The characteristics of participants
In order to explore the taxonomic composition of the gut microbiota from patients with psoriasis in comparison with healthy controls, 60 fecal samples were collected from 30 patients diagnosed with psoriasis and 30 healthy age-matched individuals for analysis. The healthy controls were composed of 20 males and 10 females, with a mean age of (43.7 ± 13.21) years old and no history of psoriasis. The psoriasis patients were composed of 20 men and 10 women, with a mean age of (43.13 ± 13.79) years old. The mean duration of the disease was (14.75 ± 11.32) years. According to the medical history and physical examinations, 18 of the 30 patients with psoriasis had the symptoms of pruritus, and the skin lesions were found to be more than 50% in 18 of the 30 patients (Table 1).
Table 1
Characteristics of patients with psoriasis (n = 30) and healthy individuals (n = 30) included in this study
| Psoriasis | Healthy |
Male/Female | 20 / 10 | 20 / 10 |
Age (years) | 43.13 ± 13.79 | 43.7 ± 13.21 |
Early-onset psoriasis (< 40 years) | 25 / 30 | - |
Duration of the disease (years) | 14.75 ± 11.32 | - |
Pustular psoriasis | 6 / 30 | - |
Pruritus | 18 / 30 | - |
Psoriasis area ≥ 50% | 18 / 30 | - |
The biochemical examination of blood in the psoriasis group found that the mean level of white blood cell (WBC) was 7.55 ± 0.52 × 109 L-1, of alanine transaminase (ALT) was (21.95 ± 3.87) U L-1, of aspartate aminotransferase (AST), was (20.18 ± 1.90) U L-1, of total cholesterol (TC), was (3.99 ± 0.18) mmol L − 1, of triglyceride (TG), was (1.62 ± 0.19) mmol L − 1, of high-density lipoprotein (HDL) was (1.02 ± 0.05) mmol L − 1, of low-density lipoprotein (LDL) was (2.68 ± 0.15) mmol L − 1, of fasting blood glucose (FBS) was (4.88 ± 0.16) mmol L − 1, and of hypersensitive c-reactive protein (hsCRP) was (11.88 ± 4.72) mg L − 1, of Immunoglobulin A (Ig A) was 2.54 ± 0.26 g L-1, of Immunoglobulin E (Ig E) was 2.54 ± 0.26 IU mL-1, of complement 3 (C3) was 1.09 ± 0.03 g L-1, of interleukin-2R (IL-2R) was 678.61 ± 106.33 U mL-1, of interleukin-6 (IL-6) was 10.91 ± 4.59 pg mL-1, of interleukin-8 (IL-8) was 45.07 ± 31.57 pg mL-1.
Fecal microbiota analysis
Bacterial DNA extracted from fecal samples was used for 16S rRNA sequencing analyses. 60 Samples Clean Reads generated a total of 7656 518 single-end reads with an average of 127608 reads per sample. Through overlap relationship between reads, we spliced reads into Tags, then clustered Tags into OTU. A total of 635 OTUs were obtained, using Venn diagrams to visually show the number of shared and unique OTUs in different groups. The results showed that there were about 465 OTUs shared in the two groups, 102 and 68 OTUs in the healthy control group (N) and the psoriasis group (P) respectively (Fig. 1A). Then the OTUs sequence and Greengenes database were annotated, and the result showed that predominant microbes were included. The top 5 taxa in relative abundance at family level include Bacteroidaceae, Lachnospiraceae, Prevotellaceae, Veillonellaceae, and Ruminococcaceae. The top 5 taxa in relative abundance at the genus level include Bacteroides, Prevotella, Roseburia, Faecalibacterium, and Lachnospira. The top 5 taxa in relative abundance at order level include Bacteroidales, Clostridiales, Enterobacteriales, Fusobacteriales, and Burkholderiales. The top 5 taxa in relative abundance at the phylum level include Bacteroidetes, Firmicutes, Proteobacteria, Fusobacteria, and Actinobacteria. The top 5 taxa in relative abundance at species level include Prevotella_copri, Bacteroides_plebeius, Faecalibacterium_prausnitzii, Roseburia_faecis, and Escherichia_coli (Fig. 1B).
The OUT Rank Abundance curves obtained for each sample tend to plateau, therefore indicating that sample biodiversity was adequately covered with the applied sequencing depth (Supplement 1). The Alpha diversity box showed that there was no significant difference based on the Wilcox Test in the microbial diversity of patients with psoriasis (P), compared with the healthy controls (N) (Supplement 2 and 3).
Moreover, the β-diversity analyses revealed significant clustering (P-value < 0.001) between healthy individuals and patients with psoriasis, supporting the theory that the gut microbiota composition differed between both groups (Fig. 2A and 2B).
Next, bacterial communities from both healthy individuals and psoriasis patients were analyzed. At the family and genus level, the microbial composition differed between the psoriasis patients and healthy individuals. We identified the presence of top 10 taxa in relative abundance at the family level and the Wilcoxon test showed that Veillonellaceae and Ruminococcaceae were relatively more abundant in psoriasis patients, whereas Lachnospiraceae were relatively less abundant in psoriasis patients (all P < 0.05). Moreover, at the genus level, Faecalibacterium and Megamonas were relatively more abundant in psoriasis patients compared with health control (all P༜0.05) (Fig. 2C and 2D). We then conducted a LEfSe comparison of the gut microbiota between the control and psoriasis groups to explore the specific bacterial taxa associated with psoriasis development. The structure and predominant bacteria of the microbiota in the control and psoriasis groups were represented in a cladogram (Fig. 2E). The greatest difference in taxa from the phylum to the genus level was identified by an LDA score (Fig. 2F). The two taxa with the highest score in the psoriasis group were Veillonellaceae and Megamonas, which is consistent with the previous one.
Correlation between gut microbiota and clinical indices
Correlation analyses were performed to further investigate identified potential associations of key microbial genera with clinical indices above (Fig. 3). Exact figures of these clinical indices were showed in Supplement 4 and 5. Complement 3 (C3) showed a negative relationship with Bacteroides (P༜0.001) and Escherichia (P༜0.01), but it showed a positive relationship with the Prevotella group (P༜0.01). Coprococcus had a great relationship with many clinical indices, and it showed a positive relationship with FBS (P༜0.001) and IgA (P༜0.001). Additionally, IL2R which is abnormal in psoriasis patients showed a positive relationship with Phascolarctobacterium (P༜0.001) and a negative relationship with the Dialister group (P༜0.001).
Different microbiota analysis between PV and PP
To compare the microbiota communities of PV (24 cases) and PP (6 cases) were compared. Heat map based on the abundance ranks of the class level was demonstrated through R (v3.1.1) gplots. Hierarchical clustering (Euclidean distance, complete linkage) showed that the PV group and healthy control group (N) tended to cluster together and the PP group is being singled out them (Fig. 4A). Then we identified the presence of the top 10 taxa in relative abundance at the class level and the Kruskal test showed that Gammaproteobacteria was relatively less abundant in PP group than PV group and N group (all P-value༜0.05) (Fig. 4B). LefSe analysis was performed to identify differentially abundant taxa in the PP group compared with the PV group (Fig. 4C). Consistent with our previous analysis, Gammaproteobacteria and Veillonellaceae had the largest LDA score indicating that Gammaproteobacteria and Veillonellaceae were consistently different between the PP group and PV group. In addition, the genus level Faecallibacterium and Anaerorhabdus were the most significant taxa in the PP group which could help us distinguish PP from PV.