# Lipid flux during autophagosome membrane biogenesis

> **NIH NIH R01** · YALE UNIVERSITY · 2021 · $335,000

## Abstract

Summary
Macro-autophagy is the intracellular stress-response pathway by which the cell packages portions of the cytosol
for delivery into the lysosome. This packaging is carried out by the de novo formation of a new organelle called
the autophagosome that grows and encapsulates cytosolic material for eventual lysosomal degradation. How
autophagosomes form, including especially from where the autophagosomes extract lipid in order to expand
their membranes, has been a core problem in the field for over 50 years. Two competing models have emerged
and suggest that either the autophagosome simply grows out of a pre-existing compartment (like the ER) or the
autophagosome forms from the continued fusion of individual vesicles recruited from many different sites in the
cell. Furthermore, lipid biogenesis pathways are intimately associated with autophagy, suggesting that one or
more organelles involved in the production of lipids might also be tightly associated to the growth of the
autophagosome. Temporal studies established over a decade ago that the autophagy protein ATG2, is needed
during membrane expansion, but how ATG2 facilitates membrane growth has remained elusive.
Our preliminary results now demonstrate that ATG2 is a member of a novel lipid-transport family of proteins and
suggest a third model for membrane expansion; the bulk delivery of lipid from organelles through protein-
mediated contact sites. Indeed, ATG2 binds up to 20 lipids at once, an order of magnitude more than virtually
any other lipid transport protein, and thus has the capacity to move a lot of lipid during biogenesis. We show
that in cells, ATG2 accumulates at an interface between autophagosomes and the ER, strongly suggesting this
organelle-organelle contact site might be the location of lipid transfer. In addition, we have developed gene-
edited knockouts of each of the ATG2 proteins in humans and discovered that in the absence of ATG2, not only
do autophagosomes not expand, but hundreds of vesicles collect at the site of autophagosome biogenesis. This
surprising observation suggests that vesicle-mediated delivery of membrane might also be essential and that
the fusion of these vesicles is specifically disrupted when ATG2-mediated lipid transport is absent.
With this proposal, we expect to describe how ATG2 works with proteins on both the autophagosome and the
ER to drive lipid flow. Likely, this will involve proteins needed to stabilize organelle-organelle contact sites and
may also involve proteins sensing or regulating lipid production in the ER. We will then establish how this lipid
flow is related to the recruitment and utilization of trafficking vesicles to describe to support autophagosome
growth.

## Key facts

- **NIH application ID:** 10111531
- **Project number:** 5R01GM135290-02
- **Recipient organization:** YALE UNIVERSITY
- **Principal Investigator:** Thomas James Melia
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $335,000
- **Award type:** 5
- **Project period:** 2020-02-19 → 2024-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10111531

## Citation

> US National Institutes of Health, RePORTER application 10111531, Lipid flux during autophagosome membrane biogenesis (5R01GM135290-02). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10111531. Licensed CC0.

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