Lineage tracing reveals transient phenotypic adaptation of tubular cells during acute kidney injury.

Tubular injury is the hallmark of acute kidney injury (AKI) with a tremendous impact on patients and health-care systems. During injury, any differentiated proximal tubular cell (PT) may transition into a specific injured phenotype, so-called "scattered tubular cell" (STC)-phenotype. To understand the fate of this specific phenotype, we generated transgenic mice allowing inducible, reversible, and irreversible tagging of these cells in a murine AKI model, the unilateral ischemia-reperfusion injury (IRI). For lineage tracing, we analyzed the kidneys using single-cell profiling during disease development at various time points. Labeled cells, which we defined by established endogenous markers, already appeared 8 h after injury and showed a distinct expression set of genes. We show that STCs re-differentiate back into fully differentiated PTs upon the resolution of the injury. In summary, we show the dynamics of the phenotypic transition of PTs during injury, revealing a reversible transcriptional program as an adaptive response during disease.

IgA nephropathy.

IgA nephropathy (IgAN), the most prevalent primary glomerulonephritis worldwide, carries a considerable lifetime risk of kidney failure. Clinical manifestations of IgAN vary from asymptomatic with microscopic or intermittent macroscopic haematuria and stable kidney function to rapidly progressive glomerulonephritis. IgAN has been proposed to develop through a 'four-hit' process, commencing with overproduction and increased systemic presence of poorly O-glycosylated galactose-deficient IgA1 (Gd-IgA1), followed by recognition of Gd-IgA1 by antiglycan autoantibodies, aggregation of Gd-IgA1 and formation of polymeric IgA1 immune complexes and, lastly, deposition of these immune complexes in the glomerular mesangium, leading to kidney inflammation and scarring. IgAN can only be diagnosed by kidney biopsy. Extensive, optimized supportive care is the mainstay of therapy for patients with IgAN. For those at high risk of disease progression, the 2021 KDIGO Clinical Practice Guideline suggests considering a 6-month course of systemic corticosteroid therapy; however, the efficacy of systemic steroid treatment is under debate and serious adverse effects are common. Advances in understanding the pathophysiology of IgAN have led to clinical trials of novel targeted therapies with acceptable safety profiles, including SGLT2 inhibitors, endothelin receptor blockers, targeted-release budesonide, B cell proliferation and differentiation inhibitors, as well as blockade of complement components.

Novel agents for treating IgA nephropathy.

PURPOSE OF REVIEW: In the past, the treatment of IgA nephropathy (IgAN), which is the most common glomerulonephritis worldwide, mostly relied on blockade of the renin-angiotensin system as a central component of so-called supportive therapy as well as on high-dose systemic corticosteroid therapy. RECENT FINDINGS: The supportive treatment arm has been expanded by the addition of sodium-glucose cotransporter-2 inhibitors, hydroxychloroquine, and, most recently, endothelin A receptor blockers. Treatment with high-dose systemic corticosteroids has become more controversial, with some studies observing no benefit and others documenting the protection of kidney function. However, all recent studies on systemic corticosteroids consistently found significant toxicity. An important novel approach to IgAN, therefore, is therapy with a targeted release formulation of budesonide with preferential release in the distal small intestine, given the mounting evidence for a gut-kidney axis in the pathophysiology of IgAN. In addition, emerging new therapeutic options include a variety of complement inhibitors as well as agents targeting B-cell proliferation and differentiation. SUMMARY: In recent years, IgAN has become the focus of a considerable number of clinical studies that will significantly advance the development of new therapy strategies.

Intestinal permeability in patients with IgA nephropathy and other glomerular diseases: an observational study.

BACKGROUND: A dysregulated 'gut-kidney axis' may contribute to immunoglobulin A nephropathy (IgAN). We studied whether IgAN patients have disturbed intestinal permeability. METHODS: In a prospective, cross sectional, pilot study we assessed intestinal permeability in 35 IgAN patients, 18 patients with non-IgAN glomerulonephritides (GNs) and 19 healthy controls. After an overnight fast, trial participants ingested a multi-sugar solution and samples were obtained from 0 to 2, 2 to 5- and 5 to 24-h urine portions. Urinary sugar concentrations were quantified using isocratic ion-exchange high performance liquid chromatography. Indices of small intestinal permeability (0-2-h lactulose/L-rhamnose (L/R) ratio), distal small intestinal and proximal colonic permeability (2-5-h sucralose/erythritol (S/E) ratio) and colonic permeability (5-24-h sucralose/erythritol (S/E) ratio) were evaluated. Associations between groups and indices of intestinal permeability were investigated by a linear mixed model. RESULTS: Small intestinal permeability (0-2 h L/R-ratio) was significantly increased in patients with glomerular diseases versus healthy controls. More precisely, increased small intestinal permeability was exclusively noted in non-IgAN GN patients, whereas IgAN patients exhibited a trend towards elevated small intestinal permeability. In total, 54% of patients with IgAN and 67% of non-IgAN GN patients had increased small intestinal permeability. Neither distal small intestinal and proximal colonic permeability nor colonic gut permeability indices (i.e., 2-5 h and 5-24 h S/E ratios) were significantly different between controls and any of the GN patient groups. CONCLUSION: The present single center pilot study suggests that disturbed intestinal permeability is common in patients with glomerular diseases and is not specific for IgAN. TRIAL REGISTRATION NUMBER: German Clinical Trials Register DRKS00021533, Date: 24.04.2020.

Large-scale extraction of interpretable features provides new insights into kidney histopathology - A proof-of-concept study.

Whole slide images contain a magnitude of quantitative information that may not be fully explored in qualitative visual assessments. We propose: (1) a novel pipeline for extracting a comprehensive set of visual features, which are detectable by a pathologist, as well as sub-visual features, which are not discernible by human experts and (2) perform detailed analyses on renal images from mice with experimental unilateral ureteral obstruction. An important criterion for these features is that they are easy to interpret, as opposed to features obtained from neural networks. We extract and compare features from pathological and healthy control kidneys to learn how the compartments (glomerulus, Bowman's capsule, tubule, interstitium, artery, and arterial lumen) are affected by the pathology. We define feature selection methods to extract the most informative and discriminative features. We perform statistical analyses to understand the relation of the extracted features, both individually, and in combinations, with tissue morphology and pathology. Particularly for the presented case-study, we highlight features that are affected in each compartment. With this, prior biological knowledge, such as the increase in interstitial nuclei, is confirmed and presented in a quantitative way, alongside with novel findings, like color and intensity changes in glomeruli and Bowman's capsule. The proposed approach is therefore an important step towards quantitative, reproducible, and rater-independent analysis in histopathology.

A Hypercaloric Diet Induces Early Podocyte Damage in Aged, Non-Diabetic Rats.

BACKGROUND/AIMS: The number of patients of older age with metabolic syndrome, obesity, and associated kidney disease, which is characterized by podocyte damage, glomerular hypertrophy, and focal segmental glomerulosclerosis (FSGS), is increasing worldwide. Animal models that would reflect the development of such kidney diseases could facilitate the testing of drugs. We investigated the renal effects of a long-term high caloric diet in aged rats and the potential effects of drugs used to treat metabolic syndrome. METHODS: We analyzed nine-month-old male and female Sprague Dawley rats fed five months with a normal diet (control group) or high-fat-high-carbohydrate diet (HFHCD group). Two additional groups were fed with HFHCD and treated with drugs used in patients with metabolic syndrome, i.e., the glucagon-like peptide receptor 1 agonist liraglutide (HFHCD+liraglutide group) or metformin (HFHCD+metformin group). RESULTS: Except an increase of waist circumference as a sign of visceral obesity, the HFHCD diet did not induce metabolic syndrome or obesity. There were no significant changes in kidney function and all groups showed similar indices of glomerular injury, i.e., no differences in glomerular size or the number of glomeruli with FSGS or with FSGS-precursor lesions quantified by CD44 expression as a marker of parietal epithelial cell (PEC) activation. Analysis of ultrastructural morphology revealed mild podocyte stress and a decrease of glomerular nestin expression in the HFHCD group, whereas podocin and desmin were not altered. HFHCD did not promote fibrogenesis, however, treatment with liraglutide led to a slightly increased tubulointerstitial damage, immune cell infiltration, and collagen IV expression compared to the control and HFHCD groups. CONCLUSION: A five-month feeding with HFHCD in aged rats induced mild podocyte injury and microinflammation, which was not alleviated by liraglutide or metformin.

The immune landscape of IgA induction in the gut.

Antibodies are key elements of protective immunity. In the mucosal immune system in particular, secretory immunoglobulin A (SIgA), the most abundantly produced antibody isotype, protects against infections, shields the mucosal surface from toxins and environmental factors, and regulates immune homeostasis and a peaceful coexistence with our microbiota. However, the dark side of IgA biology promotes the formation of immune complexes and provokes pathologies, e.g., IgA nephropathy (IgAN). The precise mechanisms of how IgA responses become deregulated and pathogenic in IgAN remain unresolved. Yet, as the field of microbiota research moved into the limelight, our basic understanding of IgA biology has been taking a leap forward. Here, we discuss the structure of IgA, the anatomical and cellular foundation of mucosal antibody responses, and current concepts of how we envision the interaction of SIgA and the microbiota. We center on key concepts in the field while taking account of both historic findings and exciting new observations to provide a comprehensive groundwork for the understanding of IgA biology from the perspective of a mucosal immunologist.

Precision medicine in immunoglobulin A nephropathy: still a journey ahead.

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerular disease worldwide and since its first description extensive research has identified a number of key central pathogenetic contributors, including genetic, immunological and environmental factors. Along with its multifaceted pathophysiology, the clinical presentation of IgAN varies, ranging from mild forms with only minor urinary findings and preserved renal function to cases that rapidly progress to end-stage renal disease. Because of this, early identification of patients at risk for a progressive course is urgently needed. The search for valid and easily accessible biomarkers showed urinary Dickkopf-3 as a promising candidate to predict the course of kidney function. In addition, a recently established IgAN risk prediction tool derived from an international cohort of IgAN patients allows estimation of the risk of a 50% loss of kidney function over several years upon diagnosis. This might serve as a significant tool to individually predict the course of renal function by combining biometric, clinical, histological and treatment information at the time of diagnosis. Today there is no doubt that a comprehensive supportive treatment regimen is the main pillar for all IgAN patients. The value of an additional immunosuppressive treatment in IgAN patients at risk for disease progression is less clear. Early risk stratification and individualized therapies would be desirable for IgAN patients to facilitate the choice of treatment strategies, which is still a matter of ongoing discussion.

Time on previous renal replacement therapy is associated with worse outcomes of COVID-19 in a regional cohort of kidney transplant and dialysis patients.

ABSTRACT: Chronic renal replacement therapy by either a kidney transplant (KTX) or hemodialysis (HD) predisposes patients to an increased risk for adverse outcomes of COVID-19. However, details on this interaction remain incomplete. To provide further characterization, we undertook a retrospective observational cohort analysis of the majority of the hemodialysis and renal transplant population affected by the first regional outbreak of severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) in Germany. In a region of 250,000 inhabitants we identified a total of 21 cases with SARS-CoV-2 among 100 KTX and 260 HD patients, that is, 7 KTX with COVID-19, 14 HD with COVID-19, and 3 HD with asymptomatic carrier status. As a first observation, KTX recipients exhibited trends for a higher mortality (43 vs 18%) and a higher proportion of acute respiratory distress syndrome (ARDS) (57 vs 27%) when compared to their HD counterparts. As a novel finding, development of ARDS was significantly associated with the time spent on previous renal replacement therapy (RRT), defined as the composite of dialysis time and time on the transplant (non-ARDS 4.3 vs ARDS 10.6 years, P = .016). Multivariate logistic regression analysis showed an OR of 1.7 per year of RRT. The association remained robust when analysis was confined to KTX patients (5.1 vs 13.2 years, P = .002) or when correlating the time spent on a renal transplant alone (P = .038). Similarly, longer RRT correlated with death vs survival (P = .0002). In conclusion our data suggest renal replacement vintage as a novel risk factor for COVID-19-associated ARDS and death. The findings should be validated by larger cohorts.

Single versus dual blockade of the renin-angiotensin system in patients with IgA nephropathy.

BACKGROUND: Inhibitors of the renin-angiotensin system (RAS) are cornerstones of supportive therapy in patients with IgA nephropathy (IgAN). We analyzed the effects of single versus dual RAS blockaQueryde during our randomized STOP-IgAN trial. METHODS: STOP-IgAN participants with available successive information on their RAS treatment regimen and renal outcomes during the randomized 3-year trial phase were stratified post hoc into two groups, i.e. patients under continuous single or dual RAS blocker therapy over the entire 3 years of the trial phase. Primary and secondary STOP-IgAN trial endpoints, i.e. frequencies of full clinical remission, eGFR-loss ≥ 15 and ≥ 30 ml/min/1.73 m2 and ESRD onset, were analyzed by logistic regression and linear mixed effects models. RESULTS: Among the 112 patients included in the present analysis, 82 (73%) were maintained on single and 30 (27%) on dual RAS inhibitor therapy throughout the trial. Neither RAS blocker strategy significantly affected full clinical remission, eGFR-loss rates, onset of ESRD. Proteinuria moderately increased in patients under dual RAS blockade by 0.1 g/g creatinine during the 3-year trial phase. This was particularly evident in patients without additional immunosuppression during the randomized trial phase, where proteinuria increased by 0.2 g/g creatinine in the dual RAS blockade group. In contrast, proteinuria decreased in patients under single RAS blocker therapy by 0.3 g/g creatinine. The course of eGFR remained stable and did not differ between the RAS treatment strategies. CONCLUSION: In the STOP-IgAN cohort, neither RAS blocker regimen altered renal outcomes. Patients on dual RAS blockade even exhibited higher proteinuria over the 3-year trial phase.

Serum concentrations of A Proliferation-Inducing Ligand (APRIL) are elevated in sepsis and predict mortality in critically ill patients.

INTRODUCTION: Inflammatory and autoimmune diseases have been associated with the tumor necrosis factor superfamily member "A PRoliferation Inducing Ligand" (APRIL). However, up to now, APRIL has not been investigated in critical illness or sepsis. We therefore analyzed APRIL serum concentrations in a large cohort of well-characterized intensive care unit patients. METHODS: Serum concentrations of APRIL were measured in 246 critically ill patients, of which 157 fulfilled sepsis criteria in comparison with 81 healthy controls. Clinical data were recorded and correlated with APRIL serum levels. RESULTS: We detected strongly elevated serum levels of APRIL in critically ill patients compared with healthy controls. Levels of APRIL were further elevated in sepsis and significantly correlated with classical markers of inflammation, bacterial infection, or multiorgan failure. Consequently, high APRIL levels were associated with an unfavorable prognosis and predicted mortality with higher diagnostic accuracy than established prognostic scoring systems such as the Acute Physiology and Chronic Health Evaluation II score. CONCLUSION: Serum levels of APRIL were significantly elevated in intensive care unit patients, with the highest concentrations in septic patients, and associated with unfavorable outcome. Besides being used as a single marker, APRIL may be implemented into established scoring systems to further improve their sensitivity and specificity in predicting patient's prognosis.

Biological responses to PDGF-AA versus PDGF-CC in renal fibroblasts.

BACKGROUND: Platelet-derived growth factors (PDGF)-AA and -CC mediate renal fibroblast proliferation and/or renal fibrosis. Whereas PDGF-CC binds to both the PDGF receptors (PDGFRs)-αα- and -αß, PDGF-AA binds more selectively to the αα-receptor, suggesting potential differences in the biological activities. METHODS: We compared signal transduction, gene expression as well as changes in the proteome induced by PDGF-AA and -CC in rat renal fibroblasts, which express both PDGFR subunits. The growth factor concentrations used were chosen based on their equipotency in inducing rat renal fibroblast proliferation. RESULTS: Both PDGF-AA and PDGF-CC induced phosphorylation and activation of extracellular signal-regulated kinase 1 (ERK1) and ERK2. Renal fibroblast proliferation induced by either PDGF-AA or -CC could be blocked by signal transduction inhibitors of the mitogen-activated protein kinase (MAPK)-, Janus-kinase (JAK)/signal transducers and activators of transcription (STAT) and phosphatidyl-inositol-3-kinase (PI3K) pathway, pointing to the involvement of all the three pathways. However, quantitative differences between both the stimulations were minor. Additive or synergistic effects by stimulating simultaneously with PDGF-AA and -CC were not observed. Using a proteomic approach we found eleven differentially expressed proteins, which were quantitatively altered after treatment with either PDGF-AA or PDGF-CC. The regulation of calreticulin and inorganic pyrophosphatase 1 could be verified by western blotting. CONCLUSIONS: PDGF-AA and -CC exhibit almost identical biological effects on signal transduction and proteome in cultured renal fibroblasts, suggesting that the ligands exert their activity essentially through the commonly bound PDGFR-αα. Nonetheless, two differentially expressed proteins were identified which might be involved in the development of renal failure.

Renal allograft failure in a hyperparathyroid patient following initiation of a calcimimetic.

BACKGROUND: A 47-year-old man with a 6-year history of chronic dialysis for end-stage renal disease of unknown etiology presented for renal transplantation. While on dialysis, he had developed secondary hyperparathyroidism, which persisted after transplantation despite treatment with cinacalcet. INVESTIGATIONS: Physical examination, serum and urine analysis, ultrasound of the renal transplant, renal biopsy, bone scintigraphy. DIAGNOSIS: Severe persistent hyperparathyroidism associated with mild hypercalcemia following renal transplantation. Initiation of a calcimimetic followed by fulminant graft failure. Extensive tubular calcinosis. MANAGEMENT: Renal transplantation (with immunosuppressant medications: basiliximab, tacrolimus, mycophenolate mofetil, prednisolone), cinacalcet (halted on day 26 after transplantation), angiotensinconverting-enzyme inhibitor, angiotensin-receptor blocker, hydrochlorothiazide, emergency dialysis, subtotal parathyroidectomy.