Yunfeng Chen

BACKGROUND: Arterial thrombotic events constitute the leading cause of mortality in hypertension. Gut dysbiosis induces endothelial dysfunction and systemic inflammation, contributing to hypertension and its associated cardiovascular complications. Whether these dysbiotic microbiota metabolites in hypertension directly regulate platelet hyperactivation and thrombosis remains unclear. METHODS: Fecal microbiota transplantation, 16S rRNA sequencing, and untargeted metabolomics were performed using samples from patients with hypertension. In vivo FeCl ₃ -induced mesenteric arteriole thrombosis model, ex vivo microfluidic whole-blood perfusion assay, and in vitro platelet functional studies defined the functional effects of acetate on platelet activation. Moreover, platelet-specific Olfr78 (olfactory receptor 78)-deficient mice were employed to explore the underlying mechanisms of acetate on platelet activation. RESULTS: Transplantation with fecal microbiota from patients with hypertension enhanced in vivo FeCl ₃ -injured mesenteric arteriole thrombosis and ex vivo whole blood thrombus formation compared with fecal microbiota from healthy normotensive subjects. Untargeted metabolomics revealed that gut microbiota-derived acetate was decreased in patients with hypertension, and plasma acetate concentration negatively correlated with integrin αIIbβ3 activation and P-selectin exposure. Acetate demonstrated superior antiplatelet efficacy against ADP-induced aggregation, dense-granule secretion, α-granule secretion, and integrin αIIbβ3 activation than collagen or thrombin-induced platelet activation. Mechanistic studies using platelet-specific Olfr78 ^−/− mice revealed that acetate bound to and activated Olfr78, a receptor not previously reported to be expressed in platelets, to elevate cAMP level and activate PKA, thereby increasing p-VASP and decreasing Ca ²⁺ mobilization as well as inactivating RhoA/ROCK2/MLC (myosin light chain) signaling to inhibit platelet activation. A high-fiber diet upregulated acetate/Olfr78 signaling in platelets to suppress microvascular thrombosis and protect against myocardial injury during myocardial infarction in mice. CONCLUSIONS: Acetate is a negative regulator of platelet hyperreactivity and thrombus formation via the Olfr78 receptor, and acetate deficiency contributes to platelet hyperreactivity in hypertension. Lifestyle modifications, particularly high-fiber dietary intervention and acetate supplementation, exhibit potent antithrombotic effects in hypertension.

Thrombosis is a pathological condition describing the abnormal accumulation of platelets and clotting factors in a blood vessel. While many works focused on platelet activation by soluble agonists as an underlying mechanism of thrombosis, it has often been overlooked that blood flow also facilitates thrombus formation. Especially, in the arteries, thrombosis is generally associated with arterial stenosis, which elevates the shear stress in the blood flow and facilitates the process of thrombogenesis, a phenomenon termed biomechanical thrombogenesis. For a long time, no bioassay was available to provide all-around and detailed insights into the process of biomechanical thrombogenesis. To address this, a thrombus profiling assay was developed by combining microfluidics with multi-color fluorescence imaging, which allows comprehensive characterization of biomechanical thrombogenesis with seven readouts covering the size and composition of the thrombus as well as platelet activation level. This thrombus profiling assay can be used to evaluate the prothrombotic tendency in humans and the efficacy of anti-thrombotic agents, and it is also useful for further understanding the mechanisms underlying arterial thrombosis.

Thrombosis is a pathological condition describing the abnormal accumulation of platelets and clotting factors in a blood vessel. While many works focused on platelet activation by soluble agonists as an underlying mechanism of thrombosis, it has often been overlooked that blood flow also facilitates thrombus formation. Especially, in the arteries, thrombosis is generally associated with arterial stenosis, which elevates the shear stress in the blood flow and facilitates the process of thrombogenesis, a phenomenon termed biomechanical thrombogenesis. For a long time, no bioassay was available to provide all-around and detailed insights into the process of biomechanical thrombogenesis. To address this, a thrombus profiling assay was developed by combining microfluidics with multi-color fluorescence imaging, which allows comprehensive characterization of biomechanical thrombogenesis with seven readouts covering the size and composition of the thrombus as well as platelet activation level. This thrombus profiling assay can be used to evaluate the prothrombotic tendency in humans and the efficacy of anti-thrombotic agents, and it is also useful for further understanding the mechanisms underlying arterial thrombosis.

Monocytes are critical in controlling tissue infections and inflammation. Monocyte dysfunction contributes to the inflammatory pathogenesis of cystic fibrosis (CF) caused by CF transmembrane conductance regulator (CFTR) mutations, making CF a clinically relevant disease model for studying the contribution of monocytes to inflammation. Although CF monocytes exhibited adhesion defects, the precise mechanism is unclear. Herein, superresolution microscopy showed that an integrin clustering but not an integrin activation defect determines the adhesion defect in CFTR-deficient monocytes, challenging the existing paradigm emphasizing an integrin activation defect in CF patient monocytes. We further found that the clustering defect is accompanied by defects in CORO1A membrane recruitment, actin cortex formation, and CORO1A engagement with integrins. Complementing canonical studies of leukocyte adhesion focusing on integrin activation, we highlight the importance of integrin clustering in cell adhesion and report that integrin clustering and activation are distinctly regulated, warranting further investigation for selective targeting in therapeutic strategy design involving leukocyte-dependent inflammation.

Arterial thrombosis is a leading cause of death and disability worldwide with no effective bioassay for clinical prediction. As a symbolic feature of arterial thrombosis, severe stenosis in the blood vessel creates a high-shear, high-gradient flow environment that facilitates platelet aggregation towards vessel occlusion. Here, we present a thrombus profiling assay that monitors the multi-dimensional attributes of thrombi forming in such biomechanical conditions. Using this assay, we demonstrate that different receptor–ligand interactions contribute distinctively to the composition and activation status of the thrombus. Our investigation into hypertensive and older individuals reveals intensified biomechanical thrombogenesis and multi-dimensional thrombus profile abnormalities, endorsing the diagnostic potential of the assay. Furthermore, we identify the hyperactivity of GPIbα-integrin α_IIbβ₃ mechanosensing axis as a molecular mechanism that contributes to hypertension-associated arterial thrombosis. By studying drug-disease interactions and inter-individual variability, our work reveals a need for personalized anti-thrombotic drug selection that accommodates each patient’s pathological profile.

Peritonitis is a common and life-threatening inflammatory disease. Myeloid cells are elevated in the peripheral blood and contribute to peritonitis, but their circulating dynamics are not clear. In vivo flow cytometry (IVFC) is a noninvasive technique for monitoring the dynamics of circulating cells in live animals. It has been extensively used to detect circulating tumor cells, but rarely for monitoring immune cells. Here, we describe a method adapting an intravital microscope for IVFC so that we can monitor LysM-EGFP-labeled circulating myeloid cells in a tumor necrosis factor (TNF) α-induced peritonitis mouse model. Using this IVFC method, we quantified the blood flow velocity and cell concentration in circulation. We observed a significant increase in LysM-EGFP+ cells in circulation after TNFα intraperitoneal (i.p.) injection, which reached a plateau in ~20 min. Conventional cytometry analysis showed that most LysM-EGFP+ cells were neutrophils. Increasing blood neutrophils were accompanied by neutrophil recruitment to the peritoneal cavity and neutrophil emigration from the bone marrow. We then monitored neutrophil CD64 expression in vivo and found a significant increase in TNFα-induced peritonitis. We also found that CD18 blockade doubled the circulating neutrophil number in TNFα-induced peritonitis, suggesting that CD18 is critical for neutrophil recruitment in peritonitis. Overall, we demonstrate that IVFC techniques are useful for studying the circulating dynamics of immune cells during inflammatory diseases.

Arterial thrombosis, which represents a critical complication of cardiovascular diseases, is a leading cause of death and disability worldwide with no effective bioassay for clinical prediction. As a symbolic feature of arterial thrombosis, severe stenosis in the blood vessel creates a high-shear, high-gradient flow environment that effectively facilitates platelet aggregation towards vessel occlusion even with platelet amplification loops inhibited. However, no approach is currently available to comprehensively characterize the size, composition and platelet activation status of thrombi forming under this biorheological condition. Here, we present a thrombus profiling assay that monitors the multi-dimensional attributes of thrombi forming in conditions mimicking the physiological scenario of arterial thrombosis. Using this platform, we demonstrate that different receptor–ligand interactions contribute distinctively to the composition and activation status of the thrombus. Our investigation into hypertensive and older individuals reveals intensified biomechanical thrombogenesis and multi-dimensional thrombus profile abnormalities, demonstrating a direct contribution of mechanobiology to arterial thrombosis and endorsing the diagnostic potential of the assay. Furthermore, we identify the hyperactivity of GPIbα-integrin α_IIbβ₃ mechanosensing axis as a molecular mechanism that contributes to hypertension-associated arterial thrombosis. By studying the interactions between anti-thrombotic inhibitors and hypertension, and the inter-individual variability in personal thrombus profiles, our work reveals a critical need for personalized anti-thrombotic drug selection that accommodates each patient’s pathological profile.

Arterial thrombosis is a prevailing and lethal pathological condition that remains difficult to treat or prevent without potentially serious side effects, mostly hemorrhagic in nature. Platelets and von Willebrand factor (VWF) have a recognized major role in the pathogenesis of arterial thrombosis. Platelets bind to surface immobilized VWF for initial adhesion to injured vascular sites, but also interact with soluble VWF to aggregate into thrombi, particularly under flow conditions creating elevated shear stress. Whether the binding of immobilized and soluble VWF to platelets is regulated by separate mechanisms and how they respectively regulate hemostasis and thrombosis remains unclear. Using targeted mutagenesis we engineered VWF to achieve modified binding kinetics with the platelet receptor glycoprotein (GP) Ibα and discovered that the interactions of immobilized and soluble VWF with platelets can be differentially regulated with distinct consequences on platelet adhesion and aggregation. Based on these results, we studied a monoclonal antibody, NMC4, known to bind to an epitope in the VWFA1 domain and to inhibit preferentially platelet aggregation under elevated shear stress conditions. We found that NMC4 was less efficient in reducing platelet adhesion to immobilized VWF than platelet aggregation mediated by soluble VWF and, surprisingly, also inhibited arterial thrombosis in a mouse model of ferric chloride-induced carotid artery occlusion at a dose that failed to prolong post-injury bleeding. Thus, our current findings help delineate interrelated biochemical and biophysical mechanisms underlying VWF function in vascular health; and suggest selective inhibition of VWF-mediated platelet aggregation as opposed to adhesion as a strategy to prevent arterial thrombosis while minimizing bleeding complications.