Nitric oxide upregulates microglia phagocytosis and increases transient receptor potential vanilloid type 2 channel expression on the plasma membrane

Abstract

Microglia phagocytosis is critical for central nervous system development, and dysregulation of phagocytosis may contribute to a variety of neurological disorders. During initial stages of phagocytosis, microglia display increased nitric oxide (NO) production via inducible nitric oxide synthase (iNOS) activity and amplified calcium entry through transient receptor potential vanilloid type 2 (TRPV2) channels. The present study investigated the regulatory role of iNOS/NO signaling in microglial phagocytosis and TRPV2 channel activation using phagocytosis assay, calcium imaging, patch clamp electrophysiology, immunocytochemistry, and immunoblot assays. Results showed that primary microglia from iNOS‐knockout (iNOS−/−) mice exhibited substantial deficits in phagocytic capacity and TRPV2 channel activity relative to wild‐type (WT) controls. Specifically, iNOS−/− microglia displayed a lower level of TRPV2 protein localized on the plasma membrane (PM) without any significant change in the mRNA levels of Fc‐gamma receptors and TRPV2. In addition, iNOS−/− microglia, unlike their WT controls, failed to elicit a calcium influx in response to application of the TRPV2‐agonist 2‐aminoethoxydiphenyl borate (2APB). Importantly, the phagocytic capacity and the PM expression and activity of TRPV2 in iNOS−/− microglia were largely corrected by pretreatment with NO‐donors. Accordingly, the 2APB‐evoked calcium influx and the PM expression of TRPV2 in WT microglia were significantly decreased by selective inhibition of iNOS, protein kinase‐G (PKG), or phosphoinositide‐3‐kinase (PI3K), respectively. Together, results from this study indicated that iNOS/NO signaling upregulates microglial phagocytosis and increases TRPV2 trafficking to the PM via PKG/PI3K dependent pathway(s).

Thermosensitive TRPV4 channels mediate temperature-dependent microglia movement

“…S1 A – C ) ( 21 , 22 ). Although TRPV2 was previously reported to be functionally expressed in microglia ( 23 ), its temperature threshold for activation exceeds the physiological range (>52 °C) ( 24 ). Thus, TRPV2 is likely not involved in temperature-dependent microglia movement, and we did not examine this channel further.…”

ChIP-seq Profiling Identifies Histone Deacetylase 2 Targeting Genes Involved in Immune and Inflammatory Regulation Induced by Calcitonin Gene-Related Peptide in Microglial Cells

“…The specific recruitment of HDAC2 to NF- κ B at target promoters and the consequent effects on acetylation status may play an important role in regulating iNOS as well as other NF- κ B-dependent genes involved in inflammation [ 27 , 34 ]. Activation of microglia displays NO production via iNOS activity which upregulates microglial phagocytosis and increases TRPV2 expression [ 35 ]. Our experiment showed that CGRP increased the expression of iNOS, NF- κ B, and RIG-I protein levels in microglia after CGRP treatment.…”

Factors and Molecular Mechanisms Influencing the Protein Synthesis, Degradation and Membrane Trafficking of ASIC1a

“…Nitric oxide (NO) is a free radical signaling molecule that regulates numerous physiological and pathological conditions. NO signaling has been shown to increase the expression of transient receptor potential vanilloid type 2, a calcium channel, and its trafficking to the plasma membrane via a PI3K dependent pathway (Maksoud et al, 2019), suggesting that NO signaling has the potential to regulate the expression of membrane proteins. Recently, differential regulatory effects of NO signaling on ASIC1a expression in the prefrontal cortex (PFC) and hippocampus have been confirmed.…”