Abstract
The human vitreous contains primarily water, but also contains proteins which have yet to be fully characterized. To gain insight into the four vitreous substructures and their potential functions, we isolated and analyzed the vitreous protein profiles of three non-diseased human eyes. The four analyzed substructures were the anterior hyaloid, the vitreous cortex, the vitreous core, and the vitreous base. Proteins were separated by multidimensional liquid chromatography and identified by tandem mass spectrometry. Bioinformatics tools then extracted the expression profiles, signaling pathways, and interactomes unique to each tissue. From each substructure, a mean of 2,062 unique proteins were identified, with many being differentially expressed in a specific substructure: 278 proteins were unique to the anterior hyaloid, 322 to the vitreous cortex, 128 to the vitreous base, and 136 to the vitreous core. When the identified proteins were organized according to relevant functional pathways and networks, key patterns appeared. The blood coagulation pathway and extracellular matrix turnover networks were highly represented. Oxidative stress regulation and energy metabolism proteins were distributed throughout the vitreous. Immune functions were represented by high levels of immunoglobulin, the complement pathway, damage-associated molecular patterns (DAMPs), and evolutionarily conserved antimicrobial proteins. The majority of vitreous proteins detected were intracellular proteins, some of which originate from the retina, including rhodopsin (RHO), phosphodiesterase 6 (PDE6), and glial fibrillary acidic protein (GFAP). This comprehensive analysis uncovers a picture of the vitreous as a biologically active tissue, where proteins localize to distinct substructures to protect the intraocular tissues from infection, oxidative stress, and energy disequilibrium. It also reveals the retina as a potential source of inflammatory mediators. The vitreous proteome catalogues the dynamic interactions between the vitreous and surrounding tissues. It therefore could be an indirect and effective method for surveying vitreoretinal disease for specific biomarkers.
Highlights
The vitreous is an optically transparent extracellular matrix that coats the retina, ciliary body, and lens.[1]
Proteins were separated by multidimensional liquid chromatography and identified by tandem mass spectrometry
A mean of 2,062 unique proteins were identified, with many being differentially expressed in a specific substructure: 278 proteins were unique to the anterior hyaloid, 322 to the vitreous cortex, 128 to the vitreous base, and 136 to the vitreous core
Summary
The vitreous is an optically transparent extracellular matrix that coats the retina, ciliary body, and lens.[1] The vitreous fills approximately 80% of the inner eye and is over 98% water.[2, 3] The remaining 2% contains proteins, polysaccharides, proteoglycans, and metabolites, but the physiologic function of this fraction is largely unknown.[4] In contrast, the pathological function of the vitreous is apparent in several retinal diseases.[2] Vitreoretinal traction, for example, underlies a number of acquired conditions that include retinal detachment, epiretinal membrane, proliferative diabetic retinopathy, macular hole, and proliferative vitreoretinopathy. Because mutations in vitreous collagens can lead to abnormal eye size and vitreoretinal degeneration,[5] a few congenital vitreoretinopathies provide some molecular insight. Surgical removal of the vitreous can be effective in managing many of these conditions, but the underlying molecular mechanisms remain poorly understood. The developmental and disease roles of the vitreous emphasize its structural function, but extracellular matrices have important biological functions that are revealed when the molecular components are known
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