Hypoxia-inducible factor-1α restricts the anabolic actions of parathyroid hormone.
The hypoxia inducible factors (Hifs) are evolutionarily conserved transcriptional factors that control homeostatic responses to low oxygen. In developing bone, Hif-1 generated signals induce angiogenesis necessary for osteoblast specification, but in mature bone, loss of Hif-1 in osteoblasts resulted in a more rapid accumulation of bone. These findings suggested that Hif-1 exerts distinct developmental functions and acts as a negative regulator of bone formation. To investigate the function of Hif-1α in osteoanabolic signaling, we assessed the effect of Hif-1α loss-of-function on bone formation in response to intermittent parathyroid hormone (PTH). Mice lacking Hif-1α in osteoblasts and osteocytes form more bone in response to PTH, likely through a larger increase in osteoblast activity and increased sensitivity to the hormone. Consistent with this effect, exposure of primary mouse osteoblasts to PTH resulted in the rapid induction of Hif-1α protein levels via a post-transcriptional mechanism. The enhanced anabolic response appears to result from the removal of Hif-1α-mediated suppression of β-catenin transcriptional activity. Together, these data indicate that Hif-1α functions in the mature skeleton to restrict osteoanabolic signaling. The availability of pharmacological agents that reduce Hif-1α function suggests the value in further exploration of this pathway to optimize the therapeutic benefits of PTH.
Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine , Baltimore, MD, USA.
Julie L
JL
Frey
Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine , Baltimore, MD, USA.
David P
DP
Stonko
Division of Nephrology, Bone & Mineral Metabolism, University of Kentucky , Lexington, KY, USA.
Marie-Claude
MC
Faugere
Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine , Baltimore, MD, USA ; Veterans Administration Medical Center , Baltimore, MD, USA.
Ryan C
RC
Riddle