Regulation of leukocyte integrin binding to Ig-family ligands

The adhesion molecules of blood cells are of great importance in the regulation of many of the most central processes of the human body, e.g. haematopoiesis, immune functions, haemostasis and wound healing, and the delivery of oxygen to the tissues. Leukocyte β2 integrins, VLA-4 integrin and members of the immunoglobulin superfamily like ICAMs (intercellular adhesion molecules) and VCAM (vascular cell adhesion molecule) are the most essential adhesion molecules of blood cells. The adhesion molecules on blood cells have many requirements that they need to fulfil in order to maintain a physiological system: they need to stay in an inactive, non-binding state for most of the time, and to be activated and thus become adhesive only when needed. In addition, they should specifically recognise their binding partners or ligands, as unnecessary binding could lead for example to clogging of the blood vessels, autoimmune diseases or allergic reactions. Still one important feature of blood cell adhesion is the ability to let go and release the adhesion, when the cell needs to move forward or continue patrolling the circulation. In my thesis work I have analysed the properties of leukocyte integrins and their ligands as well as the regulation of their interactions. We observed that the red cell adhesion molecule ICAM-4 can bind to CR4, a leukocyte integrin expressed on monocytes and macrophages, and that the I domain is the ICAM-4 binding site on leukocyte integrins (LFA-1, Mac-1 and CR4). We also characterised the phosphorylation of the cytoplasmic tail of CR4, and found that αX chain is phosphorylated on Ser1158, and that this phosphorylation is essential for CR4 inside-out activation, adhesion and phagocytosis but not for outside-in signaling initiated by CR4. Finally we analysed the regulation of VLA-4 mediated adhesion to VCAM-1 that is controlled by the β2 integrins. The findings of my studies show how leukocyte integrins are involved in numerous blood cell functions and that their functions are tightly regulated. Due to their multifold roles, they also offer attractive targets for therapeutic use. The specificity of phosphorylations or ligands may serve as distinctive factors between different integrins, even members of the same family.Veren solut hoitavat kukin omia tarkoin säädeltyjä tehtäviään elimistössä. Punasolut kuljettavat happea ja hiilidioksidia, verihiutaleet tukkivat verenvuodon ja valkosolut huolehtivat elimistön puolustusmekanismeista. Yhteistä näille kaikille soluille on että pääosan verenkierrossa viettämästään ajasta ne kulkevat huimaa vauhtia eteenpäin Toisaalta tärkeää solujen toiminnalle on pystyä tarvittaessa aistimaan muutoksia ympäristössään ja tunnistamaan tärkeitä rakenteita toisten solujen pinnalla tai solunulkoisessa materiaalissa. Myös tarttumista eli adheesiota tarvitaan jossain vaiheessa kaikkien verisolujen elämänkaaren aikana. Verisolujen tarttumistapahtumista huolehtivat suurelta osin soluadheesiomolekyylit, suuri proteiiniryhmä joka voidaan jakaa useampaan perheeseen molekyylin rakenteen ja tehtävän perusteella. Verisolujen adheesiotapahtumissa tärkeimpiä molekyylejä ovat integriinit sekä ICAM-perheen (intercellular adhesion molecules) proteiinit. Väitöskirjassani olen tutkinut näiden molekyylien välistä tarttumista sekä sen erityyppisiä säätelymekanismeja. Ensimmäisissä osajulkaisuissa selvitimme punasoluissa sekä niiden esiasteissa esiintyvän adheesiomolekyyli ICAM-4:n sitoutumista valkosolujen integriineihin ja löysimme ICAM-4:lle uuden tarttumiskumppanin, integriini CR4:n. Seuraavaksi tutkimme CR4:n toimintaan vaikuttavia solunsisäisiä mekanismeja. CR4-molekyylin on aiemmin raportoitu vaikuttavan useisiin valkosolujen tehtäviin kuten vanhentuneiden, infektoituneiden tai muuten viallisten solujen tuhoamiseen. Tutkimuksissamme huomasimme, että mikäli CR4:n solunsisäinen osa ei pysty fosforyloitumaan (siihen ei voida liittää fosfaattiryhmää), solun ulkopuolinen osa ei puolestaan pysty tarttumaan vastinmolekyyleihinsä. Viimeisessä osajulkaisussa tutkimme erityyppisten integriinien välistä vuoropuhelua saman solun sisällä. Huomasimme, että yhden integriinin fosforylaatio voi estää toisen, samassa solussa ilmentyvän integriinin tarttumista vastinmolekyyliinsä. Verisolujen tarttumistapahtumien mekanismien ja säätelyn tunnistaminen on tärkeää erilaisten sairauksien tutkimuksessa. Esim. sirppisoluanemiassa punasolut tarttuvat juurikin ICAM-4:n kautta liikaa verisuonen seinämiin, mikä aiheuttaa kiputiloja. Monissa autoimmuunisairauksissa (kuten MS-tauti, psoriasis ja Crohnin tauti) integriinit taas osallistuvat tulehdusreaktioihin joissa valkosolut hyökkäävät potilaan omia kudoksia vastaan, aiheuttaen vakavia vaurioita. Tarttumisen säätelyn tunteminen on ensiarvoisen tärkeää uusien hoitomenetelmien kehittämisessä

Verisolujen integriinit ja taudit

English summaryPeer reviewe

Verisolujen integriinit ja taudit

English summaryPeer reviewe

Beta2-Integrins and Interacting Proteins in Leukocyte Trafficking, Immune Suppression, and Immunodeficiency Disease

Beta2-integrins are complex leukocyte-specific adhesion molecules that are essential for leukocyte (e.g., neutrophil, lymphocyte) trafficking, as well as for other immunological processes such as neutrophil phagocytosis and ROS production, and T cell activation. Intriguingly, however, they have also been found to negatively regulate cytokine responses, maturation, and migratory responses in myeloid cells such as macrophages and dendritic cells, revealing new, and unexpected roles of these molecules in immunity. Because of their essential role in leukocyte function, a lack of expression or function of beta2-integrins causes rare immunodeficiency syndromes, Leukocyte adhesion deficiency type I, and type III (LAD-I and LAD-III). LAD-I is caused by reduced or lost expression of beta2-integrins, whilst in LAD-III, beta2-integrins are expressed but dysfunctional because a major integrin cytoplasmic regulator, kindlin-3, is mutated. Interestingly, some LAD-related phenotypes such as periodontitis have recently been shown to be due to an uncontrolled inflammatory response rather than to an uncontrolled infection, as was previously thought. This review will focus on the recent advances concerning the regulation and functions of beta2-integrins in leukocyte trafficking, immune suppression, and immune deficiency disease.Peer reviewe

New geophysics study programs at the University of Helsinki

Peer reviewe

A beta2-Integrin/MRTF-A/SRF Pathway Regulates Dendritic Cell Gene Expression, Adhesion, and Traction Force Generation

beta2-integrins are essential for immune system function because they mediate immune cell adhesion and signaling. Consequently, a loss of beta2-integrin expression or function causes the immunodeficiency disorders, Leukocyte Adhesion Deficiency (LAD) type I and III. LAD-III is caused by mutations in an important integrin regulator, kindlin-3, but exactly how kindlin-3 regulates leukocyte adhesion has remained incompletely understood. Here we demonstrate that mutation of the kindlin-3 binding site in the b2-integrin (TTT/AAA-b2-integrin knock-in mouse/KI) abolishes activation of the actin-regulated myocardin related transcription factor A/serum response factor (MRTF-A/SRF) signaling pathway in dendritic cells and MRTF-A/SRF-dependent gene expression. We show that Ras homolog gene family, member A (RhoA) activation and filamentous-actin (F-actin) polymerization is abolished in murine TTT/AAA-b2-integrin KI dendritic cells, which leads to a failure ofMRTF-A to localize to the cell nucleus to coactivate genes together with SRF. In addition, we show that dendritic cell gene expression, adhesion and integrin-mediated traction forces on ligand coated surfaces is dependent on the MRTF-A/SRF signaling pathway. The participation of b2-integrin and kindlin-3-mediated cell adhesion in the regulation of the ubiquitous MRTF-A/SRF signaling pathway in immune cells may help explain the role of b2-integrin and kindlin-3 in integrin-mediated gene regulation and immune system function.Peer reviewe

FT-IR-cPAS—New Photoacoustic Measurement Technique for Analysis of Hot Gases: A Case Study on VOCs

This article describes a new photoacoustic FT-IR system capable of operating at elevated temperatures. The key hardware component is an optical-readout cantilever microphone that can work up to 200 °C. All parts in contact with the sample gas were put into a heated oven, incl. the photoacoustic cell. The sensitivity of the built photoacoustic system was tested by measuring 18 different VOCs. At 100 ppm gas concentration, the univariate signal to noise ratios (1σ, measurement time 25.5 min, at highest peak, optical resolution 8 cm−1) of the spectra varied from minimally 19 for o-xylene up to 329 for butyl acetate. The sensitivity can be improved by multivariate analyses over broad wavelength ranges, which effectively co-adds the univariate sensitivities achievable at individual wavelengths. The multivariate limit of detection (3σ, 8.5 min, full useful wavelength range), i.e., the best possible inverse analytical sensitivity achievable at optimum calibration, was calculated using the SBC method and varied from 2.60 ppm for dichloromethane to 0.33 ppm for butyl acetate. Depending on the shape of the spectra, which often only contain a few sharp peaks, the multivariate analysis improved the analytical sensitivity by 2.2 to 9.2 times compared to the univariate case. Selectivity and multi component ability were tested by a SBC calibration including 5 VOCs and water. The average cross selectivities turned out to be less than 2% and the resulting inverse analytical sensitivities of the 5 interfering VOCs was increased by maximum factor of 2.2 compared to the single component sensitivities. Water subtraction using SBC gave the true analyte concentration with a variation coefficient of 3%, although the sample spectra (methyl ethyl ketone, 200 ppm) contained water from 1,400 to 100k ppm and for subtraction only one water spectra (10k ppm) was used. The developed device shows significant improvement to the current state-of-the-art measurement methods used in industrial VOC measurements

Vastasyntyneiden GBS-taudin ehkäisy – asiantuntijaryhmän suositus

B-ryhmän beetahemolyyttinen streptokokki (GBS) on vastasyntyneiden yleisin bakteremian ja meningiitin aiheuttaja. Suuri osa vastasyntyneiden varhaisista GBS-infektioista voidaan ehkäistä antamalla synnytyksenaikainen mikrobilääkeprofylaksi loppuraskauden GBS-seulonnassa positiiviseksi osoitetuille synnyttäjille. Jos GBS-seulontaviljelyä ei ole tehty, infektioriski arvioidaan synnytyksen käynnistymisen yhteydessä

Mice Lacking beta2-Integrin Function Remain Glucose Tolerant in Spite of Insulin Resistance, Neutrophil Infiltration and Inflammation

Beta2-integrins are important in leukocyte trafficking and function, and are regulated through the binding of cytoplasmic proteins, such as kindlin-3, to their intracellular domain. Here, we investigate the involvement of beta2-integrins in the regulation of metabolic disease using mice where the kindlin-3 binding site in the beta2-integrin cytoplasmic tail has been mutated (TTT/AAA-beta2-integrin knock-in (KI) mice), leading to expressed but dysfunctional beta2-integrins and significant neutrophilia in vivo. Beta2-integrin KI mice fed on a high fat diet showed normal weight gain, and normal accumulation of macrophages and lymphocytes in white adipose tissue (WAT) and liver, but increased neutrophil numbers especially in WAT. In addition, beta2-integrin KI mice fed on a high fat diet showed significantly increased peripheral insulin resistance in response to high-fat feeding. However, this was associated with improved glucose disposal following glucose load. Interestingly, beta2-integrin KI neutrophils produced more elastase in vitro, in response to stimulation. Beta2-integrin KI mice displayed variability of tissue inflammatory status, with liver and WAT exhibiting little or no difference in inflammation compared to high fat fed controls, whereas skeletal muscle demonstrated a raised inflammatory profile in association with higher elastase levels and diminished signalling through the IRS1-PKB pathway. In conclusion, although expression of dysfunctional beta2-integrins increased neutrophil production and infiltration into tissue, skeletal muscle was the most affected tissue exhibiting evidence of higher neutrophil activity and insulin resistance. Thus, beta2-integrins modulate glucose homeostasis during high fat feeding predominantly through actions on skeletal muscle to affect metabolic phenotype in vivo.Peer reviewe

Invasive Group B Streptococcal Infections in Finland: A Population-based Study

We analyzed surveillance data on group B streptococcus (GBS) infection in Finland from 1995 to 2000 and reviewed neonatal cases of early-onset GBS infection in selected hospitals in 1999 to 2000. From 1995 to 2000, 853 cases were reported (annual incidence 2.2–3.0/100,000 population). We found 32–38 neonatal cases of early-onset GBS disease per year (annual incidence 0.6–0.7/1,000 live births). In five hospitals, 35% of 26 neonatal cases of early-onset GBS infection had at least one risk factor: prolonged rupture of membranes, preterm delivery, or intrapartum fever. Five of eight mothers screened for GBS were colonized. In one case, disease developed despite intrapartum chemoprophylaxis. Although the incidence of early-onset GBS disease in Finland is relatively low, some geographic variation exists, and current prevention practices are suboptimal. Establishing national guidelines to prevent perinatal GBS is likely to reduce the incidence of the disease