Facilitated α-synuclein oligomer sharing among glial cells by a centrally acting connexin inhibitor attenuates a rapidly progressive multiple system atrophy-cerebellar type model by reducing the neuronal α-synuclein burden

Abstract

Glial connexins (Cxs) that make up astrocyte/oligodendrocyte gap junctions are extensively altered in multiple system atrophy-cerebellar type (MSA-C). Here, we investigated how Cx alterations affect the propagation of α-synuclein (α-syn) oligomers and phosphorylated (p)-α-syn aggregates in MSA-C using a centrally acting pan-Cx blocker, INI-0602. Our Plp1-tTA::tetO-SNCA*A53T transgenic (Tg) mice express mutant human A53T α-syn in oligodendrocytes after dietary doxycycline withdrawal at 8 weeks of age; they typically develop progressive ataxia around 22 weeks and die by 30 weeks. These Tg mice were intraperitoneally administered INI-0602 or vehicle from 18 to 26 weeks of age. Proximity ligation assay demonstrated that α-syn oligomers in small glial cells of the brainstem/cerebellum peaked at 10 weeks and maintained similar levels thereafter. In neuropil, α-syn oligomers appeared at 10 weeks, peaked at 16 weeks, and decreased from 24 weeks. In large cells (neuronal somata or reactive astrocytes), α-syn oligomers continuously accumulated from 10 to 30 weeks. By contrast, p-α-syn accumulated predominantly in oligodendrocytes from 24 to 30 weeks and later appeared in astrocytes, microglia, and neurons. Notably, double staining revealed that α-syn oligomers and p-α-syn were rarely colocalised. In the lesion centre with abundant p-α-syn deposits, both oligodendrocytic Cx47/Cx32 and astrocytic Cx43/Cx30 expression were extensively lost. Conversely, at the leading edges, Cx43 was upregulated despite Cx47 loss, resulting in abundant Cx43 hemichannels. INI-0602 suppressed increased hemichannel activity in the leading edges in acute slice culture and attenuated MSA-C and glial inflammation-thereby preserving Cx gap junctions-in Tg mice. INI-0602 treatment reduced neuronal α-syn oligomers and p-α-syn aggregates but facilitated α-syn oligomer dissemination throughout glial cells and neuropil. In human MSA-C, distinct distribution patterns between α-syn oligomers and p-α-syn deposits were also observed. Thus, increased sharing of α-syn oligomers via preserved Cx gap junctions may help attenuate MSA-C pathology by reducing neuronal α-syn aggregates.

Keywords: Connexin; Gap junctions; Hemichannels; Multiple system atrophy; phosphorylated α-synuclein; α-synuclein oligomers.