Structures and Functions of the Human GATOR1 Complex.

Eukaryotic cells coordinate available nutrients with their growth through the mechanistic target of rapamycin complex 1 (mTORC1) pathway, in which numerous evolutionarily conserved protein complexes survey and transmit nutrient inputs toward mTORC1. mTORC1 integrates these inputs and activates downstream anabolic or catabolic programs that are in tune with cellular needs, effectively maintaining metabolic homeostasis. The GAP activity toward Rags-1 (GATOR1) protein complex is a critical negative regulator of the mTORC1 pathway and, in the absence of amino acid inputs, is activated to turn off mTORC1 signaling. GATOR1-mediated inhibition of mTORC1 signaling is tightly regulated by an ensemble of protein complexes that antagonize or promote its activity in response to the cellular nutrient environment. Structural, biochemical, and biophysical studies of the GATOR1 complex and its interactors have advanced our understanding of how it regulates cellular metabolism when amino acids are limited. Here, we review the current research with a focus on GATOR1 structure, its enzymatic mechanism, and the growing group of proteins that regulate its activity. Finally, we discuss the implication of GATOR1 dysregulation in physiology and human diseases.

Nutrient deprivation induces mouse embryonic diapause mediated by Gator1 and Tsc2.

Embryonic diapause is a special reproductive phenomenon in mammals that helps embryos to survive various harsh stresses. However, the mechanisms of embryonic diapause induced by the maternal environment is still unclear. Here, we uncovered that nutrient deficiency in uterine fluid was essential for the induction of mouse embryonic diapause, shown by a decreased concentration of arginine, leucine, isoleucine, lysine, glucose and lactate in the uterine fluid of mice suffering from maternal starvation or ovariectomy. Moreover, mouse blastocysts cultured in a medium with reduced levels of these six components could mimic diapaused blastocysts. Our mechanistic study indicated that amino acid starvation-dependent Gator1 activation and carbohydrate starvation-dependent Tsc2 activation inhibited mTORC1, leading to induction of embryonic diapause. Our study elucidates the essential environmental factors in diapause induction.

Ictal Bradycardia and Asystole in Sleep-Related Hypermotor Epilepsy: A Study of 200 Patients.

Background: Ictal bradycardia (IB) and asystole (IA) represent a rare but potentially harmful feature of epileptic seizures. The aim of this study was to study IB/IA in patients with sleep-related hypermotor epilepsy (SHE). Methods: We retrospectively included cases with video-EEG-confirmed SHE who attended our Institute up to January 2021. We reviewed the ictal polysomnography recordings focusing on ECG and identified cases with IB (R-R interval ≥ 2 s or a ≥10% decrease of baseline heart rate) and IA (R-R interval ≥ 4 s). Results: We included 200 patients (123 males, 61.5%), with a mean age of 42 ± 16 years. Twenty patients (20%) had focal cortical dysplasia (FCD) on brain MRI. Eighteen (out of 104 tested, 17.3%) carried pathogenic variants (mTOR pathway, n = 10, nAchR subunits, n = 4, KCNT1, n = 4). We identified IB/IA in four cases (2%): three had IA (mean 10 s) and one had IB. Three patients had FCD (left fronto-insular region, left amygdala, right mid-temporal gyrus) and two had pathogenic variants in DEPDC5; both features were more prevalent in patients with IB/IA than those without (p = 0.003 and p = 0.037, respectively). Conclusions: We identified IB/IA in 2% of patients with SHE and showed that this subgroup more frequently had FCD on brain MRI and pathogenic variants in genes related to the mTOR pathway.

Why did my seizures start now? Influences of lesion connectivity and genetic etiology on age at seizure onset in focal epilepsy.

OBJECTIVE: Patients with focal, lesional epilepsy present with seizures at variable ages. Larger lesion size and overlap with sensorimotor or default mode network (DMN) have been associated with younger age at seizure onset in cohorts with mixed types of focal cortical dysplasia (FCD). Here, we studied determinants of age at seizure onset in patients with bottom-of-sulcus dysplasia (BOSD), a discrete type of FCD with highly localized epileptogenicity. METHODS: Eighty-four patients (77% operated) with BOSD were studied. Demographic, histopathologic, and genetic findings were recorded. BOSD volume and anatomical, primary versus association, rostral versus caudal, and functional network locations were determined. Normative functional connectivity analyses were performed using each BOSD as a region of interest in resting-state functional magnetic resonance imaging data of healthy children. Variables were correlated with age at seizure onset. RESULTS: Median age at seizure onset was 5.4 (interquartile range = 2-7.9) years. Of 50 tested patients, 22 had somatic and nine had germline pathogenic mammalian target of rapamycin (mTOR) pathway variants. Younger age at seizure onset was associated with greater BOSD volume (p = .002), presence of a germline pathogenic variant (p = .04), DMN overlap (p = .04), and increased functional connectivity with the DMN (p < .05, false discovery rate corrected). Location within sensorimotor cortex and networks was not associated with younger age at seizure onset in our relatively small but homogenous cohort. SIGNIFICANCE: Greater lesion size, pathogenic mTOR pathway germline variants, and DMN connectivity are associated with younger age at seizure onset in small FCD. Our findings strengthen the suggested role of DMN connectivity in the onset of FCD-related focal epilepsy and reveal novel contributions of genetic etiology.

GATOR1 Mutations Impair PI3 Kinase-Dependent Growth Factor Signaling Regulation of mTORC1.

GATOR1 (GAP Activity TOward Rag 1) is an evolutionarily conserved GTPase-activating protein complex that controls the activity of mTORC1 (mammalian Target Of Rapamycin Complex 1) in response to amino acid availability in cells. Genetic mutations in the GATOR1 subunits, NPRL2 (nitrogen permease regulator-like 2), NPRL3 (nitrogen permease regulator-like 3), and DEPDC5 (DEP domain containing 5), have been associated with epilepsy in humans; however, the specific effects of these mutations on GATOR1 function and mTORC1 regulation are not well understood. Herein, we report that epilepsy-linked mutations in the NPRL2 subunit of GATOR1, NPRL2-L105P, -T110S, and -D214H, increase basal mTORC1 signal transduction in cells. Notably, we show that NPRL2-L105P is a loss-of-function mutation that disrupts protein interactions with NPRL3 and DEPDC5, impairing GATOR1 complex assembly and resulting in high mTORC1 activity even under conditions of amino acid deprivation. Furthermore, our studies reveal that the GATOR1 complex is necessary for the rapid and robust inhibition of mTORC1 in response to growth factor withdrawal or pharmacological inhibition of phosphatidylinositol-3 kinase (PI3K). In the absence of the GATOR1 complex, cells are refractory to PI3K-dependent inhibition of mTORC1, permitting sustained translation and restricting the nuclear localization of TFEB, a transcription factor regulated by mTORC1. Collectively, our results show that epilepsy-linked mutations in NPRL2 can block GATOR1 complex assembly and restrict the appropriate regulation of mTORC1 by canonical PI3K-dependent growth factor signaling in the presence or absence of amino acids.

Clinical characteristics and analysis of diagnosis and treatment of 16 patients with GATOR1 complex-related epilepsy / 中华神经科杂志

Objective:To analyze the clinical manifestations, gene mutation characteristics and treatment effects of patients with GATOR1 complex-related epilepsy, and to explore the diagnosis and treatment of this disease.Methods:The medical history, electroencephalogram, brain imaging, genetic test results, treatment and follow-up data of patients with GATOR1 complex-related epilepsy who attended the Children′s Hospital Affiliated to Capital Institute of Pediatrics, Beijing Tsinghua Changgung Hospital, and Shanghai Deji Hospital from May 2017 to July 2022 were retrospectively analyzed.Results:A total of 16 patients with GATOR1 complex-related epilepsy were collected, including 7 males and 9 females. The age of onset of epilepsy was from 2 months to 14 years. Ten cases had focal seizures only, 2 cases had generalized seizures only, and 4 cases had coexistence of focal seizures and generalized seizures, of which generalized seizures included generalized tonic-clonic seizure, spastic seizure, and myoclonic seizure. Among the 16 patients, 2 had infantile spasms, 3 had familial focal epilepsy with variable focus, and 1 had sleep related hyperkinetic epilepsy. Electroencephalogram intervals suggested multiple brain areas discharge or diffuse discharge. A total of 13 DEPDC5 gene mutation sites, 1 NPRL2 gene mutation site, and 2 NPRL3 gene mutation sites were found; 4 sites of DEPDC5 gene were reported sites, the rest were unreported; all mutations had pathogenic significance; 8 cases had nonsense mutation, 1 case had large fragment deletion, 4 cases had frameshift mutation, 1 case had integer mutation, 2 cases had splicing mutation; 13 cases′ mutation was inherited from parents, 2 cases had new mutation, and 1 case had unverified mutation. Magnetic resonance imaging (MRI) showed 5 of the 16 patients were normal, and 11 had abnormal cerebral cortex structure, manifested as bottom-of-sulcus focal cortical dysplasia (FCD), abnormal formation of sulci and (or) gyri with or without ill-defined gray-white matter and malformation of cortical dysplasia of the bilateral brain. Seven patients underwent stereotactic electroencephalogram (SEEG) monitoring, and the SEEG showed low-amplitude fast rhythm at the beginning in 6 patients, of whom 5 cases started from the frontal lobe, and 1 case started from the parietal lobe. Eight patients were only treated with drugs, 1 with single-drug therapy and the rest with multi-drug combination therapy. Eight patients underwent surgery. Among them, 5 patients with DEPDC5 gene mutation underwent epileptogenic cortex excising after SEEG monitoring, and postoperative pathological examinations showed FCDⅡ, FCDⅢ or non-specific changes; 1 patient was waiting for surgery. One patient with NPRL3 gene mutation underwent epileptogenic foci resection and postoperative pathological examinations showed FCDⅡa; the other patient with NPRL3 gene mutation underwent radiofrequency thermocoagulation after SEEG monitoring. Follow-up showed that 3 patients were seizure-free with drug treatment, and 4 patients had fewer seizures after drug treatment. Six cases underwent epileptic foci resection. Five of them were assisted by SEEG to locate the epileptic foci before surgery and were seizure-free after the operation, but the range of surgical resection was wider than the abnormal range shown by MRI; whereas 1 case who was not assisted by SEEG showed no improvement. There was still 1 case who underwent SEEG-guided radiofrequency thermocoagulation and had no improvement after operation. Conclusions:GATOR1 complex-related epilepsy mostly manifests as focal seizures. SEEG shows that seizures originate from the frontal lobe more often, and cortical developmental abnormalities are often found. DEPDC5 gene mutations are the most common ones, mostly inherited from parents, with high incomplete penetrance rate. Therefore, genetic testing is recommended for non-acquired brain structural abnormalities. For those who are refractory to drugs, a radical cure can be obtained by resection of the epileptogenic foci after preoperative evaluation.

Clinical and genetic characteristics of focal epilepsy in children caused by GATOR1 complex gene variation / 中华儿科杂志

Objective@#To summarize the clinical and genetic characteristics of focal epilepsy in children caused by GATOR1 complex gene variation.@*Methods@#The clinical data, gene variation and treatment outcome of 12 children with focal epilepsy caused by GATOR1 complex gene variation admitted to Beijing Children′s Hospital Affiliated to Capital Medical University from June 2016 to October 2018 were retrospectively analyzed.@*Results@#There were 7 males and 5 females in 12 cases. The epilepsy onset age was 5.5 (3.0, 12.0) months, and from 11 days to 16 months of age. The epileptic seizure types were all focal motor seizures, and one case combined with epileptic spasms. The frequency of seizures in all patients was more than one time per day. Seven cases had frontal lobe epilepsy and two cases had lateral temporal lobe epilepsy. One case had a family history of febrile seizures and two had a family history of suspicious epilepsy. Epileptic form discharges were observed in 9 patients during the interictal phase by electroencephalograms (EEG), and all of them were focal discharges. Eight cases had clinical seizures detected by EEG, in 4 of whom the seizures were originated in frontal region. There were no abnormalities in brain magnetic resonance imaging in 11 cases whereas 1 case had malformation of cortical development of left frontal lobe. Eight patients had DEPDC5 gene variation, one had NPRL2 gene variation, three had NPRL3 gene variation. One case had de novo variation and the other 11 had hereditary variation. There were 11 types of gene variation, including 5 nonsense variations, 3 missense variations, 2 frame shift variations and 1 in frame deletion variation. There was no clear relationship between the clinical phenotype and the genotype. During the follow-up period from 6 months to 2 years and 6 months, 6 cases had seizure control, 3 of them were controlled by oxcarbazepine. The other 6 cases had drug-refractory epilepsy, 2 of them failed with vagus nerve stimulation and ketogenic dietary therapy as well, meanwhile combined with mental retardation.@*Conclusions@#GATOR1 complex gene variation can lead to genetic focal epilepsy, which usually has early onset with frequent seizures. Most of the patients have focal epileptic form discharges on EEG, and there is usually no structural lesion in brain imaging. Most of the patients have hereditary loss-of-function variations. Approximately half of cases are drug-resistant epilepsy.