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Articles by Khalid Iqbal
Total Records ( 7 ) for Khalid Iqbal
  Khalid Iqbal and Inge Grundke-Iqbal
  Alzheimer’s disease (AD) is multifactorial and apparently involves several different etiopathogenic mechanisms. There are at least five subgroups of AD based on cerebrospinal fluid levels of Aβ1–42, a marker of beta-amyloid (Aβ) plaques, and tau and ubiquitin, two markers of neurofibrillary tangles. These different AD subgroups may respond differently to a given disease-modifying drug, and hence, different therapeutic drugs for different disease subgroups might be required. Stratification of AD patients by disease subgroups in clinical trials is critical to the successful development of potent disease-modifying drugs. Levels of disease markers in the cerebrospinal fluid are promising, both in identifying various subgroups of AD and in monitoring the response to therapeutic drugs.
  Niklas Mattsson , Ulf Andreasson , Staffan Persson , Hiroyuki Arai , Sat Dev Batish , Sergio Bernardini , Luisella Bocchio- Chiavetto , Marinus A. Blankenstein , Maria C. Carrillo , Sonia Chalbot , Els Coart , Davide Chiasserini , Neal Cutler , Gunilla Dahlfors , Stefan Duller , Anne M. Fagan , Orestes Forlenza , Giovanni B. Frisoni , Douglas Galasko , Daniela Galimberti , Harald Hampel , Aase Handberg , Michael T. Heneka , Adrianna Z. Herskovits , Sanna-Kaisa Herukka , David M. Holtzman , Christian Humpel , Bradley T. Hyman , Khalid Iqbal , Khalid Iqbal , Stephan A. Kaeser , Elmar Kaiser , Elisabeth Kapaki , Daniel Kidd , Peter Klivenyi , Cindy S. Knudsen , Markus P. Kummer , James Lui , Albert Llado , Piotr Lewczuk , Qiao-Xin Li , Ralph Martins , Colin Masters , John McAuliffe , Marc Mercken , Abhay Moghekar , Jose Luis Molinuevo , Thomas J. Montine , William Nowatzke , Richard O’Brien , Markus Otto , George P. Paraskevas , Lucilla Parnetti , Ronald C. Petersen , David Prvulovic , Herman P.M. de Reus , Robert A. Rissman , Elio Scarpini , Alessandro Stefani , Hilkka Soininen , Johannes Schroder , Leslie M. Shaw , Anders Skinningsrud , Brith Skrogstad and Annette Spreer
  Background The cerebrospinal fluid (CSF) biomarkers amyloid β (Aβ)-42, total-tau (T-tau), and phosphorylated-tau (P-tau) demonstrate good diagnostic accuracy for Alzheimer‘s disease (AD). However, there are large variations in biomarker measurements between studies, and between and within laboratories. The Alzheimer‘s Association has initiated a global quality control program to estimate and monitor variability of measurements, quantify batch-to-batch assay variations, and identify sources of variability. In this article, we present the results from the first two rounds of the program. Methods The program is open for laboratories using commercially available kits for Aβ, T-tau, or P-tau. CSF samples (aliquots of pooled CSF) are sent for analysis several times a year from the Clinical Neurochemistry Laboratory at the Molndal campus of the University of Gothenburg, Sweden. Each round consists of three quality control samples. Results Forty laboratories participated. Twenty-six used INNOTEST enzyme-linked immunosorbent assay kits, 14 used Luminex xMAP with the INNO-BIA AlzBio3 kit (both measure Aβ-(1-42), P-tau(181P), and T-tau), and 5 used Meso Scale Discovery with the Aβ triplex (AβN-42, AβN-40, and AβN-38) or T-tau kits. The total coefficients of variation between the laboratories were 13% to 36%. Five laboratories analyzed the samples six times on different occasions. Within-laboratory precisions differed considerably between biomarkers within individual laboratories. Conclusions Measurements of CSF AD biomarkers show large between-laboratory variability, likely caused by factors related to analytical procedures and the analytical kits. Standardization of laboratory procedures and efforts by kit vendors to increase kit performance might lower variability, and will likely increase the usefulness of CSF AD biomarkers.
  Niklas Mattsson , Ulf Andreasson , Staffan Persson , Maria C. Carrillo , Steven Collins , Sonia Chalbot , Neal Cutler , Diane Dufour- Rainfray , Anne M. Fagan , Niels H.H. Heegaard , Ging-Yuek Robin Hsiung , Bradley Hyman , Khalid Iqbal , D. Richard Lachno , Alberto Lleo , Piotr Lewczuk , Jose L. Molinuevo , Piero Parchi , Axel Regeniter , Robert Rissman , Hanna Rosenmann , Giuseppe Sancesario , Johannes Schroder , Leslie M. Shaw , Charlotte E. Teunissen , John Q. Trojanowski , Hugo Vanderstichele , Manu Vandijck , Marcel M. Verbeek , Henrik Zetterberg , Kaj Blennow and Stephan A. Kaser
  Background The cerebrospinal fluid (CSF) biomarkers amyloid beta 1–42, total tau, and phosphorylated tau are used increasingly for Alzheimer's disease (AD) research and patient management. However, there are large variations in biomarker measurements among and within laboratories. Methods Data from the first nine rounds of the Alzheimer's Association quality control program was used to define the extent and sources of analytical variability. In each round, three CSF samples prepared at the Clinical Neurochemistry Laboratory (Molndal, Sweden) were analyzed by single-analyte enzyme-linked immunosorbent assay (ELISA), a multiplexing xMAP assay, or an immunoassay with electrochemoluminescence detection. Results A total of 84 laboratories participated. Coefficients of variation (CVs) between laboratories were around 20% to 30%; within-run CVs, less than 5% to 10%; and longitudinal within-laboratory CVs, 5% to 19%. Interestingly, longitudinal within-laboratory CV differed between biomarkers at individual laboratories, suggesting that a component of it was assay dependent. Variability between kit lots and between laboratories both had a major influence on amyloid beta 1–42 measurements, but for total tau and phosphorylated tau, between-kit lot effects were much less than between-laboratory effects. Despite the measurement variability, the between-laboratory consistency in classification of samples (using prehoc-derived cutoffs for AD) was high (>90% in 15 of 18 samples for ELISA and in 12 of 18 samples for xMAP). Conclusions The overall variability remains too high to allow assignment of universal biomarker cutoff values for a specific intended use. Each laboratory must ensure longitudinal stability in its measurements and use internally qualified cutoff levels. Further standardization of laboratory procedures and improvement of kit performance will likely increase the usefulness of CSF AD biomarkers for researchers and clinicians.
  Khalid Iqbal and Mohammad Aslam Chowdhary
  Combining ability studies were performed for plant height, spike length, number of spikelets per spike, number of grains per spike, grain weight per spike and 1000-grain weight in a set of diallel crosses involving five spring wheat genotypes. Significant variation was found in all six characters. General combining ability (GC), specific combining ability (SCA) and reciprocal effects were significant. Additive gene action was found for the characters under study. Best general combiners and the best cross combinations were identified for future breeding programme.
  Mahboob Akhtar , Asjad Mehmood , Jalil Ahmad and Khalid Iqbal
  Nitrogen uptake efficiency in wheat (Tritcum aestivum L.) as influenced by nitrogen level and weed-crop competition duration was determined at the Agronomic Research Area, University of Agriculture, Faisalabad during 1998-99. The data showed that yield, yield parameters of wheat, weed growth and nitrogen uptake by weeds increased with increased nitrogen application levels while weed population was not affected significantly. On the other hand yield and yield parameters in wheat decreased with an increase in the weed-crop competition durations while weed growth and nitrogen uptake by weeds increased by increasing the competition duration.
  She Chen , Bin Li , Inge Grundke-Iqbal and Khalid Iqbal
  In Alzheimer disease (AD) brain, the level of I PP2A1, a 249-amino acid long endogenous inhibitor of protein phosphatase 2A (PP2A), is increased, the activity of the phosphatase is decreased, and the microtubule-associated protein Tau is abnormally hyperphosphorylated. However, little is known about the detailed regulatory mechanism by which PP2A activity is inhibited by I PP2A1 and the consequent events in mammalian cells. In this study, we found that both I PP2A1 and its N-terminal half I PP2A(1–120)1, but neither I PP2A(1–163)1 nor I PP2A(164–249)1, inhibited PP2A activity in vitro, suggesting an autoinhibition by amino acid residues 121–163 and its neutralization by the C-terminal region. Furthermore, transfection of NIH3T3 cells produced a dose-dependent inhibition of PP2A activity by I PP2A1. I PP2A1 and PP2A were found to colocalize in PC12 cells. I PP2A1 could only interact with the catalytic subunit of PP2A (PP2Ac) and had no interaction with the regulatory subunits of PP2A (PP2A-A or PP2A-B) using a glutathione S-transferase-pulldown assay. The interaction was further confirmed by coimmunoprecipitation of I PP2A1 and PP2Ac from lysates of transiently transfected NIH3T3 cells. The N-terminal isotype specific region of I PP2A1 was required for its association with PP2Ac as well as PP2A inhibition. In addition, the phosphorylation of Tau was significantly increased in PC12/Tau441 cells transiently transfected with full-length I PP2A1 and with PP2Ac-interacting I PP2A1 deletion mutant 1–120 (I PP2A1ΔC2). Double immunofluorescence staining showed that I PP2A1 and I PP2A1ΔC2 increased Tau phosphorylation and impaired the microtubule network and neurite outgrowth in PC12 cells treated with nerve growth factor.
  Jianhua Shi , Tianyi Zhang , Chunlei Zhou , Muhammad Omar Chohan , Xiaosong Gu , Jerzy Wegiel , Jianhua Zhou , Yu-Wen Hwang , Khalid Iqbal , Inge Grundke-Iqbal , Cheng-Xin Gong and Fei Liu
  Two groups of tau, 3R- and 4R-tau, are generated by alternative splicing of tau exon 10. Normal adult human brain expresses equal levels of them. Disruption of the physiological balance is a common feature of several tauopathies. Very early in their life, individuals with Down syndrome (DS) develop Alzheimer-type tau pathology, the molecular basis for which is not fully understood. Here, we demonstrate that Dyrk1A, a kinase encoded by a gene in the DS critical region, phosphorylates alternative splicing factor (ASF) at Ser-227, Ser-234, and Ser-238, driving it into nuclear speckles and preventing it from facilitating tau exon 10 inclusion. The increased dosage of Dyrk1A in DS brain due to trisomy of chromosome 21 correlates to an increase in 3R-tau level, which on abnormal hyperphosphorylation and aggregation of tau results in neurofibrillary degeneration. Imbalance of 3R- and 4R-tau in DS brain by Dyrk1A-induced dysregulation of alternative splicing factor-mediated alternative splicing of tau exon 10 represents a novel mechanism of neurofibrillary degeneration and may help explain early onset tauopathy in individuals with DS.
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