Evolution of glucose utilization: glucokinase and glucokinase regulator protein

Pigmented paravenous chorioretinal atrophy: Updated scenario

Pigmented paravenous chorioretinal atrophy (PPCRA) is an uncommon form of chorioretinal atrophy characterized by perivenous aggregations of pigment clumps associated with peripapillary and radial zones of retinal pigment epithelial atrophy that are distributed along the retinal veins. Most patients are asymptomatic, and evidence suggest that PPCRA is slowly progressing. Unless macular involvement is present, the majority of patients usually retain a normal visual function. Our ability to diagnose PPCRA has recently improved thanks to multimodal imaging, especially with the advent of ultra-widefield (UWF) imaging. Blood tests and functional and genetic testing can help with the correct differential diagnosis of pseudo-PPCRA or other disorders with similar characteristics. Although the cause of PPCRA is unknown, it is possible that it has a genetic basis. In this review we provide a summary of the multimodal imaging characteristics of PPCRA, and discuss its possible pathogenesis, based on the genes that have been associated with this disease.

Sex-Dimorphic Effects of Hypoglycemia on Metabolic Sensor mRNA Expression in Ventromedial Hypothalamic Nucleus-Dorsomedial Division (VMNdm) Growth Hormone-Releasing Hormone Neurons

Growth hormone-releasing hormone (Ghrh) neurons in the dorsomedial ventromedial hypothalamic nucleus (VMNdm) express the metabolic transcription factor steroidogenic factor-1 and hypoglycemia-sensitive neurochemicals of diverse chemical structures, transmission modes, and temporal signaling profiles. Ghrh imposes neuromodulatory control of coexpressed transmitters. Multiple metabolic sensory mechanisms are employed in the brain, including screening of the critical nutrient glucose or the energy currency ATP. Here, combinatory laser-catapult-microdissection/single-cell multiplex qPCR tools were used to investigate whether these neurons possess molecular machinery for monitoring cellular metabolic status and if these biomarkers exhibit sex-specific sensitivity to insulin-induced hypoglycemia. Data show that hypoglycemia up- (male) or downregulated (female) Ghrh neuron glucokinase (Gck) mRNA; Ghrh gene silencing decreased baseline and hypoglycemic patterns of Gck gene expression in each sex. Ghrh neuron glucokinase regulatory protein (Gckr) transcript levels were respectively diminished or augmented in hypoglycemic male vs female rats; this mRNA profile was decreased by Ghrh siRNA in both sexes. Gene transcripts encoding catalytic alpha subunits of the energy monitor 5-AMP-activated protein kinase (AMPK), i.e., Prkaa1 and 2, were increased by hypoglycemia in males, yet only the former mRNA was hypoglycemia-sensitive in females. Ghrh siRNA downregulated baseline and hypoglycemia-associated Prkaa subunit mRNAs in males but elicited divergent changes in Prkaa2 transcripts in eu- vs hypoglycemic females. Results provide unique evidence that VMNdm Ghrh neurons express the characterized metabolic sensor biomarkers glucokinase and AMPK and that the corresponding gene profiles exhibit distinctive sex-dimorphic transcriptional responses to hypoglycemia. Data further document Ghrh neuromodulation of baseline and hypoglycemic transcription patterns of these metabolic gene profiles.

DNA methylation reprogramming mediates transgenerational diabetogenic effect induced by early-life p,p'-DDE exposure

Increasing evidence shows that an adverse environment during the early fetal development can affect the epigenetic modifications on a wide range of diabetes-related genes, leading to an increased diabetic susceptibility in adulthood or even in subsequent generations. p,p'-Dichlorodiphenoxydichloroethylene (p,p'-DDE) is a break-down product of the pesticide dichlorodiphenyltrichloroethane (DDT). p,p'-DDE has been associated with various health concerns, such as diabetogenic effect. However, the precise molecular mechanism remains unclear. In this study, p,p'-DDE was given by gavage to pregnant rat dams from gestational day (GD) 8 to GD15 to generate male germline to investiagate the transgenerational effects. We found that early-life p,p'-DDE exposure increased the transgenerational diabetic susceptibility through male germline inheritance. In utero exposure to p,p'-DDE altered the sperm DNA methylome in F1 progeny, and a significant number of those differentially methylated genes could be inherited by F2 progeny. Furthermore, early-life p,p'-DDE exposure altered DNA methylation in glucose metabolic genes Gck and G6pc in sperm and the methylation modification were also found in liver of the next generation. Our study demonstrate that DNA methylation plays a critical role in mediating transgenerational diabetogenic effect induced by early-life p,p'-DDE exposure.

Combining Protein Conformational Diversity and Phylogenetic Information Using CoDNaS and CoDNaS-Q

CoDNaS (http://ufq.unq.edu.ar/codnas/) and CoDNaS-Q (http://ufq.unq.edu.ar/codnasq) are repositories of proteins with different degrees of conformational diversity. Following the ensemble nature of the native state, conformational diversity represents the structural differences between the conformers in the ensemble. Each entry in CoDNaS and CoDNaS-Q contains a redundant collection of experimentally determined conformers obtained under different conditions. These conformers represent snapshots of the protein dynamism. While CoDNaS contains examples of conformational diversity at the tertiary level, a recent development, CoDNaS-Q, contains examples at the quaternary level. In the emerging age of accurate protein structure prediction by machine learning approaches, many questions remain open regarding the characterization of protein dynamism. In this context, most bioinformatics resources take advantage of distinct features derived from protein alignments, however, the complexity and heterogeneity of information makes it difficult to recover reliable biological signatures. Here we present five protocols to explore tertiary and quaternary conformational diversity at the individual protein level as well as for the characterization of the distribution of conformational diversity at the protein family level in a phylogenetic context. These protocols can provide curated protein families with experimentally known conformational diversity, facilitating the exploration of sequence determinants of protein dynamism. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Assessing conformational diversity with CoDNaS Alternate Protocol 1: Assessing conformational diversity at the quaternary level with CoDNaS-Q Basic Protocol 2: Exploring conformational diversity in a protein family Alternate Protocol 2: Exploring quaternary conformational diversity in a protein family Basic Protocol 3: Representing conformational diversity in a phylogenetic context.

Glucokinase activity in diabetes: too much of a good thing?

Type 2 diabetes (T2D) is a global health problem characterised by chronic hyperglycaemia due to inadequate insulin secretion. Because glucose must be metabolised to stimulate insulin release it was initially argued that drugs that stimulate glucokinase (the first enzyme in glucose metabolism) would enhance insulin secretion in diabetes. However, in the long term, glucokinase activators have been largely disappointing. Recent studies show it is hyperactivation of glucose metabolism, not glucose itself, that underlies the progressive decline in beta-cell function in diabetes. This perspective discusses if glucokinase activators exacerbate this decline (by promoting glucose metabolism) and, counterintuitively, if glucokinase inhibitors might be a better therapeutic strategy for preserving beta-cell function in T2D.

Design, Synthesis, Molecular Docking and In vitro Biological Evaluation of Benzamide Derivatives as Novel Glucokinase Activators

Background:

Glucokinase (GK) is a cytoplasmic enzyme that metabolises glucose to glucose-6-phosphate and supports adjusting blood glucose levels within the normal range in humans. In pancreatic β-cells, it plays a leading role in governing the glucose-stimulated secretion of insulin, and in liver hepatocyte cells, it controls the metabolism of carbohydrates. GK acts as a promising drug target for treating patients with type 2 diabetes mellitus (T2DM).

Objectives:

The present work has been designed to discover some novel substituted benzamide derivatives

Method:

This work involved designing novel benzamide derivatives and their screening by docking studies to determine the binding interactions for the best-fit conformations in the binding site of the GK enzyme. Based on the results of docking studies, the selected molecules were synthesized and tested for in vitro GK enzyme assay. The structures of newly synthesized products were confirmed by IR, NMR, and mass spectroscopy.

Results:

Amongst the designed derivatives, compounds 4c, 4d, 4e, 5h, 5j, 5l, 5m, 5n, 5p, and 5r have shown better binding energy than the native ligand present in the enzyme structure. The synthesized compounds were subjected to in vitro GK enzyme assay. Out of all, compounds 4c, 4d, 5h, 5l, and 5n showed more GK activation than control.

Conclusion::

From the present results, we have concluded that the synthesized derivatives can activate the human GK enzyme effectively, which can be helpful in the treatment of T2DM.

Case Report: Hypoglycemia Due to a Novel Activating Glucokinase Variant in an Adult - a Molecular Approach

We present a case of an obese 22-year-old man with activating GCK variant who had neonatal hypoglycemia, re-emerging with hypoglycemia later in life. We investigated him for asymptomatic hypoglycemia with a family history of hypoglycemia. Genetic testing yielded a novel GCK missense class 3 variant that was subsequently found in his mother, sister and nephew and reclassified as a class 4 likely pathogenic variant. Glucokinase enables phosphorylation of glucose, the rate-limiting step of glycolysis in the liver and pancreatic β cells. It plays a crucial role in the regulation of insulin secretion. Inactivating variants in GCK cause hyperglycemia and activating variants cause hypoglycemia. Spleen-preserving distal pancreatectomy revealed diffuse hyperplastic islets, nuclear pleomorphism and periductular islets. Glucose stimulated insulin secretion revealed increased insulin secretion in response to glucose. Cytoplasmic calcium, which triggers exocytosis of insulin-containing granules, revealed normal basal but increased glucose-stimulated level. Unbiased gene expression analysis using 10X single cell sequencing revealed upregulated INS and CKB genes and downregulated DLK1 and NPY genes in β-cells. Further studies are required to see if alteration in expression of these genes plays a role in the metabolic and histological phenotype associated with glucokinase pathogenic variant. There were more large islets in the patient's pancreas than in control subjects but there was no difference in the proportion of β cells in the islets. His hypoglycemia was persistent after pancreatectomy, was refractory to diazoxide and improved with pasireotide. This case highlights the variable phenotype of GCK mutations. In-depth molecular analyses in the islets have revealed possible mechanisms for hyperplastic islets and insulin hypersecretion.

Variation in the Evolution and Sequences of Proglucagon and the Receptors for Proglucagon-Derived Peptides in Mammals

The mammalian proglucagon gene (Gcg) encodes three glucagon like sequences, glucagon, glucagon-like peptide-1 (GLP-1), and glucagon-like peptide-2 that are of similar length and share sequence similarity, with these hormones having cell surface receptors, glucagon receptor (Gcgr), GLP-1 receptor (Glp1r), and GLP-2 receptor (Glp2r), respectively. Gcgr, Glp1r, and Glp2r are all class B1 G protein-coupled receptors (GPCRs). Despite their sequence and structural similarity, analyses of sequences from rodents have found differences in patterns of sequence conservation and evolution. To determine whether these were rodent-specific traits or general features of these genes in mammals I analyzed coding and protein sequences for proglucagon and the receptors for proglucagon-derived peptides from the genomes of 168 mammalian species. Single copy genes for each gene were found in almost all genomes. In addition to glucagon sequences within Hystricognath rodents (e.g., guinea pig), glucagon sequences from a few other groups (e.g., pangolins and some bats) as well as changes in the proteolytic processing of GLP-1 in some bats are suggested to have functional effects. GLP-2 sequences display increased variability but accepted few substitutions that are predicted to have functional consequences. In parallel, Glp2r sequences display the most rapid protein sequence evolution, and show greater variability in amino acids at sites involved in ligand interaction, however most were not predicted to have a functional consequence. These observations suggest that a greater diversity in biological functions for proglucagon-derived peptides might exist in mammals.

Lycopene Modulates Placental Health and Fetal Development Under High-Fat Diet During Pregnancy of Rats

Lycopene plays an important role in improving immunity, promoting antioxidant capacity, and regulating fat metabolism. The placenta, an important organ for nutrients exchange between mother and child during pregnancy, directly affects fetal development. This study aims to characterize effects of lycopene on placental health and fetal development under a high-fat diet, and utilize RNA sequencing (RNA-seq) to investigate and integrate the differences of molecular pathways and biological processes in placenta. For placental health, high-fat diet during pregnancy increases placental oxidative stress, inflammation, and fat deposition. However, lycopene reduces the negative effects of high-fat diet on placenta to some extent, and further promotes fetal development. Under high-fat diet, lycopene reduces the levels of Interleukin 17 (IL-17), Interleukin 6 (IL-6), and tumor necrosis factor α (TNF-α) in placenta (p < 0.05) through the IL-17 pathway. Furthermore, lycopene supplementation in high-fat diet increases Glutaredoxin (Glrx) gene and protein expression in the placenta (p < 0.05), increases Glutathione peroxidase (GSH-Px) and Total antioxidant capacity (T-AOC) levels (p < 0.05), decreases reactive oxygen species (ROS) (p < 0.01) and Hydrogen peroxide (H₂ O₂ ) levels (p < 0.05) in placenta. In addition, lycopene supplementation in high fat diet increases the expression of Lep gene and protein in placenta and increases the level of leptin (p < 0.05). In terms of fetal development, the average fetal weight and fetal litter weight are increased by lycopene compared to high-diet treatment.

Moonlighting Proteins: The Case of the Hexokinases

Moonlighting proteins are defined as proteins with two or more functions that are unrelated and independent to each other, so that inactivation of one of them should not affect the second one and vice versa. Intriguingly, all the glycolytic enzymes are described as moonlighting proteins in some organisms. Hexokinase (HXK) is a critical enzyme in the glycolytic pathway and displays a wide range of functions in different organisms such as fungi, parasites, mammals, and plants. This review discusses HXKs moonlighting functions in depth since they have a profound impact on the responses to nutritional, environmental, and disease challenges. HXKs’ activities can be as diverse as performing metabolic activities, as a gene repressor complexing with other proteins, as protein kinase, as immune receptor and regulating processes like autophagy, programmed cell death or immune system responses. However, most of those functions are particular for some organisms while the most common moonlighting HXK function in several kingdoms is being a glucose sensor. In this review, we also analyze how different regulation mechanisms cause HXK to change its subcellular localization, oligomeric or conformational state, the response to substrate and product concentration, and its interactions with membrane, proteins, or RNA, all of which might impact the HXK moonlighting functions.

Characterization of gustatory receptor 7 in the brown planthopper reveals functional versatility

Insect pests consume tastants as their necessary energy and nutrient sources. Gustatory receptors play important roles in insect life and can form within an extremely complicated regulatory network. However, there are still many gustatory genes that have a significant impact on insect physiology, but their functional mechanism is still unknown. Here, we purified and characterized a gustatory receptor (protein) coding gene, NlGr7, from the brown planthopper (BPH) Nilaparvata lugens, which is an important insect pest of rice. Our results revealed that NlGr7 has an active association with various ligands, such as lectins, lipids (phospho- and sphingolipid) and copper. The mass-spectrometry result showed that NlGr7 is a sugar receptor, and NlGr7 is validated by different types of insoluble polysaccharides and a varied range of tastants. Further, we observed that NlGr7-bound ATP hydrolysed on the ATPase activity assay, which indicated that NlGr7 may be associated with important biological functions in the BPH. Furthermore, an injection of NlGr7 (protein), into newly emerged female adults of BPH, showed the reduced vitellogenin in ovary. The important NlGr7 for chemoreception has now been characterized in the BPH. We showed that NlGr7 in the BPH is required for various protein-ligands, as well as protein-sugars interactions, and for regulation of fecundity marker to play crucial roles in this pest. This study will provide valuable information for further functional studies of chemoreception mechanisms in this important agricultural pest.

Glucokinase activation as antidiabetic therapy: effect of nutraceuticals and phytochemicals on glucokinase gene expression and enzymatic activity

Diabetes represents an important public health problem. Recently, new molecular targets have been identified and exploited to treat this disease. Due to its pivotal role in glucose homeostasis, glucokinase (GCK) is a promising target for the development of novel antidiabetic drugs; however, pharmacological agents that modulate GCK activity have been linked to undesirable side-effects, limiting its use. Interestingly, plants might be a valuable source of new therapeutic compounds with GCK-activating properties and presumably no adverse effects. In this review, we describe biochemical characteristics related to the physiological and pathological importance of GCK, as well as the mechanisms involved in its regulation at different molecular levels. Posteriorly, we present a compendium of findings supporting the potential use of nutraceuticals and phytochemicals in the management of diabetes through modulation of GCK expression and activity. Finally, we propose critical aspects to keep in mind when designing experiments to evaluate GCK modulation properly.

Functional Inactivation of Drosophila GCK Orthologs Causes Genomic Instability and Oxidative Stress in a Fly Model of MODY-2

Maturity-onset diabetes of the young (MODY) type 2 is caused by heterozygous inactivating mutations in the gene encoding glucokinase (GCK), a pivotal enzyme for glucose homeostasis. In the pancreas GCK regulates insulin secretion, while in the liver it promotes glucose utilization and storage. We showed that silencing the DrosophilaGCK orthologs Hex-A and Hex-C results in a MODY-2-like hyperglycemia. Targeted knock-down revealed that Hex-A is expressed in insulin producing cells (IPCs) whereas Hex-C is specifically expressed in the fat body. We showed that Hex-A is essential for insulin secretion and it is required for Hex-C expression. Reduced levels of either Hex-A or Hex-C resulted in chromosome aberrations (CABs), together with an increased production of advanced glycation end-products (AGEs) and reactive oxygen species (ROS). This result suggests that CABs, in GCK depleted cells, are likely due to hyperglycemia, which produces oxidative stress through AGE metabolism. In agreement with this hypothesis, treating GCK-depleted larvae with the antioxidant vitamin B6 rescued CABs, whereas the treatment with a B6 inhibitor enhanced genomic instability. Although MODY-2 rarely produces complications, our data revealed the possibility that MODY-2 impacts genome integrity.

Evolution of the mammalian insulin (Ins) gene; Changes in proteolytic processing

Disruption of insulin signaling in humans leads to diabetes yet changes in insulin function is tolerated in some species. Taking advantage of the large number of publicly available mammalian genome sequences I identified insulin gene (Ins) in the genomes of 151 of 156 mammalian species with well-annotated genomes, of which 141 had complete Ins coding sequences. Complete Ins coding sequences were identified from 8 additional species that lack complete genomes. Duplicated Ins genes were found in 12 rodents (9 with complete genomes) resulting in the identification of a total of 161 complete mammalian Ins coding sequences. While all 161 proinsulin protein sequences were predicted to have functional signal peptides, which should allow secretion of the hormone, unexpectedly, substitutions were found at prohormone convertase processing sites in sequences from 6 species, 2 from Chiroptera (Myotis brandtii and M. lucifugus) and 4 from Afrotheria (Chrysochloris asiatica, Echinops telfairi, Elephantulus edwardii, and Orycteropus afer). Both basic residues at the C-peptide-A-chain junction in the bats M. brandtii and M. lucifugas are replaced, which should prevent processing. Replacements of a single basic residue are found at the B-chain-C-peptide junction, in the two bats, and at the C-peptide-A-chain junction, in 4 species of Afrotheria, processing sites that suggest impaired processing. In addition, a large number of substitutions at sites that interact with the insulin receptor were found in the insulin sequences from M. brandtii and M. lucifugas suggesting a change in biological function.

High-resolution photoreceptor imaging analysis of patients with autosomal dominant retinitis pigmentosa (adRP) caused by HK1 mutation

PURPOSE

The hexokinase 1 (HK1) gene encodes one of the four human hexokinases that play essential roles in glucose metabolism. Recently, several cases of E847K mutation in the HK1 gene were reported to cause inherited retinal dystrophy. The purpose of this study was to identify the phenotypical characteristics of patients with a recurrent E847K mutation in the HK1 gene.

METHODS

Three generations of one family with autosomal dominant retinitis pigmentosa were examined. Whole exome sequencing was performed on the DNA. Fundus imaging by an adaptive optics fundus camera was used to obtain high-resolution photoreceptor images.

RESULTS

Fundus examination of the proband showed degeneration of the mid-peripheral retina, and SD-OCT images showed an absence of the ellipsoid zone (EZ) and interdigitation zone (IZ) in the parafovea and more peripherally. SD-OCT images of the mother of the proband showed an absence of the EZ and IZ, and fundus autofluorescence images showed hypo-autofluorescence surrounding the macular region. One daughter of the proband had only mild night blindness, however, the density of the cone photoreceptors was reduced in the parafoveal region. Whole exome sequencing identified a heterozygous variant, E847K, in the HK1 gene. This variant was found to co-segregate with the disease in three family members.

CONCLUSIONS

Although the systemic phenotypes were found to be associated with the HK1 mutations, only the E847K mutation can cause a non-syndromic photoreceptor degeneration. Our study strengthened the hypothesis that the amino acid E847 might play a critical role in the maintenance of the morphology and function of the photoreceptors.

Molecular tools and applications of Euglena gracilis: From biorefineries to bioremediation

Euglena gracilis is a promising source of commercially important metabolites such as vitamins, wax esters, paramylon, and amino acids. However, the molecular tools available to create improved Euglena strains are limited compared to other microorganisms that are currently exploited in the biotechnology industry. The complex poly-endosymbiotic nature of the Euglena genome is a major bottleneck for obtaining a complete genome sequence and thus represents a notable shortcoming in gaining molecular information of this organism. Therefore, the studies and applications have been more focused on using the wild-type strain or its variants and optimizing the nutrient composition and cultivation conditions to enhance the production of biomass and valuable metabolites. In addition to producing metabolites, the E. gracilis biorefinery concept also provides means for the production of biofuels and biogas as well as residual biomass for the remediation of industrial and municipal wastewater. Using Euglena for bioremediation of environments contaminated with heavy metals is of special interest due to the strong ability of the organism to accumulate and sequester these compounds. The published draft genome and transcriptome will serve as a basis for further molecular studies of Euglena and provide a guide for the engineering of metabolic pathways of relevance for the already established as well as novel applications.

Review article: the emerging role of genetics in precision medicine for patients with non-alcoholic steatohepatitis

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is a severe form of non-alcoholic fatty liver disease (NAFLD) characterised by liver fat accumulation, inflammation and progressive fibrosis. Emerging data indicate that genetic susceptibility increases risks of NAFLD, NASH and NASH-related cirrhosis.

AIMS

To review NASH genetics and discuss the potential for precision medicine approaches to treatment.

METHOD

PubMed search and inclusion of relevant literature.

RESULTS

Single-nucleotide polymorphisms in PNPLA3, TM6SF2, GCKR, MBOAT7 and HSD17B13 are clearly associated with NASH development or progression. These genetic variants are common and have moderate-to-large effect sizes for development of NAFLD, NASH and hepatocellular carcinoma (HCC). The genes play roles in lipid remodelling in lipid droplets, hepatic very low-density lipoprotein (VLDL) secretion and de novo lipogenesis. The PNPLA3 I148M variant (rs738409) has large effects, with approximately twofold increased odds of NAFLD and threefold increased odds of NASH and HCC per allele. Obesity interacts with PNPLA3 I148M to elevate liver fat content and increase rates of NASH. Although the isoleucine-to-methionine substitution at amino acid position 148 of the PNPLA3 enzyme inactivates its lipid remodelling activity, the effect of PNPLA3 I148M results from trans-repression of another lipase (ATGL/PNPLA2) by sequestration of a shared cofactor (CGI-58/ABHD5), leading to decreased hepatic lipolysis and VLDL secretion. In homozygous Pnpla3 I148M knock-in rodent models of NAFLD, targeted PNPLA3 mRNA knockdown reduces hepatic steatosis, inflammation and fibrosis.

CONCLUSION

The emerging genetic and molecular understanding of NASH paves the way for novel interventions, including precision medicines that can modulate the activity of specific genes associated with NASH.

Selective Alanine Transporter Utilization Creates a Targetable Metabolic Niche in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) evolves a complex microenvironment comprised of multiple cell types, including pancreatic stellate cells (PSC). Previous studies have demonstrated that stromal supply of alanine, lipids, and nucleotides supports the metabolism, growth, and therapeutic resistance of PDAC. Here we demonstrate that alanine cross-talk between PSCs and PDAC is orchestrated by the utilization of specific transporters. PSCs utilize SLC1A4 and other transporters to rapidly exchange and maintain environmental alanine concentrations. Moreover, PDAC cells upregulate SLC38A2 to supply their increased alanine demand. Cells lacking SLC38A2 fail to concentrate intracellular alanine and undergo a profound metabolic crisis resulting in markedly impaired tumor growth. Our results demonstrate that stromal-cancer metabolic niches can form through differential transporter expression, creating unique therapeutic opportunities to target metabolic demands of cancer. SIGNIFICANCE: This work identifies critical neutral amino acid transporters involved in channeling alanine between pancreatic stellate and PDAC cells. Targeting PDAC-specific alanine uptake results in a metabolic crisis impairing metabolism, proliferation, and tumor growth. PDAC cells specifically activate and require SLC38A2 to fuel their alanine demands that may be exploited therapeutically.This article is highlighted in the In This Issue feature, p. 890.

GCKR rs780094 Polymorphism as A Genetic Variant Involved in Physical Exercise

Exercise performance is influenced by genetics. However, there is a lack of knowledge about the role played by genetic variability in the frequency of physical exercise practice. The objective was to identify genetic variants that modulate the commitment of people to perform physical exercise and to detect those subjects with a lower frequency practice. A total of 451 subjects were genotyped for 64 genetic variants related to inflammation, circadian rhythms, vascular function as well as energy, lipid and carbohydrate metabolism. Physical exercise frequency question and a Minnesota Leisure Time Physical Activity Questionnaire (MLTPAQ) were used to qualitatively and quantitatively measure the average amount of physical exercise. Dietary intake and energy expenditure due to physical activity were also studied. Differences between genotypes were analyzed using linear and logistic models adjusted for Bonferroni. A significant association between GCKR rs780094 and the times the individuals performed physical exercise was observed (p = 0.004). The carriers of the minor allele showed a greater frequency of physical exercise in comparison to the major homozygous genotype carriers (OR: 1.86, 95% CI: 1.36-2.56). The analysis of the GCKR rs780094 variant suggests a possible association with the subjects that present lower frequency of physical exercise. Nevertheless, future studies are needed to confirm these findings.

Hypoglycemic effects of esculeoside A are mediated via activation of AMPK and upregulation of IRS-1

Background

Tomato fruit (Lycopersicon esculentum Mill.) has been suggested to be useful for the prevention of diabetes. Esculeoside A is the main saponin compounds in tomatoes. This study investigated the hypoglycemic effects and the underlying mechanism of esculeoside A in C57BLKS/Leprdb (db/db) mice.

Methods

Wild-type C57BLKS (db/dm) mice were used in the db/dm mouse group and db/db mice were randomly divided into 2 groups: untreated and treated db/db mouse groups. Esculeoside A (100 mg/kg) was administered by gavage for 56 days to the treated db/db mouse group. Distilled water was administered to the db/dm mouse group and the untreated db/db mouse group. The blood and liver biochemical parameters and the expression of liver insulin signaling-related proteins were examined.

Results

The results showed that esculeoside A reduced the fasting blood glucose (FBG) levels and improved the glucose tolerance. Further investigation revealed that hepatic protein expressions of total AMP-activated protein kinase (T-AMPK), phosphorylated AMP-activated protein kinase (p-AMPK), insulin receptor substrate-1 (IRS-1), and glucokinase (GCK) were significantly upregulated after esculeoside A treatment. In contrast, the hepatic protein expression of phosphoenolpyruvate carboxykinase (PEPCK) was significantly downregulated by esculeoside A treatment.

Conclusion

These findings suggested that esculeoside A has a potential of alleviating the metabolic abnormalities in db/db mice via regulation of AMPK/IRS-1 pathway. Our findings supported a possible application of esculeoside A as a functional supplement for diabetes treatment.

Crystal structures of rice hexokinase 6 with a series of substrates shed light on its enzymatic mechanism

Hexokinases (HXKs) have determined to be multifaceted proteins, and they are the only ones able to phosphorylate glucose in plants. However, the binding mode for ATP to plant HXKs remains unclear. Here, we report the crystal structures of rice hexokinase 6 (OsHXK6) in four different forms: (i) apo-form, (ii) binary complex with D-Glc, (iii) quaternary complex with ADP, PO₄ and Mg²⁺, and (iv) pentanary complex with D-Glc, ADP, PO₄, and Mg²⁺. The apo form is in the open state conformation, and the three others are in the closed state, indicating that glucose and ADP-PO₄ binding induces a large conformational change by domain rearrangement. The quaternary complex is a novel intermediate during the catalytic reaction we trapped for the first time, which provides a new evidence for the enzymatic mechanism of HXKs. In addition, the latter two complexes reveal the binding mode for ADP-PO₄ to plant HXKs, which provide the structural explanation for the dual-function of OsHXK6. In addition, we identified that residues Gly112, Thr261, Gly262, and Gly450 are essential to the binding between ADP-PO₄ and OsHXK6 by a series of single mutations and enzymatic assays. Our study provide structural basis for the other functional studies of OsHXK6 in rice.

Targeting hepatic glucokinase to treat diabetes with TTP399, a hepatoselective glucokinase activator

The therapeutic success of interventions targeting glucokinase (GK) activation for the treatment of type 2 diabetes has been limited by hypoglycemia, steatohepatitis, and loss of efficacy over time. The clinical characteristics of patients with GK-activating mutations or GK regulatory protein (GKRP) loss-of-function mutations suggest that a hepatoselective GK activator (GKA) that does not activate GK in β cells or affect the GK-GKRP interaction may reduce hyperglycemia in patients with type 2 diabetes while limiting hypoglycemia and liver-associated adverse effects. Here, we review the rationale for TTP399, an oral hepatoselective GKA, and its progression from preclinical to clinical development, with an emphasis on the results of a randomized, double-blind, placebo- and active-controlled phase 2 study of TTP399 in patients with type 2 diabetes. In this 6-month study, TTP399 (800 mg/day) was associated with a clinically significant and sustained reduction in glycated hemoglobin, with a placebo-subtracted least squares mean HbA1c change from baseline of −0.9% (P < 0.01). Compared to placebo, TTP399 (800 mg/day) also increased high-density lipoprotein cholesterol (3.2 mg/dl; P < 0.05), decreased fasting plasma glucagon (−20 pg/ml; P < 0.05), and decreased weight in patients weighing ≥100 kg (−3.4 kg; P < 0.05). TTP399 did not cause hypoglycemia, had no detrimental effect on plasma lipids or liver enzymes, and did not increase blood pressure, highlighting the importance of tissue selectivity and preservation of physiological regulation when targeting key metabolic regulators such as GK.

Replication of previous genome-wide association studies of HKDC1, BACE2, SLC16A11 and TMEM163 SNPs in a gestational diabetes mellitus case-control sample from Han Chinese population

Background: Four novel glucose metabolism risk loci (HKDC1 rs4746822, BACE2 rs6517656, SLC16A11 rs13342232 and TMEM163 rs998451) were identified in recent genome-wide association studies (GWAS) of Afro-Caribbean, European, Hispanic, Thai, Mexican, Latin American and Indian populations. None of the abovementioned SNPs has been reported in a Han Chinese population. Aim: To replicate the relationships between HKDC1 rs4746822, BACE2 rs6517656, SLC16A11 rs13342232 and TMEM163 rs998451 with gestational diabetes mellitus (GDM) in a Han Chinese population. Methods: This was a case-control study which enrolled 334 pregnant women with GDM and 367 pregnant women with normal glucose tolerance. The linear regression and logistic regression were used to estimate the association between SNPs with the risk of GDM, HOMA-IR and fasting insulin levels. The fasting insulin concentration and HOMA-IR were log10 transformed before analysis. Results: No significant differences in the alleles and genotypes of SLC16A11 rs13342232, HKDC1 rs4746822 and BACE2 rs6517656 were observed between cases and controls. After adjusting the weekly BMI growth, pre-pregnancy BMI and maternal age, under the additive model, SLC16A11 rs13342232 was associated with log₁₀fasting serum insulin (Beta=0.046, p=0.016), log₁₀HOMA-IR level (Beta=0.061, p=0.003) and fasting plasma glucose level (Beta=0.164, p=0.011); HKDC1 rs4746822 was associated with OGTT 2-hr plasma glucose level (Beta=0.239, p=0.016); and BACE2 rs6517656 was associated with log₁₀fasting serum insulin (Beta=-0.053, p=0.044) and log₁₀HOMA-IR level (Beta=-0.060, p=0.048). After correction for multiple testing, the associations of SLC16A11 and HKDC1 with glucose metabolism remained statistically significant. The A allele of TMEM163 rs998451 was not detected in this population. Conclusion: HKDC1 rs4746822, BACE2 rs6517656 and SLC16A11 rs13342232 are associated with glucose metabolism in pregnant women of Han Chinese.

A reassessment of the carnivorous status of salmonids: Hepatic glucokinase is expressed in wild fish in Kerguelen Islands

Salmonids belong to a high trophic level and are thus considered as strictly carnivorous species, metabolically adapted for high catabolism of proteins and low utilisation of dietary carbohydrates. However they conserved a "mammalian-type" nutritional regulation of glucokinase encoding gene and its enzymatic activity by dietary carbohydrates which remains puzzling regarding their dietary regime. The present study investigates the hypothesis that this conservation could be linked to a real consumption by trout of this nutrient in their natural habitat. To do so, brown trout were sampled in the sub-Antarctic Kerguelen Islands, a site presenting oligotrophic hydrosystems and no local freshwater fish fauna prior the introduction of salmonids fifty years ago. Qualitative and quantitative analysis of carbohydrate content within Kerguelen trout stomachs demonstrate that these animals are fed on food resources containing digestible carbohydrates. Additionally, glycaemia and more particularly gck mRNA level and gck enzymatic activity prove that Kerguelen trout digest and metabolise dietary carbohydrates. Physiological and molecular analyses performed in the present study thus strongly evidence for consumption of dietary carbohydrates by wild trout in natural environments. Investigating differences between Kerguelen individuals, we found that smaller individuals presented higher glycaemia, as well as higher carbohydrates contents in stomach. However no relationship between scaled mass index and any physiological indicator was found. Thus it appears that Kerguelen trout do not turn to carbohydrate diet because of a different condition index, or that the consumption of carbohydrates does not lead to a generally degraded physiological status. As a conclusion, our findings may explain the evolutionary conservation of a "mammalian-type" nutritional regulation of gck by dietary carbohydrates in these carnivorous fish.

The Destiny of Glucose from a MicroRNA Perspective

Glucose serves as a primary, and for some tissues the unique, fuel source in order to generate and maintain the biological functions. Hyperglycemia is a hallmark of type 2 diabetes and is the direct consequence of perturbations in the glucose homeostasis. Insulin resistance, referred to as a reduced response of target tissues to the hormone, contributes to the development of hyperglycemia. The molecular mechanisms responsible for the altered glucose homeostasis are numerous and not completely understood. MicroRNAs (miRNAs) are now recognized as regulators of the lipid and glucose metabolism and are involved in the onset of metabolic diseases. Indeed, these small non-coding RNA molecules operate in the RNA silencing and posttranscriptional regulation of gene expression and may modulate the levels of kinases and enzymes in the glucose metabolism. Therefore, a better characterization of the function of miRNAs and a deeper understanding of their role in disease may represent a fundamental step toward innovative treatments addressing the causes, not only the symptoms, of hyperglycemia, using approaches aimed at restoring either miRNAs or their specific targets. In this review, we outline the current understanding regarding the impact of miRNAs in the glucose metabolism and highlight the need for further research focused on altered key kinases and enzymes in metabolic diseases.

Glucokinase mutation-a rare cause of recurrent hypoglycemia in adults: a case report and literature review

Background

Hypoglycemia occurs frequently in patients both in the inpatient and outpatient settings. While most hypoglycemia unrelated to diabetes treatment results from excessive endogenous insulin action, rare cases involve functional and congenital mutations in glycolytic enzymes of insulin regulation.

Case

A 21-year-old obese woman presented to the emergency department with complaints of repeated episodes of lethargy, syncope, dizziness, and sweating. She was referred from an outside facility on suspicion of insulinoma, with severe hypoglycemia unresponsive to repeated dextrose infusions. Her plasma glucose was 20 mg/dl at presentation, 44 mg/dl on arrival at our facility, and remained low in spite of multiple dextrose infusions. The patient had been treated for persistent hyperinsulinemic hypoglycemia of infancy at our neonatal facility and 4 years ago was diagnosed as having an activating glucokinase (GCK) mutation. She was then treated with octreotide and diazoxide with improvement in symptoms and blood glucose levels.

Conclusion

Improved diagnostication and management of uncommon genetic mutations as typified in this patient with an activating mutation of the GCK gene has expanded the spectrum of disease in adult medicine. This calls for improved patient information dissemination across different levels and aspects of the health care delivery system to ensure cost-effective and timely health care.

Multiple Comparisons of Glucokinase Activation Mechanisms of Five Mulberry Bioactive Ingredients in Hepatocyte

Glucokinase (GK) activity, which is rapidly regulated by glucokinase regulatory protein (GKRP) in the liver, is crucial for blood glucose homeostasis. In this paper, the GK activation mechanisms of 1-deoxynojrimycin (DNJ), resveratrol (RES), oxyresveratrol (OXY), cyanidin-3-glucoside (C3G), and cyanidin-3-rutinoside (C3R) were compared. The results revealed that DNJ, RES, C3G, and C3R could differently improve glucose consumption and enhance intracellular GK activities. DNJ and RES significantly promoted GK translocation at 12.5 μM, whereas other ingredients showed moderate effects. DNJ, C3G, and C3R could rupture intramolecular hydrogen bonds of GK to accelerate its allosteric activation at early stage. RES and OXY could bind to a "hydrophobic pocket" on GK to stabilize the active GK at the final stage. Otherwise, RES, OXY, C3G, and C3R could interact with GKRP at the F1P binding site to promote GK dissociation and translocation. Enzymatic assay showed that RES (15-50 μM) and OXY (25-50 μM) could significantly enhance GK activities, which was caused by their binding properties with GK. Moreover, the most dramatic up-regulation effects on GK expression were observed in C3G and C3R groups. This work expounded the differences between GK activation mechanisms, and the new findings would help to develop new GK activators.

Genetics of Gestational Diabetes Mellitus and Maternal Metabolism

Gestational diabetes mellitus (GDM) is defined as abnormal glucose tolerance with onset or first recognition during pregnancy. Women with a history of GDM are at long-term risk for developing type 2 diabetes (T2DM), raising the question to what extent GDM and T2DM share a common genetic architecture. Meta-analysis of candidate gene studies and genome-wide association analysis (GWAS) have identified a number of genes which are reproducibly associated with GDM, including TCF7L2, GCK, KCNJ11, KCNQ1, CDKAL1, IGF2BP2, MTNR1B, and IRS1. These genes are also associated with T2DM. Candidate gene and GWAS have also identified genes associated with maternal metabolic traits, most of which are also associated with metabolic traits in the general population. Two genes, BACE2 and HKDC1, are uniquely associated with maternal metabolic traits. These studies suggest that there are similarities and differences between the genetic architecture of GDM and T2DM and metabolic quantitative traits in pregnant and non-pregnant populations.

The Association of Type 2 Diabetes Loci Identified in Genome-Wide Association Studies with Metabolic Syndrome and Its Components in a Chinese Population with Type 2 Diabetes

Metabolic syndrome (MetS) is prevalent in type 2 diabetes (T2D) patients. The comorbidity of MetS and T2D increases the risk of cardiovascular complications. The aim of the present study was to determine the T2D-related genetic variants that contribute to MetS-related components in T2D patients of Chinese ancestry. We successfully genotyped 25 genome wide association study validated T2D-related single nucleotide polymorphisms (SNPs) among 5,169 T2D individuals and 4,560 normal glycemic controls recruited from the Chinese National Diabetes and Metabolic Disorders Study (DMS). We defined MetS in this population using the harmonized criteria (2009) combined with the Chinese criteria for abdominal obesity. The associations between SNPs and MetS-related components, as well as the associations between SNPs and risk for T2D with or without MetS, were subjected to logistic regression analysis adjusted for age and sex. Results showed that the T2D risk alleles of rs243021 located near BCL11A, rs10830963 in MTNR1B, and rs2237895 in KCNQ1 were related to a lower risk for abdominal obesity in T2D patients (rs243021: 0.92 (0.84, 1.00), P = 4.42 × 10⁻²; rs10830963: 0.92 (0.85, 1.00), P = 4.07 × 10⁻²; rs2237895: 0.89 (0.82, 0.98), P = 1.29 × 10⁻²). The T2D risk alleles of rs972283 near KLF14 contributed to a higher risk of elevated blood pressure (1.10 (1.00, 1.22), P = 4.48 × 10⁻²), while the T2D risk allele of rs7903146 in TCF7L2 was related to a lower risk for elevated blood pressure (0.74 (0.61, 0.90), P = 2.56 × 10⁻³). The T2D risk alleles of rs972283 near KLF14 and rs11634397 near ZFAND6 were associated with a higher risk for elevated triglycerides (rs972283: 1.11 (1.02, 1.24), P = 1.46 × 10⁻²; rs11634397: 1.14 (1.00, 1.29), P = 4.66 × 10⁻²), while the T2D risk alleles of rs780094 in GCKR and rs7903146 in TCF7L2 were related to a lower risk of elevated triglycerides (rs780094: 0.86 (0.80, 0.93), P = 1.35 × 10⁻⁴; rs7903146: 0.82 (0.69, 0.98), P = 3.18 × 10⁻²). The genotype risk score of the 25 T2D-related SNPs was related to a lower risk for abdominal obesity (P_trend = 1.29 × 10⁻²) and lower waist circumference (P = 2.20 × 10⁻³). Genetic variants of WFS1, CDKAL1, CDKN2BAS, TCF7L2, HHEX, KCNQ1, TSPAN8/LGR5, FTO, and TCF2 were associated with the risk for T2D with MetS, as well as the risk for development of T2D with at least one of the MetS components (P < 0.05). In addition, genetic variants of BCL11A, GCKR, ADAMTS9, CDKAL1, KLF14, CDKN2BAS, TCF7L2, CDC123/CAMK1D, HHEX, MTNR1B, and KCNQ1 contributed to the risk for T2D without MetS (P < 0.05). In conclusion, these findings highlight the contribution of T2D-related genetic loci to MetS in a Chinese Han population. The study also provides insight into the pleotropic effects of genome-wide association loci of diabetes on metabolic regulation.

Genetic Variants Associated with Lipid Profiles in Chinese Patients with Type 2 Diabetes

Dyslipidemia is a strong risk factor for cardiovascular disease among patients with type 2 diabetes (T2D). The aim of this study was to identify lipid-related genetic variants in T2D patients of Han Chinese ancestry. Among 4,908 Chinese T2D patients who were not taking lipid-lowering medications, single nucleotide polymorphisms (SNPs) in seven genes previously found to be associated with lipid traits in genome-wide association studies conducted in populations of European ancestry (ABCA1, GCKR, BAZ1B, TOMM40, DOCK7, HNF1A, and HNF4A) were genotyped. After adjusting for multiple covariates, SNPs in ABCA1, GCKR, BAZ1B, TOMM40, and HNF1A were identified as significantly associated with triglyceride levels in T2D patients (P < 0.05). The associations between the SNPs in ABCA1 (rs3890182), GCKR (rs780094), and BAZ1B (rs2240466) remained significant even after correction for multiple testing (P = 8.85×10⁻³, 7.88×10⁻⁷, and 2.03×10⁻⁶, respectively). BAZ1B (rs2240466) also was associated with the total cholesterol level (P = 4.75×10⁻²). In addition, SNP rs157580 in TOMM40 was associated with the low-density lipoprotein cholesterol level (P = 6.94×10⁻³). Our findings confirm that lipid-related genetic loci are associated with lipid profiles in Chinese patients with type 2 diabetes.

Functional diversification and specialization of cytosolic 70-kDa heat shock proteins

A fundamental question in molecular evolution is how protein functional differentiation alters the ability of cells and organisms to cope with stress and survive. To answer this question we used two paralogous Hsp70s from mouse and explored whether these highly similar cytosolic molecular chaperones, which apart their temporal expression have been considered functionally interchangeable, are differentiated with respect to their lipid-binding function. We demonstrate that the two proteins bind to diverse lipids with different affinities and therefore are functionally specialized. The observed lipid-binding patterns may be related with the ability of both Hsp70s to induce cell death by binding to a particular plasma-membrane lipid, and the potential of only one of them to promote cell survival by binding to a specific lysosomal-membrane lipid. These observations reveal that two seemingly identical proteins differentially modulate cellular adaptation and survival by having acquired specialized functions via sequence divergence. Therefore, this study provides an evolutionary paradigm, where promiscuity, specificity, sub- and neo-functionalization orchestrate one of the most conserved systems in nature, the cellular stress-response.

A dominant mutation in hexokinase 1 (HK1) causes retinitis pigmentosa

PURPOSE

To identify the cause of retinitis pigmentosa (RP) in UTAD003, a large, six-generation Louisiana family with autosomal dominant retinitis pigmentosa (adRP).

METHODS

A series of strategies, including candidate gene screening, linkage exclusion, genome-wide linkage mapping, and whole-exome next-generation sequencing, was used to identify a mutation in a novel disease gene on chromosome 10q22.1. Probands from an additional 404 retinal degeneration families were subsequently screened for mutations in this gene.

RESULTS

Exome sequencing in UTAD003 led to identification of a single, novel coding variant (c.2539G>A, p.Glu847Lys) in hexokinase 1 (HK1) present in all affected individuals and absent from normal controls. One affected family member carries two copies of the mutation and has an unusually severe form of disease, consistent with homozygosity for this mutation. Screening of additional adRP probands identified four other families (American, Canadian, and Sicilian) with the same mutation and a similar range of phenotypes. The families share a rare 450-kilobase haplotype containing the mutation, suggesting a founder mutation among otherwise unrelated families.

CONCLUSIONS

We identified an HK1 mutation in five adRP families. Hexokinase 1 catalyzes phosphorylation of glucose to glucose-6-phosphate. HK1 is expressed in retina, with two abundant isoforms expressed at similar levels. The Glu847Lys mutation is located at a highly conserved position in the protein, outside the catalytic domains. We hypothesize that the effect of this mutation is limited to the retina, as no systemic abnormalities in glycolysis were detected. Prevalence of the HK1 mutation in our cohort of RP families is 1%.

β-adrenergic receptor-dependent alterations in murine cardiac transcript expression are differentially regulated by gefitinib in vivo

β-adrenergic receptor (βAR)-mediated transactivation of epidermal growth factor receptor (EGFR) has been shown to promote cardioprotection in a mouse model of heart failure and we recently showed that this mechanism leads to enhanced cell survival in part via regulation of apoptotic transcript expression in isolated primary rat neonatal cardiomyocytes. Thus, we hypothesized that this process could regulate cardiac transcript expression in vivo. To comprehensively assess cardiac transcript alterations in response to acute βAR-dependent EGFR transactivation, we performed whole transcriptome analysis of hearts from C57BL/6 mice given i.p. injections of the βAR agonist isoproterenol in the presence or absence of the EGFR antagonist gefitinib for 1 hour. Total cardiac RNA from each treatment group underwent transcriptome analysis, revealing a substantial number of transcripts regulated by each treatment. Gefitinib alone significantly altered the expression of 405 transcripts, while isoproterenol either alone or in conjunction with gefitinib significantly altered 493 and 698 distinct transcripts, respectively. Further statistical analysis was performed, confirming 473 transcripts whose regulation by isoproterenol were significantly altered by gefitinib (isoproterenol-induced up/downregulation antagonized/promoted by gefinitib), including several known to be involved in the regulation of numerous processes including cell death and survival. Thus, βAR-dependent regulation of cardiac transcript expression in vivo can be modulated by the EGFR antagonist gefitinib.