IN VIVO DUAL-MODALITY IMAGING OF MICROGLIA USING A P2Y12 RECEPTOR-TARGETED PROBE

Microglia, the resident macrophages of the central nervous system, play critical roles in psychiatric and neurological disorders. However, approaches to evaluate microglial phenotypic changes in primates remain limited. The aim of this study was to develop a novel P2Y12 receptor (P2Y12R)–targeted chemical labeling strategy that enables dual-modality in vivo imaging of microglia using two-photon imaging and magnetic resonance imaging (MRI).
We developed P2Y12R-targeted compounds based on Ticagrelor, a P2Y12R antagonist. For two-photon imaging, Ticagrelor was conjugated to the two-photon–suitable fluorescent dye SeTau647 (Tica-SeTau647). For MRI, Ticagrelor was conjugated to gadolinium (Tica-Gd). These probes were administered via intracerebroventricular injection in mice, and microglial labeling was evaluated using two-photon imaging, MRI, and immunohistochemistry.
In Cx3cr1^GFP/+ mice, Tica-SeTau647 selectively labeled microglia with high specificity in two-photon imaging without detectable effects on microglial morphology or process motility. This probe enabled enhanced visualization of microglial processes, consistent with the distribution of P2Y12R. Tica-Gd produced a robust T1 contrast effect in the regions near the cerebral ventricles, which was eliminated by pharmacological microglial ablation. In cuprizone-treated mice, a model of progressive multiple sclerosis, the T1 contrast effect of Tica-Gd in the hypothalamus was significantly reduced, consistent with microglial pathological changes observed in immunohistochemistry.
Our results demonstrate that P2Y12R-targeted probes enable dual-modality in vivo imaging of microglia and allow visualization of microglial phenotypic changes by tracking P2Y12R expression. Moreover, given its applicability to primates, including humans, this technique may open new avenues for studying the pathophysiology of psychiatric and neurological disorders.