http://hdl.handle.net/1721.1/7754 http://hdl.handle.net/1721.1/41804 Determination of the historical changes in primary and secondary risk factors for cancer using U.S. public health records Herrero Jimenez, Pablo, 1972- Overall cancer mortality rates have risen from about 4% of all deaths in the early 20th century to about 25% of all deaths by the end of the century in the United States. To assess any potential hypotheses for this increase required knowledge of the mortality rate changes specific to each form of cancer, and the time points when these rates had changed. For this purpose, population and cancer mortality data of the U.S. were collected and organized to create age-specific mortality rates for each birth decade from the 1800s forward, delineated by the organ of incidence. Concurrently, cancer survival data were collected so as to correct for any effect of improved treatment on historical changes in cancer mortality rates. To analyze these data, a mathematical model for the three-stage process of carcinogenesis (initiation, promotion, and progression) was developed to estimate for each birth decade cohort the value of the fraction of the cohort at lifetime risk for that cancer, the value of the growth rate of the respective precancerous lesion, and the values for the mutation rates of normal and precancerous cells in the organ of incidence. This methodology permits the analysis of the potential historical effect of new chemical exposures during the last century on cancer mortality rates. These chemical exposures represent potential risk factors that determine the fraction of the population at risk of developing cancer (lifetime, primary risk factor), or that hasten death by cancer by altering either mutation or cell kinetic rates (accelerating, secondary risk factor.) (cont.) COLON CANCER: Application of this model on the colon cancer mortality data resulted in the estimate that 42% of the population in the U.S. was at risk for developing colon cancer, independent of gender or race. More importantly, there was no significant historical change in the calculated fraction at risk for birthyear cohorts from 1860 to 1940, suggesting that the primary risk factors for colon cancer are not environmental. Although direct observation of in vivo mutation rates of colonic cells does not yet exist, the calculated rate for the first initiation mutation in the colon was interestingly found to be similar to the mutation rate observed for the hprt locus in human peripheral T-cells (-2.1 x 10-7 per cell year) and the spontaneous mutation rate of the hprt locus of human B-cells in culture. The estimate for initiation mutation rates increased no more than two-fold from the birthyear cohort of 1860 to the birthyear cohort of 1940, except for European American females for which calculated initiation mutation rates were historically invariant, but since the accuracy of primary data for mortality rates and survival rates cannot be ascertained, the apparent small differences might admittedly arise from unknown biases. Evaluation of the parameter of the growth rate of precancerous lesions showed no significant historical change on this parameter. Curiously, the calculated doubling rate of these lesions (-0.17-0.21) was found to be similar to the growth rate of children, suggesting that the required initiation events have the net effect of potentially reactivating pathways involved in child development. (cont.) The predominant historical change in the observed mortality rates for colon cancer occurred only at old ages. ... Thesis (Sc. D.)--Massachusetts Institute of Technology, Division of Bioengineering and Environmental Health, 2001. Includes bibliographical references (p. 346-354). Sun, 29 Oct 2000 22:58:59 GMT http://hdl.handle.net/1721.1/41586 Flow-induced mechanotransduction in cell-cell junctions of endothelial cells Rabodzey, Aleksandr Endothelial cells show an unexpected behavior shortly after the onset of laminar flow: their crawling speed decreases ~40% within the first 30 min, but only in a confluent monolayer of endothelial cells, not in subconfluent cultures, where cell-cell interactions are limited. This led us to study early shear effects on cell-cell adherens junctions. We found a 30±6% increase in the number of VE-cadherin molecules in the junctions. The strength of interactions of endothelial cells with surfaces coated with recombinant VE-cadherin protein also increased after laminar flow. These observations suggest that endothelial cell junction proteins respond to flow onset. The process of clustering may induce diffusion of monomers to the junction area, resulting in an overall increase in VE-cadherins in the junctions. To directly confirm the role of adherens junctions in the decrease in cell crawling speed, we used siRNA-knockdown technique to produce cells lacking VE-cadherin. These cells showed no decline in crawling speed under flow. Our interpretation is consistent with previous data on junction disassembly 8 hr after flow onset. The speed of endothelial cell crawling returns to the original level by that time, and junctional disassembly may explain that phenomenon. In order to understand better the change in VE-cadherin distribution under flow and during junction formation and remodelling, we developed a mathematical model of VE-cadherin redistribution in endothelial cells. This model allowed us to develop a quantitative framework for analysis of VE-cadherin redistribution and estimate the amount of protein in the junctions and on the apical surface. In addition to that, the model explains rapid junction disassembly in the leukocyte transmigration and junction formation in subconfluent cells. (cont.) These studies show that intercellular adhesion molecules are important in the force transmission and shear stress response. Their role, however, is not limited to flow mechanotransduction. Intercellular force transmission has an important application - organ development and, specifically, angiogenesis. We studied the role of VE-cadherin in vessel development in HUVECs and showed that VE-cadherin-null cells do not form vessels in the in vitro assay. This observation confirms the important role of intercellular force transmission in response to external force caused by flow or exerted by other cells. Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2006. Includes bibliographical references (leaves 86-92). Sat, 29 Oct 2005 22:58:59 GMT http://hdl.handle.net/1721.1/33869 Chondrocyte gene expression and intracellular signaling pathways in cartilage mechanotransduction Fitzgerald, Jonathan Basil Chondrocytes respond to in vivo mechanical loads by regulating the composition of the cartilage extracellular matrix. This study utilized three loading protocols that span the range of forces and flows induced by in vivo loading. Constant (static) compression of cartilage explants induces a transient hydrostatic pressure buildup and fluid exudation from the compacted matrix until relaxation leads to a new equilibrium compressed state. Dynamic compression induces cyclic matrix deformation, hydrostatic pressures, fluid flows, and streaming currents. Dynamic tissue shear causes cyclic matrix deformation only. After applying these loading protocols to intact cartilage explants for 1 to 24 hours, we used real-time PCR to measure the temporal expression profiles of selected genes associated with cartilage homeostasis. In concurrent experiments, we assessed the involvement of intracellular signaling pathways using molecular inhibitors. In order to interpret the results we developed two techniques that reliably clustered intermediate-sized datasets using principal component analysis and k-means clustering. Mechanical loading regulated a variety of genes including matrix proteins, proteases, protease inhibitors, transcription factors, cytokines, and growth factors. Static compression transiently upregulated matrix proteins, however, mRNA levels were suppressed by 24 hours. (cont.) Dynamic compression and dynamic shear increased matrix protein transcription particularly after 24 hours. In contrast, matrix proteases were upregulated by all 24 hour loading regimes, particularly static compression. Taken together these results demonstrate the functionally-coordinated regulation of chondrocyte gene transcription in response to mechanical forces, and support the hypothesis that dynamic loading is anabolic for cartilage and static loading is anti-anabolic. Intracellular calcium release, cAMP activation of protein-kinase-A, and the phosphorylation of MAP kinases (ERK1/2, p38), were all identified as signaling events necessary for mechanically-induced transcription. In addition, we measured the immediate, transient increase in mRNA levels of transcription factors downstream of the MAP kinase pathway (c-Fos and c-Jun), in response to all three loading types. The prevention of protein synthesis during static compression suppressed mechanically-induced transcription suggesting that signaling molecules are synthesized in response to mechanical forces. Comparison of this well characterized model of normal cartilage mechanotransduction to what occurs within diseased cartilage will hopefully provide insight into the mechanisms driving the progression of osteoarthritis. Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2005. Includes bibliographical references (p. 152-167). Fri, 29 Oct 2004 22:58:59 GMT http://hdl.handle.net/1721.1/41342 Studies of DNA lesion-protein interactions : toward the development of DNA repair-inhibiting chemotherapeutic agents Chen, Zheng-Huan, 1964- Thesis (Ph. D.)--Massachusetts Institute of Technology, Division of Toxicology, 1996. Vita. Includes bibliographical references (leaves 160-188). Sun, 29 Oct 1995 22:58:59 GMT