Int J Mol Sci

The role of Hedgehog (Hh) signaling in vascular biology has first been highlighted in embryos by Pepicelli et al. in 1998 and Rowitch et al. in 1999. Since then, the proangiogenic role of the Hh ligands has been confirmed in adults, especially under pathologic conditions. More recently, the Hh signaling has been proposed to improve vascular integrity especially at the blood-brain barrier (BBB). However, molecular and cellular mechanisms underlying the role of the Hh signaling in vascular biology remain poorly understood and conflicting results have been reported. As a matter of fact, in several settings, it is currently not clear whether Hh ligands promote vessel integrity and quiescence or destabilize vessels to promote angiogenesis. The present review relates the current knowledge regarding the role of the Hh signaling in vasculature development, maturation and maintenance, discusses the underlying proposed mechanisms and highlights controversial data which may serve as a guideline for future research. Most importantly, fully understanding such mechanisms is critical for the development of safe and efficient therapies to target the Hh signaling in both cancer and cardiovascular/cerebrovascular diseases

Arterioscler Thromb Vasc Biol

Evidences accumulated within the past decades identified hedgehog signaling as a new regulator of endothelium integrity. More specifically, we recently identified Dhh (desert hedgehog) as a downstream effector of Klf2 (Kruppel-like factor 2) in endothelial cells (ECs). The purpose of this study is to investigate whether hedgehog coreceptors Gas1 (growth arrest-specific 1) and Cdon (cell adhesion molecule-related/downregulated by oncogenes) may be used as therapeutic targets to modulate Dhh signaling in ECs. Approach and Results: We demonstrated that both Gas1 and Cdon are expressed in adult ECs and relied on either siRNAs- or EC-specific conditional knockout mice to investigate their role. We found that Gas1 deficiency mainly phenocopies Dhh deficiency especially by inducing VCAM-1 (vascular cell adhesion molecule 1) and ICAM-1 (intercellular adhesion molecule 1) overexpression while Cdon deficiency has opposite effects by promoting endothelial junction integrity. At a molecular level, Cdon prevents Dhh binding to Ptch1 (patched-1) and thus acts as a decoy receptor for Dhh, while Gas1 promotes Dhh binding to Smo (smoothened) and as a result potentiates Dhh effects. Since Cdon is upregulated in ECs treated by inflammatory cytokines, including TNF (tumor necrosis factor)-α and Il (interleukin)-1β, we then tested whether Cdon inhibition would promote endothelium integrity in acute inflammatory conditions and found that both fibrinogen and IgG extravasation were decreased in association with an increased Cdh5 (cadherin-5) expression in the brain cortex of EC-specific Cdon knockout mice administered locally with Il-1β. Altogether, these results demonstrate that Gas1 is a positive regulator of Dhh in ECs while Cdon is a negative regulator. Interestingly, Cdon blocking molecules may then be used to promote endothelium integrity, at least in inflammatory conditions

PLoS Biol

Inflammation of the central nervous system (CNS) induces endothelial blood-brain barrier (BBB) opening as well as the formation of a tight junction barrier between reactive astrocytes at the Glia Limitans. We hypothesized that the CNS parenchyma may acquire protection from the reactive astrocytic Glia Limitans not only during neuroinflammation but also when BBB integrity is compromised in the resting state. Previous studies found that astrocyte-derived Sonic hedgehog (SHH) stabilizes the BBB during CNS inflammatory disease, while endothelial-derived desert hedgehog (DHH) is expressed at the BBB under resting conditions. Here, we investigated the effects of endothelial Dhh on the integrity of the BBB and Glia Limitans. We first characterized DHH expression within endothelial cells at the BBB, then demonstrated that DHH is down-regulated during experimental autoimmune encephalomyelitis (EAE). Using a mouse model in which endothelial Dhh is inducibly deleted, we found that endothelial Dhh both opens the BBB via the modulation of forkhead box O1 (FoxO1) transcriptional activity and induces a tight junctional barrier at the Glia Limitans. We confirmed the relevance of this glial barrier system in human multiple sclerosis active lesions. These results provide evidence for the novel concept of "chronic neuroinflammatory tolerance" in which BBB opening in the resting state is sufficient to stimulate a protective barrier at the Glia Limitans that limits the severity of subsequent neuroinflammatory disease. In summary, genetic disruption of the BBB generates endothelial signals that drive the formation under resting conditions of a secondary barrier at the Glia Limitans with protective effects against subsequent CNS inflammation. The concept of a reciprocally regulated CNS double barrier system has implications for treatment strategies in both the acute and chronic phases of multiple sclerosis pathophysiology

La signalisation Hedgehog dans le maintien de la barrière hémato-encéphalique et la physiopathologie des troubles neurodégénératifs

Neurodegenerative diseases suchs as Alzheimer’s or Multiple Sclerosis are characterized by a progressive degeneration of the central or peripheral nervous system. The blood-brain barrier (BBB) plays a critical role in the pathophysiologie of the central nervous system, and its disruption contributes to the pathogenesis of neurodegenerative disease. Since Hedgehog (Hh) signalling is implicated in the maintenance of the BBB, and since discrepancies exist in the literature, the objective of this PhD’s thesis is to clarify the mechanisms underlying Hh ligands-dependent regulation of the BBB, in physiological and pathological (multiple sclerosis and Alzheimer’s) conditions, in the adult.We showed that Desert Hedgehog (Dhh) is expressed in endothelial cells (ECs), and is necessary to stabilize the BBB. Moreove, we showed that the deletion of Dhh in ECs, and the consequential opening of the BBB are sufficient to trigger the apparition of cognitive disorders. Our results also suggest that Dhh in ECs is downregulated in Alzheimer’s and multiple sclerosis.We also showed that in multiple sclerosis, Sonic Hedgehog (Shh) is induced in astrocytes and contributes to the opening of the BBB. Those results and other finally led us to demonstrate that depending on their post-translational maturation, Hh ligands have distinct effects on the BBB.Taken together, those results strengthen the hypothesis of using Hh signalling as a therapeutic target in the treatment of neurodegenerative diseases, and unveil new insights to consider when it comes to conceiving such therapeutical strategies.Les maladies neurodégénératives, telles que la maladie d’Alzheimer, la maladie de Parkinson ou la sclérose en plaques, sont des maladies chroniques progressives touchant le système nerveux central. La barrière hémato-encéphalique (BHE) joue un rôle critique dans la physiologie du système nerveux central et, de ce fait, sa perturbation participe à la pathogénèse des maladies neurodégénératives. Du fait de l’implication de la voie de signalisation Hedgehog (Hh) dans la régulation de la BHE, et de l’existence de résultats contradictoires dans la littérature, l’objectif de cette thèse est de revoir les mécanismes mis en jeu dans la régulation de l’intégrité de la BHE par les ligands de la voie Hh dans des conditions physiologiques et pathologiques (sclérose en plaque et maladie d’Alzheimer) chez l’adulte.Nous avons montré que Desert Hedgehog (Dhh), exprimé par les cellules endothéliales (CE), est nécessaire au maintien de l’intégrité de la BHE. De plus, nous avons montré que la perte de Dhh dans les CE et l’ouverture de la BHE qui s’ensuit suffisent à induire l’apparition de troubles cognitifs. De plus, nos résultats suggèrent que l’expression endothéliale de Dhh est réduite dans la maladie d’Alzheimer et la sclérose en plaquesPar ailleurs nous avons montré que dans la sclérose en plaque, une induction de l’expression de Sonic Hedgehog (Shh) dans les astrocytes participe à l’ouverture de la BHE. Ces résultats et d’autres nous ont finalement permis de montrer qu’en fonction de leur forme, les ligands de la voie Hh agissent différemment sur la BHE.Dans l’ensemble, ces résultats renforcent l’idée déjà existante que la voie de signalisation Hh constitue une cible d’intérêt dans la thérapeutique des maladies neurodégénératives, et apportent de nouvelles informations à prendre en compte dans l’élaboration de stratégies thérapeutiques

Role of Hedgehog signalling in the maintenance of the blood-brain barrier and in the pathophysiology of neurodegenerative diseases.

Les maladies neurodégénératives, telles que la maladie d’Alzheimer, la maladie de Parkinson ou la sclérose en plaques, sont des maladies chroniques progressives touchant le système nerveux central. La barrière hémato-encéphalique (BHE) joue un rôle critique dans la physiologie du système nerveux central et, de ce fait, sa perturbation participe à la pathogénèse des maladies neurodégénératives. Du fait de l’implication de la voie de signalisation Hedgehog (Hh) dans la régulation de la BHE, et de l’existence de résultats contradictoires dans la littérature, l’objectif de cette thèse est de revoir les mécanismes mis en jeu dans la régulation de l’intégrité de la BHE par les ligands de la voie Hh dans des conditions physiologiques et pathologiques (sclérose en plaque et maladie d’Alzheimer) chez l’adulte.Nous avons montré que Desert Hedgehog (Dhh), exprimé par les cellules endothéliales (CE), est nécessaire au maintien de l’intégrité de la BHE. De plus, nous avons montré que la perte de Dhh dans les CE et l’ouverture de la BHE qui s’ensuit suffisent à induire l’apparition de troubles cognitifs. De plus, nos résultats suggèrent que l’expression endothéliale de Dhh est réduite dans la maladie d’Alzheimer et la sclérose en plaquesPar ailleurs nous avons montré que dans la sclérose en plaque, une induction de l’expression de Sonic Hedgehog (Shh) dans les astrocytes participe à l’ouverture de la BHE. Ces résultats et d’autres nous ont finalement permis de montrer qu’en fonction de leur forme, les ligands de la voie Hh agissent différemment sur la BHE.Dans l’ensemble, ces résultats renforcent l’idée déjà existante que la voie de signalisation Hh constitue une cible d’intérêt dans la thérapeutique des maladies neurodégénératives, et apportent de nouvelles informations à prendre en compte dans l’élaboration de stratégies thérapeutiques.Neurodegenerative diseases suchs as Alzheimer’s or Multiple Sclerosis are characterized by a progressive degeneration of the central or peripheral nervous system. The blood-brain barrier (BBB) plays a critical role in the pathophysiologie of the central nervous system, and its disruption contributes to the pathogenesis of neurodegenerative disease. Since Hedgehog (Hh) signalling is implicated in the maintenance of the BBB, and since discrepancies exist in the literature, the objective of this PhD’s thesis is to clarify the mechanisms underlying Hh ligands-dependent regulation of the BBB, in physiological and pathological (multiple sclerosis and Alzheimer’s) conditions, in the adult.We showed that Desert Hedgehog (Dhh) is expressed in endothelial cells (ECs), and is necessary to stabilize the BBB. Moreove, we showed that the deletion of Dhh in ECs, and the consequential opening of the BBB are sufficient to trigger the apparition of cognitive disorders. Our results also suggest that Dhh in ECs is downregulated in Alzheimer’s and multiple sclerosis.We also showed that in multiple sclerosis, Sonic Hedgehog (Shh) is induced in astrocytes and contributes to the opening of the BBB. Those results and other finally led us to demonstrate that depending on their post-translational maturation, Hh ligands have distinct effects on the BBB.Taken together, those results strengthen the hypothesis of using Hh signalling as a therapeutic target in the treatment of neurodegenerative diseases, and unveil new insights to consider when it comes to conceiving such therapeutical strategies

Role of Hedgehog Signaling in Vasculature Development, Differentiation, and Maintenance

International audienceThe role of Hedgehog (Hh) signaling in vascular biology has first been highlighted in embryos by Pepicelli et al. in 1998 and Rowitch et al. in 1999. Since then, the proangiogenic role of the Hh ligands has been confirmed in adults, especially under pathologic conditions. More recently, the Hh signaling has been proposed to improve vascular integrity especially at the blood-brain barrier (BBB). However, molecular and cellular mechanisms underlying the role of the Hh signaling in vascular biology remain poorly understood and conflicting results have been reported. As a matter of fact, in several settings, it is currently not clear whether Hh ligands promote vessel integrity and quiescence or destabilize vessels to promote angiogenesis. The present review relates the current knowledge regarding the role of the Hh signaling in vasculature development, maturation and maintenance, discusses the underlying proposed mechanisms and highlights controversial data which may serve as a guideline for future research. Most importantly, fully understanding such mechanisms is critical for the development of safe and efficient therapies to target the Hh signaling in both cancer and cardiovascular/cerebrovascular diseases

Cardiovasc Res

The therapeutic potential of Hedgehog (Hh) signalling agonists for vascular diseases is of growing interest. However, molecular and cellular mechanisms underlying the role of the Hh signalling in vascular biology remain poorly understood. The purpose of the present paper is to clarify some conflicting literature data. : With this goal we have demonstrated that, unexpectedly, ectopically administered N-terminal Sonic Hedgehog (N-Shh) and endogenous endothelial-derived Desert Hedgehog (Dhh) induce opposite effects in endothelial cells (ECs). Notably, endothelial Dhh acts under its full-length soluble form (FL-Dhh) and activates Smoothened in ECs, while N-Shh inhibits it. At molecular level, N-Shh prevents FL-Dhh binding to Patched-1 demonstrating that N-Shh acts as competitive antagonist to FL-Dhh. Besides, we found that even though FL-Hh ligands and N-Hh ligands all bind Patched-1, they induce distinct Patched-1 localization. Finally, we confirmed that in a pathophysiological setting i.e. brain inflammation, astrocyte-derived N-Shh act as a FL-Dhh antagonist. The present study highlights for the first time that FL-Dhh and N-Hh ligands have antagonistic properties especially in ECs. As a consequence, Hh ligands or forms of Hh ligands cannot be used instead of another for therapeutic purposes

Arterioscler Thromb Vasc Biol

[Figure: see text]

Restoring Endothelial Function by Targeting Desert Hedgehog Downstream of Klf2 Improves Critical Limb Ischemia in Adults

RATIONALE: Klf (kruppel-like factor) 2 is critical to establish and maintain endothelial integrity. OBJECTIVE: Therefore, determining upstream and downstream mediators of Klf2 would lead to alternative therapeutic targets in cardiovascular disease management. METHODS AND RESULTS: Here we identify Dhh (desert hedgehog) as a downstream effector of Klf2, whose expression in endothelial cells (ECs) is upregulated by shear stress and decreased by inflammatory cytokines. Consequently, we show that Dhh knockdown in ECs promotes endothelial permeability and EC activation and that Dhh agonist prevents TNF-α (tumor necrosis factor alpha) or glucose-induced EC dysfunction. Moreover, we demonstrate that human critical limb ischemia, a pathological condition linked to diabetes mellitus and inflammation, is associated to major EC dysfunction. By recreating a complex model of critical limb ischemia in diabetic mice, we found that Dhh-signaling agonist significantly improved EC function without promoting angiogenesis, which subsequently improved muscle perfusion. CONCLUSION: Restoring EC function leads to significant critical limb ischemia recovery. Dhh appears to be a promising target, downstream of Klf2, to prevent the endothelial dysfunction involved in ischemic vascular diseases