Spatial Transcriptomics Reveals the Requirement of ADGRG6 in Maintaining Chondrocyte Homeostasis in Mouse Growth Plates

The growth plate is essential for maintaining skeletal growth; however, the mechanisms governing postnatal growth plate homeostasis are poorly understood. Here we show that ADGRG6/GPR126, a cartilage-enriched G protein-coupled receptor (GPCR), is dispensable for embryonic limb development but is required for postnatal growth plate homeostasis. Adgrg6 ablation in osteochondral progenitor cells or postnatal chondrocytes leads to reduced cellularity and impaired maintenance of the resting zone in the growth plate, coupled with increased cell death and reduced cell proliferation. Adgrg6 mutant growth plates also exhibit disorganized extracellular matrix structures and dysregulated hypertrophic differentiation. Furthermore, using a novel spatial transcriptomics workflow that applies to FFPE tissue sections of mineralized mouse knee joints, we demonstrate that Adgrg6 ablation leads to reduced SOX9 expression, induced Indian hedgehog (IHH) signaling, and a precocious chondrogenic-to-osteogenic conversion of the growth plate chondrocytes that may be driven by increased POSTN/integrin receptor signaling. We further demonstrated that ADGRG6 regulates the proper formation of the resting zone growth plate by maintaining the PTHrP and SOX9-positive cell populations. Altogether, our findings elucidate the essential role of ADGRG6 in maintaining chondrocyte fate, survival, and homeostasis of the postnatal growth plates.