# Compositional, biophysical, and functional consequences of membrane scrambling in immune cells

> **NIH NIH R21** · UNIVERSITY OF VIRGINIA · 2021 · $201,875

## Abstract

Project Summary
The asymmetric distribution of lipids between the two leaflets of the plasma membrane (PM) bilayer is a
fundamental feature of cells across the tree of life. Establishing and maintaining disparate lipid compositions
in apposing leaflets is energetically costly, implying an important physiological role for membrane asymmetry.
Classically, the lipid asymmetry has been considered largely in the context of apoptosis, where the exposure
of inner leaflet lipids on the cell surface marks dead cells for macrophagic engulfment. However, the non-
uniform transbilayer lipid distribution of the PM is also involved in a number of other cellular contexts. For
example, concentrating anionic lipids on the inner PM leaflet produces a high surface charge density and
recruits positively charged proteins. Furthermore, it has become evident that a reversible loss of lipid
asymmetry also occurs during healthy cell signaling, most notably in antigen-stimulated activation of a variety
of immune cell types. These insights reveal a central, yet poorly understood role for both steady-state
membrane asymmetry and its transient loss in immune signaling; however, they also highlight major
knowledge gaps in our understanding of PM asymmetry. Specifically, the compositions and biophysical
properties of the two leaflets of the PM bilayer are currently unknown, as are their changes during scrambling,
either induced by apoptosis or healthy cell signaling. Finally, how asymmetry contributes to immune cell
activation is almost completely not understood. We have developed a novel set of methodologies that enable
us to address these questions of fundamental importance to cell biology in general, and immune signaling in
particular. Based on extensive preliminary data, we propose that immune cells transiently scramble PM lipids
during antigen-mediated activation to regulate charge-dependent interactions of signaling proteins with the
PM. In Aim 1, we will define the changes in lipidomic and biophysical asymmetry occurring in immune cell
PMs following activation by specific antigens. These changes will be compared to the robust PM scrambling
induced by apoptotic stimuli. We will also probe the molecular mediators of these effects in both mast cells
and T-cells. In Aim 2, we assess the functional consequences of antigen-induced PM scrambling in immune
cells, and the molecular mechanisms underlying these effects. First, we will define the role of PM scrambling
in immune cell activation by measuring how various functional phenotypes (including cytokine secretion,
degranulation, and signaling protein activation) are affected by inhibition or knock-out of PM scrambling
machinery. We will then probe the mechanistic connections between PM scrambling and immune activation
by cellular, model membrane, and in silico investigations of protein-membrane interactions probing the effect
of PM charge density on association of polybasic proteins with the PM. This detailed, comprehensive
c...

## Key facts

- **NIH application ID:** 10242230
- **Project number:** 5R21AI146880-03
- **Recipient organization:** UNIVERSITY OF VIRGINIA
- **Principal Investigator:** Ilya Levental
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $201,875
- **Award type:** 5
- **Project period:** 2020-03-13 → 2022-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10242230

## Citation

> US National Institutes of Health, RePORTER application 10242230, Compositional, biophysical, and functional consequences of membrane scrambling in immune cells (5R21AI146880-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10242230. Licensed CC0.

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