John P. Dowling

Array-Based Gene Discovery with Three Unrelated Subjects Shows SCARB2/LIMP-2 Deficiency Causes Myoclonus Epilepsy and Glomerulosclerosis

Action myoclonus-renal failure syndrome (AMRF) is an autosomal-recessive disorder with the remarkable combination of focal glomerulosclerosis, frequently with glomerular collapse, and progressive myoclonus epilepsy associated with storage material in the brain. Here, we employed a novel combination of molecular strategies to find the responsible gene and show its effects in an animal model. Utilizing only three unrelated affected individuals and their relatives, we used homozygosity mapping with single-nucleotide polymorphism chips to localize AMRF. We then used microarray-expression analysis to prioritize candidates prior to sequencing. The disorder was mapped to 4q13-21, and microarray-expression analysis identified SCARB2/Limp2, which encodes a lysosomal-membrane protein, as the likely candidate. Mutations in SCARB2/Limp2 were found in all three families used for mapping and subsequently confirmed in two other unrelated AMRF families. The mutations were associated with lack of SCARB2 protein. Reanalysis of an existing Limp2 knockout mouse showed intracellular inclusions in cerebral and cerebellar cortex, and the kidneys showed subtle glomerular changes. This study highlights that recessive genes can be identified with a very small number of subjects. The ancestral lysosomal-membrane protein SCARB2/LIMP-2 is responsible for AMRF. The heterogeneous pathology in the kidney and brain suggests that SCARB2/Limp2 has pleiotropic effects that may be relevant to understanding the pathogenesis of other forms of glomerulosclerosis or collapse and myoclonic epilepsies.

Nephron Number, Renal Function, and Arterial Pressure in Aged GDNF Heterozygous Mice

Abstract—The loss of one allele for glial cell line–derived neurotrophic factor (GDNF) results in ≈30% fewer but normal sized glomeruli in young mice. Low nephron number, inherited or acquired, has been linked to increased risk of development of hypertension and renal failure. This study examines whether GDNF heterozygous mice, with an inherent reduction in nephron number, demonstrate a deterioration in renal structure and function and rise in arterial pressure in later life. Fourteen-month-old male GDNF heterozygous (n=7) and wild-type (n=6) mice were anesthetized and prepared for measurement of mean arterial pressure, glomerular filtration rate (GFR), and renal blood flow. After measurement of renal function, kidneys were fixed for stereological determination of total glomerular number and mean glomerular volume. Mean arterial pressure was, on average, 18 mm Hg higher in GDNF heterozygous (98±4 mm Hg) than wild-type mice (80±2 mm Hg;P <0.01). However, GFR (0.656±0.054 versus 0.688±0.076 mL/min per g kidney wt) and renal blood flow (5.29±0.42 versus 4.70±0.34 mL/min per g kidney wt) were not different between groups. Fourteen-month-old GDNF heterozygous mice had ≈30% fewer glomeruli than wild-type mice (9206±934 versus 13440±1275;P <0.01) and significantly larger glomeruli (4.51±0.39 versus 3.72±0.63×10−4mm3;P <0.01). Thus, aged GDNF heterozygous mice maintained a normal GFR and renal blood flow despite reduced nephron numbers. The elevated arterial pressure, glomerular hypertrophy, and hyperfiltration demonstrated in the GDNF heterozygous mice at this age may indicate a compensatory mechanism whereby GFR is maintained in the presence of a reduced nephron endowment.

Abnormal p38 mitogen-activated protein kinase signalling in human and experimental diabetic nephropathy

Aims/hypothesisInflammation and fibrosis are pathological mechanisms that are partially regulated by cell signalling through the p38 mitogen-activated protein kinase (MAPK) pathway. Elements of the diabetic milieu such as high glucose and advanced glycation end-products induce activation of this pathway in renal cells. Therefore, we examined whether p38 MAPK signalling is associated with the development of human and experimental diabetic nephropathy.MethodsImmunostaining identified phosphorylated (active) p38 MAPK in human biopsies with no abnormality (n=6) and with Type 2 diabetic nephropathy (n=12). Changes in kidney levels of phosphorylated p38 were assessed by immunostaining and western blotting in mice with streptozotocin-induced Type 1 diabetes that had been killed after 0.5, 2, 3, 4 and 8 months, and in Type 2 diabetic db/db mice at 2, 4, 6 and 8 months of age.ResultsPhosphorylated p38 was detected in some intrinsic cells in normal human kidney, including podocytes, cortical tubules and occasional interstitial cells. Greater numbers of these phosphorylated p38+ cells were observed in diabetic patients, and phosphorylated p38 was identified in accumulating interstitial macrophages and myofibroblasts. A similar pattern of p38 activation was observed in both mouse models of diabetes. In mice, kidney levels of phosphorylated p38 increased (2–6 fold) following the onset of Type 1 and Type 2 diabetes. In both mouse models, interstitial phosphorylated p38+ cells were associated with hyperglycaemia, increased HbA1c levels and albuminuria. Further assessment of streptozotocin-induced diabetic nephropathy showed that interstitial phosphorylated p38+ cells correlated with interstitial fibrosis (myofibroblasts, collagen).Conclusions/interpretationIncreased p38 MAPK signalling is a feature of human and experimental diabetic nephropathy. Time course studies in mouse models suggest that phosphorylation of p38 plays a pathological role, particularly in the development of interstitial fibrosis.

Prenatal corticosterone exposure results in altered AT1/AT2, nephron deficit and hypertension in the rat offspring.

Maternal treatment with the synthetic glucocorticoid, dexamethasone has been reported to result in a nephron deficit and development of hypertension in the offspring of rats. However, it is not known whether elevated maternal corticosterone (CORT), the natural glucocorticoid, has similar effects on blood pressure and nephron endowment. The present study investigated the effects of CORT (0.8 mg kg−1 day−1) administration on embryonic day 14 (E14) and E15 of pregnancy on: (1) nephron number at postnatal day 30 (PN30); (2) blood pressure at PN120; and (3) receptors of the renal renin–angiotensin system (RRAS) (AT1Ra, AT1Rb and AT2Ra) during both embryonic (E16, E20) and adolescent (PN30) life. Plasma CORT concentrations were approximately doubled 30 min after injection. Unbiased stereological analysis revealed that maternal CORT treatment resulted in a nephron deficit of 21 and 19% in male and female offspring, respectively. Mean arterial pressures were significantly elevated in offspring of both sexes from the CORT group. Real‐time PCR revealed that CORT treatment increased expression of AT1Ra and AT2R at E16, and at PN30. Expression of AT1Rb was downregulated in embryonic life but upregulated at PN30. We believe that these results are the first to demonstrate that maternal CORT treatment results in a nephron deficit and development of hypertension in the rat offspring. Changes in the RRAS may be contributing to these phenotypes. Critically, this study suggests that increased but physiological levels of the natural glucocorticoid can programme similar changes to those seen with pharmacological doses of the synthetic glucocorticoid. This may have important implications for women experiencing significant stress during pregnancy.

The Impact of Partial Biopsy on Histopathologic Diagnosis of Cutaneous Melanoma: Experience of an Australian Tertiary Referral Service

OBJECTIVE To compare partial and excisional biopsy techniques in the accuracy of histopathologic diagnosis and microstaging of cutaneous melanoma. DESIGN Prospective case series. SETTING Tertiary referral, ambulatory care, institutional practice. Patients Consecutive cases from 1995 to 2006. Interventions Partial and excisional biopsy. Other factors considered were anatomic site, physician type at initial management, hypomelanosis, melanoma subtype, biopsy sample size, multiple biopsies, and tumor thickness. MAIN OUTCOME MEASURES Histopathologic diagnosis (false-negative misdiagnosis-overall or with an adverse outcome-and false-positive misdiagnosis) and microstaging accuracy. Odds ratios (ORs) and 95% confidence intervals (CIs) obtained from multinomial logistic regression. RESULTS Increased odds of histopathologic misdiagnosis were associated with punch biopsy (OR, 16.6; 95% CI, 10-27) (P < .001) and shave biopsy (OR, 2.6; 95% CI, 1.2-5.7) (P = .02) compared with excisional biopsy. Punch biopsy was associated with increased odds of misdiagnosis with an adverse outcome (OR, 20; 95% CI, 10-41) (P < .001). Other factors associated with increased odds of misdiagnosis included acral lentiginous melanoma (OR, 5.1; 95% CI, 2-13) (P < .001), desmoplastic melanoma (OR, 3.8; 95% CI, 1.1-13.0) (P = .03), and nevoid melanoma (OR, 28.4; 95% CI, 7-115) (P < .001). Punch biopsy (OR, 5.1; 95% CI, 3.4-7.6) (P < .001) and shave biopsy (OR, 2.3; 95% CI, 1.5-3.6) (P < .001) had increased odds of microstaging inaccuracy over excisional biopsy. Tumor thickness was the most important determinant of microstaging inaccuracy when partial biopsy was used (odds of significant microstaging inaccuracy increased 1.8-fold for every 1 mm increase in tumor thickness; 95% CI, 1.4-2.4) (P < .001). CONCLUSIONS Among melanoma seen at a tertiary referral center, histopathologic misdiagnosis is more common for melanomas that have been assessed with punch and shave biopsy than with excisional biopsy. Regardless of biopsy method, adverse outcomes due to misdiagnosis may occur. However, such adverse events are more commonly associated with punch biopsy than with shave and excisional biopsy. The use of punch and shave biopsy also leads to increased microstaging inaccuracy.

p38 Mitogen-Activated Protein Kinase Activation and Cell Localization in Human Glomerulonephritis: Correlation with Renal Injury

Activation of the p38 mitogen-activated protein kinase (MAPK) signal transduction pathway plays an important role in the inflammatory response. It was postulated that p38 MAPK is important in the pathogenesis of human glomerulonephritis and contributes to the development of renal injury. p38 MAPK activation was examined by immunodetection for dual phosphorylated p38 (p-p38) in normal human kidney and 77 renal biopsy specimens encompassing a wide spectrum of glomerulonephritides. In normal kidney, p-p38 immunostaining was restricted to the nuclei of a small number of podocytes, parietal epithelial cells, and tubular cells. There was a dramatic increase in the number of p-p38-positive cells in glomeruli and tubules in nonproliferative and proliferative glomerulonephritis and a substantial increase in the number of interstitial p-p38-positive cells in proliferative glomerulonephritis. Double immunostaining identified p38 activation in intrinsic renal cells (podocytes and endothelial and tubular cells), infiltrating macrophage and neutrophils, and myofibroblasts. Renal failure correlated with the number of p-p38-positive glomerular, tubular, and interstitial cells. Proteinuria correlated with the number of p-p38-positive tubular and interstitial cells and the number of p-p38-positive podocytes in nonproliferative glomerulonephritis. Furthermore, glomerular p38 activation correlated with segmental proliferative and necrotic lesions, and interstitial p38 activation correlated with the degree of interstitial inflammation. In conclusion, activation of p38 MAPK in intrinsic renal cells and infiltrating leukocytes correlated with renal dysfunction and histopathology, suggesting an important pathogenic role for p38 MAPK activation in human glomerulonephritis.

A single low-fixed dose of rituximab to salvage renal transplants from refractory antibody-mediated rejection.

Rituximab may improve graft survival in renal acute antibody-mediated rejection (AMR), but data confirming efficacy and optimal dosing is lacking. High-dose regimens may be associated with significant rates of infective complications. We therefore conducted a pilot study of a single low-fixed dose (500 mg) of rituximab in seven consecutive patients with AMR resistant to standard therapy. After a mean follow-up of 21 months (range, 9.5–33 months), graft and patient survival were 100% with serum creatinine levels significantly lower than peak rejection levels (171±73 &mgr;mol/L vs. 559±358 &mgr;mol/L, P=0.028). B cells were undetectable in all patients for more than or equal to 6 months and in six of seven patients for more than or equal to 12 months after rituximab. Three patients encountered a significant infective complication including cytomegalovirus reactivation, viral pneumonia, and polyoma viral nephropathy. All have since resolved. A single low-fixed dose of rituximab may help improve graft survival in AMR and offers the potential advantage of reduced infective complications.

Activation of the Extracellular-Signal Regulated Protein Kinase Pathway in Human Glomerulopathies

Examined was extracellular-signal regulated kinase (ERK) activation in normal human kidney (n = 2) and a cohort of glomerulopathies by immunohistochemistry staining for the dual-phosphorylated form of ERK (p-ERK). Cell proliferation was determined by expression of the proliferating cell nuclear antigen (PCNA). In normal human kidney, p-ERK was largely restricted to the cytoplasm of cells of the collecting duct (CD). In glomerulopathies, glomerular ERK activation was highly variable. However, there was colocalization of cell proliferation and ERK activation in the glomerular tuft and crescents. Tubular ERK activation in the different glomerulopathies was confined to the CD in areas with normal architecture. In contrast, ERK activation was prominent in tubules and interstitial cells in areas of tubulointerstitial damage. ERK activation was observed in glomerular and interstitial alpha-smooth muscle actin-positive myofibroblasts, but few macrophages or T cells showed ERK activation. There was a significant correlation between glomerular p-ERK+ and PCNA+ cells and between tubular p-ERK+ and PCNA+ cells. Glomerular p-ERK+ cells correlated with glomerular cellularity and the percentage of glomeruli with segmental lesions. Tubular p-ERK+ cells correlated with renal dysfunction and interstitial fibrosis and tubular atrophy. In conclusion, activation of the ERK pathway in human glomerulopathies correlates with cell proliferation, histologic lesions, and renal dysfunction. ERK activation may promote renal repair through tubular proliferation while promoting renal fibrosis via proliferation of glomerular and interstitial myofibroblasts.

Production of Interleukin 1 in Glomerular Cell Cultures from Patients with Rapidly Progressive Crescentic Glomerulonephritis

Interleukin 1 (IL-1) activity was measured in glomerular culture supernatants from 3 patients with rapidly progressive crescentic glomerulonephritis (RPGN). Macrophages were present in both capillary tufts and cellular crescents as identified by OKM1-positive cells on immunoperoxidase labelling. Glomeruli from 4 rejecting renal cadaver allografts were used as a disease control, in addition to glomeruli from a normal kidney. IL-1 activity as measured by the thymocyte proliferation assay was greater in the supernatants from cultured glomerular outgrowths of patients with crescentic GN than in those from rejected renal allografts and glomeruli isolated from the normal tissue. IL-1 production from cultured glomerular cells from patients with RPGN was detectable in the serum-free conditioned media harvested after 3 days of culture and increased in a stepwise fashion over 28 days of culture. The prominent feature of the glomerular outgrowth of the glomeruli in the RPGN patients was the presence of large numbers of macrophages, which were not present in cultured control glomeruli. These findings indicate that the immunoregulatory aberration in patients with RPGN may in part be due to IL-1 production by activated macrophages.

MRI-based glomerular morphology and pathology in whole human kidneys

Nephron number (N(glom)) and size (V(glom)) are correlated with risk for chronic cardiovascular and kidney disease and may be predictive of renal allograft viability. Unfortunately, there are no techniques to assess N(glom) and V(glom) in intact kidneys. This work demonstrates the use of cationized ferritin (CF) as a magnetic resonance imaging (MRI) contrast agent to measure N(glom) and V(glom) in viable human kidneys donated to science. The kidneys were obtained from patients with varying levels of cardiovascular and renal disease. CF was intravenously injected into three viable human kidneys. A fourth control kidney was perfused with saline. After fixation, immunofluorescence and electron microscopy confirmed binding of CF to the glomerulus. The intact kidneys were imaged with three-dimensional MRI and CF-labeled glomeruli appeared as punctate spots. Custom software identified, counted, and measured the apparent volumes of CF-labeled glomeruli, with an ~6% false positive rate. These measurements were comparable to stereological estimates. The MRI-based technique yielded a novel whole kidney distribution of glomerular volumes. Histopathology demonstrated that the distribution of CF-labeled glomeruli may be predictive of glomerular and vascular disease. Variations in CF distribution were quantified using image texture analyses, which be a useful marker of glomerular sclerosis. This is the first report of direct measurement of glomerular number and volume in intact human kidneys.