Phagocytic activity of splenic macrophages is enhanced and accompanied by cytosolic alkalinization in TRPM7 kinase‐dead mice

Abstract

Transient receptor potential melastatin 7 (TRPM7) is a unique protein functioning as a cation channel as well as a serine/threonine kinase and is highly expressed in immune cells such as lymphocytes and macrophages. TRPM7 kinase-dead (KD) mouse model has been used to investigate the role of this protein in immune cells; these animals display moderate splenomegaly and ectopic hemopoiesis. The basal TRPM7 current magnitudes in peritoneal macrophages isolated from KD mice were higher; however, the maximum currents, achieved after cytoplasmic Mg 2+ washout, were not different. In the present study, we investigated the consequences of TRPM7 kinase inactivation in splenic and peritoneal macrophages. We measured the basal phagocytic activity of splenic macrophages using fluorescent latex beads, pHrodo zymosan bioparticles, and opsonized red blood cells. KD macrophages phagocytized more efficiently and had slightly higher baseline calcium levels compared to WT cells. We found no obvious differences in store-operated Ca 2+ entry between WT and KD macrophages. By contrast, the resting cytosolic pH in KD macrophages was significantly more alkaline than in WT. Pharmacological blockade of sodium hydrogen exchanger 1 (NHE1) reversed the cytosolic alkalinization and reduced phagocytosis in KD macrophages. Basal TRPM7 channel activity in KD macrophages was also reduced after NHE1 blockade. Cytosolic Mg 2+ sensitivity of TRPM7 channels measured in peritoneal macrophages was similar in WT and KD mice. The higher basal TRPM7 channel activity in KD macrophages is likely due to alkalinization. Our results identify a novel role for TRPM7 kinase as a suppressor of basal phagocytosis and a regulator of cellular pH.

NSAIDs Naproxen, Ibuprofen, Salicylate, and Aspirin Inhibit TRPM7 Channels by Cytosolic Acidification

“…This difference may be due to the dependence on TRPM7 kinase resting pH in HEK cells. We recently showed that in murine macrophages isolated from TRPM7 K1646R kinase-dead mice, the pH is more alkaline than in WT, suggesting that kinase activity may make pH i more acidic ( Beesetty et al, 2021 ). WT TRPM7 overexpressing HEK cells also respond readily to acidification in propionate and 2-APB ( Zhelay et al, 2018 ).…”

“…In addition to Mg 2+ , other metal ions, polyamines and protons, are also inhibitory ( Kozak and Cahalan, 2003 ; Kozak et al, 2005 ; Chokshi et al, 2012b ; Zhelay et al, 2018 ). Channel inhibition by Mg 2+ and protons does not depend on the kinase activity ( Kozak et al, 2005 ; Matsushita et al, 2005 ; Beesetty et al, 2021 ). TRPM7 channels have been implicated in cellular and body Mg 2+ homeostasis ( Zou et al, 2019 ).…”

Oxalate Alters Cellular Bioenergetics, Redox Homeostasis, Antibacterial Response, and Immune Response in Macrophages

“…Subsequently, macrophages were washed and fluorescent latex beads (Cat. #15702-10 Fluoresbrite ® Microparticles, Polysciences) were added to the wells (100 beads/cell reconstituted in 1x PBS) ( 38 , 39 ). Afterwards, cells were kept at 37°C for 30 minutes while shaking.…”

The Multiple Facets of Iron Recycling

“…The observation that both suppression and excessive activity of small G proteins impairs phagocytosis may be explained by the fact that the complete engulfment of large cargoes relies on both actin assembly and the subsequent rapid deactivation of G proteins and actin disassembly [ 117 ]. Finally, another recent work identified transient receptor potential melastatin 7 (TRPM7), a cation channel with kinase activity, as a suppressor of RPMs’ phagocytic activity through a mechanism that likely involves cytosolic alkalinization [ 118 ].…”