Mechanical stress enhances CD9 expression in cultured podocytes

Conditioning period impacts the morphology and proliferative effect of extracellular vesicles derived from rat adipose tissue derived stromal cell

A serum-free conditioning period is a crucial step during small extracellular vesicle (sEV) preparation ranging from 12 to 72h. There is a paucity of knowledge about downstream effects of serum-free conditioning on sEVs and the optimal duration of the conditioning period. The aim of this study was to investigate the influence of the serum-free conditioning period on the sEVs derived from primary adipose stromal cells (AdSCs) and their regenerative potential. Primary AdSCs were conditioned in serum-free medium for 72h. Conditioned medium was collected and refreshed every 24h obtaining three fractions, namely sEVs released after 24h (early), 24h to 48h (intermediate) and 48h to 72h (late). After sEV enrichment with ultracentrifugation, the sEV fractions were analyzed by their size, phenotypic expression, and morphology. Proliferation assays of primary Schwann cells after treatment with sEVs were performed. Particles meeting criteria to be classified as sEVs were detected in all fractions. However, sEVs differed by their size and phenotypic expression. A long conditioning period led to a heterogenous population of larger sEVs and increased protein per particle ratio. Moreover, the expression of tetraspanines was affected. Lastly, the proliferative effect of sEVs on Schwann cells decreased with increasing conditioning period. In conclusion, particles meeting the criteria of EVs are released by primary AdSCs over 72h under serum free conditioning. Nonetheless, they significantly differ in their proliferative effect on Schwann cells cultures.

Mechanosensing by Piezo1 and its implications in the kidney

Piezo1 is an essential mechanosensitive transduction ion channel in mammals. Its unique structure makes it capable of converting mechanical cues into electrical and biological signals, modulating biological and (patho)physiological processes in a wide variety of cells. There is increasing evidence demonstrating that the piezo1 channel plays a vital role in renal physiology and disease conditions. This review summarizes the current evidence on the structure and properties of Piezo1, gating modulation, and pharmacological characteristics, with special focus on the distribution and (patho)physiological significance of Piezo1 in the kidney, which may provide insights into potential treatment targets for renal diseases involving this ion channel.

Podocyte-Parietal Epithelial Cell Interdependence in Glomerular Development and Disease

Podocytes and parietal epithelial cells (PECs) are among the few principal cell types within the kidney glomerulus, the former serving as a crucial constituent of the kidney filtration barrier and the latter representing a supporting epithelial layer that adorns the inner wall of Bowman's capsule. Podocytes and PECs share a circumscript developmental lineage that only begins to diverge during the S-shaped body stage of nephron formation-occurring immediately before the emergence of the fully mature nephron. These two cell types, therefore, share a highly conserved gene expression program, evidenced by recently discovered intermediate cell types occupying a distinct spatiotemporal gene expression zone between podocytes and PECs. In addition to their homeostatic functions, podocytes and PECs also have roles in kidney pathogenesis. Rapid podocyte loss in diseases, such as rapidly progressive GN and collapsing and cellular subtypes of FSGS, is closely allied with PEC proliferation and migration toward the capillary tuft, resulting in the formation of crescents and pseudocrescents. PECs are thought to contribute to disease progression and severity, and the interdependence between these two cell types during development and in various manifestations of kidney pathology is the primary focus of this review.

Fibronectin is up-regulated in podocytes by mechanical stress

Hypertension is one of the central causes of kidney damage. In the past it was shown that glomerular hypertension leads to morphologic changes of podocytes and effacement and is responsible for detachment of these postmitotic cells. Because we have shown that podocytes are mechanosensitive and respond to mechanical stress by reorganization of the actin cytoskeleton in vitro, we look for mechanotransducers in podocytes. In this study, we demonstrate that the extracellular matrix protein fibronectin (Fn1) might be a potential candidate. The present study shows that Fn1 is essential for the attachment of podocytes during mechanical stress. By real-time quantitative PCR as well as by liquid chromatography-mass spectrometry, we found a significant up-regulation of Fn1 caused by mechanical stretch (3 d, 0.5 Hz, and 5% extension). To study the role of Fn1 in cultured podocytes under mechanical stress, Fn1 was knocked down (Fn1 KD) by a specific small interfering RNA. Additionally, we established a Fn1 knockout (KO) podocyte cell line (Fn1 KO) by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9). During mechanical stress, a significant loss of podocytes (>80%) was observed in Fn1 KD as well as Fn1 KO podocytes compared with control cells. Furthermore, Fn1 KO podocytes showed a significant down-regulation of the focal adhesion proteins talin, vinculin, and paxillin and a reduced cell spreading, indicating an important role of Fn1 in adhesion. Analyses of kidney sections from patients with diabetic nephropathy have shown a significant up-regulation of FN1 in contrast to control biopsies. In summary, we show that Fn1 plays an important role in the adaptation of podocytes to mechanical stress.-Kliewe, F., Kaling, S., Lötzsch, H., Artelt, N., Schindler, M., Rogge, H., Schröder, S., Scharf, C., Amann, K., Daniel, C., Lindenmeyer, M. T., Cohen, C. D., Endlich, K., Endlich, N. Fibronectin is up-regulated in podocytes by mechanical stress.

The tetraspanin CD9 controls migration and proliferation of parietal epithelial cells and glomerular disease progression

The mechanisms driving the development of extracapillary lesions in focal segmental glomerulosclerosis (FSGS) and crescentic glomerulonephritis (CGN) remain poorly understood. A key question is how parietal epithelial cells (PECs) invade glomerular capillaries, thereby promoting injury and kidney failure. Here we show that expression of the tetraspanin CD9 increases markedly in PECs in mouse models of CGN and FSGS, and in kidneys from individuals diagnosed with these diseases. Cd9 gene targeting in PECs prevents glomerular damage in CGN and FSGS mouse models. Mechanistically, CD9 deficiency prevents the oriented migration of PECs into the glomerular tuft and their acquisition of CD44 and β1 integrin expression. These findings highlight a critical role for de novo expression of CD9 as a common pathogenic switch driving the PEC phenotype in CGN and FSGS, while offering a potential therapeutic avenue to treat these conditions.

In both focal segmental glomerulosclerosis (FSGS) and crescentic glomerulonephritis (CGN), kidney injury is characterised by the invasion of glomerular tufts by parietal epithelial cells (PECs). Here Lazareth et al. identify the tetraspanin CD9 as a key regulator of PEC migration, and find its upregulation in FSGS and CGN contributes to kidney injury in both diseases.

Thrombospondin Type 1 Domain-Containing 7A Localizes to the Slit Diaphragm and Stabilizes Membrane Dynamics of Fully Differentiated Podocytes

BACKGROUND

About 3%-5% of adults with membranous nephropathy have autoantibodies directed against thrombospondin type 1 domain-containing 7A (THSD7A), a podocyte-expressed transmembrane protein. However, the temporal and spatial expression of THSD7A and its biologic function for podocytes are unknown, information that is needed to understand the effects of THSD7A autoantibodies in this disease.

METHODS

Using a variety of microscopic techniques, we analyzed THSD7A localization in postnatal, adult, and autoantibody-injected mice as well as in human podocytes. We also analyzed THSD7A function in human podocytes using confocal microscopy; Western blotting; and adhesion and migration assays.

RESULTS

We found that THSD7A expression begins on glomerular vascularization with slit diaphragm formation in development. THSD7A localizes to the basal aspect of foot processes, closely following the meanders of the slit diaphragm in human and mice. Autoantibodies binding to THSD7A localize to the slit diaphragm. In human podocytes, THSD7A expression is accentuated at filopodia and thin arborized protrusions, an expression pattern associated with decreased membrane activity of cytoskeletal regulators. We also found that, phenotypically, THSD7A expression in human podocytes is associated not only with increases in cell size, enhanced adhesion, and reduced detachment from collagen type IV-coated plates but also, with decreased ability to migrate.

CONCLUSIONS

Our findings suggest that THSD7A functions as a foot process protein involved in the stabilization of the slit diaphragm of mature podocytes and that autoantibodies to THSD7A, on the basis of their localization, might structurally and functionally alter the slit diaphragm's permeability to protein.

Expression of Slc35f1 in the murine brain

The solute carrier (SLC) group of membrane transport proteins includes about 400 members organized into more than 50 families. The SLC family that comprises nucleoside-sugar transporters is referred to as SLC35. One of the members of this family is SLC35F1. The function of SLC35F1 is still unknown; however, recent studies demonstrated that SLC35F1 mRNA is highly expressed in the brain and in the kidney. Therefore, we examine the distribution of Slc35f1 protein in the murine forebrain using immunohistochemistry. We could demonstrate that Slc35f1 is highly expressed in the adult mouse brain in a variety of different brain structures, including the cortex, hippocampus, amygdala, thalamus, basal ganglia, and hypothalamus. To examine the possible roles of Slc35f1 and its subcellular localization, we used an in vitro glioblastoma cell line expressing Slc35f1. Co-labeling experiments were performed to reveal the subcellular localization of Slc35f1. Our results indicate that Slc35f1 neither co-localizes with markers for the Golgi apparatus nor with markers for the endoplasmic reticulum. Time-lapse microscopy of living cells revealed that Slc35f1-positive structures are highly dynamic and resemble vesicles. Using super-resolution microscopy, these Slc35f1-positive spots clearly co-localize with the recycling endosome marker Rab11.

Podocytes

Podocytes are highly specialized cells of the kidney glomerulus that wrap around capillaries and that neighbor cells of the Bowman’s capsule. When it comes to glomerular filtration, podocytes play an active role in preventing plasma proteins from entering the urinary ultrafiltrate by providing a barrier comprising filtration slits between foot processes, which in aggregate represent a dynamic network of cellular extensions. Foot processes interdigitate with foot processes from adjacent podocytes and form a network of narrow and rather uniform gaps. The fenestrated endothelial cells retain blood cells but permit passage of small solutes and an overlying basement membrane less permeable to macromolecules, in particular to albumin. The cytoskeletal dynamics and structural plasticity of podocytes as well as the signaling between each of these distinct layers are essential for an efficient glomerular filtration and thus for proper renal function. The genetic or acquired impairment of podocytes may lead to foot process effacement (podocyte fusion or retraction), a morphological hallmark of proteinuric renal diseases. Here, we briefly discuss aspects of a contemporary view of podocytes in glomerular filtration, the patterns of structural changes in podocytes associated with common glomerular diseases, and the current state of basic and clinical research.

MOF maintains transcriptional programs regulating cellular stress response

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