Littoral zone primary production is under-studied relative to the pelagic zone, despite recent work indicating its importance to the lake as a whole. Benthic extracellular material, shown to be important for food web dynamics and stabilization of the surrounding ecosystem in the marine intertidal, is even less frequently studied in lakes. I examined the environmental and community level drivers of benthic primary production, and found production to increase over the summer and to decrease with disturbance. I also found that maximum photosynthesis and efficiency under sub-saturating light both increased with depth, contrary to the existing, laboratory-derived paradigm of a trade-off between the two. I also examined how benthic primary production and environmental factors were correlated with the amount of extracellular material. I found that loosely bound colloidal extracellular material decreased with in situ photosynthesis and was affected by algal community composition, whereas tightly bound capsular extracellular material was affected only by date, indicating that capsular material is refractory in lakes just as it is in marine systems. Contrary to what is seen in marine systems, however, there were no direct effects of the environmental factors, possibly the result of physical differences between these systems. I also performed the first cross-ecosystem comparison of extracellular material. Despite relatively few studies from lakes and streams, and methods which have not been standardized, I found that lakes were similar to marine intertidal zones both in their median amounts of extracellular material and their relationships between extracellular material and chlorophyll a. This relationship appeared to be quite different in streams, with very low amounts of extracellular material found at sites with either high or low chlorophyll a concentrations. While the above studies will improve future estimates of lake carbon budgets and whole-lake production, my development of a permutation test for path analysis, and a novel application of the Bayesian principal components analysis, will assist all ecological studies that are often restricted in their sample sizes or compromised by missing data.

Millions of people around the world suffer from the debilitating effects of inflammatory bone diseases characterized by excessive bone loss due to an increase in osteoclast formation and activity. Osteoclasts are multinucleated cells responsible for bone resorption in health and disease. Arthritic joints also have elevated levels of extracellular matrix proteins affecting the disease progression. The interaction between osteoclasts and the external milieu comprised of extracellular matrix proteins through integrins is essential for modulating the formation and activity of osteoclasts. The focus of this thesis was to elucidate how the interaction between the extracellular matrix proteins and osteoclasts regulates osteoclast formation and activity and the role of alphavbeta3 in this process. In primary rabbit osteoclast cultures, blocking the integrin alphavbeta3 using Vitaxin, an anti-human alphavbeta3 antibody, decreased osteoclast resorption by decreasing osteoclast attachment. Vitaxin’s inhibitory effect on osteoclast attachment was enhanced when osteoclasts were pretreated with M-CSF, a growth factor known to induce an activated conformation of the integrin alphavbeta3. Using the RAW264.7 cell line, the effects of the matrix proteins fibronectin and vitronectin on osteoclast activity were compared to those of osteopontin. Both fibronectin and vitronectin decreased the number of osteoclasts formed compared to osteopontin. Fibronectin’s effect on osteoclastogenesis was through decreasing pre-osteoclast migration and/or fusion but not through inhibiting their recruitment. In contrast, fibronectin induced resorption through increasing resorptive activity per osteoclast in comparison to vitronectin and osteopontin. These stimulatory effects were accompanied by an increase in the pro-inflammatory cytokines nitric oxide and IL-1beta Crosstalk between the signalling pathways of nitric oxide and IL-1betawas suggested by the ability of the nitric oxide inhibitor to decrease the level of IL-1beta which occurred exclusively on fibronectin. Osteoclasts on fibronectin also had a compact morphology with the smallest planar area while vitronectin increased the percentage of osteoclast with migratory morphology and osteopontin induced osteoclast spreading. The increase in compact morphology on fibronectin was associated with a decrease in extracellular pH. Low extracellular pH was found to increase the total time osteoclasts spend in a compact phase. These results show that matrix proteins differentially regulate osteoclast formation, activity and morphology.

Littoral zone primary production is under-studied relative to the pelagic zone, despite recent work indicating its importance to the lake as a whole. Benthic extracellular material, shown to be important for food web dynamics and stabilization of the surrounding ecosystem in the marine intertidal, is even less frequently studied in lakes. I examined the environmental and community level drivers of benthic primary production, and found production to increase over the summer and to decrease with disturbance. I also found that maximum photosynthesis and efficiency under sub-saturating light both increased with depth, contrary to the existing, laboratory-derived paradigm of a trade-off between the two. I also examined how benthic primary production and environmental factors were correlated with the amount of extracellular material. I found that loosely bound colloidal extracellular material decreased with in situ photosynthesis and was affected by algal community composition, whereas tightly bound capsular extracellular material was affected only by date, indicating that capsular material is refractory in lakes just as it is in marine systems. Contrary to what is seen in marine systems, however, there were no direct effects of the environmental factors, possibly the result of physical differences between these systems. I also performed the first cross-ecosystem comparison of extracellular material. Despite relatively few studies from lakes and streams, and methods which have not been standardized, I found that lakes were similar to marine intertidal zones both in their median amounts of extracellular material and their relationships between extracellular material and chlorophyll a. This relationship appeared to be quite different in streams, with very low amounts of extracellular material found at sites with either high or low chlorophyll a concentrations. While the above studies will improve future estimates of lake carbon budgets and whole-lake production, my development of a permutation test for path analysis, and a novel application of the Bayesian principal components analysis, will assist all ecological studies that are often restricted in their sample sizes or compromised by missing data.

ABCA1 is a key plasma membrane protein required for the efflux of cellular cholesterol to extracellular acceptors, particularly to apoA-I. This process is essential to maintain cholesterol homeostasis in the body. The detailed molecular mechanisms, however, are still insufficiently understood. Also, the molecular identity of ABCA1, i.e. channel, pump or flippase, remains unknown. In this study we analyzed the extracellular ATP levels in the medium of ABCA1-expressing BHK cells and RAW macrophages and compared them to the medium of relevant non-expressing cells. We found that the extracellular ATP concentrations are significantly elevated when cells express ABCA1. Importantly, a dysfunctional ABCA1 mutant (A937V), when expressed similarly as WT-ABCA1, is unable to raise extracellular ATP concentration. This suggests a causal relationship between functional ABCA1 and elevated extracellular ATP. To explore the physiological role of elevated extracellular ATP, we analyzed ABCA1-mediated cholesterol efflux under the conditions where extracellular ATP levels were modulated. We found that increasing extracellular ATP within the physiological range, i.e. < μM, promotes cholesterol efflux to apoA-I. On the other hand, removing extracellular ATP, either by adding apyrase to the medium or by expressing a plasma membrane bound ecto-nucleotidase CD39, abolishes cholesterol efflux to apoA-I. Based on these results we conclude that, through direct or indirect mechanisms, ABCA1 functions to raise ATP levels in the medium. This elevated extracellular ATP is required for ABCA1-mediated cholesterol efflux to apoA-I.

国立情報学研究所で電子化したコンテンツを使用している。

Dissertation Thesis (Ph.D.)--University of South Florida, 2007. / Title from PDF of title page. Document formatted into pages; contains 202 pages. Includes vita. Includes bibliographical references.

Diss. (sammanfattning) Göteborg : Univ. , 2007. / Härtill 3 uppsatser.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Vita. "August 2007" Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available online.