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Involvement of cyclin-dependent kinases in axotomy-induced retinal ganglion cell death
Karine Lefèvre1, Peter G H Clarke, Eve E Danthe
1Institut de Biologie Cellulaire et de Morphologie, Université de Lausanne, 1005 Lausanne, Switzerland.
Abstract:
We have tested the role of cyclin-dependent kinases (CDKs) in the type 3B death of axotomized retinal ganglion cells, by injecting intraocularly olomoucine, roscovitine, or butyrolactone I. Each of these inhibits CDK1, CDK2, and CDK5; CDK1 and CDK2 are involved in cell proliferation, whereas CDK5 is involved in neuronal differentiation. The inhibitors partially protected ganglion cells against the effects of axotomy. These agents may affect the ganglion cells directly, because CDK1, its regulatory subunit cyclin B1, and CDK5 were identified immunohistochemically in the perikarya of ganglion cells, and this was confirmed for CDK1 and CDK5 in Western blots of the ganglion cell layer. These blots showed an axotomy-induced phosphorylation of CDK5 occurring remarkably quickly (within 6 hours of axotomy) but little if any change in the phosphorylation state of CDK1. In addition, we studied the expression of proliferation markers, including proliferating cell nuclear antigen (PCNA) and the synthesis of DNA, by immunohistochemical and autoradiographic methods. Normal or axotomized ganglion cells did not express PCNA and did not synthesize DNA. Although we cannot exclude the possibility that axotomized ganglion cells may leave their quiescent state, our data show that they did not progress beyond the G1 phase of the cell cycle. Finally, in contrast to inhibitors of CDKs, cell cycle blockers with different targets than CDKs did not protect ganglion cells. Globally, our results suggest that axotomy-induced death of ganglion cells involves the activation of CDK1, CDK2, or CDK5 (most probably CDK5) but not the full cell cycle machinery.
Insights
Cyclin-dependent kinases (CDKs) play a role in retinal ganglion cell death after injury. Inhibiting CDKs, particularly CDK5, partially protected these cells, suggesting a novel therapeutic target for vision loss.
Area of Science:
- Neuroscience
- Cell Biology
- Ophthalmology
Background:
- Retinal ganglion cells (RGCs) undergo programmed cell death (type 3B) after axotomy.
- Cyclin-dependent kinases (CDKs) are crucial regulators of the cell cycle and neuronal differentiation.
- The specific role of CDKs in RGC death following optic nerve injury remains unclear.
Purpose of the Study:
- To investigate the involvement of CDK1, CDK2, and CDK5 in the death of axotomized RGCs.
- To determine if inhibiting CDKs can protect RGCs from axotomy-induced death.
- To elucidate the cell cycle status of RGCs after axotomy.
Main Methods:
- Intraocular injection of CDK inhibitors (olomoucine, roscovitine, butyrolactone I).
- Immunohistochemistry and Western blotting to detect CDK1, CDK5, and cyclin B1.
- Assessment of proliferation markers (PCNA) and DNA synthesis.
- Administration of non-CDK cell cycle blockers.
Main Results:
- CDK inhibitors partially protected RGCs from axotomy-induced death.
- CDK1, CDK5, and cyclin B1 were detected in RGCs, with rapid axotomy-induced phosphorylation of CDK5.
- Axotomized RGCs did not express PCNA or synthesize DNA, indicating cell cycle arrest in G1 phase.
- Non-CDK cell cycle blockers did not provide protection.
Conclusions:
- Axotomy-induced RGC death involves the activation of CDK1, CDK2, or CDK5, with a likely primary role for CDK5.
- Targeting CDKs, particularly CDK5, represents a potential therapeutic strategy for preventing RGC loss.
- RGCs do not re-enter the cell cycle or undergo proliferation after axotomy, despite CDK involvement in their death.