Microtubule Associated Protein 1b (MAP1B) Is a Marker of the Microtubular Cytoskeleton in Podocytes but Is Not Essential for the Function of the Kidney Filtration Barrier in Mice.

Podocytes are essential for the function of the kidney glomerular filter. A highly differentiated cytoskeleton is requisite for their integrity. Although much knowledge has been gained on the organization of cortical actin networks in podocyte's foot processes, less is known about the molecular organization of the microtubular cytoskeleton in primary processes and the cell body. To gain an insight into the organization of the microtubular cytoskeleton of the podocyte, we systematically analyzed the expression of microtubule associated proteins (Maps), a family of microtubules interacting proteins with known functions as regulator, scaffold and guidance proteins. We identified microtubule associated protein 1b (MAP1B) to be specifically enriched in podocytes in human and rodent kidney. Using immunogold labeling in electron microscopy, we were able to demonstrate an enrichment of MAP1B in primary processes. A similar association of MAP1B with the microtubule cytoskeleton was detected in cultured podocytes. Subcellular distribution of MAP1B HC and LC1 was analyzed using a double fluorescent reporter MAP1B fusion protein. Subsequently we analyzed mice constitutively depleted of MAP1B. Interestingly, MAP1B KO was not associated with any functional or structural alterations pointing towards a redundancy of MAP proteins in podocytes. In summary, we established MAP1B as a specific marker protein of the podocyte microtubular cytoskeleton

mTORC2 critically regulates renal potassium handling

The mTOR pathway orchestrates cellular homeostasis. The rapamycin-sensitive mTOR complex (mTORC1) in the kidney has been widely studied; however, mTORC2 function in renal tubules is poorly characterized. Here, we generated mice lacking mTORC2 in the distal tubule (Rictorfl/fl Ksp-Cre mice), which were viable and had no obvious phenotype, except for a 2.5-fold increase in plasma aldosterone. Challenged with a low-Na+ diet, these mice adequately reduced Na+ excretion; however, Rictorfl/fl Ksp-Cre mice rapidly developed hyperkalemia on a high-K+ diet, despite a 10-fold increase in serum aldosterone levels, implying that mTORC2 regulates kaliuresis. Phosphorylation of serum- and glucocorticoid-inducible kinase 1 (SGK1) and PKC-α was absent in Rictorfl/fl Ksp-Cre mice, indicating a functional block in K+ secretion activation via ROMK channels. Indeed, patch-clamp experiments on split-open tubular segments from the transition zone of the late connecting tubule and early cortical collecting duct demonstrated that Ba2+-sensitive apical K+ currents were barely detectable in the majority of Rictorfl/fl Ksp-Cre mice. Conversely, epithelial sodium channel (ENaC) activity was largely preserved, suggesting that the reduced ability to maintain K+ homeostasis is the result of impaired apical K+ conductance and not a reduced electrical driving force for K+ secretion. Thus, these data unravel a vital and nonredundant role of mTORC2 for distal tubular K+ handling

MTOR regulates endocytosis and nutrient transport in proximal tubular cells

Renal proximal tubular cells constantly recycle nutrients to ensure minimal loss of vital substrates into the urine. Although most of the transport mechanisms have been discovered at the molecular level, little is known about the factors regulating these processes. Here, we show that mTORC1 and mTORC2 specifically and synergistically regulate PTC endocytosis and transport processes. Using a conditional mouse genetic approach to disable nonredundant subunits of mTORC1, mTORC2, or both, we showed that mice lacking mTORC1 or mTORC1/mTORC2 but not mTORC2 alone develop a Fanconi-like syndrome of glucosuria, phosphaturia, aminoaciduria, low molecular weight proteinuria, and albuminuria. Interestingly, proteomics and phosphoproteomics of freshly isolated kidney cortex identified either reduced expression or loss of phosphorylation at critical residues of different classes of specific transport proteins. Functionally, this resulted in reduced nutrient transport and a profound perturbation of the endocytic machinery, despite preserved absolute expression of the main scavenger receptors, MEGALIN and CUBILIN. Our findings highlight a novel mTOR–dependent regulatory network for nutrient transport in renal proximal tubular cells

Europarechtsbedenkliche Vorschläge der österreichischen Parteien

Die Diplomarbeit geht der Frage nach, welchen Einfluss die Einstellung einer Partei zur europäischen Integration auf die Bereitschaft der Partei hat, europarechtsbedenkliche Vorschläge zu erstatten. Da die meisten Aussagen von Politikern meistens nicht hinreichend deutlich und konkret sind, um abschließend beurteilen zu können, ob eine von ihnen vorgeschlagene Maßnahme europarechtswidrig ist, wurde stattdessen der Begriff „europarechtsbedenklich“ gewählt. „Europarechtsbedenklich“ ist eine vorgeschlagene Maßnahme dann, wenn sie mit hoher Wahrscheinlichkeit gegen Europarecht verstoßen würde, wenn man sie in Österreich genauso umsetzen würde, wie der Politiker es fordert, ohne bestimmte andere Punkte zu berücksichtigen (wie z.B. für eine bestimmte Gruppe von Personen Ausnahmen vorzusehen). Dabei wird in einem ersten Schritt untersucht, welche Haltung die Parteien zur europäischen Integration einnehmen. Ausgehend von der Annahme, dass die Parteien die europäische Integration differenziert betrachten und daher nicht in allen Bereichen ausschließlich eine zustimmende oder ausschließlich eine ablehnende Haltung einnehmen, werden die verschiedenen Argumente der Parteien in zwei Gruppen eingeteilt: solche, die sich auf die wirtschaftlichen Aspekte beziehen (z.B. Wirtschafts-wachstum, Beschäftigung, Wohlstand, wirtschaftliche Stabilität) und solche, die sich auf die new-politics-Aspekte beziehen (z.B. Frieden, Lebensqualität, Demokratie bzw. –defizit, Korruption, Bürgernähe). Bei den wirtschaftlichen Themen wird erwartet, dass die Einstellung der Parteien zur europäischen Integration von ihrer Position auf der Links/Rechts-Achse abhängt; bei den new-politics-Themen wird der neuere GAL/TAN-Ansatz (green, alternative, liberitarian / traditional, autoritarian, nationalist) verwendet. In einem zweiten Schritt wird anschließend untersucht, ob die Parteien mit hoher Zustimmung zur europäischen Integration weniger europarechtsbedenkliche Vorschläge äußern als Parteien mit hoher Ablehnung. Drittens wird auch untersucht, wie sich Regierungs- und Oppositionsparteien hinsichtlich ihrer Einstellung zur europäischen Integration und hinsichtlich der Anzahl ihrer europarechtsbedenklichen Vorschläge voneinander unterscheiden

Absence of miR-146a in podocytes increases risk of diabetic glomerulopathy via upregulation of erbb4 and notch-1

Podocyte injury is an early event in diabetic kidney disease and is a hallmark of glomerulopathy. MicroRNA-146a (miR-146a) is highly expressed in many cell types under homeostatic conditions, and plays an important anti-inflammatory role in myeloid cells. However, its role in podocytes is unclear. Here, we show that miR-146a expression levels decrease in the glomeruli of patients with type 2 diabetes (T2D), which correlates with increased albuminuria and glomerular damage. MiR-146a levels are also significantly reduced in the glomeruli of albuminuric BTBR ob/ob mice, indicating its significant role in maintaining podocyte health. miR-146a-deficient mice (miR-146a-/-) showed accelerated development of glomerulopathy and albuminuria upon streptozotocin (STZ)-induced hyperglycemia. The miR-146a targets, Notch-1 and ErbB4, were also significantly upregulated in the glomeruli of diabetic patients and mice, suggesting induction of the downstream TGFβ-signaling. Treatment with a pan-ErbB kinase inhibitor erlotinib with nanomolar activity against ErbB4 significantly suppressed diabetic glomerular injury and albuminuria in both WT and miR-146a-/- animals. Treatment of podocytes in vitro with TGF-β1 resulted in increased expression of Notch-1, ErbB4, pErbB4 and pEGFR, the heterodimerization partner of ErbB4, suggesting increased ErbB4/EGFR signaling. TGF-β1 also increased levels of inflammatory cytokine MCP-1 and MCP-1 induced protein-1 (MCPIP1), a suppressor of miR-146a, suggesting an autocrine loop. Inhibition of ErbB4/EGFR with erlotinib co-treatment of podocytes suppressed this signaling. Our findings suggest a novel role for miR-146a in protecting against diabetic glomerulopathy and podocyte injury. They also point to Erbb4/EGFR as a novel, druggable target for therapeutic intervention, especially since several pan-ErbB inhibitors are clinically available

The FERM protein EPB41L5 regulates actomyosin contractility and focal adhesion formation to maintain the kidney filtration barrier

Podocytes form the outer part of the glomerular filter, where they have to withstand enormous transcapillary filtration forces driving glomerular filtration. Detachment of podocytes from the glomerular basement membrane precedes most glomerular diseases. However, little is known about the regulation of podocyte adhesion in vivo. Thus, we systematically screened for podocyte-specific focal adhesome (FA) components, using genetic reporter models in combination with iTRAQ-based mass spectrometry. This approach led to the identification of FERM domain protein EPB41L5 as a highly enriched podocyte-specific FA component in vivo. Genetic deletion of Epb41l5 resulted in severe proteinuria, detachment of podocytes, and development of focal segmental glomerulosclerosis. Remarkably, by binding and recruiting the RhoGEF ARGHEF18 to the leading edge, EPB41L5 directly controls actomyosin contractility and subsequent maturation of focal adhesions, cell spreading, and migration. Furthermore, EPB41L5 controls matrix-dependent outside-in signaling by regulating the focal adhesome composition. Thus, by linking extracellular matrix sensing and signaling, focal adhesion maturation, and actomyosin activation EPB41L5 ensures the mechanical stability required for podocytes at the kidney filtration barrier. Finally, a diminution of EPB41L5-dependent signaling programs appears to be a common theme of podocyte disease, and therefore offers unexpected interventional therapeutic strategies to prevent podocyte loss and kidney disease progression

Klf15 Is Critical for the Development and Differentiation of Drosophila Nephrocytes

Insect nephrocytes are highly endocytic scavenger cells that represent the only invertebrate model for the study of human kidney podocytes. Despite their importance, nephrocyte development is largely uncharacterised. This work tested whether the insect ortholog of mammalian Kidney Krüppel-Like Factor (Klf15), a transcription factor required for mammalian podocyte differentiation, was required for insect nephrocyte development. It was found that expression of Drosophila Klf15 (dKlf15, previously known as Bteb2) was restricted to the only two nephrocyte populations in Drosophila, the garland cells and pericardial nephrocytes. Loss of dKlf15 function led to attrition of both nephrocyte populations and sensitised larvae to the xenotoxin silver nitrate. Although pericardial nephrocytes in dKlf15 loss of function mutants were specified during embryogenesis, they failed to express the slit diaphragm gene sticks and stones and did not form slit diaphragms. Conditional silencing of dKlf15 in adults led to reduced surface expression of the endocytic receptor Amnionless and loss of in vivo scavenger function. Over-expression of dKlf15 increased nephrocyte numbers and rescued age-dependent decline in nephrocyte function. The data place dKlf15 upstream of sns and Amnionless in a nephrocyte-restricted differentiation pathway and suggest dKlf15 expression is both necessary and sufficient to sustain nephrocyte differentiation. These findings explain the physiological relevance of dKlf15 in Drosophila and imply that the role of KLF15 in human podocytes is evolutionarily conserve

Kidney and Colon Electrolyte Transport in CHIF Knockout Mice

Corticosteroid hormone induced factor (CHIF) is a small epithelial-specific protein regulated by aldosterone and K+ intake. It is a member of the FXYD family of single span transmembrane proteins involved in the regulation of ion transport. Recent data have suggested that CHIF interacts with the a subunit of the Na+-K+-ATPase and increases the pump's affinity to cell Na+. CHIF knockout (KO) mice have mild renal phenotype under low Na+ or high K+ diets. The present study further characterizes kidney electrolyte metabolism in CHIF KO mice and describes abnormalities in the colonic ion transport function. Kidney: KO mice were not compromised in salt and water balance under resting conditions. Fractional excretions (FE) of Na+ and K+ were normal and the animals had no deficit in the adaptation to low Na+ or high K+ intake. Glucocorticoid treatment did not unmask any difference. The effects of amiloride on Na+ absorption were not different at any treatment protocol. In contrast, FEK+ was reduced by 35% in KO mice under low Na+ intake. COLON: Amiloride inhibitable Na+ absorption was reduced in distal colon by 42%, 54% and 58% under control conditions, glucocorticoid treatment and low Na+ intake, respectively. Also, the cAMP dependent ion transport was significantly diminished. Forskolin induced equivalent short circuit current (I'SC) was reduced by 41%, 32% and 58%, under control conditions, high K+, and low Na+ intake, respectively. The present findings support a role of CHIF as an indirect modulator of several different ion transport mechanisms and are consistent with regulation of the Na+-K+-ATPase as the common denominator

Apps und ihre Anwendungsgebiete in der Rheumatologie

Zusammenfassung Mit der steigenden Verwendung von Smartphones einhergehend, nimmt auch die Nutzung von mobilen Applikationen (Apps) rapide zu. Im medizinischen Kontext könnten chronisch kranke Patienten von dem Einsatz dauerhaft profitieren. Verstärkt wird diese Entwicklung durch das Digitale-Versorgung-Gesetz (DVG), wonach Patienten ab Q4/2020 einen Rechtsanspruch auf bestimmte Apps, sog. digitale Gesundheitsanwendungen (DiGAs), haben, die von den gesetzlichen Krankenkassen erstattet werden. Besonders im Bereich der Rheumatologie bieten sich für das Management chronischer Erkrankungen und ihrer Komorbiditäten verschiedene Anknüpfungspunkte. Nicht nur unter rheumatologischen Patienten ist das Interesse an App-Angeboten groß, sondern auch unter deutschen Rheumatologen zeigt sich eine steigende Bereitschaft, Apps im Berufsalltag anzuwenden und Patienten zu empfehlen. Dieser Artikel will einen Überblick über die Entwicklung der App-Landschaft in der deutschsprachigen Rheumatologie vermitteln

Clinical and Histopathological Determinants for Kidney Allograft Survival in the Eurotransplant Senior Program (ESP) at the Time of Allocation

To address the shortage of organs for kidney transplantation, the Eurotransplant Senior Program (ESP) was established to enhance kidney allocation from elderly donors. This study aimed to evaluate post-transplant outcomes of deceased donor grafts and identify prognostic factors within the ESP population. We therefore analyzed patient data from 64 ESP recipients and their donors transplanted at our center between 2017 and 2022. Time-zero biopsies were analyzed using AI image analysis software for glomerular density and glomerulosclerosis. One-year patient and allograft survival rates were 96.9% and 85.9%. 5-year survival rate was 74.6%, as opposed to about 41.0% historically reported for patients on dialysis. Delayed Graft Function occurred in 29.7% of cases, with recipient coronary heart disease, BMI-disparities, and prolonged cold ischemia time as major predictors (P < 0.05). Histopathological analysis revealed that the degree of glomerulosclerosis and interstitial fibrosis and tubular atrophy (IFTA) were associated with graft failure in multivariable analyses (P < 0.05). Arteriolosclerosis (arteriolar hyalinosis) correlated with a higher risk for primary non-function (P < 0.05). The number of HLA mismatches was not significantly associated with graft outcome. Including prognostic baseline characteristics as well as histopathological AI analysis into individual allocation decisions during organ-acceptance process might improve allograft survival within the ESP and should prospectively be studied