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Lipidomics of human blood plasma is an emerging biomarker discovery approach that compares lipid profiles under pathological and physiologically normal conditions, but how a healthy lipidome varies within the population is poorly understood. By quantifying 281 molecular species from 27 major lipid classes in the plasma of 71 healthy young Caucasians whose 35 clinical blood test and anthropometric indices matched the medical norm, we provided a comprehensive, expandable and clinically relevant resource of reference molar concentrations of individual lipids. We established that gender is a major lipidomic factor, whose impact is strongly enhanced by hormonal contraceptives and mediated by sex hormone-binding globulin. In lipidomics epidemiological studies should avoid mixed-gender cohorts and females taking hormonal contraceptives should be considered as a separate sub-cohort. Within a gender-restricted cohort lipidomics revealed a compositional signature that indicates the predisposition towards an early development of metabolic syndrome in ca. 25% of healthy male individuals suggesting a healthy plasma lipidome as resource for early biomarker discovery.

Cold exposure greatly alters brown adipose tissue (BAT) gene expression and metabolism to increase thermogenic capacity. Here, we used RNA sequencing and mass-spectrometry-based lipidomics to provide a comprehensive resource describing the molecular signature of cold adaptation at the level of the transcriptome and lipidome. We show that short-term (3-day) cold exposure leads to a robust increase in expression of several brown adipocyte genes related to thermogenesis as well as the gene encoding the hormone irisin. However, pathway analysis shows that the most significantly induced genes are those involved in glycerophospholipid synthesis and fatty acid elongation. This is accompanied by significant changes in the acyl chain composition of triacylglycerols (TAGs) as well as subspecies-selective changes of acyl chains in glycerophospholipids. These results indicate that cold adaptation of BAT is associated with significant and highly species-selective remodeling of both TAGs and glycerophospholipids.

Biological membranes consist of several types of lipids that have important structural and functional roles. Moreover, these lipids can act as signaling molecules or affect the function of cellular proteins. Regulation of lipid homeostasis is critical for the maintenance of cellular physiology, and disturbances in lipid metabolism aspects are key components behind many diseases, including atherosclerosis. Macrophage cells play central roles in the development of atherosclerosis. The excessive uptake of modified lipoprotein particles in the vessel subendothelial space results in a proinflammatory response and the formation of macrophage foam cells. Oxysterols, oxidized cholesterol derivatives that primarily are taken up along with the modified lipoproteins, act at the crossroads of lipid metabolism and inflammation, and are important signaling lipids involved in atherogenesis. In this thesis the functions of three members of the Oxysterol Binding Protein (ORP) Family were studied in the macrophage cell type. Their role was studied by knocking down the proteins individually using lentiviruses. Moreover, the general function of these proteins was studied using other cell models. In the first part, the targeting of late endosomal protein ORP1L was investigated. ORP1L was shown to affect the motility and function of late endosomes in a sterol-dependent manner by mediating interactions between late endosomes and endoplasmic reticulum. Similar contacts between cellular compartments are also demonstrated for ORP3 and ORP8. In the second part the role of ORP8 in the macrophage was investigated by transcriptomic, biochemical and functional assays. ORP8 knockdown was shown to result in activation of several nuclear pathways and to affect cellular migration. In the third part, the lipid composition of macrophages was studied in conditions relevant for atherogenesis. The analysis revealed complex and profound changes in the cellular lipidome in the absence of ORPs, with implicat, Biologiset kalvot koostuvat erilaisista lipideistä eli rasva-aineista, joilla on tärkeitä rakenteellisia ja toiminnallisia tehtäviä. Lipiditasapainon säätely on erittäin tärkeää solujen fysiologian kannalta, ja sen häiriöt ovat keskeisessä asemassa monien tautien, kuten valtimonkovettumataudin, taustalla. ---- Makrofaagit eli syöjäsolut ovat keskeisiä soluja valtimonkovettumataudin kehittymisen kannalta, sillä ne poistavat kolesterolia valtimoiden seinämistä. Liiallisena tämä prosessi voi johtaa tulehdusreaktioon ja makrofaagien muuttumiseen vaahtosoluiksi. Kolesterolin mukana makrofaagit ottavat sisäänsä oksisteroleja, hapettuneita kolesterolijohdannaisia. Oksisterolit ovat tehokkaita signalointilipidejä, jotka säätelevät solun tulehdusreaktioita sekä rasva-aineenvaihduntaa, ja niiden määrän on havaittu kasvavan valtimonkovettumataudin edetessä. Tässä väitöskirjatyössä on tutkittu kolmen oksisteroleja sitovan proteiiniperheen (ORP) jäsenen toimintaa. ORP1L, ORP3 ja ORP8 proteiinit ilmentyvät makrofaagi-solutyypissä erityisen runsaasti. Proteiinien toimintaa tutkittiin makrofaagi-solumallissa hiljentämällä proteiineja yksi kerrallaan käyttäen hyväksi lentiviruksia. Lisäksi proteiineja tutkittiin yleisemmin käyttäen hyväksi muita solumalleja ja tekniikoita. Tutkimuksissa havaittiin, että ORP1L proteiini säätelee myöhäisten endosomien liikettä ja toimintaa solun kolesterolistatuksesta riippuvaisesti muodostamalla vuorovaikutuksen soluelinten välille. Myös ORP3- ja ORP8-proteiinien havaittiin muodostavat vastaavia vuorovaikutuksia solun eri kalvostojen välillä. ORP8:n havaittiin säätelevän eri tumankuljetusreittejä, ja vaikuttavan makrofaagien liikkuvuuteen. Kolmannessa osatyössä tutkittiin ORP-proteiinien puuttumisen vaikutusta makrofaagien lipidikoostumukseen olosuhteissa, jotka ovat olennaisia valtimonkovettumataudin kehittymisen kannalta. Proteiinien puutos aiheutti huomattavia muutoksia, mm. tulehduksellisissa lipideissä. Tulokset viittaavat siihen, että ORP-prote