Asking the Right Questions

Ingrid Eftedal studies the biological processes that may lead to DCS.

Ingrid Eftedal, Ph.D., stands beside a small hyperbaric chamber used for animal studies.

With expertise lying at the intersection of human physiology, genetics and the underwater environment, Ingrid Eftedal, Ph.D., studies the genetic and molecular mechanisms involved in the body's responses to diving. A research scientist at the Department of Circulation and Medical Imaging at the Norwegian University of Science and Technology (NTNU), Eftedal's diverse background includes work in molecular biology, forensic genetics, civil engineering, biophysics and medical technology.

Early in her career, Eftedal worked on the development of software control systems for small pressure chambers. The impact of the 1986 Chernobyl accident on northern parts of Norway influenced her doctoral research, which examined the interactions between radiation and living cells. Eftedal's doctoral work aimed to better understand how certain enzymes were able to prioritize repair of the most important parts of genetic material. Her work has since evolved into finding ways to better understand how specific stressors in diving — such as hypoxia, immersion and bubble formation — affect the expression of genes.

She now studies the interactions between genes and the environment that result from the body's response and acclimatization to diving. These interactions manifest as changes in gene expression (i.e., state of activity). Injury can occur in the diving environment because the body responds either inadequately or excessively to stressors. But not all changes in gene expression are bad. Some are adaptive and help the body maintain balance, increasing its resistance to damage or improving its ability to repair itself.

Dive safety has improved with the development of better equipment, procedures, education and awareness, but much remains to be learned about divers' risk of decompression sickness (DCS). In her current fitness-to-dive project, Eftedal focuses specifically on changes in immune-system cells. She aims to determine which cells are affected by diving, study the activity of genes within those cells and examine the outcome of those changes to better understand what is happening during breath-hold and compressed-gas diving.

Eftedal's goal is to distinguish between normal physiological responses and diving-related disease pathways. She was recently awarded the 2016 R.W. "Bill" Hamilton Scholarship, funded by the DAN Foundation and administered by the Women Divers Hall of Fame, to support her research on working saturation divers. We appreciate her willingness to talk with us about her research.

How can gene expression help us distinguish between normal physiological changes and maladaptive responses to diving?
Changes in gene expression, such as upregulation and downregulation of genes (see sidebar), can be detected before the onset of symptoms or clinical signs of DCS. This information can be used to create a profile of which genes are being expressed and how much. Such a profile provides a snapshot of the biological state or activity of any cell or tissue type after exposure to some stressor.

Measuring the gene expression of several hundred to thousands of genes reveals patterns that point to the factors instigating the changes. For example, while we usually think of our immune system in terms of host defense against things that are bad for our health, such as viruses or bacteria, I believe that the immune and inflammatory responses that we see in healthy divers are markers of successful short-term adaptation.

Perhaps the changes we see are directly involved in antioxidant defenses. Right after scuba diving we see upregulation of genes that code for essential antioxidant enzymes such as mitochondrial superoxide dismutase 2 (SOD2), glutathione peroxidase 4 (GPX4), thioredoxin-1 (TXN1) and nuclear factor kappa B (NF-kB). These factors are known to play roles in the body's defense system. It is possible that such upregulation is a defensive or adaptive response to environmentally incurred oxidative stress, an imbalance that occurs when the body cannot counteract the harmful effects of or repair damage caused by free radical production.

Eftedal works in the field as well as the lab; here a life-support supervisor shows the dive control center aboard the Skandi Arctic, the most advanced dive-support vessel in the world.

Is there a relationship between repeated diving exposures and immune-system health?
We know that repeated exposures to certain chemicals affect long-term risks of some autoimmune conditions and cancers, but we do not yet know how diving affects the immune system in the long term. Even when there are no symptoms of DCS, secondary health effects may arise from the biological defenses activated during diving to protect us from acute injury.

Changes that affect immune cells may alter our susceptibility to infections and our long-term risk to diseases. If we can identify the biological processes altered by diving and determine whether they become fixed in our immune system over time, we may be able to better prepare divers and improve medical follow-up.

What can gene expression tell us about a person's risk of DCS?
Although changes in gene expression do not yet amount to a diagnosis of DCS, in the future these changes may provide clues in the search for objective biomarkers during the diagnostic process. Understanding the biological processes involved in disease development is useful for implementing targeted prevention and treatment and is necessary for the advancement of precision medicine.

Normally, a physician detects disease through clinical evaluation, but changes in gene expression may point to risks and causes before signs or symptoms are noted. It is possible to count the number of transcripts made to determine the amount of gene activity or expression. By comparing transcriptomes (all the ribonucleic acid [RNA] transcripts within a cell) of different types of cells, one can determine a normal level of gene activity and assess how changes from that set point may contribute to disease or DCS for a given individual. Much more research will be needed before we can leverage this approach to yield useful information.

Short-term adaptive immune and inflammatory responses happen as a response to acute environmental stress, but these responses are successful only if the diver surfaces without illness. Short-term success may come at a price if acclimatization increases the risk of other diseases in the long term.

How does the study of gene expression complement other research being done to help understand the causes of DCS?
The identification of decompression-induced bubbles as a trigger for DCS is unquestionably important. The most obvious advantage of gene expression analysis is the opportunity to look into complex biological processes at a detailed level.

The process of altering gene expression is always controlled by one or more so-called transcription factors, which have been thoroughly mapped over decades. In general, we now understand what activates any particular factor in a cell. Once we observe some pattern of gene expression, we may be able to work backward to determine the cause of those changes. This may allow us to better understand which specific environmental factors are involved in the response observed.

Transcriptomics (study of transcriptome and their function), together with other "-omics" such as proteomics (study of proteins) and metabolomics (study of chemical processes and metabolites in cells), helps us understand cellular biology and physiology. This may eventually provide keys to targeted treatment of DCS.

This heat-map visualization shows messenger RNA (mRNA) levels for the top-50 differentially expressed genes in the stationary blood transcriptomes of 10 divers compared with those of nine nondivers.

Do breath-hold and scuba diving affect the immune system differently?
Both breath-hold and scuba diving (but probably not long saturation diving) appear to affect the immune system in similar ways. Oxygen is a common denominator; it is vital fuel for all cells that contain mitochondria, the organelles responsible for cellular respiration and energy production. The oxygen-triggered responses we see may play a role in susceptibility to DCS.

Both breath-hold and scuba diving cause pronounced shifts in RNA transcription patterns characteristic of specific leukocytes (white blood cells involved in the immune system). We see downregulation of cytotoxic lymphocytes, CD8+ T lymphocytes (that destroy targeted cells) and natural killer (NK) cells, and we see upregulation of genes expressed by neutrophils, monocytes and macrophages.

We see persistent changes in experienced scuba divers, and these changes are still measureable at least two weeks after their last dive. The nature of the changes we found — i.e., the total pattern of genes that were differently expressed — led us to conclude that the divers were in a lasting biological state of defense against oxidative stress. It is possible that extensive diving may cause persistent changes in pathways controlling apoptosis (programmed cell death), inflammation and innate immune responses. It remains unresolved whether breath-hold diving alters the immune system's defensive function. Data suggest that defensive responses that resolve inflammation and limit cell toxicity promote physiological balance in healthy athletes.

What are some challenges you face in interpreting and applying your results?
As long as you know which cell types you are studying, transcriptome analysis allows room to interpret data without a predetermined hypothesis. You have to consider thousands of genes, however, to make sense of the actual biology. Good software tools are available for gene expression analysis, but the challenge is determining which transcriptome data to use with these tools.

Although the software is based on everything we already know about the activity of every gene we consider, most research on human transcriptomes is concerned with diseases such as cancer or diabetes. The way genes are expressed in these disease states is not always relevant to diving. We spend an incredible amount of time poring over scientific reports to make sense of the patterns in our data and then constructing a coherent profile.

Eftedal and Andreas Møllerløkken breathe 100 percent oxygen during an
experimental chamber dive.
What insights might the research and dive communities gain from your work?
Norway has a very long coastline, and most of its major industries relate to the ocean. Offshore oil companies and fish farms employ a significant number of divers, and while the offshore industry has developed health and safety protocols in diving over several decades, there are emerging areas in aquaculture in which the methods and procedures are still evolving.

Our fitness-to-dive project studies the impact of hyperbaric exposures on the circulatory and central nervous systems of humans and animal diver models. While the fitness-to-dive project is primarily concerned with occupational saturation diving, we have done smaller projects that are relevant to the recreational community.

If we understand the biological processes that push the body toward DCS, we will be better able to develop interventions. These biological processes are likely gradual, meaning that at some point the body reaches a limit at which it can no longer compensate. I believe that gaining a detailed understanding of the progression to symptoms and learning more about the long-term effects of extensive diving is of great potential benefit to the diving community.

Occupational divers make provocative dive profiles under sometimes extreme conditions. Greater understanding of the physiological impact of these extreme profiles can help to educate recreational divers and promote safer diving behavior. The long-term effects of diving are not necessarily bad. As with other forms of exercise, there may be health benefits, but changes that involve the immune system should be followed over time since they may alter disease risk. Knowledge of immune and inflammatory responses to different situations in diving may affect the way divers' medical evaluations are done. The human body is the most complex and beautiful piece of machinery, and there is still so much we can learn about it if we ask the right questions.
Learn More
Most cells in our body contain deoxyribonucleic acid (DNA), a complex molecule that contains the necessary instructions to do and build things the body needs for development, function, maintenance and adaptation to changes in the environment. Before these instructions can be followed, they must be copied into a "readable" form called ribonucleic acid (RNA). These RNA transcripts influence everything from the structure of cells to what proteins are made.

DNA is organized into genes. As environmental conditions change, some genes may become more or less active (upregulated or downregulated). Activity can be measured by identifying both the type and quantity of all the RNA transcripts present in a cell. Changes in gene expression can provide insight into how a cell normally functions in given conditions. It may also shed light on how deviation from the norm could lead to disease, whether it is cancer or DCS. Although most cells in the body contain the same genetic instructions, not all cells follow or read the same part of the manual. Cells that make up the immune system, for example, have a completely different structure and function than cardiac cells.

© Alert Diver — Q1 Winter 2017