Page 37 - Biennial Report 2018-20 Jun 2021

HIJACKING OF HOST LIPID DROPLETS BY INTRACELLULAR PATHOGEN
Mycobacterium tuberculosis

The origin and function of foamy macrophages in TB infection remains elusive. In a study funded
by Wellcome Trust-DBT India Allaince, Sheetal Gandotra’s lab used a combination of infection
models, ranging from in vitro infection of human THP1 macrophages and human peripheral
blood monocyte derived macrophages to an in vivo guinea pig model of tuberculosis, to
understand lipid droplet
dynamics in infection.
Through this work, a role of
necrosis in the formation of
foamy macrophages during
infection was established. In
doing so, an ex vivo model of
necrosis associated foamy
macrophages was developed
that exhibited
hyperinflammatory response
to M. tuberculosis infection,
characterized by higher
expression of IL1β, IL6, and
TNFα. By silencing the
enzyme diacylglycerol O-
acyltransferase (DGAT1) in macrophages, a role for triglyceride synthesis in the heightened
inflammatory response to infection was identified. With support from SERB, this work is now
being taken forward in the C3HeB/FeJ mouse model of tuberculosis. This mouse model serves
as a preclinical model of TB research as it generates TB granulomas similar to those present in
actively infected humans. Pharmacological inhibition of DGAT1 was found to inhibit granuloma
triglyceride levels. Studies on the impact of this inhibition on inflammatory response and
bacterial control is underway.

Dr Gandotra’s lab identified key events in lipid metabolism that are targeted by M. tuberculosis.
Through this work, it was demonstrated that acute infection with M. tuberculosis does not alter
the rate of triglyceride synthesis but promotes triglyceride hydrolysis, with little effect on the
abundance and size of lipid droplets. Through quantitative proteomics of the lipid droplets
isolated from macrophages infected with live bacteria, heat killed bacteria or that were
uninfected, 86 proteins were found to be differentially and actively modulated in abundance on
the macrophage lipid droplets. These proteins largely classified in functions associated with
protein synthesis, vesicular trafficking and lipid metabolism. This work demonstrated active
manipulation of an organelle beyond the host endocytic pathway by M. tuberculosis.

LIPID TRANSPORT SYSTEMS IN Mycobacterium tuberculosis

Mycobacterial infections like TB portray an array of pathogen specific adaptive response that
prevent bacterial clearance and facilitate infection of host phagocytic cells. Its complex lipid

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