MAdCAM-1 mediates retinal neuron degeneration in experimental colitis through recruiting gut-homing CD4⁺ T cells

Extra-intestinal manifestations (EIMs) of the eyes are found in IBD patients, but the underlying pathogenesis remains unknown. To investigate the pathogenesis of IBD-associated retinal dysfunction, chronic colitis was induced in mice by oral administration of dextran sodium sulfate (DSS). Electroretinography (ERG) was performed to evaluate retinal function. Retinal neuron degeneration was analyzed by immunohistochemistry. Colitic mice displayed aberrant amplitudes of ERG a-, b-wave and oscillatory potentials (OP). Importantly, we observed severe degeneration of bipolar and ganglion cells. In contrast, outer retinal neurons (mainly photoreceptor cells) are mildly affected by colitis. Moreover, retinal inflammatory responses were significantly upregulated during colitis, including microglia activation, lymphocyte infiltration and cytokine/chemokine production. Notably, mucosal addressin cell adhesion molecule 1 (MAdCAM-1) was upregulated in retinal microvessels, especially the superficial and deep plexuses, and recruited gut-homing CD4⁺ T cells to be co-localized with bipolar and ganglion cells during colitis. Expectedly, in vivo depletion of CD4⁺ T cells or blockade of MAdCAM-1 greatly alleviated colitis-induced retinal inflammatory responses and neuron degeneration. Therefore, our data provide novel insight into the pathogenesis of IBD-associated retinal dysfunction, and targeted immune therapy directly against MAdCAM-1 might provide a novel approach in the management of eye EIM of IBD.