Smoke-Induced Mitochondrial-ER Stress in Disc Calcification

Intervertebral disc (IVD) degeneration is a leading cause of low back pain, and smoking is a major risk factor. However, the mechanisms of how smoking affects specific IVD regions remain unclear. We focused on the cartilaginous endplate (CEP) and examined whether cigarette smoke extract (CSE) drives oxidative stress that induces ER stress and mitochondrial redox disruption, leading to apoptosis and calcification. We also examined how CEP calcification alters disc-bone interface mechanics. Rat intervertebral discs were cultured ex vivo and exposed to control or CSE-treated conditions. CEP tissues were dissected for proteomic analysis. In a separate cell-based model, CEP cells treated with CSE were assessed for mitochondrial ROS, membrane potential (ΔΨm), metabolic outputs (glucose, lactate, ATP), TCA substrate utilization, and ER-stress signaling. To evaluate mechanical effects, we developed a mesoscale collagen fiber-bundle digital model to compute interface strength across calcification progression. CSE treatment increased cysteine oxidation in mitochondrial respiratory chain proteins (Complex I-V) and shifted the CEP proteome toward glycolysis, ER stress, apoptosis, and calcification. Consistent with these proteomic changes, CSE induced PERK/ATF4/CHOP signaling and mitochondrial dysfunction in CEP cells, evidenced by increased mitochondrial ROS, reduced ΔΨm, and TCA substrate utilization. This dysfunction was accompanied by elevated glycolysis (evidenced by higher glucose consumption and lactate release) and reduced ATP production. Digital simulation revealed calcified models to be stiffer and have a lower failure threshold than uncalcified models. Together, these findings link smoke exposure to CEP calcification and compromised mechanical function via mitochondrial-ER stress pathways, highlighting potential therapeutic targets.