Faculty Bibliography

Hidradenitis suppurativa (HS) is a severe chronic inflammatory skin disease affecting human apocrine sweat gland-bearing skin regions. The overall prevalence of HS ranges from 0.05-4.1% with higher occurrence among females and African Americans, and strong associations with smoking and obesity. One unique feature of HS is the development of highly immunogenic keratinized sinus tracts that grow deeply in the dermis which further complicate HS pathogenesis and treatment. Using single cell transcriptomic analyses, we finely dissected different epidermal cell types in the HS lesional skin and revealed significant dysregulation of skin barrier function in the sinus tracts. We demonstrated that sinus tract keratinocytes exhibit dual cell fates of surface epidermis and skin appendages, and derived from progenitors in infundibulum of the apocrine-pilosebaceous unit. By analyzing ligand-receptor expressions between different skin appendages and immune cells, we highlighted Th17 and TNF responses at early and late stages during HS progression, respectively. Our work provides unprecedented understanding of pathological epidermal remodeling in human inflammatory diseases and important implications for therapeutics.
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Hidradenitis suppurativa (HS) is a severe chronic inflammatory skin disease lacking effective therapeutic options due to little understanding of the complex immune response within the lesional skin. Using single-cell transcriptomic analyses, we examined the signature changes in each immune cell types during HS progression, as well as in silico ligand-receptor predictions between different immune cell types to construct the interaction network that contribute to HS pathogenesis. Our results revealed a predominant Th17 response, as well as a distinct regulatory T cells existing in the lesional skin. We found that M1-polarized macrophages likely facilitate chemotaxis and IL1B responses in perilesional skin, while regulate lymphocyte activation and tissue remodeling in the lesional skin. In addition, we identified a significant increase of CCR7 expressing dendritic cells, as well as activated stromal fibroblasts expressing CCR7-ligand CCL19, which together support the organization of tertiary lymphoid organ (TLO)-like aggregates that contribute to persistent local inflammation. Importantly, we demonstrated a dense infiltration of plasma cells near sinus tracts, and that clonal expansion of the plasma cells frequently exists in HS patients. Together, our work provides a comprehensive understanding of immune responses and cytokine networks defining disease chronicity in HS, as well as significant implications for future therapeutics.
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Hidradenitis suppurativa (HS) is a prevalent inflammatory skin disease. HS causes deep, painful, recurrent abscesses. African Americans and females are at an increased risk. A lack of effective therapies and limited knowledge about HS pathogenesis contribute to unmet needs. Unlike other common inflammatory skin diseases, there has never been a genome-wide association study (GWAS) conducted for HS. Here, we performed a first GWAS for HS using data from the eMERGE network of electronic health record linked biorepositories (project NT227). We used HS diagnosis codes to identify cases and controls. We estimated ancestry with principal component analysis using a set of 40,156 SNPs. Our final cohort consisted of 600 HS cases and 82,611 controls with comparable multi-ethnic ancestry (lambda=1.005). Our cohort recapitulated HS race and gender predilections with genetically African female participants accounting for 35% of cases, but only 10% of controls. Genotype data for 6 million variants was tested for association, adjusting for five principal components. No locus exceeded our threshold for statistical significance. Importantly, there was no evidence for HLA association supporting classification of HS as inflammatory rather than autoimmune. Several loci approached the significance threshold, suggesting that an expansion in cohort size is needed to provide adequate power to detect associations. Interestingly, the lead SNP at one of the most significant loci (rs11075745; p=8x10^-7) is an eQTL for NFAT5, a mediator of NOTCH signaling whose expression is downregulated in HS lesional skin relative to patient-matched nonlesional skin. The risk allele influences expression in tissue specific manner. Our group is constructing multi-ethnic replication cohorts that will allow us to expand this study in the near future.
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Glands in the skin are essential for various physiological functions involving exocrine secretion. Like other tissues and organs, they possess the ability to repair injury and self-renew during homeostasis. Progenitor cells in glands are mostly unipotent but include some multipotent stem cells that function when extensive remodelling or regeneration is required. In this review, using two glandular models in skin, mouse sweat gland and mammary gland, we discuss lineage restriction that develops during glandular morphogenesis, as well as the mechanisms regulating cell fate and plasticity during wound repair and regeneration. Understanding the intrinsic and extrinsic factors that control the behaviours of glandular stem cell and maintain glandular functions will provide insight into future prospects for glandular regeneration.

Tissue homeostasis and regeneration rely on resident stem cells (SCs), whose behaviour is regulated through niche-dependent crosstalk. The mechanisms underlying SC identity are still unfolding. Here, using spatiotemporal gene ablation in murine hair follicles, we uncover a critical role for the transcription factors (TFs) nuclear factor IB (NFIB) and IX (NFIX) in maintaining SC identity. Without NFI TFs, SCs lose their hair-regenerating capability, and produce skin bearing striking resemblance to irreversible human alopecia, which also displays reduced NFIs. Through single-cell transcriptomics, ATAC-Seq and ChIP-Seq profiling, we expose a key role for NFIB and NFIX in governing super-enhancer maintenance of the key hair follicle SC-specific TF genes. When NFIB and NFIX are genetically removed, the stemness epigenetic landscape is lost. Super-enhancers driving SC identity are decommissioned, while unwanted lineages are de-repressed ectopically. Together, our findings expose NFIB and NFIX as crucial rheostats of tissue homeostasis, functioning to safeguard the SC epigenome from a breach in lineage confinement that otherwise triggers irreversible tissue degeneration.

The precise pathogenic mechanisms in the development, persistence and worsening of hidradenitis suppurativa (HS) remain ill-defined. This chronic inflammatory dermatosis displays a strong Th1 and Th17 inflammatory signature with elevated levels of TNF-α, IL-1β, IL-17 and IFNγ in lesional and perilesional tissue. HS significantly differs to other chronic inflammatory dermatoses due to the development of hypertrophic scarring and dermal tunnels. The development of scarring and tunnels suggests that fibroblastic stromal cells (including myofibroblasts, fibroblasts, pericytes etc) may be involved in the development and progression of disease. Heterogeneous populations of fibroblasts have been identified in other inflammatory disorders and malignancy which contribute to inflammation and present novel therapeutic targets for fibrotic disorders. Findings in HS are consistent with these fibroblast subpopulations and may contribute to tunnel formation, aggressive squamous cell carcinoma and the phenotypic presentation of familial HS variants. We describe the existing knowledge regarding these mechanistic pathways and methods to confirm their involvement in the pathogenesis of HS.

Touch sensation is initiated by mechanosensory neurons that innervate distinct skin structures; however, little is known about how these neurons are patterned during mammalian skin development. We explored the cellular basis of touch-receptor patterning in mouse touch domes, which contain mechanosensory Merkel cell-neurite complexes and abut primary hair follicles. At embryonic stage 16.5 (E16.5), touch domes emerge as patches of Merkel cells and keratinocytes clustered with a previously unsuspected population of Bmp4-expressing dermal cells. Epidermal Noggin overexpression at E14.5 disrupted touch-dome formation but not hair-follicle specification, demonstrating a temporally distinct requirement for BMP signaling in placode-derived structures. Surprisingly, two neuronal populations preferentially targeted touch domes during development but only one persisted in mature touch domes. Finally, Keratin-17-expressing keratinocytes but not Merkel cells were necessary to establish innervation patterns during development. These findings identify key cell types and signaling pathways required for targeting Merkel-cell afferents to discrete mechanosensory compartments.

Tn5 transposase cleaves the transposon end using a hairpin intermediate on the transposon end. This involves a flipped base that is stacked against a tryptophan residue in the protein. However, many other members of the cut-and-paste transposase family, including the RAG1 protein, produce a hairpin on the flanking DNA. We have investigated the reversed polarity of the reaction for RAG recombination. Although the RAG proteins appear to employ a base-flipping mechanism using aromatic residues, the putatively flipped base is not at the expected location and does not appear to stack against any of the said aromatic residues. We propose an alternative model in which a flipped base is accommodated in a nonspecific pocket or cleft within the recombinase. This is consistent with the location of the flipped base at position -1 in the coding flank, which can be occupied by purine or pyrimidine bases that would be difficult to stabilize using a single, highly specific, interaction. Finally, during this work we noticed that the putative base-flipping events on either side of the 12/23 recombination signal sequence paired complex are coupled to the nicking steps and serve to coordinate the double-strand breaks on either side of the complex

Hypomorphic RAG mutants with severely reduced V(D)J recombination activity cause Omenn Syndrome (OS), an immunodeficiency with features of immune dysregulation and a restricted TCR repertoire. Precisely how RAG mutants produce autoimmune and allergic symptoms has been unclear. Current models posit that the severe recombination defect restricts the number of lymphocyte clones, a few of which are selected upon Ag exposure. We show that murine RAG1 R972Q, corresponding to an OS mutation, renders the recombinase hypersensitive to selected coding sequences at the hairpin formation step. Other RAG1 OS mutants tested do not manifest this sequence sensitivity. These new data support a novel mechanism for OS: by selectively impairing recombination at certain coding flanks, a RAG mutant can cause primary repertoire restriction, as opposed to a more random, limited repertoire that develops secondary to severely diminished recombination activity