HERV1-env Induces Unfolded Protein Response Activation in Autoimmune Liver Disease: A Potential Mechanism for Regulatory T Cell Dysfunction.

Photoreceptors are highly specialized neurons that depend on continuous membrane renewal and tightly regulated lipid homeostasis to maintain their visual function. Age-associated disruptions of these processes increase cellular stress and contribute to photoreceptor degeneration. Pigment epithelium-derived factor (PEDF) is a potent neuroprotective factor in the retina, and the identification of its receptor, PEDF-R (PNPLA2), has provided key mechanistic insight into how PEDF signaling is coupled to lipid metabolism. The present review examines the molecular and cellular mechanisms underlying PEDF-R function in photoreceptors and the retinal pigment epithelium (RPE). PEDF-R acts as a multifunctional enzyme with phospholipase and lipase activities that link extracellular PEDF binding to intracellular lipid remodeling. Through these activities, PEDF-R has been associated with processes essential for photoreceptor survival such as membrane phospholipid turnover, mitochondrial integrity, calcium homeostasis, and redox balance. In addition, PEDF-R contributes to retinoid metabolism and lipid processing associated with outer-segment renewal in the RPE. We further discuss how disruption of the PEDF-PEDF-R pathway impairs lipid homeostasis, promotes oxidative and inflammatory stress, and increases susceptibility to age-related retinal degeneration. These insights position PEDF-R as a key contributor to photoreceptor homeostasis and a potential therapeutic target for preserving retinal function in aging and disease.