Protective effects of acemannan-enriched Aloe polysaccharide J2 against UVA-induced autophagic cell death in retinal pigment epithelial cells

Abstract

Age-Related Macular Degeneration (AMD) is one of the leading causes of irreversible vision loss worldwide, characterized by the degeneration of the retinal pigment epithelium (RPE) and photoreceptor cells, resulting in progressive loss of central vision. RPE cells are highly specialized and essential for retinal function, and their malfunction due to genetic, environmental, or age-related factors contributes significantly to AMD pathogenesis. Ultraviolet A (UVA) radiation is recognized as a major causative factor, as it induces the accumulation of reactive oxygen species (ROS) in RPE cells, ultimately contributing to the development of AMD. On the other hand, acemannan, a D-isomer mucopolysaccharide derived from Aloe vera pulp, is known for its antioxidant and anti-inflammatory properties. In this study, we extracted a highly purified Aloe-derived polysaccharide fraction enriched in acemannan, designated Aloe polysaccharide J2 (ACJ2), to investigate its protective effects against UVA-induced RPE damage. The results showed that post-treatment with ACJ2 significantly reduced UVA-induced cell death by lowering mitochondrial ROS levels, suppressing phosphorylation of mitogen-activated protein kinases (MAPKs), including p38 MAPK, extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun N-terminal kinase (JNK), and downregulating proinflammatory mediators including tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), and inducible nitric oxide synthase (iNOS). Furthermore, ACJ2 enhanced heme oxygenase-1 (HO-1) expression and mitochondrial DNA levels, and inhibited p62/sequestosome-1 (p62) consumption and microtubule-associated protein 1 light chain 3 (LC3)-I/II conversion, thereby reducing autophagic flux. These findings demonstrate that ACJ2 mitigates UVA-induced damage and restores disrupted autophagy in RPE cells, supporting its potential as a therapeutic candidate for AMD.