LRRC8Ais dispensable for a variety of microglial functions and response to acute stroke

Abstract

Microglia, resident brain immune cells, are critical in orchestrating responses to central nervous system (CNS) injury. Many microglial functions, such as phagocytosis, motility and chemotaxis, are suggested to rely on chloride channels, including the volume‐regulated anion channel (VRAC), but studies to date have relied on the use of pharmacological tools with limited specificity. VRAC has also been proposed as a drug target for acute CNS injury, and its role in microglial function is of considerable interest for developing CNS therapeutics. This study aimed to definitively confirm the contribution of VRAC in microglia function by using conditional LRRC8A‐knockout mice, which lacked the essential VRAC subunit LRRC8A in microglia. We demonstrated that while VRAC contributed to cell volume regulation, it had no effect on phagocytic activity, cell migration or P2YR12‐dependent chemotaxis. Moreover, loss of microglial VRAC did not affect microglial morphology or the extent of ischemic damage following stroke. We conclude that VRAC does not critically regulate microglial responses to brain injury and could be targetable in other CNS cell types (e.g., astrocytes) without impeding microglial function. Our results also demonstrate a role for VRAC in cell volume regulation but show that VRAC is not involved in several major cellular functions that it was previously thought to regulate, and point to other, alternative mechanisms of chloride transport in innate immunity.

Inhibition of the LRRC8A channel promotes microglia/macrophage phagocytosis and improves outcomes after intracerebral hemorrhagic stroke

“…A recent study utilized M/Mφ-specific LRRC8A knockout mice and pharmacological inhibition of LRRC8A and demonstrated LRRC8A channel was necessary for cell volume regulation but not involved in the phagocytic activity, cell migration, or p2yr12 dependent chemotaxis of microglia. 21 This is consistent with our result that lack of LRRC8A did not affect the cell phagocytosis mediated by the AMPK-Nrf2-CD36 axis in BV2, microglia, and RAW264.7 cells. However, the inhibitory effect of LRRC8A enhanced the phagocytosis of cells cotreated with hemin.…”

“… 19 , 20 Whereas loss of the microglial LRRC8A channel did not affect microglial morphology nor the extent of brain damage. 21 In the peripheral system, the macrophagic LRRC8A channel participates in the hypotonicity-induced NLRP3 inflammasome activation and the process of pyroptotic cell swelling. 22 However, our knowledge of the expression and function of the LRRC8A channel in ICH, which is a more lethal stroke subtype where M/Mφ plays a vital role in its progression by accelerating hematoma clearance and modulating inflammation, is limited.…”

Microglial-Mediated Prevention of Axonal Degeneration in the Injured Spinal Cord: Insights from anIn VivoImaging Study

“…Then we used a non-selective VAAC inhibitor, 5-nitro-2-(3phenylpropylamino) benzonic acid (NPPB) 58 , to address whether the VAAC contributes to the microglia-node interaction after injury. Similar to PSB, VAAC blocker affects microglial ramification and impairs its laser response 60,61 . Injection of 10 ul 1.5mg/ml NPPB significantly abolished laser injury-evoked chemotaxis of microglial processes within 1.5-hour post injection (Fig.…”

ATP-releasing SWELL1 channel in spinal microglia contributes to neuropathic pain

“…Future investigations using gene expression profiling and live-cell imaging will shed more light on the detailed mechanisms underlying Swell1 channel-mediated microglia activation. Notably, using a similar cKO mouse model, a very recent study reported that loss of Swell1 did not affect morphological changes of brain microglia upon ischemic stroke injury ( 43 ). In addition, Swell1 appears to be dispensable for microglia migration and chemotaxis following focal laser injury in the brain ( 43 ).…”

“…Notably, using a similar cKO mouse model, a very recent study reported that loss of Swell1 did not affect morphological changes of brain microglia upon ischemic stroke injury ( 43 ). In addition, Swell1 appears to be dispensable for microglia migration and chemotaxis following focal laser injury in the brain ( 43 ). Thus, the regulation of microglial activation by Swell1 may be dependent on the injury type, location, and specific pathophysiological context.…”