Lipid signals help cells seal the damage from bacterial attacks, researchers discover

Epithelial cells form the body’s frontline barriers, helping keep microbes, toxins and other harmful substances out. Yet these protective cells are constantly exposed to threats, including microbial infections. Some bacteria produce pore-forming toxins that can oligomerize and act like microscopic drills, perforating the cell’s plasma membrane.

If these pores are not repaired quickly, cells can lose vital contents, suffer internal damage and eventually die. Understanding how epithelial cells rapidly repair toxin-induced membrane injuries is therefore important for understanding how tissues withstand bacterial attacks.

Testing a lipid-driven repair pathway

To investigate how cells respond to this damage, researchers Dr. Yuan Chi, Dr. Kazuko Saeki and professor Takehiko Yokomizo at Juntendo University focused on a signaling system involving 12-HHT, a bioactive lipid mediator, and BLT2, a receptor found primarily on epithelial cells.

They investigated how lipid mediator signaling promotes plasma membrane repair and protects cells from membrane-damaging insults. The study is published online in the Journal of Cell Biology.

The researchers used human lung epithelial cells, canine kidney epithelial cells and primary mouse skin epidermal keratinocytes, comparing cells with natural, increased or absent BLT2 expression. They induced membrane damage using pneumolysin, streptolysin O, α-hemolysin or digitonin and assessed membrane injury, leakage and cell survival through microscopy, fluorescent dyes to assess membrane integrity, LDH-release assays and viability tests.

Electron microscopy was used to examine cells and extracellular vesicles. To investigate the mechanism, the team tested calcium-free conditions, measured 12-HHT levels by liquid chromatography–mass spectrometry and used inhibitors targeting BLT2, Rac1, actin polymerization, acid sphingomyelinase and 12-HHT production.

BLT2 reduces damage and cell death

They found that BLT2 helps epithelial cells survive after their membranes are damaged. Under these conditions, cells with enhanced BLT2 signaling showed less membrane leakage, less visible damage, better mitochondrial health and higher survival rates. In contrast, cells lacking BLT2 were more likely to rupture and die. BLT2’s benefit was seen with all the tested toxins as well as with digitonin, suggesting that it is part of a general membrane-repair system.

“These findings identify the 12-HHT/BLT2 axis as a previously unrecognized regulator of the cellular response to plasma membrane damage,” says Chi.

Two repair actions follow calcium influx

The study showed that BLT2 does not stop toxins from attaching to the cell. Instead, it helps cells respond after injury. Calcium influx through membrane holes triggered production of 12-HHT. The 12-HHT then activated BLT2 and launched two major repair actions.

First, BLT2 helped cells pinch off damaged pieces of membrane, including toxin pores, into tiny bubbles called extracellular vesicles. Second, BLT2 activated Rac1, which reorganized actin, the cell’s internal support framework, to strengthen and reshape the injured cell. Blocking either vesicle release or Rac1-driven actin repair removed BLT2’s protective effect.

Strengthening host defenses against membrane injury

Chi notes, “By identifying the 12-HHT/BLT2 pathway as a regulator of plasma membrane repair, our research highlights that in addition to targeting the pathogen or toxin, it may also be possible to enhance the ability of host cells to withstand and repair membrane damage.”

In the long term, this knowledge could contribute to the development of host-directed therapeutic approaches for infectious diseases and other conditions associated with plasma membrane injury.

The study identifies the 12-HHT/BLT2 pathway as an emergency membrane-repair system that helps epithelial cells remove damaged membrane, restore their internal structure and survive bacterial attack. The discovery provides new insight into how cells protect themselves after their first line of defense, the plasma membrane, has been breached.

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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