Mediating a host cell signaling pathway linked to overwinter mortality offers a promising therapeutic approach for improving bee health

INTRODUCTION

Honey bees provides valuable pollination services for world food crops and wild flowering plants which are habitats of many animal species and remove carbon dioxide from the atmosphere, a powerful tool in the fight against climate change. Nevertheless, the honey bee population has been declining and the majority of colony losses occur during the winter.

OBJECTIVES

The goal of this study was to understand the mechanisms underlying overwinter colony losses and develop novel therapeutic strategies for improving bee health.

METHODS

First, pathogen prevalence in overwintering bees were screened between 2015 and 2018. Second, RNA sequencing (RNA-Seq) for transcriptional profiling of overwintering honey bees was conducted and qRT-PCR was performed to confirm the results of the differential expression of selected genes. Lastly, laboratory bioassays were conducted to measure the effects of cold challenges on bee survivorship and stress responses and to assess the effect of a novel medication for alleviating cold stress in honey bees.

RESULTS

We identified that sirtuin signaling pathway is the most significantly enriched pathway among the down-regulated differentially expressed genes (DEGs) in overwintering diseased bees. Moreover, we showed that the expression of SIRT1 gene, a major sirtuin that regulates energy and immune metabolism, was significantly downregulated in bees merely exposed to cold challenges, linking cold stress with altered gene expression of SIRT1. Furthermore, we demonstrated that activation of SIRT1 gene expression by SRT1720, an activator of SIRT1 expression, could improve the physiology and extend the lifespan of cold-stressed bees.

CONCLUSION

Our study suggests that increased energy consumption of overwintering bees for maintaining hive temperature reduces the allocation of energy toward immune functions, thus making the overwintering bees more susceptible to disease infections and leading to high winter colony losses. The novel information gained from this study provides a promising avenue for the development of therapeutic strategies for mitigating colony losses, both overwinter and annually.

Beeporter: Tools for high-throughput analyses of pollinator-virus infections

Pollinators are in decline thanks to the combined stresses of disease, pesticides, habitat loss, and climate. Honey bees face numerous pests and pathogens but arguably none are as devastating as Deformed wing virus (DWV). Understanding host-pathogen interactions and virulence of DWV in honey bees is slowed by the lack of cost-effective high-throughput screening methods for viral infection. Currently, analysis of virus infection in bees and their colonies is tedious, requiring a well-equipped molecular biology laboratory and the use of hazardous chemicals. Here we describe virus clones tagged with green fluorescent protein (GFP) or nanoluciferase (nLuc) that provide high-throughput detection and quantification of virus infections. GFP fluorescence is measured noninvasively in living bees via commonly available long-wave UV light sources and a smartphone camera, or a standard ultraviolet transilluminator gel imaging system. Nonlethal monitoring with GFP allows continuous screening of virus growth and serves as a direct breeding tool for identifying honey bee parents with increased antiviral resistance. Expression using the nLuc reporter strongly correlates with virus infection levels and is especially sensitive. Using multiple reporters, it is also possible to visualize competition, differential virulence, and host tissue targeting by co-occuring pathogens. Finally, it is possible to directly assess the risk of cross-species "spillover" from honey bees to other pollinators and vice versa.

Transferrin-mediated iron sequestration suggests a novel therapeutic strategy for controlling Nosema disease in the honey bee, Apis mellifera

Nosemosis C, a Nosema disease caused by microsporidia parasite Nosema ceranae, is a significant disease burden of the European honey bee Apis mellifera which is one of the most economically important insect pollinators. Nevertheless, there is no effective treatment currently available for Nosema disease and the disease mechanisms underlying the pathological effects of N. ceranae infection in honey bees are poorly understood. Iron is an essential nutrient for growth and survival of hosts and pathogens alike. The iron tug-of-war between host and pathogen is a central battlefield at the host-pathogen interface which determines the outcome of an infection, however, has not been explored in honey bees. To fill the gap, we conducted a study to investigate the impact of N. ceranae infection on iron homeostasis in honey bees. The expression of transferrin, an iron binding and transporting protein that is one of the key players of iron homeostasis, in response to N. ceranae infection was analysed. Furthermore, the functional roles of transferrin in iron homeostasis and honey bee host immunity were characterized using an RNA interference (RNAi)-based method. The results showed that N. ceranae infection causes iron deficiency and upregulation of the A. mellifera transferrin (AmTsf) mRNA in honey bees, implying that higher expression of AmTsf allows N. ceranae to scavenge more iron from the host for its proliferation and survival. The suppressed expression levels of AmTsf via RNAi could lead to reduced N. ceranae transcription activity, alleviated iron loss, enhanced immunity, and improved survival of the infected bees. The intriguing multifunctionality of transferrin illustrated in this study is a significant contribution to the existing body of literature concerning iron homeostasis in insects. The uncovered functional role of transferrin on iron homeostasis, pathogen growth and honey bee's ability to mount immune responses may hold the key for the development of novel strategies to treat or prevent diseases in honey bees.

Nosemosis control in European honey bees, Apis mellifera, by silencing the gene encoding Nosema ceranae polar tube protein 3

RNA interference (RNAi) is a post-transcriptional gene silencing mechanism triggered by double-stranded RNA (dsRNA) that is homologous in sequence to the silenced gene and is conserved in a wide range of eukaryotic organisms. The RNAi mechanism has provided unique opportunities for combating honey bee diseases caused by various parasites and pathogens. Nosema ceranae is a microsporidian parasite of European honey bees, Apis mellifera, and has been associated with honey bee colony losses in some regions of the world. Here we explored the possibility of silencing the expression of a N. ceranae putative virulence factor encoding polar tube protein 3 (ptp3) which is involved in host cell invasion as a therapeutic strategy for controlling Nosema parasites in honey bees. Our studies showed that the oral ingestion of a dsRNA corresponding to the sequences of N. ceranae ptp3 could effectively suppress the expression of the ptp3 gene in N. ceranae-infected bees and reduce Nosema load. In addition to the knockdown of ptp3 gene expression, ingestion of ptp3-dsRNA also led to improved innate immunity in bees infected with N. ceranae along with an improvement in physiological performance and lifespan compared with untreated control bees. These results strongly suggest that RNAi-based therapeutics hold real promise for the effective treatment of honey bee diseases in the future, and warrant further investigation.