TNF-α promotes nuclear enrichment of the transcription factor TonEBP/NFAT5 to selectively control inflammatory but not osmoregulatory responses in nucleus pulposus cells

Abstract

Intervertebral disc degeneration (IDD) causes chronic back pain and is linked to production of proinflammatory molecules by nucleus pulposus (NP) and other disc cells. Activation of tonicity-responsive enhancer-binding protein (TonEBP)/NFAT5 by non-osmotic stimuli, including proinflammatory molecules, occurs in cells involved in immune response. However, whether inflammatory stimuli activate TonEBP in NP cells and whether TonEBP controls inflammation during IDD is unknown. We show that TNF-α, but not IL-1β or LPS, promoted nuclear enrichment of TonEBP protein. However, TNF-α-mediated activation of TonEBP did not cause induction of osmoregulatory genes. RNA sequencing showed that 8.5% of TNF-α transcriptional responses were TonEBP-dependent and identified genes regulated by both TNF-α and TonEBP. These genes were over-enriched in pathways and diseases related to inflammatory response and inhibition of matrix metalloproteases. Based on RNA-sequencing results, we further investigated regulation of novel TonEBP targets ,, and TonEBP acted synergistically with TNF-α and LPS to induce-proximal promoter activity. Interestingly, this regulation required a highly conserved NF-κB-binding site but not a predicted TonE, suggesting cross-talk between these two members of the Rel family. Finally, analysis of human NP tissue showed that expression correlated with canonical osmoregulatory targets, , and, supporting findings that the inflammatory milieu during IDD does not interfere with TonEBP osmoregulation. In summary, whereas TonEBP participates in the proinflammatory response to TNF-α, therapeutic strategies targeting this transcription factor for treatment of disc disease must spare osmoprotective, prosurvival, and matrix homeostatic activities.

A New Understanding of the Role of IL-1 in Age-Related Intervertebral Disc Degeneration in a Murine Model

“…In addition to these cellular and extracellular matrix changes, inflammatory cytokine expression increases with increasing severity of disc degeneration . These cytokines promote disc degeneration by activating matrix metalloproteinases (MMPs), causing further extracellular matrix breakdown . Interleukin‐1β (IL‐1β) and tumor necrosis factor‐α (TNF‐α) are the most commonly studied inflammatory cytokines in conjunction with disc degeneration.…”

“…(8) These cytokines promote disc degeneration by activating matrix metalloproteinases (MMPs), causing further extracellular matrix breakdown. (9)(10)(11) Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) are the most commonly studied inflammatory cytokines in conjunction with disc degeneration.…”

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

“…In concert with these cellular and extracellular matrix changes, the dramatic increase in interleukin‐1β (IL‐1β) and tumor necrosis factor alpha (TNFα) expression is correlated with severity of disc degeneration . These cytokines are thought to further promote disc degeneration by activating matrix metalloproteinases (MMPs) …”

NFAT5 Has a Job in the Brain

“…CDK5, c-Abl, and ATM promote the nuclear localization of NFAT5, and, in contrast, CK1 inhibits its nuclear accumulation [19]. There are many other factors that influence the activation and expression of NFAT5, such as inflammatory cytokines [16, 77], microRNAs [50, 62, 78, 79], and transcription factors [80-83]. …”