Intranasal Transplantation of Microbiota Derived from Parkinson's Disease Mice Induced Astrocyte Activation and Neurodegenerative Pathology from Nose to Brain.

BACKGROUND: Parkinson's disease (PD) is characterized by early-onset olfactory dysfunction preceding motor symptoms, yet its mechanisms remain elusive. Based on the studies on microbiota-gut-brain axis, the microbiota-nose-brain axis might be involved in the pathogenesis of PD. However relative studies are rare. METHODS: By consecutive 14-days intranasally transplanting bacteria, we established mice models exhibiting nasal microbiota dysbiosis (NMD), including animal group received intranasal drops of fecal bacterial suspension from normal mice (NB group) and animal group received intranasal drops of fecal bacterial suspension from PD mice (PB group), with animals that only received anesthesia used as the control group. Then we analyzed the nasal microbiota composition via 16S rRNA sequencing, evaluated the olfactory and motor functions through behavioral experiments, including buried food test, open field test, pole descent test, and traction test. The neuropathology in olfactory-related and PD-related brain regions, including olfactory bulb, pyriform cortex, hippocampus, substantia nigra and striatum, was also detected by western blotting, immunofluorescence and immunohistochemical experiments using the antibodies of NeuN, TH and GFAP. RESULTS: 16S rRNA sequencing revealed that PB mice were primarily characterized by an increase in bacteria associated with inflammation and PD. Behavioral assessments revealed that mice with NMD demonstrated impairments in the buried food test and pole descent test, indicative of olfactory and motor dysfunction. By detecting NeuN and GFAP expression, we identified neuronal loss and astrocytes activation in olfactory-related brain regions and adjacent structures, including the olfactory bulb, pyriform cortex, hippocampus, substantia nigra and striatum of both NMD groups, which may contribute to the observed functional disorders. Notably, animals exposed to PD-derived bacteria exhibited more pronounced changes in nasal bacteria, with more severe neuropathology. CONCLUSIONS: We present evidence supporting the microbiota-nose-brain axis, and the NMD-induced astrocyte activation and neurodegenerative pathology along the olfactory pathway may serve as a link between nose and brain.