Rho Family GTPases and Rho GEFs in Glucose Homeostasis

Molecular signatures of longissimus dorsi differ between dairy cattle based on prepartum muscle reserves and branched-chain volatile fatty acid supplementation

Dairy cattle with high (HM) versus low muscle (LM) reserves as determined by longissimus dorsi muscle depth (LDD) in late gestation exhibit differential muscle mobilization related to subsequent milk production. Moreover, branched-chain volatile fatty acid (BCVFA) supplementation increased blood glucose levels. We hypothesized that differences in HM and LM reflect distinct muscle metabolism and that BCVFA supplementation altered metabolic pathways. At 42 days before expected calving (BEC), Holstein dairy cows were enrolled in a 2 × 2 factorial study of diet and muscle reserves, by assignment to control (CON)- or BCVFA-supplemented diets and LDD of HM (>4.6 cm) or LM (≤4.6 cm) groups: HM-CON (n = 13), HM-BCVFA (n = 10), LM-CON (n = 9), and LM-BCVFA (n = 9). Longisumus dorsi muscle was biopsied at 21 days BEC, total RNA was isolated, and protein-coding gene expression was measured with RNA sequencing. Between HM and LM, 713 genes were differentially expressed and 481 between BCVFA and CON (P < 0.05). Transcriptional signatures indicated differential distribution of type II fibers between groups, with MYH1 greater in LM cattle and MYH2 greater in HM cattle (P < 0.05). Signatures of LM cattle relative to HM cattle indicated greater activation of autophagy, ubiquitin-proteasome, and Ca2+-calpain pathways. HM cattle displayed greater expression of genes that encode extracellular matrix proteins and factors that regulate their proteolysis and turnover. BCVFA modified transcriptomes by increasing expression of genes that regulate fatty acid degradation and flux of carbons into the tricarboxylic acid cycle as acetyl CoA. Molecular signatures support distinct metabolic strategies between LM and HM cattle and that BCVFA supplementation increased substrates for energy generation.NEW & NOTEWORTHY Muscle biopsies of the longissimus dorsi of prepartum dairy cattle indicate that molecular signatures support distinct metabolic strategies between low- and high-muscle cattle and that branched-chain volatile fatty acid supplementation increased substrates for energy generation.

Effects of Commonly used Surfactants, Poloxamer 188 and Tween 80, on the Drug Transport Capacity of Intestinal Glucose Transporters

Some glycoside drugs can be transported through intestinal glucose transporters (IGTs). The surfactants used in oral drug preparations can affect the function of transporter proteins. This study aimed to investigate the effect of commonly used surfactants, Poloxamer 188 and Tween 80, on the drug transport capacity of IGTs. Previous studies have shown that gastrodin is the optimal drug substrate for IGTs. Gastrodin was used as a probe drug to evaluate the effect of these two surfactants on intestinal absorption in SD rats through pharmacokinetic and in situ single-pass intestinal perfusion. Then, the effects of the two surfactants on the expression of glucose transporters and tight-junction proteins were examined using RT-PCR and western blotting. Additionally, the effect of surfactants on intestinal permeability was evaluated through hematoxylin-eosin staining. The results found that all experimental for Poloxamer 188 (0.5%, 2.0% and 8.0%) and Tween 80 (0.1% and 2.0%) were not significantly different from those of the blank group. However, the AUC(0-∞) of gastrodin increased by approximately 32% when 0.5% Tween 80 was used. The changes in IGT expression correlated with the intestinal absorption of gastrodin. A significant increase in the expression of IGTs was observed at 0.5% Tween 80. In conclusion, Poloxamer 188 had minimal effect on the drug transport capacity of IGTs within the recommended limits of use. However, the expression of IGTs increased in response to 0.5% Tween 80, which significantly enhanced the drug transport capacity of IGTs. However, 0.1% and 2.0% Tween 80 had no significant effect.

Genomic structure analysis and construction of DNA fingerprint for four sheep populations

The Yongdeng Qishan sheep (QS) is a sheep population found locally in China. To gain in-depth knowledge of its population characteristics, three control groups were chosen, comprising the Lanzhou fat-tailed sheep (LFT), TAN sheep (TAN), and Minxian black fur sheep (MBF), inhabiting the nearby environments. This study genotyped a total of 120 individuals from four sheep populations: QS, LFT, TAN, and MBF. Using Specific-Locus Amplified Fragment Sequencing, we conducted genetic diversity, population structure, and selective sweep analysis, and constructed the fingerprint of each population. In total, there were 782 535 single nucleotide polymorphism (SNP) variations identified, with most being situated within regions that are intergenic or intronic. The genetic diversity analysis revealed that the QS population exhibited lower genetic diversity compared to the other three populations. Consistent results were obtained from the principal component, phylogenetic tree, and population structure analysis, indicating significant genetic differences between QS and the other three populations. However, a certain degree of differentiation was observed within the QS population. The linkage disequilibrium (LD) patterns among the four populations showed clear distinctions, with the QS group demonstrating the most rapid LD decline. Kinship analysis supported the findings of population structure, dividing the 90 QS individuals into two subgroups consisting of 23 and 67 individuals. Selective sweep analysis identified a range of genes associated with reproduction, immunity, and adaptation to high-altitude hypoxia. These genes hold potential as candidate genes for marker-assisted selection breeding. Additionally, a total of 86 523 runs of homozygosity (ROHs) were detected, showing non-uniform distribution across chromosomes, with chromosome 1 having the highest coverage percentage and chromosome 26 the lowest. In the high-frequency ROH islands, 79 candidate genes were associated with biological processes such as reproduction and fat digestion and absorption. Furthermore, a DNA fingerprint was constructed for the four populations using 349 highly polymorphic SNPs. In summary, our research delves into the genetic diversity and population structure of QS population. The construction of DNA fingerprint profiles for each population can provide valuable references for the identification of sheep breeds both domestically and internationally.

AMPK and Beyond: The Signaling Network Controlling RabGAPs and Contraction-Mediated Glucose Uptake in Skeletal Muscle

Impaired skeletal muscle glucose uptake is a key feature in the development of insulin resistance and type 2 diabetes. Skeletal muscle glucose uptake can be enhanced by a variety of different stimuli, including insulin and contraction as the most prominent. In contrast to the clearance of glucose from the bloodstream in response to insulin stimulation, exercise-induced glucose uptake into skeletal muscle is unaffected during the progression of insulin resistance, placing physical activity at the center of prevention and treatment of metabolic diseases. The two Rab GTPase-activating proteins (RabGAPs), TBC1D1 and TBC1D4, represent critical nodes at the convergence of insulin- and exercise-stimulated signaling pathways, as phosphorylation of the two closely related signaling factors leads to enhanced translocation of glucose transporter 4 (GLUT4) to the plasma membrane, resulting in increased cellular glucose uptake. However, the full network of intracellular signaling pathways that control exercise-induced glucose uptake and that overlap with the insulin-stimulated pathway upstream of the RabGAPs is not fully understood. In this review, we discuss the current state of knowledge on exercise- and insulin-regulated kinases as well as hypoxia as stimulus that may be involved in the regulation of skeletal muscle glucose uptake.

Hyperglycemic Stress Induces Expression, Degradation, and Nuclear Association of Rho GDP Dissociation Inhibitor 2 (RhoGDIβ) in Pancreatic β-Cells

Small G proteins (e.g., Rac1) play critical regulatory roles in islet β-cell function in health (physiological insulin secretion) and in metabolic stress (cell dysfunction and demise). Multiple regulatory factors for these G proteins, such as GDP dissociation inhibitors (GDIs), have been implicated in the functional regulation of these G proteins. The current set of investigations is aimed at understanding impact of chronic hyperglycemic stress on the expression and subcellular distribution of three known isoforms of RhoGDIs (RhoGDIα, RhoGDIβ, and RhoGDIγ) in insulin-secreting β-cells. The data accrued in these studies revealed that the expression of RhoGDIβ, but not RhoGDIα or RhoGDIγ, is increased in INS-1 832/13 cells, rat islets, and human islets. Hyperglycemic stress also promoted the cleavage of RhoGDIβ, leading to its translocation to the nuclear compartment. We also report that RhoGDIα, but not RhoGDIγ, is associated with the nuclear compartment. However, unlike RhoGDIβ, hyperglycemic conditions exerted no effects on RhoGDIα's association with nuclear fraction. Based on these observations, and our earlier findings of the translocation of Rac1 to the nuclear compartment under the duress of metabolic stress, we conclude that the RhoGDIβ-Rac1 signaling module promotes signals from the cytosolic to the nucleus, culminating in accelerated β-cell dysfunction under metabolic stress.

Vav proteins do not influence dengue virus replication but are associated with induction of phospho-ERK, IL-6, and viperin mRNA following DENV infection in vitro

IMPORTANCE

Dengue disease is characterized by an inflammatory-mediated immunopathology, with elevated levels of circulating factors including TNF-α and IL-6. If the damaging inflammatory pathways could be blocked without loss of antiviral responses or exacerbating viral replication, then this would be of potential therapeutic benefit. The study here has investigated the Vav guanine exchange factors as a potential alternative signaling pathway that may drive dengue virus (DENV)-induced inflammatory responses, with a focus on Vav1 and 2. While Vav proteins were positively associated with mRNA for inflammatory cytokines, blocking Vav signaling didn't affect DENV replication but prevented DENV-induction of p-ERK and enhanced IL-6 (inflammatory) and viperin (antiviral) mRNA. These initial data suggest that Vav proteins could be a target that does not compromise control of viral replication and should be investigated further for broader impact on host inflammatory responses, in settings such as antibody-dependent enhancement of infection and in different cell types.

Pathological mechanisms of type 1 diabetes in children: investigation of the exosomal protein expression profile

Introduction

Type 1 diabetes (T1D) is a serious autoimmune disease with high morbidity and mortality. Early diagnosis and treatment remain unsatisfactory. While the potential for development of T1D biomarkers in circulating exosomes has attracted interest, progress has been limited. This study endeavors to explore the molecular dynamics of plasma exosome proteins in pediatric T1D patients and potential mechanisms correlated with T1D progression.

Methods

Liquid chromatography-tandem mass spectrometry with tandem mass tag (TMT)6 labeling was used to quantify exosomal protein expression profiles in 12 healthy controls and 24 T1D patients stratified by age (≤ 6 years old and > 6 years old) and glycated hemoglobin (HbA1c) levels (> 7% or > 7%). Integrated bioinformatics analysis was employed to decipher the functions of differentially expressed proteins, and Western blotting was used for validation of selected proteins' expression levels.

Results

We identified 1035 differentially expressed proteins (fold change > 1.3) between the T1D patients and healthy controls: 558 in those ≤ 6-year-old and 588 in those > 6-year-old. In those who reached an HbA1c level < 7% following 3 or more months of insulin therapy, the expression levels of most altered proteins in both T1D age groups returned to levels comparable to those in the healthy control group. Bioinformatics analysis revealed that differentially expressed exosome proteins are primarily related to immune function, hemostasis, cellular stress responses, and matrix organization. Western blotting confirmed the alterations in RAB40A, SEMA6D, COL6A5, and TTR proteins.

Discussion

This study delivers valuable insights into the fundamental molecular mechanisms contributing to T1D pathology. Moreover, it proposes potential therapeutic targets for improved T1D management.

Strain differences in the drug transport capacity of intestinal glucose transporters in Sprague-Dawley versus Wistar rats, C57BL/6J versus Kunming mice

Designing oral drug delivery systems using intestinal glucose transporters (IGTs) may be one of the strategies for improving oral bioavailability of drugs. However, little is known about the biological factors affecting the drug transport capacity of IGTs. Gastrodin is a sedative drug with a structure very similar to glucose. It is a highly water-soluble phenolic glucoside. It can hardly enter the intestine through simple diffusion but exhibits good oral bioavailability of over 80%. We confirmed that gastrodin is absorbed via the intestinal glucose transport pathway. It has the highest oral bioavailability among the reported glycosides' active ingredients through this pathway. Thus, gastrodin is the most selective drug substrate of IGTs and can be used to evaluate the drug transport capacity of IGTs. Obviously, strain is one of the main biological factors affecting drug absorption. This study firstly compared the drug transport capacity of IGTs between SD rats and Wistar rats and between C57 mice and KM mice by pharmacokinetic experiments and single-pass intestinal perfusion experiments of gastrodin. Then, the sodium-dependent glucose transporter type 1 (SGLT1) and sodium-independent glucose transporters type 2 (GLUT2) in the duodenum, jejunum, ileum and colon of these animals were quantified using RT-qPCR and Western blot. The results showed that the oral bioavailability of gastrodin in Wistar rats was significantly higher than in SD rats and significantly higher in KM mice than in C57 mice. Gastrodin absorption significantly differed among different intestinal segments in SD rats, C57 mice and KM mice, except Wistar rats. RT-qPCR and Western blot demonstrated that the intestinal expression distribution of SGLT1 and GLUT2 in SD rats and C57 mice was duodenum ≈ jejunum > ileum > colon. SGLT1 expression did not differ among different intestinal segments in KM mice, whereas the intestinal expression distribution of GLUT2 was duodenum ≈ jejunum ≈ ileum > colon. However, the expression of SGLT1 and GLUT2 did not differ among different intestinal segments in Wistar rats. It was reported that the intestinal expression distribution of SGLT1 and GLUT2 in humans is duodenum > jejunum > ileum > colon. Hence, the intestinal expression distribution of SGLT1 and GLUT2 of SD rats and C57 mice was more similar to that in humans. In conclusion, the drug transport capacity of IGTs differs in different strains of rats and mice. SD rats and C57 mice are more suitable for evaluating the pharmacokinetics of glycosides' active ingredients absorbed via the intestinal glucose transport pathway.

GEF-H1 Transduces FcεRI Signaling in Mast Cells to Activate RhoA and Focal Adhesion Formation during Exocytosis

When antigen-stimulated, mast cells release preformed inflammatory mediators stored in cytoplasmic granules. This occurs via a robust exocytosis mechanism termed degranulation. Our previous studies revealed that RhoA and Rac1 are activated during mast cell antigen stimulation and are required for mediator release. Here, we show that the RhoGEF, GEF-H1, acts as a signal transducer of antigen stimulation to activate RhoA and promote mast cell spreading via focal adhesion (FA) formation. Cell spreading, granule movement, and exocytosis were all reduced in antigen-stimulated mast cells when GEF-H1 was depleted by RNA interference. GEF-H1-depleted cells also showed a significant reduction in RhoA activation, resulting in reduced stress fiber formation without altering lamellipodia formation. Ectopic expression of a constitutively active RhoA mutant restored normal morphology in GEF-H1-depleted cells. FA formation during antigen stimulation required GEF-H1, suggesting it is a downstream target of the GEF-H1-RhoA signaling axis. GEF-H1 was activated by phosphorylation in conjunction with antigen stimulation. Syk kinase is linked to the FcεRI signaling pathway and the Syk inhibitor, GS-9973, blocked GEF-H1 activation and also suppressed cell spreading, granule movement, and exocytosis. We concluded that during FcεRI receptor stimulation, GEF-H1 transmits signals to RhoA activation and FA formation to facilitate the exocytosis mechanism.

P-Rex1 is a novel substrate of the E3 ubiquitin ligase Malin associated with Lafora disease

Laforin and Malin are two proteins that are encoded by the genes EPM2A and EPM2B, respectively. Laforin is a glucan phosphatase and Malin is an E3-ubiquitin ligase, and these two proteins function as a complex. Mutations occurring at the level of one of the two genes lead to the accumulation of an aberrant form of glycogen meant to cluster in polyglucosans that go under the name of Lafora bodies. Individuals affected by the appearance of these polyglucosans, especially at the cerebral level, experience progressive neurodegeneration and several episodes of epilepsy leading to the manifestation of a fatal form of a rare disease called Lafora disease (LD), for which, to date, no treatment is available. Despite the different dysfunctions described for this disease, many molecular aspects still demand elucidation. An effective way to unknot some of the nodes that prevent the achievement of better knowledge of LD is to focus on the substrates that are ubiquitinated by the E3-ubiquitin ligase Malin. Some substrates have already been provided by previous studies based on protein-protein interaction techniques and have been associated with some alterations that mark the disease. In this work, we have used an unbiased alternative approach based on the activity of Malin as an E3-ubiquitin ligase. We report the discovery of novel bonafide substrates of Malin and have characterized one of them more deeply, namely PIP3-dependent Rac exchanger 1 (P-Rex1). The analysis conducted upon this substrate sets the genesis of the delineation of a molecular pathway that leads to altered glucose uptake, which could be one of the origin of the accumulation of the polyglucosans present in the disease.

At the Research Frontiers of Small GTPases

Small GTPases act as molecular switches in regulating a myriad of cellular signaling, cytoskeletal dynamics, vesicular trafficking, and membrane/organelle transport processes. Here, I provide an editorial overview of papers collected in this Special Issue on the "Regulation and Function of Small GTPases 2.0".

Evaluation of autoantibody signatures in pituitary adenoma patients using human proteome arrays

PURPOSE

To identify the specific diagnostic biomarkers related to pituitary adenomas (PAs), we performed serological antibody profiles for three types of PAs, namely Acromegaly, Cushing's and Nonfunctional Pituitary Adenomas (NFPAs), using the human proteome (HuProt) microarray. This is the first study describing the serum autoantibody profile of PAs.

EXPERIMENTAL DESIGN

We performed serological autoantibody profiling of four healthy controls, four Acromegaly, three Cushing's and three NFPAs patient samples to obtain their autoantibody profiles, which were used for studying expression, interaction and altered biological pathways. Further, significant autoantibodies of PAs were compared with data available for glioma, meningioma and AAgAtlas for their specificity.

RESULTS

Autoantibody profile of PAs led to the identification of differentially expressed significant proteins such as AKNAD1 (AT-Hook Transcription Factor [AKNA] Domain Containing 1), NINJ1 (Nerve injury-induced protein 1), L3HYPDH (Trans-3-hydroxy-L-proline dehydratase), RHOG (Rho-related GTP-binding protein) and PTP4A1 (Protein Tyrosine Phosphatase Type IVA 1) in Acromegaly. Protein ABR (Active breakpoint cluster region-related protein), ST6GALNAC6 (ST6 N-acetylgalactosaminide alpha-2, 6-sialyltransferase 6), NOL3 (Nucleolar protein 3), ANXA8 (Annexin A8) and POLR2H (RNA polymerase II, I and III subunit H) showed an antigenic response in Cushing's patient's serum samples. Protein dipeptidyl peptidase 3 (DPP3) and reticulon-4 (RTN4) exhibited a very high antigenic response in NFPA patients. These proteins hold promise as potential autoantibody biomarkers in PAs.

Nonredundant Rac-GEF control of actin cytoskeleton reorganization

Rac-GEFs operate in a nonredundant manner as downstream effectors of receptor tyrosine kinases to promote ruffle formation, indicative of unique modes of regulation and targeting. Current research is shedding light on the intricate signaling paradigms shaping spatiotemporal activation of the small GTPase Rac during the generation of actin-rich membrane protrusions.

Caveolin-1 Regulates Cellular Metabolism: A Potential Therapeutic Target in Kidney Disease

The kidney is an energy-consuming organ, and cellular metabolism plays an indispensable role in kidney-related diseases. Caveolin-1 (Cav-1), a multifunctional membrane protein, is the main component of caveolae on the plasma membrane. Caveolae are represented by tiny invaginations that are abundant on the plasma membrane and that serve as a platform to regulate cellular endocytosis, stress responses, and signal transduction. However, caveolae have received increasing attention as a metabolic platform that mediates the endocytosis of albumin, cholesterol, and glucose, participates in cellular metabolic reprogramming and is involved in the progression of kidney disease. It is worth noting that caveolae mainly depend on Cav-1 to perform the abovementioned cellular functions. Furthermore, the mechanism by which Cav-1 regulates cellular metabolism and participates in the pathophysiology of kidney diseases has not been completely elucidated. In this review, we introduce the structure and function of Cav-1 and its functions in regulating cellular metabolism, autophagy, and oxidative stress, focusing on the relationship between Cav-1 in cellular metabolism and kidney disease; in addition, Cav-1 that serves as a potential therapeutic target for treatment of kidney disease is also described.

Rho GTPases in Skeletal Muscle Development and Homeostasis

Rho guanosine triphosphate hydrolases (GTPases) are molecular switches that cycle between an inactive guanosine diphosphate (GDP)-bound and an active guanosine triphosphate (GTP)-bound state during signal transduction. As such, they regulate a wide range of both cellular and physiological processes. In this review, we will summarize recent work on the role of Rho GTPase-regulated pathways in skeletal muscle development, regeneration, tissue mass homeostatic balance, and metabolism. In addition, we will present current evidence that links the dysregulation of these GTPases with diseases caused by skeletal muscle dysfunction. Overall, this information underscores the critical role of a number of members of the Rho GTPase subfamily in muscle development and the overall metabolic balance of mammalian species.

Dual High-Resolution α-Glucosidase and PTP1B Inhibition Profiling Combined with HPLC-PDA-HRMS-SPE-NMR Analysis for the Identification of Potentially Antidiabetic Chromene Meroterpenoids from Rhododendron capitatum

Thirteen previously undescribed chromene meroterpenoids, capitachromenic acids A-M (3-6, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, and 11b), were identified from an ethyl acetate extract of Rhododendron capitatum, using dual high-resolution α-glucosidase and PTP1B inhibition profiling in combination with HPLC-PDA-HRMS-SPE-NMR. In addition, one known chromene meroterpenoid, daurichromenic acid (15), and its biosynthetic precursor, grifolic acid (12), two C-methylated flavanones, (2S)-5,7,4'-trihydroxy-8-methylflavanone (1) and farrerol (2), and two triterpenoids, oleanolic acid (14a) and ursolic acid (14b), were identified. New structures were elucidated by extensive 1D and 2D NMR analysis, and absolute configurations of new chromene meroterpenoids were assigned by analysis of their ECD spectra on the basis of the empirical chromane helicity rule and from Rh₂(OCOCF₃)₄-induced ECD spectra by applying the bulkiness rule. Compounds 5, 9a, 9b, 12, and 15 showed α-glucosidase inhibitory activity with IC₅₀ values ranging from 8.0 to 93.5 μM, while compounds 3, 5, 8b, 9a, 9b, 10b, 11b, 12, and 15 showed PTP1B inhibitory activity with IC₅₀ values ranging from 2.5 to 68.1 μM.

Unraveling and targeting RAS-driven metabolic signaling for therapeutic gain

RAS mutations are among the most frequent oncogenic drivers observed in human cancers. With a lack of available treatment options, RAS-mutant cancers account for many of the deadliest cancers in the United States. Recent studies established that altered metabolic requirements are a hallmark of cancer, and many of these alterations are driven by aberrant RAS signaling. Specifically, RAS-driven cancers are characterized by upregulated glycolysis, the differential channeling of glycolytic intermediates, upregulated nutrient scavenging pathways such as autophagy and macropinocytosis, and altered glutamine utilization and mitochondrial function. This unique metabolic landscape promotes tumorigenesis, proliferation, survival in nutrient deficient environments and confers resistance to conventional cytotoxic and targeted therapies. Emerging work demonstrates how these dependencies can be therapeutically exploited in vitro and in vivo with many metabolic inhibitors currently in clinical trials. This review aims to outline the unique metabolic requirements induced by aberrant RAS signaling and how these altered dependencies present opportunities for therapeutic intervention.