Pyroptosis: A Common Feature of Immune Cells of Haemodialysis Patients

NLRP-3 inflammasome activation can result in interleukin-1β (IL-1β) release and inflammatory cell death (pyroptosis). Caspase-1 is able to trigger both processes. However, other caspases, caspase-4, -5 and -8, are believed to initiate pyroptosis without affecting IL-1 secretion. In this study, we evaluated two cardiovascular risk groups, haemodialysis patients (HD) and patients with intact kidney function but high blood pressure (BP), to analyse the mechanisms driving pyroptosis. Twenty HD were age-, gender- and diabetes-matched to BP. We found a common pyroptotic pattern in both patient groups, at which pyroptosis rates but not IL-1 β levels were significantly higher in monocytes (HD vs. BP: p < 0.05), granulocytes (p < 0.01) and lymphocytes (p < 0.01) of HD patients. As uremic toxins are drivers of inflammation and regulated cell death, we applied a monocyte- and macrophage-like THP-1 model system to demonstrate that the protein-bound uremic toxin indoxyl sulfate (IS) is an inducer of pyroptotic cell death, particularly engaging caspase-4/caspase-5 and to a lesser extent caspase-8 and caspase-1. These data suggest that the uremic toxin IS can mediate pyroptosis in HD patients and the inflammatory caspase-4 and/or caspase-5 contribute to pyroptosis rates to a higher extent in comparison to caspase-1.

Rac1 promotes kidney collecting duct integrity by limiting actomyosin activity

A polarized collecting duct (CD), formed from the branching ureteric bud (UB), is a prerequisite for an intact kidney. The small Rho GTPase Rac1 is critical for actin cytoskeletal regulation. We investigated the role of Rac1 in the kidney collecting system by selectively deleting it in mice at the initiation of UB development. The mice exhibited only a mild developmental phenotype; however, with aging, the CD developed a disruption of epithelial integrity and function. Despite intact integrin signaling, Rac1-null CD cells had profound adhesion and polarity abnormalities that were independent of the major downstream Rac1 effector, Pak1. These cells did however have a defect in the WAVE2–Arp2/3 actin nucleation and polymerization apparatus, resulting in actomyosin hyperactivity. The epithelial defects were reversible with direct myosin II inhibition. Furthermore, Rac1 controlled lateral membrane height and overall epithelial morphology by maintaining lateral F-actin and restricting actomyosin. Thus, Rac1 promotes CD epithelial integrity and morphology by restricting actomyosin via Arp2/3-dependent cytoskeletal branching.

Efficacy of Ebselen Against Invasive Aspergillosis in a Murine Model

Invasive aspergillosis is one of the major causes of morbidity and mortality among invasive fungal infections. The search for new antifungal drugs becomes imperative when existing drugs are not able to efficiently treat these infections. Ebselen, is an organoselenium compound, already successfully approved in clinical trials as a repositioned drug for the treatment of bipolar disorder and prevention of noise-induced hearing loss. In this study, we aimed to reposition ebselen for the treatment of invasive aspergillosis by showing ebselen effectiveness in a murine model. For this, BALB/c mice were immunosuppressed and infected systemically with Aspergillus fumigatus. Animals were divided and treated with ebselen, voriconazole, or drug-free control, for four days. The kidneys were used for CFU count and, histopathological and cytokine analysis. Ebselen was able to significantly reduce the fungal burden in the kidneys of infected mice with efficacy comparable with voriconazole treatment as both had reductions to the same extent. The absence of hyphae and intact kidney tissue structure observed in the histopathological sections analyzed from treated groups corroborate with the downregulation of IL-6 and TNF. In summary, this study brings for the first time in vivo evidence of ebselen efficacy against invasive aspergillosis. Despite these promising results, more animal studies are warranted to evaluate the potential role of ebselen as an alternative option for the management of invasive aspergillosis in humans.

Expression of ACE2 in the Intact and Acutely Injured Kidney

Background. The actions of angiotensin-converting enzyme 2 (ACE2) oppose those of the renin-angiotensin-aldosterone system. Evidence supports ACE2 as a cytoprotectant in some tissues. This study examined ACE2 expression in models of acute kidney injury (AKI). Methods. ACE2 mRNA and protein expression, ACE2 activity, and ACE2 expression by immunofluorescence were assessed following ischemic AKI in mice. Renal ACE2 mRNA expression was evaluated in lipopolysaccharide-induced AKI in wildtype (C57BL/6J) mice, in heme oxygenase-1+/+ and heme oxygenase-1-/- mice, and following unilateral urinary tract obstruction (UUO) in wildtype mice. The effect of sex and age on renal ACE2 protein expression was also assessed. Results. In ischemic AKI, ACE2 mRNA and protein expression and ACE2 activity were reduced as compared with such indices in the intact kidney. In ischemic AKI, ACE2, which, in health, is prominently expressed in the renal tubular epithelium, especially in proximal tubules, exhibited decreased expression in these segments. Decreased ACE2 expression in AKI did not reflect reduced GFR per se as ACE2 mRNA expression was unaltered after UUO. Lipopolysaccharide induced renal ACE2 mRNA expression in wildtype mice, but this effect of lipopolysaccharide did not occur in heme oxygenase-1 deficient mice. In the intact kidney, renal ACE2 protein expression decreased in female mice as compared with male mice, but was unaltered with age. Conclusion. We conclude that renal ACE2 expression is decreased in ischemic AKI, one characterized by markedly reduced GFR and abundant cell death, but is upregulated in lipopolysaccharide-induced AKI; this latter effect requires heme oxygenase-1. Determining the significance of ACE2 expression in models of AKI merits further study. We also suggest that understanding the mechanism underlying ACE2 downregulation in AKI may offer insights relevant to COVID-19: ACE2 is downregulated after ACE2 mediates SARS-CoV-2 cellular entry; such downregulation promotes inflammation in COVID-19; and AKI commonly occurs and determines outcomes in COVID-19.

NLRP3 Inflammasome Activation in Hemodialysis and Hypertensive Patients with Intact Kidney Function

Hypertension is not only an integrative characteristic of hemodialysis (HD) patients but is also very common in the general population. There is evidence that the inflammatory cytokine IL-β, regulated by the NLRP3 inflammasome via caspase-1, contributes to the hypertensive setting. Therefore, we investigated in an observational pilot study whether IL-1β secretion and inflammatory cell death (pyroptosis) are different in HD and hypertensive patients with intact kidney function. Twenty HD patients were age-, gender-, and diabetes-mellitus-matched to patients with hypertension and intact kidney function. Caspase-1 activity and pyroptosis rates were measured by flow cytometry. IL-1β was determined by qPCR and the ELISA technique. The inflammatory status (CRP) did not differ between both groups; however, the body mass index, a classical cardiovascular risk factor, was significantly elevated in blood pressure (BP) patients. BP patients had a higher frequency of caspase-1-positive monocytes compared to HD (p < 0.001). IL1-β protein secretion was significantly enhanced in BP, but ex vivo stimulation of blood cells resulted in higher pyroptosis rates in HD compared to BP patients (p < 0.01). Therefore, HD and BP patients differ in the extent of the NLRP3 inflammasome activation. The consequences of overweight, present in BP patients, may contribute to the significantly higher inflammasomal induction level. Whether low pyroptotic rates are equivalent to a dysfunctional immune response or a high pyroptotic output corresponds to over-activation remains to be clarified.

Radiofrequency denervation of the renal arteries in patients with resistant arterial hypertension: 3 years of observation experience

Objective. To evaluate the efficiency of radiofrequency denervation of the renal arteries in patients with resi-stant arterial hypertension during a three-year follow-up. Materials and methods. The study involved 40 patients with resistant arterial hypertension aged 27 to 70 years (mean age 54.91±9.77 years) while receiving three or more antihypertensive drugs (including diuretic) in optimal doses. The conditions for inclusion in the study were considered resistant arterial hypertension with blood pressure (BP)>160/100 mm Hg, intact kidney function - glomerular filtration rate (MDRD)>45 ml/min - and the absence of secondary hypertension. All patients had sympatic radiofrequency denervation of renal arteries; its efficiency later was estimated according to the clinical measurement and ambulatory blood pressure monitoring (ABPM). Results. The level of office BP reliably differed initially and after 3 years: DSBP -34.48±6.44 mm Hg (p=0.001), DDBP - 22.29 mm Hg (p=0.001). According to ABPM results, reliable dynamics of systolic blood pressure was not observed. The data of DBP at night were significantly lower after 36 months; DDBP was -5.37±9.77 mm Hg. Conclusions. A marked decrease in the data of office SBP and DBP was observed, which proves the long-term efficiency of radiofrequency denervation of the renal arteries in patients with resistant hypertension. Accor-ding to ABPM results after 36 months, a significant decrease was registered among the DBP indicators at night and daytime.

A protocol for single-cell transcriptomics from cryopreserved renal tissue and urine for the Accelerating Medicine Partnership (AMP) RA/SLE network

ABSTRACTOBJECTIVEThere is a critical need to define the cells that mediate tissue damage in lupus nephritis. Here we aimed to establish a protocol to preserve lupus nephritis kidney biopsies and urine cell samples obtained at multiple clinical sites for subsequent isolation and transcriptomic analysis of single cells.METHODSFresh and cryopreserved kidney tissue from tumor nephrectomies and lupus nephritis kidney biopsies were disaggregated by enzymatic digestion. Cell yields and cell composition were assessed by flow cytometry. Transcriptomes of leukocytes and epithelial cells were evaluated by low-input and single cell RNA-seq.RESULTSCryopreserved kidney tissue from tumor nephrectomies and lupus nephritis biopsies can be thawed and dissociated to yield intact, viable leukocytes and epithelial cells. Cryopreservation of intact kidney tissue provides higher epithelial cell yields compared to cryopreservation of single cell suspensions from dissociated kidneys. Cell yields and flow cytometric cell phenotypes are comparable between cryopreserved kidney samples and paired kidney samples shipped overnight on wet ice. High-quality single cell and low-input transcriptomic data were generated from leukocytes from both cryopreserved lupus nephritis kidney biopsies and urine, as well as from a subset of kidney epithelial cells.CONCLUSIONThe AMP RA/SLE cryopreserved tissue analysis pipeline provides a method for centralized processing of lupus nephritis kidney biopsies and urine samples to generate robust transcriptomic analyses in multi-center studies.