Mitochondrial Dysfunction and ER Stress in CB1 Receptor Antagonist-Induced Apoptosis in Human Neuroblastoma SH-SY5Y Cells

Cannabinoid receptor type 1 (CB1R) is the key modulator of neuronal viability. In particular, CB1R antagonists provide neuroprotective effects on neurotoxicity caused by e.g. neuronal injury. However, the underlying mechanisms and potential limitations of CB1R antagonism remain unclear. Here we investigated the impact of environmental conditions on CB1R antagonist effects. Unexpectedly, we have found that cell-permeable CB1R antagonists, rimonabant and AM251, induced significant cell death in human neuroblastoma SH-SY5Y cells under serum-free conditions. Mitochondrial morphological analysis revealed mitochondrial swelling characterized by their network fragmentation and cristae reduction. Additionally, phosphoproteomics analysis showed an upregulation of phosphorylated EIF2AK3 (also known as PERK), leading to the activation of the eIF2/ATF4/CHOP pathway, indicative of endoplasmic reticulum (ER) stress. Rimonabant and AM251 treatment also triggered caspase-dependent apoptosis, evidenced by the detection of cleaved caspase 3 and cleaved PARP. These results suggest that cell-permeable CB1R antagonists promote apoptosis via mitochondrial dysfunction and ER stress under serum-free conditions in SH-SY5Y cells. Our findings indicate that while CB1R antagonists may be neuroprotective in certain conditions, they may also pose a neurotoxic risk in environments characterized by cellular stress or nutrient deprivation.