ABS 037: Astrocyte heterogeneity in the substantia nigra revealed using a novel model for Parkinson Disease risk

Navya Gullapalli ¹, Alana Colafrancesco ¹, Micah Simmons ¹ ², Jamil Saad ³, Rita Cowell ¹ ²

¹ Department of Neurology, University of Alabama at Birmingham, Birmingham, AL
² Southern Research, Birmingham, AL
³ Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL

The Van Wickle Journal (2026) Volume 2, ABS037

Introduction: More than 10 million people worldwide are diagnosed with Parkinson’s Disease (PD), a progressive neurodegenerative movement disorder characterized by alpha-synuclein aggregation and dopaminergic neuron (DAN) loss in the substantia nigra pars compacta (SNc). DANs produce the neurotransmitter dopamine, which is necessary for initiating movement. They are also known to be vulnerable to metabolic dysfunction in PD, but it is unclear as to how this develops. One possibility could be that it stems from the metabolic alterations in the neurons themselves or in astrocytes, which provide nutrients and other metabolites to neurons. Some studies have demonstrated that astrocytes are responsible for maintaining REDOX (reduction-oxidation) homeostasis. Other studies have shown activated astrocytes in the brains of PD patients. However, there is lack of direct evidence for mechanistic links between glial dysregulation and DAN loss in PD. To study the contribution of PD-related astrocytic dysfunction, we used the 2019 human genome-wide association study (GWAS) and expression Quantitative Trait Loci (eQTL) data to identify a single nucleotide polymorphism in the gene locus for cluster of differentiation 38 (Cd38). CD38, a protein involved in maintaining intra- and extracellular metabolism, is highly enriched in astrocytes and causes increased risk for PD. It converts nicotinamide adenine dinucleotide (NAD+) to nicotinamide (NAM), both of which are metabolic substrates. Without CD38, the NAD+/NAM ratio is increased, compromising neuronal energetic support. Moreover, decreased expression of CD38 is associated with the rs11724635 risk allele. Homozygous carriers of this PD risk allele exhibit a 50% reduction in Cd38 mRNA in the brain, specifically in the basal ganglia, hypothalamus, and substantia nigra. This study aims to investigate how astrocyte heterogeneity of the SN contributes to PD and how transcriptional dysregulation with CD38-deficiency increases PD risk.

Methods: We performed astrocyte immunopanning and RNA-sequencing for genes involved in glycogen metabolism (Pygb [+0.498]), mitochondrial metabolism (Ndufa10 [-0.591]), senescence (Cdkn1a [-0.637]), and inflammation (C4b [+0.8880]). To validate changes in these genes observed at the transcriptional level, we conducted fluorescent in situ hybridization (FISH) on eight mice brains (four Cd38 wildtype and four Cd38 knockout) per gene. These mice were three months of age and balanced by sex (2M, 2F). We then captured images of the FISH slides on a Nikon Eclipse Ti2 confocal microscope using the NIS-Elements Viewer software. Cell Profiler, a semiautomated program, was used to quantify transcript expression in single cells, specifically DANs and astrocytes. Then we performed statistical analyses using two-way ANOVA tests in GraphPad Prism. Next, we characterized subsets of astrocytes (Myoc+, Cst3+, and Igfbp2+) in the SNc, substantia nigra pars reticulata (SNr), and the ependyma regions using the same approaches.

Results: C4b expression showed a significant increase in Cd38 knockout mice as predicted by the RNA-sequencing data. However, Pygb, Cdkn1a, and Ndufa10 expressions showed insignificant differences between genotypes in the FISH experiments despite showing robust differences in the RNA-sequencing data. Furthermore, Cd38 deficiency altered the spatial distribution of all three astrocytic subtypes across the SNc, SNr, and ependyma. Cst3+ was more broadly expressed throughout the SN, Myoc+ was most abundant in the ependyma, and Igfbp2+ was most abundant in DANs. Both Cst3+ and Igfbp2+ showed significant genotype-dependent increases in expression while Myoc+ showed significant regional-dependent increase in expression.

Discussion: This study extends the current CD38 literature by highlighting changes in astrocyte heterogeneity. It also shows that CD38 deletion is associated with increased inflammatory signaling, which potentially induces a reactive state in astrocytes. Myoc+, which is highly expressed in the ependyma where inflammation tends to occur, might play a role in C4b astrocytic upregulation and might be linked to this inflammatory response. Therefore, targeting CD38 or related pathways in the astrocytic subtypes from this study might offer a way to fine-tune astrocyte support for dopaminergic neuron survival.