Morphological Characteristics of the Thymus and Spleen and the Subpopulation Composition of Lymphocytes in Peripheral Blood during Systemic Inflammatory Response in Male Rats with Different Resistance to Hypoxia

Molecular and phenotypic distinctions of macrophages in tolerant and susceptible to hypoxia rats

Individual hypoxia tolerance is a major influence on the course and outcome of infectious and inflammatory diseases. Macrophages, which play central roles in systemic inflammatory response and other immunity reactions, are subject to functional activation orchestrated by several transcription factors including hypoxia inducible factors (HIFs). HIF-1 expression levels and the lipopolysaccharide (LPS)-induced systemic inflammatory response severity have been shown to correlate with hypoxia tolerance. Molecular and functional features of macrophages, depending on the organisms resistance to hypoxia, can determine the severity of the course of infectious and inflammatory diseases, including the systemic inflammatory response. The purpose is the comparative molecular and functional characterization of non-activated and LPS-activated bone marrow-derived macrophages under normoxia in rats with different tolerance to oxygen deprivation. Hypoxia resistance was assessed by gasping time measurement in an 11,500 m altitude-equivalent hypobaric decompression chamber. Based on the outcome, the animals were assigned to three groups termed 'tolerant to hypoxia' (n = 12), 'normal', and 'susceptible to hypoxia' (n = 13). The 'normal' group was excluded from subsequent experiments. One month after hypoxia resistance test, the blood was collected from the tail vein to isolate monocytes. Non-activated and LPS-activated macrophage cultures were investigated by PCR, flow cytometry and Western blot methods. Gene expression patterns of non-activated cultured macrophages from tolerant and susceptible to hypoxia animals differed. We observed higher expression of VEGF and CD11b and lower expression of Tnfa, Il1b and Epas1 in non-activated cultures obtained from tolerant to hypoxia animals, whereas HIF-1α mRNA and protein expression levels were similar. LPS-activated macrophage cultures derived from susceptible to hypoxia animals expressed higher levels of Hif1a and CCR7 than the tolerant group; in addition, the activation was associated with increased content of HIF-1α in cell culture medium. The observed differences indicate a specific propensity toward pro-inflammatory macrophage polarization in susceptible to hypoxia rats.

Role of MicroRNAs in Regulation of Cellular Response to Hypoxia

Hypoxia causes changes in transcription of the genes that contribute to adaptation of the cells to low levels of oxygen. The main mechanism regulating cellular response to hypoxia is activation of hypoxia-inducible transcription factors (HIF), which include several isoforms and control expression of more than a thousand genes. HIF activity is regulated at various levels, including by small non-coding RNA molecules called microRNAs (miRNAs). miRNAs regulate cellular response to hypoxia by influencing activation of HIF, its degradation, and translation of HIF-dependent proteins. At the same time, HIFs also affect miRNAs biogenesis. Data on the relationship of a particular HIF isoform with miRNAs are contradictory, since studies have been performed using different cell lines, various types of experimental animals and clinical material, as well as at different oxygen concentrations and durations of hypoxic exposure. In addition, HIF expression may be affected by the initial resistance of organisms to lack of oxygen, which has not been taken into account in the studies. This review analyzes the data on the effect of hypoxia on biogenesis and functioning of miRNAs, as well as on the effect of miRNAs on mRNAs of the genes involved in adaptation to oxygen deficiency. Understanding the mechanisms of relationship between HIF, hypoxia, and miRNA is necessary to develop new approaches to personalized therapy for diseases accompanied by oxygen deficiency.

Cell-free immunomodulatory biomaterials mediated in situ periodontal multi-tissue regeneration and their immunopathophysiological processes

Cell-free biomaterials-inducing endogenous in situ multi-tissue regeneration is very challenging and applying advanced immunomodulatory biomaterials can be an effective strategy to overcome it. In-depth knowledge of the immunopathophysiological mechanisms should be acquired before applying such an immunomodulation strategy. In this study, we implanted different immunoregulatory cell-free biomaterials into periodontal multi-tissue defects and showed that the outcome of multi-tissue regeneration is closely regulated by the immune reaction. The underlying immunopathophysiological processes, including the blood clotting response and fibrinoid necrosis, innate and adaptive immune response, local and systemic immune reaction, growth factors release, and stem cells recruitment, were revealed. The implantation of biomaterials with anti-inflammatory properties could direct the immunopathophysiological process and make it more favorable for in situ multi-tissue regeneration, ultimately enabling the regeneration of the periodontal ligament, the acellular cementum matrix, and the alveolar bone in the periodontium. These findings further confirm the effectiveness of immunomodulatory based strategy and the unveiling of their immunopathophysiological processes could provide some favorable theoretical bases for the development of advanced cell-free immunomodulatory multi-tissue regenerative biomaterials.

Age-related differences in hypoxia-associated genes and cytokine profile in male Wistar rats

Hypoxia tolerance of the organism depends on many factors, including age. High newborn organisms tolerance and high level of oxidative stress throughout aging were demonstrated by many studies. However, there is lack of investigations reflecting the expression of key hypoxia-inducible factor HIF in different age organisms in correlation to levels of pro-inflammatory and anti-inflammatory cytokines. Liver is a sensitive to hypoxia organ, and is an important organ in providing an acute reaction to infections – it synthesizes acute inflammation phase proteins, in particular, C-reactive protein. The aim of study was to determine relationship between age-related tolerance to hypoxia and HIF-1 and PHD2 (prolyl hydroxylase domain protein) expression levels in the liver and the production of cytokines in the spleen in newborn, prepubertal and adult Wistar rats. Newborn rats are characterized by high mRNA Hif-1α expression level in the liver, accompanied by a low content of HIF-1 protein and high level of PHD2. The growth in HIF-1α protein level throughout age is accompanied by the growth of pro-inflammatory cytokines level. Prepubertal animals are the least hypoxia resistant and their HIF-1α mRNA expression level was higher than in adult animals. The PHD2 activity in prepubertal animals was significantly reduced in comparison to newborn rats, and the HIF-1α protein level did not change. Further studies require the identification of additional mechanisms, determining the regulation of the HIF-1α level in prepubertal animals.

Morphological and Functional Peculiarities of the Immune System of Male and Female Rats with Different Hypoxic Resistance

The morphological and functional peculiarities of the immune system are studied in adult male and female Wistar rats with high and low hypoxic resistance. Sex-specific differences in the subpopulation composition of the peripheral blood lymphocytes, not depending on the hypoxic resistance of animals, are detected: the males have lower absolute counts of T helpers and higher percentage of regulatory T cells than the females in the diestrus phase. Comparison of the morphofunctional status of the immune system in male and female (diestrus) rats with high resistance to hypoxia has shown a better developed subcapsular zone of the thymus, higher levels of anti-inflammatory cytokine TGF-β, and lower absolute counts of cytotoxic T lymphocytes in the peripheral blood in the males. Males with low hypoxic resistance have higher counts of phase II thymic bodies in comparison with low-resistant females. Hence, morphofunctional differences in the immune system of male and female rats with different hypoxic resistance are detected, which can determine the course of inflammatory diseases.

Differences in Tolerance to Hypoxia: Physiological, Biochemical, and Molecular-Biological Characteristics

Hypoxia plays an important role in the development of many infectious, inflammatory, and tumor diseases. The predisposition to such disorders is mostly provided by differences in basic tolerance to oxygen deficiency, which we discuss in this review. Except the direct exposure of different-severity hypoxia in decompression chambers or in highland conditions, there are no alternative methods for determining organism tolerance. Due to the variability of the detection methods, differences in many parameters between tolerant and susceptible organisms are still not well-characterized, but some of them can serve as biomarkers of susceptibility to hypoxia. At the moment, several potential biomarkers in conditions after hypoxic exposure have been identified both in experimental animals and humans. The main potential biomarkers are Hypoxia-Inducible Factor (HIF)-1, Heat-Shock Protein 70 (HSP70), and NO. Due to the different mechanisms of various high-altitude diseases, biomarkers may not be highly specific and universal. Therefore, it is extremely important to conduct research on hypoxia susceptibility biomarkers. Moreover, it is important to develop a method for the evaluation of organisms' basic hypoxia tolerance without the necessity of any oxygen deficiency exposure. This can contribute to new personalized medicine approaches' development for diagnostics and the treatment of inflammatory and tumor diseases, taking into account hypoxia tolerance differences.