Genetic Constructs for the Control of Astrocytes’ Activity

Abstract

In the current review, we aim to discuss the principles and the perspectives of using the genetic constructs based on AAV vectors to regulate astrocytes’ activity. Practical applications of optogenetic approaches utilizing different genetically encoded opsins to control astroglia activity were evaluated. The diversity of astrocytic cell-types complicates the rational design of an ideal viral vector for particular experimental goals. Therefore, efficient and sufficient targeting of astrocytes is a multiparametric process that requires a combination of specific AAV serotypes naturally predisposed to transduce astroglia with astrocyte-specific promoters in the AAV cassette. Inadequate combinations may result in off-target neuronal transduction to different degrees. Potentially, these constraints may be bypassed with the latest strategies of generating novel synthetic AAV serotypes with specified properties by rational engineering of AAV capsids or using directed evolution approach by searching within a more specific promoter or its replacement with the unique enhancer sequences characterized using modern molecular techniques (ChIP-seq, scATAC-seq, snATAC-seq) to drive the selective transgene expression in the target population of cells or desired brain regions. Realizing these strategies to restrict expression and to efficiently target astrocytic populations in specific brain regions or across the brain has great potential to enable future studies.

Optogenetic Activation of Astrocytes—Effects on Neuronal Network Function

“…For selective expression of channel rhodopsin in astrocytes we used plasmid AAV pZac2.1 GfaABC1D_ChR2(H134R)-mCherry (Addgene, #112496) that contains short version of astrocyte-specific GFAP promoter GfaABC1D [43]. Opto-a1AR encoding plasmid was generated on the basis of pZac2.1 as follows: Opto-a1AR-EYFP fragment was amplified by PCR using pcDNA3.1/opto-a1AR-EYFP plasmid (Addgene #20947) as a template, and then cloned into pZac2.1 plasmid using NheI/XbaI restriction enzymes to replace the ChR2(H134R)-mCherry fragment.…”

Novel Approaches Used to Examine and Control Neurogenesis in Parkinson′s Disease

“…As a result of activation, extracellular K+ concentrations transiently rise, astrocytes release gliotransmitters and change their mitochondrial activity and proliferative status [172][173][174]. Actually, this is a principle of optogenetic photostimulation of astroglial cells expressing ChR2 or optoGPCRs under the astroglial promoters (i.e., GFAP), which recently appeared as a new approach to control brain activity [175][176][177][178].…”

“…Higher expression of GFAP in reactive astrocytes, particularly in neurodegeneration [181], makes it possible to increase the efficacy of photostimulation in the affected brain vs. the healthy brain. Indeed, optogenetic protocols targeting astrocytes provide precise manipulation with their functional status, secretory phenotype, and interactions with mature neurons in physiological conditions and in neurodegeneration [175,177,182,183].…”

Bidirectional regulation by “star forces”: Ionotropic astrocyte's optical stimulation suppresses synaptic plasticity, metabotropic one strikes back

“…Optogenetics offers a versatile tool for precise spatial and temporal control of astrocytic activity (Adamsky et al, 2018; Borodinova et al, 2021; Chen et al, 2013; Gerasimov et al, 2021; Li et al, 2020; Mederos et al, 2019; Mederos et al, 2021; Navarrete et al, 2019; Tan et al, 2017). The classic light‐gated cation channel channelrodopsin‐2 (ChR2) and its modifications were extensively used for manipulations of astrocytic activity by inducing transmembrane influx of calcium from extracellular space (Chen et al, 2013; Navarrete et al, 2019; Tan et al, 2017; Yang et al, 2015).…”