Goto-Kakizaki Rats Research Articles

Increased COX6A2 promotes pancreatic β-cell apoptosis and is suppressed in diabetic GK rats after Roux-en-Y gastric bypass.

Roux-en-Y gastric bypass (RYGB) has been shown to inhibit β-cell apoptosis, but the underlying mechanisms are not yet fully understood. Cytochrome c oxidase subunit 6A2 (COX6A2) is expressed in β-cells. Here, we sought to investigate the role of COX6A2 in β-cell apoptosis, especially following RYGB. We found that RYGB significantly reduced β-cell apoptosis, accompanied by decreased COX6A2 expression in islets from diabetic Goto-Kakizaki (GK) rats. It is noteworthy that overexpression of COX6A2 promoted β-cell apoptosis, whereas COX6A2 deficiency suppressed it, suggesting the pro-apoptotic role of COX6A2 in β-cells. Mechanistically, increased COX6A2 interacted with and upregulated the expression of cyclophilin D (CypD), facilitating the release of cytochrome c from mitochondria to the cytoplasm, thereby promoting β-cell apoptosis. Furthermore, high-glucose-activated ChREBP epigenetically regulated COX6A2 expression by recruiting histone acetyltransferase p300 to augment histone H3 acetylation at the Cox6a2 promoter, a process inhibited by GLP-1 signaling. Given that RYGB enhances GLP-1 signaling, RYGB is likely to deactivate ChREBP by boosting GLP-1/PKA signaling, thereby reducing COX6A2 expression in islets from GK rats. These findings highlight the crucial role of the GLP-1/PKA/ChREBP axis-controlled COX6A2 in β-cell apoptosis, revealing a previously unrecognized mechanism underlying the reduction in β-cell apoptosis induced by RYGB.

Oxidative Stress and Histomorphometric Remodeling: Two Key Intestinal Features of Type 2 Diabetes in Goto–Kakizaki Rats

Gastrointestinal complications of diabetes are often overlooked, despite affecting up to 75% of patients. This study innovatively explores local glutathione levels and morphometric changes in the gut of Goto–Kakizaki (GK) rats, a type 2 diabetes animal model. Segments of the intestine, cecum, and colon were collected for histopathological analysis and glutathione quantification. A significant increase in the total thickness of the intestinal wall of GK rats was observed, particularly in the duodenum (1089.02 ± 39.19 vs. 864.19 ± 37.17 µm), ileum (726.29 ± 24.75 vs. 498.76 ± 16.86 µm), cecum (642.24 ± 34.15 vs. 500.97 ± 28.81 µm), and distal colon (1211.81 ± 51.32 vs. 831.71 ± 53.2 µm). Additionally, diabetic rats exhibited thickening of the muscular layers in all segments, except for the duodenum, which was also the only portion where the number of smooth muscle cells did not decrease. Moreover, myenteric neuronal density was lower in GK rats, suggesting neurological loss. Total glutathione levels were lower in all intestinal segments of diabetic rats (except duodenum), and the reduced/oxidized glutathione ratio (GSH/GSSG) was significantly decreased in GK rats, indicating increased oxidative stress. These findings strongly indicate that GK rats undergo significant intestinal remodeling, notable shifts in neuronal populations, and heightened oxidative stress—factors that likely contribute to the functional gastrointestinal alterations seen in diabetic patients.

Intestinal Motility Dysfunction in Goto-Kakizaki Rats: Role of the Myenteric Plexus.

The morpho-quantitative analysis of myenteric plexus neurons in the small and large intestines of 120-day-old male GK rats was investigated. The diabetes was confirmed by high fasting blood glucose levels. The myenteric plexus was evaluated through wholemount immunofluorescence. The morpho-quantitative analyses included evaluating neuronal density (neurons per ganglion) of the total neuronal population, the cholinergic and nitrergic subpopulations, and enteric glial cells per ganglion. The cell body area of 100 neurons per segment per animal was measured. The total neurons and nitrergic subpopulation were unaltered in the GK rats' small and large intestines. The cholinergic subpopulation exhibited decreased density in the three segments of the small intestine and an increased number in the proximal colon of the GK rats. The number of enteric glial cells increased in the ileum of the GK rats, which could indicate enteric gliosis caused by the intestinal inflammatory state. The area of the cell body was increased in the total neuronal population of the jejunum and ileum of the GK rats. Frequency histograms of the cell body area distribution revealed the contribution of cholinergic neurons to larger areas in the jejunum and nitrergic neurons in the ileum. The constipation previously reported in GK rats might be explained by the decrease in the density of cholinergic neurons in the small intestine of this animal model.

Evidence for a Pro-Inflammatory State of Macrophages from Non-Obese Type-2 Diabetic Goto-Kakizaki Rats

Obesity causes insulin resistance (IR) through systemic low-grade inflammation and can lead to type 2 diabetes mellitus (T2DM). However, the mechanisms that cause IR and T2DM in non-obese individuals are unclear. The Goto-Kakizaki (GK) rat develops IR spontaneously and is a model of non-obese T2DM. These rats exhibit hyperglycemia beginning at weaning and exhibit lower body mass than control Wistar rats. Herein, we tested the hypothesis that macrophages of GK rats are permanently in a pro-inflammatory state, which may be associated with a systemic inflammation condition that mimics the pathogenesis of obesity-induced T2DM. Using eighteen-week-old GK and control Wistar rats, we investigated the proportions of M1 (pro-inflammatory) and M2 (anti-inflammatory) macrophages isolated from the peritoneal cavity. Additionally, the production of inflammatory cytokines and reactive oxygen species (ROS) in cultured macrophages under basal and stimulated conditions was assessed. It was found that phorbol myristate acetate (PMA) stimulation increased GK rat macrophage ROS production 90-fold compared to basal levels. This response was also three times more pronounced than in control cells (36-fold). The production of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), tended to be upregulated in cultured macrophages from GK rats under basal conditions. Macrophages from GK rats produced 1.6 times more granulocyte-macrophage colony-stimulating factor (GM-CSF), 1.5 times more monocyte chemoattractant protein-1 (MCP-1) and 3.3 times more TNF-α than control cells when stimulated with lipopolysaccharide (LPS) (p = 0.0033; p = 0.049; p = 0.002, respectively). Moreover, compared to control cells, GK rats had 60% more M1 (p = 0.0008) and 23% less M2 (p = 0.038) macrophages. This study is the first to report macrophage inflammatory reprogramming towards a pro-inflammatory state in GK rats.

Carbohydrate response element-binding protein (ChREBP) mediates decreased SNAP25 expression in islets from diabetic Goto-Kakizaki (GK) rats.

SNAP25 plays an essential role in the glucose-stimulated insulin secretion (GSIS) of pancreatic β-cells. Carbohydrate response element-binding protein (ChREBP) is an important transcription factor in β-cells and, in this study, we aimed to explore whether ChREBP regulates SNAP25 expression in β-cells. We show that diabetic Goto-Kakizaki (GK) rats exhibited impaired insulin secretion and hyperglycemia, along with decreased SNAP25 expression and ChREBP phosphorylation in islets. SNAP25 knockdown decreased GSIS in β-cells, while SNAP25 overexpression increased GSIS in β-cells. Activation or overexpression of ChREBP led to reduced SNAP25 expression and subsequent suppression of GSIS. Conversely, ChREBP knockdown mitigated the reduction in SNAP25 expression caused by high glucose. Mechanistically, the activation of ChREBP by high glucose increased its occupancy and decreased the level of H3K4me3 at the Snap25 promoter. Our findings reveal the novel regulatory mechanisms of SNAP25 expression in β-cells and suggest that SNAP25 may be involved in the regulation of β-cell secretory function controlled by ChREBP.

KLF3 impacts insulin sensitivity and glucose uptake in skeletal muscle.

Skeletal muscle is one of the predominant sites involved in glucose disposal, accounting for approximately 80% of postprandial glucose uptake, and plays a critical role in maintaining glycemic homeostasis. Dysregulation of energy metabolism in skeletal muscle is involved in developing insulin resistance and type 2 diabetes (T2D). Transcriptomic responses of skeletal muscle to exercise found that the expression of Klf3 was increased in T2D Goto-Kakizaki (GK) rats and decreased after exercise with improved hyperglycemia and insulin resistance, implying that Klf3 might be associated with insulin sensitivity and glucose metabolism. We also found that knockdown of Klf3 promoted basal and insulin-stimulated glucose uptake in L6 myotubes, while overexpression of Klf3 resulted in the opposite. Through pairwise comparisons of L6 myotubes transcriptome, we identified 2256 and 1988 differentially expressed genes in Klf3 knockdown and overexpression groups, respectively. In insulin signaling, the expression of Slc2a4, Akt2, Insr and Sorbs1 was significantly increased by Klf3 knockdown and decreased with klf3 overexpression; Ptprf and Fasn were markedly downregulated in klf3 reduced group and upregulated in klf3 overexpressed group. Moreover, downregulation of Klf3 promoted the expression of GLUT4 and AKT proteins, as well as the translocation of GLUT4 to the cell membrane in the basal situation, and enhanced insulin sensitivity, characterized by increased insulin-stimulated GLUT4 translocation and AKT, TBC1D1 and TBC1D4 phosphorylation, while overexpression of Klf3 showed contrary results. These results suggest that Klf3 affects glucose uptake and insulin sensitivity via insulin signal transduction and intracellular metabolism, offering a novel potential treatment strategy for T2D.

Effect of exogenous free Nε-(carboxymethyl)lysine on diabetes-associated cognitive dysfunction: neuroinflammation, and metabolic disorders

Diabetes-associated cognitive dysfunction has already been attracted considerable attention. Advanced glycation end products (AGEs) from daily diets are thought to be a vital contributor to the development of this diseases. However, the effect of one of the best-characterized exogenous AGEs Nε-(carboxymethyl)lysine (CML) on cognitive function is not fully reported. In the present study, diabetical Goto-Kakizaki (GK) rats were treated with free CML for 8-weeks. It was found that oral consumption of exogenous CML significantly aggravated diabetes-associated cognitive dysfunction in behavioral test. In details, exogenous CML increased levels of oxidative stress, promoted the activation of glial cells in the brain, up-regulated the release of inflammatory cytokines interleukin-6, inhibited the protein expression of the brain-derived neurotrophic factor and thus led to neuroinflammation. Furthermore, exogenous CML promoted the amyloidogenesis in the brain of GK rats, and inhibited the expression of GLUT4. Additionally, several tricarboxylic acid cycle and glutamate-glutamine/γ-aminobutyric acid cycle intermediates including pyruvate, succinic acid, glutamine, glutamate were significantly changed in brain of GK rats treated with exogenous free CML. In conclusion, exogenous free CML is a potentially noxious compounds led to aggravated diabetes-associated cognitive dysfunction which could be possibly explained by its effects on neuroinflammation, energy and neurotransmitter amino acid homeostasis.

Targeting endothelial KCa channels in vivo restores arterial and endothelial function in type 2 diabetic rats

ObjectiveThis study tested the hypothesis that administration of the KCa channel activator SKA-31 restores endothelium-dependent vasodilation in vivo in Type 2 Diabetic (T2D) rats. BackgroundAcute treatment of isolated resistance arteries from T2D rats and humans with SKA-31 significantly improved endothelium-dependent vasodilation. However, it is unknown whether these in situ actions translate to intact vascular beds in vivo. MethodsMale Sprague Dawley (SD) and T2D Goto-Kakizaki (GK) rats (26–32 weeks of age) were injected intraperitoneally with either drug vehicle or 10 mg/kg SKA-31. Doppler ultrasound imaging was used to record reactive hyperemia/flow-mediated dilation (FMD) in the femoral artery following release of an occlusion cuff on the distal hind limb, along with diameter changes in the left main coronary artery in response to inhaled isoflurane (2 % → 5 %). ResultsVehicle treated SD rats exhibited a robust and reversible FMD response, the magnitude and time course of which did not differ in SD rats treated with SKA-31. In contrast, only a weak FMD response was observed in vehicle-treated T2D GK rats, whereas prior SKA-31 administration restored FMD to the level observed in control SD rats. Exposure of SD rats to 5 % isoflurane caused robust coronary artery dilation, which was not altered by prior treatment with SKA-31. In T2D GK rats, 5 % isoflurane inhalation alone did not increase coronary artery diameter, however, a strong vasodilatory response was observed following SKA-31 treatment. SKA-31 administration did not modify intrinsic heart rate responses in either protocol. ConclusionsEnhancement of KCa channel activity in vivo restores endothelium-dependent vasodilation in T2D rats that exhibit peripheral endothelial dysfunction.

Insulin resistance in nonobese type 2 diabetic Goto Kakizaki rats is associated with a proinflammatory Tlymphocyte profile.

Goto-Kakizaki (GK) rats develop a well-defined insulin resistance (IR) and type 2 diabetes mellitus (T2DM) without presenting obesity. The lymphocyte profile in nonobese diabetic conditions is not yet characterized. Therefore, GK rats were chosen to explore T lymphocyte (TL) dynamics at various stages (21, 60, and 120 days) compared to Wistar rats. GK rats exhibit progressive disruption of glucose regulation, with early glucose intolerance at 21 days and reduced insulin sensitivity at 60 days, confirming IR. Glucose transporter 1 (GLUT1) expression was consistently elevated in GK rats, suggesting heightened TL activation. T-regulatory lymphocyte markers diminished at 21 days. However, GK rats showed increased Th1 markers and reduced Gata-3 expression (crucial for Th2 cell differentiation) at 120 days. These findings underscore an early breakdown of anti-inflammatory mechanisms in GK rats, indicating a proinflammatory TL profile that may worsen chronic inflammation in T2DM.

Theaflavins mitigate diabetic symptoms in GK rats by modulating the INSR/PI3K-Akt/GSK-3 pathway and intestinal microbiota

Dietary management and interventions are crucial in the clinical management of diabetes. Numerous active dietary components in black tea have demonstrated positive effects on blood glucose levels and metabolic functions. However, limited research has explored the potential of theaflavins (TF), polyphenols in black tea, for diabetes management. In this study, high-purity TF was administered to Goto–Kakizaki (GK) diabetic model rats for four weeks to investigate its impact on diabetic pathology and analyze the underlying mechanisms through liver transcriptomics, hepatocyte metabolomics, and gut microbiome analysis. The findings indicated that continuous administration of TF (100 mg/kg) significantly suppressed blood glucose levels, reduced insulin resistance, and decreased the expression of oxidative stress indicators and inflammatory factors in GK rats. Further analysis revealed that TF might alleviate insulin resistance by improving hepatic glycogen conversion and reducing hepatic lipid deposition through modulation of key pathways, such as peroxisome proliferator-activated receptors and PI3K/AKT/GSK-3 pathways within the liver, thereby ameliorating diabetic symptoms. Additionally, TF intake facilitated the restoration of the intestinal microbial community structure by reducing the abundance of harmful bacteria and increasing the abundance of beneficial bacteria. It also reduced endotoxin lipopolysaccharide production, thereby lowering the chances of insulin resistance development and enhancing its efficacy in regulating blood glucose levels. These findings offer a novel perspective on the potential of black tea and its active constituents to prevent and treat diabetes and other metabolic disorders, providing valuable references for identifying and applying active dietary components from tea.

Propagermanium as a Novel Therapeutic Approach for the Treatment of Endothelial Dysfunction in Type 2 Diabetes.

Propagermanium (PG) has immune modulating activity and anti-inflammatory properties. This work aimed to study the therapeutic efficacy of PG on endothelial and perivascular dysfunction associated with type 2 diabetes. Non-obese type 2 diabetic Goto-Kakizaki (GK) rats were divided into four groups: (1) the control group; (2) the group treated with 50 mg/kg PG; (3) the group fed a high-fat diet (GKHFD); and (4) the group of GKHFD treated with 50 mg/kg PG. PG was given orally for 3 months. Several in vivo parameters and endothelial function were studied in aortas with perivascular adipose tissue PVAT (+) or without PVAT (-). We also determined the vascular inflammation and levels of CD36 in PVAT. In diabetic GK rats, PG did not affect the lipid profile or the results of the intraperitoneal glucose tolerance test. Instead, it improved the fasting glucose levels (18%, p < 0.01), insulin resistance (32%, p < 0.05), endothelial function (33 and 25% in aortas mounted with (+) or without PVAT (-), p < 0.05), and restored the anticontractile effect of the perivascular adipose tissue by reducing its inflammation (56%, p < 0.05) and oxidative stress profile (55%, p < 0.05). Due to its anti-inflammatory characteristics, PG likely improved endothelial dysfunction and restored the perivascular adipose tissue's anticontractile properties.

Are Hyperglycemia-Induced Changes in the Retina Associated with Diabetes-Correlated Changes in the Brain? A Review from Zebrafish and Rodent Type 2 Diabetes Models.

Diabetes is prevalent worldwide, with >90% of the cases identified as Type 2 diabetes. High blood sugar (hyperglycemia) is the hallmark symptom of diabetes, with prolonged and uncontrolled levels contributing to subsequent complications. Animal models have been used to study these complications, which include retinopathy, nephropathy, and peripheral neuropathy. More recent studies have focused on cognitive behaviors due to the increased risk of dementia/cognitive deficits that are reported to occur in older Type 2 diabetic patients. In this review, we collate the data reported from specific animal models (i.e., mouse, rat, zebrafish) that have been examined for changes in both retina/vision (retinopathy) and brain/cognition, including db/db mice, Goto-Kakizaki rats, Zucker Diabetic Fatty rats, high-fat diet-fed rodents and zebrafish, and hyperglycemic zebrafish induced by glucose immersion. These models were selected because rodents are widely recognized as established models for studying diabetic complications, while zebrafish represent a newer model in this field. Our goal is to (1) summarize the published findings relevant to these models, (2) identify similarities in cellular mechanisms underlying the disease progression that occur in both tissues, and (3) address the hypothesis that hyperglycemic-induced changes in retina precede or predict later complications in brain.

Pathological evaluation of the pathogenesis of diabetes mellitus and diabetic peripheral neuropathy.

Currently, there are more than 10 million patients with diabetes mellitus in Japan. Therefore, the need to explore the pathogenesis of diabetes and the complications leading to its cure is becoming increasingly urgent. Pathological examination of pancreatic tissues from patients with type 2 diabetes reveals a decrease in the volume of beta cells because of a combination of various stresses. In human type 2 diabetes, islet amyloid deposition is a unique pathological change characterized by proinflammatory macrophage (M1) infiltration into the islets. The pathological changes in the pancreas with islet amyloid were different according to clinical factors, which suggests that type 2 diabetes can be further subclassified based on islet pathology. On the other hand, diabetic peripheral neuropathy is the most frequent diabetic complication. In early diabetic peripheral neuropathy, M1 infiltration in the sciatic nerve evokes oxidative stress or attenuates retrograde axonal transport, as clearly demonstrated by in vitro live imaging. Furthermore, islet parasympathetic nerve density and beta cell volume were inversely correlated in type 2 diabetic Goto-Kakizaki rats, suggesting that diabetic peripheral neuropathy itself may contribute to the decrease in beta cell volume. These findings suggest that the pathogenesis of diabetes mellitus and diabetic peripheral neuropathy may be interrelated.

MicroRNA 29 modulates β-cell mitochondrial metabolism and insulin secretion via underlying miR-29-OXPHOS complex pathways.

MicroRNAs (miRNAs) regulate β-cell function, and β-cell mitochondria and insulin secretion are perturbed in diabetes. We aimed to identify key miRNAs regulating β-cell mitochondrial metabolism and novel β-cell miRNA-mitochondrial pathways. TargetScan (http://www.targetscan.org/) was used to predict if 16 miRNAs implicated in β-cell function target 27 cis-eGenes implicated in mitochondrial activity. The expression of candidate miRNAs and insulin secretion after 24 and 1 h pre-incubation in 2.8, 11.1- and 16.7-mM glucose was measured in clonal INS-1 832/13 β-cells. MiR-29 silenced INS-1 832/13 cells were assessed for insulin secretion (glucose, pyruvate, and K+), target cis-eGene expression (Ndufv3 and Ndufa10 components of mitochondrial complex I (CI)), OXPHOS (CI-V) protein expression, and mitochondrial OXPHOS respiration/activity. The expression of differentially expressed miR-29 miRNAs was evaluated in Goto-Kakizaki (GK) rat, db/db mouse and type 2 diabetic (T2D) human islets, as well as NMRI mouse islets cultured under glucolipotoxic conditions. MiR-29, miR-15 and miR-124 were predicted to regulate ~20 cis-eGenes, while miR-29 alone was predicted to regulate ≥12 of these in rat and human species. MiR-29 expression and insulin secretion were reduced in INS-1 832/13 cells after 24 h in elevated glucose. MiR-29 knockdown increased all tested insulin secretory responses, Nudfv3, Ndufa10, complex I and II expression, and cellular mitochondrial OXPHOS. MiR-29 expression was reduced in db/db islets but increased in GK rat and T2D human islets. We conclude miR-29 is a key miRNA in regulating β-cell mitochondrial metabolism and insulin secretion via underlying miR-29-OXPHOS complex pathways. Furthermore, we infer reduced miR-29 expression compensatorily enhances insulin secretion under glucotoxicity.

Pharmacological Targeting of Endothelial KCa Channels In Vivo Augments Vasodilatory Responses in Rat Femoral and Coronary Arteries in Health and Disease

As the primary interface between the blood and organs, the vascular endothelium functions as a key regulator of tissue blood flow by sensing chemical and mechanical stimuli and producing vasoactive signals to dynamically control intraluminal diameter in local arterioles and upstream arteries. Flow-mediated dilation (FMD) is an important physiological mechanism to modify local tissue perfusion in response to dynamic metabolic conditions, and reduced FMD responses are indicative of endothelial dysfunction, the latter being a major risk factor for cardiovascular disease. We have previously reported that pharmacological enhancement of endothelial KCa2.3 and KCa3.1 channel activity by SKA-31 augmented vasodilatory responses in small resistance arteries and intact hearts isolated from healthy and Type 2 Diabetic (T2D) rats (RC Mishra et al, 2014, 2021). In the present study, we have investigated the ability of SKA-31 to enhance endothelium-dependent vasodilation in vivo in femoral and coronary arteries of healthy and T2D male rats. Methods: FMD responses associated with reactive hyperemia were measured in a side branch of the femoral artery by high sensitivity Doppler ultrasound following release of an inflated pressure cuff placed on the distal hind limb of male Sprague Dawley (SD) and T2D Goto-Kakizaki (GK) rats (26-32 weeks of age). Rats were injected i.p. with either 10 mg/kg SKA-31 or drug vehicle ~ 3 hours prior to cuff inflation. M-mode echocardiographic imaging was used to visualize intraluminal diameter changes in the left main coronary artery in the same four treatment groups in response to an increase in inhalational isoflurane from 2% to 5%. Results: Femoral artery blood flow increased ~2-fold during reactive hyperemia in vehicle treated SD rats, as quantified by velocity-time integral, and did not increase further with SKA-31 treatment. In contrast, the FMD response in vehicle treated T2D GK rats was substantially blunted vs. SD rats, and SKA-31 administration restored this response to the level observed in healthy controls, which was still observable 15-24 hours later. In vehicle treated SD rats, exposure to 5% isoflurane increased left main coronary arterial diameter by 50-60%, which reversed to baseline following return to the original 2% isoflurane condition. SKA-31 treatment of SD rats increased basal arterial diameter by ~30%, but did not significantly modify the observed increase in arterial diameter evoked by 5% isoflurane inhalation, compared with vehicle treatment. In vehicle treated T2D GK rats, exposure to 5% isoflurane did not increase coronary artery diameter over a 10 min period, which is suggestive of endothelial dysfunction. However, SKA-31 treatment significantly increased basal coronary arterial diameter by 40-50%, and promoted a rapid and robust increase in diameter following exposure to 5% isoflurane (80-90% increase above that observed in vehicle treated T2D rats), which reversed to baseline upon return to 2% isoflurane inhalation. No enhancement of isoflurane evoked coronary vasodilation was observable in T2D GK rats 15-24 hrs post-SKA-31 treatment. In summary, these data provide the first direct demonstration that low dose administration of a KCa channel activator can enhance vasodilatory responses in vivo. This study was supported by research funding to APB from the Canadian Institutes of Health Research (MOP-142467) and NSERC (RGPIN 2017-04116). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Aberrant splicing of CaV1.2 calcium channel induced by decreased Rbfox1 enhances arterial constriction during diabetic hyperglycemia

Diabetic hyperglycemia induces dysfunctions of arterial smooth muscle, leading to diabetic vascular complications. The CaV1.2 calcium channel is one primary pathway for Ca2+ influx, which initiates vasoconstriction. However, the long-term regulation mechanism(s) for vascular CaV1.2 functions under hyperglycemic condition remains unknown. Here, Sprague–Dawley rats fed with high-fat diet in combination with low dose streptozotocin and Goto-Kakizaki (GK) rats were used as diabetic models. Isolated mesenteric arteries (MAs) and vascular smooth muscle cells (VSMCs) from rat models were used to assess K+-induced arterial constriction and CaV1.2 channel functions using vascular myograph and whole-cell patch clamp, respectively. K+-induced vasoconstriction is persistently enhanced in the MAs from diabetic rats, and CaV1.2 alternative spliced exon 9* is increased, while exon 33 is decreased in rat diabetic arteries. Furthermore, CaV1.2 channels exhibit hyperpolarized current–voltage and activation curve in VSMCs from diabetic rats, which facilitates the channel function. Unexpectedly, the application of glycated serum (GS), mimicking advanced glycation end-products (AGEs), but not glucose, downregulates the expression of the splicing factor Rbfox1 in VSMCs. Moreover, GS application or Rbfox1 knockdown dynamically regulates alternative exons 9* and 33, leading to facilitated functions of CaV1.2 channels in VSMCs and MAs. Notably, GS increases K+-induced intracellular calcium concentration of VSMCs and the vasoconstriction of MAs. These results reveal that AGEs, not glucose, long-termly regulates CaV1.2 alternative splicing events by decreasing Rbfox1 expression, thereby enhancing channel functions and increasing vasoconstriction under diabetic hyperglycemia. This study identifies the specific molecular mechanism for enhanced vasoconstriction under hyperglycemia, providing a potential target for managing diabetic vascular complications.

(−)-Epicatechin ameliorates type 2 diabetes mellitus by reshaping the gut microbiota and Gut–Liver axis in GK rats

As one of the most abundant plant polyphenols in the human diet, (−)-epicatechin (EC) can improve insulin sensitivity and regulate glucose homeostasis. However, the primary mechanisms involved in EC anti-T2DM benefits remain unclear. The present study explored the effects of EC on the gut microbiota and liver transcriptome in type 2 diabetes mellitus (T2DM) Goto–Kakizaki rats for the first time. The findings showed that EC protected glucose homeostasis, alleviated systemic oxidative stress, relieved liver damage, and increased serum insulin. Further investigation showed that EC reshaped gut microbiota structure, including inhibiting the proliferation of lipopolysaccharide (LPS)-producing bacteria and reducing serum LPS. In addition, transcriptome analysis revealed that the insulin signaling pathway may be the core pathway of the EC anti-T2DM effect. Therefore, EC may modulate the gut microbiota and liver insulin signaling pathways by the gut–liver axis to alleviate T2DM. As a diet supplement, EC has promising potential in T2DM prevention and treatment.

Melanoxetin: A Hydroxylated Flavonoid Attenuates Oxidative Stress and Modulates Insulin Resistance and Glycation Pathways in an Animal Model of Type 2 Diabetes Mellitus.

Type 2 diabetes mellitus (DM) continues to escalate, necessitating innovative therapeutic approaches that target distinct pathways and address DM complications. Flavonoids have been shown to possess several pharmacological activities that are important for DM. This study aimed to evaluate the in vivo effects of the flavonoid melanoxetin using Goto-Kakizaki rats. Over a period of 14 days, melanoxetin was administered subcutaneously to investigate its antioxidant, anti-inflammatory, and antidiabetic properties. The results show that melanoxetin reduced insulin resistance in adipose tissue by targeting protein tyrosine phosphatase 1B. Additionally, melanoxetin counteracted oxidative stress by reducing nitrotyrosine levels and modulating superoxide dismutase 1 and hemeoxygenase in adipose tissue and decreasing methylglyoxal-derived hydroimidazolone (MG-H1), a key advanced glycation end product (AGE) implicated in DM-related complications. Moreover, the glyoxalase 1 expression decreased in both the liver and the heart, correlating with reduced AGE levels, particularly MG-H1 in the heart. Melanoxetin also demonstrated anti-inflammatory effects by reducing serum prostaglandin E2 levels, and increasing the antioxidant status of the aorta wall through enhanced acetylcholine-dependent relaxation in the presence of ascorbic acid. These findings provide valuable insights into melanoxetin's therapeutic potential in targeting multiple pathways involved in type 2 DM, particularly in mitigating oxidative stress and glycation.

Jianpi Qinghua Formula Alleviates Diabetic Myocardial Injury Through Inhibiting JunB/c-Fos Expression.

Diabetic cardiomyopathy (DCM) represents a substantial risk factor for heart failure and increased mortality in individuals afflicted with diabetes mellitus (DM). DCM typically manifests as myocardial fibrosis, myocardial hypertrophy, and impaired left ventricular diastolic function. While the clinical utility of the Jianpi Qinghua (JPQH) formula has been established in treating diabetes and insulin resistance, its potential efficacy in alleviating diabetic cardiomyopathy remains uncertain. This study aims to investigate the impact and underlying molecular mechanisms of the JPQH formula (JPQHF) in ameliorating myocardial injury in nonobese diabetic rats, specifically focusing on apoptosis and inflammation. Wistar rats were assigned as the normal control group (CON), while Goto-Kakizaki (GK) rats were randomly divided into three groups: DM, DM treated with the JPQHF, and DM treated with metformin (MET). Following a 4-week treatment regimen, various biochemical markers related to glucose metabolism, cardiac function, cardiac morphology, and myocardial ultrastructure in GK rats were assessed. RNA sequencing was utilized to analyze differential gene expression and identify potential therapeutic targets. In vitro experiments involved high glucose to induce apoptosis and inflammation in H9c2 cells. Cell viability was evaluated using CCK-8 assay, apoptosis was monitored via flow cytometry, and the production of inflammatory cytokines was measured using quantitative real-time PCR (qPCR) and ELISA. Protein expression levels were determined by Western blotting analysis. The investigation also incorporated the use of MAPK inhibitors to further elucidate the mechanism at both the transcriptional and protein levels. The JPQHF group exhibited significant reductions in interventricular septal thickness at end-systole (IVSs) and left ventricular internal diameter at end-systole and end-diastole (LVIDs and LVIDd). JPQHF effectively suppressed high glucose-induced activation of IL-1β and caspase 3 in cardiomyocytes. Furthermore, JPQHF downregulated the expression of myocardial JunB/c-Fos, which was upregulated in both diabetic rats and high glucose-treated H9c2 cells. The JPQH formula holds promise in mitigating diabetic myocardial apoptosis and inflammation in cardiomyocytes by inhibiting JunB/c-Fos expression through suppressing the MAPK (p38 and ERK1/2) pathway.

High-Density Lipoprotein Is Located Alongside Insulin in the Islets of Langerhans of Normal and Rodent Models of Diabetes.

Recent studies have implicated pre-beta and beta lipoproteins (VLDL and LDL) in the etiopathogenesis of complications of diabetes mellitus (DM). In contrast, alpha lipoprotein (HDL) is protective of the beta cells of the pancreas. This study examined the distribution of HDL in the islets of Langerhans of murine models of type 1 diabetic rats (streptozotocin (STZ)-induced DM in Wistar rats) and type 2 models of DM rats (Goto-Kakizaki (GK), non-diabetic Zucker lean (ZL), and Zucker diabetic and fatty (ZDF)). The extent by which HDL co-localizes with insulin or glucagon in the islets of the pancreas was also investigated. Pancreatic tissues of Wistar non-diabetic, diabetic Wistar, GK, ZL, and ZDF rats were processed for immunohistochemistry. Pancreatic samples of GK rats fed with either a low-fat or a high-fat diet were prepared for transmission immune-electron microscopy (TIEM) to establish the cytoplasmic localization of HDL in islet cells. HDL was detected in the core and periphery of pancreatic islets of Wistar non-diabetic and diabetic, GK, ZL, and ZDF rats. The average total of islet cells immune positive for HDL was markedly (<0.05) reduced in GK and ZDF rats in comparison to Wistar controls. The number of islet cells containing HDL was also remarkably (p < 0.05) reduced in Wistar diabetic rats and GK models fed on high-fat food. The co-localization study using immunofluorescence and TIEM techniques showed that HDL is detected alongside insulin within the secretory granules of β-cells. HDL did not co-localize with glucagon. This observation implies that HDL may contribute to the metabolism of insulin.