p38 MAPK Facilitates Crosstalk Between Endoplasmic Reticulum Stress and IL-6 Release in the Intervertebral Disc

Abstract

Degenerative disc disease is associated with increased expression of pro-inflammatory cytokines in the intervertebral disc (IVD). However, it is not completely clear how inflammation arises in the IVD and which cellular compartments are involved in this process. Recently, the endoplasmic reticulum (ER) has emerged as a possible modulator of inflammation in age-related disorders. In addition, ER stress has been associated with the microenvironment of degenerated IVDs. Therefore, the aim of this study was to analyze the effects of ER stress on inflammatory responses in degenerated human IVDs and associated molecular mechanisms. Gene expression of ER stress marker GRP78 and pro-inflammatory cytokines IL-6, IL-8, IL-1β, and TNF-α was analyzed in human surgical IVD samples (n = 51, Pfirrmann grade 2–5). The expression of GRP78 positively correlated with the degeneration grade in lumbar IVDs and IL-6, but not with IL-1β and TNF-α. Another set of human surgical IVD samples (n = 25) was used to prepare primary cell cultures. ER stress inducer thapsigargin (Tg, 100 and 500 nM) activated gene and protein expression of IL-6 and induced phosphorylation of p38 MAPK. Both inhibition of p38 MAPK by SB203580 (10 µM) and knockdown of ER stress effector CCAAT-enhancer-binding protein homologous protein (CHOP) reduced gene and protein expression of IL-6 in Tg-treated cells. Furthermore, the effects of an inflammatory microenvironment on ER stress were tested. TNF-α (5 and 10 ng/mL) did not activate ER stress, while IL-1β (5 and 10 ng/mL) activated gene and protein expression of GRP78, but did not influence [Ca2+]i flux and expression of CHOP, indicating that pro-inflammatory cytokines alone may not induce ER stress in vivo. This study showed that IL-6 release in the IVD can be initiated following ER stress and that ER stress mediates IL-6 release through p38 MAPK and CHOP. Therapeutic targeting of ER stress response may reduce the consequences of the harsh microenvironment in degenerated IVD.

Quercetin Inhibits the Production of IL-1β-Induced Inflammatory Cytokines and Chemokines in ARPE-19 Cells via the MAPK and NF-κB Signaling Pathways

“…Because inflammation may be a key factor in RPE degeneration, dysfunction and loss in retinal degenerative diseases, the intracellular signaling pathways involved in initiating the release of cytokines and chemokines in RPE cells are important. One of the most widely reported signaling pathways in many cell systems is the MAPK signaling pathway, in which inflammatory stimulants contribute to the activation of MAPKs, followed by increased release of cytokines and chemokines [91,92,93]. Quercetin has been reported to have anti-inflammatory effects via inhibiting the activation of MAPKs in a number of different cell lines treated with different inflammatory stimulants [14,34,36,37].…”

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

“…The p38 signaling pathway is generally activated by stressors and is known to regulate inflammation, autophagy, apoptosis, and differentiation [ 241 ]. Numerous studies have investigated p38 in the IVD, thereby identifying hypoxia [ 245 ], hyperosmolarity [ 120 ], hyperphysiological mechanical loads [ 133 ], ER stress [ 258 ], acidity [ 257 ], high glucose levels [ 256 ], and IL-1 [ 253 ] as potent activators. Interestingly, p38 is connected to TPRV4 [ 133 ], which has previously been described to transduce mechanical, inflammatory, and pain signals in cartilage [ 259 ].…”

“…Interestingly, p38 is connected to TPRV4 [ 133 ], which has previously been described to transduce mechanical, inflammatory, and pain signals in cartilage [ 259 ]. Different research fields have shown extensive cross talk between p38 and other signaling pathways, e.g., ERK [ 258 ], TGF-β/Smad, [ 260 ] or Akt [ 261 ], which should be investigated in IVD cells. Overall, inhibition of p38 is being discussed for therapeutic approaches, potentially reducing inflammation, pain, and disc matrix catabolism [ 253 , 262 ], although ultimate outcomes may be difficult to predict due to the extensive cross talk with other pathways.…”

4‐Phenylbutyric acid, a potent endoplasmic reticulum stress inhibitor, attenuates the severity of collagen‐induced arthritis in mice via inhibition of proliferation and inflammatory responses of synovial fibroblasts

“…23 The crosstalk between ER stress and IL-6 release has been reported previously. 24 Krupkova et al showed that IL-6 release was increased following ER stress activation and that the crosstalk between ER stress and IL-6 induction was enhanced by phosphorylation of p38 F I G U R E 5 Effects of 4-phenylbutyric acid (4-PBA) on arthritis severity in collagen-induced arthritis (CIA) mice. (A) Representative front and hind paws of mice of each group, and average paw thickness score and clinical score of CIA mice treated with 4-PBA (240 mg kg −1 day −1 ) or phosphate buffered saline (PBS) (vehicle) (15 mice per group).…”