A general response to stressors by the unicellular Tetrahymena: effect of stress on the hormone levels

Dispersal plasticity driven by variation in fitness across species and environmental gradients

Dispersal plasticity, when organisms adjust their dispersal decisions depending on their environment, can play a major role in ecological and evolutionary dynamics, but how it relates to fitness remains scarcely explored. Theory predicts that high dispersal plasticity should evolve when environmental gradients have a strong impact on fitness. Using microcosms, we tested in five species of the genus Tetrahymena whether dispersal plasticity relates to differences in fitness sensitivity along three environmental gradients. Dispersal plasticity was species- and environment-dependent. As expected, dispersal plasticity was generally related to fitness sensitivity, with higher dispersal plasticity when fitness is more affected by environmental gradients. Individuals often preferentially disperse out of low fitness environments, but leaving environments that should yield high fitness was also commonly observed. We provide empirical support for a fundamental, but largely untested, assumption in dispersal theory: the extent of dispersal plasticity correlates with fitness sensitivity to the environment.

Reprogramming of the Immune System by Stress and Faulty Hormonal Imprinting

PURPOSE

Hormonal imprinting is taking place perinatally at the first encounter between the developing hormone receptors and their target hormones. However, in this crucial period when the developmental window for physiological imprinting is open, other molecules, such as synthetic hormones and endocrine disruptors can bind to the receptors, leading to faulty imprinting with life-long consequences, especially to the immune system. This review presents the factors of stress and faulty hormonal imprinting that lead to reprogramming of the immune system.

METHODS

Relevant publications from Pubmed since 1990 were reviewed and synthesized.

FINDINGS

The developing immune system is rather sensitive to hormonal effects. Faulty hormonal imprinting is able to reprogram the original developmental program present in a given cell, with lifelong consequences, manifested in alteration of hormone binding by receptors, susceptibility to certain (non-infectious) diseases, and triggering of other diseases. As stress mobilizes the hypothalamic-pituitary-adrenal axis if it occurred during gestation or perinatally, it could lead to faulty hormonal imprinting in the immune system, manifested later as allergic and autoimmune diseases or weakness of normal immune defenses. Hormonal imprinting is an epigenetic process and is carried to the offspring without alteration of DNA base sequences. This means that any form of early-life stress alone or in association with hormonal imprinting could be associated with the developmental origin of health and disease (DOHaD). As puberty is also a period of reprogramming, stress or faulty imprinting can change the original (developmental) program, also with life-long consequences.

IMPLICATIONS

Considering the continuous differentiation of immune cells (from blast-cells) during the whole life, there is a possibility of late-imprinting or stress-activated reprogramming in the immune system at any periods of life, with later pathogenetic consequences.

Provocation of life functions at a unicellular eukaryote level by extremely low doses of mammalian hormones: Evidences of hormesis

Hormones, characteristic to higher ranked animals, are synthesized, stored, and secreted by unicellular eukaryote animals. The unicells also have receptors for recognizing these materials and transmit the message into the cells for provoking response. The hormones are effective in very low concentrations (down to 10-21 M) and opposite effects of lower and higher concentrations can be observed. However, sometimes linear concentration effects can be found, which means that hormesis exists, nevertheless uncertain, as it is in the phase of formation (evolutionary experimentation). Hormesis, by transformation (fixation) of cytoplasmic receptor-like membrane components to receptors in the presence of the given hormone, likely helps the development of unicellular endocrine character and by this the evolution of endocrine system. The effect by extremely low concentrations of hormones had been forced by the watery way of unicellular life, which could establish the physiological concentrations of hormones in the blood of higher ranked animals. This means that hormetic low doses are the normal, effective concentrations and the high concentrations are artificial, consequently could be dangerous.

The hormonal system of the unicellular Tetrahymena: a review with evolutionary aspects

The unicellular ciliate, Tetrahymena has receptors for hormones of the higher ranked animals, these hormones (e.g. insulin, triiodothyronine, ACTH, histamine, etc.) are also produced by it and it has signal pathways and second messengers for signal transmission. These components are chemically and functionally very similar to that of mammalian ones. The exogenously given hormones regulate different functions, as movement, phagocytosis, chemotaxis, cell growth, secretion, excretion and the cells' own hormone production. The receptors are extremely sensitive, certain hormones are sensed (and response is provoked) at 10-21 M concentration, which makes likely that the function could work by the effect of hormones produced by the Tetrahymena itself. The signal reception is selective, it can differentiate between closely related hormones. The review is listing the hormones produced by the Tetrahymena, the receptors which can receive signals and the signal pathways and second messengers as well, as the known effects of mammalian hormones to the life functions of Tetrahymena. The possible and justified role of hormonal system in the Tetrahymena as a single cell and inside the Tetrahymena population, as a community is discussed. The unicellular hormonal system and mammalian endocrine system are compared and evolutionary conclusions are drawn.

Durable effect of heat-stress on the hormone production of Tetrahymena. Effect of insulin on the consequences of stress

The unicellular Tetrahymena pyriformis was stressed by 37°C heat for 1 h and its hormone (serotonin, histamine, triiodothyronine) content was measured by immunocytochemical flow cytometry in different time points (immediately after treatment and after 1, 2, 8, 16 weeks). The treatment increased each hormone level for two weeks, however, after 8 weeks the hormone concentration inside the cells decreased and in case of serotonin this was similar in the 16th week, while the other two hormones' level was similar to the control. Insulin further increased the hormone production during treatment, but this effect was not durable. After one week the cells behave similar to those, subjected to heath shock only. The results show that a single stress causes deep and durable changes in the hormone household of Tetrahymena which is influenced by exogenously given insulin only in the acute phase.

Thyrotropin (TSH) regulates triiodothyronine (T3) production in the unicellular Tetrahymena

The aim of the experiments was to study the regulation of triiodothyronine (T3) production in the unicellular Tetrahymena. Untreated and troph-hormone treated specimen were prepared and in different timepoints T3 content was measured and compared by immunocytochemical flow cytometry. 0.1 or 0.001 IU TSH in tryptone-yeast medium stimulated T3 synthesis at 10, 20, 30 min, but does not stimulate after 1 h. The overlapping gonadotropic hormone (GTH) also did it, however only at 10 min. In Losina salt solution (physiological for Tetrahymena) the effect was weaker, however outer amino acid source was not absolutely needed for the production of the hormone. The results show that the TSH regulation of thyroid hormone synthesis (storage, secretion) and troph-hormone overlap can be deduced to a unicellular level. This may allow the hypothesis that the endocrine mechanisms proved at a low level of phylogeny are preserved for the higher ranked organisms.

Effect of stress and stress hormones on the hormone (insulin) binding of Tetrahymena

The unicellular Tetrahymena pyriformis GL produce, store and secrete vertebrate-like hormones. In earlier experiments the effect of different stressors on the hormone levels of Tetrahymena was studied and an elevation of these was found. In the present experiments the hormone binding was investigated, using flow cytometric method. FITC-insulin binding was elevated after concentrated (5, 10, or 20 mg ml(-1)) NaCl or 0.01%, 0.1%, or 0.05% formaldehyde treatment, or after thermal stress (37 degrees C). Serotonin given together with NaCl increased and together with formaldehyde decreased the binding. Histamine always decreased the binding and insulin was indifferent. Four hours after osmotic stress, hormone binding significantly decreased and this was not influenced by hormones. However, 4 h after formaldehyde stress the binding elevated and this was further increased by repeated hormone treatments. The results show that the stress in Tetrahymena provokes an activation of its hormonal system (hormone production and binding), which is differently influenced by exogeneously given hormones.