Concurrent impairment of (Na++K+)-ATPase activity in multi-organ of type-1 diabetic NOD mice

Ion homeostasis in diabetic kidney disease

The complications of type 2 diabetes are a major global public health problem with high incidence and mortality, affecting almost all individuals with diabetes worldwide. Diabetic kidney disease (DKD) is one such primary complication and has become a leading cause of end-stage renal disease in patients with diabetes. Progression from diabetes to DKD is a complex process typically involving multiple mechanisms. Recent remarkable clinical benefits of sodium-glucose cotransporter 2 (SGLT2) inhibitors in diabetes and DKD highlight the critical impact of renal ion homeostasis on disease progression. This review comprehensively examines the impact of ion homeostasis on the transition from diabetes to DKD, outlining possible therapeutic interventions and addressing the ongoing challenges in this rapidly developing field.

Regulation of Na+-K+-ATPase leads to disturbances of isoproterenol-induced cardiac dysfunction via interference of Ca2+-dependent cardiac metabolism

Reductions in Na+-K+-ATPase (NKA) activity and expression are often observed in the progress of various reason-induced heart failure (HF). However, NKA α1 mutation or knockdown cannot cause spontaneous heart disease. Whether the abnormal NKA α1 directly contributes to HF pathogenesis remains unknown. Here, we challenge NKA α1+/- mice with isoproterenol to evaluate the role of NKA α1 haploinsufficiency in isoproterenol (ISO)-induced cardiac dysfunction. Genetic knockdown of NKA α1 accelerated ISO-induced cardiac cell hypertrophy, heart fibrosis, and dysfunction. Further studies revealed decreased Krebs cycle, fatty acid oxidation, and mitochondrial OXPHOS in the hearts of NKA α1+/- mice challenged with ISO. In ISO-treated conditions, inhibition of NKA elevated cytosolic Na+, further reduced mitochondrial Ca2+ via mNCE, and then finally down-regulated cardiac cell energy metabolism. In addition, a supplement of DRm217 alleviated ISO-induced heart dysfunction, mitigated cardiac remodeling, and improved cytosolic Na+ and Ca2+ elevation and mitochondrial Ca2+ depression in the NKA α1+/- mouse model. The findings suggest that targeting NKA and mitochondria Ca2+ could be a promising strategy in the treatment of heart disease.

O-Linked GlcNAcylation mediates the inhibition of proximal tubule (Na++K+)ATPase activity in the early stage of diabetes mellitus

BACKGROUND

Diabetic kidney disease (DKD) is a severe complication of diabetes mellitus (DM). It has been proposed that modifications in the function of proximal tubule epithelial cells (PTECs) precede glomerular damage during the onset of DKD. This study aimed to identify modifications in renal sodium handling in the early stage of DM and its molecular mechanism.

METHODS

Streptozotocin (STZ)-induced diabetic BALB/c mice (STZ group) and LLC-PK1 cells, a model of PTECs, were used. All parameters were assessed in the 4th week after an initial injection of STZ.

RESULTS

Early stage of DKD was characterized by hyperfiltration and PTEC dysfunction. STZ group exhibited increased urinary sodium excretion due to impairment of tubular sodium reabsorption. This was correlated to a decrease in cortical (Na++K+)ATPase (NKA) α1 subunit expression and enzyme activity and an increase in O-GlcNAcylation. RNAseq analysis of patients with DKD revealed an increase in expression of the glutamine-fructose aminotransferase (GFAT) gene, a rate-limiting step of hexosamine biosynthetic pathway, and a decrease in NKA expression. Incubation of LLC-PK1 cells with 10 μM thiamet G, an inhibitor of O-GlcNAcase, reduced the expression and activity of NKA and increased O-GlcNAcylation. Furthermore, 6-diazo-5-oxo-L-norleucine (DON), a GFAT inhibitor, or dapagliflozin, an SGLT2 inhibitor, avoided the inhibitory effect of HG on expression and activity of NKA associated with the decrease in O-GlcNAcylation.

CONCLUSION

Our results show that the impairment of tubular sodium reabsorption, in the early stage of DM, is due to SGLT2-mediated HG influx in PTECs, increase in O-GlcNAcylation and reduction in NKA expression and activity.

Anti-Na+/K+-ATPase DR antibody attenuates UUO-induced renal fibrosis through inhibition of Na+/K+-ATPase α1-dependent HMGB1 release

Reduced Na⁺/K⁺-ATPase (NKA) activity and NKAα1 expression are engaged in the pathologies of renal diseases. NKA-mediated Src activation is not the only reason for NKA-related renal fibrosis. In this study, we found that genetic reduction of NKAα1 exhibited exacerbated tubulointerstitial lesions and fibrosis in the UUO mice model. Activation of NKAα1 with an antibody against the extracellular DR region of the NKAα1 subunit (DRm217) prevented UUO-induced tubulointerstitial lesions, preserved kidney function, and decrease renal fibrosis. Further studies revealed that NKAα1 deficiency mice exhibited high inflammation factors expression when they suffered UUO surgery, compared with NKAα1^+/+ (WT) mice. DRm217 alleviated inflammatory cell infiltration, suppress NF-κB phosphorylation, and decreased inflammatory factors expression in the UUO mice model. Released HMGB1 can trigger the inflammatory response and contribute to renal fibrosis. Knockdown of NKA in renal tubular cells or in NKAα1^+/- mice was associated with more susceptibility to HMGB1 release in the UUO mice model. DRm217 exerted its antifibrotic effect via inhibiting HMGB1 release. Furthermore, AMPK activation participates in the effect of DRm217 on inhibiting HMGB1 release. Our findings suggest that NKAα1 is a regulator of renal fibrosis and its DR-region is a novel target on it.

Na,K-ATPase Kinetics and Oxidative Stress in Kidneys of Zucker Diabetic Fatty (fa/fa) Rats Depending on the Diabetes Severity-Comparison with Lean (fa/+) and Wistar Rats

For a better insight into relations between type 2 diabetes mellitus (T2DM) and Na,K-ATPase properties in kidneys, we aimed to characterize two subgroups of ZDF obese (fa/fa) rats, with more and less developed T2DM, and compare them with two controls: lean (fa/+) and Wistar. Na,K-ATPase enzyme kinetics were estimated by measuring the ATP hydrolysis in the range of NaCl and ATP levels. As Na,K-ATPase is sensitive to oxidative stress, we evaluated selected oxidative stress parameters in kidney homogenates. Our results suggest that thiol-disulfide redox balance in the renal medulla and Na,K-ATPase properties in the renal cortex differ between both controls, while observed measurements in lean (fa/+) rats showed deviation towards the values observed in ZDF (fa/fa) rats. In comparison with both controls, Na,K-ATPase enzyme activity was higher in the renal cortex of ZDF rats independent of diabetes severity. This might be a consequence of increased glucose load in tubular fluid. The increase in lipid peroxidation observed in the renal cortex of ZDF rats was not associated with Na,K-ATPase activity impairment. Regarding the differences between subgroups of ZDF animals, well-developed T2DM (glycemia higher than 10 mmol/L) was associated with a higher ability of Na,K-ATPase to utilize the ATP energy substrate.

Na+/K+-ATPase DR region antibody ameliorated cardiac hypertrophy and fibrosis in rats with 5/6 nephrectomy

The enzyme Na⁺/K⁺-ATPase (NKA) is important in the heart. Reductions in NKA activity and expression have often been observed in chronic kidney disease (CKD)-related heart injury. Previously, our group found that an antibody targeting the NKA1α1 subunit's DR extracellular region (⁸⁹⁷DVEDSYGQQWTYEQR⁹¹¹) stimulated NKA activities and produced cardioprotective effects against ischemic injury and isoproterenol-induced cardiac remodeling. In here, we assessed whether DRm217, a specific DR antibody, exhibits cardioprotective effects in chronic renal failure models. In 5/6 nephrectomy (5/6 Nx) surgery to mimic CKD in Sprague Dawley rat, we observed that NKA activity and expression were depressed in the hearts of 5/6 Nx rats. DRm217, an NKA DR region antibody, alleviated heart hypertrophy and cardiac fibrosis under 5/6 Nx conditions. Further studies revealed that DRm217 inhibited Src activation and reduced reactive oxygen species (ROS) levels in hearts under 5/6 Nx conditions. Our findings imply that NKA could be a treatment target in CKD-related cardiac diseases. Prevention of CKD-induced myocardial injury by DRm217 provides an appealing therapeutic alternative.

Insulin enhances renal glucose excretion: relation to insulin sensitivity and sodium-glucose cotransport

INTRODUCTION

Insulin regulates renal glucose production and utilization; both these fluxes are increased in type 2 diabetes (T2D). Whether insulin also controls urinary glucose excretion is not known.

METHODS

We applied the pancreatic clamp technique in 12 healthy subjects and 13 T2D subjects. Each participant received a somatostatin infusion and a variable glucose infusion to achieve (within 1 hour) and maintain glycemia at 22 mmol/L for 3 hours; next, a constant insulin infusion (240 pmol/min/kg) was added for another 3 hours. Urine was collected separately in each period for glucose and creatinine determination.

RESULTS

During saline, glucose excretion was lower in T2D than controls in absolute terms (0.49 (0.32) vs 0.69 (0.18) mmol/min, median (IQR), p=0.01) and as a fraction of filtered glucose (16.2 (6.4) vs 19.9 (7.5)%, p<0.001). With insulin, whole-body glucose disposal rose more in controls than T2D (183 (48) vs 101 (48) µmol/kg_FFM/min, p<0.0003). Insulin stimulated absolute and fractional glucose excretion in controls (p<0.01) but not in T2D. Sodium excretion paralleled glucose excretion. In the pooled data, fractional glucose excretion was directly related to whole-body glucose disposal and to fractional sodium excretion (r=0.52 and 0.54, both p<0.01). In another group of healthy controls, empagliflozin was administered before starting the pancreatic clamp to block sodium-glucose cotransporter 2 (SGLT2). Under these conditions, insulin still enhanced both glucose and sodium excretion.

CONCLUSIONS

Acute exogenous insulin infusion jointly stimulates renal glucose and sodium excretion, indicating that the effect may be mediated by SGLTs. This action is resistant in patients with diabetes, accounting for their increased retention of glucose and sodium, and is not abolished by partial SGLT2 inhibition by empagliflozin.

Effect of Insulin on Proximal Tubules Handling of Glucose: A Systematic Review

Renal proximal tubules reabsorb glucose from the glomerular filtrate and release it back into the circulation. Modulation of glomerular filtration and renal glucose disposal are some of the insulin actions, but little is known about a possible insulin effect on tubular glucose reabsorption. This review is aimed at synthesizing the current knowledge about insulin action on glucose handling by proximal tubules. Method. A systematic article selection from Medline (PubMed) and Embase between 2008 and 2019. 180 selected articles were clustered into topics (renal insulin handling, proximal tubule glucose transport, renal gluconeogenesis, and renal insulin resistance). Summary of Results. Insulin upregulates its renal uptake and degradation, and there is probably a renal site-specific insulin action and resistance; studies in diabetic animal models suggest that insulin increases renal SGLT2 protein content; in vivo human studies on glucose transport are few, and results of glucose transporter protein and mRNA contents are conflicting in human kidney biopsies; maximum renal glucose reabsorptive capacity is higher in diabetic patients than in healthy subjects; glucose stimulates SGLT1, SGLT2, and GLUT2 in renal cell cultures while insulin raises SGLT2 protein availability and activity and seems to directly inhibit the SGLT1 activity despite it activating this transporter indirectly. Besides, insulin regulates SGLT2 inhibitor bioavailability, inhibits renal gluconeogenesis, and interferes with Na⁺K⁺ATPase activity impacting on glucose transport. Conclusion. Available data points to an important insulin participation in renal glucose handling, including tubular glucose transport, but human studies with reproducible and comparable method are still needed.

Hyperglycemia induces mechanical hyperalgesia and depolarization of the resting membrane potential of primary nociceptive neurons: Role of ATP-sensitive potassium channels

Cumulating data suggests that ion channel alterations in nociceptive neurons might be involved in the development of diabetic painful neuropathy. In the present study we investigated the involvement of ATP-sensitive potassium (K⁺_ATP) channels in the acute effect of high glucose solution in vitro and in vivo. High glucose concentrations depolarized cultured nociceptive neurons and depolarization was blocked by the K⁺_ATP opener, diazoxide or by insulin. Glucose injection at the rat dorsal root ganglia (L5) resulted in acute mechanical hyperalgesia that was blocked by diazoxide. Mannitol injection indicates that osmolarity changes are not responsible for glucose effect. Therefore, this study suggests that K⁺_ATP channels expressed in peripheral sensory neurons might be involved in the development of diabetic painful neuropathy. Since sulfonylureas, that act by blocking K⁺_ATP are used for diabetes treatment, it is important to evaluate the possible side effects of such drugs at primary sensory neurons.

DR region specific antibody ameliorated but ouabain worsened renal injury in nephrectomized rats through regulating Na,K-ATPase mediated signaling pathways

Reduced Na⁺-K⁺-ATPase function is reported in various renal diseases. This implies that increase of Na⁺-K⁺-ATPase function may be a new target in treatment of renal injury. We previously reported that Na⁺-K⁺-ATPase was stabilized by DRm217, a specific antibody against DR region of Na⁺-K⁺-ATPase. In this study, we compared the protective effect of DRm217 and ouabain on kidney in a chronic kidney disease rat model and investigated the mechanism under it. We found that DRm217 improved renal function, alleviated glomerulus atrophy, inhibited renal tubular cells apoptosis, tubulointerstitial injury and renal fibrosis in 5/6 nephrectomized rats. Contrary to DRm217, ouabain worsened renal damage. Activated Na⁺-K⁺-ATPase /Src signaling pathway, increased oxidant stress and activated inflammasome were responsible for nephrectomized or ouabain-induced renal injury. DRm217 inhibited Na⁺-K⁺-ATPase /Src signaling pathway, retarded oxidant stress, suppressed inflammasome activation, and improved renal function, suggesting a novel approach to prevent renal damage.

Polyploidy and nuclear phenotype characteristics of cardiomyocytes from diabetic adult and normoglycemic aged mice

The frequency of polyploid nuclei in the aging human heart is in sharp contrast with that in the human liver. An inverse pattern exists between the mouse heart and liver cells. Ploidy degrees in mouse hepatocytes under hyperglycemic conditions are elevated to higher levels than those in aged hepatocytes. In this study, image analysis cytometry was used to investigate the effect of diabetes and aging on Feulgen-DNA quantities, ploidy degrees, nuclear shapes and chromatin texture in mouse cardiomyocytes compared to previously reported data for mouse hepatocytes. Adult, non-obese diabetic (NOD) hyperglycemic and normoglycemic females and 56-week-old normoglycemic BALB/c females were used. A small percentage (∼7%) of the cardiomyocyte nuclei in severely hyperglycemic NOD adult mice possessed higher ploidy values than those in the 8-week-old normoglycemic mice. Surprisingly, the Feulgen-DNA values and the frequency of nuclei belonging to the 4C and 8C ploidy classes were even higher (∼6%) in normoglycemic NOD specimens than in age-matched hyperglycemic NOD specimens. Additionally, a pronounced elongated nuclear shape was observed especially in adult normoglycemic NOD mice. In conclusion, NOD mice, irrespective of their glycemic level, exhibit a moderate increase in ploidy degrees within cardiomyocyte nuclei during the adult lifetime. As expected, aging did not affect the Feulgen-DNA values and the ploidy degrees of cardiomyocytes in BALB/c mice. The differences in ploidy degrees and chromatin textures such as absorbance variability and entropy, between adult NOD and aged BALB/c mice are consistent with other reports, indicating dissimilarities in chromatin functions between diabetes and aging.

Regulation of Na+-K+-ATPase effected high glucose-induced myocardial cell injury through c-Src dependent NADPH oxidase/ROS pathway

Depressed Na⁺/K⁺-ATPase activity has long been reported to be involved in diabetic-related cardiomyocyte death and cardiac dysfunction. However, the nature of directly regulating Na⁺-K⁺-ATPase in diabetic-related myocardial diseases remains unknown. Hyperglycemia is believed as one of major factors responsible for diabetic-related myocardial apoptosis and dysfunction. In this study, whether inhibiting Na⁺-K⁺-ATPase by ouabain or activating Na⁺-K⁺-ATPase by DRm217 has functions on high glucose (HG) -induced myocardial injury was investigated. Here we found that addition of DRm217 or ouabain to HG-treated cells had opposite effects. DRm217 decreased but ouabain increased HG-induced cell injury and apoptosis. This was mediated by changing Na⁺-K⁺-ATPase activity and Na⁺-K⁺-ATPase cell surface expression. The inhibition of Na⁺-K⁺-ATPase endocytosis alleviated HG-induced ROS accumulation. Na⁺-K⁺-ATPase·c-Src dependent NADPH oxidase/ROS pathway was also involved in the effects of ouabain and DRm217 on HG-induced cell injury. These novel results may help us to understand the important role of the Na⁺-K⁺-ATPase in diabetic cardiovascular diseases.

Activation of Na+/K+-ATPase attenuates high glucose-induced H9c2 cell apoptosis via suppressing ROS accumulation and MAPKs activities by DRm217

Hyperglycemia is one of the major factors responsible for the myocardial apoptosis and dysfunction in diabetes. Many studies have proved that there is a close relationship between decreased Na⁺/K⁺-ATPase activity and diabetic cardiomyopathy. However, the effect of directly activated Na⁺/K⁺-ATPase on high glucose-induced myocardial injury is still unknown. Here we found that DRm217, a Na⁺/K⁺-ATPase's DR-region specific monoclonal antibody and direct activator, could prevent high glucose-induced H9c2 cell injury, reactive oxygen species (ROS) release, and mitochondrial dysfunction. High glucose-treatment decreased Na⁺/K⁺-ATPase activity and increased intracellular Ca²⁺ level, whereas DRm217 increased Na⁺/K⁺-ATPase activity and alleviated Ca²⁺ overload. Inhibition of Ca²⁺ overload or closing sodium calcium exchanger (NCX channel) could reverse high glucose-induced ROS increasing and cell injury. In addition, DRm217 could significantly attenuate high glucose-induced p38, JNK and ERK1/2 phosphorylation, which were involved in high glucose-induced cell injury and ROS accumulation. Our findings suggest that DRm217 may protect against the deleterious effects of high glucose in the heart. Prevention of high glucose-induced myocardial cell injury by specific Na⁺/K⁺-ATPase activator may be an attractive therapeutic option.

Melatonin synthesis impairment as a new deleterious outcome of diabetes-derived hyperglycemia

Melatonin is a neurohormone that works as a nighttime signal for circadian integrity and health maintenance. It is crucial for energy metabolism regulation, and the diabetes effects on its synthesis are unresolved. Using diverse techniques that included pineal microdialysis and ultrahigh-performance liquid chromatography, the present data show a clear acute and sustained melatonin synthesis reduction in diabetic rats as a result of pineal metabolism impairment that is unrelated to cell death. Hyperglycemia is the main cause of several diabetic complications, and its consequences in terms of melatonin production were assessed. Here, we show that local high glucose (HG) concentration is acutely detrimental to pineal melatonin synthesis in rats both in vivo and in vitro. The clinically depressive action of high blood glucose concentration in melatonin levels was also observed in type 1 diabetes patients who presented a negative correlation between hyperglycemia and 6-sulfatoxymelatonin excretion. Additionally, high-mean-glycemia type 1 diabetes patients presented lower 6-sulfatoxymelatonin levels when compared to control subjects. Although further studies are needed to fully clarify the mechanisms, the present results provide evidence that high circulating glucose levels interfere with pineal melatonin production. Given the essential role played by melatonin as a powerful antioxidant and in the control of energy homeostasis, sleep and biological rhythms and knowing that optimal glycemic control is usually an issue for patients with diabetes, melatonin supplementation may be considered as an additional tool to the current treatment.