Epigenetic switch reshapes epithelial progenitor cell signatures and drives inflammatory pathogenesis in hidradenitis suppurativa.

Hidradenitis suppurativa (HS) is a complex inflammatory skin disease with undefined mechanistic underpinnings. Here, we investigated HS epithelial cells and demonstrated that HS basal progenitors modulate their lineage restriction and give rise to pathogenic keratinocyte clones, resulting in epidermal hyperproliferation and dysregulated inflammation in HS. When comparing to healthy epithelial stem/progenitor cells, in HS, we identified changes in gene signatures that revolve around the mitotic cell cycle, DNA damage response and repair, as well as cell-cell adhesion and chromatin remodeling. By reconstructing cell differentiation trajectory and CellChat modeling, we identified a keratinocyte population specific to HS. This population is marked by S100A7/8/9 and KRT6 family members, triggering IL1, IL10, and complement inflammatory cascades. These signals, along with HS-specific proinflammatory cytokines and chemokines, contribute to the recruitment of certain immune cells during the disease progression. Furthermore, we revealed a previously uncharacterized role of S100A8 in regulating the local chromatin environment of target loci in HS keratinocytes. Through the integration of genomic and epigenomic datasets, we identified genome-wide chromatin rewiring alongside the switch of transcription factors (TFs), which mediated HS transcriptional profiles. Importantly, we identified numerous clinically relevant inflammatory enhancers and their coordinated TFs in HS basal CD49fhigh cells. The disruption of the S100A enhancer using the CRISPR/Cas9-mediated approach or the pharmacological inhibition of the interferon regulatory transcription factor 3 (IRF3) efficiently reduced the production of HS-associated inflammatory regulators. Our study not only uncovers the plasticity of epidermal progenitor cells in HS but also elucidates the epigenetic mechanisms underlying HS pathogenesis.

Vitamin D and lumisterol derivatives can act on liver X receptors (LXRs).

The interactions of derivatives of lumisterol (L3) and vitamin D3 (D3) with liver X receptors (LXRs) were investigated. Molecular docking using crystal structures of the ligand binding domains (LBDs) of LXRα and ß revealed high docking scores for L3 and D3 hydroxymetabolites, similar to those of the natural ligands, predicting good binding to the receptor. RNA sequencing of murine dermal fibroblasts stimulated with D3-hydroxyderivatives revealed LXR as the second nuclear receptor pathway for several D3-hydroxyderivatives, including 1,25(OH)2D3. This was validated by their induction of genes downstream of LXR. L3 and D3-derivatives activated an LXR-response element (LXRE)-driven reporter in CHO cells and human keratinocytes, and by enhanced expression of LXR target genes. L3 and D3 derivatives showed high affinity binding to the LBD of the LXRα and ß in LanthaScreen TR-FRET LXRα and ß coactivator assays. The majority of metabolites functioned as LXRα/ß agonists; however, 1,20,25(OH)3D3, 1,25(OH)2D3, 1,20(OH)2D3 and 25(OH)D3 acted as inverse agonists of LXRα, but as agonists of LXRß. Molecular dynamics simulations for the selected compounds, including 1,25(OH)2D3, 1,20(OH)2D3, 25(OH)D3, 20(OH)D3, 20(OH)L3 and 20,22(OH)2L3, showed different but overlapping interactions with LXRs. Identification of D3 and L3 derivatives as ligands for LXRs suggests a new mechanism of action for these compounds.

The multiple faces of CD5.

Since its discovery, over 30 years ago, CD5 has been used as a marker to identify T cells, B1-a cells, and B cell chronic lymphocytic leukemia cells. Throughout the years, many studies have described the functional relevance of CD5 as a modulator of T and B cell receptor signaling. However, it has not been until recent years that CD5 has emerged as a functional receptor in other areas of the immune system. Here, we review some of the most important aspects of CD5 as a modulator of TCR and BCR signaling, cell survival receptor both in T and B cells during health and disease, as well as the newly discovered roles of this receptor in thymocyte selection, T cell effector differentiation, and immune tolerance. CD5 was found to promote T cell survival by protecting autoreactive T cell from activation-induced cell death, to promote de novo induction of regulatory T cells in the periphery, to modulate Th17 and Th2 differentiation, and to modulate immune responses by modulating dendritic cell functions. CD5 is overexpressed in Tregs and Bregs, which are fundamental to maintain immune homeostasis. The newly established roles of CD5 in modulating different aspects of immune responses identify this receptor as an immune checkpoint modulator, and therefore it could be used as a target for immune intervention in different pathologies such as cancer, autoimmune diseases or infections.

CD5-CK2 Signaling Modulates Erk Activation and Thymocyte Survival.

CD5 is well recognized for its importance in thymic selection. Although this property of CD5 has been attributed to its ITIM-domain dependent regulation of TCR-signal strength, the mechanism has not been established. A second major signaling domain within the cytoplasmic tail of CD5 is a CK2 binding/activation domain (CD5-CK2BD). Using a gene-targeted mouse in which the CD5-CK2BD is selectively ablated (CD5-ΔCK2BD), we determined that loss of function of CD5-CK2 signaling in a MHC-II selecting TCR transgenic (OT-II) mouse resulted in decrease in double positive (DP) thymocytes, which correlated with enhanced apoptosis. Remarkably, DP cells expressing high levels of CD5 and CD69 and single positive (CD4+SP) thymocytes were increased in CD5-ΔCK2BD mice indicating that CD5-CK2 signaling regulates positive selection and promotes survival. Consistent with this possibility, we determined that the activation and nuclear localization of ERK as well as apoptosis was greater in thymic populations from OTII CD5-ΔCK2BD mice than OTII CD5-WT mice following injection of OVA323-339-peptide. The mobilization of Ca2+, an early event of TCR activation, was not altered by the loss of CD5-CK2 signaling. Collectively, these data demonstrate that the CD5-CK2 signaling axis regulates positive selection by modulating activation of ERK and promoting survival independent of proximal TCR signals.

Functional requirement of tyrosine residue 429 within CD5 cytoplasmic domain for regulation of T cell activation and survival.

CD5 has been mainly described as a negative regulator of TCR and BCR signaling and recent evidence has shown an important role for this receptor in delivering pro-survival signals. However, the molecular mechanisms underlying these processes remain unresolved. TCR crosslinking leads to phosphorylation of three tyrosine residues within the cytoplasmic tail of CD5 (Y429, Y441 and Y463) leading to the recruitment of signaling molecules like PI3K, c-Cbl and RasGAP; nevertheless, the role of these residues in T cell survival has not yet been assessed. In this study, we show that alanine-scanning mutagenesis of such tyrosine residues, either singly or in combination, leads to an increased thymocyte cell death with or without α-CD3 stimulation. Remarkably, the T-cell death observed with each individual tyrosine mutant was Caspase 3-independent. Furthermore, Y429 mutation resulted in a hyper-phosphorylation of ERK suggesting that this tyrosine residue regulates cell survival through down modulation of TCR signaling. Mutation of Y441 or Y463 did not induce hyper-responsiveness to TCR activation, indicating that they promoted T-cell survival by a TCR signal-independent pathway. Our results show that three tyrosine-based domains within CD5 cytoplasmic tail promote T-cell survival through non-overlapping mechanisms. This study also reveals that Y429 domain of CD5, previously described as a "pseudo ITAM", is functionally an ITIM domain in T cells.