Differential effects of PTH (1-34), PTHrP (1-36) and abaloparatide on the murine osteoblast transcriptome

Teriparatide (PTH(1-34)) and its analogs, PTHrP(1-36) and abaloparatide (ABL) have been used for the treatment of osteoporosis, but their efficacy over long-term use is significantly limited. The 3 peptides exert time- and dose-dependent differential responses in osteoblasts, leading us to hypothesize that they may also differentially modulate the osteoblast transcriptome. We show that treatment of mouse calvarial osteoblasts with 1 nM of the 3 peptides for 4 h results in RNA-Seq data with PTH(1-34) regulating 367 genes, including 194 unique genes; PTHrP(1-36) regulating 117 genes, including 15 unique genes; and ABL regulating 179 genes, including 20 unique genes. There were 83 genes shared among all 3 peptides. Gene ontology analyses showed differences in Wnt signaling, cAMP-mediated signaling, bone mineralization, morphogenesis of a branching structure in biological processes; receptor ligand activity, transcription factor activity, cytokine receptor/binding activity and many other actions in molecular functions. The 3 peptides increased Vdr, Cited1 and Pde10a mRNAs in a pattern similar to Rankl , i.e., PTH(1-34) > ABL > PTHrP(1-36). mRNA abundance of other genes based on gene/pathway analyses, including Wnt4, Wnt7, Wnt11, Sfrp4, Dkk1, Kcnk10, Hdac4, Epha3, Tcf7, Crem, Fzd5, Pp2r2a , and Dvl3 showed that some genes were regulated similarly by all 3 peptides; others were not. Finally, siRNA knockdowns of SIK1/2/3 and CRTC1/2/3 in PTH(1-34)-treated cells revealed that Vdr and Wnt4 genes are regulated by SIKs and CRTCs, while others are not. Although many studies have examined PTH signaling in the osteoblast/osteocyte, ours is the first to examine the global effects of these peptides on the osteoblast transcriptome. Further delineation of which signaling events are attributable to PTH(1-34), PTHrP(1-36) or ABL exclusively and which are shared among all 3 will help improve our understanding of the effects these peptides have on the osteoblast and lead to the refinement of PTH-derived treatments for osteoporosis.