COX-2 expression mediated by calcium-TonEBP signaling axis under hyperosmotic conditions serves osmoprotective function in nucleus pulposus cells

Abstract

The nucleus pulposus (NP) of intervertebral discs experiences dynamic changes in tissue osmolarity because of diurnal loading of the spine. TonEBP/NFAT5 is a transcription factor that is critical in osmoregulation as well as survival of NP cells in the hyperosmotic milieu. The goal of this study was to investigate whether cyclooxygenase-2 (COX-2) expression is osmoresponsive and dependent on TonEBP, and whether it serves an osmoprotective role. NP cells up-regulated COX-2 expression in hyperosmotic media. The induction of COX-2 depended on elevation of intracellular calcium levels and p38 MAPK pathway, but independent of calcineurin signaling as well as MEK/ERK and JNK pathways. Under hyperosmotic conditions, both COX-2 mRNA stability and its proximal promoter activity were increased. The proximal COX-2 promoter (-1840/+123 bp) contained predicted binding sites for TonEBP, AP-1, NF-κB, and C/EBP-β. While COX-2 promoter activity was positively regulated by both AP-1 and NF-κB, AP-1 had no effect and NF-κB negatively regulated COX-2 protein levels under hyperosmotic conditions. On the other hand, TonEBP was necessary for both COX-2 promoter activity and protein up-regulation in response to hyperosmotic stimuli. disc organ culture studies using hypomorphic TonEBP mice confirmed that TonEBP is required for hyperosmotic induction of COX-2. Importantly, the inhibition of COX-2 activity under hyperosmotic conditions resulted in decreased cell viability, suggesting that COX-2 plays a cytoprotective and homeostatic role in NP cells for their adaptation to dynamically loaded hyperosmotic niches.

Differential Effect of Long-Term Systemic Exposure of TNFα on Health of the Annulus Fibrosus and Nucleus Pulposus of the Intervertebral Disc

“…TNFα may be involved in maintaining cell viability and matrix homeostasis in the physiologically challenging disc niche that is hypoxic, hyperosmolar, and under mechanical stress . Earlier work from our group found that TNFα expression is maintained in the postnatal NP cells by tonicity‐responsive binding‐protein (TonEBP); this transcription factor controls cell adaptive responses in the hyperosmolar disc environment likely in part by regulating the expression of pro‐survival and anabolic matrix genes . Additionally, complete removal of IL‐1β, another cytokine closely related to disc degeneration, renders mice more susceptible to age‐related disc degeneration, further reinforcing the importance of the physiological role that certain cytokines play in the preservation of disc health .…”

The Role of p38 MAPK in Triacylglycerol Accumulation during Apoptosis

“…Based on this, we decided to investigate the role of p38 MAPK on the regulation of DGATs at the mRNA level. We used a small molecule inhibitor SB‐202190, which inhibits p38 MAPKα and p38 MAPKβ, and investigated the effect of p38 MAPK inhibition on DGAT1 expression during apoptosis. We collected control, SB‐202190‐treated, 5‐FU‐treated and 5‐FU+SB‐202190‐treated cells, and measured the expression of genes of interest in these conditions.…”

Selective inhibition of cyclooxygenase‐2 protects porcine aortic endothelial cells from human antibody‐mediated complement‐dependent cytotoxicity

“…54 In addition, the induction of COX-2 is dependent on elevation of intracellular calcium levels in nucleus pulposus cells under hyperosmotic conditions. 55 Calcium activation of tonicity-responsive enhancer binding protein (TonEBP) is required for regulation of COX-2 in nucleus pulposus cells. We then examined whether elevated Ca 2+ was responsible for the upregulation of COX-2.…”