Cloning and in vivo expression of vascular endothelial growth factor receptor 2 (Flk1) in the naturally hypoxia-tolerant subterranean mole rat

The hypoxia adaptation of small mammals to plateau and underground burrow conditions

Oxygen is one of the important substances for the survival of most life systems on the earth, and plateau and underground burrow systems are two typical hypoxic environments. Small mammals living in hypoxic environments have evolved different adaptation strategies, which include increased oxygen delivery, metabolic regulation of physiological responses and other physiological responses that change tissue oxygen utilization. Multi-omics predictions have also shown that these animals have evolved different adaptations to extreme environments. In particular, vascular endothelial growth factor (VEGF) and erythropoietin (EPO), which have specific functions in the control of O2 delivery, have evolved adaptively in small mammals in hypoxic environments. Naked mole-rats and blind mole-rats are typical hypoxic model animals as they have some resistance to cancer. This review primarily summarizes the main living environment of hypoxia tolerant small mammals, as well as the changes of phenotype, physiochemical characteristics and gene expression mode of their long-term living in hypoxia environment.

Vascular endothelial growth factor (VEGF), mast cells and inflammation

Vascular endothelial growth factor (VEGF) is one of the most important inducers of angiogenesis, therefore blocking angiogenesis has led to great promise in the treatment of various cancers and inflammatory diseases. VEGF, expressed in response to soluble mediators such as cytokines and growth factors, is important in the physiological development of blood vessels as well as development of vessels in tumors. In cancer patients VEGF levels are increased, and the expression of VEGF is associated with poor prognosis in diseases. VEGF is a mediator of angiogenesis and inflammation which are closely integrated processes in a number of physiological and pathological conditions including obesity, psoriasis, autoimmune diseases and tumor. Mast cells can be activated by anti-IgE to release potent mediators of inflammation and can also respond to bacterial or viral antigens, cytokines, growth factors and hormones, leading to differential release of distinct mediators without degranulation. Substance P strongly induces VEGF in mast cells, and IL-33 contributes to the stimulation and release of VEGF in human mast cells in a dose-dependent manner and acts synergistically in combination with Substance P. Here we report a strong link between VEGF and mast cells and we depict their role in inflammation and immunity.

Living with stress: regulation of antioxidant defense genes in the subterranean, hypoxia-tolerant mole rat, Spalax

Lack of oxygen is life threatening for most mammals. It is therefore of biomedical interest to investigate the adaptive mechanisms which enable mammalian species to tolerate extremely hypoxic conditions. The subterranean mole rat Spalax survives substantially longer periods of hypoxia than the laboratory rat. We hypothesized that genes of the antioxidant defense, detoxifying harmful reactive oxygen species generated during hypoxia and hyperoxia, are involved in Spalax underground adaptation. Using quantitative RT-PCR, we analyzed the mRNA expression levels of seven antioxidant defense genes (catalase, glutathione peroxidase 1, glutathione-S-transferase Pi1, heme oxygenase 1, superoxide dismutase 1 and 2) and a master regulator of this stress pathway, nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in several tissues of two Israeli Spalax species, S. galili (2n=52) and S. judaei (2n=60), and rat. We also studied the differential expression of these genes after experimental hypoxia and hyperoxia as oxidative stress treatments. We found that mRNA levels and transcriptional responses are species and tissue specific. There are constitutively higher transcript levels of antioxidant genes and their transcription factor Nrf2 in Spalax tissue as compared to rat, suggesting an increased ability in the mole rat to withstand hypoxic/hyperoxic insults. In contrast to Spalax, the rat reacts to experimental oxidative stress by changes in gene regulation. In addition, Spalax Nrf2 reveals unique amino acid changes, which may be functionally important for this transcription factor and indicate positive (Darwinian) selection. Antioxidant defense genes are therefore important targets for adaptive change during evolution of hypoxia tolerance in Spalax.

Expression of FLK1 and CD146 at day 7 following reperfused acute myocardial infarction

OBJECTIVES

To investigate the expression of FLK1, CD146 and microvessel density of angiogenesis at the first week of reperfused acute myocardial infarction (AMI).

METHODS

16 of mini-swines (20 to 30 Kg) were randomly assigned to the sham-operated group and the AMI group. Pathologic myocardial tissue was collected at day 7 following reperfusion and detected by dual immunochemistry, real-time quantitative polymerase chain reaction and western blot.

RESULTS

The infarcted area had higher FLK1 mRNA expression than the sham-operated area and the normal area (all P < 0.05), and the infarcted and marginal areas showed higher CD146 protein expression than the sham-operated area (all P < 0.05), but the microvessel density (CD31 positive expression of microvessels/HP) was not significantly different between the infarcted area and the sham-operated area (8.92 ± 3.05 vs 6.43 ± 1.54)(P > 0.05).

CONCLUSION

FLK1 and CD146 expression significantly increase in the infarcted and marginal areas, and the microvessel density of angiogenesis in the infarcted area is similar to normal microvessel density of healthy heart tissue, suggesting that FLK1 and CD146 are possible associated with angiogenesis at day 7 following reperfused acute myocardial infarction.

Tolerance to oxygen nutrient deprivation in the hippocampal slices of the naked mole rats

Hypoxia tolerance in the naked mole rats (Heterocephalus glaber) represents a unique physiological phenomenon characterized by the capability to regulate oxygen demand to attenuate energetically costly response to low oxygen condition. Several aspects of tolerance to hypoxia in the naked mole rat are consistent with a state of neuroprotection; however, it remains to be established if such protective capability is expressed in the brain cells of mole rats subjected to hypoxia insults. The objective of this study was to determine whether evidence of tolerance to oxygen nutrient deprivation exists in the chronic cultures of the naked mole rats hippocampal slices. We used oxygen nutrient deprivation (OND), an in vitro model of hypoxia tolerance, to determine neuronal survival in the hippocampal slices of mole rats and rats (Rattus sp.). Our results indicate that hippocampal slices of mole rats kept in hypoxic condition consistently tolerate OND right from the onset time of 5 hrs and the tolerance to OND is maintained for 24 hrs, suggesting that there is evidence of tolerance to OND in hippocampal slices of mole rats.

Adaptive features of skeletal muscles of mole rats (Spalax ehrenbergi) to intensive activity under subterranean hypoxic conditions

Mole rats of the Spalax ehrenbergi superspecies are blind subterranean rodents that live under fluctuating oxygen supply, reduced to a measured 6% O(2), and mostly probably lower, during the rainy season. Fiber typing of muscles of the neck (trapezius) and leg (gastrocnemius, quadriceps) using standard histochemical techniques (succinic dehydrogenase, myosin ATPase) showed that the muscle fibers of mole rats in natural settings, as well as after extended captivity, were predominantly type IIa. The same muscles in laboratory rats showed the full range of fiber types. In contrast, the hearts of the mole rats and the laboratory rats were very similar. Our results indicate that skeletal muscle in the mole rats appears to have evolved in response to specific environmental demands to permit intensive endurance burrowing activities under conditions of severe or chronic hypoxia.

The injured nervous system: a Darwinian perspective

Much of the permanent damage that occurs in response to nervous system damage (trauma, infection, ischemia, etc.) is mediated by endogenous secondary processes that can contribute to cell death and tissue damage (excitotoxicity, oxidative damage and inflammation). For humans to evolve mechanisms to minimize secondary pathophysiological events following CNS injuries, selection must occur for individuals who survive such insults. Two major factors limit the selection for beneficial responses to CNS insults: for many CNS disease states the principal risk factor is advanced, post-reproductive age and virtually all severe CNS traumas are fatal in the absence of modern medical intervention. An alternative hypothesis for the persistence of apparently maladaptive responses to CNS damage is that the secondary exacerbation of damage is the result of unavoidable evolutionary constraints. That is, the nervous system could not function under normal conditions if the mechanisms that caused secondary damage (e.g., excitotoxicity) in response to injury were decreased or eliminated. However, some vertebrate species normally inhabit environments (e.g., hypoxia in underground burrows) that could potentially damage their nervous systems. Yet, neuroprotective mechanisms have evolved in these animals indicating that natural selection can occur for traits that protect animals from nervous system damage. Many of the secondary processes and regeneration-inhibitory factors that exacerbate injuries likely persist because they have been adaptive over evolutionary time in the healthy nervous system. Therefore, it remains important that researchers consider the role of the processes in the healthy or developing nervous system to understand how they become dysregulated following injury.