Loss-of-function variants of TREM2 are associated with increased risk of Alzheimer’s disease (AD), suggesting that activation of this innate immune receptor may be a useful therapeutic strategy. Here we describe a high-affinity human TREM2-activating antibody engineered with a monovalent transferrin receptor (TfR) binding site, termed antibody transport vehicle (ATV), to facilitate blood–brain barrier transcytosis. Upon peripheral delivery in mice, ATV:TREM2 showed improved brain biodistribution and enhanced signaling compared to a standard anti-TREM2 antibody. In human induced pluripotent stem cell (iPSC)-derived microglia, ATV:TREM2 induced proliferation and improved mitochondrial metabolism. Single-cell RNA sequencing and morphometry revealed that ATV:TREM2 shifted microglia to metabolically responsive states, which were distinct from those induced by amyloid pathology. In an AD mouse model, ATV:TREM2 boosted brain microglial activity and glucose metabolism. Thus, ATV:TREM2 represents a promising approach to improve microglial function and treat brain hypometabolism found in patients with AD.

Regulation of gene transcription is controlled in part by nuclear receptors that function coordinately with coregulator proteins. The human constitutive androstane receptor (CAR; NR1I3) is expressed primarily in liver and regulates the expression of genes involved in xenobiotic metabolism as well as hormone, energy, and lipid homeostasis. In this report, DAX-1, a nuclear receptor family member with corepressor properties, was identified as a potent CAR regulator. Results of transaction and mutational studies demonstrated that both DAX-1's downstream LXXLL and its PCFQVLP motifs were critical contributors to DAX-1's corepression activities, although two other LXXM/LL motifs located nearer the N terminus had no impact on the CAR functional interaction. Deletion of DAX-1's C-terminal transcription silencing domain restored CAR1 transactivation activity in reporter assays to approximately 90% of control, demonstrating its critical function in mediating the CAR repression activities. Furthermore, results obtained from mammalian two-hybrid experiments assessing various domain configurations of the respective receptors showed that full-length DAX-1 inhibited the CAR-SRC1 interaction by approximately 50%, whereas the same interaction was restored to 90% of control when the DAX-1 transcription silencing domain was deleted. Direct interaction between CAR and DAX-1 was demonstrated with both alpha-screen and coimmunoprecipitation experiments, and this interaction was enhanced in the presence of the CAR activator 6-(4-chlorophenyl)imidazo[2,1-b]thiazole-5-carbaldehyde O- (3,4-dichlorobenzyl)oxime (CITCO). Results obtained in primary human hepatocytes further demonstrated DAX-1 inhibition of CAR-mediated CITCO induction of the CYP2B6 target gene. The results of this investigation identify DAX-1 as a novel and potent CAR corepressor and suggest that DAX-1 functions as a coordinate hepatic regulator of CAR's biological function.

The human constitutive androstane receptor (CAR) is a nuclear receptor (NR) primarily expressed in liver that regulates genes involved in xenobiotic metabolism, as well as lipid and energy homeostasis. Screening a panel of phage display peptides identified DAX‐1, a NR with corepressor properties, as a potential CAR coregulator. We next determined that DAX‐1 dose‐dependently inhibited CAR‐mediated transactivation. Directed mutation studies of DAX‐1 NR interaction domains showed that mutation of two N terminal domain ‘LXXM/LL’ motifs had no impact on DAX‐1 repression of CAR activity, whereas mutation of downstream ‘LXXLL’ or ‘PCFQVLP’ motifs restored CAR activity to 50% or 65% of control, respectively. Further, deletion of a transcription silencing domain (TSD) located in the DAX‐1 carboxy‐terminal region restored CAR transactivation to 90% of control levels. Two‐hybrid data demonstrated that full length DAX‐1 inhibited CAR‐SRC1 interaction by 50%, while the interaction was once again restored to 90% of control upon deletion of the TSD. Results of an alpha screen assay corroborated a direct interaction between CAR and DAX‐1 that was enhanced by CAR ligands. To examine ex vivo effects of DAX‐1, primary human hepatocytes were transfected with DAX‐1 and subsequent RT‐PCR analyses established that DAX‐1 inhibited CAR‐mediated induction of the CYP2B6 target gene by CITCO. In summary, these studies show that DAX‐1 is a functional corepressor of CAR transcriptional activity. Supported by NIH GM066411