GLEPP1, a renal glomerular epithelial cell (podocyte) membrane protein-tyrosine phosphatase. Identification, molecular cloning, and characterization in rabbit

Glucagon receptor activation contributes to the development of kidney injury

The underlying causes of diabetic kidney disease are still largely unknown. New insights into the contributing causes of diabetic nephropathy are important to prevent this complication. Hyperglycemia and hypertension are some of the risk factors for diabetic nephropathy. However, the incidence of diabetic nephropathy is increasing despite efforts to normalize blood glucose levels and blood pressure. Therefore, other factors should be investigated as causes of diabetic nephropathy. We investigated whether long-term increased plasma levels of glucagon contribute to the development of pathophysiological changes in kidney function as seen in patients with diabetic nephropathy. Using mouse models of chronic activation and inactivation of glucagon receptor signaling, we investigated whether glucagon is involved in changes in renal function, renal structure, and transcriptional changes. We found several histopathological changes in the kidney, such as thickening of the parietal layer of Bowman's capsule, glomerular mesangial cell expansion, and significant albuminuria in the mice with activated glucagon receptor signaling. Opposite effects on mesangial area expansion and the development of albuminuria were demonstrated in mice with glucagon receptor inactivation. RNA sequencing data revealed that transcription of genes related to fatty acid metabolism, podocytes, Na+-K+-ATPase, and sodium/glucose transport was significantly changed in mice with activated glucagon receptor signaling. These data implicate that glucagon receptor signaling is involved in the development of kidney injury, as seen in type 2 diabetes, and that glucagon receptor is a potential therapeutic target in the treatment of diabetes. NEW & NOTEWORTHY This study suggests that the glucagon receptor is a potential therapeutic target in the treatment of diabetic kidney disease. We show, in mice, that long-term treatment with a glucagon analog showed not only pathophysiological changes and changes in renal function but also transcriptional changes in the kidneys, whereas opposite effects were demonstrated in mice with glucagon receptor inactivation. Therefore, the use of glucagon in a treatment regimen requires investigation of possible metabolic and renal abnormalities.

PTPRO inhibits LPS-induced apoptosis in alveolar epithelial cells

Acute lung injury (ALI) and its severe manifestation, acute respiratory distress syndrome (ARDS), represent critical clinical syndromes with multifactorial origins, notably stemming from sepsis within intensive care units (ICUs). Despite their high mortality rates, no selective cure is available beside ventilation support. Apoptosis plays a complex and pivotal role in the pathophysiology of acute lung injury. Excessive apoptosis of alveolar epithelial and microvascular endothelial cells can lead to disruption of lung epithelial barrier integrity, impairing the body's ability to exchange blood and gas. At the same time, apoptosis of damaged or dysfunctional cells, including endothelial and epithelial cells, can help maintain tissue integrity and accelerate recovery from organ pro-inflammatory stress. The balance between pro-survival and pro-apoptotic signals in lung injury determines patient outcomes, making the modulation of apoptosis an area of intense research in the quest for more effective therapies. Here we found that protein tyrosine phosphatase receptor type O (PTPRO), a poorly understood receptor-like protein tyrosine phosphatase, is consistently upregulated in multiple tissue types of mice under septic conditions and in the lung alveolar epithelial cells. PTPRO reduction by its selective short-interfering RNA (siRNA) leads to excessive apoptosis in lung alveolar epithelial cells without affecting cell proliferation. Consistently PTPRO overexpression by a DNA construct attenuates apoptotic signaling induced by LPS. These effects of PTPTO on cellular apoptosis are dependent on an ErbB2/PI3K/Akt/NFκB signaling pathway. Here we revealed a novel regulatory pathway of cellular apoptosis by PTPRO in lung alveolar epithelial cells during sepsis.

Protein tyrosine phosphatase PTPRO represses lung adenocarcinoma progression by inducing mitochondria-dependent apoptosis and restraining tumor metastasis

Emerging evidence indicates that protein activities regulated by receptor protein tyrosine phosphatases (RPTPs) are crucial for a variety of cellular processes, such as proliferation, apoptosis, and immunological response. Protein tyrosine phosphatase receptor type O (PTPRO), an RPTP, has been revealed as a putative suppressor in the development of particular tumors. However, the function and the underlying mechanisms of PTPRO in regulating of lung adenocarcinoma (LUAD) are not well understood. In this view, the present work investigated the role of PTPRO in LUAD. Analysis of 90 pairs of clinical LUAD specimens revealed significantly lower PTPRO levels in LUAD compared with adjacent non-tumor tissue, as well as a negative correlation of PTPRO expression with tumor size and TNM stage. Survival analyses demonstrated that PTPRO level can help stratify the prognosis of LUAD patients. Furthermore, PTPRO overexpression was found to suppress the progression of LUAD both in vitro and in vivo by inducing cell death via mitochondria-dependent apoptosis, downregulating protein expression of molecules (Bcl-2, Bax, caspase 3, cleaved-caspase 3/9, cleaved-PARP and Bid) essential in cell survival. Additionally, PTPRO decreased LUAD migration and invasion by regulating proteins involved in the epithelial-to-mesenchymal transition (E-cadherin, N-cadherin, and Snail). Moreover, PTPRO was shown to restrain JAK2/STAT3 signaling pathways. Expression of PTPRO was negatively correlated with p-JAK2, p-STAT3, Bcl-2, and Snail levels in LUAD tumor samples. Furthermore, the anti-tumor effect of PTPRO in LUAD was significant but compromised in STAT3-deficient cells. These data support the remarkable suppressive role of PTPRO in LUAD, which may represent a viable therapeutic target for LUAD patients.

Developmental roles of glomerular epithelial protein-1 in mice molar morphogenesis

Glomerular epithelial protein-1 (Glepp1), a R3 subtype family of receptor-type protein tyrosine phosphatases, plays important role in the activation of Src family kinases and regulates cellular processes such as cell proliferation, differentiation, and apoptosis. In this study, we firstly examined the functional evaluation of Glepp1 in tooth development and morphogenesis. The precise expression level and developmental function of Glepp1 were examined by RT-qPCR, in situ hybridization, and loss and gain of functional study using a range of in vitro organ cultivation methods. Expression of Glepp1 was detected in the developing tooth germs in cap and bell stage of tooth development. Knocking down Glepp1 at E13 for 2 days showed the altered expression levels of tooth development-related signaling molecules, including Bmps, Dspp, Fgf4, Lef1, and Shh. Moreover, transient knock down of Glepp1 revealed alterations in cellular physiology, examined by the localization patterns of Ki67 and E-cadherin. Similarly, knocking down of Glepp1 showed disrupted enamel rod and interrod formation in 3-week renal transplanted teeth. In addition, due to attrition of odontoblastic layers, the expression signals of Dspp and the localization of NESTIN were almost not detected after knock down of Glepp1; however, their expressions were increased after Glepp1 overexpression. Thus, our results suggested that Glepp1 plays modulating roles during odontogenesis by regulating the expression levels of signaling molecules and cellular events to achieve the proper structural formation of hard tissue matrices in mice molar development.

Age-related decline in hippocampal tyrosine phosphatase PTPRO is a mechanistic factor in chemotherapy-related cognitive impairment

Chemotherapy-related cognitive impairment (CRCI) or "chemo brain" is a devastating neurotoxic sequela of cancer-related treatments, especially for the elderly individuals. Here we show that PTPRO, a tyrosine phosphatase, is highly enriched in the hippocampus, and its level is tightly associated with neurocognitive function but declined significantly during aging. To understand the protective role of PTPRO in CRCI, a mouse model was generated by treating Ptpro-/- female mice with doxorubicin (DOX) because Ptpro-/- female mice are more vulnerable to DOX, showing cognitive impairments and neurodegeneration. By analyzing PTPRO substrates that are neurocognition-associated tyrosine kinases, we found that SRC and EPHA4 are highly phosphorylated/activated in the hippocampi of Ptpro-/- female mice, with increased sensitivity to DOX-induced CRCI. On the other hand, restoration of PTPRO in the hippocampal CA3 region significantly ameliorate CRCI in Ptpro-/- female mice. In addition, we found that the plant alkaloid berberine (BBR) is capable of ameliorating CRCI in aged female mice by upregulating hippocampal PTPRO. Mechanistically, BBR upregulates PTPRO by downregulating miR-25-3p, which directly targeted PTPRO. These findings collectively demonstrate the protective role of hippocampal PTPRO against CRCI.

Renal cell markers: lighthouses for managing renal diseases

Kidneys, one of the vital organs in our body, are responsible for maintaining whole body homeostasis. The complexity of renal function (e.g., filtration, reabsorption, fluid and electrolyte regulation, and urine production) demands diversity not only at the level of cell types but also in their overall distribution and structural framework within the kidney. To gain an in depth molecular-level understanding of the renal system, it is imperative to discern the components of kidney and the types of cells residing in each of the subregions. Recent developments in labeling, tracing, and imaging techniques have enabled us to mark, monitor, and identify these cells in vivo with high efficiency in a minimally invasive manner. In this review, we summarize different cell types, specific markers that are uniquely associated with those cell types, and their distribution in the kidney, which altogether make kidneys so special and different. Cellular sorting based on the presence of certain proteins on the cell surface allowed for the assignment of multiple markers for each cell type. However, different studies using different techniques have found contradictions in cell type-specific markers. Thus, the term "cell marker" might be imprecise and suboptimal, leading to uncertainty when interpreting the data. Therefore, we strongly believe that there is an unmet need to define the best cell markers for a cell type. Although the compendium of renal-selective marker proteins presented in this review is a resource that may be useful to researchers, we acknowledge that the list may not be necessarily exhaustive.

Regulatory Functions of Protein Tyrosine Phosphatase Receptor Type O in Immune Cells

The members of the protein tyrosine phosphatase (PTP) family are key regulators in multiple signal transduction pathways and therefore they play important roles in many cellular processes, including immune response. As a member of PTP family, protein tyrosine phosphatase receptor type O (PTPRO) belongs to the R3 receptor-like protein tyrosine phosphatases. The expression of PTPRO isoforms is tissue-specific and the truncated PTPRO (PTPROt) is mainly observed in hematopoietic cells, including B cells, T cells, macrophages and other immune cells. Therefore, PTPROt may play an important role in immune cells by affecting their growth, differentiation, activation and immune responses. In this review, we will focus on the regulatory roles and underlying molecular mechanisms of PTPRO/PTPROt in immune cells, including B cells, T cells, and macrophages.

Mitotic Catastrophe Causes Podocyte Loss in the Urine of Human Diabetics

Mitotic catastrophe (MC) is a major cause of podocyte loss in vitro and in vivo. We evaluated urine samples (n = 184 urine samples from diabetic patients; n = 41 patients) from diabetic patients and determined the presence of podocytes in the urine and studied their characteristics, specifically asking whether apoptosis versus MC is present. We also evaluated diabetic glomeruli in renal biopsy specimens by electron microscopy (n = 54). A battery of stains including the antibody to podocalyxin (PCX) were used. PCX and podocytes (PCX+podo) showed nuclear morphologies such as a i) mononucleated normal shape (8.7%), ii) large and abnormal shape (3.8%), iii) multinucleated with or without micronucleoli (31.2%), iv) mitotic spindles (8.2%), v) single nucleus and denucleation combined (10.3%), and vi) denucleation only (37.0%). Large size/abnormal shape, multinucleation, mitotic spindles, and a combination of single nucleus and denucleation were considered features of MC (53.5%). Dual staining of PCX+podo was positive for Glepp 1 (50%), whereas none of PCX+podo were positive for nephrin, podocin, leukocyte, or parietal epithelial cell markers (cytokeratin 8), annexin V, cleaved caspase-3, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling. Ten percent of PCX+podo were positive for phosphorylated vimentin. Electron microscopy identified cellular and nuclear podocyte changes characteristic of MC. The majority of urine podocytes in diabetic patients showed MC, not apoptosis. This noninvasive approach may be clinically useful in determining progressive diabetic nephropathy or response to therapeutic intervention.

Oestrogen inhibits PTPRO to prevent the apoptosis of renal podocytes

Podocytes are a major component of the glomerular filtration membrane, and their apoptosis is involved in a variety of nephrotic syndromes. In the current study, the effects and molecular mechanisms of oestrogen on the proliferation and apoptosis of podocytes were investigated to elucidate the role of oestrogen in the pathogenesis of childhood nephrotic syndrome. The cell proliferation of mouse renal podocytes (MPC-5) and human primary renal podocytes was promoted by 17β-oestradiol (E2) in what appear to be a time-dependent manner. Apoptosis was inhibited by E2 and promoted by the E2 antagonist, tamoxifen. The expression of protein tyrosine phosphatase receptor type O (PTPRO) decreased with the increasing dosage of E2, but increased with the increasing dosage tamoxifen in MPC-5 and human podocytes. The protein, oestrogen receptor (ER)α, was not expressed in MPC-5 and human podocytes. E2 binding to ERβ completely eliminated PTPRO expression in MPC-5. In podocytes, PTPRO was phosphorylated by E2 at the Y1007 and associated with tyrosine-protein kinase JAK2 (JAK2) activation, rather than JAK1 activation. PTPRO was involved in the binding of E2 to signal transducer and activator of transcription (STAT)3 at the Y705 and S727 sites, resulting in the phosphorylation of STAT3 in podocytes. Through PTPRO, E2 also regulated the proliferation and apoptosis of podocytes. In conclusion, oestrogen binding to ERβ, rather than ERα, promoted the proliferation of podocytes and inhibited the apoptosis of podocytes by inhibiting the expression of PTPRO. The mechanism may be associated with the activation of the JAK2/STAT3 signalling pathway. The current study may provide a novel direction for the treatment of childhood nephrotic syndrome.

Apelinergic system in the kidney: implications for diabetic kidney disease

The bioactive peptides of the apelinergic system and its receptor APJ have been shown to play a protective role in experimental cardiovascular and diabetic kidney disease (DKD). Mechanisms of this renoprotective effect remain to be elucidated. In this study, we examined the localization of APJ within the normal kidney and its kidney expression in the db/db model of DKD. The effect of hyperglycemia and angiotensin II on APJ was examined in cultured podocytes. In the glomerulus, APJ colocalized with podocyte but not endothelial cell markers. In podocytes stimulated with Pyr1 Apelin-13, a change in the phosphorylation status of the signaling proteins, AKT, ERK, and p70S6K, was observed with an increase 15 min after stimulation. Apelin-13 decreased activity of Caspase-3 in podocytes after high glucose treatment reflecting an antiapoptotic effect of APJ stimulation. In podocytes, APJ mRNA was downregulated in high glucose, when compared to normal glucose conditions and exposure to angiotensin II led to a further significant decrease in APJ mRNA. APJ and preproapelin mRNA levels in kidneys from db/db mice were markedly decreased along with decreased tubular APJ protein by western blotting and immunostaining when compared to db/m controls. In conclusion, the apelinergic system is decreased in kidneys from db/db mice. Within the glomerulus, APJ is mainly localized in podocytes and in this cell type its activation by Apelin-13 abolishes the proapoptotic effect of high glucose, suggesting a potential therapeutic role of apelin and emerging agonists with extended half-life for therapy of DKD.

The Roles of Protein Tyrosine Phosphatases in Hepatocellular Carcinoma

The protein tyrosine phosphatase (PTP) family is involved in multiple cellular functions and plays an important role in various pathological and physiological processes. In many chronic diseases, for example cancer, PTP is a potential therapeutic target for cancer treatment. In the last two decades, dozens of PTP inhibitors which specifically target individual PTP molecules were developed as therapeutic agents. Hepatocellular carcinoma (HCC) is one of the most common malignant tumors and is the second most lethal cancer worldwide due to a lack of effective therapies. Recent studies have unveiled both oncogenic and tumor suppressive functions of PTP in HCC. Here, we review the current knowledge on the involvement of PTP in HCC and further discuss the possibility of targeting PTP in HCC.

Compulsive methamphetamine taking in the presence of punishment is associated with increased oxytocin expression in the nucleus accumbens of rats

Methamphetamine addiction is mimicked in rats that self-administer the drug. However, these self-administration (SA) models do not include adverse consequences that are necessary to reach a diagnosis of addiction in humans. Herein, we measured genome-wide transcriptional consequences of methamphetamine SA and footshocks in the rat brain. We trained rats to self-administer methamphetamine for 20 days. Thereafter, lever-presses for methamphetamine were punished by mild footshocks for 5 days. Response-contingent punishment significantly reduced methamphetamine taking in some rats (shock-sensitive, SS) but not in others (shock-resistant, SR). Rats also underwent extinction test at one day and 30 days after the last shock session. Rats were euthanized one day after the second extinction test and the nucleus accumbens (NAc) and dorsal striatum were collected to measure gene expression with microarray analysis. In the NAc, there were changes in the expression of 13 genes in the SRvsControl and 9 genes in the SRvsSS comparison. In the striatum, there were 9 (6 up, 3 down) affected genes in the SRvsSS comparison. Among the upregulated genes was oxytocin in the NAc and CARTpt in the striatum of SR rats. These observations support a regional role of neuropeptides in the brain after a long withdrawal interval when animals show incubation of methamphetamine craving.

Regulation of receptor-type protein tyrosine phosphatases by their C-terminal tail domains

Protein tyrosine phosphatases (PTPs) perform specific functions in vivo, despite being vastly outnumbered by their substrates. Because of this and due to the central roles PTPs play in regulating cellular function, PTP activity is regulated by a large variety of molecular mechanisms. We review evidence that indicates that the divergent C-terminal tail sequences (C-terminal domains, CTDs) of receptor-type PTPs (RPTPs) help regulate RPTP function by controlling intermolecular associations in a way that is itself subject to physiological regulation. We propose that the CTD of each RPTP defines an 'interaction code' that helps determine molecules it will interact with under various physiological conditions, thus helping to regulate and diversify PTP function.

ALCAM a novel biomarker in patients with type 2 diabetes mellitus complicated with diabetic nephropathy

BACKGROUND & AIM

Activated leukocyte cell adhesion molecule (ALCAM/CD166) functions analogue to the receptor of advanced glycation end products, which has been implicated in the development of diabetic nephropathy (DN). We investigated the expression of ALCAM and its ligand S100B in patients with DN.

METHODS

A total of 34 non-diabetic patients, 29 patients with type 2 diabetes and normal albuminuria and 107 patients with type 2 diabetes complicated with DN were assessed for serum concentration of soluble ALCAM (sALCAM) by ELISA. Expression of ALCAM and S100B in kidney histology from patients with DN was determined by immunohistochemistry. Cell expression of ALCAM and S100B was analyzed through confocal immunofluorescence microscopy.

RESULTS

Serum concentration of sALCAM was increased in diabetic patients with DN compared to non-diabetic (59.85±14.99ng/ml vs. 126.88±66.45ng/ml, P<0.0001). Moreover sALCAM correlated positively with HbA1c (R=0.31, P<0.0001), as well as with the stages of chronic kidney disease and negatively correlated with eGFR (R=-0.20, P<0.05). In diabetic patients with normal albuminuria sALCAM was increased compared to patients with DN (126.88±66.45ng/ml vs. 197.50±37.17ng/ml, P<0.0001). In diabetic patients, ALCAM expression was significantly upregulated in both the glomeruli and tubules (P<0.001). ALCAM expression in the glomeruli correlated with presence of sclerosis (R=0.25, P<0.001) and localized mainly in the podocytes supporting the hypothesis that membrane bound ALCAM drives diabetic nephropathy and thus explaining sALCAM decrease in diabetic patients with DN. The expression of S100B was increased significantly in the glomeruli of diabetic patients (P<0.001), but not in the tubules. S100B was as well localized in the podocytes.

CONCLUSIONS

This study identifies for the first time ALCAM as a potential mediator in the late complications of diabetes in the kidney.

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.

Reduced Glomerular Epithelial Protein 1 Expression and Podocyte Injury in Immunoglobulin a Nephropathy

Expression of glomerular epithelial protein 1 (GLEPP1), a receptor tyrosine phosphatase present on the apical cell surface of the glomerular podocyte, and podocyte morphology were investigated in renal specimens from 51 patients with biopsy-diagnosed immunoglobulin A nephropathy (IgAN) and 11 controls. Clinical parameters, such as daily proteinuria were obtained from the patients' records and pathological manifestations of IgAN in the specimens were graded. GLEPP1 was strongly expressed and diffusely distributed in the glomeruli of control specimens. GLEPP1 expression was reduced in IgAN, especially in patients with nephrotic proteinuria and severe pathological manifestations. Podocyte injury was evident in IgAN and was associated with lower GLEPP1 expression and higher pathological grade. GLEPP1 expression was also significantly associated with clinical parameters. The results of this study suggest that GLEPP1 expression may be a useful marker of podocyte injury in IgAN, and may be predictive of clinical and pathological severity.

The proepicardium keeps a potential for glomerular marker expression which supports its evolutionary origin from the pronephros

The proepicardium is the embryonic primordium of the epicardium. This transient structure is essential for cardiac development giving rise to the epicardium and supplying the heart with vascular and cardiac connective tissue progenitors. However, their nature and evolutionary origin are poorly-known. We have suggested elsewhere (Pombal et al. Evol. Dev. 10: 210-216, 2008; Cano et al., J. Dev. Biol. 1: 3-19, 2013) that the proepicardium is an evolutionary derivative of the primordium of an ancient external pronephric glomerulus, devoid of its original excretory function. In this study, we describe for the first time expression of two podocyte markers in the chick proepicardium (glepp1 and synaptopodin) and we have shown how these podocyte markers as well as the intermediate mesoderm marker Pax2 are strongly upregulated when the proepicardium is cultured with nephrogenic inducers. Retinoic acid treatment also induced in the proepicardium expression of Hoxb4, a gene which confers to intermediate mesoderm competence to respond to nephrogenic signals. Thus, a latent nephrogenic potential persists in the proepicardium and also that its original glomerular fate can be partially rescued. The transcription factor Wt1, essential for kidney and epicardial development, plays opposite roles in both tissues, inducing epithelial-mesenchymal transition in the proepicardium and promoting epithelialization in the kidneys (Essafi et al., Dev. Cell 21: 559-574, 2011). Consistently with this antithetical function of Wt1, we have observed an upregulation of podocalyxin in the epicardium of mouse embryos with conditional deletion of the Wt1 gene, while this protein is transcriptionally activated by Wt1 in podocytes.

Tumor-Suppression Mechanisms of Protein Tyrosine Phosphatase O and Clinical Applications

Tyrosine phosphorylation plays an important role in regulating human physiological and pathological processes. Functional stabilization of tyrosine phosphorylation largely contributes to the balanced, coordinated regulation of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Research has revealed PTPs play an important suppressive role in carcinogenesis and progression by reversing oncoprotein functions. Receptor-type protein tyrosine phosphatase O (PTPRO) as one member of the PTPs family has also been identified to have some roles in tumor development. Some reports have shown PTPRO over-expression in tumors can not only inhibit the frequency of tumor cell division and induce tumor cell death, but also suppress migration. However, the tumor-suppression mechanisms are very complex and understanding is incomplete, which in some degree blocks the further development of PTPRO. Hence, in order to resolve this problem, we here have summarized research findings to draw meaningful conclusions. We found tumor-suppression mechanisms of PTPRO to be diverse, such as controlling G0/G1 of the tumor cell proliferation cycle, inhibiting substrate phosphorylation, down-regulating transcription activators and other activities. In clinical anticancer efforts, expression level of PTPRO in tumors can not only serve as a biomarker to monitor the prognosis of patients, but act as an epigenetic biomarker for noninvasive diagnosis. In addition, the re-activation of PTPRO in tumor tissues, not only can induce tumor volume reduction, but also enhance the susceptibility to chemotherapy drugs. So, we can propose that these research findings of PTPRO will not only support new study ideas and directions for other tumor- suppressors, importantly, but also supply a theoretical basis for researching new molecular targeting agents in the future.

Proteomic analysis of formalin-fixed paraffin-embedded glomeruli suggests depletion of glomerular filtration barrier proteins in two-kidney, one-clip hypertensive rats

Background

It is well known that hypertension may cause glomerular damage, but the molecular mechanisms involved are still incompletely understood.

Methods

In the present study, we used formalin-fixed paraffin-embedded (FFPE) tissue to investigate changes in the glomerular proteome in the non-clipped kidney of two-kidney one-clip (2K1C) hypertensive rats, with special emphasis on the glomerular filtration barrier. 2K1C hypertension was induced in 6-week-old Wistar Hannover rats (n = 6) that were sacrificed 23 weeks later and compared with age-matched sham-operated controls (n = 6). Tissue was stored in FFPE tissue blocks and later prepared on tissue slides for laser microdissection. Glomeruli without severe morphological damage were isolated, and the proteomes were analysed using liquid chromatography–tandem mass spectrometry.

Results

2K1C glomeruli showed reduced abundance of proteins important for slit diaphragm complex, such as nephrin, podocin and neph1. The podocyte foot process had a pattern of reduced abundance of transmembrane proteins but unchanged abundances of the podocyte cytoskeletal proteins synaptopodin and α-actinin-4. Lower abundance of important glomerular basement membrane proteins was seen. Possible glomerular markers of damage with increased abundance in 2K1C were transgelin, desmin and acyl-coenzyme A thioesterase 1.

Conclusions

Microdissection and tandem mass spectrometry could be used to investigate the proteome of isolated glomeruli from FFPE tissue. Glomerular filtration barrier proteins had reduced abundance in the non-clipped kidney of 2K1C hypertensive rats.

Podocyte injury in pure membranous and proliferative lupus nephritis: distinct underlying mechanisms of proteinuria?

Proteinuria is a major feature of lupus nephritis (LN) and reflects podocyte injury. Analysis of podocyte biomarkers was performed attempting to identify if podocyte phenotype is distinct in pure membranous and proliferative LN. Expression of synaptopodin, Wilms tumor protein 1 (WT1), glomerular epithelial protein 1 (GLEPP1) and nephrin was evaluated in 52 LN biopsies by immunohistochemistry. Preserved synaptopodin expression was observed in only 10 (19.2%) of all biopsies while 42 (80.8%) had reduced expression. Both groups had comparable proteinuria at the time of biopsy (p = 0.22); however, in the mean follow-up of four years there was a tendency toward lower mean levels of proteinuria in patients with preserved synaptopodin staining (0.26±0.23 vs. 0.84±0.90 g/24 h, p = 0.05) compared with those with diminished expression. Thirty-nine (75%) biopsies were classified as proliferative and 13 (25%) as pure membranous. Comparison of podocyte biomarkers demonstrated a predominance of preserved staining of synaptopodin (69.2%), WT1 (69.2%), GLEPP1 (53.9%) and nephrin (60%) in the pure membranous group whereas only <10% of the proliferative showed preserved expression. Our data suggest that in proliferative forms there seems to occur structural podocyte damage, whereas in the pure membranous the predominant preserved pattern suggests a dysfunctional podocyte lesion that may account for the better long-term prognosis of proteinuria outcome.

A compendium of urinary biomarkers indicative of glomerular podocytopathy

It is well known that glomerular podocyte injury and loss are present in numerous nephropathies and that the pathophysiologic consecution of disease hinges upon the fate of the podocyte. While multiple factors play a hand in glomerulopathy progression, basic logic lends that if one monitors the podocyte's status, that may reflect the status of disease. Recent investigations have focused on what one can elucidate from the noninvasive collection of urine, and have proven that certain, specific biomarkers of podocytes can be readily identified via varying techniques. This paper has brought together all described urinary biomarkers of podocyte injury and is made to provide a concise summary of their utility and testing in laboratory and clinical theatres. While promising in the potential that they hold as tools for clinicians and investigators, the described biomarkers require further comprehensive vetting in the form of larger clinical trials and studies that would give their value true weight. These urinary biomarkers are put forth as novel indicators of glomerular disease presence, disease progression, and therapeutic efficacy that in some cases may be more advantageous than the established parameters/measures currently used in practice.

Real-Time Monitoring of the Dephosphorylating Activity of Protein Tyrosine Phosphatases Using Microarrays with 3-Nitrophosphotyrosine Substrates

Phosphatases and kinases regulate the crucial phosphorylation post-translational modification. In spite of their similarly important role in many diseases and therapeutic potential, phosphatases have received arguably less attention. One reason for this is a scarcity of high-throughput phosphatase assays. Herein, a new real-time, dynamic protein tyrosine phosphatase (PTP) substrate microarray assay measuring product formation is described. PTP substrates comprising a novel 3-nitrophosphotyrosine residue are immobilized in discrete spots. After reaction catalyzed by a PTP a 3-nitrotyrosine residue is formed that can be detected by specific, sequence-independent antibodies. The resulting microarray was successfully evaluated with a panel of recombinant PTPs and cell lysates, which afforded results comparable to data from other assays. Its parallel nature, convenience, and low sample requirements facilitate investigation of the therapeutically relevant PTP enzyme family.

Estrogen-sensitive PTPRO expression represses hepatocellular carcinoma progression by control of STAT3

Protein tyrosine phosphatase receptor type O (PTPRO), one of the receptor types of phosphotyrosine phosphatases (PTP), was recently described as a tumor suppressor in various kinds of cancers. We aimed to clarify the role of PTPRO in hepatocellular carcinoma (HCC). It was demonstrated in 180 pairs (120 male and 60 female) of clinical HCC specimens that the PTPRO level was significantly reduced, as compared with adjacent tissue, and the PTPRO level in male adjacent tissue was lower than in female. We further found that estrogen receptor alpha (ERα) could up-regulate PTPRO expression as a transcription factor. Moreover, an in vitro study showed that cell proliferation was inhibited and apoptosis was promoted in PTPRO-transduced HCC cell lines, whereas an in vivo study represented that tumor number and size was increased in ptpro(-/-) mice. As a result of its tumor-suppressive position, PTPRO was proved to down-regulate signal transducers and activators of transcription (STAT3) activity dependent on Janus kinase 2 (JAK2) and phosphoinositide 3-kinase (PI3K) dephosphorylation.

CONCLUSIONS

PTPRO expression results in pathological deficiency and gender bias in HCC, which could be attributed to ERα regulation. The suppressive role of PTPRO in HCC could be ascribed to STAT3 inactivation.

Protein tyrosine phosphatase receptor type O (Ptpro) regulates cerebellar formation during zebrafish development through modulating Fgf signaling

Protein activities controlled by receptor protein tyrosine phosphatases (RPTPs) play comparably important roles in transducing cell surface signals into the cytoplasm by protein tyrosine kinases. Previous studies showed that several RPTPs are involved in neuronal generation, migration, and axon guidance in Drosophila, and the vertebrate hippocampus, retina, and developing limbs. However, whether the protein tyrosine phosphatase type O (ptpro), one kind of RPTP, participates in regulating vertebrate brain development is largely unknown. We isolated the zebrafish ptpro gene and found that its transcripts are primarily expressed in the embryonic and adult central nervous system. Depletion of zebrafish embryonic Ptpro by antisense morpholino oligonucleotide knockdown resulted in prominent defects in the forebrain and cerebellum, and the injected larvae died on the 4th day post-fertilization (dpf). We further investigated the function of ptpro in cerebellar development and found that the expression of ephrin-A5b (efnA5b), a Fgf signaling induced cerebellum patterning factor, was decreased while the expression of dusp6, a negative-feedback gene of Fgf signaling in the midbrain-hindbrain boundary region, was notably induced in ptpro morphants. Further analyses demonstrated that cerebellar defects of ptpro morphants were partially rescued by inhibiting Fgf signaling. Moreover, Ptpro physically interacted with the Fgf receptor 1a (Fgfr1a) and dephosphorylated Fgfr1a in a dose-dependant manner. Therefore, our findings demonstrate that Ptpro activity is required for patterning the zebrafish embryonic brain. Specifically, Ptpro regulates cerebellar formation during zebrafish development through modulating Fgf signaling.

Expression profiling during mammary epithelial cell three-dimensional morphogenesis identifies PTPRO as a novel regulator of morphogenesis and ErbB2-mediated transformation

Identification of genes that are upregulated during mammary epithelial cell morphogenesis may reveal novel regulators of tumorigenesis. We have demonstrated that gene expression programs in mammary epithelial cells grown in monolayer cultures differ significantly from those in three-dimensional (3D) cultures. We identify a protein tyrosine phosphate, PTPRO, that was upregulated in mature MCF-10A mammary epithelial 3D structures but had low to undetectable levels in monolayer cultures. Downregulation of PTPRO by RNA interference inhibited proliferation arrest during morphogenesis. Low levels of PTPRO expression correlated with reduced survival for breast cancer patients, suggesting a tumor suppressor function. Furthermore, we showed that the receptor tyrosine kinase ErbB2/HER2 is a direct substrate of PTPRO and that loss of PTPRO increased ErbB2-induced cell proliferation and transformation, together with tyrosine phosphorylation of ErbB2. Moreover, in patients with ErbB2-positive breast tumors, low PTPRO expression correlated with poor clinical prognosis compared to ErbB2-positive patients with high levels of PTPRO. Thus, PTPRO is a novel regulator of ErbB2 signaling, a potential tumor suppressor, and a novel prognostic marker for patients with ErbB2-positive breast cancers. We have identified the protein tyrosine phosphatase PTPRO as a regulator of three-dimensional epithelial morphogenesis of mammary epithelial cells and as a regulator of ErbB2-mediated transformation. In addition, we demonstrated that ErbB2 is a direct substrate of PTPRO and that decreased expression of PTPRO predicts poor prognosis for ErbB2-positive breast cancer patients. Thus, our results identify PTPRO as a novel regulator of mammary epithelial transformation, a potential tumor suppressor, and a predictive biomarker for breast cancer.

Aging in the glomerulus

Kidney function declines with age in the majority of the population. Although very few older people progress to end stage, the consequences of doing so are burdensome for the patient and very expensive for the society. Although some of the observed decline is likely due to changes in the vasculature, much is associated with the development of age-associated glomerulosclerosis. This article will review the well-established structural and functional changes in the glomerulus with age. The role of calorie restriction in modifying age-related pathology will be discussed. The importance of the podocyte as a critical cell in the aging process is considered using animal models and human biopsy material. Newer data on changes in gene expression driven by nuclear factor kappa beta (NFkB) and possible changes in biology in the glomerulus are discussed. The relationship between pathways involved in aging and the decline in kidney function is reviewed. There is speculation on the significance of these changes in relation to normal and pathological aging.

An overview of molecular mechanism of nephrotic syndrome

Podocytopathies (minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS)) together with membranous nephropathy are the main causes of nephrotic syndrome. Some changes on the expression of nephrin, podocin, TGF-β, and slit diaphragm components as well as transcription factors and transmembrane proteins have been demonstrated in podocytopathies. Considering the pathogenesis of proteinuria, some elucidations have been directed towards the involvement of epithelial-mesenchymal transition. Moreover, the usefulness of some markers such as TGF-β1, nephrin, synaptopodin, dystroglycans, and malondialdehyde have been determined in the differentiation between MCD and FSGS. Experimental models and human samples indicated an essential role of autoantibodies in membranous glomerulonephritis, kidney damage, and proteinuria events. Megalin and phospholipase-A2-receptor have been described as antigens responsible for the formation of the subepithelial immune complexes and renal disease occurrence. In addition, the complement system seems to play a key role in basal membrane damage and in the development of proteinuria in membranous nephropathy. This paper focuses on the common molecular changes involved in the development of nephrotic proteinuria.

An osteoclastic protein-tyrosine phosphatase regulates the β3-integrin, syk, and shp1 signaling through respective src-dependent phosphorylation in osteoclasts

This study utilized the glutathione transferase (GST) pull-down assay to identify novel substrates of an osteoclastic protein-tyrosine phosphatase, PTP-oc. Consistent with the previous findings that the phosphorylated tyr-527 (pY527) of Src is a substrate of PTP-oc, the major protein pulled down with the phosphatase-deficient (PD)-PTP-oc-GST trapping mutant in RAW264.7 cells was Src. The GST-PD-PTP-oc also pulled down pY-Syk and pY-β(3)-integrin, but not after PP2 pretreatment. However, PTP-oc transgenic osteoclasts or PTP-oc-overexpressing RAW264.7 cells had elevated, and not reduced, levels of pY525/526-Syk and pY759-β(3) integrin, and the PTP-oc siRNA treatment drastically reduced levels of pY525/526 Syk and pY759-β(3)-integrin in RAW264.7 cells. These findings are incompatible with the premise that they are substrates of PTP-oc. The PTP-oc-dependent increases in pY525/526-Syk and pY759-β(3)-integrin levels were completely blocked by PP2, indicating that these effects are secondary to PTP-oc-mediated activation of the Src protein-tyrosine kinase (PTK). Overexpression of PTP-oc increased, and siRNA-mediated suppression of PTP-oc reduced, pY160-Vav1, pY173-Vav3, and pY783-PLCγ levels, and Rac1 activation, which are downstream mediators of the ITAM/Syk signaling. Overexpression of PTP-oc also increased, and PTP-oc siRNA treatment decreased, the pY-Shp1 levels, which were blocked by PP2. Since Shp1 is a negative regulator of osteoclast activity and is a key mediator of the ITIM signaling, these findings suggest that PTP-oc is an upstream suppressor of the ITIM/Shp1 signaling through PTP-oc-induced Src-dependent Shp1 phosphorylation. In summary, PTP-oc plays a central regulatory role in the concerted regulation of the β(3)-integrin, the ITAM/Syk, and the ITIM/Shp1 signaling indirectly through activation of Src PTK.

Aberrant methylation of the PTPRO gene in peripheral blood as a potential biomarker in esophageal squamous cell carcinoma patients

Epigenetic inactivation of protein tyrosine phosphatase receptor-type O (PTPRO), a new member of the PTP family, has been described in several forms of cancer. We evaluated PTPRO promoter hypermethylation as a potential biomarker in esophageal squamous cell carcinoma (ESCC). This alteration was observed in 27 (75%) of 36 primary tumors and correlated significantly with depth of invasion (T-stage, P = 0.013). Among matched peripheral blood samples from ESCC patients, 13 (36.1%) of 36 exhibited detectable methylated PTPRO in plasma, while 15 (41.7%) of 36 had this abnormality in buffy coat. No methylated PTPRO was observed in normal peripheral blood samples from 10 healthy individuals. In addition, demethylation by 5-aza-dC treatment led to gene reactivation in PTPRO-methylated and -silenced ESCC cell lines. To our knowledge, this is the first report of methylated PTPRO as a noninvasive tumor biomarker in peripheral blood. These findings suggest that hypermethylated PTPRO occurs frequently in ESCC. Further, detection in peripheral blood of ESCC patients suggests potential clinical application for noninvasive diagnosis and disease monitoring.

Genome-wide study identifies PTPRO and WDR72 and FOXQ1-SUMO1P1 interaction associated with neurocognitive function

BACKGROUND

Several aspects of neurocognitive function have high heritability, but the molecular genetic mechanisms underlying neurocognition are not known. We performed a genome-wide association study (GWAS) to identify genes associated with neurocognition.

METHODS

700 Subjects (schizophrenia spectrum disorder, n=190, bipolar disorder n=157 and healthy individuals n=353) were tested with an extensive neuropsychological test battery, and genotyped using the Affymetrix Genome-Wide Human SNP Array 6.0. After quality control, linear regression analysis of each of the 24 cognitive tests on the SNP dosage was performed, including age, gender, education and disease group as covariates. Additionally, 9 SNPs trending toward genome-wide significance were considered for epistatic interactions.

RESULTS

Four SNPs and 2 independent association signals achieving genome-wide significance were identified. Three intronic SNPs in PTPRO were associated with learning and memory (CVLT-II LDFR) (rs17222089, p=1.55×10(-8); rs11056571, p=1.68×10(-8); and rs2300290, p=1.09×10(-8)). rs719714 downstream of WDR72 was associated with executive functioning (CW-3: Inhibition, D-KEFS) (p=4.32×10(-8)). A highly significant epistatic interaction was found between rs9378605 upstream of FOXQ1 and rs11699311 downstream of SUMO1P1 for the Grooved Pegboard test (p=7.6×10(-14)).

CONCLUSIONS

We identified four novel loci associated with neurocognitive function and one novel epistatic interaction. The findings should be replicated in independent samples, but indicate a role of PTPRO in learning and memory, WDR72 with executive functioning, and an interaction between FOXQ1 and SUMO1P1 for psychomotor speed.

Podocyte Protein, Nephrin, Is a Substrate of Protein Tyrosine Phosphatase 1B

Glomerular podocytes are critical for the barrier function of the glomerulus in the kidney and their dysfunction causes protein leakage into the urine (proteinuria). Nephrin is a key podocyte protein, which regulates the actin cytoskeleton via tyrosine phosphorylation of its cytoplasmic domain. Here we report that two protein tyrosine phosphatases, PTP1B and PTP-PEST negatively regulate nephrin tyrosine phosphorylation. PTP1B directly binds to and dephosphorylates nephrin, while the action of PTP-PEST is indirect. The two phosphatases are also upregulated in the glomerulus in the rat model of puromycin aminonucleoside nephrosis. Both overexpression and inhibition of PTP1B deranged the actin cytoskeleton in cultured mouse podocytes. Thus, protein tyrosine phosphatases may affect podocyte function via regulating nephrin tyrosine phosphorylation.

Identification of ptpro as a novel target gene of Wnt signaling and its potential role as a receptor for Wnt

Wnt/β-catenin signaling plays critical roles in embryonic development and tissue homeostasis in adults by controlling the expression of target genes. We found that expression of ptpro, which encodes a protein tyrosine phosphatase receptor type O (PTPRO), was induced by Wnt/β-catenin signaling in a T cell factor/lymphoid enhancer factor dependent manner. Biochemical assays found that PTPRO interacted with Wnt via its extracellular domain. In addition, ectopic expression of this extracellular domain inhibited Wnt-mediated reporter activity. These results suggest that ptpro is a target gene of Wnt/β-catenin signaling and that PTPRO may function as a novel receptor for Wnt.

Expression, localization, and biological function of the R3 subtype of receptor-type protein tyrosine phosphatases in mammals

The R3 subtype of receptor-type protein tyrosine phosphatases (RPTPs) includes VE-PTP, DEP-1, PTPRO, and SAP-1. All of these enzymes share a similar structure, with a single catalytic domain and putative tyrosine phosphorylation sites in the cytoplasmic region and fibronectin type III-like domains in the extracellular region. The expression of each R3 RPTP is largely restricted to a single or limited number of cell types, with VE-PTP and DEP-1 being expressed in endothelial or hematopoietic cells, PTPRO in neurons and in podocytes of the renal glomerulus, and SAP-1 in gastrointestinal epithelial cells. In addition, these RPTPs are localized specifically at the apical surface of polarized cells. The structure, expression, and localization of the R3 RPTPs suggest that they perform tissue-specific functions and that they might act through a common mechanism that includes activation of Src family kinases. In this review, we describe recent insights into R3-subtype RPTPs, particularly those of mammals.

Molecular make-up of the glomerular filtration barrier

The glomerular filtration barrier is composed of glomerular endothelial cells, the glomerulus basement membrane and the podocyte cell layer. The filtration barrier is a target of injury in several systemic and renal diseases, and this often leads to progressive renal disease and kidney failure. Therefore, it is essential to understand the molecular biology of the glomerulus. During the last two decades, a lot of new information about molecular components of the glomerulus filtration barrier has been generated. Many of the key discoveries have been obtained through studies on the genetic background of inherited glomerular diseases. These studies have emphasized the role of podocytes in the filtration barrier function. During the last decade, the use of knockout mouse technology has become more available and given important new insights into the functional significance of glomerular components. Large-scale approaches, such as microarray profiling, have also given data about molecules involved in the biology and pathology of the glomerulus. In the coming decade, the use of global expression profiling platforms, transgenic mouse lines, and other in vivo gene delivery methods will rapidly expand our understanding of biology and pathology of the glomerular filtration barrier, and hopefully expose novel target molecules for therapy in progressive renal diseases.

SIRP-alpha-CD47 system functions as an intercellular signal in the renal glomerulus

The renal glomerulus consists of endothelial cells, podocytes, and mesangial cells. These cells cooperate with each other for glomerular filtration; however, the intercellular signaling molecules between glomerular cells are not fully determined. Tyrosine phosphorylation of slit diaphragm molecules is a key to the detection of the signal to podocytes from other cells. Although src kinase is involved in this event, the molecules working for dephosphorylation remain unclear. We demonstrate that signal-inhibitory regulatory protein (SIRP)-alpha, which recruits a broadly distributed tyrosine dephosphorylase SHP-2 to the plasma membrane, is located in podocytes. SIRP-alpha is a type I transmembrane glycoprotein, which has three immunoglobulin-like domains in the extracellular region and two SH2 binding motifs in the cytoplasm. This molecule functions as a scaffold for many proteins, especially the SHP-2 molecule. SIRP-alpha is concentrated in the slit diaphragm region of normal podocytes. CD47, a ligand for SIRP-alpha, is also expressed in the glomerulus. CD47 is located along the plasma membrane of mesangial cells, but not on podocytes. CD47 is markedly decreased during mesangiolysis, but increased in mesangial cells in the restoration stage. SIRP-alpha is heavily tyrosine phosphorylated under normal conditions; however, tyrosine phosphorylation of SIRP-alpha was markedly decreased during mesangiolysis induced by Thy1.1 monoclonal antibody injection. It is known that the cytoplasmic domain of SIPR-alpha is dephosphorylated when CD47 binds to the extracellular domain of SIRP-alpha. The data suggest that the CD47-SIRP-alpha interaction may be functionally important in cell-cell communication in the diseased glomerulus.

Notch signaling, wt1 and foxc2 are key regulators of the podocyte gene regulatory network in Xenopus

Podocytes are highly specialized cells in the vertebrate kidney. They participate in the formation of the size-exclusion barrier of the glomerulus/glomus and recruit mesangial and endothelial cells to form a mature glomerulus. At least six transcription factors (wt1, foxc2, hey1, tcf21, lmx1b and mafb) are known to be involved in podocyte specification, but how they interact to drive the differentiation program is unknown. The Xenopus pronephros was used as a paradigm to address this question. All six podocyte transcription factors were systematically eliminated by antisense morpholino oligomers. Changes in the expression of the podocyte transcription factors and of four selected markers of terminal differentiation (nphs1, kirrel, ptpru and nphs2) were analyzed by in situ hybridization. The data were assembled into a transcriptional regulatory network for podocyte development. Although eliminating the six transcription factors individually interfered with aspects of podocyte development, no single gene regulated the entire differentiation program. Only the combined knockdown of wt1 and foxc2 resulted in a loss of all podocyte marker gene expression. Gain-of-function studies showed that wt1 and foxc2 were sufficient to increase podocyte gene expression within the glomus proper. However, the combination of wt1, foxc2 and Notch signaling was required for ectopic expression in ventral marginal zone explants. Together, this approach demonstrates how complex interactions are required for the correct spatiotemporal execution of the podocyte gene expression program.

Tyrosine phosphorylation of R3 subtype receptor-type protein tyrosine phosphatases and their complex formations with Grb2 or Fyn

Post-translational modification of protein tyrosine phosphatases (PTPs) is implicated in functional modulation of these enzymes. Stomach cancer-associated protein tyrosine phosphatase-1 (SAP-1), as well as protein tyrosine phosphatase receptor type O (PTPRO) and vascular endothelial-protein tyrosine phosphatase (VE-PTP) are receptor-type PTPs (RPTPs), which belong to the R3 subtype RPTP family. Here, we have shown that the carboxyl (COOH)-terminal region of SAP-1 undergoes tyrosine phosphorylation by the treatment with a PTP inhibitor. Src family kinases are important for the tyrosine phosphorylation of SAP-1. Either Grb2 or Fyn, through their Src homology-2 domains, bound to the tyrosine-phosphorylated SAP-1. Moreover, both PTPRO and VE-PTP underwent tyrosine phosphorylation in their COOH-terminal regions. Tyrosine phosphorylation of VE-PTP or PTPRO also promoted their complex formations with Grb2 or Fyn. Forced expression of SAP-1, PTPRO or VE-PTP promoted cell spreading and lamellipodium formation of fibroblasts that expressed an activated form of Ras. In contrast, such effects of non-tyrosine-phosphorylated forms of these RPTPs were markedly smaller than those of wild-type RPTPs. Our results thus suggest that tyrosine phosphorylation of R3 subtype RPTPs promotes their complex formations with Grb2 or Fyn and thus participates in the regulation of cell morphology.

Expression of PTPRO in the interneurons of adult mouse olfactory bulb

PTPRO is a receptor-type protein tyrosine phosphatase (PTP) with a single catalytic domain in its cytoplasmic region and multiple fibronectin type III-like domains in its extracellular region. In the chick, PTPRO mRNA has been shown to be particularly abundant in embryonic brain, and PTPRO is implicated in axon growth and guidance during embryonic development. However, the temporal and spatial expression of PTPRO protein in the mammalian CNS, particularly in the juvenile and adult mammalian brain, has not been evaluated in any detail. By immunohistofluorescence analysis with a monoclonal antibody to PTPRO, we show that PTPRO is widely expressed throughout the mouse brain from embryonic day 16 to postnatal day 1, while expression is largely confined to the olfactory bulb (OB) and olfactory tubercle in the adult brain. In the OB, PTPRO protein is expressed predominantly in the external plexiform layer, the granule cell layer, and the glomerular layer (GL). In these regions, expression of PTPRO is predominant in interneurons such as gamma-aminobutyric acid (GABA)-ergic or calretinin (CR)-positive granule cells. In addition, PTPRO is expressed in GABAergic, CR-positive, tyrosine hydroxylase-positive, or neurocalcin-positive periglomerular cells in the GL. Costaining of PTPRO with other neuronal markers suggests that PTPRO is likely to be localized to the dendrites or dendritic spines of these olfactory interneurons. Thus, PTPRO might participate in regulation of dendritic morphology or synapse formation of interneurons in the adult mouse OB.

Podocytes and glomerular function with aging

Kidney function declines with age in association with the development of age-associated glomerulosclerosis. The well-established structural and functional changes with age are reviewed briefly. The modification of aging pathology by calorie restriction is discussed. The role of the podocyte as a critical cell in the aging process is considered, using animal models and human biopsy material. Newer data on changes in gene expression and possible changes in biology in the glomerulus are discussed. There is speculation on the implications of this change in biology for human disease and progression.

Dimerization of tyrosine phosphatase PTPRO decreases its activity and ability to inactivate TrkC

Receptor-protein tyrosine phosphatases (RPTPs), like receptor tyrosine kinases, regulate neuronal differentiation. While receptor tyrosine kinases are dimerized and activated by extracellular ligands, the extent to which RPTPs dimerize, and the effects of dimerization on phosphatase activity, are poorly understood. We have examined a neuronal type III RPTP, PTPRO; we find that PTPRO can form dimers in living cells, and that disulfide linkages in PTPROs intracellular domain likely regulate dimerization. Dimerization of PTPROs transmembrane and intracellular domains, achieved by ligand binding to a chimeric fusion protein, decreases activity toward artificial peptides and toward a putative substrate, tropomyosin-related kinase C (TrkC). Dephosphorylation of TrkC by PTPRO may be physiologically relevant, as it is efficient, and TrkC and PTPRO can be co-precipitated from transfected cells. Inhibition of PTPROs phosphatase activity by dimerization is interesting, as dimerization of a related RPTP, CD148/PTPRJ, increases activity. Thus, our results suggest a complex relationship between dimerization and activity in type III RPTPs.

Decreased nephrin and GLEPP-1, but increased VEGF, Flt-1, and nitrotyrosine, expressions in kidney tissue sections from women with preeclampsia

Renal injury is a common pathophysiological feature in women with preeclampsia as evidenced by increased protein leakage (proteinuria) and glomerular injury (glomerular endotheliosis). Recently, podocyturia was found in preeclampsia, suggesting podocyte shedding occurs in this pregnancy disorder. However, podocyte function in preeclampsia is poorly understood. In this study, the authors have examined podocyte-specific protein expressions for nephrin, glomerular epithelial protein 1 (GLEPP-1), and ezrin in kidney biopsy tissue sections from women with preeclampsia. Expressions for vascular endothelial growth factor (VEGF) and its receptor Flt-1 and oxidative stress marker nitrotyrosine and antioxidant CuZn-superoxide dismutase (CuZn-SOD) were also examined. Kidney tissue sections from nonhypertensive and chronic hypertensive participants were stained as controls. The findings were (1) nephrin and GLEPP-1 were mainly expressed in glomerular podocytes; (2) ezrin was expressed in both glomerular podocytes and tubular epithelial cells; (3) compared to tissue sections from nonhypertensive and chronic hypertensive participants, nephrin and GLEPP-1 expressions were much reduced in tissue sections from preeclampsia and ezrin expression was reduced in podocytes; (4) enhanced VEGF, Flt-1, and nitrotyrosine, but reduced CuZn-SOD, expressions were observed in both glomerular podocytes and endothelial cells in tissue sections from preeclampsia; and (5) the expression pattern for nephrin, GLEPP-1, ezrin, VEGF, Flt-1, and CuZn-SOD were similar between tissue sections from nonhypertensive and chronic hypertensive participants. Although the authors could not conclude from this biopsy study whether the podocyte injury is the cause or effect of the preeclampsia phenotype, the data provide compelling evidence that podocyte injury accompanied by altered angiogenesis process and increased oxidative stress occurs in kidney of patients with preeclampsia.

A human glomerular SAGE transcriptome database

Background

To facilitate in the identification of gene products important in regulating renal glomerular structure and function, we have produced an annotated transcriptome database for normal human glomeruli using the SAGE approach.

Description

The database contains 22,907 unique SAGE tag sequences, with a total tag count of 48,905. For each SAGE tag, the ratio of its frequency in glomeruli relative to that in 115 non-glomerular tissues or cells, a measure of transcript enrichment in glomeruli, was calculated. A total of 133 SAGE tags representing well-characterized transcripts were enriched 10-fold or more in glomeruli compared to other tissues. Comparison of data from this study with a previous human glomerular Sau3A-anchored SAGE library reveals that 47 of the highly enriched transcripts are common to both libraries. Among these are the SAGE tags representing many podocyte-predominant transcripts like WT-1, podocin and synaptopodin. Enrichment of podocyte transcript tags SAGE library indicates that other SAGE tags observed at much higher frequencies in this glomerular compared to non-glomerular SAGE libraries are likely to be glomerulus-predominant. A higher level of mRNA expression for 19 transcripts represented by glomerulus-enriched SAGE tags was verified by RT-PCR comparing glomeruli to lung, liver and spleen.

Conclusion

The database can be retrieved from, or interrogated online at http://cgap.nci.nih.gov/SAGE. The annotated database is also provided as an additional file with gene identification for 9,022, and matches to the human genome or transcript homologs in other species for 1,433 tags. It should be a useful tool for in silico mining of glomerular gene expression.

Antibodies to protein tyrosine phosphatase receptor type O (PTPro) increase glomerular albumin permeability (P(alb))

Glomerular capillary filtration barrier characteristics are determined in part by the slit-pore junctions of glomerular podocytes. Protein tyrosine phosphatase receptor-O (PTPro) is a transmembrane protein expressed on the apical surface of podocyte foot processes. Tyrosine phosphorylation of podocyte proteins including nephrin may control the filtration barrier. To determine whether PTPro activity is required to maintain glomerular macromolecular permeability, albumin permeability (P(alb)) was studied after incubation of glomeruli from normal animals with a series of monoclonal (mAb) and polyclonal antibodies. Reagents included mAbs to rabbit and rat PTPro and polyclonal rabbit immune IgG to rat PTPro. mAb 4C3, specific to the amino acid core of PTPro, decreased its phosphatase activity and increased P(alb) of rabbit glomeruli in a time- and concentration-dependent manner. In contrast, mAb P8E7 did not diminish phosphatase activity and did not alter P(alb). Preincubation of 4C3 with PTPro extracellular domain fusion protein blocked glomerular binding and abolished permeability activity. In parallel experiments, P(alb) of rat glomeruli was increased by two mAbs (1B4 and 1D1) or by polyclonal anti-rat PTPro. We conclude that PTPro interaction with specific antibodies acutely increases P(alb). The identity of the normal ligand for PTPro and of its substrate, as well as the mechanism by which phosphatase activity of this receptor affects the filtration barrier, remain to be determined.

GLEPP1/protein-tyrosine phosphatase phi inhibitors block chemotaxis in vitro and in vivo and improve murine ulcerative colitis

We describe novel, cell-permeable, and bioavailable salicylic acid derivatives that are potent and selective inhibitors of GLEPP1/protein-tyrosine phosphatase . Two previously described GLEPP1 substrates, paxillin and Syk, are both required for cytoskeletal rearrangement and cellular motility of leukocytes in chemotaxis. We show here that GLEPP1 inhibitors prevent dephosphorylation of Syk1 and paxillin in resting cells and block primary human monocyte and mouse bone marrow-derived macrophage chemotaxis in a gradient of monocyte chemotactic protein-1. In mice, the GLEPP1 inhibitors also reduce thioglycolate-induced peritoneal chemotaxis of neutrophils, lymphocytes, and macrophages. In murine disease models, the GLEPP1 inhibitors significantly reduce severity of contact hypersensitivity, a model for allergic dermatitis, and dextran sulfate sodium-induced ulcerative colitis, a model for inflammatory bowel disease. Taken together, our data provide confirmation that GLEPP1 plays an important role in controlling chemotaxis of multiple types of leukocytes and that pharmacological inhibition of this phosphatase may have therapeutic use.

SAP-1 is a microvillus-specific protein tyrosine phosphatase that modulates intestinal tumorigenesis

SAP-1 (PTPRH) is a receptor-type protein tyrosine phosphatase (RPTP) with a single catalytic domain in its cytoplasmic region and fibronectin type III-like domains in its extracellular region. The cellular localization and biological functions of this RPTP have remained unknown, however. We now show that mouse SAP-1 mRNA is largely restricted to the gastrointestinal tract and that SAP-1 protein localizes to the microvilli of the brush border in gastrointestinal epithelial cells. The expression of SAP-1 in mouse intestine is minimal during embryonic development but increases markedly after birth. SAP-1-deficient mice manifested no marked changes in morphology of the intestinal epithelium. In contrast, SAP-1 ablation inhibited tumorigenesis in mice with a heterozygous mutation of the adenomatous polyposis coli gene. These results thus suggest that SAP-1 is a microvillus-specific RPTP that regulates intestinal tumorigenesis.