Morphogen pathways in systemic sclerosis.

The morphogen pathways Wnt, hedgehog, and Notch are key regulators of organ development and tissue homeostasis. In adults, the tightly regulated activity of morphogen pathways is essential for cell renewal and tissue regeneration. Loss of control and persistent activation of morphogen pathways, however, can lead to a variety of diseases, including malignancy and fibrotic disorders. In recent years, pathological activation of Wnt, hedgehog, and Notch pathways have been described in systemic sclerosis (SSc) and other fibrotic diseases. Experimental models reveal that morphogen pathways drive fibroblast activation and collagen release. In these model systems, genetic or pharmacological blockade of morphogen pathways inhibits collagen release and reduces experimental fibrosis. Importantly, inhibitors for Wnt, hedgehog, and Notch are already in clinical evaluation, thereby emphasizing the translational implications of these findings. Further experimental studies, however, should deepen our knowledge before initiating clinical trials with inhibitors of morphogen pathways.