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DARPP32, a target of hyperactive mTORC1 in the retinal pigment epithelium

ABSTRACT: The mechanistic target of rapamycin (mTOR) is assembled into signaling complexes of mTORC1 or mTORC2, and plays key roles in cell metabolism, stress response, nutrient and growth factor sensing. Accumulating evidence from human and animal model studies has demonstrated a pathogenic role of hyperactive mTORC1 in age-related macular degeneration (AMD). The retinal pigment epithelium (RPE) is a primary injury site in AMD. In mouse models of RPE-specific deletion of Tuberous sclerosis 1 (Tsc1), which encodes an upstream suppressor of mTORC1, the hyperactivated mTORC1 metabolically reprogrammed the RPE and led to the degeneration of the outer retina and choroid (CH). In the current study, we used single-cell RNA sequencing (scRNA-seq) to identify a novel RPE mTORC1 downstream protein, dopamine and cyclic AMP-regulated phosphoprotein of molecular weight 32,000 (DARPP-32). DARPP-32 was not found in healthy RPE but localized to drusen and basal linear deposits in human AMD eyes. In animal models, overexpressing DARPP-32 by adeno-associated virus (AAV) led to abnormal RPE structure and function. The data indicate that DARPP-32 is a previously unidentified signaling protein subjected to mTORC1 regulation and may contribute to RPE degeneration in AMD.

ORGANISM(S): Mus musculus

PROVIDER: GSE209908 | GEO | 2022/07/29

REPOSITORIES: GEO

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Project description:Background: Age-related macular degeneration (AMD) is caused by the degeneration of the macular photoreceptors. This is preceded by development of subretinal protein aggregates (drusen) and degeneration of the macular retinal pigment epithelium (RPE). The underlying pathogenesis remains unknown, but the immune system is suspected to play a key role in it. Aging of the immune system, immunosenescence, includes changes in T cell sub-populations and results in low-level chronic inflammation. Because AMD exclusively occurs in patients over 55 years of age, we hypothesize that aging of the T cell compartment may be implicated in AMD pathogenesis. Methodology and principal findings: Using an in vitro co-culture system, we investigated the effects of activated T cells on a human RPE cell line (ARPE-19). Differential gene expression in the RPE cells of complement factor genes was identified using microarrays, and selected gene transcripts from the alternative complement pathway were validated by q-RT-PCR. Protein expression was determined by ELISA and immunoblotting. Co-culture with activated T cells increased RPE mRNA and protein expression of complement component C3, factors B, H, H-like 1, CD46, CD59, and clusterin, in a dose-dependent manner. Conclusions: RPE cells responded to inflammatory assault caused by exposure to T cell-derived cytokines by upregulating expression of many complement factors from the alternative pathway. This may have implications for RPE ability to deal with complement attack, and opsonization and removal of debris from the RPE-choroidal interface. We speculate that regulation of the complement system in response to inflammatory assault may play a vital role in RPE pathology and drusen biogenesis. Experiment Overall Design: 10 samples investigating variations of co-cultures of RPE cells and T-cells. Variable parameters include the cell type, the co-culturing of the counter-part cell type and the orientation of the system (apical vs basolateral).

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DARPP32, a target of hyperactive mTORC1 in the retinal pigment epithelium

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