The gut microbiome is a key player in the immunomodulatory and protumorigenic microenvironment during colorectal cancer (CRC), as different gut-derived bacteria can induce tumour growth. However, the crosstalk between the gut microbiome and the host in relation to tumour cell metabolism remains largely unexplored. Here we show that formate, a metabolite produced by the CRC-associated bacterium Fusobacterium nucleatum, promotes CRC development. We describe molecular signatures linking CRC phenotypes with Fusobacterium abundance. Cocultures of F. nucleatum with patient-derived CRC cells display protumorigenic effects, along with a metabolic shift towards increased formate secretion and cancer glutamine metabolism. We further show that microbiome-derived formate drives CRC tumour invasion by triggering AhR signalling, while increasing cancer stemness. Finally, F. nucleatum or formate treatment in mice leads to increased tumour incidence or size, and Th17 cell expansion, which can favour proinflammatory profiles. Moving beyond observational studies, we identify formate as a gut-derived oncometabolite that is relevant for CRC progression.

Several mutations in leucine-rich repeat kinase-2 (LRRK2) have been associated with Parkinson's disease (PD). The most common substitution, G2019S, interferes with LRRK2 kinase activity, which is regulated by autophosphorylation. Yet, the penetrance of this gain-of-function mutation is incomplete, and thus far, few factors have been correlated with disease status in carriers. This includes (i) LRRK2 autophosphorylation in urinary exosomes, (ii) serum levels of the antioxidant urate, and (iii) abundance of mitochondrial DNA (mtDNA) transcription-associated 7S DNA. In light of a mechanistic link between LRRK2 kinase activity and mtDNA lesion formation, we previously investigated mtDNA integrity in fibroblasts from manifesting (LRRK2+/PD+) and non-manifesting carriers (LRRK2+/PD−) of the G2019S mutation as well as from aged-matched controls. In our published study, mtDNA major arc deletions correlated with PD status, with manifesting carriers presenting the highest levels. In keeping with these findings, we now further explored mitochondrial features in fibroblasts derived from LRRK2+/PD+ (n = 10), LRRK2+/PD− (n = 21), and control (n = 10) individuals. In agreement with an accumulation of mtDNA major arc deletions, we also detected reduced NADH dehydrogenase activity in the LRRK2+/PD+ group. Moreover, in affected G2019S carriers, we observed elevated mitochondrial mass and mtDNA copy numbers as well as increased expression of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which regulates antioxidant signaling. Taken together, these results implicate mtDNA dyshomeostasis-possibly as a consequence of impaired mitophagy-in the penetrance of LRRK2-associated PD. Our findings are a step forward in the pursuit of unveiling markers that will allow monitoring of disease progression of LRRK2 mutation carriers.

Accumulating evidence suggests that dysbiosis, a state of pathologic imbalance in the human gut microbiome, is present in patients suffering from colorectal cancer (CRC). Several microbiome studies identified specific bacteria that are associated with CRC, among which Fusobacteria were shown to directly interact with cancer or immune cells of their host. However, only a limited number of CRC-associated microbes have been studied for host-microbial interactions; hence, the role of bacteria in the etiology of the disease remains unknown. Accordingly, our work aims at the development of a methodologic workflow for studying CRC-associated bacteria and their role in colon cancer tumor initiation and progression. In a first step, we identified CRC-associated bacteria that are enriched at the tumor site of CRC patients. Therefore, we used publicly available datasets and an in-house patient sample collection. Then, we predicted and optimized bacterial growth in silico by using a genome-scale metabolic reconstruction model combined with a constraint-based modeling approach. Finally, we implemented CRC-associated bacteria together with established primary CRC patient cultures into the microfluidics-based human-microbial crosstalk model (HuMiX). Our workflow allowed to analyze host-microbial interaction mechanisms of CRC-associated bacteria on a transcriptomic, proteomic, and metabolomic level. Citation Format: Dominik Ternes, Martine Schmitz, Léa Grandmougin, Mina Tsenkova, Eric Koncina, Aurélien Ginolhac, Jessica Karta, Diana Kuhn, Javier Ramiro Garcia, Kacy Greenhalgh, Paul Wilmes, Elisabeth Letellier, Serge Haan. Understanding the role of colorectal cancer-associated microbes in colorectal cancer [abstract]. In: Proceedings of the AACR Special Conference on the Microbiome, Viruses, and Cancer; 2020 Feb 21-24; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2020;80(8 Suppl):Abstract nr A09.

The human body is colonized by at least the same number of microbial cells as it is composed of human cells, and most of these microorganisms are located in the gut.Though the interplay between the gut microbiome and the host has been extensively studied, how the gut microbiome interacts with the enteric nervous system remains largely unknown. To date, a physiologically representative in vitro model to study gut microbiome-nervous system interactions does not exist.To fill this gap, we further developed the human-microbial crosstalk (HuMiX) guton-chip model by introducing induced pluripotent stem cell-derived enteric neurons into the device. The resulting model, 'neuroHuMiX', allows for the co-culture of bacterial, epithelial, and neuronal cells across microfluidic channels, separated by semi-permeable membranes. Despite separation of the different cell types, the cells can communicate with each other through soluble factors, simultaneously providing an opportunity to study each cell type separately. This setup allows for first insights into how the gut microbiome affects the enteric neuronal cells. This is a critical first step in studying and understanding the human gut microbiome-nervous system axis.