A groundbreaking study led by a global research consortium offers new hope for patients with mycetoma, a neglected tropical disease. Researchers using an insect model and transcriptome analysis have unraveled the mechanism of iron regulation between host tissue and the mycetoma grain, a fungal mass characteristic of the disease. This discovery illuminates how the causative fungus invades and develops these protective grains within subcutaneous tissue, paving the way for new drug development and less invasive treatment strategies beyond surgical removal, potentially reducing the burden on patients significantly.
Mycetoma, a chronic infectious disease affecting impoverished communities, is characterized by the development of black grains within infected tissue. These grains shield the causative fungus from the immune system and antifungal agents, making treatment challenging and often requiring surgery or amputation. Until now, the process of grain formation has remained largely unknown.
A research group led by Specially Appointed Professor Imad Abugessaisa(full time), in collaboration with Associate Professor Wendy van de Sande from Erasmus University Medical Center in the Netherlands, headed a consortium from RIKEN IMS (Japan), Erasmus MC (Netherlands), Maynooth University (Ireland), and the Mycetoma Research Center (WHO collaborating center on Mycetoma and Skin Neglected Tropical Diseases, Sudan). The team used state-of-the-art histology techniques, omics technologies, and computational biology to unravel the formation and development of mycetoma grains.
In their study, the consortium used an invertebrate model, Galleria mellonella, in which they could follow grain formation over time. By performing RNA analysis at different time points, they demonstrated that iron homeostasis in both host and pathogen plays an important role in mycetoma grain formation. These findings are an important milestone in the field of mycetoma research. Although the presence of grains was documented as early as 1840, how these grains form and which processes in both host and pathogen contribute have remained a mystery until now.
In this extensive study, the consortium showed that the primary mycetoma causative agent produces siderophores, fungal molecules that are excreted to scavenge iron and bring it back to the fungal cell. Furthermore, the amount of iron within the host appears to be important in either containing the fungus inside the grain or allowing it to grow actively outside the grain. Therefore, interfering with iron uptake might be a promising target for drug discovery.
Reflecting on the journey leading to this achievement, Professor Imad Abugessaisa stated, "In Wad Onsa, Sudan, a village with the world's highest prevalence of mycetoma, the disease leaves many disabled and impoverished, especially young people. Determined to make a difference, I partnered with Dr. Wendy van de Sande and secured funding from various organizations, including RIKEN, Erasmus MC, JSPS, and the GHIT Fund, to research this neglected disease. This publication highlights the importance of collaboration in achieving scientific breakthroughs and addressing societal needs."
Research background
Mycetoma is a chronic, neglected tropical infectious disease. It affects the poorest of the poor in chronically neglected communities. The disease is characterized by a large subcutaneous mass and the formation of black grains in the infected tissue (Figure 1). Treatment for mycetoma is disappointing as 25-50% of the patients' recurrences are noted and up to 15% of patients will have to undergo amputation [PMID: 25667234]. The main reason behind this poor treatment response is the formation of protective structures by the pathogen upon entering the human body. These structures are called grains (Figure 1) and provide a strong barrier for antifungal agents. Although grains are the hallmark of mycetoma, it is currently not known how these grains are formed. To improve the current therapy, it is important to gain insights about grain formation.
In the research paper, a team lead by S.A. Prof. Abugessaisa and associate professor W.W.J. van de Sande and collaborators have discovered that iron homeostasis of both host and pathogen plays an important role in mycetoma grain formation.
This research will be published in Nature Communications on June 25, 2025 in Japan time.
Details of the Research paper
To map the processes leading to Mycetoma grain formation, we used a G. mellonella larvae infection model and time-course transcriptomic profiling. G. mellonella was infected with M. mycetomatis genome strain mm55. At 4h, day 1, day 3 and day 7 post-inoculation, RNA was extracted from larval content for transcriptomics profiling (In vivo study). At the same time, we monitored grain development and size by histology, counting number of grains and monitoring G. mellonella survival (Figure 2).
An immediate change was observed in the host transcriptomics as response to infection. The transcriptomics analysis revealed that genes related to iron transport were highly expressed by both in the host (transferrin and ferritin) and pathogen (SidA, SidD and SidI). Network analysis revealed that all siderophore (small, iron-chelating molecules produced by microorganisms to scavenge iron from the environment) genes in M. mycetomatis are differentially expressed. We observed that L-ornithine N(5)-monooxygenase (SidA), Acyl-CoA ligase (SidI) and Nonribosomal peptide synthetase (SidD) are highly expressed in all timepoints with significant upregulation one day after the infection compared to the rest of the genes involved in the siderophore pathway. These findings lead us to analyze the impacts of iron related genes in pathogen growth (in vitro) and in the development of grain (toxicity & survival (every day), monitor grain by histology, number and size of grains, and transcriptomics profiling) (in vivo) (Figure 2). In response to the withdrawal of iron from hemolymph by G. mellonella (host) the pathogen needs to alter its iron regulation. We therefore first established that pathogen could obtain iron from holoferritin in the presence of iron chelator 2'2 bipiridyl. Furthermore, we characterized iron genes (siderophore) in the pathogen using advanced proteomics and metabolomics analysis (in vitro) (Figure 2).
The study proposed a model of iron regulation in G. mellonella during infection with M. mycetomatis pathogen (Figure 3). During translation and in healthy G. mellonella, in the absence of iron (Fe2+), the The iron-responsive element-binding proteins IRP1 and IRP2 form a complex, which can bind to Iron Responsive Elements (IRE) in the 5' prime UTR region of the ferritin subunits coding transcripts LOC13510017 (Ferritin) and LOC13510018 (Ferritin, EC 1 16 3 1), preventing translation of the mRNA to form ferritin. In the presence of iron (Fe2+), 4Fe-4S is formed, binding to IRP1. The IRP1/4Fe-4S complex prevents binding to the IRE, enabling translation of both LOC13510017 and LOC13510018, forming ferritin. Ferritin will bind Fe2+ for transportation and storage. During infection, increased expression of aconitate hydratase results in increased formation of the 4Fe-4S complex, binding of IRP1 and thus the translation of both subunits of ferritin for the binding of Fe2+, creating an iron-derived environment. In response to the limited available iron, the pathogen shows significantly increased expression of the siderophore-related biosynthesis pathway for the production of siderophores needed for sequestering Fe2+, which is essential for the survival of the fungus.
In this study, we developed a method to integrate, analyze and interpret multi-Omics time-course data from in vivo and in vitro systems to map host and pathogen interaction, and to monitor the development of the mycetoma grain (subcutaneous tumor-like) during infection. The methods will be utilized in iPSC and Organoid research to study non-infection human diseases and will contribute to the development of WPI-PRIMe research.
Social impact of the research（the meaning of the research）
Our study addresses SDG3's targets 3.3 which aims to end among other neglected tropical disease (NTDs) and the World Health Organization (WHO) 2021-2030 roadmap for (NTDs). This study highlights the importance of iron acquisition pathways during mycetoma grain formation, suggesting potential avenues for development of new diagnostic and therapeutic strategies for mycetoma, therefore reduce the number of amputations needed and could shorten the treatment duration.
Fig. 1
Grain formation in the host was visualized 40 times magnified using H&E staining and light microscopy
Credit: 2025, Imad Abugessaisa et al., Iron regulatory pathways differentially expressed during Madurella mycetomatis grain development in Galleria mellonella, Nature Communications
Fig. 2
Overall view of the study. In vivo and in vitro, study of the grain development and impact of iron.
Credit: 2025, Imad Abugessaisa et al., Iron regulatory pathways differentially expressed during Madurella mycetomatis grain development in Galleria mellonella, Nature Communications
Fig. 3
Snapshot of different analysis showing gene expression changes, expression of iron genes and impacts of iron on pathogen growth
Credit: 2025, Imad Abugessaisa et al., Iron regulatory pathways differentially expressed during Madurella mycetomatis grain development in Galleria mellonella, Nature Communications
The article, "Iron regulatory pathways differentially expressed during Madurella mycetomatis grain development in Galleria mellonella," was published in Nature Communications at DOI: https://doi.org/10.1038/s41467-025-60875-2.
