Calcium overload and reactive oxygen species accumulation induced by selenium deficiency promote autophagy in swine small intestine

Selenium(Se)deficiency can seriously affect the small intestine of swine,and cause diarrhea in swine.However,the specific mechanism of Se deficiency-induced swine diarrhea has rarely been reported.Here,to explore the damage of Se deficiency on the calcium homeostasis and autophagy mechanism of swine,in vivo and in vitro models of swine intestinal Se deficiency were established.Twenty-four pure line castrated male Yorkshire pigs(45 d old,12.50±1.32 kg,12 full-sibling pairs)were divided into 2 equal groups and fed Se-deficient diet(0.007 mg Se/kg)as the Se-deficiency group,or fed Se-adequate diet(0.3 mg Se/kg)as the control group for 16 weeks.The intestinal porcine enterocyte cell line(IPEC-J2)was divided into 2 groups,and cultured by Se-deficient medium as the Se-deficient group,or cultured by normal medium as the control group.Morphological observations showed that compared with the control group,intestinal cells in the Se-deficiency group were significantly damaged,and autophagosomes increased.Autophagy staining and cytoplasmic calcium staining results showed that in the Sedeficiency group,autophagy increased and calcium homeostasis was destroyed.According to the reactive oxygen species(ROS)staining results,the percentage of ROS in the Se-deficiency group was higher than that in the control group in the in vitro model.Compared with the control group,the protein and mRNA expressions of autophagy-calcium-related genes including Beclin 1,microtubule-associated proteins 1 A(LC3-1),microtubule-associated proteins 1 B(LC3-2),autophagy-related protein 5(ATG5),autophagy-related protein 12(ATG12),autophagy-related protein 16(ATG16),mammalian target of rapamycin(mTOR),calmodulin-dependent protein kinase kinaseβ(CAMKK-β),adenosine 5’-monophosphate-activated protein kinase(AMPK),sarco(endo)plasmic reticulum Ca2+-ATPase(SERCA),and calpain in the Se-deficiency group were significantly increased which was consistent in vivo and in vitro(P<0.05).Altogether,our results indicated that Se deficiency could destroy the calcium homeostasis of the swine small intestine to trigger cell autophagy and oxidative stress,which was helpful to explain the mechanism of Se deficiency-induced diarrhea in swine.

Influence of Long-Term Fertilization on Selenium Accumulation in Soil and Uptake by Crops

Continuous applications of organic and inorganic fertilizers can affect soil and food quality with respect to selenium （Se） concen- trations. A long-term （over 20 years） experimental field study, started in 1989, was conducted to investigate the changes in soil Se fractions and its uptake by crops, as affected by different fertilizer practices, in the North China Plain with an annual crop rotation of winter wheat and summer maize. The long-term experiment was arranged in a complete randomized block design consisting of 4 replications with 7 fertilizer treatments： 1） organic compost （OC）, 2） half organic compost plus half N-P-K chemical fertilizers （OC ＋ NPK）, 3） N-P-K fertilizers （NPK）, 4） N-P fertilizers （NP）, 5） P-K fertilizers （PK）, 6） N-K fertilizers （NK）, and 7） an un-amended control. Soil samples from the surface （20 cm） were collected in 1989, 1994, 1999, 2004 and 2009 to characterize Se and other soil properties. In 2009, the average soil Se concentrations in the treatments （149 ± 8 beg kg-1） were higher than those in the soil samples collected in 1989 at the beginning of the experiment （112 4- 4 beg kg-1）, and decreased in the order of OC 〉 OC ＋ NPK 〉 NPK NP 〉 PK NK 〉 control. Sequential extraction showed the oxidizable fraction （50.06%± 3.94%） was the dominant form of Se in the soil, followed by the residual fraction （24.12% ± 2.89%）, exchangeable fraction （15.09% ± 4.34%） and Fe-Mn oxides fraction （10.73%±4.04%）. With an increase of soil K, the exchangeable Se concentrations in the soil increased. The Se concentrations in the soil tillage layer （0-20 cm） were mainly related to soil organic carbon （SOC）, although different contributions came from atmospheric deposition, irrigation and fertilizers. With the accumulation of SOC, the uptakes of soil Se by two crops were inhibited. For the OC and OC ＋ NPK treatments, Se concentrations in wheat grains were lower than the critical standard of Se in stable food （100 μg kg·1]. Additionallv. Se concentrations in grains were also decreased by the deficiencies of major soil nutrients, especially P.