Repeated and Interrupted Resistance Exercise Induces the Desensitization and Re-Sensitization of mTOR-Related Signaling in Human Skeletal Muscle Fibers

The acute resistance exercise (RE)-induced phosphorylation of mTOR-related signaling proteins in skeletal muscle can be blunted after repeated RE. The time frame in which the phosphorylation (_p) of mTOR^S2448, p70S6k^T421/S424, and rpS6^S235/236 will be reduced during an RE training period in humans and whether progressive (PR) loading can counteract such a decline has not been described. (1) To enclose the time frame in which _pmTOR^S2448, _prpS6^S235/236, and _pp70S6k^T421/S424 are acutely reduced after RE occurs during repeated RE. (2) To test whether PR will prevent that reduction compared to constant loading (CO) and (3) whether 10 days without RE may re-increase blunted signaling. Fourteen healthy males (24 ± 2.8 yrs.; 1.83 ± 0.1 cm; 79.3 ± 8.5 kg) were subjected to RE with either PR (n = 8) or CO (n = 6) loading. Subjects performed RE thrice per week, conducting three sets with 10–12 repetitions on a leg press and leg extension machine. Muscle biopsies were collected at rest (T0), 45 min after the first (T1), seventh (T7), 13th (T13), and 14th (X-T14) RE session. No differences were found between PR and CO for any parameter. Thus, the groups were combined, and the results show the merged values. _prpS6^S235/236 and _pp70s6k^T421/S424 were increased at T1, but were already reduced at T7 and up to T13 compared to T1. Ten days without RE re-increased _prpS6^S235/236 and _pp70S6k^T421/S424 at X-T14 to a level comparable to that of T1. _pmTOR^S2448 was increased from T1 to X-T14 and did not decline over the training period. Single-fiber immunohistochemistry revealed a reduction in _prpS6^S235/236 in type I fibers from T1 to T13 and a re-increase at X-T14, which was more augmented in type II fibers at T13 (p < 0.05). The entity of myofibers revealed a high heterogeneity in the level of _prpS6^S235/236, possibly reflecting individual contraction-induced stress during RE. The type I and II myofiber diameter increased from T0 and T1 to T13 and X-T14 (p < 0.05) _prpS6^S235/236 and _pp70s6k^T421/S424 reflect RE-induced states of desensitization and re-sensitization in dependency on frequent loading by RE, but also by its cessation.     

桑黄多糖调控PI3K/AKT/mTOR通路抑制肝癌腹水荷瘤小鼠及对化疗的减毒增效作用

目的:研究桑黄多糖通过调控PI3K/AKT/mTOR通路对肝癌腹水荷瘤小鼠化疗的增效减毒作用。方法:SPF级雄性昆明种小鼠90只,随机分为正常组、模型组、环磷酰胺组、桑黄多糖组及桑黄多糖+环磷酰胺组。制备肝癌腹水荷瘤小鼠,各给药组分别给予30 mg/kg的环磷酰胺或（和）200 mg/kg的桑黄多糖,灌胃给药。正常组及模型组灌胃10 mL/kg的生理盐水。观察小鼠抑瘤率、肝脏、脾脏等指数、肿瘤组织内VEGF与炎性因子含量、PI3K/AKT/mTOR通路相关蛋白表达。结果:环磷酰胺组、桑黄多糖组及桑黄多糖+环磷酰胺组小鼠体质量、瘤体质量、肿瘤组织内血管内皮生长因子（VEGF）、肿瘤坏死因子（TNF-α）、白介素（IL）-6、PI3K、AKT及mTOR磷酸化水平均低于模型组,IL-1β水平高于模型组;桑黄多糖+环磷酰胺组小鼠体质量、抑瘤率、肿瘤组织内VEGF、TNF-α、IL-6、PI3K、AKT及mTOR磷酸化水平高于桑黄多糖组及环磷酰胺组,瘤体质量及IL-1β水平低于桑黄多糖组及环磷酰胺组(P<0.05)。结论:桑黄多糖联合环磷酰胺可有效抑制肝癌腹水荷瘤小鼠肿瘤的增殖,发挥减毒增效作用,其机制可能与下调PI3K/AKT/mTOR通路的表达有关。     

mTOR Signaling and Potential Therapeutic Targeting in Meningioma

Meningiomas are the most frequent primary tumors arising in the central nervous system. They typically follow a benign course, with an excellent prognosis for grade I lesions through surgical intervention. Although radiotherapy is a good option for recurrent, progressive, or inoperable tumors, alternative treatments are very limited. mTOR is a protein complex with increasing therapeutical potential as a target in cancer. The current understanding of the mTOR pathway heavily involves it in the development of meningioma. Its activation is strongly dependent on PI3K/Akt signaling and the merlin protein. Both factors are commonly defective in meningioma cells, which indicates their likely function in tumor growth. Furthermore, regarding molecular tumorigenesis, the kinase activity of the mTORC1 complex inhibits many components of the autophagosome, such as the ULK1 or Beclin complexes. mTOR contributes to redox homeostasis, a vital component of neoplasia. Recent clinical trials have investigated novel chemotherapeutic agents for mTOR inhibition, showing promising results in resistant or recurrent meningiomas.     

Lysosomes at the Crossroads of Cell Metabolism,Cell Cycle,and Stemness

Initially described as lytic bodies due to their degradative and recycling functions, lysosomes play a critical role in metabolic adaptation to nutrient availability. More recently, the contribution of lysosomal proteins to cell signaling has been established, and lysosomes have emerged as signaling hubs that regulate diverse cellular processes, including cell proliferation and cell fate. Deciphering these signaling pathways has revealed an extensive crosstalk between the lysosomal and cell cycle machineries that is only beginning to be understood. Recent studies also indicate that a number of lysosomal proteins are involved in the regulation of embryonic and adult stem cell fate and identity. In this review, we will focus on the role of the lysosome as a signaling platform with an emphasis on its function in integrating nutrient sensing with proliferation and cell cycle progression, as well as in stemness-related features, such as self-renewal and quiescence.     

Autophagy Signaling by Neural-Induced Human Adipose Tissue-Derived Stem Cell-Conditioned Medium during Rotenone-Induced Toxicity in SH-SY5Y Cells

Rotenone (ROT) inhibits mitochondrial complex I, leading to reactive oxygen species formation, which causes neurodegeneration and alpha-synuclein (α-syn) aggregation and, consequently, Parkinson’s disease. We previously found that a neurogenic differentiated human adipose tissue-derived stem cell-conditioned medium (NI-hADSC-CM) was protective against ROT-induced toxicity in SH-SY5Y cells. In the present study, ROT significantly decreased the phospho (p)-mTORC1/total (t)-mTOR, p-mTORC2/t-mTOR, and p-/t-ULK1 ratios and the ATG13 level by increasing the DEPTOR level and p-/t-AMPK ratio. Moreover, ROT increased the p-/t-Akt ratio and glycogen synthase kinase-3β (GSK3β) activity by decreasing the p-/t-ERK1/2 ratios and beclin-1 level. ROT also promoted the lipidation of LC3B-I to LC3B-II by inducing autophagosome formation in Triton X-100-soluble and -insoluble cell lysate fractions. Additionally, the levels of ATG3, 5, 7, and 12 were decreased, along with those of lysosomal LAMP1, LAMP2, and TFEB, leading to lysosomal dysfunction. However, NI-hADSC-CM treatment increased the p-mTORC1, p-mTORC2, p-ULK1, p-Akt, p-ERK1/2, ATG13, and beclin-1 levels and decreased the p-AMPK level and GSK3β activity in response to ROT-induced toxicity. Additionally, NI-hADSC-CM restored the LC3B-I level, increased the p62 level, and normalized the ATG and lysosomal protein amounts to control levels. Autophagy array revealed that the secreted proteins in NI-hADSC-CM could be crucial in the neuroprotection. Taken together, our results showed that the neuroprotective effects of NI-hADSC-CM on the autophagy signaling pathways could alleviate the aggregation of α-syn in Parkinson’s disease and other neurodegenerative disorders.     

Abnormal mTOR Activity in Pediatric Autoimmune Neuropsychiatric and MIA-Associated Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by the early onset of communication and behavioral problems. ASD is highly heritable; however, environmental factors also play a considerable role in this disorder. A significant part of both syndromic and idiopathic autism cases could be attributed to disorders caused by mammalian target of rapamycin (mTOR)-dependent translation deregulation. This narrative review analyzes both bioinformatic and experimental evidence that connects mTOR signaling to the maternal autoantibody-related (MAR) autism spectrum and autoimmune neuropsychiatric disorders simultaneously. In addition, we reconstruct a network presenting the interactions between the mTOR signaling and eight MAR ASD genes coding for ASD-specific maternal autoantibody target proteins. The research discussed in this review demonstrates novel perspectives and validates the need for a subtyping of ASD on the grounds of pathogenic mechanisms. The utter necessity of designing ELISA-based test panels to identify all antibodies related to autism-like behavior is also considered.     

mTOR Signaling Components in Tumor Mechanobiology

Mechanistic target of rapamycin (mTOR) is a central signaling hub that integrates networks of nutrient availability, cellular metabolism, and autophagy in eukaryotic cells. mTOR kinase, along with its upstream regulators and downstream substrates, is upregulated in most human malignancies. At the same time, mechanical forces from the tumor microenvironment and mechanotransduction promote cancer cells’ proliferation, motility, and invasion. mTOR signaling pathway has been recently found on the crossroads of mechanoresponsive-induced signaling cascades to regulate cell growth, invasion, and metastasis in cancer cells. In this review, we examine the emerging association of mTOR signaling components with certain protein tools of tumor mechanobiology. Thereby, we highlight novel mechanisms of mechanotransduction, which regulate tumor progression and invasion, as well as mechanisms related to the therapeutic efficacy of antitumor drugs.     

Functional Characterization of FH Mutation c.557G>A Underlies Uterine Leiomyomas

The FH gene encodes the fumarate hydratase of the Krebs cycle and functions as a homotetramer to catalyze the hydration of fumarate to malate. Mutations in FH result in uterine leiomyomas, a rare autosomal dominant inherited metabolic disease. However, how FH mutations result in this disease is poorly understood. Here, the FH mutation c.557G>A (p.S186N) was identified in a family with uterine leiomyomas phenotype. A series of studies were performed to confirm the pathogenicity of this mutation. Results showed that the FH mutant exhibited significantly lower fumarase enzyme activity and increased the fumarates level compared with the wildtype, which might be due to the impaired homotetramer formation in the native gel electrophoresis. Interestingly, the immunofluorescence study revealed that the overexpressed FH mutant exhibited puncta structures compared with the evenly expressed FH wildtype in cytoplasm suggesting that the altered amino acid might result in dysfunctional proteins which were accumulated to reduce its cytotoxicity. Importantly, the cells overexpressing the FH mutant exhibited higher proliferation and extracellular acidification rate value (ECAR) which might be caused by the upregulated HIF-1α indicating the tumor phenotype. Notably, phospho-mTOR was significantly increased and autophagy was inhibited in the FH mutant overexpression cells compared with the wildtype. Our work provides new insight into the FH mutation c.557G>A (p.S186N) underlies uterine leiomyomas and important information for accurate genetic counseling and clinical diagnosis of the disease.