Multiple environmental stressors induce complex transcriptomic responses indicative of phenotypic outcomes in Western fence lizard

Unraveling molecular mechanistic disparities in pathogenic visceral Leishmania resistance between reptiles and mammals through comparative transcriptomic analyses

Leishmaniasis is one of the most important neglected tropical parasitic diseases, manifesting various clinical forms depending on the parasite species and the genetic background of the host. In order to elucidate the underlying mechanisms of reptilian defense against pathogenic Leishmania species and to delineate the global gene expression profile alterations during host-pathogen interaction, we established experimental animal and cell models using both heterothermic lizards (Phrynocephalus przewalskii) and homothermic mammals (BALB/c mice) infected with pathogenic Leishmania infantum (high virulence HCZ strain) and Leishmania donovani (low virulence 801 strain). Overall, the lizards didn't show any obvious clinical symptoms or immune responses in vivo. Using RNA-seq methodology, differentially expressed genes identified in the HCZ and 801-comparison groups of P. przewalskii were primarily associated with arginine biosynthesis, the MAPK signaling pathway and the PI3K-Akt signaling pathway. In contrast, higher parasite loads, exacerbated hepatic inflammatory lesions and enhanced immune responses were observed in BALB/c mice, with DEGs predominantly associated with immunological diseases, innate and adaptive immune responses. By integrating transcriptional data from reptile and mammalian hosts, we elucidated the pivotal role of amino acid metabolism and lipid metabolism in parasite control. In contrast to findings from animal experiments, Leishmania parasites effectively infected peritoneal macrophages of lizards in vitro, demonstrating a high infection rate. Furthermore, we used RT-qPCR to detect changes in cytokine expression in macrophages and found that Th1-type cytokines were significantly upregulated in lizards, facilitating the clearance of the HCZ strain 24 hours post-infection. Conversely, cytokine expression was generally suppressed in BALB/c mice, allowing immune evasion by the parasites.

Key challenges and developments in wildlife ecological risk assessment: Problem formulation

Problem formulation (PF) is a critical initial step in planning risk assessments for chemical exposures to wildlife, used either explicitly or implicitly in various jurisdictions to include registration of new pesticides, evaluation of new and existing chemicals released to the environment, and characterization of impact when chemical releases have occurred. Despite improvements in our understanding of the environment, ecology, and biological sciences, few risk assessments have used this information to enhance their value and predictive capabilities. In addition to advances in organism-level mechanisms and methods, there have been substantive developments that focus on population- and systems-level processes. Although most of the advances have been recognized as being state-of-the-science for two decades or more, there is scant evidence that they have been incorporated into wildlife risk assessment or risk assessment in general. In this article, we identify opportunities to consider elevating the relevance of wildlife risk assessments by focusing on elements of the PF stage of risk assessment, especially in the construction of conceptual models and selection of assessment endpoints that target population- and system-level endpoints. Doing so will remain consistent with four established steps of existing guidance: (1) establish clear protection goals early in the process; (2) consider how data collection using new methods will affect decisions, given all possibilities, and develop a decision plan a priori; (3) engage all relevant stakeholders in creating a robust, holistic conceptual model that incorporates plausible stressors that could affect the targets defined in the protection goals; and (4) embrace the need for iteration throughout the PF steps (recognizing that multiple passes may be required before agreeing on a feasible plan for the rest of the risk assessment). Integr Environ Assess Manag 2024;20:658-673. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Adaptive Immunity in Reptiles: Conventional Components but Unconventional Strategies

Recent studies have established that the innate immune system of reptiles is broad and robust, but the question remains: What role does the reptilian adaptive immune system play? Conventionally, adaptive immunity is described as involving T and B lymphocytes that display variable receptors, is highly specific, improves over the course of the response, and produces a memory response. While reptiles do have B and T lymphocytes that utilize variable receptors, their adaptive response is relatively non-specific, generates a prolonged antibody response, and does not produce a typical memory response. This alternative adaptive strategy may allow reptiles to produce a broad adaptive response that complements a strong innate system. Further studies into reptile adaptive immunity cannot only clarify outstanding questions on the reptilian immune system but can shed light on a number of important immunological concepts, including the evolution of the immune system and adaptive immune responses that take place outside of germinal centers.

Accumulation of Insensitive Munition Compounds in the Earthworm Eisenia andrei from Amended Soil: Methodological Considerations for Determination of Bioaccumulation Factors

The present study investigates the bioaccumulation of the insensitive munition compounds 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), developed for future weapons systems to replace current munitions containing sensitive explosives. The earthworm Eisenia andrei was exposed to sublethal concentrations of DNAN or NTO amended in Sassafras sandy loam. Chemical analysis indicated that 2- and 4-amino-nitroanisole (2-ANAN and 4-ANAN, respectively) were formed in DNAN-amended soils. The SumDNAN (sum of DNAN, 2-ANAN, and 4-ANAN concentrations) in soil decreased by 40% during the 14-d exposure period. The SumDNAN in the earthworm body residue increased until day 3 and decreased thereafter. Between days 3 and 14, there was a 73% decrease in tissue uptake that was greater than the 23% decrease in the soil concentration, suggesting that the bioavailable fraction may have decreased over time. By day 14, the DNAN concentration accounted for only 45% of the SumDNAN soil concentration, indicating substantial DNAN transformation in the presence of earthworms. The highest bioaccumulation factor (BAF; the tissue-to-soil concentration ratio) was 6.2 ± 1.0 kg/kg (dry wt) on day 3 and decreased to 3.8 ± 0.8 kg/kg by day 14. Kinetic studies indicated a BAF of 2.3 kg/kg, based on the earthworm DNAN uptake rate of 2.0 ± 0.24 kg/kg/d, compared with the SumDNAN elimination rate of 0.87 d^-1 (half-life = 0.79 d). The compound DNAN has a similar potential to bioaccumulate from soil compared with trinitrotoluene. The NTO concentration in amended soil decreased by 57% from the initial concentration (837 mg NTO/kg dry soil) during 14 d, likely due to the formation of unknown transformation products. The bioaccumulation of NTO was negligible (BAF ≤ 0.018 kg/kg dry wt). Environ Toxicol Chem 2021;40:1713-1725. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Genomic investigations of acute munitions exposures on the health and skin microbiome composition of leopard frog (Rana pipiens) tadpoles

Natural communities of microbes inhabiting amphibian skin, the skin microbiome, are critical to supporting amphibian health and disease resistance. To enable the pro-active health assessment and management of amphibians on Army installations and beyond, we investigated the effects of acute (96h) munitions exposures to Rana pipiens (leopard frog) tadpoles and the associated skin microbiome, integrated with RNAseq-based transcriptomic responses in the tadpole host. Tadpoles were exposed to the legacy munition 2,4,6-trinitrotoluene (TNT), the new insensitive munition (IM) formulation, IMX-101, and the IM constituents nitroguinidine (NQ) and 1-methyl-3-nitroguanidine (MeNQ). The 96h LC50 values and 95% confidence intervals were 2.6 (2.4, 2.8) for ΣTNT and 68.2 (62.9, 73.9) for IMX-101, respectively. The NQ and MeNQ exposures caused no significant impacts on survival in 96h exposures even at maximum exposure levels of 3560 and 5285 mg/L, respectively. However, NQ and MeNQ, as well as TNT and IMX-101 exposures, all elicited changes in the tadpole skin microbiome profile, as evidenced by significantly increased relative proportions of the Proteobacteria with increasing exposure concentrations, and significantly decreased alpha-diversity in the NQ exposure. The potential for direct effects of munitions exposure on the skin microbiome were observed including increased abundance of munitions-tolerant phylogenetic groups, in addition to possible indirect effects on microbial flora where transcriptional responses suggestive of changes in skin mucus-layer properties, antimicrobial peptide production, and innate immune factors were observed in the tadpole host. Additional insights into the tadpole host's transcriptional response to munitions exposures indicated that TNT and IMX-101 exposures significantly enriched transcriptional expression within type-I and type-II xenobiotic metabolism pathways, where dose-responsive increases in expression were observed. Significant enrichment and increased transcriptional expression of heme and iron binding functions in the TNT exposures served as likely indicators of known mechanisms of TNT toxicity including hemolytic anemia and methemoglobinemia. The significant enrichment and dose-responsive decrease in transcriptional expression of cell cycle pathways in the IMX-101 exposures was consistent with previous observations in fish, while significant enrichment of immune-related function in response to NQ exposure were consistent with potential immune suppression at the highest NQ exposure concentration. Finally, the MeNQ exposures elicited significantly decreased transcriptional expression of keratin 16, type I, a gene likely involved in keratinization processes in amphibian skin. Overall, munitions showed the potential to alter tadpole skin microbiome composition and affect transcriptional profiles in the amphibian host, some suggestive of potential impacts on host health and immune status relevant to disease susceptibility.

Example of Adverse Outcome Pathway Concept Enabling Genome-to-Phenome Discovery in Toxicology

The following article represents a mini-review of an intensive 10-year progression of genome-to-phenome (G2P) discovery guided by the adverse outcome pathway (AOP) concept. This example is presented as a means to stimulate crossover of this toxicological concept to enhance G2P discovery within the broader biological sciences community. The case study demonstrates the benefits of the AOP approach for establishing causal linkages across multiple levels of biological organization ultimately linking molecular initiation (often at the genomic scale) to organism-level phenotypes of interest. The case study summarizes a US military effort to identify the mechanism(s) underlying toxicological phenotypes of lethargy and weight loss in response to nitroaromatic munitions exposures, such as 2,4,6-trinitrotoluene. Initial key discoveries are described including the toxicogenomic results that nitrotoluene exposures inhibited expression within the peroxisome proliferator activated receptor α (PPARα) pathway. We channeled the AOP concept to test the hypothesis that inhibition of PPARα signaling in nitrotoluene exposures impacted lipid metabolic processes, thus affecting systemic energy budgets, ultimately resulting in body weight loss. Results from a series of transcriptomic, proteomic, lipidomic, in vitro PPARα nuclear signaling, and PPARα knock-out investigations ultimately supported various facets of this hypothesis. Given these results, we next proceeded to develop a formalized AOP description of PPARα antagonism leading to body weight loss. This AOP was refined through intensive literature review and polished through multiple rounds of peer-review leading to final international acceptance as an Organisation for Economic Cooperation and Development-approved AOP. Briefly, that AOP identifies PPARα antagonist binding as the molecular initiating event (MIE) leading to a series of key events including inhibition of nuclear transactivation for genes controlling lipid metabolism and ketogenesis, inhibition of fatty acid beta-oxidation and ketogenesis dynamics, negative energy budget, and ultimately the adverse outcome (AO) of body-weight loss. Given that the PPARα antagonism MIE represented a reliable indicator of AO progression within the pathway, a phylogenetic analysis was conducted which indicated that PPARα amino acid relatedness generally tracked species relatedness. Additionally, PPARα amino acid relatedness analysis using the Sequence Alignment to Predict Across Species Susceptibility predicted susceptibility to the MIE across vertebrates providing context for AOP extrapolation across species. Overall, we hope this illustrative example of how the AOP concept has benefited toxicology sows a seed within the broader biological sciences community to repurpose the concept to facilitate enhanced G2P discovery in biology.