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

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. Overall design: Single-cell suspension of RPE/choroid tissue prepared from 10-week-old animals was used for single-cell RNAseq experiments. Each sample includes tissues pooled from one male and one female. TSC1 flox (Tsc1tm1Djk/J) and the RPE-specific TSC1 KO (Tsc1tm1Djk/J; Best-Cre) were analyzed and compared. The scRNA experiments were performed using 10 X genomics chromium platforms.