Progression of glomerular diseases: is the podocyte the culprit?

Parietal cells-new perspectives in glomerular disease

In normal glomeruli, parietal epithelial cells (PECs) line the inside of Bowman's capsule and form an inconspicuous sheet of flat epithelial cells in continuity with the proximal tubular epithelial cells (PTECs) at the urinary pole and with the podocytes at the vascular pole. PECs, PTECs and podocytes have a common mesenchymal origin and are the result of divergent differentiation during embryogenesis. Podocytes and PTECs are highly differentiated cells with well-established functions pertaining to the maintenance of the filtration barrier and transport, respectively. For PECs, no specific function other than a structural one has been known until recently. Possible important functions for PECs in the fate of the glomerulus in glomerular disease have now become apparent: (1) PECs may be involved in the replacement of lost podocytes; (2) PECs form the basis of extracapillary proliferative lesions and subsequent sclerosis in glomerular disease. In addition to the acknowledgement that PECs are crucial in glomerular disease, knowledge has been gained regarding the molecular processes driving the phenotypic changes and behavior of PECs. Understanding these molecular processes is important for the development of specific therapeutic approaches aimed at either stimulation of the regenerative function of PECs or inhibition of the pro-sclerotic action of PECs. In this review, we discuss recent advances pertaining to the role of PECs in glomerular regeneration and disease and address the major molecular processes involved.

Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a leading cause of kidney disease worldwide. The presumed etiology of primary FSGS is a plasma factor with responsiveness to immunosuppressive therapy and a risk of recurrence after kidney transplant-important disease characteristics. In contrast, adaptive FSGS is associated with excessive nephron workload due to increased body size, reduced nephron capacity, or single glomerular hyperfiltration associated with certain diseases. Additional etiologies are now recognized as drivers of FSGS: high-penetrance genetic FSGS due to mutations in one of nearly 40 genes, virus-associated FSGS, and medication-associated FSGS. Emerging data support the identification of a sixth category: APOL1 risk allele-associated FSGS in individuals with sub-Saharan ancestry. The classification of a particular patient with FSGS relies on integration of findings from clinical history, laboratory testing, kidney biopsy, and in some patients, genetic testing. The kidney biopsy can be helpful, with clues provided by features on light microscopy (e.g, glomerular size, histologic variant of FSGS, microcystic tubular changes, and tubular hypertrophy), immunofluorescence (e.g, to rule out other primary glomerulopathies), and electron microscopy (e.g., extent of podocyte foot process effacement, podocyte microvillous transformation, and tubuloreticular inclusions). A complete assessment of renal histology is important for establishing the parenchymal setting of segmental glomerulosclerosis, distinguishing FSGS associated with one of many other glomerular diseases from the clinical-pathologic syndrome of FSGS. Genetic testing is beneficial in particular clinical settings. Identifying the etiology of FSGS guides selection of therapy and provides prognostic insight. Much progress has been made in our understanding of FSGS, but important outstanding issues remain, including the identity of the plasma factor believed to be responsible for primary FSGS, the value of routine implementation of genetic testing, and the identification of more effective and less toxic therapeutic interventions for FSGS.

The Tubulointerstitial Pathophysiology of Progressive Kidney Disease

Accumulating evidence suggests that the central locus for the progression of CKD is the renal proximal tubule. As injured tubular epithelial cells dedifferentiate in attempted repair, they stimulate inflammation and recruit myofibroblasts. At the same time, tissue loss stimulates remnant nephron hypertrophy. Increased tubular transport workload eventually exceeds the energy-generating capacity of the hypertrophied nephrons, leading to anerobic metabolism, acidosis, hypoxia, endoplasmic reticulum stress, and the induction of additional inflammatory and fibrogenic responses. The result is a vicious cycle of injury, misdirected repair, maladaptive responses, and more nephron loss. Therapy that might be advantageous at one phase of this progression pathway could be deleterious during other phases. Thus, interrupting this downward spiral requires narrowly targeted approaches that promote healing and adequate function without generating further entry into the progression cycle.

Renoprotection From Diabetic Complications in OVE Transgenic Mice by Endothelial Cell Specific Overexpression of Metallothionein: A TEM Stereological Analysis

We previously demonstrated that OVE transgenic diabetic mice are susceptible to chronic complications of diabetic nephropathy (DN) including substantial oxidative damage to the renal glomerular filtration barrier (GFB). Importantly, the damage was mitigated significantly by overexpression of the powerful antioxidant, metallothionein (MT) in podocytes. To test our hypothesis that GFB damage in OVE mice is the result of endothelial oxidative insult, a new JTMT transgenic mouse was designed in which MT overexpression was targeted specifically to endothelial cells. At 60 days of age, JTMT mice were crossed with age-matched OVE diabetic mice to produce bi-transgenic OVE-JTMT diabetic progeny that carried the endothelial targeted JTMT transgene. Renal tissues from the OVE-JTMT progeny were examined by unbiased TEM stereometry for possible GFB damage and other alterations from chronic complications of DN. In 150 day-old OVE-JTMT mice, blood glucose and HbA1c were indistinguishable from age-matched OVE mice. However, endothelial-specific MT overexpression in OVE-JTMT mice mitigated several DN complications including significantly increased non-fenestrated glomerular endothelial area, and elimination of glomerular basement membrane thickening. Significant renoprotection was also observed outside of endothelial cells, including reduced podocyte effacement, and increased podocyte and total glomerular cell densities. Moreover, when compared to OVE diabetic animals, OVE-JTMT mice showed significant mitigation of nephromegaly, glomerular hypertrophy, increased mesangial cell numbers and increased total glomerular cell numbers. These results confirm the importance of oxidative stress to glomerular damage in DN, and show the central role of endothelial cell injury to the pathogenesis of chronic complications of diabetes. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:560-576, 2017. © 2016 Wiley Periodicals, Inc.

Notoginsenoside R1 attenuates glucose-induced podocyte injury via the inhibition of apoptosis and the activation of autophagy through the PI3K/Akt/mTOR signaling pathway

Injury to terminally differentiated podocytes contributes ignificantly to proteinuria and glomerulosclerosis. The aim of this study was to examine the protective effects of notoginsenoside R1 (NR1) on the maintenance of podocyte number and foot process architecture via the inhibition of apoptosis, the induction of autophagy and the maintenance pf podocyte biology in target cells. The effects of NR1 on conditionally immortalized human podocytes under high glucose conditions were evaluated by determining the percentage apoptosis, the percentage autophagy and the expression levels of slit diaphragm proteins. Our results revealed that NR1 protected the podocytes against high glucose-induced injury by decreasing apoptosis, increasing autophagy and by promoting cytoskeletal recovery. The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway was further investigated in order to elucidate the mechanisms responsible for the protective effects of NR1 on podocytes. Our data indicated that treatment with NR increased the phosphorylation levels of PI3K, Akt and mTOR, leading to the activation of the PI3K/Akt/mTOR signaling pathway in podocytes. To the best of our knowledge, this is the first in vitro study to demonstrate that NR1 protects podocytes by activating the PI3K/Akt/mTOR pathway.

Diabetes-Induced Reactive Oxygen Species: Mechanism of Their Generation and Role in Renal Injury

Diabetes induces the onset and progression of renal injury through causing hemodynamic dysregulation along with abnormal morphological and functional nephron changes. The most important event that precedes renal injury is an increase in permeability of plasma proteins such as albumin through a damaged glomerular filtration barrier resulting in excessive urinary albumin excretion (UAE). Moreover, once enhanced UAE begins, it may advance renal injury from progression of abnormal renal hemodynamics, increased glomerular basement membrane (GBM) thickness, mesangial expansion, extracellular matrix accumulation, and glomerulosclerosis to eventual end-stage renal damage. Interestingly, all these pathological changes are predominantly driven by diabetes-induced reactive oxygen species (ROS) and abnormal downstream signaling molecules. In diabetic kidney, NADPH oxidase (enzymatic) and mitochondrial electron transport chain (nonenzymatic) are the prominent sources of ROS, which are believed to cause the onset of albuminuria followed by progression to renal damage through podocyte depletion. Chronic hyperglycemia and consequent ROS production can trigger abnormal signaling pathways involving diverse signaling mediators such as transcription factors, inflammatory cytokines, chemokines, and vasoactive substances. Persistently, increased expression and activation of these signaling molecules contribute to the irreversible functional and structural changes in the kidney resulting in critically decreased glomerular filtration rate leading to eventual renal failure.

Prohibitin Signaling at the Kidney Filtration Barrier

The kidney filtration barrier consists of three well-defined anatomic layers comprising a fenestrated endothelium, the glomerular basement membrane (GBM) and glomerular epithelial cells, the podocytes. Podocytes are post-mitotic and terminally differentiated cells with primary and secondary processes. The latter are connected by a unique cell-cell contact, the slit diaphragm. Podocytes maintain the GBM and seal the kidney filtration barrier to prevent the onset of proteinuria. Loss of prohibitin-1/2 (PHB1/2) in podocytes results not only in a disturbed mitochondrial structure but also in an increased insulin/IGF-1 signaling leading to mTOR activation and a detrimental metabolic switch. As a consequence, PHB-knockout podocytes develop proteinuria and glomerulosclerosis and eventually loss of renal function. In addition, experimental evidence suggests that PHB1/2 confer additional, extra-mitochondrial functions in podocytes as they localize to the slit diaphragm and thereby stabilize the unique intercellular contact between podocytes required to maintain an effective filtration barrier.

Regulation of Nephrin Phosphorylation in Diabetes and Chronic Kidney Injury

Diabetes is the leading cause of microalbuminuria and end-stage renal failure in industrial countries. Disruption of the filtration barrier, seen in almost all nephrotic diseases and diabetes, is the result of the loss or effacement of the podocyte foot process, notably damage of proteins within the slit diaphragm such as nephrin. For many years, nephrin has been viewed as a structural component of the slit diaphragm. It is now well recognized that nephrin contains several tyrosine residues in its cytoplasmic domain, which influences the development of glomerular injury. In this review, we propose an overview of nephrin signaling pathways in kidney injury.

Podocyte number and density changes during early human life

BACKGROUND

Podocyte depletion, which drives progressive glomerulosclerosis in glomerular diseases, is caused by a reduction in podocyte number, size or function in the context of increasing glomerular volume.

METHODS

Kidneys obtained at autopsy from premature and mature infants who died in the first year of life (n = 24) were used to measure podometric parameters for comparison with previously reported data from older kidneys.

RESULTS

Glomerular volume increased 4.6-fold from 0.13 ± 0.07 μm³ x10⁶ in the pre-capillary loop stage, through 0.35 μm³ x10⁶ at the capillary loop, to 0.60 μm³ x10⁶ at the mature glomerular stage. Podocyte number per glomerulus increased from 326 ± 154 per glomerulus at the pre-capillary loop stage to 584 ± 131 per glomerulus at the capillary loop stage of glomerular development to reach a value of 589 ± 166 per glomerulus in mature glomeruli. Thus, the major podocyte number increase occurs in the early stages of glomerular development, in contradistinction to glomerular volume increase, which continues after birth in association with body growth.

CONCLUSIONS

As glomeruli continue to enlarge, podocyte density (number per volume) rapidly decreases, requiring a parallel rapid increase in podocyte size that allows podocyte foot processes to maintain complete coverage of the filtration surface area. Hypertrophic stresses on the glomerulus and podocyte during development and early rapid growth periods of life are therefore likely to play significant roles in determining how and when defects in podocyte structure and function due to genetic variants become clinically manifest. Therapeutic strategies aimed at minimizing mismatch between these factors may prove clinically useful.

Podocyte and Parietal Epithelial Cell Interactions in Health and Disease

The glomerulus has 3 resident cells namely mesangial cells that produce the mesangial matrix, endothelial cells that line the glomerular capillaries, and podocytes that cover the outer surface of the glomerular basement membrane. Parietal epithelial cells (PrECs), which line the Bowman's capsule are not part of the glomerular tuft but may have an important role in the normal function of the glomerulus. A significant progress has been made in recent years regarding our understanding of the role and function of these cells in normal kidney and in kidneys with various types of glomerulopathy. In crescentic glomerulonephritis necrotizing injury of the glomerular tuft results in activation and leakage of fibrinogen which provides the trigger for excessive proliferation of PrECs giving rise to glomerular crescents. In cases of collapsing glomerulopathy, podocyte injury causes collapse of the glomerular capillaries and activation and proliferation of PrECs, which accumulate within the urinary space in the form of pseudocrescents. Many of the noninflammatory glomerular lesions such as focal segmental glomerulosclerosis and global glomerulosclerosis also result from podocyte injury which causes variable loss of podocytes. In these cases podocyte injury leads to activation of PrECs that extend on to the glomerular tuft where they cause segmental and/or global sclerosis by producing excess matrix, resulting in obliteration of the capillary lumina. In diabetic nephropathy, in addition to increased matrix production in the mesangium and glomerular basement membranes, increased loss of podocytes is an important determinant of long-term prognosis. Contrary to prior belief there is no convincing evidence for an active podocyte proliferation in any of the above mentioned glomerulopathies.

MicroRNA-30e targets BNIP3L to protect against aldosterone-induced podocyte apoptosis and mitochondrial dysfunction

MicroRNAs are essential for the maintenance of podocyte homeostasis. Emerging evidence has demonstrated a protective role of microRNA-30a (miR-30a), a member of the miR-30 family, in podocyte injury. However, the roles of other miR-30 family members in podocyte injury are unclear. The present study was undertaken to investigate the contribution of miR-30e to the pathogenesis of podocyte injury induced by aldosterone (Aldo), as well as the underlying mechanism. After Aldo treatment, miR-30e was reduced in a dose-and time-dependent manner. Notably, overexpression of miR-30e markedly attenuated Aldo-induced apoptosis in podocytes. In agreement with this finding, miR-30e silencing led to significant podocyte apoptosis. Mitochondrial dysfunction (MtD) has been shown to be an early event in Aldo-induced podocyte injury. Here we found that overexpression of miR-30e improved Aldo-induced MtD while miR-30e silencing resulted in MtD. Next, we found that miR-30e could directly target the BCL2/adenovirus E1B-interacting protein 3-like (BNIP3L) gene. Aldo markedly enhanced BNIP3L expression in podocytes, and silencing of BNIP3L largely abolished Aldo-induced MtD and cell apoptosis. On the contrary, overexpression of BNIP3L induced MtD and apoptosis in podocytes. Together, these findings demonstrate that miR-30e protects mitochondria and podocytes from Aldo challenge by targeting BNIP3L.

FAK contributes to proteinuria in hypercholesterolaemic rats and modulates podocyte F-actin re-organization via activating p38 in response to ox-LDL

Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase that regulates cell adhesion, proliferation and differentiation. In the present study, a rat model of high fat diet-induced hypercholesterolaemia was established to investigate the involvement of FAK in lipid disorder-related kidney diseases. We showed focal fusion of podocyte foot process that occurred at as early as 4 weeks in rats consuming high fat diet, preceding the onset of proteinuria when aberrant phosphorylation of FAK was found. These abnormalities were ameliorated by dietary intervention of TAE226, a reported inhibitor of FAK. FAK is also an adaptor protein initiating cascades of intracellular signals including c-Src, Rho GTPase and mitogen-activated protein kinase (MAPK). P38 MAPK belongs to the latter and is centrally involved in kidney diseases. Our cell culture data revealed oxidized low-density lipoprotein (ox-LDL) triggered hyper-phosphorylation of FAK and p38, ectopic expression of cellular markers (manifested as decreased WT1, podocin and NEPH1, and increased vimentin and mmp9), and re-arrangement of F-actin filaments with enhanced cell motility; these mutations were significantly rectified by FAK shRNA. Notably, pre-treatment of p38 inhibitor did not alter FAK activation, albeit its deletion of p38 hyper-activity and attenuation of cellular abnormalities, demonstrating that p38 acted as a downstream effector of FAK signalling and ox-LDL damaged podocytes in a FAK/p38-dependent manner. This was further identified by animal data that p38 activation was also abrogated by TAE226 treatment in hypercholesterolaemic rats, suggesting that FAK/p38 axis might also be involved in in vivo events. These findings provided a potential early mechanism of hypercholesterolaemia-related podocyte damage and proteinuria.

The role of mechanistic target of rapamycin in maintenance of glomerular epithelial cells

PURPOSE OF REVIEW

Recent studies have emerged to reveal the pivotal roles of mechanistic target of rapamycin (mTOR) signaling not only in the maintenance of the physiological functions of renal cells but also in the pathogenesis of renal cell dysfunctions and kidney diseases. We introduce the current understanding of mTOR signaling, and its crucial roles in glomerular epithelial cell biology and the pathophysiology related to kidney diseases.

RECENT FINDINGS

mTOR, a Ser/Thr kinase, forms two distinct functional complexes, mTORC1 and mTORC2. Recent studies revealed that physiologic levels of mTORC1 and mTORC2 activity play key roles in maintaining podocyte and glomerular functions. However, aberrant activation of mTORC1 or loss of mTORC2 activity in podocytes may underlie the pathogenesis of glomerular disorders, including diabetic kidney disease.

SUMMARY

An effective treatment for mTORC1-associated podocyte and glomerular dysfunction may require the attenuation of mTORC1 activity in the setting of both an intact mTORC2 pathway and normal basal mTORC1 activity in order to preserve physiologic podocyte functions.

Anti-fibrotic effects of valproic acid: role of HDAC inhibition and associated mechanisms

Tissue injuries and pathological insults produce oxidative stress, genetic and epigenetic alterations, which lead to an imbalance between pro- and anti-fibrotic molecules, and subsequent accumulation of extracellular matrix, thereby fibrosis. Various molecular pathways play a critical role in fibroblasts activation, which promotes the extracellular matrix production and accumulation. Recent reports highlighted that histone deacetylases (HDACs) are upregulated in various fibrotic disorders and play a central role in fibrosis, while HDAC inhibitors exert antifibrotic effects. Valproic acid is a first-line anti-epileptic drug and a proven HDAC inhibitor. This review provides the current research and novel insights on antifibrotic effects of valproic acid in various fibrotic conditions with an emphasis on the possible strategies for treatment of fibrosis.

CNDP1 genotype and renal survival in pediatric nephropathies

BACKGROUND

The risk of developing type II diabetic nephropathy (DN) is lower in patients carrying the CNDP1 Mannheim polymorphism (homozygosity for the five leucine repeat), resulting in decreased activity of the histidine-dipeptide metabolizing enzyme carnosinase. The role of CNDP1 in other nephropathies is still unknown.

METHODS

To evaluate the impact of the CNDP1 Mannheim allele on pediatric chronic kidney disease (CKD), we prospectively followed the long-term clinical outcome of 272 children with non-diabetic kidney disease (glomerulopathies n=32, non-glomerular kidney disease n=240).

RESULTS

Renal failure progression was independent of CNDP1 genotype in the total cohort of CKD children. However, in patients with glomerulopathies, only 39% of patients homozygous for the CNDP1 Mannheim polymorphism attained the primary renal endpoint as compared to 77% of patients with any other CNDP1 genotype (p=0.06).

CONCLUSIONS

Our findings in pediatric CKD patients suggest that the nephroprotective effect of the CNDP1 Mannheim variant is not restricted to patients with diabetic nephropathy.

Glomerular pathology and the progression of chronic kidney disease

Structural studies of the glomerulus, largely undertaken in animal models, have informed our understanding of the progression of chronic kidney disease (CKD) for decades. A fundamental tenet of that understanding is that a loss of podocytes underlies progression in many or most cases of progressive CKD. Recent attempts have been made to reconcile earlier findings from glomerular physiology (the primacy of glomerular capillary hypertension in causation of secondary glomerular sclerosis) with structural findings and have suggested a more detailed model of the mechanisms underlying podocyte detachment as viable cells. A new appreciation of the main locus of mechanical challenges to the podocyte (in the filtration slit) may both explain the renoprotective action of some current therapies and help to suggest novel therapeutic strategies.

Quantitative podocyte parameters predict human native kidney and allograft half-lives

BACKGROUND

Kidney function decreases with age. A potential mechanistic explanation for kidney and allograft half-life has evolved through the realization that linear reduction in glomerular podocyte density could drive progressive glomerulosclerosis to impact both native kidney and allograft half-lives.

METHODS

Predictions from podometrics (quantitation of podocyte parameters) were tested using independent pathologic, functional, and outcome data for native kidneys and allografts derived from published reports and large registries.

RESULTS

With age, native kidneys exponentially develop glomerulosclerosis, reduced renal function, and end-stage kidney disease, projecting a finite average kidney life span. The slope of allograft failure rate versus age parallels that of reduction in podocyte density versus age. Quantitative modeling projects allograft half-life at any donor age, and rate of podocyte detachment parallels the observed allograft loss rate.

CONCLUSION

Native kidneys are designed to have a limited average life span of about 100-140 years. Allografts undergo an accelerated aging-like process that accounts for their unexpectedly short half-life (about 15 years), the observation that older donor age is associated with shorter allograft half-life, and the fact that long-term allograft survival has not substantially improved. Podometrics provides potential readouts for these processes, thereby offering new approaches for monitoring and intervention.

FUNDING

National Institutes of Health.

Podocyte Depletion in Thin GBM and Alport Syndrome

The proximate genetic cause of both Thin GBM and Alport Syndrome (AS) is abnormal α3, 4 and 5 collagen IV chains resulting in abnormal glomerular basement membrane (GBM) structure/function. We previously reported that podocyte detachment rate measured in urine is increased in AS, suggesting that podocyte depletion could play a role in causing progressive loss of kidney function. To test this hypothesis podometric parameters were measured in 26 kidney biopsies from 21 patients aged 2–17 years with a clinic-pathologic diagnosis including both classic Alport Syndrome with thin and thick GBM segments and lamellated lamina densa [n = 15] and Thin GBM cases [n = 6]. Protocol biopsies from deceased donor kidneys were used as age-matched controls. Podocyte depletion was present in AS biopsies prior to detectable histologic abnormalities. No abnormality was detected by light microscopy at <30% podocyte depletion, minor pathologic changes (mesangial expansion and adhesions to Bowman’s capsule) were present at 30–50% podocyte depletion, and FSGS was progressively present above 50% podocyte depletion. eGFR did not change measurably until >70% podocyte depletion. Low level proteinuria was an early event at about 25% podocyte depletion and increased in proportion to podocyte depletion. These quantitative data parallel those from model systems where podocyte depletion is the causative event. This result supports a hypothesis that in AS podocyte adherence to the GBM is defective resulting in accelerated podocyte detachment causing progressive podocyte depletion leading to FSGS-like pathologic changes and eventual End Stage Kidney Disease. Early intervention to reduce podocyte depletion is projected to prolong kidney survival in AS.

Podometrics as a Potential Clinical Tool for Glomerular Disease Management

Chronic kidney disease culminating in end-stage kidney disease is a major public health problem costing in excess of $40 billion per year with high morbidity and mortality. Current tools for glomerular disease monitoring lack precision and contribute to poor outcome. The podocyte depletion hypothesis describes the major mechanisms underlying the progression of glomerular diseases, which are responsible for more than 80% of cases of end-stage kidney disease. The question arises of whether this new knowledge can be used to improve outcomes and reduce costs. Podocytes have unique characteristics that make them an attractive monitoring tool. Methodologies for estimating podocyte number, size, density, glomerular volume and other parameters in routine kidney biopsies, and the rate of podocyte detachment from glomeruli into urine (podometrics) now have been developed and validated. They potentially fill important gaps in the glomerular disease monitoring toolbox. The application of these tools to glomerular disease groups shows good correlation with outcome, although data validating their use for individual decision making is not yet available. Given the urgency of the clinical problem, we argue that the time has come to focus on testing these tools for application to individualized clinical decision making toward more effective progression prevention.

Multi-scale imaging of anticancer platinum(iv) compounds in murine tumor and kidney

Nano-scale secondary ion mass spectrometry (NanoSIMS) enables trace element and isotope analyses with high spatial resolution. This unique capability has recently been exploited in several studies analyzing the subcellular distribution of Au and Pt anticancer compounds. However, these studies were restricted to cell culture systems. To explore the applicability to the in vivo setting, we developed a combined imaging approach consisting of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), NanoSIMS and transmission electron microscopy (TEM) suitable for multi-scale detection of the platinum distribution in tissues. Applying this approach to kidney and tumor samples upon administration of selected platinum(iv) anticancer prodrugs revealed uneven platinum distributions on both the organ and subcellular scales. Spatial platinum accumulation patterns were quantitatively assessed by LA-ICP-MS in histologically heterogeneous organs (e.g., higher platinum accumulation in kidney cortex than in medulla) and used to select regions of interest for subcellular-scale imaging with NanoSIMS. These analyses revealed cytoplasmic sulfur-rich organelles accumulating platinum in both kidney and malignant cells. Those in the tumor were subsequently identified as organelles of lysosomal origin, demonstrating the potential of the combinatorial approach for investigating therapeutically relevant drug concentrations on a submicrometer scale.

Chronic effects of soft drink consumption on the health state of Wistar rats: A biochemical, genetic and histopathological study

The present study was performed to examine the effects of chronic soft drink consumption (SDC) on oxidative stress, biochemical alterations, gene biomarkers and histopathology of bone, liver and kidney. Free drinking water of adult male Wistar rats was substituted with three different soft drinks: Coca‑Cola, Pepsi and 7‑Up, for three consecutive months. The serum and organs were collected for examining the biochemical parameters associated with bone, liver and kidney functions. Semi‑quantitative reverse transcription polymerase chain reaction was used to observe the changes in the expression of genes in the liver and kidney, which are associated with oxidative stress resistance. Histopathological investigations were performed to determine the changes in bone, liver and kidney tissues using hematoxylin and eosin stains. SDC affected liver, kidney and bone function biomarkers. Soft drinks increased oxidative stress, which is represented by an increase in malondialdehyde and a decrease in antioxidant levels. SDC affected serum mineral levels, particularly calcium and phosphorus. Soft drinks downregulated the expression levels of glutathione‑S‑transferase and super oxide dismutase in the liver compared with that of control rats. Rats administered Coca‑Cola exhibited a hepatic decrease in the mRNA expression of α2‑macroglobulin compared with rats administered Pepsi and 7‑Up. On the other hand, SDC increased the mRNA expression of α1‑acid glycoprotein. The present renal studies revealed that Coca‑Cola increased the mRNA expression levels of desmin, angiotensinogen and angiotensinogen receptor compared with the other groups, together with mild congestion in renal histopathology. Deleterious histopathological changes were reported predominantly in the bone and liver of the Coca‑Cola and Pepsi groups. In conclusion, a very strict caution must be considered with SDC due to the increase in oxidative stress biomarkers and disruption in the expression of certain genes associated with the bio‑vital function of both the liver and kidney.

Endoglin regulates mural cell adhesion in the circulatory system

The circulatory system is walled off by different cell types, including vascular mural cells and podocytes. The interaction and interplay between endothelial cells (ECs) and mural cells, such as vascular smooth muscle cells or pericytes, play a pivotal role in vascular biology. Endoglin is an RGD-containing counter-receptor for β1 integrins and is highly expressed by ECs during angiogenesis. We find that the adhesion between vascular ECs and mural cells is enhanced by integrin activators and inhibited upon suppression of membrane endoglin or β1-integrin, as well as by addition of soluble endoglin (SolEng), anti-integrin α5β1 antibody or an RGD peptide. Analysis of different endoglin mutants, allowed the mapping of the endoglin RGD motif as involved in the adhesion process. In Eng (+/-) mice, a model for hereditary hemorrhagic telangectasia type 1, endoglin haploinsufficiency induces a pericyte-dependent increase in vascular permeability. Also, transgenic mice overexpressing SolEng, an animal model for preeclampsia, show podocyturia, suggesting that SolEng is responsible for podocytes detachment from glomerular capillaries. These results suggest a critical role for endoglin in integrin-mediated adhesion of mural cells and provide a better understanding on the mechanisms of vessel maturation in normal physiology as well as in pathologies such as preeclampsia or hereditary hemorrhagic telangiectasia.

Podocyte Detachment Is Associated with Renal Prognosis in ANCA-Associated Glomerulonephritis: A Retrospective Cohort Study

The prognosis of antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (ANCA-GN) is unfavorable despite immunosuppressive therapy. It has been suggested that the loss of podocytes is a hallmark of progressive kidney disease. However, it is unclear about podocyte injuries and their predictive values on the prognosis in ANCA-GN. Therefore, the current study aimed to investigate the podocyte injury in renal histopathology and its association with renal prognosis of patients with ANCA-GN. A total of 170 patients with ANCA-GN were recruited in this study. Morphometric investigation of podocytes by electron microscopy including foot process width (FPW), podocyte density per glomerulus (Nv), and glomerular basement membrane (GBM) width were measured and calculated in ANCA-GN patients. Cox regression analysis was used to analyze the association between podocyte injuries and prognosis of patients with ANCA-GN. Foot processes broadening, podocyte detachment, and GBM thickening could be observed in electron micrographs in the specimens of 158/170 (92.9%), 142/170 (83.5%), and 150/170 (88.2%) patients, respectively. Compared with normal controls, FPW and GBM width in ANCA-GN patients was significantly higher (1269.39 ± 680.19 vs 585.81 ± 77.16, P = 0.004; 668.23 ± 208.73 vs 354.23 ± 52.70, P = 0.000, respectively), while the podocyte density was significantly lower (55.90 ± 36.32 vs 255.23 ± 47.29, P = 0.000). The podocyte density was independently associated with the recovery of renal function in logistic regression analysis (OR, 1.083; 95% CI, 1.025-1.440; P = 0.005). Furthermore, multivariate analysis revealed that podocyte density was an independent predictor of end-stage renal disease (ESRD) (model A: HR, 0.950; 95% CI, 0.919-1.982; P = 0.002; model B: HR, 0.953; 95% CI, 0.922-0.985; P = 0.004). Podocyte structural damage and detachment occurred frequently in patients with ANCA-GN. Moreover, podocyte detachment was an independent predictor of renal outcomes.

Vitamin D and its receptor regulate lipopolysaccharide-induced transforming growth factor-β, angiotensinogen expression and podocytes apoptosis through the nuclear factor-κB pathway

AIMS/INTRODUCTION

To investigate the effects of vitamin D and its receptor on cytokines expression and podocytes apoptosis.

MATERIALS AND METHODS

Cultured mouse podocytes were pre-incubated with vitamin D or transiently transfected with small interfering ribonucleic acid (RNA) to knock down the vitamin D receptor. Lipopolysaccharide was used to mimic the inflammation status of diabetes.

RESULTS

In a lipopolysaccharide-induced state, expressions of transforming growth factor-β, angiotensinogen and vascular endothelial growth factor were similarly increased. Transforming growth factor-β and angiotensinogen levels originally elevated by lipopolysaccharide challenge were distinctly reduced after pre-incubation with vitamin D. Whereas after vitamin D receptor small interfering (si)RNA transfection, the aforementioned cytokines had opposite changes as expected. However, neither vitamin D pretreatment nor vitamin D receptor siRNA transfection influenced the previously increased vascular endothelial growth factor expression at messenger RNA or protein levels. When pretreated with vitamin D, decreases were observed for phosphorylated inhibitor-κB and the inhibitor kinase proteins. After siRNA transfection, those proteins levels were further elevated. The originally increased transforming growth factor-β and angiotensinogen levels as a result of lipopolysaccharide stimulation were reduced at both the messenger RNA and protein levels after the specific inhibition of the nuclear factor-κB pathway with pyrrolidine dithiocarbamate. The apoptosis rate of podocytes was decreased in a parallel manner after vitamin D pre-incubation, and increased after siRNA transfection, which was also suppressed by pyrrolidine dithiocarbamate.

CONCLUSIONS

Vitamin D and its receptor might be involved in the progression of diabetic nephropathy by regulating transforming growth factor-β, angiotensinogen expression and apoptosis of podocytes. The processes are mediated through the signaling of nuclear factor-κB pathway.

Podocyte injury and its consequences

Podocytes maintain the glomerular filtration barrier, and the stability of this barrier depends on their highly differentiated postmitotic phenotype, which also defines the particular vulnerability of the glomerulus. Recent podocyte biology and gene disruption studies in vivo indicate a causal relationship between abnormalities of single podocyte molecules and proteinuria and glomerulosclerosis. Podocytes live under various stresses and pathological stimuli. They adapt to maintain homeostasis, but excessive stress leads to maladaptation with complex biological changes including loss of integrity and dysregulation of cellular metabolism. Podocyte injury causes proteinuria and detachment from the glomerular basement membrane. In addition to "sick" podocytes and their detachment, our understanding of glomerular responses following podocyte loss needs to address the pathways from podocyte injury to sclerosis. Studies have found a variety of glomerular responses to podocyte dysfunction in vivo, such as disruption of podocyte-endothelial cross talk and activation of podocyte-parietal cell interactions, all of which help us to understand the complex scenario of podocyte injury and its consequences. This review focuses on the cellular aspects of podocyte dysfunction and the adaptive or maladaptive glomerular responses to podocyte injury that lead to its major consequence, glomerulosclerosis.

Counting glomeruli and podocytes: rationale and methodologies

PURPOSE OF REVIEW

There is currently much interest in the numbers of both glomeruli and podocytes. This interest stems from a greater understanding of the effects of suboptimal fetal events on nephron endowment, the associations between low nephron number and chronic cardiovascular and kidney disease in adults, and the emergence of the podocyte depletion hypothesis.

RECENT FINDINGS

Obtaining accurate and precise estimates of glomerular and podocyte number has proven surprisingly difficult. When whole kidneys or large tissue samples are available, design-based stereological methods are considered gold standard because they are based on principles that negate systematic bias. However, these methods are often tedious and time consuming, and oftentimes inapplicable when dealing with small samples such as biopsies. Therefore, novel methods suitable for small tissue samples, and innovative approaches to facilitate high throughput measurements, such as MRI to estimate glomerular number and flow cytometry to estimate podocyte number, have recently been described.

SUMMARY

This review describes current gold-standard methods for estimating glomerular and podocyte number, as well as methods developed in the past 3 years. We are now better placed than ever before to accurately and precisely estimate glomerular and podocyte number, and examine relationships between these measurements and kidney health and disease.

Toll-like Receptor 9 Can be Activated by Endogenous Mitochondrial DNA to Induce Podocyte Apoptosis

Toll-like receptor 9 (TLR9) senses bacterial DNA characteristic of unmethylated CpG motifs to induce innate immune response. TLR9 is de novo expressed in podocytes of some patients with glomerular diseases, but its role in podocyte injury remains undetermined. Since TLR9 activates p38 MAPK and NFkB that are known to mediate podocyte apoptosis, we hypothesized that TLR9 induces podocyte apoptosis in glomerular diseases. We treated immortalized podocytes with puromycin aminonucleosides (PAN) and observed podocyte apoptosis, accompanied by TLR9 upregulation. Prevention of TLR9 upregulation by siRNA significantly attenuated NFκB p65 or p38 activity and apoptosis, demonstrating that TLR9 mediates podocyte apoptosis. We next showed that endogenous mitochondrial DNA (mtDNA), whose CpG motifs are also unmethylated, is the ligand for TLR9, because PAN induced mtDNA accumulation in endolysosomes where TLR9 is localized, overexpression of endolysosomal DNase 2 attenuated PAN-induced p38 or p65 activity and podocyte apoptosis, and DNase 2 silencing was sufficient to activate p38 or p65 and induce apoptosis. In PAN-treated rats, TLR9 was upregulated in the podocytes, accompanied by increase of apoptosis markers. Thus, de novo expressed TLR9 may utilize endogenous mtDNA as the ligand to facilitate podocyte apoptosis, a novel mechanism underlying podocyte injury in glomerular diseases.

Glomerular Function and Structure in Living Donors: Lessons from Single Nephron Studies

One third of the kidney transplants performed in the USA come from living kidney donors. The long-term outcome of healthy individuals who donate kidneys is mostly excellent, although recent studies have suggested that living donation is associated with a small absolute increase in the risk of end stage renal failure. Much of our understanding about the progression of kidney disease comes from experimental models of nephron loss. For this reason, living kidney donation has long been of great interest to renal physiologists. This review will summarize the determinants of glomerular filtration and the physiology that underlies post-donation hyperfiltration. We describe the 'remnant kidney' model of kidney disease and the reasons why such progressive kidney disease very rarely ensues in healthy humans following uninephrectomy. We also review some of the methods used to determine glomerular number and size and outline their associations.

HIV Promotes NLRP3 Inflammasome Complex Activation in Murine HIV-Associated Nephropathy

Dysregulated growth and loss of podocytes are important features of HIV-associated nephropathy. Recently, HIV was reported to induce a new type of programed cell death, pyroptosis, in T lymphocytes through induction of Nod-like receptor protein 3 (NLRP3) inflammasome complexes. We evaluated the role of HIV in podocyte NLRP3 inflammasome formation both in vivo and in vitro. Renal cortical sections of HIV-transgenic mice (Tg26) displayed increased expression of NLRP3, ASC (a CARD protein), caspase-1, and IL-1β proteins, confirming NLRP3 inflammasome complex formation in podocytes of Tg26 mice. Renal tissues of Tg26 mice also displayed enhanced mRNA levels and protein expressions of inflammasome markers (NLRP3, ASC, and caspase-1, and IL-1β). Serum of Tg26 mice also showed elevated concentrations of IL-1β cytokine compared with FVBN mice. HIV induced pyroptosis in a dose- and time-dependent manner within podocytes, a phenotype of inflammasome activation. Caspase-1 inhibitor not only attenuated podocyte expression of caspase-1 and IL-1β but also provided protection against pyroptosis, suggesting that HIV-induced podocyte injury was mediated by caspase-1 activation. Interestingly, HIV-induced podocyte pyroptosis could be partially inhibited by Tempol (a superoxide dismutase-mimetic agent) and by glyburide (an inhibitor of potassium efflux). These findings suggest that generation of reactive oxygen species and potassium efflux contribute to HIV-induced pyroptosis and NLRP3 inflammasome activation in podocytes.

Reactive oxygen species-initiated autophagy opposes aldosterone-induced podocyte injury

Evidence has demonstrated that aldosterone (Aldo) is involved in the development and progression of chronic kidney diseases. The purpose of the present study was to investigate the role of autophagy in Aldo-induced podocyte damage and the underlying mechanism. Mouse podocytes were treated with Aldo in the presence or absence of 3-methyladenine and N-acetylcysteine. Cell apoptosis was investigated by detecting annexin V conjugates, apoptotic bodies, caspase-3 activity, and alterations of the podocyte protein nephrin. Autophagy was evaluated by measuring the expressions of light chain 3, p62, beclin-1, and autophagy-related gene 5. Aldo (10^-7 mol/l) induced podocyte apoptosis, autophagy, and downregulation of nephrin protein in a time-dependent manner. Aldo-induced apoptosis was further promoted by the inhibition of autophagy via 3-methyladenine and autophagy-related gene 5 small interfering RNA pretreatment. Moreover, Aldo time dependently increased ROS generation, and H₂O₂ (10^-4 mol/l) application remarkably elevated podocyte autophagy. After treatment with N-acetylcysteine, the autophagy induced by Aldo or H₂O₂ was markedly attenuated, suggesting a key role of ROS in mediating autophagy formation in podocytes. Inhibition of ROS could also lessen Aldo-induced podocyte injury. Taken together, our findings suggest that ROS-triggered autophagy played a protective role against Aldo-induced podocyte injury, and targeting autophagy in podocytes may represent a new therapeutic strategy for the treatment of podocytopathy.

Carboxymethyl lysine induces EMT in podocytes through transcription factor ZEB2: Implications for podocyte depletion and proteinuria in diabetes mellitus

Advanced glycation end-products (AGEs) are implicated in the pathogenesis of diabetic nephropathy (DN). N-carboxymethyl-lysine (CML) is one of the predominant AGEs that accumulate in all renal compartments of diabetic patients. Nevertheless, the direct effect of CML on podocyte biology has not been explored. In this study, we demonstrate the induction of the transcription factor Zeb2 in podocytes upon exposure to CML through activation of NF-kB signaling cascade. Zeb2 orchestrates epithelial-mesenchymal transformation (EMT), during which cell-cell and cell-extracellular matrix interactions are feeble and enable epithelial cells to become invasive. CML treatment induced both NF-kB and Zeb2 promoter activity and suppressed E-cadherin promoter activity. Inhibition of NF-kB activity prevented CML dependent induction of Zeb2 and loss of E-cadherin. While the exposure of podocytes to CML results in increased podocyte permeability, shRNA-mediated knockdown of Zeb2 expression abrogated CML-mediated podocyte permeability. Further, in vivo findings of elevated CML levels concurrent with increased expression of ZEB2 in glomeruli and proteinuria in diabetic rats confirm that CML-mediated manifestations in the kidney under chronic diabetes conditions. These in vitro and in vivo results envisage the novel axis of NFkB-ZEB2 in podocytes playing a significant role in eliciting EMT and pathogenesis of DN.

MiR-30a Inhibits the Epithelial--Mesenchymal Transition of Podocytes through Downregulation of NFATc3

MicroRNAs (miRNAs) possess an important regulating effect among numerous renal diseases, while their functions in the process of epithelial-to-mesenchymal transition (EMT) after podocyte injury remain unclear. The purpose of our study is to identify the potential functions of miR-30a in EMT of podocytes and explore the underlying mechanisms of miR-30a in the impaired podocytes. The results revealed that downregulation of miR-30a in podocyte injury animal models and patients, highly induced the mesenchymal markers of EMT including Collagen I, Fibronectin and Snail. Furthermore, overexpression of miR-30a enhances epithelial markers (E-cadherin) but diminished mesenchymal markers (Collagen I, Fibronectin and Snail) in podocytes. In addition, we established miR-30a target NFATc3, an important transcription factor of Non-canonical Wnt signaling pathway. More importantly, our findings demonstrated that the augmentation of miR-30a level in podocytes inhibits the nuclear translocation of NFATc3 to protect cytoskeleton disorder or rearrangement. In summary, we uncovered the protective function of miR30a targeting NFATc3 in the regulation of podocyte injury response to EMT.

MicroRNA-30 family members regulate calcium/calcineurin signaling in podocytes

Calcium/calcineurin signaling is critical for normal cellular physiology. Abnormalities in this pathway cause many diseases, including podocytopathy; therefore, understanding the mechanisms that underlie the regulation of calcium/calcineurin signaling is essential. Here, we showed that critical components of calcium/calcineurin signaling, including TRPC6, PPP3CA, PPP3CB, PPP3R1, and NFATC3, are the targets of the microRNA-30 family (miR-30s). We found that these 5 genes are highly expressed as mRNA, but the level of the proteins is low in normal podocytes. Conversely, protein levels were markedly elevated in podocytes from rats treated with puromycin aminonucleoside (PAN) and from patients with focal segmental glomerulosclerosis (FSGS). In both FSGS patients and PAN-treated rats, miR-30s were downregulated in podocytes. In cultured podocytes, PAN or a miR-30 sponge increased TRPC6, PPP3CA, PPP3CB, PPP3R1, and NFATC3 expression; calcium influx; intracellular Ca2+ concentration; and calcineurin activity. Moreover, NFATC3 nuclear translocation, synaptopodin degradation, integrin β3 (ITGB3) activation, and actin fiber loss, which are downstream of calcium/calcineurin signaling, were induced by miR-30 reduction but blocked by the calcineurin inhibitor FK506. Podocyte-specific expression of the miR-30 sponge in mice increased calcium/calcineurin pathway component protein expression and calcineurin activity. The mice developed podocyte foot process effacement and proteinuria, which were prevented by FK506. miR-30s also regulated calcium/calcineurin signaling in cardiomyocytes. Together, our results identify miR-30s as essential regulators of calcium/calcineurin signaling.

MOF maintains transcriptional programs regulating cellular stress response

MOF (MYST1, KAT8) is the major H4K16 lysine acetyltransferase (KAT) in Drosophila and mammals and is essential for embryonic development. However, little is known regarding the role of MOF in specific cell lineages. Here we analyze the differential role of MOF in proliferating and terminally differentiated tissues at steady state and under stress conditions. In proliferating cells, MOF directly binds and maintains the expression of genes required for cell cycle progression. In contrast, MOF is dispensable for terminally differentiated, postmitotic glomerular podocytes under physiological conditions. However, in response to injury, MOF is absolutely critical for podocyte maintenance in vivo. Consistently, we detect defective nuclear, endoplasmic reticulum and Golgi structures, as well as presence of multivesicular bodies in vivo in podocytes lacking Mof following injury. Undertaking genome-wide expression analysis of podocytes, we uncover several MOF-regulated pathways required for stress response. We find that MOF, along with the members of the non-specific lethal but not the male-specific lethal complex, directly binds to genes encoding the lysosome, endocytosis and vacuole pathways, which are known regulators of podocyte maintenance. Thus, our work identifies MOF as a key regulator of cellular stress response in glomerular podocytes.

[Urinary biomarkers for podocyte injury: Significance for evaluating the course and prognosis of chronic glomerulonephritis]

AIM

To estimate the degree of podocyte injury in patients with different types of chronic glomerulonephritis (CGN) from the urinary level of podocyte markers and to determine the significance of these indicators as criteria for disease activity and prognosis.

SUBJECTS AND METHODS

Seventy-three patients with CGN, including 20 with inactive nephritis (Group 1), 23 with obvious urological syndrome (Group 2), 30 with nephrotic syndrome (NS) (Group 3), among them there were 7 patients with severe NS and 7 with NS concurrent with acute nephritic syndrome, were examined. A control group consisted of 8 healthy individuals. In the examined groups, the degree of podocyturia (PCU) was investigated by flow cytometry using podocalyxin-labeled antibodies and the levels of nephrinuria (NU), heat shock protein 27 (HSP27) in urine, interleukin 6 (IL-6), caspase 9, and vascular endothelial growth factor (VEGF) were estimated by ELISA.

RESULTS

The patients with active CGN were found to have a high level of markers for podocyte injury: PCU and NU, which correlate with the magnitude of proteinuria, severity of NS, and degree of podocytopenia. Those with the severest NS, that concurrent with renal dysfunction in particular, were observed to have a progressive imbalance of inflammatory (IL-6), apoptotic (caspase-9), and defensive (HSP27 and VEGF) factors, which displays the incompetence of self-defense mechanisms in podocytes and contributes to the torpid course of CGN. Progressive PCU and NU are a poor prognostic sign indicating the risk of glomerulonephritis.

CONCLUSION

The indicators considered are universal for all patients with CGN running with proteinuria and may be used to monitor the course of the disease; moreover, the damaging factors should be considered in conjunction with the defensive factors.

Molecular and Histopathological Study on the Ameliorative Effects of Curcumin Against Lead Acetate-Induced Hepatotoxicity and Nephrototoxicity in Wistar Rats

Lead (Pb(2+)) toxicity is the most common form of heavy metal intoxication in humans and animals. Therefore, the current study was conducted to evaluate the potential ameliorative effects of curcumin on lead acetate (LA)-induced deleterious effects in the liver and kidney. Forty male Wistar rats were divided into four equal groups; first group was used as a control and given both corn oil orally and vehicle of lead acetate intraperitoneally (i.p). Groups from 2-4 were treated with lead acetate (LA; 50 mg/kg BW i.p), curcumin (200 mg/kg BW orally), and curcumin plus lead acetate, respectively. Curcumin was administered 3 weeks before LA injection for 7 days. Pb(2+)-intoxicated rats have higher Pb(2+) levels compared to other treated groups. Results revealed that lead acetate significantly increased the serum levels of hepatic transaminases (GPT and GOT), urea and creatinine, while albumin was significantly decreased. In parallel, serum IgG, IgM, and IgA were significantly decreased in LA-injected rats. LA groups showed decrease in messenger RNA (mRNA) expression of catalase, SOD, GST, GPx, and alpha-1 acid glycoprotein (AGP), while the gene expression of desmin, vimentin, transforming growth factor-β1 (TGF-β1), monocyte chemoattractant protein-1 (MCP-1), and alpha-2 macroglobulin (α-2M) was increased. Prior and coadministration of curcumin with LA for 7 days significantly improved the ameliorated changes in liver and kidney, immunoglobulins, and mRNA expression. Moreover, curcumin ameliorated LA-induced congestion of hepatic and renal blood vessels and decreased fibrous tissue proliferation and necrosis of hepatocytes. In the kidney, LA-induced degeneration in tubular epithelium and intraluminal hyaline casts and prior curcumin administration restored normal renal structure with mild congestion of renal blood vessels. The results clarify the potential of curcumin to counteract the immunosuppressive alteration in gene expression as well as hepatic and renal damage occurred after Pb(2+) intoxication.

Podocyte and endothelial injury in focal segmental glomerulosclerosis: an ultrastructural analysis

Podocyte injury contributes to the development of focal segmental glomerulosclerosis (FSGS). Endocapillary hypercellularity, which is one of the pathological characteristics of FSGS, suggests that glomerular endothelial injury may also be involved in the pathogenesis of FSGS. In electron micrographs of patients with FSGS (n = 43), we conducted morphometric measurements of foot process width (FPW) and podocyte detachment (PD) as markers of podocyte injury and subendothelial widening (SW) of the glomerular basement membrane as a marker of endothelial injury and compared them to those in patients with minimal change nephrotic syndrome (MCNS; n = 11) and control kidney donors (n = 5). Associations between ultrastructural and clinical parameters were analyzed according to the FSGS variants defined by the Columbia classification. FPW was significantly higher in the FSGS group than that in the MCNS and control groups, particularly in the collapsing, tip, and cellular variants of FSGS. Percentage of glomerular basement membrane (GBM) length showing PD and SW was significantly increased in the FSGS group, especially in the collapsing, cellular, and not otherwise specified variants. In FSGS, FPW was inversely correlated with disease duration, but not with proteinuria. Finally, the percentage of GBM length with SW significantly correlated with clinical parameters indicative of poor prognosis, such as lower remission rate and lower estimated glomerular filtration rate at the final observation. Quantitative measurement of podocyte and endothelial injury by electron microscopy might be useful for evaluating histological activity and predicting prognosis in FSGS.

Following specific podocyte injury captopril protects against progressive long term renal damage

BACKGROUND

Angiotensin converting enzyme inhibitors (ACEi) reduce proteinuria and preserve kidney function in proteinuric renal diseases. Their nephroprotective effect exceeds that attributable to lowering of blood pressure alone. This study examines the potential of ACEi to protect from progression of injury after a highly specific injury to podocytes in a mouse model.

METHODS

We created transgenic (Podo-DTR) mice in which graded specific podocyte injury could be induced by a single injection of diphtheria toxin. Transgenic and wild-type mice were given the ACEi captopril in drinking water, or water alone, commencing 24h after toxin injection. Kidneys were examined histologically at 8 weeks and injury assessed by observers blinded to experimental group.

RESULTS

After toxin injection, Podo-DTR mice developed acute proteinuria, and at higher doses transient renal impairment, which subsided within 3 weeks to be followed by a slow glomerular scarring process. Captopril treatment in Podo-DTR line 57 after toxin injection at 5ng/g body weight reduced proteinuria and ameliorated glomerular scarring, matrix accumulation and glomerulosclerosis almost to baseline (toxin: 17%; toxin + ACEi 10%, p<0.04; control 7% glomerular scarring). Podocyte counts were reduced after toxin treatment and showed no recovery irrespective of captopril treatment (7.1 and 7.3 podocytes per glomerular cross section in water and captopril-treated animals compared with 8.2 of wild-type controls, p<0.05).

CONCLUSIONS

Observations in Podo-DTR mice support the hypothesis that continuing podocyte dysfunction is a key abnormality in proteinuric disease. Our model is ideal for studying strategies to protect the kidney from progressive injury following podocyte depletion. Demonstrable protective effects from captopril occur, despite indiscernible preservation or restoration of podocyte counts, at least after this degree of relatively mild injury.

Glomerular Aging and Focal Global Glomerulosclerosis: A Podometric Perspective

Kidney aging is associated with an increasing proportion of globally scarred glomeruli, decreasing renal function, and exponentially increasing ESRD prevalence. In model systems, podocyte depletion causes glomerulosclerosis, suggesting age-associated glomerulosclerosis could be caused by a similar mechanism. We measured podocyte number, size, density, and glomerular volume in 89 normal kidney samples from living and deceased kidney donors and normal poles of nephrectomies. Podocyte nuclear density decreased with age due to a combination of decreased podocyte number per glomerulus and increased glomerular volume. Compensatory podocyte cell hypertrophy prevented a change in the proportion of tuft volume occupied by podocytes. Young kidneys had high podocyte reserve (podocyte density >300 per 10(6) µm(3)), but by 70-80 years of age, average podocyte nuclear density decreased to, <100 per 10(6) µm(3), with corresponding podocyte hypertrophy. In older age podocyte detachment rate (urine podocin mRNA-to-creatinine ratio) was higher than at younger ages and podocytes were stressed (increased urine podocin-to-nephrin mRNA ratio). Moreover, in older kidneys, proteinaceous material accumulated in the Bowman space of glomeruli with low podocyte density. In a subset of these glomeruli, mass podocyte detachment events occurred in association with podocytes becoming binucleate (mitotic podocyte catastrophe) and subsequent wrinkling of glomerular capillaries, tuft collapse, and periglomerular fibrosis. In kidneys of young patients with underlying glomerular diseases similar pathologic events were identified in association with focal global glomerulosclerosis. Podocyte density reduction with age may therefore directly lead to focal global glomerulosclerosis, and all progressive glomerular diseases can be considered superimposed accelerators of this underlying process.

Urine podocyte mRNAs mark disease activity in IgA nephropathy

BACKGROUND

Podocyte depletion is a major mechanism driving glomerulosclerosis. We and others have previously projected from model systems that podocyte-specific mRNAs in the urine pellet might serve as glomerular disease markers. We evaluated IgA nephropathy (IgAN) to test this concept.

METHODS

From 2009 to 2013, early morning voided urine samples and kidney biopsies from IgAN patients (n = 67) were evaluated in comparison with urine samples from healthy age-matched volunteers (n = 28). Urine podocyte (podocin) mRNA expressed in relation to either urine creatinine concentration or a kidney tubular marker (aquaporin 2) was tested as markers.

RESULTS

Urine podocyte mRNAs were correlated with the severity of active glomerular lesions (segmental glomerulosclerosis and acute extracapillary proliferation), but not with non-glomerular lesions (tubular atrophy/interstitial fibrosis) or with clinical parameters of kidney injury (serum creatinine and estimated glomerular filtration rate), or with degree of accumulated podocyte loss at the time of biopsy. In contrast, proteinuria correlated with all histological and clinical markers. Glomerular tuft podocyte nuclear density (a measure of cumulative podocyte loss) correlated with tubular atrophy/interstitial fibrosis, estimated-glomerular filtration rate and proteinuria, but not with urine podocyte markers. In a subset of the IgA cohort (n = 19, median follow-up period = 37 months), urine podocyte mRNAs were significantly decreased after treatment, in contrast to proteinuria which was not significantly changed.

CONCLUSIONS

Urine podocyte mRNAs reflect active glomerular injury at a given point in time, and therefore provide both different and additional clinical information that can complement proteinuria in the IgAN decision-making paradigm.

Alteration in the podoplanin-ezrin-cytoskeleton linkage is an important initiation event of the podocyte injury in puromycin aminonucleoside nephropathy, a mimic of minimal change nephrotic syndrome

Podoplanin was identified as a protein associated with the transformation of arborized foot processes of glomerular epithelial cells (podocytes) to flat feet. However, the function of podoplanin in the podocyte is not yet fully clarified. In this study, we analyzed the molecular nature of podoplanin, and its expression in rat nephrotic models and patients with minimal change nephrotic syndrome (MCNS). We demonstrated here that podoplanin has two forms: one contains abundant sialic acid and the other a lesser amount of sialic acid. Podoplanin bound ezrin to interact with the cytoskeleton. The silencing of podoplanin in cultured podocytes caused a change in the cell shape and the distribution of ezrin and actin. The expression of podoplanin was clearly reduced before the onset of proteinuria in puromycin aminonucleoside (PAN) nephropathy, a mimic of MCNS, and the decrease in the expression of podoplanin became more evident at the proteinuric stage. Podoplanin was detected in normal urine samples, and the amount of urinary podoplanin markedly increased on day 1 of PAN nephropathy. Urinary ezrin was also detected. The amount of the phosphorylated ezrin was reduced, while the amount of the podoplanin-interacting ezrin increased. The podoplanin expression was reduced in a patient with active-phase MCNS. It is conceivable that the alteration of the podoplanin-ezrin-cytoskeleton linkage is an important event of the podocyte injury in MCNS.

Early-onset diabetic E1-DN mice develop albuminuria and glomerular injury typical of diabetic nephropathy

The transgenic E1-DN mice express a kinase-negative epidermal growth factor receptor in their pancreatic islets and are diabetic from two weeks of age due to impaired postnatal growth of β-cell mass. Here, we characterize the development of hyperglycaemia-induced renal injury in the E1-DN mice. Homozygous mice showed increased albumin excretion rate (AER) at the age of 10 weeks; the albuminuria increased over time and correlated with blood glucose. Morphometric analysis of PAS-stained histological sections and electron microscopy images revealed mesangial expansion in homozygous E1-DN mice, and glomerular sclerosis was observed in the most hyperglycaemic mice. The albuminuric homozygous mice developed also other structural changes in the glomeruli, including thickening of the glomerular basement membrane and widening of podocyte foot processes that are typical for diabetic nephropathy. Increased apoptosis of podocytes was identified as one mechanism contributing to glomerular injury. In addition, nephrin expression was reduced in the podocytes of albuminuric homozygous E1-DN mice. Tubular changes included altered epithelial cell morphology and increased proliferation. In conclusion, hyperglycaemic E1-DN mice develop albuminuria and glomerular and tubular injury typical of human diabetic nephropathy and can serve as a new model to study the mechanisms leading to the development of diabetic nephropathy.

Common histological patterns in glomerular epithelial cells in secondary focal segmental glomerulosclerosis

Parietal epithelial cells (PECs) are involved in the development of sclerotic lesions in primary focal and segmental glomerulosclerosis (FSGS). Here, the role of PECs was explored in the more common secondary FSGS lesions in 68 patient biopsies, diagnosed with 11 different frequently or rarely encountered glomerular pathologies and additional secondary FSGS lesions. For each biopsy, one section was quadruple stained for PECs (ANXA3), podocytes (synaptopodin), PEC matrix (LKIV69), and Hoechst (nuclei), and a second was quadruple stained for activated PECs (CD44 and cytokeratin-19), PEC matrix, and nuclei. In all lesions, cellular adhesions (synechiae) between Bowman's capsule and the tuft were formed by cells expressing podocyte and/or PEC markers. Cells expressing PEC markers were detected in all FSGS lesions independent of the underlying glomerular disease and often stained positive for markers of activation. Small FSGS lesions, which were hardly identified on PAS sections previously, were detectable by immunofluorescent staining using PEC markers, potentially improving the diagnostic sensitivity to identify these lesions. Thus, similar patterns of cells expressing podocyte and/or PEC markers were found in the formation of secondary FSGS lesions independent of the underlying glomerular disease. Hence, our findings support the hypothesis that FSGS lesions follow a final cellular pathway to nephron loss that includes involvement of cells expressing PEC markers.

Podocyte injury-driven intracapillary plasminogen activator inhibitor type 1 accelerates podocyte loss via uPAR-mediated β1-integrin endocytosis

Podocyte-endothelial cell cross-talk is paramount for maintaining the filtration barrier. The present study investigated the endothelial response to podocyte injury and its subsequent role in glomerulosclerosis using the podocyte-specific injury model of NEP25/LMB2 mice. NEP25/LMB2 mice showed proteinuria and local podocyte loss accompanied by thrombotic microangiopathy on day 8. Mice showed an increase of glomerular plasminogen activator inhibitor type 1 (PAI-1) mRNA and aberrant endothelial PAI-1 protein already on day 1, before thrombosis and proteinuria. A PAI-1-specific inhibitor reduced proteinuria and thrombosis and preserved podocyte numbers in NEP25/LMB2 mice by stabilization of β1-integrin translocation. Heparin loading significantly reduced thrombotic formation, whereas proteinuria and podocyte numbers were unchanged. Immortalized podocytes treated with PAI-1 and the urokinase plasminogen activator (uPA) complex caused significant cell detachment, whereas podocytes treated with PAI-1 or uPA alone or with the PAI-1/uPA complex pretreated with an anti-uPA receptor (uPAR) antibody failed to cause detachment. Confocal microscopy and cell surface biotinylation experiments showed that internalized β1-integrin was found together with uPAR in endocytotic vesicles. The administration of PAI-1 inhibitor or uPAR-blocking antibody protected cultured podocytes from cell detachment. In conclusion, PAI-1/uPA complex-mediated uPAR-dependent podocyte β1-integrin endocytosis represents a novel mechanism of glomerular injury leading to progressive podocytopenia. This aberrant cross-talk between podocytes and endothelial cells represents a feedforward injury response driving podocyte loss and progressive glomerulosclerosis.

Retinal microvascular abnormalities and risk of renal failure in Asian populations

BACKGROUND

Retinal microvascular signs may provide insights into the structure and function of small vessels that are associated with renal disease. We examined the relationship of retinal microvascular signs with both prevalent and incident end-stage renal disease (ESRD) in a multi-ethnic Asian population.

METHODS

A total of 5763 subjects (aged ≥ 40 years) from two prospective population-based studies (the Singapore Malay Eye Study and the Singapore Prospective Study) were included for the current analysis. Retinopathy was graded using the modified Airlie House classification system. Retinal vascular parameters were measured using computer-assisted programs to quantify the retinal vessel widths (arteriolar and venular caliber) and retinal vascular network (fractal dimension). Data on ESRD was obtained by record linkage with the ESRD cases registered by National Registry of Diseases Office, Singapore. Multi-variable adjusted regression analyses were performed to assess the associations of baseline retinal vascular parameters and prevalent and incident ESRD.

RESULTS

At baseline, 21(0.36%) persons had prevalent ESRD. During a median follow-up of 4.3 years, 33 (0.57%) subjects developed ESRD. In our analyses, retinopathy was associated with prevalent ESRD (multi-variable adjusted odds ratio [OR], 3.21, 95% confidence interval [CI]: 1.28-8.05) and incident ESRD (multi-variable adjusted hazard ratio [HR], 2.51, 95%CI: 1.14-5.54). This association was largely seen in person with diabetes (HR, 2.60, 95%CI: 1.01-6.66) and not present in persons without diabetes (HR, 1.65, 95%CI: 0.14-18.98). Retinal arteriolar caliber, retinal venular caliber and retinal vascular fractal dimension were not associated with ESRD.

CONCLUSION

Retinopathy signs in persons with diabetes are related to an increased risk of ESRD; however, other microvascular changes in the retina are not associated with ESRD.

Ret is critical for podocyte survival following glomerular injury in vivo

Podocyte injury and loss directly cause proteinuria and the progression to glomerulosclerosis. Elucidation of the mechanisms of podocyte survival and recovery from injury is critical for designing strategies to prevent the progression of glomerular diseases. Glial cell line-derived neurotrophic factor (GDNF) and its receptor tyrosine kinase, Ret, are upregulated in both nonimmune and immune-mediated in vitro and in vivo models of glomerular diseases. We investigated whether Ret, a known receptor tyrosine kinase critical for kidney morphogenesis and neuronal growth and development, is necessary for glomerular and podocyte development and survival in vivo. Since deletions of both GDNF and Ret result in embryonic lethality due to kidney agenesis, we examined the role of Ret in vivo by generating mice with a conditional deletion of Ret in podocytes (Ret(flox/flox); Nphs2-Cre). In contrast to the lack of any developmental and maintenance deficits, Ret(flox/flox); Nphs2-Cre mice showed a significantly enhanced susceptibility to adriamycin nephropathy, a rodent model of focal segmental glomerulosclerosis. Thus, these findings demonstrated that the Ret signaling pathway is important for podocyte survival and recovery from glomerular injury in vivo.