Functional and Morphological Plasticity of the Endolysosomal System: Pigment Organelles at the Crossroads of Physiology and Pathology.

The endolysosomal system is a highly dynamic and versatile network of organelles essential for maintaining cellular and tissue homeostasis. Its functional diversity relies on a high degree of plasticity, driven by tightly regulated membrane remodeling and intracellular trafficking events. In certain specialized cells, this plasticity enables the formation of lysosome-related organelles, like melanosomes in pigment cells, through the repurposing of ubiquitous membrane trafficking machineries. Disruption of these pathways can lead to pathological conditions, including genetic disorders. In this review, we explore how endolysosomal plasticity underlies key adaptive cellular strategies at the cellular and tissue levels. Focusing on melanocytes, which synthesize melanin, and keratinocytes, which receive and store it, we illustrate how trafficking and membrane dynamics events coordinate between these two cell types for skin pigmentation and photoprotection, and how mutations affecting these processes lead to genetic forms of albinism. By using skin pigmentation as a model of cell- and tissue-specific adaptation, this review highlights the broader physiological and pathological implications of endolysosomal membrane morphodynamics.