Podocyte detachment in type 2 diabetic nephropathy

How Stem and Progenitor Cells Can Affect Renal Diseases

Stem and progenitor cells have been observed to contribute to regenerative processes in acute renal failure and chronic kidney disease. Recent research has delved into the intricate mechanisms by which stem and progenitor cells exert their influence on kidney diseases. Understanding how these cells integrate with the existing renal architecture and their response to injury could pave the way for innovative treatment strategies aimed at promoting kidney repair and regeneration. Overall, the role of stem and progenitor cells in kidney diseases is multifaceted, with their ability to contribute to tissue regeneration, immune modulation, and the maintenance of renal homeostasis. Here, we review the studies that we have available today about the involvement of stem and progenitor cells both in regenerative therapies and in the causes of renal diseases, as well as in natural healing mechanisms, taking into account the main kidney disorders, such as IgA nephropathy, lupus nephritis, diabetic nephropathy, C3 glomerulopathy, focal segmental glomerulosclerosis, idiopathic membranous nephropathy, anti-glomerular basement membrane glomerulonephritis, and ANCA-associated crescentic glomerulonephritis. Moreover, based on the comprehensive data available in the framework of the specific kidney diseases on stem cells and renal progenitors, we hypothesize a possible role of adult renal progenitors in exacerbating or recovering the illness.

The Human Phospholipase B-II Precursor (HPLBII-P) in Urine as a Novel Biomarker of Glomerular Activity in COVID-19 and Diabetes Mellitus

Background: The human phospholipase B-II precursor (HPLBII-P) was originally purified from white blood cells but is also found in other cellular structures, such as kidney glomeruli and tubuli. The objective of this report was to investigate the relationship of HPLBII-P in urine to acute kidney injury in patients with COVID-19. Methods: Urine was collected at admission from 132 patients with COVID-19 admitted to the intensive care units (ICUs) because of respiratory failure. HPLBII-P was measured using a sensitive ELISA. For comparison, human neutrophil lipocalin (HNL) was measured in urine, using the ELISA configured with the monoclonal antibody 763/8F, as a sign of tubular affection in addition to routine biomarkers of kidney disease. Results: Overall, the concentrations of urinary HPLBII-P were almost 3-fold higher in patients with COVID-19 compared to healthy controls (p < 0.0001) and with significantly higher concentrations even in patients with COVID-19 without signs of acute kidney injury (AKI) (p < 0.001). HPLBII-P was further increased in patients with AKI (p < 0.02). HPLBII-P was significantly increased in patients with diabetes mellitus (p = 0.0008) and correlated to plasma glucose (r = 0.29, p = 0.001) and urine albumin concentrations (r = 0.55, p < 0.001). Conclusions: Urine concentrations of HPLBII-P are highly raised in the urine of patients with COVID-19 and relate to AKI and diabetes mellitus. HPLBII-P may reflect glomerular injury and/or increased glomerular cell activity in SARS-CoV-2 infections.

Modes of podocyte death in diabetic kidney disease: an update

Diabetic kidney disease (DKD) accounts for a large proportion of end-stage renal diseases that require renal replacement therapies including dialysis and transplantation. Therefore, it is critical to understand the occurrence and development of DKD. Podocytes are mainly injured during the development of DKD, ultimately leading to their extensive death and loss. In turn, the injury and death of glomerular podocytes are also the main culprits of DKD. This review introduces the characteristics of podocytes and summarizes the modes of their death in DKD, including apoptosis, autophagy, mitotic catastrophe (MC), anoikis, necroptosis, and pyroptosis. Apoptosis is characterized by nuclear condensation and the formation of apoptotic bodies, and it exerts a different effect from autophagy in mediating DKD-induced podocyte loss. MC mediates a faulty mitotic process while anoikis separates podocytes from the basement membrane. Moreover, pyroptosis activates inflammatory factors to aggravate podocyte injuries whilst necroptosis drives signaling cascades, such as receptor-interacting protein kinases 1 and 3 and mixed lineage kinase domain-like, ultimately promoting the death of podocytes. In conclusion, a thorough knowledge of the modes of podocyte death in DKD can help us understand the development of DKD and lay the foundation for strategies in DKD disease therapy.

Repurposing a clinically approved prescription Colquhounia root tablet to treat diabetic kidney disease via suppressing PI3K/AKT/NF-kB activation

Background

Growing clinical evidences show the potentials of Colquhounia root tablet (CRT) in alleviating diabetic kidney disease (DKD). However, its pharmacological properties and underlying mechanisms remain unclear.

Methods

‘Drug target-Disease gene’ interaction network was constructed and the candidate network targets were screened through evaluating node genes' topological importance. Then, a DKD rat model induced by high-fat diet/streptozotocin was established and used to determine pharmacological effects and network regulatory mechanisms of CRT against DKD, which were also verified using HK2 cell model induced by high glucose.

Results

The candidate network targets of CRT against DKD were involved into various type II diabetes-related and nephropathy-related pathways. Due to the topological importance of the candidate network targets and the important role of the imbalance between immunity and inflammation in the pathogenesis of DKD, PI3K/AKT/NF-кB signaling-mediated immune-modulatory and anti-inflammatory actions of CRT were selected to be experimentally verified. On the basis of high-fat diet (HFD) / streptozotocin (STZ)-induced DKD rat model, CRT effectively reduced the elevated level of blood glucose, decreased the accumulation of renal lipid, suppressed inflammation and the generation of ECM proteins, and ameliorated kidney function and the renal histopathology through inhibiting the activation of PI3K, AKT and NF-кB proteins, reducing the nuclear accumulation of NF-кB protein and the serum levels of downstream cytokines, which were in line with the in vitro findings.

Conclusions

Our data suggest that CRT may be the promising candidate drug for treating DKD via reversing the imbalance of immune-inflammation system mediated by the PI3K/AKT/NF-кB/IL-1β/TNF-α signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00563-7.

Elevated serum leptin levels are associated with lower renal function among middle-aged and elderly adults in Taiwan, a community-based, cross-sectional study

BACKGROUND

Plasma leptin is considered a risk factor for obesity and cardio-metabolic disease, but the link between serum leptin and renal function is still under evaluation. In our study, we focused on the relationship between serum leptin and renal function, and we investigated the relationship in more detail.

METHODS

The 396 middle-aged and elderly Taiwanese adults recruited for our health survey were the subject of our research. All participants agreed to participate and signed a consent form before they joined and completed our study. We divided the participants into three groups according to eGFR tertiles and analyzed the parameters between each group. Then, we used Pearson's correlation test to investigate the relationship between eGFR levels and cardio-metabolic risk factors with adjustment for age. The scatter plot indicates the trend between serum leptin levels and eGFR levels. Participants were reclassified into three subgroups according to their leptin levels and the bar chart reveals the prevalence of chronic kidney disease (CKD) in each group. Finally, we used multivariate linear regression to evaluate the relationship between serum leptin and eGFR levels with adjustment for age, sex, smoking status, drinking status, body mass index (BMI), uric acid levels, hypertension (HTN), diabetes mellitus (DM), and dyslipidemia.

RESULTS

In our study, we analyzed the data from 396 eligible participants. A total of 41.4% of the participants were male, and the average age of all participants was 64.81 years ( ± 8.78). The participants in the high eGFR group were more likely to have lower serum leptin levels. Furthermore, eGFR values were negatively correlated with serum leptin levels even after adjustment for age. The prevalence of CKD in the high serum leptin group was higher than that in the low serum leptin group. Serum leptin levels showed significant negative correlations with eGFR levels (β=-0.14, p<0.01) in the multivariate linear regression after adjusting for age, sex, smoking status, drinking status, BMI, uric acid levels, HTN, DM, and dyslipidemia.

CONCLUSION

According to our study, serum leptin levels show a negative relationship with eGFR levels in middle-aged and elderly people in Taiwan. In addition, high serum leptin levels could be an novel marker to survey kidney failure in clinical practices.

Marein ameliorates diabetic nephropathy by inhibiting renal sodium glucose transporter 2 and activating the AMPK signaling pathway in db/db mice and high glucose-treated HK-2 cells

Marein, an active component of the Coreopsis tinctoria Nutt. plant, is known to improve diabetic nephropathy (DN). However, its anti-diabetic functions in DN and potential mechanisms remain unclear. The aim of this study was to elucidate the effects and mechanisms of Marein in diabetic db/db mice with DN, and in high glucose-treated HK-2 cells. In vivo, treating diabetic db/db mice with Marein for 12 consecutive weeks restored diabetes-induced hyperglycemia and dyslipidemia, and ameliorated renal function deterioration, glomerulosclerosis, and renal ectopic lipid deposition. Marein exerted renoprotective effects by directly inhibiting renal tubule sodium glucose transporter 2 (SGLT2) expression, and then activating the AMP-activated protein kinase (AMPK)/acetyl CoA carboxylase (ACC)/peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) pathway in db/db mice. Meanwhile, Marein ameliorated fibrosis and inflammation by suppressing the pro-inflammatory factors interleukin-6 (IL-6) and monocyte chemotactic protein-1 (MCP-1), and expression of the extracellular matrix proteins, fibronectin (FN) and collagen 1 (COL1) in diabetic mice. In vitro, MDCK monolayer cells were established to explore the characteristics of Marein transmembrane transport. Marein was found to be absorbed across the membrane at a medium level that involved active transport and this was mediated by SGLTs. In HK-2 cells, Marein decreased uptake of the fluorescent glucose analog, 2-NBDG, by 22 % by inhibiting SGLT2 expression. In high glucose-treated HK-2 cells, Marein decreased SGLT2 expression and increased phosphorylated (p)-AMPK/p-ACC to improve high glucose-induced cellular dysfunction. Furthermore, Marein treatment decreased SGLT2 expression in SGLT2-overexpressing HK-2 cells. In addition, molecular docking and dynamics analysis revealed that SGLT2 was a direct target of Marein. Collectively, our results demonstrated that Marein ameliorates DN by inhibiting renal SGLT2 and activating p-AMPK, suggesting Marein can potentially prevent DN by suppressing renal SGLT2 expression directly.

Loss of Roundabout Guidance Receptor 2 (Robo2) in Podocytes Protects Adult Mice from Glomerular Injury by Maintaining Podocyte Foot Process Structure

Roundabout guidance receptor 2 (ROBO2) plays an important role during early kidney development. ROBO2 is expressed in podocytes, inhibits nephrin-induced actin polymerization, down-regulates nonmuscle myosin IIA activity, and destabilizes kidney podocyte adhesion. However, the role of ROBO2 during kidney injury, particularly in mature podocytes, is not known. Herein, we report that loss of ROBO2 in podocytes [Robo2 conditional knockout (cKO) mouse] is protective from glomerular injuries. Ultrastructural analysis reveals that Robo2 cKO mice display less foot process effacement and better-preserved slit-diaphragm density compared with wild-type littermates injured by either protamine sulfate or nephrotoxic serum (NTS). The Robo2 cKO mice also develop less proteinuria after NTS injury. Further studies reveal that ROBO2 expression in podocytes is up-regulated after glomerular injury because its expression levels are higher in the glomeruli of NTS injured mice and passive Heymann membranous nephropathy rats. Moreover, the amount of ROBO2 in the glomeruli is also elevated in patients with membranous nephropathy. Finally, overexpression of ROBO2 in cultured mouse podocytes compromises cell adhesion. Taken together, these findings suggest that kidney injury increases glomerular ROBO2 expression that might compromise podocyte adhesion and, thus, loss of Robo2 in podocytes could protect from glomerular injury by enhancing podocyte adhesion that helps maintain foot process structure. Our findings also suggest that ROBO2 is a therapeutic target for podocyte injury and podocytopathy.

Pro-inflammatory cytokines are associated with podocyte damage and proximal tubular dysfunction in the early stage of diabetic kidney disease in type 2 diabetes mellitus patients

AIMS

To evaluate if there is a link between inflammation (expressed by inflammatory cytokines) and the early stage of diabetic kidney disease (DKD), as shown by markers of podocyte damage and proximal tubular (PT) dysfunction.

METHODS

In this study were enrolled 117 type 2 DM patients (36-normoalbuminuria, 42-microalbuminuria, 39- macroalbuminuria), and 11 healthy subjects. Serum and urinary IL-1 alpha, IL-8, IL-18, urinary albumin:creatinine ratio (UACR), eGFR, biomarkers of podocyte damage (podocalyxin, synaptopodin, nephrin) and of PT dysfunction (KIM-1, NAG) were assessed.

RESULTS

In multivariable regression urinary Il-1 alpha correlated positively with podocalyxin and NAG (p < 0.0001, R²= 0.57); urinary IL-8 correlated directly with synaptopodin, NAG, nephrin, and KIM-1 (p < 0.0001, R² = 0.67); urinary IL-18 correlated directly with synaptopodin, NAG, and nephrin (p < 0.0001, R² = 0.59). Serum IL-1 alpha correlated positively with nephrin, synaptopodin, NAG (P < 0.0001, R² = 0.68); serum IL-8 correlated directly with synaptopodin and NAG (p < 0.0001, R² = 0.66); serum IL-18 correlated directly with NAG, KIM-1, and podocalyxin (p < 0.0001, R²=0.647).

CONCLUSIONS

Pro-inflammatory interleukins are associated with podocyte injury and PT dysfunction in early DKD. These could exert a key role in the pathogenesis of early DKD, before the development of albuminuria.

The protective effect and mechanism of catalpol on high glucose-induced podocyte injury

BACKGROUND

Catalpol, a natural iridoid glycoside in Rehmannia glutinosa, can alleviate proteinuria associated with diabetic nephropathy (DN), however, whether catalpol has a protective effect against podocyte injury in DN remains unclear.

METHODS

In this study, we used a high glucose (HG)-induced podocyte injury model to evaluate the protective effect and mechanism of catalpol against HG-induced podocyte injury. Cell viability was determined by the 3-(4,5-dimethylthiazolyl-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The levels of lactate dehydrogenase (LDH), superoxide dismutase (SOD) and malondialdehyde (MDA) were measured by commercial assay kits. Cell apoptosis and reactive oxygen species (ROS) were determined by using flow cytometry. Tumour necrosis factor α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) levels were determined by enzyme-linked immunosorbent assay (ELISA). The protein expression levels of B-cell lymphoma-2 (Bcl-2), Bcl2-associated x (Bax), cleaved caspase-3, nicotinamide adenine dinucleotide phosphate oxidase enzyme 4 (NOX4), toll-like receptor 4 (TLR4), myeloid differentiation primary response gene 88 (MyD88), p38 mitogen-activated protein kinase (p38 MAPK), phosphorylated p38 MAPK (p-p38 MAPK), nuclear factor kappa B inhibitor alpha (IκBα) and phosphorylated IκBα (p-IκBα) were measured by western blotting. In addition, Bcl-2, Bax, caspase-3 and nuclear factor kappa B (NF-κB) levels were determined by immunofluorescence staining.

RESULTS

Catalpol significantly increased cell viability and decreased LDH release in HG-induced podocyte injury. Catalpol significantly decreased ROS generation, apoptosis, level of MDA, levels of inflammatory cytokine TNF-α, IL-1β, and IL-6 and increased SOD activity in HG-induced podocyte injury. Moreover, catalpol significantly decreased expression of cleaved caspase-3, Bax, NOX4, TLR4, MyD88, p-p38 MAPK, p-IκBα and NF-κB nuclear translocation, as well as increased Bcl-2 expression in HG-induced podocyte injury.

CONCLUSION

Catalpol can protect against podocyte injury by ameliorating apoptosis and inflammation. These protective effects may be attributed to the inhibition of NOX4, which alleviates ROS generation and suppression of the TLR4/MyD88 and p38 MAPK signaling pathways to prevent NF-κB activation. Therefore, catalpol could be a promising drug for the prevention of DN.

[Ultrastructural study of podocyte alterations in non proliferative glomerulopathy]

Ultrastructural changes in podocytes are an important diagnostic and prognostic marker for nephropathies. However, the biomedical understanding of detected submicroscopic changes in podocytes remains controversial.

OBJECTIVE

To investigate the relationship between the ultrastructural changes of podocytes (fusion of cytopodia and denudation of the basement membrane as a result of their desquamation) with a number of clinical and laboratory indicators of kidney dysfunction in case of non-proliferative glomerulopathies (NPGP). Thirty-seven patients (23 men, 14 women) with NPGP, including 8 with focal segmental glomerulosclerosis (FSGS), 17 with membranous nephropathy (MN), and 12 with minimal change disease (MCD), were examined.

SUBJECT AND METHODS

All the patients underwent standard laboratory and instrumental studies: determinations of the levels of total serum cholesterol (mmol/l), total serum protein (g/l); serum albumin (g/l); CKD-EPI glomerular filtration rate (GFR) (ml/min/1.73 m²), and daily protein loss (g/day). Light optical changes were measured; completely sclerotic and/or focally segmentally sclerotic glomeruli were taken into account. Quantitative ultrastructural stereological analysis was carried out estimating the cytopodium width (CPW) and the degree of glomerular basement membrane denudation (GBMD) (%).

RESULTS

NPGP cases showed the largest number of sclerotic glomeruli in FSGS, which was accompanied by the lowest level of daily proteinuria and GFR. Quantitative values of CPW were associated with the level of daily protein loss (r=0.47; p < 0.05) and serum albumin (r=-0.57; p <0.05) in patients with nephrotic syndrome. In MN, the absolute value of CPW was larger than that in the other two patient groups. A correlation analysis of CPW and GBMD values among patients with NPGP revealed a statistically insignificant negative relation between these morphometric parameters. However, when a subgroup of patients with podocytopathies (only MCD and FSGS) was identified in the study group, this relationship was found to be significant (r=-0.54; p=0.012).

CONCLUSION

The patients with NPGP exhibited a relationship between the severity of nephrotic syndrome and proteinuria/hypoalbuminemia, on the one hand, and CPW, on the other. The established negative relationship between CPW and the percentage of GBMD in the subgroup of patients with podocytopathies may be due to the early stages of podocyte injury, which are accompanied by transient GBMD.

Effects of insulin and metformin on fetal kidney development of streptozotocin-induced gestational diabetic albino rats

Gestational diabetes mellitus is one of common medical complications of pregnancy. Hyperglycemia in utero impairs renal development and produces renal anomalies. Metformin has antioxidant properties and better glycemic control. Aim: assessment insulin and metformin effects on renal development of streptozotocin-induced gestational diabetic albino rats. Sixty virgin female albino rats were used. Once pregnancy confirmed, animals were randomly assigned into control, metformin, diabetic, diabetic plus insulin, diabetic plus metformin and diabetic plus insulin and metformin treated groups. Rats were sacrificed on the 20th day of gestation; fetuses were extracted and weighted. Fetal kidneys were extracted prepared for light, morphometric and electron microscopic examination. Diabetic followed by diabetic plus metformin treated groups revealed retardation of glomerular development in the cortical and Juxtaglomerular zones with a significant increase in the early immature glomerular stages and immature to mature glomerular ratio compared to other groups. Diabetic group also showed morphometric changes, shrunken and empty glomeruli, vacuolar degeneration and hemorrhage. Diabetic plus metformin group showed minimal improvement while diabetic plus insulin and diabetic plus insulin and metformin groups showed developmental, histopathological and morphometric improvement with best results in the combination group. Gestational diabetes mellitus (GDM) possess deleterious effects on fetal kidney development. Insulin improves the glycemic state and decreases GDM effects on fetal kidneys. Metformin produces mild protection while the combination of insulin and metformin produces the best glycemic control and protect fetal kidneys.

Podocyte injury elicits loss and recovery of cellular forces

In the healthy kidney, specialized cells called podocytes form a sophisticated blood filtration apparatus that allows excretion of wastes and excess fluid from the blood while preventing loss of proteins such as albumin. To operate effectively, this filter is under substantial hydrostatic mechanical pressure. Given their function, it is expected that the ability to apply mechanical force is crucial to the survival of podocytes. However, to date, podocyte mechanobiology remains poorly understood, largely because of a lack of experimental data on the forces involved. We perform quantitative, continuous, nondisruptive, and high-resolution measurements of the forces exerted by differentiated podocytes in real time using a recently introduced functional imaging modality for continuous force mapping. Using an accepted model for podocyte injury, we find that injured podocytes experience near-complete loss of cellular force transmission but that this loss of force is reversible under certain conditions. The observed changes in force correlate with F-actin rearrangement and reduced expression of podocyte-specific proteins. By introducing robust and high-throughput mechanical phenotyping and by demonstrating the significance of mechanical forces in podocyte injury, this research paves the way to a new level of understanding of the kidney. In addition, in an advance over established force mapping techniques, we integrate cellular force measurements with immunofluorescence and perform continuous long-term force measurements of a cell population. Hence, our approach has general applicability to a wide range of biomedical questions involving mechanical forces.

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.

WT1 ameliorates podocyte injury via repression of EZH2/β-catenin pathway in diabetic nephropathy

Epigenetic modulation of podocyte injury plays a pivotal role in diabetic nephropathy (DN). Wilm's tumor 1 (WT1) has been found to have opposing roles with β-catenin in podocyte biology. Herein, we asked whether the histone methyltransferase enzyme enhancer of zeste homolog 2 (EZH2) promotes WT1-induced podocyte injury via β-catenin activation and the underlying mechanisms. We found that WT1 antagonized EZH2 and ameliorated β-catenin-mediated podocyte injury as demonstrated by attenuated podocyte mesenchymal transition, maintenance of podocyte architectural integrity, decreased podocyte apoptosis and oxidative stress. Further, we provided mechanistical evidence that EZH2 was required in WT1-mediated β-catenin inactivation via repression of secreted frizzled-related protein 1 (SFRP-1), a Wnt antagonist. Moreover, EZH2-mediated silencing of SFRP-1 was due to increased histone 3 lysine 27 trimethylation (H3K27me3) on its promoter region. WT1 favored renal function and decreased podocyte injury in diabetic rats and DN patients. Notably, WT1 exhibited clinical and biological relevance as it was linked to dropped serum creatinine, decreased proteinuria and elevated estimated glomerular filtration rate (eGFR). We propose an epigenetic process via the WT1/EZH2/β-catenin axis in attenuating podocyte injury in DN. Targeting WT1 and EZH2 could be potential therapeutic approaches for DN.

Combination of Tripterygium wilfordii Hook F and angiotensin receptor blocker synergistically reduces excretion of urinary podocytes in patients with type 2 diabetic kidney disease

The aim of this study was to investigate whether Tripterygium wilfordii Hook F (TwHF) and irbesartan could synergistically affect the urinary excretion of podocytes and proteins in type 2 diabetic kidney disease (DKD) patients and the underlying mechanisms. Forty DKD patients were divided into a DI group (DKD patients treated with irbesartan alone) and a DTI group (DKD patients treated with Tripterygium wilfordii Hook F and irbesartan). Urinary podocytes were observed by immunofluorescence. Urinary levels of connective tissue growth factor (CTGF) and transforming growth factor-β₁ (TGF-β₁) were detected by enzyme-linked immunosorbent assay. Immunofluorescence indicated that shed podocytes were not detected in urine samples of normal controls, whereas the detection rate of urinary podocytes was 82.5% in DKD patients. Urinary CTGF and TGF-β₁ levels were significantly higher in urinary podocyte-positive DKD patients than in urinary podocyte-negative patients. Furthermore, urinary podocyte excretion was closely correlated with urinary protein excretion and urinary CTGF/TGF-β₁ levels. Treatments with TwHF and irbesartan significantly reduced the urinary excretion of proteins and podocytes, and decreased the urinary levels of CTGF and TGF-β₁. Our results suggest that urinary podocyte excretion might serve as a predictor for DKD progression. TwHF/irbesartan combination could reduce the urinary excretion of proteins and podocytes synergistically in DKD patients, which might result from the synergistic inhibition of CTGF and TGF-β₁ in urine.

MicroRNA-21 in glomerular injury

TGF-β(1) is a pleotropic growth factor that mediates glomerulosclerosis and podocyte apoptosis, hallmarks of glomerular diseases. The expression of microRNA-21 (miR-21) is regulated by TGF-β(1), and miR-21 inhibits apoptosis in cancer cells. TGF-β(1)-transgenic mice exhibit accelerated podocyte loss and glomerulosclerosis. We determined that miR-21 expression increases rapidly in cultured murine podocytes after exposure to TGF-β(1) and is higher in kidneys of TGF-β(1)-transgenic mice than wild-type mice. miR-21-deficient TGF-β(1)-transgenic mice showed increased proteinuria and glomerular extracellular matrix deposition and fewer podocytes per glomerular tuft compared with miR-21 wild-type TGF-β(1)-transgenic littermates. Similarly, miR-21 expression was increased in streptozotocin-induced diabetic mice, and loss of miR-21 in these mice was associated with increased albuminuria, podocyte depletion, and mesangial expansion. In cultured podocytes, inhibition of miR-21 was accompanied by increases in the rate of cell death, TGF-β/Smad3-signaling activity, and expression of known proapoptotic miR-21 target genes p53, Pdcd4, Smad7, Tgfbr2, and Timp3. In American-Indian patients with diabetic nephropathy (n=48), albumin-to-creatinine ratio was positively associated with miR-21 expression in glomerular fractions (r=0.6; P<0.001) but not tubulointerstitial fractions (P=0.80). These findings suggest that miR-21 ameliorates TGF-β(1) and hyperglycemia-induced glomerular injury through repression of proapoptotic signals, thereby inhibiting podocyte loss. This finding is in contrast to observations in murine models of tubulointerstitial kidney injury but consistent with findings in cancer models. The aggravation of glomerular disease in miR-21-deficient mice and the positive association with albumin-to-creatinine ratio in patients with diabetic nephropathy support miR-21 as a feedback inhibitor of TGF-β signaling and functions.

Gremlin aggravates hyperglycemia-induced podocyte injury by a TGFβ/smad dependent signaling pathway

Gremlin is a bone morphogenic protein (BMP) antagonist and is elevated in diabetic kidney tissues. In the early course of diabetic nephropathy (DN), podocyte are injured. We studied the protein and gene expression of gremlin in mice podocytes cultured in hyperglycemia ambient. The role of gremlin on podocyte injury and the likely signaling pathways involved were determined. Expression of gremlin was visualized by confocal microscopy. Recombinant mouse gremlin and small interfering RNA (siRNA) targeting to gremlin1 identified the role played by gremlin on podocytes. Study of canonical (smad2/3) and non-canonical (p38MAPK and JNK1/2) transforming growth factor beta (TGFβ)/smad mediated signaling revealed the putative signaling mechanisms involved. Smad2/3 siRNA and TGFβ receptor inhibition (SB431542) were used to probe canonical TGFβ/smad signaling in gremlin-induced podocyte injury. Apoptosis of podocytes was measured by TUNEL assay. Gremlin expression was enhanced in high glucose cultured mouse podocytes, and was localized predominantly in the cytoplasm and negligibly on the cell membrane. Not only expression of nephrin and synaptopodin were decreased on treatment with gremlin, but also synaptopodin rearrangement and nephrin relocalization were evident. Knockdown gremlin1 or smad2/3 by siRNA, and inhibition of TGFβR (SB431542) attenuated podocyte injury. Inhibition of canonical TGF-β signal blocked the injury of gremlin on podocytes. In conclusion, gremlin was clearly elevated in high glucose cultured mouse podocytes, and likely employed endogenous canonical TGFβ1/Smad signaling to induce podocyte injury. Knockdown gremlin1 by siRNA may be clinically useful in the attenuation of podocyte injury.

Transforming growth factor-β-induced cross talk between p53 and a microRNA in the pathogenesis of diabetic nephropathy

Elevated p53 expression is associated with several kidney diseases including diabetic nephropathy (DN). However, the mechanisms are unclear. We report that expression levels of transforming growth factor-β1 (TGF-β), p53, and microRNA-192 (miR-192) are increased in the renal cortex of diabetic mice, and this is associated with enhanced glomerular expansion and fibrosis relative to nondiabetic mice. Targeting miR-192 with locked nucleic acid-modified inhibitors in vivo decreases expression of p53 in the renal cortex of control and streptozotocin-injected diabetic mice. Furthermore, mice with genetic deletion of miR-192 in vivo display attenuated renal cortical TGF-β and p53 expression when made diabetic, and have reduced renal fibrosis, hypertrophy, proteinuria, and albuminuria relative to diabetic wild-type mice. In vitro promoter regulation studies show that TGF-β induces reciprocal activation of miR-192 and p53, via the miR-192 target Zeb2, leading to augmentation of downstream events related to DN. Inverse correlation between miR-192 and Zeb2 was observed in glomeruli of human subjects with early DN, consistent with the mechanism seen in mice. Our results demonstrate for the first time a TGF-β-induced feedback amplification circuit between p53 and miR-192 related to the pathogenesis of DN, and that miR-192-knockout mice are protected from key features of DN.

Temporal profile of diabetic nephropathy pathologic changes

Diabetic nephropathy, by far, is the most common cause of end stage renal disease in the US and many other countries. In type 1 diabetes, the natural history of diabetic nephropathy is tightly linked to evolution of classic lesions of the disease, namely glomerular basement membrane thickening, increased mesangial matrix, and reduced glomerular filtration surface density. These lesions progress in parallel and correlate with increased albumin excretion rate and reduced glomerular filtration rate across a wide range of renal function. In fact, the vast majority of the variances of albumin excretion and glomerular filtration rates can be explained by these glomerular lesions alone in type 1 diabetic patients. Although, classic lesions of diabetic nephropathy, indistinguishable from those of type 1 diabetes, also occur in type 2 diabetes, renal lesions are more heterogeneous in type 2 diabetic patients with some patients developing more advanced vascular or chronic tubulointerstitial lesions than diabetic glomerulopathy. More research biopsy longitudinal studies, especially in type 2 diabetic patients, are needed to better understand various pathways of renal injury in diabetic nephropathy.

The podocyte's response to stress: the enigma of foot process effacement

Progressive loss of podocytes is the most frequent cause accounting for end-stage renal failure. Podocytes are complex, terminally differentiated cells incapable of replicating. Thus lost podocytes cannot be replaced by proliferation of neighboring undamaged cells. Moreover, podocytes occupy a unique position as epithelial cells, adhering to the glomerular basement membrane (GBM) only by their processes, whereas their cell bodies float within the filtrate in Bowman's space. This exposes podocytes to the danger of being lost by detachment as viable cells from the GBM. Indeed, podocytes are continually excreted as viable cells in the urine, and the rate of excretion dramatically increases in glomerular diseases. Given this situation, it is likely that evolution has developed particular mechanisms whereby podocytes resist cell detachment. Podocytes respond to stress and injury by undergoing tremendous changes in shape. Foot process effacement is the most prominent and, yet in some ways, the most enigmatic of those changes. This review summarizes the various structural responses of podocytes to injury, focusing on foot process effacement and detachment. We raise the hypothesis that foot process effacement represents a protective response of podocytes to escape detachment from the GBM.

New urinary biomarkers for diabetic kidney disease

Diabetic kidney disease is the leading cause of end-stage renal disease in developed and developing countries. Microalbuminuria is the gold standard for detection and prediction of diabetic kidney disease and cardiovascular risk disease in clinical practice. However, microalbuminuria has several limitations, such as lower sensitive, larger variability. It is urgent to explore higher sensitivity and specificity for earlier detection of diabetic kidney disease and more accurate prediction of the progression to end stage renal disease. We reviewed some new and important urinary biomarkers, such as: transferrin, immunoglobulin G, immunoglobulin M, Cystanic C, podocytes, type IV collagen, 8-oxo-7, 8-dihydro-2'-deoxyguanosine, ceruloplasmin, monocyte chemoattractant protein-1 and so on. We need good quality, long-term, large longitudinal trials to validate published biomarkers and find new biomarkers, considering biomarkers reviewed here are from small cross-sectional studies.

Renal progenitors in non-diabetic and diabetic nephropathies

Chronic kidney disease represents a major health problem worldwide. Although the kidney has the ability to repopulate structures that have sustained some degree of injury, the mechanisms underlying its regenerative capacity have been unclear. Recent evidence now supports the existence of a renal progenitor system able to replace podocytes and tubular cells, localized within the urinary pole of Bowman's capsule and along the tubule. Altered growth or differentiation of renal progenitors has been reported in several renal disorders including diabetic nephropathy. Pharmacological modulation of renal progenitor growth or differentiation can enhance kidney regeneration, suggesting that treatments aimed at reversing kidney injury are possible. Renal progenitors may represent a novel target in diabetic nephropathy and other kidney disorders.

Podocyte detachment and reduced glomerular capillary endothelial fenestration promote kidney disease in type 2 diabetic nephropathy

Podocyte detachment and reduced endothelial cell fenestration and relationships between these features and the classic structural changes of diabetic nephropathy have not been described in patients with type 2 diabetes. Here we studied these relationships in 37 Pima Indians with type 2 diabetes of whom 11 had normal albuminuria, 16 had microalbuminuria, and 10 had macroalbuminuria. Biopsies from 10 kidney donors (not American Indians) showed almost undetectable (0.03%) podocyte detachment and 43.5% endothelial cell fenestration. In patients with type 2 diabetes, by comparison, the mean percentage of podocyte detachment was significantly higher in macroalbuminuria (1.48%) than in normal albuminuria (0.41%) or microalbuminuria (0.37%). Podocyte detachment correlated significantly with podocyte number per glomerulus and albuminuria. The mean percentage of endothelial cell fenestration was significantly lower in macroalbuminuria (19.3%) than in normal albuminuria (27.4%) or microalbuminuria (27.2%) and correlated significantly with glomerular basement membrane thickness, albuminuria, fractional mesangial area, and the glomerular filtration rate (iothalamate clearance). Podocyte detachment and diminished endothelial cell fenestration were not correlated, but were related to classic lesions of diabetic nephropathy. Thus, our findings confirm the important role these injuries play in the development and progression of kidney disease in type 2 diabetes, just as they do in type 1 diabetes. Whether podocyte detachment creates conduits for proteins to escape the glomerular circulation and reduced endothelial fenestration lowers glomerular hydraulic permeability requires further study.