ABSTRACT
Inherited defects in retinal photoreceptor structure impair visual transduction, disrupt relationship with the retinal pigment epithelium (RPE), and compromise cell viability. A variety of progressive retinal degenerative diseases can result, and knowledge of disease etiology remains incomplete. To investigate pathogenic mechanisms in such instances, we have characterized rod photoreceptor and retinal gene expression changes in response to a defined insult to photoreceptor structure, using the retinal degeneration slow (rds) mouse model. Global gene expression profiling was performed on flow-sorted rds and wild-type rod photoreceptors immediately prior and subsequent to times at which OSs are normally elaborated. Dysregulated genes were identified via microarray hybridization, and selected candidates were validated using quantitative PCR analyses. Both the array and qPCR data revealed that gene expression changes were generally modest and dispersed amongst a variety of known functional networks. Although genes showing major (>5-fold) differential expression were identified in a few instances, nearly all displayed transient temporal profiles, returning to WT levels by postnatal day (P) 21. These observations suggest that major defects in photoreceptor cell structure may induce early homeostatic responses, which function in a protective manner to promote cell viability. We identified a single key gene, Egr1, that was dysregulated in a sustained fashion in rds rod photoreceptors and retina. Egr1 upregulation was associated with microglial activation and migration into the outer retina at times subsequent to the major peak of photoreceptor cell death. Interestingly, this response was accompanied by neurotrophic factor upregulation. We hypothesize that activation of Egr1 and neurotrophic factors may represent a protective immune mechanism which contributes to the characteristically slow retinal degeneration of the rds mouse model.
Subject(s)
Gene Expression Regulation , Genetic Diseases, Inborn/genetics , Genetic Diseases, Inborn/prevention & control , Photoreceptor Cells, Vertebrate/pathology , Retinal Degeneration/genetics , Retinal Degeneration/prevention & control , Animals , Antigens, CD/metabolism , Antigens, Differentiation, Myelomonocytic/metabolism , Disease Models, Animal , Early Growth Response Protein 1/metabolism , Gene Expression Profiling , Genetic Diseases, Inborn/immunology , Genetic Diseases, Inborn/pathology , Homeostasis/genetics , Mice , Mice, Inbred C57BL , Microglia/metabolism , Microglia/pathology , Nerve Growth Factors/genetics , Nerve Growth Factors/metabolism , Neuroprotective Agents/metabolism , Oligonucleotide Array Sequence Analysis , Photoreceptor Cells, Vertebrate/immunology , Photoreceptor Cells, Vertebrate/metabolism , Polymerase Chain Reaction , Reproducibility of Results , Retinal Degeneration/immunology , Retinal Degeneration/pathology , Up-Regulation/geneticsABSTRACT
Secreted Wnt proteins play essential roles in many biological processes during development and diseases. However, little is known about the mechanism(s) controlling Wnt secretion. Recent studies have identified Wntless (Wls) and the retromer complex as essential components involved in Wnt signaling. While Wls has been shown to be essential for Wnt secretion, the function(s) of the retromer complex in Wnt signaling is unknown. Here, we have examined a role of Vps35, an essential retromer subunit, in Wnt signaling in Drosophila and mammalian cells. We provide compelling evidence that the retromer complex is required for Wnt secretion. Importantly, Vps35 colocalizes in endosomes and interacts with Wls. Wls becomes unstable in the absence of retromer activity. Our findings link Wls and retromer functions in the same conserved Wnt secretion pathway. We propose that retromer influences Wnt secretion by recycling Wntless from endosomes to the trans-Golgi network (TGN).
