PROJECT SUMMARY
Few therapeutic options exist for patients with age-related macular degeneration (AMD), and no FDA
approved drugs are available for the most common subtype, dry AMD. Longitudinal imaging studies have
identified the accumulation of drusen near the fovea as the single greatest anatomic risk factor for progression
to severe disease, suggesting that loss of lipid homeostasis in the retinal pigmented epithelium (RPE) and
choroid is a critical disease mechanism underlying AMD. Moreover, histologic and molecular studies have shown
that inflammation of the macular RPE/choroid is an early, unifying feature of AMD. Yet, the molecular and cellular
mechanisms responsible for the accumulation of lipid and inflammation in the RPE/choroid remain poorly
understood. Using publicly available bulk and single-cell RNA-sequencing data from 150 human donors, we
demonstrate that choroidal macrophages—a critical component of the choroidal ecosystem required for
maintenance of the choriocapillaris and RPE function—are decreased and dysfunctional in the macular
RPE/choroid in AMD. We detail novel transcriptomic observations related to the molecular underpinnings of
choroidal macrophages in humans, demonstrating that they are robustly anti-inflammatory and express several
key modules involved in lipid clearance. Of note is the expression of triggering receptor expressed on myeloid
cells 2 (TREM2), a liporeceptor that mediates lipid homeostasis and immunosuppression in a range of tissues
and is lost in several diseases involving accumulation of extracellular material. Using choroidal tissue from mice,
we employ a variety of techniques to validate key findings related to choroidal macrophages. We show that
choroidal macrophages are important in maintaining lipid homeostasis in the choroid during times of chronic lipid
challenge, as these cells expand and contain nearly all of the excess lipid after 9 weeks of high-fat diet. These
findings led us to our core hypothesis that TREM2+ choroidal macrophages modulate lipid homeostasis in the
RPE/choroid and suppress inflammation and choroidal neovascularization. We propose two Aims using TREM2
knock-out mice to interrogate the role of TREM2 signaling in choroidal macrophages with respect to lipid
metabolism and immune and neovascular suppression in the RPE/choroid. We anticipate the findings from this
proposal will expand our understanding of the role of choroidal macrophages in the choroidal ecosystem and will
identify TREM2 as a novel drug target in AMD.
The proposed training plan for the PI, Seth Fortmann, is sponsored by his mentor, Dr. Maria Grant MD.
The overall goal of the training plan is to provide the PI with a strong scientific foundation for a successful career
as a physician-scientist ophthalmologist. Included in the training plan are experiences that will help the PI: 1)
gain competence in a variety of techniques including bioinformatics, flow cytometry, primary cell culture, and
ex vivo imaging of human donor eyes; 2) develop hypothesis-driven research; 3) present data in an oral and
written format; 4) effectively integrate research with the clinic; 5) collaborate with other scientists; and 6)
responsibly conduct research.