Astrocyte-specific transcriptome analysis using the ALDH1L1 bacTRAP mouse reveals novel biomarkers of astrogliosis in response to neurotoxicity.

Lindsay T Michalovicz,Diane B Miller,Saurabh Vashishtha,Rotem Ben‐Hamo,Kimberly A Kelly,Sol Efroni,James P O’Callaghan,Gordon Broderick,Alicia R Locker,Julie V Miller,Kimberly Sullivan

doi:10.1111/jnc.14800

Abstract

Neurotoxicology is hampered by the inability to predict regional and cellular targets of toxicant‐induced damage. Evaluating astrogliosis overcomes this problem because reactive astrocytes highlight the location of toxicant‐induced damage. While enhanced expression of glial fibrillary acidic protein is a hallmark of astrogliosis, few other biomarkers have been identified. However, bacterial artificial chromosome ‐ translating ribosome affinity purification (bacTRAP) technology allows for characterization of the actively translating transcriptome of a particular cell type; use of this technology in aldehyde dehydrogenase 1 family member L1 (ALDH1L1) bacTRAP mice can identify genes selectively expressed in astrocytes. The aim of this study was to characterize additional biomarkers of neurotoxicity‐induced astrogliosis using ALDH1L1 bacTRAP mice. The known dopaminergic neurotoxicant 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP; 12.5 mg/kg s.c.) was used to induce astrogliosis. Striatal tissue was obtained 12, 24, and 48 h following exposure for the isolation of actively translating RNA. Subsequently, MPTP‐induced changes in this RNA pool were analyzed by microarray and 184 statistically significant, differentially expressed genes were identified. The dataset was interrogated by gene ontology, pathway, and co‐expression network analyses, which identified novel genes, as well as those with known immune and inflammatory functions. Using these analyses, we were directed to several genes associated with reactive astrocytes. Of these, TIMP1 and miR‐147 were identified as candidate biomarkers because of their robust increased expression following both MPTP and trimethyl tin exposures. Thus, we have demonstrated that bacTRAP can be used to identify new biomarkers of astrogliosis and aid in the characterization of astrocyte phenotypes induced by toxicant exposures.Open Science Badges This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14518.

Highlights

These observations suggest that astrogliosis is a common response to all types of neurotoxic exposures and that glial fibrillary acidic protein (GFAP) and other markers of ‘reactive’ astrocytes serve as biomarkers of neurotoxicity
aldehyde dehydrogenase 1 family member L1 (ALDH1L1) levels are unaffected across different models of neurotoxicity Astrogliosis, the reactive state of astrocytes, is the hallmark of all types of central nervous system (CNS) injuries and damage, and enhanced expression of the intermediate filament protein of astrocytes, GFAP, is the characteristic feature
Does ALDH1L1 colocalize to GFAP + astrocytes in both the striatum and hippocampus, but histological evaluation following MPTP exposure confirms the measured increase in GFAP expression as well as the morphological hypertrophy and increased number of activated astrocytes associated with astrogliosis following exposure

Summary

Introduction

Several studies have utilized the ALDH1L1 bacTRAP transgenic mice to evaluate different aspects of normal astrocyte gene expression, including regional or subcellular distribution and effects of the sleep–wake cycle (Bellesi et al, 2015; Boulay et al, 2017; Morel et al, 2017), as well as gene expression changes related to temporal lobe epilepsy (Clasadonte et al, 2016) and chronic stress (Simard et al, 2018). These mice have not been used to evaluate astrogliosis related to neurotoxicity. Additional analysis of these genes revealed that many had strong associations with known inflammatory and immune response pathways and that their expression changes were conserved across different neurotoxicant exposures, regardless of brain area or rodent species

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