Induction of autophagy through the activating transcription factor 4 (ATF4)-dependent amino acid response pathway in maternal skeletal muscle may function as the molecular memory in response to gestational protein restriction to alert offspring to maternal nutrition

Research progress on the effects of adverse exposure during pregnancy on skeletal muscle function in the offspring

Skeletal muscle plays a crucial role in maintaining metabolism, energy homeostasis, movement, as well as endocrine function. The gestation period is a critical stage for myogenesis and development of the skeletal muscle. Adverse environmental exposures during pregnancy may impose various effects on the skeletal muscle health of the offspring. Maternal obesity during pregnancy can mediate lipid deposition in the skeletal muscle of the offspring by affecting fetal skeletal muscle metabolism and inflammation-related pathways. Poor dietary habits during pregnancy, such as high sugar and high fat intake, can affect autophagy of skeletal muscle mitochondria and reduce the quality of the offspring skeletal muscle. Nutritional deficiencies during pregnancy can affect the development of the offspring skeletal muscle through epigenetic modifications. Gestational diabetes may affect the function of the offspring skeletal muscle by upregulating the levels of miR-15a and miR-15b in the offspring. Exposure to environmental endocrine disruptors during pregnancy may impair skeletal muscle function by interfering with insulin receptor-related signaling pathways. This article reviews the research progress on effects and possible mechanisms of adverse maternal exposures during pregnancy on the offspring skeletal muscle function based on clinical and animal studies, aiming to provide scientific evidence for the prevention and treatment strategies of birth defects in the skeletal muscle.

Single-Cell RNA Sequencing (scRNA-seq) Identifies L1CAM as a Key Mediator between Epithelial Tuft Cell and Innate Lymphoid Cell in the Colon of Hnrnp I Knockout Mice

(1) Background: Knockout (KO) of heterogeneous nuclear ribonucleoprotein I (Hnrnp I) in mouse intestinal epithelial cells (IECs) induced a severe inflammatory response in the colon, followed by hyperproliferation. This study aimed to investigate the epithelial lineage dynamics and cell-cell communications that underlie inflammation and colitis. (2) Methods: Single cells were isolated from the colons of wildtype (WT) and KO mice and used in scRNA-seq. Whole colons were collected for immunofluorescence staining and cytokine assays. (3) Results: from scRNA-seq, the number of DCLK1 + colonic tuft cells was significantly higher in the Hnrnp I KO mice compared to the WT mice. This was confirmed by immunofluorescent staining of DCLK1. The DCLK1 + colonic tuft cells in KO mice developed unique communications with lymphocytes via interactions between surface L1 cell adhesion molecule (L1CAM) and integrins. In the KO mice colons, a significantly elevated level of inflammatory cytokines IL4, IL6, and IL13 were observed, which marks type-2 immune responses directed by group 2 innate lymphoid cells (ILC2s). (4) Conclusions: This study demonstrates one critical cellular function of colonic tuft cells, which facilitates type-2 immune responses by communicating with ILC2s via the L1CAM-integrins interaction. This communication promotes pro-inflammatory signaling pathways in ILC2, leading to the increased secretion of inflammatory cytokines.

Combined prenatal to postnatal protein restriction augments protein quality control processes and proteolysis in the muscle of rat offspring

Several human epidemiological and animal studies suggest that a maternal low-protein (MLP) diet affects skeletal muscle (SM) health in the offspring. However, effect of combined prenatal to postnatal protein restriction (chronic PR) and prenatal to perinatal protein restriction (PR) with postnatal rehabilitation maternal protein restriction (MPR) on protein quality control (PQC) processes and proteolysis in the offspring remains poorly understood. The current study explored the impact of chronic PR and MPR on SM protein degradation rates, chaperones, unfolded protein response (UPR), ubiquitin-proteasome system (UPS), autophagy, and apoptosis, in the adult offspring. Wistar rats were randomly assigned to a normal protein (NP; 20% casein), or low-protein (LP; 8% casein) isocaloric diets from 7 weeks prior to breeding through weaning. Offspring born to NP dams received the same diet (NP offspring) while a group of LP offspring remained on LP diet and another group was rehabilitated with NP diet (LPR offspring) from weaning for 16 weeks. LP offspring displayed lower body weight, lean mass, and myofiber cross-sectional area than NP. Furthermore, LP offspring demonstrated increased total protein degradation, urinary 3-methyl histidine, ER stress, autophagy, UPS components, proteasomal activity, muscle atrophy markers, and apoptosis-related proteins than NP. However, MPR showed little or no effect on muscle proteolysis, UPR, UPS, autophagy, apoptosis, and muscle atrophy in LPR offspring. These results indicate that exposure to chronic PR diets induces muscle atrophy and accelerates SM proteolysis via augmenting PQC processes in the offspring, while MPR shows little or no effect.

Gestational low dietary protein induces intrauterine inflammation and alters the programming of adiposity & insulin sensitivity in the adult offspring

Malnutrition associated with low dietary protein can induce gestational inflammation and sets a long-lasting metabolic impact on the offspring even after replenishment. The work investigated whether a low-protein diet (LPD) during pregnancy and lactation induces intrauterine inflammation and predisposes offspring to adiposity and insulin resistance in their adult life. Female Golden Syrian hamsters were fed LPD (10.0% energy from protein) or a control diet (CD, 20.0 % energy from protein) from preconception until lactation. All pups were switched to CD after lactation and continued until the end. Maternal LPD increased intrauterine inflammation by enhancing neutrophil infiltration, amniotic hsCRP, oxidative stress, and mRNA expression of NFκβ, IL8, COX2, and TGFβ in the chorioamniotic membrane (P<.05). The prepregnancy body weight, placental, and fetal weights, serum AST and ALT were decreased, while blood platelets, lymphocytes, insulin, and HDL were significantly increased in LPD-fed dams (P<.05). A postnatal switch to an adequate protein could not prevent hyperlipidemia in the 6-months LPD/CD offspring. The lipid profile and liver functions were restored over 10 months of protein feeding but failed to normalize fasting glucose and body fat accumulation compared to CD/CD. LPD/CD showed elevated GLUT4 expression & activated pIRS1 in the skeletal muscle and increased expression of IL6, IL1β, and p65-NFκB proteins in the liver (P<.05). In conclusion, present data suggest that maternal protein restriction may induce intrauterine inflammation and affect liver inflammation in the adult offspring by an influx of fats from adipose that may alter lipid metabolism and reduce insulin sensitivity in skeletal muscle.

Maternal diet induces persistent DNA methylation changes in the muscle of beef calves

Maternal nutrition during pregnancy can induce epigenetic alterations in the fetal genome, such as changes in DNA methylation. It remains unclear whether these epigenetic alterations due to changes in maternal nutrition are transitory or persist over time. Here, we hypothesized that maternal methionine supplementation during preconception and early pregnancy could alter the fetal epigenome, and some of these alterations could persist throughout different developmental stages of the offspring. Beef cows were randomly assigned to either a control or a methionine-rich diet from - 30 to + 90 d, relative to the beginning of the breeding season. The methylome of loin muscle from the same bull calves (n = 10 per maternal diet) at 30 and 200 days of age were evaluated using whole-genome bisulfite sequencing. Notably, a total of 28,310 cytosines showed persistent methylation differences over time between maternal diets (q-value < 0.10, methylation change > 20%). These differentially methylated cytosines were in the transcription start sites, exons, or splice sites of 341 annotated genes. Over-representation analysis revealed that these differentially methylated genes are involved in muscle contraction, DNA and histone methylation, mitochondrial function, reactive oxygen species homeostasis, autophagy, and PI3K signaling pathway, among other functions. In addition, some of the persistently, differentially methylated cytosines were found in CpG islands upstream of genes implicated in mitochondrial activities and immune response. Overall, our study provides evidence that a maternal methionine-rich diet altered fetal epigenome, and some of these epigenetic changes persisted over time.

A maternal low-protein diet during gestation induces hepatic autophagy-related gene expression in a sex-specific manner in Sprague-Dawley rats

This study investigates the mechanism by which maternal protein restriction induces hepatic autophagy-related gene expression in the offspring of rats. Pregnant Sprague-Dawley rats were fed either a control diet (C, 18 % energy from protein) or a low-protein diet (LP, 8·5 % energy from protein) during gestation, followed by the control diet during lactation and post-weaning. Liver tissue was collected from the offspring at postnatal day 38 and divided into four groups according to sex and maternal diet (F-C, F-LP, M-C and M-LP) for further analysis. Autophagy-related mRNA and protein levels were determined by real-time PCR and Western blotting, respectively. In addition, chromatin immunoprecipitation (ChIP) was performed to investigate the interactions between transcription factors and autophagy-related genes. Protein levels of p- eukaryotic translation initiation factor 2a and activating transcription factor 4 (ATF4) were increased only in the female offspring born to dams fed the LP diet. Correlatively, the mRNA expression of hepatic autophagy-related genes including Map1lc3b, P62/Sqstm1, Becn1, Atg3, Atg7 and Atg10 was significantly greater in the F-LP group than in the F-C group. Furthermore, ChIP results showed greater ATF4 and C/EBP homology protein (CHOP) binding at the regions of a set of autophagy-related genes in the F-LP group than in the F-C group. Our data demonstrated that a maternal LP diet transcriptionally programmed hepatic autophagy-related gene expression only in female rat offspring. This transcriptional programme involved the activation of the eIF2α/ATF4 pathway and intricate regulation by transcription factors ATF4 and CHOP.

Effects of maternal branched-chain amino acid and alanine supplementation on growth and biomarkers of protein metabolism in dams fed a low-protein diet and their offspring

A considerable number of studies have reported that maternal protein restriction may disturb fetal growth and organ development due to a lower availability of amino acids. Leucine, one of branched-chain amino acid (BCAA) promotes protein synthesis through mechanistic target of rapamycin signaling. Here, we investigated the effects of BCAA supplementation in the dams fed a low-protein diet on serum and hepatic biochemical parameters of protein metabolism of dams and their offspring. Female ICR mice were fed a control (20% casein), a low-protein (10% casein), a low-protein with 2% BCAAs or a low-protein with 2% alanine diet for 2 weeks before mating and then throughout pregnancy and lactation. Alanine was used as an amino nitrogen control for the BCAA. Dams and their male offspring were sacrificed at postnatal day 21. There were no changes in body weight and fat mass in low-protein fed dams; however, BCAA supplementation significantly increased fat mass and serum leptin levels. Low-protein diet consumption reduced maternal protein synthesis based on biochemical analysis of serum albumin and hepatic protein levels and immunoblotting of S6 protein, which were increased by BCAA and alanine supplementation. Offspring from dams fed a low-protein diet exhibited lower body and organ weights. Body weight and hepatic protein levels of the offspring were increased by alanine supplementation. However, the decreased serum biochemical parameters, including glucose, triglyceride, total protein and albumin levels in the low-protein offspring group were not changed in response to BCAA or alanine supplementation. A reduced density of the hepatic vessel system in the offspring from dams fed a low-protein diet was restored in the offspring from dams fed either BCAA and alanine-supplemented diet. These results suggest that supplementation of amino nitrogen per se may be responsible for inducing hepatic protein synthesis in the dams fed a low-protein diet and alleviating the distorted growth and liver development of their offspring.

Maternal malnutrition and anaemia in India: dysregulations leading to the 'thin-fat' phenotype in newborns

Maternal and child malnutrition and anaemia remain the leading factors for health loss in India. Low birth weight (LBW) offspring of women suffering from chronic malnutrition and anaemia often exhibit insulin resistance and infantile stunting and wasting, together with increased risk of developing cardiometabolic disorders in adulthood. The resulting self-perpetuating and highly multifactorial disease burden cannot be remedied through uniform dietary recommendations alone. To inform approaches likely to alleviate this disease burden, we implemented a systems-analytical approach that had already proven its efficacy in multiple published studies. We utilised previously published qualitative and quantitative analytical results of rural and urban field studies addressing maternal and infantile metabolic and nutritional parameters to precisely define the range of pathological phenotypes encountered and their individual biological characteristics. These characteristics were then integrated, via extensive literature searches, into metabolic and physiological mechanisms to identify the maternal and foetal metabolic dysregulations most likely to underpin the 'thin-fat' phenotype in LBW infants and its associated pathological consequences. Our analyses reveal hitherto poorly understood maternal nutrition-dependent mechanisms most likely to promote and sustain the self-perpetuating high disease burden, especially in the Indian population. This work suggests that it most probably is the metabolic consequence of 'ill-nutrition' - the recent and rapid dietary shifts to high salt, high saturated fats and high sugar but low micronutrient diets - over an adaptation to 'thrifty metabolism' which must be addressed in interventions aiming to significantly alleviate the leading risk factors for health deterioration in India.

A Low Protein Diet during Gestation and Lactation Increases Hepatic Lipid Accumulation through Autophagy and Histone Deacetylase

The present study examined the mechanism of a low protein (LP) diet on hepatic lipid metabolism during gestation and lactation. Timed-pregnant Sprague-Dawley rats were fed a control or an LP diet during gestation and lactation. LP dams had increased hepatic triglyceride accumulation and significantly higher aspartate/alanine transaminase ratio, accompanied by a decrease in circulating very low-density/low-density lipoprotein ratio. LC3B (Microtubule Associated Protein 1 Light Chain 3 Beta) expression was stimulated in LP dams along with increased histone acetylation. LP diet-induced co-localization of the LC3 binding motif-interacting proteins APOB or MTTP with LC3B, suggesting autophagic degradation. HDAC3 is found necessary to prevent lipid accumulation in response to amino acid deprivation in HepG2 cells. LC3B-mediated APOB protein degradation is related to increases in lipid accumulation. Conclusion: HDAC3 regulated LC3B-induced lipid accumulation potentially through autophagic degradation of APOB and MTTP in response to amino acid limitation caused by a low protein diet.

Epigenetic Mechanisms of Maternal Dietary Protein and Amino Acids Affecting Growth and Development of Offspring

Nutrients can regulate metabolic activities of living organisms through epigenetic mechanisms, including DNA methylation, histone modification, and RNA regulation. Since the nutrients required for early embryos and postpartum lactation are derived in whole or in part from maternal and lactating nutrition, the maternal nutritional level affects the growth and development of fetus and creates a profound relationship between disease development and early environmental exposure in the offspring's later life. Protein is one of the most important biological macromolecules, involved in almost every process of life, such as information transmission, energy processing and material metabolism. Maternal protein intake levels may affect the integrity of the fetal genome and alter DNA methylation and gene expression. Most amino acids are supplied to the fetus from the maternal circulation through active transport of placenta. Some amino acids, such as methionine, as dietary methyl donor, play an important role in DNA methylation and body's one-carbon metabolism. The purpose of this review is to describe effects of maternal dietary protein and amino acid intake on fetal and neonatal growth and development through epigenetic mechanisms, with examples in humans and animals.

Maternal and Post-weaning High-Fat Diets Produce Distinct DNA Methylation Patterns in Hepatic Metabolic Pathways within Specific Genomic Contexts

Calorie-dense high-fat diets (HF) are associated with detrimental health outcomes, including obesity, cardiovascular disease, and diabetes. Both pre- and post-natal HF diets have been hypothesized to negatively impact long-term metabolic health via epigenetic mechanisms. To understand how the timing of HF diet intake impacts DNA methylation and metabolism, male Sprague–Dawley rats were exposed to either maternal HF (MHF) or post-weaning HF diet (PHF). At post-natal week 12, PHF rats had similar body weights but greater hepatic lipid accumulation compared to the MHF rats. Genome-wide DNA methylation was evaluated, and analysis revealed 1744 differentially methylation regions (DMRs) between the groups with the majority of the DMR located outside of gene-coding regions. Within differentially methylated genes (DMGs), intragenic DNA methylation closer to the transcription start site was associated with lower gene expression, whereas DNA methylation further downstream was positively correlated with gene expression. The insulin and phosphatidylinositol (PI) signaling pathways were enriched with 25 DMRs that were associated with 20 DMGs, including PI3 kinase (Pi3k), pyruvate kinase (Pklr), and phosphodiesterase 3 (Pde3). Together, these results suggest that the timing of HF diet intake determines DNA methylation and gene expression patterns in hepatic metabolic pathways that target specific genomic contexts.

Protein restriction and cancer

Protein restriction without malnutrition is currently an effective nutritional intervention known to prevent diseases and promote health span from yeast to human. Recently, low protein diets are reported to be associated with lowered cancer incidence and mortality risk of cancers in human. In murine models, protein restriction inhibits tumor growth via mTOR signaling pathway. IGF-1, amino acid metabolic programing, FGF21, and autophagy may also serve as potential mechanisms of protein restriction mediated cancer prevention. Together, dietary intervention aimed at reducing protein intake can be beneficial and has the potential to be widely adopted and effective in preventing and treating cancers.

Amino acid starvation-induced autophagy is involved in reduced subcutaneous fat deposition in weaning piglets derived from sows fed low-protein diet during gestation and lactation : Autophagy is involved in reduced fat deposition in maternal low-protein piglets

PURPOSE

The study aimed to determine the effects of maternal low-protein (LP) diet on subcutaneous fat deposition of weaning piglets and the potential mechanism.

METHODS

Sows were fed either a standard protein (SP, 15 and 18% crude protein) or a LP diet (50% protein levels of SP) throughout pregnancy and lactation. Subcutaneous fat and blood were sampled from male piglets at 28 days of age. Serum biochemical metabolites and hormone concentrations were detected with the enzymatic colorimetric methods. Serum-free amino acid (FAA) levels were measured by amino acid auto-analyzer. The mRNA and protein were measured by qRT-PCR and Western blot.

RESULTS

Body weight, back fat thickness, triglycerides concentrations in subcutaneous fat tissue, and serum, as well as FFA concentrations were significantly reduced in LP piglets when compared with SP piglets. Further studies showed that mRNA and protein expression of acetyl-CoA carboxylase and fatty acid synthetase, two key enzymes of de novo lipogenesis, were significantly reduced in LP piglets, while mRNA expression and the lipolytic enzymes activities of lipolysis genes, adipose triglyceride lipase and hormone-sensitive lipase, were significantly increased. Furthermore, expression of autophagy-related gene 7 and autophagy maker gene microtubule-associated protein 1A/1B-light chain 3 (LC 3) as well as the conversion of LC3I to LC3II were significantly elevated, along with the expression of activating transcription factor-4 and eukaryotic translation initiation factor-2a.

CONCLUSION

These results indicate that amino acid starvation-induced autophagy is involved in reduced subcutaneous fat deposition in maternal LP weaning piglets, demonstrating links between maternal protein restriction and offspring fat deposition.

LC3/GABARAP family proteins: autophagy-(un)related functions

From yeast to mammals, autophagy is an important mechanism for sustaining cellular homeostasis through facilitating the degradation and recycling of aged and cytotoxic components. During autophagy, cargo is captured in double-membraned vesicles, the autophagosomes, and degraded through lysosomal fusion. In yeast, autophagy initiation, cargo recognition, cargo engulfment, and vesicle closure is Atg8 dependent. In higher eukaryotes, Atg8 has evolved into the LC3/GABARAP protein family, consisting of 7 family proteins [LC3A (2 splice variants), LC3B, LC3C, GABARAP, GABARAPL1, and GABARAPL2]. LC3B, the most studied family protein, is associated with autophagosome development and maturation and is used to monitor autophagic activity. Given the high homology, the other LC3/GABARAP family proteins are often presumed to fulfill similar functions. Nevertheless, substantial evidence shows that the LC3/GABARAP family proteins are unique in function and important in autophagy-independent mechanisms. In this review, we discuss the current knowledge and functions of the LC3/GABARAP family proteins. We focus on processing of the individual family proteins and their role in autophagy initiation, cargo recognition, vesicle closure, and trafficking, a complex and tightly regulated process that requires selective presentation and recruitment of these family proteins. In addition, functions unrelated to autophagy of the LC3/GABARAP protein family members are discussed.-Schaaf, M. B. E., Keulers, T. G, Vooijs, M. A., Rouschop, K. M. A. LC3/GABARAP family proteins: autophagy-(un)related functions.

Does skeletal muscle have an 'epi'-memory? The role of epigenetics in nutritional programming, metabolic disease, aging and exercise

Skeletal muscle mass, quality and adaptability are fundamental in promoting muscle performance, maintaining metabolic function and supporting longevity and healthspan. Skeletal muscle is programmable and can ‘remember’ early‐life metabolic stimuli affecting its function in adult life. In this review, the authors pose the question as to whether skeletal muscle has an ‘epi’‐memory? Following an initial encounter with an environmental stimulus, we discuss the underlying molecular and epigenetic mechanisms enabling skeletal muscle to adapt, should it re‐encounter the stimulus in later life. We also define skeletal muscle memory and outline the scientific literature contributing to this field. Furthermore, we review the evidence for early‐life nutrient stress and low birth weight in animals and human cohort studies, respectively, and discuss the underlying molecular mechanisms culminating in skeletal muscle dysfunction, metabolic disease and loss of skeletal muscle mass across the lifespan. We also summarize and discuss studies that isolate muscle stem cells from different environmental niches in vivo (physically active, diabetic, cachectic, aged) and how they reportedly remember this environment once isolated in vitro. Finally, we will outline the molecular and epigenetic mechanisms underlying skeletal muscle memory and review the epigenetic regulation of exercise‐induced skeletal muscle adaptation, highlighting exercise interventions as suitable models to investigate skeletal muscle memory in humans. We believe that understanding the ‘epi’‐memory of skeletal muscle will enable the next generation of targeted therapies to promote muscle growth and reduce muscle loss to enable healthy aging.

Mechanisms of protein balance in skeletal muscle

Increased global demand for adequate protein nutrition against a backdrop of climate change and concern for animal agriculture sustainability necessitates new and more efficient approaches to livestock growth and production. Anabolic growth is achieved when rates of new synthesis exceed turnover, producing a positive net protein balance. Conversely, deterioration or atrophy of lean mass is a consequence of a net negative protein balance. During early life and periods of growth, muscle mass is driven by increases in protein synthesis at the level of mRNA translation. Throughout life, muscle mass is further influenced by degradative processes such as autophagy and the ubiquitin proteasome pathway. Multiple signal transduction networks guide and coordinate these processes alongside quality control mechanisms to maintain protein homeostasis (proteostasis). Genetics, hormones, and environmental stimuli each influence proteostasis control, altering capacity and/or efficiency of muscle growth. An overview of recent findings and current methods to assess muscle protein balance and proteostasis is presented. Current efforts to identify novel control points have the potential through selective breeding design or development of hormetic strategies to better promote growth and health span during environmental stress.