bims-tubesc 2022-06-19 papers

bims-tubesc

Biomed News

on Molecular mechanisms in tuberous sclerosis

Issue of 2022–06–19
eleven papers selected by

Identification of a Novel Canonical Splice Site Variant TSC2 c.2967-1G>T That is Not Associated With Tuberous Sclerosis Pathogenesis.
Analysis of Clinical Features and Next-Generation Sequencing of 12 Tuberous Sclerosis Families in China.
Interictal Discharge Pattern in Preschool-Aged Children With Tuberous Sclerosis Complex Before and After Resective Epilepsy Surgery.
A Rare Cause of Chronic Hip Pain From PEComa: An Aggressive Mesenchymal Sarcoma.
Nuclear-targeted 4E-BP1 is dephosphorylated, induces nuclear translocation of eIF4E, and alters mRNA translation.
mTORC1 function in hippocampal parvalbumin interneurons: regulation of firing and long-term potentiation of intrinsic excitability but not long-term contextual fear memory and context discrimination.
Ubiquitin E3 ligase Atrogin-1 protein is regulated via the rapamycin-sensitive mTOR-S6K1 signaling pathway in C2C12 muscle cells.
Rapid symptomatic and structural improvement of a retinal astrocytic hamartoma in response to anti-VEGF therapy: A case report.
Chylomicron production is repressed by RPTOR knockdown, R-α-lipoic acid and 4-phenylbutyric acid in human enterocyte-like Caco-2 cells.
Vps33B controls Treg cell suppressive function through inhibiting lysosomal nutrient sensing complex-mediated mTORC1 activation.
Genomics in the presurgical epilepsy evaluation.

Front Genet. 2022 ;13 904224

Identification of a Novel Canonical Splice Site Variant TSC2 c.2967-1G>T That is Not Associated With Tuberous Sclerosis Pathogenesis.

Jing Duan, Yuanzhen Ye, Zhanqi Hu, Xia Zhao, Jianxiang Liao, Li Chen.

  Tuberous sclerosis, also known as tuberous sclerosis complex (TSC), is an autosomal dominant defect characterized by hamartomas in multiple organ systems. Inactivating variants cause this defect in either the TSC1 gene or the TSC2 gene, leading to hamartin or tuberin protein dysfunction, thus resulting in TSC. The diagnostic criteria for TSC suggest that it can be diagnosed by identifying a heterozygous pathogenic variant of TSC1 or TSC2, even in the absence of clinical signs. In a 4-year-old girl, we identified a splicing variant (NM_000548.4: c.2967-1G>T) that she inherited from her father. Neither the girl (patient) nor her father showed typical features of TSC. This variant is located in a NAGNAG acceptor, which can produce mRNA isoforms that differ by a three-nucleotide indel. Reverse transcription polymerase chain reaction analysis of the patient and both parents' blood RNA samples suggested two different splicing patterns, and these two splicing patterns differed in the presence or absence of the first codon of exon 27, thus providing two splicing products designated as isoforms A and B, respectively. Furthermore, the proportions of these two patterns varied between the patient and either parent. A minigene assay further confirmed that the c.2967-1G>T variant led to the absence of isoform A (including the first codon of exon 27). The finding of our study demonstrates this variant, c.2967-1G>T, disrupts the balance of an alternative splice event which involves the use of two tandem alternatives acceptors and is not associated with typical symptoms of tuberous sclerosis. Our finding is of importance for genetic counseling and suggests that we need to be vigilant to avoid misdiagnosis when we encounter such a site.

Keywords:  NAGNAG acceptor; TSC2; alternative splicing; c.2967-1G>T; splicing variant; tuberous sclerosis

DOI:  https://doi.org/10.3389/fgene.2022.904224
Front Med (Lausanne). 2022 ;9 840709

Analysis of Clinical Features and Next-Generation Sequencing of 12 Tuberous Sclerosis Families in China.

Xu Wang, Wenda Wang, Yang Zhao, Zhan Wang, Yushi Zhang.

   Background: Tuberous sclerosis complex (TSC) is a rare autosomal dominant genetic disease with systemic organ involvement. So far, only a few TSC families in China have been reported. Therefore, more data on the clinical and genetic features of TSC families are required.
Materials and Methods: We retrospectively analyzed 12 TSC family probands and their family members. Next-generation sequencing (NGS) has been applied to confirm the type of TSC mutation along with a detailed physical examination.
Results: In this study, twenty-seven patients in 12 TSC families were reported, including 12 male and 15 female patients, aged 8-67 years. Skin lesions were detected among all patients with TSC, including 25 cases of facial angiofibromas, 18 cases of hypomelanotic macules, 15 cases of ungual fibromas, and 13 cases of shagreen patch. Other clinical features were also revealed: 14 cases of renal angiomyolipoma, 6 cases of subependymal nodules (SENs), and 3 cases of lymphangioleiomyomatosis. All twenty-seven patients with TSC were tested by NGS. Totally, TSC2 mutations were reported in 19 cases (7 frameshift mutations, 10 nonsense mutations, and 2 missense mutations), TSC1 mutations were reported in 4 cases (4 nonsense mutations), and 4 cases were genetically negative. The novel causal mutations (TSC2: c.208dup, c.1874C > G, c.1852del) identified in three families were first reported in TSC.
Conclusion: Our findings expand the mutation spectrum of patients with TSC in China. The clinical characteristics can vary among patients with TSC with the same pathogenic mutation. The genetic results and summary of clinical features of 12 TSC families contribute to a more accurate diagnosis and further genetic counseling.

Keywords:  clinical feature; family; gene mutation; next-generation sequencing; tuberous sclerosis complex

DOI:  https://doi.org/10.3389/fmed.2022.840709
Front Neurol. 2022 ;13 868633

Interictal Discharge Pattern in Preschool-Aged Children With Tuberous Sclerosis Complex Before and After Resective Epilepsy Surgery.

Liu Yuan, Yangshuo Wang, Shuhua Cheng, Junchen Zhang, Shaohui Zhang, Tinghong Liu, Guojun Zhang, Shuli Liang.

   Objective: To analyze the interictal discharge (IID) patterns on pre-operative scalp electroencephalogram (EEG) and compare the changes in IID patterns after removal of epileptogenic tubers in preschool children with tuberous sclerosis complex (TSC)-related epilepsy.
Methods: Thirty-five preschool children who underwent resective surgery for TSC-related epilepsy were enrolled retrospectively, and their EEG data collected before surgery to 3 years after surgery were analyzed.
Results: Twenty-three (65.7%) patients were seizure-free post-operatively at 1-year follow-up, and 37-40% of post-operative patients rendered non-IID on scalp EEGs, and patients with focal IIDs or generalized IID patterns on pre-operative EEG presented a high percentage of normal post-operative scalp EEGs. IID patterns on pre-operative scalp EEGs did not influence the outcomes of post-operative seizure controls, while patients with non-IID and focal IID on post-operative EEGs were likely to achieve post-operative seizure freedom. Patients with new focal IIDs presented a significantly lower percentage of seizure freedom than those without new focal IIDs on post-operative EEGs at 3-year follow-up.
Conclusion: Over 1/3 children with TSC presented normal scalp EEGs after resective epileptsy surgery. Patients with post-operative seizure freedom were more likely to have non-IIDs on post-operative EEGs. New focal IIDs were negative factors for seizure freedom at the 3-year follow-up.

Keywords:  epilepsy; epileptogenic tuber; interictal discharge (IID); scalp electroencephalographs (EEGs); tuberous sclerosis complex (TSC)

DOI:  https://doi.org/10.3389/fneur.2022.868633
J Investig Med High Impact Case Rep. 2022 Jan-Dec;10:10 23247096221103385

A Rare Cause of Chronic Hip Pain From PEComa: An Aggressive Mesenchymal Sarcoma.

Samender Randhawa, Jessica Pinsker, Madhurya Amirapu, Metlapalli Venkata Sravanthi, Prashanth Ashok Kumar, Komal Akhtar.

  Perivascular epithelioid cell tumors (PEComas) are related to the tuberous sclerosis complex (TSC) and are commonly benign. When malignant, they can be aggressive with local invasion and metastatic spread. Conventional PEComas do not have TFE3 gene rearrangement and are associated with TSC with a preference for an occurrence at a younger age. We report a case of a young male who had progressive chronic hip pain and was found to have a TFE3-associated PEComa in his pelvic region.

Keywords:  PEComa; TFE3; epithelioid; hip pain; mesenchymal; metastatic; sarcoma; sirolimus; tumor

DOI:  https://doi.org/10.1177/23247096221103385
Exp Cell Res. 2022 Jun 10. pii: S0014-4827(22)00239-7. [Epub ahead of print] 113246

Nuclear-targeted 4E-BP1 is dephosphorylated, induces nuclear translocation of eIF4E, and alters mRNA translation.

Sho Takahashi, Shusaku Shibutani, Hiroyuki Iwata.

  Mechanistic target of rapamycin complex 1 (mTORC1) phosphorylates and inhibits eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1). This leads to the release of eIF4E from 4E-BP1 and the initiation of eIF4E-dependent mRNA translation. In this study, we examined the expression of a 4E-BP1-based reporter (mTORC1 activity reporter; TORCAR) with various localization signal tags to clarify the relationship between the localization of 4E-BP1 and its phosphorylation. Phosphorylation of 4E-BP1 at threonine 37/46 and serine 65 was efficient at lysosomes and the plasma membrane, whereas it was significantly decreased in the nucleus. In addition, the localization of endogenous eIF4E shifted from the cytoplasm to the nucleus only when nuclear-localized TORCAR was expressed. Nuclear-localized TORCAR decreased cyclin D1 protein levels and altered cell cycle distribution. These data provide an experimental tool to manipulate the localization of endogenous eIF4E without affecting mTORC1 and highlight the important role of nuclear-cytoplasmic shuttling of eIF4E.

Keywords:  4E-BP1; NLS; TORCAR; Translation; eIF4E

DOI:  https://doi.org/10.1016/j.yexcr.2022.113246
Mol Brain. 2022 Jun 17. 15(1): 56

mTORC1 function in hippocampal parvalbumin interneurons: regulation of firing and long-term potentiation of intrinsic excitability but not long-term contextual fear memory and context discrimination.

Abdessattar Khlaifia, Eve Honoré, Julien Artinian, Isabel Laplante, Jean-Claude Lacaille.

  Hippocampal CA1 parvalbumin-expressing interneurons (PV INs) play a central role in controlling principal cell activity and orchestrating network oscillations. PV INs receive excitatory inputs from CA3 Schaffer collaterals and local CA1 pyramidal cells, and they provide perisomatic inhibition. Schaffer collateral excitatory synapses onto PV INs express Hebbian and anti-Hebbian types of long-term potentiation (LTP), as well as elicit LTP of intrinsic excitability (LTPIE). LTPIE requires the activation of type 5 metabotropic glutamate receptors (mGluR5) and is mediated by downregulation of potassium channels Kv1.1. It is sensitive to rapamycin and thus may involve activation of the mammalian target of rapamycin complex 1 (mTORC1). LTPIE facilitates PV INs recruitment in CA1 and maintains an excitatory-inhibitory balance. Impaired CA1 PV INs activity or LTP affects network oscillations and memory. However, whether LTPIE in PV INs plays a role in hippocampus-dependent memory remains unknown. Here, we used conditional deletion of the obligatory component of mTORC1, the Regulatory-Associated Protein of mTOR (Raptor), to directly manipulate mTORC1 in PV INs. We found that homozygous, but not heterozygous, conditional knock-out of Rptor resulted in a decrease in CA1 PV INs of mTORC1 signaling via its downstream effector S6 phosphorylation assessed by immunofluorescence. In whole-cell recordings from hippocampal slices, repetitive firing of CA1 PV INs was impaired in mice with either homozygous or heterozygous conditional knock-out of Rptor. High frequency stimulation of Schaffer collateral inputs that induce LTPIE in PV INs of control mice failed to do so in mice with either heterozygous or homozygous conditional knock-out of Rptor in PV INs. At the behavioral level, mice with homozygous or heterozygous conditional knock-out of Rptor showed similar long-term contextual fear memory or contextual fear memory discrimination relative to control mice. Thus, mTORC1 activity in CA1 PV INs regulates repetitive firing and LTPIE but not consolidation of long-term contextual fear memory and context discrimination. Our results indicate that mTORC1 plays cell-specific roles in synaptic plasticity of hippocampal inhibitory interneurons that are differentially involved in hippocampus-dependent learning and memory.

Keywords:  CA1 hippocampus; Contextual fear conditioning; GABA interneurons; Raptor conditional knock-out mice; Whole-cell recordings

DOI:  https://doi.org/10.1186/s13041-022-00941-8
Am J Physiol Cell Physiol. 2022 Jun 15.

Ubiquitin E3 ligase Atrogin-1 protein is regulated via the rapamycin-sensitive mTOR-S6K1 signaling pathway in C2C12 muscle cells.

Yusuke Nishimura, Jitpisute Chunthorng-Orn, Samuel Lord, Ibrahim Musa, Peter Dawson, Lars Holm, Yu-Chiang Lai.

  Atrogin-1 and MuRF1 are highly expressed in multiple conditions of skeletal muscle atrophy. The PI3K/Akt/FoxO signaling pathway is well known to regulate Atrogin-1 and MuRF1 gene expressions. However, Akt activation also activates the mammalian target of rapamycin complex 1 (mTORC1) which induces skeletal muscle hypertrophy. Whether mTORC1-dependent signaling has a role in regulating Atrogin-1 and/or MuRF1 gene and protein expression is currently unclear. In this study, we showed that activation of insulin-mediated Akt signaling suppresses both Atrogin-1 and MuRF1 protein contents and that inhibition of Akt increases both Atrogin-1 and MuRF1 protein contents in C2C12 myotubes. Interestingly, inhibition of mTORC1 using a specific mTORC1 inhibitor, rapamycin, increased Atrogin-1, but not MuRF1, protein content. Furthermore, activation of AMP-activated protein kinase (AMPK), a negative regulator of the mTORC1 signaling pathway, also showed distinct time-dependent changes between Atrogin-1 and MuRF1 protein contents, suggesting differential regulatory mechanisms between Atrogin-1 and MuRF1 protein content. To further explore the downstream of mTORC1 signaling, we employed a specific S6K1 inhibitor, PF-4708671. We found that Atrogin-1 protein content was dose-dependently increased with PF-4708671 treatment, whereas MuRF1 protein content was decreased at 50 μM of PF-4708671 treatment. However, MuRF1 protein content was unexpectedly increased when treated with PF-4708671 for a longer period. Overall, our results indicate that Atrogin-1 and MuRF1 protein contents are regulated by different mechanisms, the downstream of Akt, and that Atrogin-1 protein content can be regulated by rapamycin-sensitive mTOR-S6K1 dependent signaling pathway.

Keywords:  Skeletal muscle; The ubiquitin proteasome system; mTORC1

DOI:  https://doi.org/10.1152/ajpcell.00384.2021
Am J Ophthalmol Case Rep. 2022 Sep;27 101606

Rapid symptomatic and structural improvement of a retinal astrocytic hamartoma in response to anti-VEGF therapy: A case report.

Kevin C Allan, Hong-Uyen Hua, Arun D Singh, Alex Yuan.

   Purpose: To describe a patient with bilateral peripapillary astrocytic hamartomas with exudation of subretinal fluid into the macula and loss of vision without evidence of choroidal neovascularization. The patient rapidly responded to intravitreal bevacizumab injections resulting in reduced subretinal fluid and clinical improvement.
Observation: A 70-year-old female presented with worsening vision in her left eye due to subretinal fluid exudation from a peripapillary astrocytic hamartoma. The patient was treated with two doses of bevacizumab with rapid improvement in vision and resolution of subretinal fluid. Genetic testing was negative for common pathogenic variants for tuberous sclerosis and neurofibromatosis, which are highly associated with bilateral optic nerve and retinal astrocytic hamartomas.
Conclusion: Astrocytic hamartomas with exudation may be responsive to bevacizumab suggesting a dependence of these lesions on vascular endothelial growth factor (VEGF) independent of secondary choroidal neovascularization. Furthermore, this case describes a patient with bilateral astrocytic hamartomas without genetic or clinical confirmation of associated phakomatoses, such as tuberous sclerosis and neurofibromatosis.

Keywords:  Anti-VEGF; Neurofibromatosis; Retinal astrocytic hamartoma; Retinal astrocytoma; Subretinal fluid; Tuberous sclerosis

DOI:  https://doi.org/10.1016/j.ajoc.2022.101606
J Nutr Biochem. 2022 Jun 09. pii: S0955-2863(22)00158-9. [Epub ahead of print] 109087

Chylomicron production is repressed by RPTOR knockdown, R-α-lipoic acid and 4-phenylbutyric acid in human enterocyte-like Caco-2 cells.

Bo He, Zhigang Wang, Régis Moreau.

  Although the role of mechanistic target of rapamycin complex 1 (mTORC1) in lipid metabolism has been the subject of previous research, its function in chylomicron production is not known. In this study, we created three stable human colorectal adenocarcinoma Caco-2 cell lines exhibiting normal, low or high mTORC1 kinase activity, and used these cells to investigate the consequences of manipulating mTORC1 activity on enterocyte differentiation and chylomicron-like particle production. Constitutively active mTORC1 induced Caco-2 cell proliferation and differentiation (as judged by alkaline phosphatase activity) but weakened transepithelial electrical resistance (TEER). Repressed mTORC1 activity due to the knockdown of RPTOR significantly decreased the expression of lipogenic genes FASN, DGAT1 and DGAT2, lipoprotein assembly genes APOB and MTTP, reduced protein expression of APOB, MTTP and FASN, downregulated the gene expression of very long-chain fatty acyl-CoA ligase (FATP2), acyl-CoA binding protein (DBI), and prechylomicron transport vesicle-associated proteins VAMP7 (vesicle-associated membrane protein 7) and SAR1B (secretion associated Ras related GTPase 1B) resulting in the repression of apoB-containing triacylglycerol-rich lipoprotein secretion. Exposure of Caco-2 cells harboring a constitutively active mTORC1 to short-chain fatty acid derivatives, R-α-lipoic acid and 4-phenylbutyric acid, downregulated chylomicron-like particle secretion by interfering with the lipidation and assembly of the particles, and concomitantly repressed mTORC1 activity with no change to Raptor abundance or PRAS40 (Thr246) phosphorylation. R-α-lipoic acid and 4-phenylbutyric acid may be useful to mitigate intestinal lipoprotein overproduction and associated postprandial inflammation.

Keywords:  apolipoprotein B; dietary fat; lacteal; lipogenesis; mTORC1; triacylglycerol

DOI:  https://doi.org/10.1016/j.jnutbio.2022.109087
Cell Rep. 2022 Jun 14. pii: S2211-1247(22)00725-2. [Epub ahead of print]39(11): 110943

Vps33B controls Treg cell suppressive function through inhibiting lysosomal nutrient sensing complex-mediated mTORC1 activation.

Hongrui Xiang, Yuexiao Tao, Zhenyan Jiang, Xian Huang, Huizi Wang, Wei Cao, Jia Li, Rui Ding, Mingyi Shen, Ru Feng, Linsen Li, Chenyang Guan, Jiamin Liu, Jun Ni, Lei Chen, Zhengting Wang, Youqiong Ye, Qing Zhong, Junling Liu, Qiang Zou, Xuefeng Wu.

  The suppressive function of regulatory T (Treg) cells is tightly controlled by nutrient-fueled mechanistic target of rapamycin complex 1 (mTORC1) activation, yet its dynamics and negative regulation remain unclear. Here we show that Treg-specific depletion of vacuolar protein sorting 33B (Vps33B) in mice results in defective Treg cell suppressive function and acquisition of effector phenotype, which in turn leads to disturbed T cell homeostasis and boosted antitumor immunity. Mechanistically, Vps33B binds with lysosomal nutrient-sensing complex (LYNUS) and promotes late endosome and lysosome fusion and clearance of the LYNUS-containing late endosome/lysosome, and therefore suppresses mTORC1 activation. Vps33B deficiency in Treg cells results in disordered endosome lysosome fusion, which leads to accumulation of LYNUS that causes elevated mTORC1 activation and hyper-glycolytic metabolism. Taken together, our study reveals that Vps33B maintains Treg cell suppressive function through sustaining endolysosomal homeostasis and therefore restricting amino acid-licensed mTORC1 activation and metabolism.

Keywords:  CP: Immunology; CP: Metabolism; Foxp3; Treg; Vps33B; endolysosomal system; mTORC1

DOI:  https://doi.org/10.1016/j.celrep.2022.110943
Epilepsy Res. 2022 May 30. pii: S0920-1211(22)00102-4. [Epub ahead of print]184 106951

Genomics in the presurgical epilepsy evaluation.

Patrick B Moloney, Patricia Dugan, Peter Widdess-Walsh, Orrin Devinsky, Norman Delanty.

  Epilepsy surgery should be considered in all patients with drug-resistant focal epilepsy. The diagnostic presurgical evaluation aims to delineate the epileptogenic zone and its relationship to eloquent brain regions. Genetic testing is not yet routine in presurgical evaluations, despite many monogenic causes of severe epilepsies, including some focal epilepsies. This review highlights genomic data that may inform decisions regarding epilepsy surgery candidacy and strategy. Focal epilepsies due to pathogenic variants in mechanistic target of rapamycin pathway genes are amenable to surgery if clinical, electroencephalography and imaging data are concordant. Epilepsy surgery outcomes are less favourable in patients with pathogenic variants in ion channel genes such as SCN1A. However, genomic data should not be used in isolation to contraindicate epilepsy surgery and should be considered alongside other diagnostic modalities. The additional role of somatic mosaicism in the pathogenesis of focal epilepsies may have implications for surgical planning and prognostication. Here, we advocate for including genomic data in the presurgical evaluation and multidisciplinary discussion for many epilepsy surgery candidates. We encourage neurologists to perform genetic testing in patients with focal non-lesional epilepsy, epilepsy in the setting of intellectual disability and epilepsy due to specific malformations of cortical development. The integration of genomics into the presurgical evaluation assists selection of patients for resective surgery and fosters a personalised medicine approach, where precision or targeted therapies are considered alongside surgical procedures.

Keywords:  Epilepsy surgery; Genetic testing; Monogenic epilepsy; Next-generation sequencing; Presurgical evaluation

DOI:  https://doi.org/10.1016/j.eplepsyres.2022.106951