Title: STAT3 drives GFAP expression and accumulation in a mouse model of Alexander disease
Legend: (A) Immunolabeling of phosphorylated STAT3 (red) demonstrates nuclear localization (blue) and activation of the transcription factor in GFAP labeled astrocytes (green) from the Gfap+/R236H mouse model of Alexander disease (right panel) compared with wild-type Gfap+/+ mice (left panel, hippocampus shown, scale bar = 10 µm). (B) Genetic knockout of STAT3 (Stat3 -/-) specifically in astrocytes prevents GFAP protein accumulation and pathology that occurs in Gfap+/R236H mice (Stat3 +/+), as shown by GFAP quantification (enzyme-linked immunosorbent assay). Both males and females were tested, ****p-value < 0.0001 represents Sidak’s post-tests, two-way ANOVA.
Citation: Hagemann, T. L., Coyne, S., Levin, A., Wang, L., Feany, M. B., & Messing, A. (2023). STAT3 Drives GFAP Accumulation and Astrocyte Pathology in a Mouse Model of Alexander Disease. Cells, 12(7), 978. https://doi.org/10.3390/cells12070978
Abstract: Alexander disease (AxD) is caused by mutations in the gene for glial fibrillary acidic protein (GFAP), an intermediate filament expressed by astrocytes in the central nervous system. AxD-associated mutations cause GFAP aggregation and astrogliosis, and GFAP is elevated with the astrocyte stress response, exacerbating mutant protein toxicity. Studies in mouse models suggest disease severity is tied to Gfap expression levels, and signal transducer and activator of transcription (STAT)-3 regulates Gfap during astrocyte development and in response to injury and is activated in astrocytes in rodent models of AxD. In this report, we show that STAT3 is also activated in the human disease. To determine whether STAT3 contributes to GFAP elevation, we used a combination of genetic approaches to knockout or reduce STAT3 activation in AxD mouse models. Conditional knockout of Stat3 in cells expressing Gfap reduced Gfap transactivation and prevented protein accumulation. Astrocyte-specific Stat3 knockout in adult mice with existing pathology reversed GFAP accumulation and aggregation. Preventing STAT3 activation reduced markers of reactive astrocytes, stress-related transcripts, and microglial activation, regardless of disease stage or genetic knockout approach. These results suggest that pharmacological inhibition of STAT3 could potentially reduce GFAP toxicity and provide a therapeutic benefit in patients with AxD.
About the Lab: The Alexander Disease Research Lab focuses on the role of astrocytes in neurodegenerative disease and the cellular consequences of their dysfunction. Astrocytes have traditionally been thought of as support cells that maintain ion and neurotransmitter homeostasis in the central nervous system (CNS). However, research over the past few decades has revealed more complex functions including the regulation of neurogenesis, synaptogenesis, neurotransmission and remyelination. In addition, astrocytes control blood flow, maintain the blood brain barrier, and contribute to the distribution and clearance of compounds through the CNS glymphatic system.
Astrocytes take on another critical role of reacting to CNS injury by activating anti-stress and neuroinflammatory pathways in both acute insults and chronic disease. Reactive astrocytes are heterogeneous in their response and can either promote or prevent regeneration and repair. Given the complexities of astrocyte function in the healthy CNS and their sometimes paradoxical role in brain and spinal cord injury, it can be difficult to dissect the effects of astrogliosis on other neural cell types from the primary insult.
To better understand astrocyte function in neurodegenerative disease, we have focused on one of the few examples of a primary disorder of astrocytes, Alexander disease. Alexander disease (AxD) is caused by mutations in the gene for glial fibrillary acidic protein (GFAP), an astrocyte specific intermediate filament protein, that lead to protein aggregation, activation of stress response genes, including GFAP, and reactive gliosis. AxD can affect all ages but is most severe in children, who often present with seizures, motor and cognitive delay, and a general failure to thrive. We have generated several rodent models with missense mutations homologous to those found in patients with the disease. These models allow us to study the effects of astrocyte dysfunction on other cell types in the mammalian CNS, including neurons and oligodendrocytes and their progenitors. As with other injuries, the astrocyte response to mutant GFAP is also heterogeneous, and a second goal is to identify the molecular networks controlling regional differences in astrocyte reactivity. Finally we hope that understanding the mechanisms behind Alexander disease pathology will lead to therapeutic strategies for this devastating disorder as well as other diseases with astropathology.
Investigator: Tracy L. Hagemann, PhD