Medizinische Universität Graz - Research portal
Selected Publication:
Madhusudhan, N.
Microbiota alterations during epithelial tumor evolution and their functional consequences.
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Graz Medical University; 2020. pp. 141
[OPEN ACCESS]
FullText
- Authors Med Uni Graz:
- Advisor:
- Becker Jürgen Christian
- Gorkiewicz Gregor
- Wolf Peter
- Altmetrics:
- Abstract:
- Malignant tumors develop from specific pre-invasive neoplastic lesions, which have been described for most epithelial organs, e.g. actinic keratosis (AK) for squamous cell carcinoma (SCC) of the skin and adenomatous polyps for colorectal cancer (CRC). They harbor genetic aberrations, immune and stromal cells as well as microbes. During tumor development, the host-microbiota equilibrium is altered leading to a pro-inflammatory resident microbiota which could drive cancer progression. Given the central importance of microbiome in health and disease, elucidating mechanisms that maintain the microbiome homeostasis at cutaneous (skin) and mucosal (GI) surfaces as well as factors leading to microbiome disturbance (dysbiosis) and ultimately to chronic inflammation will improve our understanding of cancer initiation and progression. Skin harbors a considerable number of microbes that play an important role in health and disease. Nevertheless, their contribution to skin tumorigenesis has not been well studied. Therefore, we comparatively assessed the microbial community compositions in human keratinocyte skin tumors, AK, SCC and basal cell carcinoma (BCC). Our study shows that skin tumors are characterized by markedly different microbial community structures. AK and SCC, unlike BCC exhibit a significantly increased bacterial biomass. Markedly, Staphylococcus aureus was overabundant in the hyperkeratotic regions of SCC. Further, skin tumors showed an altered expression of antimicrobial peptides (AMPs), wherein human ß-defensin-2 (hBD-2) was elevated in SCC. Interestingly, this AMP is known to induce proliferation of squamous epithelia. To that end, we challenged SCC cells with S. aureus in vitro and observed specific induction of hBD-2 expression, which also promoted the growth of SCC cells. Thus, our studies demonstrate that a microbial community composition possibly favored due to the alteration of the microbial habitat (niche) perpetuates cancer development. In the case of SCC, increased S. aureus likely promotes tumor cell growth via specific induction of hBD-2, thus perpetuating the neoplastic process. Another organ system wherein the microbiota contributes to cancer development is the GI tract. Fusobacterium species typically colonizing the oral cavity but also the GI tract, have shown to be increased in GI tumors and can promote their growth. Part of this thesis validated an increased abundance of tumor-promoting Fusobacterium and F. nucleatum in adenomatous polyps and CRC compared to normal tissue. Interestingly we also observed a decreased expression of FadA from adenomas to carcinoma suggesting a possible down-regulation of this microbial colonization factor. Also, another aspect of this thesis aimed at addressing critical issues in fungal compartment of the microbiota which includes fungal DNA extraction and PCR amplification using the internal transcribed spacer (ITS) regions from human skin FFPE specimens. The tools used for microbial community analysis are typically developed for bacterial components and often fall short if applied to fungal data. Hence, we first aimed at attaining an ideal method to isolate fungal DNA from human skin FFPE, which represents the typical specimens for histopathology. We further sought to optimize PCR amplification of fungal ribosomal DNA using the ITS1 and -2 regions which are highly variable sequences used to distinguish fungal species. We showed that mechanical cell disruption during DNA isolation significantly lowered the DNA yield leading to a significant decrease in signal-to-noise ratio in ITS PCR. We also observed increased PCR performance using ITS2 primers in comparison to ITS1. In summary, this thesis points out that changes in microbiota emerging during carcinogenesis could promote tumor cell growth, modulated by diverse host and microbial factors such as alteration of AMP expression in cSCC progression or via regulation of microbial colonization factor such as in CRC.