Psoriasis is a highly prevalent and chronic inflammatory skin disorder. According to the latest epidemiological survey, the annual incidence rate of psoriasis in European countries is about 0.96 per thousand[38]. This disease is often chronic and recurrent in nature, which offers different degrees of negative impact on the life of patients, involving physiology, psychology, daily life, social contact, family and other aspects. A foreign survey on psoriatic patients revealed that 79% of the patients agreed that the disease had a negative impact on their lives, and 10% of the patients entertained the idea of suicide[39]. Unfortunately, despite the availability of multiple therapeutics for psoriasis, this disease remains incurable and a vast majority of treated patients experience adverse reactions to psoriatic drugs. As a result, there is great urgency in the development of highly specific and efficient psoriatic biomarkers. Here, we utilized bioinformatics analysis of three separate microarray data sets, involving a total of 265 psoriatic vs. 213 healthy samples, to identify genes specific to the pathogenesis of psoriasis. Among the DEGs studied, CXCL8 showed the largest fold change and is intimately linked to viral defense, type I interferon axis, and its corresponding cellular response. We further delineated the CXCL8 role in psoriasis by assessing its overall expression profile along with evaluating its underlying mechanism of action.
Multiple studies have demonstrated CXCL8 to be an essential cytokine. It often regulates tumor growth, invasion, and neovascularization and can be found in excess in tissues from skin squamous cell carcinoma patients[40]. Earlier reports have also indicated that CXCL8 modulates the formation of psoriasis Munro micro abscess. We, therefore, assessed CXCL8 expression in patients with psoriasis. Given that the role of CXCL8 in psoriasis has not been fully elucidated, we also explored the underlying function of CXCL8 in psoriasis.
Here, we conducted a comprehensive analysis of three microarray data sets to retrieve DEGs involved with psoriasis verses healthy skin specimen. We discovered 187 DEGs in total among the 3 data sets. We further explored interrelationships between DEGs, using GO and KEGG enrichment analyses. Moreover, we conducted analysis with the STRING database to verify the links among the DEGs. 30 DEGs were chosen as hub genes carrying degrees ≥20. Among them, CXCL8 exhibited the largest node degrees with 76, indicating its strong importance in the development and/or progression of psoriasis. Furthermore, using GO enrichment analysis, we demonstrated that alterations in the markedly obvious modules occurred in response to virus, type I interferon axis and its corresponding cellular response. Conversely, using KEGG, it was shown that the DEGs were mainly in the NOD-like receptor axis, interaction between cytokine and cytokine receptor and the IL−17 axis. Multiple studies have reported a strong relation between the IL−17 axis and psoriasis. In fact, IL−17 expression is markedly elevated in the psoriatic skin, compared to healthy skin[41]. It was also shown in keratinocytes that IL-17 stimulated the production of pro-inflammatory cytokines like IL-6 and IL-8, which exacerbated psoriasis[42]. Moreover, topical administration of imiquimod, a Toll-like receptor (TLR) 7/8 ligand and powerful immunologic stimulator, resulted in psoriasis-resembling dermatitis in mice, with simultaneous increases in IL-17A and IL-17F levels[43]. Alternately, both CsA and anti-TNF-a agents downregulated IL-17A, IL-23p19, and chemokine (C-C motif) ligand 20 in psoriatic skin, thereby improving eruptions[42.44-46]. Collectively, these evidences suggest a strong involvement of IL-17A in the progression of psoriasis.
Interleukin-22 (IL-22) belongs to the IL-10 cytokine family[47-48] and is intimately linked to psoriatic inflammation (Fig. 1). It is primarily made by Th17 cells. However, T22 have also been shown to exclusively produce IL-22. The IL-22 receptor can be found on keratinocytes, wherein IL-22 stimulates epidermal hyperplasia via a rise in keratinocyte proliferation. Clinically, serum IL-22 is markedly elevated in psoriatic patients, as opposed to healthy individuals[49]. Additionally, IL-22 is known to be highly expressed in psoriatic lesions and the levels fall with anti-psoriatic therapy[39]. Based on these data, IL-22 not only plays a crucial role in keratinocyte proliferation, but also regulates pasoriasis development and progression.
Dendritic cells produce interleukin (IL)-23, which regulates Th17 proliferation. The TH17 cells, in turn, are responsible for stimulating a variety of cytokines, including IL-17A, IL-17F, and IL-22. Among them, IL-17A and IL-22 was reported to be involved in keratinocyte proliferation and positively regulate tumor necrosis factor (TNF)-a, chemokine (C-X-C motif) ligand (CXCL)1, and CXCL8. Taken together, these conclusions suggest the involvement of these genes in multiple mmune-provoked disease states.
Using single gene ROC analysis, we revealed that CXCL8 has great potential to serve as a bio-marker for psoriatic diagnosis (AUC values>0.7). Moreover, based on CXCL8 predictions from starBase, miRDB and miRWalk, we generated a CXCL8-ceRNA network that included hsa-miR-1294, hsa-miR-140-3p, hsa-miR-185-5p, hsa-miR-4306, hsa-miR-4644, and hsa-miR-493-5p. lncRNAs modulate immune and inflammatory pathways via multi-mechanistic regulation of gene expression [50]. Among these mechanisms, the ceRNA axis has been widely investigated. Based on the ceRNA theory, lncRNA activates target gene expression by sequestering miRNA that would otherwise suppress gene activation. [51]. Qiao et. al. [52], for instance, revealed a lncRNA‑MSX2P1 axis that stimulates S100A71 and facilitates IL‑22‑induced keratinocytes production via depressing miR‑6731‑5p action. Similarly, Li et al [53] reported that lncRNA H19 modulates keratinocyte differentiation by sequesteting miR‑130b‑3p and augmenting desmoglein 1 expression. Consistent with these studies, our work also demonstrated a strong involvement of ceRNA in the development and progression of psoriasis via sequestering multiple potential miRNAs.
This study highlighted a promising bio-marker for psoriasis. Nevertheless, our work had some notable limitations. Firstly, the stratification analysis and interaction between factors did not receive detailed investigation. Moreover, due to its retrospective nature, we also couldn’t rule out selective and recall biases. Hence, we propose prospective future studies to increase the statistical power and obtain more reliable conclusions. Secondly, apart from bioinformatics being a powerful tool for genome-wide studies, inadequate knowledge of underlying mechanisms may have limited our identification of effective psoriatic bio-markers. Hence, CXCL8 must be examined extensively at the molecular, cellular, and organismal level to confirm its significance in psoriatic diagnosis.