Intracortical astrocyte subpopulations defined by astrocyte reporter Mice in the adult brain

Abstract

Although historically regarded as a homogeneous cell population, astrocytes in different brain regions exhibit differences in their physiological properties, such as gap‐junction coupling, glutamate uptake dynamics, and intracellular Ca2+ response. Recent in vivo RNA profiles have further demonstrated the molecular heterogeneity of astrocytes in the adult CNS. Astrocyte heterogeneity exists not only inter‐regionally but also intra‐regionally. Despite the characteristic laminal organization of cortical layers and multiple sources of radial glia progenitors for (astro)gliogenesis, the molecular profile and functional properties of astroglial subpopulations in the adult cerebral cortex remain essentially undefined. Using two astrocyte reporter mouse lines: eaat2‐tdTomato and Bac aldh1l1‐eGFP, we identified tdT−eGFP+, tdTloweGFP+, and tdThigheGFP+ astroglial subpopulations (in an approximate 1:7:2 ratio) within the cortex. The tdT−eGFP+ astrocyte population is selectively localized at layers I–II and exhibits increased resting membrane potential and membrane resistance but reduced functional expression of the potassium channel Kir4.1. We also isolated individual astrocyte subpopulations through fluorescence activated cell sorting (FACS) and examined their transcriptome differences by RNA‐seq. We found that the whole‐genome transcriptional profiles of tdT−eGFP+ astrocytes are drastically different from that of tdTloweGFP+ and tdThigheGFP+ astrocytes. Particularly, elevated levels of several nonastrocyte genes that are typically specific to other glial cells, such as mog, mobp, Iba1, and pdgfrα, are observed in tdT−eGFP+ astrocytes, suggesting a less‐specific molecular identity of these astrocytes. Overall, our study has unveiled molecular differences between adult cortical astroglial subpopulations, shedding new light on understanding their unique functions in the adult cortex.

Regionally encoded functional heterogeneity of astrocytes in health and disease: A perspective

“…Interestingly, evidence of intraregional astrocytic functional heterogeneity was also raised in this study as dorsal versus ventral parts of the striatum exhibited graded expression of specific factors (Chai et al, 2017). This builds on morphological (Oberheim, Goldman, & Nedergaard, 2012) and molecular evidence from recent single cell RNA sequencing (Batiuk et al, 2020;Bayraktar et al, 2020) (Martín, Bajo-Grañeras, Moratalla, Perea, & Araque, 2015;Morel et al, 2019) and in their ability to support synaptogenesis (John Lin et al, 2017), suggesting that intraregional functional heterogeneity occurs throughout the CNS.…”

A Dual Nanosensor Approach to Determine the Cytosolic Concentration of ATP in Astrocytes

“…Astrocytes are a heterogenous cell population which also includes heterogeneity of metabolism (Bittner et al, 2010;Matyash and Kettenmann, 2010;Zhang and Barres, 2010;Bayraktar et al, 2015;Farmer and Murai, 2017;Köhler et al, 2018Köhler et al, , 2019Miller, 2018;Morel et al, 2018;Batiuk et al, 2020). Therefore, information on the heterogeneity of [ATP] 0 within the astrocytic cell population is of major interest.…”

No Longer Underappreciated: The Emerging Concept of Astrocyte Heterogeneity in Neuroscience

“…A partial GLT1/EAAT2 promoter fragment drives TdTomato expression in a subgroup of astrocytes in cortical layer 5 [58], which express the synaptogenic protein Norrin (and see Section 7). A double reporter line (GLT1/EAAT2-TdTomato: Aldh1l1-eGFP) identifies three distinct classes of cortical astrocytes [59], with unique transcriptomes, tissue locations and electrophysiological characteristics. Staining with antibodies specific for CD51, CD63 and C71 in the Aldh1l1-eGFP mouse identifies five astrocyte subpopulations present in cortex, olfactory bulb, brain stem, thalamus, cerebellum and spinal cord [60], albeit in differing proportions.…”