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Oxidative stress induces caspase-independent retinal apoptosis in vitro
1Tumour Biology Laboratory, Department of Biochemistry, Lee Maltings, University College Cork, Cork, Ireland.
Abstract:
Apoptosis is the mode of cell death in retinitis pigmentosa (RP), a heterogeneous group of retinal degenerations. The activation of the caspase proteases forms a pivotal step in the initiation and execution phase of apoptosis in many cells. Inhibition of caspases has been reported to prevent apoptosis in many model systems. However, we demonstrate the absence of caspase activation during retinal cell apoptosis in vitro which involves phosphatidylserine (PS) externalisation, DNA nicking and cell shrinkage. In addition, zVAD-fmk, DEVD-CHO and BD-fmk, inhibitors of the caspases, were unable to alter the characteristics or kinetics of apoptosis, implying that retinal cell death in vitro follows a caspase-independent pathway. We have previously demonstrated the ability of reactive oxygen species (ROS) to act as mediators of retinal cell apoptosis in vitro as well as the ability of antioxidants to prevent retinal cell apoptosis. Here we demonstrate the oxidative inactivation of caspases in this model of retinal apoptosis and provide evidence for an oxidative stress driven cell death pathway that does not involve caspase activity and which retains key features of apoptotic cell death. Furthermore, our data indicates that apoptotic events such as PS exposure, DNA nicking and cell shrinkage may occur independently of caspase activity.
Insights
Retinal cell death in retinitis pigmentosa (RP) occurs independently of caspase activation, suggesting a novel, oxidative stress-driven pathway. Antioxidants may prevent RP by targeting this caspase-independent apoptosis.
Area of Science:
- Cell Biology
- Neuroscience
- Ophthalmology
Background:
- Apoptosis is a key cell death mechanism in retinitis pigmentosa (RP).
- Caspase activation is typically crucial for apoptosis initiation and execution.
- Previous research suggested caspases mediate retinal cell death.
Purpose of the Study:
- To investigate the role of caspases in retinal cell apoptosis in vitro.
- To explore the involvement of oxidative stress in retinal cell death.
- To determine if key apoptotic events can occur independently of caspases.
Main Methods:
- Inducing apoptosis in retinal cells in vitro.
- Assessing caspase activation using specific inhibitors (zVAD-fmk, DEVD-CHO, BD-fmk).
- Evaluating markers of apoptosis like phosphatidylserine (PS) externalization, DNA nicking, and cell shrinkage.
- Investigating the role of reactive oxygen species (ROS) and antioxidants.
Main Results:
- Retinal cell apoptosis in vitro showed no caspase activation.
- Caspase inhibitors did not alter the characteristics or kinetics of apoptosis.
- Oxidative inactivation of caspases was observed.
- Key apoptotic features occurred independently of caspase activity, driven by oxidative stress.
Conclusions:
- Retinal cell death in RP involves a caspase-independent pathway.
- Oxidative stress drives this non-caspase apoptotic pathway.
- Apoptotic events like PS exposure and DNA nicking can occur without caspase activity.