The lysosome represents an important regulatory platform within numerous vesicle trafficking pathways including the endocytic, phagocytic, and autophagic pathways. Its ability to fuse with endosomes, ...phagosomes, and autophagosomes enables the lysosome to break down a wide range of both endogenous and exogenous cargo, including macromolecules, certain pathogens, and old or damaged organelles. Due to its center position in an intricate network of trafficking events, the lysosome has emerged as a central signaling node for sensing and orchestrating the cells metabolism and immune response, for inter-organelle and inter-cellular signaling and in membrane repair. This review highlights the current knowledge of general lysosome function and discusses these findings in their implication for renal glomerular cell types in health and disease including the involvement of glomerular cells in lysosomal storage diseases and the role of lysosomes in nongenetic glomerular injuries.
Chronic renal failure is a growing public health problem. Experimental and clinical data suggest that the loss of functional renal mass itself is a major driver for the progression of renal failure. ...Surprisingly, mice appear to be largely resistant to this pathogenic mechanism. In patients, chronic renal failure usually develops slowly over years, and increased arterial blood pressure and an activated renin‐angiotensin system are common comorbidities of the clinical phenotype. Hence, we formulated the hypothesis that coexistence of both changes over a prolonged period is required to induce sensitivity to a reduction in renal mass in mouse kidneys. To test this, we examined the effects of a moderate reduction in renal mass (unilateral nephrectomy) in SV‐129 renin transgenic mice, which have chronically elevated blood pressure levels subsequent to a genetically clamped high renin. The reduction in renal mass induced albuminuria and histopathological changes (glomerulosclerosis and protein casts) in renin transgenic animals, which were further enhanced when the mice were fed a high‐salt diet. In contrast, fibrosis of the myocardium and aortic wall was not increased in renin‐transgenic compared with control animals. We conclude that loss of renal mass can be an effective pathogenic factor in the development of chronic renal damage in mice. Renin transgenic mice may be a relevant model for chronic renal failure associated with high‐renin hypertension.
Protein homeostasis strongly depends on the targeted and selective removal of unneeded or flawed proteins, of protein aggregates, and of damaged or excess organelles by the two main intracellular ...degradative systems, namely the ubiquitin proteasomal system (UPS) and the autophagosomal lysosomal system. Despite representing completely distinct mechanisms of degradation, which underlie differing regulatory mechanisms, growing evidence suggests that the UPS and autophagy strongly interact especially in situations of overwhelming and impairment, and that both are involved in podocyte proteostasis and in the pathogenesis of podocyte injury. The differential impact of autophagy and the UPS on podocyte biology and on podocyte disease development and progression is not understood. Recent advances in understanding the role of the UPS and autophagy in podocyte biology are reviewed here.
Intracellular proteins continuously turn over by degradation and synthesis in all organ tissues. Owing to its irreversible nature, protein degradation is a highly selective process to avoid ...irreparable breakdown of cellular constituents, thereby disrupting cellular stability, integrity and signalling. The majority of intracellular proteins are degraded by the ubiquitin-proteasome system (UPS), a multi-enzyme process that involves the covalent conjugation of ubiquitin to a substrate protein and its recognition and degradation by the core multicomponent proteolytic complex of the UPS, the proteasome. In addition to labelling misfolded, damaged, aggregation-prone and intact but unneeded proteins for proteasomal degradation, ubiquitylation regulates a multitude of cellular processes, such as transcription, translation, endocytosis, and receptor activity and subcellular localization. In addition, the proteasome generates peptides for antigen presentation in the immune system and for further degradation by peptidases to provide amino acids for protein biosynthesis and gluconeogenesis. Alterations of the UPS or of protein substrates that render them more or less susceptible to degradation are responsible for disorders associated with renal cell dysfunction. In this Review, we provide insight into the elegant and complex nature of UPS-mediated proteostasis and focus on its established and potential roles in renal cell physiology and pathophysiology.
Complement may drive the pathology of hypertension through effects on innate and adaptive immune responses. Recently an injurious role for the anaphylatoxin receptors C3aR (complement component 3a ...receptor) and C5aR1 (complement component 5a receptor) in the development of hypertension was shown through downregulation of Foxp3
(forkhead box protein 3) regulatory T cells. Here, we deepen our understanding of the therapeutic potential of targeting both receptors in hypertension.
Data from the European Renal cDNA Bank, single cell sequencing and immunohistochemistry were examined in hypertensive patients. The effect of C3aR or C3aR/C5aR1 double deficiency was assessed in two models of Ang II (angiotensin II)-induced hypertension in knockout mice.
We found increased expression of C3aR, C5aR1 and Foxp3 cells in kidney biopsies of patients with hypertensive nephropathy. Expression of both receptors was mainly found in myeloid cells. No differences in blood pressure, renal injury (albuminuria, glomerular filtration rate, glomerular and tubulointerstitial injury, inflammation) or cardiac injury (cardiac fibrosis, heart weight, gene expression) between control and mutant mice was discerned in C3aR
as well as C3aR/C5aR1
double knockout mice. The number of renal Tregs was not decreased in Ang II as well as in DOCA salt induced hypertension.
Hypertensive nephropathy in mice and men is characterized by an increase of renal regulatory T cells and enhanced expression of anaphylatoxin receptors. Our investigations do not corroborate a role for C3aR/C5aR1 axis in Ang II-induced hypertension hence challenging the concept of anaphylatoxin receptor targeting in the treatment of hypertensive disease.
Abstract
Immune cells at sites of inflammation are continuously activated by local antigens and cytokines, and regulatory mechanisms must be enacted to control inflammation. The stepwise hydrolysis ...of extracellular ATP by ectonucleotidases CD39 and CD73 generates adenosine, a potent immune suppressor. Here we report that human effector CD8 T cells contribute to adenosine production by releasing CD73-containing extracellular vesicles upon activation. These extracellular vesicles have AMPase activity, and the resulting adenosine mediates immune suppression independently of regulatory T cells. In addition, we show that extracellular vesicles isolated from the synovial fluid of patients with juvenile idiopathic arthritis contribute to T cell suppression in a CD73-dependent manner. Our results suggest that the generation of adenosine upon T cell activation is an intrinsic mechanism of human effector T cells that complements regulatory T cell-mediated suppression in the inflamed tissue. Finally, our data underscore the role of immune cell-derived extracellular vesicles in the control of immune responses.
Idiopathic membranous nephropathy is associated with autoantibodies against the phospholipase A2 receptor (PLA2R1) in about 70% of patients. This study identifies another antigen, thrombospondin ...type-1 domain-containing 7A (THSD7A), which accounts for about 10% of cases.
Idiopathic membranous nephropathy is an autoimmune disease and a common cause of the nephrotic syndrome in adults.
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In 2009, the phospholipase A2 receptor 1 (PLA2R1), a protein that is expressed in glomerular podocytes, was discovered as the major antigen involved in the pathogenesis of adult idiopathic membranous nephropathy.
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As confirmed by a number of subsequent studies, about 70% of patients with idiopathic membranous nephropathy have circulating autoantibodies against PLA2R1.
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The remaining patients, approximately 30% of those with idiopathic membranous nephropathy, have no obvious secondary cause of the disease, and it is thought that other endogenous glomerular antigens may be . . .
The phospholipase A2 receptor 1 (PLA2R1) is the major autoantigen in patients suffering from membranous nephropathy. To date, the lack of endogenous glomerular expression of PLA2R1 in mice and rats ...has impeded the establishment of PLA2R1-dependent animal models of this disease. Here, we generated a transgenic mouse line expressing murine full-length PLA2R1 in podocytes. Furthermore, expression of murine PLA2R1 did not result in any morphological disturbance as high-resolution confocal microscopy demonstrated an intact nephrin distribution with normal foot processes. Transfer of rabbit anti-mPLA2R1 antibodies to these mice induced nephrotic range proteinuria, hypercholesterolemia, and histomorphological signs of membranous nephropathy. Immunohistochemical and immunofluorescence analyses revealed enhanced staining for murine PLA2R1 in the presence of unaffected staining for murine thrombospondin type-1 domain-containing 7A in the diseased mice, resembling what is classically found in patients with PLA2R1-associated membranous nephropathy Thus, our mouse model of membranous nephropathy will allow investigation of PLA2R1-specific pathomechanisms and may help to develop and assess antigen-specific treatments in vivo.
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Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults, and one-third of patients develop end-stage renal disease (ESRD). Circulating autoantibodies against the podocyte ...surface antigens phospholipase A2 receptor 1 (PLA2R1) and the recently identified thrombospondin type 1 domain-containing 7A (THSD7A) are assumed to cause the disease in the majority of patients. The pathogenicity of these antibodies, however, has not been directly proven. Here, we have reported the analysis and characterization of a male patient with THSD7A-associated MN who progressed to ESRD and subsequently underwent renal transplantation. MN rapidly recurred after transplantation. Enhanced staining for THSD7A was observed in the kidney allograft, and detectable anti-THSD7A antibodies were present in the serum before and after transplantation, suggesting that these antibodies induced a recurrence of MN in the renal transplant. In contrast to PLA2R1, THSD7A was expressed on both human and murine podocytes, enabling the evaluation of whether anti-THSD7A antibodies cause MN in mice. We demonstrated that human anti-THSD7A antibodies specifically bind to murine THSD7A on podocyte foot processes, induce proteinuria, and initiate a histopathological pattern that is typical of MN. Furthermore, anti-THSD7A antibodies induced marked cytoskeletal rearrangement in primary murine glomerular epithelial cells as well as in human embryonic kidney 293 cells. Our findings support a causative role of anti-THSD7A antibodies in the development of MN.
Ion channels are desirable therapeutic targets, yet ion channel-directed drugs with high selectivity and few side effects are still needed. Unlike small-molecule inhibitors, antibodies are highly ...selective for target antigens but mostly fail to antagonize ion channel functions. Nanobodies-small, single-domain antibody fragments-may overcome these problems. P2X7 is a ligand-gated ion channel that, upon sensing adenosine 5'-triphosphate released by damaged cells, initiates a proinflammatory signaling cascade, including release of cytokines, such as interleukin-1β (IL-1β). To further explore its function, we generated and characterized nanobodies against mouse P2X7 that effectively blocked (13A7) or potentiated (14D5) gating of the channel. Systemic injection of nanobody 13A7 in mice blocked P2X7 on T cells and macrophages in vivo and ameliorated experimental glomerulonephritis and allergic contact dermatitis. We also generated nanobody Dano1, which specifically inhibited human P2X7. In endotoxin-treated human blood, Dano1 was 1000 times more potent in preventing IL-1β release than small-molecule P2X7 antagonists currently in clinical development. Our results show that nanobody technology can generate potent, specific therapeutics against ion channels, confirm P2X7 as a therapeutic target for inflammatory disorders, and characterize a potent new drug candidate that targets P2X7.
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