Refeeding with a standard diet after a 48-h fast elicits an inflammatory response in the mouse liver

Aging Induces Hepatic Oxidative Stress and Nuclear Proteomic Remodeling in Liver from Wistar Rats

Aging is a continuous, universal, and irreversible process that determines progressive loss of adaptability. The liver is a critical organ that supports digestion, metabolism, immunity, detoxification, vitamin storage, and hormone signaling. Nevertheless, the relationship between aging and the development of liver diseases remains elusive. In fact, although prolonged fasting in adult rodents and humans delays the onset of the disease and increases longevity, whether prolonged fasting could exert adverse effects in old organisms remains incompletely understood. In this work, we aimed to characterize the oxidative stress and nuclear proteome in the liver of 3-month- and 24-month-old male Wistar rats upon 36 h of fasting and its adaptation in response to 30 min of refeeding. To this end, we analyzed the hepatic lipid peroxidation levels (TBARS) and the expression levels of genes associated with fat metabolism and oxidative stress during aging. In addition, to gain a better insight into the molecular and cellular processes that characterize the liver of old rats, the hepatic nuclear proteome was also evaluated by isobaric tag quantitation (iTRAQ) mass spectrometry-based proteomics. In old rats, aging combined with prolonged fasting had great impact on lipid peroxidation in the liver that was associated with a marked downregulation of antioxidant genes (Sod2, Fmo3, and Cyp2C11) compared to young rats. Besides, our proteomic study revealed that RNA splicing is the hepatic nuclear biological process markedly affected by aging and this modification persists upon refeeding. Our results suggest that aged-induced changes in the nuclear proteome could affect processes associated with the adaptative response to refeeding after prolonged fasting, such as those involved in the defense against oxidative stress.

Macronutrient modulation of mRNA and microRNA function in animals: A review

Dietary macronutrients have been regarded as a basic source of energy and amino acids that are necessary for the maintenance of cellular homeostasis, metabolic programming as well as protein synthesis. Due to the emergence of “nutrigenomics”, a unique discipline that combines nutritional and omics technologies to study the impacts of nutrition on genomics, it is increasingly evident that macronutrients also have a significant role in the gene expression regulation. Gene expression is a complex phenomenon controlled by several signaling pathways and could be influenced by a wide variety of environmental and physiological factors. Dietary macronutrients are the most important environmental factor influencing the expression of both genes and microRNAs (miRNA). miRNA are tiny molecules of 18 to 22 nucleotides long that regulate the expression of genes. Therefore, dietary macronutrients can influence the expression of genes in both direct and indirect manners. Recent advancements in the state-of-the-art technologies regarding molecular genetics, such as next-generation sequencing, quantitative PCR array, and microarray, allowed us to investigate the occurrence of genome-wide changes in the expression of genes in relation to augmented or reduced dietary macronutrient intake. The purpose of this review is to accumulate the current knowledge focusing on macronutrient mediated changes in the gene function. This review will discuss the impact of altered dietary carbohydrate, protein, and fat intake on the expression of coding genes and their functions. In addition, it will also summarize the regulation of miRNA, both cellular and extracellular miRNA, expression modulated by dietary macronutrients.

Refeeding with glucose rather than fructose elicits greater hepatic inflammatory gene expression in mice

OBJECTIVE

We previously reported that refeeding after a 48-h fast, used as a study model of starvation and refeeding, promotes acute liver inflammatory gene expression, which is at least partly mediated by toll-like receptor 2 (TLR2). We also previously demonstrated that dietary carbohydrates play critical roles in this process. The aim of this study was to compare the outcomes of refeeding with different carbohydrate sources.

METHODS

Mice were fasted for 46 h and then refed with 1.5% (w/w) agar gel containing 19% carbohydrate (sources: α-cornstarch, glucose, sucrose, or fructose). The liver expression of inflammatory and other specific genes was then sequentially measured for the first 14 h after refeeding initiation.

RESULTS

Fasting for 46 h up-regulated the liver expression of endogenous ligands for TLRs (HspA5, Hsp90 aa1, and Hspd1). Refeeding with agar gel containing α-cornstarch or glucose increased the liver expression of Tlr2, proinflammatory genes (Cxcl2, Cxcl10, Cxcl1, Nfkb1, Nfkb2, RelB, Sectm1α, Il1β), stress response genes (Atf3, Asns, Gadd45 a, Perk, Inhbe), detoxification genes (Hmox1, Gsta1, Abca8b), genes involved in tissue regeneration (Gdf15, Krt23, Myc, Tnfrsf12a, Mthfd2), and genes involved in tumor suppression (p53, Txnrd1, Btg2). This refeeding also moderately but significantly elevated the serum levels of alanine aminotransferase. These effects were attenuated in mice refed with agar gel containing sucrose or fructose.

CONCLUSION

Dietary glucose, rather than fructose, plays a critical role in refeeding-induced acute liver inflammatory gene expression and moderate hepatocyte destruction. Further studies are recommended regarding the role of these effects in liver inflammation and, consequently, liver dysfunction.

Defective autophagy impairs ATF3 activity and worsens lung injury during endotoxemia

Autophagy has emerged as a key regulator of the inflammatory response. To examine the role of autophagy in the development of organ dysfunction during endotoxemia, wild-type and autophagy-deficient (Atg4b-null) mice were challenged with lipopolysaccharide. Animals lacking Atg4b showed increased mortality after endotoxemia. Among the different organs studied, only the lungs showed significant differences between genotypes, with increased damage in mutant animals. Autophagy was activated in lungs from wild-type, LPS-treated mice. Similarly, human bronchial cells show an increased autophagy when exposed to serum from septic patients. We found an increased inflammatory response (increased neutrophilic infiltration, higher levels of Il6, Il12p40, and Cxcl2) in the lungs from knockout mice and identified perinuclear sequestration of the anti-inflammatory transcription factor ATF3 as the putative mechanism responsible for the differences between genotypes. Finally, induction of autophagy by starvation before LPS exposure resulted in a dampened pulmonary response to LPS in wild-type, but not knockout, mice. Similar results were found in human bronchial cells exposed to LPS. Our results demonstrate the central role of autophagy in the regulation of the lung response to endotoxemia and sepsis and its potential modulation by nutrition.

KEY MESSAGES

Endotoxemia and sepsis trigger autophagy in lung tissue. Defective autophagy increases mortality and lung inflammation after endotoxemia. Impairment of autophagy results is perinuclear ATF3 sequestration. Starvation ameliorates lung injury by an autophagy-dependent mechanism.