injury, including the stimulation and recruitment of glial cells. P2Y2R activation induces the phosphorylation of the epidermal growth factor receptor (EGFR), a response dependent upon the presence of a SH3 binding domain in the intracellular C terminus of the P2Y2R that promotes Src binding and transactivation of EGFR, a pathway that regulates the proliferation of cortical astrocytes. Other studies indicate that P2Y2R activation increases astrocyte migration. P2Y2R activation by UTP increases the expression in astrocytes of αVβ3/5 integrins that bind directly to the P2Y2R via an Arg-Gly-Asp (RGD) motif in the first extracellular loop of the P2Y2R, an interaction required for Go and G12 protein-dependent astrocyte migration. In rat primary cortical neurons (rPCNs) P2Y2R expression is increased by stimulation with interleukin-1β (IL-1β), a pro-inflammatory cytokine whose levels are elevated in AD, in part due to nucleotide-stimulated release from glial cells. Other results indicate that oligomeric β-amyloid peptide (Aβ1-42), a contributor to AD, increases nucleotide release from astrocytes, which would serve to activate upregulated P2Y2Rs in neurons. Data with rPCNs suggest that P2Y2R upregulation by IL-1β and subsequent activation by UTP are neuroprotective, since this increases the non-amyloidogenic cleavage of amyloid precursor protein. Furthermore, activation of IL-1β-upregulated P2Y2Rs in rPCNs increases the phosphorylation of cofilin, a cytoskeletal protein that stabilizes neurite outgrowths. Thus, activation of pro-inflammatory P2Y2Rs in glial cells can promote neuroprotective responses, suggesting that P2Y2Rs represent a novel pharmacological target in neurodegenerative and other pro-inflammatory diseases.