The phosphorylation of eukaryotic initiation factor 2 (p-eIF2) during dietary amino acid insufficiency reduces protein synthesis and alters gene expression via the integrated stress response (ISR). We explored whether a Met-restricted (MR) diet activates the ISR to reduce body fat and regulate protein balance. Male and female mice aged 3-6 mo with either whole-body deletion of general control nonderepressible 2 () or liver-specific deletion of protein kinase R-like endoplasmic reticulum kinase () alongside wild-type or floxed control mice were fed an obesogenic diet sufficient in Met (0.86%) or an MR (0.12% Met) diet for ≤5 wk. Ala enrichment with deuterium was measured to calculate protein synthesis rates. The guanine nucleotide exchange factor activity of eIF2B was measured alongside p-eIF2 and hepatic mRNA expression levels at 2 d and 5 wk. Metabolic phenotyping was conducted at 4 wk, and body composition was measured throughout. Results were evaluated with the use of ANOVA ( < 0.05). Feeding an MR diet for 2 d did not increase hepatic p-eIF2 or reduce eIF2B activity in wild-type or mice, yet many genes transcriptionally regulated by the ISR were altered in both strains in the same direction and amplitude. Feeding an MR diet for 5 wk increased p-eIF2 and reduced eIF2B activity in wild-type but not mice, yet ISR-regulated genes altered in both strains similarly. Furthermore, the MR diet reduced mixed and cytosolic but not mitochondrial protein synthesis in both the liver and skeletal muscle regardless of status. Despite the similarities between strains, the MR diet did not increase energy expenditure or reduce body fat in mice. Finally, feeding the MR diet to mice with deleted in the liver increased hepatic p-eIF2 and altered body composition similar to floxed controls. Hepatic activation of the ISR resulting from an MR diet does not require p-eIF2. status influences body fat loss but not protein balance when Met is restricted.

Background Dietary sulfur amino acid restriction (SAAR) improves body composition and metabolic health across several model organisms in part through induction of the integrated stress response (ISR). Objective We investigate the hypothesis that activating transcription factor 4 (ATF4) acts as a converging point in the ISR during SAAR. Methods Using liver-specific or global gene ablation strategies, in both female and male mice, we address the role of ATF4 during dietary SAAR. Results We show that ATF4 is dispensable in the chronic induction of the hepatokine fibroblast growth factor 21 while being essential for the sustained production of endogenous hydrogen sulfide. We also affirm that biological sex, independent of ATF4 status, is a determinant of the response to dietary SAAR. Conclusions Our results suggest that auxiliary components of the ISR, which are independent of ATF4, are critical for SAAR-mediated improvements in metabolic health in mice.

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The inorganic anion nitrate (NO3 (-)), which is naturally enriched in certain vegetables (e.g., spinach and beetroot), has emerged as a dietary component that can regulate diverse bodily functions, including blood pressure, mitochondrial efficiency, and skeletal muscle force. It is not known if dietary nitrate improves cardiac contractility. To test this, mice were supplemented for 1-2 weeks with sodium nitrate in the drinking water at a dose similar to a green diet. The hearts from nitrate-treated mice showed increased left ventricular pressure and peak rate of pressure development as measured with the Langendorff heart technique. Cardiomyocytes from hearts of nitrate-treated and control animals were incubated with the fluorescent indicator Fluo-3 to measure cytoplasmic free [Ca(2+)] and fractional shortening. Cardiomyocytes from nitrate-treated mice displayed increased fractional shortening, which was linked to larger Ca(2+) transients. Moreover, nitrate hearts displayed increased protein expression of the L-type Ca(2+) channel/dihydropyridine receptor and peak L-type Ca(2+) channel currents. The nitrate-treated hearts displayed increased concentration of cAMP but unchanged levels of cGMP compared with controls. These findings provide the first evidence that dietary nitrate can affect the expression of important Ca(2+) handling proteins in the heart, resulting in increased cardiomyocyte Ca(2+) signaling and improved left ventricular contractile function. Our observation shows that dietary nitrate impacts cardiac function and adds understanding to inorganic nitrate as a physiological modulator.

Intestinal-fatty acid binding protein (IFABP; FABP2) is a 15-kDa intracellular protein abundantly present in the cytosol of the small intestinal (SI) enterocyte. High-fat (HF) feeding of IFABP−/− mice resulted in reduced weight gain and fat mass relative to wild-type (WT) mice. Here, we examined intestinal properties that may underlie the observed lean phenotype of high fat-fed IFABP−/− mice. No alterations in fecal lipid content were found, suggesting that the IFABP−/− mice are not malabsorbing dietary fat. However, the total excreted fecal mass, normalized to food intake, was increased for the IFABP−/− mice relative to WT mice. Moreover, intestinal transit time was more rapid in the IFABP−/− mice. IFABP−/− mice displayed a shortened average villus length, a thinner muscularis layer, reduced goblet cell density, and reduced Paneth cell abundance. The number of proliferating cells in the crypts of IFABP−/− mice did not differ from that of WT mice, suggesting that the blunt villi phenotype is not due to alterations in proliferation. IFABP−/− mice were observed to have altered expression of genes and proteins related to intestinal structure, while immunohistochemical analyses revealed increased staining for markers of inflammation. Taken together, these studies indicate that the ablation of IFABP, coupled with high-fat feeding, leads to changes in gut motility and morphology, which likely contribute to the relatively leaner phenotype occurring at the whole-body level. Thus, IFABP is likely involved in dietary lipid sensing and signaling, influencing intestinal motility, intestinal structure, and nutrient absorption, thereby impacting systemic energy metabolism. NEW & NOTEWORTHY Intestinal fatty acid binding protein (IFABP) is thought to be essential for the efficient uptake and trafficking of dietary fatty acids. In this study, we demonstrate that high-fat-fed IFABP−/− mice have an increased fecal output and are likely malabsorbing other nutrients in addition to lipid. Furthermore, we observe that the ablation of IFABP leads to marked alterations in intestinal morphology and secretory cell abundance.