Microglia processes block the spread of damage in the brain and require functional chloride channels

Abstract

Microglia cells exhibit two forms of motility, constant movement of filopodia probing surrounding brain tissue, and outgrowth of larger processes in response to nearby damage. The mechanisms and functions of filopodia sensing and process outgrowth are not well characterized but are likely critical for normal immune function in the brain. Using two photon laser scanning microscopy we investigated microglia process outgrowth in response to damage, and explored the relationship between process outgrowth and filopodia movement. Further, we examined the roles of Cl(-) or K(+) channel activation, as well as actin polymerization in these two distinct processes, because mechanistic understanding could provide a strategy to modulate microglia function. We found that volume sensitive Cl(-) channel blockers (NPPB, tamoxifen, DIDS) prevented the rapid process outgrowth of microglia observed in response to damage. In contrast, filopodia extension during sensing was resistant to Cl(-) channel inhibitors, indicating that these motile processes have different cellular mechanisms. However, both filopodia sensing and rapid process outgrowth were blocked by inhibition of actin polymerization. Following lesion formation under control conditions, rapidly outgrowing processes contacted the damaged area and this was associated with a 37% decrease in lesion volume. Inhibition of process outgrowth by Cl(-) channel block, prevention of actin polymerization, or by selectively ablating microglia all allowed lesion volume to increase and spread into the surrounding tissue. Therefore, process outgrowth in response to focal brain damage is beneficial by preventing lesion expansion and suggests microglia represent a front line defence against damage in the brain.

Chondroitin Sulfate Proteoglycans Potently Inhibit Invasion and Serve as a Central Organizer of the Brain Tumor Microenvironment

“…We also observed the identical staining pattern for the DSD-1 antibody (Fig. 2 H, I,M ), which binds to a uniquely sulfated CS-GAG and is only poorly detected by CS-56 and WFALectin (Ito et al, 2005). The absence of DSD-1 immunostaining from the invasive tumors ruled out the possibility that the invasive tumors may have switched to a CS-GAG expression profile unrecognized by our labeling methods.…”

“…4D) are highly reminiscent of injury-associated microglia. Because these microglia are know to play a critical role in cordoning off and inhibiting further spread of damage away from sites of CNS injury, we speculate that these tumor-adjacent microglia may likewise serve a noninfiltrative function (Nimmerjahn et al, 2005;Lalancette-Hébert et al, 2007;Rolls et al, 2008;Hines et al, 2009). Overall, our findings placed in context with the literature suggest that distinct microglial states, modulated through the ECM, may in turn result in pro-or anti-invasive contributions to the tumor microenvironment.…”

Decreased connexin 43 in astrocytes inhibits the neuroinflammatory reaction in an acute mouse model of neonatal sepsis

“…In the situation of trauma, the astrocytes are the first to sense injury, and the activation of microglia is triggered by astrocytic ATP release. Lack of Cx43 hemichannels causes reduced leakage of ATP and thus inhibits the activation of microglia [25][26][27] . The release of TNF-α and IL-1β from LPS-activated microglia targets astrocytes mainly through Cx43 hemichannels [28,29] .…”

Integrin-Kindlin3 requirements for microglial motility in vivo are distinct from those for macrophages

“…Therefore, delayed and diminished extensions of microglial processes in Kindlin3-knockin mice are likely to be a consequence of diminished post-ligand-binding events, including Y397 FAK phosphorylation. Defects in early microglial response to injury were shown to increase lesion volume and promote its spreading into the surrounding tissues (51). In addition, microglial response to injury was shown to contribute to the timely restoration of blood-brain barrier (52).…”