Mouse background genetics in biomedical research: The devil's in the details

Genetically modified mice as a tool for the study of human diseases

Modeling a human disease is an essential part of biomedical research. The recent advances in the field of molecular genetics made it possible to obtain genetically modified animals for the study of various diseases. Not only monogenic disorders but also chromosomal and multifactorial disorders can be mimicked in lab animals due to genetic modification. Even human infectious diseases can be studied in genetically modified animals. An animal model of a disease enables the tracking of its pathogenesis and, more importantly, to test new therapies. In the first part of this paper, we review the most common DNA modification technologies and provide key ideas on specific technology choices according to the task at hand. In the second part, we focus on the application of genetically modified mice in studying human diseases.

Erythropoietin downregulates red blood cell clearance, increasing transfusion efficacy in severely anemic recipients

Red blood cells (RBC) transfusion is used to alleviate symptoms and prevent complications in anemic patients by restoring oxygen delivery to tissues. RBC transfusion efficacy, that can be measured by a rise in hemoglobin (Hb) concentration, is influenced by donor-, product-, and recipient-related characteristics. In some studies, severe pre-transfusion anemia is associated with a greater than expected Hb increment following transfusion but the biological mechanism underpinning this relationship remains poorly understood. We conducted a prospective study in critically ill patients and quantified Hb increment following one RBC transfusion. In a murine model, we investigated the possibility that, in conjunction with the host erythropoietic response, the persistence of transfused donor RBC is improved to maintain a highest RBC biomass. We confirmed a correlation between a greater Hb increment and a deeper pre-transfusion anemia in a cohort of 17 patients. In the mouse model, Hb increment and post-transfusion recovery were increased in anemic recipients. Post-transfusion RBC recovery was improved in hypoxic mice or those receiving an erythropoiesis-stimulating agent and decreased in those treated with erythropoietin (EPO)-neutralizing antibodies, suggesting that EPO signaling is necessary to observe this effect. Irradiated recipients also showed decreased post-transfusion RBC recovery. The EPO-induced post-transfusion RBC recovery improvement was abrogated in irradiated or in macrophage-depleted recipients, but maintained in splenectomized recipients, suggesting a mechanism requiring erythroid progenitors and macrophages, but which is not spleen-specific. Our study highlights a physiological role of EPO in downregulating post-transfusion RBC clearance, contributing to maintain a vital RBC biomass to rapidly cope with hypoxemia.

Deciphering Nucleic Acid Binding Proteome of Mouse Immune Organs Reveals Hub Proteins for Aging

Profiling the nucleic acid-binding proteins (NABPs) during aging process is critical to elucidate its roles in biological systems as well as transcriptional and translational regulation. Here, we developed a comprehensive strategy to survey the NABPs of mouse immune organs by using single cell preparation and selective capture technology-based proteomics. Our approach provided a global view of tissue NABPs from different organs under normal physiological conditions with extraction specificity of 70 to 90%. Through quantitative proteomics analysis of mouse spleen and thymus at 1, 4, 12, 24, 48, and 72 weeks, we investigated the molecular features of aging-related NABPs. A total of 2674 proteins were quantified in all six stages, demonstrating distinct and time-specific expression pattern of NABPs. Thymus and spleen exhibited unique aging signatures, and differential proteins and pathways were enriched across the mouse lifespan. Three core modules and 16 hub proteins associated with aging were revealed through weighted gene correlation network analysis. Significant candidates were screened for immunoassay verification, and six hub proteins were confirmed. The integrated strategy pertains the capability to decipher the dynamic functions of NABPs in aging physiology and benefit further mechanism research.

Red Blood Cell Metabolism In Vivo and In Vitro

Red blood cells (RBC) are the most abundant cell in the human body, with a central role in oxygen transport and its delivery to tissues. However, omics technologies recently revealed the unanticipated complexity of the RBC proteome and metabolome, paving the way for a reinterpretation of the mechanisms by which RBC metabolism regulates systems biology beyond oxygen transport. The new data and analytical tools also informed the dissection of the changes that RBCs undergo during refrigerated storage under blood bank conditions, a logistic necessity that makes >100 million units available for life-saving transfusions every year worldwide. In this narrative review, we summarize the last decade of advances in the field of RBC metabolism in vivo and in the blood bank in vitro, a narrative largely influenced by the authors' own journeys in this field. We hope that this review will stimulate further research in this interesting and medically important area or, at least, serve as a testament to our fascination with this simple, yet complex, cell.

Red Blood Cell Omics and Machine Learning in Transfusion Medicine: Singularity Is Near

Background

Blood transfusion is a life-saving intervention for millions of recipients worldwide. Over the last 15 years, the advent of high-throughput, affordable omics technologies - including genomics, proteomics, lipidomics, and metabolomics - has allowed transfusion medicine to revisit the biology of blood donors, stored blood products, and transfusion recipients.

Summary

Omics approaches have shed light on the genetic and non-genetic factors (environmental or other exposures) impacting the quality of stored blood products and efficacy of transfusion events, based on the current Food and Drug Administration guidelines (e.g., hemolysis and post-transfusion recovery for stored red blood cells). As a treasure trove of data accumulates, the implementation of machine learning approaches promises to revolutionize the field of transfusion medicine, not only by advancing basic science. Indeed, computational strategies have already been used to perform high-content screenings of red blood cell morphology in microfluidic devices, generate in silico models of erythrocyte membrane to predict deformability and bending rigidity, or design systems biology maps of the red blood cell metabolome to drive the development of novel storage additives.

Key Message

In the near future, high-throughput testing of donor genomes via precision transfusion medicine arrays and metabolomics of all donated products will be able to inform the development and implementation of machine learning strategies that match, from vein to vein, donors, optimal processing strategies (additives, shelf life), and recipients, realizing the promise of personalized transfusion medicine.

Norecopa: A global knowledge base of resources for improving animal research and testing

There are good ethical, legal and scientific reasons for ensuring that our use of animals in research and testing is limited to the lowest number of animals, and that those which are used are treated as humanely as possible, while at the same time providing reliable, reproducible and translatable data which is adequately reported. Unfortunately, there is widespread evidence that there is room for improvement in all these areas. This paper describes the Norecopa website, which offers links to global resources which can be used to resolve these issues. Much of the website content is linked to the PREPARE guidelines for planning any research or testing which appears to need animals. Attention to detail on all steps of the pathway from early planning to manuscript submission should lead to better science, improved animal welfare, and fewer health and safety accidents. This will also minimize the chances of manuscript rejection due to inadequate planning, avoiding a waste of human resources and animal lives.

Hypoxic storage of murine red blood cells improves energy metabolism and post-transfusion recoveries

BACKGROUND

The Red blood cell (RBC) storage lesion results in decreased circulation and function of transfused RBCs. Elevated oxidant stress and impaired energy metabolism are a hallmark of the storage lesion in both human and murine RBCs. Although human studies don't suffer concerns that findings may not translate, they do suffer from genetic and environmental variability amongst subjects. Murine models can control for genetics, environment, and much interventional experimentation can be carried out in mice that is neither technically feasible nor ethical in humans. However, murine models are only useful to the extent that they have similar biology to humans. Hypoxic storage has been shown to mitigate the storage lesion in human RBCs, but has not been investigated in mice.

MATERIALS AND METHODS

RBCs from a C57BL6/J mouse strain were stored under normoxic (untreated) or hypoxic conditions (SO2 ~ 26%) for 1h, 7 and 12 days. Samples were tested for metabolomics at steady state, tracing experiments with 1,2,3-¹³C₃-glucose, proteomics and end of storage post transfusion recovery.

RESULTS

Hypoxic storage improved post-transfusion recovery and energy metabolism, including increased steady state and ¹³C₃-labeled metabolites from glycolysis, high energy purines (adenosine triphosphate) and 2,3-diphospholgycerate. Hypoxic storage promoted glutaminolysis, increased glutathione pools, and was accompanied by elevation in the levels of free fatty acids and acyl-carnitines.

DISCUSSION

This study isolates hypoxia, as a single independent variable, and shows similar effects as seen in human studies. These findings also demonstrate the translatability of murine models for hypoxic RBC storage and provide a pre-clinical platform for ongoing study.

FcγRIV is required for IgG2c mediated enhancement of RBC alloimmunization

Passive immunization with anti-D can prevent maternal alloimmunization to RhD thereby preventing hemolytic disease of the fetus and newborn. Unexpectedly, anti-D fails in some cases and some monoclonal anti-D preparations paradoxically enhances alloimmunization. The underlying mechanisms modulating humoral alloimmunization by anti-D are unknown. We previously reported that IgG antibody subclasses differentially regulate alloimmunity in response to red blood cell (RBC) transfusions in a mouse model; in particular, IgG2c significantly enhanced RBC alloantibody responses. Initial mechanistic studies revealed that IgG2c:RBC immune complexes were preferentially consumed by the splenic dendritic cell (DC) subsets that play a role in RBC alloimmunization. The deletion of activating Fc-gamma receptors (FcγRs) (i.e., FcγRI, FcγRIII, and FcγRIV) on DCs abrogated IgG2c-mediated enhanced alloimmunization. Because DCs express high levels of FcγRIV, which has high affinity for the IgG2c subclass, we hypothesized that FcγRIV was required for enhanced alloimmunization. To test this hypothesis, knockout mice and blocking antibodies were used to manipulate FcγR expression. The data presented herein demonstrate that FcγRIV, but not FcγRI or FcγRIII, is required for IgG2c-mediated enhancement of RBC alloantibody production. Additionally, FcγRI is alone sufficient for IgG2c-mediated RBC clearance but not for increased alloimmunization, demonstrating that RBC clearance can occur without inducing alloimmunization. Together, these data, combined with prior observations, support the hypothesis that passive immunization with an RBC-specific IgG2c antibody increases RBC alloantibody production through FcγRIV ligation on splenic conventional DCs (cDCs). This raises the question of whether standardizing antibody subclasses in immunoprophylaxis preparations is desirable and suggests which subclasses may be optimal for generating monoclonal anti-D therapeutics.

Adriamycin-Induced Nephropathy is Robust in N and Modest in J Substrain of C57BL/6

Adriamycin (ADR)-induced nephropathy remains the leading model to study human primary focal segmental glomerulosclerosis (FSGS), a common pathway for podocyte damage and glomerular loss of function that leads to chronic kidney disease. However, the use of this model for reverse genetics is limited by historical categorization of C57BL/6 mice as an ADR-resistant strain, which is also the most common genetically modified strain. Additionally, conflicting reports exist utilizing C57BL/6 for ADR-nephrosis due to lack of understanding of substrain differences (J/N) and variability in ADR dosage, timing, and frequency to induce damage. We have undertaken a systematic approach to elucidate the specifics of ADR-nephrosis in C57BL/6 N and J substrains. We induced nephropathy with 2 doses of ADR, and measured albuminuria for 6 weeks and performed histological evaluations. Our findings revealed induction of robust and modest proteinuria in N and J substrains, respectively. The serum creatinine levels were elevated in N, but not J substrain. Both the substrains showed reduction in body weight with N greater than J, although mortality remained at 0% in both substrains. Histological analysis showed worse renal lesions in the N than the J substrain. Podocyte markers synaptopodin, nephrin, podocin, and WT1 were reduced to a greater extent in the N than the J substrain. In summary, we provide the nephrology community with a reproducible mouse model for FSGS, in a strain otherwise assumed to be ADR-resistant and highlight the differences between J and N substrains. This enables future studies, especially concerning genetically manipulated animal models in C57BL/6.

ZOOMICS: Comparative Metabolomics of Red Blood Cells From Guinea Pigs, Humans, and Non-human Primates During Refrigerated Storage for Up to 42 Days

Unlike other rodents, guinea pigs (Cavia porcellus) have evolutionarily lost their capacity to synthesize vitamin C (ascorbate) de novo and, like several non-human primates and humans, rely on dietary intake and glutathione-dependent recycling to cope with oxidant stress. This is particularly relevant in red blood cell physiology, and especially when modeling blood storage, which exacerbates erythrocyte oxidant stress. Herein we provide a comprehensive metabolomics analysis of fresh and stored guinea pig red blood cell concentrates (n = 20), with weekly sampling from storage day 0 through 42. Results were compared to previously published ZOOMICS studies on red blood cells from three additional species with genetic loss of L-gulonolactone oxidase function, including humans (n = 21), olive baboons (n = 20), and rhesus macaques (n = 20). While metabolic trends were comparable across all species, guinea pig red blood cells demonstrated accelerated alterations of the metabolic markers of the storage lesion that are consistent with oxidative stress. Compared to the other species, guinea pig red blood cells showed aberrant glycolysis, pentose phosphate pathway end product metabolites, purine breakdown products, methylation, glutaminolysis, and markers of membrane lipid remodeling. Consistently, guinea pig red blood cells demonstrated higher end storage hemolysis, and scanning electron microscopy confirmed a higher degree of morphological alterations of their red blood cells, as compared to the other species. Despite a genetic inability to produce ascorbate that is common to the species evaluated, guinea pig red blood cells demonstrate accelerated oxidant stress under standard storage conditions. These data may offer relevant insights into the basal and cold storage metabolism of red blood cells from species that cannot synthesize endogenous ascorbate.