Identification of cellular and molecular risk signatures for progression to late-stage age-related macular degeneration using the 9-step Minnesota Grading System
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Age-related macular degeneration (AMD) is a complex multifactorial disease, and the molecular mechanisms underpinning the progression of intermediate AMD to geographic atrophy are not fully understood. To better understand mechanisms driving progression, we performed bulk RNA sequencing on dissected macular and peripheral RPE/choroid and neural retina tissue from postmortem human eyes graded using the 9-step Minnesota Grading System (MGS). Binning of intermediate AMD cases into three distinct groups (AMD3L, AMD3M, AMD3H) based on the 5-year risk of progression enabled identification of distinct gene and pathway changes associated with progression to late-stage disease. Identified changes in gene expression were validated using ELISA or histological methods. RPE-specific genes and lipid metabolic pathways showed a transient increase in AMD3L followed by a pronounced decrease in AMD3H. In AMD3H, immune response genes such as C3 , TREM2 , and OLR1 were upregulated when compared to AMD3L samples, as well as genes specific to Müller glia/astrocytes (NGFR, SPP1, GPX3 ). Our findings support complement inhibition as a promising therapeutic option for slowing conversion to advanced AMD and identify macrophage and Müller/astrocyte genes as potential cell types to target in AMD. Further, we demonstrate the value of combining emerging, outcomes-based, clinically relevant grading systems with profiling technologies to generate new insights into ocular diseases.
Highlights
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Intermediate AMD (AMD3) can be further divided into 3 stages - AMD3L (low risk), AMD3M (intermediate risk), AMD3H (high risk) – using the MGS9 grading system based on the risk of disease progression to late AMD.
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RNA sequencing of the macular RPE/choroid shows opposing changes in gene expression of multiple biological pathways for both RPE and immune cells between AMD3L and AMD3H stages.
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In the macular neural retina, most biological pathways were downregulated in AMD2 (early AMD) but upregulated in AMD4 (late AMD) compared to AMD1 (non-AMD control).
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Molecular and cellular signatures associated with a high risk of progression to AMD4 include activation of complement C3, two subtypes of macrophages expressing either TREM2 or OLR1, and Müller glia/astrocytes as evidenced by the upregulation of GFAP and NGFR.
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Understanding the roles of these high-risk associated genes in AMD progression will facilitate the development of new treatments that prevent or delay the irreversible central vision loss in AMD patients.
