[Cell-Free Epigenome]
Genome and Epigenome Analysis of Circulating Nucleic Acid-based Liquid Biopsy

RESEARCH OVERVIEW

• The human body works differently in space, as compared to on Earth. To understand the changes on a genetic level, it is important to analyze gene expression under spaceflight conditions.
• The Genome and Epigenome Analysis of Circulating Nucleic Acid-based Liquid Biopsy (Cell-Free Epigenome) investigation uses a newly developed blood test method to analyze molecules called “cell-free DNA (cfDNA) and circulating RNA”, which are released from cells inside the body. Chemical modifications of DNA can reflect cellular status of internal organs corresponding to origin of cfDNA, while RNA contents indicates gene expression. By combining information from DNA and RNA, scientists can estimate genetic events in various tissues without direct access to these organs.
• This study may provide important clues about genetic and cellular processes that play important roles in adaptation of the human body to the space environment. Such information is useful for developing advanced methods to accurately measure health of astronauts.

DESCRIPTION

Unlike conventional bulk DNA profiling from blood, which mainly observes blood cells, cell-free DNA (cfDNA) and circulating RNA (cRNA) profiling detects the cellular status of internal body without invasive operation. This is because cfDNA and cRNA represent genetic and epigenetic information released from cells in tissue. When cells are damaged or targeted by the immune system, the original cellular DNA and RNA are thought to be released into circulating blood flow. Therefore, cfDNA and cRNA profiling can be used as “liquid biopsy” to assess cellular status and integrity of tissue inside the body.

The Genome and Epigenome Analysis of Circulating Nucleic Acid-based Liquid Biopsy (Cell-Free Epigenome) investigation compares the cfDNA and cRNA profile among samples collected on Earth and during spaceflight. The results should provide key information including (i) low-frequency gene mutation events in internal tissue cells, (ii) cellular origin of cfDNA which represents sites of cellular damage or excessive tissue turnover by alteration of stem cell activity or cell death, and (iii) cRNA expression profile to screen gene-specific biomarker of stress response.

Direct sequencing of cfDNA by ultra-high throughput sequencing could detect mutations in DNA. When combined with advanced methods to reduce sequencing error, DNA mutations detected by sequencing can be a reliable indicator of genetic damage by space radiation in the human body under normal DNA repair function.

The Research Team also performs detection and quantification of epigenetic modification (methylation) of cfDNA. Since the methylation pattern of DNA is specific for cell types, this information can be used to identify the cellular origins of cfDNA. The cRNA expression profile indicates cellular pathways that respond against environmental stress. If there are any genes specifically up or downregulated during flight, these genes could be important to enhance environmental tolerance. Such genes may be targets for drug development, or specific biomarker candidates.

SPACE APPLICATIONS

Better methods of detecting stress biomarkers – measurable, specific characteristics – in astronauts living and working in the space environment advances crew health monitoring and countermeasure development. Comparing human data from this study with previous mouse project data adds to a better understanding of mammalian response to the space environment, and may lead to identification of genetic changes useful as biomarkers.

EARTH APPLICATIONS

Results also contribute to understanding how cells work to maintain bodily functions on Earth. This supports development of medical treatments for issues associated with aging, and understanding of biological responses to radiation and microgravity exposure, that cause aging-related symptoms.

OPERATIONAL REQUIREMENTS AND PROTOCOLS

Cold Stowage requirement: Blood tubes are stored in the Minus-Eighty Freezer for ISS (MELFI) until return to Earth.

• Blood drawings of 5 ml are performed 3 times during preflight, 4 times in flight, and 4 times during postflight for plasma sampling.
• The blood tubes are centrifuged, then, stored at -80°C.
• One extra vial of 5 ml blood is collected for genome sequencing at first pre-BDC. It is inverted and frozen at -80°C.