Institute for Ophthalmic Research

Neurodegenerative diseases are an ever increasing health concern in the ageing human
populations. The understanding of these diseases requires the use of reliable model systems
which can satisfy diverse research needs. The retina as an integral part of the central nervous
system (CNS) combines easy access with a large number of animal models available for
investigations of development, function and pathology. We use the retina as a model system
to investigate neuronal degeneration with a particular focus on photoreceptor cell death and a
group of inherited retinal degenerations collectively termed Retinitis Pigmentosa (RP).
RP affects predominantly photoreceptors and in the developed world it is the prevalent cause
of blindness in the working age population. Although the underlying genetic mutations have
been identified in many cases, the degeneration mechanisms are still unknown and at present
there is no treatment available. A precise knowledge of the mechanisms at play is, however,
essential for the development of rational therapies. The hope is that once we understand the
mechanisms underlying retinal degeneration we will be able to use this knowledge to develop
treatments for RP and related diseases that affect photoreceptors.

Current projects

For our studies we use different animal models for RP such as the rd1 mouse as well as retinal
explant cultures and cell cultures to study signaling pathways that are involved in
photoreceptor cell death or survival. Different neuroprotective strategies are evaluated for
their capacity to prevent or delay photoreceptor cell death. The following topics are currently
being investigated:

1. Activities of Poly-ADP-ribose polymerase (PARP) and poly-ADP-glycohydrolase
   (PARG) in retinal function and disease.      
   Ayse Sahaboglu-Tekgöz

2. The 661W cell line as model system for cone photoreceptor degeneration.
   Stine Menc

3. Cone photoreceptor cell death mechanisms.
   Dragana Trifunovic

4. Mechanisms of photoreceptor degeneration in rhodopsin mutant (P23H, S334ter) rat
   models for retinal degeneration
   Blanca Arango-Gonzalez & Jasvir Kaur

5. cGMP metabolism, activity of protein kinase G (PKG) and calpains in retinal degeneration.
   François Paquet-Durand

Research interests

We are studying cell death pathways using pharmacological and genetic manipulations on
retinal degeneration models, specific knock-out animals, organotypic retinal tissue cultures
and neuronal cell cultures. Experimental manipulations are evaluated using methods that
allow high spatiotemporal resolution of metabolic processes in living retinal tissues. This is
supplemented by studies at the tissue level using biochemical and proteomic approaches.

Figure 1: Differential regulation of metabolic markers at the onset of rd1 mouse
retinal degeneration:In wild-type (wt) mice (upper panel) PDE6 beta is expressed in the outer
segments of photoreceptors. In rd1 photoreceptors (lower panel) the PDE6 mutation leads to
a loss of expression and a dramatic accumulation of cGMP at post-natal day 11 when
compared with wt. cGMP accumulation coincides with increased activation of CaMKII and
PKC theta in rd1 photoreceptor segments. In the rd1 situation a subpopulation of
photoreceptor cell bodies shows strong increases in calpain activity, oxidatively damaged
DNA, and PARP activity. Degenerating rd1 photoreceptors also show nuclear translocation
of AIF and a positive reaction in the TUNEL assay. The images shown here are
representative of at least 3 different specimens from each genotype. ONL/INL stands for
outer/inner nuclear layer, respectively; figure modified after Sancho-Pelluz et al., 2008.

Processes under investigation concern regulation of cyclic nucleotide synthesis and
degradation, activities and expression of protein kinases A and G (PKA, PKG), calpains,
poly-ADP-ribose-polymerase (PARP), histone deacetylases (HDAC) as well as factors
implicated with oxidative stress (Figure 1). Particular emphasis is put on assessing metabolic
activity rather than gene/protein expression. New data generated is used to model
degenerative pathways active during retinal neurodegeneration (for an example see figure 2)
and serves as basis for the development of novel experimental treatments on in vitro retinal
explants and where appropriate on in vivo animal models.

Recent Publications

Paquet-Durand F, Beck S, Michalakis S, Goldmann T, Huber G, Mühlfriedel R, Trifunović D, Fischer MD, Fahl E, Duetsch G, Becirovic E, Wolfrum U, van Veen T, Biel M, Tanimoto N, Seeliger MW. (2011) A key role for cyclic nucleotide gated (CNG) channels in cGMP-related retinitis pigmentosa. Human Molecular Genetics, 20:941-7.
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Del Río P, Irmler M, Arango-González B, Favor J, Bobe C, Bartsch U, Vecino E, Beckers J, Hauck SM, Ueffing M. (2011) GDNF-induced osteopontin from Müller glial cells promotes photoreceptor survival in the Pde6brd1 mouse model of retinal degeneration. Glia 59:821-32. 
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Arango-Gonzalez B, Szabó A, Pinzon-Duarte G, Lukáts A, Guenther E, Kohler K (2010), "In vivo and in vitro development of S- and M-cones in rat retina.", Investigative Ophthalmology and Vision Science, May 12.  [Epub ahead of print]

Trifunović  D, Dengler  K, Michalakis S, Zrenner E, Wissinger B, Paquet-Durand F (2010)
"cGMP-dependent cone photoreceptor degeneration in the cpfl1 mouse retina.", Journal of Comparative Neurology, 518(17):3604-17.
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Sancho-Pelluz J, Alavi MV, Sahaboglu A, Kustermann S, Farinelli P, Azadi S, van Veen T,
Romero FJ, Paquet-Durand F, Ekström P (2010), "Excessive HDAC activation is critical for neurodegeneration in the rd1 mouse.", Cell Death & Disease, 1: e24; doi:10.1038/cddis.2010.4
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Selected Publications

Arango-González B, Cellerino A, Kohler K (2009), "Exogenous brain-derived neurotrophic factor (BDNF) reverts phenotypic changes in the retinas of transgenic mice lacking the BDNF gene.", Investigative Ophthalmology and  Vision Science, 50:1416-22.
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Paquet-Durand F, Hauck SM, van Veen T, Ueffing M, Ekström P (2009), "PKG activity causes photoreceptor cell death in two retinitis pigmentosa models.", Journal of Neurochemistry, 108:796-810.
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Sancho-Pelluz J, Arango-Gonzalez B, Kustermann S, Romero FJ,  van Veen T, Zrenner E, Ekström P, Paquet-Durand F (2008), "Photoreceptor cell death mechanisms in inherited retinal degeneration.", Molecular Neurobiology, 38:253-269.

Paquet-Durand F, Silva J, Talukdar T, Johnson L, Azadi S, Hauck S, Ueffing M, van Veen T, Ekström P (2007), "Excessive activation of poly (ADP-ribose) polymerase (PARP) contributes to inherited photoreceptor degeneration in the rd1 mouse.", Journal of Neuroscience, 27:10311-10319.
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Paquet-Durand, F., Azadi, S., Hauck, S. M., Ueffing, M., van Veen, T.,
Ekström, P. (2006): “Calpain is activated in degenerating photoreceptors
in the rd1 mouse”, Journal of Neurochemistry 96: 802-814.
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