Activating\xa0mutations in BRAF\xa0disrupt the hypothalamo-pituitary axis leading to hypopituitarism in mice and humans

Angelica Gualtieri,James Blackburn,Wolfgang Högler,Maria Lillina Vignola,Shannon W Davis,Nikolina Kyprianou,Pedro Casado,Andrey Gagunashvili,I Karen Temple,Sally A Camper,Mehul Dattani ,Evelien Gevers ,James Nicholson ,Shinichi Inoue ,Rachel E J Besser ,Iain C A F Robinson ,Justin H Davies ,Fernando Abollo-Jiménez ,Louise Gregory ,Yoko Aoki,Rachael Tan,Valeria Scagliotti,Eugenia Marinelli,Pedro R Cutillas,Carles Gaston‐Massuet

doi:10.1038/s41467-021-21712-4

Abstract

Germline mutations in BRAF and other components of the MAPK pathway are associated with the congenital syndromes collectively known as RASopathies. Here, we report the association of Septo-Optic Dysplasia (SOD) including hypopituitarism and Cardio-Facio-Cutaneous (CFC) syndrome in patients harbouring mutations in BRAF. Phosphoproteomic analyses demonstrate that these genetic variants are gain-of-function mutations leading to activation of the MAPK pathway. Activation of the MAPK pathway by conditional expression of the BrafV600E/+ allele, or the knock-in BrafQ241R/+ allele (corresponding to the most frequent human CFC-causing mutation, BRAF p.Q257R), leads to abnormal cell lineage determination and terminal differentiation of hormone-producing cells, causing hypopituitarism. Expression of the BrafV600E/+ allele in embryonic pituitary progenitors leads to an increased expression of cell cycle inhibitors, cell growth arrest and apoptosis, but not tumour formation. Our findings show a critical role of BRAF in hypothalamo-pituitary-axis development both in mouse and human and implicate mutations found in RASopathies as a cause of endocrine deficiencies in humans.

Highlights

Germline mutations in BRAF and other components of the MAPK pathway are associated with the congenital syndromes collectively known as RASopathies
All had characteristic features of CFC encompassing facial dysmorphism, growth failure, feeding problems, structural cardiac abnormalities, neurodevelopmental delay and CNS abnormalities detected on magnetic resonance imaging (MRI)
Due to the endocrine profile from these patients clearly showing endocrinopathies associated with brain and eye abnormalities characteristic of Septo-Optic Dysplasia (SOD), we reasoned that mutations in novel genes or known hypopituitarism or SOD causative genes, other than the reported BRAF variants, could be responsible for the observed clinical phenotype

Summary

Introduction

RASopathies are a class of developmental syndromes that result from germline mutations in components of the Ras–RAF–MEK–ERK/mitogen-activated protein kinase signalling pathway (ERK/MAPK pathway hereafter). Raf), which in turn phosphorylates and activates MEK1/2 leading to phosphorylation and activation of ERK1/2-MAPK This results in different cellular events from proliferation, changes in cell differentiation, apoptosis and senescence[13]. 90% of activating BRAF mutations present in neoplasms are the result of substitution of a valine to glutamic acid at position 600: BRAF p.V600E This mutation results in increased protein kinase activity leading to a constitutively active ERK/MAPK pathway[15]. The differences between papillary craniopharyngioma (a non-secreting benign tumour) and ACTH-secreting adenomas with the same underlying genetic driver, BRAF p.V600E, reflect different, yet unknown, roles of oncogenic BRAF in different pituitary cell types leading to tumorigenesis. The precise role for the ERK/MAPK pathway in the pathogenesis of endocrine deficiencies that are a component of the clinical phenotype of RASopathies has not been established

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Conclusion