The amino acid sensor MetRS is required for methionine-induced milk protein synthesis in a domestic pigeon model.

This study was conducted to investigate whether methionyl-tRNA synthetase (MetRS) is a mediator of Met-induced crop milk protein synthesis via the janus kinase 2 (JAK2)/signal transducer and activator of transcription 5 (STAT5) signalling pathway in breeding pigeons. In Experiment 1, a total of 216 pairs of breeding pigeons were divided into 3 groups (control, Met-deficient, and Met-rescue groups). In Experiments 2 and 3, forty pairs of breeding pigeons from each experiment were allocated into 4 groups. The 2nd experiment included a control group and 3 MetRS inhibitor (REP8839) groups. The 3rd experiment included a Met-deficient group, Met-sufficient group, REP8839 + Met-deficient group, and REP8839 + Met-sufficient group. Experiment 1 showed that Met supplementation increased crop development, crop milk protein synthesis, the protein expression of MetRS and JAK2/STAT5 signalling pathway, and improved squab growth. Experiment 2 showed that crop development, crop milk protein synthesis, and the protein expression of MetRS and the JAK2/STAT5 signalling pathway were decreased, and squab growth was inhibited by the injection of 1.0 mg/kg BW REP8839, which was the selected dose for the 3rd experiment. These results showed that Met supplementation increased crop development, crop milk protein synthesis, and the expression of MetRS and JAK2/STAT5 signalling pathway and rescued squab growth after the injection of REP8839. Moreover, the Co-IP results showed that there was an interaction between MetRS and JAK2. Taken together, these findings indicate that MetRS mediates Met-induced crop milk protein synthesis via the JAK2/STAT5 signalling pathway, resulting in improved squab growth in breeding pigeons.

L-glutamate requires ß-catenin signalling through Frizzled7 to stimulate porcine intestinal stem cell expansion.

Intestinal stem cells (ISCs) decode and coordinate various types of nutritional information from the diet to support the crypt-villus axis architecture, but how specific dietary molecules affect intestinal epithelial homeostasis remains unclear. In the current study, L-glutamate (Glu) supplementation in either a nitrogen-free diet (NFD) or a corn-soybean meal diet (CSMD) stimulated gut growth and ISC expansion in weaned piglets. Quantitative proteomics screening identified the canonical Wnt signalling pathway as a central regulator of intestinal epithelial development and ISC activity in vivo. Importantly, the Wnt transmembrane receptor Frizzled7 (FZD7) was upregulated in response to dietary Glu patterns, and its perturbations in intestinal organoids (IOs) treated with a specific inhibitor and in FZD7-KO IPEC-J2 cells disrupted the link between Glu inputs and ß-catenin signalling and a subsequent reduction in cell viability. Furthermore, co-localization, coimmunoprecipitation (Co-IP), isothermal titration calorimetry (ITC), and microscale thermophoresis (MST) revealed that Glu served as a signalling molecule directly bound to FZD7. We propose that FZD7-mediated integration of the extracellular Glu signal controls ISC proliferation and differentiation, which provides new insights into the crosstalk of nutrients and ISCs.

Dietary supplementation with probiotics increases growth performance, improves the intestinal mucosal barrier and activates the Wnt/ß-catenin pathway activity in chicks.

BACKGROUND: Probiotics comprise effective feed additives that can replace antibiotics in animal livestock production. However, mono-strain probiotics appear less effective because of their instability. Therefore, the present study aimed to investigate dietary supplementation with compound probiotics (CPP) on growth performance, diarrhea rate and intestinal mucosal barrier, as well as the possible molecular mechanism, in chicks. In total, 360 1-day-old chicks of the Hy-Line Brown Chicks were randomly divided into the control group (CON, basal diet), chlortetracycline group (500 mg kg-1 CTC) and compound probiotics group (1000 mg kg-1 CPP, consisting of Bacillus subtilis, Bacillus licheniformis, Enterococcus faecium and yeast). The experiment period was 56 days. RESULTS: The results showed that, in comparison with the CON group, CPP significantly increased the average daily feed intake and average daily gain of chicks and reduced diarrhea (P < 0.05). The probiotic group exhibited increased immune organ (i.e. spleen and thymus) mass and increased levels of serum immunoglobulin (Ig)A, IgM and IgG (P < 0.05) compared to the CTC group. In addition, the jejunal mass and morphology were improved in the probiotic group (P < 0.05). Moreover, CPP reinforced jejunal barrier function, as indicated by increased transepithelial electrical resistance, protein expression of occludin and claudin-1, and diamine oxidase levels in the jejunum (P < 0.05). Likewise, enhanced fluorescence signals of proliferating cell nuclear antigen-labeled mitotic cells and villin-labeled absorptive cells in the jejunum (P < 0.05) suggested that CPP promoted intestinal stem cells activity. Mechanistically, the Wnt/ß-catenin signaling pathway, including ß-catenin, TCF4, c-Myc, cyclin D1 and Lgr5, was amplified in the jejunum by CPP addition (P < 0.05). CONCLUSION: The present study demonstrated that dietary supplementation with CPP reinforced the jejunal epithelial integrity by activating Wnt/ß-catenin signaling and enhanced immune function in chicks. © 2023 Society of Chemical Industry.

Heat-stable enterotoxin inhibits intestinal stem cell expansion to disrupt the intestinal integrity by downregulating the Wnt/ß-catenin pathway.

Enterotoxigenic Escherichia coli causes severe infectious diarrhea with high morbidity and mortality in newborn and weanling pigs mainly through the production of heat-stable enterotoxins (STs). However, the precise regulatory mechanisms involved in ST-induced intestinal epithelium injury remain unclear. Consequently, we conducted the experiments in vivo (mice), ex vivo (mouse and porcine enteroids), and in vitro (MODE-K and IPEC-J2 cells) to explore the effect of STp (one type of STa) on the integrity of the intestinal epithelium. The results showed that acute STp exposure led to small intestinal edema, disrupted intestinal integrity, induced crypt cell expansion into spheroids, and downregulated Wnt/ß-catenin activity in the mice. Following a similar trend, the enteroid-budding efficiency and the expression of Active ß-catenin, ß-catenin, Lgr5, PCNA, and KRT20 were significantly decreased after STp treatment, as determined ex vivo. In addition, STp inhibited cell proliferation, induced cell apoptosis, destroyed cell barriers, and reduced Wnt/ß-catenin activity by downregulating its membrane receptor Frizzled7 (FZD7). In contrast, Wnt/ß-catenin reactivation protected the IPEC-J2 cells from STp-induced injury. Taking these findings together, we conclude that STp inhibits intestinal stem cell expansion to disrupt the integrity of the intestinal mucosa through the downregulation of the Wnt/ß-catenin signaling pathway.

Wnt/ß-catenin-mediated heat exposure inhibits intestinal epithelial cell proliferation and stem cell expansion through endoplasmic reticulum stress.

Heat stress induced by continuous high ambient temperatures or strenuous exercise in humans and animals leads to intestinal epithelial damage through the induction of intracellular stress response. However, the precise mechanisms involved in the regulation of intestinal epithelial cell injury, especially intestinal stem cells (ISCs), remain unclear. Thereby, in vitro a confluent monolayer of IPEC-J2 cells was exposed to the high temperatures (39, 40, and 41°C), the IPEC-J2 cell proliferation, apoptosis, differentiation, and barrier were determined, as well as the expression of GRP78, which is a marker protein of endoplasmic reticulum stress (ERS). The Wnt/ß-catenin pathway-mediated regenerative response was validated using R-spondin 1 (Rspo1). And ex-vivo, three-dimensional cultured enteroids were developed from piglet jejunal crypt and employed to assess the ISC activity under heat exposure. The results showed that exposure to 41°C for 72 hr, rather than 39°C and 40°C, decreased IPEC-J2 cell viability, inhibited cell proliferation and differentiation, induced ERS and cell apoptosis, damaged barrier function and restricted the Wnt/ß-catenin pathway. Nevertheless, Wnt/ß-catenin reactivation via Rspo1 protects the intestinal epithelium from heat exposure-induced injury. Furthermore, exposure to 41°C for 24 hr reduced ISC activity, stimulated crypt-cell apoptosis, upregulated the expression of GRP78 and caspase-3, and downregulated the expression of ß-catenin, Lgr5, Bmi1, Ki67, KRT20, ZO-1, occludin, and claudin-1. Taken together, we conclude that heat exposure induces ERS and downregulates the Wnt/ß-catenin signaling pathway to disrupt epithelial integrity by inhibiting the intestinal epithelial cell proliferation and stem cell expansion.

Dietary supplementation with pioglitazone hydrochloride improves intramuscular fat, fatty acid profile, and antioxidant ability of thigh muscle in yellow-feathered chickens.

BACKGROUND: Muscle fat content and fatty acid composition play an important role in poultry flavor and taste. To investigate the effects of pioglitazone hydrochloride (PGZ) on growth performance and thigh muscle quality in yellow-feathered chickens, 360 female chickens were randomly divided into three groups and treated with three doses of PGZ (0, 7.5, and 15 mg kg-1 ) for 28 days. Each group had six replicates of 20 chickens. RESULTS: The results showed that dietary supplementation with 15 mg kg-1 PGZ increased average daily feed intake (ADFI) and the average daily gain (ADG) from 0 to 14 days. Furthermore, the triglyceride (TG) level was decreased by 15 mg kg-1 PGZ, whereas the eviscerated yield was increased. The relative weight of the heart and kidneys showed a linear increase with dietary PGZ supplementation, and the drip loss of the thigh muscle was significantly decreased by 15 mg kg-1 PGZ supplementation. Moreover, a* value, intramuscular fat (IMF), and polyunsaturated fatty acids (PUFAs) showed a linear increase, and pH24 h and drip loss showed a quadratic influence with the levels of PGZ supplementation. In particular, the PUFA proportion was increased by 7.63% and 9.14% in the 7.5 mg kg-1 PGZ and 15 mg kg-1 PGZ groups, respectively. Additionally, 15 mg kg-1 of PGZ increased the total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-PX ) activity. CONCLUSION: In summary, 15 mg kg-1 PGZ has substantial effects on growth performance and meat quality, particularly by decreasing drip loss and increasing IMF content, PUFA proportions, and antioxidant ability. © 2019 Society of Chemical Industry.

Dietary supplementation with pioglitazone hydrochloride and chromium methionine manipulates lipid metabolism with related genes to improve the intramuscular fat and fatty acid profile of yellow-feathered chickens.

BACKGROUND: Intramuscular fat (IMF) and polyunsaturated fatty acids (PUFAs) have been thought to play a crucial role in improving meat quality. Considering the ability of pioglitazone hydrochloride (PGZ) to deposit fat, and the anti-stress capability of chromium methionine (CrMet), we combined these compounds to produce higher quality meat in poultry. A total of 3000 female chickens were divided into four groups (five replicates, each with 150 chickens): control, control plus15 mg·kg-1 PGZ, control plus 200 µg·kg-1 CrMet, and control plus15 mg·kg-1 PGZ plus 200 µg·kg-1 CrMet. The experiment lasted for 28 days. RESULTS: Compared to the control group and the PGZ group, the average daily gain (ADG) was significantly increased in the PGZ plus CrMet group, whereas the feed-to-gain ratio (F/G) was decreased from 0 to 14 days. Meanwhile, the redness value of breast muscle and IMF of thigh muscle increased in the PGZ plus CrMet group compared with the control group and these detections in the PGZ plus CrMet group exhibited highest value among the four groups. The cooking loss decreased in the breast muscle and thigh muscle after PGZ combined with CrMet in diets. The percentages of C16:1, C18:2n-6 and PUFAs increased in the PGZ plus CrMet group. The mRNA abundance of peroxisome proliferator activated receptor (PPAR) γ, PPAR coactivator 1 α, and fatty acid binding protein 3 was significantly enhanced with PGZ plus CrMet supplementation. CONCLUSION: Collectively, dietary supplementation with PGZ plus CrMet improved growth performance and meat quality by decreasing the cooking loss and increasing the IMF and PUFA levels. © 2019 Society of Chemical Industry.

mTORC1 signaling activation increases intestinal stem cell activity and promotes epithelial cell proliferation.

The crypt-villus axis of the intestine undergoes a continuous renewal process that is driven by intestinal stem cells (ISCs). However, the homeostasis is disturbed under constant exposure to high ambient temperatures, and the precise mechanism is unclear. We found that both EdU+ and Ki67+ cell ratios were significantly reduced after exposure to 41°C, as well as the protein synthesis rate of IPEC-J2 cells, and the expression of ubiquitin and heat shock protein 60, 70, and 90 were significantly increased. Additionally, heat exposure decreased enteroid expansion and budding efficiency, as well as induced apoptosis after 48 hr; however, no significant difference was observed in the apoptosis ratio after 24 hr. In the process of heat exposure, the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway was significantly inhibited in both IPEC-J2 cells and enteroids. Correspondingly, treatment of IPEC-J2 and enteroids with the mTORC1 agonist MHY1485 at 41°C significantly attenuated the inhibition of proliferation and protein synthesis, increased the ISC activity, and promoted expansion and budding of enteroid. In summary, we conclude that the mTORC1 signaling pathway regulates intestinal epithelial cell and stem cell activity during heat exposure-induced injury.

LGR5 and BMI1 Increase Pig Intestinal Epithelial Cell Proliferation by Stimulating WNT/ß-Catenin Signaling.

Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) and B-cell-specific Moloney murine leukemia virus insertion site 1 (BMI1) are markers of fast-cycling and quiescent intestinal stem cells, respectively. To determine the functions of these proteins in large animals, we investigated their effects on the proliferation of intestinal epithelial cells from pigs. Our results indicated that LGR5 and BMI1 are highly conserved proteins and that the pig proteins have greater homology with the human proteins than do mouse proteins. Overexpression of either LGR5 or BMI1 promoted cell proliferation and WNT/ß-catenin signaling in pig intestinal epithelial cells (IPEC-J2). Moreover, the activation of WNT/ß-catenin signaling by recombinant human WNT3A protein increased cell proliferation and LGR5 and BMI1 protein levels. Conversely, inhibition of WNT/ß-catenin signaling using XAV939 reduced cell proliferation and LGR5 and BMI1 protein levels. This is the first report that LGR5 and BMI1 can increase proliferation of pig intestinal epithelial cells by activating WNT/ß-catenin signaling.

CDX2 Stimulates the Proliferation of Porcine Intestinal Epithelial Cells by Activating the mTORC1 and Wnt/ß-Catenin Signaling Pathways.

Caudal type homeobox 2 (CDX2) is expressed in intestinal epithelial cells and plays a role in gut development and homeostasis by regulating cell proliferation. However, whether CDX2 cooperates with the mammalian target of rapamycin complex 1 (mTORC1) and Wnt/ß-catenin signaling pathways to stimulate cell proliferation remains unknown. The objective of this study was to investigate the effect of CDX2 on the proliferation of porcine jejunum epithelial cells (IPEC-J2) and the correlation between CDX2, the mTORC1 and Wnt/ß-catenin signaling pathways. CDX2 overexpression and knockdown cell culture models were established to explore the regulation of CDX2 on both pathways. Pathway-specific antagonists were used to verify the effects. The results showed that CDX2 overexpression increased IPEC-J2 cell proliferation and activated both the mTORC1 and Wnt/ß-catenin pathways, and that CDX2 knockdown decreased cell proliferation and inhibited both pathways. Furthermore, the mTORC1 and Wnt/ß-catenin pathway-specific antagonist rapamycin and XAV939 (3,5,7,8-tetrahydro-2-[4-(trifluoromethyl)]-4H -thiopyrano[4,3-d]pyrimidin-4-one) both suppressed the proliferation of IPEC-J2 cells overexpressing CDX2, and that the combination of rapamycin and XAV939 had an additive effect. Regardless of whether the cells were treated with rapamycin or XAV939 alone or in combination, both mTORC1 and Wnt/ß-catenin pathways were down-regulated, accompanied by a decrease in CDX2 expression. Taken together, our data indicate that CDX2 stimulates porcine intestinal epithelial cell proliferation by activating the mTORC1 and Wnt/ß-catenin signaling pathways.

Low dose of IGF-I increases cell size of skeletal muscle satellite cells via Akt/S6K signaling pathway.

The objective of this study was to investigate the effect of insulin growth factor-I (IGF-I) on the size of pig skeletal muscle satellite cells (SCs). Using microarray, real-time RT-PCR, radioimmunoassay analysis and western blot, we first showed that supplementation of low-dose of IGF-I in culture medium resulted in enlarged cell size of Lantang SCs, only Akt and S6K were up-regulated at both the mRNA and protein levels among almost all of the mTOR pathway key genes, but had no effect on cell number. To elucidate the signaling mechanisms responsible for regulating cell size under low-dose of IGF-I treatment, we blocked Akt and S6K activity with the specific inhibitors MK2206 and PF4708671, respectively. Both inhibitors caused a decrease in cell size. In addition, MK2206 lowered the protein level of p-Akt (Ser473), p-S6K (Thr389), and p-rpS6 (Ser235/236), whereas PF4708671 lowered the protein level of p-S6K (Thr389) and p-rpS6 (Ser235/236). However, low dose of IGF-I didn't affect the protein level of p-mTOR (Ser2448) and p-mTOR (Ser2481). When both inhibitors were applied simultaneously, the effect was the same as that of the Akt inhibition alone. Taken together, we report for the first time that low-dose of IGF-I treatment increases cell size via Akt/S6K signaling pathway.

Matrine reduced intestinal stem cell damage in eimeria necatrix-infected chicks via blocking hyperactivation of Wnt signaling.

BACKGROUND: Coccidiosis is a rapidly spreading and acute parasitic disease that seriously threatening the intestinal health of poultry. Matrine from leguminous plants has anthelmintic and anti-inflammatory properties. PURPOSE: This assay was conducted to explore the protective effects of Matrine and the AntiC (a Matrine compound) on Eimeria necatrix (EN)-infected chick small intestines and to provide a nutritional intervention strategy for EN injury. STUDY DESIGN: The in vivo (chick) experiment: A total of 392 one-day-old yellow-feathered broilers were randomly assigned to six groups in a 21-day study: control group, 350 mg/kg Matrine group, 500 mg/kg AntiC group, EN group, and EN + 350 mg/kg Matrine group, EN + 500 mg/kg AntiC group. The in vitro (chick intestinal organoids, IOs): The IOs were treated with PBS, Matrine, AntiC, 3 µM CHIR99021, EN (15,000 EN sporozoites), EN + Matrine, EN + AntiC, EN + Matrine + CHIR99021, EN + AntiC + CHIR99021. METHODS: The structural integrity of chicks jejunal crypt-villus axis was evaluated by hematoxylin and eosin (H&E) staining and transmission electron microscopy (TEM). And the activity of intestinal stem cells (ISCs) located in crypts was assessed by in vitro expansion advantages of a primary in IOs model. Then, the changes of Wnt/ß-catenin signaling in jejunal tissues and IOs were detected by Real-Time qPCR,Western blotting and immunohistochemistry. RESULTS: The results showed that dietary supplementation with Matrine or AntiC rescued the jejunal injury caused by EN, as indicated by increased villus height, reduced crypt hyperplasia, and enhanced expression of tight junction proteins. Moreover, there was less budding efficiency of the IOs expanded from jejunal crypts of chicks in the EN group than that in the Matrine and AntiC group, respectively. Further investigation showed that AntiC and Matrine inhibited EN-stimulated Wnt/ß-catenin signaling. The fact that Wnt/ß-catenin activation via CHIR99021 led to the failure of Matrine and AntiC to rescue damaged ISCs confirmed the dominance of this signaling. CONCLUSION: Our results suggest that Matrine and AntiC inhibit ISC proliferation and promote ISC differentiation into absorptive cells by preventing the hyperactivation of Wnt/ß-catenin signaling, thereby standardizing the function of ISC proliferation and differentiation, which provides new insights into mitigating EN injury by Matrine and AntiC.

Succinate metabolism and its regulation of host-microbe interactions.

Succinate is a circulating metabolite, and the relationship between abnormal changes in the physiological concentration of succinate and inflammatory diseases caused by the overreaction of certain immune cells has become a research focus. Recent investigations have shown that succinate produced by the gut microbiota has the potential to regulate host homeostasis and treat diseases such as inflammation. Gut microbes are important for maintaining intestinal homeostasis. Microbial metabolites serve as nutrients in energy metabolism, and act as signal molecules that stimulate host cell and organ function and affect the structural balance between symbiotic gut microorganisms. This review focuses on succinate as a metabolite of both host cells and gut microbes and its involvement in regulating the gut - immune tissue axis by activating intestinal mucosal cells, including macrophages, dendritic cells, and intestinal epithelial cells. We also examined its role as the mediator of microbiota - host crosstalk and its potential function in regulating intestinal microbiota homeostasis. This review explores feasible ways to moderate succinate levels and provides new insights into succinate as a potential target for microbial therapeutics for humans.

Heat stress disrupts intestinal stem cell migration and differentiation along the crypt-villus axis through FAK signaling.

During heat stress (HS), the intestinal epithelium suffers damage due to imbalance of tissue homeostasis. However, the specific mechanism by which intestinal stem cells (ISCs) migrate and differentiate along the crypt-villus axis to heal lesions upon insult is unclear. In our study, C57BL/6 mice and IPEC-J2 cells were subjected to normal ambient conditions (25 °C for 7 days in vivo and 37 °C for 18 h in vitro) or 41 °C. The results showed that HS impaired intestinal morphology and barrier function. The numbers of ISCs (SOX9+ cells), mitotic cells (PCNA+ cells), and differentiated cells (Paneth cells marked by lysozyme, absorptive cells marked by Villin, goblet cells marked by Mucin2, enteroendocrine cells marked by Chromogranin A, and tuft cells marked by DCAMKL1) were reduced under high temperature. Importantly, BrdU incorporation confirmed the decreased migration ability of jejunal epithelial cells exposed to 41 °C. Furthermore, intestinal organoids (IOs) expanded from jejunal crypt cells in the HS group exhibited greater growth disadvantages. Mechanistically, the occurrence of these phenotypes was accompanied by FAK/paxillin/F-actin signaling disruption in the jejunum. The fact that the FAK agonist ZINC40099027 reversed the HS-triggered inhibition of IPEC-J2 cell differentiation and migration further confirmed the dominant role of FAK in response to high-temperature conditions. Overall, the present investigation is the first to reveal a major role of FAK/paxillin/F-actin signaling in HS-induced ISC migration and differentiation along the crypt-villus axis, which indicates a new therapeutic target for intestinal epithelial regeneration after heat injuries.

l-Malic Acid Facilitates Stem Cell-Driven Intestinal Epithelial Renewal through the Amplification of ß-Catenin Signaling by Targeting Frizzled7 in Chicks.

l-Malic acid (l-MA) contributes to energy metabolism and nutrient digestion, which is an alternative to antibiotics for livestock; however, it is not clear whether l-MA can replace antibiotics to promote intestinal development in chicks. To investigate the effects of l-MA on intestinal stem cells (ISCs) driving epithelial renewal, we employed in vivo chick feeding experiments, chick intestinal organoid (IO) models, and in vitro chick intestinal epithelial cell models. The results showed that the feed conversion rate and diarrhea scores were decreased with improved jejunal morphology and barrier function in the 0.5% l-MA group. l-MA promoted the proliferation and differentiation of ISCs, inhibited the cell apoptosis, increased the IO formation efficiency, surface area, budding efficiency, and number of buds, suggesting that l-MA promoted the expansion of ISCs. Furthermore, l-MA treatment dramatically upregulated the Wnt/ß-catenin signaling pathway in the jejunum. Importantly, Wnt transmembrane receptor Frizzled7 (FZD7) mRNA abundance was increased in response to dietary 0.5% l-MA. In addition, molecular docking analysis using Autodock software and isothermal titration calorimetry revealed that l-MA binds to Lys91 of FZD7 with high affinity, indicating a spontaneous interaction. The chick intestinal epithelial cells treated with 10 µM l-MA significantly increased cell viability, and the Wnt/ß-catenin signaling pathway was activated, but l-MA failed to upregulate the Wnt/ß-catenin signaling when treated with the FZD7-specific inhibitor Fz7-21 in chick intestinal epithelial cells, indicating that FZD7 is indispensable for l-MA activation of the Wnt/ß-catenin signaling. Collectively, l-MA stimulated ß-catenin signaling by targeting transmembrane receptor FZD7, which promoted ISC expansion and inhibited cell apoptosis to accelerate intestinal epithelial renewal in chicks.

Chemical composition of pigeon crop milk and factors affecting its production: a review.

Pigeons are important commercial poultry in addition to being ornamental birds. In 2021, more than 111 million pairs of breeding pigeons were kept in stock and 1.6 billion squabs were slaughtered for meat in China. However, in many countries, pigeons are not domestic birds; thus, it is necessary to elucidate the factors involved in their growth and feeding strategy due to their economic importance. Pigeons are altricial birds, so feedstuffs cannot be digested by squabs, which instead are fed a mediator named pigeon crop milk. During lactation, breeding pigeons (both female and male) ingest diets and generate crop milk to feed squabs. Thus, research on squab growth is more complex than that on chicken and other poultry. To date, research on the measurement of crop milk composition and estimation of the factors affecting its production has not ceased, and these results are worth reviewing to guide production. Moreover, some studies have focused on the formation mechanism of crop milk, reporting that the synthesis of crop milk is controlled by prolactin and insulin-activated pathways. Furthermore, the Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) pathway, target of rapamycin (TOR) pathway and AMP-activated protein kinase (AMPK) pathway were also reported to be involved in crop milk synthesis. Therefore, this review focuses on the chemical composition of pigeon crop milk and factors affecting its production during lactation. This work explores novel mechanisms and provides a theoretical reference for improving production in the pigeon industry, including for racing, ornamental purposes, and production of meat products.

New horizons for selenium in animal nutrition and functional foods.

Selenium (Se), one of the indispensable nutrients for both human health and animal growth, participates in various physiological functions, such as antioxidant and immune responses and metabolism. The role of dietary Se, in its organic and inorganic forms, has been well documented in domestic animals. Furthermore, many feeding strategies for different animals have been developed to increase the Se concentration in animal products to address Se deficiency and even as a potential nutritional strategy to treat free radical-associated diseases. Nevertheless, studies on investigating the optimum addition of Se in feed, the long-term consequences of Se usage in food for animal nutrition, the mechanism of metallic Se nanoparticle (SeNP) transformation in vivo, and the nutritional effects of SeNPs on feed workers and the environment are urgently needed. Starting from the absorption and metabolism mechanism of Se, this review discusses the antioxidant role of Se in detail. Based on this characteristic, we further investigated the application of Se in animal health and described some unresolved issues and unanswered questions warranting further investigation. This review is expected to provide a theoretical reference for improving the quality of food animal meat as well as for the development of Se-based biological nutrition enhancement technology.

DL-methionine and DL-methionyl-DL-methionine increase intestinal development and activate Wnt/ß-catenin signaling activity in domestic pigeons (Columba livia).

This experiment was undertaken to investigate the effects of parental dietary DL-methionine (DL-Met) and DL-methionyl-DL-methionine (DL-Met-Met) supplementation on the intestinal development of young squabs. A total of 108 pairs of breeding pigeons and 432 one-day-old squabs were randomly divided into 3 groups: the control group (CON) was fed a basal diet (CP = 15%) and the experimental groups were fed a basal diet supplemented with 0.3% DL-Met or DL-Met-Met. Each pair of breeding pigeons nourished 4 young squabs, and 8 squabs from each treatment were randomly sampled at the end of the experiment. The results indicated that DL-Met and DL-Met-Met supplementation improved the intestinal morphology and structure in the squabs, as reflected by the increased relative intestinal weight of each small intestinal segment, villus height, and villus to crypt ratio. In addition, DL-Met and DL-Met-Met supplementation significantly increased the protein expression of cell proliferation markers (Ki67 and PCNA) and tight junction proteins (ZO-1 and Claudin-1) in the jejunum and strengthened the fluorescence signal intensity of Ki67, PCNA and Villin. Moreover, the expression of Wnt/ß-catenin signaling pathway-related proteins (Frizzled 7 [FZD7], p-GSK-3ß, Active ß-catenin, ß-catenin, TCF4, c-Myc, and Cyclin D1), and intestinal peptide transporter 1 (PepT1) in the jejunum was considerably higher in the treatment group than in the CON group (P < 0.05), with the DL-Met-Met group having the highest expression. Consistently, the molecular docking results predicted the possibility that DL-Met or DL-Met-Met binds to the membrane receptor FZD7, which mediates Wnt/ß-catenin signaling. Collectively, the improvement of the intestinal development in squabs after parental dietary 0.3% DL-Met and DL-Met-Met supplementation could be through activation of Wnt/ß-catenin signaling pathway, and DL-Met-Met is superior to DL-Met. Our findings may provide basic data for further optimizing the feeding formula of breeding pigeons and improving the growth and development of squabs.

Lysine Interacts with Frizzled7 to Activate ß-Catenin in Satellite Cell-Participated Skeletal Muscle Growth.

This work provided an interesting finding of lysine (Lys) control on skeletal muscle growth besides protein synthesis. According to the isobaric tag for relative and absolute quantitation and molecular docking analyses, we found both in in vivo skeletal muscle and in vitro muscle satellite cells (MuSCs) that the frizzled7 (FZD7) expression level was positively correlated with Lys levels and this was consistent with the activation of the Wnt/ß-catenin pathway. On the other hand, FZD7 inhibition suppressed the Lys-rescued Wnt/ß-catenin pathway, FZD7 knockdown caused cell proliferation, and Wnt/ß-catenin pathway restrictions could not be compensated for by Lys or Wnt3a. Furthermore, the combination between Lys and recombinant pig frizzled7 (rpFZD7) protein was confirmed by isothermal titration calorimetry. This finding displayed concrete evidence that Lys is not only a molecular block of protein synthesis but is also a ligand for FZD7 to activate ß-catenin to stimulate MuSCs in promoting skeletal muscle growth.

Recombinant Porcine R-Spondin 1 Facilitates Intestinal Stem Cell Expansion along the Crypt-Villus Axis through Potentiating Wnt/ß-Catenin Signaling in Homeostasis and Deoxynivalenol Injury.

R-spondin 1 (RSPO1) is a ligand for the intestinal stem cell (ISC) marker Lgr5 in the crypt, which functions to amplify canonical Wnt signaling to stimulate the division of ISCs. Despite the crucial role of recombinant human RSPO1 (rhRSPO1) in homeostasis and regeneration, little is known about RSPO1 among different species. Here, we cloned the porcine RSPO1 (pRSPO1) gene and obtained rpRSPO1 protein through the expression system of the recombinant Escherichia coli Rosetta (DE3) chemical competent cells. Using the in vitro IPEC-J2 model that combines cell proliferation evaluation approaches, we identified the rpRSPO1 activity in stimulating jejunal epithelial cells. And upon deoxynivalenol challenge in mice, we found that rpRSPO1 ameliorated their growth retardation and jejunal epithelial integrity. Importantly, the ISCs in the jejunum had greater proliferation and differentiation potential that was accompanied by Wnt/ß-catenin pathway activation after rpRSPO1 modulation. Subsequently, the jejunal organoids expanded from these ISCs ex vivo presented robust growth advantages. And the rpRSPO1 was able to guide Wnt/ß-catenin activity to increase ISC activity. Our work systematically demonstrates that rpRSPO1 facilitates ISC expansion by potentiating Wnt/ß-catenin signaling during homeostasis and responding to deoxynivalenol perturbations.