The structural and functional integrity of rod photoreceptor ribbon synapses depends on redundant actions of dynamins 1 and 3.

Vertebrate vision begins with light absorption by rod and cone photoreceptors, which transmit signals from their synaptic terminals to second-order neurons: bipolar and horizontal cells. In mouse rods, there is a single presynaptic ribbon-type active zone at which release of glutamate occurs tonically in the dark. This tonic glutamatergic signaling requires continuous exo- and endocytosis of synaptic vesicles. At conventional synapses, endocytosis commonly requires dynamins: GTPases encoded by three genes (Dnm1-3), which perform membrane scission. Disrupting endocytosis by dynamin deletions impairs transmission at conventional synapses, but the impact of disrupting endocytosis and the role(s) of specific dynamin isoforms at rod ribbon synapses are understood incompletely. Here, we used cell-specific knockouts of the neuron-specific Dnm1 and Dnm3 to investigate the functional roles of dynamin isoforms in rod photoreceptors in mice of either sex. Analysis of synaptic protein expression, synapse ultrastructure, and retinal function via electroretinograms showed that dynamins 1 and 3 act redundantly and are essential for supporting the structural and functional integrity of rod ribbon synapses. Single Dnm3 knockout showed no phenotype, and single Dnm1 knockout only modestly reduced synaptic vesicle density without affecting vesicle size and overall synapse integrity; whereas, double Dnm1/Dnm3 knockout impaired vesicle endocytosis profoundly, causing enlarged vesicles, reduced vesicle density, reduced ERG responses, synaptic terminal degeneration, and disassembly and degeneration of postsynaptic processes. Concurrently, cone function remained intact. These results show the fundamental redundancy of dynamins 1 and 3 in regulating the structure and function of rod ribbon synapses.Significance Statement The process of vision starts with the capturing of light by rod and cone photoreceptors within the retina. Photoreceptors communicate with downstream retinal neurons at specialized sites called ribbon synapses, where vesicles of the neurotransmitter glutamate are released and recycled. The synaptic vesicle recycling process at conventional synapses commonly requires specialized proteins for membrane scission, typically dynamins 1 and 3. The role of dynamins in vesicle cycling at photoreceptor ribbon synapses, however, is not fully understood. Here, we specifically deleted dynamins 1 and 3 in rod photoreceptors using a conditional gene knockout approach and demonstrated the redundant role of dynamins 1 and 3 in maintaining rod photoreceptor ribbon synapse structure and function.

Polarized Desmosome and Hemidesmosome Shedding via Small Extracellular Vesicles is an Early Indicator of Outer Blood-Retina Barrier Dysfunction.

The retinal pigmented epithelium (RPE) constitutes the outer blood-retinal barrier, enables photoreceptor function of the eye, and is constantly exposed to oxidative stress. As such, dysfunction of the RPE underlies pathology leading to development of age-related macular degeneration (AMD), the leading cause of vision loss among the elderly in industrialized nations. A major responsibility of the RPE is to process photoreceptor outer segments, which relies on the proper functioning of its endocytic pathways and endosomal trafficking. Exosomes and other extracellular vesicles (EVs) from RPE are an essential part of these pathways and may be early indicators of cellular stress. To test the role of small EVs (sEVs) including exosomes, that may underlie the early stages of AMD, we used a polarized primary RPE cell culture model under chronic subtoxic oxidative stress. Unbiased proteomic analyses of highly purified basolateral sEVs from oxidatively stressed RPE cultures revealed changes in proteins involved in epithelial barrier integrity. There were also significant changes in proteins accumulating in the basal-side sub-RPE extracellular matrix during oxidative stress, that could be prevented with an inhibitor of sEV release. Thus, chronic subtoxic oxidative stress in primary RPE cultures induces changes in sEV content, including basal-side specific desmosome and hemidesmosome shedding via sEVs. These findings provide novel biomarkers of early cellular dysfunction and opportunity for therapeutic intervention in age-related retinal diseases (e.g., AMD).

Src family kinases engage differential pathways for encapsulation into extracellular vesicles.

Extracellular vesicles (EVs) are heterogeneous biological nanoparticles secreted by all cell types. Identifying the proteins preferentially encapsulated in secreted EVs will help understand their heterogeneity. Src family kinases including Src and Fyn are a group of tyrosine kinases with fatty acylation modifications and/or multiple lysine residues (contributing charge interaction) at their N-terminus. Here, we demonstrate that Src and Fyn kinases were preferentially encapsulated in EVs and fatty acylation including myristoylation and palmitoylation facilitated their encapsulation. Genetic loss or pharmacological inhibition of myristoylation suppressed Src and/or Fyn kinase levels in EVs. Similarly, loss of palmitoylation reduced Fyn levels in EVs. Additionally, mutation of lysine at sites 5, 7, and 9 of Src kinase also inhibited the encapsulation of myristoylated Src into EVs. Knockdown of TSG101, which is a protein involved in the endosomal sorting complexes required for transport (ESCRT) protein complex mediated EVs biogenesis and led to a reduction of Src levels in EVs. In contrast, filipin III treatment, which disturbed the lipid raft structure, reduced Fyn kinase levels, but not Src kinase levels in EVs. Finally, elevated levels of Src protein were detected in the serum EVs of host mice carrying constitutively active Src-mediated prostate tumors in vivo. Collectively, the data suggest that different EVs biogenesis pathways exist and can regulate the encapsulation of specific proteins into EVs. This study provides an understanding of the EVs heterogeneity created by different EVs biogenesis pathways.

Polarized Desmosome and Hemidesmosome Shedding via Exosomes is an Early Indicator of Outer Blood-Retina Barrier Dysfunction.

The retinal pigmented epithelium (RPE) constitutes the outer blood-retinal barrier, enables photoreceptor function of the eye, and is constantly exposed to oxidative stress. As such, dysfunction of the RPE underlies pathology leading to development of age-related macular degeneration (AMD), the leading cause of vision loss among the elderly in industrialized nations. A major responsibility of the RPE is to process photoreceptor outer segments, which relies on the proper functioning of its endocytic pathways and endosomal trafficking. Exosomes and other extracellular vesicles from RPE are an essential part of these pathways and may be early indicators of cellular stress. To test the role of exosomes that may underlie the early stages of AMD, we used a polarized primary RPE cell culture model under chronic subtoxic oxidative stress. Unbiased proteomic analyses of highly purified basolateral exosomes from oxidatively stressed RPE cultures revealed changes in proteins involved in epithelial barrier integrity. There were also significant changes in proteins accumulating in the basal-side sub-RPE extracellular matrix during oxidative stress, that could be prevented with an inhibitor of exosome release. Thus, chronic subtoxic oxidative stress in primary RPE cultures induces changes in exosome content, including basal-side specific desmosome and hemidesmosome shedding via exosomes. These findings provide novel biomarkers of early cellular dysfunction and opportunity for therapeutic intervention in age-related retinal diseases, (e.g., AMD) and broadly from blood-CNS barriers in other neurodegenerative diseases.

AAV Gene Augmentation of Truncated Complement Factor H Differentially Rescues Ocular Complement Dysregulation in a Mouse Model.

Purpose: Complement dysregulation in the eye has been implicated in the pathogenesis of age-related macular degeneration (AMD), and genetic variants of complement factor H (CFH) are strongly associated with AMD risk. We therefore aimed to untangle the role of CFH and its splice variant, factor H-like 1 (FHL-1), in ocular complement regulation derived from local versus circulating sources. We assessed the therapeutic efficacy of adeno-associated viruses (AAVs) expressing human FHL-1 and a truncated version of CFH (tCFH), which retains the functional N- and C-terminal ends of the CFH protein, in restoring the alternative complement pathway in Cfh-/- mouse eyes and plasma. Methods: Using Cfh-/- mice as a model of complement dysregulation, AAV vectors expressing tCFH or FHL-1 were injected subretinally or via tail vein, and the efficacy of the constructs was evaluated. Results: Following subretinal injections, tCFH expression rescued factor B (FB) retention in the eye, but FHL-1 expression did not. By contrast, both constructs restored FB detection in plasma following tail vein injections. Both tCFH and FHL-1 proteins accumulated in the posterior eyecup from the circulation following liver transduction; however, neither was able to significantly regulate local ocular complement. Conclusions: Our findings demonstrate that the C-terminus of human CFH is necessary for complement regulation in the murine eye. Furthermore, exogenous CFH must be synthesized locally to maximize complement regulation in the retina. These findings establish a critical foundation for development of CFH augmentation-based gene therapies for the eye.

Distinct Phenotypic Consequences of Pathogenic Mutants Associated with Late-Onset Retinal Degeneration.

A pathologic feature of late-onset retinal degeneration caused by the S163R mutation in C1q-tumor necrosis factor-5 (C1QTNF5) is the presence of unusually thick deposits between the retinal pigmented epithelium (RPE) and the vascular choroid, considered a hallmark of this disease. Following its specific expression in mouse RPE, the S163R mutant exhibits a reversed polarized distribution relative to the apically secreted wild-type C1QTNF5, and forms widespread, prominent deposits that gradually increase in size with aging. The current study shows that S163R deposits expand to a considerable thickness through a progressive increase in the basolateral RPE membrane, substantially raising the total RPE height, and enabling their clear imaging as a distinct hyporeflective layer by noninvasive optical coherence tomography in advanced age animals. This phenotype bears a striking resemblance to ocular pathology previously documented in patients harboring the S163R mutation. Therefore, a similar viral vector-based gene delivery approach was used to also investigate the behavior of P188T and G216C, two novel pathogenic C1QTNF5 mutants recently reported in patients for which histopathologic data are lacking. Both mutants primarily impacted the RPE/photoreceptor interface and did not generate basal laminar deposits. Distinct distribution patterns and phenotypic consequences of C1QTNF5 mutants were observed in vivo, which suggested that multiple pathobiological mechanisms contribute to RPE dysfunction and vision loss in this disorder.

Continuous Hypoxia Reduces Retinal Ganglion Cell Degeneration in a Mouse Model of Mitochondrial Optic Neuropathy.

Purpose: To test whether continuous hypoxia is neuroprotective to retinal ganglion cells (RGCs) in a mouse model of mitochondrial optic neuropathy. Methods: RGC degeneration was assessed in genetically modified mice in which the floxed gene for the complex I subunit NDUFS4 is deleted from RGCs using Vlgut2-driven Cre recombinase. Beginning at postnatal day 25 (P25), Vglut2-Cre;ndufs4loxP/loxP mice and control littermates were housed under hypoxia (11% oxygen) or kept under normoxia (21% oxygen). Survival of RGC somas and axons was assessed at P60 and P90 via histological analysis of retinal flatmounts and optic nerve cross-sections, respectively. Retinal tissue was also assessed for gliosis and neuroinflammation using western blot and immunofluorescence. Results: Consistent with our previous characterization of this model, at least one-third of RGCs had degenerated by P60 in Vglut2-Cre;ndufs4loxP/loxP mice remaining under normoxia. However, continuous hypoxia resulted in complete rescue of RGC somas and axons at this time point, with normal axonal myelination observed on electron microscopy. Though only partial, hypoxia-mediated rescue of complex I-deficient RGC somas and axons remained significant at P90. Hypoxia prevented reactive gliosis at P60, but the retinal accumulation of Iba1+ mononuclear phagocytic cells was not substantially reduced. Conclusions: Continuous hypoxia achieved dramatic rescue of early RGC degeneration in mice with severe mitochondrial dysfunction. Although complete rescue was not durable to P90, our observations suggest that investigating the mechanisms underlying hypoxia-mediated neuroprotection of RGCs may identify useful therapeutic strategies for optic neuropathies resulting from less profound mitochondrial impairment, such as Leber hereditary optic neuropathy.

Encapsulating Cas9 into extracellular vesicles by protein myristoylation.

CRISPR/Cas9 genome editing is a very promising avenue for the treatment of a variety of genetic diseases. However, it is still very challenging to encapsulate CRISPR/Cas9 machinery for delivery. Protein N-myristoylation is an irreversible co/post-translational modification that results in the covalent attachment of the myristoyl-group to the N-terminus of a target protein. It serves as an anchor for a protein to associate with the cell membrane and determines its intracellular trafficking and activity. Extracellular vesicles (EVs) are secreted vesicles that mediate cell-cell communication. In this study, we demonstrate that myristoylated proteins were preferentially encapsulated into EVs. The octapeptide derived from the leading sequence of the N-terminus of Src kinase was a favourable substrate for N-myristoyltransferase 1, the enzyme that catalyzes myristoylation. The fusion of the octapeptide onto the N-terminus of Cas9 promoted the myristoylation and encapsulation of Cas9 into EVs. Encapsulation of Cas9 and sgRNA-eGFP inside EVs was confirmed using protease digestion assays. Additionally, to increase the transfection potential, VSV-G was introduced into the EVs. The encapsulated Cas9 in EVs accounted for 0.7% of total EV protein. Importantly, the EVs coated with VSV-G encapsulating Cas9/sgRNA-eGFP showed up to 42% eGFP knock out efficiency with limited off-target effects in recipient cells. Our study provides a novel approach to encapsulate CRISPR/Cas9 protein and sgRNA into EVs. This strategy may open an effective avenue to utilize EVs as vehicles to deliver CRISPR/Cas9 for genome-editing-based gene therapy.

Electrochemical micro-aptasensors for exosome detection based on hybridization chain reaction amplification.

Exosomes are cell-derived nanovesicles that have recently gained popularity as potential biomarkers in liquid biopsies due to the large amounts of molecular cargo they carry, such as nucleic acids and proteins. However, most existing exosome-based analytical sensing methods struggle to achieve high sensitivity and high selectivity simultaneously. In this work, we present an electrochemical micro-aptasensor for the highly sensitive detection of exosomes by integrating a micropatterned electrochemical aptasensor and a hybridization chain reaction (HCR) signal amplification method. Specifically, exosomes are enriched on CD63 aptamer-functionalized electrodes and then recognized by HCR products with avidin-horseradish peroxidase (HRP) attached using EpCAM aptamers as bridges. Subsequently, the current signal that is generated through the enzyme reaction between the HRP enzyme and 3,3',5,5'-tetramethylbenzidine (TMB)/H2O2 directly correlates to the amount of bound HRP on the HCR products and thus to the number of target exosomes. By introducing anti-EpCAM aptamers, micro-aptasensors can detect cancerous exosomes with high specificity. Due to the micropatterned electrodes and HCR dual-amplification strategy, the micro-aptasensors achieve a linear detection response for a wide range of exosome concentrations from 2.5×103 to 1×107 exosomes/mL, with a detection limit of 5×102 exosomes/mL. Moreover, our method successfully detects lung cancer exosomes in serum samples of early-stage and late-stage lung cancer patients, showcasing the great potential for early cancer diagnosis.

Complement-mediated release of fibroblast growth factor 2 from human RPE cells.

PURPOSE: Complement activation is associated with choroidal neovascularization (CNV) in age-related macular degeneration (AMD). Fibroblast growth factor 2 (FGF2) and membrane attack complex (MAC) are present in eyes of patients with CNV. Herein, we investigated the effect of complement activation on FGF2 release in human retinal pigment epithelial (RPE) cells. METHODS: Cultured human RPE cells were primed with an anti-RPE antibody and then treated with C1q-depleted human serum in the presence or absence of Tec kinases inhibitor (LFM-A13). 38 cytokines/chemokines levels were measured by Luminex technology. Secretion of FGF2 and interleukin (IL)-6 was assessed by ELISA. Tec protein was measured by Western blot. mRNA expression of FGF2, chemokine (C-X-C motif) ligand 1 (CXCL-1), and family members of Tec kinases was evaluated by qPCR. Cell viability and MAC deposition were determined by WST-1 assay and flow cytometry, respectively. RESULTS: Complement activation caused increased FGF2 and IL-6 release. FGF2 was released when C6-depleted human serum was reconstituted with C6. Anti-C5 antibody significantly attenuated complement-mediated FGF2 release, but not IL-6. FGF2 mRNA levels were not affected, while CXCL-1 mRNA levels were increased by complement activation. FGF2-containing extracellular vesicles were detected in response to complement challenge. Tec mRNA and protein were expressed in RPE cells. In the presence of LFM-A13, secretion of FGF2, but not IL-6, and MAC deposition were significantly decreased and cell viability was significantly increased in complement-treated cells when compared to controls. CONCLUSIONS: Complement plays an important role to release FGF2 from RPE cells. Tec kinase is involved in MAC formation and complement-mediated FGF2 release. This information suggests a role for complement activation to mediate neovascularization in conditions such as AMD, and may elucidate potential therapeutic targets.

Progressive optic atrophy in a retinal ganglion cell-specific mouse model of complex I deficiency.

Optic atrophy resulting from retinal ganglion cell (RGC) degeneration is a prominent ocular manifestation of mitochondrial dysfunction. Although transgenic mice lacking the mitochondrial complex I accessory subunit NDUFS4 develop early-onset optic atrophy, severe systemic mitochondrial dysfunction leads to very early death and makes this mouse line impractical for studying the pathobiology of mitochondrial optic neuropathies. Theoretically, RGC-specific inactivation of ndufs4 would allow characterization of RGC degeneration over a longer time course, provided that RGC death from mitochondrial dysfunction is a cell-autonomous process. We demonstrate that the vesicular glutamate transporter VGLUT2 may be exploited to drive robust Cre recombinase expression in RGCs without any expression observed in directly neighboring retinal cell types. Deletion of ndufs4 in RGCs resulted in reduced expression of NDUFS4 protein within the optic nerves of Vglut2-Cre;ndufs4loxP/loxP mice. RGC degeneration in Vglut2-Cre;ndufs4loxP/loxP retinas commenced around postnatal day 45 (P45) and progressed to loss of two-thirds of RGCs by P90, confirming that intrinsic complex I dysfunction is sufficient to induce RGC death. The rapidly-developing optic atrophy makes the Vglut2-Cre;ndufs4loxP/loxP mouse line a promising preclinical model for testing therapies for currently untreatable mitochondrial optic neuropathies such as Leber Hereditary Optic Neuropathy.

High-density lipoproteins are a potential therapeutic target for age-related macular degeneration.

Strong evidence suggests that dysregulated lipid metabolism involving dysfunction of the retinal pigmented epithelium (RPE) underlies the pathogenesis of age-related macular degeneration (AMD), the leading cause of irreversible blindness in the elderly. A hallmark of AMD is the overproduction of lipid- and protein-rich extracellular deposits that accumulate in the extracellular matrix (Bruch's membrane (BrM)) adjacent to the RPE. We analyzed apolipoprotein A-1 (ApoA-1)-containing lipoproteins isolated from BrM of elderly human donor eyes and found a unique proteome, distinct from high-density lipoprotein (HDL) isolated from donor plasma of the same individuals. The most striking difference is higher concentrations of ApoB and ApoE, which bind to glycosaminoglycans. We hypothesize that this interaction promotes lipoprotein deposition onto BrM glycosaminoglycans, initiating downstream effects that contribute to RPE dysfunction/death. We tested this hypothesis using two potential therapeutic strategies to alter the lipoprotein/protein profile of these extracellular deposits. First, we used short heparan sulfate oligosaccharides to remove lipoproteins already deposited in both the extracellular matrix of RPE cells and aged donor BrM tissue. Second, an ApoA-1 mimetic, 5A peptide, was demonstrated to modulate the composition and concentration of apolipoproteins secreted from primary porcine RPE cells. Significantly, in a mouse model of AMD, this 5A peptide altered the proteomic profile of circulating HDL and ameliorated some of the potentially harmful changes to the protein composition resulting from the high-fat, high-cholesterol diet in this model. Together, these results suggest that targeting HDL interactions with BrM represents a new strategy to slow AMD progression in humans.

Isolation of Retinal Exosome Biomarkers from Blood by Targeted Immunocapture.

The retinal pigmented epithelium (RPE) forms the outer blood-retinal barrier, provides nutrients, recycles visual pigment, and removes spent discs from the photoreceptors, among many other functions. Because of these critical roles in visual homeostasis, the RPE is a principal location of disease-associated changes in age-related macular degeneration (AMD), emphasizing its importance for study in both visual health and disease. Unfortunately, there are no early indicators of AMD or disease progression, a void that could be filled by the development of early AMD biomarkers. Exosomes are lipid bilayer membrane vesicles of nanoscale sizes that are released in a controlled fashion by cells and carry out a number of extra- and intercellular activities. In the RPE they are released from both the apical and basal sides, and each source has a unique signature/content. Exosomes released from the basolateral side of RPE cells enter the systemic circulation via the choroid and thus represent a potential source of retinal disease biomarkers in blood. Here we discuss the potential of targeted immunocapture of eye-derived exosomes and other small extracellular vesicles from blood for eye disease biomarker discovery.

Photoreceptors in a mouse model of Leigh syndrome are capable of normal light-evoked signaling.

Mitochondrial dysfunction is an important cause of heritable vision loss. Mutations affecting mitochondrial bioenergetics may lead to isolated vision loss or life-threatening systemic disease, depending on a mutation's severity. Primary optic nerve atrophy resulting from death of retinal ganglion cells is the most prominent ocular manifestation of mitochondrial disease. However, dysfunction of other retinal cell types has also been described, sometimes leading to a loss of photoreceptors and retinal pigment epithelium that manifests clinically as pigmentary retinopathy. A popular mouse model of mitochondrial disease that lacks NADH:ubiquinone oxidoreductase subunit S4 (NDUFS4), a subunit of mitochondrial complex I, phenocopies many traits of the human disease Leigh syndrome, including the development of optic atrophy. It has also been reported that ndufs4-/- mice display diminished light responses at the level of photoreceptors or bipolar cells. By conducting electroretinography (ERG) recordings in live ndufs4-/- mice, we now demonstrate that this defect occurs at the level of retinal photoreceptors. We found that this deficit does not arise from retinal developmental anomalies, photoreceptor degeneration, or impaired regeneration of visual pigment. Strikingly, the impairment of ndufs4-/- photoreceptor function was not observed in ex vivo ERG recordings from isolated retinas, indicating that photoreceptors with complex I deficiency are intrinsically capable of normal signaling. The difference in electrophysiological phenotypes in vivo and ex vivo suggests that the energy deprivation associated with severe mitochondrial impairment in the outer retina renders ndufs4-/- photoreceptors unable to maintain the homeostatic conditions required to operate at their normal capacity.

Microglial Function Is Distinct in Different Anatomical Locations during Retinal Homeostasis and Degeneration.

Microglia from different nervous system regions are molecularly and anatomically distinct, but whether they also have different functions is unknown. We combined lineage tracing, single-cell transcriptomics, and electrophysiology of the mouse retina and showed that adult retinal microglia shared a common developmental lineage and were long-lived but resided in two distinct niches. Microglia in these niches differed in their interleukin-34 dependency and functional contribution to visual-information processing. During certain retinal-degeneration models, microglia from both pools relocated to the subretinal space, an inducible disease-associated niche that was poorly accessible to monocyte-derived cells. This microglial transition involved transcriptional reprogramming of microglia, characterized by reduced expression of homeostatic checkpoint genes and upregulation of injury-responsive genes. This transition was associated with protection of the retinal pigmented epithelium from damage caused by disease. Together, our data demonstrate that microglial function varies by retinal niche, thereby shedding light on the significance of microglia heterogeneity.

Microglia are not required for prion-induced retinal photoreceptor degeneration.

Degeneration of photoreceptors in the retina is a major cause of blindness in humans. Often retinal degeneration is due to inheritance of mutations in genes important in photoreceptor (PR) function, but can also be induced by other events including retinal trauma, microvascular disease, virus infection or prion infection. The onset of apoptosis and degeneration of PR neurons correlates with invasion of the PR cellular areas by microglia or monocytes, suggesting a causal role for these cells in pathogenesis of PR degenerative disease. To study the role of microglia in prion-induced retinal disease, we fed prion-infected mice a CSF-1 receptor blocking drug, PLX5622, to eliminate microglia in vivo, and the effects on retinal degeneration were analyzed over time. In mice not receiving drug, the main inflammatory cells invading the degenerating PR areas were microglia, not monocytes. Administration of PLX5622 was highly effective at ablating microglia in retina. However, lack of microglia during prion infection did not prevent degeneration of PR cells. Therefore, microglia were not required for the PR damage process during prion infection. Indeed, mice lacking microglia had slightly faster onset of PR damage. Similar results were seen in C57BL/10 mice and transgenic mice expressing GFP or RFP on microglia and monocytes, respectively. These results were supported by experiments using prion-infected Cx3cr1 knockout mice without PLX5622 treatment, where microglial expansion in retina was delayed, but PR degeneration was not. Contrary to predictions, microglia were not a causative factor in retinal damage by prion infection. Instead, newly generated PrPSc accumulated around the inner segment region of the PR cells and appeared to correlate with initiation of the pathogenic process in the absence of microglia.

Human complement factor H Y402H polymorphism causes an age-related macular degeneration phenotype and lipoprotein dysregulation in mice.

One of the strongest susceptibility genes for age-related macular degeneration (AMD) is complement factor H (CFH); however, its impact on AMD pathobiology remains unresolved. Here, the effect of the principal AMD-risk-associated CFH variant (Y402H) on the development and progression of age-dependent AMD-like pathologies was determined in vivo. Transgenic mice expressing equal amounts of the full-length normal human CFH Y402 (CFH-Y/0) or the AMD-risk associated CFH H402 (CFH-H/H) variant on a Cfh-/- background were aged to 90 weeks and switched from normal diet (ND) to a high fat, cholesterol-enriched (HFC) diet for 8 weeks. The resulting phenotype was compared with age-matched controls maintained on ND. Remarkably, an AMD-like phenotype consisting of vision loss, increased retinal pigmented epithelium (RPE) stress, and increased basal laminar deposits was detected only in aged CFH-H/H mice following the HFC diet. These changes were not observed in aged CFH-Y/0 mice or in younger (36- to 40-week-old) CFH mice of both genotypes fed either diet. Biochemical analyses of aged CFH mice after HFC diet revealed genotype-dependent changes in plasma and eyecup lipoproteins, but not complement activation, which correlated with the AMD-like phenotype in old CFH-H/H mice. Specifically, apolipoproteins B48 and A1 are elevated in the RPE/choroid of the aged CFH-H/H mice compared with age-matched control CFH-Y/0 fed a HFC diet. Hence, we demonstrate a functional consequence of the Y402H polymorphism in vivo, which promotes AMD-like pathology development and affects lipoprotein levels in aged mice. These findings support targeting lipoproteins as a viable therapeutic strategy for treating AMD.

Author Correction: Directional Exosome Proteomes Reflect Polarity-Specific Functions in Retinal Pigmented Epithelium Monolayers.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Polarized Exosome Release from the Retinal Pigmented Epithelium.

The retinal pigmented epithelium (RPE) forms the outer blood-retinal barrier and provides nutrients and recycling of visual pigment to the photoreceptors, among many other functions. The RPE is also a key site of pathophysiological changes in age-related macular degeneration, making it an important focus of study in both visual health and disease. Exosomes are nanometer-sized vesicles that are released by cells in a controlled fashion and mediate a range of extra- and intercellular activities. Some key exosome actions include cell-cell communication, immune modulation, extracellular matrix turnover, stem cell division/differentiation, neovascularization, and cellular waste removal. While much is known about their role in cancer and cardiovascular disease, exosome function in the many specialized tissues of the eye is just beginning to undergo rigorous study. Here we review current knowledge of the functions and roles of exosomes and other small extracellular vesicles released from the RPE. In particular, we discuss the potential role and importance of polarized exosome release from the RPE.