Current Protein and Peptide Science - Volume 18, Issue 6, 2017

Dietary protein is the main source of the body needed protein for animals. A great number of domestic animals including cattle, sheep, goats, pigs and chicken and other species are raised in the world to supply meat, milk and eggs that contain high quality of protein for human consumption. Domestic animals consume a great amount of feeds and water and excrete a large amount of faeces and urine. The conversion rate of dietary nitrogen (N, mainly dietary protein) to product N in livestock is low and the amount of N excretion is high and the nitrogenous compounds in excreta can be used as materials for nitrous oxide (N2O) formation in the processes of nitrification and denitrification in storage of excreta. Hence livestock farms and grazing pastures are important sources of N2O. N2O is a potent greenhouse gas and the key factor that damages the ozonosphere of the earth. Therefore, it is urgent to reveal the dietary protein metabolism processes and the regulation mechanism, which will help to reduce N2O emission. The nutritional options to reduce N excretion from livestock and consequently N2O emission include feeding low N rations and supplementing essential amino acid (AA) such as lysine and methionine to balance the AA profile of rations for pigs and ruminants. Other options include regulating partition of N excretion from urine to faeces and urinary nitrogenous constituents by decreasing urea N and increasing hippuric acid in ruminants. Supplementing tannic acid in the ration of ruminants has the potential to decrease the ratio of urinary N/faecal N and regulate the urinary nitrogenous components of ruminants and possibly reduce N2O emission in storage of excreta.

Biogenic amines in the gastrointestinal tract are important metabolites of dietary protein and amino acids with the help of gut digestive enzymes and microbes, which play a crucial role in the regulation of intestinal functions, including digestion, absorption, and local immunity. However, high concentrations of biogenic amines can induce adverse reactions and are harmful to animal's health. Therefore, it is crucial to have a clear understanding of how different biogenic amines interact with a body's intestinal function signaling pathways and to monitor the content of biogenic amines in the gastrointestinal tract. And in turn, the proper concentration of dietary protein and balanced amino acids for humans and livestock could be given. Though numerous methods have been developed and improved for the detection of biogenic amines in foods or wines much less attention has been paid directly to the determination of amine levels in the gastrointestinal tract. In this article, we mainly focus on the interaction of amines with the intestinal function signaling pathway and the broad impacts on animal physiology, and our modified method to accurately and quickly detect the biogenic amines in the digesta of an animal intestine.

Gastrointestinal homeostasis is a dynamic balance under the interaction between the host, GI tract, nutrition and energy metabolism. Glucose is the main energy source in living cells. Thus, glucose metabolic disorders can impair normal cellular function and endanger organisms’ health. Diseases that are associated with glucose metabolic disorders such as obesity, diabetes, hypertension, and other metabolic syndromes are in fact life threatening. Digestive system is responsible for food digestion and nutrient absorption. It is also involved in neuronal, immune, and endocrine pathways. In addition, the gut microbiota plays an essential role in initiating signal transduction, and communication between the enteric and central nervous system. Gut-brain axis is composed of enteric neural system, central neural system, and all the efferent and afferent neurons that are involved in signal transduction between the brain and gut-brain. Gut-brain axis is influenced by the gut-microbiota as well as numerous neurotransmitters. Properly regulated gut-brain axis ensures normal digestion, absorption, energy production, and subsequently maintenance of glucose homeostasis. Understanding the underlying regulatory mechanisms of gut-brain axis involved in gluose homeostasis would enable us develop more efficient means of prevention and management of metabolic disease such as diabetic, obesity, and hypertension.

Research efforts focusing on metabolic diseases have established a close conjunction between glucolipid abnormalities and nuclear receptors, a large superfamily of receptors including classic peroxisome proliferation-activated receptors (PPARs), liver X receptors (LXRs), farnesoid X receptors (FXRs) and glucocorticoid receptors (GRs) together with burgeoning retinoic acid receptor-related orphan receptors (RORs) and REV-ERBs. Nuclear receptors are identified to control a series of physiological and pathological processes of glucose and lipid metabolism and also implicated to mediate the long-term effects of early environmental and nutritional experiences on the formation of adult chronic metabolic disorders in human and animals. Thus, nuclear receptors play profound roles in fetal programming and adult regulation of glucolipid metabolism. In this review, we provide an overview on the recent advances in the field of nuclear receptors focusing on their roles in lipid and glucose metabolism during early and late life courses. We hope that this knowledge may shed new lights on identifying the novel target molecules or pathways for the prevention and treatment of metabolic disorders involving disrupted glucose and lipid homeostasis in human and animals.

AMP-activated protein kianse (AMPK) is a master sensor of cellular energy levels and a crucial regulator of nutrient metabolism such as the synthesis of fatty acids, glucose and protein as well as their oxidation to CO2 and water . Thus, AMPK signaling has important implications for fat deposition and glucose homeostasis in animals and humans. Much experimental and clinical evidence show that AMPK is a key therapeutic target for the prevention of diseases such as obesity, diabetes, cancer, inflammation and cardiac dysfunction. In this review we highlight recent advances on the upstream and downstream targets of AMPK, as well as the specific mechanisms whereby AMPK regulates digestive functions and chronic energy balance in animals and humans.

Myogenic stem cells are composed of satellite cells, multipotential muscle-derived stem cells and bone-marrow mesenchymal stem cells. They are multipotential stem cells that can differentiate into different cell lineages. Usually, they have the ability to commit to myogenesis, adipogenesis, and osteogenesis, which is important for the tissue growth and regeneration and even the cure of diseases. Signal proteins are major members of each signaling pathway. They transmit mass signals in or between cells and regulate gene expression, so ensure the homeostasis of the organism. Here, we review the origin, properties and applications of myogenic stem cells, and the vital signal proteins involved in myogenic stem cells differentiation will be referred to as well.

Pork is one of the most economical sources of animal protein for human consumption. Meat quality is an important economic trait for the swine industry, which is primarily determined by prenatal muscle development and postnatal growth. Identification of the molecular mechanisms underlying skeletal muscle development is a key priority. MicroRNAs (miRNAs) are a class of small noncoding RNAs that have emerged as key regulators of skeletal muscle development. A number of muscle-related miRNAs have been identified by functional gain and loss experiments in mouse model. However, determining miRNA-mRNA interactions involved in pig skeletal muscle still remains a significant challenge. For a comprehensive understanding of miRNA-mediated mechanisms underlying muscle development, miRNAome analyses of pig skeletal muscle have been performed by deep sequencing. Additionally, porcine miRNA single nucleotide polymorphisms have been implicated in muscle fiber types and meat quality. The present review provides an overview of current knowledge on recently identified miRNAs involved in myogenesis, muscle fiber type and muscle protein metabolism. Undoubtedly, further systematic understanding of the functions of miRNAs in pig skeletal muscle development will be helpful to expand the knowledge of basic skeletal muscle biology and be beneficial for the genetic improvement of meat quality traits.

New fat cells originate from a preexisting population of undifferentiated progenitor cells named preadipocytes. The process in which preadipocytes proliferate and differentiate into mature adipocytes under certain circumstances is called adipogenesis. In the past decade, many epigenetic factors have been shown to be pivotal for the appropriate timing of adipogenesis. A large number of coregulators at critical gene promoters set up specific patterns of DNA methylation, histone methylation and RNA methylation, which act as an epigenetic code to modulate the correct progress of adipocyte differentiation and adipogenesis. In this review, we focus on the functions and roles of epigenetic processes in preadipocyte differentiation and adipogenesis.

Type 2 diabetes has become a global public health problem affecting approximately 380 million people throughout the world. It can cause many complications and lead to greater mortality. At present, there is no available medicine for effectively preventing diabetes. L-arginine, a functional amino acid, the precursor of nitric oxide, plays a crucial role in maintenance, reproduction, growth, anti-aging and immunity for animals. Growing clinical evidence indicates that dietary L-arginine supplementation can reduce obesity, decrease arterial blood pressure, resist oxidation and normalize endothelial dysfunction to bring about remission of type 2 diabetes. The potential molecular mechanism may play a role in modulating glucose homeostasis, promoting lipolysis, maintaining hormone levels, ameliorating insulin resistance, and fetal programing in early stages. The possible signaling pathway of the beneficial effects of L-arginine likely involves L-arginine-nitric oxide pathway through which cell signal protein can be activated. Accumulating studies have indicated that L-arginine may have potential to prevent and/or relieve type 2 diabetes via restoring insulin sensitivity in vivo.

Glucose and lipid are the major energy sources, and pivotal components of organic metabolism in mammals. Inappropriate diet directly influences the metabolic rate, and can alter the body’s homeostasis. The underlying changes in energy storage and utilization would manifest as metabolic syndrome including obesity and high blood pressure, and high blood glucose, which are predisposing factors that significantly increase the risk for cardiovascular diseases and Type 2 Diabetes (T2D). Thus, it is essential to identify the genes that are involved in the process of glucose and lipid metabolism. Utilizing current advanced scientific methodology and technology, as well as computational resources has led to discovery of many novel genes with major roles in energy metabolism. In addition, many studies have focused on the functional analysis of the novel genes. Nowadays, uncovering the genes that are involved in glucose and lipid storage and utilization, as well as underlying pathways that regulate expression of those genes is an area of ongoing research. Here, we summarize the current research related to the novel genes regulating glucose and lipid metabolisms, which enable us to develop more efficient means of prevention and management of metabolic diseases such as T2D, obesity, high blood glucose, and hypertension.

Clinical observations support the postulate that chronic low-grade inflammation underlies metabolic diseases and inflammatory mediators can trigger some metabolic diseases. In disorder condition, what is the first one: metabolic diseases cause inflammation or conversely? This “chicken or egg” type question was hard to answer. However, instead of focusing on this difficult issue, we should ask another challenging question: what are the links between inflammation and metabolic diseases? Seizing the key from this chaos may be the best way to solve the problem and break the cycle. To answer this question, we review the regulators (such as NF-Κ ;B, PPARs, mTOR, and STAT3) that have important roles in both metabolism and inflammation. These “bridge proteins” that link metabolic diseases and inflammation not only increase our understanding of these two diseases, but also provide potential targets for therapeutics and practical clinical applications.

X-box binding protein1 (XBP1) especially exerts its fundamental effects in the cellular organelle endoplasmic reticulum (ER) via affecting three trans-membrane stress sensor proteins: PKRlike ER kinase (PERK), inositol-requiring enzyme 1(IRE1) and activating transcription factor 6(ATF6). At the center of XBP1’s broad effects is its remarkable metabolic housekeeper function. XBP1 decreased glucose dysfunction via funneling its effects on improving insulin sensitivity and stimulating insulin secretion. However, XBP1 also yields its double-edged effects, driving the transformation from excess glucose to lipid, which is a key contribution to obesity and T2DM. In this review, we highlight the vital mechanism of XBP1 in manipulating glucose and lipid metabolism involved by multiple signaling pathways.

Protein is an important yet the most expensive dietary component for farm ruminant animals. Understanding the mechanism behind protein utilization in animals for maintenance and milk production is critical for raising animals efficiently. Once the protein has been ingested, it undergoes various transformations in the gut before it is absorbed into blood and its precursors are harnessed by the mammary gland for milk protein synthesis in lactating animals. Several signaling pathways are involved both in absorption and in milk protein biosynthesis. Protein metabolism and signal pathway regulation in various tissues of ruminant are thus reviewed with emphasis on two particular tissues, the rumen and the mammary gland.