SLC2A2 gene expression in kidney of diabetic rats is regulated by HNF-1alpha and HNF-3beta

S100A2 promotes clear cell renal cell carcinoma tumor metastasis through regulating GLUT2 expression

Clear cell renal cell carcinoma (ccRCC) is the predominant subtype of renal cancer and is highly malignant. Despite advances in diagnostics and treatment, the prognosis for ccRCC remains poor. The dual nature (promotion or inhibition) of S100A2 in different cancer types shows the complex involvement of its tumorigenesis, but its effect in ccRCC remains unclear. In this study, we first elucidate the tumor-promoting function of S100A2 in ccRCC by reprogramming glycolysis. Mechanistically, we demonstrate that S100A2 accelerates cancer progression through its interaction with the transcription factor HNF1A, leading to activating GLUT2 transcription. The upregulation of GLUT2 significantly enhances glucose uptake by cancer cells, thereby fueling augmented glucose metabolism and fostering the malignant progression of ccRCC. Collectively, our findings highlight the pivotal role of the S100A2-HNF1A-GLUT2 axis in promoting migration and invasion of ccRCC by amplifying glycolysis and suggest that targeting the S100A2-HNF1A-GLUT2 axis is clinically relevant for the treatment of metastatic ccRCC.

The pivotal role of glucose transporter 1 in diabetic kidney disease

Diabetes mellitus (DM) is a significant public health problem. Diabetic kidney disease (DKD) is the most common complication of DM, and its incidence has been increasing with the increasing prevalence of DM. Given the association between DKD and mortality in patients with DM, DKD is a significant burden on public health resources. Despite its significance in DM progression, the pathogenesis of DKD remains unclear. Aberrant glucose uptake by cells is an important pathophysiological mechanism underlying DKD renal injury. Glucose is transported across the bilayer cell membrane by a glucose transporter (GLUT) located on the cell membrane. Multiple GLUT proteins have been identified in the kidney, and GLUT1 is one of the most abundantly expressed isoforms. GLUT1 is a crucial regulator of intracellular glucose metabolism and plays a key pathological role in the phenotypic changes in DKD mesangial cells. In an attempt to understand the pathogenesis of DKD better, we here present a review of studies on the role of GLUT1 in the development and progression of DKD.

Monitoring glucose levels in urine using FTIR spectroscopy combined with univariate and multivariate statistical methods

The development of novel platforms for non-invasive continuous glucose monitoring applied in the screening and monitoring of diabetes is crucial to improve diabetes surveillance systems. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy of urine can be an alternative as a sustainable, label-free, fast, non-invasive, and highly sensitive analysis to detect changes in urine promoted by diabetes and insulin treatment. In this study, we used ATR-FTIR to evaluate the urinary components of non-diabetic (ND), diabetic (D), and diabetic insulin-treated (D + I) rats. As expected, insulin treatment was capable to revert changes in glycemia, 24-h urine collection volume, urine creatinine, urea, and glucose excretion promoted by diabetes. Several differences in the urine spectra of ND, D, and D + I were observed, with urea, creatinine, and glucose analytes being related to these changes. Principal components analysis (PCA) scores plots allowed for the discrimination of ND and D + I from D with an accuracy of ∼ 99 %. The PCA loadings associated with PC1 confirmed the importance of urea and glucose vibrational modes for this discrimination. Univariate analysis of second derivative spectra showed a high correlation (r: 0.865, p < 0.0001) between the height of 1074 cm-1 vibrational mode with urinary glucose concentration. In order to estimate the amount of glucose present in the infrared spectra from urine, multivariate curve resolution-alternating least square (MCR-ALS) was applied and a higher predicted concentration of glucose in the urine was observed with a correlation of 78.9 % compared to urinary glucose concentration assessed using enzyme assays. In summary, ATR-FTIR combined with univariate and multivariate chemometric analyses provides an innovative, non-invasive, and sustainable approach to diabetes surveillance.

Transcription factor c-Maf deletion improves streptozotocin-induced diabetic nephropathy by directly regulating Sglt2 and Glut2

The transcription factor c-Maf has been widely studied and has been reported to play a critical role in embryonic kidney development; however, the postnatal functions of c-Maf in adult kidneys remain unknown as c-Maf-null C57BL/6J mice exhibit embryonic lethality. In this study, we investigated the role of c-Maf in adult mouse kidneys by comparing the phenotypes of tamoxifen-inducible (TAM-inducible) c-Maf-knockout mice (c-Maffl/fl; CAG-Cre-ERTM mice named "c-MafΔTAM") with those of c-Maffl/fl control mice, 10 days after TAM injection [TAM(10d)]. In addition, we examined the effects of c-Maf deletion on diabetic conditions by injecting the mice with streptozotocin, 4 weeks before TAM injection. c-MafΔTAM mice displayed primary glycosuria caused by sodium-glucose cotransporter 2 (Sglt2) and glucose transporter 2 (Glut2) downregulation in the kidneys without diabetes, as well as morphological changes and life-threatening injuries in the kidneys on TAM(10d). Under diabetic conditions, c-Maf deletion promoted recovery from hyperglycemia and suppressed albuminuria and diabetic nephropathy by causing similar effects as did Sglt2 knockout and SGLT2 inhibitors. In addition to demonstrating the potentially unique gene regulation of c-Maf, these findings highlight the renoprotective effects of c-Maf deficiency under diabetic conditions and suggest that c-Maf could be a novel therapeutic target gene for treating diabetic nephropathy.

Kidney Proximal Tubule GLUT2-More than Meets the Eye

Tubulopathy plays a central role in the pathophysiology of diabetic kidney disease (DKD). Under diabetic conditions, the kidney proximal tubule cells (KPTCs) are exposed to an extensive amount of nutrients, most notably glucose; these nutrients deteriorate KPTCs function and promote the development and progression of DKD. Recently, the facilitative glucose transporter 2 (GLUT2) in KPTCs has emerged as a central regulator in the pathogenesis of DKD. This has been demonstrated by identifying its specific role in enhancing glucose reabsorption and glucotoxicity, and by deciphering its effect in regulating the expression of the sodium-glucose transporter 2 (SGLT2) in KPTCs. Moreover, reduction/deletion of KPTC-GLUT2 has been recently found to ameliorate DKD, raising the plausible idea of considering it as a therapeutic target against DKD. However, the underlying molecular mechanisms by which GLUT2 exerts its deleterious effects in KPTCs remain vague. Herein, we review the current findings on the proximal tubule GLUT2 biology and function under physiologic conditions, and its involvement in the pathophysiology of DKD. Furthermore, we shed new light on its cellular regulation during diabetic conditions.

Renoprotective Effects of SGLT2 Inhibitors

SGLT2 inhibitors can protect the kidneys of patients with and without type 2 diabetes from failing. This includes blood glucose dependent and independent mechanisms. SGLT2 inhibitors lower glomerular pressure and filtration, thereby reducing the physical stress on the filtration barrier and the oxygen demand for tubular reabsorption. This improves cortical oxygenation, which, together with lesser tubular glucotoxicity and improved mitochondrial function and autophagy, can reduce proinflammatory and profibrotic signaling and preserve tubular function and GFR in long term. By shifting transport downstream, SGLT2 inhibitors may mimic systemic hypoxia and stimulate erythropoiesis, which improves oxygen delivery to the kidney and other organs.

Up-Date on Diabetic Nephropathy

Diabetes is one of the leading causes of kidney disease. Diabetic kidney disease (DKD) is a major cause of end-stage kidney disease (ESKD) worldwide, and it is linked to an increase in cardiovascular (CV) risk. Diabetic nephropathy (DN) increases morbidity and mortality among people living with diabetes. Risk factors for DN are chronic hyperglycemia and high blood pressure; the renin-angiotensin-aldosterone system blockade improves glomerular function and CV risk in these patients. Recently, new antidiabetic drugs, including sodium-glucose transport protein 2 inhibitors and glucagon-like peptide-1 agonists, have demonstrated additional contribution in delaying the progression of kidney disease and enhancing CV outcomes. The therapeutic goal is regression of albuminuria, but an atypical form of non-proteinuric diabetic nephropathy (NP-DN) is also described. In this review, we provide a state-of-the-art evaluation of current treatment strategies and promising emerging treatments.

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.

Opposite physiological and pathological mTORC1-mediated roles of the CB1 receptor in regulating renal tubular function

Activation of the cannabinoid-1 receptor (CB₁R) and the mammalian target of rapamycin complex 1 (mTORC1) in the renal proximal tubular cells (RPTCs) contributes to the development of diabetic kidney disease (DKD). However, the CB₁R/mTORC1 signaling axis in the kidney has not been described yet. We show here that hyperglycemia-induced endocannabinoid/CB₁R stimulation increased mTORC1 activity, enhancing the transcription of the facilitative glucose transporter 2 (GLUT2) and leading to the development of DKD in mice; this effect was ameliorated by specific RPTCs ablation of GLUT2. Conversely, CB₁R maintained the normal activity of mTORC1 by preventing the cellular excess of amino acids during normoglycemia. Our findings highlight a novel molecular mechanism by which the activation of mTORC1 in RPTCs is tightly controlled by CB₁R, either by enhancing the reabsorption of glucose and inducing kidney dysfunction in diabetes or by preventing amino acid uptake and maintaining normal kidney function in healthy conditions.

Renal proximal tubules modulate whole-body homeostasis by sensing various nutrients. Here the authors describe the existence and importance of a unique CB1/mTORC1/GLUT2 signaling axis in regulating nutrient homeostasis in healthy and diseased kidney.

Renal Tubular Handling of Glucose and Fructose in Health and Disease

The proximal tubule of the kidney is programmed to reabsorb all filtered glucose and fructose. Glucose is taken up by apical sodium-glucose cotransporters SGLT2 and SGLT1 whereas SGLT5 and potentially SGLT4 and GLUT5 have been implicated in apical fructose uptake. The glucose taken up by the proximal tubule is typically not metabolized but leaves via the basolateral facilitative glucose transporter GLUT2 and is returned to the systemic circulation or used as an energy source by distal tubular segments after basolateral uptake via GLUT1. The proximal tubule generates new glucose in metabolic acidosis and the postabsorptive phase, and fructose serves as an important substrate. In fact, under physiological conditions and intake, fructose taken up by proximal tubules is primarily utilized for gluconeogenesis. In the diabetic kidney, glucose is retained and gluconeogenesis enhanced, the latter in part driven by fructose. This is maladaptive as it sustains hyperglycemia. Moreover, renal glucose retention is coupled to sodium retention through SGLT2 and SGLT1, which induces secondary deleterious effects. SGLT2 inhibitors are new anti-hyperglycemic drugs that can protect the kidneys and heart from failing independent of kidney function and diabetes. Dietary excess of fructose also induces tubular injury. This can be magnified by kidney formation of fructose under pathological conditions. Fructose metabolism is linked to urate formation, which partially accounts for fructose-induced tubular injury, inflammation, and hemodynamic alterations. Fructose metabolism favors glycolysis over mitochondrial respiration as urate suppresses aconitase in the tricarboxylic acid cycle, and has been linked to potentially detrimental aerobic glycolysis (Warburg effect). © 2022 American Physiological Society. Compr Physiol 12:2995-3044, 2022.

Effects of SGLT2 Inhibitors on Kidney and Cardiovascular Function

SGLT2 inhibitors are antihyperglycemic drugs that protect kidneys and the heart of patients with or without type 2 diabetes and preserved or reduced kidney function from failing. The involved protective mechanisms include blood glucose-dependent and -independent mechanisms: SGLT2 inhibitors prevent both hyper- and hypoglycemia, with expectedly little net effect on HbA1C. Metabolic adaptations to induced urinary glucose loss include reduced fat mass and more ketone bodies as additional fuel. SGLT2 inhibitors lower glomerular capillary hypertension and hyperfiltration, thereby reducing the physical stress on the filtration barrier, albuminuria, and the oxygen demand for tubular reabsorption. This improves cortical oxygenation, which, together with lesser tubular gluco-toxicity, may preserve tubular function and glomerular filtration rate in the long term. SGLT2 inhibitors may mimic systemic hypoxia and stimulate erythropoiesis, which improves organ oxygen delivery. SGLT2 inhibitors are proximal tubule and osmotic diuretics that reduce volume retention and blood pressure and preserve heart function, potentially in part by overcoming the resistance to diuretics and atrial-natriuretic-peptide and inhibiting Na-H exchangers and sympathetic tone.

Perspective of SGLT2 Inhibition in Treatment of Conditions Connected to Neuronal Loss: Focus on Alzheimer's Disease and Ischemia-Related Brain Injury

Sodium-glucose co-transporter 2 inhibitors (SGLT2i) are oral anti-hyperglycemic agents approved for the treatment of type 2 diabetes mellitus. Some reports suggest their presence in the central nervous system and possible neuroprotective properties. SGLT2 inhibition by empagliflozin has shown to reduce amyloid burden in cortical regions of APP/PS1xd/db mice. The same effect was noticed regarding tau pathology and brain atrophy volume. Empagliflozin presented beneficial effect on cognitive function, which may be connected to an increase in cerebral brain-derived neurotrophic factor. Canagliflozin and dapagliflozin may possess acetylcholinesterase inhibiting activity, resembling in this matter Alzheimer’s disease-registered therapies. SGLT2 inhibitors may prove to impact risk factors of atherosclerosis and pathways participating both in acute and late stage of stroke. Their mechanism of action can be related to induction in hepatocyte nuclear factor-1α, vascular endothelial growth factor-A, and proinflammatory factors limitation. Empagliflozin may have a positive effect on preservation of neurovascular unit in diabetic mice, preventing its aberrant remodeling. Canagliflozin seems to present some cytostatic properties by limiting both human and mice endothelial cells proliferation. The paper presents potential mechanisms of SGLT-2 inhibitors in conditions connected with neuronal damage, with special emphasis on Alzheimer’s disease and cerebral ischemia.

Glucose transporters in the kidney in health and disease

The kidneys filter large amounts of glucose. To prevent the loss of this valuable fuel, the tubular system of the kidney, particularly the proximal tubule, has been programmed to reabsorb all filtered glucose. The machinery involves the sodium-glucose cotransporters SGLT2 and SGLT1 on the apical membrane and the facilitative glucose transporter GLUT2 on the basolateral membrane. The proximal tubule also generates new glucose, particularly in the post-absorptive phase but also to enhance bicarbonate formation and maintain acid-base balance. The glucose reabsorbed or formed by the proximal tubule is primarily taken up into peritubular capillaries and returned to the systemic circulation or provided as an energy source to further distal tubular segments that take up glucose by basolateral GLUT1. Recent studies provided insights on the coordination of renal glucose reabsorption, formation, and usage. Moreover, a better understanding of renal glucose transport in disease states is emerging. This includes the kidney in diabetes mellitus, when renal glucose retention becomes maladaptive and contributes to hyperglycemia. Furthermore, enhanced glucose reabsorption is coupled to sodium retention through the sodium-glucose cotransporter SGLT2, which induces secondary deleterious effects. As a consequence, SGLT2 inhibitors are new anti-hyperglycemic drugs that can protect the kidneys and heart from failing. Recent studies discovered unique roles for SGLT1 with implications in acute kidney injury and glucose sensing at the macula densa. This review discusses established and emerging concepts of renal glucose transport, and outlines the need for a better understanding of renal glucose handling in health and disease.

The tubular hypothesis of nephron filtration and diabetic kidney disease

Kidney size and glomerular filtration rate (GFR) often increase with the onset of diabetes, and elevated GFR is a risk factor for the development of diabetic kidney disease. Hyperfiltration mainly occurs in response to signals passed from the tubule to the glomerulus: high levels of glucose in the glomerular filtrate drive increased reabsorption of glucose and sodium by the sodium-glucose cotransporters SGLT2 and SGLT1 in the proximal tubule. Passive reabsorption of chloride and water also increases. The overall capacity for proximal reabsorption is augmented by growth of the proximal tubule, which (alongside sodium-glucose cotransport) further limits urinary glucose loss. Hyperreabsorption of sodium and chloride induces tubuloglomerular feedback from the macula densa to increase GFR. In addition, sodium-glucose cotransport by SGLT1 on macula densa cells triggers the production of nitric oxide, which also contributes to glomerular hyperfiltration. Although hyperfiltration restores sodium and chloride excretion it imposes added physical stress on the filtration barrier and increases the oxygen demand to drive reabsorption. Tubular growth is associated with the development of a senescence-like molecular signature that sets the stage for inflammation and fibrosis. SGLT2 inhibitors attenuate the proximal reabsorption of sodium and glucose, normalize tubuloglomerular feedback signals and mitigate hyperfiltration. This tubule-centred model of diabetic kidney physiology predicts the salutary effect of SGLT2 inhibitors on hard renal outcomes, as shown in large-scale clinical trials.

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.

Dual SGLT1/SGLT2 Inhibitor Phlorizin Ameliorates Non-Alcoholic Fatty Liver Disease and Hepatic Glucose Production in Type 2 Diabetic Mice

PURPOSE

NAFLD is a hepatic component of type 2 diabetes mellitus (T2D), in which impaired hepatic glucose production plays an important role. Inhibitors of sodium glucose transporter 2 (SGLT2) reduce glycemia and exert beneficial effects on diabetic complications. Recently, dual SGLT1/2 inhibition has been proposed to be more effective in reducing glycemia. We hypothesized that improving hepatic glucose metabolism induced by SGLT1/2 inhibition could be accompanied by beneficial effects on NAFLD progression.

METHODS

Glycemic homeostasis, hepatic glucose production and NAFLD features were investigated in obese T2D mice, treated with SGLT1/2 inhibitor phlorizin for 1 week.

RESULTS

T2D increased glycemia; insulinemia; hepatic expression of phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6Pase) and glucose transporter 2 (Slc2a2 gene); hepatocyte nuclear factors 1A/4A/3B-binding activity in Slc2a2; endogenous glucose production; liver weight, plasma transaminase concentration as well as hepatic inflammation markers, and induced histological signals of non-alcoholic steatohepatitis (NASH, according to NASH-CRN Pathology Committee System). Phlorizin treatment restored all these parameters (mean NASH score reduced from 5.25 to 2.75 P<0.001); however, plasma transaminase concentration was partially reverted and some hepatic inflammation markers remained unaltered.

CONCLUSION

NAFLD accompanies altered hepatic glucose metabolism in T2D mice and that greatly ameliorated through short-term treatment with the dual SGLT1/2 inhibitor. This suggests that altered hepatic glucose metabolism participates in T2D-related NAFLD and highlights the pharmacological inhibition of SGLTs as a useful approach not only for controlling glycemia but also for mitigating development and/or progression of NAFLD.

Modulation of Renal GLUT2 by the Cannabinoid-1 Receptor: Implications for the Treatment of Diabetic Nephropathy

Altered glucose reabsorption via the facilitative glucose transporter 2 (GLUT2) during diabetes may lead to renal proximal tubule cell (RPTC) injury, inflammation, and interstitial fibrosis. These pathologies are also triggered by activating the cannabinoid-1 receptor (CB₁R), which contributes to the development of diabetic nephropathy (DN). However, the link between CB₁R and GLUT2 remains to be determined. Here, we show that chronic peripheral CB₁R blockade or genetically inactivating CB₁Rs in the RPTCs ameliorated diabetes-induced renal structural and functional changes, kidney inflammation, and tubulointerstitial fibrosis in mice. Inhibition of CB₁R also downregulated GLUT2 expression, affected the dynamic translocation of GLUT2 to the brush border membrane of RPTCs, and reduced glucose reabsorption. Thus, targeting peripheral CB₁R or inhibiting GLUT2 dynamics in RPTCs has the potential to treat and ameliorate DN. These findings may support the rationale for the clinical testing of peripherally restricted CB₁R antagonists or the development of novel renal-specific GLUT2 inhibitors against DN.

A homozygous point mutation in the GH1 promoter (c.-223C>T) leads to reduced GH1 expression in siblings with isolated GH deficiency (IGHD)

CONTEXT

Mutations in the GH1 promoter are a rare cause of isolated growth hormone deficiency (IGHD).

OBJECTIVE

To identify the molecular aetiology of a family with IGHD.

DESIGN

DNA sequencing, electromobility shift (EMSA) and luciferase reporter assays.

SETTING

University Hospital.

PATIENTS

Three siblings (2M) born to consanguineous parents presented with IGHD with normal pituitary on MRI.

METHODS

The GH1 proximal promoter, locus control region, five exons and four introns as well as GHRHR gene were sequenced in genomic DNA by Sanger method. DNA-protein interaction was evaluated by EMSA in nuclear extracts of GH3 pituitary cells. Dual-luciferase reporter assays were performed in cells transiently transfected with plasmids containing four different combinations of GH1 allelic variants (AV).

RESULTS

The patients harboured two homozygous variants (c.-185T>C and c.-223C>T) in the GH1 promoter within a highly conserved region and predicted binding sites for POU1F1/SP1 and SP1 respectively. The parents and brother were carriers and these variants were absent in 100 controls. EMSA demonstrated absent binding of GH3 nuclear extract to the c.-223C>T variant and normal binding of both POU1F1 protein and GH3 nuclear extract to the c.-185T>C variant. In contrast to GH1 promoter with AV only at c.-185, the GH1 promoter containing the AV only at c.-223 and at both positions drove significantly less expression of luciferase compared with the promoter containing either positions wild type in luciferase reporter assays.

CONCLUSION

To our knowledge, c.-223C>T is the first homozygous point mutation in the GH1 promoter that leads to short stature due to IGHD.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Increased SGLT1 expression in salivary gland ductal cells correlates with hyposalivation in diabetic and hypertensive rats

BACKGROUND

Oral health complications in diabetes and hypertension include decreased salivary secretion. The sodium-glucose cotransporter 1 (SGLT1) protein, which transports 1 glucose/2 Na+/264 H2O molecules, is described in salivary glands. We hypothesized that changes in SGLT1 expression in the luminal membrane of ductal cell may be related to an altered salivary flow.

FINDINGS

By immunohistochemistry, we investigated SGLT1 expression in ductal cells of parotid and submandibular glands from Wistar Kyoto rats (WKY), diabetic WKY (WKY-D), spontaneously hypertensive rats (SHR) and diabetic SHR (SHR-D), as well as in parotid glands from WKY subjected to sympathetic stimulation, with or without previous propranolol blockade. Diabetes and hypertension decreased the salivary secretion and increased SGLT1 expression in the luminal membrane of ductal cells, and their association exacerbated the regulations observed. After 30 min of sympathetic stimulation, SGLT1 increased in the luminal membrane of ductal cells, and that was blocked by previous injection of propranolol.

CONCLUSIONS

SGLT1 expression increases in the luminal membrane of salivary gland ductal cells and the salivary flow decreases in diabetic and hypertensive rats, which may be related to sympathetic activity. This study highlights the water transporter role of SGLT1 in salivary glands, which, by increasing ductal water reabsorption, may explain the hyposalivation of diabetic and hypertensive subjects.

Identification of nuclear factor-κB sites in the Slc2a4 gene promoter

Glucose transporter GLUT4 protein, codified by Slc2a4 gene plays a key role in glycemic homeostasis. Insulin resistance, as in obesity, has been associated to inflammatory state, in which decreased GLUT4 is a feature. Inflammatory NF-κB transcriptional factor has been proposed as a repressor of Slc2a4; although, the binding site(s) in Slc2a4 promoter and the direct repressor effect have never been reported yet. A motif-based sequence analysis of mouse Slc2a4 promoter revealed two putative κB sites located inside -83/-62 and -134/-113 bp. Eletrophoretic mobility assay showed that p50 and p65 NF-κB subunits bind to both putative κB sites. Chromatin immunoprecipitation assay using genomic DNA from adipocytes confirmed p50- and p65-binding to Slc2a4 promoter. Moreover, transfection experiments revealed that NF-κB binds to the -134/-113bp region of the mouse Slc2a4 gene promoter, inhibiting the Slc2a4 gene transcription. The current findings demonstrate the existence of two κB sites in Slc2a4 gene promote, and that NF-κB has a direct repressor effect upon the Slc2a4 gene, providing an important link between insulin resistance and inflammation.

Cocoa flavanol metabolites activate HNF-3β, Sp1, and NFY-mediated transcription of apolipoprotein AI in human cells

SCOPE

To identify the mechanisms by which cocoa induces HDL levels and since apolipoprotein AI (ApoAI) is the major protein in HDLs, we analyzed, upon incubation with cocoa metabolites, ApoAI mRNA levels, its transcriptional regulation, and the levels of the transcription factors involved in this process.

METHODS AND RESULTS

Epicatechin and cocoa metabolites caused an increase in ApoAI expression in HepG2 cells. Electrophoretic mobility shift assays revealed the involvement of Sites A and B of the ApoAI promoter in the induction of ApoAI mRNA upon incubation with cocoa metabolites. Using supershift assays, we demonstrated the binding of HNF-3β, HNF-4, ER-α, and RXR-α to Site A and the binding of HNF-3β, NFY, and Sp1 to Site B. Luciferase assays performed with a construct containing Site B confirmed its role in the upregulation of ApoAI by cocoa metabolites. Incubation with 3-methyl-epicatechin led to an increase in HNF-3β mRNA, HNF-3β, ER-α, Sp1, and NFY protein levels and the activation of ApoAI transcription mediated by NFY, Sp1, and ER-α.

CONCLUSION

The activation of ApoAI transcription through Site B by cocoa flavanol metabolites is mainly mediated by an increase in HNF-3β, with a significant contribution of Sp1 and NFY, as a mechanism for the protective role of these compounds in cardiovascular diseases.

Renal function in diabetic disease models: the tubular system in the pathophysiology of the diabetic kidney

Diabetes mellitus affects the kidney in stages. At the onset of diabetes mellitus, in a subset of diabetic patients the kidneys grow large, and glomerular filtration rate (GFR) becomes supranormal, which are risk factors for developing diabetic nephropathy later in life. This review outlines a pathophysiological concept that focuses on the tubular system to explain these changes. The concept includes the tubular hypothesis of glomerular filtration, which states that early tubular growth and sodium-glucose cotransport enhance proximal tubule reabsorption and make the GFR supranormal through the physiology of tubuloglomerular feedback. The diabetic milieu triggers early tubular cell proliferation, but the induction of TGF-β and cyclin-dependent kinase inhibitors causes a cell cycle arrest and a switch to tubular hypertrophy and a senescence-like phenotype. Although this growth phenotype explains unusual responses like the salt paradox of the early diabetic kidney, the activated molecular pathways may set the stage for tubulointerstitial injury and diabetic nephropathy.

A fluorescence method for measurement of glucose transport in kidney cells

BACKGROUND

Diabetes may alter renal glucose reabsorption by sodium (Na(+))-dependent glucose transporters (SGLTs). Radiolabeled substrates are commonly used for in vitro measurements of SGLT activity in kidney cells. We optimized a method to measure glucose uptake using a fluorescent substrate, 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG).

METHODS

Uptake buffers for 2-NBDG were the same as for (14)C-labeled α-methyl-d-glucopyranoside ([(14)C]AMG). Cell lysis buffer was optimized for fluorescence of 2-NBDG and Hoechst DNA stain. Uptake was performed on cultures of primary mouse kidney cells (PMKCs), the LLC-PK(1) proximal tubule cell line, or COS-7 cells transiently overexpressing mouse SGLT1 or SGLT2 by incubating cells at 37°C in buffer containing 50-200 μM 2-NBDG. Microscopy was performed to visualize uptake in intact cells, while a fluorescence microplate reader was used to measure intracellular concentration of 2-NBDG ([2-NBDG](i)) in cell homogenates.

RESULTS

Fluorescent cells were observed in cultures of PMKCs and LLC-PK(1) cells exposed to 2-NBDG in the presence or absence of Na(+). In LLC-PK(1) cells, 2-NBDG transport in the presence of Na(+) had a maximum rate of 0.05 nmol/min/μg of DNA. In these cells, Na(+)-independent uptake of 2-NBDG was blocked with the GLUT inhibitor, cytochalasin B. The Na(+)-dependent uptake of 2-NBDG decreased in response to co-exposure to the SGLT substrate, AMG, and it could be blocked with the SGLT inhibitor, phlorizin. Immunocytochemistry showed overexpression of SGLT1 and SGLT2 in COS-7 cells, in which, in the presence of Na(+), [2-NBDG](i) was fivefold higher than in controls.

CONCLUSION

Glucose transport in cultured kidney cells can be measured with the fluorescence method described in this study.

Metabolomics reveals attenuation of the SLC6A20 kidney transporter in nonhuman primate and mouse models of type 2 diabetes mellitus

To enhance understanding of the metabolic indicators of type 2 diabetes mellitus (T2DM) disease pathogenesis and progression, the urinary metabolomes of well characterized rhesus macaques (normal or spontaneously and naturally diabetic) were examined. High-resolution ultra-performance liquid chromatography coupled with the accurate mass determination of time-of-flight mass spectrometry was used to analyze spot urine samples from normal (n = 10) and T2DM (n = 11) male monkeys. The machine-learning algorithm random forests classified urine samples as either from normal or T2DM monkeys. The metabolites important for developing the classifier were further examined for their biological significance. Random forests models had a misclassification error of less than 5%. Metabolites were identified based on accurate masses (<10 ppm) and confirmed by tandem mass spectrometry of authentic compounds. Urinary compounds significantly increased (p < 0.05) in the T2DM when compared with the normal group included glycine betaine (9-fold), citric acid (2.8-fold), kynurenic acid (1.8-fold), glucose (68-fold), and pipecolic acid (6.5-fold). When compared with the conventional definition of T2DM, the metabolites were also useful in defining the T2DM condition, and the urinary elevations in glycine betaine and pipecolic acid (as well as proline) indicated defective re-absorption in the kidney proximal tubules by SLC6A20, a Na(+)-dependent transporter. The mRNA levels of SLC6A20 were significantly reduced in the kidneys of monkeys with T2DM. These observations were validated in the db/db mouse model of T2DM. This study provides convincing evidence of the power of metabolomics for identifying functional changes at many levels in the omics pipeline.

The proximal tubule in the pathophysiology of the diabetic kidney

Diabetic nephropathy is a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved in the early changes of the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. This review focuses on the proximal tubule in the early diabetic kidney, particularly on its exposure and response to high glucose levels, albuminuria, and other factors in the diabetic glomerular filtrate, the hyperreabsorption of glucose, the unique molecular signature of the tubular growth phenotype, including aspects of senescence, and the resulting cellular and functional consequences. The latter includes the local release of proinflammatory chemokines and changes in proximal tubular salt and fluid reabsorption, which form the basis for the strong tubular control of glomerular filtration in the early diabetic kidney, including glomerular hyperfiltration and odd responses like the salt paradox. Importantly, these early proximal tubular changes can set the stage for oxidative stress, inflammation, hypoxia, and tubulointerstitial fibrosis, and thereby for the progression of diabetic renal disease.

Sodium-glucose transport: role in diabetes mellitus and potential clinical implications

PURPOSE OF REVIEW

Current options for glycemic control are less than optimal in terms of efficacy and to reduce complications in the diabetic population. Selective inhibition of SGLT2 in the proximal tubule increases urinary glucose excretion thereby reducing plasma glucose levels, which may present a novel therapeutic approach.

RECENT FINDINGS

SGLT2 inhibitors enhance glucose excretion and improve glycemic control in patients with type 2 diabetes in the absence of clinically relevant hypoglycemia or sustained changes in volume status or glomerular filtration rate. This is associated with lowering of body weight and may reduce systolic blood pressure. The increased glucosuria appears to increase the risk of genital infections but may not increase the risk of urinary tract infections.

SUMMARY

The ability of SGLT2 inhibitors to reduce plasma glucose without inducing increased insulin secretion, clinically relevant hypoglycemia, or weight gain constitutes a major advance. The ability to increase glucose excretion provides a powerful means to treat caloric excess conditions. Important questions remain to be resolved and more clinical research is needed on the long-term effects of SGLT2 inhibition. Potential extrarenal effects need to be explored in order to determine the safety of these compounds. It also remains to be determined whether these drugs lower the toxicity of glucose directly on renal cells, independent of hyperglycemia, which may slow or prevent the progressive nature of diabetic nephropathy.

Transcriptional regulation of glucose sensors in pancreatic β-cells and liver: an update

Pancreatic β-cells and the liver play a key role in glucose homeostasis. After a meal or in a state of hyperglycemia, glucose is transported into the β-cells or hepatocytes where it is metabolized. In the β-cells, glucose is metabolized to increase the ATP:ADP ratio, resulting in the secretion of insulin stored in the vesicle. In the hepatocytes, glucose is metabolized to CO(2), fatty acids or stored as glycogen. In these cells, solute carrier family 2 (SLC2A2) and glucokinase play a key role in sensing and uptaking glucose. Dysfunction of these proteins results in the hyperglycemia which is one of the characteristics of type 2 diabetes mellitus (T2DM). Thus, studies on the molecular mechanisms of their transcriptional regulations are important in understanding pathogenesis and combating T2DM. In this paper, we will review a recent update on the progress of gene regulation of glucose sensors in the liver and β-cells.