3.6 UVB inhibits negative regulators and activates functional and developmental genes to promote Treg induction
To study the mechanisms underlying the effects of UVB on antigen-specific Treg induction, we collected Tregs from UVB-untreated/treated skin of mice with imiquimod-induced psoriasiform dermatitis. RNA sequencing (RNA-seq) of Tregs from two independent experiments of UVB-untreated and treated skin samples was performed to investigate differentially expressed genes (DEGs) related to UVB treatment. Compared to UVB-untreated Tregs, UVB-treated Tregs showed alterations in 880 upregulated DEGs and 243 downregulated DEGs, after false discovery rate (FDR <0.05) correction and |log2-fold change| ≥ 1. Principle component analysis (PCA) unveiled an altered transcriptional profile in UVB-treated Tregs relative to UVB-untreated Tregs (Figure S6A). Gene ontology analysis of the significantly upregulated DEGs revealed biological functions of cellular homeostasis, cell proliferation, and cell motility (Figure 5A). These findings suggest that UVB-treated Tregs show stable cell fate, high proliferative ability, and sustainable cellular location in the skin.
We performed single-cell RNA sequencing (scRNA-seq) on blood samples from two psoriasis patients whose disease was greatly mitigated by UVB treatment to investigate the underlying molecular mechanisms. Samples from the two patients yielded 4,832 CD4+ T cells, averaging 39,811 genes per cell, and comprised of 3,045 and 1,787 CD4+ T cells, which were well-distributed across the UMAP (Figure S6B). No distribution bias across cell clusters was evident in either the pre- (n = 2,502) or post-UVB (n = 2,330) treatment cells (Figure 5B). Subsequent analysis of CD4+ T cell phenotypic heterogeneity identified several clusters, which were annotated as naive T, T memory (Tmem), T effector (Teff), and Tregs based on known gene markers (Figure 5C). We identified different gene profiles between Tregs derived from UVB-untreated/treated skin of mice and before UVB/after UVB human blood samples, respectively (Figure 5D). Thirty-one genes were identified and were categorized into three gene sets. The first gene set, including FOXO3 , AHR , andSP1 , is involved in Treg differentiation, maintenance, and function. These genes were upregulated in both mouse skin and human blood Tregs upon UVB treatment, indicating Treg cellular functional improvement. The second gene set is classified as negative regulators. These genes were downregulated upon UVB treatment, supporting the examined Treg cell expansion. Notably, the changes in the expression ofIDH1 (p = 0.03), VAV1 (p = 0.02), and RAB35 (p = 0.04) were significant, a finding that merits further mechanistic investigation (Figure 5D,E). The last gene set, including HAVCR2 ,NFKB1 , and TIGIT , is involved in TCR activation. Most of these genes were upregulated upon UVB treatment (Figure 5D). Overall, these genes indicate that UVB promotes Treg differentiation and expansion by cultivating Treg functional and developmental genes and inhibiting negative regulators.