Senp1 drives hypoxia-induced polycythemia via GATA1 and Bcl-xL in subjects with Monge's disease.

In this study, because excessive polycythemia is a predominant trait in some high-altitude dwellers (chronic mountain sickness [CMS] or Monge's disease) but not others living at the same altitude in the Andes, we took advantage of this human experiment of nature and used a combination of induced pluripotent stem cell technology, genomics, and molecular biology in this unique population to understand the molecular basis for hypoxia-induced excessive polycythemia. As compared with sea-level controls and non-CMS subjects who responded to hypoxia by increasing their RBCs modestly or not at all, respectively, CMS cells increased theirs remarkably (up to 60-fold). Although there was a switch from fetal to adult HgbA0 in all populations and a concomitant shift in oxygen binding, we found that CMS cells matured faster and had a higher efficiency and proliferative potential than non-CMS cells.

Quantitative evaluation of the mitochondrial proteomes of Drosophila melanogaster adapted to extreme oxygen conditions.

Mitochondria are the primary organelles that consume oxygen and provide energy for cellular activities. To investigate the mitochondrial mechanisms underlying adaptation to extreme oxygen conditions, we generated Drosophila strains that could survive in low- or high-oxygen environments (LOF or HOF, respectively), examined their mitochondria at the ultrastructural level via transmission electron microscopy, studied the activity of their respiratory chain complexes, and quantitatively analyzed the protein abundance responses of the mitochondrial proteomes using Isobaric tag for relative and absolute quantitation (iTRAQ). A total of 718 proteins were identified with high confidence, and 55 and 75 mitochondrial proteins displayed significant differences in abundance in LOF and HOF, respectively, compared with the control flies.

Whole-genome sequencing uncovers the genetic basis of chronic mountain sickness in Andean highlanders.

The hypoxic conditions at high altitudes present a challenge for survival, causing pressure for adaptation. Interestingly, many high-altitude denizens (particularly in the Andes) are maladapted, with a condition known as chronic mountain sickness (CMS) or Monge disease. To decode the genetic basis of this disease, we sequenced and compared the whole genomes of 20 Andean subjects (10 with CMS and 10 without).

Hypoxia-adaptation involves mitochondrial metabolic depression and decreased ROS leakage.

Through long-term laboratory selection, we have generated a Drosophila melanogaster population that tolerates severe, normally lethal, level of hypoxia. This strain lives perpetually under severe hypoxic conditions (4% O(2)). In order to shed light on the mechanisms involved in this adaptation, we studied the respiratory function of isolated mitochondria from the thorax of hypoxia-adapted flies (AF) using polarographic oxygen consumption while monitoring superoxide generation by electron paramagnetic resonance (EPR) techniques.

Does hyperoxia selection cause adaptive alterations of mitochondrial electron transport chain activity leading to a reduction of superoxide production?

Prolonged hyperoxia exposure generates excessive reactive oxygen species (ROS) and potentially leads to oxidative injury in every organ. We have previously generated Drosophila melanogaster flies that tolerate extreme oxidative stress (90%-95% O₂), a lethal condition to naive flies, through a long-term laboratory selection. We found that hyperoxia-selected (S(O2)A) flies had a significantly longer lifespan in hyperoxia and paraquat-induced oxidative stress.

Antimicrobial peptides increase tolerance to oxidant stress in Drosophila melanogaster.

It is well appreciated that reactive oxygen species (ROS) are deleterious to mammals, including humans, especially when generated in abnormally large quantities from cellular metabolism. Whereas the mechanisms leading to the production of ROS are rather well delineated, the mechanisms underlying tissue susceptibility or tolerance to oxidant stress remain elusive. Through an experimental selection over many generations, we have previously generated Drosophila melanogaster flies that tolerate tremendous oxidant stress and have shown that the family of antimicrobial peptides (AMPs) is over-represented in these tolerant flies.

Experimental selection for Drosophila survival in extremely high O2 environments.

Although oxidative stress is deleterious to mammals, the mechanisms underlying oxidant susceptibility or tolerance remain to be elucidated. In this study, through a long-term laboratory selection over many generations, we generated a Drosophila melanogaster strain that can live and reproduce in very high O(2) environments (90% O(2)), a lethal condition to naïve flies. We demonstrated that tolerance to hyperoxia was heritable in these flies and that these hyperoxia-selected flies exhibited phenotypic differences from naïve flies, such as a larger body size and increased weight by 20%.

Arctic ground squirrel (Spermophilus parryii) hippocampal neurons tolerate prolonged oxygen-glucose deprivation and maintain baseline ERK1/2 and JNK activation despite drastic ATP loss.

Oxygen-glucose deprivation (OGD) initiates a cascade of intracellular responses that culminates in cell death in sensitive species. Neurons from Arctic ground squirrels (AGS), a hibernating species, tolerate OGD in vitro and global ischemia in vivo independent of temperature or torpor. Regulation of energy stores and activation of mitogen-activated protein kinase (MAPK) signaling pathways can regulate neuronal survival.

Distribution of NMDA receptor subunit NR1 in arctic ground squirrel central nervous system.

Hibernation is a natural model of neuroprotection and adult synaptic plasticity. NMDA receptors (NMDAR), which play key roles in excitotoxicity and synaptic plasticity, have not been characterized in a hibernating species. Tolerance to excitotoxicity and cognitive enhancement in Arctic ground squirrels (AGS, Spermophilus parryii) suggests that NMDAR expression may decrease in hibernation and increase upon arousal.

Decreased NR1 phosphorylation and decreased NMDAR function in hibernating Arctic ground squirrels.

Heterothermic mammals such as ground squirrels tolerate ischemia and N-methyl-D-aspartate (NMDA) better than homeothermic mammals such as rats both in vivo and in vitro, and this tolerance is enhanced in the hibernating state. However, the cellular mechanisms underlying this tolerance remain unclear. NMDA receptors (NMDAR) play a key role in excitotoxicity.

Persistent tolerance to oxygen and nutrient deprivation and N-methyl-D-aspartate in cultured hippocampal slices from hibernating Arctic ground squirrel.

Hibernating Arctic ground squirrel (hAGS), Spermophilus parryii, survive profound decreases in cerebral perfusion during torpor and return to normal blood flow during intermittent rewarming periods without neurologic damage. Hibernating AGS tolerate traumatic brain injury in vivo, and acute hippocampal slices from hibernating animals tolerate oxygen and glucose deprivation. It remains unclear, however, if neuroprotection results from intrinsic tissue properties or from differences in response to acute trauma associated with slice preparation.

Arousal from hibernation alters contextual learning and memory.

Hibernation is a unique and highly regulated physiological state characterized by profound, albeit periodically reversible, depression in body temperature, metabolism, and consciousness. Hippocampal synapses undergo pronounced remodeling in concert with torpor and arousal. During hibernation, the number of postsynaptic densities, apical dendritic branches, and spine densities decreases substantially in the hippocampus.

MAPKs are differentially modulated in arctic ground squirrels during hibernation.

Hibernating animals are very tolerant of trauma to the central nervous system such that dramatic fluctuations in cerebral blood flow occur during hibernation and arousal without apparent damage. Indeed, it was demonstrated that Arctic ground squirrels (AGS) experience acute and severe systemic hypoxia along with the dramatic fluctuation in cerebral blood flow when the animals are aroused from hibernation. While initial hypotheses concerned protective mechanisms in the hibernating state, recent evidence of sustained elevation of HIF1alpha in euthermic AGS from our laboratory suggests that a preparatory program of protective gene expression is chronically expressed in euthermic AGS.

Ascorbate distribution during hibernation is independent of ascorbate redox state.

Distribution of ascorbate into tissues is an essential process in ascorbate antioxidant defense. Hibernating animals are studied as a model of tolerance to ischemia-reperfusion because of their tolerance to fluctuations in blood flow associated with prolonged torpor and periodic arousal episodes. Throughout hibernation, plasma ascorbate concentration ([Asc](p)) repetitively increases during torpor, then falls during periodic arousal bouts.