Molecular signatures of regional vulnerability to tauopathy in excitatory cortical neurons.

Tauopathies are characterized by the aggregation and accumulation of hyperphosphorylated tau proteins that correlates with cognitive impairment in affected individuals. The presence of tauopathy follows a temporospatial spreading pattern in which certain neuronal cell types in specific brain regions are more vulnerable to tau accumulation and atrophy. However, the mechanisms underlying the selective vulnerability of these neurons and regions to pathological tau accumulation are not fully understood. Here, we characterized the presence of phosphorylated tau in excitatory and inhibitory neurons in post-mortem prefrontal cortex of tauopathy patients, including Alzheimer's disease, progressive supranuclear palsy, corticobasal degeneration, and frontotemporal lobar dementia due to a MAPT mutation. We observed that neuronal tau accumulation across these tauopathies occurs predominantly in excitatory neurons compared to inhibitory neurons. Next, we performed viral translating ribosome affinity purification (vTRAP) from vulnerable and resistant brain regions on vGLUT1^CRE+ and GAD2^CRE+ PS19 mice to understand molecular signatures of tau vulnerability. We observed that both vulnerable regions and vulnerable neurons are characterized by alterations in synaptic transmission and neuronal excitability. Transcription factor Mef2c (myocyte enhancer factor 2c) was identified as an upstream regulator affecting myelination and synaptic organization in vulnerable brain regions in PS19 mice. The relevance of these findings was validated in human tauopathies via coexpression network analysis. Concordantly, we observed tau-induced changes in spontaneous postsynaptic currents of excitatory neurons in mice especially in the prefrontal cortex. Taken together, we conclude that selective vulnerability to tau could arise from changes in neurotransmission and synaptic compositions, potentially due to an altered Mef2c transcriptional network.