Abstract
Purpose :
Mutations in the transmembrane transporter and receptor STRA6 cause Matthew-Wood syndrome in human, characterized by microphthalmia-anophthalmia, heart defects and diaphragmatic hernia. STRA6 is the only known ocular receptor for RBP4-retinol, and facilitates bidirectional transport of retinol into the retinal pigment epithelium (RPE) from circulating blood. In nonocular cells, STRA6 has been proposed to mediate cytokine signaling to the JAK-STAT, p53 and Wnt/β-catenin pathways. Though these pathways have been shown to have important roles in the retina and RPE for survival, immune status, visual cycle regulation, and cytokine response, no study of the role of STRA6 signaling in the eye has been undertaken. Deletion of the entire stra6 gene in the cone-rich zebrafish provides valuable insight into the signaling cascades mediated through this membrane-bound receptor.
Methods :
Following CRISPR/Cas9 of zebrafish stra6 to establish a viable mutant line, adult stra6-/- mutant and wild-type RPEs transcriptomes were analyzed by bulk RNAseq. Subsequently, unbiased gene-set enrichment analysis was used to determine pathways up- or downregulated following loss of Stra6. Finally, nicotinamide-matured human wild-type and STRA6-/- ARPE-19 cells were functionally assessed for mitochondrial function using Seahorse analysis.
Results :
We see that several pathways associated with mitochondrial activity and function are downregulated in stra6-/- RPE: oxidative phosphorylation, electron transport chain, assembly of multiple mitochondrial complexes. Conversely, only the epithelial-mesenchymal transition pathway was significantly upregulated with stra6 deletion. Finally, loss of STRA6 in human ARPE-19 cells greatly diminished maximum respiratory oxygen consumption, likely indicating mitochondrial dysfunction.
Conclusions :
Loss of STRA6 from RPE in both whole eye and cultured cells is associated with pathological changes that likely reduce its function to support photoreceptors. Without normal RPE functional support, photoreceptors suffer, with consequences mirroring blinding pathologies such as age-related macular degeneration and retinitis pigmentosa, whose earliest defects are often seen in the RPE. Characterizing the signaling pathways mediated through STRA6 in the RPE will reveal important sites of therapeutic intervention to treat or prevent visual diseases affecting the RPE and photoreceptors.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.