Cathepsin proteases mediate photoreceptor cell degeneration in Drosophila
ABSTRACT Endocytosis-mediated cell death is a form of degeneration displayed in several Drosophila mutants. This form of degeneration is displayed in several Drosophila mutant lines including flies lacking the eye-specific PLC (norpA). The cell death pathway is initiated by the stabilization of complexes between rhodopsin and arrestin which undergo massive endocytosis into the cell body. The internalized rhodopsin becomes insoluble and builds up in the late endosomal system, wherein it triggers cell death. Cathepsins are resident late endosome/lysosome proteases that have been shown to mediate apoptosis in many disease models. Therefore we sought to test the involvement of cathepsins in endocytosis-mediated retinal degeneration. Here we show that cathepsins mediate cell death in light-exposed norpA eyes. Moreover, we show that the cathepsin L-like cysteine protease, CP1, specifically mediates retinal degeneration, while the aspartyl protease, cathepsin D, does not. Furthermore, eye-specific expression of pan-cathepsin inhibitors also blocks cell death. Western blot analysis demonstrates that cathepsin L levels remain unchanged during retinal degeneration. However, whole mount immunohistochemistry performed on light-exposed retinas revealed a decrease in cathepsin L levels and a loss of rhodopsin/ CP1 colocalization, suggesting that cathepsin L translocates during the degeneration process. Lastly, we show that the retinal degeneration can be enhanced by the overexpression of cathepsin L in the sensitized norpA background. Together these data show that cathepsins play a crucial role in endocytosis-mediated retinal degeneration and are consistent with a model where rhodopsin internalization and accumulation in the endosomal/lysosomal system triggers cathepsin translocation to the cytosol.
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ABSTRACT: Cysteine cathepsins are a family of proteases involved in intracellular protein turnover and extracellular matrix degradation. Cathepsin B (Ctsb) and cathepsin Z (Ctsz) promote tumorigenesis and Ctsb is a known modulator of tumor angiogenesis. We therefore investigated the angiomodulatory function of these cathepsins in vitro as well as in a mouse model of laser-induced choroidal neovascularization (laser-CNV). Ctsb(-/-), Ctsz(-/-), Ctsb/Ctsz double-knockout (Ctsb/z DKO), and wild type (WT) mice underwent argon laser treatment to induce choroidal neovascularization (CNV). The neovascularized area was quantified individually for each lesion at 14 days after laser coagulation. In vitro the effects of cathepsin inhibitors on angiogenesis were analysed by endothelial cell (EC) spheroid sprouting and EC invadosome assays. Retinas from cathepsin KO mice did not show gross morphological abnormalities. In the laser CNV model, however, Ctsb/z DKO mice displayed a significantly reduced neovascularized area compared to WT (0.027mm(2) vs. 0.052mm(2); p=0.012), while single knockouts did not differ significantly from WT. In line, VEGF-induced EC spheroid sprouting and invadosome formation were not significantly altered by a specific cathepsin B inhibitor alone, but significantly suppressed when more than one cathepsin was inhibited. Our results demonstrate that laser-CNV formation is significantly reduced in Ctsb/z DKO mice. In line, EC sprouting and invadosome formation are blunted when more than one cathepsin is inhibited in vitro. These results reveal an angiomodulatory potential of cathepsins with partial functional redundancies between different cathepsin family members.Experimental Eye Research 06/2013; 115. DOI:10.1016/j.exer.2013.06.014 · 3.02 Impact Factor
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ABSTRACT: Cathepsin L is a cysteine protease which degrades connective tissue proteins including collagen, elastin, and fibronectin. In this study, five well-characterized cathepsin L proteins from different arthropods were used as query sequences for the Drosophila genome database. The search yielded 10 cathepsin L-like sequences, of which eight putatively represent novel cathepsin L-like proteins. To understand the phylogenetic relationship among these cathepsin L-like proteins, a phylogenetic tree was constructed based on their sequences. In addition, models of the tertiary structures of cathepsin L were constructed using homology modeling methods and subjected to molecular dynamics simulations to obtain reasonable structure to understand its dynamical behavior. Our findings demonstrate that all of the potential Drosophila cathepsin L-like proteins contain at least one cathepsin propeptide inhibitor domain. Multiple sequence alignment and homology models clearly highlight the conservation of active site residues, disulfide bonds, and amino acid residues critical for inhibitor binding. Furthermore, comparative modeling indicates that the sequence/structure/function profiles and active site architectures are conserved.Journal of biomolecular Structure & Dynamics 12/2012; 31(12). DOI:10.1080/07391102.2012.745379 · 2.98 Impact Factor
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ABSTRACT: Purpose: Mutations in the CLN6 gene cause variant late-infantile neuronal ceroid lipofuscinosis, a lysosomal storage disorder clinically characterized by progressive loss of vision, dementia, seizures and early death. Here, we analyzed the time course of photoreceptor loss and the role of lysosomes in nclf mice, an animal model of the human CLN6 disease. Methods: Labeling of apoptotic cells, activated astrocytes and Müller cells, and expression analyses of glial fibrillary acidic protein, rhodopsin and lysosomal proteins were performed on nclf mice during the course of retinal degeneration. In addition, the distribution and variability of storage material was examined at the ultrastructural level. Results: Progressive apoptotic loss of photoreceptor cells was observed in nclf mice resulting in reduction of the outer nuclear layer to ~3 rows of photoreceptor cells at 9 months of age. Onset of reactive gliosis was observed in 1 month old nclf mice. Ultrastructural analysis revealed lysosomal storage material containing curvilinear and fingerprint-like inclusions in various retinal cell types. Expression levels of soluble mannose 6-phosphate-containing lysosomal enzymes such as cathepsin D and the lysosomal membrane protein Lamp1 were increased in retinal cells of nclf mice. Conclusions: Accumulation of heterogeneous non-degraded macromolecules in dysfunctional lysosomes and autolysosomes impairs photoreceptor cells, ultimately leading to early-onset apoptotic death with subsequent activation of astrocytes and Müller cells in the retina of nclf mice. The defined steps of photoreceptor degeneration suggest that nclf mice might serve as an ideal animal model for experimental therapeutic approaches aimed at attenuating vision loss in neuronal ceroid lipofuscinosis.Investigative ophthalmology & visual science 10/2013; 54(10). DOI:10.1167/iovs.13-12945 · 3.66 Impact Factor