Mammalian Dive Reflex, Hibernation: Cooling is Good for Cells

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photo by Carol Duff

Health Editor’s Note: Often when someone has become comatose after an out of hospital cardiac arrest (heart has stopped beating), he or she will be cooled (body temperature wise) to 32-34 degrees Centigrade for 12 to 24 hours.

During a cardiac arrest, there is decreased oxygen delivered to the brain tissues due to lack of movement of blood (heart pumps and moves blood) and a decreased blood pressure.  A brain without oxygen begins to swell so when the heart is restarted swelling of the brain will harm the brain so there may be brain deficits even though the heart has been restarted. If the person has been cooled and rewarmed slowly, there will be less swelling of the brain cells. The cooling slowed the need for oxygen (each degree  below normal reduces the need for oxygen by 6%).  The same process will also save brain cells (neurons) from damage due to a traumatic brain injury.  Decrease the need for oxygen which leads to a decrease in brain tissue reaction to lack of oxygen (swelling) and cells will suffer little to no damage.   

Just as cooling keep foods from decomposing, cooling tissues will increase the chances that cells will keep functioning.  Transplanted organs, that are kept cold before the transplantation, have a greater chance of functioning when they are placed into the host’s body.  How do many animals adjust to cold weather?  They hibernate.  Placing cells into a state of hibernation will insure that cells will be able to overcome adversity that may other wise damage them. 

This reaction to cooling of cells could be related to the mammalian dive reflex that occurs when mammals are exposed to very cold water.  A submersion in ice water, such as falling into a pond during the winter, will cause the body to shut down processes in order to have more energy for survival.  The diving reflex is the body’s physiological response to submersion in cold water and includes selectively shutting down parts of the body in order to conserve energy to improve chances of survival. It is the reason why a child may be pulled out of freezing water, with no heartbeat, resuscitation begins, and the child is slowly warmed, heart beat and spontaneous breathing returns, and the child will have no deficits. I believe the younger the individual, the more successful the diving reflex is in saving the person from deficits.

Discovering exactly how a cell responds to hibernation will lead to increased life/time for human body organs that are destined for transplantation……Carol    

NIH researchers develop “hibernation in a dish” to study how animals adapt to the cold

Findings may help expand window for storing organs before transplantation, therapeutic hypothermia.

Researchers at the National Eye Institute have discovered cellular mechanisms that help the 13-lined ground squirrel survive hibernation. Their findings could be a step to extending storage of human donor tissues awaiting transplantation and protecting traumatic brain injury patients who undergo induced hypothermia. NEI is part of the National Institutes of Health. The findings were published in the May 3 issue of Cell.

During hibernation, the 13-lined ground squirrel endures near freezing temperatures, dramatically slowing its heart rate and respiration. How the squirrel’s tissues adapt to the cold and metabolic stress has confounded researchers.

A structure in cells known to be vulnerable to cold is the microtubule cytoskeleton. This network of small tubes within a cell provides structural support and acts as a kind of inner cellular railway system, transporting organelles and molecular complexes vital for a cell’s survival.

In a series of experiments, the research team led by Wei Li, Ph.D., a senior investigator in the NEI Retinal Neurophysiology Section and Jingxing Ou, Ph.D., a postdoctoral scientist in Li’s lab, compared cells from non-hibernators to cells from the ground squirrel to determine differences in their response to cold. They found that in ground squirrel neurons the microtubule cytoskeleton remains intact while it deteriorates in the neurons of humans and other non-hibernating animals, including rats.

Freshly fixed renal cells from a mouse kidney (top) show the microtubule structure is intact. After 24 hours at 4° Celsius and rewarming, the microtubule structure is no longer visible (middle). Microtubule structure in the cells pretreated with the drug combination before cooling and rewarming closely resemble that of the freshly fixed cells.

To investigate the biological factors supporting the squirrel’s cold adaptation, researchers created “hibernation in a dish”. They took cells from a newborn ground squirrel and reprogrammed them to become stem cells, which are undifferentiated cells capable of becoming any type of tissue in the body. Importantly, these lab-made cells, also known as induced pluripotent stem cells (iPSCs), retained the intrinsic cold-adaptive characteristics of the adult squirrel’s cells, thus providing a type of platform for studying how various kinds of the rodent’s cells adapt to the cold.

Next, they compared gene expression of stem cell-derived neurons from ground squirrels and humans. Cold exposure revealed distinct differences in the reaction of mitochondria, organelles that provide energy to the cell in the form of adenosine, triphosphate (ATP). They found that cold-exposed human stem cell-derived neurons tended to overproduce a byproduct of metabolism known as reactive oxygen species (ROS). The overabundance of ROS in human neurons appeared to cause proteins along the microtubules to oxidize, wreaking havoc with the microtubule structure. By comparison, ground squirrel ROS levels remained relatively low and their microtubules remained intact.

Cold exposure also interfered with the human stem cell-derived neurons’ ability to dispose of the toxic oxidized proteins via its protein quality control system. Under normal conditions, lysosomes envelop oxidized proteins and digest them via enzymes called proteases, but in the cold-exposed human neurons, the proteases leaked from the lysosomes and digested nearby microtubules.

The researchers then treated non-hibernating cells prior to cold exposure with two drugs to alter the course of the cold-induced damage. One of the drugs, BAM15, inhibits the production of ATP, which reduces the production of ROS. The second drug inhibited protease activity.

After bathing a variety of cell types from non-hibernators in both drugs, Li and his team exposed them to 4-degrees Celsius for four to 24 hours. The drug combination preserved microtubule structure in human stem cell-derived neurons, and rat retina—the light sensitive tissue at the back of the eye. Subsequent tests showed that the rat retina also remained functional.

They found that the drug combination also preserved nonneural tissue. Microtubules in renal cells from mouse kidneys showed improved structural integrity after cooling and rewarming.

In addition to the implications for organ transplantation, these findings pave the way for future studies looking at possible therapeutic applications. For example, inducing hypothermia is a commonly used strategy to protect the brain following a traumatic injury, but the potential benefits are weighed against the potential harm from cold-induced cellular damage.

“By understanding the biology of cold adaptation in hibernation, we may be able to improve and broaden the applications of induced hypothermia in the future, and perhaps prolong the viability of organs prior to transplantation,” Li said. “Kidneys, for example, are typically stored for no more than 30 hours. After that, the tissue starts to deteriorate, impairing the organ’s ability to function properly after its been rewarmed and reperfused. Heart, lungs and livers have an even shorter shelf life.”

The findings also suggest that stem cell-derived neurons from the ground squirrel can serve as a platform for studying other aspects of hibernation adaption, a field of research that has been limited by a lack of transgenic animal models and the inability to induce hibernation in the animal.

The study was funded in part by the Intramural Research Programs of NEI, the National Institute of Neurological Disorders and Stroke, and Center for Human Immunology, Autoimmunity and Inflammation, also part of NIH. It is a collaboration with a bioinformatics team led by Zhi Xie, Ph.D., of the Zhongshan Ophthalmic Center, Ouzhuang, China; Dana Merriman, Ph.D., a hibernation biologist at the University of Wisconsin-Oshkosh, and Barbara Mallon, D.Phil., technical director of the NIH Stem Cell Unit.

By studying the molecular tricks employed by a hibernating squirrel, Li and colleagues uncover cold-adaptive strategies that have the potential to improve the shelf-life of organs for transplantation. J. Ou, J.M. Ball, Y. Luan, T. Zhao, K.J. Miyagishima, Y. Xu, H. Zhou, J. Chen, D.K. Merriman, Z. Xie, et al. (2018) iPSCs from a Hibernator Provide a Platform for Studying Cold Adaptation and Its Potential Medical Applications. Cell 173.

By studying the molecular tricks employed by a hibernating squirrel, Li and colleagues uncover cold-adaptive strategies that have the potential to improve the shelf-life of organs for transplantation. J. Ou, J.M. Ball, Y. Luan, T. Zhao, K.J. Miyagishima, Y. Xu, H. Zhou, J. Chen, D.K. Merriman, Z. Xie, et al. (2018) iPSCs from a Hibernator Provide a Platform for Studying Cold Adaptation and Its Potential Medical Applications. Cell 173.

This press release describes a basic research finding. Basic research increases our understanding of human behavior and biology, which is foundational to advancing new and better ways to prevent, diagnose, and treat disease. Science is an unpredictable and incremental process — each research advance builds on past discoveries, often in unexpected ways. Most clinical advances would not be possible without the knowledge of fundamental basic research.

NEI leads the federal government’s research on the visual system and eye diseases. NEI supports basic and clinical science programs that result in the development of sight-saving treatments. For more information, visit https://www.nei.nih.gov.

NINDS is the nation’s leading funder of research on the brain and nervous system. The mission of NINDS is to seek fundamental knowledge about the brain and nervous system and to use that knowledge to reduce the burden of neurological disease. For more information, visit https://www.ninds.nih.gov.

About the National Institutes of Health (NIH): NIH, the nation’s medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.

Reference

Ou J, Ball JM, Luan Y, Zhao T, Miyagishima KJ, Xu Y, Zhou H, Chen J, Merriman D, Xie Z, Mallon BS, Li W. 2018. PSCs from a hibernator provide a platform for studying cold adaptation and its potential medical applications. Cell. 173:1-13. May 3. doi.org/10.1016/j.cell.2018.03.010

Biography
Carol graduated from Riverside White Cross School of Nursing in Columbus, Ohio and received her diploma as a registered nurse. She attended Bowling Green State University where she received a Bachelor of Arts Degree in History and Literature. She attended the University of Toledo, College of Nursing, and received a Master’s of Nursing Science Degree as an Educator.

She has traveled extensively, is a photographer, and writes on medical issues. Carol has three children RJ, Katherine, and Stephen – two daughters-in-law; Suzy and Katie – two granddaughters; Isabella Marianna and Zoe Olivia – and one grandson, Alexander Paul. She also shares her life with husband Gordon Duff, many cats, and two rescue pups.

Carol’s Archives 2009-2013
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