Date of Award
Doctor of Philosophy (PhD)
Terminally differentiated keratinocytes are essential for skin barrier function and are surrounded by an involucrin (IVL)-rich cornified envelope. Increased IVL expression in the epidermis is associated with recent positive selection in European populations, yet the functional significance of this finding is unclear. An upstream enhancer of IVL, the 923 enhancer, regulates IVL expression, and the impact of IVL enhancer variants on involucrin expression in modifying the penetrance of filaggrin (FLG) loss-of-function variants associated with atopic dermatitis (AD) has not been explored. I hypothesize involucrin to modulate the environmentally sensitive Vitamin D receptor (Vdr) activity in the epidermis and involucrin enhancer variants to modify the penetrance of FLG LOF in atopic dermatitis. I investigated Vdr activity in both Ivl -/- and wild-type (WT) mice using vitamin D agonist (MC903) treatment that gives rise to MC903- mediated skin inflammation and observed a significant reduction in skin inflammation in MC903-treated Ivl -/- mice. Using scRNA-seq, I evaluated the dampened immune cellular response and observed a decrease in significant reductions in CD4+ T cells, basophils, macrophages, and monocytes in Ivl -/- mouse skin. Reduced expression of CD4+ T cells and basophils was validated by flow cytometry of MC903-treated skin. The reduced Vdr-mediated inflammation correlates with decreased nuclear Vdr immunostaining activity in MC903-treated Ivl -/- primary keratinocytes. I further investigated the impact of Ivl deficiency and MC903 treatment on the skin microbiome using 16S bacterial phylotyping and discovered dysbiosis in untreated Ivl -/- mice with decreased Muribaculaceae, and increased Aerococcus and Streptococcus, that persisted after MC903 treatment. In order to determine potential candidates linking Ivl to Vdr, I employed a multi-omics approach integrating ATAC-seq, RNA-seq, and LC/MS proteomics analyses in newborn Ivl -/- vs. WT mouse skin and identified Casein Kinase 1 epsilon (Csnk1e) as a top candidate. I discovered a closed differentially accessible region (DAR) at the transcriptional 3’ end of Csnk1e, corresponding to an ENCODE distal enhancer mouse and human cCRE bound by the Ep300 transcription factor. The finding coincides with the discovery for decreased Csnk1e ENSMUST00000230599 isoform expression containing the serine/threonine kinase activity domain in Ivl -/- mice. The reduction of isoform ENSMUST00000230599 was confirmed in a western blot analysis of WT and Ivl -/- newborn skin. The impact of IVL enhancer variants associated with decreased IVL expression in the context of FLG-LOF AD was examined using targeted sequencing for FLG and the 923 IVL enhancer in a cohort of AD patients. Of the discovered IVL enhancer variants, seven are known GTEx IVL eQTLs associated with decreased skin IVL that were considerably enriched in FLG LOF-AD patients vs. GTEx FLG LOF-unaffected controls. These studies identify a functional role for involucrin to regulate Vdr activity in the skin, microbial niche composition, and likely penetrance of FLG-LOF AD, which together highlight the adaptivity of IVL for epidermal function.
Chair and Committee
Cristina de Guzman Strong
Schmidt, Alina, "Understanding the role of involucrin in skin inflammation" (2022). Arts & Sciences Electronic Theses and Dissertations. 2687.