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Congenital macrothrombocytopenia with focal myelofibrosis due to mutations in human G6b-B is rescued in humanized mice.

ABSTRACT: Unlike primary myelofibrosis (PMF) in adults, myelofibrosis in children is rare. Congenital (inherited) forms of myelofibrosis (cMF) have been described, but the underlying genetic mechanisms remain elusive. Here we describe 4 families with autosomal recessive inherited macrothrombocytopenia with focal myelofibrosis due to germ line loss-of-function mutations in the megakaryocyte-specific immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptor G6b-B (G6b, C6orf25, or MPIG6B). Patients presented with a mild-to-moderate bleeding diathesis, macrothrombocytopenia, anemia, leukocytosis and atypical megakaryocytes associated with a distinctive, focal, perimegakaryocytic pattern of bone marrow fibrosis. In addition to identifying the responsible gene, the description of G6b-B as the mutated protein potentially implicates aberrant G6b-B megakaryocytic signaling and activation in the pathogenesis of myelofibrosis. Targeted insertion of human G6b in mice rescued the knockout phenotype and a copy number effect of human G6b-B expression was observed. Homozygous knockin mice expressed 25% of human G6b-B and exhibited a marginal reduction in platelet count and mild alterations in platelet function; these phenotypes were more severe in heterozygous mice that expressed only 12% of human G6b-B. This study establishes G6b-B as a critical regulator of platelet homeostasis in humans and mice. In addition, the humanized G6b mouse will provide an invaluable tool for further investigating the physiological functions of human G6b-B as well as testing the efficacy of drugs targeting this receptor.

SUBMITTER: Hofmann I

PROVIDER: S-EPMC6161765 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Congenital macrothrombocytopenia with focal myelofibrosis due to mutations in human G6b-B is rescued in humanized mice.

Hofmann Inga I Geer Mitchell J MJ Vögtle Timo T Crispin Andrew A Campagna Dean R DR Barr Alastair A Calicchio Monica L ML Heising Silke S van Geffen Johanna P JP Kuijpers Marijke J E MJE Heemskerk Johan W M JWM Eble Johannes A JA Schmitz-Abe Klaus K Obeng Esther A EA Douglas Michael M Freson Kathleen K Pondarré Corinne C Favier Rémi R Jarvis Gavin E GE Markianos Kyriacos K Turro Ernest E Ouwehand Willem H WH Mazharian Alexandra A Fleming Mark D MD Senis Yotis A YA

Blood 20180613 13

Unlike primary myelofibrosis (PMF) in adults, myelofibrosis in children is rare. Congenital (inherited) forms of myelofibrosis (cMF) have been described, but the underlying genetic mechanisms remain elusive. Here we describe 4 families with autosomal recessive inherited macrothrombocytopenia with focal myelofibrosis due to germ line loss-of-function mutations in the megakaryocyte-specific immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptor G6b-B (<i>G6b</i>, <i>C6orf25</i>, ...[more]

PMID: 29898956

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Project description:The importance of glucokinase (GK) in the regulation of insulin secretion has been highlighted by the phenotypes of individuals with activating and inactivating mutations in the glucokinase gene (GCK). Here we report 10 individuals with congenital hyperinsulinism (HI) caused by eight unique activating mutations of GCK. Six are novel and located near previously identified activating mutations sites. The first recognized episode of hypoglycemia in these patients occurred between birth and 24 years, and the severity of the phenotype was also variable. Mutant enzymes were expressed and purified for enzyme kinetics in vitro. Mutant enzymes had low glucose half-saturation concentration values and an increased enzyme activity index compared with wild-type GK. We performed functional evaluation of islets from the pancreata of three children with GCK-HI who required pancreatectomy. Basal insulin secretion in perifused GCK-HI islets was normal, and the response to glyburide was preserved. However, the threshold for glucose-stimulated insulin secretion in perifused glucokinase hyperinsulinism (GCK-HI) islets was decreased, and glucagon secretion was greatly suppressed. Our evaluation of novel GCK disease-associated mutations revealed that the detrimental effects of these mutations on glucose homeostasis can be attributed not only to a lowering of the glucose threshold of insulin secretion but also to a decreased counterregulatory glucagon secretory response.Article highlightsOur evaluation of six novel and two previously published activating GCK mutations revealed that the detrimental effects of these mutations on glucose homeostasis can be attributed not only to a lowering of the glucose threshold of insulin secretion but also to a decreased counterregulatory glucagon secretory response. These studies provide insights into the pathophysiology of GCK-hyperinsulinism and the dual role of glucokinase in β-cells and α-cells to regulate glucose homeostasis.

Dataset Information

Congenital macrothrombocytopenia with focal myelofibrosis due to mutations in human G6b-B is rescued in humanized mice.

Publications

Congenital macrothrombocytopenia with focal myelofibrosis due to mutations in human G6b-B is rescued in humanized mice.

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