Translational Factor eIF4G1 Regulates Glucose Homeostasis and Pancreatic β-Cell Function

EIF4G1 Is a Potential Prognostic Biomarker of Breast Cancer

BACKGROUND

Breast cancer (BRCA) is one of the most common cancers in women worldwide and a leading cause of death from malignancy. This study was designed to identify a novel biomarker for prognosticating the survival of BRCA patients.

METHODS

The prognostic potential of eukaryotic translation initiation factor 4 gamma 1 (EIF4G1) was assessed using RNA sequencing (RNA-seq) data from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) as training cohort and validation set, respectively. The functional enrichment analysis of differentially expressed genes (DEGs) was performed. The relationship between EIF4G1 and tumor microenvironment (TME) was analyzed. Immunotherapy responses were explored by the immunophenoscores (IPS) and tumor immune dysfunction and exclusion (TIDE) score. The Connectivity Map (CMap) was used to discover potentially effective therapeutic molecules against BRCA. Immunohistochemistry (IHC) was applied to compare the protein levels of EIF4G1 in normal and cancer tissues and to verify the prognostic value of EIF4G1.

RESULTS

BRCA patients with increased expression of EIF4G1 had a shorter overall survival (OS) in all cohorts and results from IHC. EIF4G1-related genes were mainly involved in DNA replication, BRCA metastasis, and the MAPK signaling pathway. Infiltration levels of CD4⁺-activated memory T cells, macrophages M0, macrophages M1, and neutrophils were higher in the EIF4G1 high-expression group than those in the EIF4G1 low-expression group. EIF4G1 was positively correlated with T cell exhaustion. Lower IPS was revealed in high EIF4G1 expression patients. Five potential groups of drugs against BRCA were identified.

CONCLUSION

EIF4G1 might regulate the TME and affect BRCA metastasis, and it is a potential prognostic biomarker and therapeutic target for BRCA.

Pancreatic β-cell hyper-O-GlcNAcylation leads to impaired glucose homeostasis in vivo

Protein O-GlcNAcylation is a nutrient and stress-sensitive protein post-translational modification (PTM). The addition of an O-GlcNAc molecule to proteins is catalyzed by O-GlcNAc transferase (OGT), whereas O-GlcNAcase (OGA) enzyme is responsible for removal of this PTM. Previous work showed that OGT is highly expressed in the pancreas, and we demonstrated that hypo-O-GlcNAcylation in β-cells cause severe diabetes in mice. These studies show a direct link between nutrient-sensitive OGT and β-cell health and function. In the current study, we hypothesized that hyper-O-GlcNAcylation may confer protection from β-cell failure in high-fat diet (HFD)-induced obesity. To test this hypothesis, we generated a mouse model with constitutive β-cell OGA ablation (βOGAKO) to specifically increase O-GlcNAcylation in β-cells. Under normal chow diet, young male and female βOGAKO mice exhibited normal glucose tolerance but developed glucose intolerance with aging, relative to littermate controls. No alteration in β-cell mass was observed between βOGAKO and littermate controls. Total insulin content was reduced despite an increase in pro-insulin to insulin ratio in βOGAKO islets. βOGAKO mice showed deficit in insulin secretion in vivo and in vitro. When young animals were subjected to HFD, both male and female βOGAKO mice displayed normal body weight gain and insulin tolerance but developed glucose intolerance that worsened with longer exposure to HFD. Comparable β-cell mass was found between βOGAKO and littermate controls. Taken together, these data demonstrate that the loss of OGA in β-cells reduces β-cell function, thereby perturbing glucose homeostasis. The findings reinforce the rheostat model of intracellular O-GlcNAcylation where too much (OGA loss) or too little (OGT loss) O-GlcNAcylation are both detrimental to the β-cell.

Lactiplantibacillus plantarum 299v supplementation modulates β-cell ER stress and antioxidative defense pathways and prevents type 1 diabetes in gluten-free BioBreeding rats

The increasing incidence of Type 1 diabetes has coincided with the emergence of the low-fiber, high-gluten Western diet and other environmental factors linked to dysbiosis. Since Lactiplantibacillus plantarum 299 v (Lp299v) supplementation improves gut barrier function and reduces systemic inflammation, we studied its effects in spontaneously diabetic DRlyp/lyp rats provided a normal cereal diet (ND) or a gluten-free hydrolyzed casein diet (HCD). All rats provided ND developed diabetes (62.5±7.7 days); combining ND with Lp299v did not improve survival. Diabetes was delayed by HCD (72.2±9.4 days, p = .01) and further delayed by HCD+Lp299v (84.9±14.3 days, p < .001). HCD+Lp299v pups exhibited increased plasma propionate and butyrate levels, which correlated with enriched fecal Bifidobacteriaceae and Clostridiales taxa. Islet transcriptomic and histologic analyses at 40-days of age revealed that rats fed HCD expressed an autophagy profile, while those provided HCD+Lp299v expressed ER-associated protein degradation (ERAD) and antioxidative defense pathways, including Nrf2. Exposing insulinoma cells to propionate and butyrate promoted the antioxidative defense response but did not recapitulate the HCD+Lp299v islet ERAD transcriptomic profile. Here, both diet and microbiota influenced diabetes susceptibility. Moreover, Lp299v supplement modulated antioxidative defense and ER stress responses in β-cells, potentially offering a new therapeutic direction to thwart diabetes progression and preserve insulin secretion.

Different Protein Sources Enhance 18FDG-PET/MR Uptake of Brown Adipocytes in Male Subjects

Background: The unique ability of brown adipocytes to increase metabolic rate suggests that they could be targeted as an obesity treatment. Objective: The objective of the study was to search for new dietary factors that may enhance brown adipose tissue (BAT) activity. Methods: The study group comprised 28 healthy non-smoking males, aged 21–42 years old. All volunteers underwent a physical examination and a 75 g oral glucose tolerance test (75g-OGTT). Serum atrial and brain natriuretic peptide (ANP, BNP), PRD1-BF1-RIZ1 homologous domain containing 16 (PRDM16) and eukaryotic translation initiation factor 4E (eIF4E) measurements were taken, and 3-day food intake diaries were completed. Body composition measurements were assessed using dual-energy X-ray absorptiometry (DXA) scanning and bioimpedance methods. An fluorodeoxyglucose-18 (FDG-18) uptake in BAT was assessed by positron emission tomography/magnetic resonance (PET/MR) in all participants after 2 h cold exposure. The results were adjusted for age, daily energy intake, and DXA lean mass. Results: Subjects with detectable BAT (BAT⁽⁺⁾) were characterized by a higher percentage of energy obtained from dietary protein and fat and higher muscle mass (p = 0.01, p = 0.02 and p = 0.04, respectively). In the BAT⁽⁺⁾ group, animal protein intake was positively associated (p= 0.04), whereas the plant protein intake negatively correlated with BAT activity (p = 0.03). Additionally, the presence of BAT was inversely associated with BNP concentration in the 2 h of cold exposure (p = 0.002). Conclusion: The outcomes of our study suggest that different macronutrient consumption may be a new way to modulate BAT activity leading to weight reduction.

Advances in The Study of RNA-binding Proteins in Diabetic Complications

Background

It has been reported that diabetes mellitus affects 435 million people globally as a primary health care problem. Despite many therapies available, many diabetes remains uncontrolled, giving rise to irreversible diabetic complications that pose significant risks to patients’ wellbeing and survival.

Scope of Review

In recent years, as much effort is put into elucidating the posttranscriptional gene regulation network of diabetes and diabetic complications; RNA binding proteins (RBPs) are found to be vital. RBPs regulate gene expression through various post-transcriptional mechanisms, including alternative splicing, RNA export, messenger RNA translation, RNA degradation, and RNA stabilization.

Major Conclusions

Here, we summarized recent studies on the roles and mechanisms of RBPs in mediating abnormal gene expression in diabetes and its complications. Moreover, we discussed the potential and theoretical basis of RBPs to treat diabetes and its complications.

• Mechanisms of action of RBPs involved in diabetic complications are summarized and elucidated.

• We discuss the theoretical basis and potential of RBPs for the treatment of diabetes and its complications.

• We summarize the possible effective drugs for diabetes based on RBPs promoting the development of future therapeutic drugs.

OGT Regulates Mitochondrial Biogenesis and Function via Diabetes Susceptibility Gene Pdx1

O-GlcNAc transferase (OGT), a nutrient sensor sensitive to glucose flux, is highly expressed in the pancreas. However, the role of OGT in the mitochondria of β-cells is unexplored. In this study, we identified the role of OGT in mitochondrial function in β-cells. Constitutive deletion of OGT (βOGTKO) or inducible ablation in mature β-cells (iβOGTKO) causes distinct effects on mitochondrial morphology and function. Islets from βOGTKO, but not iβOGTKO, mice display swollen mitochondria, reduced glucose-stimulated oxygen consumption rate, ATP production, and glycolysis. Alleviating endoplasmic reticulum stress by genetic deletion of Chop did not rescue the mitochondrial dysfunction in βOGTKO mice. We identified altered islet proteome between βOGTKO and iβOGTKO mice. Pancreatic and duodenal homeobox 1 (Pdx1) was reduced in in βOGTKO islets. Pdx1 overexpression increased insulin content and improved mitochondrial morphology and function in βOGTKO islets. These data underscore the essential role of OGT in regulating β-cell mitochondrial morphology and bioenergetics. In conclusion, OGT couples nutrient signal and mitochondrial function to promote normal β-cell physiology.

eIF2A-knockout mice reveal decreased life span and metabolic syndrome

Eukaryotic initiation factor 2A (eIF2A) is a 65 kDa protein that functions in minor initiation pathways, which affect the translation of only a subset of messenger ribonucleic acid (mRNAs), such as internal ribosome entry site (IRES)-containing mRNAs and/or mRNAs harboring upstream near cognate/non-AUG start codons. These non-canonical initiation events are important for regulation of protein synthesis during cellular development and/or the integrated stress response. Selective eIF2A knockdown in cellular systems significantly inhibits translation of such mRNAs, which rely on alternative initiation mechanisms for their translation. However, there exists a gap in our understanding of how eIF2A functions in mammalian systems in vivo (on the organismal level) and ex vivo (in cells). Here, using an eIF2A-knockout (KO) mouse model, we present evidence implicating eIF2A in the biology of aging, metabolic syndrome and central tolerance. We discovered that eIF2A-KO mice have reduced life span and that eIF2A plays an important role in maintenance of lipid homeostasis, the control of glucose tolerance, insulin resistance and also reduces the abundance of B lymphocytes and dendritic cells in the thymic medulla of mice. We also show the eIF2A KO affects male and female mice differently, suggesting that eIF2A may affect sex-specific pathways. Interestingly, our experiments involving pharmacological induction of endoplasmic reticulum (ER) stress with tunicamycin did not reveal any substantial difference between the response to ER stress in eIF2A-KO and wild-type mice. The identification of eIF2A function in the development of metabolic syndrome bears promise for the further identification of specific eIF2A targets responsible for these changes.

Anti-cancer actions of carnosine and the restoration of normal cellular homeostasis

Carnosine is a naturally occurring dipeptide found in meat. Alternatively it can be formed through synthesis from the amino acids, β-alanine and L-histidine. Carnosine has long been advocated for use as an anti-oxidant and anti-glycating agent to facilitate healthy ageing, and there have also been reports of it having anti-proliferative effects that have beneficial actions against the development of a number of different cancers. Carnosine is able to undertake multiple molecular processes, and it's mechanism of action therefore remains controversial - both in healthy tissues and those associated with cancer or metabolic diseases. Here we review current understanding of its mechanistic role in different physiological contexts, and how this relates to cancer. Carnosine turns over rapidly in the body due to the presence of both serum and tissue carnosinase enzymes however, so its use as a dietary supplement would require ingestion of multiple daily doses. Strategies are therefore being developed that are based upon either resistance of carnosine analogs to enzymatic turnover, or else β-alanine supplementation, and the development of these potential therapeutic agents is discussed.

Placental mTOR complex 1 regulates fetal programming of obesity and insulin resistance in mice

Fetal growth restriction, or low birth weight, is a strong determinant for eventual obesity and type 2 diabetes. Clinical studies suggest placental mechanistic target of rapamycin (mTOR) signaling regulates fetal birth weight and the metabolic health trajectory of the offspring. In the current study, we used a genetic model with loss of placental mTOR function (mTOR-KO^Placenta) to test the direct role of mTOR signaling on birth weight and metabolic health in the adult offspring. mTOR-KO^Placenta animals displayed reduced placental area and total weight, as well as fetal body weight at embryonic day (E) 17.5. Birth weight and serum insulin levels were reduced; however, β cell mass was normal in mTOR-KO^Placenta newborns. Adult mTOR-KO^Placenta offspring, under a metabolic high-fat challenge, displayed exacerbated obesity and metabolic dysfunction compared with littermate controls. Subsequently, we tested whether enhancing placental mTOR complex 1 (mTORC1) signaling, via genetic ablation of TSC2, in utero would improve glucose homeostasis in the offspring. Indeed, increased placental mTORC1 conferred protection from diet-induced obesity in the offspring. In conclusion, placental mTORC1 serves as a mechanistic link between placental function and programming of obesity and insulin resistance in the adult offspring.

Disruption of O-Linked N-Acetylglucosamine Signaling in Placenta Induces Insulin Sensitivity in Female Offspring

Placental dysfunction can lead to fetal growth restriction which is associated with perinatal morbidity and mortality. Fetal growth restriction increases the risk of obesity and diabetes later in life. Placental O-GlcNAc transferase (OGT) has been identified as a marker and a mediator of placental insufficiency in the setting of prenatal stress, however, its role in the fetal programming of metabolism and glucose homeostasis remains unknown. We aim to determine the long-term metabolic outcomes of offspring with a reduction in placental OGT. Mice with a partial reduction and a full knockout of placenta-specific OGT were generated utilizing the Cre-Lox system. Glucose homeostasis and metabolic parameters were assessed on a normal chow and a high-fat diet in both male and female adult offspring. A reduction in placental OGT did not demonstrate differences in the metabolic parameters or glucose homeostasis compared to the controls on a standard chow. The high-fat diet provided a metabolic challenge that revealed a decrease in body weight gain (p = 0.02) and an improved insulin tolerance (p = 0.03) for offspring with a partially reduced placental OGT but not when OGT was fully knocked out. Changes in body weight were not associated with changes in energy homeostasis. Offspring with a partial reduction in placental OGT demonstrated increased hepatic Akt phosphorylation in response to insulin treatment (p = 0.02). A partial reduction in placental OGT was protective from weight gain and insulin intolerance when faced with the metabolic challenge of a high-fat diet. This appears to be, in part, due to increased hepatic insulin signaling. The findings of this study contribute to the greater understanding of fetal metabolic programming and the effect of placental OGT on peripheral insulin sensitivity and provides a target for future investigation and clinical applications.