Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Christopher A. Lowry

Second Advisor

Dylan J. Taatjes

Third Advisor

Hubert Yin

Fourth Advisor

Robin Dowell

Fifth Advisor

Xuedong Liu

Abstract

In modern urban environments there is an increased prevalence of allergies, asthma, inflammatory bowel diseases (IBD), and anxiety disorders. The underlying cause for these disorders, as postulated by the Hygiene Hypothesis, is chronic inflammation, and the imbalance in the immune system is caused by a lack of interaction with microbes that have been removed from the urban space and lifestyle. One such microbe is the environmental saprophyte, Mycobacterium vaccae. In animal models, immunization with M. vaccae protects against the development of these prevalent inflammatory disorders. This immunoregulatory effect has been shown to occur due to the expansion of regulatory T cells, but it is still unclear how M. vaccae is interacting with the immune cells.

To better understand the mechanisms of immune suppression, we screened secreted molecules and whole cell preparations for anti-inflammatory properties. We were able to isolate and determine the structure of a single fatty acid, 10(Z)-hexadecenoic acid. The fatty acid was an effective immunosuppressant both in vivo in a murine model of allergic asthma, and ex vivo, as observed by decreased release of proinflammatory cytokines, like interleukin-5 from splenocytes.

We next investigated how the anti-inflammatory effects are achieved using macrophages as a model system. The mRNA transcriptional profile of macrophages treated with 10(Z)-hexadecenoic acid suggested that peroxisome proliferator-activated receptor (PPAR)α was mediating the effects. It was subsequently confirmed, using transfection assays, that 10(Z)-hexadecenoic acid increases PPARα signaling. Furthermore, PPARα was demonstrated to be necessary for the anti-inflammatory effects, as a PPARα antagonist blocked the effects of 10(Z)-hexadecenoic acid, and 10(Z)-hexadecenoic acid had no effect in macrophages isolated from PPARα-/- mice.

Collectively, these data define 10(Z)-hexadecenoic acid as an immunosuppressant metabolite that may contribute to the immunomodulatory effects of M. vaccae immunization. Furthermore, to our knowledge, 10(Z)-hexadecenoic acid is not synthesized de novo in mammals, and its biosynthesis appears to be unique to mycobacteria. This is also the first instance where a Mycobacterium or Mycobacterium-derived molecule has been shown to have anti-inflammatory effects mediated through PPARα.

Included in

Biochemistry Commons

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