Selenium Deficiency Affects the mRNA Expression of Inflammatory Factors and Selenoprotein Genes in the Kidneys of Broiler Chicks.

The aim of this study was to investigate the influence of Se deficiency on the transcription of inflammatory factors and selenoprotein genes in the kidneys of broiler chicks. One hundred fifty 1-day-old broiler chicks were randomly assigned to two groups fed with either a low-Se diet (L group, 0.033 mg/kg Se) or an adequate Se diet (C group, 0.2 mg/kg Se). The levels of uric acid (UA) and creatinine (Cr) in the serum and the mRNA levels of 6 inflammatory factors and 25 selenoprotein genes in the kidneys were measured as the clinical signs of Se deficiency occurred at 20 days old. The results indicated that the contents of UA and Cr in the serum increased in L group (p < 0.05), and the mRNA levels of the inflammatory factors (NF-κB, iNOS, COX-2, and TNF-α) increased in L group (p < 0.05). Meanwhile, the mRNA levels of PTGEs and HO-1 were not changed. In addition, 25 selenoprotein transcripts displayed ubiquitous expression in the kidneys of the chicks. The mRNA levels of 14 selenoprotein genes (Dio1, Dio2, GPx3, Sepp1, SelH, SelI, SelK, Sepn1, SelO, SelW, Sep15, SelT, SelU, and SelS) decreased, and 9 selenoprotein genes (GPx1, GPx2, GPx4, SelPb, Txnrd1, Txnrd2, Txnrd3, SPS2, and SelM) increased in L group (p < 0.05), but the Dio3 and Sepx1 mRNA levels did not change. The results indicated that Se deficiency resulted in kidney dysfunction, activation of the NF-κB pathway, and a change in selenoprotein gene expression. The changes of inflammatory factor and selenoprotein gene expression levels were directly related to the abnormal renal functions induced by Se deficiency.

Protective roles of selenium on nitric oxide-mediated apoptosis of immune organs induced by cadmium in chickens.

Little is known about the influence of subchronic cadmium exposure on apoptosis in the immune organs of birds and the protective effects on apoptosis by selenium against cadmium. The aim of this study was to investigate the effect of subchronic cadmium exposure on nitric oxide and apoptosis in the immune organs of chicken and the protective roles of selenium against cadmium-induced apoptosis. Two hundred ten 30-day-old chickens were randomly assigned to three groups and were fed a basal diet, cadmium+selenium (as 150 mg of CdCl2 per kg of diet+10 mg of Na2SeO3 per kg of diet ) or cadmium (as 150 mg of CdCl2 per kg of diet) in basic diets for 15, 30, 45, and 60 days. Then, the production of nitric oxide, messenger RNA (mRNA level), and the activity of inducible nitric oxide synthase, ultrastructural changes, TUNEL assay, and flow cytometric analysis of apoptosis and Bcl-2 and p53 mRNA levels in the immune organs were examined. The results showed that cadmium exposure caused ultrastructural damage and increased production of nitric oxide, mRNA level, and activity of inducible nitric oxide synthase, the degree, and the number of apoptotic cells in a time-dependent manner. Cadmium exposure decreased Bcl-2 mRNA level and increased p53 mRNA level in a time-dependent manner. Selenium supplementation during dietary cadmium reduced the production of nitric oxide, the mRNA level, and activity of inducible nitric oxide synthase, ultrastructural damage, and apoptosis in the immune organs of chicken. It indicated that cadmium induced nitric oxide-mediated apoptosis of immune organs, and selenium played protective effects against cadmium-induced apoptosis in the immune organs of chickens.

Protective effects of selenium on cadmium-induced brain damage in chickens.

Selenium (Se) is an important dietary micronutrient with antioxidative roles. Cadmium (Cd), a ubiquitous environmental pollutant, is known to cause brain lesion in rats and humans. However, little is reported about the deleterious effects of subchronic Cd exposure on the brain of poultry and the protective roles on the brain by Se against Cd. The aim of this study was to investigate the protective effects of Se on Cd-induced brain damage in chickens. One hundred twenty 100-day-old chickens were randomly assigned to four groups and were fed a basal diet, or Se (as 10 mg Na2SeO3/kg dry weight of feed), Cd (as 150 mg CdCl2/kg dry weight of feed), or Cd + Se in their basic diets for 60 days. Then, concentrations of Cd and Se, production of nitric oxide (NO), messenger RNA (mRNA) level and activity of inducible NO synthase (iNOS), level of oxidative stress, and histological and ultrastructural changes of the cerebrum and cerebellum were examined. The results showed that Cd exposure significantly increased Cd accumulation, NO production, iNOS activities, iNOS mRNA level, and MDA content in the cerebrum and cerebellum. Cd treatment obviously decreased Se content and antioxidase activities and caused histopathological changes in the cerebrum and cerebellum. Se supplementation during dietary Cd obviously reduced Cd accumulation, NO production, mRNA level and activity of iNOS, oxidative stress, and histopathological damage in the cerebrum and cerebellum of chickens. It indicated that Se ameliorates Cd-induced brain damage in chickens by regulating iNOS-NO system changes, and oxidative stress induced by Cd and Se can serve as a potential therapeutic for Cd-induced brain lesion of chickens.

Effects of dietary selenium deficiency or excess on gene expression of selenoprotein N in chicken muscle tissues.

Previous studies have determined the effects of dietary selenium (Se) supplementation on selenoprotein N (SelN, SEPN1), selenophosphate synthetase-1 (SPS1), and selenocysteine-synthase (SecS) mRNA abundance in chicken skeletal and cardiac muscles. To investigate collective responses of these genes to dietary Se concentrations ranging from deficiency to moderately high level in muscle tissues of chicken, 1-day-old chickens were exposed to a diet of deficient Se and supplemented with Se (0.15 mg Se/kg and 1.50 mg Se/kg) as sodium selenite in the feed for 35 days. Muscle tissues (flight, breast, leg, and cardiac muscles) were collected and examined for Se content and mRNA levels of SelN on days 1, 15, 25, and 35 days, respectively. Moreover, SPS1 and SecS mRNA levels were analyzed. The results showed that the expression of SelN gene in cardiac muscle responded to dietary Se concentrations. SelN gene was downregulated in the Se deficiency group (L group), and upregulated in the Se excess group (H group) compared with the moderate Se group (M group) (P < 0.05) in cardiac muscle. Se deficiency mainly unregulated SelN mRNA level in skeletal muscles compared with M group. Excess dietary Se mainly resulted in the upregulation of SelN mRNA level in skeletal muscles compared with the M group. SecS mRNA levels responded to dietary Se concentrations showed a similar change compared with SelN in cardiac muscle. SPS1 mRNA levels responded to dietary Se concentrations showed a downregulation in L group and upregulation in H group. However, SelN mRNA levels displayed a different expression pattern in different skeletal and cardiac muscles. Moreover, Se also regulated the levels of SPS1 and SecS mRNAs. In summary, Se regulated the expression of SelN gene and affected the mRNA levels of SecS and SPS1. The level of Se in the feed may regulate SelN biosynthesis by affecting the levels of SPS1 and SecS mRNA.

The effect of Se-deficient diet on gene expression of inflammatory cytokines in chicken brain.

Selenium (Se) plays an important role in the brain development, function, and degeneration, nutritional encephalomalacia is closely related with dietary Se in avian. However, there is little evidence on the relationship between inflammation and encephalomalacia in avian and the mechanism which Se regulates the inflammatory response in brain tissues remains to be unclear. The present paper describes the effects of Se-deficient granulated diet on one transcription factor-nuclear factor kappaB and four pro-inflammatory cytokines-tumor necrosis factor, cyclooxygenase2, inducible nitric oxide synthase and Prostaglandin E synthase mRNA expression in the chicken brain tissues associated encephalomalacia. One hundred male chickens (1 day old; Weiwei Co. Ltd., Harbin, China) were divided into two groups (50 chickens per group). The expression levels in the brain tissues (cerebral gray matter, cerebral white matter, marrowbrain, cerebellum, thalamus and brain stem) were determined by real-time PCR on days 15, 25, 35, 45, and 55, respectively. The results showed the productions of pro-inflammatory mediators were increased following Se-deficiency. These data indicate the correlations between nutritional encephalomalacia and inflammatory response and the activity of inflammatory response in chicken brain may be induced by Se-deficiency.

Gene expression of endoplasmic reticulum resident selenoproteins correlates with apoptosis in various muscles of se-deficient chicks.

Dietary selenium (Se) deficiency causes muscular dystrophy in various species, but the molecular mechanism remains unclear. Our objectives were to investigate: 1) if dietary Se deficiency induced different amounts of oxidative stress, lipid peroxidation, and cell apoptosis in 3 skeletal muscles; and 2) if the distribution and expression of 4 endoplasmic reticulum (ER) resident selenoprotein genes (Sepn1, Selk, Sels, and Selt) were related to oxidative damages in these muscles. Two groups of day-old layer chicks (n = 60/group) were fed a corn-soy basal diet (33 µg Se/kg; produced in the Se-deficient area of Heilongjiang, China) or the diet supplemented with Se (as sodium selenite) at 0.15 mg/kg for 55 d. Dietary Se deficiency resulted in accelerated (P < 0.05) cell apoptosis that was associated with decreased glutathione peroxidase activity and elevated lipid peroxidation in these muscles. All these responses were stronger in the pectoral muscle than in the thigh and wing muscles (P < 0.05). Relative distribution of the 4 ER resident selenoprotein gene mRNA amounts and their responses to dietary Se deficiency were consistent with the resultant oxidative stress and cell apoptosis in the 3 muscles. Expression of Sepn1, Sels, and Selt in these muscles was correlated with (r > 0.72; P < 0.05) that of Sepsecs encoding a key enzyme for biosynthesis of selenocysteine (selenocysteinyl-tRNA synthase). In conclusion, the pectoral muscle demonstrated unique expression patterns of the ER resident selenoprotein genes and GPx activity, along with elevated susceptibility to oxidative cell death, compared with the other skeletal muscles. These features might help explain why it is a primary target of Se deficiency diseases in chicks.

Effect of oxygen free radicals and nitric oxide on apoptosis of immune organ induced by selenium deficiency in chickens.

Selenium is an essential element with antioxidant roles in immune regulation, but there is little understanding of how Se acts in apoptosis in the immune organs of birds. The aim of study was to evaluate the influence of Se deficiency on oxygen free radicals, NO and apoptosis in immune organ of chickens. 160 1-day-old chickens were randomly assigned to two groups of 80 each and were fed on a low-Se diet (0.032 mg/kg Se) or a control diet (0.282 mg/kg Se), respectively. OFR production in blood was determined on days 30, 45, 60 and 75, respectively. The iNOS-NO system activity in immune organ (thymus, spleen, bursa of fabricius) was identified by NO content and NOS activity assay on days 30, 45, 60 and 75, respectively. Apoptosis was measured by DNA ladder analysis, ultrastructural observations, TdT-mediated dUTP nick end labeling TUNEL assay and flow cytometric analysis of apoptotic DNA. The transcription of factor-associated suicide, caspase-3 mRNA was tested by fluorescence quantitative PCR. The results showed that OFR production, NO and inducible NO synthases (iNOS) activity in the low-Se group were significantly increased (p < 0.05) than in the control group. In addition, apoptosis was observed in chicken immune organ in the low-Se group. The degree and the number of apoptotic cells rose in a time-dependent manner. The expression of Fas and caspase-3 mRNA increased (p < 0.05) than in the control group. It indicated that the oxidative stress and NO played a causative role in the apoptosis of immune tissues induced by selenium deficiency.

The oxidative damage and disbalance of calcium homeostasis in brain of chicken induced by selenium deficiency.

Dietary selenium (Se) deficiency can influence the function of the brain. Our objective was to investigate the effects of Se deficiency on oxidative damage and calcium (Ca) homeostasis in brain of chicken. In the present study, 1-day-old chickens were fed either a commercial diet (as control group) with 0.15 mg/kg Se or a Se-deficient diet (as L group) with 0.033 mg/kg Se for 75 days. Then, brain injury biomarkers were examined, including histological analysis, ultrastructure assay, and apoptosis assay. We also examined the effect of Se deficiency on the Se-containing antioxidative enzyme glutathione peroxidase (GSH-Px), the level of glutathione (GSH), and the Ca homeostasis in brain of chicken. The results showed that the levels of Se and GSH and activity of GSH-Px are seriously reduced by 33.8-96 % (P < 0.001), 24.51-27.84 % (P < 0.001), and 20.70-64.24 % (P < 0.01), respectively. In the present study, we also perform histological analysis and ultrastructure assay and find that Se deficiency caused disorganized histological structure, damage to the mitochondria, fusion of nuclear membrane and nucleus shrinkage, higher apoptosis rate (P < 0.001), and increase of Ca homeostasis (P < 0.05 or P < 0.01 or P < 0.001) in the brain of chicken. In conclusion, the results demonstrated that Se deficiency induced oxidative damage and disbalance of Ca homeostasis in the brain of chicken. Similar to mammals, chickens brain is also extremely susceptible to oxidative damage and selenium deficiency.

Effects of oxidative stress on immunosuppression induced by selenium deficiency in chickens.

Selenium (Se) is an important nutritional trace element possessing immune-stimulatory properties. The aim of this 75-day study was to investigate effect of oxidative stress on immunosuppression induced by selenium deficiency by determining antioxidative function, morphological changes, DNA damage, and immune function in immune organ of chickens. One hundred sixty 1-day-old chickens (egg-type birds) were randomly assigned to two groups of 80 each and were fed on a low-Se diet (0.032 mg/kg Se) or a control diet (0.282 mg/kg Se, sodium selenite), respectively. Se contents in blood and immune organ (thymus, spleen, bursa of Fabricius) were determined on days 30, 45, 60, and 75, respectively. Antioxidative function was examined by total antioxidant capacity (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and xanthine oxidase (XOD), and oxidative damage was examined by malondialdehyde (MDA) detection. DNA damage was measured by comet assay, and immune function was examined by determining serum interleukin-1ß (IL-1ß), interleukin-2 (IL-2), and tumor necrosis factor (TNF) contents. The results showed that Se concentrations in the low-Se group were significantly lower (P < 0.05) than in the control group. Low-Se diet caused a decrease in the activities of T-AOC, SOD, GSH-Px, and an increase in XOD activity and MDA content. Pathological lesions and DNA damage of immune tissues were observed in low-Se group, while the serum IL-1ß and IL-2 contents decreased, and TNF content increased. The present study demonstrated that chickens fed deficient in Se diets exhibited lesions in immune organs, decreased serum IL-1ß, IL-2 content, and serum TNF content, indicating that oxidative stress inhibited the development of immune organs and finally impaired the immune function of chickens.

Priority in selenium homeostasis involves regulation of SepSecS transcription in the chicken brain.

O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase (SepSecS) is critical for the biosynthesis and transformation of selenocysteine (Sec) and plays an important role in the biological function of Se through the regulation of selenoprotein synthesis. Selenium (Se) and Selenoprotein play a pivotal role in brain function. However, how intake of the micronutrient Se affects gene expression and how genetic factors influence Se metabolism in the brain is unknown. To investigate the regulation of SepSecS transcription induced by Se in the chicken brain, we determined the Se content of brain tissue, SepSecS gene expression levels and mRNA stability in the chicken brain and primary cultured chicken embryos neurons receiving Se supplements. These results showed that Se content in the brain remains remarkably stable during Se supplementation. A significant increase in SepSecS mRNA levels was observed in all of the brain tissues of chickens fed diets containing 1-5 mg/kg sodium selenite. Most strikingly, significant changes in SepSecS mRNA levels were not observed in neurons treated with Se. However, Se altered the SepSecS mRNA half-life in cells. These data suggest that Se could regulate SepSecS mRNA stability in the avian brain and that SepSecS plays an important role in Se homeostasis regulation.

Dietary selenium regulation of transcript abundance of selenoprotein N and selenoprotein W in chicken muscle tissues.

Selenium (Se), selenoprotein N (SelN) and selenoprotein W (SelW) play a crucial role in muscle disorders. Se status highly regulates selenoprotein mRNA levels. However, few attempts have been performed on the effect of dietary Se supplementation on muscle SelN and SelW mRNA levels in birds. To investigate the effects of Se on the regulation of SelN and SelW mRNA levels in muscle tissues, one-day-old male chickens were fed either a commercial diet or a Se-supplemented diet containing 1.0, 2.0, 3.0 or 5.0 mg/kg sodium selenite for 90 days. Muscle tissues (breast, flight, thigh, shank and cardiac muscles) were collected and examined for Se content and mRNA levels of SelN and SelW. Moreover, Selenophosphate synthetase-1 (SPS-1) and selenocysteine-synthase (SecS) mRNA levels were analyzed. Significant increases in SelN mRNA levels were obtained in breast, thigh and shank muscles treated with Se, with maximal effects at 3.0 mg Se/kg diet, but 2.0 mg Se/kg diet resulted in peak levels of Sel N mRNA in flight muscles. Changes in SelW mRNA abundance in thigh and shank muscles increased in response to Se supply. After reaching a maximal level, higher Se supplementation led to a reduction in both SelN and SelW mRNAs. However, SelN and SelW mRNA levels displayed a different expression pattern in different skeletal and cardiac muscles. Thus, it suggested that skeletal and cardiac muscles SelN and SelW mRNA levels were highly regulated by Se supplementation and different muscle tissues showed differential sensitivity. Moreover, Se supplementation also regulated the levels of SPS1 and SecS mRNAs. The mRNA levels of SPS1 and SecS were enhanced in the Se supplemented groups. These data indicate that Se regulates the expression of SelN and SelW gene and affect the mRNA levels of SecS and SPS1.

Effects of dietary selenium on selenoprotein W gene expression in the chicken immune organs.

Selenoprotein W (SelW) is expressed in the immune systems of mammals. However, its pattern of expression in the immune organs of birds is still unclear. To investigate the distribution of SelW and effects of dietary Se levels on the SelW mRNA expression in the immune organs of birds, 1-day-old male chickens were fed either a commercial diet or an Se-supplemented diet containing 0.601, 1.058, 1.514, or 2.427 mg Se per kilogram, and 1.0, 2.0, 3.0 or 5.0 mg sodium selenite per kilogram for 90 days. The immune organs (spleen, thymus, and bursa of Fabricius) were collected and examined for Se content and SelW mRNA levels. The mRNA expression of SelW was detected in all the tissues. Although Se content was the highest in the spleen, the remarkable stability of the SelW mRNA level was observed in this organ during different times of dietary Se supplementation. Se-supplemented diet can make the SelW expression levels higher within a certain range in thymus and bursa of Fabricius. The present study demonstrates that SelW is widely expressed in immune organs of birds and that Se-supplementation of the feed increases SelW expression in the thymus and the bursa of Fabricius.