Laboratory for Neuron-Glia Circuitry, RIKEN Center for Brain Science, Wako 351-0106, Saitama, Japan.
Center for Translational Neuromedicine, Faculty of Medical and Health Sciences, University of Copenhagen, 1172 Copenhagen, Denmark.
Int J Mol Sci. 2023 Sep 2;24(17):13590. doi: 10.3390/ijms241713590.
Activation of Gq-type G protein-coupled receptors (GPCRs) gives rise to large cytosolic Ca elevations in astrocytes. Previous in vitro and in vivo studies have indicated that astrocytic Ca elevations are closely associated with diameter changes in the nearby blood vessels, which astrocytes enwrap with their endfeet. However, the causal relationship between astrocytic Ca elevations and blood vessel diameter changes has been questioned, as mice with diminished astrocytic Ca signaling show normal sensory hyperemia. We addressed this controversy by imaging cortical vasculature while optogenetically elevating astrocyte Ca in a novel transgenic mouse line, expressing Opto-Gq-type GPCR Optoα1AR (Astro-Optoα1AR) in astrocytes. Blue light illumination on the surface of the somatosensory cortex induced Ca elevations in cortical astrocytes and their endfeet in mice under anesthesia. Blood vessel diameter did not change significantly with Optoα1AR-induced Ca elevations in astrocytes, while it was increased by forelimb stimulation. Next, we labeled blood plasma with red fluorescence using AAV8-P3-Alb-mScarlet in Astro-Optoα1AR mice. We were able to identify arterioles that display diameter changes in superficial areas of the somatosensory cortex through the thinned skull. Photo-stimulation of astrocytes in the cortical area did not result in noticeable changes in the arteriole diameters compared with their background strain C57BL/6. Together, compelling evidence for astrocytic Gq pathway-induced vasodiameter changes was not observed. Our results support the notion that short-term (<10 s) hyperemia is not mediated by GPCR-induced astrocytic Ca signaling.
Gq 型 G 蛋白偶联受体 (GPCR) 的激活会导致星形胶质细胞内的胞质钙离子大幅升高。先前的体外和体内研究表明，星形胶质细胞钙离子升高与附近血管的直径变化密切相关，星形胶质细胞的足突包裹着这些血管。然而，星形胶质细胞钙离子升高与血管直径变化之间的因果关系一直存在争议，因为具有减弱的星形胶质细胞钙离子信号的小鼠表现出正常的感觉性充血。我们通过在一种新型转基因小鼠系中对星形胶质细胞进行光遗传学钙升高来解决这一争议，该小鼠系在星形胶质细胞中表达光遗传学 Gq 型 GPCR Optoα1AR（Astro-Optoα1AR）。在麻醉状态下，对体感皮层表面进行蓝光照射会诱导皮层星形胶质细胞及其足突中的钙离子升高。Optoα1AR 诱导的星形胶质细胞钙离子升高不会导致血管直径发生显著变化，但前肢刺激会增加血管直径。接下来，我们使用 AAV8-P3-Alb-mScarlet 在 Astro-Optoα1AR 小鼠中对血浆进行红色荧光标记。我们能够通过颅骨变薄识别出在体感皮层浅层区域显示直径变化的小动脉。与背景品系 C57BL/6 相比，对皮层区域的星形胶质细胞进行光刺激不会导致小动脉直径发生明显变化。没有观察到星形胶质细胞 Gq 途径诱导的血管直径变化的有力证据。我们的结果支持这样一种观点，即短期（<10 秒）充血不是由 GPCR 诱导的星形胶质细胞钙离子信号介导的。
