In-depth examination of the zinc-mitigation of the molecular effects of heat stress-induced intestinal damage in broilers.

Three experiments were conducted to elucidate the protective mechanisms of zinc (Zn) as ZnSO4.7H2O (ZnSO4) or Zn proteinate with moderate chelation strength (Zn-Prot M) against heat stress (HS)-induced damage to broiler intestine or jejunal organoids. In experiment 1, under high temperature (HT: 34 ± 1°C, 8 h/d; 28 ± 1°C, 16 h/d), a control (HT-CON) and four groups from a 2 (Zn sources: Zn-Prot M and ZnSO4) × 2 (added Zn levels: 30 and 60 mg/kg) factorial arrangement were designed. Under normal temperature (NT: 23 ± 1°C, 24 h/d), a control (NT-CON) and a pair-fed group were included. HS increased (P < 0.04) broiler serum diamine oxidase activity and fluorescein isothiocyanate dextran content. However, dietary added Zn, notably at 60 mg/kg, decreased (P < 0.02) these elevated serum indices in HS-broilers. In experiment 2, transcriptome sequencing was conducted in jejunal tissues collected from the broilers in the groups of NT-CON, HT-CON, HT-ZnSO4 and HT-Zn-Prot M at 60 mg/kg. Dietary supplemental Zn, especially Zn-Prot M, mitigated the HS-induced inhibitions of the phosphatidylinositol 3-kinase (PI3K)/serine threonine kinase (AKT), mitogen activated protein kinase (MAPK), and cell cycle pathways. In experiment 3, broiler jejunal organoids were maintained under NT (40°C, CON) and HT (44°C, 12 h, HS). The HT groups comprised a control and a 2 × 2 factorial arrangement of added Zn sources (Zn-Prot M and ZnSO4) and levels (50 and 100 μmol/L). Supplemental Zn, especially Zn-Prot M at 50 μmol/L, mitigated (P < 0.05) HS-induced inhibitions of mRNA or protein expression levels of occludin, junctional adhesion molecule 1/3, zonula occludens-1, Zn finger protein A20 (A20) and cyclin-B1/D1, and promotions of mRNA or protein expression levels of nuclear factor kappa-B (NF-κB) p65 and matrix metalloproteinase (MMP)-2/9. In conclusion, the optimal supplemental Zn, particularly Zn-Prot M, could effectively mitigate HS-induced damage to broiler intestine or jejunal organoids possibly by promoting cell proliferation and the expression of tight junction proteins via the PI3K/AKT, MAPK, A20/NF-κB p65/MMP-2/9 and cell cycle pathways.