ABSTRACT
Bile acids (BAs) metabolism has a significant impact on the pathogenesis of Alzheimer's disease (AD). We found that deoxycholic acid (DCA) increased in brains of AD mice at an early stage. The enhanced production of DCA induces the up-regulation of the bile acid receptor Takeda G protein-coupled receptor (TGR5), which is also specifically increased in neurons of AD mouse brains at an early stage. The accumulation of exogenous DCA impairs cognitive function in wild-type mice, but not in TGR5 knockout mice. This suggests that TGR5 is the primary receptor mediating these effects of DCA. Furthermore, excitatory neuron-specific knockout of TGR5 ameliorates Aß pathology and cognition impairments in AD mice. The underlying mechanism linking TGR5 and AD pathology relies on the downstream effectors of TGR5 and the APP production, which is succinctly concluded as a "p-STAT3-APH1-γ-secretase" signaling pathway. Our studies identified the critical role of TGR5 in the pathological development of AD.
Subject(s)
Alzheimer Disease , Amyloid beta-Protein Precursor , Neurons , Receptors, G-Protein-Coupled , Animals , Humans , Mice , Alzheimer Disease/metabolism , Alzheimer Disease/pathology , Alzheimer Disease/genetics , Amyloid beta-Protein Precursor/metabolism , Amyloid beta-Protein Precursor/genetics , Amyloid Precursor Protein Secretases/metabolism , Amyloid Precursor Protein Secretases/genetics , Brain/metabolism , Brain/pathology , Deoxycholic Acid/pharmacology , Disease Models, Animal , Mice, Knockout , Neurons/metabolism , Neurons/pathology , Receptors, G-Protein-Coupled/metabolism , Receptors, G-Protein-Coupled/genetics , Signal TransductionABSTRACT
Depressive symptoms usually precede the cognitive decline in Alzheimer disease (AD) and worsen the clinical outcome. However, the neural circuitry mediating early emotional dysfunction, especially depressive symptoms in AD, remains elusive. Anterior cingulate cortex (ACC) is closely related to depression and vulnerable in AD. By quantitative whole-brain mapping and electrophysiological recording, we found that the decreased axonal calcium activity in neurons of ACC and the glutamatergic projection from ACC to the ventral hippocampal CA1 (vCA1) is significantly impaired in 3-month-old 5×FAD mice, which exhibit depressive-like phenotype before cognition defects in early stage. The activation of ACC-vCA1 circuit by chemogenetic manipulation efficiently ameliorated the early depressive-like behaviors in 5×FAD mice. We further identified the upregulated neuregulin-1 (Nrg1) in ACC impaired the excitatory synaptic transmission from the ACC to vCA1 in AD. Our work reveals the role of ACC-vCA1 circuit in regulating AD associated depression symptom in a mouse model of AD.
