A polygenetic rat model of divergent aerobic capacity reveals a liver-brain interaction impacting Alzheimer's disease-like phenotypes.

Abstract

The interaction between liver and brain health is an emerging complex relationship implicated in Alzheimer's disease (AD). Divergence in aerobic capacity influences liver and brain health independently; however, whether these factors converge to influence AD risk is mechanistically unknown. Bile acid metabolism has been implicated as a link between liver and brain health and is modulated by aerobic capacity. Here, we examined rats selectively bred for high vs. low intrinsic aerobic capacity [high and low-capacity runner (HCR or LCR)] on indices of hepatic metabolism and brain health following a chronic low-fat, high-fat, or high-fat diet with bile acid sequestrant from 6 to 12 months of age. Pre- and post-diet measures included learning, memory, and brain volume metabolite levels. We additionally quantified brain and liver Aβ and proteins associated with Aβ production and clearance, as well as liver and brain mitochondrial energetics and liver bile acid species. We found that not only did aerobic capacity and diet influence mitochondrial function, but also it modified Aβ levels across the liver and brain. Additionally, aerobic capacity and diet altered bile acid profiles and brain hippocampal metabolite levels. The addition of bile acid sequestrant lowered brain Aβ levels in a sexually dimorphic manner. Aerobic capacity but not diet altered cognitive outcomes. Our results indicate that aerobic capacity and diet-induced liver health alterations modulate brain health with respect to metabolism and AD-like pathologies, whereas a stimulation of faecal bile acid loss could have positive effects on lowering brain Aβ. KEY POINTS: Aerobic capacity and diet-induced alterations to liver function alter liver bile acid species and faecal energy loss. Aerobic capacity and diet alter both brain and liver Aβ homeostasis. Aerobic capacity modulates brain and hippocampal volume in addition to brain metabolism. Aerobic capacity influences learning in middle-aged rats.