Natural history and early diagnosis of LAD-1/variant syndrome

The syndrome of leukocyte adhesion deficiency (LAD) combined with a severe Glanzmann-type bleeding disorder has been recognized as a separate disease entity. The variability in clinical and cell biological terms has remained largely unclear. We present data on 9 cases from 7 unrelated families, with 3 patients being actively followed for more than 12 years. The disease entity, designated LAD-1/variant syndrome, presents early in life and consists of nonpussing infections from bacterial and fungal origin, as well as a severe bleeding tendency. This is compatible with 2 major blood cell types contributing to the clinical symptoms (ie, granulocytes and platelets). In granulocytes of the patients, we found adhesion and chemotaxis defects, as well as a defect in NADPH oxidase activity triggered by unopsonized zymosan. This last test can be used as a screening test for the syndrome. Many proteins and genes involved in adhesion and signaling, including small GTPases such as Rap1 and Rap2 as well as the major Rap activity-regulating molecules, were normally present. Moreover, Rap1 activation was intact in patients' blood cells. Defining the primary defect awaits genetic linkage analysis, which may be greatly helped by a more precise understanding and awareness of the disease combined with the early identification of affected patients.     

A frequently occurring mutation in the lipoprotein lipase gene (Asn291Ser) contributes to the expression of familial combined hyperlipidemia

We performed denaturing gradient gel electrophor-esis (DGGE)of exons 4, 5, 6 and their exon-intron boundaries of the LPL-genein 169 unrelated male patients suffering from familial combinedhyperlipide-mia (FCH). Twenty patients were found to carry anucleotide substitution in exon 6. Sequence and PCR/ digestionanalysis revealed one common mutation (Asn291Ser) in all thesecases. This mutation was also present in 215 male controls,albeit at a lower frequency than in FCH patients (10/215 = 4.6% vs. 20/ 169 = 11. 8% p <0. 02). Analysis of lipid, lipoproteinand apolipoprotein levels demonstrated an association betweenthe presence of this Asn291Ser substitution and decreased HDL-cholesterol(0. 94 ± 0. 31 vs. 1. 12 ± 0. 26 mmol/ l; p <0. 04) in our controls. FCH patients carrying this mutationshowed decreased HDL-cholesterol (0.75 ± 0. 16 vs. 0.95 ± 0.36 mmol/l; p = 0. 05) and increased triglyceridelevels (5. 96 ± 4. 12 vs. 3.48 ± 1.78 mmol/ l;p < 0. 005) compared to non-carriers. The high triglycerideand low HDL-cholesterol phenotype in carriers of this substitutionwas most obvious when BMI exceded 27 kg/ m². Our study of maleFCH patients revealed the presence of a common mutation in theLPL-gene that is associated with lipoprotein abnormalities,indicating that defective LPL is at least one of the factorscontributing to the FCH-phenotype.     

Hermansky–Pudlak syndrome type 2: Aberrant pre‐mRNA splicing and mislocalization of granule proteins in neutrophils

Hermansky–Pudlak syndrome type 2 (HPS2) is a syndrome caused by mutations in the beta‐3A subunit of the adaptor protein (AP)‐3 complex (AP3B1 gene). We describe five unreported cases with four novel mutations, one of which caused aberrant pre‐mRNA splicing. A point mutation c.2702C>G in exon 23 of the AP3B1 gene caused deletion of 112 bp in the mRNA in two siblings. This mutation activates a cryptic donor splice site that overrules the wild‐type donor splice site of this exon. Three other novel mutations in AP3B1 were identified, that is, a nonsense mutation c.716G>A (p.Trp239Ter), a 1‐bp and a 4‐bp deletion c.177delA and c.1839_1842delTAGA, respectively, both causing frameshift and premature termination of translation. Mass spectrometry in four of these HPS2 patients demonstrated the (near) absence of all AP‐3 complex subunits. Immunoelectron microscopy on the neutrophils of two of these patients showed abnormal granule formation. We found clear mislocalization of myeloperoxidase in the neutrophils even though the content of this protein but not the activity seemed to be present at normal levels. In sum, HPS2 is the result of the absence of the entire AP‐3 complex, which results in severe neutropenia with a defect in granule formation as the major hematological finding.     

Granulocyte colony-stimulating factor inhibits the mitochondria-dependent activation of caspase-3 in neutrophils.

The exact mechanism of apoptosis in neutrophils (PMNs) and the explanation for the antiapoptotic effect of granulocyte colony-stimulating factor (G-CSF) in PMNs are unclear. Using specific fluorescent mitochondrial staining, immunofluorescent confocal microscopy, Western blotting, and flow cytometry, this study found that PMNs possess an unexpectedly large number of mitochondria, which are involved in apoptosis. Spontaneous PMN apoptosis was associated with translocation of the Bcl-2-like protein Bax to the mitochondria and subsequent caspase-3 activation, but not with changes in the expression of Bax. G-CSF delayed PMN apoptosis and prevented both associated events. These G-CSF effects were inhibited by cycloheximide. The general caspase inhibitor z-Val-Ala-DL-Asp-fluoromethylketone (zVAD-fmk) prevented caspase-3 activation and apoptosis in PMNs, but not Bax redistribution. PMN-derived cytoplasts, which lack a nucleus, granules, and mitochondria, spontaneously underwent caspase-3 activation and apoptosis (phosphatidylserine exposure), without Bax redistribution. zVAD-fmk inhibited both caspase-3 activation and phosphatidylserine exposure in cultured cytoplasts. Yet, G-CSF prevented neither caspase-3 activation nor apoptosis in cytoplasts, confirming the need for protein synthesis in the G-CSF effects. These data demonstrate that (at least) 2 routes regulate PMN apoptosis: one via Bax-to-mitochondria translocation and a second mitochondria-independent pathway, both linked to caspase-3 activation. Moreover, G-CSF exerts its antiapoptotic effect in the first, that is, mitochondria-dependent, route and has no impact on the second.     

Human saliva stimulates skin and oral wound healing in vitro

Despite continuous exposure to environmental pathogens, injured mucosa within the oral cavity heals faster and almost scar free compared with skin. Saliva is thought to be one of the main contributing factors. Saliva may possibly also stimulate skin wound healing. If so, it would provide a novel therapy for treating skin wounds, for example, burns. This study aims to investigate the therapeutic wound healing potential of human saliva in vitro. Human saliva from healthy volunteers was filter sterilized before use. Two different in vitro wound models were investigated: (a) open wounds represented by 2D skin and gingiva cultures were used to assess fibroblast and keratinocyte migration and proliferation and (b) blister wounds represented by introducing freeze blisters into organotypic reconstructed human skin and gingiva. Re‐epithelialization and differentiation (keratin K10, K13, K17 expression) under the blister and inflammatory wound healing mediator secretion was assessed. Saliva‐stimulated migration of skin and oral mucosa fibroblasts and keratinocytes, but only fibroblast proliferation. Topical saliva application to the blister wound on reconstructed skin did not stimulate re‐epithelization because the blister wound contained a dense impenetrable dead epidermal layer. Saliva did promote an innate inflammatory response (increased CCL20, IL‐6, and CXCL‐8 secretion) when applied topically to the flanking viable areas of both wounded reconstructed human skin and oral mucosa without altering the skin specific keratin differentiation profile. Our results show that human saliva can stimulate oral and skin wound closure and an inflammatory response. Saliva is therefore a potential novel therapeutic for treating open skin wounds.     

Human CalDAG-GEFI gene (RASGRP2) mutation affects platelet function and causes severe bleeding

The nature of an inherited platelet disorder was investigated in three siblings affected by severe bleeding. Using whole-exome sequencing, we identified the culprit mutation (cG742T) in the RAS guanyl-releasing protein-2 (RASGRP2) gene coding for calcium- and DAG-regulated guanine exchange factor-1 (CalDAG-GEFI). Platelets from individuals carrying the mutation present a reduced ability to activate Rap1 and to perform proper αIIbβ3 integrin inside-out signaling. Expression of CalDAG-GEFI mutant in HEK293T cells abolished Rap1 activation upon stimulation. Nevertheless, the PKC- and ADP-dependent pathways allow residual platelet activation in the absence of functional CalDAG-GEFI. The mutation impairs the platelet’s ability to form thrombi under flow and spread normally as a consequence of reduced Rac1 GTP-binding. Functional deficiencies were confined to platelets and megakaryocytes with no leukocyte alteration. This contrasts with the phenotype seen in type III leukocyte adhesion deficiency caused by the absence of kindlin-3. Heterozygous did not suffer from bleeding and have normal platelet aggregation; however, their platelets mimicked homozygous ones by failing to undergo normal adhesion under flow and spreading. Rescue experiments on cultured patient megakaryocytes corrected the functional deficiency after transfection with wild-type RASGRP2. Remarkably, the presence of a single normal allele is sufficient to prevent bleeding, making CalDAG-GEFI a novel and potentially safe therapeutic target to prevent thrombosis.Inherited platelet disorders are rare diseases that give rise to bleeding when platelets fail to fulfill their hemostatic function upon vessel injury. Clinical manifestations include mainly mucocutaneous bleeding, menometrorrhagia and excessive bleeding after surgical intervention or trauma. The study of these diseases allows a better understanding of normal platelet biochemistry and physiology. These inherited disorders include abnormalities of platelet receptors, granules, or signal transduction (Nurden and Nurden, 2011). Signal transduction dysfunction is thought to be the most common cause of platelet inherited disorders; however, only a few have been successfully genotyped.Here, we have identified and characterized the first mutation of RASGRP2 (RAS guanyl-releasing protein-2) in a family suffering severe bleeding. RASGRP2 codes for a major signaling molecule in platelets, calcium-and-DAG-regulated guanine exchange factor-1 (CalDAG-GEFI). It is a guanine nucleotide exchange factor (GEF) that is critical for Ras-like GTPase activation whose target is mainly Rap1 in platelets (Crittenden et al., 2004; Bergmeier et al., 2007; Cifuni et al., 2008; Stefanini et al., 2009). Rap1 is one of the most predominant small GTPases in platelets and constitutes a key signaling element that governs platelet activation by directly regulating integrin-mediated aggregation and granule secretion (Chrzanowska-Wodnicka et al., 2005; Zhang et al., 2011). Mice lacking CalDAG-GEFI not only have major defects in platelet function, with a reduced ability to form thrombi upon vascular injury, but they also have impaired neutrophil functions (Crittenden et al., 2004; Bergmeier et al., 2007; Carbo et al., 2010). To date, no pathological mutation in RASGRP2 has been reported in man and knowledge about the phenotype linked to human CalDAG-GEFI deficiency is lacking.     

A reversion of an IL2RG mutation in combined immunodeficiency providing competitive advantage to the majority of CD8+ T cells

Mutations in the common gamma chain (γ_c, CD132, encoded by the IL2RG gene) can lead to B⁺T⁻NK⁻ X-linked severe combined immunodeficiency, as a consequence of unresponsiveness to γc-cytokines such as interleukins-2, -7 and -15. Hypomorphic mutations in CD132 may cause combined immunodeficiencies with a variety of clinical presentations. We analyzed peripheral blood mononuclear cells of a 6-year-old boy with normal lymphocyte counts, who suffered from recurrent pneumonia and disseminated mollusca contagiosa. Since proliferative responses of T cells and NK cells to γc -cytokines were severely impaired, we performed IL2RG gene analysis, showing a heterozygous mutation in the presence of a single X-chromosome. Interestingly, an IL2RG reversion to normal predominated in both naïve and antigen-primed CD8⁺ T cells and increased over time. Only the revertant CD8⁺ T cells showed normal expression of CD132 and the various CD8⁺ T cell populations had a different T-cell receptor repertoire. Finally, a fraction of γδ⁺ T cells and differentiated CD4⁺CD27⁻ effector-memory T cells carried the reversion, whereas NK or B cells were repeatedly negative. In conclusion, in a patient with a novel IL2RG mutation, gene-reverted CD8⁺ T cells accumulated over time. Our data indicate that selective outgrowth of particular T-cell subsets may occur following reversion at the level of committed T progenitor cells.