Objective-Because culprit atherosclerotic plaques contain proteases, we hypothesized that the diminished heat shock protein 27 (HSP27) released by atherosclerotic plaques could be due to proteolysis. We assessed the role of HSP27 in human vascular smooth muscle cells (VSMCs) under proteolytic injury. Methods and Results-Active plasmin is present in culprit atherosclerotic plaques. Recombinant HSP27 was cleaved by plasmin and this effect was prevented by different inhibitors. Fragments and aggregated forms of HSP27 appeared after incubation of mammary control endarteries with plasmin. Coincubation of atherosclerotic plaques with recombinant HSP27 or mammary endarteries led to HSP27 proteolysis. After incubation of VSMCs with plasmin, HSP27 was overexpressed, phosphorylated, aggregated, and redistributed from the cytoskeleton to the cytosol, nucleus, and cell membrane. Plasmin-induced VSMC apoptosis was significantly higher in VSMCs treated by HSP27 siRNA. Immunohistochemical analysis of atherosclerotic plaques showed that plasmin(ogen) and apoptotic cells are localized in the core/shoulder whereas HSP27 and VSMCs are mainly expressed in the cap/media. Conclusions-Extracellular HSP27 can be degraded by enzymes released from atherosclerotic plaques and may reflect a proteolytic imbalance. Intracellular HSP27 downregulation decreases VSMCs resistance to proteolytically-induced apoptosis. HSP27 might play a pivotal role in the prevention of plaque instability and rupture.

Among legumes (Fabaceae) capable of nitrogen-fixing nodulation, several Aeschynomene spp. use a unique symbiotic process that is independent of Nod factors and infection threads. They are also distinctive in developing root and stem nodules with photosynthetic bradyrhizobia. Despite the significance of these symbiotic features, their understanding remains limited. To overcome such limitations, we conduct genetic studies of nodulation in Aeschynomene evenia, supported by the development of a genome sequence for A. evenia and transcriptomic resources for 10 additional Aeschynomene spp. Comparative analysis of symbiotic genes substantiates singular mechanisms in the early and late nodulation steps. A forward genetic screen also shows that AeCRK, coding a receptor-like kinase, and the symbiotic signaling genes AePOLLUX, AeCCamK, AeCYCLOPS, AeNSP2, and AeNIN are required to trigger both root and stem nodulation. This work demonstrates the utility of the A. evenia model and provides a cornerstone to unravel mechanisms underlying the rhizobium–legume symbiosis.