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68.3.2 Morphology
Cpfl1 mice undergo a progressive selective degeneration of cone photoreceptor cells with age. To analyse morphological changes in the retina, in vivo cSLO and SDOCT analyses were performed. Since only about 3% of the murine photoreceptors are cones and these are widely spaced, no differences between wt and cpfl1 mice could be detected in native en face (cSLO) and cross sectional imaging (SD-OCT). In particular, no enhanced fundus autofluorescence as indicator of cumulative photoreceptor degeneration (Seeliger et al. 2005) was detected. To specifically analyse the fate of the cone photoreceptor cells in vivo, we cross-bred cpfl1 mice with the RG-GFP mouse line selectively expressing green fluorescent protein under control of a red-green opsin promotor (Fei and Hughes 2001). This allowed non-invasive imaging of individual cone photoreceptors in the autofluorescence mode of the cSLO. Timeline analysis of numbers and distribution of GFP positive cone photoreceptors in wild type and double mutant RG-GFP/cpfl1 mice revealed no change in the control animals (Fig. 68.2, top row), but a marked decrease in GFP expression over time in the RG-GFP/cpfl1 animals, leading to an almost complete loss of GFP expressing cells in the ventral region and a strong reduction in the dorsal region (Fig. 68.2, bottom row).
Fig. 68.2 Time course of GFP expression in RG-GFP mice and RG-GFP/cpfl1 mice analyzed by cSLO. In RG-GFP mice, the GFP expression remains constant between 3 and 8 weeks of age. Conversely, the expression decreases considerably over time in RG-GFP/cpfl1 mice with some reduction visible at 4 weeks and drastic changes at 6 weeks of age. At 8 weeks only few cones can be detected by GFP expression. V = ventral; D = dorsal
68.4 Discussion
The cpfl1 mouse model is known for a lack of cone mediated ERG responses (Chang et al. 2001; Chang et al. 2002). However, stringent ERG testing revealed a minimally intense photopic response indicating a low degree of residual cone photoreceptor
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function. Latter contrasts this line from an established functional rod-only model such as the Cnga3–/– mice (Biel et al. 1999).
In vivo imaging of cpfl1 mice demonstrated progressive cone photoreceptor degeneration with a marked reduction between 4 and 8 weeks of age, i.e. the functional deficit and the physical loss are independent in time. Already at 4 weeks of age, the cone system functions were strongly reduced in cpfl1 mice, although only a slight decrease in GFP expression could be observed in cSLO imaging of double mutant RG-GFP/cpfl1 mice at 4 weeks of age. This also explains why the respective human disease due to mutations in the PDE6C gene is usually classified as achromatopsia, clinically manifesting as a lack of cone function from birth (Wissinger et al. 2007), and not as a cone dystrophy, where cone function more closely follows the actual physical loss. Nevertheless, the processes involved may well be studied in the cpfl1 mouse model.
Structurally, the impact of cone degeneration on general retinal morphology remains limited. In cSLO and in the SD-OCT derived virtual cross sections, retinal architecture was seemingly unchanged (Fig. 68.3). This can at least partly be explained by the relatively slow degenerative process and the low number and sparse distribution of cones in the afoveate murine retina, whose remains may be removed without persistent degradation products often seen in rod degenerations as areas of enhanced fundus autofluorescence.
Fig. 68.3 In vivo imaging of cpfl1 mouse retinae shows essentially normal retinal configuration in the course of progressive cone photoreceptor degeneration. Left panels show normal fundus appearance of cpfl1 mice aged 4 (top) and 8 (bottom) weeks similar to WT mice (not shown) in native cSLO imaging modes. V = ventral; D = dorsal; λ 514 nm = argon laser (reflectance mode); λ 488 nm = argon laser (autofluorescence mode); white circles indicate orientation of respective SD-OCT scans shown in the right panels. SD-OCT derived virtual cross sections display essentially intact retinal architecture in cpfl1 mice at both time points similar to WT mice (not shown)
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In this work, we present in vivo functional and structural characteristics of the retina in the cpfl1 mouse model for cone dystrophy. In addition, we present a noninvasive method to follow the fate of single photoreceptors over time in individual mice and provide new aspects of residual cone function in the cpfl1 mouse model.
References
Chang B, Hawes NL, Hurd RE et al (2002) Retinal degeneration mutants in the mouse. Vis Res 42:517–525
Chang B, Hawes NL, Hurd RE et al (2001) A new mouse model of cone photoreceptor function loss (cpfl1) Invest Ophthalmol Vis Sci 42:ARVO E-Abstract S527
Seeliger MW, Grimm C, Stahlberg F et al (2001) New views on RPE65 deficiency: the rod system is the source of vision in a mouse model of Leber congenital amaurosis. Nat Genet 29:70–74 Seeliger MW, Beck SC, Pereyra-Munoz N et al (2005) In vivo confocal imaging of the retina in
animal models using scanning laser ophthalmoscopy. Vis Res 45:3512–3519 Wolf-Schnurrbusch UE, Enzmann V, Brinkmann CK et al (2008) Morphological changes in
patients with geographic atrophy assessed with a novel spectral OCT-SLO combination. Invest Ophthalmol Vis Sci 49:3095–3099
Biel M, Seeliger M, Pfeifer A et al (1999) Selective loss of cone function in mice lacking the cyclic nucleotide-gated channel CNG3. Proc Natl Acad Sci U S A 96:7553–7557
Jaissle GB, May CA, Reinhard J et al (2001) Evaluation of the rhodopsin knockout mouse as a model of pure cone function. Invest Ophthalmol Vis Sci 42:506–513
Fei Y, Hughes TE (2001) Transgenic expression of the jellyfish green fluorescent protein in the cone photoreceptors of the mouse. Vis Neurosci 18:615–623
Tanimoto N, Muehlfriedel RL, Fischer MD et al (2009) Vision tests in the mouse: functional phenotyping with electroretinography. Front Biosci 14:2730–2737
Wissinger B, Chang B, Dangel S et al. (2007) Cone phosphodiesterase defects in the murine cpfl1 mutant and human achromatopsia patients Invest Ophthalmol Vis Sci 48:ARVO E-Abstract B122
Chapter 69
The Differential Role of Jak/Stat Signaling
in Retinal Degeneration
C. Lange, M. Thiersch, M. Samardzija, and C. Grimm
Abstract Retinal degenerative diseases are a major cause of severe visual impairment or blindness in humans. To develop therapeutic strategies it is of particular importance to understand the molecular mechanisms taking place during the progression of the disease. Genes and proteins of the Janus kinase/Signal Transducer and Activator of Transcription (Jak/STAT) signaling pathway have been shown to play an important role in models of retinal degeneration (RD). Here we investigated the expression of additional genes involved in the Jak/STAT pathway in an induced (light exposure) and an inherited (rd1 mouse) model of RD. We show that STAT mRNAs as well as the Jak2/shp-1 pathway are differentially regulated in the two models. In contrast, we show that Jak3 mRNA is upregulated in both, the light damaged and the degenerative retina of the rd1 mouse. This common answer to probably different apoptotic stimuli suggests a prominent role for Jak3 in the damaged retina and could therefore be interesting for further investigations.
69.1 Introduction
Retinal degenerative diseases like retinitis pigmentosa (RP) are a frequent cause of severe visual impairment or blindness in human patients. They are characterized by the progressive loss of visual cells by apoptosis. Understanding the molecular mechanisms underlying the processes of photoreceptor degeneration and identifying endogenous rescue pathways is of fundamental importance to develop successful therapeutic strategies for this group of diseases.
There are various animal models, induced as well as inherited, to study retinal degenerations. In one model for induced retinal degeneration mice are exposed to bright light which causes photoreceptors to die by apoptosis (Reme et al. 1998; Grimm et al. 2000; Wenzel et al. 2005). Depending on the light intensity used and
C. Lange (B)
Lab for Retinal Cell Biology, Department of Ophthalmology, University of Zurich, Zurich, Switzerland
e-mail: christina.lange@usz.ch
R.E. Anderson et al. (eds.), Retinal Degenerative Diseases, Advances in Experimental |
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Medicine and Biology 664, DOI 10.1007/978-1-4419-1399-9_69,C Springer Science+Business Media, LLC 2010