Spinal Muscular Atrophy (SMA) is an autosomal, recessive form of childhood motor neuron disease and the most common genetic cause of infant mortality in the western world. SMA displays the characteristic hallmarks of a motor neuron disease, including loss of motor neurons in the spinal cord and atrophy of skeletal muscles. However, mounting evidence suggests that multiple tissues and body systems, beyond the neuromuscular system, are affected in SMA. Previous studies have highlighted alterations in the vascular system in both SMA patients and in a variety of mouse models of the disease, reporting alterations in vessel structure and perfusion abnormalities in peripheral tissues. In this project a detailed morphological investigation of the capillary beds of skeletal muscle and the spinal cord, two of the key pathological tissues in SMA was undertaken. This work was conducted in the Smn-/-;SMN2, Smn-/-;SMN2tg/+ and Smn-/-;SMN2;Δ7 mouse models of SMA. Significant alterations in the form and extent of the skeletal muscle and spinal cord capillary bed in SMA mice were identified, the most striking of which being a reduction in capillary density in SMA tissue when compared to control littermate tissue. In skeletal muscle, this reduction in capillary density was found to be a postnatal phenomenon, which occurred independently of denervation, in a variety of phenotypically distinct muscles and in all three SMA mouse models investigated. In the spinal cord, the capillary defect was seen to develop in a similar postnatal pattern to that observed in skeletal muscle. Importantly, a reduction in capillary density was observed in the ventral horn of the spinal cord, which houses motor neuron cell bodies, a known pathological target in SMA. These motor neurons were seen to be surrounded by fewer capillaries than their control counterparts. Using an injectable marker of hypoxia, it was determined that the cells of the ventral horn of SMA spinal cords are hypoxic. This suggests that the capillary defect identified has a functional impact on the tissues it is observed in. Having established the presence of capillary defect in SMA tissue, the effect of potential SMA therapeutics on the capillary defect was then investigated. The effect of HDAC inhibitors, which have been successfully shown to increase the levels of the disease causing Smn protein, was investigated. Treatment with the HDAC inhibitor SAHA was found to ameliorate the capillary defect, significantly improving capillary density in SMA skeletal muscle. This implies that the capillary defect is related to Smn levels in tissue and is amenable to therapeutics which increase Smn levels. Having characterised the capillary defect in SMA tissues in detail, a selection of tools were then used to investigate the underlying mechanisms resulting in the defect. First, using primary cell cultures, the growth and morphology of the key cellular component of capillaries, the endothelial cell, was examined. While displaying reduced levels of the Smn protein, endothelial cells isolated from SMA tissues showed no difference in growth rate, morphology or endothelial cell marker expression when compared to endothelial cells isolated from control tissue. This suggests that the defects seen in SMA capillary beds are not the result of defects in the structure and growth of endothelial cells. Second, retinas from SMA mice were found to exhibit similar capillary defects to those observed in SMA skeletal muscle and spinal cord. Given the entirely postnatal development of the retinal capillary network, the retina was identified as a useful experimental preparation for the further investigation of the mechanisms underlying the capillary defect in SMA. In summary, this work highlights the incidence and importance of capillary defects in mouse models of spinal muscular atrophy.

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Thesis (Ph.D.)--Ohio University, November, 2007. / Title from PDF t.p. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri--Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves: 139-147). Also available on the Internet.

The analysis of hemodynamic parameters and functional reactivity of cerebral capillaries is still controversial. The detailed mapping of tissue oxygen levels on the scale of micrometers cannot be obtained by means of an experimental approach, necessitating the use of theoretical methods in this investigating field. To assess the hemodynamics and oxygen transport in the cortical capillary network, 2D and 3D generic models are constructed (non-tree like) using random voronoi tessellation in which each edge represents a capillary segment. The modelling presented here is based on morphometric parameters extracted from physiological data of the cortex in which the spatial distribution of the diameter of the capillary is based on a Modified Murray method. This method led to a proper link between the diameter topology and flow pattern such that the maximum efficiency for flowing blood is concluded in the model of cortical capillary network. The approach is capable of creating an appropriate generic, realistic model of a cerebral capillary network relating to each part of the brain cortex because its geometrical density is able to vary the capillary density. The pertinent hemodynamic parameters are obtained by numerical simulation based on effective blood viscosity as a function of hematocrit and microvessel diameter, ESL (endothelial surface layer) effect, phase separation and plasma skimming effects. Using a solution method of the Green's function, the model is numerically developed to provide different simulations of oxygen transport for varying perfusion and metabolism in a mesoscale model of the cortical capillary network, bridging smaller and larger scale phenomena. The analysis of hemodynamic parameters (blood flow rate, velocity and hematocrit) demonstrates a consistency with the experimental observation. The distribution pattern of wall shear stress (WSS) in the network model supports the physiological data which in turn represents a proper matching between the hemodynamics and morphometrics in the cerebral capillary network. The distributions of blood flow throughout the 2D and 3D models seem to confirm the hypothesis in which all capillaries in a cortical network are recruited at rest (normal condition). The predictions showed a heterogeneous distribution in the flow pathways (aspect of length and inflow) and the pertinent transit time of red blood cell (RBC) in the network model which is dependent on varying perfusion rates. The analyses of oxygen transport in the model has demonstrated that oxygen levels in the tissue are sensitively dependent on the microvascular architecture and flow distribution. Unlike the homogeneous compartmental models, the mesoscale model presented in this study led to a prediction of tissue PO2 gradients throughout the tissue and a spatial distribution of tissue PO2 on the micron-scale for varying perfusion and metabolism. The predicted nonlinear changes in the oxygen extraction fraction (OEF) of the model as a function of the perfusion rate provide a basis for the quantitative interpretation of functional magnetic resonance imaging (fMRI) studies in terms of changes in local perfusion. The model is capable of predicting the brain oxygen metabolism under both normal and disease states, particularly, local hypoxia and local ischemia caused by misery perfusion syndrome. The hypoxic states for different perfusion rates and oxygen consumption rates demonstrated that in a significant decrease in brain perfusion (as can occur in stroke), the tissue hypoxia can be avoided by a moderate reduction in oxygen consumption rate. Increasing oxygen consumption rates (a realization of spatiotemporal stimulation of neural tissue) with respect to maintaining the tissue PO2 in the model led to a predicted flow-metabolism coupling in the model which supports the experimental studies of somatosensory and visual stimulation in humans by positron emission tomography (PET) and functional MRI (magnetic resonance imaging). A disproportionately large increase in blood supply is required for a small increase in the metabolic utilization (oxygen consumption rate) which in turn, is strongly dependent on the resting OEF such that the magnitude of the blood flow increases in the higher resting OEF.

A mathematical model has been developed which describes the fluid exchange from a capillary network of realistic topology, and calculates the spatial distribution of extravascular pressure. In this model, the capillaries are represented by a superposition of sources and sinks, resulting from a D'Arcy's Law description of flow in tissue of uniform fluid conductivity. The combination of this representation and Starling's Hypothesis, which relates the forces influencing transmural fluid exchange, yields an integral equation of the second kind which is solved numerically for the source strength distribution. Two important features of this approach are that: (i) it allows for interaction between the local tissue pressure field and fluid exchange (the model is called, therefore, the tissue pressure interaction model); and (ii) complex network morphologies are easily modeled. In single capillaries, this interaction, which decreases the predicted fluid exchange, increases with the magnitude of the ratio of capillary wall to extravascular fluid conductivities. For multiple capillaries, in addition to the "self" interaction of a capillary with the local extravascular pressure field, there is the possibility of interaction between capillaries ("capillary-capillary" interaction). The ratio of conductivities, and the additional factors of intercapillary distance and the number of capillaries, also affect interaction in capillary networks. Although interaction is only a weak function of intercapillary distance, it depends strongly on the number of capillaries. The major result from this work is that for the entire physiological range of conductivity ratios, interaction cannot be neglected in predicting fluid exchange. Although tissue pressure interaction affects the magnitude of fluid exchange, it does not greatly alter the pattern of extravascular flow. Therefore, previous models which neglected interaction are not invalidated by the present findings. The effect of interaction on planar capillary networks within a semi-infinite tissue space was also investigated. Flow boundary conditions were imposed at opposed planar boundaries, parallel with the capillary network. Interaction was found to decrease with decreasing distance between the boundary and plane of the capillaries. It still exerted a large effect, however, for distances greater than one-fourth the reference capillary length.

Recent investigations into the permeability of the kidney capillaries have produced conflicting reports. This study was an attempt to better describe the permeability of the kidney capillaries by using narrow-range macromolecular dextran fractions in four molecular sizes: MW 61,400, MW 77,000, MW 118,000, and MW 147,000. Permeability was measured by dextran concentration differences in plasma and kidney lymph. Permeability decreased as the dextran molecular weight increased. Molecular weights 61,400 and 77,000 penetrated into the kidney lymph. Molecular weight 118,000 exhibited greater difficulty in penetrating to the lymph. The largest fraction penetrated into the kidney lymph with greatest difficulty. Plasma expansion by saline infusion increased the permeability of all dextran fractions.

Objetivos. Analisar prospectivamente os dados de capilaroscopiaperiungueal (CPU) em pacientes com dermatomiosite recém-diagnosticada (DM) e correlacioná-los com citocinas angiogênicas séricas e características clínicas e laboratoriais. Métodos. Vinte e três pacientes com DM com < 12 meses de sintomas foram incluídos no estudo. Para avaliar os níveis de citocinas séricas, os pacientes foram pareados 23 voluntários saudáveis por idade, sexo e etnia. As características da CPU e os parâmetros da atividade da DM foram analisados. Resultados. Foram observados níveis aumentados de angiogenina (ANG) e de fator de crescimento de endotélio vascular-1 (VEGF1) séricos de forma significativa em pacientes com DM em comparação com os controles saudáveis. Os níveis de ANG sérica correlacionaram-se positiva e negativamente, respectivamente, com a densidade capilar e as áreas avasculares. Além disso, a densidade capilar correlacionou-se inversamente com o número de capilares ectasiados, capilares gigantes e áreas avasculares. O número de capilares ectasiados correlacionou-se positivamente com a Escala Visual Analógica (EVA) do paciente e do médico, a presença de eritema facial, capilares gigantes e micro-hemorragias. Os capilares gigantes apresentaram correlação positiva com EVA do médico e da atividade cutânea, capilares ectasiados, áreas avasculares, micro-hemorragias e capilares em forma de arbustos e correlação negativa com a densidade capilar. Micro-hemorragias correlacionaram-se positivamente com o sinal de \"V do decote\" e EVA do médico. O VEGF1 sérico não mostrou relação com os parâmetros da CPU ou com características clínicas e laboratoriais relacionadas a DM. Além disso, 15 dos 23 pacientes foram avaliados prospectivamente após 3,21 anos. Todos os pacientes tiveram resposta clínica com melhora significativa em todos os parâmetros da CPU, exceto em relação a capilares ectasiados e número de capilares em forma de arbustos. Conclusões. A CPU pode ser uma ferramenta útil para avaliar a atividade da doença em DM de início recente e a sua correlação com a ANG sérica sugere a participação desta citocina na neoangiogênese da doença / Objectives. To prospectively analyze nailfold capillaroscopy (NC) findings in new-onset dermatomyositis (DM) and to correlate NC findings with serum angiogenic cytokines and DM clinical and laboratory features. Methods. Twenty-three patients with DM who experienced < 12 months of symptoms were included in the study. To assess serum cytokine levels, 23 age-, sexand ethnicity-matched healthy volunteers were used. NC characteristics and DM activity parameters were analyzed. Results. Significantly higher serum angiogenin (ANG) and vascular endothelial growth factor-1 (VEGF1) levels were observed in DM patients than in controls. Capillary density and avascular areas correlated positively and negatively, respectively, with serum levels of ANG. Moreover, the capillary density correlated inversely with the number of enlarged and giant capillaries and avascular areas. The number of enlarged capillaries correlated positively with patient and physician VAS, the presence of a facial rash, giant capillaries and microhemorrhages. Giant capillaries had a positive correlation with physician and cutaneous VAS, enlarged capillaries, avascular areas, microhemorrhages and bushy capillaries and a negative correlation with capillary density. Microhemorrhages correlated positively with the \"V-neck\" sign and physician VAS. VEGF1 showed no relationship with the NC parameters with DMrelated clinical and laboratory features. Additionally, 15 out of 23 patients were assessed prospectively after 3.21 years. All patients had a major clinical response with significant improvement in all NC parameters, except for enlarged and bushy capillaries. Conclusions. The NC may be a useful tool to assess disease activity in recent-onset DM, and it can also reinforce the role of ANG in the angiogenesis of this myopathy