Impact of neuromelanin and Tau accumulation during aging and disease on local gene expression in the human locus coeruleus using spatially-resolved transcriptomics with protein detection - PROJECT SUMMARY The locus coeruleus (LC) is a small bilateral nucleus located in the dorsal pons of the brainstem, and serves as the brain’s primary site for producing the neuromodulator norepinephrine (NE). NE-producing neurons in the LC project to many regions of the central nervous system to modulate highly divergent functions including cognition, arousal, and mood. The LC is one of the earliest sites of degeneration in Alzheimer’s disease (AD), and profound loss of LC-NE neurons accelerates with disease progression. Several unique anatomical, morphological and neurochemical properties likely contribute to vulnerability of LC-NE neurons. First, LC-NE neurons synthesize neuromelanin (NM), a property shared by only a few cell types in the human brain. NM accumulates with aging, and one hypothesis is that it initially protects LC-NE neurons by sequestering or chelating neurotoxic substances. However, in late life and disease states, NM deposition may be detrimental when it overwhelms cellular machinery, and accumulated toxins are released from degenerating cells. Second, accumulation of phosphorylated tau (pTau), a primary AD neuropathology, is detected in the LC prior to any other brain region. In this application, we generate transcriptomic-scale spatial maps that incorporate localization of NM and pTau in the human LC in brain donors diagnosed with AD and contrast these expression patterns to both middle-aged and age-matched elderly neurotypical donors. We will use the 10x Genomics Visium Spatial Gene Expression and the Visium Spatial Proteogenomics platforms, which combine transcriptome-wide RNA sequencing with detailed high-resolution histology and immunofluorescence imaging to segment and quantify NM and pTau, respectively. We will computationally align adjacent tissue sections from the same donor across platforms to determine how joint accumulation of NM and pTau during aging and disease impacts the local tissue microenvironment in the human LC. Results will be validated and extended using complementary in situ hybridization platforms with cellular resolution and simultaneous protein detection. Accumulation of NM and pTau represent two key biological hypotheses underlying the vulnerability and resiliency of LC-NE neurons to neurodegeneration in the human brain. Hence, generation of these data are important because understanding the molecular sequelae downstream of this accumulation is critical to develop strategies to target cells in the LC for disease treatment or prevention.
