Effects of temperature on the innate immune response on Antarctic and sub-Antarctic fish Harpagifer antarcticus and Harpagifer bispinis challenged with two immunostimulants, LPS and Poly I:C: In vivo and in vitro approach

Rising ocean temperatures due to climate change combined with the intensification of anthropogenic activity can drive shifts in the geographic distribution of species, with the risks of introducing new diseases. In a changing environment, new host-pathogen interactions or changes to existing dynamics represent a major challenge for native species at high latitudes. Notothenioid fish constitute a unique study system since members of this group are found inside and outside Antarctica, are highly adapted to cold and particularly sensitive to temperature increments. However, data about their immune response remains scarce. Here, we aimed to evaluate the innate immune response under thermal stress in two species of Notothenioid fish, Harpagifer antarcticus and Harpagifer bispinis. Adult individuals from both species were collected on King George Island (Antarctica), and Punta Arenas (Chile), respectively. Specimens were assigned to a control group or injected with one of two agents (LPS and Poly I:C) to simulate either a bacterial or viral infection, and subjected to three different temperatures 2, 5 and 8 °C for 1 week. In parallel, we established leukocytes primary cell cultures from head kidney, which were also subjected to the immunostimulants at the same three temperatures, and incubated for 0.5, 1, 3, 6, 12, 24, and 48 h. We evaluated the relative gene expression of genes involved in the innate immune response (TLR1, TLR3, NF-kB, MYD88, IFNGR e IL-8) through real time qPCR. We found differences between species mainly in vivo, where H. antarcticus exhibited upregulation at high temperatures and H. bispinis seemed to have reached their physiological minimum at 2 °C. Although temperature had a strong effect during the in vivo assay for both species, it was negligible for primary cell cultures, which responded primarily to condition and time. Moreover, while leukocytes responded with fluctuations across time points, in vivo both species manifested strong and clear patterns of gene expression. These results highlight the importance of evaluating the effect of multiple stressors and set a precedent for future research.

Quantitative Proteomics and Network Analysis of Differentially Expressed Proteins in Proteomes of Icefish Muscle Mitochondria Compared with Closely Related Red-Blooded Species

Simple Summary

Antarctic icefish are unusual in that they are the only vertebrates that survive without the protein haemoglobin. One way to try and understand the biological processes that support this anomaly is to record how proteins are regulated in these animals and to compare what we find to closely related Antarctic fish that do still retain haemoglobin. The part of the cell that most clearly utilises oxygen, which is normally transported by haemoglobin, is the mitochondrion. Therefore, we chose to catalogue all the proteins and their relative quantities in the mitochondria (pl.) from two different muscle types in two species of icefish and two species of red-blooded notothenioids. We used an approach called mass spectrometry to reveal relative amounts of the proteins from the muscles of each fish. We present analysis that shows how the connections and relative quantities of proteins differ between these species.

Abstract

Antarctic icefish are extraordinary in their ability to thrive without haemoglobin. We wanted to understand how the mitochondrial proteome has adapted to the loss of this protein. Metabolic pathways that utilise oxygen are most likely to be rearranged in these species. Here, we have defined the mitochondrial proteomes of both the red and white muscle of two different icefish species (Champsocephalus gunnari and Chionodraco rastrospinosus) and compared these with two related red-blooded Notothenioids (Notothenia rossii, Trematomus bernacchii). Liquid Chromatography-Mass spectrometry (LC-MS/MS) was used to generate and examine the proteomic profiles of the two groups. We recorded a total of 91 differentially expressed proteins in the icefish red muscle mitochondria and 89 in the white muscle mitochondria when compared with the red-blooded related species. The icefish have a relatively higher abundance of proteins involved with Complex V of oxidative phosphorylation, RNA metabolism, and homeostasis, and fewer proteins for striated muscle contraction, haem, iron, creatine, and carbohydrate metabolism. Enrichment analyses showed that many important pathways were different in both red muscle and white muscle, including the citric acid cycle, ribosome machinery and fatty acid degradation. Life in the Antarctic waters poses extra challenges to the organisms that reside within them. Icefish have successfully inhabited this environment and we surmise that species without haemoglobin uniquely maintain their physiology. Our study highlights the mitochondrial protein pathway differences between similar fish species according to their specific tissue oxygenation idiosyncrasies.

Adaptations and Diversity of Antarctic Fishes: A Genomic Perspective

Antarctic notothenioid fishes are the classic example of vertebrate adaptive radiation in a marine environment. Notothenioids diversified from a single common ancestor ∼25 Mya to more than 140 species today, and they represent ∼90% of fish biomass on the continental shelf of Antarctica. As they diversified in the cold Southern Ocean, notothenioids evolved numerous traits, including osteopenia, anemia, cardiomegaly, dyslipidemia, and aglomerular kidneys, that are beneficial or tolerated in their environment but are pathological in humans. Thus, notothenioids are models for understanding adaptive radiations, physiological and biochemical adaptations to extreme environments, and genetic mechanisms of human disease. Since 2014, 16 notothenioid genomes have been published, which enable a first-pass holistic analysis of the notothenioid radiation and the genetic underpinnings of novel notothenioid traits. Here, we review the notothenioid radiation from a genomic perspective and integrate our insights with recent observations from other fish radiations. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Does geographic variation in thermal tolerance in Daphnia represent trade-offs or conditional neutrality?

Geographic variation in thermal tolerance in Daphnia seems to represent genetic load at the loci specifically responsible for heat tolerance resulting from conditional neutrality. We see no evidence of trade-offs between fitness-related traits at 25 °C vs. 10 °C or between two algal diets across Daphnia magna clones from a variety of locations representing the opposite ends of the distribution of long-term heat tolerance. Likewise, we found no evidence of within-environment trade-offs between heat tolerance and fitness-related traits in any of the environments. Neither short-term and long-term heat tolerance shows any consistent relationship with lipid fluorescence polarization and lipid peroxidation across clones or environments. Pervasive positive correlations between fitness-related traits indicate differences in genetic load rather than trade-off based local adaptation or thermal specialization. For heat tolerance such differences may be caused by either relaxation of stabilizing selection due to lower exposure to high temperature extremes, i.e., conditional neutrality, or by small effective population size followed by the recent range expansion.

Developmental constraint shaped genome evolution and erythrocyte loss in Antarctic fishes following paleoclimate change

In the frigid, oxygen-rich Southern Ocean (SO), Antarctic icefishes (Channichthyidae; Notothenioidei) evolved the ability to survive without producing erythrocytes and hemoglobin, the oxygen-transport system of virtually all vertebrates. Here, we integrate paleoclimate records with an extensive phylogenomic dataset of notothenioid fishes to understand the evolution of trait loss associated with climate change. In contrast to buoyancy adaptations in this clade, we find relaxed selection on the genetic regions controlling erythropoiesis evolved only after sustained cooling in the SO. This pattern is seen not only within icefishes but also occurred independently in other high-latitude notothenioids. We show that one species of the red-blooded dragonfish clade evolved a spherocytic anemia that phenocopies human patients with this disease via orthologous mutations. The genomic imprint of SO climate change is biased toward erythrocyte-associated conserved noncoding elements (CNEs) rather than to coding regions, which are largely preserved through pleiotropy. The drift in CNEs is specifically enriched near genes that are preferentially expressed late in erythropoiesis. Furthermore, we find that the hematopoietic marrow of icefish species retained proerythroblasts, which indicates that early erythroid development remains intact. Our results provide a framework for understanding the interactions between development and the genome in shaping the response of species to climate change.

Our climate is rapidly changing. To better understand how species can adapt to major climate disturbance, we looked back into the past at a group of fishes that have encountered dramatic climate upheavals and thrived: Antarctic notothenioid fishes. In particular, we focus on the icefishes, which lost the ability to produce red blood cells in the frigid environment of the Southern Ocean. By integrating past climate records with a large genetic dataset of Antarctic fishes, we show that the loss of red blood cells occurred only after sustained cooling of the Southern Ocean. As cooling continued into the modern era, we discover that even some of the “red-blooded” relatives of the icefishes show early genetic and morphological signs of erythrocyte loss. This cooling event left a non-random imprint on the genome of icefishes. With few exceptions, the genetic toolkit underlying red cell development has remained intact in icefishes because many “erythroid” genes perform important functions in other tissues. Rather, mutations have accumulated in gene regulatory regions near genes that control terminal erythroid maturation, such that icefishes continue to produce red cell progenitors but not mature erythrocytes. These results show that the genetic constraints regulating embryonic development shaped the evolutionary response of this fish group to climate change.

What Is Next in This "Age" of Heme-Driven Pathology and Protection by Hemopexin? An Update and Links with Iron

This review provides a synopsis of the published literature over the past two years on the heme-binding protein hemopexin (HPX), with some background information on the biochemistry of the HPX system. One focus is on the mechanisms of heme-driven pathology in the context of heme and iron homeostasis in human health and disease. The heme-binding protein hemopexin is a multi-functional protectant against hemoglobin (Hb)-derived heme toxicity as well as mitigating heme-mediated effects on immune cells, endothelial cells, and stem cells that collectively contribute to driving inflammation, perturbing vascular hemostasis and blood–brain barrier function. Heme toxicity, which may lead to iron toxicity, is recognized increasingly in a wide range of conditions involving hemolysis and immune system activation and, in this review, we highlight some newly identified actions of heme and hemopexin especially in situations where normal processes fail to maintain heme and iron homeostasis. Finally, we present preliminary data showing that the cytokine IL-6 cross talks with activation of the c-Jun N-terminal kinase pathway in response to heme-hemopexin in models of hepatocytes. This indicates another level of complexity in the cell responses to elevated heme via the HPX system when the immune system is activated and/or in the presence of inflammation.