Life at the Extreme: Physiological Adaptation Gary Sieck
Physiology 30:84-85, 2015. doi:10.1152/physiol.00001.2015 You might find this additional info useful... This article cites 8 articles, 8 of which can be accessed free at: /content/30/2/84.full.html#ref-list-1 Updated information and services including high resolution figures, can be found at: /content/30/2/84.full.html Additional material and information about Physiology can be found at: http://www.the-aps.org/publications/physiol
This information is current as of April 9, 2015.
Downloaded from on April 9, 2015
Physiology (formerly published as News in Physiological Science) publishes brief review articles on major physiological developments. It is published bimonthly in January, March, May, July, September, and November by the American Physiological Society, 9650 Rockville Pike, Bethesda, MD 20814-3991. Copyright © 2015 by the American Physiological Society. ISSN: 1548-9213, ESSN: 1548-9221. Visit our website at http://www.the-aps.org/.
PHYSIOLOGY IN PERSPECTIVE Gary Sieck, Editor-in-Chief Mayo Clinic, Rochester, Minnesota
PHYSIOLOGY 30: 84 – 85, 2015; doi:10.1152/physiol.00001.2015
Life at the Extreme: Physiological Adaptation
84
common among polar vertebrates, although how these species avoid the metabolic pathologies typically associated with clock dysregulation is unknown. Thermophiles are microorganisms that survive the high temperatures of environments such as hot springs and compost. What is it about thermophile physiology that allows them to thrive in temperatures above 60°C? Studies on the survival mechanisms of thermophiles help to understand how life can thrive under extreme temperatures, and how early life may have evolved on Earth. In their review (7), Wang and colleagues discuss the survival physiology of thermophiles from an “omics” perspective (genomic, transcriptomic, and proteomic) to provide some clues regarding the adaptive ability of thermophiles. A better understanding of thermophile physiology may provide insights that will lead to thermo-resistant products and provide strategies to help humans better tolerate heat stress. Each year, the bar-headed goose makes its journey from Central Asia to winter in India; a trek requiring flight over the highest mountain range in the world–the Himalayas. At altitudes reaching over 8,800 m, the oxygen levels in the air are dangerously low (containing only onethird to one-half of the oxygen available at sea level); yet bar-headed geese accomplish their metabolically costly flights in this extremely low-oxygen environment. In their review (6), Scott and colleagues explore the physiological adaptations (primarily cardiorespiratory) that permit bar-headed geese to fly at extremely high elevations. The lessons learned from the bar-headed goose provide a basic understanding of hypoxia tolerance overall, while informing us about the importance of studying avian evolution. People who suffer from obstructive sleep apnea experience the equivalent of flying over the Himalayas every night, with periodic reductions in their blood oxygen levels. These individuals must adapt to this change in their internal environment, which if left unchecked would present a significant risk to their health
1548-9213/15 ©2015 Int. Union Physiol. Sci./Am. Physiol. Soc.
Downloaded from on April 9, 2015
Many of us in North America, Europe, and Asia are looking forward to the end of winter and the emergence of spring and renewed life. But a closer look would reveal the robust existence of life that has adapted to winter’s coldness and the shorter periods of sunlight. Physiological adaptations are all around us. They are a part of our existence and a natural driving force of biology. How can we help but be curious? Indeed, physiology is for the curious, those who ask questions and explore the world that surrounds them. In this issue of Physiology, several reviews take a closer look at physiological adaptation to nature’s extremes. As illustrated by the cover of the March issue of Physiology, biological circadian clocks are ubiquitous adaptations that enable organisms to anticipate and exploit favorable conditions for daily activities through the temporal coordination and phasing of biochemical, physiological, and behavioral processes. In their review (8), Williams et al. discuss a very unique situation in which polar vertebrates cope with an environment that periodically lacks the strongest time-giver, or zeitgeber, of circadian organization–robust, cyclical oscillations between light and darkness. The light/dark cycle is thought to be the primary driver for the emergence and evolution of circadian clocks. Subsequently, a variety of physiological processes, including metabolic homeostasis, are now tightly linked to circadian regulation with dysregulation of circadian rhythms being associated with a multitude of disease states. When internal circadian coordination is disrupted in humans, such as in shift workers, in various sleep disorders, and in individuals suffering from Seasonal Affective Disorder, their cognitive abilities and long-term health can be compromised. Many polar vertebrates maintain entrained daily rhythms of physiology and behavior throughout the year. In contrast, humans do not seem to be capable of maintaining entrained daily rhythms during the constancy of the polar day or night. Seasonal absence of circadian rhythmicity is also
and survival. It is well known that nitric oxide (NO) and its oxidative product nitrite are essential signaling molecules involved in the control of blood flow and protection of the heart against oxygen deprivation. However, it is not well understood how such important protective signaling pathways evolved. In their review (1), Fago and Jensen focused on selected vertebrate species that have evolved to tolerate periodic events of extreme oxygen deprivation. Indeed, certain animals are able to survive months of extremely low oxygen levels during the winter. Elevations of nitrite concentrations in the hearts of some ectotherm vertebrate species, including the crucian carp and the freshwater turtle during anoxia (i.e., a complete absence of oxygen) indicate that nitrite is part of the natural cellular defense against the lack of oxygen. These animal species are wonderful models to extend our knowledge of how NO and nitrite are used in the adaptive response to hypoxia in maintaining and defending a functional cardio-circulatory system. Further study may lead to new therapies for diseases where oxygen supply is compromised, including heart attacks, cardiocirculatory insufficiency, and stroke. Fluids comprise a significant proportion of our body mass and volume, and the neurohypophyseal system plays a key role in body fluid homeostasis. In addition to its role in cardiovascular control, NO and other gaseous molecules such as carbon monoxide (CO) and hydrogen sulfide (H2S) are produced by the brain to regulate endocrine function. In their review (5), Ruginsk and colleagues discuss the main findings linking NO, CO, and H2S to the control of body fluid homeostasis by the hypothalamic neurohypophyseal system through production and secretion of the hormones vasopressin and oxytocin. The analysis of the behavior of these gaseous neuromodulators under diverse physiological conditions strongly suggests that their main molecular mechanisms and targets are shared, underlying a complex and interconnected regulatory mechanism. This area of research contributes to our overall understanding of how the brain is able to produce and release hormones to rapidly adapt to the
sympathetic and parasympathetic neural activity. It is known that sympathetic activation is involved in the pathogenesis of primary hypertension and heart failure, disease states associated with baroreflex dysfunction. In their review, Lohmeier and Iliescu (4) explore whether alterations in the baroreflex play a role in the long-term control of sympathetic activity and arterial pressure. They describe chronic neurohormonal and cardiovascular responses to natural activation of the baroreflex in hypertension. In addition, they explore the use of chronic electrical stimulation of the carotid baroreflex, which suppresses central sympathetic outflow and thereby lowers the blood pressure response during baroreflex activation. Together, these experimental results support the contention that the baroreflex plays a role in the long-term regulation of sympathetic activity and arterial pressure. Furthermore, these studies provide mechanistic insight into which patients will likely benefit the most in current clinical trials designed to evaluate the efficacy of baroreflex activation therapy in the treatment of resistant hypertension and heart failure, disorders in which the pathogenesis is linked to activation of the sympathetic nervous system. Plants display a high degree of adaptation (plasticity) in their growth and development that allows them to respond to light, gravity, physical obstructions, water, and soil-bound nutrients. Plant growth occurs through the coordinated expansion of tightly adherent cells, driven by regulated softening of cell walls. It is an intrinsically multiscale
process, with the integrated properties of multiple cell walls shaping the whole tissue. In their review (2), Jensen and Fozard discuss the use of multiscale models to encode physical relationships and bring new understanding to plant physiology and development. Multicellular models of plant growth and development are moving toward threedimensional representations of plant tissues, thereby incorporating more realistic details of cell wall mechanics. Further studies in this area promise the development of models that capture the full architecture of rooting and branching systems of plants, while preserving the cross talk with molecular processes that underlie structural adaptations. 䡲
References 1.
Fago A, Jensen FB. Hypoxia tolerance, nitric oxide and nitrite: lessons from extreme animals. Physiology 30: 116 –126, 2015.
2.
Jensen OE, Fozard JA. Multiscale models in the biomechanics of plant growth. Physiology 30: 159 –166, 2015.
3.
Johnson AC, Cipolla MJ. The cerebral circulation during pregnancy: adapting to preserve normalcy. Physiology 30: 139 –147, 2015.
4.
Lohmeier TE, Iliescu R. The baroreflex as a longterm controller of arterial pressure. Physiology 30: 148 –158, 2015.
5.
Ruginsk SG, Mecawi AS, da Silva MP, Reis WL, Coletti R, de Lima JBM, Elias LLK, Antunes-Rodrigues J. Gaseous modulators in the control of the hypothalamic neurohypophyseal system. Physiology 30: 127–138, 2015.
6.
Scott GR, Hawkes LA, Frappell PB, Butler PJ, Bishop CM, Milsom WK. How bar-headed geese fly over the Himalayas. Physiology 30: 107–115, 2015.
7.
Wang Q, Cen Z, Zhao J. The survival mechanisms of thermophiles at high temperatures: an angle of omics. Physiology 30: 97–106, 2015.
8.
Williams CT, Barnes BM, Buck CL. Persistence, entrainment, and function of circadian rhythms in polar vertebrates. Physiology 30: 86 –96, 2015.
PHYSIOLOGY • Volume 30 • March 2015 • www.physiologyonline.org
85
Downloaded from on April 9, 2015
constantly changing demands of the body. Pregnancy is a state of tremendous physiological change requiring adaptations to accommodate the needs of both the mother and the fetus. The adaptation of the cerebral circulation to pregnancy is unique since, compared with other organs, the brain requires relatively constant blood flow and tightly regulated water and solute composition to maintain healthy function. To do this, the cerebral circulation adapts to become less responsive to circulating hormones and neurotransmitters that would otherwise cause increased flow and permeability. Thus a major adaptation of the maternal cerebral circulation to pregnancy is to maintain normalcy in the face of expanded plasma volume, increased cardiac output, and high levels of permeability factors. In addition, the limits of cerebral blood flow autoregulation are extended on both ends of the arterial pressure range, potentially providing protection from hemorrhage and acute hypertension. In their review (3), Johnson and Cipolla discusses these adaptive changes in cerebral circulation during pregnancy. Advancing knowledge of the mechanisms that control maternal cerebral circulation could lead to diagnostic and therapeutic strategies for women at risk for preeclampsia and eclampsia, common hypertensive disorders of pregnancy with high maternal and fetal mortality. The arterial baroreflex is a powerful adaptive mechanism that counteracts short-term fluctuations in arterial pressure by mediating reciprocal changes in
Physiology 30:84-85, 2015. doi:10.1152/physiol.00001.2015 You might find this additional info useful... This article cites 8 articles, 8 of which can be accessed free at: /content/30/2/84.full.html#ref-list-1 Updated information and services including high resolution figures, can be found at: /content/30/2/84.full.html Additional material and information about Physiology can be found at: http://www.the-aps.org/publications/physiol
This information is current as of April 9, 2015.
Downloaded from on April 9, 2015
Physiology (formerly published as News in Physiological Science) publishes brief review articles on major physiological developments. It is published bimonthly in January, March, May, July, September, and November by the American Physiological Society, 9650 Rockville Pike, Bethesda, MD 20814-3991. Copyright © 2015 by the American Physiological Society. ISSN: 1548-9213, ESSN: 1548-9221. Visit our website at http://www.the-aps.org/.
PHYSIOLOGY IN PERSPECTIVE Gary Sieck, Editor-in-Chief Mayo Clinic, Rochester, Minnesota
PHYSIOLOGY 30: 84 – 85, 2015; doi:10.1152/physiol.00001.2015
Life at the Extreme: Physiological Adaptation
84
common among polar vertebrates, although how these species avoid the metabolic pathologies typically associated with clock dysregulation is unknown. Thermophiles are microorganisms that survive the high temperatures of environments such as hot springs and compost. What is it about thermophile physiology that allows them to thrive in temperatures above 60°C? Studies on the survival mechanisms of thermophiles help to understand how life can thrive under extreme temperatures, and how early life may have evolved on Earth. In their review (7), Wang and colleagues discuss the survival physiology of thermophiles from an “omics” perspective (genomic, transcriptomic, and proteomic) to provide some clues regarding the adaptive ability of thermophiles. A better understanding of thermophile physiology may provide insights that will lead to thermo-resistant products and provide strategies to help humans better tolerate heat stress. Each year, the bar-headed goose makes its journey from Central Asia to winter in India; a trek requiring flight over the highest mountain range in the world–the Himalayas. At altitudes reaching over 8,800 m, the oxygen levels in the air are dangerously low (containing only onethird to one-half of the oxygen available at sea level); yet bar-headed geese accomplish their metabolically costly flights in this extremely low-oxygen environment. In their review (6), Scott and colleagues explore the physiological adaptations (primarily cardiorespiratory) that permit bar-headed geese to fly at extremely high elevations. The lessons learned from the bar-headed goose provide a basic understanding of hypoxia tolerance overall, while informing us about the importance of studying avian evolution. People who suffer from obstructive sleep apnea experience the equivalent of flying over the Himalayas every night, with periodic reductions in their blood oxygen levels. These individuals must adapt to this change in their internal environment, which if left unchecked would present a significant risk to their health
1548-9213/15 ©2015 Int. Union Physiol. Sci./Am. Physiol. Soc.
Downloaded from on April 9, 2015
Many of us in North America, Europe, and Asia are looking forward to the end of winter and the emergence of spring and renewed life. But a closer look would reveal the robust existence of life that has adapted to winter’s coldness and the shorter periods of sunlight. Physiological adaptations are all around us. They are a part of our existence and a natural driving force of biology. How can we help but be curious? Indeed, physiology is for the curious, those who ask questions and explore the world that surrounds them. In this issue of Physiology, several reviews take a closer look at physiological adaptation to nature’s extremes. As illustrated by the cover of the March issue of Physiology, biological circadian clocks are ubiquitous adaptations that enable organisms to anticipate and exploit favorable conditions for daily activities through the temporal coordination and phasing of biochemical, physiological, and behavioral processes. In their review (8), Williams et al. discuss a very unique situation in which polar vertebrates cope with an environment that periodically lacks the strongest time-giver, or zeitgeber, of circadian organization–robust, cyclical oscillations between light and darkness. The light/dark cycle is thought to be the primary driver for the emergence and evolution of circadian clocks. Subsequently, a variety of physiological processes, including metabolic homeostasis, are now tightly linked to circadian regulation with dysregulation of circadian rhythms being associated with a multitude of disease states. When internal circadian coordination is disrupted in humans, such as in shift workers, in various sleep disorders, and in individuals suffering from Seasonal Affective Disorder, their cognitive abilities and long-term health can be compromised. Many polar vertebrates maintain entrained daily rhythms of physiology and behavior throughout the year. In contrast, humans do not seem to be capable of maintaining entrained daily rhythms during the constancy of the polar day or night. Seasonal absence of circadian rhythmicity is also
and survival. It is well known that nitric oxide (NO) and its oxidative product nitrite are essential signaling molecules involved in the control of blood flow and protection of the heart against oxygen deprivation. However, it is not well understood how such important protective signaling pathways evolved. In their review (1), Fago and Jensen focused on selected vertebrate species that have evolved to tolerate periodic events of extreme oxygen deprivation. Indeed, certain animals are able to survive months of extremely low oxygen levels during the winter. Elevations of nitrite concentrations in the hearts of some ectotherm vertebrate species, including the crucian carp and the freshwater turtle during anoxia (i.e., a complete absence of oxygen) indicate that nitrite is part of the natural cellular defense against the lack of oxygen. These animal species are wonderful models to extend our knowledge of how NO and nitrite are used in the adaptive response to hypoxia in maintaining and defending a functional cardio-circulatory system. Further study may lead to new therapies for diseases where oxygen supply is compromised, including heart attacks, cardiocirculatory insufficiency, and stroke. Fluids comprise a significant proportion of our body mass and volume, and the neurohypophyseal system plays a key role in body fluid homeostasis. In addition to its role in cardiovascular control, NO and other gaseous molecules such as carbon monoxide (CO) and hydrogen sulfide (H2S) are produced by the brain to regulate endocrine function. In their review (5), Ruginsk and colleagues discuss the main findings linking NO, CO, and H2S to the control of body fluid homeostasis by the hypothalamic neurohypophyseal system through production and secretion of the hormones vasopressin and oxytocin. The analysis of the behavior of these gaseous neuromodulators under diverse physiological conditions strongly suggests that their main molecular mechanisms and targets are shared, underlying a complex and interconnected regulatory mechanism. This area of research contributes to our overall understanding of how the brain is able to produce and release hormones to rapidly adapt to the
sympathetic and parasympathetic neural activity. It is known that sympathetic activation is involved in the pathogenesis of primary hypertension and heart failure, disease states associated with baroreflex dysfunction. In their review, Lohmeier and Iliescu (4) explore whether alterations in the baroreflex play a role in the long-term control of sympathetic activity and arterial pressure. They describe chronic neurohormonal and cardiovascular responses to natural activation of the baroreflex in hypertension. In addition, they explore the use of chronic electrical stimulation of the carotid baroreflex, which suppresses central sympathetic outflow and thereby lowers the blood pressure response during baroreflex activation. Together, these experimental results support the contention that the baroreflex plays a role in the long-term regulation of sympathetic activity and arterial pressure. Furthermore, these studies provide mechanistic insight into which patients will likely benefit the most in current clinical trials designed to evaluate the efficacy of baroreflex activation therapy in the treatment of resistant hypertension and heart failure, disorders in which the pathogenesis is linked to activation of the sympathetic nervous system. Plants display a high degree of adaptation (plasticity) in their growth and development that allows them to respond to light, gravity, physical obstructions, water, and soil-bound nutrients. Plant growth occurs through the coordinated expansion of tightly adherent cells, driven by regulated softening of cell walls. It is an intrinsically multiscale
process, with the integrated properties of multiple cell walls shaping the whole tissue. In their review (2), Jensen and Fozard discuss the use of multiscale models to encode physical relationships and bring new understanding to plant physiology and development. Multicellular models of plant growth and development are moving toward threedimensional representations of plant tissues, thereby incorporating more realistic details of cell wall mechanics. Further studies in this area promise the development of models that capture the full architecture of rooting and branching systems of plants, while preserving the cross talk with molecular processes that underlie structural adaptations. 䡲
References 1.
Fago A, Jensen FB. Hypoxia tolerance, nitric oxide and nitrite: lessons from extreme animals. Physiology 30: 116 –126, 2015.
2.
Jensen OE, Fozard JA. Multiscale models in the biomechanics of plant growth. Physiology 30: 159 –166, 2015.
3.
Johnson AC, Cipolla MJ. The cerebral circulation during pregnancy: adapting to preserve normalcy. Physiology 30: 139 –147, 2015.
4.
Lohmeier TE, Iliescu R. The baroreflex as a longterm controller of arterial pressure. Physiology 30: 148 –158, 2015.
5.
Ruginsk SG, Mecawi AS, da Silva MP, Reis WL, Coletti R, de Lima JBM, Elias LLK, Antunes-Rodrigues J. Gaseous modulators in the control of the hypothalamic neurohypophyseal system. Physiology 30: 127–138, 2015.
6.
Scott GR, Hawkes LA, Frappell PB, Butler PJ, Bishop CM, Milsom WK. How bar-headed geese fly over the Himalayas. Physiology 30: 107–115, 2015.
7.
Wang Q, Cen Z, Zhao J. The survival mechanisms of thermophiles at high temperatures: an angle of omics. Physiology 30: 97–106, 2015.
8.
Williams CT, Barnes BM, Buck CL. Persistence, entrainment, and function of circadian rhythms in polar vertebrates. Physiology 30: 86 –96, 2015.
PHYSIOLOGY • Volume 30 • March 2015 • www.physiologyonline.org
85
Downloaded from on April 9, 2015
constantly changing demands of the body. Pregnancy is a state of tremendous physiological change requiring adaptations to accommodate the needs of both the mother and the fetus. The adaptation of the cerebral circulation to pregnancy is unique since, compared with other organs, the brain requires relatively constant blood flow and tightly regulated water and solute composition to maintain healthy function. To do this, the cerebral circulation adapts to become less responsive to circulating hormones and neurotransmitters that would otherwise cause increased flow and permeability. Thus a major adaptation of the maternal cerebral circulation to pregnancy is to maintain normalcy in the face of expanded plasma volume, increased cardiac output, and high levels of permeability factors. In addition, the limits of cerebral blood flow autoregulation are extended on both ends of the arterial pressure range, potentially providing protection from hemorrhage and acute hypertension. In their review (3), Johnson and Cipolla discusses these adaptive changes in cerebral circulation during pregnancy. Advancing knowledge of the mechanisms that control maternal cerebral circulation could lead to diagnostic and therapeutic strategies for women at risk for preeclampsia and eclampsia, common hypertensive disorders of pregnancy with high maternal and fetal mortality. The arterial baroreflex is a powerful adaptive mechanism that counteracts short-term fluctuations in arterial pressure by mediating reciprocal changes in
