Gene

Osteoblast

Cell biology

Heterotopic ossification

Biology

Endocrinology

Signal transduction

Cancer research

Downregulation and upregulation

Genetics

Ossification

GNAS complex locus

Anatomy

Mathematics

In vitro

Internal medicine

Loop (graph theory)

Combinatorics

Sonic hedgehog

Medicine

Fibrodysplasia ossificans progressiva

Hedgehog signaling pathway

Bone morphogenetic protein

Science Translational Medicine

Heterotopic ossification (HO) occurs as a common complication after injury or in genetic disorders. The mechanisms underlying HO remain incompletely understood, and there are no approved prophylactic or secondary treatments available. Here, we identify a self-amplifying, self-propagating loop of Yes-associated protein (YAP)-Sonic hedgehog (SHH) as a core molecular mechanism underlying diverse forms of HO. In mouse models of progressive osseous heteroplasia (POH), a disease caused by null mutations in GNAS, we found that Gnas-/- mesenchymal cells secreted SHH, which induced osteoblast differentiation of the surrounding wild-type cells. We further showed that loss of Gnas led to activation of YAP transcription activity, which directly drove Shh expression. Secreted SHH further induced YAP activation, Shh expression, and osteoblast differentiation in surrounding wild-type cells. This self-propagating positive feedback loop was both necessary and sufficient for HO expansion and could act independently of Gnas in fibrodysplasia ossificans progressiva (FOP), another genetic HO, and nonhereditary HO mouse models. Genetic or pharmacological inhibition of YAP or SHH abolished HO in POH and FOP and acquired HO mouse models without affecting normal bone homeostasis, providing a previously unrecognized therapeutic rationale to prevent, reduce, and shrink HO.

A self-amplifying loop of YAP and SHH drives formation and expansion of heterotopic ossification