Molecular approaches for manipulating astrocytic signaling in vivo

Abstract

Astrocytes are the predominant glial type in the central nervous system and play important roles in assisting neuronal function and network activity. Astrocytes exhibit complex signaling systems that are essential for their normal function and the homeostasis of the neural network. Altered signaling in astrocytes is closely associated with neurological and psychiatric diseases, suggesting tremendous therapeutic potential of these cells. To further understand astrocyte function in health and disease, it is important to study astrocytic signaling in vivo. In this review, we discuss molecular tools that enable the selective manipulation of astrocytic signaling, including the tools to selectively activate and inactivate astrocyte signaling in vivo. Lastly, we highlight a few tools in development that present strong potential for advancing our understanding of the role of astrocytes in physiology, behavior, and pathology.

New Transgenic Mouse Lines for Selectively Targeting Astrocytes and Studying Calcium Signals in Astrocyte Processes In Situ and In Vivo

“…From this perspective much attention has focussed on genetic methods to selectively target astrocytes (Davila et al, 2013; Xie et al, 2015). Cell type specific expression of Cre recombinase (Cre) is frequently used to achieve gene expression and deletion by exploiting the Cre-loxP system (Sauer, 1994; Tsien, 2016).…”

“…Cell type specific expression of Cre recombinase (Cre) is frequently used to achieve gene expression and deletion by exploiting the Cre-loxP system (Sauer, 1994; Tsien, 2016). However, existing mouse lines expressing Cre under the control of astrocyte promoters are neither selective for astrocytes, nor are they pan-astrocytic (Khakh and Sofroniew, 2015; Xie et al, 2015; Zhang and Barres, 2010). Furthermore, several of the commonly used mouse lines express Cre from birth, which vitiates inducible gene expression/deletion in adult mice and complicates analyses of complex behaviors and disease mechanisms.…”

“…Overall, existing astrocyte Cre lines display some, several or all of these shortcomings, and thus fall short of minimal experimental requirements for cell specificity (Xie et al, 2015). For example, widely used hGfap -Cre lines target large populations of neurons (Sun et al, 2016; Zhuo et al, 2001) and several mGfap -Cre and Slc1a3 -Cre/ERT2 lines target neural progenitors that give rise to neurons in the olfactory bulb and hippocampus (Garcia et al, 2004; Gregorian et al, 2009; Niu et al, 2013; Slezak et al, 2007) and smaller populations of neurons elsewhere (Xie et al, 2015). This problem is shared with mice constitutively expressing Cre under the control of the Aldh1l1 promoter (Foo and Dougherty, 2013).…”

Targeting sympathetic glia for treating cardiovascular diseases

“…More recent optogenetic methods paired with targeted viral delivery can selectively elevate intracellular calcium in GFAP + glia, mimicking one of the downstream signaling effects following Gq-GPCR activation in these cells. However, optogenetic manipulation in GFAP + glia fails to activate the extensive network of Gq-GPCR signaling pathway in GFAP + glia [11] . Moreover, the activation of optogenetic channels on GFAP + glia leads to strong depolarization and acidification [12] , which are not present in physiological glial Gq-GPCR activation.…”

“…Glial Gq-GPCR signaling is essential to neuron-glia interaction in the CNS [10] . The challenge to studying the role of Gq-GPCR signaling in GFAP + glia is that neurons and GFAP + glia express overlapping GPCRs [11] . Traditional pharmacological stimulation leads to Gq-GPCR activation in both neurons and GFAP + glia, causing difficulties in dissecting the contribution of GPCR activation specifically in GFAP + glia.…”