Serum and nutrient deprivation increase autophagic flux in intervertebral disc annulus fibrosus cells: an in vitro experimental study

Yurube, Takashi; Buchser, William J.; Moon, Hong Joo; Hartman, Robert A.; Takayama, Koji; Kawakami, Yoshiyuki; Nishida, Kotaro; Kurosaka, Masahiro; Vo, Nam; Kang, James D.; Lotze, Michael T.; Sowa, Gwendolyn

doi:10.1007/s00586-019-05910-9

Cited by 33 publications

(53 citation statements)

References 26 publications

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“…This brief review describes the current understanding of autophagy and mTOR signaling in the intervertebral disc. 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 .…”

Section: Resultsmentioning

confidence: 96%

“…We used rabbit cells due to reduced phenotypic variability, including age, sex, and degeneration grade, compared with surgically obtained human cells. Hence, the objective of our first study was to clarify the fundamental relationships between nutrient supply and autophagy, apoptosis, and senescence levels in rabbit disc AF cells (Figure ) …”

Section: Serum and Nutrient Deprivation In Rabbit Disc Cellsmentioning

confidence: 99%

“…Disc AF cells responded to nutrient deprivation by reducing cell proliferation and metabolism. Further investigations aim to identify the optimal culture conditions for rabbit disc AF cells in 5% O 2 , although DMEM containing 5% FBS resulted in the highest normalized cell metabolic activity …”

Section: Serum and Nutrient Deprivation In Rabbit Disc Cellsmentioning

confidence: 99%

“…25 Therefore, as a preliminary study, we carefully and systematically examined intervertebral disc cell fate, in vitro. 67 We conducted time-course experiments to measure autophagic flux in rabbit disc AF cells under F I G U R E 2 Schematic illustration of the RNA interference (RNAi)-mediated and pharmacological modulation of disc cellular mTOR signaling. The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that detects nutrients to signal the execution of cell growth and division.…”

Section: Serum and Nutrient Deprivation In Rabbit Disc Cellsmentioning

confidence: 99%

“…Hence, the objective of our first study was to clarify the fundamental relationships between nutrient supply and autophagy, apoptosis, and senescence levels in rabbit disc AF cells ( Figure 1). 67 Subsequently, we examined the co-localization of autophagy and senescence markers in cells positive for an apoptotic marker by multicolor immunofluorescence. After the withdrawal of FBS, "apoptotic" nuclear cleaved caspase-3-positive cells presented a higher percentage of immunopositivity for "autophagic" cytoplasmic LC3 than for "senescent" nuclear p16/INK4A.…”

Section: Serum and Nutrient Deprivation In Rabbit Disc Cellsmentioning

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: 96%

Section: Serum and Nutrient Deprivation In Rabbit Disc Cellsmentioning

confidence: 99%

Section: Serum and Nutrient Deprivation In Rabbit Disc Cellsmentioning

confidence: 99%

Section: Serum and Nutrient Deprivation In Rabbit Disc Cellsmentioning

confidence: 99%

Section: Serum and Nutrient Deprivation In Rabbit Disc Cellsmentioning

confidence: 99%

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Autophagy and mTOR signaling during intervertebral disc aging and degeneration

et al. 2020

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Role of autophagy in intervertebral disc degeneration

Kritschil

Scott

Sowa

et al. 2021

Journal Cellular Physiology

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Intervertebral disc degeneration (IDD) is a leading contributor to low back pain. The intervertebral disc (IVD) is composed of three tissue types: the central gelatinous nucleus pulposus (NP) tissue, the surrounding annulus fibrosus (AF) tissue, and the inferior and superior cartilage endplates. The IVD microenvironment is hypoxic, acidic, hyperosmotic, and low in nutrients because it is mostly avascular. The cellular processes that underlie IDD initiation and progression are still poorly understood. Specifically, a lack of understanding regarding NP cell metabolism and physiology hinders the development of effective therapeutics to treat IDD patients. Autophagy is a vital intracellular degradation process that removes damaged organelles, misfolded proteins, and intracellular pathogens and recycles the degraded components for cellular energy and function. NP cells have adapted to survive within their harsh tissue microenvironment using processes that are largely unknown, and we postulate autophagy is one of these undiscovered mechanisms. In this review, we describe unique features of the IVD tissue, review how physiological stressors impact autophagy in NP cells in vitro, survey the current understanding of autophagy regulation in the IVD, and assess the relationship between autophagy and IDD. Published studies confirm autophagy markers are present in IVD tissue, and IVD cells can regulate autophagy in response to cellular stressors in vitro. However, data are still lacking to determine the exact mechanisms regulating autophagy in IVD cells. More in‐depth research is needed to establish whether autophagy is necessary to maintain IVD cell health and validate autophagy as a relevant therapeutic target for treating IDD.

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Similarity and difference between aging and puncture‐induced intervertebral disc degeneration

Zhang

Zhou

et al. 2022

Journal Orthopaedic Research

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The purpose of our study was to investigate the changes in micromorphology and mechanical properties of intervertebral discs degeneration induced by aging and puncture. Normal group (NG), 2 weeks post‐puncture degeneration group (PDG) and aging degeneration group (ADG) each included 10 rats. Plain film, magnetic resonance imaging, and histological testing were utilized to assess intervertebral disc degeneration. Atomic force microscope was utilized to analyze the microstructure and elastic modulus of the intervertebral disc, while immunohistochemistry was employed to assess alterations in the cell matrix using collagen I, collagen II, matrix metalloproteinase‐3 (MMP‐3), and tumour necrosis factor‐α (TNF‐α). The results showed that the disc height ratio between PDG and ADG decreased. In the PDG and ADG group, histological scores both increased, the gray value of the T2 signal decreased, the proportion of MMP‐3 and TNF‐positive cells in intervertebral disc tissues was higher (p < 0.05) and the IOD values of COL‐2 lower in intervertebral disc tissues (p < 0.05). The elastic modulus of PDG and ADG annulus fibers (AF) increased compared to the NG (p < 0.05); when compared to PDG, the elastic modulus of ADG AF decreased (p < 0.05). The elastic modulus of PDG and ADG collagen increased in the nucleus pulposus (NP, p < 0.05); ADG had a greater AF diameter than NG and PDG (p < 0.05). The results indicated that ADG fiber diameter thickens, and chronic inflammation indicators rise; PDG suffers from severe extracellular matrix loss. The degeneration of the ADG and PDG intervertebral discs is different. The results provide foundation for clinical research.

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Serum and nutrient deprivation increase autophagic flux in intervertebral disc annulus fibrosus cells: an in vitro experimental study

Cited by 33 publications

References 26 publications

Autophagy and mTOR signaling during intervertebral disc aging and degeneration

Autophagy and mTOR signaling during intervertebral disc aging and degeneration

Role of autophagy in intervertebral disc degeneration

Similarity and difference between aging and puncture‐induced intervertebral disc degeneration

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