Inhibition of Hif1α prevents both trauma-induced and genetic heterotopic ossification

S Agarwal, S Loder, C Brownley… - Proceedings of the …, 2016 - National Acad Sciences
S Agarwal, S Loder, C Brownley, D Cholok, L Mangiavini, J Li, C Breuler, HH Sung, S Li…
Proceedings of the National Academy of Sciences, 2016National Acad Sciences
Pathologic extraskeletal bone formation, or heterotopic ossification (HO), occurs following
mechanical trauma, burns, orthopedic operations, and in patients with hyperactivating
mutations of the type I bone morphogenetic protein receptor ACVR1 (Activin type 1
receptor). Extraskeletal bone forms through an endochondral process with a cartilage
intermediary prompting the hypothesis that hypoxic signaling present during cartilage
formation drives HO development and that HO precursor cells derive from a mesenchymal …
Pathologic extraskeletal bone formation, or heterotopic ossification (HO), occurs following mechanical trauma, burns, orthopedic operations, and in patients with hyperactivating mutations of the type I bone morphogenetic protein receptor ACVR1 (Activin type 1 receptor). Extraskeletal bone forms through an endochondral process with a cartilage intermediary prompting the hypothesis that hypoxic signaling present during cartilage formation drives HO development and that HO precursor cells derive from a mesenchymal lineage as defined by Paired related homeobox 1 (Prx). Here we demonstrate that Hypoxia inducible factor-1α (Hif1α), a key mediator of cellular adaptation to hypoxia, is highly expressed and active in three separate mouse models: trauma-induced, genetic, and a hybrid model of genetic and trauma-induced HO. In each of these models, Hif1α expression coincides with the expression of master transcription factor of cartilage, Sox9 [(sex determining region Y)-box 9]. Pharmacologic inhibition of Hif1α using PX-478 or rapamycin significantly decreased or inhibited extraskeletal bone formation. Importantly, de novo soft-tissue HO was eliminated or significantly diminished in treated mice. Lineage-tracing mice demonstrate that cells forming HO belong to the Prx lineage. Burn/tenotomy performed in lineage-specific Hif1α knockout mice (Prx-Cre/Hif1αfl:fl) resulted in substantially decreased HO, and again lack of de novo soft-tissue HO. Genetic loss of Hif1α in mesenchymal cells marked by Prx-cre prevents the formation of the mesenchymal condensations as shown by routine histology and immunostaining for Sox9 and PDGFRα. Pharmacologic inhibition of Hif1α had a similar effect on mesenchymal condensation development. Our findings indicate that Hif1α represents a promising target to prevent and treat pathologic extraskeletal bone.
National Acad Sciences