GNAQ/GNA11 Mosaicism Causes Aberrant Calcium Signaling Susceptible to Targeted Therapeutics

Phenotypic Spectrum of GNA11 R183C Mosaicism

BACKGROUND

Many vascular anomalies harbor postzygotic somatic variants in GNAQ and GNA11; however, the phenotype of specific G-protein variants has not been well described. We report the clinical characteristics of 17 patients with a GNA11 R183C variant.

METHODS

This case series is derived from a multinational cohort of vascular anomaly patients whose pathogenic mutations were identified using high-depth next generation sequencing. Data include vascular anomaly features, imaging reports, and extracutaneous manifestations of the GNA11 R183C variant.

RESULTS

We identified 17 subjects (median age 18 years [range 6-67]) with somatic GNA11 R183C variant. All patients had vascular lesions of the skin that presented as pink-to-red in children and deeper red in adults. Most lesions were large, poorly demarcated, and reticulated patches that were often bilaterally distributed. Nevus anemicus was observed in 53% (N = 9) and dermal melanocytosis in 13.3% (N = 2) of individuals. 82% (N = 14) of patients had limb growth discrepancies, and 1 patient had marked thoracic hypoplasia. 47% (N = 8) of patients had facial involvement, and 41% (N = 7) had forehead involvement. One patient experienced seizures due to right hemispheric leptomeningeal angiomatosis consistent with Sturge-Weber syndrome. Other findings included glaucoma (29%, N = 5) and psychomotor delay (29%, N = 5).

CONCLUSION

These findings contribute to our understanding of the clinical spectrum of GNA11 R183C capillary malformations (CMs); patients characteristically present with extensive, bilateral, poorly demarcated, pink-to-red CMs associated with nevus anemicus. Glaucoma and growth discrepancies (overgrowth or undergrowth) are common. Leptomeningeal angiomatosis and developmental delay can occur, appearing potentially less prevalent and severe than GNAQ-associated disease.

MAPK Signaling and Angiopoietin-2 Contribute to Endothelial Permeability in Capillary Malformations

Capillary malformations (CM) are slow-flow vascular abnormalities present at birth and predominantly manifest as cutaneous lesions. In the rare neurocutaneous disorder known as Sturge Weber Syndrome (SWS), individuals exhibit CM not only on the skin but also within the leptomeninges of the brain and the choroid of the eye. >90% of CM are caused by a somatic R183Q mutation in GNAQ, the gene encoding Gαq - a heterotrimeric G-protein subunit. The somatic GNAQ mutation is notably enriched in endothelial cells (ECs) isolated from CM-affected regions. Here we show blood vessels in cutaneous and leptomeningeal SWS lesions exhibit extravascular fibrin indicating a compromised endothelial barrier. Longitudinal MRI of the brain in one SWS patient further suggests vascular permeability. To explore this pathological phenotype, we employed the trans-endothelial electrical resistance (TEER) assay to measure permeability of the EC-EC barrier in vitro . Human EC CRISPR edited to create a GNAQ R183Q allele (EC-R183Q) exhibited a reduced barrier compared to mock edited EC (EC-WT). We sought to identify signaling molecules needed for EC barrier formation. Knockdown of angiopoietin-2 (ANGPT2), known to be significantly increased in EC-R183Q and in CM, partially yet significantly restored the barrier, while an anti-ANGPT2 function blocking antibody did not. We next tested the MEK1,2 inhibitor (Trametinib) because MAPK signaling is increased by GNAQ mutation. MEK1,2 inhibitors partially restored the EC barrier, implicating involvement of MAPK/ERK signaling. The combination of ANGPT2 knockdown and Trametinib significantly restored the EC barrier to near EC-WT levels. The additive impacts of ANGPT knockdown and MEK1,2 inhibition indicate the two operate in separate pathways. In summary, we discovered that GNAQ p.R183Q ECs exhibit compromised endothelial barrier formation, reflecting the compromised EC barrier in CM lesions, and that ANGPT2 knockdown combined with Trametinib effectively restores the EC-EC barrier.

NONSTANDARD ABBREVIATIONS AND ACRONYMS

NOVELTY AND SIGNIFICANCE

What is known?: The mutant Gαq-R183Q in endothelial cells activates phospholipase β3, contributing to increased angiopoietin-2, a pro-angiogenic, proinflammatory molecule that contributes to vascular permeability.Endothelial Gαq-R183Q is sufficient to drive formation of enlarged blood vessels akin to what is observed in CM. ANGPT2 shRNA knockdown prevented the enlarged vessel phenotype in a xenograft model.An EC-specific GNAQ p.R183Q mouse model showed permeability in brain vessels, detected by perfusion of Evans Blue dye, indicating reduced vascular integrity.What New Information Does This Article Contribute?: Reduced vascular integrity in CM is confirmed by Martius Scarlet Blue staining and longitudinal MRI imaging of SWS brain. GNAQ p.R183Q EC form a weaker endothelial barrier in vitro compared to control ECs. The weakened endothelial barrier in the mutant ECscan be rescued by Gαq inhibitor, YM254890, confirming the compromised barrier is a consequence of the mutant Gαq. Titration experiments modeling the mosaic nature of the GNAQ p.R183Q in CMshow that 5- 10% GNAQ p.R183Q EC in the monolayer is sufficient to reduce endothelial barrier formation. Knockdown of ANGPT2 or MEK1,2 inhibition partially restored the endothelial barrier in GNAQ p.R183Q EC. Combining knockdown of ANGPT2 and addition of a MEK inhibitor, Trametinib, restored the endothelial barrier to near what is seen in wild type ECs.What is the translational message?: Sturge Weber Syndrome (SWS) is a neurocutaneous disorder that involves atypical blood vessel overgrowth in the skin, brain and eye. It is associated with facial CM (aka port wine birthmark), leptomeningeal CM in the brain visible with MRI, and glaucoma. Theneurological sequalae involve seizures, cerebral atrophies and calcification, and intellectual disorders. Currently there are no molecularly targeted therapies for non-syndromic CM or SWS. Our study shows the involvement of MAPK pathway and the proinflammatory molecule ANGPT2 in endothelial permeability and suggests a path to target GNAQ p.R183Q driven CM.

A Comprehensive Review of Electrolyte Imbalances and Their Applied Aspects in Dermatology

Electrolytes play a pivotal role in the maintenance of neutrality in the minerals of the cells - also, the generation and conduction of action potentials in neurons and muscles. Key electrolytes include sodium, potassium, chloride, magnesium, calcium, and phosphate. Electrolyte imbalances can result in elevated or diminished levels. Abnormal electrolyte levels, whether raised or decreased, interfere with normal physiological activities and may result in life-threatening consequences. Electrolyte imbalances are common in critical care units, although they are less frequent in dermatological conditions. Dermatologists should, however, be knowledgeable about the skin disorders and medications that are related to or may increase the risk of electrolyte imbalance to ensure that appropriate treatments are implemented immediately to avoid negative results. The objective of this review is to narrate the dermatological features of disorders involving abnormalities of sodium, potassium, calcium, phosphorus, and magnesium.

Sturge-Weber syndrome: updates in translational neurology

Sturge-Weber syndrome (SWS) is a rare congenital neurovascular disorder that initially presents with a facial port-wine birthmark (PWB) and most commonly associated with a R183Q somatic mosaic mutation in the gene GNAQ. This mutation is enriched in endothelial cells. Contrast-enhanced magnetic resonance imaging (MRI) diagnoses brain abnormalities including leptomeningeal vascular malformation, an enlarged choroid plexus, and abnormal cortical and subcortical blood vessels. Mouse SWS models identify dysregulated proteins important for abnormal vasculogenesis and blood brain barrier permeability. Recent clinical research has focused on early diagnosis, biomarker development, presymptomatic treatment, and development of novel treatment strategies. Prospective pilot clinical drug trials with cannabidiol (Epidiolex) or with sirolimus, an mTOR inhibitor, indicate possible reductions in seizure frequency and improved cognitive outcome. This review connects the most recent molecular research in SWS cell culture and animal models to developing new treatment methods and identifies future areas of research.

Sturge-Weber syndrome: an update for the pediatrician

BACKGROUND

Sturge-Weber syndrome (SWS) is a rare congenital neurocutaneous disorder characterized by the simultaneous presence of both cutaneous and extracutaneous capillary malformations. SWS usually presents as a facial port-wine birthmark, with a varying presence of leptomeningeal capillary malformations and ocular vascular abnormalities. The latter may lead to significant neurological and ocular morbidity such as epilepsy and glaucoma. SWS is most often caused by a somatic mutation involving the G protein subunit alpha Q or G protein subunit alpha 11 gene causing various alterations in downstream signaling pathways. We specifically conducted a comprehensive review focusing on the current knowledge of clinical practices, the latest pathophysiological insights, and the potential novel therapeutic avenues they provide.

DATA SOURCES

A narrative, non-systematic review of the literature was conducted, combining expert opinion with a balanced review of the available literature. A search of PubMed, Google Scholar and Embase was conducted, using keywords "Sturge-Weber Syndrome" OR "SWS", "Capillary malformations", "G protein subunit alpha 11" OR "G protein subunit alpha Q".

RESULTS

One of the hallmark features of SWS is the presence of a port-wine birthmark at birth, and forehead involvement is most indicative for SWS. The most common ocular manifestations of SWS are glaucoma and choroidal hemangioma. Glaucoma presents in either in infancy (0-3 years of age) or later in life. Neurological complications are common in SWS, occurring in about 70%-80% of patients, with seizures being the most common one. SWS significantly impacts the quality of life for patients and their families, and requires a multidisciplinary approach for diagnosis and treatment. Currently, no disease-modifying therapies exist, and treatment is mostly focused on symptoms or complications as they arise.  CONCLUSIONS: SWS remains a complex and heterogeneous disorder. Further research is needed to optimize diagnostic and therapeutic strategies, and to translate insights from molecular pathogenesis to clinical practice.