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Chronic kidney disease (CKD) is characterized by inflammation and fibrosis in the kidney. Renal biopsies and estimated glomerular filtration rate (eGFR) remain the standard of care, but these endpoints have limitations in detecting the stage, progression, and spatial distribution of fibrotic pathology in the kidney. MRI diffusion tensor imaging (DTI) has emerged as a promising noninvasive technology to evaluate renal fibrosis in vivo both in clinical and preclinical studies. However, these imaging studies have not systematically identified fibrosis particularly deeper in the kidney where biopsy sampling is limited, or completed an extensive analysis of whole organ histology, blood biomarkers, and gene expression to evaluate the relative strengths and weaknesses of MRI for evaluating renal fibrosis. In this study, we performed DTI in the sodium oxalate mouse model of CKD. The DTI parameters fractional anisotropy, apparent diffusion coefficient, and axial diffusivity were compared between the control and oxalate groups with region of interest (ROI) analysis to determine changes in the cortex and medulla. In addition, voxel-based analysis (VBA) was implemented to systematically identify local regions of injury over the whole kidney. DTI parameters were found to be significantly different in the medulla by both ROI analysis and VBA, which also spatially matched with collagen III immunohistochemistry (IHC). The DTI parameters in this medullary region exhibited moderate to strong correlations with histology, blood biomarkers, hydroxyproline, and gene expression. Our results thus highlight the sensitivity of DTI to the heterogeneity of renal fibrosis and importance of whole kidney noninvasive imaging. NEW & NOTEWORTHY: Chronic kidney disease (CKD) can be characterized by inflammation and fibrosis of the kidney. Although standard of care methods have been limited in scope, safety, and spatial distribution, MRI diffusion tensor imaging (DTI) has emerged as a promising noninvasive technology to evaluate renal fibrosis in vivo. In this study, we performed DTI in an oxalate mouse model of CKD to systematically identify local kidney injury. DTI parameters strongly correlated with histology, blood biomarkers, hydroxyproline, and gene expression. [ABSTRACT FROM AUTHOR]

The article discusses how the nucleolar protein DCAF13 plays a role in T cell activation by accelerating ribosomal maturation through liquid-liquid phase separation with nucleophosmin 1 (NPM1).

Focal segmental glomerulosclerosis (FSGS) is a syndrome that involves kidney podocyte dysfunction and causes chronic kidney disease. Multiple factors including chemical toxicity, inflammation, and infection underlie FSGS; however, highly penetrant disease genes have been identified in a small fraction of patients with a family history of FSGS. Variants of apolipoprotein L1 (APOL1) have been linked to FSGS in African Americans with HIV or hypertension, supporting the proposal that genetic factors enhance FSGS susceptibility. Here, we used sequencing to investigate whether genetics plays a role in the majority of FSGS cases that are identified as primary or sporadic FSGS and have no known cause. Given the limited number of biopsy-proven cases with ethnically matched controls, we devised an analytic strategy to identify and rank potential candidate genes and used an animal model for validation. Nine candidate FSGS susceptibility genes were identified in our patient cohort, and three were validated using a high-throughput mouse method that we developed. Specifically, we introduced a podocyte-specific, doxycycline-inducible transactivator into a murine embryonic stem cell line with an FSGS-susceptible genetic background that allows shRNA-mediated targeting of candidate genes in the adult kidney. Our analysis supports a broader role for genetic susceptibility of both sporadic and familial cases of FSGS and provides a tool to rapidly evaluate candidate FSGS-associated genes., Introduction The glomerulus of the kidney is a specialized capillary bed that generates an ultrafiltrate that, after modification by the kidney tubule system, becomes urine. Diseases of the glomerulus often [...]

Podocytes are specialized epithelial cells In the kidney glomerulus that play Important structural and functional roles In maintaining the filtration barrier. Nephrotic syndrome results from a breakdown of the kidney filtration barrier and is associated with proteinuria, hyperlipidemia, and edema. Additionally, podocytes undergo changes in morphology and internalize plasma proteins in response to this disorder. Here, we used fluid-phase tracers in murine models and determined that podocytes actively internalize fluid from the plasma and that the rate of internalization is increased when the filtration barrier is disrupted. In cultured podocytes, the presence of free fatty acids (FFAs) associated with serum albumin stimulated macropinocytosis through a pathway that involves FFA receptors, the G[beta]/G[gamma] complex, and RAC1. Moreover, mice with elevated levels of plasma FFAs as the result of a high-fat diet were more susceptible to Adriamycin-induced proteinuria than were animals on standard chow. Together, these results support a model in which podocytes sense the disruption of the filtration barrier via FFAs bound to albumin and respond by enhancing fluid-phase uptake. The response to FFAs may function in the development of nephrotic syndrome by amplifying the effects of proteinuria., Introduction The kidney glomerular filter functions to remove small molecular wastes from the blood without the loss of large plasma proteins into the urine. The filter is composed of 3 [...]

Background Two coding variants-G1 and G2-in the apolipoprotein L-1 (APOL1) gene are associated with increased incidence of end-stage renal disease (ESRD) in the adult African American population. These variants associate with hypertension-attributed renal disease, focal segmental glomerulosclerosis (FSGS), and HIV-associated nephropathy. We hypothesized that as a genetic disease, APOL1 nephropathy has a pediatric phenotype. Methods We investigated the incidence of APOL1 variants in young African Americans with hypertension or FSGS and a family history of ESRD by conducting a case-control study of 93 pediatric and young adult African Americans with hypertension or FSGS to determine the association with APOL1 risk variants, G1, and G2 using custom-made TaqMan-based allelic discrimination assays. Results Forty of the 61 cases (66 %) with a family history of kidney disease had two APOL1 risk variants, significantly higher than the prevalence in controls and the general African American population (p < 0.001); 24 of 29 patients with hypertension-attributed kidney disease had two APOL1 risk variants, while none of nine hypertensive patients without kidney disease had more than one risk allele. Conclusions Although it was a small study cohort, our findings strongly suggest for the first time that two APOL1 risk alleles in young hypertensive African Americans with a family history of ESRD are strongly associated with kidney disease., Author(s): Elizabeth I. Anyaegbu[sup.1] , Andrey S. Shaw[sup.2] , Keith A. Hruska[sup.1] [sup.3] , Sanjay Jain[sup.2] [sup.3] Author Affiliations: (1) Department of Pediatrics (Pediatric Nephrology), Washington University School of Medicine, [...]

The specialized epithelial cell of the kidney, the podocyte, has a complex actinbased cytoskeleton. Dynamic regulation of this cytoskeleton is required for efficient barrier function of the kidney. Podocytes are a useful cell type to study the control of the actin cytoskeleton in vivo, because disruption of components of the cytoskeleton results in podocyte damage, cell loss, and a prototypic injury response called focal segmental glomerulosclerosis (FSGS). Searching for actin regulatory proteins that are expressed in podocytes, we identified a RhoA-activated Rac1 GTPase-activating protein (Rac1-GAP), Arhgap24, that was upregulated in podocytes as they differentiated, both in vitro and in vivo. Increased levels of active Rac1 and Cdc42 were measured in Arhgap24 knockdown experiments, which influenced podocyte cell shape and membrane dynamics. Consistent with a role for Arhgap24 in normal podocyte functioning in vivo, sequencing of the ARHGAP24 gene in patients with FSGS identified a mutation that impaired its Rac1-GAP activity and was associated with disease in a family with FSGS. Thus, Arhgap24 contributes to the careful balancing of RhoA and Rac1 signaling in podocytes, the disruption of which may lead to kidney disease., Introduction The kidneys filter plasma and reabsorb solutes and nutrients to maintain the appropriate extracellular environment. The proximal component of the nephron, the glomerulus, is the primary filtration barrier that [...]

Kidney podocytes are highly differentiated epithelial cells that form interdigitating foot processes with bridging slit diaphragms (SDs) that regulate renal ultrafiltration. Podocyte injury results in proteinuric kidney disease, and genetic deletion of SD-associated CD2-associated protein (CD2AP) leads to progressive renal failure in mice and humans. Here, we have shown that CD2AP regulates the TGF-β1-dependent translocation of dendrin from the SD to the nucleus. Nuclear dendrin acted as a transcription factor to promote expression of cytosolic cathepsin L (CatL). CatL proteolyzed the regulatory GTPase dynamin and the actinassociated adapter synaptopodin, leading to a reorganization of the podocyte microfilament system and consequent proteinuria. CD2AP itself was proteolyzed by CatL, promoting sustained expression of the protease during podocyte injury, and in turn increasing the apoptotic susceptibility of podocytes to TGF-β1. Our study identifies CD2AP as the gatekeeper of the podocyte TGF-β response through its regulation of CatL expression and defines a molecular mechanism underlying proteinuric kidney disease., Introduction Several hundred million people worldwide-about 1 in 15 adults-have some form of kidney damage, and every year, millions die prematurely of cardiovascular or renal complications linked to chronic kidney [...]

Injury and loss of podocytes are leading factors of glomerular disease and renal failure. The postmitotic podocyte is the primary glomerular target for toxic, immune, metabolic, and oxidant stress, but little is known about how this cell type copes with stress. Recently, autophagy has been identified as a major pathway that delivers damaged proteins and organelles to lysosomes in order to maintain cellular homeostasis. Here we report that podocytes exhibit an unusually high level of constitutive autophagy. Podocyte-specific deletion of autophagy-related 5 (Atg5) led to a glomerulopathy in aging mice that was accompanied by an accumulation of oxidized and ubiquitinated proteins, ER stress, and proteinuria. These changes resulted ultimately in podocyte loss and late-onset glomerulosclerosis. Analysis of pathophysiological conditions indicated that autophagy was substantially increased in glomeruli from mice with induced proteinuria and in glomeruli from patients with acquired proteinuric diseases. Further, mice lacking Atg5 in podocytes exhibited strongly increased susceptibility to models of glomerular disease. These findings highlight the importance of induced autophagy as a key homeostatic mechanism to maintain podocyte integrity. We postulate that constitutive and induced autophagy is a major protective mechanism against podocyte aging and glomerular injury, representing a putative target to ameliorate human glomerular disease and aging-related loss of renal function., Introduction The kidney filtration barrier is a unique structure characterized by a complex 3-dimensional framework of podocytes and endothelial cells. Podocytes form fine interdigitating foot processes, which envelope the glomerular [...]

Primary defects in either podocytes or the glomerular basement membrane (GBM) cause proteinuria, a fact that complicates defining the barrier to albumin. Laminin [beta]2 (LAMB2) is a GBM component required [...]

Focal segmental glomerulosclerosis (FSGS) is the most common primary glomerular diagnosis resulting in end-stage renal disease. Defects in several podocyte proteins have been implicated in the etiology of FSGS, including [...]

Abstract Mice lacking CD2-associated protein (CD2AP-/-) develop glomerular lesions resembling human focal segmental glomerulosclerosis (FSGS) between 3-4 weeks of age and die approximately 2 weeks later from massive proteinuria and [...]

The docking protein CD2AP (CD2-associated protein) serves a nonredundant function in podocytes as CD2AP knockout mice die of renal failure at the age of 6-7 wk. Furthermore, haploinsufficiency due to mutation of the CD2AP gene is associated with focal segmental glomerulosclerosis in humans. Although CD2AP has been shown to interact with proteins regulating actin polymerization, with proteins of the slit diaphragm, and with the endocytic machinery, its critical function in podocytes remains unclear. In conditionally immortalized mouse podocytes, we demonstrate that CD2AP colocalizes with cortactin and F-actin in spots of [is less than or equal to] 0.5-[micro]m diameter. Confocal time-lapse microscopy in living podocytes expressing GFP-CD2AP or GFP-actin revealed that spots are motile, possess a limited lifetime, and are frequently associated with vesicles. A significant portion of spot-associated vesicles belongs to a later endosomal-sorting compartment, characterized by delayed uptake of fluorescent dextran (10 kDa) and by colocalization with Rab4, but not Rab5 and AP-2. Rapid accumulation of microinjected G-actin in spots and abrogation of spot motility by jasplakinolide demonstrate that spot movements depend on actin polymerization. Furthermore, a high turnover (half-time < 10 s) of CD2AP in spots was demonstrated by FRAP (fluorescence recovery after photobleaching). Our results demonstrate that CD2AP is associated with dynamic actin in a specific late endosomal compartment in podocytes, suggesting that CD2AP might be crucially involved in endosomal sorting and/or trafficking via regulation of actin assembly on vesicles. glomerular epithelial cells; CMS; green fluorescent protein

A study showed that CD2 binding to ligand results to protein segregation, CD2 clustering and T cell polarization. The protein segregation is independent of the cytoplasmic domain of CD2, while the CD2 clustering and cytoskeleton polarization are mediated by binding of the CD2 cytoplasmic domain with a new SH3-containing protein called CD2-associated protein (CD2AP). These indicate that the CD2AP seems to promote receptor patterning and cytoskeletal polarization in the T cell contact area.

The T cell receptor (TCR) [Alpha]Β heterodimer interacts with its ligands with high specificity, but surprisingly low affinity. The role of the [Zeta] component of the murine TCR in contributing to the fidelity of antigen recognition was examined. With sequence-specific phosphotyrosine antibodies, it was found that [Zeta] undergoes a series of ordered phosphorylation events upon TCR engagement. Completion of phosphorylation steps is dependent on the nature of the TCR ligand. Thus, the phosphorylation steps establish thresholds for T cell activation. This study documents the sophisticated molecular events that follow the engagement of a low-affinity receptor., The [Alpha]Β TCR is part of a large protein complex composed of the CD3 [Gamma] Δ, [Epsilon], and [Zeta] chains. These chains contain signaling motifs called ITAMs (immune receptor tyrosinebased [...]