Effects of SMMSC on MUC2 mRNA and protein level in IPEC-J2 cells
As can be seen from Fig 1 and 2, the mRNA and protein level of MUC2 in the medium concentration and high concentration groups were significantly increased compared with the control group (
p<0.05). The mRNA and protein level of MUC2 in the low concentration group were also increased, though it was not significant (
p>0.05).
Effects of SMMSC on mRNA and protein level of EGF, TGF-b1, GLP-2 and IGF-1 in IPEC-J2 cells
As shown in Fig 3, the mRNA and protein level of EGF and IGF-1 in the groups with SMMSC were significantly increased compared with the control group (
p<0.05). The mRNA and protein level of TGF-b
1 in the groups with SMMSC were significantly decreased compared with the control group (
p<0.05). The mRNA and protein level of GLP-2 in the medium concentration and high concentration groups but not low concentration group were significantly increased compared with the control group (
p<0.05).
Intestinal tract is an important organ for digestion and nutrient absorption and recently was reported to maintain the stability of the internal environment because it works as an important barrier to protect the body from antigens, toxins and pathogens
(Arrieta et al., 2006). The integrity of intestinal structure and function is maintained by the regularly proliferation and differentiation of intestinal epithelial cells
(Okamoto et al., 2006). Malnutrition and environmental stress can easily lead to morphological and structural changes of intestinal mucosa, resulting in secretion disorder of cytokines and antibodies in intestinal mucosal immune system, leading to intestinal diseases of livestock and poultry. Intestinal diseases will affect both quantity and quality of livestock and poultry and bring significant economic losses. Therefore, how to use feed additives or other ways to improve the intestinal health of young animals and to reduce intestinal diseases occurrence has become a focus for scholars.
Amino acids play an important role in regulating the balance of intestinal dynamic, maintaining intestinal health and preventing intestine from diseases
(Gottardo et al., 2016). Sulfur-containing amino acids (SAA) plays essential role in the growth of livestock and poultry. Changes in dietary SAA will affect the metabolism, gene expression and function of intestinal cells
(Tesseraud et al., 2009). The one carbon metabolite of Methionine (Met), a kind of SAA, is S-adenosylmethionine (SAM). SAM is a key mediator to control intestinal metabolic homeostasis and it’s also an important regulator of the activity of intestinal stem cells (ISCs)
(Burgess et al., 2014; Shoveller et al., 2005; Tang et al., 2017). Notably, SMMSC can also be synthesized from methionine and SAM and SAM plays an important role in protecting the integrity of intestinal epithelial structure and function
(Yan et al., 2018).
Decreased dietary Met or SAM has been reported to affect growth performance (
Elango, 2020;
Elshorbagy et al., 2013; Jin et al., 2007), lipid metabolism
(Jha et al., 2014) and translation ability of animals
(Laxman et al., 2013). Consistent with our previous report that SMMSC can promote the proliferation and reduce apoptosis of jejunal epithelial cells in piglets. We hypothesized that SMMSC may affect cell survival, proliferation and differentiation, growth and apoptosis by regulating epidermal growth factor (EGF), insulin-like growth factor (IGF), TGF-b
1 and glucagon-like peptide 2 (GLP2) (
Arda-Pirincci and Bolkent, 2014;
Houle et al., 1997; Huang and Huang, 2005;
Iwabu et al., 2004; Massague et al., 2000; Petersen et al., 2003; Xu et al., 2020). Thus, relevant experiments were carried out in this study.
Our results showed that different concentrations of SMMSC can significantly improve the expression of EGF and IGF-1 in both mRNA and protein level in IPEC-J2 cells. The expression of EGF and IGF-1 in IPEC-J2 cells were more significantly improved in the SMMSC concentration of 0.5 mM, indicating that 0.5 mM SMMSC functions better in changing the level of MUC2 and the growth factors. These results indicated that SMMSC play an important role in intestinal development and therefore affected the nutrient absorption, cell proliferation and intestinal repair in piglet jejunal epithelial cells. These were consistent with previous studies that SMMSC affected intestinal development via regulating EGF and IGF-1
(Kim et al., 2010; Xu et al., 1994). The role of SMMSC in intestinal development may due to its function as the methyl donor, regulating of SAM, increasing the activity of S-adenosyll homocysteine and stimulating the methylation process
(Kim et al., 2010; Lee et al., 2012). However, the detail molecular mechanism needs to be further investigated.
Moreover, we found that 0.1 mM SMMSC had no significant effect on the expression of GLP-2 in IPEC-J2 cells while 0.5 and 1 mM SMMSC significantly increased the expression of GLP-2 in IPEC-J2 cells. These results indicated that SMMSC have anti-inflammatory and anti-injury function and can increase intestinal barrier function by regulating GLP-2 expression in a dose dependent manner, which was also consistent with previous findings (
Brubaker, 2006;
Yang et al., 2021). TGF-b
1 was revealed to induce apoptosis of the intestinal cells
(Hao et al., 2019; Seoane and Gomis, 2017). Accordingly, the addition of 0.5 or 1 mM SMMSC significantly reduced the expression of TGF-b
1 in IPEC-J2 cells and therefore improved the activity of IPEC-J2 cells.
The integrity of the mucus barrier is the first line of gastrointestinal protection. Intestinal mucus layer plays a major role in preventing intestinal mechanical, chemical and biological attack and helps maintain the dynamic balance of the intestine
(Cornick et al., 2015; Etienne-Mesmin et al., 2019).
Currently, the physical barrier role and immunomodulatory function of mucus barrier has attracted increasing attention of scientists. MUC2 is secreted by goblet cells of the small intestine and colon and it’s a major component of intestinal mucus. MUC2 is secreted when goblet cells were stimulated by different hormones, neurotransmitters (
e.g., vasoactive intestinal peptide, acetylcholine) or lipids (
e.g., bile acid, prostaglandin, butyric acid)
(Herath et al., 2020; Kim and Ho, 2010;
Yamashita and Melo, 2018). Studies have shown that EGF promotes the secretion of MUC2 by stimulating the proliferation and differentiation of intestinal goblet cells
Bedford et al., (2015). Butyrate was proved to change the expression of MUC2 in a dose-dependent manner
Hatayama et al., (2007). Animal studies have shown that Threonine can increase the expression of MUC2 in small intestine of weaned piglets
Wang et al., (2010). The present study showed that SMMSC could up-regulate the expression of MUC2 in IPEC-J2 cells in a dose-dependent manner and 0.5 mM SMMSC had the most significant effect on the mRNA and protein of MUC2 in IPEC-J2 cells. These results indicated that SMMSC could regulate MUC2 so as to affect intestinal mucosal barrier function.