Algae-derived polysaccharides supplementation ameliorates heat stress-induced impairment of bursa of Fabricius via modulating NF-κB signaling pathway in broilers

This study aimed to investigate the protective effects of dietary algae-derived polysaccharides (ADP) from Enteromorpha prolifera against heat stress (HS)-induced bursa of Fabricius injure in broilers, and to elucidate the molecular mechanisms underlying the protective effect. A total of 144 8-week-old male yellow-feathered broilers were randomly allocated into 3 treatments of 6 replicates each (8 broilers per replicate): thermoneutral zone group (TN, fed basal diet); heat stress group (HS, fed basal diet); heat stress + ADP group (HSA, basal diet supplemented with 1,000 mg/kg ADP). Broilers in TN group were raised at 23.6 +/- 1.8 degrees C during the whole study. Broilers in HS and HSA groups were exposed to 33.2 +/- 1.5 degrees C for 10 h/day. The experimental period lasted for four weeks. The results showed that HS and dietary ADP had no significant effects on bursa of Fabricius index (P > 0.05). HS exposure increased the apoptosis rate of bursa of Fabricius (P < 0.05), and the apoptosis rate was reduced by dietary ADP (P < 0.05). Besides, broilers in HS and HSA groups had a lower glutathione-S transferase (GST) activity and total anti -oxidation capacity (T-AOC), whereas had a higher malondialdehyde (MDA) levels of bursa of Fabricius than those in TN group (P < 0.05). HS exposure elevated the concentration of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 beta, IL-4, and IL-6, while decreased the concentration of interferon-gamma (INF-gamma) and IL-2 (P < 0.05), and dietary inclusion of ADP reduced the IL-1 beta level and increased the IL-2 level of bursa of Fabricius (P < 0.05). Compared with TN group, broilers in HS and HSA groups had lower relative mRNA expression of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and GSTT1 in bursa of Fabricius (P < 0.05). Additionally, HS exposure down-regulated the mRNA expression of inhibitor kappa B alpha (I kappa B alpha), IFN-gamma, and IL-2, while up-regulated the mRNA expression of nuclear factor-kappa B (NF-kappa B) p65, TNF-alpha, IL-1 beta, and IL-6 in bursa of Fabricius (P < 0.05). However, dietary inclusion of ADP up-regulated the mRNA expression of I kappa B alpha and down-regulated the mRNA expression of NF-kappa B p65, TNF-alpha, and IL-6 in bursa of Fabricius (P < 0.05). Furthermore, HS exposure increased the relative protein expression levels of total and nuclear NF-kappa B p65 (P < 0.05), but dietary ADP supplementation reduced the relative protein expression levels of total and nuclear NF-kappa B p65 in bursa of Fabricius (P < 0.05). Collectively, dietary ADP ameliorated the impairment of histology, cell apoptosis and immune balance in bursa of Fabricius of heat stressed broilers, which is involved in modulation of NF-kappa B signaling pathway.

Automated summary

This study demonstrated the protective effect of ADP on heat stress-induced bursa of Fabricius injury in broilers, by modulating the NF-kappa B signaling pathway to alleviate histological damage, cell apoptosis, and immune imbalance.