Inhibition of AhR improves cortical bone and skeletal muscle function via preservation of neuromuscular junctions

The aryl hydrocarbon receptor (AhR) is proposed to mediate the frailty-promoting effects of the tryptophan metabolite kynurenine (Kyn), which increases with age in mice and humans. The goal of the current study was to test whether administration of pharmacological AhR inhibitors, BAY2416964 and CH-223191, could abrogate musculoskeletal decline in aging mice. Female C57BL/6 mice (18 months old) were treated with vehicle (VEH) or BAY2416964 (30 mg/kg) via daily oral gavage 5 days/week for 8 weeks. A second AhR antagonist, CH-223191, was administered to 16-month-old male and female C57BL/6 mice via intraperitoneal injections (3.3mg/kg) 3 days/week for 12 weeks. While grip strength declined over time in VEH-treated mice, BAY2416964 preserved grip strength in part by improving integrity of neuromuscular junctions, an effect replicated during in vitro studies with siRNA against AhR. Cortical bone mass was also greater in BAY2416964- than VEH-treated mice. Similarly, CH- 223191 treatment improved cortical bone and showed beneficial effects in skeletal muscle, including reducing oxidative stress as compared to VEH-treated animals. Transcriptomic and proteomic data from BAY2416964-treated mice supported a positive impact of BAY2416964 on molecular targets that affect neuromuscular junction function. Taken together, these data support AhR as a therapeutic target for improving musculoskeletal health during aging. RNA-seq profiling of tibialis anterior (TA) muscle and cortical bone shafts in vehicle- and BAY2416964-treated aged mice. For TA muscles, bulk RNA-seq was performed using total RNA extracted by Maxwell RSC simplyRNA Tissue kit; libraries were generated with Illumina Stranded mRNA Prep kit. For cortical bone, RNA was extracted with TRIzol. Sequencing was performed on Illumina platform. Transcript counts were aligned to the mm39 genome using STAR aligner and analyzed using Partek Flow and DESeq2. n=4 mice per group.