Locoweed is a poisonous plant that severely harms the development of grass-land and animal husbandry throughout the world. Oxytropis and Astragalus are the Latin names for the poisonous plants commonly known as locoweed. The main toxic substance in these plants is swainsonine. It is a strong inhibitor of lysosomal α-mannosidase I and Golgi body α-mannosidase II, resulting in the accumulation of oligosaccharides and glycoproteins in lysosomes, interfering with the molecular and cellular recognition of glycans, and causing tissue-cell vacuolar degeneration. Livestock shows a series of clinical and pathological symptoms, mainly for the decline of reproductive performance. The effects in dams are abortion, weak fetus, and fetal malformations. The key step in maintaining pregnancy in dams is early endometrial decidualization, because reproductive hormones, decidual cell apoptosis, endoplasmic reticulum (ER) stress, and other immune factors are negatively affected by swainsonine. This article addresses the modifications that occur through glycan processing and glycosylation resulting in the change of post-translational modification of the protein and the activity of the glycoprotein, and then direct and indirect mechanisms of ER stress, apoptosis, reproductive hormones, immune factors, and cell cycle and other pathways. Our aim is to find new methods of prevention and treatment of swainsonine poisoning in grassland animals.
Locoweed (Astragalus spp. and Oxytropis spp.) is a perennial flowering plant found frequently in the rangelands of the western United States, Asia, and South America. It is one of the most poisonous weeds and harms grassland and animal husbandry development worldwide [
Locoweed, known by the Latin names Astragalus and Oxytropisis a poisonous plant that affects the world’s animal husbandry, causing performance degradation and even death [
Locoweed reduces other vegetation due to its own good growth characteristics (drought resistance, cold resistance, resistance to poverty, resistance to insect pests, early greening, late withered). It cause the soil nutrients decreased, productive forces, utilization rate down, grassland degradation faster, lawn effective stocking becoming low, changing herd structure and other issues. Due to the serious degeneration of naturally available herbage and the spread of locoweed, livestock have to eat locoweed and then caused poisoning phenomenon. Therefore, pastoralists carried out a series of locoweed control work. However, the unreasonable prevention and control of locoweed, for example unreasonable using the herbicide can also lead to deterioration of the grassland, even accumulation in the food chain and endanger human health. Tibet has used Xinjiang fine wool sheep, cigai sheep and caucasian sheep to improve native breed of sheep since 1977. Although the improved sheep improve production performance, their recognition of poisonous grass are greatly reducing and are more poisoning than local varieties. Coupled with abortion and other factors after poisoning, the action hinder the improvement of breeding.
The Leguminosae Oxytropis spp plant contains indoxylidine alkaloids toxic
Direct damage (impact in animals) | Indirect losses (management cost) |
---|---|
Dead | Fence establishment and maintenance |
Abortion | Increased feed requirements |
Malfortion | Increased medical treatments |
Abspecken | Altered grazing programs |
Lengthened calving interval | Decreased forage availability |
Decreased fertility | Decreased land values |
Decreased immune response | Opportunity costs |
Dccrcased function | Lost time to management |
Loss of breeding stock | Stress to management |
components that can cause chronic neurological dysfunction in animals, manifested as mania; thus, the plant was referred to as locoweed. Earlier studies suggested that the reason for livestock poisoning caused by Oxytropis is excessive selenium. However, the study by Zhang Shengmin et al. found that the symptoms and lesions of Gansu Oxytropis poisoning and selenium poisoning are not exactly the same in Qinghai area livestock through incidence, poisoning symptoms, and pathological changes. They first put forward that Oxytropis poisoning in China is not caused by selenium. Cauch (1929) isolated a kind of locoweed toxin from the Lambertian Oxytropis that can cause cat locoweed disease. He described the toxin as a stable nitrogen-containing compound with multiple hydroxyl groups. It can dissolve in water but not in chloroform, ether, and hydrocarbon solvents. However, due to the conditions at that time, they failed to identify its structure. Colegate (1979) used α-mannosidase as a tool to isolate a pure toxin for the first time from the gray bitter horse beans and identified it as indolizidine alkaloids―swainonine [
The molecular formula of swainonine is C8H15NO3.There are three hydroxyl groups on the molecular structure.
The typical symptom of swainsonine poisoning is to affect the reproductive performance of livestock. It not only has negative effects on the reproductive
performance of adult males and females, but also causes toxic effects on young animals. Poisoned dams not only frequently miscarry, but also can give birth to a weak fetus, a stillborn fetus, a deformed fetus, or a rotten fetus. Gansu Oxytropis and black calyx Oxytropis poison female deer, making it difficult for them to become pregnant. Pregnant mares may miscarry. Oxytropis sericea bean poisoning in the goat causes placenta dysplasia, inhibited uterine vascular development, and fetal malformations, but no poisonous addiction [
Male animals affected by swainsonine show testicular damage, and testicular and epididymal weight loss. Decreased testosterone induces loss of libido. Testicular spermatogenic cells and epididymal epithelial cytoplasm show extensive vacuolar degeneration. The nucleoli of spermatogenic cells are broken and present vacuolar degeneration. Cytoplasmic granules show vacuolization. Epididymal tubular cell nuclei show degeneration. Mitochondria show swelling and vacuolization. Sperm cells show deformity. JB Richards et al. conducted a 21-day locoweed feeding experiment on male lambs, finding that luteinizing hormone levels in serum were basically stable but testosterone levels decreased after injection of gonadotropin-releasing hormone on the day 22. On day 50, lamb serum luteinizing hormone began to decrease, and the testosterone area under the curve (AUC) was numerically lower in locoweed-fed rams than in control animals [
Visible swainsonine not only affects the function of germ cells, but also have an impact on the relevant reproductive hormones.
The molecular weight of SW is smaller. It can be metabolized through breast milk, leading to young animals poisoning by sucking breast milk. Oxytropis glabra poisoning ewes, lambs Because of its breast feed their symptoms occur only mild symptoms [
A large dose of swainsonine has a strong cytotoxicity to the body cells, but a small dose of swainsonine also has the ability to regulate the immune system, protect the cells, inhibit bacteria, and act as an antiviral. Swainsonine can also inhibit tumor metastasis, and play a role in cell diffusion and cell apoptosis. Swainsonine is the major toxic component of Astragalus and Oxytropis poisonous plants. Because of its cationic spatial structure similar to the mannose cationic semi-chair-like structure formed during the hydrolysis of mannoside and its very high affinity for α-mannosidase, it inhibits the activities of lysosomal α-mannosidase I (LAM I), GM II, and cytoplasmic α-mannosidase. In particular, the hydrolase activity is lost. Swainsonine changes the cell surface oligosaccharide structure and metabolism (
Because of SW cationic spatial structure similar to the mannose catalyzed semi-chair-like structure formed during the hydrolysis of mannoside and its very high affinity for α-mannosidase. Causing cell degeneration occurs.
Studies have shown that, Golgi marker enzymes are glycosyltransferases, wherein a variety of proteins involved in cell proliferation, differentiation, migration, apoptosis and tumor metastasis and transmitting signals [
O-connecting N-acetylglucosamine modification (O-GlcNAc) is a protein post-translational modification that is ubiquitous in eukaryotic cells [
transferase OGT (O-G1cNAc transferases) belongs to the GT41 family of polysaccharide transferases. The human OGT gene is located on the X Chromosome [
The role of OGT is to link acetylglucosamine to the serine or threonine hydroxyl of the target protein. The role of OGA is to remove the modification.
N-linked sugar chains extend from the ER to the Golgi apparatus. Polysaccharides embedded in the ER are a starting point for N-polysaccharification. N-polysaccharification contains 14 monosaccharides. They are respectively three glucose, nine mannose, and two N-acetylglucosamine. In the ER and the Golgi apparatus, there are specific glycosidases and glycosyltransferases to catalyze them [
In humans, livestock, birds, insects, microorganisms, and plants, a variety of organelles distribute α-mannosidase, such as the ER, the Golgi apparatus, lysosomes, and cytoplasm [
conservative sequence, it is possible to specifically cut the α-1,3 and α-1,6 linked mannose residues on GlcNA2Man5GlcNAc.The structure of the glycosyl moiety is formed by the cleaved sequence and serves as a basic precursor for further incorporation of N-acetylglucosamine units [
The N-acetylglucosamine transferase exists in the Golgi body. Its primary function is to develop it into a multi-branched structure based on the core pentasaccharide. GlcNAc(Gn) glycans in the donor substrate UDP-N-acetylphthalopyranoside (UDP-G1cNAc) are transferred to two mannose saccharides at the core of the N-glycan pentasaccharide to participate in the synthesis of asparagine-linked glycans (N-glycans) or serine/threonine-linked glycans (O-glycans) (
The oligosaccharide precursor during the maturation of N-glycans is GLc3Man9GlcNAc2. The distal three glucosyl groups are first specifically excised by glucosyltransferase, producing Man9GlcNAc2 and then hydrolyzed by class I a mannosidase to remove four mannose formations. Man5GLcNAc2. Man5GLcNAc2 is modified by N-acetylglucosamine transferase I, which is linked to an N-acetylglucose to form GlcMan5GlcNAc2, which is transported to the Golgi apparatus and cut by type IIa-mannosidase to remove two nectars. The sugar
forms GLcMan3GlcNAc2, which is transported by the glycosyltransferase to the terminal of the oligosaccharide branch sugar chain. The N-glycan is processed and the processed N-glycan is transported to specific tissues and organs to perform physiological functions.
The reducing end of the glycosyl or sugar chain is linked to the oxygen atom (O) of the hydroxyl group of Ser, Thr, or hydroxylysine residues in the protein peptide chain as an O-linked sugar group or sugar chain. Mucins are the major type of O-glycosylated glycoprotein and are enriched with highly O-glycosylated Ser/Thr/Pro tandem repeat regions.
Swainsonine Inhibit Golgi α-Mannosidase II (GMII) and then leads to N-glycan glycosylation abnormalities and the expression of specific membrane glycoproteins. Therefore, the structure of oligosaccharide in cell membrane is changed [
Most cell adhesion molecules are in the form of N-glycan glycosylated. Swainsonine acts as an N-glycan glycosylation inhibitor to block the N-glycan glycosylation pathway and then it causes lesions. Swainsonine, an inhibitor of N-glycan processing, reduces the N-glycan branch of cellular glycoproteins, including N-glycans linked to the Na-K ATPase, and the normal branch of N-glycans decreases Cell pump permeability is significantly reduced, resulting in increased cell-cell tightness and stability [
glycoprotein and the accumulation of oligosaccharides in lysosomes. Then, it causes cell vacuolar degeneration, tissue and organ damage, and even dysfunction.
The CD40-CD40L system is known to rescue germinal center B cells from apoptosis through up-regulation of bcl-2 family proteins, such as bcl-XL, or regulate germinal center B cell differentiation. Others have reported that the CD40-CD40L system protects B lymphoma cells from apoptotic signals through up-regulation of bcl-2 oncoprotein. Recent studies showed that human B lymphoma cells survive through the autocrine action of CD40L, which results in autonomous cell growth. IgM has five N-glycosylation sites.
Uterine decidualization is a temporary process of heterogeneous tissue composed of multiple cells during pregnancy. Decidualization protects the fetus from maternal rejection and plays an important role in the maintenance of early pregnancy. In most mammals, stromal cells surrounding the blastocyst begin to proliferate and differentiate immediately on adhesion of the blastula and uterine cavity epithelium. This process causes a change in the morphology and function of the stroma (decidualization), and the volume and weight of the site of implantation of the embryo is rapidly increased so that the blastocyst can be completely embedded into the sub-matrix [
Early in the primate and rodent pregnancy, successful implantation is the result of the ability of the implanted blastocyst to interact with the uterus of the recipient, where free blastocysts must adhere to the uterine cavity epithelium and invade the uterine stroma. Then, the stromal cells, beginning interstitial loosening to ensure the smooth implantation of embryos [
A potential model for stromal cell proliferation, differentiation, and terminal differentiation for polyploidization during the progression of uterine decidualization.
Uterine decidualization occurs by hormones, cytokines, transcription factors, and other factors [
embryo implantation occurs. E2 is necessary for embryo implantation, and the dose required is small and sensitive [
Pre-implantation hormone secretion patterns are divided into three stages: 1) Pre-ovulatory estrogen peaks (preoestrus estrogens) exist in the early estrus of
mice, and progesterone is almost absent during this period; 2) Two days after ovulation (which is also the time when mating occurs in mice), both estrogen and progesterone levels are very low; 3) After this period, progesterone levels are rapidly increasing with the formation of the corpus luteum. Increased (days 3 to 4), while estrogen secretion also showed a small peak on the fourth day of pregnancy, lutein-phase estrogen (luteal-phaseestrogen, day 4).
In primates, the decrease of progesterone during menstruation is the key factor that causes necrosis, disintegration, and hemorrhage of endometrial decidua. The physiological (P4) effects of progesterone progestins on endometrial stromal cells is mediated by interaction of the hormone with specific intracellular progesterone receptors (PGR) that are expressed from a single gene as two protein isoforms. PGR has two subtypes, PGR-α and PGR-β, and although PGR-? is 164-amino acids shorter at its N-terminus than PGR-β, its molecular weight is smaller, and it plays a major role in the uterus [
Working model for the cellular function of Luman recruitment into the LRF nuclear bodies. Luman is a type II transmembrane protein which is normally bound to the ER. During cellular stress responses such as the UPR, Luman undergoes regulated intramembrane proteolysis, and subsequently the N-terminal region of Luman translocates to the nucleus. In the absence of interaction with LRF, nuclear Luman binds to the cofactor HCF-1 and forms a transcription
activation complex, leading to the activation of downstream target genes, such as the UPR-related Herp and EDEM. At a point of the UPR where the cellular environment changes and the level of LRF in the nucleus rises to a threshold, Luman may be recruited in the LRF bodies and sequestered from HCF-1, which results in accelerated proteasomal degradation and repression of the transactivation function of Luman.
The mammalian uterus is the target organ for changes in morphology and function of the organization by hypothalamic-pituitary-gonadal axis precision regulation of sex hormones. Hormones are the key regulators of physiological and pathological functions, given the high levels of early pregnancy estrogen to suppress the endometrial decidualization process. E2 can induce uterine epithelial apoptosis in rodent uterus; P4 has an opposite effect; and the ER stress pathway can induce the expression of P4. Meanwhile, it is confirmed that ER stress GRP78 is regulated by E2 in the rat uterus [
Apoptosis is considered a vital component of various processes including normal cell turnover, proper development and functioning of the immune system, hormone-dependent atrophy, embryonic development and chemical-induced cell death [
caspase pathway or its analogues. Caspase is a class of cysteine aspartate-specific protease that plays a key role in the process of apoptosis. Its common active site is cysteine residues, aspartate residues, and peptide bonds. Normally, caspase is an inactive proenzyme consisting of an N-terminal pre-region and a small subunit. When the apoptotic signal is stimulated, the peptide bond following the aspartic acid residue of the zymogen molecule breaks, exposing the active site, dissociating the large and small subunits, and polymerizing into an active tetrameric form [
Mitochondrial apoptosis pathway is also called endogenous apoptotic pathway. Mitochondria control the life and death of cells under aerobic conditions and are the main sites for cellular ATP production. Death receptor pathway: This pathway is an apoptotic pathway induced by extracellular signals and is therefore also referred to as an exogenous apoptotic pathway. There are at least 8 death receptors on the surface of mammalian cells: Fas, TNFR1, TNFR2, DR3, DR4, DR5, Dc R1, and Dc R2, all of which are members of the tumor necrosis factor alpha receptor family. The most typical of these death receptors are Fas and TNFRs. Endoplasmic reticulum pathway: At present, there are three pathways known to induce apoptosis of endoplasmic reticulum stress: 1) Activation of CHOP/GADD153 gene transcription; 2) JNK activation pathway; 3) Endoplasmic reticulum-specific Cysteine protease Caspase-12 activation pathway.
In the primate menstrual cycle, the follicular atresia and the corpus luteum are parts of the process of apoptosis, and genital organs atrophying due to hormonal insufficiency will also undergo apoptosis. Apoptosis in reproductive organs and tissues during pregnancy is essential. However, abnormal apoptosis can result in abnormal pregnancy, causing various pathological phenomena, such as habitual abortion, gestational trophoblastic disease, and intrauterine growth retardation. During early pregnancy, endometrial decidualization, endometrial differentiation, and apoptosis limit trophoblast cells, so that they cannot over-invade the endometrium [
There are many ways to trigger apoptosis in decidual tissue: most cyclins are activated protein-dependent kinases, which are involved in decidualized protein phosphorylation and are positive regulators of the cell cycle during decidualization. However, not all of the cyclins play a positive regulatory role in regulating the cell cycle. Cyclin G2, for example, induces apoptosis in endometrial cells with a negative effect on the cell cycle in decidualization [
Swainsonine poisoning can make caspase-3,9,12 increase to a certain extent, and can promote apoptosis in medium and high doses. Fas is also a member of the TNF superfamily, which quickly combines with its ligand to form apoptosis-inducing complex, activates the downstream caspase-8, and induces apoptosis. Thus, swainsonine has a certain influence on apoptosis, and can activate some apoptosis factors and induce apoptosis. There is a significant impact on the expression of apoptosis-related genes and proteins in swainsonine-poisoned animal tissues. Qiubo Yu, in early decidual tissue gene expression profiles and proteome results, shows that natural abortion decidual tissue compared with normal, apoptosis-related genes an increase of 55, a decrease of 27 [
The ER is an important organelle that plays a key role not only in protein synthesis, folding, and secretion, but also in the lipid biosynthesis process [
proteins. The three pathways are pancreatic ER kinase (PERK), activating transcription factor 6 (ATF6), and inositol requiring enzyme 1 a (IRE1a), which is the endoplasmic reticulum stress repair pathway.
ER stress and UPR activation have important roles in the pathogenesis of many diseases. The induction of ER stress in vivo is attributable to both intrinsic and extrinsic factors. For example, gene mutations can cause defects in the folding and transport of certain proteins. The loss of function and toxicity that is associated with the accumulation of mutant protein in the ER leads to genetic and developmental disorders and neurodegenerative diseases. Environmental or lifestyle insults that trigger ER stress in neurons also contribute to the development of neurodegenerative diseases. More often, however, environmental insults such as an excess of nutrients or inflammation induce protein misfolding in the ER, which compromises cell function and triggers cell death and the development of metabolic and inflammatory diseases. NASH, non-alcoholic steatohepatitis. The UPR is mediated by three ER stress sensors. Binding of unfolded proteins to GRP78 within the ER lumen allows activation of PERK, ATF6 and IRE1. PERK dimerises and autophosphorylates. It phosphorylates eIF2α and thus general Cap-dependent translation is inhibited. Cap-independent translation allows the translation of certain proteins such as ATF4 which activates CHOP transcription. One of the genes induced by CHOP is GADD34 which regulates protein phosphatase 1 (PP1), which can dephosphorylate eIF2α. Activation of ATF6 allows its translocation to the Golgi where it undergoes cleavage by S1P and S2P proteases. Cleaved ATF6 activates XBP1 transcription. Active IRE1 is a dual kinase and endonuclease. One of its targets is XBP1 mRNA which undergoes splicing to produce an active transcription factor, XBP1s. One of the targets of XBP1s is p58IPK.
ER stress has a wide range of roles in mammalian reproduction, including the formation of decidualization, which is important for embryo implantation. Many ER-stress-related gene expressions change during embryo implantation, suggesting that ER stress may be an essential step in embryo implantation. On day 5 of pregnancy in mice, the GRP78 protein was more highly observed around the implanted embryo at the implantation site, and we understand that the change of GRP78 expression means the occurrence of ER stress [
The most important reason that swainsonine causes animal poisoning is as an inhibitor of α-mannosidase activity, which affects the glycosylation process and causes the accumulation of oligosaccharides. The effect on glycosylation will inevitably lead to abnormal glycoprotein synthesis, and may lead to ER stress. Second, α-mannosidases play an important role in protein degradation and are selectively degraded when proteins are incorrectly folded, mutated, processed, or modified in the ER [
Normal decidual tissue consists of many cells, such as extra-trophoblast cells, endometrial cells, and bone-marrow-derived cells, including T cells and a small number of B cells [
To sum up, the main causes of dam abortion caused by swainsonine poisoning are the following. First, swainsonine acts through a variety of pathways to change the secretion of early pregnancy hormones, affecting the process of decidualization. Second, swainsonine directly or indirectly affects the decidual cell apoptosis caused by decidual changes. Third, swainsonine directly or indirectly causes ER stress, leading to abnormal decidualization. Fourth, some other factors, including immune factors and cell cycle changes, lead to abnormal decidualization. These four reasons are all due to the influence of swainsonine on glycan processing and glycosylation modification. Glycosylation modification is an indispensable factor in the process of synthesis, secretion, binding, and function of glycoprotein. Swainsonine disturbance to this process can directly or indirectly affect ER stress, apoptosis, hormone disorders, immune dysfunction, cell cycle disorders, and other pathways, triggering abnormal pregnancy decidualization, and then leading to the poisoning of animals and abortion.
National natural science foundation-youth project (31302153), Shaanxi provincial natural science foundation―youth project (2017JQ3012).
The authors declare no conflicts of interest regarding the publication of this paper.
Wang, Y., Gao, X., Peng, M., You, Y.F., Shi, F.Y., Guo, Y.Z., Zhao, B.Y. and Wu, C.C. (2018) The Mechanism of Swainsonine Causing Early Pregnancy Abnormal Decidualization and Inducing Abortion by Changing Glycosylation Modification. Advances in Reproductive Sciences, 6, 70-101. http://dx.doi.org/10.4236/arsci.2018.63007