Mamdouh Albaqumi

Histidine Phosphorylation of the Potassium Channel KCa3.1 by Nucleoside Diphosphate Kinase B Is Required for Activation of KCa3.1 and CD4 T Cells

The Ca2+ -activated K+ channel KCa3.1 is required for Ca2+ influx and the subsequent activation of B and T cells. Inhibitors of KCa3.1 are in development to treat autoimmune diseases and transplant rejection, underscoring the importance in understanding how these channels are regulated. We show that nucleoside diphosphate kinase B (NDPK-B), a mammalian histidine kinase, functions downstream of PI(3)P to activate KCa3.1. NDPK-B directly binds and activates KCa3.1 by phosphorylating histidine 358 in the carboxyl terminus of KCa3.1. Endogenous NDPK-B is also critical for KCa3.1 channel activity and the subsequent activation of CD4 T cells. These findings provide one of the best examples whereby histidine phosphorylation regulates a biological process in mammals, and provide an example whereby a channel is regulated by histidine phosphorylation. The critical role for NDPK-B in the reactivation of CD4 T cells indicates that understanding NDPK-B regulation should uncover novel pathways required for T cell activation.

Protein histidine phosphatase 1 negatively regulates CD4 T cells by inhibiting the K+ channel KCa3.1

The calcium activated K+ channel KCa3.1 plays an important role in T lymphocyte Ca2+ signaling by helping to maintain a negative membrane potential, which provides an electrochemical gradient to drive Ca2+ influx. We previously showed that nucleoside diphosphate kinase beta (NDPK-B), a mammalian histidine kinase, is required for KCa3.1 channel activation in human CD4 T lymphocytes. We now show that the mammalian protein histidine phosphatase (PHPT-1) directly binds and inhibits KCa3.1 by dephosphorylating histidine 358 on KCa3.1. Overexpression of wild-type, but not a phosphatase dead, PHPT-1 inhibited KCa3.1 channel activity. Decreased expression of PHPT-1 by siRNA in human CD4 T cells resulted in an increase in KCa3.1 channel activity and increased Ca2+ influx and proliferation after T cell receptor (TCR) activation, indicating that endogenous PHPT-1 functions to negatively regulate CD4 T cells. Our findings provide a previously unrecognized example of a mammalian histidine phosphatase negatively regulating TCR signaling and are one of the few examples of histidine phosphorylation/dephosphorylation influencing a biological process in mammals.

KCa3.1 potassium channels are critical for cAMP-dependent chloride secretion and cyst growth in autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is characterized by numerous fluid-filled kidney cysts. Net fluid secretion into renal cysts is caused by transepithelial transport mediated by the apical cystic fibrosis transmembrane conductance regulator chloride channel, which leads to cyst enlargement. Here we found that forskolin, a potent adenylyl cyclase agonist, stimulated anion secretion by monolayers of kidney cells derived from patients with ADPKD. TRAM-34, a specific KCa3.1 potassium channel blocker, inhibited this current, and in vitro cyst formation and enlargement by the cells cultured within a collagen gel. Net chloride secretion was enhanced by the KCa3.1 activator DCEBIO and both chloride secretion and in vitro cyst growth were inhibited by overexpression of myotubularin-related protein-6, a phosphatase that specifically inhibits KCa3.1 channel activity. Our study suggests that KCa3.1 channels play a critical role in transcellular chloride secretion and net fluid transport into the kidney cysts of patients with ADPKD by maintaining the electrochemical driving force for chloride efflux through apical chloride channels. Pharmacological inhibitors of KCa3.1 channels may provide a novel and effective therapy to delay progression to kidney failure in patients with ADPKD.

Specificity of the Myotubularin Family of Phosphatidylinositol-3-phosphatase Is Determined by the PH/GRAM Domain

Myotubularins (MTM) are a large subfamily of lipid phosphatases that specifically dephosphorylate at the D3 position of phosphatidylinositol 3-phosphate (PI(3)P) in PI(3)P and PI(3,5)P2. We recently found that MTMR6 specifically inhibits the Ca2+-activated K+ channel, KCa3.1, by dephosphorylating PI(3)P. We now show that inhibition is specific for MTMR6 and other MTMs do not inhibit KCa3.1. By replacing either or both of the coiled-coil (CC) and pleckstrin homology/GRAM (PH/G) domains of MTMs that failed to inhibit KCa3.1 with the CC and PH/G domains of MTMR6, we found that chimeric MTMs containing both the MTMR6 CC and PH/G domains functioned like MTMR6 to inhibit KCa3.1 channel activity, whereas chimeric MTMs containing either domain alone did not. Immunofluorescent microscopy demonstrated that both the MTMR6 CC and PH/G domains are required to co-localize MTMR6 to the plasma membrane with KCa3.1. These findings support a model in which two specific low affinity interactions are required to co-localize MTMR6 with KCa3.1: 1) between the CC domains on MTMR6 and KCa3.1 and (2) between the PH/G domain and a component of the plasma membrane. Our inability to detect significant interaction of the MTMR6 G/PH domain with phosphoinositides suggests that this domain may bind a protein. Identifying the specific binding partners of the CC and PH/G domains on other MTMs will provide important clues to the specific functions regulated by other MTMs as well as the mechanism(s) whereby loss of some MTMs lead to disease.

Transplant tourism outcome: a single center experience.

Background. Transplant tourism is the term used for patients who travel abroad for transplantation. Transplant tourism has always been surrounded with controversy regarding how these organs were obtained, the donors care after transplantation, and the recipient outcome. Many authors have found that the outcome of the recipients in transplant tourism is inferior to those transplanted in their own countries. However, most these studies were small, with the latest one including only 33 patients. Here, we describe the outcome of 93 patients who were transplanted abroad compared with local transplantation. Material and Methods. All transplant patients who were followed up at our Nephrology Clinic from 1998 until 2008 were identified using our data base system. We selected patients transplanted from 2003 and forward because the computerized system for laboratory and electronic records began operation that year. Results. A total of 165 patients were identified (93 in the tourist group and 72 in the local one). Transplant tourists had a higher rate of acute rejection in the first year compared with local transplantation (27.9% vs. 9.9, P=0.005), higher mean creatinine at 6 months and 1 year (120 vs. 101 &mgr;mol/L, P=0.0007, 113 vs. 98 &mgr;mol/L, P=0.008). There was no statistical difference in graft or patient survival in 1 or 2 years after transplantation. However, transplant tourist had a higher rate of cytomegalovirus infection (15.1% vs. 5.6%, P=0.05) and hepatitis C seroconversion (7.5% vs. 0%, P=0.02). Conclusion. Transplant tourists had a more complex posttransplantation course with higher incidence of acute rejection and infectious complications.

Regression of brown tumor of the maxilla in a patient with secondary hyperparathyroidism after a parathyroidectomy

Brown tumors or osteoclastomas are erosive bony lesions arising as a complication of hyperparathyroidism. In patients with end‐stage renal disease, brown tumors are uncommon skeletal manifestations that are usually seen in severe forms of secondary hyperparathyroidism. Initial treatment involves the correction of hyperparathyroidism, which usually leads to regression of the tumors. We report a case of brown tumors of the maxilla in a 24‐year‐old female referred to us by a local hospital, where she had been on regular hemodialysis for >10 years. After a complete biochemical and radiological workup, she underwent a total parathyroidectomy, which subsequently resulted in significant regression of her tumor.

Proteomic analysis of Class IV lupus nephritis

BACKGROUND There have been several attempts to standardize the definition and increase reproducibility in classifying lupus nephritis (LN). The last was made by the International Society of Nephrology and Renal Pathology Society in 2003 where the introduction of Class IV subcategories (global and segmental) was introduced. METHODS We investigated whether this subdivision is important using a proteomics approach. All patients with renal biopsies along with their clinical outcome of LN were identified and regrouped according to the above 2003 classifications. Fresh-frozen renal biopsies of Class IV LN (global and segmental), antineutrophil cytoplasmic antibody-associated vasculitis and normal tissue were analyzed using two-dimensional gel electrophoresis (2-DE) and mass spectrometry. Differentially expressed proteins were identified and subjected to principal component analysis (PCA), and post hoc analysis for the four sample groups. RESULTS PCA of 72 differentially expressed spots separated Class IV global and Class IV segmental from both normal and antineutrophil cytoplasmic antibody-associated vasculitis (ANCA). The 28 identified proteins were used in a post hoc analysis, and showed that IV-global and IV-segmental differ in several protein expression when compared with normal and ANCA. To confirm the proteomic results, a total of 78 patients (50 Class IV-Global and 28 Class IV-Segmental) were re-classified according to 2003 classification. There was no difference in therapy between the groups. The renal survival and patient survivals were similar in both groups. CONCLUSIONS There is no strong evidence to support a different outcome between the two subcategories of Class-IV LN and, they should thus be treated the same until further studies indicate otherwise.

Vascular access types in patients starting hemodialysis after failed kidney transplant: does close nephrology follow-up matter?

Background Native arteriovenous fistulae (AVFs) are preferred while central venous catheters (CVCs) are least suitable vascular access (VA) in patients requiring hemodialysis (HD). Unfortunately, around 80% of patients start HD with CVCs. Late referral to nephrologist is thought to be a factor responsible for this. We retrospectively analyzed the types of VA at HD initiation in renal transplant recipients followed by nephrologists with failed transplant. If early referral to nephrologist improves AVF use, these patients should have higher prevalence of AVF at HD initiation. Methods All patients who failed their kidney transplants from January 2002 to April 2013 were included in the study. Data regarding planning of VA by nephrologist, documented discussion about renal replacement therapy (RRT), estimated glomerular filtration rate (eGFR) at 6 months and last clinic visit before HD initiation, time of VA referral, and subsequent VA at dialysis initiation were gathered and analyzed. Results Eighty-three patients failed their transplants during study period. Data were inaccessible in six patients. Eleven patients started peritoneal dialysis (PD) while 66 started HD. Thirty-two had previous functioning VA while 34 needed VA. There were 11/34 patients (32%) with eGFR <15 mL/min at six months while 21/34 (61%) had eGFR <15 mL/min at last clinic visit before HD initiation. Only 11/34 (32%) had documented RRT discussion, 8/34 (24%) had VA referral, and 7/34 (21%) had vein mapping. A total of 30/34 (88.3%) started HD with CVC while 4/34 (11.3%) started HD with AVF (p<0.0001). Conclusions Early referral to nephrologist by itself may not improve VA care amongst patient with end-stage renal disease.

Peritoneal Dialysis Catheter Placement with Peritoneoscopic Technique and Successful Initiation of Peritoneal Dialysis in a Patient with Diastasis Recti

Preserved anatomical integrity of the anterior abdominal wall is considered important in the presurgical evaluation of a patient who is being considered for placement of a peritoneal dialysis (PD) catheter. Diastasis recti abdominis (DRA) is the excessive widening or separation between the two bellies of the rectus abdominis muscle. The separation can occur anywhere along the linea alba and at times has been found to span the entire length from the xiphosternal angle to the pubic bone. Presence of DRA can pose a surgical challenge in the peritoneoscopic placement of peritoneal dialysis catheter. In this report, we discuss a case of successful placement of peritoneal dialysis catheter with peritoneoscope technique and successful initiation of peritoneal dialysis in a chronic kidney disease patient with DRA.