Upregulation Of Renal GLUT2 And SGLT2 Is Involved In High-Fat Diet-Induced Gestational Diabetes In Mice

Fufang Zhenzhu Tiaozhi (FTZ) capsule ameliorates diabetic kidney disease in mice via inhibiting the SGLT2/glycolysis pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Fufang Zhenzhu Tiaozhi (FTZ) capsule is a hospital preparation of a patented traditional Chinese medicine compound. FTZ has been clinically used for nearly 13 years in the treatment of diabetes and glycolipid metabolic diseases. With the significant benefits of SGLT2 inhibitor in patients with diabetic kidney disease (DKD), it provides a research avenue to explore the mechanism of FTZ in treating this disease based on glycolysis pathway.

AIM OF THE STUDY

To explore the pharmacological characteristics of FTZ in DKD mice and its impact on the glycolysis pathway.

MATERIALS AND METHODS

We induced a DKD model in C57BL/6 mice by injection of streptozotocin (STZ) combined with long-term high-fat diet. We administered three doses of FTZ for 12 weeks of treatment. Kidney function, blood lipid levels, glucose tolerance, and key glycolytic enzymes were evaluated. Renal pathological changes were observed using HE, MASSON, and PAS staining. The potential targets of the active ingredients of FTZ in the glycolysis pathway were predicted using network pharmacology and molecular docking. Validation was performed using immunohistochemistry and Western blotting.

RESULTS

FTZ effectively reduces blood glucose, total cholesterol, triglyceride, low density lipoprotein cholesterol, 24 h proteinuria, serum creatinine, blood urea nitrogen, and increases urinary glucose levels. Glucose tolerance and renal pathological changes were significantly improved by FTZ treatment. Pinusolidic acid, a component of FTZ, shows good binding affinity with three active pockets of SGLT2. WB and immunohistochemistry revealed that FTZ significantly inhibits the expression of SGLT2 and its glycolytic related proteins (GLUT2/PKM2/HK2). Hexokinase, pyruvate kinase, and lactate dehydrogenase in the kidney were also significantly inhibited by FTZ in a dose-dependent manner.

CONCLUSION

FTZ may alleviate the progression of DKD by inhibiting the activation of the SGLT2/glycolytic pathway. Our study provides new insights into the clinical application of FTZ in DKD.

Suppression of certain intestinal microbiota metabolites may lead to gestational diabetes in mice fed a high-fat diet

Background

We aim to establish a gestational diabetes mellitus (GDM) mouse model with mice fed with a high-fat diet (HFD) in comparison with pregnant mice with normal blood glucose levels to investigate the role of intestinal microbiota in the development of HFD-induced GDM.

Methods

We divided healthy 6-week-old female C57BL mice into an HFD-induced GDM group and a normal diet group. Their bacterial flora and metabolites in intestinal fecal exosomes were co-analyzed using 16 s multi-region sequencing and compared.

Findings

Alpha (α) diversity was lower within the model group compared to the control group. Beta (β) diversity was significantly different between the two groups. The relative abundances of Lactobacillus, Actinomyces, Rothia, and Bacteroidetes were significantly different between the two groups. Fermentation and nitrate consumption were significantly higher in the GDM group. Multiple bacteria were associated with glycerophosphocholine, S-methyl-5'-thioadenosine, quinolinate, galactinol, deoxyadenosine, DL-arginine, and 2-oxoadenic acid.

Interpretation

Imbalances in the production of Lactobacillus, Bacteroidetes, Actinomyces, and Rothia and their related metabolites may lead to metabolic disturbances in GDM. These indicators may be used to assess changes affecting the intestinal microbiota during pregnancy and thus help modulate diet and alter blood glucose.

Phenotypes of streptozotocin-induced gestational diabetes mellitus in mice

Gestational diabetes mellitus (GDM) in human patients disrupts glucose metabolism post-pregnancy, affecting fetal development. Although obesity and genetic factors increase GDM risk, a lack of suitable models impedes a comprehensive understanding of its pathology. To address this, we administered streptozotocin (STZ, 75 mg/kg) to C57BL/6N mice for two days before pregnancy, establishing a convenient GDM model. Pregnant mice exposed to STZ (STZ-pregnant) were compared with STZ-injected virgin mice (STZ-virgin), citrate buffer-injected virgin mice (CB-virgin), and pregnant mice injected with citrate buffer (CB-pregnant). STZ-pregnant non-obese mice exhibited elevated blood glucose levels on gestational day 15.5 and impaired glucose tolerance. They also showed fewer normal fetuses compared to CB-pregnant mice. Additionally, STZ-pregnant mice had the highest plasma C-peptide levels, with decreased pancreatic islets or increased alpha cells compared to CB-pregnant mice. Kidneys isolated from STZ-pregnant mice did not display histological alterations or changes in gene expression for the principal glucose transporters (GLUT2 and SGLT2) and renal injury-associated markers. Notably, STZ-pregnant mice displayed decreased gene expression of insulin-receiving molecules (ISNR and IGFR1), indicating heightened insulin resistance. Liver histology in STZ-pregnant mice remained unchanged except for a pregnancy-related increase in lipid droplets within hepatocytes. Furthermore, the duodenum of STZ-pregnant mice exhibited increased gene expression of ligand-degradable IGFR2 and decreased expression of GLUT5 and GLUT12 (fructose and glucose transporters, respectively) compared to STZ-virgin mice. Thus, STZ-pregnant mice displayed GDM-like symptoms, including fetal abnormalities, while organs adapted to impaired glucose metabolism by altering glucose transport and insulin reception without histopathological changes. STZ-pregnant mice offer a novel model for studying mild onset non-obese GDM and species-specific differences in GDM features between humans and animals.

In situ microwave fixation provides an instantaneous snapshot of the brain metabolome

Brain glucose metabolism is highly heterogeneous among brain regions and continues postmortem. In particular, we demonstrate exhaustion of glycogen and glucose and an increase in lactate production during conventional rapid brain resection and preservation by liquid nitrogen. In contrast, we show that these postmortem changes are not observed with simultaneous animal sacrifice and in situ fixation with focused, high-power microwave. We further employ microwave fixation to define brain glucose metabolism in the mouse model of streptozotocin-induced type 1 diabetes. Using both total pool and isotope tracing analyses, we identified global glucose hypometabolism in multiple brain regions, evidenced by reduced 13C enrichment into glycogen, glycolysis, and the tricarboxylic acid (TCA) cycle. Reduced glucose metabolism correlated with a marked decrease in GLUT2 expression and several metabolic enzymes in unique brain regions. In conclusion, our study supports the incorporation of microwave fixation for more accurate studies of brain metabolism in rodent models.

Metabolic reprogramming: A novel therapeutic target in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most common microvascular complications of diabetes mellitus. However, the pathological mechanisms contributing to DKD are multifactorial and poorly understood. Diabetes is characterized by metabolic disorders that can bring about a series of changes in energy metabolism. As the most energy-consuming organs secondary only to the heart, the kidneys must maintain energy homeostasis. Aberrations in energy metabolism can lead to cellular dysfunction or even death. Metabolic reprogramming, a shift from mitochondrial oxidative phosphorylation to glycolysis and its side branches, is thought to play a critical role in the development and progression of DKD. This review focuses on the current knowledge about metabolic reprogramming and the role it plays in DKD development. The underlying etiologies, pathological damages in the involved cells, and potential molecular regulators of metabolic alterations are also discussed. Understanding the role of metabolic reprogramming in DKD may provide novel therapeutic approaches to delay its progression to end-stage renal disease.

Berberine Ameliorates Insulin Resistance by Inhibiting IKK/NF-κB, JNK, and IRS-1/AKT Signaling Pathway in Liver of Gestational Diabetes Mellitus Rats

Introduction: Berberine is derived from rhizoma coptidis, a well-known Traditional Chinese herbal Medicine that has been found to be effective in the treatment of type 2 diabetes mellitus in recent years. The aim of the present study was to investigate the effects of berberine on a gestational diabetes mellitus (GDM) rat model and the related mechanisms. Methods: GDM was induced in Sprague-Dawley rats using a high-fat diet before and during pregnancy. Berberine (100 mg/kg/day) was administered from the 7th to 20th day of pregnancy. Insulin resistance (IR), glucose tolerance, and maternal, fetal, and placental weight were determined. Liver histopathological analysis, as well as analysis of C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), inhibitor kappa B kinaseβ (IKKβ), nuclear factor kappa-B (NF-κB), c-Jun N-terminal kinase (JNK), insulin receptor substrate-1 (IRS-1), and protein kinase B (AKT), was performed at the end of pregnancy. Results: Treatment of GDM rats with berberine markedly decreased IR, the number of dead and absorptive fetuses, maternal body weight gain, and fetal and placental weight compared with GDM without berberine. Furthermore, berberine decreased CRP and TNF-α levels, IKKβ expression, NF-κB P65 nuclear translocation, and changed the phosphorylation of JNK, IRS-1, and AKT in the liver of GDM rats. Conclusions: Berberine improved IR and maternal-fetal outcomes of GDM rats, possibly through modulation of IKK/NF-κB, JNK, and IRS-1/AKT signaling pathways in the liver. Therefore, berberine may be a potential GDM treatment.

Loss of function of renal Glut2 reverses hyperglycaemia and normalises body weight in mouse models of diabetes and obesity

AIMS/HYPOTHESIS

Renal GLUT2 is increased in diabetes, thereby enhancing glucose reabsorption and worsening hyperglycaemia. Here, we determined whether loss of Glut2 (also known as Slc2a2) specifically in the kidneys would reverse hyperglycaemia and normalise body weight in mouse models of diabetes and obesity.

METHODS

We used the tamoxifen-inducible CreERT2-Lox system in mice to knockout Glut2 specifically in the kidneys (Ks-Glut2 KO) to establish the contribution of renal GLUT2 to systemic glucose homeostasis in health and in insulin-dependent as well as non-insulin-dependent diabetes. We measured circulating glucose and insulin levels in response to OGTT or IVGTT under different experimental conditions in the Ks-Glut2 KO and their control mice. Moreover, we quantified urine glucose levels to explain the phenotype of the mice independently of insulin actions. We also used a transcription factor array to identify mechanisms underlying the crosstalk between renal GLUT2 and sodium-glucose cotransporter 2 (SGLT2).

RESULTS

The Ks-Glut2 KO mice exhibited improved glucose tolerance and massive glucosuria. Interestingly, this improvement in blood glucose control was eliminated when we knocked out Glut2 in the liver in addition to the kidneys, suggesting that the improvement is attributable to the lack of renal GLUT2. Remarkably, induction of renal Glut2 deficiency reversed hyperglycaemia and normalised body weight in mouse models of diabetes and obesity. Longitudinal monitoring of renal glucose transporters revealed that Sglt2 (also known as Slc5a2) expression was almost abolished 3 weeks after inducing renal Glut2 deficiency. To identify a molecular basis for this crosstalk, we screened for renal transcription factors that were downregulated in the Ks-Glut2 KO mice. Hnf1α (also known as Hnf1a) was among the genes most downregulated and its recovery restored Sglt2 expression in primary renal proximal tubular cells isolated from the Ks-Glut2 KO mice.

CONCLUSIONS/INTERPRETATION

Altogether, these results demonstrate a novel crosstalk between renal GLUT2 and SGLT2 in regulating systemic glucose homeostasis via glucose reabsorption. Our findings also indicate that inhibiting renal GLUT2 is a potential therapy for diabetes and obesity.

Lower ATG7 Levels are Associated with a Higher Risk of Gestational Diabetes Mellitus: A Cross-Sectional Study

OBJECTIVE

This study aimed to investigate ATG7 levels in pregnant women with and without gestational diabetes mellitus (GDM) and explore the potential associations between ATG7 levels and GDM.

METHODS

This was a cross-sectional study conducted in a large tertiary hospital in Chengdu, China. The ATG7 levels in pregnant women at between 24 and 28 weeks of gestation with (n=84) and without GDM (n=649) were measured by using an ELISA kit. Glucose, HbA1c, total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) levels were measured by an automatic biochemistry analyser. The homeostasis model assessment of insulin resistance (HOMA-IR) and insulin secretion (HOMA-β) were calculated according to published formulas. The associations of ATG7 levels with laboratory parameters, GDM, and insulin resistance were evaluated using correlation analysis or a regression model.

RESULTS

The ATG7 levels were significantly lower in pregnant women with GDM than in those without GDM. The correlation analyses found that ATG7 levels correlated positively with HOMA-β but correlated negatively with HOMA-IR, oral glucose tolerance test (OGTT) glucose levels, TGs, and LDL-C. There were no significant correlations between ATG7 levels and HbA1c, HDL-C, or TC. After adjusting for potential confounders, lower ATG7 levels were shown to be associated with a higher risk of GDM. Furthermore, multiple linear regression analyses showed that ATG7 levels were negatively associated with insulin resistance.

CONCLUSION

ATG7 levels are significantly lower in pregnant women with GDM than in those without GDM, and lower ATG7 levels are associated with a higher risk of GDM. ATG7 levels were negatively associated with insulin resistance. Autophagy deficiency, which is caused by lower ATG7 levels, may be the underlying mechanism that mediates insulin resistance in the development of GDM.

Understanding the Mechanism of Dysglycemia in a Fanconi-Bickel Syndrome Patient

Fanconi-Bickel Syndrome (FBS) is a rare disorder of carbohydrate metabolism that is characterized mainly by the accumulation of glycogen in the liver and kidney. It is inherited as an autosomal recessive disorder caused by mutations in the SLC2A2 gene, which encodes for GLUT2. Patients with FBS have dysglycemia but the molecular mechanisms of dysglycemia are still not clearly understood. Therefore, we aimed to understand the underlying molecular mechanisms of dysglycemia in a patient with FBS. Genomic DNA was isolated from a peripheral blood sample and analyzed by whole genome and Sanger sequencing. CRISPR-Cas9 was used to introduce a mutation that mimics the patient's mutation in a human kidney cell line expressing GLUT2 (HEK293T). Mutant cells were used for molecular analysis to investigate the effects of the mutation on the expression and function of GLUT2, as well as the expression of other genes implicated in dysglycemia. The patient was found to have a homozygous nonsense mutation (c.901C>T, R301X) in the SLC2A2 gene. CRISPR-Cas9 successfully mimicked the patient's mutation in HEK293T cells. The mutant cells showed overexpression of a dysfunctional GLUT2 protein, resulting in reduced glucose release activity and enhanced intracellular glucose accumulation. In addition, other glucose transporters (SGLT1 and SGLT2 in the kidney) were found to be induced in the mutant cells. These findings suggest the last loops (loops 9-12) of GLUT2 are essential for glucose transport activity and indicate that GLUT2 dysfunction is associated with dysglycemia in FBS.

Adaptive Changes in single-nephron GFR, Tubular Morphology, and Transport in a Pregnant Rat Nephron: Modeling and Analysis

Normal pregnancy is characterized by massive increases in plasma volume and electrolyte retention. Given that the kidneys regulate homeostasis of electrolytes and volume, the organ undergoes major adaptations in morphology, hemodynamics, and transport to achieve the volume and electrolyte retention required in pregnancy. These adaptations are complex, sometimes counterintuitive, and not fully understood. In addition, the demands of the developing fetus and placenta change throughout the pregnancy. For example, during late pregnancy, K⁺ retention and thus enhanced renal K⁺ reabsorption is required despite many kaliuretic factors. The goal of this study is to unravel how known adaptive changes along the nephrons contribute to the ability of the kidney to meet volume and electrolyte requirements in mid- and late pregnancy. We developed computational models of solute and water transport in the superficial nephron of the kidney of a rat in mid- and late pregnancy. The mid-pregnant and late-pregnant rat superficial nephron models predict that morphological adaptations and increased activity of the sodium hydrogen exchanger 3 (NHE3) and epithelial sodium channel (ENaC) are essential for enhanced Na⁺ reabsorption observed during pregnancy. Model simulations showed that for sufficient K⁺ reabsorption, increased H ⁺-K ⁺-ATPase activity and decreased K⁺ secretion along the distal segments is required in both mid- and late-pregnancy. Furthermore, certain known sex differences in renal transporter pattern (e.g., the higher NHE3 protein abundance but lower activity in the proximal tubules of virgin female rats compared to male) may serve to better prepare the female for the increased transport demand in pregnancy.

Mitochondria in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end stage renal disease (ESRD) in the USA. The pathogenesis of DKD is multifactorial and involves activation of multiple signaling pathways with merging outcomes including thickening of the basement membrane, podocyte loss, mesangial expansion, tubular atrophy, and interstitial inflammation and fibrosis. The glomerulo-tubular balance and tubule-glomerular feedback support an increased glomerular filtration and tubular reabsorption, with the latter relying heavily on ATP and increasing the energy demand. There is evidence that alterations in mitochondrial bioenergetics in kidney cells lead to these pathologic changes and contribute to the progression of DKD towards ESRD. This review will focus on the dialogue between alterations in bioenergetics in glomerular and tubular cells and its role in the development of DKD. Alterations in energy substrate selection, electron transport chain, ATP generation, oxidative stress, redox status, protein posttranslational modifications, mitochondrial dynamics, and quality control will be discussed. Understanding the role of bioenergetics in the progression of diabetic DKD may provide novel therapeutic approaches to delay its progression to ESRD.

Renal lipid accumulation induced by high-fat diet regulates glucose homeostasis via sodium-glucose cotransporter 2

AIMS

Visceral lipid accumulation is involved in a variety of physiological aberrations. In the current study, we aimed to investigate whether lipid accumulation had an impact on glucose reabsorption in the kidney.

METHODS

We examined renal lipid content and renal threshold for glucose (RT_G) of each subject. We compared sodium-glucose cotransporter 2 (SGLT2) and sterol regulatory element-binding protein 1c (SREBP1c) levels in kidneys between rats fed with high fat diet (HFD) and normal chow diet. In vitro, HK2 cells were treated with palmitic acid (PA). Intracellular lipid droplet deposition, glucose uptake, SGLT2 and SREBP1c expression were examined.

RESULTS

Renal fat fraction was positively associated with RT_G among the recruited subjects. Moreover, renal lipid content was significantly increased in HFD rats, as well as SGLT2 expression. Accompanied with lipid droplet deposition in HK2 cells, PA stimulated SGLT2 expression and glucose uptake. In addition, after PA treatment, SREBP1c expression was significantly enhanced. However, transfection with siRNA-SREBP1c resulted in significant amelioration of lipid accumulation induced by PA in HK2 cells. Further examination indicated that accompanied with improvement of lipid deposition, SGLT2 expression and glucose uptake were attenuated.

CONCLUSIONS

The results of our study demonstrate the involvement of renal lipid accumulation in glucose homeostasis.

Resveratrol ameliorates the glucose uptake and lipid metabolism in gestational diabetes mellitus mice and insulin-resistant adipocytes via miR-23a-3p/NOV axis

BACKGROUND

Resveratrol improves insulin-resistance (IR) of gestational diabetes mellitus (GDM) mice. Low-expressed miR-23a-3p in diabetes patients regulates IR of adipocytes. Hence, we speculated the effect of Res on GDM mice was realized through regulating miR-23a-3p.

METHODS

The GDM model was established in mice by high-fat diet, treated with miR-23a-3p antagomiR, and further performed with glucose and insulin tolerance tests. The bodyweight, serum glucose and serum insulin, and the expressions of miR-23a-3p and nephroblastoma overexpressed (NOV) in mouse adipose tissues were detected. MiR-23a-3p target was identified by Starbase and dual-luciferase reporter. Then, an IR adipocyte model was established by dexamethasone-inducing and further treated with Resveratrol or transfected with miR-23a-3p inhibitor or siNOV. The cell glucose intake was detected by radioimmunoassay. The expressions of miR-23a-3p, NOV, Adiponectin, Leptin, p-PI3K, PI3K, p-Akt, and Akt in the adipocytes were determined by qPCR or Western blot.

RESULTS

Resveratrol decreased bodyweight, glucose level, insulin level, and the expressions of miR-23a-3p and NOV in the GDM mice, which was reversed by miR-23a-3p antagomiR. MiR-23a-3p targeted NOV. Resveratrol increased the glucose intake and the expressions of miR-23a-3p, Adiponectin, Leptin, p-PI3K, and p-Akt, decreased NOV expression in the IR adipocytes. The effect of the miR-23a-3p inhibitor on adipocytes with IR was opposite to Resveratrol, and the effects siNOV was the same as Resveratrol, except for its effect on miR-23a-3p expression. Effect of Res on the adipocytes with IR was counteracted by miR-23a-3p inhibitor whose effect was reversed by siNOV.

CONCLUSION

Resveratrol ameliorated glucose uptake and lipid metabolism of the GDM mice and adipocytes with IR by regulating miR-23a-3p/NOV axis.

Sodium-Glucose Co-Transporter 2 Inhibitors Correct Metabolic Maladaptation of Proximal Tubular Epithelial Cells in High-Glucose Conditions

Glucose filtered in the glomerulus is actively reabsorbed by sodium-glucose co-transporter 2 (SGLT2) in proximal tubular epithelial cells (PTEC) and passively returned to the blood via glucose transporter 2 (GLUT2). Healthy PTEC rely primarily on fatty acid beta-oxidation (FAO) for energy. In phase III trials, SGLT2 inhibitors improved outcomes in diabetic kidney disease (DKD). Tubulointerstitial renal fibrosis due to altered metabolic reprogramming of PTEC might be at the root of the pathogenesis of DKD. Here, we investigated the molecular mechanism of SGLT2 inhibitors’ renoprotective effect by examining transcriptional activity of Spp1, which encodes osteopontin, a key mediator of tubulointerstitial renal fibrosis. With primary cultured PTEC from Spp1-enhanced green fluorescent protein knock-in mice, we proved that in high-glucose conditions, increased SGLT2- and GLUT-mediated glucose uptake is causatively involved in aberrant activation of the glycolytic pathway in PTEC, thereby increasing mitochondrial reactive oxygen species (ROS) formation and transcriptional activation of Spp1. FAO activation did not play a direct role in these processes, but elevated expression of a tubular-specific enzyme, myo-inositol oxygenase, was at least partly involved. Notably, canagliflozin blocked overexpression of myo-inositol oxygenase. In conclusion, SGLT2 inhibitors exerted renoprotective effects by inhibiting aberrant glycolytic metabolism and mitochondrial ROS formation in PTEC in high-glucose conditions.