Two human brain systems micro-structurally associated with obesity

Area of Science:

• Neuroimaging
• Obesity Research
• Genetics

Background:

• The intricate relationship between obesity and human brain structure remains poorly understood.
• Microstructural MRI metrics offer insights into brain tissue composition.

Purpose of the Study:

• To investigate the association between obesity (waist-to-hip ratio) and brain microstructural metrics (isotropic volume fraction and intra-cellular volume fraction).
• To explore the genetic underpinnings and inflammatory correlations of these obesity-associated brain changes.

Main Methods:

• Utilized diffusion-weighted MRI data from approximately 30,000 UK Biobank participants.
• Analyzed associations between waist-to-hip ratio and isotropic volume fraction (free water) and intra-cellular volume fraction (neurite density).
• Examined genetic correlations and relationships with C-reactive Protein (CRP) maps.

Main Results:

• Identified two distinct brain systems associated with obesity: a prefrontal/temporal/striatal system for isotropic volume fraction and a medial temporal/occipital/striatal system for intra-cellular volume fraction.
• Observed distinct gene expression patterns and receptor densities within these systems.
• Found a significant genetic correlation between waist-to-hip ratio and intra-cellular volume fraction, but not isotropic volume fraction.

Conclusions:

• Obesity is associated with distinct alterations in brain water content and neurite density in specific neural systems.
• Findings support a bidirectional model where brain structure may influence obesity risk (neurite density) and obesity may impact brain structure (water content via immune activation).
• Suggests a potential role for innate immune pathways in mediating obesity's effects on brain water content.