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

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.

HDAC2 and 7 down-regulation induces senescence in dermal fibroblasts.

Originally simply reported to be in a stable and irreversible growth arrest in vitro, senescent cells are now clearly associated with normal and pathological ageing in vivo. They are characterized by several biomarkers and changes in gene expression that may depend on epigenetic factors, such as histone acetylation, involving a balance between histone acetyltransferases (HATs) and histone deacetylases (HDACs). In this study, we investigate the expression and the role of HDACs on the senescent phenotype of dermal fibroblasts. We report that during replicative senescence, most canonical HDACs are less expressed. Moreover, treatment with SAHA, a histone deacetylase inhibitor (HDACi) also known as Vorinostat, or the specific downregulation of HDAC2 or HDAC7 by siRNA, induces the appearance of senescence biomarkers of dermal fibroblasts. Conversely, the ectopic re-expression of HDAC7 by lentiviral transduction in pre-senescent dermal fibroblasts extends their proliferative lifespan. These results demonstrate that HDACs expression can modulate the senescent phenotype, highlighting their pharmaceutical interest in the context of healthy ageing.