bims-tubesc 2022-03-20 papers

bims-tubesc

Biomed News

on Molecular mechanisms in tuberous sclerosis

Issue of 2022–03–20
nine papers selected by

Single serine on TSC2 exerts biased control over mTORC1 activation mediated by ERK1/2 but not Akt.
Sirolimus treatment for tuberous sclerosis complex prior to epilepsy: Evidence from a registry-based real-world study.
Rheb regulates nuclear mTORC1 activity independent of farnesylation.
Prevalence of thoracoabdominal imaging findings in tuberous sclerosis complex.
Convolutional Neural Network-aided Tuber Segmentation in Tuberous Sclerosis Complex Patients Correlates with EEG.
Identification of defined structural elements within TOR2 kinase required for TOR Complex 2 assembly and function in S. cerevisiae.
eIF3a regulation of mTOR signaling and translational control via HuR in cellular response to DNA damage.
The Role of Zinc in Axon Formation via the mTORC1 Pathway.
Autistic-like behavior and cerebellar dysfunction in Bmal1 mutant mice ameliorated by mTORC1 inhibition.

Life Sci Alliance. 2022 Jun;pii: e202101169. [Epub ahead of print]5(6):

Single serine on TSC2 exerts biased control over mTORC1 activation mediated by ERK1/2 but not Akt.

Brittany L Dunkerly-Eyring, Shi Pan, Miguel Pinilla-Vera, Desirae McKoy, Sumita Mishra, Maria I Grajeda Martinez, Christian U Oeing, Mark J Ranek, David A Kass.

Tuberous sclerosis complex-2 (TSC2) negatively regulates mammalian target of rapamycin complex 1 (mTORC1), and its activity is reduced by protein kinase B (Akt) and extracellular response kinase (ERK1/2) phosphorylation to activate mTORC1. Serine 1364 (human) on TSC2 bidirectionally modifies mTORC1 activation by pathological growth factors or hemodynamic stress but has no impact on resting activity. We now show this modification biases to ERK1/2 but not Akt-dependent TSC2-mTORC1 activation. Endothelin-1-stimulated mTORC1 requires ERK1/2 activation and is bidirectionally modified by phospho-mimetic (S1364E) or phospho-silenced (S1364A) mutations. However, mTORC1 activation by Akt-dependent stimuli (insulin or PDGF) is unaltered by S1364 modification. Thrombin stimulates both pathways, yet only the ERK1/2 component is modulated by S1364. S1364 also has negligible impact on mTORC1 regulation by energy or nutrient status. In vivo, diet-induced obesity, diabetes, and fatty liver couple to Akt activation and are also unaltered by TSC2 S1364 mutations. This contrasts to prior reports showing a marked impact of both on pathological pressure-stress. Thus, S1364 provides ERK1/2-selective mTORC1 control and a genetic means to modify pathological versus physiological mTOR stimuli.

DOI: https://doi.org/10.26508/lsa.202101169
Seizure. 2022 Mar 08. pii: S1059-1311(22)00049-8. [Epub ahead of print]97 23-31

Sirolimus treatment for tuberous sclerosis complex prior to epilepsy: Evidence from a registry-based real-world study.

Yan-Wen Shen, Yang-Yang Wang, Meng-Na Zhang, Yong Xu, Qian Lu, Wen He, Hui-Min Chen, Li-Ying Liu, Ling-Yu Pang, Qiu-Hong Wang, Shuo Dun, Yu-Fen Li, Jing Gao, Fang Han, Li-Ping Zou.

   OBJECTIVE: To evaluate whether sirolimus treatment could relieve the later burden of new-onset seizures in patients with tuberous sclerosis complex (TSC) prior to epilepsy.
METHODS: A real-world matched case-control study was nested in another registry cohort study. Infants with TSC (<12 months old) without seizures whose parents agreed on sirolimus treatment for other symptoms were eligible for inclusion to the early sirolimus (ES) group. These patients were enrolled from 2015 to 2018. Controls in the late sirolimus (LS) group were matched from the registry cohort database for 2015-2018. Age and genotype were used as the initial stratifying criteria and other symptoms as the greedy matching criteria at a matching ratio of 1:4. None of the preventive drugs were introduced before seizure onset or before 2 years of age in the LS group. Both groups were followed up until June 2020. The primary objective was a comparison of the characteristics of the first seizure between the two groups. The secondary objective was the assessment of the final seizure status at the endpoint.
RESULTS: There were 42 and 168 patients with TSC in the ES and LS groups, respectively. Early sirolimus treatment significantly reduced the seizure onset, especially in the patients aged <6 months. The mean onset-age was significantly delayed by sirolimus treatment (11.34±7.93 months vs. 6.94±6.03 months, P<0.001). The subtype of seizures that benefited the most was spastic (onset) seizures (all were infantile spasms) [5/42 (11.90%) vs. 73/168 (43.45%), P<0.001]; these seizures were either eliminated or alleviated. The sirolimus treatment addition prior to seizures was more effective than its addition after seizures in reducing drug-resistant epilepsy [10/42 (23.81%) vs. 70/147 (47.62%), P=0.004].
CONCLUSION: Early sirolimus treatment for TSC effectively modified the disease by preventing infantile spasms, delaying seizure onset, and relieving its severity. The anti-epileptogenic effect of sirolimus may be time- and dose-dependent.

Keywords:  Focal onset seizure; Infantile spasm; Sirolimus; Tuberous sclerosis complex

DOI:  https://doi.org/10.1016/j.seizure.2022.03.003
Cell Chem Biol. 2022 Mar 04. pii: S2451-9456(22)00087-3. [Epub ahead of print]

Rheb regulates nuclear mTORC1 activity independent of farnesylation.

Yanghao Zhong, Xin Zhou, Kun-Liang Guan, Jin Zhang.

  The small GTPase Ras homolog enriched in brain (Rheb) plays a critical role in activating the mechanistic target of rapamycin complex 1 (mTORC1), a signaling hub that regulates various cellular functions. We recently observed nuclear mTORC1 activity, raising an intriguing question as to how Rheb, which is known to be farnesylated and localized to intracellular membranes, regulates nuclear mTORC1. In this study, we found that active Rheb is present in the nucleus and required for nuclear mTORC1 activity. We showed that inhibition of farnesyltransferase reduced cytosolic, but not nuclear, mTORC1 activity. Furthermore, a farnesylation-deficient Rheb mutant, with preferential nuclear localization and specific lysosome tethering, enables nuclear and cytosolic mTORC1 activities, respectively. These data suggest that non-farnesylated Rheb is capable of interacting with and activating mTORC1, providing mechanistic insights into the molecular functioning of Rheb as well as regulation of the recently observed, active pool of nuclear mTORC1.

Keywords:  Compartmentation; PTM; TSC; biosensor; lipid modification; mTOR; small GTPase

DOI:  https://doi.org/10.1016/j.chembiol.2022.02.006
Orphanet J Rare Dis. 2022 Mar 15. 17(1): 124

Prevalence of thoracoabdominal imaging findings in tuberous sclerosis complex.

David M Ritter, Bailey K Fessler, Daniel Ebrahimi-Fakhari, Jun Wei, David N Franz, Darcy A Krueger, Andrew T Trout, Alexander J Towbin.

   BACKGROUND: Tuberous sclerosis complex (TSC) results in neurodevelopmental phenotypes, benign tumors, and cysts throughout the body. Recent studies show numerous rare findings in TSC. Guidelines suggest routine abdominal and chest imaging to monitor these thoracoabdominal findings, but imaging is not uniformly done across centers. Thus, the prevalence of many findings is unknown. To answer this, we categorized the clinical reads of 1398 thoracoabdominal scans from 649 patients of all ages in the Cincinnati Children's Hospital TSC Repository Database.
RESULTS: Typical TSC findings were present in many patients: kidney cysts (72%), kidney fat-containing angiomyolipomas (51%), kidney lipid-poor angiomyolipomas (27%), liver angiomyolipomas (19%), and lung nodules thought to represent multifocal micronodular pneumocyte hyperplasia (MMPH) (18%). While many features were more common in TSC2 patients, TSC1 patients had a higher prevalence of MMPH than TSC2 patients (24% versus 13%, p = 0.05). Many rare findings (e.g., lymphatic malformations and liver masses) are more common in TSC than in the general population. Additionally, most thoracoabdominal imaging findings increased with age except kidney cysts which decreased, with the 0-10 years age group having the highest percentage (69% 0-10 years, 49% 10-21 years, 48% 21 + years, p < 0.001). Finally, in our population, no patients had renal cell carcinoma found on abdominal imaging.
CONCLUSIONS: These results show that regular thoracoabdominal scans in TSC may show several findings that should not be ignored or, conversely, over-reacted to when found in patients with TSC. Female sex, TSC2 mutation, and age are risk factors for many thoracoabdominal findings. The data suggest novel interactions of genetic mutation with pulmonary nodules and age with renal cysts. Finally, in agreement with other works, these findings indicate that several rare thoracoabdominal imaging findings occur at higher rates in the TSC population than in the general population. This work supports obtaining detailed thoracoabdominal imaging in patients with TSC.

Keywords:  CT; MRI; Pulmonary nodules; Renal angiomyolipomas; Renal cysts; TSC1; TSC2; Tuberous sclerosis

DOI:  https://doi.org/10.1186/s13023-022-02277-x
Epilepsia. 2022 Mar 17.

Convolutional Neural Network-aided Tuber Segmentation in Tuberous Sclerosis Complex Patients Correlates with EEG.

David K Park, Woojoong Kim, Olivia Thornburg, Danielle McBrian, Guy McKhann, Neil Feldstein, Alexis Maddocks, Elena Gonzalez, Min Y Shen, Cigdem Akman, Frank Provenzano.

   OBJECTIVE: One of the clinical hallmarks of tuberous sclerosis complex is radiologically-identified cortical tubers present in most patients. Intractable epilepsy may require surgery, often involving invasive diagnostic procedures such as intracranial EEG. Identifying the location of the dominant tuber responsible for generating epileptic activities, is a critical issue. However, the link between cortical tubers and epileptogenesis is poorly understood. Given this, we hypothesized that tuber voxel intensity may be an indicator of the dominant epileptogenic tuber. Also, via tuber segmentation based on deep learning, we explore whether an automatic quantification of the tuber burden is feasible.
METHODS: We annotated tubers from structural MRIs across 29 TSC subjects, summarized tuber statistics in eight brain lobes, and determined suspected epileptogenic lobes from the same group using EEG monitoring data. Then logistic regression analyses are performed to demonstrate the linkage between the statistics of cortical tuber and the epileptogenic zones. Furthermore, we test the ability of a neural network to identify and quantify tuber burden.
RESULTS: Logistic regression analyses show that the volume and count of tubers per lobe, not the mean or variance of tuber voxel intensity, are positively correlated with electrophysiological data. In 47.6% of subjects, the lobe with the largest tuber volume concurred with the epileptic brain activity. A neural network model on the test dataset shows a sensitivity of 0.83 for localizing individual tubers. The predicted masks from the model highly correlated with the neurologist labels, thus may be a useful tool for determining tuber burden and searching for epileptogenic zone.
SIGNIFICANCE: we prove the feasibility of an automatic segmentation of tubers and a derivation of tuber burden across brain lobes. Our method may provide crucial insights in the treatment and outcome of TSC patients.

Keywords:  Deep Learning; Epilepsy; Neuroimaging; Tuber Burden; Tuberous Sclerosis Complex

DOI:  https://doi.org/10.1111/epi.17227
Mol Biol Cell. 2022 Mar 16. mbcE21120611

Identification of defined structural elements within TOR2 kinase required for TOR Complex 2 assembly and function in S. cerevisiae.

Jennifer Tsverov, Kristina Yegorov, Ted Powers.

mTOR is a large protein kinase that assembles into two multi-subunit protein complexes, mTORC1 and mTORC2, to regulate cell growth in eukaryotic cells. While significant progress has been made in our understanding of the composition and structure of these complexes, important questions remain regarding the role of specific sequences within mTOR important for complex formation and activity. To address these issues, we have used a molecular genetic approach to explore TOR Complex assembly in budding yeast, where two closely related TOR paralogs, TOR1 and TOR2, partition preferentially into TORC1 versus TORC2, respectively. We previously identified a ∼500 amino acid segment within the N-terminal half of each protein, termed the Major Assembly Specificity (MAS) Domain, which can govern specificity in formation of each complex. In this study, we have extended the use of chimeric TOR1-TOR2 genes as a "sensitized" genetic system to identify specific subdomains rendered essential for TORC2 function, using synthetic lethal interaction analyses. Our findings reveal important design principles underlying the dimeric assembly of TORC2, as well as identify specific segments within the MAS domain critical for TORC2 function, to a level approaching single amino acid resolution. Together these findings highlight the complex and cooperative nature of TOR Complex assembly and function.

DOI: https://doi.org/10.1091/mbc.E21-12-0611
Oncogene. 2022 Mar 12.

eIF3a regulation of mTOR signaling and translational control via HuR in cellular response to DNA damage.

Shijie Ma, Zizheng Dong, Yanfei Huang, Jing-Yuan Liu, Jian-Ting Zhang.

eIF3a (eukaryotic translation initiation factor 3a), a subunit of the eIF3 complex, has been suggested to play a regulatory role in protein synthesis and in cellular response to DNA-damaging treatments. S6K1 is an effector and a mediator of mTOR complex 1 (mTORC1) in regulating protein synthesis and integrating diverse signals into control of cell growth and response to stress. Here, we show that eIF3a regulates S6K1 activity by inhibiting mTORC1 kinase via regulating Raptor synthesis. The regulation of Raptor synthesis is via eIF3a interaction with HuR (human antigen R) and binding of the eIF3a-HuR complex to the 5'-UTR of Raptor mRNA. Furthermore, mTORC1 may mediate eIF3a function in cellular response to cisplatin by regulating synthesis of NER proteins and NER activity. Taken together, we conclude that the mTOR signaling pathway may also be regulated by translational control and mediate eIF3a regulation of cancer cell response to cisplatin by regulating NER protein synthesis.

DOI: https://doi.org/10.1038/s41388-022-02262-5
Mol Neurobiol. 2022 Mar 15.

The Role of Zinc in Axon Formation via the mTORC1 Pathway.

Seunghyuk Choi, Donghyeon Kang, Jieun Kang, Dae Ki Hong, Beom Seok Kang, A Ra Kho, Bo Young Choi, Sung-Oh Huh, Sang Won Suh.

  Zinc is an essential micronutrient required for proper function during neuronal development because it can modulate neuronal function and structure. A fully functional description of zinc in axonal processing in the central nervous system remains elusive. Here, we define the role of intracellular zinc in axon formation and elongation, involving the mammalian target of rapamycin complex 1 (mTORC1). To investigate the involvement of zinc in axon growth, we performed an ex vivo culture of mouse hippocampal neurons and administrated ZnCl2 as a media supplement. At 2 days in vitro, the administration of zinc induced the formation of multiple and elongated axons in the ex vivo culture system. A similar outcome was witnessed in callosal projection neurons in a developing mouse brain. Treatment with extracellular zinc activated the mTORC1 signaling pathway in mouse hippocampal neuronal cultures. The zinc-dependent enhancement of neuronal processing was inhibited either by the deactivation of mTORC1 with RAPTOR shRNA or by mTOR-insensitive 4EBP1 mutants. Additionally, zinc-dependent mTORC1 activation enhanced the axonal translation of TC10 and Par3 may be responsible for axonal growth. We identified a promising role of zinc in controlling axonogenesis in the developing brain, which, in turn, may indicate a novel structural role of zinc in the cytoskeleton and developing neurons.

Keywords:  Axon; Primary neuron; Zinc; mTORC1

DOI:  https://doi.org/10.1007/s12035-022-02785-8
Mol Psychiatry. 2022 Mar 17.

Autistic-like behavior and cerebellar dysfunction in Bmal1 mutant mice ameliorated by mTORC1 inhibition.

Dong Liu, Carmen Nanclares, Konstanze Simbriger, Kun Fang, Ethan Lorsung, Nam Le, Inês Silva Amorim, Kleanthi Chalkiadaki, Salil Saurav Pathak, Jin Li, Jonathan C Gewirtz, Victor X Jin, Paulo Kofuji, Alfonso Araque, Harry T Orr, Christos G Gkogkas, Ruifeng Cao.

Although circadian and sleep disorders are frequently associated with autism spectrum disorders (ASD), it remains elusive whether clock gene disruption can lead to autistic-like phenotypes in animals. The essential clock gene Bmal1 has been associated with human sociability and its missense mutations are identified in ASD. Here we report that global Bmal1 deletion led to significant social impairments, excessive stereotyped and repetitive behaviors, as well as motor learning disabilities in mice, all of which resemble core behavioral deficits in ASD. Furthermore, aberrant cell density and immature morphology of dendritic spines were identified in the cerebellar Purkinje cells (PCs) of Bmal1 knockout (KO) mice. Electrophysiological recordings uncovered enhanced excitatory and inhibitory synaptic transmission and reduced firing rates in the PCs of Bmal1 KO mice. Differential expression of ASD- and ataxia-associated genes (Ntng2, Mfrp, Nr4a2, Thbs1, Atxn1, and Atxn3) and dysregulated pathways of translational control, including hyperactivated mammalian target of rapamycin complex 1 (mTORC1) signaling, were identified in the cerebellum of Bmal1 KO mice. Interestingly, the antidiabetic drug metformin reversed mTORC1 hyperactivation and alleviated major behavioral and PC deficits in Bmal1 KO mice. Importantly, conditional Bmal1 deletion only in cerebellar PCs was sufficient to recapitulate autistic-like behavioral and cellular changes akin to those identified in Bmal1 KO mice. Together, these results unveil a previously unidentified role for Bmal1 disruption in cerebellar dysfunction and autistic-like behaviors. Our findings provide experimental evidence supporting a putative role for dysregulation of circadian clock gene expression in the pathogenesis of ASD.

DOI: https://doi.org/10.1038/s41380-022-01499-6