Histological Stratification of Thick and Thin Plaque Psoriasis Explores Molecular Phenotypes with Clinical Implications

Abstract

Psoriasis, which presents as red, scaly patches on the body, is a common, autoimmune skin disease that affects 2 to 3 percent of the world population. To leverage recent molecular findings into the personalized treatment of psoriasis, we need a strategy that integrates clinical stratification with molecular phenotyping. In this study, we sought to stratify psoriasis patients by histological measurements of epidermal thickness, and to compare their molecular characterizations by gene expression, serum cytokines, and response to biologics. We obtained histological measures of epidermal thickness in a cohort of 609 psoriasis patients, and identified a mixture of two subpopulations-thick and thin plaque psoriasis-from which they were derived. This stratification was verified in a subcohort of 65 patients from a previously published study with significant differences in inflammatory cell infiltrates in the psoriatic skin. Thick and thin plaque psoriasis shared 84.8% of the meta-analysis-derived psoriasis transcriptome, but a stronger dysregulation of the meta-analysis-derived psoriasis transcriptome was seen in thick plaque psoriasis on microarray. RT-PCR revealed that gene expression in thick and thin plaque psoriasis was different not only within psoriatic lesional skin but also in peripheral non-lesional skin. Additionally, differences in circulating cytokines and their changes in response to biologic treatments were found between the two subgroups. All together, we were able to integrate histological stratification with molecular phenotyping as a way of exploring clinical phenotypes with different expression levels of the psoriasis transcriptome and circulating cytokines.

Fig 1

(A) Difference in epidermal thickness between lesional and non-lesional skin. Expectation maximization algorithm identifies two underlying distributions of the epidermal thickness difference (thick and thin plaque psoriasis). (B) Epidermal thickness of thick and thin plaque psoriasis. Epidermal thickness is significantly different between thick and thin plaque psoriasis in the lesional skin (n = 609 lesional and non-lesional matched biopsies, p <0.05, ANOVA, Tukey’s HSD test). (C) Inflammatory cell infiltrates in the dermis of thick and thin plaque psoriasis. CD3 ⁺ T cells and CD11c ⁺ dendritic cells are significantly different between thick and thin plaque psoriasis in the lesional skin (n = 65, p <0.05). Bars represent means; error bars represent standard error of the mean (SEM).

Fig 2. Comparison of differentially expressed genes (DEGs) between thick and thin plaque psoriasis.

(A) Heatmap that displays the 12,001 differentially expressed probesets (FCH >2.0, p <0.05, and FDR < 0.05). The distance matrix was built based on Euclidean distances and the McQuitty algorithm was used for clustering. (B) Scatter plot that displays the high correlation of DEGs between thick and thin plaque psoriasis (log₂ fold change). (C) Area-proportional Venn diagram comparing DEGs between thick and thin plaque psoriasis (>2-fold change and <0.05 false discovery rate). (D) Differentially expressed genes among the meta-analysis derived transcriptome genes (MAD3, Tian et al., 2012).

Fig 3. Comparison of psoriasis transcriptome scores between thick and thin plaque psoriasis.

Based on psoriasis transcriptome references, psoriasis transcriptome scores are calculated by the combined z-score gene set variation analysis (GSVA) method. The absolute values of psoriasis transcriptome scores are consistently higher in thick plaque psoriasis compared to those of thin plaque psoriasis (*p <0.1, **p <0.05, ***p <0.01).

Fig 4. Comparison of psoriatic gene expression normalized to the house-keeping gene, human acidic ribosomal protein (hARP).

(A) Gene expression is significantly different only within lesional skin. (B) Gene expression is not significantly different within both lesional and non-lesional skin. (C) Gene expression is significantly different only within non-lesional skin (n = 16 for thick plaque psoriasis, n = 20 for thin plaque psoriasis; *p < 0.05; bars represent means; error bars represent SEM).

Fig 5. Comparison of serum TNF-α, IL-6, and IL-8 between thick and thin plaque psoriasis.

Serum levels of TNF-α were not significantly different (p = 0.11), but its downstream cytokines, IL-6 and IL-8, were significantly higher in thick plaque psoriasis compared to thin plaque psoriasis (p = 0.0035 for IL-6, p = 0.0036 for IL-8) for a mixed effect model with a random intercept for the cohort (n = 19 for thick plaque psoriasis, n = 7 for thin plaque psoriasis; bars represent means; error bars represent SEM).

Fig 6. Comparison of treatment response between thick and thin plaque psoriasis.

(A) Percent improvement in Psoriasis Area Severity Index (PASI) is compared between Etanercept (12 with thick plaque psoriasis and 15 with thin plaque psoriasis) and Ustekinumab 90 mg treatment (12 with thick plaque psoriasis and with 12 thin plaque psoriasis). (B) Serum TNF-α increased more in thick plaque psoriasis after 12 weeks of Etanercept treatment (p = 0.04). In contrast, it decreased with Ustekinumab treatment and there was no significant difference between thick and thin plaque psoriasis (p >0.05). Bars represent means; error bars represent SEM.