bims-tubesc Biomed News
on Molecular mechanisms in tuberous sclerosis
Issue of 2021‒02‒14
ten papers selected by
Marti Cadena Sandoval

  1. Mol Cell Biochem. 2021 Feb 11.
      Since its initial discovery as the gene altered in Tuberous Sclerosis Complex (TSC), an autosomal dominant disorder, the interest in TSC1 (Tuberous Sclerosis Complex 1) has steadily risen. TSC1, an essential component of the pro-survival PI3K/AKT/MTOR signaling pathway, plays an important role in processes like development, cell growth and proliferation, survival, autophagy and cilia development by co-operating with a variety of regulatory molecules. Recent studies have emphasized the tumor suppressive role of TSC1 in several human cancers including liver, lung, bladder, breast, ovarian, and pancreatic cancers. TSC1 perceives inputs from various signaling pathways, including TNF-α/IKK-β, TGF-β-Smad2/3, AKT/Foxo/Bim, Wnt/β-catenin/Notch, and MTOR/Mdm2/p53 axis, thereby regulating cancer cell proliferation, metabolism, migration, invasion, and immune regulation. This review provides a first comprehensive evaluation of TSC1 and illuminates its diverse functions apart from its involvement in TSC genetic disorder. Further, we have summarized the physiological functions of TSC1 in various cellular events and conditions whose dysregulation may lead to several pathological manifestations including cancer.
    Keywords:  Cancer; Cell proliferation; Hamartin; Migration; PI3K/AKT/MTOR; TSC; TSC1; miRNAs
  2. Cell Death Discov. 2020 Jun 15. 6(1): 52
      Tuberous sclerosis complex (TSC) is characterized by hamartomatous lesions in multiple organs, with most patients developing polycystic kidney disease and leading to a decline of renal function. TSC is caused by loss-of-function mutations in either Tsc1 or Tsc2 gene, but currently, there is no effective treatment for aberrant kidney growth in TSC patients. By generating a renal proximal tubule-specific Tsc1 gene-knockout (Tsc1ptKO) mouse model, we observed that Tsc1ptKO mice developed aberrantly enlarged kidneys primarily due to hypertrophy and proliferation of proximal tubule cells, along with some cystogenesis, interstitial inflammation, and fibrosis. Mechanistic studies revealed inhibition of AMP-activated protein kinase (AMPK) phosphorylation at Thr-172 and activation of Akt phosphorylation at Ser-473 and Thr-308. We therefore treated Tsc1ptKO mice with the AMPK activator, metformin, by daily intraperitoneal injection. Our results indicated that metformin increased the AMPK phosphorylation, but decreased the Akt phosphorylation. These signaling modulations resulted in inhibition of proliferation and induction of apoptosis in the renal proximal tubule cells of Tsc1ptKO mice. Importantly, metformin treatment effectively prevented aberrant kidney enlargement and cyst growth, inhibited inflammatory response, attenuated interstitial fibrosis, and protected renal function. The effects of metformin were further confirmed by in vitro experiments. In conclusion, this study indicates a potential therapeutic effect of metformin on Tsc1 deletion-induced kidney pathology, although currently metformin is primarily prescribed to treat patients with type 2 diabetes.
  3. Cureus. 2021 Jan 04. 13(1): e12481
      Tuberous sclerosis (TS) is a rare genetic disorder of autosomal-dominant inheritance. Mutations on either of the two genes Tuberous Sclerosis Complex 1 (TSC1) or Tuberous Sclerosis Complex 2 (TSC2) play a role and result in hamartomas involving many organs, like the brain, heart, kidneys, skin, lungs, and liver. This case report is about a four-year-old boy with facial angiofibromas, hypo-pigmented skin lesions on the lower back and dorsum of the right wrist, and previous history of seizures who was referred to the radiology department of the Korle Bu Teaching Hospital for Magnetic Resonance Imaging (MRI) of the brain. The MRI of the brain revealed subependymal giant cell astrocytomas, subependymal nodules, and cortical tubers. Ultrasonography of the abdomen also showed multiple angiomyolipomas and multiple simple cysts in both kidneys. The aim of this case report is to present the imaging findings and create awareness that this rare genetic disorder does exist in Ghana and advocate for formation of support groups for parents with children with tuberous sclerosis.
    Keywords:  angiofibromas; renal angiomyolipomas; seizures; subependymal giant cell astrocytoma; tuberous sclerosis
  4. Front Oncol. 2020 ;10 610858
      Background: To evaluate the efficacy and safety of everolimus, a mTOR inhibitor, on invasive malignant renal epithelioid angiomyolipoma (EAML).Materials and Methods: From Oct 2014 to May 2019, we collected data from seven patients with a definite (clinical and pathological) diagnosis of EAML received everolimus in our hospital. Targeted sequence capture array technique with next-generation of high throughput sequencing (NGS) were performed to detect mutations of TSC1/2 genes. All patients had received surgery and everolimus. The clinical efficacy and safety of the therapy were evaluated.
    Results: Mutations of TSC1 and TSC2 were detected in two and three patients though targeted sequence capture array technique with NGS, respectively. Among seven patients, three had missense mutations, one had nonsense mutation, and one had the large fragment deletion mutation. Five patients accompanied with tuberous sclerosis complex (TSC) were identified. All patients were administered 10mg everolimus once daily, the treatment duration lasted for 3 to 28 months. The objective response was assessed 3 months later, five partial response, two stable disease (SD), the mean greatest tumor diameter of all patients decreased from 9.6 to 5.2cm. Six patients stayed SD and one patient died during follow up. Patients accompanying with TSC had better responses to everolimus compared with non-TSC.
    Conclusion: The mTOR inhibitor can be an effective treatment for patients with invasive malignant renal EAML. Patients with TSC may benefit more from the therapy.
    Keywords:  everolimus; mutation; next-generation sequencing; renal epithelioid angiomyolipoma; tuberous sclerosis complex
  5. Neuropediatrics. 2021 Feb 12.
      Sleep-related hypermotor epilepsy (SHE) is a rare syndrome that presents with hyperkinetic asymmetric tonic/dystonic seizures with vegetative signs, vocalization, and emotional facial expression, mainly during light non-rapid eye movement sleep stages. The role of various genes (CHRNA4, CHRNB2, CHRNA2, KCNT1, DEPDC5, NPRL2, NPRL3, and PRIMA1) has previously been reported, though genetic etiology is assessed in less than 10% of cases. We report the case of a 5-year-old female carrying the TSC1 variant c.843del p.(Ser282Glnfs*36) who presented with a mild phenotype of tuberous sclerosis, including carbamazepine-responsive SHE, normal neurocognitive functioning, hypomelanotic macules, no abnormalities outside the central nervous system, and tubers at neuroimaging. The presented case extends the list of SHE-related genes to include TSC1, thus suggesting a central pathogenic role of mammalian target of rapamycin (mTOR) cascade dysfunction in SHE and introducing a possible use of mTOR inhibitors in this epileptic syndrome.
  6. J Eur Acad Dermatol Venereol. 2021 Feb 10.
      BACKGROUND: Tuberous sclerosis complex (TSC) is a hamartoma syndrome characterized by multiple skin lesions, such as angiofibromas, shagreen patch, and miliary fibromas (MiF).OBJECTIVE: To determine the clinical and histological features of MiF.
    METHODS: A retrospective analysis was conducted on 133 adults with TSC. Photography was used to characterize the appearance and location of MiF. Histological features in 5 skin samples from 4 individuals were evaluated by a board-certified dermatopathologist.
    RESULTS: MiF were observed in 19 of 133 (14%) individuals with TSC. MiF were 1 to 3 mm skin-colored, sessile papules scattered on the back and rarely buttocks or thighs. Most were scattered in a bilaterally symmetric distribution, but others were asymmetric or associated with a shagreen patch. Histological features of MiF included expansion of the papillary and periadnexal dermis with variable hamartomatous abnormalities involving adjacent epithelial components.
    CONCLUSIONS: MiF are distinct from other cutaneous lesions in TSC such as shagreen patches and angiofibromas. Recognition of this entity is important in defining the spectrum of TSC disease and reassuring individuals with TSC that these lesions are benign.
    Keywords:  MiF; TSC; miliary fibroma; tuberous sclerosis complex
  7. Zhonghua Yi Xue Yi Chuan Xue Za Zhi. 2021 Feb 10. 38(2): 154-157
      OBJECTIVE: To explore the genetic basis for Chinese pedigree affected with tuberous sclerosis complex (TSC).METHODS: The proband and his family members were subjected to Sanger sequencing for variants of the TSC1 and TSC2 genes.
    RESULTS: The proband was found to harbor a c.2837+1dupG splicing variant at a donor site of the TSC2 gene. The same variant was not found among his family members and the fetus during his mother's subsequent pregnancy.
    CONCLUSION: The c.2837+1dupG splicing variant of the TSC2 gene has probably predisposed to the TSC in this pedigree. Above finding has enriched the spectrum of pathogenic variants associated with this disease.
  8. Biochem Biophys Res Commun. 2021 Feb 06. pii: S0006-291X(21)00121-2. [Epub ahead of print]545 183-188
      The mechanistic target of rapamycin complex 1 (mTORC1) signaling is the prototypical pathway regulating protein synthesis and cell proliferation. The level of mTORC1 activity is high in intestinal stem cells located at the base of the crypts and thought to gradually decrease as transit-amplifying cells migrate out of the crypts and differentiate into enterocytes, goblet cells or enteroendocrine cells along the epithelium. The unknown mechanism responsible for the silencing of intestinal epithelium mTORC1 during cell differentiation was investigated in Caco-2 cells, which spontaneously differentiate into enterocytes in standard growth medium. The results show that TSC2, an upstream negative regulator of mTORC1 was central to mTORC1 silencing in differentiated Caco-2 cells. AMPK-mediated activation of TSC2 (Ser1387) and repression of Raptor (Ser792), an essential component of mTORC1, were stimulated in differentiated Caco-2 cells. ERK1/2-mediated repression of TSC2 (Ser664) seen in undifferentiated Caco-2 cells was lifted in differentiated cells. IRS-1-mediated activation of AKT (Thr308) phosphorylation was stimulated in differentiated Caco-2 cells and may be involved in cross-pathway repression of ERK1/2. Additionally, PRAS40 (Thr246) phosphorylation was decreased in differentiated Caco-2 cells compared to undifferentiated cells allowing dephosphorylated PRAS40 to displace Raptor thereby repressing mTORC1 kinase activity.
    Keywords:  AKT; ERK; Enterocyte; PRAS40; Raptor; Tight junction protein
  9. Mol Cancer Res. 2021 Feb 11. pii: molcanres.MCR-20-0637-E.2020. [Epub ahead of print]
      Malignant mesothelioma (MM) is an aggressive tumor that typically develops after a long latency following asbestos exposure. Although mechanistic target of rapamycin complex 1 (mTORC1) activation enhances MM cell growth, the mTORC1 inhibitor everolimus has shown limited efficacy in clinical trials of MM patients. We explored the mechanism underlying mTORC1 activation in MM cells and its effects on cell proliferation and progression. Analysis of the expression profiles of 87 MMs from The Cancer Genome Atlas revealed that 40 samples (46%) displayed altered expression of RPTOR (mTORC1 component) and genes immediately upstream that activate mTORC1. Among them, we focused on RHEB and RHEBL1, which encode direct activators of mTORC1. Exogenous RHEBL1 expression enhanced MM cell growth, indicating that RHEB-mTORC1 signaling acts as a pro-oncogenic cascade. We investigated molecules that directly activate RHEBs, identifying SmgGDS as a novel RHEB-binding protein. SmgGDS knockdown reduced mTORC1 activation and inhibited the proliferation of MM cells with mTORC1 activation. Interestingly, SmgGDS displayed high binding affinity with inactive GDP-bound RHEBL1, and its knockdown reduced cytosolic RHEBL1 without affecting its activation. These findings suggest that SmgGDS retains GDP-bound RHEBs in the cytosol, whereas GTP-bound RHEBs are localized on intracellular membranes to promote mTORC1 activation. We revealed a novel role for SmgGDS in the RHEB-mTORC1 pathway and its potential as a therapeutic target in MM with aberrant mTORC1 activation. Implications: Our data showing that SmgGDS regulates RHEB localization to activate mTORC1 indicate that SmgGDS can be used as a new therapeutic target for MM exhibiting mTORC1 activation.
  10. Cells. 2021 Jan 29. pii: 262. [Epub ahead of print]10(2):
      Neurodegenerative disorders are spreading worldwide and are one of the greatest threats to public health. There is currently no adequate therapy for these disorders, and therefore there is an urgent need to accelerate the discovery and development of effective treatments. Although neurodegenerative disorders are broad ranging and highly complex, they may share overlapping mechanisms, and thus potentially manifest common targets for therapeutic interventions. Glycogen synthase kinase-3 (GSK-3) is now acknowledged to be a central player in regulating mood behavior, cognitive functions, and neuron viability. Indeed, many targets controlled by GSK-3 are critically involved in progressing neuron deterioration and disease pathogenesis. In this review, we focus on three pathways that represent prominent mechanisms linking GSK-3 with neurodegenerative disorders: cytoskeleton organization, the mammalian target of rapamycin (mTOR)/autophagy axis, and mitochondria. We also consider the challenges and opportunities in the development of GSK-3 inhibitors for treating neurodegeneration.
    Keywords:  GSK-3; GSK-3 inhibitors; autophagy; lysosome; mTOR; microtubules; mitochondria; neurodegeneration