About our work
The mission of our section (NGIRDS) is to explore and understand the fundamental biological mechanisms underlying retinal diseases and translate these findings into proof-of-concept clinical studies to discover new therapies. We have the following starting point: that discovering the interactions between the cellular (neuronal and glia) components of the retina and elucidating how these may be pathological altered are central to the understanding and management of retinal disease. Because many retinal diseases such as diabetic retinopathy, retinal vein occlusions, age-related macular degeneration, involve a key inflammatory component, NGIRDS has focused on the study of the resident immune cell in the retina, the microglial cell, and how it interacts with other retinal cells in the healthy and diseased retina. We have summarized some or our perspectives on how microglia function in the retina in a recent review (Silverman and Wong, Annu Rev Vis Sci., 2018).
Our unit operates at 3 levels with a central focus on retinal microglia:
- Basic scientific study of the retina, addressing the cellular mechanisms in the healthy retina: Basic study of the microglia cell in the retina, involving its morphology, physiology, and cellular interactions with other retinal cell types
- Translational study of the retina in disease models: Preclinical study of the involvement of retinal microglia in the aging retina, and in models of retinal disease
- Clinical study of retinal diseases and its manifestations: Clinical study of the inflammatory involvement in common retinal diseases, including the targeting inflammation and microglial activation as a therapeutic strategy in proof-of-concept Phase I/II clinical trials.
Our key areas of work are:
Understanding the basic physiology of microglia in the retina
Given that microglia are the primary resident immune cell type in the retina, we aim to investigate the following questions: What everyday roles do microglia play in the healthy adult retina? What kinds of communications exist between microglia and the surrounding retina neurons and glia? What signals arising from retinal cells help organize the distribution, morphology, and activation states of microglia and maintain their homeostasis? The answers are central to elucidating the basic function of microglia and are relevant to establishing a foundation for the development of therapeutic approaches aimed at microglial modulation as a strategy for retinal diseases.
Previous research from our unit has shown that “resting” retinal microglia possess a highly ordered distribution in the laminated structure of the retina, forming a regularly-tiled network of morphologically ramified cells. We have found that processes of retinal microglia are dynamically motile, providing extensive coverage of the surrounding parenchyma (Lee et al., IOVS, 2008). We discovered that retinal microglial morphology, behavior, and activation are not regulated solely by cell-autonomous mechanisms but involve external signals from surrounding neurons and macroglia (Müller cells and astrocytes). These signals include: (1) neurotransmission via glutamatergic, GABAergic, and purinergic signaling (Fontainhas et al., PLoS One, 2011; Wong et al., Neuron Glia Biol.), (2) CX3CL1 chemokine signaling from retinal neurons (Liang et al., IOVS, 2009), and (3) signals from Müller glia via inflammatory cytokine and DBI-TSPO signaling that regulate microglial activation (Wang et al., J. Neuroinflammation, 2011; Wang, Zhao, et al., J. Neurosci., 2014; Wang and Wong, Adv Exp Med Biol., 2014).
What constitutive functions do microglia play in the healthy adult retina? We had examined how microglia contribute to normal neuronal function in the uninjured adult retina by depleting microglia in a genetic model (Wang, Zhao et al., J. Neurosci., 2016) over a sustained period of time. We found no significant changes in the: (1) laminar appearance or thickness in the retina, (2) densities of neuronal populations (RGCs, amacrine cells, bipolar cells, horizontal cells, rod or cone photoreceptors, or (3) morphology of retinal neurons and macroglia (astrocytes and Müller cells). However, on functional evaluation, we found that sustained microglial depletion resulted in the progressive deterioration in the electroretinographic (ERG) response, which were correlated with synaptic degeneration that was appreciable on the level of electron microscopy. Our study was the first to show a requirement for microglia in the maintenance of synaptic integrity in the CNS, and reveal the place that microglia have in the healthy function of the retina.
The requirement for microglia in the healthy retina is also evident in the mechanisms that maintain microglial homeostasis under normal conditions. We found that perturbations, such as depleting the retina of microglia, induces a spontaneous recovery of microglial numbers and organization that fully recapitulates the status quo. This response is driven by the proliferation and migration of residual microglia, under the guidance of neuron-to-microglia signals, such as CX3CL1-CX3CR1 signaling (Zhang, Zhao, et al., Science Advances, 2018).
To understand how microglia undergo change in the aging retina and how this contributes to age-related retinal disease
Our research in Focus Area 1 revealed that microglia in the young healthy adult retina are highly integrated into their environment and continually exchange signals with retinal cells in functionally significant ways. With aging, both microglia and their environment can undergo progressive senescent changes that alter the balance of this relationship. As retinal microglia are long lived cells with tenures extending across much of an animal’s lifespan, we explore in this focus area the following hypotheses:(1) microglia features are not static but instead develop aging phenotypes that are functionally significant, (2) the development of aging phenotypes in microglia are driven by cell-autonomous and environmental factors, and (3) microglial senescent changes help confer on the aged retina an increased vulnerability to disease. In our previous work, we demonstrated that retinal microglia in mouse models do indeed demonstrate senescent changes in terms of their morphology, dynamic process motility, and distribution (Damani et al., Aging Cell, 2011). We discovered that aged microglia display an altered response to injury signals, being slower to respond to acute injury but also slower to revert back to a resting state following injury resolution. These aging phenotypes support the notion that aged microglia decline in their ability to carry out constitutive functions, and respond to injury in a more dysregulated and less reversible way, contributing to greater chronic pro-inflammatory activation states associated with aging (Wong, Front Cell Neurosci. 2013; Ma and Wong, Adv Exp Med Biol., 2016). We discovered through gene profiling studies that retinal microglia demonstrate progressive changes in the expression of genes involved in immune function, angiogenesis, trophic factors, and complement regulation (Ma et al., Neurobiology of Aging, 2013a). We also found that aging microglia accumulate (1) A2E, the primary bisretinoid constitutent of ocular lipofuscin, and (2) 7-ketocholesterol, an oxidized lipid. These factors whose levels increase with aging in the retina, conferred onto microglia a phenotype favoring greater pro-inflammatory and pro-angiogenic influences, and increased complement activation (Ma et al., Neurobiology of Aging, 2013b, Indaram et al., Scientific Reports, 2015).
To understand how microglia are altered in retinal disease, how they may drive disease progression, and how they can be inhibited in preclinical experiments and in clinical trials
In Focus Area 3, we study how microglia and other innate immune cells in the retina are altered in the context of retinal disease and contribute to disease progression. We are interested in (1) understanding the cellular and molecular mechanisms involved in the pathological interactions between microglia and affected retinal cells, (2) discovering therapeutic agents and new strategies for intervention, and (3) conducting proof-of-concept clinical studies that can demonstrate microglial modulation as a therapeutic strategy. We have previously discovered in a mouse model for retinitis pigmentosa (RP) that microglia can contribute non-cell autonomously to the overall rate of photoreceptor degeneration in RP via phagocytosis and pro-inflammatory mechanisms (Zhao, Zabel et al., EMBO Mol. Med. 2015). We discovered that the following molecular mechanisms are involved: (1) phagocytosis via the vitronectin receptor, (2) production of the inflammatory cytokine IL1β, and (3) CX3CL1-CX3CR1 signaling between retinal neurons and microglia that regulates microglial phagocytosis and activation (Zabel, Zhao et al., Glia, 2016). We also recently discovered that tamoxifen, a drug previously associated with retinal toxicity, paradoxically conferred protection to photoreceptors via its ability to suppress microglia activation (Wang et al., J. Neuroscience, 2017). These studies together outline the contributions that retinal microglia can make to photoreceptor degeneration and highlight some candidate pathways and pharmacological agents that can be exploited for the therapeutic strategy of microglial modulation to ameliorate photoreceptor loss in a variety of retinal diseases.
In addition, we are also interested in further investigating the roles of resident microglia vs. infiltrating monocytes in modulating overall immune responses in the injured retina. Our recent work has uncovered the presence of infiltrating monocytes in different models of retinal injury (Ma et al., Sci. Reports, 2018; Zhao, Zabel., EMBO Mol. Med. 2015), that respond to both neural injury and the need to restore homeostasis to the myeloid cell population in the retina. How these populations and responses contribute in disease and how they should be modulated form part of our future translational goals.
Silverman, S. M., Wong, W.T.Microglia in the Retina: Roles in Development, Maturity, and Disease. Annual Reviews in Vision Science, 2018; 4:45-77.doi: 10.1146/annurev-vision-091517-034425.
Zhang, Y, Zhao, L, Wang, X, Ma, W, Lazere, A, Qian, H.-h, Zhang, J, Abu-Asab, M., Fariss, R.N., Roger, J.E., Wong, W.T.* Repopulating microglia restore endogenous organization and function under CX3CL1-CX3CR1 regulation. Science Advances,2018, 21;4:eaap8492. PMCID: PMC5943055.https://www.drugtargetreview.com/news/30654/microglia-retina-regenerate/(link is external)https://www.nih.gov/news-events/nih-research-matters/immune-cell-regeneration-mouse-retina(link is external)
Ma, W., Zhang, Y., Gao, C., Fariss, R.N., Tam, J., Wong, W.T.Monocyte infiltration and proliferation reestablish myeloid cell homeostasis in the mouse retina following retinal pigment epithelial cell injury.Scientific Reports, 2017; 7:8433. PMC5559448
Wang, X., Zhao, L., Zhang, Y., Ma, W., Gonzalez, S., Fan, J., Kretschmer, F., Badea, T., Qian, H-h., Wong, W.T. Tamoxifen provides structural and functional rescue in murine models of photoreceptor degeneration. Journal of Neuroscience, 2017; 37:3294-3310.PMC5373119. https://www.eurekalert.org/pub_releases/2017-03/sfn-jhf032217.php(link is external)
Singaravelu, J., Zhao, L., Fariss, R.N., Nork, T. M., Wong, W.T.* Microglia in the primate macula: Specializations in microglial distribution and morphology with retinal position and with aging.Brain Structure Function; 2017; 222:2759-2771. PMC5542874
Zabel, M.Kǂ., Zhao, Lǂ., Zhang ,Y., Gonzalez, S.R., Ma, W., Wang, X., Fariss, R.N., Wong, W.T.* Microglial phagocytosis and activation underlying photoreceptor degeneration is regulated by CX3CL1-CX3CR1 signaling in a mouse model of retinitis pigmentosa. Glia, 2016; 64(9):1479-1491. (ǂ indicates equal contribution). PMC 4958518
Wang Xǂ, Zhao Lǂ, Zhang J, Fariss RN, Ma W, Kretschmer F, Wang M, Qian HH, Badea TC, Diamond JS, Gan WB, Roger JE, Wong WT.* Requirement for Microglia for the Maintenance of Synaptic Function and Integrity in the Mature Retina. Journal of Neuroscience, 2016; 36:2827-42. (ǂ indicates equal contribution) (Cover Article). PMC4879218
Zhao, L.ǂ, Zabel, M.K. ǂ, Wang, X., Ma, W., Shah, P., Fariss, R.N., Qian, H., Parkhurst, C.N., Gan, W-B., Wong, W.T.* Microglial phagocytosis of living photoreceptors contributes to inherited retinal degeneration. EMBO Molecular Medicine, 2015, 7:1179-1197 (ǂ indicates equal contribution)(Cover Article). https://nei.nih.gov/news/pressrelease/blinding_eye_disease PMC4568951
Indaram M‡, Ma W‡, Zhao L, Fariss RN, Rodriguez IR, Wong WT. 7-Ketocholesterol Increases Retinal Microglial Migration, Activation, and Angiogenicity: A Potential Pathogenic Mechanism Underlying Age-related Macular Degeneration. Scientific Reports, 2015, 5:9144. (‡ indicates equal contribution).
Wang, M, Wang, X, Zhao, L, Ma, W, Rodriguez, IR, Fariss, RN, Wong, WT. Macroglia-Microglia Interactions via TSPO Signaling Regulates Microglial Activation in the Mouse Retina. Journal of Neuroscience, 2014, 34:3793-3806.
Kumar, A., Zhao, L., Fariss, R.N., McMenamin, P.G., Wong, W.T. Vascular associations and dynamic process motility in perivascular myeloid cells of the mouse choroid: implications for function and senescent change. Investigative Ophthalmology and Visual Science, 2014, 55:1787-96.
Wong, W.T. Microglial Aging in the Healthy CNS: Phenotypes, Drivers, and Rejuvenation. Frontiers in Cellular Neuroscience, 2013, 7:22.
Ma, W., Cojocaru, R., Gotoh, N., Gieser, L., Villasmil, R., Cogliati, T., Swaroop, A., Wong, W.T. Gene expression changes in aging retinal microglia: relationship to microglial support functions and regulation of activation. Neurobiology of Aging, 2013, 34:2310-21.
Condren, A.B., Kumar, A., Mettu, P., Liang, K.J., Zhao, L., Tsai, J-Y., Fariss, R.N., Wong, W.T. Perivascular mural cells of the mouse choroid demonstrate morphological diversity that is correlated with vasoregulatory function. PLoS One, 2013;8(1):e53386.
Ma, W., Coon, S., Zhao, L., Fariss, R.N., Wong, W.T. A2E accumulation influences retinal microglial activation and complement regulation. Neurobiology of Aging, 2013, 34(3):943-60.
Wang, M., Ma, W., Zhao, L., Fariss, R.N., Wong, W.T. Adaptive Muller Cell Responses to Microglial Activation Mediate Neuroprotection and Coordinate Inflammation in the Retina. Journal of Neuroinflammation, 2011; 8:173.
Zhao, L, Ma, W.X., Fariss, R.N., Wong, W.T. Minocycline attenuates photoreceptor degeneration in a mouse model of subretinal hemorrhage: microglial inhibition as a potential therapeutic strategy. American Journal of Pathology, 2011; 179:1265-77.
Damani, M., Zhao, L., Fontainhas, A.M., Amaral, J., Fariss, R.N., Wong, W.T. Age-related Alterations in the Dynamic Behavior of Microglia. Aging Cell, 2011;10:263-76.
Wong, W.T., Wang, M., Li, W. Regulation of Microglia by Ionotropic Glutamatergic and GABAergic Neurotransmission. Neuron Glia Biology, 2011; 14:1-6.
Petrou PA, Cunningham D, Shimel K, Harrington M, Hammel K, Cukras CA, Ferris FL, Chew EY, Wong WT. Intravitreal sirolimus for the treatment of geographic atrophy: results of a phase I/II clinical trial. Invest Ophthalmol Vis Sci. 2014, 56:330-8
Toy, B.C., Krishnadev, N., Indaram, M., Cunningham, D., Cukras, C.A., Chew, E.Y., Wong, W.T. Drusen regression is associated with local changes in fundus autofluorescence in intermediate age-related macular degeneration. American Journal of Ophthalmology, 2013;156:532-542
Wong, W.T., Dresner, S., Forooghian, F., Glaser, T., Doss, L., Zhou, M., Cunningham, D., Shimel, K., Harrington, M., Hammel, K., Cukras, C.A., Ferris, F.L., Chew, E.Y. Treatment of Geographic Atrophy with Subconjunctival Sirolimus: Results of a Phase I/II Clinical Trial. Investigative Ophthalmology and Visual Science, 2013, 54:2941-50.
Meleth, A.D., Toy, B.C., Nigam, D., Agron, E., Chew, E.Y., Wong, W.T. Prevalence and Progression of Pigment Clumping Associated with Idiopathic Macular Telangiectasia Type 2 (IMT2). Retina, 2013, 33:762-70.
Toy, B.C., Agrón, E., Nigam, D., Chew, E.Y., Wong, W.T. Longitudinal Analysis of Retinal Hemangioblastomatosis and Visual Function in Ocular von Hippel-Lindau Disease. Ophthalmology, 2012, 119(12):2622-30.
Cukras, C.A., Petrou, P., Chew, E.Y., Meyerle, C.B., Wong, W.T. Oral Minocycline for the Treatment of Diabetic Macular Edema (DME): Results of a Phase I/II Clinical Study. Investigative Ophthalmology and Visual Science, 2012, 22: 3865-74.
Meleth, A.D., Mettu, P., Agron, E., Chew, E.Y., Sadda, S.R., Ferris, F.L., Wong, W.T. Changes in Retinal Sensitivity in Geographic Atrophy Progression as Measured by Microperimetry. Investigative Ophthalmology and Visual Science, 2011;52:1119-26.
Forooghian, F., Chew, E.Y., Meyerle, C.B., Cukras, C., Wong, W.T. Investigation of the Role of Neutralizing Antibodies Against Bevacizumab as Mediators of Tachyphylaxis. Acta Ophthalmologica, 2011; 89:e206-7.
Wong, W.T., Kam, W, Cunningham D., Harrington, M., Hammel, K., Meyerle, C.B., Cukras, C., Chew, E.Y., Sadda, S.R., Ferris, F.L. Treatment of Geographic Atrophy by the Topical Administration of OT-551: Results of a Phase II Clinical Trial. Investigative Ophthalmology and Visual Science, 2010; 51:6131-9.