Effect of mutant HTT on the development and maturation of astrocytes

Project Summary / Abstract: Astrocytes are known to be dysfunctional in Huntington’s disease (HD); however, further research is needed to understand how these star-like cells develop in the context of HD. HD is a devastating, progressive, genetic neurodegenerative disease, and recent work suggests mutant Huntingtin (mHTT), the cause of disease, may

trigger early molecular and cellular changes during neurodevelopment that sets up susceptibility. Data suggests mHTT impacts the maturation of neural cells into adult life and throughout disease progression. While HD is primarily characterized by the degeneration of medium spiny neurons in the striatum and atrophy of the cortex,

astrocytes have become a prominent cell type of interest as a contributor to the onset and progression of the disease. Astrocytes guard and support the brain by stabilizing the blood-brain barrier, responding to stressors, and regulating ions and neurotransmitter homeostasis, all of which are dysregulated in HD. Our lab at UC Irvine

has shown developmental deficits using single-nuclei RNA sequencing (snRNAseq) in HD human induced PSC- derived astrocytes (iAstros) and in rapidly progressing R6/2 HD mouse cortex and striatum. We also confirmed that HD iAstros have decreased RNA and protein of transcription factors (TFs) SOX9 and ATF3, results that

support a role for these TFs in dysregulated maturation and developmental pathways. Lacking in the snRNAseq from mice is spatial information, thus I conducted spatial transcriptomics of postnatal day 0 (P0), 4-week and 12- week-old control and R6/2 mice and found early dysregulation of astrocytic developmental genes and a possible

role for neuronal-derived signaling factors in astrocyte developmental impairment. Several questions remain: 1) whether HD astrocyte dysmaturation is an initial delay of maturation or a persistent impairment, 2) what is mechanistically driving spatial maturation impairments, and 3) what the impact is of astrocyte deficits on

neighboring cells. I hypothesize that early impairments in astrocyte maturation set up susceptibility to HD progression later in life. To begin to address these gaps in knowledge, in Aim 1, I will investigate the role of dysregulated TFs, SOX9 and ATF3, with overexpression and knockdown in iAstros and assess cellular

maturation, function, morphology, and transcriptomic pathways. Aim 2 then utilizes the spatial transcriptomics data integrated with snRNAseq to evaluate temporal and spatial regulators of regional changes with a focus on astrocyte development and maturation, and the contributions of neuronal-astrocyte signaling. I will infer cellular

communication between neurons and astrocytes through ligand-receptor analysis and functionally validate my preliminary findings in vitro with iAstros. This proposal uses innovative approaches to provide the scientific community with a novel investigation of dysfunctional astrocytic developmental trajectories in HD with the aim of

influencing early therapeutic interventions to impact the onset or progression of disease. My laboratory environment at UCI and individualized mentorship from my sponsors supporting my research skills in perturbing in vitro cell models and bioinformatics analysis will help to burgeon my growth as a young scientist.