Hyperosmotic stress represents a major threat to cellular integrity and may lead to cell death via apoptosis. Accordingly, each cell reacts to hyperosmolarity with a set of functional and structural compensatory responses. Recently it has been shown that the mitochondria remodel during hyperosmotic stress. Although changes in mitochondrial dynamics could be crucial for both adaptation and apoptosis, hyperosmolarity-induced mitochondrial remodeling has not been characterized. We found that hyperosmotic stress translocates dynamin like protein 1 (DLP-1) to the mitochondria and induces DLP-1 mediated, F-actin-modulated, Rac-dependent fragmentation of these organelles in LLC-PK1 cells. Downregulation of DLP-1 mitigates the activation of the osmotic response element and increases the susceptibility of tubular cells to hyperosmotically-induced apoptosis, suggesting that DLP-1 (or mitochondrial fragmentation) may have a protective role during osmotic stress. The hyperosmolarity-triggered remodeling of the mitochondrion represents a hitherto unrecognized response to osmotic shock, which may have significant impact on adaptation and apoptosis.

Hyperosmotic stress represents a major threat to cellular integrity and may lead to cell death via apoptosis. Accordingly, each cell reacts to hyperosmolarity with a set of functional and structural compensatory responses. Recently it has been shown that the mitochondria remodel during hyperosmotic stress. Although changes in mitochondrial dynamics could be crucial for both adaptation and apoptosis, hyperosmolarity-induced mitochondrial remodeling has not been characterized. We found that hyperosmotic stress translocates dynamin like protein 1 (DLP-1) to the mitochondria and induces DLP-1 mediated, F-actin-modulated, Rac-dependent fragmentation of these organelles in LLC-PK1 cells. Downregulation of DLP-1 mitigates the activation of the osmotic response element and increases the susceptibility of tubular cells to hyperosmotically-induced apoptosis, suggesting that DLP-1 (or mitochondrial fragmentation) may have a protective role during osmotic stress. The hyperosmolarity-triggered remodeling of the mitochondrion represents a hitherto unrecognized response to osmotic shock, which may have significant impact on adaptation and apoptosis.

Mitochondria have evolved to play a vital role in both the life and death of a eukaryotic cell, through involvement in numerous cellular functions, such as the proficient production of energy from ATP biosynthesis and the regulation of programmed cell death. As a result, dysfunction in the biochemical processes housed within this organelle is implicated in diverse diseases, including cancer, diabetes, and neurodegenerative disorders. Advancing mitochondrial medicine by probing the subcellular biochemistry or targeting therapeutics into this organelle has motivated the development of effective mitochondrial delivery vectors. Thus, the rational design of novel mitochondrial-specific molecules, inspired by the success of cell-penetrating peptides, is described, whereby short synthetic peptides that retain the ability to traverse the plasma membrane, yet with mitochondrial-specificity were engineered. By modulating the overall physicochemical properties, through substitutions with both natural and synthetic amino acids, and monitoring the intracellular localization by confocal fluorescence microscopy, the requisite thresholds for achieving mitochondrial accumulation with a cationic peptide were elucidated. These systematic studies led to the development of a novel class of cationic yet lipophilic peptides, referred to as mitochondria-penetrating peptides (MPPs), which are readily cell permeable and preferentially localize into the mitochondria of living mammalian cells. The mechanisms of cellular uptake and mitochondrial matrix accumulation were investigated and the results from these studies suggest that MPPs utilize the negative membrane potential across these biological membranes to drive translocation. In addition, the effects of various chemical perturbations on the cellular and mitochondrial uptake, such as sequence, structure of the cation moiety, and chirality, were examined. The information obtained from these studies provided insight into the important features of these peptides and led to the design of an optimized molecule displaying pyridinium salt side chains. Moreover, MPPs were shown to be effective mitochondrial delivery vectors for diverse and bioactive small molecule cargo. In conclusion, the extensive biological and chemical characterization of MPPs revealed the importance of balancing the opposing characteristics of positive charge and lipophilicity to attain preferential sequestration into mitochondria, as well as provided evidence that these peptides will be suitable as mitochondrial delivery vectors.

Population studies and species identification based on morphological characteristics are often ambiguous. A different approach, e.g. molecular information, may be used to clarify the ambiguities . In this thesis, two categories of organisms, fish and corals, were chosen for study. The Danioninae, Candidia barbata and Opsariichthys pachycephalus, are extremely diversified morphologically among the Henchun peninsula and the northern Taiwan populations. Six geographic population of C. barbata were found using the mitochondrial D-loop DNA sequences. The sequences data also confirmed that the Henchun peninsula population was the most divergent group. On the other side of Taiwan strait, Opsariichthys bidens and Zacco platypus in northern Fujian province were also found to be divergent. It is likely that the Danioninae fishes migrated through the basins due to lowering of sea level during glacial stages. The discrepancies of morphological classification and molecular phylogenetics should be re-examined. The five coral mitochondrial genomes sequenced were Euphyllia ancora (19084 bp), Tubastrea aurea (18770 bp), Stylophora pistillata (17169 bp), Montipora aequituberculata (17886 bp), and Junceella fragilis (18724 bp). The gene organization of Octocorallia and Hexacorallia were highly conserved. All the stony corals contain a group I intron in the ND5 gene. In addition, the COI gene of Tubastrea aurea contains an extra intron, which consists an ORF of the LAGLI-DADG gene family. Of all the genes analysed, the transition rates were saturated except COI, COIII, Cytb and ND3; on the other hand, only 12S and ATP8 were saturated for the transversion rates. The results might refer to new gene markers for future species identification of corals.

Thesis (M. Med. Sc.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 53-59)f.

Thesis (Ph. D.)--University of Wisconsin--Madison, 2000. / Includes bibliographical references (leaves 213-223). Also available on Internet.

Thesis (M. Phil.)--University of Hong Kong, 1982.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

abstract / Anatomy / Doctoral / Doctor of Philosophy

Not available / text