[Gq-GPCR upregulation in reactive astrocytes: implication for neurological disorders]

Astrocytes are essential glial cells that maintain brain homeostasis. Upon brain injury, they become reactive astrocytes with altered morphology, gene expression, and function, including dysregulated Ca²⁺ signaling implicated in disease development and progression. P2Y1 receptor (P2Y1R), one of Gq-GPCRs, is upregulated in reactive astrocytes across multiple brain disorders, including Alzheimer's disease, epilepsy, and stroke; however, how this upregulation contributes to pathology has remained unclear. To address this question, we generated astrocyte-specific P2Y1R-overexpressing transgenic mice. P2Y1R overexpression in astrocytes induced neuronal hyperexcitability, as evidenced by increased hippocampal neuronal firing, abnormal EEG spikes, and heightened susceptibility to pilocarpine-induced seizures. Dual-color Ca²⁺ imaging of neurons and astrocytes, electrophysiology, transcriptome analysis of astrocytes, immunohistochemistry, and CRISPR/Cas9-mediated astrocyte-specific knockdown revealed that P2Y1R overexpression amplified both neuron-to-neuron and neuron-to-astrocyte signaling, with astrocytes becoming hypersensitive to neuronal activity-derived ATP. Astrocyte-specific transcriptomic analysis identified insulin-like growth factor binding protein 2 (IGFBP2) as a key downstream effector. IGFBP2, a secreted protein selectively expressed in astrocytes, enhanced glutamatergic synaptic transmission. Furthermore, co-upregulation of P2Y1R and IGFBP2 was confirmed in reactive astrocytes in both kainate-induced epilepsy and middle cerebral artery occlusion stroke models. These findings identify the P2Y1R-IGFBP2 signaling axis as a common pathological feature of reactive astrocytes across brain diseases and establish IGFBP2 as a novel glial-derived factor that could promote neuronal hyperexcitability.