Mouzaaber, C. | Search bioRxiv

bioRxiv2026

Peroxisome dysfunction alters metabolism of photoreceptor outer segments in human retinal pigment epithelium

Peroxisomes are ubiquitous organelles that compartmentalize metabolic reactions including lipid catabolism and cellular detoxification. Pathogenic variants in PEX1 and PEX6 disrupt essential peroxisome functions and cause profound neurodegenerative diseases called peroxisome biogenesis disorders (PBDs). Despite retinal degeneration and blindness occurring frequently in PBDs, precisely how impaired peroxisome activity disrupts retinal function remains to be fully explored. To address this, we differentiated PEX1-/-, PEX6-/-, and wildtype human induced pluripotent stem cells into retinal pigment epithelium (iRPE) to study the consequences of peroxisome dysfunction in this disease-relevant cell type. Despite exhibiting impaired peroxisome matrix protein import, PEX1-/- and PEX6-/-iRPE had comparable morphology, tight junctions, and expression of proteins characteristic of RPE compared to wildtype iRPE. Targeted lipid profiling revealed reduced docosahexaenoic acid, a polyunsaturated fatty acid (PUFA) essential for retinal function, and elevated lipid species exclusively metabolized by peroxisomes in PEX1-/- and PEX6-/- iRPE. Following a photoreceptor outer segment (POS) challenge, PEX1-/- and PEX6-/- iRPE demonstrated disrupted PUFA retroconversion and lipid droplet accumulation. Additionally, PEX1-/- and PEX6-/-iRPE had impaired rhodopsin degradation, lysosomal dysfunction, and reduced transepithelial electrical resistance. These findings suggest that dysregulated POS metabolism in the RPE is a potential mechanism driving retinal degeneration in patients with PBDs. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/701576v2_ufig1.gif" ALT="Figure 1"> View larger version (99K): org.highwire.dtl.DTLVardef@bf2389org.highwire.dtl.DTLVardef@b62e1forg.highwire.dtl.DTLVardef@8e0b21org.highwire.dtl.DTLVardef@17cb332_HPS_FORMAT_FIGEXP M_FIG C_FIG Schematic summarizing the consequences of PEX1 and PEX6 knockout on iRPE biology, including the presence of import-incompetent peroxisomes, impaired {omega}3 and {omega}6 fatty acid retroconversion, lipid droplet accumulation, and defective photoreceptor outer segment phagocytosis.

cell biology↗

bioRxiv2023

Development and characteristics of photoreceptor actin-based apical processes in zebrafish (Danio rerio)

Vertebrate photoreceptors detect light through a large cilium-based outer segment, which is filled with photopigment-laden membranous discs. Surrounding the base of the outer segment are microvilli-like calyceal processes (CPs). While CP disruption has been associated with altered outer segment morphology and photoreceptor degeneration, the role of the processes remains elusive. Here, we used zebrafish as a model to characterize CPs. We quantified CP parameters and report a strong disparity in outer segment coverage between photoreceptor subtypes. CP length is stable across light and dark conditions, while heat shock inducible expression of tagged actin revealed rapid turnover of the CP actin core. Detailed imaging of the embryonic retina uncovered substantial remodeling of the developing photoreceptor apical surface, including a transition from dynamic tangential processes to vertically-oriented CPs immediately prior to outer segment formation. Remarkably, we also found a direct connection between apical extensions of the Muller glia and retinal pigment epithelium, arranged as bundles around the ultraviolet sensitive cones. In summary, our data characterize the structure, development, and surrounding environment of photoreceptor microvilli in the zebrafish retina.

cell biology↗