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Macrophage triglyceride synthesis in TB infection comparison, the T863 group exhibited control at
Necrotizing granulomas are a hallmark of human the transcript level also. Together, these data
tuberculosis pathology. Macrophages containing point towards a balance achieved by granuloma
large deposits of neutral lipids, termed foamy triglyceride lowering, between the pro-
macrophages, are present around the central inflammatory and anti-bacterial eicosanoids,
necrotic core. The peculiar placement of these accompanied by lowering the inflammatory
cells in the structured granuloma, their being response and bacterial burden.
laden with bacteria, and forming an interface
between lymphocytes and the necrotic core has
raised interest in the origin and function of these
cells, with the goal to ameliorate pathology and
improve granuloma outcome with this knowledge.
Triglycerides are the major neutral lipid present in
these cells. To understand whether triglyceride
synthesis in these macrophages plays a role in the
progression of disease, we used a susceptible
mouse model of infection which exhibits this
characteristic pathology found in human TB. We
generated a high dose model of C3HeB/FeJ aerosol
infection with Mycobacterium tuberculosis (Mtb)
which exhibited development of necrotic
granulomas containing foamy macrophages. The A schematic representation of the key effects in
accumulation of neutral lipid was preceded by T863 treated mice
increased expression of diacylglycerol O-
acyltransferase 1 (DGAT1) which is the last enzyme This data provides proof-of-concept that inhibition
involved in triglyceride synthesis. Treating mice of triglyceride synthesis is a potential avenue for
with a DGAT1 specific inhibitor (T863) led to host directed therapy in tuberculosis. This field will
reduction in the neutral lipid content of benefit a great deal by understanding the
pulmonary granulomas, revealing a key role for mechanism of neutral lipid storage and
this enzyme in granuloma neutral lipid mobilization in macrophages.
accumulation. Surprisingly, mice treated with
T863 generated two distinct phenotypes in terms Lipid droplet proteins: key to lipid storage and
of bacterial growth in the lungs. Five out of eleven mobilization
animals responded to T863 treatment by lowering Cells store neutral lipids such as triglycerides and
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bacterial burden between 25-97% (T863 ) of the cholesterol esters in the form of specialized
vehicle group while the other six animals did not organelles called lipid droplets. Lipid droplets (LDs)
respond in this manner (T863 ). To understand exhibit a cell type specific proteome. In the past
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the correlates of bacterial control that are driven we have defined the proteome of LDs from human
by triglyceride lowering, we performed global THP1 macrophage cell line and studied the impact
transcriptome profiling. T863 animals had of Mtb infection on this proteome. This led to our
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reduced neutrophil infiltration and reduced discovery that Mtb actively manipulates the
expression of pro-inflammatory cytokines and macrophage LD proteome. One of the pathways
their upstream signaling molecules. Using multiple differentially modulated by Mtb on the LD
reaction monitoring, we measured eicosanoid proteome was vesicular trafficking. We are
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levels in lung extracts and found that T863 currently focusing on the small GTPase ARL8B
animals had higher levels of lipoxygenase products which we found to be increased in abundance on
compared to the vehicle treated animals and that LDs of live Mtb infected animals. Having found
this was solely driven at the metabolite level. In that preventing the formation of LDs in
Annual Report 2020-21 128
