Piezo1 stretch-activated channel activity differs between murine bone marrow-derived and cardiac tissue-resident...

Macrophages (MΦ) play pivotal roles in tissue homeostasis and repair. Their mechanical environment has been identified as a key modulator of various cell functions, and MΦ mechanosensitivity is likely to be critical - in particular in a rhythmically contracting organ such as the heart. Cultured MΦ, differentiated in vitro from bone marrow (MΦ_BM), form a popular research model. This study explores the activity of mechanosensitive ion channels (MSC) in murine MΦ_BM and compares it to MSC activity in MΦ enzymatically isolated from cardiac tissue (tissue-resident MΦ; MΦ_TR). We show that MΦ_BM and MΦ_TR have stretch-induced currents, indicating the presence of functional MSC in their plasma membrane. The current profiles in MΦ_BM and in MΦ_TR show characteristics of cation non-selective MSC such as Piezo1 or transient receptor potential channels. While Piezo1 ion channel activity is detectable in the plasma membrane of MΦ_BM using the patch-clamp technique, or by measuring cytosolic calcium concentration upon perfusion with the Piezo1 channel agonist Yoda1, no Piezo1 channel activity was observed in MΦ_TR. The selective transient receptor potential vanilloid 4 (TRPV4) channel agonist GSK1016790A induces calcium entry in MΦ_TR and in MΦ_BM. In MΦ isolated from left-ventricular scar tissue 28 days after cryoablation, stretch-induced current characteristics are not significantly different compared to non-injured control tissue, even though scarred ventricular tissue is expected to be mechanically remodelled and to contain an altered composition of pre-existing cardiac and circulation-recruited MΦ. Our data suggest that the in vitro differentiation protocols used to obtain MΦ_BM generate cells that differ from MΦ recruited from the circulation during tissue repair in vivo. Further investigations are needed to explore MSC identity in lineage-traced MΦ in scar tissue, and to compare mechanosensitivity of circulating monocytes with that of MΦ_BM. KEY POINTS: Bone marrow-derived (MΦ_BM) and tissue resident (MΦ_TR) macrophages have stretch-induced currents, indicating expression of functional mechanosensitive channels (MSC) in their plasma membrane. Stretch-activated current profiles show characteristics of cation non-selective MSC; and mRNA coding for MSC, including Piezo1 and TRPV4, is expressed in murine MΦ_BM and in MΦ_TR. Calcium entry upon pharmacological activation of TRPV4 confirms functionality of the channel in MΦ_TR and in MΦ_BM. Piezo1 ion channel activity is detected in the plasma membrane of MΦ_BM but not in MΦ_TR, suggesting that MΦ_BM may not be a good model to study the mechanotransduction of MΦ_TR. Stretch-induced currents, Piezo1 mRNA expression and response to pharmacological activation are not significantly changed in cardiac MΦ 28 days after cryoinjury compared to sham operated mice.