Myeloid CCR2 Promotes Atherosclerosis after AKI.

BACKGROUND: The risk of cardiovascular events rises after AKI. Leukocytes promote atherosclerotic plaque growth and instability. We established a model of enhanced remote atherosclerosis after renal ischemia-reperfusion (IR) injury and investigated the underlying inflammatory mechanisms. METHODS: Atherosclerotic lesions and inflammation were investigated in native and bone marrow-transplanted LDL receptor-deficient (LDLr-/- ) mice after unilateral renal IR injury using histology, flow cytometry, and gene expression analysis. RESULTS: Aortic root atherosclerotic lesions were significantly larger after renal IR injury than in controls. A gene expression screen revealed enrichment for chemokines and their cognate receptors in aortas of IR-injured mice in early atherosclerosis, and of T cell-associated genes in advanced disease. Confocal microscopy revealed increased aortic macrophage proximity to T cells. Differential aortic inflammatory gene regulation in IR-injured mice largely paralleled the pattern in the injured kidney. Single-cell analysis identified renal cell types that produced soluble mediators upregulated in the atherosclerotic aorta. The analysis revealed a marked early increase in Ccl2, which CCR2+ myeloid cells mainly expressed. CCR2 mediated myeloid cell homing to the post-ischemic kidney in a cell-individual manner. Reconstitution with Ccr2-/- bone marrow dampened renal post-ischemic inflammation, reduced aortic Ccl2 and inflammatory macrophage marker CD11c, and abrogated excess aortic atherosclerotic plaque formation after renal IR. CONCLUSIONS: Our data introduce an experimental model of remote proatherogenic effects of renal IR and delineate myeloid CCR2 signaling as a mechanistic requirement. Monocytes should be considered as mobile mediators when addressing systemic vascular sequelae of kidney injury.

Induction of ferroptosis selectively eliminates senescent tubular cells.

The accumulation of senescent cells is an important contributor to kidney aging, chronic renal disease, and poor outcome after kidney transplantation. Approaches to eliminate senescent cells with senolytic compounds have been proposed as novel strategies to improve marginal organs. While most existing senolytics induce senescent cell clearance by apoptosis, we observed that ferroptosis, an iron-catalyzed subtype of regulated necrosis, might serve as an alternative way to ablate senescent cells. We found that murine kidney tubular epithelial cells became sensitized to ferroptosis when turning senescent. This was linked to increased expression of pro-ferroptotic lipoxygenase-5 and reduced expression of anti-ferroptotic glutathione peroxidase 4 (GPX4). In tissue slice cultures from aged kidneys low dose application of the ferroptosis-inducer RSL3 selectively eliminated senescent cells while leaving healthy tubular cells unaffected. Similar results were seen in a transplantation model, in which RSL3 reduced the senescent cell burden of aged donor kidneys and caused a reduction of damage and inflammatory cell infiltration during the early post-transplantation period. In summary, these data reveal an increased susceptibility of senescent tubular cells to ferroptosis with the potential to be exploited for selective reduction of renal senescence in aged kidney transplants.

Comparison of Different Selection Strategies for Tolvaptan Eligibility among Autosomal Dominant Polycystic Kidney Disease Patients.

BACKGROUND: Tolvaptan can slow down renal function decline in autosomal dominant polycystic kidney disease (-ADPKD). While there is consensus across international recommendations that the drug should only be used in patients with high risk of rapid progression, identification criteria for rapid progression vary. Here, we investigated different assessment strategies using a real-life ADPKD cohort. METHODS: Observational retrospective cohort analysis. The study included 131 ADPKD patients aged 19-78 years who were referred to the Hannover Medical School outpatient clinic for evaluation of tolvaptan treatment. Six different assessment strategies for tolvaptan eligibility were tested for each patient. Comparative analysis for different assessments was performed in the total study population, the subpopulation with available computed tomography/magnetic resonance imaging data, and the genotyped subpopulation. RESULTS: Comparing 6 assessment strategies revealed strong variations in the individual selection processes resulting in treatment recommendations for 14.5-64.9% of patients. The highest patient number was selected by the Scottish and the lowest by the Japanese approach. Few patients had positive recommendations by all 6 systems, but strong congruency was observed between the Scottish, U.K. and Canadian patient selection. The lowest number of overlapping patients was found between the Japanese and the ERA-EDTA selection. Important discrepancies were also found between the ERA-EDTA and the U.S. system due to different emphases on parameters of kidney function versus kidney volume. Limitations of the study included the restricted sample size, heterogeneity in parameter availability and lack of outcome data. CONCLUSIONS: The study draws attention to important discrepancies between different decision algorithms for tolvaptan eligibility in ADPKD patients.

Claudin 19 Is Regulated by Extracellular Osmolality in Rat Kidney Inner Medullary Collecting Duct Cells.

The inner medullary collecting duct (IMCD) is subject to severe changes in ambient osmolality and must either allow water transport or be able to seal the lumen against a very high osmotic pressure. We postulate that the tight junction protein claudin-19 is expressed in IMCD and that it takes part in epithelial adaptation to changing osmolality at different functional states. Presence of claudin-19 in rat IMCD was investigated by Western blotting and immunofluorescence. Primary cell culture of rat IMCD cells on permeable filter supports was performed under different osmotic culture conditions and after stimulation by antidiuretic hormone (AVP). Electrogenic transepithelial transport properties were measured in Ussing chambers. IMCD cells cultivated at 300 mosm/kg showed high transepithelial resistance, a cation selective paracellular pathway and claudin-19 was mainly located in the tight junction. Treatment by AVP increased cation selectivity but did not alter transepithelial resistance or claudin-19 subcellular localization. In contrast, IMCD cells cultivated at 900 mosm/kg had low transepithelial resistance, anion selectivity, and claudin-19 was relocated from the tight junctions to intracellular vesicles. The data shows osmolality-dependent transformation of IMCD epithelium from tight and sodium-transporting to leaky, with claudin-19 expression in the tight junction associated to tightness and cation selectivity under low osmolality.

Corticomedullary difference in the effects of dietary Ca²âº on tight junction properties in thick ascending limbs of Henle's loop.

The thick ascending limb of Henle's loop (TAL) drives an important part of the reabsorption of divalent cations. This reabsorption occurs via the paracellular pathway formed by the tight junction (TJ), which in the TAL shows cation selectivity. Claudins, a family of TJ proteins, determine the permeability and selectivity of this pathway. Mice were fed with normal or high-Ca(2+) diet, and effects on the reabsorptive properties of cortical and medullary TAL segments were analysed by tubule microdissection and microperfusion. Claudin expression was investigated by immunostaining and quantitative PCR. We show that the TAL adapted to high Ca(2+) load in a sub-segment-specific manner. In medullary TAL, transcellular NaCl transport was attenuated. The transepithelial voltage decreased from 10.9 ± 0.6 mV at control diet to 8.3 ± 0.5 mV at high Ca(2+) load, thereby reducing the driving force for Ca(2+) and Mg(2+) uptake. Cortical TAL showed a reduction in paracellular Ca(2+) and Mg(2+) permeabilities from 8.2 ± 0.7 to 6.2 ± 0.5 ∙ 10(-4) cm/s and from 4.8 ± 0.5 to 3.0 ± 0.2 · 10(-4) cm/s at control and high-Ca(2+) diet, respectively. Expression, localisation and regulation of claudins 10, 14, 16 and 19 differed along the corticomedullary axis: Towards the cortex, the main site of divalent cation reabsorption in TAL, high-Ca(2+) intake led to a strong upregulation of claudin-14 within TAL TJs while claudin-16 and -19 were unaltered. Towards the inner medulla, only claudin-10 was present in TAL TJ strands. In summary, high-Ca(2+) diet induced a reduction of divalent cation reabsorption via a diminution of NaCl transport and driving force in mTAL and via decreased paracellular permeabilities in cTAL. We reveal an important regulatory pattern along the corticomedullary axis and improve the understanding how the kidney disposes of detrimental excess Ca(2+).

Heterogeneity of tight junctions in the thick ascending limb.

Renal tubular transport mechanisms are optimized to be energy efficient and tailored to local gradients and transport rates. The combined transcellular action of ion channels, transporters, and pumps, together with the paracellular pathway, enables kidney function. Monogenetic diseases and mouse models indicate that both trans- and paracellular proteins can become disease-causing candidates and may be targets for future therapeutic approaches. Recent advances in tight junction research have provided new insights into their structure, function, and regulation. The thick ascending limb (TAL) is a nephron segment with specific requirements for the paracellular pathway. It has to fuel the generation of the corticomedullary concentration gradient, to be watertight, and to provide a highly selective permeability for Na+ and divalent cations. Tight junction composition and function in the TAL is organized along the corticomedullary axis. Even on the level of a seemingly homogeneous tubular epithelium like the TAL, there is a separation of tight junction protein expression in the strands between the respective tricellular nexus of the junctional network. Here, we highlight some new insights from our recent work and that of others in this context. In addition, we provide some perspectives for the further study of paracellular transport mechanisms.