Blunted Neuronal Calcium Response to Hypoxia in Naked Mole-Rat Hippocampus

Naked mole-rats are highly social and strictly subterranean rodents that live in large communal colonies in sealed and chronically oxygen-depleted burrows. Brain slices from naked mole-rats show extreme tolerance to hypoxia compared to slices from other mammals, as indicated by maintenance of synaptic transmission under more hypoxic conditions and three fold longer latency to anoxic depolarization. A key factor in determining whether or not the cellular response to hypoxia is reversible or leads to cell death may be the elevation of intracellular calcium concentration. In the present study, we used fluorescent imaging techniques to measure relative intracellular calcium changes in CA1 pyramidal cells of hippocampal slices during hypoxia. We found that calcium accumulation during hypoxia was significantly and substantially attenuated in slices from naked mole-rats compared to slices from laboratory mice. This was the case for both neonatal (postnatal day 6) and older (postnatal day 20) age groups. Furthermore, while both species demonstrated more calcium accumulation at older ages, the older naked mole-rats showed a smaller calcium accumulation response than even the younger mice. A blunted intracellular calcium response to hypoxia may contribute to the extreme hypoxia tolerance of naked mole-rat neurons. The results are discussed in terms of a general hypothesis that a very prolonged or arrested developmental process may allow adult naked mole-rat brain to retain the hypoxia tolerance normally only seen in neonatal mammals

Time domains of the hypoxic ventilatory response in ectothermic vertebrates

Over a decade has passed since Powell et al. (Respir Physiol 112:123–134, 1998) described and defined the time domains of the hypoxic ventilatory response (HVR) in adult mammals. These time domains, however, have yet to receive much attention in other vertebrate groups. The initial, acute HVR of fish, amphibians and reptiles serves to minimize the imbalance between oxygen supply and demand. If the hypoxia is sustained, a suite of secondary adjustments occur giving rise to a more long-term balance (acclimatization) that allows the behaviors of normal life. These secondary responses can change over time as a function of the nature of the stimulus (the pattern and intensity of the hypoxic exposure). To add to the complexity of this process, hypoxia can also lead to metabolic suppression (the hypoxic metabolic response) and the magnitude of this is also time dependent. Unlike the original review of Powell et al. (Respir Physiol 112:123–134, 1998) that only considered the HVR in adult animals, we also consider relevant developmental time points where information is available. Finally, in amphibians and reptiles with incompletely divided hearts the magnitude of the ventilatory response will be modulated by hypoxia-induced changes in intra-cardiac shunting that also improve the match between O2 supply and demand, and these too change in a time-dependent fashion. While the current literature on this topic is reviewed here, it is noted that this area has received little attention. We attempt to redefine time domains in a more ‘holistic’ fashion that better accommodates research on ectotherms. If we are to distinguish between the genetic, developmental and environmental influences underlying the various ventilatory responses to hypoxia, however, we must design future experiments with time domains in mind

Taking advantage of tumor cell adaptations to hypoxia for developing new tumor markers and treatment strategies

Cancer cells in hypoxic areas of solid tumors are to a large extent protected against the action of radiation as well as many chemotherapeutic drugs. There are, however, two different aspects of the problem caused by tumor hypoxia when cancer therapy is concerned: One is due to the chemical reactions that molecular oxygen enters intoin therapeutically targeted cells. This results in a direct chemical protection against therapy by the hypoxic microenvironment which has little to do with cellular biological regulatory processes. This part of the protective effect of hypoxia has been known for more than half a century and has been studied extensively. However, in recent years more focus has been put into the other aspect of hypoxia, namely the effect of this microenvironmental condition on selecting cells with certain genetical pre-requisites that are negative with respect to patient prognosis. There are adaptive mechanisms, where hypoxia induces regulatory cascades in cells resulting in a changed metabolism or changes in extra cellular signalling. These processes may lead to changes in cellular intrinsic sensitivity to treatment irrespective of oxygenation and furthermore, may also have consequences for tissue organization. Thus, the adaptive mechanisms induced by hypoxia itself may have a selective effect on cells with a fine-tuned protection against damage and stress of many kinds. It therefore could be that the adaptive mechanisms may be taken advantage of for new tumor labelling/imaging and treatment strategies. One of the Achilles’ heels of hypoxia research has always been exact measurements of tissue oxygenation as well as control of oxygenation in biological tumor models. Thus, development of technology that can ease this control is vital in order to study mechanisms and perform drug development under relevant conditions. An integrated EU Framework project 2004-2009, termed Euroxy, demonstrates several pathways involved in transcription and translation control of the hypoxic cell phenotype and evidence of cross talk with responses to pH and redox changes. The carbon anhydrase isoenzyme CA IX was selected for further studies due to its expression on the surface of many types of hypoxic tumors. The effort has lead to marketable culture flaks with sensors and incubation equipment and the synthesis of new drug candidates against new molecular targets. New labelling/imaging methods for cancer diagnosing and imaging of hypoxic cancer tissue now are being tested in xeno-graft models and also are in early clinical testing while new potential anticancer drugs are undergoing tests using xenografted tumor cancers. The present paper describes the above results in individual consortium partner presentations