Mechanisms of skin vascular maturation and maintenance captured by longitudinal imaging of live mice.

A functional network of blood vessels is essential for organ growth and homeostasis, yet how the vasculature matures and maintains homeostasis remains elusive in live mice. By longitudinally tracking the same neonatal endothelial cells (ECs) over days to weeks, we found that capillary plexus expansion is driven by vessel regression to optimize network perfusion. Neonatal ECs rearrange positions to evenly distribute throughout the developing plexus and become positionally stable in adulthood. Upon local ablation, adult ECs survive through a plasmalemmal self-repair response, while neonatal ECs are predisposed to die. Furthermore, adult ECs reactivate migration to assist vessel repair. Global ablation reveals coordinated maintenance of the adult vascular architecture that allows for eventual network recovery. Lastly, neonatal remodeling and adult maintenance of the skin vascular plexus are orchestrated by temporally restricted, neonatal VEGFR2 signaling. Our work sheds light on fundamental mechanisms that underlie both vascular maturation and adult homeostasis in vivo.

Targeting lymphoid-derived IL-17 signaling to delay skin aging.

Skin aging is characterized by structural and functional changes that contribute to age-associated frailty. This probably depends on synergy between alterations in the local niche and stem cell-intrinsic changes, underscored by proinflammatory microenvironments that drive pleotropic changes. The nature of these age-associated inflammatory cues, or how they affect tissue aging, is unknown. Based on single-cell RNA sequencing of the dermal compartment of mouse skin, we show a skew towards an IL-17-expressing phenotype of T helper cells, γδ T cells and innate lymphoid cells in aged skin. Importantly, in vivo blockade of IL-17 signaling during aging reduces the proinflammatory state of the skin, delaying the appearance of age-related traits. Mechanistically, aberrant IL-17 signals through NF-κB in epidermal cells to impair homeostatic functions while promoting an inflammatory state. Our results indicate that aged skin shows signs of chronic inflammation and that increased IL-17 signaling could be targeted to prevent age-associated skin ailments.

Isolation and Sorting of Epidermal Interfollicular Stem Cells for the Study of Circadian Rhythms.

Epidermal and interfollicular stem cell proliferation and differentiation are controlled in a circadian manner, in order to anticipate the daily environmental challenges. For this reason, examining the circadian transcriptome of interfollicular stem cells has become a central technique for functional skin studies. In this chapter, we describe a widely adopted protocol for the isolation and analysis of circadian rhythms in adult stem cells of the epidermis.