292172 Bacterial Metabolites As Regulators of Inflammation and Adipogenesis

Monday, October 29, 2012
Hall B (Convention Center )
Pallavi Nair, Texas A&M University, College Station, TX

Our driving motivation for this research is obesity, which can be considered a low-grade inflammation. If tryptophan-derived molecules such as indole influence inflammation in adipocytes, they could help us combat the disease. Though there is prior research on the intestinal natural flora and the metabolites produced by them, these metabolites have not been studied as inflammation regulators yet.

Bacterial Metabolites as Regulators of Inflammation and Adipogenesis

Wikoff et al. [1] showed that mammalian metabolism and microbial metabolism are linked through bacterial metabolites that potentially circulate throughout the body. In addition, a clinical study showed that fecal levels of tryptophan are strongly related to Crohn’s disease [2], an inflammatory intestinal disease, suggesting that those with this disease are not utilizing tryptophan or converting it to other compounds and thus may have an imbalance of tryptophan-derived bacterial metabolites. Together, these studies imply that the gut microbiota may be connected to inflammatory disease through the circulation of tryptophan-derived metabolites and their interaction with molecules that regulate adipocyte function (transcription factors). This link is the focus of our proposed research.

Bacteria-derived metabolites could present a novel way to treat inflammatory diseases. Using these molecules in the treatment of obesity is of particular interest because obesity is an inflammatory disease that affects a large population and because obesity is tied to other health problems like diabetes and cardiovascular disease. Additionally, the tryptophan-related metabolites are naturally present in the human intestinal tract, so using them to combat disease may be safer than treatments that use synthetic (i.e., non-natural) compounds to do so.  Understanding what bacteria-derived molecules adipocytes respond to will allow us to determine the role microbes play in obesity. In addition, determining the function of various transcription factors in adipogenesis and how they interact with these metabolites will enable us to improve our understanding of the disease and give us new ways to remediate it as well as further expand our understanding of the gut microbiota.

This work is part of a larger goal to understand the role bacterial metabolites play in disease. This research will also improve our understanding of how human cells recognize bacterial metabolites. Not only is this significant in discerning the role these metabolites play in disease, but it is also key to understanding the impact of microbial metabolites on human health in general.


It is well understood that intestinal microbes play important roles in digestion and immunity, however recent studies have shown that bacteria-derived molecules affect intestinal cells and even organs like the brain [3][4]. If these molecules affect tissues outside of the gastro-intestinal (GI) tract, they may also play a role in disease.

Based on the aforementioned previously published work, the Jayaraman Research group hypothesizes that metabolites derived from intestinal microbes are important mediators of inflammation. Adipocytes are specifically being tested because their inflammation in the intestinal region plays a key role in obesity. Qualitative examination of lipid accumulation in adipose cells will also allow us to visually determine if indole impacts adipogenesis.

Prior work by the Jayaraman Research Team has shown that the protein Nr4A, a nuclear receptor that binds directly to DNA and acts as a transcription factor, is involved in inflammation. The study concluded that as the expression of the Nr4A gene increases in the cell, the amount on inflammation increases and adipogenesis decreases. However, it has been observed that the expression of Nr4A decreases in the presence of Indole. Since the addition of Indole to adipocytes decreases the expression of Nr4A which in turn reduces inflammation in cells, we expect that adipogenesis will increase in the presence of indole.

PPAR-γ is one of the most important transcription factor for activating the genes for adipogenesis. After being induced, the transcription factor binds to the DNA to transcribe an mRNA for the enzyme luciferase. This will result in the synthesis of luciferase and its secretion outside the cell, into the media. The activity of luciferase can be monitored by the addition of the substrate Luciferin, and by measuring the photon emission of the reaction using a luminometer. Hence, adipogenesis, which is regulated by PPAR-γ, is indirectly measured through the photon emission data from luciferase. If the presence of indole does indeed affect adipogenesis, then more enzyme will be produced, and the photon emission data will be higher than the control group with no indole present.

We therefore hypothesize that indole and other metabolites will increase the expression of the key adipogenesis-associated transcription factors such as PPAR-γ, CEBP, CREB, and SREBP. We will also determine if the transcription factors influence one another in their interactions or act individually. Our results can be used to help us determine whether indole directly affects adipogenesis by their presence or if they affect adipogenesis indirectly through their regulation of inflammation.

Our results suggest that indole addition does indeed cause an increase in both PPAR and CREB reporter expression compared to the control experimental set. This translates to an increase in adipogenesis as proposed by our hypothesis. In addition, by using Oil Red O staining to qualitatively monitor adipogenesis via lipid accumulation we found that cells treated with indole while differentiating do in fact experience increased lipid production. The visual images and the transcription factor expression results go hand in hand in supporting our hypothesis in showing that indole, a bacterial metabolite, can be used to control inflammation and consequently combat obesity.

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