Biology subjects

Anthony W Segal

Publications and source records attributed to Anthony W Segal.

3 recordsLinked to original sources

bioRxiv2016

Insights into the genetic epidemiology of Crohn’s and rare diseases in the Ashkenazi Jewish population

As part of a broader collaborative network of exome sequencing studies, we developed a jointly called data set of 5,685 Ashkenazi Jewish exomes. We make publicly available a resource of site and allele frequencies, which should serve as a reference for medical genetics in the Ashkenazim. We estimate that 30% of protein-coding alleles present in the Ashkenazi Jewish population at frequencies greater than 0.2% are significantly more frequent (mean 7.6-fold) than their maximum frequency observed in other reference populations. Arising via a well-described founder effect, this catalog of enriched alleles can contribute to differences in genetic risk and overall prevalence of diseases between populations. As validation we document 151 AJ enriched protein-altering alleles that overlap with \"pathogenic\" ClinVar alleles, including those that account for 10-100 fold differences in prevalence between AJ and non-AJ populations of some rare diseases including Gaucher disease (GBA, p.Asn409Ser, 8-fold enrichment); Canavan disease (ASPA, p.Glu285Ala, 12-fold enrichment); and Tay-Sachs disease (HEXA, c.1421+1G>C, 27-fold enrichment; p.Tyr427IlefsTer5, 12-fold enrichment). We next sought to use this catalog, of well-established relevance to Mendelian disease, to explore Crohns disease, a common disease with an estimated two to four-fold excess prevalence in AJ. We specifically evaluate whether strong acting rare alleles, enriched by the same founder-effect, contribute excess genetic risk to Crohns disease in AJ, and find that ten rare genetic risk factors in NOD2 and LRRK2 are strongly enriched in AJ, including several novel contributing alleles, show evidence of association to CD. Independently, we find that genomewide common variant risk defined by GWAS shows a strong difference between AJ and non-AJ European control population samples (0.97 s.d. higher, p<10-16). Taken together, the results suggest coordinated selection in AJ population for higher CD risk alleles in general. The results and approach illustrate the value of exome sequencing data in case-control studies along with reference data sets like ExAC to pinpoint genetic variation that contributes to variable disease predisposition across populations.

Genetics↗

bioRxiv2015

The NADPH oxidase and microbial killing by neutrophils, with a particular emphasis on the proposed antimicrobial role of myeloperoxidase within the phagocytic vacuole

This review is devoted to a consideration of the way in which the NADPH oxidase of neutrophils, NOX2, functions to enable the efficient killing of bacteria and fungi. It includes a critical examination of the current dogma that its primary purpose is the generation of hydrogen peroxide as substrate for myeloperoxide catalysed generation of hypochlorite. Instead it is demonstrated that NADPH oxidase functions to optimise the ionic and pH conditions within the vacuole for the solubilisation and optimal activity of the proteins released into this compartment from the cytoplasmic granules, which kill and digest the microbes. The general role of other NOX systems as electrochemical generators to alter the pH and ionic composition in compartments on either side of a membrane in plants and animals will also be examined.

Immunology↗

bioRxiv2014

The HVCN1 channel conducts protons into the phagocytic vacuole of neutrophils to produce a physiologically alkaline pH

Activation of the NADPH oxidase (NOX2) of the phagocytic vacuole of neutrophils is essential for innate immunity. Sustained activity of the oxidase requires that charge movements across the membrane are balanced. A role for the proton channel, HVCN1, has been proposed but not proven. Using the ratiometric pH indicator SNARF, introduced into the cytosol and separately into the vacuole coupled to Candida, we used confocal microscopy to measure changes in pH in these two compartments in human and mouse neutrophils. Shortly after phagocytosis by human cells, the vacuolar pH rose to ~9, at which it was maintained for ~20 minutes, while the cytosol showed a small acidification of ~0.25 pH unit. Alkalinisation has important consequences for the microbicidal and digestive functions of vacuolar enzymes. In HVCN1 knock out mouse neutrophils, the phagocytosis induced respiratory burst was halved to ~3 fmols per Candida, the vacuolar pH rose to >11 and the cytosol acidified excessively to pH ~6.75. These changes were prevented by the protonophore CCCP. The rate of extrusion of protons into the extracellular medium following phagocytosis was not significantly different from wild type neutrophils suggesting that cytoplasmic acidification resulted from the loss of the proton sink into the vacuole. HVCN1 phagocytic vacuoles showed considerable swelling, and this was blocked by CCCP and decreased by valinomycin. Stoichiometric considerations indicated that the HVCN1 channel compensates 90-95% of the oxidase-induced charge in normal cells, and in its absence, charge is carried by ions other than protons, including K+.

Cell Biology↗