N-acetylcysteine regulates the endoplasmic reticulum stress response in CEP-like chondrocytes exposed to proinflammatory cytokines.

BACKGROUND

Intervertebral disc degeneration (IVDD) is characterized by chronic inflammation and redox imbalance, which compromise cartilage endplate (CEP) cells and essential organelles such as the endoplasmic reticulum (ER), leading to protein misfolding and altered calcium homeostasis. To counteract this, cells activate the unfolded protein response (UPR) through the ATF6α, IRE1α, and PERK/eIF2α pathways. Due to its antioxidant properties, N-acetylcysteine (NAC) has been proposed as a modulator of these stress responses under proinflammatory conditions. However, the impact of NAC on IVDD remains poorly understood.

OBJECTIVE

This study aimed to analyse UPR signaling, calcium homeostasis, and ER stress-associated caspase activation in differentiated ATDC5 chondrocytes used as a CEP-like model under inflammatory stress, and to evaluate their modulation by NAC.

METHODS

Differentiated ATDC5 cells were exposed to IL-1α, IL-1β, and TNF (1 ng/mL) for 24 h in the presence or absence of NAC (100 μM). Oxidative status and ER stress-associated pathways were assessed using biochemical assays.

RESULTS

Proinflammatory cytokines induced redox imbalance, elevated cytosolic calcium levels, and upregulated HSP90. The ER stress response was intensified, as indicated by increased expression of IRE1α and ATF6α, along with increased caspase-12 expression under IL-1β stimulation, which is consistent with the activation of ER stress-associated caspase signaling. NAC treatment restored redox balance, normalized calcium levels and HSP90 expression, attenuated ATF6α activation, and reduced ER stress-associated caspase signaling.

CONCLUSIONS

NAC mitigates inflammation-induced oxidative and ER stress responses in CEP-like chondrocytes. These findings support redox-ER modulation as a potential strategy to preserve disc cell homeostasis during early IVDD and highlight NAC as a promising pharmacological approach to slow disease progression.