Click on the 'Resources' tab to download the ePoster. 

Macrophage NFAT Signaling Drives Angiogenesis in Response to Mycobacterial Infection

Mycobacterial infection is defined by the multitude of ways in which the pathogen succeeds in subverting the host immune response and persisting in their obligate hosts and spreading to new hosts. One notable method of immunological subversion in tuberculosis, which has been long noted histologically but understudied in a functional way, is the induction of host angiogenesis. This process of inducing newly elaborated blood vessels is shared by other bacterial and fungal pathogens, but can, principally, serve either a host-beneficial (delivery of immune cells, antimicrobial peptides, or exogenous antibiotic therapies) or host-detrimental (increased availability of host cells for intracellular replication and immunological evasion, increased oxygen and nutrient delivery, or inefficient delivery of antibiotics to the site of infection with abnormal blood vessels) role. Our group (Oehlers et al. 2015) and others (Datta et al. 2015) have identified a host-detrimental (or bacterially-beneficial) role for this angiogenesis, which suggests the potential for a specific bacterial mechanism for inducing angiogenesis.

More recently, our group (Walton et al. 2018) identified a particular modification of the mycobacterial cell wall glycolipid trehalose 6-6’-dimycolate (TDM) as both necessary and sufficient for inducing pathological angiogenesis. Using the zebrafish-Mycobacterium marinum model we identified the specific induction of VEGF (vascular endothelial growth factor, the master angiogenic chemokine) in response to both active mycobacterial infection or cis-cyclopropanated TDM alone. However, we still do not understand the mechanism by which TDM results in the transcription of VEGF and this work seeks to identify the intracellular immune signaling events that result in VEGF induction. Canonically, TDM can be detected by either toll-like receptor 2 (TLR2; Bowdish et al. 2009) or the C-type lectin receptors Mcl/Mincle (Ishikawa et al. 2009). Previous work and preliminary results indicated that the critical TLR adaptor protein Myd88 was dispensable so we focused further efforts on the downstream events from C-type lectin signaling. Three major pathways are known to be induced by Mcl/Mincle binding to TDM: CARD9-NF-κB induction, ASC-dependent inflammasome assembly and IL-1β processing and release, and ER calcium release activating calcineurin-NFAT. Preliminary results suggested the dispensability of both CARD9 and ASC, focusing our further efforts on NFAT.

The nuclear factor of activated T cells (NFAT) is a developmentally critical pathway with wide tissue distribution that is governed by 4 major NFAT genes. Little is known of this pathway in macrophages and less still in the host innate immune response to mycobacteria and no connection has ever been drawn between NFAT induction in macrophages and angiogenesis. To assess the role of this pathway strictly in macrophages, we developed a transgenic approach to inhibiting the induction of NFAT and found that this was sufficient to abolish the induction of angiogenesis to either infection or TDM treatment. This novel reagent and others in development offer us the ability to dissect the contribution of this pathway to both the angiogenic response in tuberculosis as well as the broader effects of inhibiting NFAT on host outcomes, opening the potential for new host-directed therapeutic options.