bims-tubesc Biomed News
on Molecular mechanisms in tuberous sclerosis
Issue of 2021‒04‒25
fourteen papers selected by
Marti Cadena Sandoval

  1. Proc Natl Acad Sci U S A. 2021 Apr 13. pii: e2025522118. [Epub ahead of print]118(15):
      The mechanistic/mammalian target of rapamycin complex 1 (mTORC1) integrates multiple signals to regulate critical cellular processes such as mRNA translation, lipid biogenesis, and autophagy. Germline and somatic mutations in mTOR and genes upstream of mTORC1, such as PTEN, TSC1/2, AKT3, PIK3CA, and components of GATOR1 and KICSTOR complexes, are associated with various epileptic disorders. Increased mTORC1 activity is linked to the pathophysiology of epilepsy in both humans and animal models, and mTORC1 inhibition suppresses epileptogenesis in humans with tuberous sclerosis and animal models with elevated mTORC1 activity. However, the role of mTORC1-dependent translation and the neuronal cell types mediating the effect of enhanced mTORC1 activity in seizures remain unknown. The eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and 2 (4E-BP2) are translational repressors downstream of mTORC1. Here we show that the ablation of 4E-BP2, but not 4E-BP1, in mice increases the sensitivity to pentylenetetrazole (PTZ)- and kainic acid (KA)-induced seizures. We demonstrate that the deletion of 4E-BP2 in inhibitory, but not excitatory neurons, causes an increase in the susceptibility to PTZ-induced seizures. Moreover, mice lacking 4E-BP2 in parvalbumin, but not somatostatin or VIP inhibitory neurons exhibit a lowered threshold for seizure induction and reduced number of parvalbumin neurons. A mouse model harboring a human PIK3CA mutation that enhances the activity of the PI3K-AKT pathway (Pik3ca H1047R-Pvalb ) selectively in parvalbumin neurons shows susceptibility to PTZ-induced seizures. Our data identify 4E-BP2 as a regulator of epileptogenesis and highlight the central role of increased mTORC1-dependent translation in parvalbumin neurons in the pathophysiology of epilepsy.
    Keywords:  epilepsy; mRNA translation; mTORC1
  2. Mol Cancer Res. 2021 Apr 22. pii: molcanres.MCR-20-1046-A.2020. [Epub ahead of print]
      Tuberous sclerosis complex (TSC) is caused by mutations of either the TSC1 or TSC2 tumor suppressor gene. TSC causes tumors of the brain, heart, kidney, lung and skin. Here we report that the TSC2 protein physically binds to high-density lipoprotein binding protein (HDLBP), also called vigilin, a core stress granule (SG) protein, and that TSC2 localizes to SGs. SGs contain mRNAs and translation initiation complexes, and regulate gene expression by sequestering specific transcripts, thereby serving a cytoprotective role. TSC2 has never before been shown to localize to SGs and knocking down vigilin impacts SG translocation of TSC2. TSC2-deficient cells showed a striking increase in the number of SGs after thermal shock and arsenite treatment relative to Tsc2-expressing cells. Our findings also show that murine kidney lysates from a model of TSC have increased levels of SG components including G3BP1 and Caprin1. G3BP1 and Caprin are elevated in renal angiomyolipomas (a renal tumor common in TSC patients) compared to control normal kidney. G3BP1 is also elevated in TSC-associated Subependymal Giant Cell Astrocytomas. We found that genetic inhibition of G3BP1 inhibits the proliferation of TSC2- deficient cells in vitro. Finally, in a mouse model of TSC, genetic inhibition of SGs suppresses cell growth, suggesting that targeting SGs may have efficacy in the therapy of TSC. Implications: This study demonstrates that TSC2 physically interacts with HDLBP/vigilin, a component of stress granules, that TSC2 localizes to SG and that TSC2-deficient cells have more SGs, suggesting that SGs represent a novel therapeutic target in TSC.
  3. PLoS One. 2021 ;16(4): e0248380
      Inactivating mutations in either TSC1 or TSC2 cause Tuberous Sclerosis Complex, an autosomal dominant disorder, characterized by multi-system tumor and hamartoma development. Mutation and loss of function of TSC1 and/or TSC2 also occur in a variety of sporadic cancers, and rapamycin and related drugs show highly variable treatment benefit in patients with such cancers. The TSC1 and TSC2 proteins function in a complex that inhibits mTORC1, a key regulator of cell growth, which acts to enhance anabolic biosynthetic pathways. In this study, we identified and validated five cancer cell lines with TSC1 or TSC2 mutations and performed a kinase inhibitor drug screen with 197 compounds. The five cell lines were sensitive to several mTOR inhibitors, and cell cycle kinase and HSP90 kinase inhibitors. The IC50 for Torin1 and INK128, both mTOR kinase inhibitors, was significantly increased in three TSC2 null cell lines in which TSC2 expression was restored. Rapamycin was significantly more effective than either INK128 or ganetespib (an HSP90 inhibitor) in reducing the growth of TSC2 null SNU-398 cells in a xenograft model. Combination ganetespib-rapamycin showed no significant enhancement of growth suppression over rapamycin. Hence, although HSP90 inhibitors show strong inhibition of TSC1/TSC2 null cell line growth in vitro, ganetespib showed little benefit at standard dosage in vivo. In contrast, rapamycin which showed very modest growth inhibition in vitro was the best agent for in vivo treatment, but did not cause tumor regression, only growth delay.
  4. Front Immunol. 2021 ;12 664344
      Using a targeted transcriptomics approach, we have analyzed resected brain tissue from a cohort of 53 pediatric epilepsy surgery cases, and have found that there is a spectrum of involvement of both the innate and adaptive immune systems as evidenced by the differential expression of immune-specific genes in the affected brain tissue. The specimens with the highest expression of immune-specific genes were from two Rasmussen encephalitis cases, which is known to be a neuro-immunological disease, but also from tuberous sclerosis complex (TSC), focal cortical dysplasia, and hemimegalencephaly surgery cases. We obtained T cell receptor (TCR) Vβ chain sequence data from brain tissue and blood from patients with the highest levels of T cell transcripts. The clonality indices and the frequency of the top 50 Vβ clonotypes indicated that T cells in the brain were clonally restricted. The top 50 Vβ clonotypes comprised both public and private (patient specific) clonotypes, and the TCR Vβ chain third complementarity region (CDR3) of the most abundant public Vβ clonotype in each brain sample was strikingly similar to a CDR3 that recognizes an immunodominant epitope in either human cytomegalovirus or Epstein Barr virus, or influenza virus A. We found that the frequency of 14 of the top 50 brain Vβ clonotypes from a TSC surgery case had significantly increased in brain tissue removed to control recurrent seizures 11 months after the first surgery. Conversely, we found that the frequency in the blood of 18 of the top 50 brain clonotypes from a second TSC patient, who was seizure free, had significantly decreased 5 months after surgery indicating that T cell clones found in the brain had contracted in the periphery after removal of the brain area associated with seizure activity and inflammation. However, the frequency of a public and a private clonotype significantly increased in the brain after seizures recurred and the patient underwent a second surgery. Combined single cell gene expression and TCR sequencing of brain-infiltrating leukocytes from the second surgery showed that the two clones were CD8 effector T cells, indicating that they are likely to be pathologically relevant.
    Keywords:  Rasmussen encephalitis; T cell receptor; epilepsy; focal cortical dysplasia; tuberous sclerosis complex
  5. Histopathology. 2021 Apr 21.
      BACKGROUND: Fibrous cephalic plaques (FCPs) in individuals with tuberous sclerosis complex (TSC) may be excised for cosmetic reasons or biopsied to confirm lesion identification and TSC diagnosis.AIM: To determine the range of histopathological features of FCPs.
    METHODS: A retrospective analysis was conducted on 119 adults with TSC. Twenty-one lesions from 16 individuals were evaluated by a dermatopathologist. Additionally, we assessed if lesion color or histology varied by anatomical location.
    RESULTS: Seventy-six lesions were observed in 36/119 individuals. Erythematous lesions were more commonly found on the forehead, face, or neck than the scalp (OR=12.6, p=0.0001). Thickened and disorganized collagen fiber bundles were present in 95% (20/21). Perifollicular fibrosis was observed in 95% (20/21), enhanced vascularity in 52% (11/21), and features of fibrofolliculoma in 43% (9/21) of lesions. Other abnormalities included features similar to trichofolliculoma, follicular-derived, infundibular-type cysts, and abnormally arranged primitive hair follicles.
    CONCLUSIONS: FCPs in TSC exhibit thickened bundles of collagen and hamartomatous changes involving hair follicles. Recognition of these histopathological features may raise the possibility of unsuspected TSC or confirm FCP identification.
    Keywords:  Tuberous sclerosis complex; fibrofolliculoma; fibrous cephalic plaque; genodermatosis; hamartoma
  6. Semin Pediatr Neurol. 2021 Apr;pii: S1071-9091(21)00003-6. [Epub ahead of print]37 100875
      Affecting approximately 1 per 6000-10,000 individuals, tuberous sclerosis complex (TSC) is a neurocutaneous disorder that is not only uncommon but at risk to go underrecognized. Similar to other phakomatoses, TSC is a disorder of cellular proliferation and migration producing hamartomas-benign tumors or malignant cancers affecting the skin and brain-and also involving the heart, kidneys, lungs and eyes in ways that can vary across the lifetime. It also occurs and varies across generations. Among medical subspecialists, the pediatric neurologist is often responsible for making the initial diagnosis when the affected individual presents with infantile spasms or another early-onset epilepsy syndrome. In recent decades, the identification of the responsible genes and gene products forming the mechanistic target of rapamycin complex, previously termed the mammalian target of rapamycin, not only has expanded our understanding of tuberous sclerosis pathophysiology, but has also inspired the search for targeted interventions.
  7. Am J Respir Crit Care Med. 2021 Apr 21.
      RATIONALE: Lymphangioleiomyomatosis is a multisystem disease causing lung cysts and respiratory failure. Loss of tuberous sclerosis complex (TSC) gene function results in a clone of 'LAM cells' with dysregulated mTOR activity. LAM cells and fibroblasts form lung nodules that also contain mast cells although their significance is unknown.OBJECTIVES: To understand the mechanism of mast cell accumulation and their role in the pathogenesis of LAM. Methods, Measurements and Main Results: Transcriptional profiling, quantitative RT-PCR and ELISA showed that LAM derived cell / fibroblast co-cultures induced multiple CXC chemokines in fibroblasts. Compared with normal tissue, LAM lungs had increased tryptase positive mast cells expressing CXC chemokine receptors (p<0.05). Mast cells located around the periphery of LAM nodules were positively associated with rate of lung function loss (p=0.016). In vitro, LAM spheroid TSC2 null cell / fibroblast co-cultures attracted mast cells, which was inhibited by pharmacologic and CRISPR-cas9 inhibition of CXCR1 and 2. LAM spheroids caused mast cell tryptase release, which induced fibroblast proliferation and increased LAM spheroid size (1.36±0.24 fold, p=0.0019). The tryptase inhibitor APC366 and sodium cromoglycate inhibited mast cell induced spheroid growth. Using an immuno-competent Tsc2 null murine homograft model, sodium cromoglycate markedly reduced mast cell activation and Tsc2 null lung tumour burden (vehicle: 32.5.3%±23.6 and cromoglycate: 5.5%±4.3. p=0.0035).
    CONCLUSIONS: LAM cell / fibroblast interactions attract mast cells where tryptase release contributes to disease progression. Repurposing sodium cromoglycate for use in LAM should be studied as an alternative or adjunct to mTOR inhibitor therapy.
    Keywords:  Tissue remodelling; chemokine; serine protease; tuberous sclerosis
  8. Pediatr Dent. 2021 Mar 15. 43(2): 140-144
      Purpose: The purpose of this descriptive study was to describe oral manifestations and oral health quality of life (QOL) in children aged six months to six years, 11 months with tuberous sclerosis complex (TSC). Methods: Parents of participants completed an oral health QOL survey. The presence of oral lesions associated with TSC was assessed. Results: Sixty-two participants enrolled between February 2015 and March 2017. Among the significant oral health findings, 11 (17.7 percent) had enamel pitting, 33 (53 percent) had no previous dental examination, eight (12.9 percent) did not brush their teeth, and eight (12.9 percent) had caries present. Per the QOL survey results, 18 (31 percent) had difficulty sleeping, 22 (37.3 percent) experienced irritability/frustration, and 15 (29.4 percent) had difficulty pronouncing words. Developmental delays were present in 40 (70.2 percent), seizures occurred within the last three months in 37 (59.7 percent), and a mammalian target of rapamycin inhibitor medication was used for 22 (35.4 percent). Conclusions: Enamel pitting was observed in 17.7 percent of children in the primary dentition. Oral health quality of life in this tuberous sclerosis complex cohort was significantly reduced.
  9. Neurosciences (Riyadh). 2021 Apr;26(2): 207-211
      Blue rubber bleb nevus syndrome (BRBNS) is a rare disorder that is characterized by multiple dome-shaped cutaneous venous malformations on the skin and visceral organs. Typical extra-cutaneous lesions have the appearance of blueish nipple-shaped nodules that can easily compress and refill. We described a rare case of a 23-year-old female with BRBNS and tuberous sclerosis complex (TSC) that presented with central nervous system (CNS) involvement including unprovoked focal impaired awareness seizure. Her BRBNS presents with hemangiomas involving multiple organs in the body including the brain, gastrointestinal (GI) system, and skin. This case highlights the importance of studying and understanding the association between BRBNS and TSC as it may lead to improved understanding.
  10. Sci Rep. 2021 Apr 19. 11(1): 8493
      Renal angiomyolipomas hemorrhage is associated with their size and vascular constitution. The effects of sirolimus on different components of angiomyolipomas was analyzed in patients with tuberous sclerosis complex, sporadic lymphangioleiomyomatosis and multiple sporadic angiomyolipomas. Thirty angiomyolipomas from 14 patients treated with sirolimus were retrospectively evaluated. A Hounsfield-unit threshold was used to classify angiomyolipomas in fat-rich, fat-poor and intermediate-fat tumors, and to categorize tumor compartments in fat rich, fat poor, intermediate fat and highly vascularized. Diameter variations were measured to assess the effects on aneurysmatic/ectatic vascular formations. Volume reduction following treatment with sirolimus was higher in fat-poor than fat-rich angiomyolipomas. Tumor reduction was mainly determined by decrease of the fat-poor and highly-vascularized compartments while the volume of the fat-rich compartment increased. Broad liposubstitution was observed in some tumors. A median reduction of 100% (75 to 100) in the diameter of aneurysmatic/ectatic vascular structures was observed. Our study showed that sirolimus reduces the size of angiomyolipomas by decreasing primarily their highly-vascularized and fat-poor compartments. This effect is associated with a remarkable reduction of tumoral aneurysms/ectatic vessels, revealing the likely mechanism responsible for the risk-decreasing effect of mTOR inhibitors on angiomyolipoma bleeding. These findings support the role of mTOR in the development of angiomyolipoma blood vessels.
  11. Orphanet J Rare Dis. 2021 Apr 17. 16(1): 181
      BACKGROUND: The tuberous sclerosis-associated neuropsychiatric disorders (TAND) have not previously been studied in China. We aimed to assess the psychiatric level of individuals with TAND using the Mini International Neuropsychiatric Interview for Children (MINI-KID) in China.RESULTS: A total of 83.16% of individuals (79/95) had at least one TAND, and 70.53% (67/95) had an intellectual disability. The MINI-KID tool diagnosed 16 neuropsychiatric diseases, the most common of which were attention-deficit/hyperactivity disorder (ADHD) (51.58%, 49/95) and social anxiety disorder (30.53%, 29/95). The number of children with psychiatric diseases in the tuberous sclerosis complex (TSC) group was significantly greater than the number in the typically developing group (P < 0.0001). Notably, 69.47% (66/95) had two or more psychiatric disorders. Pervasive developmental disorder (PDD) was often co-morbid with other psychiatric disorders.
    CONCLUSIONS: This study used the structured and systematic MINI-KID scale to determine the diagnosis of psychiatric co-morbidities in a relatively large sample, suggesting a higher rate. By comparing the status of individuals with TSC with typically developing children, the results suggests that neuropsychiatric co-morbidities are significantly higher in individuals with TSC. Research has revealed the frequent presence of two, three or more neuropsychiatric diseases in individuals with TSC.
    Keywords:  ADHD; Child; MINI-KID; Psychiatric disorders; TAND; TSC
  12. Cell Signal. 2021 Apr 16. pii: S0898-6568(21)00098-X. [Epub ahead of print] 110010
      Activation of the protein kinase mechanistic target of rapamycin (mTOR) in both complexes 1 and 2 (mTORC1/2) in the liver is repressed during fasting and rapidly stimulated in response to a meal. The effect of feeding on hepatic mTORC1/2 is attributed to an increase in plasma levels of nutrients, such as amino acids, and insulin. By contrast, fasting is associated with elevated plasma levels of glucagon, which is conventionally viewed as having a counter-regulatory role to insulin. More recently an expanded role for glucagon action in post-prandial metabolism has been demonstrated. Herein we investigated the impact of insulin and glucagon on mTORC1/2 activation. In H4IIE and HepG2 cultures, insulin enhanced phosphorylation of the mTORC1 substrates S6K1 and 4E-BP1. Surprisingly, the effect of glucagon on mTORC1 was biphasic, wherein there was an acute increase in phosphorylation of S6K1 and 4E-BP1 over the first hour of exposure, followed by latent suppression. The transient stimulatory effect of glucagon on mTORC1 was not additive with insulin, suggesting convergent signaling. Glucagon enhanced cAMP levels and mTORC1 stimulation required activation of the glucagon receptor, PI3K/Akt, and exchange protein activated by cAMP (EPAC). EPAC acts as the guanine nucleotide exchange factor for the small GTPase Rap1. Rap1 expression enhanced S6K1 phosphorylation and glucagon addition to culture medium promoted Rap1-GTP loading. Signaling through mTORC1 acts to regulate protein synthesis and we found that glucagon promoted an EPAC-dependent increase in protein synthesis. Overall, the findings support that glucagon elicits acute activation of mTORC1/2 by an EPAC-dependent increase in Rap1-GTP.
    Keywords:  Cyclic AMP; Diabetes; Glucagon; Insulin; Liver; Protein synthesis
  13. Epilepsy Behav. 2021 Apr 15. pii: S1525-5050(21)00195-5. [Epub ahead of print] 107961
      Despite the availability of 28 antiseizure medications (ASMs), one-third of people with epilepsy fail to achieve sustained freedom from seizures. Clinical outcome is even poorer for children with developmental and epileptic encephalopathies (DEEs), many of which are due to single-gene mutations. Discovery of causative genes, however, has paved the way to understanding the molecular mechanism underlying these epilepsies, and to the rational application, or development, of precision treatments aimed at correcting the specific functional defects or their consequences. This article provides an overview of current progress toward precision medicine (PM) in the management of monogenic pediatric epilepsies, by focusing on four different scenarios, namely (a) rational selection of ASMs targeting specifically the underlying pathogenetic mechanisms; (b) development of targeted therapies based on novel molecules; (c) use of dietary treatments or food constituents aimed at correcting specific metabolic defects; and (d) repurposing of medications originally approved for other indications. This article is part of the Special Issue "Severe Infantile Epilepsies".
    Keywords:  Children; Drug resistant epilepsy; Epileptic encephalopathy; Monogenic epilepsies; Precision medicine; Seizure disorder
  14. Front Cell Dev Biol. 2021 ;9 646482
      Skeletal muscle anabolic resistance (i.e., the decrease in muscle protein synthesis (MPS) in response to anabolic stimuli such as amino acids and exercise) has been identified as a major cause of age-related sarcopenia, to which blunted nutrition-sensing contributes. In recent years, it has been suggested that a leucine sensor may function as a rate-limiting factor in skeletal MPS via small-molecule GTPase. Leucine-sensing and response may therefore have important therapeutic potential in the steady regulation of protein metabolism in aging skeletal muscle. This paper systematically summarizes the three critical processes involved in the leucine-sensing and response process: (1) How the coincidence detector mammalian target of rapamycin complex 1 localizes on the surface of lysosome and how its crucial upstream regulators Rheb and RagB/RagD interact to modulate the leucine response; (2) how complexes such as Ragulator, GATOR, FLCN, and TSC control the nucleotide loading state of Rheb and RagB/RagD to modulate their functional activity; and (3) how the identified leucine sensor leucyl-tRNA synthetase (LARS) and stress response protein 2 (Sestrin2) participate in the leucine-sensing process and the activation of RagB/RagD. Finally, we discuss the potential mechanistic role of exercise and its interactions with leucine-sensing and anabolic responses.
    Keywords:  age-related sarcopenia; anabolic resistance; leucine response; leucine-sensing; protein synthesis