In vivo phenotypic and molecular characterization of retinal degeneration in mouse models of three ciliopathies

Abstract

Cilia are highly conserved and ubiquitously expressed organelles. Ciliary defects of genetic origins lead to ciliopathies, in which retinal degeneration (RD) is one cardinal clinical feature. In order to efficiently find and design new therapeutic strategies the underlying mechanism of retinal degeneration of three murine model was compared. The rodent models correspond to three emblematic ciliopathies, namely: Bardet-Biedl Syndrome (BBS), Alström Syndrome (ALMS) and CEP290-mediated Leber Congenital Amaurosis (LCA). Scotopic rodent electroretinography (ERG) was used to test the retinal function of mice, Transmitted Electron microscopy (T.E.M) was performed to assess retinal structural defects and real-time PCR for targeted genes was used to monitor the expression levels of the major apoptotic Caspase-related pathways in retinal extracts to identify pathological pathways driving the RD in order to identify potential therapeutic targets. We found that BBS and CEP290-mediated LCA mouse models exhibit perinatal retinal degeneration associated with rhodopsin mislocalization in the photoreceptor and the induction of an Endoplasmic Reticulum (ER) stress. On the other hand, the tested ALMS mouse model, displayed a slower degeneration phenotype, with no Rhodopsin mislocalization nor ER-stress activity. Our data points out that behind the general phenotype of vision loss associated with these ciliopathies, the mechanisms and kinetics of disease progression are different.

Mouse Models of Inherited Retinal Degeneration with Photoreceptor Cell Loss

“…ALMS1 encodes a 460kDa protein that when disrupted results in the Alström syndrome (ALMS) [81,82]. Mice with a gene trap, frameshift, and nonsense mutations recapitulate human ALMS disease features such as obesity, diabetes, and neurosensory deficits [21,83,84]. The proper formation of the connecting cilium and the slow progression of PR cell loss in Alms1 Gt(XH152)Byg [83], Alms1 foz [84], and Alms1 tvrm102 [21] models suggests that ALMS1 is not essential for ciliary biogenesis but necessary for overall PR homeostasis.…”

Translational readthrough of ciliopathy genes BBS2 and ALMS1 restores protein, ciliogenesis and function in patient fibroblasts

“…ALMS1 is a basal body protein localised to the proximal end of the centriole and is therefore involved in ciliary protein transport and maintenance [ 29 , [31] , [32] , [33] ]. ALMS1 has a role in retinal development, guiding photoreceptor maturation and correct organisation, however its precise disease mechanism remains unclear [34] , [35] , [36] , [37] , [38] .…”

Magnetically Assisted Drug Delivery of Topical Eye Drops Maintains Retinal Function In Vivo in Mice

“…The mice were kept and bred in humidity-and temperature-controlled rooms on a 12-h light/dark cycle, on normal chow and water ad libitum. These three mouse models share the same UPR mechanism behind the apoptosis of the photoreceptors, and similar disease progression [11,12]. An extensive table with the mice and their genetic backgrounds in the experiments is found in Table S3.…”

“…Previously, we and others [10,11] demonstrated using mouse models that BBS-associated retinal degeneration was related to the pro-apoptotic activation of the unfolded protein response (UPR) associated with the gradual flattening of elettroretinogram (ERG) recordings, the thinning of the outer nuclear layer (ONL), and endoplasmic reticulum (ER) swelling. Different Bbs KO mice models have been shown to share similar UPR-related responses [11]. Based on these findings, we successfully repositioned two historical drugs: namely valproic acid (VPA) and guanabenz (GBZ), an anti-epileptic and anti-hypertensive drug, respectively.…”