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Review 3: "Lipid droplets fuels SARS-CoV-2 replication and inflammatory response"

This study claims infection-mediated lipid droplet biogenesis contributes to SARS-CoV-2 replication while suppressing lipid droplet formation restricts infection. However, these are not fully substantiated by the data offered due to lack of proper controls.

Published onSep 21, 2020
Review 3: "Lipid droplets fuels SARS-CoV-2 replication and inflammatory response"
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key-enterThis Pub is a Review of
Lipid droplets fuel SARS-CoV-2 replication and production of inflammatory mediators
Lipid droplets fuel SARS-CoV-2 replication and production of inflammatory mediators

Viruses are obligate intracellular parasites that make use of the host metabolic machineries to meet their biosynthetic needs, identifying the host pathways essential for the virus replication may lead to potential targets for therapeutic intervention. The mechanisms and pathways explored by SARS-CoV-2 to support its replication within host cells are not fully known. Lipid droplets (LD) are organelles with major functions in lipid metabolism and energy homeostasis, and have multiple roles in infections and inflammation. Here we demonstrate that monocytes from COVID-19 patients have an increased LD accumulation compared to SARS-CoV-2 negative donors. In vitro, SARS-CoV-2 infection modulates pathways of lipid synthesis and uptake, as CD36, SREBP-1, PPARγ and DGAT-1 in human monocytes and triggered LD formation in different human cells. LDs were found in close apposition with SARS-CoV-2 proteins and double-stranded (ds)-RNA. The pharmacological modulation of LD formation by inhibition of DGAT-1 with A922500 significantly inhibited SARS-CoV-2 replication as well as reduced production of pro-inflammatory mediators. Taken together, we demonstrate the essential role of lipid metabolic reprograming and LD formation in SARS-CoV-2 replication and pathogenesis, opening new opportunities for therapeutic strategies to COVID-19.

RR:C19 Evidence Scale rating by reviewer:

  • Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.



The manuscript by Dias et al shows an increased in lipid droplets in monocytes from COVID-19 patients. The same phenomenon was also observed in human monocytes and other cell lines infected with SARS-CoV2 in vitro. This increase in lipid droplets is probably explained by increases in expression of a number of genes involved in lipid uptake and synthesis. It was hypothesized that the virus induces these changes to promote viral replication and that lipid droplets play an important in viral replication. Applying an inhibitor of fatty acid synthesis could reduce the number of lipid droplets in infected cell and the viral output as well as production of proinflammatory cytokines. The authors also tried to show co-localization between lipid droplets and viral antigens / dsRNA in infected cells.

Except for the co-localization, the data seem to be reliable and trustworthy and in agreement with previous publications on a number of other viruses, which induced lipid synthesis and relied on the increased availability of intracellular lipid for optimal viral replication. While there are some co-localized areas between the viral antigens and lipid droplets, many areas of viral antigen do not co-localized with lipid droplet. This has to be better described and explained. Because the viral antigen detection was done using serum, which might react to many antigens and positive areas might contain different antigens. This may explain the lack of co-localization of some antigen signal. The co-localization with dsRNA looks less convincing as only a few co-localized dots were shown. The description and interpretation should be more cautiously stated. It is possible that inhibition of DGAT simply reduce the viral replication by reducing availability of intracellular lipid. Availability of lipid and number of lipid droplets is related but may not be the same thing.

In addition, more information should be given on the COVID-19 patients, whose blood monocytes are shown in Fig. 1. How many patients were the data derived from, and what were their clinical conditions? Was there any correlation between the levels of lipid droplets and clinical severity?

Mark Cooper:

The authors provide micrographic evidence that some developing Covid-Virions associate with Lipid Droplets (LDs) in Covid-Infected Monocytes. It is possible that Covid Replication-Organelles (ROs) are also in contact with tubules of the Endoplasmic Reticulum. Use of a lipophilic vital-stain, BODIPY TR methyl ester, could help visualize the entire complement of endomembraneous-organelles in Covid-Infected Cells. After solvation in DMSO, BODIPY TR methyl ester is able to permeate cell membranes, and become localized in organelle membranes by a diffusion-trap mechanism. The dye is also fixable. Fixed or live Covid-Infected Cells, stained with this fluorescent dye, could be examined with Confocal, Deconvolution, or Light-Sheet Microscopes. Associations of Covid ROs with Lipid Droplets could also be examined in combinations with other vital-stains (e.g. BODIPY 493/503 for LDs; SYTO RNAselect for viral RNA). The actions of the DGAT-1 Inhibitor, A922500, could then be examined using time-lapse recordings. The 300nm diameter Covid Replication-Organelles should be visible after vital-staining, using advanced fluorescent imaging methods. ER tubules, which are 60nm in diameter, can be discerned in live cells using BODIPY TR methyl ester staining. see: