Abstract
Differentiating keratinocytes break down their organelles and nuclei to become the compacted cornified layers of the epidermal barrier in a poorly understood catabolic process. Live confocal imaging of stratified human organotypic epidermis revealed endoplasmic reticulum (ER) fragmentation and lysosomal engulfment in the cornifying layers, where we found up-regulation of TEX264, a receptor that mediates selective autophagy of the ER (reticulophagy). TEX264 expression was increased by ER stress, which caused precocious cornification of organotypic epidermis. In undifferentiated keratinocytes, ectopic TEX264 was sufficient to fragment the ER, while in highly differentiated keratinocytes, it accelerated ER elimination and induced nuclear shrinkage; these effects were abolished by mutating the LC3 interacting region required for its autophagic function. Knockout of TEX264 or inhibiting its activation disrupted maturation of organotypic cultures, pointing to a critical role for reticulophagy in cornification. Finally, in patient biopsies and an organotypic model of Darier disease, a genetic cornification disorder linked to ER dysfunction, we found increased TEX264 in areas of premature cornification (dyskeratosis). Our results identified TEX264 as a key driver of epidermal differentiation and led us to propose a novel model of cornification in which keratinocytes activate selective autophagy receptors to orchestrate orderly organelle elimination during cutaneous barrier formation.