MECHANISMS AND EFFECTS OF MITOCHONDRIAL DNA INSTABILITY AND COPY NUMBER MANIPULATION

Defects in mitochondrial DNA (mtDNA) maintenance cause a range of human diseases, including autosomal dominant progressive external ophthalmoplegia (adPEO). This study aimed to clarify the molecular background of adPEO. We discovered that deoxynucleoside triphosphate (dNTP) metabolism plays a crucial in mtDNA maintenance and were thus prompted to search for therapeutic strategies based on the modulation of cellular dNTP pools or mtDNA copy number. Human mtDNA is a 16.6 kb circular molecule present in hundreds to thousands of copies per cell. mtDNA is compacted into nucleoprotein clusters called nucleoids. mtDNA maintenance diseases result from defects in nuclear encoded proteins that maintain the mtDNA. These syndromes typically afflict highly differentiated, post-mitotic tissues such as muscle and nerve, but virtually any organ can be affected. adPEO is a disease where mtDNA molecules with large-scale deletions accumulate in patients tissues, particularly in skeletal muscle. Mutations in five nuclear genes, encoding the proteins ANT1, Twinkle, POLG, POLG2 and OPA1, have previously been shown to cause adPEO. Here, we studied a large North American pedigree with adPEO, and identified a novel heterozygous mutation in the gene RRM2B, which encodes the p53R2 subunit of the enzyme ribonucleotide reductase (RNR). RNR is the rate-limiting enzyme in dNTP biosynthesis, and is required both for nuclear and mitochondrial DNA replication. The mutation results in the expression of a truncated form of p53R2, which is likely to compete with the wild-type allele. A change in enzyme function leads to defective mtDNA replication due to altered dNTP pools. Therefore, RRM2B is a novel adPEO disease gene. The importance of adequate dNTP pools and RNR function for mtDNA maintenance has been established in many organisms. In yeast, induction of RNR has previously been shown to increase mtDNA copy number, and to rescue the phenotype caused by mutations in the yeast mtDNA polymerase. To further study the role of RNR in mammalian mtDNA maintenance, we used mice that broadly overexpress the RNR subunits Rrm1, Rrm2 or p53R2. Active RNR is a heterotetramer consisting of two large subunits (Rrm1) and two small subunits (either Rrm2 or p53R2). We also created bitransgenic mice that overexpress Rrm1 together with either Rrm2 or p53R2. In contrast to the previous findings in yeast, bitransgenic RNR overexpression led to mtDNA depletion in mouse skeletal muscle, without mtDNA deletions or point mutations. The mtDNA depletion was associated with imbalanced dNTP pools. Furthermore, the mRNA expression levels of Rrm1 and p53R2 were found to correlate with mtDNA copy number in two independent mouse models, suggesting nuclear-mitochondrial cross talk with regard to mtDNA copy number. We conclude that tight regulation of RNR is needed to prevent harmful alterations in the dNTP pool balance, which can lead to disordered mtDNA maintenance. Increasing the copy number of wild-type mtDNA has been suggested as a strategy for treating PEO and other mitochondrial diseases. Only two proteins are known to cause a robust increase in mtDNA copy number when overexpressed in mice; the mitochondrial transcription factor A (TFAM), and the mitochondrial replicative helicase Twinkle. We studied the mechanisms by which Twinkle and TFAM elevate mtDNA levels, and showed that Twinkle specifically implements mtDNA synthesis. Furthermore, both Twinkle and TFAM were found to increase mtDNA content per nucleoid. Increased mtDNA content in mouse tissues correlated with an age-related accumulation of mtDNA deletions, depletion of mitochondrial transcripts, and progressive respiratory dysfunction. Simultaneous overexpression of Twinkle and TFAM led to a further increase in the mtDNA content of nucleoids, and aggravated the respiratory deficiency. These results suggested that high mtDNA levels have detrimental long-term effects in mice. These data have to be considered when developing and evaluating treatment strategies for elevating mtDNA copy number.

En undersökning om typografins betydelse för läsbarhet av ord i rörelse

The purpose of this work was to determine how important a word’s setting was for the readability of typography in motion. Facts regarding how reading works and the importance of the words formation for the readability were used to form a computer test. This test was performed by 15 test persons and the results were analyzed. The results show that the serif was easier to read than the sanserif. The words of the serif which were easiest to read were the words with positive tracking and the words with capital letters. Also for the sanserif, these words were the easiest to read.

Hela och halva samtal : Olika samtalsformers inverkan på arbetsprestationen

Denna studie grundar sig på en undersökning av hur 58 gymnasieelevers arbetsförmåga påverkades av exponering för dels ett traditionellt samtal mellan två personer och dels ett mobiltelefonsamtal. Utifrån teorier om den proaktiva hjärnan och det resursmässigt begränsade korttidsminnet utformades studiens huvudsakliga hypoteser; att mobilsamtal stör mer än vanliga samtal samt att denna distraktion blir mer påtaglig då försökspersonen utför uppgifter av mer komplex karaktär. Resultaten visade sig ge stöd åt hypotesen att mobiltelefonsamtal distraherar personer i högre utsträckning än vad traditionella samtal gör. Studien kunde dock inte påvisa att denna distraktion blir mer tydlig då personer utför mer komplexa uppgifter även om resultatet hade en tendens att gå i den riktningen. Författaren menar att studier likt denna ger ett viktigt vetenskapligt inlägg till debatten om hur öppna kontorslandskap (där de anställda ständigt exponeras för kollegors samtal) påverkar människors arbetsprestationer.

The role of semantic context and attentional resource distribution in semantic comprehension in Swedish pre-schoolers

Research on semantic processing focused mainly on isolated units in language, which does not reflect the complexity of language. In order to understand how semantic information is processed in a wider context, the first goal of this thesis was to determine whether Swedish pre-school children are able to comprehend semantic context and if that context is semantically built up over time. The second goal was to investigate how the brain distributes attentional resources by means of brain activation amplitude and processing type. Swedish preschool children were tested in a dichotic listening task with longer children’s narratives. The development of event-related potential N400 component and its amplitude were used to investigate both goals. The decrease of the N400 in the attended and unattended channel indicated semantic comprehension and that semantic context was built up over time. The attended stimulus received more resources, processed the stimuli in more of a top-down manner and displayed prominent N400 amplitude in contrast to the unattended stimulus. The N400 and the late positivity were more complex than expected since endings of utterances longer than nine words were not accounted for. More research on wider linguistic context is needed in order to understand how the human brain comprehends natural language. 

Djurterapins inverkan på människor med demenssjukdom och andra kognitiva sjukdomar- en litteraturöversikt

Bakgrund: I Sverige insjuknar varje år ungefär 25 000 människor i någon form av demenssjukdom, en sjukdom som ökar världen över och troligtvis kommer att fördubblas inom de närmsta 20 åren. Demenssjukdom drabbar hjärnan vilket påverkar minnet och den kognitiva förmågan och kan ge beteendemässiga och psykiska symtom (BPSD). Studier visar att nio av tio personer någon gång kommer att visa symtom som ångest, oro, vandrande och aggressiva beteenden. Läkemedelsadministrering för att behandla symtom som oro, ångest och agiterande beteenden är inte ovanligt. Dock kan läkemedel ofta orsaka biverkningar hos äldre människor. Att istället använda djurterapi för att behandla symtom som kan uppstå vid demenssjukdomar kan ses som ett positivt alternativ då studier visat att djurterapi har en positiv inverkan på människan med demenssjukdom och andra kognitiva sjukdomar. Syfte: Syftet med denna studie var att beskriva vilken inverkan djurterapi har på människor med demenssjukdom och andra kognitiva sjukdomar. Metod: Studien är en litteraturöversikt baserad på artiklar med kvantitativ och kvalitativ ansats (n=15). Resultat: Resultatet av denna litteraturstudie visar att djurterapi ger minskad stressnivå, minskat uppvisande av aggressiva beteenden, färre vanföreställningar, minskad ångest, nedstämdhet, sorgsenhet, depressiva symtom och apatiska beteenden samt ökning av glädje, lycka, engagemang, vakenhet, medvetenhet, verbala uttryck samt ökat minne. Konklusion: Resultatet tyder på att djurterapi med fördel kan användas som alternativ eller kompletterande behandling för människor med demenssjukdom. Dock ser författarna att utökad forskning behövs för att se långvarig inverkan av djurterapins effekter.