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TRPV1 stimulation triggers apoptotic cell death of rat cortical neurons
Hisashi Shirakawa1, Tomoko Yamaoka, Kazuaki Sanpei
1Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida-shimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan.
Abstract:
Transient receptor potential vanilloid 1 (TRPV1) functions as a polymodal nociceptor and is activated by several vanilloids, including capsaicin, protons and heat. Although TRPV1 channels are widely distributed in the brain, their roles remain unclear. Here, we investigated the roles of TRPV1 in cytotoxic processes using TRPV1-expressing cultured rat cortical neurons. Capsaicin induced severe neuronal death with apoptotic features, which was completely inhibited by the TRPV1 antagonist capsazepine and was dependent on extracellular Ca(2+) influx. Interestingly, nifedipine, a specific L-type Ca(2+) channel blocker, attenuated capsaicin cytotoxicity, even when applied 2-4 h after the capsaicin. ERK inhibitor PD98059 and several antioxidants, but not the JNK and p38 inhibitors, attenuated capsaicin cytotoxicity. Together, these data indicate that TRPV1 activation triggers apoptotic cell death of rat cortical cultures via L-type Ca(2+) channel opening, Ca(2+) influx, ERK phosphorylation, and reactive oxygen species production.
Insights
Activation of the Transient Receptor Potential Vanilloid 1 (TRPV1) channel triggers neuronal death in rat cortical cultures. This cell death involves calcium influx, ERK activation, and reactive oxygen species, and can be blocked by TRPV1 antagonists.
Area of Science:
- Neuroscience
- Cell Biology
- Pharmacology
Background:
- Transient Receptor Potential Vanilloid 1 (TRPV1) channels are widely expressed in the brain.
- The precise functions of TRPV1 channels in neuronal processes, particularly cytotoxicity, remain largely undetermined.
Purpose of the Study:
- To investigate the role of TRPV1 channels in cytotoxic processes within cultured rat cortical neurons.
- To elucidate the molecular mechanisms underlying TRPV1-mediated neuronal cell death.
Main Methods:
- Utilized TRPV1-expressing cultured rat cortical neurons.
- Administered capsaicin to activate TRPV1 channels.
- Assessed neuronal death and employed specific inhibitors for TRPV1 (capsazepine), L-type Ca(2+) channels (nifedipine), ERK (PD98059), JNK, and p38.
- Measured extracellular Ca(2+) influx and reactive oxygen species (ROS) production.
Main Results:
- Capsaicin induced significant neuronal death with apoptotic features.
- This capsaicin-induced cytotoxicity was completely inhibited by capsazepine and dependent on extracellular Ca(2+) influx.
- Nifedipine attenuated capsaicin cytotoxicity, even when administered hours later.
- PD98059 (ERK inhibitor) and antioxidants reduced neuronal death, while JNK and p38 inhibitors had no significant effect.
Conclusions:
- TRPV1 activation initiates apoptotic cell death in rat cortical neurons.
- The process involves L-type Ca(2+) channel opening, subsequent Ca(2+) influx, ERK phosphorylation, and reactive oxygen species generation.
- These findings highlight TRPV1 as a key mediator of neuronal cytotoxicity with potential therapeutic implications.
