Non-senescent keratinocytes organize in plasma membrane submicrometric lipid domains enriched in sphingomyelin and involved in re-epithelialization

• Sphingomyelin and cholesterol concentrate into lipid submicrometric domains in membranes of keratinocytes.
• Sphingomyelin is suppressed in membranes during replicative senescence of human keratinocytes.
• Keratinocyte migration decreases with senescence, as well as a consequence of sphingomyelin or cholesterol depletion.

Membrane lipid raft model has long been debated, but recently the concept of lipid submicrometric domains has emerged to characterize larger (micrometric) and more stable lipid membrane domains. Such domains organize signaling platforms involved in normal or pathological conditions. In this study, adhering human keratinocytes were investigated for their ability to organize such specialized lipid domains. Successful fluorescent probing of lipid domains, by either inserting exogenous sphingomyelin (BODIPY-SM) or using detoxified fragments of lysenin and theta toxins fused to mCherry, allowed specific, sensitive and quantitative detection of sphingomyelin and cholesterol and demonstrated for the first time submicrometric organization of lipid domains in living keratinocytes. Potential functionality of such domains was additionally assessed during replicative senescence, notably through gradual disappearance of SM-rich domains in senescent keratinocytes. Indeed, SM-rich domains were found critical to preserve keratinocyte migration before senescence, because sphingomyelin or cholesterol depletion in keratinocytes significantly alters lipid domains and reduce migration ability.