IgA nephropathy (IgAN) is the most common glomerulonephritis in the world, affecting close to a million people. Circulating galactose-deficient IgA (gd-IgA), present in patients with IgAN, form immune complex deposits in the glomerular mesangium causing local proliferation and matrix expansion. Intriguing though, individuals having gd-IgA deposits in the kidneys do not necessarily have signs of glomerular disease. Recurrence of IgAN only occurs in less than half of transplanted patients with IgAN, indicating that gd-IgA is not the only factor driving the disease. We hypothesize that, in addition to IgA complexes, patients with IgAN possess a subtype of mesangial cells highly susceptible to gd-IgA induced cell proliferation. To test the hypothesis, we designed a technique to culture primary mesangial cells from renal biopsies obtained from IgAN patients and controls. The cell response to gd-IgA treatment was then measured both on gene and protein level and the proliferation rate of the cells in response to PDGF was investigated. When treated with gd-IgA, mesangial cells from patients with IgAN express and release more PDGF compared to controls. In addition, the mesangial cells from patients with IgAN were more responsive to treatment with PDGF resulting in an increased proliferation rate of the cells compared to control. Mesangial cells cultured from patients with IgAN expressed and released more IL-6 than controls and had a higher expression of matrix genes. Both mesangial cells derived from patients with IgAN and controls increased their expressed TGFβ1 and CCL5 when treated with gd-IgA. We conclude that mesangial cells derived from IgAN patients have a mesangioproliferative phenotype with increased reactivity to IgA and that these cellular intrinsic properties may be important for the development of IgA nephropathy.

Accidental intake of mushrooms of the Cortinarius species (deadly webcap) may cause irreversible renal damage and the need for dialysis or transplantation. The species is found in forests of Northern Europe, Scandinavia and North America and may be mistaken for other edible mushrooms. The highly selective nephrotoxic compound of the mushroom is called orellanine. Very little is known about the long-term effects of the nephrotoxin. We identified patients who ingested deadly webcap in the period of 1979 to 2012. Informed consent and medical records were obtained for 28 of the 39 cases that occurred during the 34-year period. A case control group was also studied based on sex, age and initiation of dialysis or transplantation. The average age at time of the accidental intake was 40 ± 3 (n = 28) years. 64% of patients were male, and 22 of 28 patients developed acute kidney injury requiring dialysis. Serum creatinine peaked at 1 329 ± 133 μmol/l, and serum urea was 31 ± 3.5 mmol/l. No signs of acute damage were present in any other organ. The average time of follow-up was 16.9 ± 2.1 years (1.24–34.3 years, n = 28). 15 patients were transplanted and 3 also had a second graft. At follow-up, 23 patients were alive, and five had died at ages of 67 ± 5 (range 54–84). The outcome was similar in the case control group with 6 deaths in 20 patients. We conclude that the long-term prognosis for patients poisoned by deadly webcap who lost their renal function is not different compared to other patients in active uremic care.

Orellanine is a nephrotoxin found in mushrooms of the Cortinarius family. Accidental intake of this substance may cause renal failure. Orellanine is specific for proximal tubular cells and could, therefore, potentially be used as treatment for metastatic renal cancer, which originates from these cells. However, more information is needed about the distribution and elimination of orellanine from the body to understand its potential use for therapy. In this study, 5 mg/kg orellanine (unlabeled and ³H-labeled) was injected intravenously in rats (Wistar and Sprague Dawley). Distribution was measured (Wistar rats, n = 10, n = 12) using radioluminography and the highest amount of orellanine was found in the kidney cortex and bladder at all time-points investigated. The pharmacokinetic properties of orellanine was investigated using LC-MS/MS and β-scintillation to measure the amount of orellanine in plasma. Three groups of rats were investigated: control rats with intact kidneys (n = 10) and two groups with bilateral renal artery ligation (n = 7) where animals in one of these groups were treated with peritoneal dialysis (n = 8). Using LC-MS/MS, the half-life of orellanine was found to be 109 ± 6 min in the controls. In the groups with ligated renal arteries, orellanine had a half-life of 756 ± 98 min without and 238 ± 28 min with dialysis. Thus, orellanine was almost exclusively eliminated by glomerular filtration as well as by peritoneal dialysis.

Recent studies have demonstrated that the transcription factor hepatocyte nuclear factor 4α (HNF4A) drives epithelial differentiation in the renal proximal tubules (PT) and is critical for maintaining a mature PT phenotype. Furthermore, HNF4A downregulation has been observed following kidney injury in mouse models. The aim of the present work was to investigate the role of HNF4A during acute and chronic human kidney disease and the loss of the mature PT phenotype in cultured PT cells. By immunohistochemistry, we discovered that loss of HNF4A expression and gain of vimentin expression is reciprocal and gradual during both acute and chronic kidney disease. Healthy human kidneys demonstrated partial or total loss of HNF4A expression in vimentin-positive scattered tubular cells. Primary cell isolation and subculture of PT cells recapitulated HNF4A-associated loss of the PT phenotype. Re-expression of HNF4A in cultured PT cells by adenoviral transduction increased transcripts related to brush border formation as well as absorptive and transport processes, as shown by RNA sequencing and gene set enrichment analyses. Thus, the reduction of HNF4A and increase of vimentin expression is connected to both acute and chronic kidney disease and represent a stereotypic injury response of the PT, resulting in dedifferentiation. HNF4A re-expression in cultured primary PT cells could provide a more reliable and predictive in vitro model to study PT function and injury.

Podocytes are kidney glomerular cells that depend on rigorously regulated cytoskeleton components and integrins to form and maintain the so-called foot processes, apparatuses that attach podocytes to the glomerular basement membrane and connect them to neighboring podocytes. In diabetic kidney disease (DKD) these foot processes are effaced as a result of cytoskeleton dysregulation, a phenomenon that gradually reduces glomerular filtration. Cytoskeleton-associated protein 4 (CKAP4) is a known linker between the endoplasmic reticulum, integrins, and microtubular cytoskeleton. Since CKAP4 gene expression is downregulated in glomeruli from patients with DKD but not in other chronic kidney diseases, we hypothesized a role for CKAP4 in the mechanisms leading to foot process effacement (FPE) in DKD. CKAP4 mRNA reduction in podocytes in DKD was demonstrated in human kidney biopsies. Knockdown of CKAP4 in vivo in zebrafish resulted in edema, proteinuria, and foot process effacement, all typical features of DKD. Knockdown of CKAP4 in vitro led to disruption of the actin cytoskeleton and of the microtubular orientation. Moreover, it caused a downregulation of several integrins. These findings indicate that CKAP4 is crucial for foot process dynamics of podocytes. Its reduction, unique to DKD, is mechanistically connected to the pathophysiological processes leading to podocyte FPE.

Brain damage caused by hypoxia-ischemia is a serious complication for a newborn with possible life-long sequelae. To develop targeted neuroprotective strategies, it is essential to understand the mechanisms of injury, particularly the role of microglial phagocytosis, which may contribute to neuronal loss after hypoxia-ischemia. The aim was to evaluate neuronal cell death by phagocytosis in neonatal hypoxia-ischemia by investigating key signaling molecules and the effect of gene deletion of the phagocytic receptor Myeloid-epithelial-reproductive tyrosine kinase (MerTK) in a neonatal mouse model. MerTK, growth arrest–specific 6, and genes related to phagoptosis were regulated in the brain 6–72 h after hypoxic ischemia. Brain injury was reduced in MerTK knock-out vs. wild-type mice by 48% in gray matter (p = 0.002) and by 32% in white matter (p = 0.04). There was a near 40% reduction in NeuN immunoreactivity in microglia in MerTK knock-out mice vs. wild-type (p = 0.03) indicating attenuation of neuronal phagocytosis by microglia. In summary, the reduction in microglial neuronal engulfment and brain injury in MerTK-deficient mice strongly indicates that phagoptosis contributes to neuronal loss after neonatal hypoxia-ischemia. This insight suggests that targeting MerTK-mediated phagocytosis may represent a potential therapeutic approach in neonatal hypoxia-ischemic brain injury.