Hedgehog proteins activate pro-angiogenic responses in endothelial cells through non-canonical signaling pathways

Abstract

The Hedgehog (Hh) pathway orchestrates developmental and homeostatic angiogenesis. the three Hh isoforms--Sonic Hedgehog (Shh), Indian Hedgehog (Ihh) and Desert Hedgehog (Dhh)--signal through patched-1 (ptCH1) and Smoothened (SMo), to activate the Gli transcription factors with a characteristic rank of potency (Shh >> Ihh > Dhh). To dissect the mechanisms through which Hh proteins promote angiogenesis, we analyzed processes inherent to vessel formation in endothelial cells. We found that none of the Hh ligands were able to induce Gli-target genes in human umbilical vein (HUVeC) or human cardiac microvascular endothelial cells (HMVeC), suggesting that endothelial cells do not respond to Hh through the canonical pathway. However, our results show that the three Hh proteins promote endothelial cell tubulogenesis in 3D cultures in a SMo- and Gi protein-dependent manner. Consistent with the required cytoskeletal re-arrangement for tubulogenesis, Shh, Ihh and Dhh all stimulated the small GTPase RhoA and the formation of actin stress fibers. This effect, which was mediated by SMO, Gi proteins and Rac1, defines a new non-canonical Hh pathway. In addition to regulating the actin cytoskeleton, the Hh ligands promoted survival through inhibition of the pro-apoptotic effect of PTCH1 in a SMO-independent manner. Altogether, our results support the existence of Gli-independent Hh responses in endothelial cells that regulate tubulogenesis and apoptosis. The identification of novel non-canonical responses elicited by Hh proteins in endothelial cells highlights the complexity of the Hh signaling pathway and reveals striking differences in ligand strength for transcriptional and non-transcriptional responses

Sonic hedgehog signaling in kidney fibrosis: a master communicator

“…However, all three hedgehog proteins promote endothelial cell tubulogenesis in 3D cultures in a Smo-dependent manner (Polizio et al, 2011). Consistent with the required cytoskeletal rearrangement for tubulogenesis, Shh, Ihh and Dhh all stimulate the small GTPase RhoA and actin stress fibers formation (Chinchilla et al, 2010). This effect, mediated by Smo and G proteins, defines a new non-canonical hedgehog pathway.…”

“…Another non-canonical Shh signaling mainly controls endothelial cells cytoskeletal reorganization and fibroblast migration through activating small GTPases and regulating fluctuations of calcium ions upon stimulation of Shh (Chinchilla et al, 2010; El-Zaatari et al, 2010; Polizio et al, 2011). It has been demonstrated that none of the three hedgehog ligands are able to induce Gli-target genes in human umbilical vein (HUVeC) or human cardiac microvascular endothelial cells (HMVeC), indicating that endothelial cells do not respond to hedgehog through the canonical pathway.…”

T Cell Development Critically Depends on Prethymic Stromal Patched Expression

“…Recently, the immediate signaling partner of Ptch, Smo, was shown to be dispensable for adult HSC differentiation and specification of the T cell lineage (27). The discrepancy between the role of Smo and its immediate signaling partner Ptch in T cell development can be explained by the fact that Ptch also acts on molecular processes without the involvement of the Smo/Gli axis (28)(29)(30). For example, it was demonstrated that Ptch functions as a dependence receptor, which induces apoptosis in the absence of Hh, whereas its proapoptotic activity is blocked the presence of Hh (29).…”

Rescue Effects and Underlying Mechanisms of IntraglandShhGene Delivery on Irradiation-Induced Hyposalivation

“…12 In addition to the Glidependent canonical Hh pathway, the binding of Hh ligands with Ptch also activates several noncanonical pathways such as Rho small GTPases and phosphoinositide 3-kinase (PI3K)/Akt pathways. 13,14 We have found that IR did not activate Hh/Gli signaling, whereas transient activation of the Hh pathway in salivary gland by inducible expression of Shh transgene in Keratin5…”