bims-tubesc Biomed News
on Molecular mechanisms in tuberous sclerosis
Issue of 2023‒02‒26
ten papers selected by
Marti Cadena Sandoval
Columbia University
  1. Epileptogenesis in tuberous sclerosis complex-related developmental and epileptic encephalopathy.
  2. Peripheral Neuropathy: An Early Indication for Systemic Disease that Involves the Mechanistic Target of Rapamycin (mTOR).
  3. The role of programmed mitophagy in germline mitochondrial DNA quality control.
  4. Metabolic signatures of lymphangioleiomyomatosis in biofluids: nuclear magnetic resonance (NMR)-based metabonomics of blood plasma: a case-control study.
  5. HDAC6-G3BP2 promotes lysosomal-TSC2 and suppresses mTORC1 under ETV4 targeting-induced low-lactate stress in non-small cell lung cancer.
  6. Amino acid sensing and lysosomal signaling complexes.
  7. Enhanced liquidity of p62 droplets mediated by Smurf1 links Nrf2 activation and autophagy.
  8. In Vitro Delivery of mTOR inhibitors by Kidney-Targeted Micelles for Autosomal Dominant Polycystic Kidney Disease.
  9. Loss of pex5 sensitizes zebrafish to fasting due to deregulated mitochondria, mTOR, and autophagy.
  10. NRF3 activates mTORC1 arginine-dependently for cancer cell viability.
  1. Brain. 2023 Feb 20. pii: awad048. [Epub ahead of print]
    Epileptogenesis in tuberous sclerosis complex-related developmental and epileptic encephalopathy.
    Eleonora Aronica, Nicola Specchio, Mark J Luinenburg, Paolo Curatolo.
      Epileptogenesis in infants with tuberous sclerosis complex (TSC) is a gradual and dynamic process leading to early onset and difficult-to-treat seizures. Several cellular, molecular, and pathophysiologic mechanisms, including mammalian target of rapamycin (mTOR) dysregulation, GABAergic dysfunction, and abnormal connectivity, may play a role in this epileptogenic process, and may also contribute to the associated developmental encephalopathy. Disease specific antiseizure medications or drugs targeting the mTOR pathway have proved to be effective in TSC-associated epilepsy. Pre-symptomatic administration of vigabatrin, a GABAergic drug, delays seizure onset and reduces the risk of a subsequent epileptic encephalopathy, such as infantile spasms syndrome or Lennox-Gastaut syndrome. Everolimus, a rapamycin-derived mTOR inhibitor, reduces seizures frequency especially in younger patients. This evidence suggests that everolimus should be considered early in the course of epilepsy. Future trials are needed to optimize the use of everolimus and to determine whether earlier correction of the mTOR dysregulation can prevent the progression to developmental and epileptic encephalopathies or mitigate their severity in infants with TSC. Clinical trials of several other potential antiseizure drugs (cannabidiol and ganaxolone) that target contributing mechanisms are also underway. This review provides an overview of the different biological mechanisms occurring in parallel and interacting throughout the life course, even beyond the epileptogenic process, in individuals with TSC. These complexities highlight the facing challenges in the prevention and treatment of TSC-related developmental and epileptic encephalopathy.
    Keywords:  animal model; developmental and epileptic encephalopathy; epileptogenesis; mTOR; tuberous sclerosis complex
    DOI:  https://doi.org/10.1093/brain/awad048
  2. Curr Neurovasc Res. 2023 Feb 20.
    Peripheral Neuropathy: An Early Indication for Systemic Disease that Involves the Mechanistic Target of Rapamycin (mTOR).
    Kenneth Maiese.
      
    DOI:  https://doi.org/10.2174/1567202620999230220094137
  3. Autophagy. 2023 Feb 20.
    The role of programmed mitophagy in germline mitochondrial DNA quality control.
    Jonathan M Palozzi, Thomas R Hurd.
      Mitochondrial DNA (mtDNA) is prone to the accumulation of mutations. To prevent harmful mtDNA mutations from being passed on to the next generation, the female germline, through which mtDNA is exclusively inherited, has evolved extensive mtDNA quality control. To dissect the molecular underpinnings of this process, we recently performed a large RNAi screen in Drosophila and uncovered a programmed germline mitophagy (PGM) that is essential for mtDNA quality control. We found that PGM begins as germ cells enter meiosis, induced, at least in part, by the inhibition of the mTor (mechanistic Target of rapamycin) complex 1 (mTorC1). Interestingly, PGM requires the general macroautophagy/autophagy machinery and the mitophagy adaptor BNIP3, but not the canonical mitophagy genes Pink1 and park (parkin), even though they are critical for germline mtDNA quality control. We also identified the RNA-binding protein Atx2 as a major regulator of PGM. This work is the first to identify and implicate a programmed mitophagy event in germline mtDNA quality control, and it highlights the utility of the Drosophila ovary for studying developmentally regulated mitophagy and autophagy in vivo.
    Keywords:  Drosophila; autophagy; germline; mitochondria; mitochondrial DNA; mitophagy; mtDNA; purifying selection
    DOI:  https://doi.org/10.1080/15548627.2023.2182595
  4. Ann Transl Med. 2023 Jan 31. 11(2): 76
    Metabolic signatures of lymphangioleiomyomatosis in biofluids: nuclear magnetic resonance (NMR)-based metabonomics of blood plasma: a case-control study.
    Weili Gu, Yingxin Pan, Wei Zhao, Jie Liu, Ying Meng.
      Background: Our aim was to analyze and compare the characteristics and differences of blood metabolites between lymphangioleiomyomatosis (LAM) patients and healthy controls, in order to find biomarkers that can be used for the diagnosis and classification of LAM.Methods: Between January 2020 to January 2022, 61 eligible LAM patients [51 sporadic LAM (S-LAM) and 10 tuberous sclerosis complex LAM (TSC-LAM)] from the First Affiliated Hospital of Guangzhou Medical University and 30 healthy controls were enrolled. Blood samples were taken for nuclear magnetic resonance (NMR) detection. Data analysis was performed by the umbrella program, and Wilcoxon analysis was used for comparisons between groups. The difference indicators were modeled by logistic regression. Diagnostic accuracy of the best predictive parameters was evaluated by the area under the receiver operating characteristic (ROC) curve (AUC), and the sensitivity and specificity were calculated.
    Results: The indexes differed between LAM patients and healthy controls, S-LAM patients and healthy controls, and between TSC-LAM patients and healthy controls. There were two different metabolic indexes between S-LAM and TSC-LAM patients. After logistic regression modeling and ROC analysis, methionine (AUC =0.929, sensitivity =73.8%, specificity =100%, cut-off value =0.011 mmol/L) and acetic acid (AUC =0.966, sensitivity =95.1%, specificity =90%, cut-off value =0.006 mmol/L) had the highest diagnostic efficiency in LAM patients, and could be used to distinguish between affected and healthy people. Methionine was significantly associated with pneumothorax (P<0.05), and creatinine was significantly correlated with hysteromyoma (P<0.05).
    Conclusions: Methionine and acetic acid in the plasma of LAM patients are potential biomarkers. Methionine was also associated with pneumothorax in LAM patients. Also, acetone and creatinine were promising metabolic markers to distinguish S-LAM from TSC-LAM. NMR as a new non-invasive diagnostic method had a good discriminatory power for LAM.
    Keywords:  Biomarkers; lipoprotein; lymphangioleiomyomatosis (LAM); metabolites; metabonomics
    DOI:  https://doi.org/10.21037/atm-22-6420
  5. Oncogene. 2023 Feb 23.
    HDAC6-G3BP2 promotes lysosomal-TSC2 and suppresses mTORC1 under ETV4 targeting-induced low-lactate stress in non-small cell lung cancer.
    Bei Liu, Jiaxi Zhang, Xue Meng, Shelly M Xie, Fang Liu, Heli Chen, Demin Yao, Minglei Li, Minghui Guo, Haitao Shen, Xianghong Zhang, Lingxiao Xing.
      TSC-mTORC1 inhibition-mediated translational reprogramming is a major adaptation mechanism upon many stresses, such as low-oxygen, -ATP, and -amino acids. But how cancer cells hijack the adaptive pathway to survive under low-lactate stress when targeting glycolysis-related signaling remains uncertain. ETV4 is an oncogenic transcription factor frequently dysregulated in human cancer. We previously found that ETV4 is associated with tumor progression and poor prognosis in non-small cell lung cancer (NSCLC). In this study, we report that ETV4 controls HK1 expression and glycolysis-lactate production to activate mTORC1 by relieving TSC2 repression of Rheb in NSCLC cells. Targeting ETV4-induced low-lactate stress is an important input for TSC2 to inhibit mTORC1 and global protein synthesis, while the core stress granule components G3BP2 and HDAC6 are selectively translated. Mechanistically, G3BP2 recruits lysosomal-TSC2 to suppress mTORC1. HDAC6 deacetylates TSC2 to sustain protein stability and associates with G3BP2 to facilitate more recruiting of TSC2 to inactivate mTORC1. In addition, the microtubule retrograde transport activity of HDAC6 drives the aggregate-like perinuclear-mTOR distribution paralleled by lower mTORC1 activity under stress. Thus, HDAC6-G3BP2 is the key complex that promotes lysosomal-TSC2 and suppresses mTORC1 when targeting ETV4, which might represent a critical adaptive mechanism for cell survival under low-lactate challenges.
    DOI:  https://doi.org/10.1038/s41388-023-02641-6
  6. Curr Opin Struct Biol. 2023 Feb 16. pii: S0959-440X(23)00018-0. [Epub ahead of print]79 102544
    Amino acid sensing and lysosomal signaling complexes.
    Zhicheng Cui, Aaron M N Joiner, Rachel M Jansen, James H Hurley.
      Amino acid pools in the cell are monitored by dedicated sensors, whose structures are now coming into view. The lysosomal Rag GTPases are central to this pathway, and the regulation of their GAP complexes, FLCN-FNIP and GATOR1, have been worked out in detail. For FLCN-FNIP, the entire chain of events from the arginine transporter SLC38A9 to substrate-specific mTORC1 activation has been visualized. The structure GATOR2 has been determined, hinting at an ordering of amino acid signaling across a larger size scale than anticipated. The centerpiece of lysosomal signaling, mTORC1, has been revealed to recognize its substrates by more nuanced and substrate-specific mechanisms than previous appreciated. Beyond the well-studied Rag GTPase and mTORC1 machinery, another lysosomal amino acid sensor/effector system, that of PQLC2 and the C9orf72-containing CSW complex, is coming into structural view. These developments hold promise for further insights into lysosomal physiology and lysosome-centric therapeutics.
    DOI:  https://doi.org/10.1016/j.sbi.2023.102544
  7. Cell Biosci. 2023 Feb 21. 13(1): 37
    Enhanced liquidity of p62 droplets mediated by Smurf1 links Nrf2 activation and autophagy.
    Qin Xia, Yang Li, Wanting Xu, Chengwei Wu, Hanfei Zheng, Liqun Liu, Lei Dong.
      BACKGROUND: Macro-autophagy/Autophagy is an evolutionarily well-conserved recycling process to maintain the balance through precise spatiotemporal regulation. However, the regulatory mechanisms of biomolecular condensates by the key adaptor protein p62 via liquid-liquid phase separation (LLPS) remain obscure.RESULTS: In this study, we showed that E3 ligase Smurf1 enhanced Nrf2 activation and promoted autophagy by increasing p62 phase separation capability. Specifically, the Smurf1/p62 interaction improved the formation and material exchange of liquid droplets compared with p62 single puncta. Additionally, Smurf1 promoted the competitive binding of p62 with Keap1 to increase Nrf2 nuclear translocation in p62 Ser349 phosphorylation-dependent manner. Mechanistically, overexpressed Smurf1 increased the activation of mTORC1 (mechanistic target of rapamycin complex 1), in turn leading to p62 Ser349 phosphorylation. Nrf2 activation increased the mRNA levels of Smurf1, p62, and NBR1, further promoting the droplet liquidity to enhance oxidative stress response. Importantly, we showed that Smurf1 maintained cellular homeostasis by promoting cargo degradation through the p62/LC3 autophagic pathway.
    CONCLUSIONS: These findings revealed the complex interconnected role among Smurf1, p62/Nrf2/NBR1, and p62/LC3 axis in determining Nrf2 activation and subsequent clearance of condensates through LLPS mechanism.
    Keywords:  Protein homeostasis; Smurf1; p62-liquid droplets
    DOI:  https://doi.org/10.1186/s13578-023-00978-9
  8. SLAS Technol. 2023 Feb 17. pii: S2472-6303(23)00011-0. [Epub ahead of print]
    In Vitro Delivery of mTOR inhibitors by Kidney-Targeted Micelles for Autosomal Dominant Polycystic Kidney Disease.
    Alysia Cox, Madelynn Tung, Hui Li, Kenneth R Hallows, Eun Ji Chung.
      Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic kidney disease and is characterized by the formation of renal cysts and the eventual development of end-stage kidney disease. One approach to treating ADPKD is through inhibition of the mammalian target of rapamycin (mTOR) pathway, which has been implicated in cell overproliferation, contributing to renal cyst expansion. However, mTOR inhibitors, including rapamycin, everolimus, and RapaLink-1, have off-target side effects including immunosuppression. Thus, we hypothesized that the encapsulation of mTOR inhibitors in drug delivery carriers that target the kidneys would provide a strategy that would enable therapeutic efficacy while minimizing off-target accumulation and associated toxicity. Toward eventual in vivo application, we synthesized cortical collecting duct (CCD) targeted peptide amphiphile micelle (PAM) nanoparticles and show high drug encapsulation efficiency (>92.6 %). In vitro analysis indicated that drug encapsulation into PAMs enhanced the anti-proliferative effect of all three drugs in human CCD cells. Analysis of in vitro biomarkers of the mTOR pathway via western blotting confirmed that PAM encapsulation of mTOR inhibitors did not reduce their efficacy. These results indicate that PAM encapsulation is a promising way to deliver mTOR inhibitors to CCD cells and potentially treat ADPKD. Future studies will evaluate the therapeutic effect of PAM-drug formulations and ability to prevent off-target side effects associated with mTOR inhibitors in mouse models of ADPKD.
    Keywords:  ADPKD; MTOR; Micelles; Rapalogs; Targeted
    DOI:  https://doi.org/10.1016/j.slast.2023.02.001
  9. Cell Mol Life Sci. 2023 Feb 23. 80(3): 69
    Loss of pex5 sensitizes zebrafish to fasting due to deregulated mitochondria, mTOR, and autophagy.
    Sushil Bhandari, Yong-Il Kim, In-Koo Nam, KwangHeum Hong, Yunju Jo, Kyeong-Won Yoo, Weifang Liao, Jae-Young Lim, Seong-Jin Kim, Jae-Young Um, Peter K Kim, Ho Sub Lee, Dongryeol Ryu, Seok-Hyung Kim, SeongAe Kwak, Raekil Park, Seong-Kyu Choe.
      Animal models have been utilized to understand the pathogenesis of Zellweger spectrum disorders (ZSDs); however, the link between clinical manifestations and molecular pathways has not yet been clearly established. We generated peroxin 5 homozygous mutant zebrafish (pex5-/-) to gain insight into the molecular pathogenesis of peroxisome dysfunction. pex5-/- display hallmarks of ZSD in humans and die within one month after birth. Fasting rapidly depletes lipids and glycogen in pex5-/- livers and expedites their mortality. Mechanistically, deregulated mitochondria and mechanistic target of rapamycin (mTOR) signaling act together to induce metabolic alterations that deplete hepatic nutrients and accumulate damaged mitochondria. Accordingly, chemical interventions blocking either the mitochondrial function or mTOR complex 1 (mTORC1) or a combination of both improve the metabolic imbalance shown in the fasted pex5-/- livers and extend the survival of animals. In addition, the suppression of oxidative stress by N-acetyl L-cysteine (NAC) treatment rescued the apoptotic cell death and early mortality observed in pex5-/-. Furthermore, an autophagy activator effectively ameliorated the early mortality of fasted pex5-/-. These results suggest that fasting may be detrimental to patients with peroxisome dysfunction, and that modulating the mitochondria, mTORC1, autophagy activities, or oxidative stress may provide a therapeutic option to alleviate the symptoms of peroxisomal diseases associated with metabolic dysfunction.
    Keywords:  Autophagy; Fasting; Mitochondria; Zellweger spectrum disorder; mTOR; pex5
    DOI:  https://doi.org/10.1007/s00018-023-04700-3
  10. iScience. 2023 Feb 17. 26(2): 106045
    NRF3 activates mTORC1 arginine-dependently for cancer cell viability.
    Shuuhei Hirose, Tsuyoshi Waku, Misato Tani, Haruka Masuda, Keiko Endo, Sanae Ashitani, Iori Aketa, Hina Kitano, Sota Nakada, Ayaka Wada, Atsushi Hatanaka, Tsuyoshi Osawa, Tomoyoshi Soga, Akira Kobayashi.
      Cancer cells coordinate the mTORC1 signals and the related metabolic pathways to robustly and rapidly grow in response to nutrient conditions. Although a CNC-family transcription factor NRF3 promotes cancer development, the biological relevance between NRF3 function and mTORC1 signals in cancer cells remains unknown. Hence, we showed that NRF3 contributes to cancer cell viability through mTORC1 activation in response to amino acids, particularly arginine. NRF3 induced SLC38A9 and RagC expression for the arginine-dependent mTORC1 recruitment onto lysosomes, and it also enhanced RAB5-mediated bulk macropinocytosis and SLC7A1-mediated selective transport for arginine loading into lysosomes. Besides, the inhibition of the NRF3-mTORC1 axis impaired mitochondrial function, leading to cancer cell apoptosis. Consistently, the aberrant upregulation of the axis caused tumor growth and poor prognosis. In conclusion, this study sheds light on the unique function of NRF3 in arginine-dependent mTORC1 activation and the pathophysiological aspects of the NRF3-mTORC1 axis in cancer development.
    Keywords:  Cancer; Cell biology; Cellular physiology
    DOI:  https://doi.org/10.1016/j.isci.2023.106045
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