Responses and adaptations of intervertebral disc cells to microenvironmental stress: a possible central role of autophagy in the adaptive mechanism

Figures & data

Figure 1. Autophagy induction and execution in disc cells. Under different stresses and following rapamycin treatment, disc cells produce a double-membrane structure termed as a phagophore, which engulfs dysfunctional organelles and proteins. As the vesicle elongates, the phagophore becomes the autophagosome, which fuses with the lysosome, producing the autolysosome and degrading the sequestered contents with proteolytic enzymes.

Table 1. Responses and adaptations of disc cells to starvation.

Research style	Species	Animal or cell model	Starvation time	Cell specify	Key findings	Authors
In vitro 3-D culture	Bovine	Special chamber Treated with no-glucose medium	0 d–12 d	NP cells	Viability and GAG production decreased by distance, density and glucose-free medium	Horner et al. (32)
In vitro 3-D culture	Bovine	No-glucose medium	5 h–48 h	NP cells	No glucose inhibited cell viability	Bibby et al. (33)
In vitro	Wistar rats	Serum-free medium	12 h–24 h	NP cells	No serum induced cell apoptosis	Risbud et al. (34)
In vitro	SD rats	Serum -free medium	6 h, 48 h	NP cells	Starvation induced apoptosis, cycle arrest and a group of related genes	Sudo et al. (37)
In vitro	Rats	Serum -free medium	6 h, 48 h	NP cells	Starvation inhibited expression of Col-II and aggrecan and induced apoptosis Overexpression of bcl-2 reversed the effect	Sudo et al. (38)
In vitro	Human	Serum-free medium	0 h–48 h	NP cells	Transfection of hTERT attenuated the negative influence of starvation	Liang et al. (35)
In vitro	SD rats	Serum-free medium EBSS	12 h, 24 h 2 h	AF cells NP cells	Autophagy protected disc cells from apoptosis induced by starvation	Jiang and Shen (28,45)

NP, nucleus pulposus; AF, annulus fibrosus; GAG, glycosaminoglycans; hTERT, human telomerase reverse transcriptase; EBSS, Earle’s Balanced Salt Solution.

Table 2. Responses and adaptations of disc cells to acidic stress.

Research style	Species	Animal or cell model	Cell specify	Key finding	Authors
In vitro	SD rats	Cells treated with HCl pH: 6.4, 7.4	Endplate chondrocyte	Acid promoted apoptosis via OGR1	Yuan et al. (52)
In vitro 3-D culture	Bovine	Treated with HCl pH: 6.3–7.5	NP cells	Acid inhibited GAG, TIMP-1 production	Razaq et al. (54)
In vitro 3-D culture	Bovine	Treated with HCl pH: 6.5, 6.8, 7.2	NP cells	Acid inhibited mRNA of aggrecan, collagen-I, collagen-II	Neidlinger-Wilke et al. (56)
In vitro 3-D culture	Bovine	Adjusted to pH: 6.2, 6.7, 7.4	NP cells	Low pH inhibited cell viability with or without oxygen	Bibby et al. (33)
Ex-vivo	Human and bovine	Treated with lactic acid or HCl pH: 6.3–7.4	NP cells	Acid suppressed proteoglycan synthesis	Ohshima et al. (55)
In vitro 3-D culture	Bovine	Adjusted to pH: 6.0, 7.4	NP cells	Low PH inhibited cell viability	Horner et al. (32)
In vitro	SD rats	Treated with lactic acid 2 mM, 6 mM	NP cells	Lactic acid promoted autophagy	Wu et al. (69)

NP, nucleus pulposus; OGR1, ovarian cancer G protein-coupled receptor 1; GAG, glycosaminoglycans; TIMPs, tissue inhibitors of metalloproteinases.

Table 3. Responses and adaptations of disc cells to hyperglycemia stress.

Research style	Species	Animal or cell model	Cell specify	Key findings	Authors
In vitro	SD rats	Cells treated with high glucose	Notochordal cells NP cells	High glucose promoted apoptosis and MMPs, inhibited cell proliferation	Park, Yang et al. (76,80)
In vitro	SD rats	Cells treated with high glucose	Notochordal cells	High glucose impaired mitochondria and enhanced ROS and autophagy	Park, Yanget et al. (81)
In vitro	SD rats	Streptozotocin-induced Type I diabetes	NP cells	Diabetes induced apoptosis, senescence, and autophagy	Jiang et al. (73)
In vitro	OLETF rats	Spontaneously diabetes	Notochordal cells	Diabetes induced apoptosis and MMPs expression	Won et al. (74)
In vitro	SD rats human	Cells from diabetic discs	NP cells	AGEs increased RAGE, MMP2 and p-ERK	Tsai et al. (79)
In vivo	ROP Os/+ mice	Streptozotocin-induced Type I diabetes	NP cells and AF cells	PYR and PPS attenuated disc degeneration	Illien-Junger et al. (75)

MMPs, matrix metalloproteinase; ROS, reactive oxygen species; AGEs, advanced glycation end products; PYR, Pyridoxamine; PPS, Pentosan Polysulphate; NP, nucleus pulposus; AF, annulus fibrosus.

Table 4. Responses and adaptations of disc cells to mechanical stress.

Research style	Species	Animal or cell model	Cell specify	Key findings	Authors
In vivo and in vitro	SD rats	Compressive loading on the tail disc and scaffold	NP cells	Excessive magnitude, duration and frequency of compressive loading accelerated the apoptosis via mitochondrial pathway	Kuo et al. (100)
In vitro	SD rats	Cultured cells treated with air pressure	NP cells	1.0 Mpa static compression reduced cell viability and induced apoptosis in a time-dependent manner via mitochondrial pathway	Ding et al. (101)
In vitro	SD rats	Compressive loading on the tail disc	Notochordal cells	1.3 MPa static compression reduced notochordal cells, increased apoptosis and induced catabolic metabolism	Hirata et al. (106)
In vitro	Pigs	Compressive loading on the cultured disc	NP and AF cells	10% compressive static and dynamic strain increased the total ATP and lactate content in the IVD	Wang et al. (107)
In vitro	Bovine	Cyclic compression and torsion on the cultured disc	NP and AF cells	Combined dynamic compression and axial torsion promoted NP cell death compared with the pure loading	Chan et al. (102)
In vitro	SD rats	Cultured cells treated with cyclic tension loading	AF cells	0.5 Hz 20% stretch induced AF cells apoptosis via endoplasmic reticulum stress through nitric oxide production	Zhang et al. (104)
In vitro	Human	Cyclic compression on the cultured NP tissues	NP ells	The dynamic compression induced the increase of ADAMTS and decrease of aggrecan	Huang et al. (108)

NP, nucleus pulposus; AF, annulus fibrosus; IVD, intervertebral disc; ATP, adenosine 5′-triphosphate; ADAMTS, a disintegrin and metalloproteinase with thrombospondin motifs; ATP, adenosine 5′-triphosphate.

Figure 2. The central role of autophagy in regulating the adaptive mechanism of disc cells under different stresses. Compression, starvation, acid, hypoxia and high glucose have all been reported to induce autophagy in disc cells. The dotted line indicates that the pathway has been demonstrated in chondrocyte but not yet in disc cells.

Horner HA, Urban JP. Volvo Award Winner in basic science studies: effect of nutrient supply on the viability of cells from the nucleus pulposus of the intervertebral disc. Spine (Phila Pa 1976) 2001;26:2543–9

 PubMed Web of Science ®Google Scholar

Bibby SR, Urban JP. Effect of nutrient deprivation on the viability of intervertebral disc cells. Eur Spine J 2004;13:695–701

 PubMed Web of Science ®Google Scholar

Risbud MV, Fertala J, Vresilovic EJ, Albert TJ, Shapiro IM. Nucleus pulposus cells upregulate PI3K/Akt and MEK/ERK signaling pathways under hypoxic conditions and resist apoptosis induced by serum withdrawal. Spine (Phila Pa 1976) 2005;30:882–9

 PubMedGoogle Scholar

Sudo H, Yamada K, Iwasaki K, Higashi H, Ito M, Minami A, Iwasaki N. Global identification of genes related to nutrient deficiency in intervertebral disc cells in an experimental nutrient deprivation model. PLoS One 2013;8:e58806

 Google Scholar

Sudo H, Minami A. Regulation of apoptosis in nucleus pulposus cells by optimized exogenous Bcl-2 overexpression. J Orthop Res 2010;28:1608–13

 PubMed Web of Science ®Google Scholar

Liang W, Ye D, Dai L, Shen Y, Xu J. Overexpression of hTERT extends replicative capacity of human nucleus pulposus cells, and protects against serum starvation-induced apoptosis and cell cycle arrest. J Cell Biochem 2012;113:2112–21

 PubMed Web of Science ®Google Scholar

Shen C, Yan J, Jiang LS, Dai LY. Autophagy in rat annulus fibrosus cells: evidence and possible implications. Arthritis Res Ther 2011;13:R132

 PubMed Web of Science ®Google Scholar

Jiang L, Zhang X, Xu H. Protective effect of autophagy on nucleus pulposus cells under starvation. Chin J Pathophysiol 2012;28:1302–7

 Google Scholar

Yuan FL, Wang HR, Yuan W, Zhao MD, Cao L, Duan PG, Jiang YQ, Li XL, Dong J. Ovarian cancer G protein-coupled receptor 1 is involved in acid-induced apoptosis of endplate chondrocytes in intervertebral discs. J Bone Miner Res 2014;29:67–77

 Web of Science ®Google Scholar

Razaq S, Wilkins RJ, Urban JP. The effect of extracellular pH on matrix turnover by cells of the bovine nucleus pulposus. Eur Spine J 2003;12:341–9

 PubMed Web of Science ®Google Scholar

Neidlinger-Wilke C, Mietsch A, Rinkler C, Wilke HJ, Ignatius A, Urban J. Interactions of environmental conditions and mechanical loads have influence on matrix turnover by nucleus pulposus cells. J Orthop Res 2012;30:112–21

 PubMed Web of Science ®Google Scholar

Ohshima H, Urban JP. The effect of lactate and pH on proteoglycan and protein synthesis rates in the intervertebral disc. Spine (Phila Pa 1976) 1992;17:1079–82

 PubMed Web of Science ®Google Scholar

Wu W, Zhang X, Hu X, Wang X, Sun L, Zheng X, Jiang L, Ni X, Xu C, Tian N, Zhu S, Xu H. Lactate down-regulates matrix systhesis and promotes apoptosis and autophagy in rat nucleus pulposus cells. J Orthop Res 2014;32:253–61

 PubMed Web of Science ®Google Scholar

Park EY, Park JB. Dose- and time-dependent effect of high glucose concentration on viability of notochordal cells and expression of matrix degrading and fibrotic enzymes. Int Orthop 2013;37:1179–86

 PubMed Web of Science ®Google Scholar

Yang L, Zhu L, Dong W, Cao Y, Lin L, Rong Z, Zhang Z, Wu G. Reactive oxygen species-mediated mitochondrial dysfunction plays a critical role in high glucose-induced nucleus pulposus cell injury. Int Orthop 2013;38:205–6

 Web of Science ®Google Scholar

Park EY, Park JB. High glucose-induced oxidative stress promotes autophagy through mitochondrial damage in rat notochordal cells. Int Orthop 2013;37:2507–14

 Google Scholar

Jiang L, Zhang X, Zheng X, Ru A, Ni X, Wu Y, Tian N, Huang Y, Xue E, Wang X, Xu H. Apoptosis, senescence, and autophagy in rat nucleus pulposus cells: Implications for diabetic intervertebral disc degeneration. J Orthop Res 2013;31:692–702

 PubMed Web of Science ®Google Scholar

Won HY, Park JB, Park EY, Riew KD. Effect of hyperglycemia on apoptosis of notochordal cells and intervertebral disc degeneration in diabetic rats. J Neurosurg Spine 2009;11:741–8

 PubMed Web of Science ®Google Scholar

Tsai TT, Ho NY, Lin YT, Lai PL, Fu TS, Niu CC, Chen LH, Chen WJ, Pang JH. Advanced glycation end products in degenerative nucleus pulposus with diabetes. J Orthop Res 2014;32:238–44

 PubMed Web of Science ®Google Scholar

Illien-Junger S, Grosjean F, Laudier DM, Vlassara H, Striker GE, Iatridis JC. Combined anti-inflammatory and anti-age drug treatments have a protective effect on intervertebral discs in mice with diabetes. PLoS One 2013;8:e64302

 PubMed Web of Science ®Google Scholar

Adams MA, Roughley PJ. What is intervertebral disc degeneration, and what causes it? Spine (Phila Pa 1976) 2006;31:2151–61

 PubMed Web of Science ®Google Scholar

Kuo YJ, Wu LC, Sun JS, Chen MH, Sun MG, Tsuang YH. Mechanical stress-induced apoptosis of nucleus pulposus cells: an in vitro and in vivo rat model. J Orthop Sci 2014;19:313–22

 PubMed Web of Science ®Google Scholar

Xie M, Yang S, Win HL, Xiong L, Huang J, Zhou J. Rabbit annulus fibrosus cell apoptosis induced by mechanical overload via a mitochondrial apoptotic pathway. J Huazhong Univ Sci Technol Med Sci 2010;30:379–84

 PubMed Web of Science ®Google Scholar

Hirata H, Yurube T, Kakutani K, Maeno K, Takada T, Yamamoto J, Kurakawa T, Akisue T, Kuroda R, Kurosaka M, Nishida K. A rat tail temporary static compression model reproduces different stages of intervertebral disc degeneration with decreased notochordal cell phenotype. J Orthop Res 2014;32:455–63

 PubMed Web of Science ®Google Scholar

Ding F, Shao ZW, Yang SH, Wu Q, Gao F, Xiong LM. Role of mitochondrial pathway in compression-induced apoptosis of nucleus pulposus cells. Apoptosis 2012;17:579–90

 PubMed Web of Science ®Google Scholar

Zhu Q, Jackson AR, Gu WY. Cell viability in intervertebral disc under various nutritional and dynamic loading conditions: 3d finite element analysis. J Biomech 2012;45:2769–77

 PubMed Web of Science ®Google Scholar

Wang C, Gonzales S, Levene H, Gu W, Huang CY. Energy metabolism of intervertebral disc under mechanical loading. J Orthop Res 2013;31:1733–8

 PubMed Web of Science ®Google Scholar