bims-tubesc Biomed News
on Molecular mechanisms in tuberous sclerosis
Issue of 2021‒01‒24
thirteen papers selected by
Marti Cadena Sandoval

  1. Biochem Biophys Res Commun. 2021 Jan 19. pii: S0006-291X(21)00068-1. [Epub ahead of print]541 84-89
      Tuberous sclerosis complex 2 (TSC2) is a tumor-suppressor protein that is partially regulated by insulin, energy, oxygen, and growth factors. Mutations in the TSC2 gene and loss of TSC2 promote cell growth by the mammalian target of rapamycin complex 1 (mTORC1) activation. Furthermore, S-adenosylmethionine (SAM) sensor upstream of mTORC1 indirectly inhibits mTORC1 activity via the methionine metabolite SAM. Here, we investigated the effects of methionine on insulin/TSC2/mTORC1 activity. Our results showed that methionine affected TSC2 stability and abolished TSC2 localization to the lysosome. Moreover, activation of insulin signaling contributed to TSC2 degradation in a methionine deprivation-dependent manner. Thus, methionine and insulin crosstalk occurred via TSC2.
    Keywords:  AKT; Amino acid; Mammalian target of rapamycin complex 1; Methionine; S-adenosylmethionine; Tuberous sclerosis complex 2
  2. Neuroradiology. 2021 Jan 22.
      Tuberous sclerosis complex (TSC) is an autosomal dominant condition clinically presenting with heterogenous clinical features. Multiple neuroradiological manifestations have been associated with TSC, such as tubers, radial migration lines, subependymal nodules, subependymal giant cell astrocytomas, and cyst-like lesions of the white matter (CLLWMs). The latter have been described as non-enhancing well-defined cysts whose pathogenesis is still unknown. We describe 2 TSC patients with CLLWM showing contrast enhancement after Gadolinium injection, a previously unreported entity.
    Keywords:  Magnetic resonance imaging; Pediatric neuroradiology; Phakomatosis; Tuberous sclerosis complex
  3. Cell Death Differ. 2021 Jan 19.
      Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies and cause of death from cancer in China. Previous studies showed that autophagy and apoptosis inhibition are critical for the survival of ESCC cells. However, the underlying mechanisms remain to be clarified. Recently, we found that PIWIL2, a novel cancer testis protein, is highly expressed in ESCC and associated with high T-stage and poor 5-year survival rate in patients. Our further study showed that PIWIL2 can directly bind to IKK and promote its phosphorylation, leading to phosphorylation of IκB and subsequently nuclear translocation of NF-κB for apoptosis inhibition. Meanwhile, PIWIL2 competitively inhibits binding of IKK to TSC1, and thus deactivate mTORC1 pathway which suppresses ULK1 phosphorylation and initiation of autophagy. The mouse xenograft model suggested that PIWIL2 can promote ESCC growth in an IKK-dependent manner. This present work firstly revealed that PIWIL2 can play a role in regulating autophagy and apoptosis, and is associated with poor prognosis in ESCC patients, providing novel insights into the roles of PIWIL2 in tumorigenesis.
  4. Transl Pediatr. 2020 Dec;9(6): 757-767
      Background: Tuberous sclerosis complex (TSC) is a rare genetic disease which leads to formation of benign tumors in the brain and other organs of the body. Ultrasound (US) can detect the location, quantity, size and internal echo of TSC-associated renal diseases, liver angiomyolipoma (AML), and co-existing lesions, providing important diagnostic basis for clinical diagnosis. The aim of the present study was to investigate the abdominal ultrasonographic features of pediatric TSC and explore the advantages of abdominal ultrasonography in clinical practice.Methods: Data of children with TSC, who presented to the Second Affiliated Hospital and Yuying Children's Hospital, Wenzhou Medical University, between January 2016 and November 2018, were analyzed by a retrospective chart review. The cases were identified from electronic medical records (EMR) system and underwent ultrasonography, we yielded a total of 12 patients.
    Results: The 12 pediatric patients, including 5 boys and 7 girls, ranged in age from 9 months to 13 years old. And they all had a history of epilepsy. All the patients underwent brain magnetic resonance imaging (MRI) or computed tomography (CT) examination, which revealed a scattered distribution of multiple hyperintense nodules. Of the 12 patients, 10 had TSC-associated bilateral renal AMLs, 5 had hepatic AML, and 4 had renal cysts.
    Conclusions: US is a useful and non-invasive tool for the detection of TSC-associated renal and liver lesions and for clinical follow-up among pediatric patients.
    Keywords:  Tuberous sclerosis complex (TSC); angiomyolipoma (AML); pediatric patients; ultrasound (US)
  5. Placenta. 2021 Jan 12. pii: S0143-4004(21)00018-7. [Epub ahead of print]104 267-276
      INTRODUCTION: High-altitude (>2500 m) residence augments the risk of intrauterine growth restriction (IUGR) and preeclampsia likely due, in part, to uteroplacental hypoperfusion. Previous genomic and transcriptomic studies in humans and functional studies in mice and humans suggest a role for AMP-activated protein kinase (AMPK) pathway in protecting against hypoxia-associated IUGR. AMPK is a metabolic sensor activated by hypoxia that is ubiquitously expressed in vascular beds and placenta.METHODS: We measured gene expression and protein levels of AMPK and its upstream regulators and downstream targets in human placentas from high (>2500 m) vs. moderate (~1700 m) and low (~100 m) altitude.
    RESULTS: We found that phosphorylated AMPK protein levels and its downstream target TSC2 were increased in placentas from high and moderate vs. low altitude, whereas the phosphorylated form of the downstream target translation repressor protein 4E-BP1 was increased in high compared to moderate as well as low altitude placentas. Mean birth weights progressively fell with increasing altitude but no infants, by study design, were clinically growth-restricted. Gene expression analysis showed moderate increases in PRKAG2, encoding the AMPK γ2 subunit, and mechanistic target of rapamycin, MTOR, expression.
    DISCUSSION: These results highlight a differential regulation of placental AMPK pathway activation in women residing at low, moderate or high altitude during pregnancy, suggesting AMPK may be serving as a metabolic regulator for integrating hypoxic stimuli with placental function.
    Keywords:  AMPK; High altitude; Hypoxia; Placenta; Pregnancy
  6. Nat Commun. 2021 01 20. 12(1): 476
      Endonuclease G (ENDOG), a mitochondrial nuclease, is known to participate in many cellular processes, including apoptosis and paternal mitochondrial elimination, while its role in autophagy remains unclear. Here, we report that ENDOG released from mitochondria promotes autophagy during starvation, which we find to be evolutionally conserved across species by performing experiments in human cell lines, mice, Drosophila and C. elegans. Under starvation, Glycogen synthase kinase 3 beta-mediated phosphorylation of ENDOG at Thr-128 and Ser-288 enhances its interaction with 14-3-3γ, which leads to the release of Tuberin (TSC2) and Phosphatidylinositol 3-kinase catalytic subunit type 3 (Vps34) from 14-3-3γ, followed by mTOR pathway suppression and autophagy initiation. Alternatively, ENDOG activates DNA damage response and triggers autophagy through its endonuclease activity. Our results demonstrate that ENDOG is a crucial regulator of autophagy, manifested by phosphorylation-mediated interaction with 14-3-3γ, and its endonuclease activity-mediated DNA damage response.
  7. Curr Top Behav Neurosci. 2021 Jan 17.
      Epilepsy is commonly associated with cognitive and behavioral deficits that dramatically affect the quality of life of patients. In order to identify novel therapeutic strategies aimed at reducing these deficits, it is critical first to understand the mechanisms leading to cognitive impairments in epilepsy. Traditionally, seizures and epileptiform activity in addition to neuronal injury have been considered to be the most significant contributors to cognitive dysfunction. In this review we however highlight the role of a new mechanism: alterations of neuronal dynamics, i.e. the timing at which neurons and networks receive and process neural information. These alterations, caused by the underlying etiologies of epilepsy syndromes, are observed in both animal models and patients in the form of abnormal oscillation patterns in unit firing, local field potentials, and electroencephalogram (EEG). Evidence suggests that such mechanisms significantly contribute to cognitive impairment in epilepsy, independently of seizures and interictal epileptiform activity. Therefore, therapeutic strategies directly targeting neuronal dynamics rather than seizure reduction may significantly benefit the quality of life of patients.
    Keywords:  Cognitive comorbidities; Epilepsy; Gamma; High frequency oscillations; Hippocampus; Oscillations; Sharp wave ripples; Theta
  8. Cell Death Dis. 2021 Jan 18. 12(1): 88
      Inducing autophagy and inhibiting apoptosis may provide a therapeutic treatment for atherosclerosis (AS). For the treatment of progressive AS, arsenic trioxide (ATO) has been used to coat vascular stents. However, the effect of ATO on autophagy of macrophages is still unknown. Therefore, the aims of this study were to characterize the effects and the mechanism of actions of ATO on autophagy in macrophages. Our results showed that ATO-induced activation of autophagy was an earlier event than ATO-induced inhibition of the expression of apoptosis markers in macrophages and foam cells. Nuclear transcription factor EB (TFEB) prevents atherosclerosis by activating macrophage autophagy and promoting lysosomal biogenesis. Here, we report that ATO triggered the nuclear translocation of TFEB, which in turn promoted autophagy and autophagosome-lysosome fusion. Both the latter events were prevented by TFEB knockdown. Moreover, ATO decreased the p-AKT and p-mTOR in the PI3K/AKT/mTOR signaling pathway, thus inducing autophagy. Correspondingly, treatment with the autophagy inhibitor 3-methyladenine (3-MA) abolished the autophagy-inducing effects of ATO. Meanwhile, PI3K inhibitor (LY294002) and mTOR inhibitor (rapamycin) cooperated with ATO to induce autophagy. Furthermore, reactive oxygen species (ROS) were generated in macrophages after treatment with ATO. The ROS scavenger N-acetyl-1-cysteine (NAC) abolished ATO-induced nuclear translocation of TFEB, as well as changes in key molecules of the AKT/mTOR signaling pathway and downstream autophagy. More importantly, ATO promoted autophagy in the aorta of ApoE-/- mice and reduced atherosclerotic lesions in early AS, which were reversed by 3-MA treatment. In summary, our data indicated that ATO promoted ROS induction, which resulted in nuclear translocation of TFEB and inhibition of the PI3K/AKT/mTOR pathway. These actions ultimately promoted macrophage autophagy and reduced atherosclerotic lesions at early stages. These findings may provide a new perspective for the clinical treatment of early-stage atherosclerosis and should be further studied.
  9. Proc Natl Acad Sci U S A. 2021 Jan 26. pii: e2022120118. [Epub ahead of print]118(4):
      In mammalian cells, nutrients and growth factors signal through an array of upstream proteins to regulate the mTORC1 growth control pathway. Because the full complement of these proteins has not been systematically identified, we developed a FACS-based CRISPR-Cas9 genetic screening strategy to pinpoint genes that regulate mTORC1 activity. Along with almost all known positive components of the mTORC1 pathway, we identified many genes that impact mTORC1 activity, including DCAF7, CSNK2B, SRSF2, IRS4, CCDC43, and HSD17B10 Using the genome-wide screening data, we generated a focused sublibrary containing single guide RNAs (sgRNAs) targeting hundreds of genes and carried out epistasis screens in cells lacking nutrient- and stress-responsive mTORC1 modulators, including GATOR1, AMPK, GCN2, and ATF4. From these data, we pinpointed mitochondrial function as a particularly important input into mTORC1 signaling. While it is well appreciated that mitochondria signal to mTORC1, the mechanisms are not completely clear. We find that the kinases AMPK and HRI signal, with varying kinetics, mitochondrial distress to mTORC1, and that HRI acts through the ATF4-dependent up-regulation of both Sestrin2 and Redd1. Loss of both AMPK and HRI is sufficient to render mTORC1 signaling largely resistant to mitochondrial dysfunction induced by the ATP synthase inhibitor oligomycin as well as the electron transport chain inhibitors piericidin and antimycin. Taken together, our data reveal a catalog of genes that impact the mTORC1 pathway and clarify the multifaceted ways in which mTORC1 senses mitochondrial dysfunction.
    Keywords:  CRISPR-Cas9 screen; mTORC1; mitochondria
  10. Cancer Biother Radiopharm. 2021 Jan 20.
      Background: Glioma is a devastating disease with the worst prognosis among human malignant tumors. Although temozolomide (TMZ) improves the overall survival of glioma patients, there are still many glioma patients who are resistant to TMZ. In this study, we focused on the effect of apigenin (API) and TMZ on glioma cells in vitro and in vivo, and we studied the underlying molecular mechanisms. Materials and Methods: To investigate the effect of API on glioblastoma cell proliferation, cell viability was assessed after glioma cells were incubated with various concentrations of API with or without TMZ using MTT assays. Then, we explored the synergistic effect of API and TMZ on glioma cell cycle, apoptosis, and migration. To investigate the molecular mechanism behind the synergism of API and TMZ, we examined the related genes of the major signaling pathways involved in glioma pathogenesis by Western blotting. Results: In this study, we found that API significantly suppressed the proliferation of glioma cells in a dose- and time-dependent manner. Combining API and TMZ significantly induced glioma cells arrest at the G2 phase and inhibited glioma cells proliferation compared with API or TMZ alone. In addition, API promoted the ability of TMZ to induce glioma cells apoptosis and inhibit glioma cells invasion. Furthermore, compared with treatment with individual agents, the combination of API and TMZ significantly inhibited the growth of subcutaneous tumors in mice. These results implied that API could synergistically suppress the growth of glioma cells when combined with TMZ. Combining API and TMZ significantly inhibited the protein expression of p-AKT, cyclin D1, Bcl-2, Matrix Metallopeptidase 2, and Matrix Metallopeptidase 9. Conclusion: API and TMZ synergistically inhibited glioma growth through the PI3K/AKT pathway.
    Keywords:  AKT; apigenin; glioma; proliferation; temozolomide
  11. Orphanet J Rare Dis. 2021 Jan 21. 16(1): 39
      BACKGROUND: Mucolipidosis type IV (MLIV), an ultra-rare neurodevelopmental and neurodegenerative disorder, is caused by mutations in the MCOLN1 gene, which encodes the late endosomal/lysosomal transient receptor potential channel TRPML1 (mucolipin 1). The precise pathophysiogical pathways that cause neurological disease in MLIV are poorly understood. Recently, the first post-mortem brain sample became available from a single MLIV patient, and in the current study we performed mass spectrometry (MS)-based proteomics on this tissue with a view to delineating pathological pathways, and to compare with previously-published data on MLIV, including studies using the Mcoln1-/- mouse.RESULTS: A number of pathways were altered in two brain regions from the MLIV patient, including those related to the lysosome, lipid metabolism, myelination, cellular trafficking and autophagy, mTOR and calmodulin, the complement system and interferon signaling. Of these, levels of some proteins not known previously to be associated with MLIV were altered, including APOD, PLIN4, ATG and proteins related to interferon signaling. Moreover, when proteins detected by proteomics in the human brain were compared with their orthologs detected in the Mcoln1-/- mouse by RNAseq, the results were remarkably similar. Finally, analysis of proteins in human and mouse CSF suggest that calbindin 1 and calbindin 2 might be useful as biomarkers to help chart the course of disease development.
    CONCLUSIONS: Despite the sample size limitations, our findings are consistent with the relatively general changes in lysosomal function previously reported in MLIV, and shed light on new pathways of disease pathophysiology, which is required in order to understand the course of disease development and to determine the efficacy of therapies when they become available for this devastating disease.
    Keywords:  Autophagy; Brain; Calbindin; Lysosome; Neuroinflammation; Neuropathology; TRPML1
  12. eNeuro. 2021 Jan 14. pii: ENEURO.0183-20.2021. [Epub ahead of print]
      Excessive activation of mTOR in microglia impairs CNS homeostasis and causes severe epilepsy. Autophagy constitutes an important part of mTOR signaling. The contribution of microglial autophagy to CNS homeostasis and epilepsy remains to be determined. Here we report that ATG7KO mice deficient for autophagy in microglia display a marked increase of myelination markers, a higher density of mature oligodendrocytes, and altered lengths of the nodes of Ranvier. Moreover, we found that deficiency of microglial autophagy (ATG7KO) leads to increased seizure susceptibility in three seizure models (pilocarpine, kainic acid, and amygdala kindling). We demonstrated that ATG7KO mice develop severe generalized seizures and display nearly 100% mortality to convulsions induced by pilocarpine and kainic acid. In the amygdala kindling model, we observed significant facilitation of contralateral propagation of seizures, a process underlying the development of generalized seizures. Taken together, our results reveal impaired microglial autophagy as a novel mechanism underlying altered homeostasis of oligodendrocytes and increased susceptibility to severe and fatal generalized seizures.Significance statement Microglia play a critical role in CNS homeostasis, predominantly by impinging on neurons and astrocytes. A role for microglia in the development of oligodendrocytes has begun to be recognized, but the mechanism remains largely unknown. The present study uncovered a novel role of microglial autophagy in oligodendrocyte homeostasis. Importantly, we found that deficiency of microglial autophagy causes severe forms of generalized seizures and high mortality, pointing to a strong association of altered oligodendrocyte homeostasis and epilepsy. Our findings have implications in understanding severe forms of epilepsy.
    Keywords:  autophagy; epilepsy; mTOR; microglia; myelination; seizure
  13. Exp Mol Med. 2021 Jan 22.
      Posttranslational modifications of proteins, such as acetylation, are essential for the regulation of diverse physiological processes, including metabolism, development and aging. Autophagy is an evolutionarily conserved catabolic process that involves the highly regulated sequestration of intracytoplasmic contents in double-membrane vesicles called autophagosomes, which are subsequently degraded after fusing with lysosomes. The roles and mechanisms of acetylation in autophagy control have emerged only in the last few years. In this review, we describe key molecular mechanisms by which previously identified acetyltransferases and deacetylases regulate autophagy. We highlight how p300 acetyltransferase controls mTORC1 activity to regulate autophagy under starvation and refeeding conditions in many cell types. Finally, we discuss how altered acetylation may impact various neurodegenerative diseases in which many of the causative proteins are autophagy substrates. These studies highlight some of the complexities that may need to be considered by anyone aiming to perturb acetylation under these conditions.