Atypical Vascular Inflammation in Retinal Vasculopathies: Targeting p38 Signaling

Abstract

Purpose : Mitogen-activated protein kinase (MAPK) p38 plays a central role in retinal diseases, but broad-spectrum p38 therapeutics often hinder physiological signaling. Atypical p38, activated solely in response to disease signaling, emerges as a potential therapeutic target. This project aims to model and selectively target atypical p38 signaling, offering a complementary approach to anti-VEGF therapies for retinal diseases.

Methods : Using a C57BL6 mouse model of oxygen-induced retinopathy (OIR), we compared wild-type (WT) mice with a mutant Tab1^KI mouse defective for atypical p38 activation. Post-natal day 7 (p7) mice were exposed to 75% oxygen for five days, followed by five days in room air before retina collection. Assessment methods included flat mounting, isolectin B4 labeling, immunohistochemistry for microglia and neuronal cells, and RNAseq analysis. Room-air mice were collected at p7, p12, and p21 for comparison. We also assessed human retinal endothelial cells (HREC) for atypical p38 signaling by immunoblotting after stimulation with known atypical p38 activators, including prostaglandin E2 (PGE₂) and Histamine +/- p38 kinase inhibitors

Results : At p17, WT mice exhibited vaso-obliteration and hyperproliferative responses including, excessive vascular growth, tufting, and edema. Tab1^KI mice showed significantly reduced vaso-obliteration (5% vs. ~15% in WT) and decreased vascular tufting (5% vs. 10% in WT). Immunohistochemistry revealed changes in microglial activity in the Tab1^KI OIR retina. A bioinformatic analysis of these retinal tissues is ongoing to support identified morphological phenotypes. Atypical p38 signaling persisted in HREC after PGE₂ and histamine stimulation, inducing proinflammatory cytokine expression.

Conclusions : Our data reveal unperturbed retinal vascular development in Tab1^KI mice, with significant protection against vascular damage in OIR. Inhibition of atypical p38 blocks pro-inflammatory responses in both mouse and human samples. The spatially biased loss of atypical p38 signaling reduces pro-inflammatory and proangiogenic signaling. These findings support the development of selective therapeutics targeting atypical p38 in retinal vascular diseases, including diabetic retinopathy, retinopathy of prematurity, and age-related macular degeneration.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.