Faculty Bibliography

Cross-linking of the IgE receptor (FcepsilonRI) on mast cells plays a critical role in IgE-dependent allergy, including allergic rhinitis, asthma, anaphylaxis, and immediate-type hypersensitivity reactions. Previous studies have demonstrated that the K(+) channel, KCa3.1, plays a critical role in IgE-stimulated Ca(2+) entry and degranulation in both human and mouse mast cells. We now have shown that the class II phosphatidylinositol-3-kinase C2beta (PI3KC2beta) is necessary for FcepsilonRI-stimulated activation of KCa3.1, Ca(2+) influx, cytokine production, and degranulation of bone marrow-derived mast cells (BMMC). In addition, we found that the E3 ubiquitin ligase, tripartite motif containing protein 27 (TRIM27), negatively regulates FcepsilonRI activation of KCa3.1 and downstream signaling by ubiquitinating and inhibiting PI3KC2beta. TRIM27(-/-) mice are also more susceptible in vivo to acute anaphylaxis. These findings identify TRIM27 as an important negative regulator of mast cells in vivo and suggest that PI3KC2beta is a potential new pharmacologic target to treat IgE-mediated disease.

Lymphocyte function is regulated by a network of ion channels and transporters in the plasma membrane of B and T cells. These proteins modulate the cytoplasmic concentrations of diverse cations, such as calcium, magnesium and zinc ions, which function as second messengers to regulate crucial lymphocyte effector functions, including cytokine production, differentiation and cytotoxicity. The repertoire of ion-conducting proteins includes calcium release-activated calcium (CRAC) channels, P2X receptors, transient receptor potential (TRP) channels, potassium channels, chloride channels and magnesium and zinc transporters. This Review discusses the roles of ion conduction pathways in lymphocyte function and immunity.

Antibodies to myeloperoxidase (MPO) and proteinase 3 (PR3) have been demonstrated to mediate anti-neutrophil cytoplasmic antibody (ANCA)-associated disease. For membranous nephropathy, antibodies to the podocyte-expressed phospholipase A(2) receptor (anti-PLA(2)R) are highly associated with disease activity and have been reported in at least 70% of patients with idiopathic membranous nephropathy (IMN). We present a case of a 56-year-old male with a 1 year history of hypertension, leg edema, and proteinuria, who presented with advanced renal failure and was found to have both ANCA-associated glomerulonephritis (GN) and IMN on kidney biopsy. Consistent with the idea that this is due to the chance occurrence of two independent diseases, we found both anti-MPO and anti-PLA(2)R antibodies in the patient's sera. Treatment with methylprednisolone, plasmapheresis, and cyclophosphamide resulted in improvement in kidney function and proteinuria, together with the simultaneous decrease in both autoantibodies. This is the first demonstration of two pathogenic antibodies giving rise to ANCA-associated GN and IMN in the same patient. It confirms the importance of classifying disease based upon the underlying mechanism, in addition to renal histopathology, to both optimize therapy and predict prognosis.

The K(+) channel KCa3.1 is required for Ca(2+) influx and the subsequent activation of CD4 T cells. The class II phosphatidylinositol 3 kinase C2beta (PI3KC2beta) is activated by the T-cell receptor (TCR) and is critical for KCa3.1 channel activation. Tripartite motif containing protein 27 (TRIM27) is a member of a large family of proteins that function as Really Interesting New Gene (RING) E3 ubiquitin ligases. We now show that TRIM27 functions as an E3 ligase and mediates lysine 48 polyubiquitination of PI3KC2beta, leading to a decrease in PI3K enzyme activity. By inhibiting PI3KC2beta, TRIM27 also functions to negatively regulate CD4 T cells by inhibiting KCa3.1 channel activity and TCR-stimulated Ca(2+) influx and cytokine production in Jurkat, primary human CD4 T cells, and Th0, Th1, and Th2 CD4 T cells generated from TRIM27(-/-) mice. These findings provide a unique mechanism for regulating class II PI3Ks, and identify TRIM27 as a previously undescribed negative regulator of CD4 T cells

Micro-RNAs (miRNAs) are short (average 22 nucleotides) noncoding regulatory RNAs that inhibit gene expression by targeting complementary 3'-untranslated regions of protein-encoding mRNAs for translational repression or degradation. miRNAs play key roles in both the function and differentiation of many cell types. Drosha and Dicer, two RNAase III enzymes, function in a stepwise manner to generate a mature miRNA. Previous studies have shown that podocyte-specific deletion of Dicer during development results in proteinuric renal disease and collapsing glomerulopathy (CG); however, Dicer has functions other than the generation of miRNAs. Here we found that the podocyte-specific deletion of Drosha results in a similar phenotype to Dicer mutants, confirming that the Dicer mutant phenotype is due to the loss of miRNAs. Moreover, the inducible deletion of Drosha in 2- to 3-month-old mice (Tet-On system) resulted in CG. Thus, continuous generation of miRNAs are required for the normal function of mature podocytes and their loss leads to CG. Identifying these miRNAs may provide new insight into disease pathogenesis and novel therapeutic targets in various podocytopathies

OBJECTIVES: Several studies have shown comparable results in long-term graft and patient survival, comparing a tacrolimus-based therapy to cyclosporine, while other studies have shown that a tacrolimus-based regimen had a better renal function with fewer episodes of acute rejection. Most of these studies were in a white population. We describe our experiences comparing tacrolimus versus cyclosporine maintenance therapy in a Saudi population. MATERIALS AND METHODS: All patients from 2003 until 2008 in our transplant clinic were evaluated. A retrospective analysis was done comparing patient and graft survival, kidney function, and metabolic profile. RESULTS: There was no statistical difference in acute rejection rate between the cyclosporine group and the tacrolimus group (18.7% vs 20.9%; P = .756). Mean serum creatinine was not statistically different between the 2 groups. Patient and graft survival at 1 and 2 years also were similar. Although patient and graft survival were similar, the cyclosporine group had a higher level of cholesterol compared with the tacrolimus group (4.6 +/- 1.03 mmol/L vs 4.1 +/- 0.80 mmol/L; P = .010). CONCLUSIONS: There is no difference in 1- or 2-year patient and graft survival between patients maintained on cyclosporine compared with tacrolimus. However, patients on cyclosporine had a higher blood pressure and serum cholesterol level

PURPOSE: To assess the accuracy of glomerular filtration rate (GFR) measurements obtained with low-contrast agent dose dynamic contrast material-enhanced magnetic resonance (MR) renography in patients with liver cirrhosis who underwent routine liver MR imaging, with urinary clearance of technetium 99m ((99m)Tc) pentetic acid (DTPA) as the reference standard. MATERIALS AND METHODS: This HIPAA-compliant study was institutional review board approved. Written informed patient consent was obtained. Twenty patients with cirrhosis (14 men, six women; age range, 41-70 years; mean age, 54.6 years) who were scheduled for routine 1.5-T liver MR examinations to screen for hepatocellular carcinoma during a 6-month period were prospectively included. Five-minute MR renography with a 3-mL dose of gadoteridol was performed instead of a routine test-dose timing examination. The GFR was estimated at MR imaging with use of two kinetic models. In one model, only the signal intensities in the aorta and kidney parenchyma were considered, and in the other, renal cortical and medullary signal intensities were treated separately. The GFR was also calculated by using serum creatinine levels according to the Cockcroft-Gault and modification of diet in renal disease (MDRD) formulas. All patients underwent a (99m)Tc-DTPA urinary clearance examination on the same day to obtain a reference GFR measurement. The accuracies of all MR- and creatinine-based GFR estimations were compared by using Wilcoxon signed rank tests. RESULTS: The mean reference GFR, based on (99m)Tc-DTPA clearance, was 74.9 mL/min/1.73 m(2) +/- 27.7 (standard deviation) (range, 10.3-120.7 mL/min/1.73 m(2)). With both kinetic models, 95% of MR-based GFRs were within 30% of the reference values, whereas only 40% and 60% of Cockcroft-Gault- and MDRD-based GFRs, respectively, were within this range. MR-based GFR estimates were significantly more accurate than creatinine level-based estimates (P < .001). CONCLUSION: GFR assessment with MR imaging, which outperformed the Cockcroft-Gault and MDRD formulas, adds less than 10 minutes of table time to a clinically indicated liver MR examination without ionizing radiation. Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101338/-/DC1

Nucleoside diphosphate kinases (NDPKs) are encoded by the Nme (non-metastatic cell) gene family. Although they comprise a family of 10 genes, NDPK-A and -B are ubiquitously expressed and account for most of the NDPK activity. We previously showed that NDPK-B activates the K(+) channel KCa3.1 via histidine phosphorylation of the C terminus of KCa3.1, which is required for T cell receptor-stimulated Ca(2+) flux and proliferation of activated naive human CD4 T cells. We now report the phenotype of NDPK-B(-/-) mice. NDPK-B(-/-) mice are phenotypically normal at birth with a normal life span. Although T and B cell development is normal in NDPK-B(-/-) mice, KCa3.1 channel activity and cytokine production are markedly defective in T helper 1 (Th1) and Th2 cells, whereas Th17 function is normal. These findings phenocopy studies in the same cells isolated from KCa3.1(-/-) mice and thereby support genetically that NDPK-B functions upstream of KCa3.1. NDPK-A and -B have been linked to an astonishing array of disparate cellular and biochemical functions, few of which have been confirmed in vivo in physiological relevant systems. NDPK-B(-/-) mice will be an essential tool with which to definitively address the biological functions of NDPK-B. Our finding that NDPK-B is required for activation of Th1 and Th2 CD4 T cells, together with the normal overall phenotype of NDPK-B(-/-) mice, suggests that specific pharmacological inhibitors of NDPK-B may provide new opportunities to treat Th1- and Th2-mediated autoimmune diseases

Chronic kidney disease (CKD) accelerates cardiovascular disease. The mechanisms that explain this independent, excess risk associated with CKD have not been fully elucidated. OBJECTIVES: We propose that impaired regression of atherosclerosis in renal disease represents a novel risk factor for the heightened morbidity and mortality and resistance to treatment observed in patients with CKD. METHODS AND RESULTS: Using a transplant model to study atherosclerosis regression, we transplanted atheromatous aortic segments generated in Apolipoprotein E knock-out (ApoE(-/-)) mice, into either control or moderately uremic, normolipidemic, wild-type mice. In non-uremic mice, lesions regressed 55%, whereas lesions in uremic mice increased in size by 17% (p<0.01 for control vs. uremic). The lesions in uremic mice were also characterized by a greater presence of macrophages (36,300 microm(2) vs. 12,600 microm(2), p<0.01). This finding was despite upregulation of chemokine receptor 7 (CCR7), normally a migration factor, in uremic lesion macrophages. Gene expression analysis of lesion macrophages showed relative down-regulation of serum response factor (SRF) target genes in the uremic group, consistent with impaired CCR7 signaling. CONCLUSION: Moderate kidney disease inhibits regression of atherosclerosis in a mouse transplant model. This inhibition may be a result of impaired CCR7 signaling