CANNABINOID RECEPTOR TYPE 1-REGULATED CELL DEATH DEPENDING ON ITS SUBCELLULAR LOCALIZATION IN HUMAN NEUROBLASTOMA CELL
Authors: Mori *Kazuaki , Asahi Toru , Kataoka Kosuke 
Published: February 2025

Abstract

Background
The cannabinoid receptor, a major component of the endocannabinoid system, plays a significant role in fine-tuning the physiological processes including cell death, particularly in the brain. The cannabinoid receptor type 1 (CB1) in neurons and astrocytes is expressed on the mitochondrial outer mitochondrial membrane (mtCB1) as well as on the plasma membrane (pmCB1) (Hebert-Chatelain et al., 2016).
Depending on its sub-cellular localization, CB1 receptors can act differently in synaptic transmission (Soria-Gomez et al., 2021). However, little is known about the role of sub-cellular localization of CB1 receptors in neuronal cell death.

Aims & Objectives
Our primary objective was to investigate how the sub-cellular localization of CB1 receptors affects neuronal mitochondrial function and cell death.

Method
Human neuroblastoma cell line SH-SY5Y was treated with three selective ligands with different cell membrane permeabilities: arachidonyl-2'-chloroethylamide (ACEA; a cell-permeable selective agonist), rimonabant (a cell-permeable selective inverse agonist), and hemopressin (a cell-impermeable selective inverse agonist).

Results
ACEA treatment for 1 hour diminished mitochondrial membrane potential (Δ&Psi;m) and induced reactive oxygen species (ROS) production accompanied by a decrease in NAD/NADH ratio. In contrast, rimonabant treatment not only diminished Δ&Psi;m but also induced mitochondrial fragmentation without the effects on ROS and NAD/NADH ratio. Interestingly rimonabant treatment for 12 hours led to significant cell death characterized by an increase in intracellular Fe2+ levels, which was inhibited by iron chelator, a 2,2'-bipyridyl, indicating that rimonabant-induced cell death was ferroptosis. In contrast, ACEA caused cell death without the ferroptotic features. Furthermore, Hemopressin treatment also slightly elevated the cellular Fe2+ level, but had no effect on cell death or mitochondrial function, suggesting that pmCB1 inhibition had a minor effect on mitochondria and cell death.

Discussion & Conclusion
These results highlight that both overactivation and inhibition of mtCB1 can lead to neuronal cell death following mitochondrial dysfunction. Notably, the underlying mechanisms differ based on the specific cannabinoids used. To determine whether the observed mitochondrial dysfunction and cell death are CB1 receptor-dependent, further experiments involving pharmacological or genetic manipulation are necessary. In summary, our research expands the understanding of the multifaceted roles of CB1 receptors in regulating neuronal mitochondrial function and cell death, possibly providing insights into the psychoactive effects of cannabinoids.

References
Hebert-Chatelain, E. et al. (2016) “A cannabinoid link between mitochondria and memory,” Nature 539, pp. 555–559. doi: https://doi.org/10.1038/nature20127.
Soria-Gomez, E. et al. (2021) “Subcellular specificity of cannabinoid effects in striatonigral circuits,”
Neuron 109 (9), pp. 1513-1526.e11. doi: https://doi.org/10.1016/j.neuron.2021.03.007.