Related Experiment Video
Updated: Mar 1, 2026
Two-photon Imaging of Microglial Processes' Attraction Toward ATP or Serotonin in Acute Brain Slices
Published on: January 31, 2019
The Arp2/3 complex is required for in situ haptotactic response of microglia to iC3b
Summer G Paulson1,2, Isabella Swafford1,2, Fritz W Lischka2,3,4
1Uniformed Services University of the Health Sciences, Department of Biochemistry, Bethesda, MD, 20814, USA.
Abstract:
Microglia maintain brain homeostasis via iC3b-mediated synaptic pruning. The Arp2/3 complex has been implicated in iC3b-mediated macrophage phagocytosis, but it is unclear whether it is similarly required in microglia in the CNS. We examined the question of CR3-dependent clearance of iC3b in microglia using a combination of in vitro and in situ physical confinement studies. Arp2/3 inhibition decreased iC3b phagocytosis and cell motility in vitro. Furthermore, microglia-like cells remove immobilized iC3b from the substrate in an Arp2/3-dependent fashion, in a process reminiscent of trogocytic synaptic pruning. We also used a novel approach to immobilize an iC3b gradient onto a substrate and demonstrate Arp2/3-dependent haptotactic migration toward increasing iC3b concentrations. While Arp2/3-deficient microglia robustly respond to ATP via chemotaxis within mouse hippocampal slices, they demonstrate a persistent inability to stably interact with iC3b-coated beads. The present study establishes new approaches to systematically interrogate molecular pathways relevant to synaptic pruning, advances the understanding of iC3b phagocytosis as a haptotactic response, and confirms that the Arp2/3-dependent haptotactic response is important for microglia function in the CNS microenvironment.
Insights
The Arp2/3 complex is crucial for microglia to clear debris and migrate towards targets in the brain. This finding is vital for understanding brain homeostasis and synaptic pruning.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia are essential for maintaining brain homeostasis through processes like synaptic pruning, which involves the clearance of complement-tagged debris (iC3b).
- The Arp2/3 complex is known to be involved in phagocytosis by macrophages, but its role in microglia-mediated iC3b clearance within the central nervous system (CNS) remained unclear.
Purpose of the Study:
- To investigate the requirement of the Arp2/3 complex in complement receptor 3 (CR3)-dependent clearance of iC3b by microglia.
- To explore the Arp2/3 complex's role in microglial migration and interaction with iC3b in the CNS microenvironment.
Main Methods:
- Employed in vitro and in situ physical confinement studies to examine microglial interactions with iC3b.
- Utilized Arp2/3 inhibition to assess its impact on iC3b phagocytosis and cell motility.
- Developed a novel method to immobilize an iC3b gradient on a substrate to study haptotactic migration.
Main Results:
- Inhibition of Arp2/3 significantly reduced iC3b phagocytosis and motility in microglia-like cells.
- Microglia demonstrated Arp2/3-dependent removal of immobilized iC3b, resembling trogocytic synaptic pruning.
- Arp2/3-deficient microglia showed impaired haptotactic migration towards iC3b gradients and failed to stably interact with iC3b-coated beads, despite normal chemotaxis to ATP.
Conclusions:
- The Arp2/3 complex is essential for Arp2/3-dependent haptotactic migration of microglia towards iC3b.
- This study establishes new methods for studying molecular pathways in synaptic pruning and advances the understanding of iC3b phagocytosis as a haptotactic response.
- Confirms the importance of the Arp2/3-dependent haptotactic response for effective microglia function within the CNS.
Related Concept Videos
01:11IP3/DAG Signaling Pathway
01:32Assembly of Complex Microtubule Structures
01:14Generation of Straight or Branched Actin Filaments
Arp2/3 Complex
Arp2/3 complex is a seven-subunit complex consisting of two proteins similar to actin- Arp2 and Arp3, and five other subunits that help keep Arp2 and Arp3 inactive. When required, the complex is...