Parathyroid Hormone Signaling in Adiponectin+ Bone Marrow Cells Decreases Bone Mass and Restricts the Anabolic Response to Teriparatide

Objectives The parathyroid hormone (PTH) and its related peptide (PTHrP) are critical for skeletal development and homeostasis, acting on several cell types in bone/bone marrow via their receptor, Pth1r. A bioactive form (PTH [1-34], teriparatide) is one of the few anabolic treatments approved for use in osteoporosis and has been used for the treatment of medication-related osteonecrosis of the jaw. Adiponectin-positive (Adipoq+) marrow cells have been reported to suppress osteogenesis and enhance osteoclastogenesis. Previously, we showed that deletion of Pth1r in Adipoq+ cells increases bone mass by favoring osteogenesis. Here, we characterize the transcriptomic profiles of Adipoq+ cells lacking Pth1r and their effects on neighboring cells. Moreover, we assess the response to the teriparatide treatment in mice lacking Pth1r in Adipoq+ cells. Methods AdipoqCre, Pth1rfl/fl mice were used, where Pth1r is deleted only in Adipoq+ cells (AdipoqΔPth1r). Bulk RNA-seq was performed on sorted Adipoq+ cells. scRNA-seq was performed on all stromal cells. Teriparatide was administered daily to 8-week-old mice for 4 weeks and skeletal phenotype was characterized by micro-computed tomography (mCT). Results Bulk RNA-seq analysis identified 549 upregulated and 423 downregulated genes in AdipoqΔPth1r mice. Genes implicated in monocyte regulation such as colony stimulating factor 1 (Csf1) were downregulated in AdipoqΔPth1r mice. scRNA-seq analysis identified 14 cell populations; cluster 10 was labeled by Adipoq. Pth1r deletion in cluster 10 altered the expression of genes implicated in bone and adipocyte biology. Furthermore, receptor-ligand interactions between Adipoq+ cluster and Adipoq-negative clusters were affected by Pth1r deletion resulting in changes in the proportions of Adipoq-negative clusters. Lastly, we analyzed the skeletal response to teriparatide treatment in AdipoqΔPth1r mice and their littermate controls. Teriparatide treatment induced a 2-fold greater increase in vertebral bone volume in AdipoqΔPth1r mice (8.38%) compared to control mice (4.08%, p=0.0006). Conclusions PTH and PTHrP activate the Pth1r in both the osteogenic and adipogenic lineages. Whereas Pth1r activation in the osteogenic lineage favors bone formation and increases bone mass, its activation in the adipogenic lineage exerts a negative influence on the skeleton, affects the bone marrow environment, and restricts the anabolic response to teriparatide treatment. The parathyroid hormone (PTH) and its related peptide (PTHrP) are critical for skeletal development and homeostasis, acting on several cell types in bone/bone marrow via their receptor, Pth1r. A bioactive form (PTH [1-34], teriparatide) is one of the few anabolic treatments approved for use in osteoporosis and has been used for the treatment of medication-related osteonecrosis of the jaw. Adiponectin-positive (Adipoq+) marrow cells have been reported to suppress osteogenesis and enhance osteoclastogenesis. Previously, we showed that deletion of Pth1r in Adipoq+ cells increases bone mass by favoring osteogenesis. Here, we characterize the transcriptomic profiles of Adipoq+ cells lacking Pth1r and their effects on neighboring cells. Moreover, we assess the response to the teriparatide treatment in mice lacking Pth1r in Adipoq+ cells. AdipoqCre, Pth1rfl/fl mice were used, where Pth1r is deleted only in Adipoq+ cells (AdipoqΔPth1r). Bulk RNA-seq was performed on sorted Adipoq+ cells. scRNA-seq was performed on all stromal cells. Teriparatide was administered daily to 8-week-old mice for 4 weeks and skeletal phenotype was characterized by micro-computed tomography (mCT). Bulk RNA-seq analysis identified 549 upregulated and 423 downregulated genes in AdipoqΔPth1r mice. Genes implicated in monocyte regulation such as colony stimulating factor 1 (Csf1) were downregulated in AdipoqΔPth1r mice. scRNA-seq analysis identified 14 cell populations; cluster 10 was labeled by Adipoq. Pth1r deletion in cluster 10 altered the expression of genes implicated in bone and adipocyte biology. Furthermore, receptor-ligand interactions between Adipoq+ cluster and Adipoq-negative clusters were affected by Pth1r deletion resulting in changes in the proportions of Adipoq-negative clusters. Lastly, we analyzed the skeletal response to teriparatide treatment in AdipoqΔPth1r mice and their littermate controls. Teriparatide treatment induced a 2-fold greater increase in vertebral bone volume in AdipoqΔPth1r mice (8.38%) compared to control mice (4.08%, p=0.0006). PTH and PTHrP activate the Pth1r in both the osteogenic and adipogenic lineages. Whereas Pth1r activation in the osteogenic lineage favors bone formation and increases bone mass, its activation in the adipogenic lineage exerts a negative influence on the skeleton, affects the bone marrow environment, and restricts the anabolic response to teriparatide treatment.