Multiple System Atrophy: Identifying Cells that Accelerate Disease Progression

There is currently no cure for the rare neurodegenerative disorder multiple system atrophy (MSA), and its rarity has made it difficult to understand how the disease progresses. Now a research team has created a successful mouse model of aggressive cerebellar-type MSA and identified new populations of glial cells in the brain that exacerbate disease progression. MSA, similar to Parkinson’s disease, affects the motor system as well as the autonomic nervous system including blood pressure control, eventually leading to death. It is characterized by abnormal accumulations of the protein α-synuclein (α-syn) in a type of central nervous system cell called oligodendrocytes. Researchers bred transgenic mice which expressed the ultra-accumulative A53T mutation of human α-syn when triggered by removal of doxycycline from their diet. The mice showed disease progression similar to humans. Disease symptoms could be fully reversed with the reintroduction of doxycycline to the diet after 23 weeks (soon after development of symptoms) but recovery was only partial if doxycycline was reintroduced after 27 weeks. In addition to cells already known to be involved in disease progression, the researchers identified a cluster of migroglial cells that, in transgenic mice, highly expressed the genes for proteins Sdc4, Tgm2, Tlr2, Arg1 and inflammatory cytokines involved in TNF signaling, NF-kappa B signaling, cytokine-cytokine receptor interaction, Toll-like receptor signaling, and chemokine signaling. A successful mouse model means more research can be performed in the absence of many human patients, and the newly identified factors in disease progression may provide future therapeutic avenues.

Full abstract, to be presented at the American Neurological Association 2022 Annual Meeting, October 22-25, 2022 in Chicago and published in Annals of Neurology:

Synucleionopathy-Associated Microglia Uncovered by a Novel Multiple System Atrophy-Cerebellar Type (MSA-c) Mouse Model

Jun-ichi Kira, MD, PhD, International University of Health and Welfare, Fukuoka, Japan

Co-authors: Dai Matsuse, MD, PhD, Katsuhisa Masaki, MD, PhD, Noriko Isobe, MD, PhD

Backgrounds: α-synuclein (α-syn) accumulation in oligodendrocytes plays a pivotal role in multiple system atrophy (MSA). Early intrathecal glial activation is associated with aggressive progression of MSA.

Objective: To identify glial populations exacerbating MSA pathology.

Methods: We generated transgenic (Tg) mice, in which A53T human α-syn (h-α-syn), a mutant protein with enhanced aggregability, was produced in oligodendrocytes under the control of Plp promoter by the Tet-Off System since 8 weeks of age by removing doxycycline (DOX) from the diet after myelination.

Results: Tg mice developed ataxia shown by increased hind paw width and stride length at around 22 weeks and rapidly progressed to death by 30 weeks. Phosphorylated α-syn (p-α-syn) aggregates started to accumulate in the brainstem and spinal cord from 16 weeks. These lesions, also visible in vivo on MRI, showed pronounced demyelination with loss of myelin basic protein, together with neuroaxonal loss, increased infiltration of Iba1-positive microglia expressing arginase-1 (Arg1) and toll-like receptor 2, and glial fibrillary acidic protein-positive astrogliosis. Re-inhibition of h-α-syn expression by DOX diet at 23 weeks (23WDOX+) resulted in full recovery but 27WDOX+ showed only partial recovery. In 23 and 27WDOX+ Tg mice, p-α-syn deposition markedly decreased while demyelination improved in 23WDOX+ but persisted in 27WDOX+ mice. Arg1-positive microglia disappeared in the lesions of 23WDOX+ mice but only partially decreased in those of 27WDOX+ mice. RNA microarray from the brain stem/cerebellum at 16 and 24 weeks indicated a robust inflammatory response and cytokine/chemokine production in both microglia and astroglia in Tg mice. Single cell RNA-sequence of CD11b+ cells isolated from Tg mouse brain at 22 and 26 weeks identified 10 clusters. Custer 0 highly expressed Sdc4, Tgm2, Tlr2, Arg1 and inflammatory cytokines while Cluster 2 corresponded to disease-associated microglia previously reported. The enriched KEGG pathways for all differentially expressed genes in Cluster 0 included TNF signaling, NF-kappa B signaling, Cytokine-cytokine receptor interaction, Toll-like receptor signaling, and Chemokine signaling. Treatment of BLZ945, a colony-stimulating factor 1 receptor inhibitor, just before the onset of motor symptoms, exacerbated both motor symptoms and pathology. BLZ945-treated Tg mice had higher proportions of Cluster 0 compared with vehicle-treated controls. By volcano and scatter plots, Cluster 0 had higher expression of Ccl2 and Ccl12 in BLZ945-treated than vehicle-treated Tg mice.

Conclusion: We successfully developed an aggressive adult MSA-cerebellar type mouse model and identified synucleinopathy-associated microglia that exacerbate the disease.

All abstracts from ANA2022 will be available in Annals of Neurology starting at 3:01 p.m. U.S. Eastern Time on October 14. This research is under embargo until that time. Contact Katherine Pflaumer ([email protected]) for additional highlighted abstracts, full meeting abstracts, and call-in information for the ANA2022 Media Roundtable (Oct. 25, 11 a.m. U.S. Central).