PhD Scientific Days 2024

Molecular Medicine III.

The role of serotonin in the intratumoral cellular heterogeneity of colorectal cancer

Text of the abstract

Colorectal cancer (CRC) is a leading cause of cancer-related mortality. In recent years, intratumoral heterogeneity, a major factor modifying drug responses and survival, has emerged as an interesting scientific question. This can be studied with patient-derived organoids (PDOs) that maintain the cellular heterogeneity of the original tissue. CRC is classically clustered in the microsatellite unstable (MSI) and microsatellite stable (MSS) groups. In addition, the consensus molecular subtyping system (CMS) is based on gene expression profiles and shows great potential for diagnostic and prognostic purposes. CMS4, a gene expression-based consensus molecular subtyping system (CMS) subgroup, is characterized by epithelial-mesenchymal transition (EMT), fibroblast accumulation, significant HTR2B serotonin receptor expression, and the worst prognosis. The accumulation of collagen is also associated with a bad outcome.

Thus, in my experiments, I focused on the role of serotonin in the intratumoral cellular heterogeneity of CRC.

CRC cells and PDOs were cultured in 2D or 3D (Matrigel or collagen). We applied RT-qPCR, flow cytometry, and immunocytochemistry to study gene expression.

We found that neither fibroblasts nor CRC cells produced serotonin in different conditions. Compared to normal colon organoids, we observed a reduced expression of TPH1, the rate-limiting enzyme of serotonin synthesis in CRC. In contrast, CRC organoids had a higher expression of SLC6A4, involved in serotonin re-uptake, and both normal colon and CRC organoids had a high level of the serotonin-degrading MAOA enzyme. In addition, we observed the heterogeneous expression of HTR2B and a low level of the mesenchymal marker α-SMA in CRC epithelial cells. Interestingly, α-SMA was also present in PDOs and MSI and MSS cell lines. Serotonin and HTR2B agonist modified the percentage of cells with mesenchymal markers in both 2D and 3D in MSI and MSS. In addition, serotonin had a major influence on PDO morphology in collagen.

Thus, although CRC cells are not a major source of serotonin, they can take it up and degrade it. Modulating the activity of HTR2B may critically affect the molecular heterogeneity of CRC.

This research was financed by OTKA-K 137554 and TKP2021-EGA-24. Ethical permission: TUKEB 51323-4/2015/EKU.