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Enhanced cGMP Interactor Rap Guanine Exchange Factor 4 (EPAC2) Expression and Activity in Degenerating
Michel Rasmussen1, Jiaming Zhou1, Frank Schwede2
1Department of Clinical Sciences Lund, Faculty of Medicine, Lund University, 22184 Lund, Sweden.
Abstract:
The disease retinitis pigmentosa (RP) leads to photoreceptor degeneration by a yet undefined mechanism(s). In several RP mouse models (i.e., rd mice), a high cyclic GMP (cGMP) level within photoreceptors is detected, suggesting that cGMP plays a role in degeneration. The rap guanine exchange factor 4 (EPAC2) is activated by cyclic AMP (cAMP) and is an accepted cGMP-interacting protein. It is unclear whether and how cGMP interacts with EPAC2 in degenerating photoreceptors; we therefore investigated EPAC2 expression and interactions with cGMP and cAMP in retinas of the rd1 and rd10 models for retinal degeneration. EPAC2 expression in the photoreceptor layer increased significantly during rd1 and rd10 degeneration, and an increase in EPAC2 interactions with cGMP but not cAMP in the rd1 was also seen via a proximity ligation assay on histological sections. Retinal explant cultures revealed that pharmacological inhibition of the EPAC2 activity reduced the photoreceptor layer thickness in the rd10 retina, suggesting that EPAC2 inhibition promotes degeneration. Taken together, our results support the hypothesis that high degeneration-related cGMP leads to increased EPAC2 and cGMP interactions, inhibiting EPAC2. By inference, EPAC2 could have neuroprotective capacities that may be exploited in the future.
Insights
High cyclic GMP (cGMP) levels in retinitis pigmentosa (RP) correlate with increased EPAC2 interactions, suggesting EPAC2 may protect photoreceptors. Inhibiting EPAC2 appears to worsen degeneration in RP mouse models.
Area of Science:
- Ophthalmology
- Molecular Biology
- Neuroscience
Background:
- Retinitis pigmentosa (RP) causes photoreceptor degeneration through unknown mechanisms.
- Elevated cyclic guanosine monophosphate (cGMP) levels are observed in RP mouse models, implicating cGMP in degeneration.
- EPAC2, a cyclic adenosine monophosphate (cAMP)-activated protein, is known to interact with cGMP.
Purpose of the Study:
- To investigate the expression and interaction of EPAC2 with cGMP and cAMP in degenerating photoreceptors of RP mouse models (rd1 and rd10).
Main Methods:
- Quantitative analysis of EPAC2 expression in photoreceptor layers.
- Proximity ligation assay to detect EPAC2 interactions with cGMP and cAMP in retinal sections.
- Pharmacological inhibition of EPAC2 activity in retinal explant cultures.
Main Results:
- EPAC2 expression significantly increased in photoreceptor layers during degeneration in both rd1 and rd10 models.
- Increased interaction between EPAC2 and cGMP (but not cAMP) was observed in rd1 retinas.
- Inhibition of EPAC2 activity reduced photoreceptor layer thickness in rd10 retinal explants, suggesting a pro-degenerative effect.
Conclusions:
- The study supports a hypothesis where degeneration-related cGMP increases EPAC2 interaction, potentially inhibiting EPAC2.
- Findings suggest EPAC2 may possess neuroprotective properties in photoreceptors.
- EPAC2's role warrants further investigation for potential therapeutic strategies in RP.
