Gamma-Glutamyl Transferase and Cognitive Outcomes: A Cross-Species Analysis and Hepatic Transcriptomic Signature

Cognitive impairment is a major public health concern, and the liver–brain axis has attracted growing interest. Gamma-glutamyl transferase (GGT) is a serum marker of liver function, but its association with cognitive outcomes remains uncertain. We conducted a cross-species analysis. In 5xFAD mice (n = 52), we examined serum liver markers and spatial cognition using the Morris water maze. In NHANES 2011–2014 (n = 3181, aged ≥60 years), we evaluated liver markers and low cognitive performance (LCP) using multivariable logistic regression. We also performed virtual hepatic GGT1 knockout in a human liver single-cell atlas and integrated GTEx liver co-expression, transcription factor enrichment, and WGCNA analyses. In mice, GGT–cognition associations largely attenuated after strain adjustment, but a positive association with platform crossings emerged (r = 0.321, p = 0.02). In NHANES, serum GGT was inversely associated with LCP (Q4 vs. Q1 OR = 0.54, p < 0.001), with a nonlinear association and an inflection point near 19 U/L. Virtual hepatic GGT1 knockout identified eight immunoglobulin-related genes associated with SPI1 and oxidative stress-related pathways. These parallel findings are hypothesis-generating. A testable hypothesis is that lower hepatic GGT1 activity or serum GGT is associated with upregulated cholangiocyte immunoglobulin-related programs and poorer cognition.