Heat Stress Weakens the Skin Barrier Function in Sturgeon by Decreasing Mucus Secretion and Disrupting the Mucosal Microbiota

Abstract

Heat stress induced by global warming has damaged the well-being of aquatic animals. The skin tissue plays a crucial role as a defense barrier to protect organism, however, little is known about the effect of heat stress on fish skin, particularly in cold-water fish species. Here, we investigated the effects of mild heat stress (24°C, MS) and high heat stress (28°C, HS) on Siberian sturgeon skin using RNA-seq, histological observation, and microbial diversity analysis. In RNA-seq, 8,819 differentially expressed genes (DEGs) in MS vs. C group and 12,814 DEGs in HS vs. C group were acquired, of which the MS vs. C and HS vs. C groups shared 3,903 DEGs, but only 1,652 DEGs were successfully annotated. The shared DEGs were significantly enriched in pathways associating with mucins synthesis. Histological observation showed that the heat stresses significantly reduced the number of skin mucous cells and induced the damages of epidermis. The microbial diversity analysis elicited that heat stress markedly disrupted the diversity and abundance of skin microbiota by increasing of potential pathogens (Vibrionimonas, Mesorhizobium, and Phyllobacterium) and decreasing of probiotics (Bradyrhizobium and Methylovirgula). In conclusion, this study reveals that heat stress causes adverse effects on sturgeon skin, reflecting in decreasing the mucus secretion and disordering the mucosal microbiota, which may contribute to develop the preventive strategy for heat stress caused by global warming.

Keywords: Siberian sturgeon; heat stress; microbial diversity; mucous cells; skin.

FIGURE 1

Venn diagram, KEGG enrichment analysis of the shared DEGs in MS vs. C and HS vs. C groups. (A) Venn diagram showed the 8,818 in MS vs. C group and 12,813 DEGs in HS vs. C group, and 1,652 shared annotated DEGs. (B) Scatter diagram of KEGG enrichment analysis of the shared DEGs. X-axis (enrichment factor) indicates the enrichment level of DEGs in each pathway, while Y-axis represents the reliability of enrichment analysis of each pathway.

FIGURE 2

Venn diagram and KEGG enrichment analysis of the non-shared DEGs in MS vs. C and HS vs. C groups. (A) Venn diagram showed 1,494 and 3,032 non-shared annotated DEGs in MS vs. C and HS vs. C groups, respectively. (B,C) Scatter diagram of KEGG enrichment analysis. X-axis (enrichment factor) indicates the enrichment level of DEGs in each pathway, while Y-axis represents the reliability of enrichment analysis of each pathway.

FIGURE 3

Histological changes in the skin of Siberian sturgeon after exposure to the heat stresses. (A–C) indicates hematoxylin and eosin (H&E) staining, (D–F) represents Periodic Acid-Schiff (PAS) staining. (A,E) 20°C group, (B,F) 24°C group, (C,G) 28°C group, scale bar = 100 μm. The exfoliated cells are shown by the white arrows, black arrows delegate mucus cells. (D) Skin health status (organ index) of sturgeon in different groups. (H) Mucus cell count between different groups, *p < 0.05 indicates a significant difference compared to the control group.

FIGURE 4

Species composition analysis among different groups. (A) Venn comparison diagram of different groups. (B) Principal Component Analysis (PCA).

FIGURE 5

The relative abundance of phylum (A) and genus (B) under the heat stresses, only classes that are present at abundances >1% in at least one sample are shown.

FIGURE 6

LEfSe analysis of the differences in skin microbiota of Siberian sturgeon. (A) Taxonomic characterization of differences in skin microbiota of Siberian sturgeon under different temperature treatments, the concentric circles from the inside to the outside stand for different taxonomic classes (phylum to family). Different color areas point to different groups (the red nodes in the branches represented microbial taxa that play an important role in the control group, the blue nodes indicate microbial taxa that plays a vital role in the MS group, the green nodes mean microbial taxa that play a key role in the HS group, while the yellow nodes show no significant difference). Abundance of skin microbiota were revealed by the size of each node. (B) Linear discriminant analysis (LDA) for three groups, scores for remarkable abundant of skin microbiota. (C) The relative proportion of species under different temperatures, only classes that are present at abundances >1% in at least one sample are shown. *p < 0.05, indicates a significant difference compared to the group C.