PATHOPHYSIOLOGY OF THE COSTELLO SYNDROME: STUDY IN MICE AND CELL MODELS – COSMIT

This "COSMIT" project focuses on a rare disease, the Costello syndrome (CS), the underlying mechanisms of which are not understood and for which no treatment is available. This rare disease is revealed in the first months of life and is characterized by postnatal growth retardation, thick lines, intellectual deficit and skin abnormalities, with muscle and heart alterations. Our aim is to elucidate the biological mechanisms responsible for this syndrome caused by a mutation (G12S) in the HRAS gene. Other less frequent mutations in this gene are the cause of rare diseases grouped under the term "rasopathies" as well as many cancers (HRASG12V). The fact that the French Association of Costello Syndrome and CFC based in Bordeaux has funded a novel mouse model of that disease (HRASG12S generated by the Mouse Clinical Institute) makes the context of this project particularly interesting, competitive and innovative. Indeed, we propose here to explore several facets of the pathophysiology of CS using this mice, but also skin fibroblasts obtained from patients, induced-pluripotent stem cells (iPSCs) and neural-crest derivatives. While current effort on the study of CS pathophysiology focus on the HRAS-related ERK signaling pathway, we discovered that HRAS constitutive activation in human fibroblasts inhibits the activity of both LKB1-kinase and its main target, the AMP-activated protein kinase (AMPK). This triggers both a metabolic reprogramming and an alteration of focal adhesion and cytoskeleton potientally involved in CS patophysiology notably during neural crest differentiation. Interestingly, the AMPK inhibition induced by HRAS can be reversed by using a pharmacological activator of AMPK, suggesting that a therapeutic approach could be derived from our observations. In addition, we explored the mice and found an alteration of muscle strength, locomotor activity, heart function, macrocephalia and hypertension. Further imaging analysis that are still ongoing confirmed the existence of potential cranio-facial changes in the mice that need to be further characterized. In addition, a transgenic mouse model of the cancer-associated HRASG12V mutation unexpectedly triggered the CS in mice, raising a fundamental question on the possible dose-effect of HRAS constitutive activation in Rasopathies, since the G12V mutation triggers a stronger biochemical activity of HRAS as compared to the G12S mutation. Therefore, we will compare the effect of those two mutations of HRAS on cell models, looking more closely at the impact on LKB1-AMPK and ERK signaling. We will perform an indepth analysis of HRASG12S mice through metabolic, cardiac and cognitive phenotyping and embryogenesis, with an emphasis on neural crest cells development. Since drugs are available to stimulate AMPK in human and mice, as resveratrol or AICAR, we will test their therapeutic effect on the mice model of CS. Inhibitors of RAS constitutive activation will also be tested as the Zopra cocktail developped by team 2. Lastly, we will evaluate the alteration of senescence in those mice and cell models of CS, since AMPK could regulate progerin levels via SRSF1 and because alteration in working memory was found in the HRASG12S mice and CS patients, a feature previously reported in patients with accelerated aging. Our project thus fits perfectly in the challenge "Health and Wellbeing" because we are studying the mechanisms of a rare disease on an original mouse model and patient-derived cell models, and we propose to evaluate two therapeutic approaches. We regrouped a consortium of internationally recognized experts in energy metabolism (R. Rossignol), mice generation and phenotypic characterization (Y. Herault) and rare diseases pathophysiology and therapy (N. Levy), along with a patient association to achieve the general aim of this project and disseminate our findings.