Aberrant RPE mTORC1 signaling in dysregulation of choroid homeostasis

The overall goal of the project is to delineate the cellular and molecular mechanisms that link dysfunction of the
retinal pigment epithelium (RPE) to degeneration of the choriocapillaris (CC). Choroidal atrophy is an early
pathological change in age-related macular degeneration (AMD), a leading cause of blindness in elderly
people. The RPE produces a number of trophic factors that support the structural integrity of the choroidal
vasculature. Aging and age-related degeneration can interfere with the functional interactions between the
RPE and CC. The underlying disease mechanisms are largely unclear. We found that the mouse model of
RPE-specific overactivation of the mechanistic target of rapamycin complex 1 (mTORC1) recapitulated many
of the clinical features of CC dropout. RPE cells with high mTORC1 activity had increased release of
angiopoietin 2 (ANGPT2), a vascular destabilizing factor that is usually produced by endothelial cells (ECs)
and exerts autocrine effects on its receptor TIE2. We further identified that the secretion of ANGPT2 from RPE
was likely mediated by the upregulation and activation of a phosphoprotein DARPP-32. Based on these novel
findings, we hypothesize that ANGPT2 production and secretion from the RPE contribute to the degeneration
of choroid under pathological conditions that involve dysregulated mTORC1 signaling. The hypothesis will be
tested in three specific aims. Aim 1 is to determine whether mTORC1 activation in the RPE will stimulate
ANGPT2 secretion via DARPP-32-dependent mechanisms. Aim 2 is to examine whether ANGPT2 can
regulate the function of choroidal ECs via TIE2-dependent or independent pathways. Aim 3 is to determine
whether genetic knockout of ANGPT2 in the RPE, or AAV-mediated overexpression of ANGPT2 will influence
the CC atrophy in the mouse model of mTORC1 hyperactivation. The results from these studies will provide
insights on how the AMD-related signaling events in the RPE impact its support to the CC. The newly identified
ANGPT2-TIE2 axis between the RPE and choroidal ECs can be a molecular pathway for the therapeutic
intervention of choroidal atrophy.

Grant Number: 7R01EY026999-10
NIH Institute/Center: NIH
Principal Investigator: Yan Chen