GSK1016790A

To investigate whether cardiac mast cells (MCs) participate in pressure overload-induced myocardial hypertrophy through the regulation of transient receptor potential vanilloid 4 (TRPV4).

Pressure overload-induced myocardial hypertrophy was induced via abdominal aortic constriction (AAC). Myocardial hypertrophy was evaluated by measuring the heart weight index (HW/BW), lung weight index (LW/BW), ratio of heart weight to tibia length (HW/TL), ratio of lung weight to tibia length (LW/TL), and cross-sectional area of myocardial cells. qRT-PCR was used to detect the mRNA expression of TRPV4. Western blotting was used to detect the protein expression of TRPV4, mast cell tryptase, myosin heavy chain beta (β-MHC), calcineurin A (CnA), and nuclear factor of activated T-cell c3 (NFATc3). ELISA was used to measure the levels of brain natriuretic peptide (BNP) and histamine. Fluo4 AM was used to detect the calcium signal in H9c2 myocardial cells.

Compared with those of the sham rats, the myocardial mast cells, tryptase, HW/BW, LW/BW, HW/TL, and LW/TL, the cross-sectional area of the myocardial cells, and the expression of β-MHC, TRPV4, CnA, and NFATc3 in the myocardial tissue and the serum BNP of the AAC-treated rats increased significantly, whereas the MC stabilizer cromolyn sodium (CS) reversed these indicators. In H9c2 cardiomyocytes, treatment with histamine and the TRPV4 agonist GSK1016790A upregulated the expression of TRPV4, β-MHC, BNP, CnA and NFATc3 and increased calcium ion influx, whereas these effects were inhibited by the H2 receptor inhibitor famotidine and the TRPV4 inhibitor HC067047.

Cardiac MCs participate in pressure overload-induced myocardial hypertrophy through the upregulation of TRPV4 via its mediator histamine, and the Ca²⁺/CnA/NFATc3 signaling pathway is involved in this process.

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 (MΦBM), form a popular research model. This study explores the activity of mechanosensitive ion channels (MSC) in murine MΦBM and compares it to MSC activity in MΦ enzymatically isolated from cardiac tissue (tissue‐resident MΦ; MΦTR). We show that MΦBM and MΦTR have stretch‐induced currents, indicating the presence of functional MSC in their plasma membrane. The current profiles in MΦBM and in MΦTR 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 MΦBM 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 MΦTR. The selective transient receptor potential vanilloid 4 (TRPV4) channel agonist GSK1016790A induces calcium entry in MΦTR and in MΦBM. 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 MΦBM 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 MΦBM. image

Bone marrow‐derived (MΦBM) and tissue resident (MΦTR) 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 MΦBM and in MΦTR.Calcium entry upon pharmacological activation of TRPV4 confirms functionality of the channel in MΦTR and in MΦBM.Piezo1 ion channel activity is detected in the plasma membrane of MΦBM but not in MΦTR, suggesting that MΦBM may not be a good model to study the mechanotransduction of MΦTR.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.