Spectrum of Renal Diseases Associated with Extreme Forms of Insulin Resistance

Inhibition of phosphodiesterase 5A by tadalafil improves SIRT1 expression and activity in insulin-resistant podocytes

A decrease in intracellular levels of 3',5'-cyclic guanosine monophosphate (cGMP) has been implicated in the progression of diabetic nephropathy. Hyperglycemia significantly inhibits cGMP-dependent pathway activity in the kidney, leading to glomerular damage and proteinuria. The enhancement of activity of this pathway that is associated with an elevation of cGMP levels may be achieved by inhibition of the cGMP specific phosphodiesterase 5A (PDE5A) using selective inhibitors, such as tadalafil. Hyperglycemia decreased the insulin responsiveness of podocytes and impaired podocyte function. These effects were associated with lower protein amounts and activity of the protein deacetylase sirtuin 1 (SIRT1) and a decrease in the phosphorylation of adenosine monophosphate-dependent protein kinase (AMPK). We found that PDE5A protein levels increased in hyperglycemia, and PDE5A downregulation improved the insulin responsiveness of podocytes with reestablished SIRT1 expression and activity. PDE5A inhibitors potentiate nitric oxide (NO)/cGMP signaling, and NO modulates the activity and expression of SIRT1. Therefore, we investigated the effects of tadalafil on SIRT1 and AMPK in the context of improving the insulin sensitivity in podocytes and podocyte function in hyperglycemia. Our study revealed that tadalafil restored SIRT1 expression and activity and activated AMPK by increasing its phosphorylation. Tadalafil also restored stimulating effect of insulin on glucose transport in podocytes with high glucose-induced insulin resistance. Additionally, tadalafil improved the function of podocytes that were exposed to high glucose concentrations. Our results display novel mechanisms involved in the pathogenesis of glomerulopathies in diabetes, which may contribute to the development of more effective treatment strategies for diabetic nephropathy.

Lipodystrophy for the Diabetologist-What to Look For

PURPOSE OF REVIEW

Genetic or acquired lipodystrophies are characterized by selective loss of body fat along with predisposition towards metabolic complications of insulin resistance, such as diabetes mellitus, hypertriglyceridemia, hepatic steatosis, polycystic ovarian syndrome, and acanthosis nigricans. In this review, we discuss the various subtypes and when to suspect and how to diagnose lipodystrophy.

RECENT FINDINGS

The four major subtypes are autosomal recessive, congenital generalized lipodystrophy (CGL); acquired generalized lipodystrophy (AGL), mostly an autoimmune disorder; autosomal dominant or recessive familial partial lipodystrophy (FPLD); and acquired partial lipodystrophy (APL), an autoimmune disorder. Diagnosis of lipodystrophy is mainly based upon physical examination findings of loss of body fat and can be supported by body composition analysis by skinfold measurements, dual-energy x-ray absorptiometry, and whole-body magnetic resonance imaging. Confirmatory genetic testing is helpful in the proband and at-risk family members with suspected genetic lipodystrophies. The treatment is directed towards the specific comorbidities and metabolic complications, and there is no treatment to reverse body fat loss. Metreleptin should be considered as the first-line therapy for metabolic complications in patients with generalized lipodystrophy and for prevention of comorbidities in children. Metformin and insulin therapy are the best options for treating hyperglycemia and fibrates and/or fish oil for hypertriglyceridemia. Lipodystrophy should be suspected in lean and muscular subjects presenting with diabetes mellitus, hypertriglyceridemia, non-alcoholic fatty liver disease, polycystic ovarian syndrome, or amenorrhea. Diabetologists should be aware of lipodystrophies and consider genetic varieties as an important subtype of monogenic diabetes.

The role of protein tyrosine phosphatase 1B (PTP1B) in the pathogenesis of type 2 diabetes mellitus and its complications

Insulin resistance, the most important characteristic of the type 2 diabetes mellitus (T2DM), is mostly caused by impairment in the insulin receptor (IR) signal transduction pathway. Protein tyrosine phosphatase 1B (PTP1B), one of the main negative regulators of the IR signaling pathway, is broadly expressed in various cells and tissues. PTP1B decreases the phosphorylation of the IR resulting in insulin resistance in various tissues. The evidence for the physiological role of PTP1B in regulation of metabolic pathways came from whole-body PTP1B-knockout mice. Whole-body and tissue-specific PTP1B-knockout mice showed improvement in adiposity, insulin resistance, and glucose tolerance. In addition, the key role of PTP1B in the pathogenesis of T2DM and its complications was further investigated in mice models of PTP1B deficient/overexpression. In recent years, targeting PTP1B using PTP1B inhibitors is being considered an attractive target to treat T2DM. PTP1B inhibitors improve the sensitivity of the insulin receptor and have the ability to cure insulin resistance-related diseases. We herein summarized the biological functions of PTP1B in different tissues in vivo and in vitro. We also describe the effectiveness of potent PTP1B inhibitors as pharmaceutical agents to treat T2DM.

GPR43 deficiency protects against podocyte insulin resistance in diabetic nephropathy through the restoration of AMPKα activity

Rationale: Albuminuria is an early clinical feature in the progression of diabetic nephropathy (DN). Podocyte insulin resistance is a main cause of podocyte injury, playing crucial roles by contributing to albuminuria in early DN. G protein-coupled receptor 43 (GPR43) is a metabolite sensor modulating the cell signalling pathways to maintain metabolic homeostasis. However, the roles of GPR43 in podocyte insulin resistance and its potential mechanisms in the development of DN are unclear.

Methods: The experiments were conducted by using kidney tissues from biopsied DN patients, streptozotocin (STZ) induced diabetic mice with or without global GPR43 gene knockout, diabetic rats treated with broad-spectrum oral antibiotics or fecal microbiota transplantation, and cell culture model of podocytes. Renal pathological injuries were evaluated by periodic acid-schiff staining and transmission electron microscopy. The expression of GPR43 with other podocyte insulin resistance related molecules was checked by immunofluorescent staining, real-time PCR, and Western blotting. Serum acetate level was examined by gas chromatographic analysis. The distribution of gut microbiota was measured by 16S ribosomal DNA sequencing with faeces.

Results: Our results demonstrated that GPR43 expression was increased in kidney samples of DN patients, diabetic animal models, and high glucose-stimulated podocytes. Interestingly, deletion of GPR43 alleviated albuminuria and renal injury in diabetic mice. Pharmacological inhibition and knockdown of GPR43 expression in podocytes increased insulin-induced Akt phosphorylation through the restoration of adenosine 5'-monophosphate-activated protein kinase α (AMPKα) activity. This effect was associated with the suppression of AMPKα activity through post-transcriptional phosphorylation via the protein kinase C-phospholipase C (PKC-PLC) pathway. Antibiotic treatment-mediated gut microbiota depletion, and faecal microbiota transplantation from the healthy donor controls substantially improved podocyte insulin sensitivity and attenuated glomerular injury in diabetic rats accompanied by the downregulation of the GPR43 expression and a decrease in the level of serum acetate.

Conclusion: These findings suggested that dysbiosis of gut microbiota-modulated GPR43 activation contributed to albuminuria in DN, which could be mediated by podocyte insulin resistance through the inhibition of AMPKα activity.

The good, the bad, and the ugly facets of insulin resistance

Insulin is a potent anabolic hormone, and binding to its receptor activates downstream intracellular signaling pathways that regulate the nutrient metabolism, fluid homeostasis, growth, ionic transport, maintenance of vascular tone, and other functions. Insulin resistance (IR) is a condition characterized by subnormal cellular response to physiological levels of insulin. The IR is divided into three types (prereceptor, receptor, and postreceptor) based on the site of pathology. Beta cells attempt to overcome the IR by increasing the release of insulin, leading to hyperinsulinemia. IR is the predisposing factor for many metabolic and cardiovascular disorders. From the evolutionary perspective, the presence of IR offers a survival advantage in the face of starvation or stress. In this brief review, we discuss the different facets of insulin resistance and appraise the readers about the hitherto neglected beneficial advantages.

A review of non-immune mediated kidney disease in systemic lupus erythematosus: A hypothetical model of putative risk factors

About half of patients with systemic lupus erythematosus (SLE) are diagnosed with lupus nephritis (LN). Patients with SLE are also at increased risk for diabetes, hypertension and obesity, which together account for >70% of end-stage renal disease in the general population. The frequencies of non-LN related causes of kidney disease, and their contribution to kidney disease development and progression among patients with SLE have been inadequately studied. We hypothesize that a substantial, and increasing proportion of kidney pathology in patients with SLE might not directly relate to LN but instead might be explained by non-immune mediated factors such as diabetes, hypertension, and obesity. The goal of the manuscript is to draw attention to hypertension, diabetes and obesity as potential alternative causes of kidney damage in patients with SLE. Further, we suggest that misclassification of kidney disease etiology in patients with SLE might have important ramifications for clinical trial recruitment, epidemiologic investigation, and clinical care. Future studies aiming to elucidate and distinguish discrete causes of kidney disease - both clinically and histologically - among patients with SLE are desperately needed as improved understanding of disease mechanisms is paramount to advancing therapeutic discovery. Collaboration among rheumatologists, pathologists, nephrologists, and endocrinologists, and the availability of dedicated research funding, will be critical to the success of such efforts.

Metabolomic Analysis of the Effects of Leptin Replacement Therapy in Patients with Lipodystrophy

Context and Objective

Leptin treatment has dramatic clinical effects on glucose and lipid metabolism in leptin-deficient patients with lipodystrophy. Further elucidation of metabolic effects of exogenous leptin therapy will shed light on understanding leptin physiology in humans. Our objective was to utilize metabolomic profiling to examine the changes associated with administration of short-term metreleptin therapy in patients with lipodystrophy.

Study Design

We conducted a pre-post-treatment study in 19 patients (75% female) with varying forms of lipodystrophy (congenital generalized lipodystrophy, n = 10; acquired generalized lipodystrophy, n = 1; familial partial lipodystrophy, n = 8) who received daily subcutaneous metreleptin injections for a period of 16 to 23 weeks. A 3-hour oral glucose tolerance test and body composition measurements were conducted before and after the treatment period, and fasting blood samples were used for metabolomic profiling. The study outcome aimed at measuring changes in physiologically relevant metabolites before and after leptin therapy.

Results

Metabolomic analysis revealed changes in pathways involving branched-chain amino acid metabolism, fatty acid oxidation, protein degradation, urea cycle, tryptophan metabolism, nucleotide catabolism, vitamin E, and steroid metabolism. Fold changes in pre- to post-treatment metabolite levels indicated increased breakdown of fatty acids, branched chain amino acids proteins, and nucleic acids.

Conclusions

Leptin replacement therapy has significant effects on important metabolic pathways implicated in patients with lipodystrophy. Continued metabolomic studies may provide further insight into the mechanisms of action of leptin replacement therapy and provide novel biomarkers of lipodystrophy.Abbreviations: 1,5-AG, 1,5-anhydroglucitol; 11βHSD1, 11-β hydroxysteroid dehydrogenase 1; BCAA, branched-chain amino acid; FFA, free fatty acid; GC-MS, gas chromatography mass spectrometry; IDO, indoleamine 2,3-dioxygenase; IFN-γ, interferon-γ; m/z, mass to charge ratio; OGTT, oral glucose tolerance test; TDO, tryptophan 2,3-dioxygenase; TNF-α, tumor necrosis factor-α; UPLC-MS/MS, ultra-performance liquid chromatography-tandem mass spectrometry.

Effects of metreleptin on proteinuria in patients with lipodystrophy

CONTEXT

Patients with lipodystrophy have high prevalence of proteinuria.

OBJECTIVE

To assess kidney disease in patients with generalized (GLD) versus partial lipodystrophy (PLD), and effects metreleptin on proteinuria in patients with lipodystrophy.

DESIGN/SETTING/PATIENTS/INTERVENTION

Prospective, open-label studies of metreleptin treatment in patients with GLD and PLD at the National Institutes of Health, Bethesda, MD.

OUTCOME MEASURES

24-hour urinary albumin and protein excretion rates, estimated glomerular filtration rate (eGFR), and creatinine clearance (CrCl) were measured at baseline and during up to 24 months of metreleptin treatment. Patients with increases in medications affecting outcome measures were excluded.

RESULTS

At baseline, patients with GLD had significantly greater albuminuria, proteinuria, eGFR, and CrCl compared to patients with PLD. CrCl was above the normal range in 69% of patients with GLD, and 39% with PLD (P=0.02). With up to 24 months of metreleptin treatment, there were significant reductions in albuminuria and proteinuria in patients with GLD, but not in those with PLD. No changes in eGFR or CrCl were observed in patients with GLD or PLD during metreleptin treatment.

CONCLUSIONS

Patients with GLD had significantly greater proteinuria than those with PLD, which improved with metreleptin treatment. The mechanisms leading to proteinuria in lipodystrophy and improvements in proteinuria with metreleptin are not clear. Hyperfiltration was also more common in GLD versus PLD but did not change with metreleptin.

Renal complications of lipodystrophy: A closer look at the natural history of kidney disease

OBJECTIVES

Lipodystrophy syndromes are a group of heterogeneous disorders characterized by adipose tissue loss. Proteinuria is a remarkable finding in previous reports.

STUDY DESIGN

In this multicentre study, prospective follow-up data were collected from 103 subjects with non-HIV-associated lipodystrophy registered in the Turkish Lipodystrophy Study Group database to study renal complications in treatment naïve patients with lipodystrophy.

METHODS

Main outcome measures included ascertainment of chronic kidney disease (CKD) by studying the level of proteinuria and the estimated glomerular filtration rate (eGFR). Kidney volume was measured. Percutaneous renal biopsies were performed in 9 patients.

RESULTS

Seventeen of 37 patients with generalized and 29 of 66 patients with partial lipodystrophy had CKD characterized by proteinuria, of those 12 progressed to renal failure subsequently. The onset of renal complications was significantly earlier in patients with generalized lipodystrophy. Patients with CKD were older and more insulin resistant and had worse metabolic control. Increased kidney volume was associated with poor metabolic control and suppressed leptin levels. Renal biopsies revealed thickening of glomerular basal membranes, mesangial matrix abnormalities, podocyte injury, focal segmental sclerosis, ischaemic changes and tubular abnormalities at various levels. Lipid vacuoles were visualized in electron microscopy images.

CONCLUSIONS

CKD is conspicuously frequent in patients with lipodystrophy which has an early onset. Renal involvement appears multifactorial. While poorly controlled diabetes caused by severe insulin resistance may drive the disease in some cases, inherent underlying genetic defects may also lead to cell autonomous mechanisms contributory to the pathogenesis of kidney disease.

Renal injury in Seipin-deficient lipodystrophic mice and its reversal by adipose tissue transplantation or leptin administration alone: adipose tissue-kidney crosstalk

Seipin deficiency is responsible for type 2 congenital generalized lipodystrophy with severe loss of adipose tissue (AT) and could lead to renal failure in humans. However, the effect of Seipin on renal function is poorly understood. Here we report that Seipin knockout (SKO) mice exhibited impaired renal function, enlarged glomerular and mesangial surface areas, renal depositions of lipid, and advanced glycation end products. Elevated glycosuria and increased electrolyte excretion were also detected. Relative renal gene expression in fatty acid oxidation and reabsorption pathways were impaired in SKO mice. Elevated glycosuria might be associated with reduced renal glucose transporter 2 levels. To improve renal function, AT transplantation or leptin administration alone was performed. Both treatments effectively ameliorated renal injury by improving all of the parameters that were measured in the kidney. The treatments also rescued insulin resistance and low plasma leptin levels in SKO mice. Our findings demonstrate for the first time that Seipin deficiency induces renal injury, which is closely related to glucolipotoxicity and impaired renal reabsorption in SKO mice, and is primarily caused by the loss of AT and especially the lack of leptin. AT transplantation and leptin administration are two effective treatments for renal injury in Seipin-deficient mice.-Liu, X.-J., Wu, X.-Y., Wang, H., Wang, S.-X., Kong, W., Zhang, L., Liu, G., Huang, W. Renal injury in Seipin-deficient lipodystrophic mice and its reversal by adipose tissue transplantation or leptin administration alone: adipose tissue-kidney crosstalk.

Glucose Transporters in Diabetic Kidney Disease-Friends or Foes?

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes and a common cause of end-stage renal disease worldwide. DKD manifests as an increased urinary protein excretion (albuminuria). Multiple studies have shown that insulin resistance correlates with the development of albuminuria in non-diabetic and diabetic patients. There is also accumulating evidence that glomerular epithelial cells or podocytes are insulin sensitive and that insulin signaling in podocytes is essential for maintaining normal kidney function. At the cellular level, the mechanisms leading to the development of insulin resistance include mutations in the insulin receptor gene, impairments in the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway, or perturbations in the trafficking of glucose transporters (GLUTs), which mediate the uptake of glucose into cells. Podocytes express several GLUTs, including GLUT1, GLUT2, GLUT3, GLUT4, and GLUT8. Of these, the most studied ones are GLUT1 and GLUT4, both shown to be insulin responsive in podocytes. In the basal state, GLUT4 is preferentially located in perinuclear and cytosolic vesicular structures and to a lesser extent at the plasma membrane. After insulin stimulation, GLUT4 is sorted into GLUT4-containing vesicles (GCVs) that translocate to the plasma membrane. GCV trafficking consists of several steps, including approaching of the GCVs to the plasma membrane, tethering, and docking, after which the lipid bilayers of the GCVs and the plasma membrane fuse, delivering GLUT4 to the cell surface for glucose uptake into the cell. Studies have revealed novel molecular regulators of the GLUT trafficking in podocytes and unraveled unexpected roles for GLUT1 and GLUT4 in the development of DKD, summarized in this review. These findings pave the way for better understanding of the mechanistic pathways associated with the development and progression of DKD and aid in the development of new treatments for this devastating disease.

The Evolving Importance of Insulin Signaling in Podocyte Health and Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease worldwide, occuring in approximately one-third of diabetic patients. One of the earliest hallmarks of DKD is albuminuria, often occurring following disruptions to the glomerular filtration barrier. Podocytes are highly specialized cells with a central role in filtration barrier maintenance; hence, podocyte dysfunction is a major cause of albuminuria in many settings, including DKD. Numerous studies over the last decade have highlighted the importance of intact podocyte insulin responses in the maintenance of podocyte function. This review summarizes our current perspectives on podocyte insulin signaling, highlighting evidence to support the notion that dysregulated podocyte insulin responses contribute toward podocyte damage, particularly during the pathogenesis of DKD.

Prolonged exposure of mouse and human podocytes to insulin induces insulin resistance through lysosomal and proteasomal degradation of the insulin receptor

AIMS/HYPOTHESIS

Podocytes are insulin-responsive cells of the glomerular filtration barrier and are key in preventing albuminuria, a hallmark feature of diabetic nephropathy. While there is evidence that a loss of insulin signalling to podocytes is detrimental, the molecular mechanisms underpinning the development of podocyte insulin resistance in diabetes remain unclear. Thus, we aimed to further investigate podocyte insulin responses early in the context of diabetic nephropathy.

METHODS

Conditionally immortalised human and mouse podocyte cell lines and glomeruli isolated from db/db DBA/2J mice were studied. Podocyte insulin responses were investigated with western blotting, cellular glucose uptake assays and automated fluorescent imaging of the actin cytoskeleton. Quantitative (q)RT-PCR was employed to investigate changes in mRNA. Human cell lines stably overproducing the insulin receptor (IR) and nephrin were also generated, using lentiviral constructs.

RESULTS

Podocytes exposed to a diabetic environment (high glucose, high insulin and the proinflammatory cytokines TNF-α and IL-6) become insulin resistant with respect to glucose uptake and activation of phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signalling. These podocytes lose expression of the IR as a direct consequence of prolonged exposure to high insulin concentrations, which causes an increase in IR protein degradation via a proteasome-dependent and bafilomycin-sensitive pathway. Reintroducing the IR into insulin-resistant human podocytes rescues upstream phosphorylation events, but not glucose uptake. Stable expression of nephrin is also required for the insulin-stimulated glucose uptake response in podocytes and for efficient insulin-stimulated remodelling of the actin cytoskeleton.

CONCLUSIONS/INTERPRETATION

Together, these results suggest that IR degradation, caused by high levels of insulin, drives early podocyte insulin resistance, and that both the IR and nephrin are required for full insulin sensitivity of this cell. This could be highly relevant for the development of nephropathy in individuals with type 2 diabetes, who are commonly hyperinsulinaemic in the early phases of their disease.

Sodium Glucose Cotransporter-2 Inhibition in Heart Failure: Potential Mechanisms, Clinical Applications, and Summary of Clinical Trials

Despite current established therapy, heart failure (HF) remains a leading cause of hospitalization and mortality worldwide. Novel therapeutic targets are therefore needed to improve the prognosis of patients with HF. The EMPA-REG OUTCOME trial ([Empagliflozin] Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients) demonstrated significant reductions in mortality and HF hospitalization risk in patients with type 2 diabetes mellitus (T2D) and cardiovascular disease with the antihyperglycemic agent, empagliflozin, a sodium glucose cotransporter 2 (SGLT2) inhibitor. The CANVAS trial (Canagliflozin Cardiovascular Assessment Study) subsequently reported a reduction in 3-point major adverse cardiovascular events and HF hospitalization risk. Although SGLT2 inhibition may have potential application beyond T2D, including HF, the mechanisms responsible for the cardioprotective effects of SGLT2 inhibitors remain incompletely understood. SGLT2 inhibition promotes natriuresis and osmotic diuresis, leading to plasma volume contraction and reduced preload, and decreases in blood pressure, arterial stiffness, and afterload as well, thereby improving subendocardial blood flow in patients with HF. SGLT2 inhibition is also associated with preservation of renal function. Based on data from mechanistic studies and clinical trials, large clinical trials with SGLT2 inhibitors are now investigating the potential use of SGLT2 inhibition in patients who have HF with and without T2D. Accordingly, in this review, we summarize the key pharmacodynamic effects of SGLT2 inhibitors and the clinical evidence that support the rationale for the use of SGLT2 inhibitors in patients with HF who have T2D. Because these favorable effects presumably occur independent of blood glucose lowering, we also explore the potential use of SGLT2 inhibition in patients without T2D with HF or at risk of HF, such as in patients with coronary artery disease or hypertension. Finally, we provide a detailed overview and summary of ongoing cardiovascular outcome trials with SGLT2 inhibitors.

Deficient Insulin-mediated Upregulation of the Equilibrative Nucleoside Transporter 2 Contributes to Chronically Increased Adenosine in Diabetic Glomerulopathy

Deficient insulin signaling is a key event mediating diabetic glomerulopathy. Additionally, diabetic kidney disease has been related to increased levels of adenosine. Therefore, we tested a link between insulin deficiency and dysregulated activity of the equilibrative nucleoside transporters (ENTs) responsible for controlling extracellular levels of adenosine. In ex vivo glomeruli, high D-glucose decreased nucleoside uptake mediated by ENT1 and ENT2 transporters, resulting in augmented extracellular levels of adenosine. This condition was reversed by exposure to insulin. Particularly, insulin through insulin receptor/PI3K pathway markedly upregulated ENT2 uptake activity to restores the extracellular basal level of adenosine. Using primary cultured rat podocytes as a cellular model, we found insulin was able to increase ENT2 maximal velocity of transport. Also, PI3K activity was necessary to maintain ENT2 protein levels in the long term. In glomeruli of streptozotocin-induced diabetic rats, insulin deficiency leads to decreased activity of ENT2 and chronically increased extracellular levels of adenosine. Treatment of diabetic rats with adenosine deaminase attenuated both the glomerular loss of nephrin and proteinuria. In conclusion, we evidenced ENT2 as a target of insulin signaling and sensitive to dysregulation in diabetes, leading to chronically increased extracellular adenosine levels and thereby setting conditions conducive to kidney injury.

Familial partial lipodystrophy and proteinuric renal disease due to a missense c.1045C > T LMNA mutation

Proteinuric renal disease is prevalent in congenital or acquired forms of generalized lipodystrophy. In contrast, an association between familial partial lipodystrophy (FPLD) and renal disease has been documented in very few cases. A 22-year-old female patient presented with impaired glucose tolerance, hyperinsulinemia, hirsutism and oligomenorrhea. On examination, there was partial loss of subcutaneous adipose tissue in the face, upper and lower limbs, bird-like facies with micrognathia and low set ears and mild acanthosis nigricans. Laboratory investigations revealed hyperandrogenism, hyperlipidemia, elevated serum creatine kinase and mild proteinuria. A clinical diagnosis of FPLD of the non-Dunnigan variety was made; genetic testing revealed a heterozygous c.1045C > T mutation in exon 6 of the LMNA gene, predicted to result in an abnormal LMNA protein (p.R349W). Electromyography and muscle biopsy were suggestive of non-specific myopathy. Treatment with metformin and later with pioglitazone was initiated. Due to worsening proteinuria, a renal biopsy was performed; histological findings were consistent with mild focal glomerular mesangioproliferative changes, and the patient was started on angiotensin-converting enzyme inhibitor therapy. This is the fourth report of FPLD associated with the c.1045C > T missense LMNA mutation and the second with co-existent proteinuric renal disease. Patients carrying this specific mutation may exhibit a phenotype that includes partial lipodystrophy, proteinuric nephropathy, cardiomyopathy and atypical myopathy.

Persistent Insulin Resistance in Podocytes Caused by Epigenetic Changes of SHP-1 in Diabetes

Poor glycemic control profoundly affects protein expression and the cell signaling action that contributes to glycemic memory and irreversible progression of diabetic nephropathy (DN). We demonstrate that SHP-1 is elevated in podocytes of diabetic mice, causing insulin unresponsiveness and DN. Thus, sustained SHP-1 expression caused by hyperglycemia despite systemic glucose normalization could contribute to the glycemic memory effect in DN. Microalbuminuria, glomerular filtration rate, mesangial cell expansion, and collagen type IV and transforming growth factor-β expression were significantly increased in diabetic Ins2^+/C96Y mice compared with nondiabetic Ins2^+/+ mice and remained elevated despite glucose normalization with insulin implants. A persistent increase of SHP-1 expression in podocytes despite normalization of systemic glucose levels was associated with sustained inhibition of the insulin signaling pathways. In cultured podocytes, high glucose levels increased mRNA, protein expression, and phosphatase activity of SHP-1, which remained elevated despite glucose concentration returning to normal, causing persistent insulin receptor-β inhibition. Histone posttranslational modification analysis showed that the promoter region of SHP-1 was enriched with H3K4me1 and H3K9/14ac in diabetic glomeruli and podocytes, which remained elevated despite glucose level normalization. Hyperglycemia induces SHP-1 promoter epigenetic modifications, causing its persistent expression and activity and leading to insulin resistance, podocyte dysfunction, and DN.

High Glucose Impairs Insulin Signaling in the Glomerulus: An In Vitro and Ex Vivo Approach

Objective

Chronic hyperglycaemia, as seen in type II diabetes, results in both morphological and functional impairments of podocytes in the kidney. We investigated the effects of high glucose (HG) on the insulin signaling pathway, focusing on cell survival and apoptotic markers, in immortalized human glomerular cells (HGEC; podocytes) and isolated glomeruli from healthy rats.

Methods and Findings

HGEC and isolated glomeruli were cultured for various time intervals under HG concentrations in the presence or absence of insulin. Our findings indicated that exposure of HGEC to HG led to downregulation of all insulin signaling markers tested (IR, p-IR, IRS-1, p-Akt, p-Fox01,03), as well as to increased sensitivity to apoptosis (as seen by increased PARP cleavage, Casp3 activation and DNA fragmentation). Short insulin pulse caused upregulation of insulin signaling markers (IR, p-IR, p-Akt, p-Fox01,03) in a greater extent in normoglycaemic cells compared to hyperglycaemic cells and for the case of p-Akt, in a PI3K-dependent manner. IRS-1 phosphorylation of HG-treated podocytes was negatively regulated, favoring serine versus tyrosine residues. Prolonged insulin treatment caused a significant decrease of IR levels, while alterations in glucose concentrations for various time intervals demonstrated changes of IR, p-IR and p-Akt levels, suggesting that the IR signaling pathway is regulated by glucose levels. Finally, HG exerted similar effects in isolated glomeruli.

Conclusions

These results suggest that HG compromises the insulin signaling pathway in the glomerulus, promoting a proapoptotic environment, with a possible critical step for this malfunction lying at the level of IRS-1 phosphorylation; thus we herein demonstrate glomerular insulin signaling as another target for investigation for the prevention and/ or treatment of diabetic nephropathy.

Metreleptin for injection to treat the complications of leptin deficiency in patients with congenital or acquired generalized lipodystrophy

The lipodystrophies represent a class of diseases characterized by leptin deficiency. Leptin deficiency is associated with a severe form of the metabolic syndrome characterized by dyslipidemia, insulin resistance, diabetes, and ovarian dysfunction. Metreleptin is the pharmaceutical derived product that has been approved by the Food and Drug Administration (FDA) to treat the severe metabolic abnormalities of the generalized forms of lipodystrophy. Herein we describe the properties of metreleptin, its use in patients, which includes the administration of the drug and how it may be acquired by medical professionals as well as its safety, tolerability, and properties. Finally, we speculate on future uses and development of metreleptin.

Insulin signaling: implications for podocyte biology in diabetic kidney disease

PURPOSE OF REVIEW

Several key elements of the insulin signaling cascade contribute to podocyte function and survival. While it was initially thought that the consequences of altered insulin signaling to podocyte function was strictly related to altered glucose uptake, it has become clear that upstream signaling events involved in cell survival, lipid metabolism or nutrient sensing and modulated by insulin are strong independent contributors to podocyte function.

RECENT FINDINGS

Akt2, the major isoform of Akt activated following cellular insulin stimulation, protects against the progression of renal disease in nephron-deficient mice, and podocyte-specific deletion of Akt2 results in a more rapid progression of experimental glomerular disease. In diabetes, podocyte mammalian target of rapamycin activation clearly contributes to podocyte injury and regulated autophagy. Furthermore, podocyte-specific glucose transporter type 4 (GLUT4) deficiency protects podocytes by preventing mammalian target of rapamycin signaling independently of glucose uptake. Finally, intracellular lipids have been recently recognized as major modulators of podocyte insulin signaling and as a new therapeutic target.

SUMMARY

The identification of new contributors to podocyte insulin signaling is of extreme translational value as it may lead to new drug development strategies for diabetic kidney disease, as well as for other proteinuric kidney diseases.

Podocyte-specific GLUT4-deficient mice have fewer and larger podocytes and are protected from diabetic nephropathy

Podocytes are a major component of the glomerular filtration barrier, and their ability to sense insulin is essential to prevent proteinuria. Here we identify the insulin downstream effector GLUT4 as a key modulator of podocyte function in diabetic nephropathy (DN). Mice with a podocyte-specific deletion of GLUT4 (G4 KO) did not develop albuminuria despite having larger and fewer podocytes than wild-type (WT) mice. Glomeruli from G4 KO mice were protected from diabetes-induced hypertrophy, mesangial expansion, and albuminuria and failed to activate the mammalian target of rapamycin (mTOR) pathway. In order to investigate whether the protection observed in G4 KO mice was due to the failure to activate mTOR, we used three independent in vivo experiments. G4 KO mice did not develop lipopolysaccharide-induced albuminuria, which requires mTOR activation. On the contrary, G4 KO mice as well as WT mice treated with the mTOR inhibitor rapamycin developed worse adriamycin-induced nephropathy than WT mice, consistent with the fact that adriamycin toxicity is augmented by mTOR inhibition. In summary, GLUT4 deficiency in podocytes affects podocyte nutrient sensing, results in fewer and larger cells, and protects mice from the development of DN. This is the first evidence that podocyte hypertrophy concomitant with podocytopenia may be associated with protection from proteinuria.

Cosegregation of focal segmental glomerulosclerosis in a family with familial partial lipodystrophy due to a mutation in LMNA

BACKGROUND AND AIM

Focal segmental glomerulosclerosis (FSGS) is a common cause of idiopathic nephrotic syndrome in adults (35%). A number of genetic and familial forms of FSGS have been recognized. Here, we report a large pedigree with a pathogenic mutation in LMNA (R349W) in which four members were found to have biopsy-proven FSGS. The LMNA gene codes for lamins A and C, major components of the nuclear lamina which function in nuclear architecture, integrity and the regulation of gene expression.

METHODS

Pedigree screening and mutation analysis of LMNA gene in all family members. Renal biopsies were performed in proteinuric patients. A molecular 3D model of the familial LMNA mutation was constructed.

RESULTS

There were a total of 16 affected members from four generations, 12 of whom were found to carry the germline LMNA mutation. All affected adults had clinical features of familial partial lipodystrophy (FPLD) of the non-Dunnigan variety. Four patients within the same generation presented with a variable degree of renal impairment and proteinuria. Renal biopsies from all four revealed FSGS. The familial mutation is a missense change (R349W) in exon 6 of LMNA (c.1045C>T).

CONCLUSIONS

We report a genetic link between LMNA and biopsy-proven FSGS in a large pedigree with FPLD. This unexpected association extends the disease spectrum of LMNA to the kidney and suggests that the physiological role of LMNA could be relevant to the maintenance of glomerular structure and function.

Expression of SHP-1 induced by hyperglycemia prevents insulin actions in podocytes

Renal podocyte apoptosis is an early event of diabetic nephropathy progression. Insulin action is critical for podocyte survival. Previous studies demonstrated that Src homology-2 domain-containing phosphatase-1 (SHP-1) is elevated in renal cortex of type 1 diabetic mice; we hypothesized that hyperglycemia-induced SHP-1 expression may affect insulin actions in podocytes. Type 1 diabetic Akita mice (Ins2(+/C96Y)) developed elevated foot process effacement and podocyte apoptosis compared with control littermate mice (Ins2(+/+)). In contrast to Ins2(+/+) mice, insulin-stimulated protein kinase B (Akt) and extracellular signal-regulated kinase (ERK) phosphorylation were remarkably reduced in renal podocytes of Akita mice. This renal insulin resistance was associated with elevated SHP-1 expression in the glomeruli. Cultured podocytes exposed to high glucose concentration (HG; 25 mM) for 96 h exhibited high levels of apoptotic markers and caspase-3/7 enzymatic activity. HG exposure raised mRNA and protein levels of SHP-1 and reduced the insulin-signaling pathway in podocytes. Overexpression of dominant-negative SHP-1 in podocytes prevented HG effects and restored insulin actions. Elevated SHP-1 expression induced by high glucose levels was directly associated with insulin receptor-β in vitro and in vivo to prevent insulin-stimulated Akt and ERK phosphorylation. In conclusion, our results showed that high levels of SHP-1 expression in glomeruli cause insulin resistance and podocyte loss, thereby contributing to diabetic nephropathy.

Insulin signalling to the kidney in health and disease

Ninety-one years ago insulin was discovered, which was one of the most important medical discoveries in the past century, transforming the lives of millions of diabetic patients. Initially insulin was considered only important for rapid control of blood glucose by its action on a restricted number of tissues; however, it has now become clear that this hormone controls an array of cellular processes in many different tissues. The present review will focus on the role of insulin in the kidney in health and disease.

Exploring metabolic dysfunction in chronic kidney disease

Impaired kidney function and chronic kidney disease (CKD) leading to kidney failure and end-stage renal disease (ESRD) is a serious medical condition associated with increased morbidity, mortality, and in particular cardiovascular disease (CVD) risk. CKD is associated with multiple physiological and metabolic disturbances, including hypertension, dyslipidemia and the anorexia-cachexia syndrome which are linked to poor outcomes. Specific hormonal, inflammatory, and nutritional-metabolic factors may play key roles in CKD development and pathogenesis. These include raised proinflammatory cytokines, such as interleukin-1 and −6, tumor necrosis factor, altered hepatic acute phase proteins, including reduced albumin, increased C-reactive protein, and perturbations in normal anabolic hormone responses with reduced growth hormone-insulin-like growth factor-1 axis activity. Others include hyperactivation of the renin-angiotensin aldosterone system (RAAS), with angiotensin II and aldosterone implicated in hypertension and the promotion of insulin resistance, and subsequent pharmacological blockade shown to improve blood pressure, metabolic control and offer reno-protective effects. Abnormal adipocytokine levels including leptin and adiponectin may further promote the insulin resistant, and proinflammatory state in CKD. Ghrelin may be also implicated and controversial studies suggest activities may be reduced in human CKD, and may provide a rationale for administration of acyl-ghrelin. Poor vitamin D status has also been associated with patient outcome and CVD risk and may indicate a role for supplementation. Glucocorticoid activities traditionally known for their involvement in the pathogenesis of a number of disease states are increased and may be implicated in CKD-associated hypertension, insulin resistance, diabetes risk and cachexia, both directly and indirectly through effects on other systems including activation of the mineralcorticoid receptor. Insight into the multiple factors altered in CKD may provide useful information on disease pathogenesis, clinical assessment and treatment rationale such as potential pharmacological, nutritional and exercise therapies.

The long-term renal and cardiovascular consequences of prematurity

Infants born prematurely at <37 weeks' gestation account for over 80% of infants weighing <2,500 g at birth-low birth weight (LBW) infants. This designation remains the surrogate marker for developmental origins of adult disease. Landmark studies spanning four decades have shown that individuals born with a LBW are more likely to develop cardiovascular and renal disease in later life, which is believed to be related to 'developmental programming' of such adult disease during vulnerable periods of growth in utero and in the early postnatal period. There has long been ambiguity regarding the distinction between infants with intrauterine growth restriction and preterm infants since both show a low nephron endowment that is associated with subsequent hypertension and chronic kidney disease. Knowledge is growing specific to the preterm infant and the developmental associations of being born preterm with the interruption of normal organogenesis relative to the vascular tree and kidney. Both systems develop by branching morphogenesis and interruptions lead to considerable deficits in their structure and function. These developmental aberrations can lead to endothelial dysfunction, hypertension, proteinuria and metabolic abnormalities that persist throughout life. This Review will examine the effect of preterm birth on the development of cardiovascular and kidney disease in later life and will also discuss potential early interventions to alter the progression of disease.

Insulin and metformin may prevent renal injury in young type 2 diabetic Goto-Kakizaki rats

Type 2 diabetes is increasing at epidemic proportions throughout the world, and diabetic nephropathy is the principal cause of end stage renal failure. Approximately 40% of patients with type 2 diabetes may progress to nephropathy and a good metabolic control can prevent the development of diabetic renal injury. The aim of our study was to evaluate, in young type 2 diabetic Goto-Kakizaki (GK) rats fed with atherogenic diet, the effects of the anti-diabetic compounds insulin, metformin and gliclazide on renal damage. GK rats fed with atherogenic diet showed increased body weight and fasting blood glucose, total cholesterol, triglycerides, C-reactive protein and protein carbonyl levels and lower HDL-cholesterol concentration; renal markers of inflammation and fibrosis were also elevated. All the anti-diabetic agents ameliorated fasting glycaemia and insulin resistance but only insulin and metformin were able to improve glycoxidation, fibrosis and inflammation kidney parameters. Our data suggest that insulin and metformin treatments, improving glicoxidative, inflammatory and fibrotic renal damage markers, play a key role in the prevention of diabetic nephropathy.

Renal Doppler indices in diabetic children with insulin resistance syndrome

End-stage renal failure is still a leading cause of mortality among type 1 diabetes patients. Insulin resistance plays a larger role in type 1 diabetes disease process than is commonly recognized. Detection of diabetic nephropathy as early as possible currently offers the best chance of delaying or possibly preventing progression to end-stage disease. Renal resistive index (RI) and pulsatility index (PI), measured using renal Doppler ultrasonography, reflect intrarenal vascular resistance. The present work aimed at examining renal Doppler indices (RI and PI) in type 1 diabetic children and their relation to features of insulin resistance and other established parameters of early diabetic nephropathy as microalbuminuria. One hundred diabetic children with a mean age of 13.4 ± 2.9 yr and an average diabetes duration of (7.2 ± 2.5 yr) were included. Thirty healthy children served as controls. All renal Doppler indices were significantly higher in children with type 1 diabetes mellitus (p ≤ 0.01). The worst parameters were observed in children diagnosed with insulin resistance syndrome (IRS) (38%), hypertensive (12%), and obese (4%) children. Resistive index showed a significant correlation to blood pressure (r = 0.2, p = 0.04), waist-hip ratio (r = 0.5, p = 0.02), insulin dose (r = 0.2, p = 0.02) and estimated glucose disposal rate (r = -0.5, p = 0.01). No correlation was noted to microalbuminuria, HbA1c, or duration of diabetes. The present work concluded that renal Doppler indices are worse in diabetic children and particularly those with IRS. These children appear to be at graver risk for diabetic nephropathy. In these patients adding renal Doppler assessment to their work up, might diagnose diabetic nephropathy at a prealbuminuric stage.

Efficacy of leptin therapy in the different forms of human lipodystrophy

AIMS/HYPOTHESIS

Lipodystrophy is a rare disorder characterised by loss of adipose tissue, hypoleptinaemia, severe insulin resistance, diabetes and dyslipidaemia. The aims of this study were to determine whether leptin replacement in lipodystrophy patients ameliorates their metabolic abnormalities over an extended period of time and whether leptin therapy is effective in the different forms of lipodystrophy.

METHODS

We conducted an open-label prospective study of patients with acquired forms of lipodystrophy and inherited forms of lipodystrophy secondary to mutations in the AGPAT2, SEIPIN (also known as BSCL2), LMNA and PPARgamma (also known as PPARG) genes. Between July 2000 and November 2008, 48 patients with lipodystrophy were treated with s.c. recombinant methionyl human leptin.

RESULTS

Serum triacylglycerol and HbA(1c) levels declined dramatically with leptin therapy. Among 35 patients with data at baseline and 12 months, serum triacylglycerol fell by 59% (from 10.18 +/- 2.67 mmol/l to 4.16 +/- 0.99 mmol/l [means +/- SE]; p = 0.008) and HbA(1c) decreased by 1.5 percentage points (from 8.4 +/- 0.3% to 6.9 +/- 0.3%; p < 0.001). A significant reduction was seen in total cholesterol and a trend towards reduction was observed in LDL-cholesterol at 12 months. HDL-cholesterol was unchanged. Among generalised lipodystrophy patients, proteinuria diminished with leptin replacement. Patients with both acquired and inherited forms of lipodystrophy experienced decreases in serum triacylglycerol and HbA(1c) levels.

CONCLUSIONS/INTERPRETATION

Leptin replacement in lipodystrophy patients leads to significant and sustained improvements in glycaemic control and dyslipidaemia. Leptin is effective in the various forms of lipodystrophy, whether they are acquired or inherited, generalised or partial.

TRIAL REGISTRATION

ClinicalTrials.gov ID NCT00025883

FUNDING

This work was supported by intramural research funding from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the National Institutes of Health (NIH).

Role of altered insulin signaling pathways in the pathogenesis of podocyte malfunction and microalbuminuria

PURPOSE OF REVIEW

In diabetic nephropathy, insulin resistance and hyperinsulinemia correlate with the development of albuminuria. The possibility that altered insulin signaling in glomerular cells and particularly podocytes contributes to the development of diabetic nephropathy will be discussed.

RECENT FINDINGS

Whereas normal podocytes take up glucose in response to insulin, diabetic podocytes become insulin resistant in experimental diabetic nephropathy prior to the development of significant albuminuria. Both clinical and experimental data suggest that insulin sensitizers may be renoprotective independent of their systemic effects on the metabolic control of diabetes.

SUMMARY

We will review the clinical and experimental evidence that altered insulin signaling correlates with the development of diabetic nephropathy in both type 1 and type 2 diabetes, and that insulin sensitizers may be superior to other hypoglycemic agents in the prevention of diabetic nephropathy. We will then review potential mechanisms by which altered podocyte insulin signaling may contribute to the development of diabetic nephropathy. Understanding the role of podocytes in glucose metabolism is important because it may lead to the discovery of novel pathogenetic mechanisms of diabetic nephropathy, it may affect current strategies for prevention and treatment of diabetic nephropathy, and it may allow the identification of novel therapeutic targets.

A case of Dunnigan-type familial partial lipodystrophy (FPLD) due to lamin A/C (LMNA) mutations complicated by end-stage renal disease

Dunnigan-type familial partial lipodystrophy (FPLD) is a rare monogenic adipose tissue disorder in which the affected subjects have increased predisposition to insulin resistance and related metabolic complications, such as glucose intolerance, diabetes, dyslipidemia, and hepatic steatosis. Our patient was a 35-year-old female who had been receiving insulin injection therapy for diabetes mellitus and was transferred to our hospital. She was diagnosed with FPLD on the basis of the following symptoms: increase in subcutaneous fat in the face, neck, and upper trunk; loss of subcutaneous fat in the lower limbs and the gluteal region. We found a heterozygous CGG to CAG transition in codon 482 of exon 8 in the gene encoding lamin A/C (LMNA), which leads to an arginine to glutamine substitution (R482Q). At the time of admission, her serum creatinine level was 8.4 mg/dl, and her blood urea nitrogen (BUN) level was 81 mg/dl. Her serum creatinine level was elevated and hemodialysis was performed twice every week. However, she died of cerebral hemorrhage 9 months after hemodialysis. Although it is uncommon for patients with FPLD to exhibit renal dysfunction and require hemodialysis, this case suggests the need for careful analysis of renal function in a patient with FPLD.

Inhibition of C-jun N-terminal kinase improves insulin sensitivity but worsens albuminuria in experimental diabetes

C-jun N-terminal kinase (JNK) regulates both the development of insulin resistance and inflammation. Podocytes of the widely used db/db mouse model of diabetic nephropathy lose their ability to respond to insulin as albuminuria develops, in comparison to control db/+ mice. Here we tested whether JNK inhibition or its gene deletion would prevent albuminuria in experimental diabetes. Phosphorylated/total JNK was significantly increased in vivo in glomeruli of db/db compared to db/+ mice. Treatment of podocytes isolated from these two strains of mice with tumor necrosis factor-alpha caused greater phosphorylation of JNK in those obtained from diabetic animals. When db/db mice were treated with a cell-permeable TAT-JNK inhibitor peptide, their insulin sensitivity and glycemia significantly improved compared to controls. We induced diabetes in JNK1 knockout mice with streptozotocin and found that they had significantly better insulin sensitivity compared to diabetic wild-type or JNK2 knockout mice. Albuminuria was, however, worse in all mice treated with the JNK inhibitor and in diabetic JNK2 knockout mice compared to controls. Nephrin expression was also reduced in JNK inhibitor-treated mice compared to controls. A similar degree of mesangial expansion was found in all diabetic mice. Our study shows that targeting JNK to improve systemic insulin sensitivity does not necessarily prevent diabetic nephropathy.