PT  - JOURNAL ARTICLE
AU  - Manfred G Kitzbichler
AU  - Daniel Martins
AU  - Richard AI Bethlehem
AU  - Richard Dear
AU  - Rafael Romero-Garcia
AU  - Varun Warrier
AU  - Jakob Seidlitz
AU  - Ottavia Dipasquale
AU  - Federico Turkheimer
AU  - Mara Cercignani
AU  - Edward T Bullmore
AU  - Neil A Harrison
TI  - Two human brain systems micro-structurally associated with obesity
AID  - 10.1101/2022.11.25.517981
DP  - 2023 Jan 01
TA  - bioRxiv
PG  - 2022.11.25.517981
4099  - http://biorxiv.org/content/early/2023/05/26/2022.11.25.517981.short
4100  - http://biorxiv.org/content/early/2023/05/26/2022.11.25.517981.full
AB  - The relationship between obesity and brain structure is incompletely understood. Using diffusion-weighted MRI from ∼30,000 UK Biobank participants we test the hypothesis that obesity (waist-to-hip ratio, WHR) is associated with regional differences in two micro-structural MRI metrics: isotropic volume fraction (ISOVF), an index of free water, and intra-cellular volume fraction (ICVF), an index of neurite density. We observed significant associations with obesity in two coupled but distinct brain systems: a prefrontal-temporal-striatal system associated with ISOVF and a medial temporal-occipital-striatal system associated with ICVF. The ISOVF∼WHR system colocated with expression of genes enriched for innate immune functions, decreased glial density, and high mu opioid (MOR) and other neurotransmitter receptor density. Conversely, the ICVF∼WHR system co-located with expression of genes enriched for G-protein coupled receptors and decreased density of MOR and other receptors. To test whether these distinct brain phenotypes might differ in terms of their underlying shared genetics or relationship to maps of the inflammatory marker C-reactive Protein (CRP), we estimated the genetic correlations between WHR and ISOVF (rg = 0.026, P = 0.36) and ICVF (rg = 0.112, P < 9 × 10−4) as well as comparing correlations between WHR maps and equivalent CRP maps for ISOVF and ICVF (p<0.05). These correlational results are consistent with a two-way mechanistic model whereby genetically determined differences in neurite density in the medial temporal system may contribute to obesity, whereas water content in the prefrontal system could reflect a consequence of obesity mediated by innate immune system activation.Competing Interest StatementThe authors have declared no competing interest.