Sepsis is among the most prevalent diagnosed critical illnesses in the United States today. Although advances have reduced the overall morbidity and mortality associated with this illness, the enormous number of deaths associated with it shows a need for improved diagnostic and therapeutic optionsgent. Our laboratory has utilized RNA based technologies to aid in the treatment of histone induced multiple organ dysfunction syndrome seen in sepsis. Histones are proteins found in the nucleus of every cell in our body and have been shown to be released during sepsis. Such release induces damage to other cells, causing a feed forward cycle that results in organ failure and death. Several therapeutics have been utilized to neutralize histones but have shown considerable toxicity. This thesis describes the generation of single stranded RNA aptamers to bind and neutralize histone mediate damage without unwanted toxicity. We demonstrate that our aptamers selectively bind to histones but not serum proteins. In addition, we establish that our aptamers can neutralize all histone mediated cellular response in vitro and in vivo. Finally, we determined that our aptamers are able inhibit the histone feed forward cycle in a temporal fashion in our murine model of multiple organ dysfunction. This novel therapeutic demonstrates the selectivity and effectiveness needed to inhibit histones in several critical illnesses.

Final publication is available at http://ajp.amjpathol.org/ / 京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19583号 / 医博第4090号 / 新制||医||1014(附属図書館) / 32619 / 京都大学大学院医学研究科医学専攻 / (主査)教授 小池 薫, 教授 中山 健夫, 教授 福田 和彦 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DGAM

Histones are chromatin-associated proteins localized to the nucleus. However, extracellular histones are present in biofluids from healthy individuals and become elevated under disease conditions, such as neurodegeneration and cancer. Hence, extracellular histones may have important biological functions in healthy and diseased states, which are not understood. Histones have been reported in the proteomes of extracellular vesicles (EVs), including microvesicles and exosomes. The main aim of this thesis was to determine whether or not extracellular histones are secreted via EVs/exosomes. In an initial study (Paper I), I optimized methods for human embryonic kidney (HEK293) cell culture, transfection and protein detection using western blotting. In the main study (Paper II), I used oligodendrocyte cell lines (rat OLN-93 and mouse Oli-neu) to investigate the localization of histones to EVs. Western blotting of EVs purified from OLN-93 cell-conditioned media confirmed the presence of linker and core histones in them. Immunolocalization and transmission electron microscopy confirmed that histones are localized to EVs, as well as intraluminal vesicles (ILVs) within multivesicular bodies (MVBs). This suggests that histones are secreted via the MVB/exosome pathway. Localization of histones in EVs was investigated by biochemical/proteolytic degradation and purification followed by western blotting. Surprisingly, histones were associated with the membrane but not the luminal fraction. Overexpression of tagged histones in HEK293 cells confirmed their conserved, membrane localization. OLN-93 cell EVs contained both double stranded and single stranded DNA but nuclease and protease digestion showed that the association of histones and DNA with EVs was not interdependent. The abundance of histones in EVs was not affected by differentiation in Oli-neu cells. However, histone release was upregulated as an early response to cellular stress in OLN-93 cells and occurred before the release of markers of stress including heat shock proteins. Interestingly, a notable upregulation in secretion of small diameter (50-100 nm) EVs was observed following heat stress, suggesting that a sub-population of vesicles may be involved specifically in histone secretion in response to stress. Proteomic analyses identified the downregulation of endosomal sorting complex required for transport (ESCRT) as a possible mechanism underlying increased histone secretion. In Paper III, I developed methods to quantify extracellular histone proteins in human ascites samples from ovarian cancer patients.   In summary, we show for the first time that membrane-associated histones are secreted via the MVB/exosome pathway. We demonstrate a novel pathway for extracellular histone release that may have a role in both health and disease.