Skin aging is driven by intrinsic and extrinsic factors impacting on skin functionality with progressive age. One factor of this multifaceted process is cellular senescence, as it has recently been identified to contribute to a declining tissue functionality in old age. In the skin, senescent cells have been found to markedly accumulate with age, and thus might impact directly on skin characteristics. Especially the switch from young, extracellular matrix-building fibroblasts to a senescence-associated secretory phenotype (SASP) could alter the microenvironment in the skin drastically and therefore promote skin aging. In order to study the influence of senescence in human skin, 3D organotypic cultures are a well-suited model system. However, only few "aged" skinequivalent (SE) models are available, requiring complex and long-term experimental setups. Here, we adapted a previously published full-thickness SE model by seeding increasing ratios of stress-induced premature senescent versus normal fibroblasts into the collagen matrix, terming these SE "senoskin". Immunohistochemistry stainings revealed a shift in the balance between proliferation (Ki67) and differentiation (Keratin 10 and Filaggrin) of keratinocytes within our senoskin equivalents, as well as partial impairment of skin barrier function and changed surface properties. Monitoring of cytokine levels of known SASP factors confirmedly showed an upregulation in 2D cultures of senescent cells and at the time of seeding into the skin equivalent. Surprisingly, we find a blunted response of cytokines in the senoskin equivalent over time during 3D differentiation.

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Langerhans cell histiocytosis (LCH) is a MAPK pathway-driven disease characterized by the accumulation of CD1a + langerin + cells of unknown origin. We have previously reported that the Notch signaling pathway is active in LCH lesions and that the Notch ligand Jagged2 (JAG2) induces CD1a and langerin expression in monocytes in vitro. Here we show that Notch signaling induces monocytes to acquire an LCH gene signature and that Notch inhibition suppresses the LCH phenotype.In contrast, while also CD1c + dendritic cells or IL-4-stimulated CD14 + monocytes acquire CD1a and langerin positivity in culture, their gene expression profiles and surface phenotypes are more different from primary LCH cells. We propose a model where CD14 + monocytes serve as LCH cell precursor and JAG2-mediated activation of the Notch signaling pathway initiates a differentiation of monocytes toward LCH cells in selected niches and thereby contributes to LCH pathogenesis. K E Y W O R D SBRAFV600E, notch pathway, pediatric neoplasm BRAFV600E mutation alone is not instructive for a cell to develop an LCH phenotype.We have previously shown that the Notch pathway is active in LCH and that stimulation of the Notch pathway in the presence of

The engagement of the herpesvirus entry mediator (HVEM, TNFRSF14) by the B and T lymphocyte attenuator (BTLA) represents a unique interaction between an activating receptor of the TNFR-superfamily and an inhibitory receptor of the Ig-superfamily. BTLA and HVEM have both been implicated in the regulation of human T cell responses, but their role is complex and incompletely understood. Here, we have used T cell reporter systems to dissect the complex interplay of HVEM with BTLA and its additional ligands LIGHT and CD160. Co-expression with LIGHT or CD160, but not with BTLA, induced strong constitutive signaling via HVEM. In line with earlier reports, we observed that in cis interaction of BTLA and HVEM prevented HVEM co-stimulation by ligands on surrounding cells. Intriguingly, our data indicate that BTLA mediated inhibition is not impaired in this heterodimeric complex, suggesting a dominant role of BTLA co-inhibition. Stimulation of primary human T cells in presence of HVEM ligands indicated a weak costimulatory capacity of HVEM potentially owed to its in cis engagement by BTLA. Furthermore, experiments with T cell reporter cells and primary T cells demonstrate that HVEM antibodies can augment T cell responses by concomitantly acting as checkpoint inhibitors and co-stimulation agonists.

Saturated very long-chain fatty acids (VLCFA, ≥ C22), enriched in brain myelin and innate immune cells, accumulate in X-linked adrenoleukodystrophy (X-ALD) due to inherited dysfunction of the peroxisomal VLCFA transporter ABCD1. In its severest form, X-ALD causes cerebral myelin destruction with infiltration of pro-inflammatory skewed monocytes/macrophages. How VLCFA levels relate to macrophage activation is unclear. Here, whole transcriptome sequencing of X-ALD macrophages indicated that VLCFAs prime human macrophage membranes for inflammation and increased expression of factors involved in chemotaxis and invasion. When added externally to mimic lipid release in demyelinating X-ALD lesions, VLCFAs did not activate toll-like receptors in primary macrophages. In contrast, VLCFAs provoked pro-inflammatory responses through scavenger receptor CD36-mediated uptake, cumulating in JNK signalling and expression of matrix-degrading enzymes and chemokine release. Following pro-inflammatory LPS activation, VLCFA levels increased also in healthy macrophages. With the onset of the resolution, VLCFAs were rapidly cleared in control macrophages by increased peroxisomal VLCFA degradation through liver-X-receptor mediated upregulation of ABCD1. ABCD1 deficiency impaired VLCFA homeostasis and prolonged pro-inflammatory gene expression upon LPS treatment. Our study uncovers a pivotal role for ABCD1, a protein linked to neuroinflammation, and associated peroxisomal VLCFA degradation in regulating macrophage plasticity.