Pharmacological inhibition of mTORC1 but not mTORC2 protects against human disc cellular apoptosis, senescence, and extracellular matrix catabolism through Akt and autophagy induction

Kakiuchi, Yuji; Yurube, Takashi; Kakutani, Kenichiro; Takada, Toru; Ito, Masaaki; Takeoka, Yoshiki; Kanda, Yutaro; Miyazaki, Shingo; Kuroda, R.; Nishida, Kotaro

doi:10.1016/j.joca.2019.01.009

Cited by 67 publications

(93 citation statements)

References 53 publications

(81 reference statements)

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“…In vitro serum and nutrient deprivation reduced rabbit disc AF cell proliferation and metabolic activity, induced the dynamic activation of disc cellular autophagy, and increased apoptosis and senescence . The selective RNAi‐mediated mTORC1/RAPTOR suppression and the pharmacological mTORC1 inhibition were both protective against inflammation‐induced apoptosis, senescence, and matrix catabolism and were associated with Akt and autophagy induction in human disc NP cells . These effects were primarily Akt phosphorylation‐dependent, resulting from negative feedback following mTORC1 suppression .…”

Section: Resultsmentioning

confidence: 97%

“…Then, mTORC1 inhibition‐mediated relief of this negative feedback loop activates IRS1, PI3K, Akt, and ERK in some cell types . This feedback system has been found in a variety of cancers and also non‐malignant intervertebral disc cells (Figure A) …”

Section: Rnai‐mediated Mtor Signaling Modulation In Human Disc Cellsmentioning

confidence: 85%

“…We examined the in vivo involvement of mTOR signaling in human disc NP surgical specimens. Western blotting showed the expression of mTOR, RAPTOR, RICTOR, p70/S6K, and Akt and the phosphorylation of mTOR, p70/S6K, and Akt in all patient samples with 19 to 81 in ages and 2 to 5 in degeneration grades . Regression analysis demonstrated age‐dependent decreases in Akt expression and phosphorylation levels .…”

Section: Clinical Relevance Of Mtor Signaling In Human Disc Tissuesmentioning

confidence: 92%

“…A natural polyphenol from the rhizomes of turmeric, curcumin, has also been reported to inhibit mTOR signaling in various cancer cells . Therefore, we performed an additional in vitro study to identify the most suitable mTORC1 inhibitor for human degenerative disc disease treatment . We also tested more recently developed second‐generation mTOR inhibitors: a dual mTORC1 and mTORC2 inhibitor, INK‐128, and a dual PI3K and mTOR inhibitor, NVP‐BEZ235 .…”

Section: Pharmacological Mtor Signaling Modulation In Human Disc Cellsmentioning

confidence: 99%

“…Regression analysis demonstrated age‐dependent decreases in Akt expression and phosphorylation levels . Furthermore, mTOR, p70/S6K, and Akt expression and phosphorylation were increased in Pfirrmann grade‐3 discs . Despite the elevated interest in mTOR signaling, its involvement in disc degeneration remains largely unknown.…”

Section: Clinical Relevance Of Mtor Signaling In Human Disc Tissuesmentioning

confidence: 99%

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Autophagy and mTOR signaling during intervertebral disc aging and degeneration

et al. 2020

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Degenerative disc disease is a highly prevalent, global health problem that represents the primary cause of back pain and is associated with neurological disorders, including radiculopathy, myelopathy, and paralysis, resulting in worker disability and socioeconomic burdens. The intervertebral disc is the largest avascular organ in the body, and degeneration is suspected to be linked to nutritional deficiencies. Autophagy, the process through which cells self‐digest and recycle damaged components, is an important cell survival mechanism under stress conditions, especially nutrient deprivation. Autophagy is negatively controlled by the mammalian target of rapamycin (mTOR) signaling pathway. mTOR is a serine/threonine kinase that detects nutrient availability to trigger the activation of cell growth and protein synthesis pathways. Thus, resident disc cells may utilize autophagy and mTOR signaling to cope with harsh low‐nutrient conditions, such as low glucose, low oxygen, and low pH. We performed rabbit and human disc cell and tissue studies to elucidate the involvement and roles played by autophagy and mTOR signaling in the intervertebral disc. In vitro serum and nutrient deprivation studies resulted in decreased disc cell proliferation and metabolic activity and increased apoptosis and senescence, in addition to increased autophagy. The selective RNA interference‐mediated and pharmacological inhibition of mTOR complex 1 (mTORC1) was protective against inflammation‐induced disc cellular apoptosis, senescence, and extracellular matrix catabolism, through the induction of autophagy and the activation of the Akt‐signaling network. Although temsirolimus, a rapamycin derivative with improved water solubility, was the most effective mTORC1 inhibitor tested, dual mTOR inhibitors, capable of blocking multiple mTOR complexes, did not rescue disc cells. In vivo, high levels of mTOR‐signaling molecule expression and phosphorylation were observed in human intermediately degenerated discs and decreased with age. A mechanistic understanding of autophagy and mTOR signaling can provide a basis for the development of biological therapies to treat degenerative disc disease.

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Section: Resultsmentioning

confidence: 97%

Section: Rnai‐mediated Mtor Signaling Modulation In Human Disc Cellsmentioning

confidence: 85%

Section: Clinical Relevance Of Mtor Signaling In Human Disc Tissuesmentioning

confidence: 92%

Section: Pharmacological Mtor Signaling Modulation In Human Disc Cellsmentioning

confidence: 99%

Section: Clinical Relevance Of Mtor Signaling In Human Disc Tissuesmentioning

confidence: 99%

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Autophagy and mTOR signaling during intervertebral disc aging and degeneration

et al. 2020

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lncRNA HOTAIR upregulates autophagy to promote apoptosis and senescence of nucleus pulposus cells

Zhan

Wang

Xiang

et al. 2019

Journal Cellular Physiology

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Intervertebral disc degeneration (IDD) is a complex and chronic disease that involves disc cell senescence, death, and extracellular matrix (ECM) degradation. HOTAIR, a long non-coding RNA (lncRNA) is reportedly associated with autophagy, whereas autophagy is shown to promote IDD. However, how it affects nucleus pulposus (NP) cells, the primary component of intervertebral discs is still unclear. We hypothesized that HOTAIR promotes NP cell apoptosis and senescence through upregulating autophagy. Thus, silencing HOTAIR should inhibit autophagy and exert a therapeutic effect on IDD. Our in vitro experiments in human NP cells revealed that HOTAIR expression positively correlated with IDD grade, and overexpression enhanced autophagy. Autophagy inhibition via 3-methyladenine reversed HOTAIR stimulatory effects on apoptosis, senescence, and ECM catabolism, while the AMP-activated protein kinase (AMPK) inhibitor Compound C suppressed HOTAIR-induced autophagy through regulating AMPK/mTOR/ULK1 pathways. Our in vivo experiment then illustrated that silencing HOTAIR ameliorates IDD in rats. Collectively, we demonstrated that HOTAIR stimulates autophagy to promote NP cell apoptosis, senescence, and ECM catabolism. Therefore, silencing HOTAIR has the potential to become a treatment option for IDD.

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Autophagy‐activated nucleus pulposus cells deliver exosomal miR‐27a to prevent extracellular matrix degradation by targeting MMP‐13

Zhang

et al. 2020

Journal Orthopaedic Research

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Although autophagy may be beneficial for maintaining the metabolic balance of the extracellular matrix (ECM) in the nucleus pulposus (NP) and its vitality under inflammation, the underlying mechanism still remains unclear. A previous study found that autophagy activation stimulated the release of exosomes in normal chondrocytes, which are located in a similar avascular environment and share many common features with those of nucleus pulposus cells (NPCs). This study explored the protective effect on matrix degradation in the NP by exosomes derived from autophagy-activated NPCs and exosomal microRNAs. NPCs-derived exosomes (NPCs-Exos) were isolated from culture medium of either normal NPCs or rapamycin-treated NPCs and quantified by nanoparticle tracking analysis. The effect of rapamycin-treated NPC-derived exosomes on NPCs were assessed by coculture with interleukin 1β (IL-1β)-stimulated NPCs. After examination of six major proteinases of the ECM, matrix metalloproteinase 13 (MMP-13) was chosen for further study. miR-27a, which targets MMP-13, was investigated through previous studies and bioinformatics tool. The levels of miR-27a were upregulated in both rapamycintreated NPCs and their exosomes, compared to the control. When exosomal miR-27a was transferred into NPCs, it alleviated IL-1β-induced degradation of the NPC ECM by targeting MMP-13. Autophagy activation may promote the release of NPCs-derived exosomes and thereby prevent the NPC matrix from degradation.Autophagy activation also alleviates intervertebral disc degeneration (IDD), at least partly via exosomal miR-27a, which restrains MMP-13 expression under IL-1β stimulation. Our work elucidates a new mechanism for how autophagy may participate in preventing IDD, which may be a promising therapeutic strategy.

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Pharmacological inhibition of mTORC1 but not mTORC2 protects against human disc cellular apoptosis, senescence, and extracellular matrix catabolism through Akt and autophagy induction

Cited by 67 publications

References 53 publications

Autophagy and mTOR signaling during intervertebral disc aging and degeneration

Autophagy and mTOR signaling during intervertebral disc aging and degeneration

lncRNA HOTAIR upregulates autophagy to promote apoptosis and senescence of nucleus pulposus cells

Autophagy‐activated nucleus pulposus cells deliver exosomal miR‐27a to prevent extracellular matrix degradation by targeting MMP‐13

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