Reversibility of structural and functional damage in a model of advanced diabetic nephropathy

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 Injury Repair: How About the Role of Stem Cells

Renal failure is one of the most important causes of mortality and morbidity all over the world. Acute kidney injury (AKI) is a major clinical problem that affects up to 5% of all hospitalized patients. Although the kidney has a remarkable capacity for regeneration after acute injury, the mortality among patients with severe AKI remains dismally high, and in clinical practice, most patients cannot be cured completely and suffer from chronic kidney disease (CKD). Recently, the incidence and prevalence of CKD have increased, largely as a result of the enhanced prevalence of diabetes and obesity. The progressive nature of CKD and the ensuing end-stage renal disease (ESRD) place a substantial burden on global healthcare resources. Currently, dialysis and transplantation remain the only treatment options. Finding new therapeutic methods to fight AKI and CKD remains an ongoing quest. Although the human renal histological structure is complex, stem cell therapies have been applied to repair injured kidneys. The curative effects of mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), induced pluripotent stem cells (iPSCs), and nephron progenitor cells (NPCs) on renal repair have also been reported by researchers. This review focuses on stem cell therapy and mechanisms for renal injury repair.

Mathematical model of hemodynamic mechanisms and consequences of glomerular hypertension in diabetic mice

Many preclinically promising therapies for diabetic kidney disease fail to provide efficacy in humans, reflecting limited quantitative translational understanding between rodent models and human disease. To quantitatively bridge interspecies differences, we adapted a mathematical model of renal function from human to mice, and incorporated adaptive and pathological mechanisms of diabetes and nephrectomy to describe experimentally observed changes in glomerular filtration rate (GFR) and proteinuria in db/db and db/db UNX (uninephrectomy) mouse models. Changing a small number of parameters, the model reproduced interspecies differences in renal function. Accounting for glucose and Na⁺ reabsorption through sodium glucose cotransporter 2 (SGLT2), increasing blood glucose and Na⁺ intake from normal to db/db levels mathematically reproduced glomerular hyperfiltration observed experimentally in db/db mice. This resulted from increased proximal tubule sodium reabsorption, which elevated glomerular capillary hydrostatic pressure (P_gc) in order to restore sodium balance through increased GFR. Incorporating adaptive and injurious effects of elevated P_gc, we showed that preglomerular arteriole hypertrophy allowed more direct transmission of pressure to the glomerulus with a smaller mean arterial pressure rise; Glomerular hypertrophy allowed a higher GFR for a given P_gc; and P_gc-driven glomerulosclerosis and nephron loss reduced GFR over time, while further increasing P_gc and causing moderate proteinuria, in agreement with experimental data. UNX imposed on diabetes increased P_gc further, causing faster GFR decline and extensive proteinuria, also in agreement with experimental data. The model provides a mechanistic explanation for hyperfiltration and proteinuria progression that will facilitate translation of efficacy for novel therapies from mouse models to human.

Many drugs for diabetic kidney disease appear to work in rodents, but fail in humans, reflecting incomplete understanding of disease processes. A team led by Melissa Hallow at the University of Georgia has developed a mathematical model that explains how elevated blood glucose in diabetes causes kidney injury in mice. They first showed that normal human, rat, or mouse kidney physiology could be reproduced with the same model by changing a small number of parameters. They then showed that diabetes-induced increases in sodium reabsorption cause unintuitive changes in kidney function that increase pressure on glomerular capillaries, causing protein leakage and nephron loss. The model reproduced faster disease progression observed in diabetic mice who have had one kidney removed. This mathematical understanding of diabetic kidney injury may improve translation of novel therapies from mice to human.

Donor-related diabetic nephropathy: a comprehensive clinicopathological study

Knowledge on renal involvement in kidney donors with diabetes, that is, diabetic nephropathy (DN), is limited. During the 7 years (2010-2017), 921 postperfusion biopsies were performed for living donors (14%) or deceased donors (86%). The Renal Pathology Society classification schema for DN (class 0-IV) was used. Biopsies with light microscopic changes of DN (at least class IIa) were selected for study. Eleven biopsies (1.2%) showed DN, all from deceased donors (class IIa in 8, class IIb in 2, and class III in 1 biopsy). The glomerular basement membrane thickness ranged from 439 ± 52 to 725 ± 82 nm. These biopsies also displayed arterionephrosclerosis. They were from 9 deceased donors (fulfilling clinical criteria for acceptance in all, diabetes ;[>6 years] in 8, hypertension in 6, and proteinuria [1+] in all). Follow-up biopsies (5-342 weeks after transplant) showed DN of the same class (7 biopsies), probably progression (1), or progression (3). At follow-up (15-416 weeks), all recipients were alive. One graft was lost at 76 weeks because of progressive DN. The other 10 grafts were functioning, but the serum creatinine reached 2.0 to 2.7 mg/dL in 5 of them. Although diabetes is frequent in kidney donors, donor-related DN is unusual. It is observed only in deceased donors, but the risk factors for its development are not known. Donor-related DN may be stable or progress. Whether it resolves, especially for DN in early phase, remains unknown. It may adversely impact the graft outcome with a magnitude proportional to the severity of the tissue injury in the postperfusion biopsies.

Targeting inflammation in diabetic nephropathy: a tale of hope

INTRODUCTION

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD). Beyond the new anti-diabetic drugs that possess markedly cardiovascular and renal protective effects, no novel direct therapies for DN have become available on the market in the last twenty years. Recently well-designed clinical trials for the treatment of DN, with attractive pathogenetic rationale, e.g. bardoxolone and atrasentan, were canceled or stopped because of safety concerns or lack of reaching the end points, respectively.

AREAS COVERED

In this review, we focus on the involvement of inflammation in the pathogenesis of DN. We update information from recent experimental and clinical studies that reported beneficial effects of several agents targeting chemokines, cytokines, transcription factors and kinases as well as several compounds with anti-inflammatory properties on DN.

EXPERT OPINION

Inflammation plays a key role in the DN progression. Preclinical studies have identified several anti-inflammatory molecules that effective decrease albuminuria and/or proteinuria. However, limited clinical trials in humans have been performed to confirm these results. Inhibitors of CCL2/CCR2, IL-1β and JAK/STAT pathways, and Nrf2 inducers are promising therapeutic options to improve the renal outcome of patients with DN, but appropriate clinical trials are necessary.

Kidney-derived c-kit+ progenitor/stem cells contribute to podocyte recovery in a model of acute proteinuria

Kidney-derived c-kit⁺ cells exhibit progenitor/stem cell properties and can regenerate epithelial tubular cells following ischemia-reperfusion injury in rats. We therefore investigated whether c-kit⁺ progenitor/stem cells contribute to podocyte repair in a rat model of acute proteinuria induced by puromycin aminonucleoside (PAN), the experimental prototype of human minimal change disease and early stages of focal and segmental glomerulosclerosis. We found that c-kit⁺ progenitor/stem cells accelerated kidney recovery by improving foot process effacement (foot process width was lower in c-kit group vs saline treated animals, P = 0.03). In particular, these cells engrafted in small quantity into tubules, vessels, and glomeruli, where they occasionally differentiated into podocyte-like cells. This effect was related to an up regulation of α-Actinin-4 and mTORC2-Rictor pathway. Activation of autophagy by c-kit⁺ progenitor/stem cells also contributed to kidney regeneration and intracellular homeostasis (autophagosomes and autophagolysosomes number and LC3A/B-I and LC3A/B-II expression were higher in the c-kit group vs saline treated animals, P = 0.0031 and P = 0.0009, respectively). Taken together, our findings suggest that kidney-derived c-kit⁺ progenitor/stem cells exert reparative effects on glomerular disease processes through paracrine effects, to a lesser extent differentiation into podocyte-like cells and contribution to maintenance of podocyte cytoskeleton after injury. These findings have clinical implications for cell therapy of glomerular pathobiology.

Inflammation and Immunity Pathways Regulate Genetic Susceptibility to Diabetic Nephropathy

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease worldwide, but its molecular pathogenesis is not well defined, and there are no specific treatments. In humans, there is a strong genetic component determining susceptibility to DN. However, specific genes controlling DN susceptibility in humans have not been identified. In this study, we describe a mouse model combining type 1 diabetes with activation of the renin-angiotensin system (RAS), which develops robust kidney disease with features resembling human DN: heavy albuminuria, hypertension, and glomerulosclerosis. Additionally, there is a powerful effect of genetic background regulating susceptibility to nephropathy; the 129 strain is susceptible to kidney disease, whereas the C57BL/6 strain is resistant. To examine the molecular basis of this differential susceptibility, we analyzed the glomerular transcriptome of young mice early in the course of their disease. We find dramatic differences in regulation of immune and inflammatory pathways, with upregulation of proinflammatory pathways in the susceptible (129) strain and coordinate downregulation in the resistant (C57BL/6) strain. Many of these pathways are also upregulated in rat models and in humans with DN. Our studies suggest that genes controlling inflammatory responses, triggered by hyperglycemia and RAS activation, may be critical early determinants of susceptibility to DN.

Aberrant activation of Notch-1 signaling inhibits podocyte restoration after islet transplantation in a rat model of diabetic nephropathy

Signaling abnormalities play important roles during podocyte injury and have been indicated as crucial events for triggering many glomerular diseases. There is emerging evidence demonstrating significant improvements in preventing renal injury and restoring podocytes after islet transplantation. However, whether signaling abnormalities affect the therapeutic efficacy of islet transplantation remain unclear. This study was established to investigate the impact of Notch-1 signaling activation on renal injury and podocyte restoration after islet transplantation. Experiments were performed in vivo and in vitro under conditions of diabetic nephropathy and high-glucose medium, respectively. Podocyte injury in vitro was induced by high-glucose concentration, and expression levels of genes associated with the Notch-1 pathway were also regulated by Jagged-1/FC and N-[N-(3,5-Difluorophenacetyl)-L-alanyl]- S-phenylglycine t-butyl ester (DAPT). Podocytes were co-cultured with islets to investigate the protective effect of islets in high-glucose conditions. Histopathological staining and transmission electron microscopy were performed to assess pathological changes in podocytes in glomeruli. The results from this study showed that Notch-1 signaling in podocytes was significantly decreased by functional islet cells in vivo and in vitro. Compared with the co-cultured group and transplanted group, highly activated Notch-1 signaling significantly moderated the effect of islets in affecting podocyte restoration and renal injury. Renal damage and podocyte injury were alleviated after DAPT treatment. Furthermore, the balance between apoptosis and autophagy was diverse under different treatments. All the data in this study showed that highly activated Notch-1 signaling could affect the therapeutic efficacy of islet transplantation on renal injury and podocyte restoration in high-glucose conditions. The balance between apoptosis and autophagy was also closely associated with the degree of podocyte restoration. This finding may suggest that the in vivo microenvironment plays a critical role in podocyte restoration after islet transplantation, which provides a promising and individual assessment and targeting treatment for different diabetic nephropathy patients after islet transplantation into the future.

Therapeutic effects of Salvia miltiorrhiza injection combined with telmisartan in patients with diabetic nephropathy by influencing collagen IV and fibronectin: A case-control study

Involvement of collagen IV (ColIV) and fibronectin (FN) in the occurrence and development of diabetic nephropathy (DN) and the effects of telmisartan and Salvia miltiorrhiza injection in the treatment of the patients were investigated. Two hundred and fifty-eight patients with stage IV DN were selected as the case group, and another 110 normal healthy subjects were incorporated as the control group. Involved patients were subdivided into different groups according to different treatment therapies; patients in the telmisartan group (T group) were given oral telmisartan; patients in the Salvia miltiorrhiza injection + telmisartan (S + T group) were administered with Salvia miltiorrhiza injection combined with telmisartan treatment, and there was a group of patients who received no intervention as the placebo group. After intervention, levels of glycemic indexes and renal damage indexes indicated downwards trends both in the T group and the S + T group when compared to the placebo group; besides, levels in the S + T group were much lower than those in the T group (all P<0.05). Additionally, in comparison among the above three intervention groups, differences in the fasting blood glucose, 2 h post-prandial blood glucose, glycosylated hemoglobin, blood urea nitrogen, serum creatinine and urinary albumin excretion rate were significant after treatment (all P<0.05). Further, before intervention, both Co1IV and FN in the urine were increased in the case group compared to the control group (all P<0.05). After intervention, both levels were apparently decreased. There were remarkable differences of Co1IV and FN levels in the urine when compared among three different intervention groups after treatment (P<0.05). Increased ColIV and FN levels may be partially responsible for the development of DN. Salvia miltiorrhiza injection with telmisartan have beneficial synergistic effects for DN patients through attenuating the increase in ColIV and FN, reversing hyperglycemia state and postponing ultrastructure changes of glomerular basement membrane.

Regenerating the kidney using human pluripotent stem cells and renal progenitors

INTRODUCTION

Chronic kidney disease is a major health-care problem worldwide and its cost is becoming no longer affordable. Indeed, restoring damaged renal structures or building a new kidney represents an ambitious and ideal alternative to renal replacement therapy. Streams of research have explored the possible application of pluripotent stem cells (SCs) (embryonic SCs and induced pluripotent SCs) in different strategies aimed at regenerate functioning nephrons and at understanding the mechanisms of kidney regeneration.

AREAS COVERED

In this review, we will focus on the main potential applications of human pluripotent SCs to kidney regeneration, including those leading to rebuilding new kidneys or part of them (organoids, scaffolds, biological microdevices) as well as those aimed at understanding the pathophysiological mechanisms of renal disease and regenerative processes (modeling of kidney disease, genome editing). Moreover, we will discuss the role of endogenous renal progenitors cells in order to understand and promote kidney regeneration, as an attractive alternative to pluripotent SCs.

EXPERT OPINION

Opportunities and pitfalls of all these strategies will be underlined, finally leading to the conclusion that a deeper knowledge of the biology of pluripotent SCs is mandatory, in order to allow us to hypothesize their clinical application.

Lineage tracing aged mouse kidneys shows lower number of cells of renin lineage and reduced responsiveness to RAAS inhibition

Blocking the renin-angiotensin-aldosterone system (RAAS) remains a mainstay of therapy in hypertension and glomerular diseases. With the population aging, our understanding of renin-producing cells in kidneys with advanced age is more critical than ever. Accordingly, we administered tamoxifen to Ren1cCreERxRs-tdTomato-R mice to permanently fate map cells of renin lineage (CoRL). The number of Td-tomato-labeled CoRL decreased significantly in aged mice (24 mo of age) compared with young mice (3.5 mo of age), as did renin mRNA levels. To determine whether aged CoRL responded less to RAAS blockade, enalapril and losartan were administered over 25 days following uninephrectomy in young and aged mice. The number of CoRL increased in young mice in response to enalapril and losartan. However, this was significantly lower in aged mice compared with young mice due to limited proliferation, but not recruitment. Gene expression analysis of laser-captured CoRL showed a substantial increase in mRNA levels for proapoptotic and prosenescence genes, and an increase in a major prosenescence protein on immunostaining. These results show that CoRL are lower in aged mice and do not respond to RAAS inhibition to the same extent as young mice.

Pathology identifies glomerular treatment targets in diabetic nephropathy

The development of the glomerular injury in diabetic nephropathy involves interactions between podocytes, endothelium, and the mesangium. Loss of podocytes is an early and critical step in the development of diabetic nephropathy, and analysis of structural lesions within the mesangium such as mesangiolysis implicate the loss of podocytes as a key mediating event. The BTBR ob/ob mouse has proved a useful tool to demonstrate that restoration of podocyte density, once thought to be an absolute barrier to glomerular repair, can be achieved with replacement of the hormone leptin that is constitutively absent in these mice. Restoration of podocyte density is associated with reversal of the structural lesions of morphologically advanced diabetic glomerular injury in this model. This finding, in conjunction with the demonstration in human diabetic patients with morphologically advanced diabetic nephropathy and with long-standing functioning pancreatic transplants of ten years duration that their diabetic nephropathy can be reversed, suggests that restoration of podocyte number and density is an appropriate target for the development of new therapeutics for diabetic nephropathy.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

Can podocytes be regenerated in adults?

PURPOSE OF REVIEW

Podocytes are critical components of the nephron filtration barrier and are depleted in many kidney injuries and disease states. Terminally differentiated adult podocytes are highly specialized, postmitotic cells, raising the question of whether the body has any ability to regenerate lost podocytes. This timely question has recently been illuminated by a series of innovative studies. Here, we review recent progress on this topic of significant interest and debate.

RECENT FINDINGS

The innovation of genetic labeling techniques enables fate tracing of individual podocytes, providing the strongest evidence yet that podocytes can be replaced by nearby progenitor cells. In particular, two progenitor pools have recently been identified in multiple studies: parietal epithelial cells and cells of renin lineage. These studies furthermore suggest that podocyte regeneration can be enhanced using ex-vivo or pharmacological interventions.

SUMMARY

Recent studies indicate that the podocyte compartment is more dynamic than previously believed. Bidirectional exchange with neighboring cellular compartments provides a mechanism for podocyte replacement. Based on these findings, we propose a set of criteria for evaluating podocyte regeneration and suggest that restoration of podocyte number to a subsclerotic threshold be targeted as a potentially achievable clinical goal.

A new model of diabetic nephropathy in C57BL/6 mice challenged with advanced oxidation protein products

There remains a lack of robust mouse models with key features of advanced human diabetic nephropathy (DN). Few options of murine models of DN require mutations to be superimposed to obtain desired phenotypic characteristics. Most genetically modified mice are on the C57BL/6 background; however, they are notorious for resistance to develop DN. To overcome these conundrums, this study reports a novel DN model by challenging with advanced oxidation protein products (AOPPs) in streptozotocin-induced diabetic C57BL/6 mice. AOPPs-challenged diabetic C57BL/6 mice were more sensitive to develop progressive proteinuria, causing a 5.59-fold increase in urine albumin to creatinine ratio as compared to diabetic controls by 24 weeks. Typical lesions were present as demonstrated by significant diffuse mesangial expansion, diffuse podocyte foot process effacement, increased glomerular basement membrane thickness, focal arteriolar hyalinosis, mesangiolysis, and mild interstitial fibrosis. These changes were alleviated by losartan treatment. Collectively, these results suggest that AOPPs can accelerate the progression of DN in the resistant C57BL/6 mouse strain. Our studies offer a novel model for studying the pathogenesis of DN that resembles human diabetic kidney disease. It also makes it possible to interrogate the role of specific genetic modifications and to evaluate novel therapeutics to treat DN in preclinical setting.

Early and late scanning electron microscopy findings in diabetic kidney disease

Diabetic nephropathy (DN), the single strongest predictor of mortality in patients with type 2 diabetes, is characterized by initial glomerular hyperfiltration with subsequent progressive renal function loss with or without albuminuria, greatly accelerated with the onset of overt proteinuria. Experimental and clinical studies have convincingly shown that early interventions retard disease progression, while treatment if started late in the disease course seldom modifies the slope of GFR decline. Here we assessed whether the negligible renoprotection afforded by drugs in patients with proteinuric DN could be due to loss of glomerular structural integrity, explored by scanning electron microscopy (SEM). In diabetic patients with early renal disease, glomerular structural integrity was largely preserved. At variance SEM documented that in the late stage of proteinuric DN, glomerular structure was subverted with nearly complete loss of podocytes and lobular transformation of the glomerular basement membrane. In these circumstances one can reasonably imply that any form of treatment, albeit personalized, is unlikely to reach a given cellular or molecular target. These findings should persuade physicians to start the putative renoprotective therapy soon after the diagnosis of diabetes or in an early phase of the disease before structural integrity of the glomerular filter is irreversibly compromised.

Gremlin Regulates Podocyte Apoptosis via Transforming Growth Factor-β (TGF-β) Pathway in Diabetic Nephropathy

BACKGROUND Gremlin has been reported to be up-regulated in glomerular mesangial cells in diabetic nephropathy (DN). However, the regulation of gremlin in podocytes is still rarely reported. This study aimed to investigate the underlying mechanisms by which gremlin mediates the pathogenesis of DN via transforming growth factor-β (TGF-β) signaling pathways. MATERIAL AND METHODS Lentiviral and RNAi transfection were performed to increase and decrease gremlin expression in high-glucose conditions. Expression at the mRNA and protein level was detected by RT-qPCR and Western blotting. RESULTS The expression of gremlin was significantly higher in high-glucose (HG, 30mM) than normal-glucose (NG, 5.5 mM) conditions. The gremlin overexpression significantly suppressed the expression of nephrin and synaptopodin. The phosphorylation of canonical TGF-b signaling pathway components, including Smad2/3 and MKK, was increased in the gremlin-overexpressing group. In addition, the expression levels of Bax and cleaved caspase-3 were also higher in the gremlin-overexpressing group. TGF-β pathway inhibitor (SB505124) significantly inhibited TGF-β pathway activity and enhanced the expression of nephrin and synaptopodin. CONCLUSIONS These results indicate that gremlin can aggravate podocyte lesions through the TGF-β signaling pathway, providing a novel therapeutic target for DN.

Early Growth Response 1 (Egr1) Is a Transcriptional Activator of NOX4 in Oxidative Stress of Diabetic Kidney Disease

BACKGROUND

NADPH oxidase 4 (NOX4) plays a major role in renal oxidative stress of diabetic kidney disease (DKD). NOX4 was significantly increased in Egr1-expressing fibroblasts, but the relationship between Egr1 and NOX4 in DKD is unclear.

METHODS

For the evaluation of the potential relationship between Egr1 and NOX4, both were detected in HFD/STZ-induced mice and HK-2 cells treated with TGF-β1. Then, changes in NOX4 expression were detected in HK-2 cells and mice with overexpression and knockdown of Egr1. The direct relationship between Egr1 and NOX4 was explored via chromatin immunoprecipitation (ChIP).

RESULTS

We found increased levels of Egr1, NOX4, and α-SMA in the kidney cortices of diabetic mice and in TGF-β1-treated HK-2 cells. Overexpression or silencing of Egr1 in HK-2 cells could upregulate or downregulate NOX4 and α-SMA. ChIP assays revealed that TGF-β1 induced Egr1 to bind to the NOX4 promoter. Finally, Egr1 overexpression or knockdown in diabetic mice could upregulate or downregulate the expression of NOX4 and ROS, and α-SMA was also changed.

CONCLUSION

Our study provides strong evidence that Egr1 is a transcriptional activator of NOX4 in oxidative stress of DKD. Egr1 contributes to DKD by enhancing EMT, in part by targeting NOX4.

A Novel Type 2 Diabetes Mouse Model of Combined Diabetic Kidney Disease and Atherosclerosis

Diabetic kidney disease and atherosclerotic disease are major causes of morbidity and mortality associated with type 2 diabetes (T2D), and diabetic kidney disease is a major cardiovascular risk factor. The black and tan, brachyury (BTBR) mouse strain with leptin deficiency (Lep^ob) has emerged as one of the best models of human diabetic kidney disease. However, no T2D mouse model of combined diabetic kidney disease and atherosclerosis exists. Our goal was to generate such a model. To this end, the low-density lipoprotein (LDL) receptor was targeted for degradation via inducible degrader of the LDL receptor (IDOL) overexpression, using liver-targeted adenoassociated virus serotype DJ/8 (AAV-DJ/8) in BTBR wild-type and BTBR Lep^ob mice. Liver-targeted IDOL-AAV-DJ/8 increased plasma LDL cholesterol compared with the control enhanced green fluorescent protein AAV-DJ/8. IDOL-induced dyslipidemia caused formation of atherosclerotic lesions of an intermediate stage, which contained both macrophages and smooth muscle cells. BTBR Lep^ob mice exhibited diabetic kidney disease. IDOL-induced dyslipidemia worsened albuminuria and glomerular macrophage accumulation but had no effect on mesangial expansion or podocyte numbers. Thus, by inducing hepatic degradation of the LDL receptor, we generated a T2D model of combined kidney disease and atherosclerosis. This model provides a new tool to study mechanisms, interactions, and treatment strategies of kidney disease and atherosclerosis in T2D.

The effects of dual PPARα/γ agonism compared with ACE inhibition in the BTBRob/ob mouse model of diabetes and diabetic nephropathy

The leptin‐deficient BTBRob/ob mouse develops progressive albuminuria and morphological lesions similar to human diabetic nephropathy (DN), although whether glomerular hyperfiltration, a recognized feature of early DN that may contribute to renal injury, also occurs in this model is not known. Leptin replacement has been shown to reverse the signs of renal injury in this model, but in contrast, the expected renoprotection by angiotensin‐converting enzyme (ACE) inhibition in BTBRob/ob mice seems to be limited. Therefore, to investigate the potential renal benefits of improved metabolic control in this model, we studied the effect of treatment with the dual peroxisome proliferator‐activated receptor (PPAR) α/γ agonist AZD6610 and compared it with the ACE inhibitor enalapril. AZD6610 lowered plasma glucose and triglyceride concentrations and increased liver size, but had no significant effect in reducing albuminuria, whereas enalapril did have an effect. Nephrin and WT1 mRNA expression decreased in the kidneys of BTBRob/ob mice, consistent with podocyte injury and loss, but was unaffected by either drug treatment: at the protein level, both nephrin and WT1‐positive cells per glomerulus were decreased. Mesangial matrix expansion was reduced in AZD6610‐treated mice. GFR, measured by creatinine clearance, was increased in BTBRob/ob mice, but unaffected by either treatment. Unexpectedly, enalapril‐treated mice showed intrarenal arteriolar vascular remodeling with concentric thickening of vessel walls. In summary, we found that the BTBRob/ob mouse model shows some similarities to the early changes seen in human DN, but that ACE inhibition or PPARα/γ agonism afforded limited or no kidney protection.

Chronic kidney disease

Chronic kidney disease (CKD) is defined by persistent urine abnormalities, structural abnormalities or impaired excretory renal function suggestive of a loss of functional nephrons. The majority of patients with CKD are at risk of accelerated cardiovascular disease and death. For those who progress to end-stage renal disease, the limited accessibility to renal replacement therapy is a problem in many parts of the world. Risk factors for the development and progression of CKD include low nephron number at birth, nephron loss due to increasing age and acute or chronic kidney injuries caused by toxic exposures or diseases (for example, obesity and type 2 diabetes mellitus). The management of patients with CKD is focused on early detection or prevention, treatment of the underlying cause (if possible) to curb progression and attention to secondary processes that contribute to ongoing nephron loss. Blood pressure control, inhibition of the renin-angiotensin system and disease-specific interventions are the cornerstones of therapy. CKD complications such as anaemia, metabolic acidosis and secondary hyperparathyroidism affect cardiovascular health and quality of life, and require diagnosis and treatment.

Modelling diabetic nephropathy in mice

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease in the developed world. Accordingly, an urgent need exists for new, curative treatments as well as for biomarkers to stratify risk of DN among individuals with diabetes mellitus. A barrier to progress in these areas has been a lack of animal models that faithfully replicate the main features of human DN. Such models could be used to define the pathogenesis, identify drug targets and test new therapies. Owing to their tractability for genetic manipulation, mice are widely used to model human diseases, including DN. Questions have been raised, however, about the general utility of mouse models in human drug discovery. Standard mouse models of diabetes typically manifest only modest kidney abnormalities, whereas accelerated models, induced by superimposing genetic stressors, recapitulate key features of human DN. Incorporation of systems biology approaches and emerging data from genomics and metabolomics studies should enable further model refinement. Here, we discuss the current status of mouse models for DN, their limitations and opportunities for improvement. We emphasize that future efforts should focus on generating robust models that reproduce the major clinical and molecular phenotypes of human DN.

Tracking the stochastic fate of cells of the renin lineage after podocyte depletion using multicolor reporters and intravital imaging

Podocyte depletion plays a major role in focal segmental glomerular sclerosis (FSGS). Because cells of the renin lineage (CoRL) serve as adult podocyte and parietal epithelial cell (PEC) progenitor candidates, we generated Ren1cCre/R26R-ConfettiTG/WT and Ren1dCre/R26R-ConfettiTG/WT mice to determine CoRL clonality during podocyte replacement. Four CoRL reporters (GFP, YFP, RFP, CFP) were restricted to cells in the juxtaglomerular compartment (JGC) at baseline. Following abrupt podocyte depletion in experimental FSGS, all four CoRL reporters were detected in a subset of glomeruli at day 28, where they co-expressed de novo four podocyte proteins (podocin, nephrin, WT-1 and p57) and two glomerular parietal epithelial cell (PEC) proteins (claudin-1, PAX8). To monitor the precise migration of a subset of CoRL over a 2w period following podocyte depletion, intravital multiphoton microscopy was used. Our findings demonstrate direct visual support for the migration of single CoRL from the JGC to the parietal Bowman's capsule, early proximal tubule, mesangium and glomerular tuft. In summary, these results suggest that following podocyte depletion, multi-clonal CoRL migrate to the glomerulus and replace podocyte and PECs in experimental FSGS.

Carnosine Attenuates the Development of both Type 2 Diabetes and Diabetic Nephropathy in BTBR ob/ob Mice

We previously demonstrated that polymorphisms in the carnosinase-1 gene (CNDP1) determine the risk of nephropathy in type 2 diabetic patients. Carnosine, the substrate of the enzyme encoded by this gene, is considered renoprotective and could possibly be used to treat diabetic nephropathy (DN). In this study, we examined the effect of carnosine treatment in vivo in BTBR (Black and Tan, BRachyuric) ob/ob mice, a type 2 diabetes model which develops a phenotype that closely resembles advanced human DN. Treatment of BTBR ob/ob mice with 4 mM carnosine for 18 weeks reduced plasma glucose and HbA1c, concomitant with elevated insulin and C-peptide levels. Also, albuminuria and kidney weights were reduced in carnosine-treated mice, which showed less glomerular hypertrophy due to a decrease in the surface area of Bowman's capsule and space. Carnosine treatment restored the glomerular ultrastructure without affecting podocyte number, resulted in a modified molecular composition of the expanded mesangial matrix and led to the formation of carnosine-acrolein adducts. Our results demonstrate that treatment with carnosine improves glucose metabolism, albuminuria and pathology in BTBR ob/ob mice. Hence, carnosine could be a novel therapeutic strategy to treat patients with DN and/or be used to prevent DN in patients with diabetes.

A biomimetic gelatin-based platform elicits a pro-differentiation effect on podocytes through mechanotransduction

Using a gelatin microbial transglutaminase (gelatin-mTG) cell culture platform tuned to exhibit stiffness spanning that of healthy and diseased glomeruli, we demonstrate that kidney podocytes show marked stiffness sensitivity. Podocyte-specific markers that are critical in the formation of the renal filtration barrier are found to be regulated in association with stiffness-mediated cellular behaviors. While podocytes typically de-differentiate in culture and show diminished physiological function in nephropathies characterized by altered tissue stiffness, we show that gelatin-mTG substrates with Young’s modulus near that of healthy glomeruli elicit a pro-differentiation and maturation response in podocytes better than substrates either softer or stiffer. The pro-differentiation phenotype is characterized by upregulation of gene and protein expression associated with podocyte function, which is observed for podocytes cultured on gelatin-mTG gels of physiological stiffness independent of extracellular matrix coating type and density. Signaling pathways involved in stiffness-mediated podocyte behaviors are identified, revealing the interdependence of podocyte mechanotransduction and maintenance of their physiological function. This study also highlights the utility of the gelatin-mTG platform as an in vitro system with tunable stiffness over a range relevant for recapitulating mechanical properties of soft tissues, suggesting its potential impact on a wide range of research in cellular biophysics.

Critical role of the cAMP-PKA pathway in hyperglycemia-induced epigenetic activation of fibrogenic program in the kidney

Hyperglycemia is a major pathogenic factor that promotes diabetic nephropathy, but the underlying mechanism remains incompletely understood. Here, we show that high glucose induced cAMP response element-binding protein (CREB)-binding protein (CBP)-mediated H3K9/14 hyperacetylation in approximately 5000 gene promoters in glomerular mesangial cells, including those of Tgfb1, Tgfb3, and Ctgf, the major profibrotic factors that are known to drive diabetic renal fibrogenesis. In these promoters, H3K9/14 hyperacetylation was closely associated with NF-κB or CREB motifs. Chromatin immunoprecipitation assays confirmed that hyperglycemia promoted phospho-p65 or phospho-CREB and CBP bindings and RNA polymerase II recruitment to these promoters in mesangial cells as well as in glomeruli that were purified from type I and type II diabetic mice. Under hyperglycemia, cAMP production and PKA activity were markedly increased as a result of glucose transporter 1-mediated glucose influx that drives glucose metabolism and ATP production, which led to increased phosphorylation of p65 and CREB. Inhibition of adenylyl cyclase or PKA activity blocked p65 and CREB phosphorylation, CBP recruitment, and histone acetylation in these promoters. Collectively, these data demonstrate that the cAMP-PKA pathway plays a key role in epigenetic regulation of key profibrotic factors in diabetes.-Deb, D. K., Bao, R., Li, Y. C. Critical role of the cAMP-PKA pathway in hyperglycemia-induced epigenetic activation of fibrogenic program in the kidney.

Activated ERK1/2 increases CD44 in glomerular parietal epithelial cells leading to matrix expansion

The glycoprotein CD44 is barely detected in normal mouse and human glomeruli, but is increased in glomerular parietal epithelial cells following podocyte injury in focal segmental glomerulosclerosis (FSGS). To determine the biological role and regulation of CD44 in these cells, we employed an in vivo and in vitro approach. Experimental FSGS was induced in CD44 knockout and wild-type mice with a cytotoxic podocyte antibody. Albuminuria, focal and global glomerulosclerosis (periodic acid-Schiff stain), and collagen IV staining were lower in CD44 knockout compared with wild-type mice with FSGS. Parietal epithelial cells had lower migration from Bowman's capsule to the glomerular tuft in CD44 knockout mice with disease compared with wild type mice. In cultured murine parietal epithelial cells, overexpressing CD44 with a retroviral vector encoding CD44 was accompanied by significantly increased collagen IV expression and parietal epithelial cell migration. Because our results showed de novo co-staining for activated ERK1/2 (pERK) in parietal epithelial cells in experimental FSGS, and also in biopsies from patients with FSGS, two in vitro strategies were employed to prove that pERK regulated CD44 levels. First, mouse parietal epithelial cells were infected with a retroviral vector for the upstream kinase MEK-DD to increase pERK, which was accompanied by increased CD44 levels. Second, in CD44-overexpressing parietal epithelial cells, decreasing pERK with U0126 was accompanied by reduced CD44. Finally, parietal epithelial cell migration was higher in cells with increased and reduced in cells with decreased pERK. Thus, pERK is a regulator of CD44 expression, and increased CD44 expression leads to a pro-sclerotic and migratory parietal epithelial cell phenotype.

Mesenchymal Stem Cells as Therapeutic Candidates for Halting the Progression of Diabetic Nephropathy

Mesenchymal stem cells (MSCs) possess pleiotropic properties that include immunomodulation, inhibition of apoptosis, fibrosis and oxidative stress, secretion of trophic factors, and enhancement of angiogenesis. These properties provide a broad spectrum for their potential in a wide range of injuries and diseases, including diabetic nephropathy (DN). MSCs are characterized by adherence to plastic, expression of the surface molecules CD73, CD90, and CD105 in the absence of CD34, CD45, HLA-DR, and CD14 or CD11b and CD79a or CD19 surface molecules, and multidifferentiation capacity in vitro. MSCs can be derived from many tissue sources, consistent with their broad, possibly ubiquitous distribution. This article reviews the existing literature and knowledge of MSC therapy in DN, as well as the most appropriate rodent models to verify the therapeutic potential of MSCs in DN setting. Some preclinical relevant studies are highlighted and new perspectives of combined therapies for decreasing DN progression are discussed. Hence, improved comprehension and interpretation of experimental data will accelerate the progress towards clinical trials that should assess the feasibility and safety of this therapeutic approach in humans. Therefore, MSC-based therapies may bring substantial benefit for patients suffering from DN.

Pentraxin-3 Attenuates Renal Damage in Diabetic Nephropathy by Promoting M2 Macrophage Differentiation

As one of the most important long-term complications of diabetes, diabetic nephropathy (DN) is the major cause of end-stage renal disease and high mortality in diabetic patients. The long pentraxin 3 (Ptx3) is a member of a superfamily of conserved proteins characterized by a cyclic multimeric structure and a conserved C-terminal domain. Several clinical investigations have demonstrated that elevated plasma Ptx3 levels are associated with cardiovascular and chronic kidney diseases (CKD). However, the therapeutic effect of Ptx3 on DN has never been investigated. In our current study, we showed a crucial role for Ptx3 in attenuating renal damage in DN. In our mouse hyperglycemia-induced nephropathy model, Ptx3 treatment showed significantly increased expression of nephrin, acetylated nephrin, and Wilm's tumor-1 protein (WT-1) when compared with control. The number of CD4(+) T cells, CD8(+) T cells, Ly6G(+) neutrophils, and CD11b(+) macrophages were all significantly lower in the Ptx3-treated group than that in the control group in DN. The IL-4 and IL-13 levels in the Ptx3-treated group were markedly higher than that in the control group in DN. Correspondingly, the Ptx3-treated group showed increased numbers of Arg1- or CD206-expressing macrophages compared with the control group. Furthermore, inhibition of Ptx3-treated macrophages abrogated the alleviated renal damage induced by Ptx3 treatment. In conclusion, Ptx3 attenuates renal damage in DN by promoting M2 macrophage differentiation.

Renin-Angiotensin-Aldosterone System Inhibition Increases Podocyte Derivation from Cells of Renin Lineage

Because adult podocytes cannot proliferate and are therefore unable to self-renew, replacement of these cells depends on stem/progenitor cells. Although podocyte number is higher after renin-angiotensin-aldosterone system (RAAS) inhibition in glomerular diseases, the events explaining this increase are unclear. Cells of renin lineage (CoRL) have marked plasticity, including the ability to acquire a podocyte phenotype. To test the hypothesis that RAAS inhibition partially replenishes adult podocytes by increasing CoRL number, migration, and/or transdifferentiation, we administered tamoxifen to Ren1cCreERxRs-tdTomato-R CoRL reporter mice to induce permanent labeling of CoRL with red fluorescent protein variant tdTomato. We then induced experimental FSGS, typified by abrupt podocyte depletion, with a cytopathic antipodocyte antibody. RAAS inhibition by enalapril (angiotensin-converting enzyme inhibitor) or losartan (angiotensin-receptor blocker) in FSGS mice stimulated the proliferation of CoRL, increasing the reservoir of these cells in the juxtaglomerular compartment (JGC). Compared with water or hydralazine, RAAS inhibition significantly increased the migration of CoRL from the JGC to the intraglomerular compartment (IGC), with more glomeruli containing RFP⁺CoRL and, within these glomeruli, more RFP⁺CoRL. Moreover, RAAS inhibition in FSGS mice increased RFP⁺CoRL transdifferentiation in the IGC to phenotypes, consistent with those of podocytes (coexpression of synaptopodin and Wilms tumor protein), parietal epithelial cells (PAX 8), and mesangial cells (α8 integrin). These results show that in the context of podocyte depletion in FSGS, RAAS inhibition augments CoRL proliferation and plasticity toward three different glomerular cell lineages.

Partial podocyte replenishment in experimental FSGS derives from nonpodocyte sources

The current studies used genetic fate mapping to prove that adult podocytes can be partially replenished following depletion. Inducible NPHS2-rtTA/tetO-Cre/RS-ZsGreen-R reporter mice were generated to permanently label podocytes with the ZsGreen reporter. Experimental focal segmental glomerulosclerosis (FSGS) was induced with a cytotoxic podocyte antibody. On FSGS day 7, immunostaining for the podocyte markers p57, synaptopodin, and podocin were markedly decreased by 44%, and this was accompanied by a decrease in ZsGreen fluorescence. The nuclear stain DAPI was absent in segments of reduced ZsGreen and podocyte marker staining, which is consistent with podocyte depletion. Staining for p57, synaptopodin, podocin, and DAPI increased at FSGS day 28 and was augmented by the ACE inhibitor enalapril, which is consistent with a partial replenishment of podocytes. In contrast, ZsGreen fluorescence did not return and remained significantly low at day 28, indicating replenishment was from a nonpodocyte origin. Despite administration of bromodeoxyuridine (BrdU) thrice weekly throughout the course of disease, BrdU staining was not detected in podocytes, which is consistent with an absence of proliferation. Although ZsGreen reporting was reduced in the tuft at FSGS day 28, labeled podocytes were detected along the Bowman's capsule in a subset of glomeruli, which is consistent with migration from the tuft. Moreover, more than half of the migrated podocytes coexpressed the parietal epithelial cell (PEC) proteins claudin-1, SSeCKS, and PAX8. These results show that although podocytes can be partially replenished following abrupt depletion, a process augmented by ACE inhibition, the source or sources are nonpodocyte in origin and are independent of proliferation. Furthermore, a subset of podocytes migrate to the Bowman's capsule and begin to coexpress PEC markers.

An Update on the Use of Animal Models in Diabetic Nephropathy Research

In the current review, we discuss limitations and recent advances in animal models of diabetic nephropathy (DN). As in human disease, genetic factors may determine disease severity with the murine FVB and DBA/2J strains being more susceptible to DN than C57BL/6J mice. On the black and tan, brachyuric (BTBR) background, leptin deficient (ob/ob) mice develop many of the pathological features of human DN. Hypertension synergises with hyperglycemia to promote nephropathy in rodents. Moderately hypertensive endothelial nitric oxide synthase (eNOS(-/-)) deficient diabetic mice develop hyaline arteriosclerosis and nodular glomerulosclerosis and induction of renin-dependent hypertension in diabetic Cyp1a1mRen2 rats mimics moderately severe human DN. In addition, diabetic eNOS(-/-) mice and Cyp1a1mRen2 rats recapitulate many of the molecular pathways activated in the human diabetic kidney. However, no model exhibits all the features of human DN; therefore, researchers should consider biochemical, pathological, and transcriptomic data in selecting the most appropriate model to study their molecules and pathways of interest.

Cells of renin lineage express hypoxia inducible factor 2α following experimental ureteral obstruction

BACKGROUND

Recent studies indicate that mural cells of the preglomerular vessels, known as cells of renin lineage (CoRL), contribute to repair and regeneration of injured kidney glomeruli. However, their potential roles in tubulointerstitial disease are less understood. The aim of this study was to better understand CoRL number and distribution following UUO so that future mechanistic studies could be undertaken.

METHODS

We mapped the fate of CoRL in adult Ren1cCreER x Rs-tdTomato-R reporter mice that underwent UUO. Kidney biopsies from sham and UUO-subjected mice on days 3, 7, and 14 were evaluated by immunohistochemistry.

RESULTS

In sham animals, CoRL were restricted to juxtaglomerular location. At day 7 following UUO, CoRL increased two-fold, were perivascular in location, and co-expressed pericyte markers (PDGFßR, NG2), but did not express renin. At day 14 post UUO, labeled CoRL detached from vessels and were present in the interstitium, in areas of fibrosis, where they now expressed the myofibroblast marker alpha-smooth muscle actin. The increase in CoRL was likely due to proliferation as marked by BrdU labeling, and migration from the cortex. Following UUO starting from day 3, active hypoxia inducible factor-2α was detected in nuclei in labeled CoRL, in the cortex, but not those cells found in medulla.

CONCLUSIONS

We have demonstrated that arteriolar CoRL are potential kidney progenitors that may contribute to the initial vascular regeneration. However, in chronic kidney injury (≥14 days post UUO), perivascular CoRL transition to myofibroblast-like cells.

Reversal of Early Diabetic Nephropathy by Islet Transplantation under the Kidney Capsule in a Rat Model

Objective. Diabetic nephropathy (DN) is a common microvascular complication of diabetes mellitus, and insulin therapy has many side effects in the treatment of DN. Islet transplantation has emerged as a promising therapy for diabetic patients. This study was established to investigate its advantageous effects in a rat model of early DN. Methods. Streptozotocin was administered to the rats to induce diabetes. Twelve weeks later, the diabetic rats were divided into 3 groups: the islet-transplanted group (IT group), the insulin-treated group (IN group), and the untreated group (DN group). Renal injury and kidney structure were assessed by urinalysis and transmission electron microscopy (TEM) detection. Immunohistochemical staining and western blotting were performed to assess renal fibrosis levels. Results. The early DN features were reversed and the glomerular filtration barrier and basement membrane structures were improved at 4 weeks after islet transplantation. The urine microalbumin-to-creatinine ratio (ACR), protein-to-creatinine ratio, and mean thickness of the glomerular basement membrane (GBM) were significantly decreased in the IT group. The expression of renal fibrotic factors was also significantly decreased. Conclusions. These data suggest that early DN can be reversed after islet transplantation, and they may facilitate the development of a clinical therapeutic strategy for human diabetes mellitus.

MicroRNA-155 deficiency promotes nephrin acetylation and attenuates renal damage in hyperglycemia-induced nephropathy

MiR-155 has been reported to be involved in both innate and adaptive immune responses. But the role of miR-155 in hyperglycemia-induced nephropathy is still unknown. In our current study, 3-month-old male wild-type C57 mice and Mir-155(-/-) mice were used to establish hyperglycemia-induced nephropathy. In our hyperglycemia-induced nephropathy model, the expression of podocyte injury marker desmin was markedly increased in the diabetes group when compared with control. Diabetes also significantly decreased the levels of nephrin and acetylated nephrin, whereas the expression of miR-155 was markedly increased in diabetes group when compared with control. MiR-155(-/-) mice showed significantly increased expression of nephrin, acetylated nephrin, and Wilm's tumor-1 protein (WT-1) when compared with wild-type control. MiR-155 deficiency results in significantly decrease in IL-17A expression both in vivo and in vitro. And the increased expression of WT-1, nephrin, and ac-nephrin was reversed with additional treatment of rmIL-17. Furthermore, we found that the inhibited Th17 differentiation induced by miR-155 deficiency was dependent on increased expression of SOCS1. In conclusion, miR-155 deficiency promotes nephrin acetylation and attenuates renal damage in hyperglycemia-induced nephropathy. This was associated with inhibited IL-17 production through enhancement of SOCS1 expression.

The phenotypes of podocytes and parietal epithelial cells may overlap in diabetic nephropathy

Reversal of diabetic nephropathy (DN) has been achieved in humans and mice, but only rarely and under special circumstances. Since progression of DN is related to podocyte loss, reversal of DN requires restoration of podocytes. Here we identified and quantified potential glomerular progenitor cells that could be a source for restored podocytes. DN was identified in 31 human renal biopsy cases and separated into morphologically early or advanced lesions. Markers of podocytes (WT-1, p57), parietal epithelial cells (claudin-1) and cell proliferation (Ki-67) were identified by immunohistochemistry. Podocyte density was progressively reduced with DN. Cells marking as podocytes (p57) were present infrequently on Bowman's capsule in controls, but significantly increased in histologically early DN. Ki-67 expressing cells were identified on the glomerular tuft and Bowman's capsule in DN, but rarely in controls. Cells marking as PECs were present on the glomerular tuft, particularly in morphologically advanced DN. These findings show evidence of phenotypic plasticity in podocyte and PEC populations and are consistent with studies in the BTBR ob/ob murine model in which reversibility of DN occurs with podocytes potentially regenerating from PEC precursors. Thus, our findings support, but do not prove, that podocytes may regenerate from PEC progenitors in human DN. If so, progression of DN may represent a modifiable net balance between podocyte loss and regeneration.

Podocyte Regeneration Driven by Renal Progenitors Determines Glomerular Disease Remission and Can Be Pharmacologically Enhanced

Podocyte loss is a general mechanism of glomerular dysfunction that initiates and drives the progression of chronic kidney disease, which affects 10% of the world population. Here, we evaluate whether the regenerative response to podocyte injury influences chronic kidney disease outcome. In models of focal segmental glomerulosclerosis performed in inducible transgenic mice where podocytes are tagged, remission or progression of disease was determined by the amount of regenerated podocytes. When the same model was established in inducible transgenic mice where renal progenitors are tagged, the disease remitted if renal progenitors successfully differentiated into podocytes, while it persisted if differentiation was ineffective, resulting in glomerulosclerosis. Treatment with BIO, a GSK3s inhibitor, significantly increased disease remission by enhancing renal progenitor sensitivity to the differentiation effect of endogenous retinoic acid. These results establish renal progenitors as critical determinants of glomerular disease outcome and a pharmacological enhancement of their differentiation as a possible therapeutic strategy.

Tight blood glycaemic and blood pressure control in experimental diabetic nephropathy reduces extracellular matrix production without regression of fibrosis

AIMS

Regression of albuminuria and renal fibrosis occurs in patients with diabetic nephropathy (DN) following tight control of blood glucose and blood pressure, however the pathways that promote regression remain poorly understood and we wished to characterize these using a rodent model.

METHODS

Diabetes was induced with streptozotocin in Cyp1a1mRen2 rats and hypertension was generated by inducing renin transgene expression with dietary indole-3-carbinol (I-3-C) for 28 weeks. At this point an 'injury cohort' was culled, while in a 'reversal cohort' glycaemia was tightly controlled using insulin implants and blood pressure normalized by withdrawing dietary I-3-C for a further 8 weeks. Pathways activated during and following reversal of diabetes and hypertension were assessed by microarray profiling.

RESULTS

Tight control of blood glucose and blood pressure reduced albuminuria and renal hypertrophy, but had no impact on renal fibrosis. 85 genes were up-regulated specifically during the injury phase, including genes encoding multiple myofibroblast and extracellular matrix (ECM) proteins. Conversely, 314 genes remained persistently elevated during reversal including genes linked to innate/adaptive immunity, phagocytosis, lysosomal processing and degradative metalloproteinases (MMPs). Despite increased MMP gene expression, MMP activity was suppressed during both injury and reversal, in association with up-regulation of tissue inhibitor of metalloproteinase-1 (TIMP-1) protein. Physical separation of the TIMP-1/MMP complexes during zymography of tissue homogenate restored MMP activity.

CONCLUSION

Normalization of blood glucose and pressure ameliorates albuminuria and inhibits excess ECM production, however persistent TIMP-1 expression hinders attempts at ECM remodelling. Therapies which counteract the action of TIMPs may accelerate scar resolution.