Rémi Peyronnet

Vascular smooth muscle cells (VSMCs) play a key role in aortic aneurysm formation. Bone morphogenetic proteins (BMPs) have been implicated as important regulators of VSMC phenotype, and dysregulation of the BMP pathway has been shown to be associated with vascular diseases. The aim of this study was to investigate for the first time the effects of BMP-4 on the VSMC phenotype and to understand its role in the development of thoracic aortic aneurysms (TAAs). Using the angiotensin II (AngII) osmotic pump model in mice, aortas from mice with VSMC-specific BMP-4 deficiency showed changes similar to AngII-infused aortas, characterised by a loss of contractile markers, increased fibrosis, and activation of matrix metalloproteinase 9. When BMP-4 deficiency was combined with AngII infusion, there was a significantly higher rate of apoptosis and aortic dilatation. In vitro, VSMCs with mRNA silencing of BMP-4 displayed a dedifferentiated phenotype with activated canonical BMP signalling. In contrast, BMP-2-deficient VSMCs exhibited the opposite phenotype. The compensatory regulation between BMP-2 and BMP-4, with BMP-4 promoting the contractile phenotype, appeared to be independent of the canonical signalling pathway. Taken together, these results demonstrate the impact of VSMC-specific BMP-4 deficiency on TAA development.

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 . image 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