Important anatomical, age-related, and species considerations regarding ocular fibulin-3 (EFEMP1) analysis

PurposeFibulin-3 (F3) or EFEMP1 is a secreted extracellular matrix glycoprotein implicated in several ocular diseases. Little is known about the native biology of this protein. Thus, our study aims to determine expression and localization characteristics of F3 utilizing a range of mammalian species as well as F3-associated changes with age. MethodsGene expression analyses for fibulins as well as immunohistochemistry for F3 were conducted in ocular tissue from mice, pigs, non-human primates (NHPs), and humans (n = 3-5). Age-based F3 expression study along with changes in ECM remodeling enzymes was also evaluated in mice. ResultsWithin the mouse retina, F3 staining was consistent throughout the entirety of the retina (far-periphery, mid-periphery, and central), being enriched in the ganglion cell layer and inner nuclear layer (INL). However, in humans, the F3 staining pattern was quite unique; enriched in the RPE, INL, and outer nuclear layer (ONL) in the peripheral retina, but then shifting to predominantly outer plexiform layer (OPL) staining in the central retina and macula with waning RPE immunoreactivity approaching the fovea. We demonstrate that F3 expression in the mouse retina significantly increases with age, and the levels of extracellular F3 degrading enzymes produced by the RPE and retina (e.g., Mmp2 and Htra1) decrease with age. ConclusionsThese findings demonstrate that F3 has distinct species-dependent as well as ocular region-specific expression and localization patterns. We also show that F3 and ECM enzyme dynamics favor F3 accumulation in the retina and RPE with increasing age.