Developing Treatment Paradigms for Age-Related Macular Degeneration

Project Overview

Age-related macular degeneration (AMD) is one of the leading causes of blindness among the elderly affecting over 30 million individuals world-wide. AMD initiates in the back of the eye because of dysfunctions in the retinal pigment epithelium (RPE), a monolayer of cells that maintains vision through maintenance of photoreceptor healthy and integrity. AMD can lead to severe vision loss and blindness in advanced stages – “dry” and “wet” forms. In the dry stage, the death of RPE cells triggers photoreceptor cell death and atrophy of the choroidal blood supply causing vision loss. It is thought that RPE cell death in AMD is triggered by the formation of sub-RPE protein/lipid deposits called drusen. Our recent work shows that drusen formation is initiated by reduced autophagic flux in RPE cells resulting in reduced ability of RPE cells to process intracellular “debris” that eventually gets secreted as drusen deposits. TFEB, a member of MiT family of transcription factors is a known master regulator of autophagy. Here, we propose to investigate the activity of transcription factor TEFB in our AMD cellular models of iPSC-derived RPE cells. We hypothesize that autophagy downregulation is triggered by post-translational changes in TFEB that affect its sub-cellular localization and reduce its transcriptional activity. Here, we propose to identify those changes in TEFB and discover signaling pathways that lead to its altered activity. Lastly, we will test the ability of our recently discovered FDA-approved drugs that stimulate TEFB activity to reduce drusen formation by increasing autophagy in iPSC-RPE AMD models. This work will lead to a better understanding of AMD pathogenesis and potentially retool existing  drugs to treat AMD patients.

Training Opportunities

This project will provide opportunities to undertake research aimed at retooling FDA-approved drugs for treatment of AMD. The project will not only decipher the mode of action of the drugs already identified in our screen by focussing on their effects on signaling pathways regulating TFEB sub-cellular localization and autophagy, but will also use our recently discovered marker of dormant stem cells to identify and characterise RPE and retinal stem cells. We have also developed a novel fluorescence radiometric stem cell reporter that will be tested for the isolation of live RPE/retinal stem cells cells and their characterisation.Techniques and tools available include high-resolution microscopy, single cell mRNA-sequencing and proteomics as well as standard molecular and cell biology tools. 

Theme

Physiology, Cellular & Molecular Biology

Admissions

Project reference number: 980

Funding and admissions information

Supervisors

Name Department Institution Country Email
Professor Colin R Goding Oxford Ludwig Institute Oxford University, Old Road Campus Research Building GBR colin.goding@ludwig.ox.ac.uk
Dr Kapil Bharti Occular Stem Cell &Translational Research National Institutes of Health USA kapil.bharti@nih.gov

Falletta P, Sanchez-Del-Campo L, Chauhan J, Effern M, Kenyon A, Kershaw CJ, Siddaway R, Lisle R, Freter R, Daniels MJ, Lu X, Tüting T, Middleton M, Buffa FM, Willis AE, Pavitt G, Ronai ZA, Sauka-Spengler T, Hölzel M, Goding CR. 2017. Translation reprogramming is an evolutionarily conserved driver of phenotypic plasticity and therapeutic resistance in melanoma. Genes Dev., 31 (1), pp. 18-33. Read abstract | Read more

The intratumor microenvironment generates phenotypically distinct but interconvertible malignant cell subpopulations that fuel metastatic spread and therapeutic resistance. Whether different microenvironmental cues impose invasive or therapy-resistant phenotypes via a common mechanism is unknown. In melanoma, low expression of the lineage survival oncogene microphthalmia-associated transcription factor (MITF) correlates with invasion, senescence, and drug resistance. However, how MITF is suppressed in vivo and how MITF-low cells in tumors escape senescence are poorly understood. Here we show that microenvironmental cues, including inflammation-mediated resistance to adoptive T-cell immunotherapy, transcriptionally repress MITF via ATF4 in response to inhibition of translation initiation factor eIF2B. ATF4, a key transcription mediator of the integrated stress response, also activates AXL and suppresses senescence to impose the MITF-low/AXL-high drug-resistant phenotype observed in human tumors. However, unexpectedly, without translation reprogramming an ATF4-high/MITF-low state is insufficient to drive invasion. Importantly, translation reprogramming dramatically enhances tumorigenesis and is linked to a previously unexplained gene expression program associated with anti-PD-1 immunotherapy resistance. Since we show that inhibition of eIF2B also drives neural crest migration and yeast invasiveness, our results suggest that translation reprogramming, an evolutionarily conserved starvation response, has been hijacked by microenvironmental stress signals in melanoma to drive phenotypic plasticity and invasion and determine therapeutic outcome. Hide abstract

Li L, Friedrichsen HJ, Andrews S, Picaud S, Volpon L, Ngeow K, Berridge G, Fischer R, Borden KLB, Filippakopoulos P, Goding CR. 2018. A TFEB nuclear export signal integrates amino acid supply and glucose availability. Nat Commun, 9 (1), pp. 2685. Read abstract | Read more

How cells coordinate the response to fluctuating carbon and nitrogen availability required to maintain effective homeostasis is a key issue. Amino acid limitation that inactivates mTORC1 promotes de-phosphorylation and nuclear translocation of Transcription Factor EB (TFEB), a key transcriptional regulator of lysosome biogenesis and autophagy that is deregulated in cancer and neurodegeneration. Beyond its cytoplasmic sequestration, how TFEB phosphorylation regulates its nuclear-cytoplasmic shuttling, and whether TFEB can coordinate amino acid supply with glucose availability is poorly understood. Here we show that TFEB phosphorylation on S142 primes for GSK3β phosphorylation on S138, and that phosphorylation of both sites but not either alone activates a previously unrecognized nuclear export signal (NES). Importantly, GSK3β is inactivated by AKT in response to mTORC2 signaling triggered by glucose limitation. Remarkably therefore, the TFEB NES integrates carbon (glucose) and nitrogen (amino acid) availability by controlling TFEB flux through a nuclear import-export cycle. Hide abstract

May-Simera HL, Wan Q, Jha BS, Hartford J, Khristov V, Dejene R, Chang J, Patnaik S, Lu Q, Banerjee P, Silver J, Insinna-Kettenhofen C, Patel D, Lotfi M, Malicdan M, Hotaling N, Maminishkis A, Sridharan R, Brooks B, Miyagishima K, Gunay-Aygun M, Pal R, Westlake C, Miller S, Sharma R, Bharti K. 2018. Primary Cilium-Mediated Retinal Pigment Epithelium Maturation Is Disrupted in Ciliopathy Patient Cells. Cell Rep, 22 (1), pp. 189-205. Read abstract | Read more

Primary cilia are sensory organelles that protrude from the cell membrane. Defects in the primary cilium cause ciliopathy disorders, with retinal degeneration as a prominent phenotype. Here, we demonstrate that the retinal pigment epithelium (RPE), essential for photoreceptor development and function, requires a functional primary cilium for complete maturation and that RPE maturation defects in ciliopathies precede photoreceptor degeneration. Pharmacologically enhanced ciliogenesis in wild-type induced pluripotent stem cells (iPSC)-RPE leads to fully mature and functional cells. In contrast, ciliopathy patient-derived iPSC-RPE and iPSC-RPE with a knockdown of ciliary-trafficking protein remain immature, with defective apical processes, reduced functionality, and reduced adult-specific gene expression. Proteins of the primary cilium regulate RPE maturation by simultaneously suppressing canonical WNT and activating PKCδ pathways. A similar cilium-dependent maturation pathway exists in lung epithelium. Our results provide insights into ciliopathy-induced retinal degeneration, demonstrate a developmental role for primary cilia in epithelial maturation, and provide a method to mature iPSC epithelial cells for clinical applications. Hide abstract

Bharti K. 2018. Patching the retina with stem cells. Nat. Biotechnol., 36 (4), pp. 311-313. | Read more