Bacterial extracellular vesicles (BEVs) are small membrane vesicles secreted by a diverse range of bacteria that act as bioactive nanocarriers of a high diversity of proteins, lipids and nucleic acids. BEVs have mostly been studied in pathogenic bacterial models, owing to their causal role in pathogenicity. Compared to other microbial features, such as taxa, genes or metabolites, BEVs secreted by the large diversity of commensal bacterial species of the human gut microbiota have received little attention so far, leaving their influence upon gut microbial ecology and human health almost entirely unknown. We hypothesize that gut BEVs and their molecular cargos (i.e. the gut bacterial vesiculome) play critical roles in bacteria-bacteria and host-microbiome interactions, and in shaping phenotypes of host-microbiome systems. Our project will enable a comprehensive profiling of BEV molecular diversity across a large number of gut bacterial taxa, and a functional analysis of their impact on inter-species and inter-kingdom interactions. We intend to tackle these objectives through three aims: 1) characterize the origin, diversity and evolution of the human gut bacterial vesiculome; 2) investigate the role of BEVs in promoting horizontal gene transfers among bacterial species in the gut microbiome; and 3) investigate the role of BEVs on bacteria-bacteria and host-bacteria interactions. We will tackle each of these aims from three diversity perspectives: investigating multiple bacterial species, including geographically-distinct healthy human populations, and comparing healthy vs. disease. The project will expand our basic understanding of the evolution and function of bacterial vesiculation. It will also generate the first atlas of BEV profiles across gut bacterial taxa and host cohorts, providing key resources to mine for vesicular characteristics and functions that have translational potential for biomedicine.

Obesity and metabolic diseases are a top priority challenge for health systems. Monitoring changes in the bodys energy levels is a task of the hypothalamus (HpT) which integrates the actions of peripheral hormones and nutrients with neural information. However, this regulation is complex, and the causes and biological mechanisms leading to metabolic disorders remain to be explored. Among the cells involved, tanycytes play a key role. They are glial cells that line the third ventricle and mediate information about changes in the circulation to various HpT nuclei. They regulate important neuroendocrine functions such as food intake and energy balance. Although tanycytes are known to integrate external and internal signals, the specific cellular organelles through which they sense these cues remain unknown. Primary cilia (PC) are one such compartment crucial for perceiving peripheral signals, and they are indeed present in tanycytes. We have coined the name tanycilia for them. However, the function of tanycilia is still unclear. Here, we hypothesize that cilia may act as antennae for tanycytes, sensing nutrients or hormones, enabling adaptive cellular responses, and transmitting metabolic information to neurons. This project aims to I) characterize tanycilia morphology for the first time; II) identify their functions, primarily in the regulation of metabolism; and III) examine them in pathological contexts like obesity and anorexia. To achieve these goals, we will employ immunohistochemical techniques to characterize tanycilia in wild-type mice. To investigate their function, we will genetically manipulate tanycilia using inducible mouse models in combination with tanycyte-specific adeno-associated viruses (rAAV). The discovery of tanycilia's roles in integrating peripheral signals to regulate neuroendocrine functions holds promise for understanding and treating metabolic disorders.

The microbiota has an enormous influence on human health. CD4+ T cells play a central role in controlling the interaction with the microbiota. By specifically reacting against individual microbial species, T cells enable a mutualistic co-existence with microbes. Inappropriate T cell responses against microbes are in turn associated with inflammatory diseases. Thus, the combination of T cell specificity and functionality form the key determinant for physiological versus pathological host-microbiota interactions. So far, research on T cell-microbiota interaction is almost exclusively focussed on functional T cell subsets, whereas antigen-specificity is rarely addressed. This is a significant roadblock for developing targeted therapeutic interventions for microbiota-associated diseases. The interaction with the microbiota poses two particular challenges for adaptive immunity: first, the extremely high diversity of microbial species, and thus potential T cell targets; second, microbes are persistent and thus probably encountered chronically. Currently, we do not know (1) which microbes are targets of specific T cell reactivity in humans, (2) how the (chronic) interaction with the huge number of different microbial species is regulated by T cell specificity and function, and (3) how alterations of these parameters contribute to microbiota-associated diseases. I developed a highly sensitive technology to detect and deeply characterize microbe-specific T cells directly from human samples. MicroT will identify microbial target species of human T cells and unravel the molecular mechanisms regulating chronic interaction of T cells with the highly diverse microbiota. I will define the impact of specific T cell-microbiota interactions on chronic inflammatory diseases and upon ageing. Answering these fundamental questions of microbiota-T cell interaction will identify specific immune or microbial targets as an essential basis for rational development of novel targeted therapies.