The linkage of heterodimeric (␣/␤) integrin receptors with their extracellular matrix ligands and intracellular actin cytoskeleton is a fundamental step for controlling cell adhesion and migration.Binding of the actin-linking protein, talin, to integrin ␤ cytoplasmic tails (CTs) induces high affinity ligand binding (integrin activation), whereas binding of another actinlinking protein, filamin, to the integrin ␤ CTs negatively regulates this process by blocking the talin-integrin interaction. Here we show structurally that migfilin, a novel cytoskeletal adaptor highly enriched in the integrin adhesion sites, strongly interacts with the same region in filamin where integrin ␤ CTs bind. We further demonstrate that the migfilin interaction dissociates filamin from integrin and promotes the talin/integrin binding and integrin activation. Migfilin thus acts as a molecular switch to disconnect filamin from integrin for regulating integrin activation and dynamics of extracellular matrix-actin linkage.

The need for more specific and selective contrast agents for magnetic resonance imaging motivated us to prepare a new nanoparticle agent based on high-density lipoproteins (HDL). This second generation contrast agent can be prepared in three different ways. The HDL nanoparticles (rHDL) were fully characterized by FPLC and gel electrophoresis. The flexibility of the platform also allows us to incorporate optical probes into rHDL for localization ex vivo by confocal fluorescence microscopy. The contrast-agent-containing nanoparticles were injected into mice that develop atherosclerotic lesions. Magnetic resonance imaging of the animals showed clear enhancement of the atherosclerotic plaques.

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The infusion of coronavirus disease 2019 (COVID-19) patients with mesenchymal stem cells (MSCs) potentially improves clinical symptoms, but the underlying mechanism remains unclear. We conducted a randomized, single-blind, placebo-controlled (29 patients/group) phase II clinical trial to validate previous findings and explore the potential mechanisms. Patients treated with umbilical cord-derived MSCs exhibited a shorter hospital stay (P = 0.0198) and less time required for symptoms remission (P = 0.0194) than those who received placebo. Based on chest images, both severe and critical patients treated with MSCs showed improvement by day 7 (P = 0.0099) and day 21 (P = 0.0084). MSC-treated patients had fewer adverse events. MSC infusion reduced the levels of C-reactive protein, proinflammatory cytokines, and neutrophil extracellular traps (NETs) and promoted the maintenance of SARS-CoV-2-specific antibodies. To explore how MSCs modulate the immune system, we employed single-cell RNA sequencing analysis on peripheral blood. Our analysis identified a novel subpopulation of VNN2+ hematopoietic stem/progenitor-like (HSPC-like) cells expressing CSF3R and PTPRE that were mobilized following MSC infusion. Genes encoding chemotaxis factors — CX3CR1 and L-selectin — were upregulated in various immune cells. MSC treatment also regulated B cell subsets and increased the expression of costimulatory CD28 in T cells in vivo and in vitro. In addition, an in vivo mouse study confirmed that MSCs suppressed NET release and reduced venous thrombosis by upregulating kindlin-3 signaling. Together, our results underscore the role of MSCs in improving COVID-19 patient outcomes via maintenance of immune homeostasis.

Cardiovascular disease is one of the prime causes of mortality throughout the world and there is a need for targeted and effective contrast agents to allow noninvasive imaging of the cholesterol-rich atherosclerotic plaques in arteries. A new, fully synthetic, high-density lipoprotein (HDL)-mimicking MRI contrast agent is developed, which enhances macrophage-rich areas of plaque in a mouse model of atherosclerosis by 94%. Confirmation of the targeting of this nanoparticulate agent is achieved using confocal microscopy by tracking a fluorescent lipid incorporated into the nanoparticle.

Integrin activation is crucial for numerous cellular responses, including cell adhesion, migration, and survival. Recent studies in mice have specifically emphasized the vital role of kindlin-3 in integrin activation. Kindlin-3 deficiency in humans also has now been documented and includes symptoms of bleeding, frequent infections, and osteopetrosis, which are consequences of an inability to activate β1, β2, and β3 integrins. To date, kindlin-3 was thought to be restricted to hematopoietic cells. In this article, we demonstrate that kindlin-3 is present in human endothelial cells derived from various anatomical origins. The mRNA and protein for KINDLIN-3 was detected in endothelial cells by reverse transcription-PCR and Western blots. When subjected to sequencing by mass spectrometry, the protein was identified as authentic kindlin-3 and unequivocally distinguished from KINDLIN-1 and KINDLIN-2 or any other known protein. By quantitative real time PCR, the level of kindlin-3 in endothelial cells was 20–50% of that of kindlin-2. Using knockdown approaches, we show that kindlin-3 plays a role in integrin-mediated adhesion of endothelial cells. This function depends upon the integrin and substrate and is distinct from that of kindlin-2. Formation of tube-like structures in Matrigel also was impaired by kindlin-3 knockdown. Mechanistically, the distinct functions of the kindlins can be traced to differences in their subcellular localization in integrin-containing adhesion structures. Thus, the prevailing view that individual kindlins exert their functions in a cell type-specific manner must now be modified to consider distinct functions of the different family members within the same cell type.

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Kindlins play an important role in supporting integrin activation by cooperating with talin; however, the mechanistic details remain unclear. Here, we show that kindlins interacted directly with paxillin and that this interaction could support integrin αIIbβ3 activation. An exposed loop in the N-terminal F 0 subdomain of kindlins was involved in mediating the interaction. Disruption of kindlin binding to paxillin by structure-based mutations significantly impaired the function of kindlins in supporting integrin αIIbβ3 activation. Both kindlin and talin were required for paxillin to enhance integrin activation. Interestingly, a direct interaction between paxillin and the talin head domain was also detectable. Mechanistically, paxillin, together with kindlin, was able to promote the binding of the talin head domain to integrin, suggesting that paxillin complexes with kindlin and talin to strengthen integrin activation. Specifically, we observed that crosstalk between kindlin-3 and the paxillin family in mouse platelets was involved in supporting integrin αIIbβ3 activation and in vivo platelet thrombus formation. Taken together, our findings uncover a novel mechanism by which kindlin supports integrin αIIbβ3 activation, which might be beneficial for developing safer anti-thrombotic therapies.