Selective Vulnerability of Brainstem Nuclei in Distinct Tauopathies: A Postmortem Study

Area of Science:

• Neuroscience
• Neuropathology
• Neurodegenerative Diseases

Background:

• The brainstem reticular formation (RF) is crucial for homeostasis, behavior, and cognition.
• RF degeneration is observed in tauopathies like Alzheimer disease (AD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD).
• Distinct clinical phenotypes associated with RF degeneration suggest differential vulnerability patterns among these diseases despite similar tau pathology burdens.

Purpose of the Study:

• To compare the selective vulnerability patterns of specific RF nuclei in AD, CBD, and PSP.
• To investigate how tauopathies differentially affect RF nuclei.
• To establish a foundation for understanding the clinical consequences of RF degeneration in tauopathies.

Main Methods:

• Analysis of 5 RF nuclei in post-mortem brain tissue from 14 AD, 14 CBD, 10 PSP, and 3 control cases.
• Multidimensional quantitative analysis of tau inclusion burden and neuronal loss.
• Comparative assessment of tau pathology and neuronal populations across different tauopathy subtypes.

Main Results:

• Discernible differences in RF nuclei vulnerability to AD, CBD, and PSP were identified.
• Locus coeruleus showed higher tau burden in PSP and CBD compared to AD, but extreme neuronal loss in AD limited aggregate formation.
• Gigantocellular nucleus had low tau burden in AD and high in PSP, with fewer GABAergic neurons in AD, challenging its role in REM behavioral disorders in AD.

Conclusions:

• RF nuclei exhibit distinct vulnerability patterns in different tauopathies.
• Neuronal loss, not just tau burden, influences the presentation of RF degeneration.
• Findings provide a basis for characterizing clinical consequences and guiding tailored treatments for tauopathies affecting the RF.