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Final Report Summary - DENDRITIC CELLS (Identification and targeting of metabolic pathways in dendritic cells that regulate their immune polarizing function)

Dendritic cells (DCs) are key regulators of both immunity and tolerance by controlling activation and polarization of effector T helper cells (Th) and regulatory T cell responses (Treg). Therefore, there is a major focus on developing approaches to manipulate DC function for immunotherapy. It is well known that changes in cellular activation are coupled to profound changes in cellular metabolism. However, only recently, based on studies with T cells and macrophages, the picture is emerging that manipulation of cellular metabolism can be used to shape immune responses. This field of immunometabolism is rapidly evolving as one of the new frontiers in science. Nonetheless, still little is known about the metabolic processes that support DC activation or about the metabolic requirements for DCs to drive Th1, Th2 or Treg responses. My proposal aimed to fill this gap and focused on the novel concept that cellular metabolism regulates the immune-polarizing properties of DCs. Specifically I hypothesized that conditioning of DCs by bacterial products results in a shift to glycolytic metabolism to acquire a Th1-polarizing phenotype, whereas Th2-DCs and Tol-DCs will display a shift towards mitochondrial OXPHOS fueled by FAO, that these states of metabolism are required for optimal Th1 and Th2/Treg polarization by these DCs, respectively and that manipulation of these metabolic pathways can be used in therapeutic settings to improve DC-based vaccinations

The main objectives of this proposal were the following:
Key objective 1): Characterize the metabolic profiles of Th1-, Th2- and Treg- promoting DCs.
Key objective 2): Determine whether glycolytic and mitochondrial metabolism in DCs are required for their Th1 and Th2/Treg-polarizing capacity, respectively
Key objective 3): Determine if manipulation of glycolytic or mitochondrial metabolism in DCs can be used to improve efficacy of DC-based immunotherapy

To address objective 1, we have performed detailed metabolic and transcriptomic analyses of human monocyte-derived DCs (moDCs), that have been stimulated with Th1, Th17, Th2 and Treg polarizing compounds. This has resulted in the identification of specific metabolic pathways that are characteristic of different Th-cell polarizing DCs. Specifically we found that Th1 and Th17-promoting DCs have increased glycolytic metabolism, with little changes in oxidative metabolism. In contrast, we observed that Th2 polarizing-DCs have suppressed glycolytic metabolism and instead appear to have heightened oxidative phosphorylation fueled by fatty-acid oxidation. Interestingly, unbiased integration of metabolic and transcriptomic data identified the UDP-GlcNAc synthesis pathway as a key defining metabolic property of Th2-priming moDCs. Finally, preliminary experiments suggest that Treg-inducing DCs are metabolically characterized by both increased glycolytic and mitochondrial metabolism.

To address objective 2, we have targeted these different metabolic pathways in dendritic cells pharmacologically in vitro and assessed the effects of those treatments on their ability to polarize different T cell responses. This has yielded very interesting data. Consistent with the observation that glycolysis was increased in Th1-polarizing DCs, but suppressed in Th2-priming DCs, we found that inhibition of glycolysis alone was sufficient to condition DCs for Th2 polarization. Conversely we found that when fatty acid oxidation was impaired in Th2-polarizing DCs, their ability to prime Th2 responses was compromised. Finally, inhibition of O-GlcNAcylation, the posttranslational modification for which UDP-GlcNAc is used, resulted in a selective impairment of Th2 priming of DCs, without comprising their ability to drive Th1 or Th17 responses.

As thoroughly addressing these first 2 aims has taken longer than expected, we have unfortunately within the timeframe of this grant not been able to evaluate if manipulation of glycolytic or mitochondrial metabolism in DCs can be used to improve efficacy of DC-based immunotherapy. With additional funding I aim to address this in the near future.

Together, the findings show that DCs with different T cell polarizing properties have different metabolic characteristics and that these metabolic differences are functionally important as targeting or manipulation of these metabolic pathways change the ability of these cells to prime certain Th cell responses.
This is highly relevant, given the fact that last 5 decades have seen an alarming rise in the incidence of several major diseases, such as cardiovascular diseases (CVD), cancer, type 2 diabetes (T2D), and allergies, which for a large part stem from inappropriate immune polarization - either too strong Th1/Type 1 immune responses (CVD and T2D) or too strong Th2/Type 2 inflammation (allergies, cancer). Furthermore, particularly in developing countries, infectious diseases are also still a major health burden and an important cause of death (WHO, 2015). Yet, vaccines or therapeutics to treat these illnesses are in most cases still insufficiently effective, partly due to lack of tools to manipulate Immune. Thus one of the major challenges we are currently facing is the development of novel ways to prevent and treat these diseases.
Hence, given the striking effects of metabolic manipulation of DCs on their capacity to prime and polarize Th cell responses as revealed in this project, we believe that these fundamental data provide a convincing proof of concept that targeting metabolism of DCs can be exploited in the future as a highly promising and novel approach to modulate immune polarization in therapeutic settings and contribute to the development of more efficacious types of immunotherapy in which DCs play a central role. This can be done alone or in synergy with other immunemodulating therapeutics, to improve vaccine efficacy and to become a key element of successful therapies for several diseases that are characterized by dysregulated immune polarization, as exemplified above. Therefore, the knowledge generated by my project can benefit patients as well as medical specialists from the fields of cardiology, oncology, metabolic diseases, and allergology.

Background and contact information
I have set up a webpage that explains my research interests and goals that encompass this project:

My contact details are:
Bart Everts, PhD
Department of Parasitology
Leiden University Medical Center
Room P4-37
Albinusdreef 2, 2333 ZA Leiden
The Netherlands
Tel # +31 (0)71 5265070

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