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The interplay between prior selection, mild intermittent exposure, and acute severe exposure in phenotypic and transcriptional response to hypoxia

ABSTRACT: Hypoxia has profound and diverse effects on aerobic organisms, disrupting oxidative phosphorylation and activating several protective pathways. Predictions have been made that exposure to mild intermittent hypoxia may be protective against more severe exposure and may extend lifespan. Here we report the lifespan effects of chronic, mild, intermittent hypoxia and short-term survival in acute severe hypoxia in four clones of Daphnia magna originating from either permanent or intermittent habitats. We test the hypothesis that acclimation to chronic mild intermittent hypoxia can extend lifespan through activation of antioxidant and stress-tolerance pathways and increase survival in acute severe hypoxia through activation of oxygen transport and storage proteins and adjustment to carbohydrate metabolism. Unexpectedly, we show that chronic hypoxia extended the lifespan in the two clones originating from intermittent habitats but had the opposite effect in the two clones from permanent habitats, which also showed lower tolerance to acute hypoxia. Exposure to chronic hypoxia did not protect against acute hypoxia; to the contrary, Daphnia from the chronic hypoxia treatment had lower acute hypoxia tolerance than normoxic controls. Few transcripts changed their abundance in response to the chronic hypoxia treatment in any of the clones. After 12 hours of acute hypoxia treatment, the transcriptional response was more pronounced, with numerous protein-coding genes with functionality in oxygen transport, mitochondrial and respiratory metabolism, and gluconeogenesis, showing up-regulation. While clones from intermittent habitats showed somewhat stronger differential expression in response to acute hypoxia than those from permanent habitats, contrary to predictions, there were no significant hypoxia-by-habitat of origin or chronic-by-acute treatment interactions. GO enrichment analysis revealed a possible hypoxia tolerance role by accelerating the molting cycle and regulating neuron survival through up-regulation of cuticular proteins and neurotrophins, respectively.

ORGANISM(S): Daphnia magna

PROVIDER: GSE207385 | GEO | 2022/07/05

REPOSITORIES: GEO

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Project description:Background: Constant hypoxia (CH) and intermittent hypoxia (IH) occur during several pathological conditions such as asthma and obstructive sleep apnea. Our research is focused on understanding the molecular mechanisms that lead to injury or adaptation to hypoxic stress using Drosophila as a model system. Our current genome-wide study is designed to investigate gene expression changes and identify protective mechanism(s) in D. melanogaster after exposure to severe (1% O2) intermittent or constant hypoxia. Methodology/Principal Findings: Our microarray analysis has identified multiple gene families that are up- or down-regulated in response to acute CH or IH. We observed distinct responses to IH and CH in gene expression that varied in the number of genes and type of gene families. We then studied the role of candidate genes (up-or down-regulated) in hypoxia tolerance (adult survival) for longer periods (CH-7 days, IH-10 days) under severe CH or IH. Heat shock proteins up-regulation (specifically Hsp23 and Hsp70) led to a significant increase in adult survival (as compared to controls) of P-element lines during CH. In contrast, during IH treatment the up-regulation of Mdr49 and l(2)08717 genes (P-element lines) provided survival advantage over controls. This suggests that the increased transcript levels following treatment with either paradigm play an important role in tolerance to severe hypoxia. Furthermore, by over-expressing Hsp70 in specific tissues, we found that up-regulation of Hsp70 in heart and brain play critical role in tolerance to CH in flies. Conclusions/Significance: We observed that the gene expression response to IH or CH is specific and paradigm-dependent. We have identified several genes Hsp23, Hsp70, CG1600, l(2)08717 and Mdr49 that play an important role in hypoxia tolerance whether it is in CH or IH. These data provide further clues about the mechanisms by which IH or CH lead to cell injury and morbidity or adaptation and survival. Expression profiles were determined by expression arrays in Drosophila melanogaster following acute constant or intermittent hypoxia. Three groups of samples were included in this analysis (3 x control, 3x CH treated and 3 x IH treated samples).

Project description:The long-term effects of neonatal intermittent hypoxia (IH), an accepted model of apnea-induced hypoxia, are unclear. We have previously shown lasting “programming” effects on the HPA axis in adult rats exposed to neonatal IH. We hypothesized that neonatal rat exposure to IH will subsequently result in a heightened inflammatory state in the adult. Rat pups were exposed to normoxia (control) or six cycles of 5% IH or 10% IH over one hour daily from postnatal day 2 – 6. Plasma samples from blood obtained at 114 days of age were analyzed by assessing the capacity to induce transcription in a healthy peripheral blood mononuclear cell (PBMC) population and read using a high-density microarray. The analysis of plasma from adult rats previously exposed to neonatal 5% IH vs. 10% IH resulted in 2,579 significantly regulated genes including increased expression of Cxcl1, Cxcl2, Ccl3, Il1a, and Il1b. We conclude that neonatal exposure to intermittent hypoxia elicits a long-lasting programming effect in the adult resulting in an upregulation of inflammatory-related genes. Apnea is the most common cause of neonatal hypoxia affecting about 50% of preterm births (30 – 31 weeks), usually due to immature respiratory development. Upregulation of inflammatory genes and pathways in children 7 – 10 years of age has been shown, and there is a known increased risk of insulin resistance in adulthood when the fetus is exposed to maternal hypoxia, but the mechanism is unclear. The long-term metabolic, endocrine, and immunological effects of neonatal intermittent hypoxia (IH) exposure, an accepted model of apnea-induced hypoxia, have not been thoroughly evaluated. Recent studies in rats have shown that perinatal IH exposure can result in oxidative stress, causing a permanent immune response subsequently resulting in features of diabetes mellitus. We have previously examined adult rats exposed to neonatal intermittent hypoxia and perinatal continuous hypoxia, and have found lasting “programming” effects on the HPA axis. We now assess the long term effects of an accepted model of apnea-induced hypoxia using a validated transcriptional bioassay to study the extracellular milieu of adult rats exposed to neonatal intermittent hypoxia. We hypothesize that exposure to neonatal intermittent hypoxia will result in an increased inflammatory state in the adult as a result of long-lasting programming.

Project description:The long-term effects of neonatal intermittent hypoxia (IH), an accepted model of apnea-induced hypoxia, are unclear. We have previously shown lasting âprogrammingâ effects on the HPA axis in adult rats exposed to neonatal IH. We hypothesized that neonatal rat exposure to IH will subsequently result in a heightened inflammatory state in the adult. Rat pups were exposed to normoxia (control) or six cycles of 5% IH or 10% IH over one hour daily from postnatal day 2 â 6. Plasma samples from blood obtained at 114 days of age were analyzed by assessing the capacity to induce transcription in a healthy peripheral blood mononuclear cell (PBMC) population and read using a high-density microarray. The analysis of plasma from adult rats previously exposed to neonatal 5% IH vs. 10% IH resulted in 2,579 significantly regulated genes including increased expression of Cxcl1, Cxcl2, Ccl3, Il1a, and Il1b. We conclude that neonatal exposure to intermittent hypoxia elicits a long-lasting programming effect in the adult resulting in an upregulation of inflammatory-related genes. Apnea is the most common cause of neonatal hypoxia affecting about 50% of preterm births (30 Ã¢ÂÂ 31 weeks), usually due to immature respiratory development. Upregulation of inflammatory genes and pathways in children 7 Ã¢ÂÂ 10 years of age has been shown, and there is a known increased risk of insulin resistance in adulthood when the fetus is exposed to maternal hypoxia, but the mechanism is unclear. The long-term metabolic, endocrine, and immunological effects of neonatal intermittent hypoxia (IH) exposure, an accepted model of apnea-induced hypoxia, have not been thoroughly evaluated. Recent studies in rats have shown that perinatal IH exposure can result in oxidative stress, causing a permanent immune response subsequently resulting in features of diabetes mellitus. We have previously examined adult rats exposed to neonatal intermittent hypoxia and perinatal continuous hypoxia, and have found lasting Ã¢ÂÂprogrammingÃ¢ÂÂ effects on the HPA axis. We now assess the long term effects of an accepted model of apnea-induced hypoxia using a validated transcriptional bioassay to study the extracellular milieu of adult rats exposed to neonatal intermittent hypoxia. We hypothesize that exposure to neonatal intermittent hypoxia will result in an increased inflammatory state in the adult as a result of long-lasting programming. Sprague-Dawley (SD) rat pups were treated with neonatal normoxia (21% O2, control), 5% intermittent hypoxia (IH), or 10% IH on postnatal days (PD) 2-6, daily over 1 hr. They were reared normally by birth dams and weaned at PD22. Males were allowed to mature and sacrificed at age PD114 after an overnight fast. Whole blood collected by decapitation into tubes with EDTA, and plasma saved for further analysis. Two adult (~180 day) male Brown Norway (BN) rats served as PBMC donors. Cells were incubated with 20% plasma that was either autologous BN (self-control), or one of 3 pools: a) SD normoxic N=8, b) SD 5% IH treated N=5, and c) SD 10% IH N=3.

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The interplay between prior selection, mild intermittent exposure, and acute severe exposure in phenotypic and transcriptional response to hypoxia

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