Les molécules classiques du CMH de classe II sont responsables de la présentation de peptides exogènes par les cellules présentatrices d’antigène aux lymphocytes T CD4+. Cette présentation antigénique est essentielle à l’établissement d’une réponse immunitaire adaptative. Cependant, la reconnaissance d’auto-antigènes ainsi que l’élimination des cellules du Soi sont des problèmes à l’origine de nombreuses maladies auto-immunes. Notamment, le diabète et la sclérose en plaque. D’éventuels traitements de ces maladies pourraient impliquer la manipulation de la présentation antigénique chez les cellules dont la reconnaissance et l’élimination engendrent ces maladies. Il est donc primordial d’approfondir nos connaissances en ce qui concerne les mécanismes de régulation de la présentation antigénique. La présentation antigénique est régulée tant au niveau transcriptionnel que post-traductionnel. Au niveau post-traductionnel, diverses cytokines affectent le processus. Parmi celles-ci, l’IL-10, une cytokine anti-inflammatoire, cause une rétention intracellulaire des molécules du CMH II. Son mécanisme d’action consiste en l’ubiquitination de la queue cytoplasmique de la chaîne bêta des molécules de CMH II. Cette modification protéique est effectuée par MARCH1, une E3 ubiquitine ligase dont l’expression est restreinte aux organes lymphoïdes secondaires. Jusqu’à tout récemment, il y avait très peu de connaissance concernant la structure et les cibles de MARCH1. Considérant son impact majeur sur la présentation antigénique, nous nous sommes intéressé à la structure-fonction de cette molécule afin de mieux caractériser sa régulation ainsi que les diverses conditions nécessaires à son fonctionnement. Dans un premier article, nous avons étudié la régulation de l’expression de MARCH1 au niveau protéique. Nos résultats ont révélé l’autorégulation de la molécule par formation de dimères et son autoubiquitination. Nous avons également démontré l’importance des domaines transmembranaires de MARCH1 dans la formation de dimères et l’interaction avec le CMH II. Dans un second article, nous avons investigué l’importance de la localisation de MARCH1 pour sa fonction. Les résultats obtenus montrent la fonctionnalité des motifs de localisation de la portion C-terminale de MARCH1 ainsi que la présence d’autres éléments de localisation dans la portion N-terminale de la protéine. Les nombreux mutants utilisés pour ce projet nous ont permis d’identifier un motif ‘‘VQNC’’, situé dans la portion cytoplasmique C-terminale de MARCH1, dont la valine est requise au fonctionnement optimal de la molécule. En effet, la mutation de la valine engendre une diminution de la fonction de la molécule et des expériences de BRET ont démontré une modification de l’orientation spatiale des queues cytoplasmiques. De plus, une recherche d’homologie de séquence a révélé la présence de ce même motif dans d’autres ubiquitines ligases, dont Parkin. Parkin est fortement exprimée dans le cerveau et agirait, entre autre, sur la dégradation des agrégats protéiques. La dysfonction de Parkin cause l’accumulation de ces agrégats, nommés corps de Lewy, qui entraînent des déficiences au niveau du fonctionnement neural observé chez les patients atteints de la maladie de Parkinson. La valine comprise dans le motif ‘’VQNC’’ a d’ailleurs été identifiée comme étant mutée au sein d’une famille où cette maladie est génétiquement transmise. Nous croyons que l’importance de ce motif ne se restreint pas à MARCH1, mais serait généralisée à d’autres E3 ligases. Ce projet de recherche a permis de caractériser des mécanismes de régulation de MARCH1 ainsi que de découvrir divers éléments structuraux requis à sa fonction. Nos travaux ont permis de mieux comprendre les mécanismes de contrôle de la présentation antigénique par les molécules de CMH II. / Classical MHC class II molecules are responsible for the presentation of exogenous peptides to CD4+ T cells, which is essential for the establishment of the adaptive immune response. However, problems with recognition of auto-antigens and the subsequent cell elimination are at the root of numerous autoimmune diseases. Manipulation of the antigen presentation pathway in order to eliminate cells that present self-antigens could serve as potential treatments of many autoimmune disorders. It is therefore essential to deepen our knowledge regarding the mechanisms regulating antigen presentation. Antigen presentation is regulated both transcriptionally and post-translationally. Whereas many cytokines affect the latter, IL-10, an anti-inflammatory cytokine, causes the intracellular retention of MHC II molecules. This phenotype is the result of the ubiquitination of MHC II -chain cytoplasmic tail by MARCH1. MARCH1 is an E3 ubiquitin ligase expressed in secondary lymphoid organs. Until recently, little was known about the structure-function and the targets of MARCH1. Considering its major impact on antigen presentation, we were interested to study this E3 ligase in order to reveal how it is regulated and what are the required conditions for its function. In a first report, we have investigated the regulation of MARCH1’s protein expression. Our results revealed its autoregulation via dimer formation and autoubiquitination. In addition, we have demonstrated the involvement of MARCH1’s transmembrane domains for dimerization and MHC II interaction. In a second article, we highlighted the importance of MARCH1 localization for its function. Our results indicated that localization motifs in the C-terminal portion of MARCH1 were functional and revealed the presence of some sorting elements in the N-terminal portion of the molecule. A panel of mutant were used and allowed us to identify a ‘’VQNC’’ motif, located in the C-terminal cytoplasmic portion of MARCH1, in which the valine is central for the molecule’s function. Indeed, point-mutation of the valine led to a decrease in MARCH1 ability to relocate MHC II whereas BRET experiments revealed a modification in the spatial organization of the cytoplasmic tails. Moreover, a blast of sequence homology showed the presence or that same motif in others ubiquitine ligases, one of which is Parkin. Parkin is highly expressed in the brain and seems to be implicated in protein aggregates’ degradation. It was reported that malfunction of Parkin leads to the accumulation of aggregates, called Lewy bodies, responsible for the neural functions deficiencies observed in patients with Parkinson disease. Interestingly, a family for which the sickness was genetically transmitted has a mutated valine in the VQNC motif. We believe that the importance of this motif is not restricted to MARCH1 and could be generalized to others E3 ubiquitin ligases. This project enabled us to characterize the regulation mechanisms of MARCH1. In addition, we discovered various structural elements required for its function. Altogether, our data allows for a better understanding of the mechanisms controlling MHC II molecules antigen presentation.

Die Familie der NFAT-Transkriptionsfaktoren (NFATc1-c4) ist im Zuge einer Immunreaktion endscheidend an der transkriptionellen Regulation der Genexpression beteiligt. Wurden NFAT-Faktoren zunächst als T-zell-spezifische Aktivatoren von Zytokinpromotoren beschrieben, so hat sich inzwischen gezeigt, dass sie in einer Vielzahl von Geweben eine wichtige Rolle spielen. Als Beispiele seien die Herzklappenentwicklung, die Bildung von Blutgefässen, die Ausbildung neuronaler Axone oder die Osteoklastendifferenzierung genannt [10, 24]. In der hier vorliegenden Arbeit zeigen wir, dass die starke Expression der kurzen Isoform NFATc1/αA in Effektor-T-Lymphozyten durch die induzierbare Aktivität des Promoters P1 kontrolliert wird. Die P1 Aktivierung führt zum Splicing des Exon 1 zu 3 (α-Isoformen) und endet meist durch Benutzung der Polyadenylierungsstelle pA1 hinter Exon 9 (A-Isoformen). Der zweite, schwächerer Promoter P2 befindet sich vor dem zweiten Exon und ist für die konstitutive Synthese der β-Isoformen verantwortlich. Der Transkriptionstart am zweiten Exon geht meist mit der Benutzung einer zweiten, hinter dem 11. Exon gelegenen Polyadenylierungsstelle pA2 einher, die durch alternatives Splicing zur Synthese der Isoformen B und C führt. Insgesamt können so vom nfatc1-Lokus sechs verschiedene Isoformen (αA, αB, αC, βA, βB und βC) generiert werden. Die induzierbare Aktivität des P1-Promoters ist, im Gegensatz zum eher konstitutiv aktiven P2-Promoter, NFAT-abhängig und somit eine Form der Autoregulation. In ruhenden T-Lymphozyten sind einzig die Transkripte der NFATc1/β-Isoformen nachweisbar. Nach einer T-Zell-Aktivierung nimmt ihre Häufigkeit dann ab, während nun die α-Isoformen dominant werden. In dieser Arbeit wird gezeigt, dass es nach Induktion primärer Effektor-T-Helfer-Zellen oder in T-Zell-Linien zu einer 15-20-fachen Akkumulation der NFATc1/αA mRNA bzw. einer 2-5-fachen Zunahme der NFATc1/αB und C mRNAs kommt. Zur maximalen Induktion des P1-Promotors bedarf es zum einen eines anhaltenden Anstiegs der intrazellulären Kalziumkonzentration, die zur Aktivierung der Phosphatase Calcineurin und damit zur Kernlokalisation der NFAT-Faktoren führt. Zum anderen ist die Aktivierung der Proteinkinase C-Enzyme und der MAP-Kinasen notwendig, wie sie durch Phorbolester in der Zelle vermittelt wird. Dies lässt darauf schließen, dass für eine optimale Aktivierung des P1-Promotors sowohl Signale des T-Zell-Rezeptors als auch Signale von Korezeptoren - wie von CD28 - notwendig sind. Da die Induktion von NFATc1/αA in NFATc2/NFATc3 doppeldefizienten Mäusen normal erfolgt, kann man schlussfolgern, dass NFATc1 in Form einer Autoregulation die Aktivität des P1-Promoters und damit die Synthese der α-Isoformen kontrolliert. Die NFAT-vermittelte Aktivierung des P1-Promoters erfolgt über zwei tandemartig angeordnete NFAT-Bindungsstellen der Nukleotidsequenz TGGAAA, an die jeweils ein NFAT-Protein binden kann. Daneben enthält der Promoter konservierte Bindemotive für CREB-, AP-1, Sp-, NF-kB- und GATA-Faktoren, die wahrscheinlich an der komplexen Kontrolle dieses induzierbaren NFATc1-Promoters beteiligt sind. Zusammengefasst ergibt sich aus diesen Daten das folgende Modell. Die Transkription im nfatc1-Genlokus erfolgt in naiven und in ruhenden Effektor-T-Zellen konstitutiv und gesteuert durch den P2-Promotor. In Folge einer Aktivierung der Zelle verringert sich die Aktivität des P2-Promotors, während gleichzeitig der P1-Promotor induziert wird, der zusammen mit einer verstärkten Nutzung der pA1-Polyadenylierungssequenz für die massive Zunahme der NFATc1/αA-Isoform verantwortlich ist. Dies deutet auf eine besondere Bedeutung dieser kurzen Isoform in der Effektorphase der T-Zell-Aktivierung hin, insbesondere in Th1-Zellen, die NFATc1/αA in hohen Konzentrationen produzieren. / NFAT transcription factors play critical roles in gene transcription during immune responses. Besides regulation of lymphokine promoters in T lymphocytes, NFAT factors are also expressed in other cell types and regulate the activity of numerous genes that control the generation of cardiac septa and valves in embryonic heart, the formation of blood vessels, the outgrowth of neuronal axons and the differentiation of osteoclasts during bone formation [10, 24]. Here we show that the induction of NFATc/αA in effector T cells is controlled by a strong inducible promoter, P1. It results in splicing of exon 1 to exon 3 transcripts and, in concert with the activity of a poly A site downstream of exon 9, leads to the massive synthesis of NFATc/αA in effector Th1 cells. A second, weak promoter, P2, lies in front of exon 2 and directs the synthesis of longer NFAT β isoforms. Both P1 and P2 direct the synthesis of three different RNAs: αA, αB, αC and βA, βB, βC correspondingly. The B and C isoforms arise from alternative splicing and poly A addition at the distal site pA2. P1 but not P2 activity is autoregulated by NFAT factors which bind to two tandemly arranged NFAT sites within P1 and enhance its induction. In resting T cells, the NFATc1/β RNAs are the most prominent nfatc1 transcripts and their synthesis is reduced upon T-cell activation. However, following activation in primary effector T cells or in T-cell lines of human or murine origin, a 15–20-fold induction of NFATc1/αA RNA was detected, whereas only a 2–5-fold increase was observed for the NFATc1/αB or NFATc1/αC RNAs. Optimal induction of P1 promoter require involving of a persistent increase in free cytosolic Ca2+ induced by ionomycin, which stimulates the nuclear translocation and transcriptional activation of all NFATc factors and phorbol esters, which activate protein kinase C and other protein kinase pathways in T cells. This suggests that both TCR and co-receptor signals contribute to give full P1 nfatc1 induction. Because NFATc1/αA induction is unaffected in NFATc2+c3 double-deficient T cells, NFATc1 autoregulates its own synthesis by controlling P1 activity and NFATc1/αA induction. P1 promoter contains tandemly arranged NFAT core binding motif TGGAAA to witch bind monomeric NFATc1 proteins and numerous conservative binding sites of other transcriptional factors like CREB, Fos, ATF-2, Sp1, NF-kB and GATA suggesting complex multi-factor regulation of NFATc1 gene. We also highlight that initial phase of nfatc1 transcription in naive CD4+ T cells is controlled by the promoter P2 which is constitutively active in resting T cells. The activation of resting T cells results in a decrease of P2 and the induction of P1 activity and, under optimal conditions, in the predominant synthesis of NFATc1/αA in effector T cells. In addition to the high concentrations of poly A factors required for optimal pA1 function, the levels of transcription factors, in particular NFATs, must also increase for P1 induction. That could be explained by achievement of certain threshold levels for transcriptional activation. Finally, the altered transactivation potential of NFATc1/αA suggests a specific role for this NFATc1 protein in gene control, such as in Th1 effector cells where NFATc1/αA is synthesized at high concentrations.

La réussite de la transition vers la concurrence effective du marché des services de télécommunications dépend essentiellement des conditions optimales de l'interconnexion des opérateurs de réseau. Les opérateurs négocient les tarifs d'interconnexion qui peuvent être réciproques ou asymétriques. Les tarifs asymétriques sont présents, d'une part entre la boucle locale fixe et la boucle locale mobile et, d'autre part entre les opérateurs notifiés puissants sur le marché et les opérateurs non puissants. Nous étudions l'impact de l'asymétrie des tarifs d'interconnexion sur le développement concurrentiel du marché. Nous avons essayé de concevoir un environnement réglementaire favorable à l'autorégulation du marché de l'interconnexion. Nos travaux aboutissent à un modèle conceptuel cherchant à maintenir un juste équilibre entre le principe de laissez faire et le principe de réglementation des tarifs d'interconnexion.

Purpose: To determine the vascular reactivity (VR) capacity and visual function (VF) response to potent vasoconstrictor and vasodilatory provocations of retinal arterioles in healthy subjects. Methods: One hyperoxic hypocapnic and two graded hypoxic hypercapnic stimuli were administered. VR in response to gas provocation was assessed using the Canon Laser Blood Flowmeter. VF was assessed using high and low contrast ETDRS logMAR charts, Medmont C-100, and H.R.R. Pseudoisochromatic Plates. Results: Flow reduced by 23% (p=0.0001) during hyperoxic hypocapnia and increased by 18% (p=0.0129) during hypoxic hypercapnia. During hyperoxic hypocapnia, high contrast VA improved by -0.026 (p=0.0372). During hypoxic hypercapnia, high and low contrast VA were reduced (+0.033, p=0.0110; +0.025, p=0.0058, respectively). Colour vision was unaffected. Conclusions: The retinal arterioles demonstrated a greater capacity for vasoconstriction than vasodilation in response to the stimuli used in our study. Hyperoxic hypocapnia improved high contrast VA while hypoxic hypercapnia reduced high and low contrast VA.

Purpose: To determine the vascular reactivity (VR) capacity and visual function (VF) response to potent vasoconstrictor and vasodilatory provocations of retinal arterioles in healthy subjects. Methods: One hyperoxic hypocapnic and two graded hypoxic hypercapnic stimuli were administered. VR in response to gas provocation was assessed using the Canon Laser Blood Flowmeter. VF was assessed using high and low contrast ETDRS logMAR charts, Medmont C-100, and H.R.R. Pseudoisochromatic Plates. Results: Flow reduced by 23% (p=0.0001) during hyperoxic hypocapnia and increased by 18% (p=0.0129) during hypoxic hypercapnia. During hyperoxic hypocapnia, high contrast VA improved by -0.026 (p=0.0372). During hypoxic hypercapnia, high and low contrast VA were reduced (+0.033, p=0.0110; +0.025, p=0.0058, respectively). Colour vision was unaffected. Conclusions: The retinal arterioles demonstrated a greater capacity for vasoconstriction than vasodilation in response to the stimuli used in our study. Hyperoxic hypocapnia improved high contrast VA while hypoxic hypercapnia reduced high and low contrast VA.

Developement of a procedure to calculate intracranial pressure by means of arterial blood pressure and blood flow velocity in a big cerebral artery. Methods of systems theory are used. / Entwicklung eines Verfahrens zur Berechnung des Hirndrucks aus dem Bludrucksignal und der Blutströmungsgeschwindigkeit in einer großen Hirnarterie. Es werden Methoden der Systemtheorie verwendet.

Les molécules classiques du CMH de classe II sont responsables de la présentation de peptides exogènes par les cellules présentatrices d’antigène aux lymphocytes T CD4+. Cette présentation antigénique est essentielle à l’établissement d’une réponse immunitaire adaptative. Cependant, la reconnaissance d’auto-antigènes ainsi que l’élimination des cellules du Soi sont des problèmes à l’origine de nombreuses maladies auto-immunes. Notamment, le diabète et la sclérose en plaque. D’éventuels traitements de ces maladies pourraient impliquer la manipulation de la présentation antigénique chez les cellules dont la reconnaissance et l’élimination engendrent ces maladies. Il est donc primordial d’approfondir nos connaissances en ce qui concerne les mécanismes de régulation de la présentation antigénique. La présentation antigénique est régulée tant au niveau transcriptionnel que post-traductionnel. Au niveau post-traductionnel, diverses cytokines affectent le processus. Parmi celles-ci, l’IL-10, une cytokine anti-inflammatoire, cause une rétention intracellulaire des molécules du CMH II. Son mécanisme d’action consiste en l’ubiquitination de la queue cytoplasmique de la chaîne bêta des molécules de CMH II. Cette modification protéique est effectuée par MARCH1, une E3 ubiquitine ligase dont l’expression est restreinte aux organes lymphoïdes secondaires. Jusqu’à tout récemment, il y avait très peu de connaissance concernant la structure et les cibles de MARCH1. Considérant son impact majeur sur la présentation antigénique, nous nous sommes intéressé à la structure-fonction de cette molécule afin de mieux caractériser sa régulation ainsi que les diverses conditions nécessaires à son fonctionnement. Dans un premier article, nous avons étudié la régulation de l’expression de MARCH1 au niveau protéique. Nos résultats ont révélé l’autorégulation de la molécule par formation de dimères et son autoubiquitination. Nous avons également démontré l’importance des domaines transmembranaires de MARCH1 dans la formation de dimères et l’interaction avec le CMH II. Dans un second article, nous avons investigué l’importance de la localisation de MARCH1 pour sa fonction. Les résultats obtenus montrent la fonctionnalité des motifs de localisation de la portion C-terminale de MARCH1 ainsi que la présence d’autres éléments de localisation dans la portion N-terminale de la protéine. Les nombreux mutants utilisés pour ce projet nous ont permis d’identifier un motif ‘‘VQNC’’, situé dans la portion cytoplasmique C-terminale de MARCH1, dont la valine est requise au fonctionnement optimal de la molécule. En effet, la mutation de la valine engendre une diminution de la fonction de la molécule et des expériences de BRET ont démontré une modification de l’orientation spatiale des queues cytoplasmiques. De plus, une recherche d’homologie de séquence a révélé la présence de ce même motif dans d’autres ubiquitines ligases, dont Parkin. Parkin est fortement exprimée dans le cerveau et agirait, entre autre, sur la dégradation des agrégats protéiques. La dysfonction de Parkin cause l’accumulation de ces agrégats, nommés corps de Lewy, qui entraînent des déficiences au niveau du fonctionnement neural observé chez les patients atteints de la maladie de Parkinson. La valine comprise dans le motif ‘’VQNC’’ a d’ailleurs été identifiée comme étant mutée au sein d’une famille où cette maladie est génétiquement transmise. Nous croyons que l’importance de ce motif ne se restreint pas à MARCH1, mais serait généralisée à d’autres E3 ligases. Ce projet de recherche a permis de caractériser des mécanismes de régulation de MARCH1 ainsi que de découvrir divers éléments structuraux requis à sa fonction. Nos travaux ont permis de mieux comprendre les mécanismes de contrôle de la présentation antigénique par les molécules de CMH II. / Classical MHC class II molecules are responsible for the presentation of exogenous peptides to CD4+ T cells, which is essential for the establishment of the adaptive immune response. However, problems with recognition of auto-antigens and the subsequent cell elimination are at the root of numerous autoimmune diseases. Manipulation of the antigen presentation pathway in order to eliminate cells that present self-antigens could serve as potential treatments of many autoimmune disorders. It is therefore essential to deepen our knowledge regarding the mechanisms regulating antigen presentation. Antigen presentation is regulated both transcriptionally and post-translationally. Whereas many cytokines affect the latter, IL-10, an anti-inflammatory cytokine, causes the intracellular retention of MHC II molecules. This phenotype is the result of the ubiquitination of MHC II -chain cytoplasmic tail by MARCH1. MARCH1 is an E3 ubiquitin ligase expressed in secondary lymphoid organs. Until recently, little was known about the structure-function and the targets of MARCH1. Considering its major impact on antigen presentation, we were interested to study this E3 ligase in order to reveal how it is regulated and what are the required conditions for its function. In a first report, we have investigated the regulation of MARCH1’s protein expression. Our results revealed its autoregulation via dimer formation and autoubiquitination. In addition, we have demonstrated the involvement of MARCH1’s transmembrane domains for dimerization and MHC II interaction. In a second article, we highlighted the importance of MARCH1 localization for its function. Our results indicated that localization motifs in the C-terminal portion of MARCH1 were functional and revealed the presence of some sorting elements in the N-terminal portion of the molecule. A panel of mutant were used and allowed us to identify a ‘’VQNC’’ motif, located in the C-terminal cytoplasmic portion of MARCH1, in which the valine is central for the molecule’s function. Indeed, point-mutation of the valine led to a decrease in MARCH1 ability to relocate MHC II whereas BRET experiments revealed a modification in the spatial organization of the cytoplasmic tails. Moreover, a blast of sequence homology showed the presence or that same motif in others ubiquitine ligases, one of which is Parkin. Parkin is highly expressed in the brain and seems to be implicated in protein aggregates’ degradation. It was reported that malfunction of Parkin leads to the accumulation of aggregates, called Lewy bodies, responsible for the neural functions deficiencies observed in patients with Parkinson disease. Interestingly, a family for which the sickness was genetically transmitted has a mutated valine in the VQNC motif. We believe that the importance of this motif is not restricted to MARCH1 and could be generalized to others E3 ubiquitin ligases. This project enabled us to characterize the regulation mechanisms of MARCH1. In addition, we discovered various structural elements required for its function. Altogether, our data allows for a better understanding of the mechanisms controlling MHC II molecules antigen presentation.

Smegenų kraujotakos autoreguliacija (SKAR) – viena svarbiausių gyvybinių organizmo funkcijų, t.y. smegenų savybė moduliuoti apsirūpinimą krauju, išlaikant nekintamą kraujotaką,skirtingo smegenų perfuzinio spaudimo sąlygomis (Paulson et al., 1990). Perfuzinis spaudimas,įveikiantis išorinį pasipriešinimą (vidinį kaukolės slėgį ) ir vidinį (arteriolių sienelių tonusą,reguliuojamą vazomotorų) palaiko smegenų kraujotaką (Steiner et al., 2003b). Sveikame organizme garantuojamas smegenų kraujotakos pastovumas ir regioninis pasiskirstymas pagal metabolinius- funkcinius poreikius (Sato et al., 2009). Fizinio ar emocinio krūvio metu pakinta įprastinė organizmo sistemų veikla. Fizinis krūvis paveikia kiekvieną kardiovaskulinės sistemos komponentą. Fizinio krūvio metu padidėja aktyviai dirbančių raumenų metabolinis poreikis, sukeliama lokali vazodilatacija, kuri garantuoja adekvačią kraujo perfuziją ir sukelia bendro periferinio pasipriešinimo sumažėjimą (Sprangers et al., 1991; Brys et al., 2003), tuo pat metu padidėja sistolinis širdies tūris ir širdies susitraukimų dažnis (Brys et al., 2003; Duncker and Bache, 2008; Laughlin et al., 2011). Ilgalaikės treniruotės veikia kraujo spaudimą dėl lėtinio autonominės kontrolės mechanizmų poveikio ir kraujagyslių remodeliavimo (Pescatello et al., 2004b). Pasipriešinimo pratimai padidina periferinį kraujagyslių pasipriešinimą ir kairiojo skilvelio pokrūvį (Leddy and Izzo, 2009). Fizinio krūvio pradžioje būna smegenų kraujotakos padidėjimas... [toliau žr. visą tekstą] / Cerebrovasvular autoregulation (CA), i.e. an intrinsic ability of the brain to regulate its blood supply, maintaining stable blood flow within the wide range of cerebral perfusion pressure (CPP), is one of the most important vital functions in a living organism (Paulson et al., 1990). Perfusion pressure maintains cerebral blood flow by overcoming external (i.e. intracranial pressure) as well as internal resistance (i.e. vasomotor regulated tone of the arteriolar wall) (Steiner et al., 2003b). In healthy body, constant cerebral blood flow and regional distribution is maintained in accordance tometabolic and functional needs (Sato et al., 2009). Physical and emotional stress alters regular activity of organism. Physical exercise affects every component of cardiovascular system. Metabolic demand of actively exercising muscles increases during physical exercise; local vasodilatation develops, thus adequate blood perfusion is maintained and total peripheral resistance decreases (Sprangers et al., 1991; Brys et al., 2003). Meanwhile, systolic blood pressure and heart rate increases (Brys et al., 2003; Duncker and Bache, 2008; Laughlin et al., 2011). Due to long-term effect of autonomous control mechanisms and blood vessel remodeling, long-term physical training affects blood pressure (Pescatello et al., 2004b). Resistance exercises increase peripheral resistance of blood vessels and left ventricle afterload (Leddy and Izzo, 2009). At the onset of exercise, there is... [to full text]

<p>One of the key mechanisms that mediate renal autoregulation is the tubuloglomerular feedback (TGF) system, which is a negative feedback loop in the kidney that balances glomerular filtration with tubular reabsorptive capacity. In this dissertation, we develop several mathematical models of the TGF system to study TGF-mediated model dynamics. </p><p>First, we develop a mathematical model of compliant thick ascending limb (TAL) of a short loop of Henle in the rat kidney, called TAL model, to investigate the effects of spatial inhomogeneous properties in TAL on TGF-mediated dynamics. We derive a characteristic equation that corresponds to a linearized TAL model, and conduct a bifurcation analysis by finding roots of that equation. Results of the bifurcation analysis are also validated via numerical simulations of the full model equations. </p><p>We then extend the TAL model to explicitly represent an entire short-looped nephron including the descending segments and having compliant tubular walls, developing a short-looped nephron model. A bifurcation analysis for the TGF loop-model equations is similarly performed by computing parameter boundaries, as functions of TGF gain and delay, that separate differing model behaviors. We also use the loop model to better understand the effects of transient as well as sustained flow perturbations on the TGF system and on distal NaCl delivery.</p><p>To understand the impacts of internephron coupling on TGF dynamics, we further develop a mathematical model of a coupled-TGF system that includes any finite number of nephrons coupled through their TGF systems, coupled-nephron model. Each model nephron represents a short loop of Henle having compliant tubular walls, based on the short-looped nephron model, and is assumed to interact with nearby nephrons through electrotonic signaling along the pre-glomerular vasculature. The characteristic equation is obtained via linearization of the loop-model equations as in TAL model. To better understand the impacts of parameter variability on TGF-mediated dynamics, we consider special cases where the relation between TGF delays and gains among two coupled nephrons is specifically chosen. By solving the characteristic equation, we determine parameter regions that correspond to qualitatively differing model behaviors. </p><p>TGF delays play an essential role in determining qualitatively and quantitatively different TGF-mediated dynamic behaviors. In particular, when noise arising from external sources of system is introduced, the dynamics may become significantly rich and complex, revealing a variety of model behaviors owing to the interaction with delays. In our next study, we consider the effect of the interactions between time delays and noise, by developing a stochastic model. We begin with a simple time-delayed transport equation to represent the dynamics of chloride concentration in the rigid-TAL fluid. Guided by a proof for the existence and uniqueness of the steady-state solution to the deterministic Dirichlet problem, obtained via bifurcation analysis and the contraction mapping theorem, an analogous proof for stochastic system with random boundary conditions is presented. Finally we conduct multiscale analysis to study the effect of the noise, specifically when the system is in subcritical region, but close enough to the critical delay. To analyze the solution behaviors in long time scales, reduced equations for the amplitude of solutions are derived using multiscale method.</p> / Dissertation

In today’s aging population, cerebrovascular health plays a pivotal role in maintaining independence. The identification of early markers of change might help to plan more appropriate preventative and/or therapeutic measures. Recent focus has been placed on the relationship between peripheral vascular characteristics and cerebral hemodynamics. Given the compliant nature of the cerebral circulation, examination of passive properties, including critical closing pressure (CrCP) and resistance area product (RAP), might provide sensitive information about early functional changes. The purpose of this thesis was to provide a comprehensive view of peripheral vascular and cerebrovascular regulation in community-living older adults. In doing so, the thesis covered a spectrum, ranging from an examination of lifestyle factors, including habitual physical activity and sleep quality, to the impact of cerebrovascular health on functional status, characterized by gait speed. Key findings included the observation that while participants showed the ability to regulate cerebral blood flow (CBF) appropriately in most circumstances, the underlying mechanisms used to achieve this regulation was dependent on baseline vascular tone. During sit-to-stand transitions, individuals with lower baseline resistance relied primarily on fluctuations in RAP, which have been suggested to more closely reflect myogenic pathways. In contrast, individuals with elevated resistance had lower baseline CBF and relied relatively more on fluctuations in CrCP during the dynamic transition. The greater reliance on CrCP might indicate that these individuals were required to tap further into reserve pools to avoid hypoperfusion during the transition. Notably, those who exhibited a smaller dynamic RAP response during the posture change also had slower gait speed and higher occurrence of falls over the past year. These results provide evidence that passive cerebrovascular dynamics are sensitive markers linking peripheral and cerebrovascular properties with functional consequences for brain health in the elderly.