Toward Postgenomics Ophthalmology: A Proteomic Map of the Human Choroid–Retinal Pigment Epithelium Tissue

Aldehyde oxidase 1 activity and protein expression in human, rabbit, and pig ocular tissues

Aldehyde oxidase (AOX) is a cytosolic drug-metabolizing enzyme which has attracted increasing attention in drug development due to its high hepatic expression, broad substrate profile and species differences. In contrast, there is limited information on the presence and activity of AOX in extrahepatic tissues including ocular tissues. Because several ocular drugs are potential substrates for AOX, we performed a comprehensive analysis of the AOX1 expression and activity profile in seven ocular tissues from humans, rabbits, and pigs. AOX activities were determined using optimized assays for the established human AOX1 probe substrates 4-dimethylamino-cinnamaldehyde (DMAC) and phthalazine. Inhibition studies were undertaken in conjunctival and retinal homogenates using well-established human AOX1 inhibitors menadione and chlorpromazine. AOX1 protein contents were quantitated with targeted proteomics and confirmed by immunoblotting. Overall, DMAC oxidation rates varied over 10-fold between species (human ˃˃ rabbit ˃ pig) and showed 2- to 6-fold differences between tissues from the same species. Menadione seemed a more potent inhibitor of DMAC oxidation across species than chlorpromazine. Human AOX1 protein levels were highest in the conjunctiva, followed by most posterior tissues, whereas anterior tissues showed low levels. The rabbit AOX1 expression was high in the conjunctiva, retinal pigment epithelial (RPE), and choroid while lower in the anterior tissues. Quantification of pig AOX1 was not successful but immunoblotting confirmed the presence of AOX1 in all species. DMAC oxidation rates and AOX1 contents correlated quite well in humans and rabbits. This study provides, for the first time, insights into the ocular expression and activity of AOX1 among multiple species.

Proteomic Analysis of Human Breast Cancer MCF-7 Cells to Identify Cellular Targets of the Anticancer Pigment OR3 from Streptomyces coelicolor JUACT03

Search for ideal compounds with known pathways of anticancer mechanism is still a priority research focus for cancer, as it continues to be a major health challenge across the globe. Hence, in the present study, anticancer potential of a yellow pigment fraction, OR3, isolated from Streptomyces coelicolor JUACT03 was assessed on the breast cancer cell line MCF-7. TLC-fractionated OR3 pigment was subjected to HPLC and GC-MS analysis for characterization and identification of the bioactive component. MCF-7 cells were treated with IC₅₀ concentration of OR3 and the molecular alterations were analyzed using mass spectrometry-based quantitative proteomic analysis. Bioinformatics tools such as STRING analysis and Ingenuity Pathway Analysis were performed to analyze proteomics data and to identify dysregulated signaling pathways. As per our obtained data, OR3 treatment decreased cell proliferation and induced apoptotic cell death due to significant dysregulation of protein expressions in MCF-7 cells. Altered expression included the ribosomal, mRNA processing and vesicle-mediated transport proteins as a result of OR3 treatment. Downregulation of MAPK proteins, NFkB, and estradiol signaling was identified in OR3-treated MCF-7 cells. Mainly eIF2, mTOR, and eIF4 signaling pathways were altered in OR3-treated cells. GC-MS data indicated the presence of novel compounds in OR3 fraction. It can be concluded that OR3 exhibits potent anticancer activity on the breast cancer cells mainly through altering the expression and affecting the signaling proteins which are involved in different cell proliferation/apoptotic pathways thereby causing inhibition of cancer cell proliferation, survival and metastasis.

Retinal Pigment Epithelium-Secreted VEGF-A Induces Alpha-2-Macroglobulin Expression in Endothelial Cells

Alpha-2-macroglobulin (A2M) is a protease inhibitor that regulates extracellular matrix (ECM) stability and turnover. Here, we show that A2M is expressed by endothelial cells (ECs) from human eye choroid. We demonstrate that retinal pigment epithelium (RPE)-conditioned medium induces A2M expression specifically in ECs. Experiments using chemical inhibitors, blocking antibodies, and recombinant proteins revealed a key role of VEGF-A in RPE-mediated A2M induction in ECs. Furthermore, incubation of ECs with RPE-conditioned medium reduces matrix metalloproteinase-2 gelatinase activity of culture supernatants, which is partially restored after A2M knockdown in ECs. We propose that dysfunctional RPE or choroidal blood vessels, as observed in retinal diseases such as age-related macular degeneration, may disrupt the crosstalk mechanism we describe here leading to alterations in the homeostasis of choroidal ECM, Bruch's membrane and visual function.

Immune modulation by the macrophage migration inhibitory factor (MIF) family: D-dopachrome tautomerase (DDT) is not (always) a backup system

Human macrophage migration inhibition factor (MIF) is a protein with cytokine and chemokine properties that regulates a diverse range of physiological functions related to innate immunity and inflammation. Most research has focused on the role of MIF in different inflammatory diseases. D-dopachrome tautomerase (DDT), a different molecule with structural similarities to MIF, which shares receptors and biological functions, has recently been reported, but little is known about its roles and mechanisms. In this review, we sought to understand the similarities and differences between these molecules by summarizing what is known about their different structures, receptors and mechanisms regulating their expression and biological activities with an emphasis on immunological aspects.

Plasma proteomic profiles differ between European and North American myotid bats colonized by Pseudogymnoascus destructans

Emerging fungal diseases have become challenges for wildlife health and conservation. North American hibernating bat species are threatened by the psychrophilic fungus Pseudogymnoascus destructans (Pd) causing the disease called white-nose syndrome (WNS) with unprecedented mortality rates. The fungus is widespread in North America and Europe, however, disease is not manifested in European bats. Differences in epidemiology and pathology indicate an evolution of resistance or tolerance mechanisms towards Pd in European bats. We compared the proteomic profile of blood plasma in healthy and Pd-colonized European Myotis myotis and North American Myotis lucifugus in order to identify pathophysiological changes associated with Pd colonization, which might also explain the differences in bat survival. Expression analyses of plasma proteins revealed differences in healthy and Pd-colonized M. lucifugus, but not in M. myotis. We identified differentially expressed proteins for acute phase response, constitutive and adaptive immunity, oxidative stress defence, metabolism and structural proteins of exosomes and desmosomes, suggesting a systemic response against Pd in North American M. lucifugus but not European M. myotis. The differences in plasma proteomic profiles between European and North American bat species colonized by Pd suggest European bats have evolved tolerance mechanisms towards Pd infection.

The Human Eye Proteome Project: Updates on an Emerging Proteome

The human eye is a complex organ consisting of multiple compartments with unique and specialized properties that reflect their varied functions. Although there have been advancements in ocular imaging and therapeutics over the past decade, the pathogenesis of many common eye diseases remains poorly understood. Proteomics is an invaluable tool to gain insight into pathogenesis, diagnosis, and treatment of eye diseases. By 2013, when the Human Eye Proteome Project (also known as the EyeOme) was founded, there were 4842 nonredundant proteins identified in the human eye. Twenty-three recent papers on the human eye proteome were identified in PubMed searches. These papers were used to compile an updated resource of 9782 nonredundant proteins in the human eye. This updated catalogue sheds light on the molecular makeup of previously undescribed proteomes within the human eye, including optic nerve, sclera, iris, and ciliary body, while adding additional proteins to previously characterized proteomes such as aqueous humor, lens, vitreous, retina, and retinal pigment epithelium/choroid. Although considerable advances have been made to characterize the complete proteome of the human eye, additional high-quality data are needed to confirm and quantify previously discovered eye proteins in both health and disease.

Human Optic Nerve: An Enhanced Proteomic Expression Profile

Ophthalmology and visual health are new frontiers for postgenomic research and technologies such as proteomics. In this context, the optic nerve and retina extend as the outgrowth of the brain, wherein the latter receives the optical input and the former relays the information for processing. While efforts to understand the optic nerve proteome have been made earlier, there exists a lacuna in its biochemical composition and molecular functions. We report, in this study, a high-resolution mass spectrometry-based approach using an Orbitrap Fusion Tribrid mass spectrometer to elucidate the human optic nerve proteomic profile. Raw spectra were searched against NCBI Human RefSeq 75 database using SEQUEST HT and MASCOT algorithms. We identified nearly 35,000 peptides in human optic nerve samples, corresponding to 5682 proteins, of which 3222 proteins are being reported for the first time. Label-free quantification using spectral abundance pointed out to neuronal structural proteins such as myelin basic protein, glial fibrillary acidic protein, and proteolipid protein 1 as the most abundant proteins. We also identified several neurotransmitter receptors and postsynaptic density synaptosomal scaffold proteins. Pathway analysis revealed that a majority of the proteins are structural proteins and have catalytic and binding activity. This study is one of the largest proteomic profiles of the human optic nerve and offers the research community an initial baseline optic nerve proteome for further studies. This will also help understand the protein dynamics of the human optic nerve under normal conditions.

Proteomic Analysis of the Human Olfactory Bulb

The importance of olfaction to human health and disease is often underappreciated. Olfactory dysfunction has been reported in association with a host of common complex diseases, including neurological diseases such as Alzheimer's disease and Parkinson's disease. For health, olfaction or the sense of smell is also important for most mammals, for optimal engagement with their environment. Indeed, animals have developed sophisticated olfactory systems to detect and interpret the rich information presented to them to assist in day-to-day activities such as locating food sources, differentiating food from poisons, identifying mates, promoting reproduction, avoiding predators, and averting death. In this context, the olfactory bulb is a vital component of the olfactory system receiving sensory information from the axons of the olfactory receptor neurons located in the nasal cavity and the first place that processes the olfactory information. We report in this study original observations on the human olfactory bulb proteome in healthy subjects, using a high-resolution mass spectrometry-based proteomic approach. We identified 7750 nonredundant proteins from human olfactory bulbs. Bioinformatics analysis of these proteins showed their involvement in biological processes associated with signal transduction, metabolism, transport, and olfaction. These new observations provide a crucial baseline molecular profile of the human olfactory bulb proteome, and should assist the future discovery of biomarker proteins and novel diagnostics associated with diseases characterized by olfactory dysfunction.