About

David S. Paul is a Research Assistant Professor in the Department of Biochemistry and Biophysics at the University of North Carolina at Chapel Hill. He is affiliated with the Bergmeier Lab, located in the Mary Ellen Jones Building. His contact information includes a phone number (919) 962-7332 and an email address, david_paul@med.unc.edu. The department is situated at 120 Mason Farm Road, Campus Box 7260, Chapel Hill, NC 27599. The page does not provide additional details about his research focus, background, or key contributions.

Research topics

• Immunology
• Biology
• Biochemistry
• Medicine
• Internal medicine
• Chemistry
• Andrology
• Cell biology
• Pharmacology
• Molecular biology
• Endocrinology

Selected publications

• Loss of P2Y1 receptor desensitization does not impact hemostasis or thrombosis despite increased platelet reactivity in vitro

  UNC Libraries · 2025-09-27

  articleOpen access
  PublisherDOI

• Coagulation factor XII haploinsufficiency is protective against venous thromboembolism in a population-scale multidimensional analysis

  Nature Communications · 2025-09-01 · 6 citations

  articleOpen access

  Coagulation factor XII has been identified as a potential drug target that could prevent thrombosis without increasing the risk of bleeding. However, human data to support the development of factor XII-directed therapeutics are lacking. To assess the role of factor XII in venous thromboembolism, we examine genetic variation in the coding region of the F12 locus across 703,745 participants in the UK Biobank and NIH All of Us biorepositories. We find that heterozygous carriers of nonsense, frameshift, and essential splice site variants in F12 are protected against venous thromboembolism without an increased risk of bleeding or infection. We also show that F12 variant carriers generally experience a quantitative (type I) defect in circulating factor XII levels, though a subset of participants was also identified with possible qualitative (type II) deficiency. In vitro plasma-based thrombin generation is reduced at factor XII concentrations reflective of those seen in F12 variant carriers. We also show that F12 heterozygous mice are protected against venous thromboembolism and display an intermediate phenotype between wild-type and F12-null animals. We conclude that heterozygous loss of F12 represents a haploinsufficient state characterized by protection against venous thromboembolism and that therapeutically inhibiting factor XII is likely to be safe and effective.

  PublisherOA PDFDOI

• Mitochondrial Calcium Uniporter Regulates ITAM-Dependent Platelet Activation

  Circulation Research · 2025-07-01 · 9 citations

  article

  BACKGROUND: Platelet activation relies on changes in cytoplasmic calcium flux. However, little is known about the role mitochondrial calcium flux plays in platelet activation. Activation induces release of calcium from intracellular stores, which enters the mitochondrial matrix through the MCU (mitochondrial calcium uniporter) to regulate bioenergetics and reactive oxygen species (ROS) formation, as demonstrated in other cells. However, whether MCU contributes to platelet function is unclear. METHODS: We generated platelet-specific Mcu-deficient mice ( Mcu plt −/− ) and compared them to littermate wild-type controls ( Mcu plt+/+ ). In vitro approaches assessed mitochondrial calcium flux and platelet activation responses to stimulation of immunoreceptor tyrosine-based activation motif (ITAM) receptors and GPCRs (G protein–coupled receptors). In addition, we examined in vivo hemostasis and thrombosis. We also treated human platelets with MCU inhibitors, and platelet function was assessed. RESULTS: Mcu plt −/ − platelets had significantly reduced mitochondrial calcium flux in response to activation of ITAM receptors, whereas mitochondrial calcium flux in response to GPCR activation was unchanged. Platelet aggregation was significantly reduced by ITAM activation in Mcu plt −/ − platelets, but GPCR-induced aggregation was unchanged. Similar findings were observed when MCU was inhibited in human platelets. In vivo, Mcu plt −/ − mice had reduced arterial thrombosis and less ischemic stroke brain injury. Hemostasis was mildly altered in Mcu plt −/ − mice. Mechanistically, mitochondrial ROS generation was significantly reduced in Mcu plt −/ − platelets compared with Mcu plt+/+ platelets after ITAM-dependent activation, but not GPCR activation. Reduced mitochondrial ROS was associated with decreased ITAM signaling based on p-Syk (phospho–spleen tyrosine kinase) and p-PLCγ2 (phospho–phospholipase C-gamma 2) in Mcu plt −/ − platelets. Inhibiting mitochondrial ROS decreased aggregation as well as downstream ITAM signaling in Mcu plt+/+ platelets. Conversely, treating Mcu plt −/ − platelets with MitoParaquat to induce mitochondrial ROS increased platelet ITAM-dependent aggregation and signaling. CONCLUSIONS: Our data support a role for mitochondrial calcium flux in regulating ITAM-dependent platelet activation through the generation of mitochondrial ROS.

  PublisherDOI

• Coagulation factor XII haploinsufficiency is protective against venous thromboembolism in a population-scale multidimensional analysis

  Open MIND · 2025-01-01

  article

  Coagulation factor XII has been identified as a potential drug target that could prevent thrombosis without increasing the risk of bleeding. However, human data to support the development of factor XII-directed therapeutics are lacking. To assess the role of factor XII in venous thromboembolism, we examine genetic variation in the coding region of the F12 locus across 703,745 participants in the UK Biobank and NIH All of Us biorepositories. We find that heterozygous carriers of nonsense, frameshift, and essential splice site variants in F12 are protected against venous thromboembolism without an increased risk of bleeding or infection. We also show that F12 variant carriers generally experience a quantitative (type I) defect in circulating factor XII levels, though a subset of participants was also identified with possible qualitative (type II) deficiency. In vitro plasma-based thrombin generation is reduced at factor XII concentrations reflective of those seen in F12 variant carriers. We also show that F12 heterozygous mice are protected against venous thromboembolism and display an intermediate phenotype between wild-type and F12-null animals. We conclude that heterozygous loss of F12 represents a haploinsufficient state characterized by protection against venous thromboembolism and that therapeutically inhibiting factor XII is likely to be safe and effective.Lowering the levels of coagulation factor XII may prevent thrombosis without increasing the risk of bleeding. Here, Haj et al. use a large human dataset to show that this is the case for people carrying mutations that lower the levels of factor XII.

• Platelet priming in MPN triggers pro-thrombotic intermediate affinity state in αIIbβ3 integrin

  Blood · 2025-11-03

  article

  Abstract Introduction: Myeloproliferative neoplasms (MPN) are associated with both a higher risk of thrombosis and bleeding. Interestingly, both hyper- and hypo-reactivity in platelets is characteristic for MPN patients, the latter being the result of cellular exhaustion. The majority (>90%) of MPN have activating mutations in JAK2, a kinase operating downstream of the platelet/megakaryocyte receptor for thrombopoietin (TPO), c-Mpl. JAK2 mutations or TPO binding to c-Mpl lead to intracellular signaling in platelets, including phosphoinositide-3-kinase (PI3K). However, TPO is a platelet “primer”, i.e. it does not cause platelet aggregation itself, but synergizes with other agonists in converting the main platelet integrin, αIIbβ3, from a bent, low affinity (B+) to an extended, high affinity state (E+H+). If and how altered JAK2 signaling affects platelet adhesive function and thrombotic plug formation are significant knowledge gaps in our understanding of MPN. Aims: Here, we aimed to determine whether JAK2 mutations or TPO binding to c-Mpl can enhance platelet adhesiveness via transition of αIIbβ3 to an intermediate affinity state (E+H-), and whether altered platelet adhesive function mediated by E+H- αIIbβ3 contributes to increased VT response in a murine MPN model. Methods: Platelet function was investigated in blood samples from a well-characterized mouse model with a 13 copy human JAK2V617F transgene driven by the vav1 promoter, and from JAK2V617F MPN patients. The inferior vena cava stenosis and femoral vein electrolytic injury models were used to study venous thrombosis in JAK2V617F or control mice. Microfluidics studies were performed to assess platelet adhesive behavior under flow conditions on fibrin or captured VWF. Platelet rolling, stable adhesion, and thrombus formation were analyzed using a custom machine learning model. A novel flow cytometry-based Förster Resonance Energy Transfer (FRET) assay was established to monitor extension of murine αIIbβ3 integrin. E+H+αIIbβ3 was detected using JON/A-PE antibody. Platelets positive for αIIbβ3 extension but negative for JON/A-PE staining were classified as expressing αIIbβ3 in the E+H- state. Results: In vivo, a significant increase in venous thrombosis was observed in JAK2V617F expressing mice when compared to controls. JAK2V617F platelets also showed increased, αIIbβ3 -dependent adhesiveness when perfused over fibrin (2.7 fold increase), suggesting that the integrin is present in a pre-activated form on circulating platelets in these mice. A novel FRET assay to assess αIIbβ3 extension revealed αIIbβ3-integrins in an intermediate affinity conformation (E+H-) in circulating JAK2V617F platelets, but not WT platelets. Mechanistic studies were conducted to elucidate how the JAK2V617F mutation induces E+H-αIIbβ3 in platelets. Pre-incubation of WT platelets with the TPO-mimetic, romiplostim, induced E+H-αIIbβ3 and adhesion to fibrin under flow (6-fold increase in comparison to vehicle). Similarly, increased platelet adhesion to fibrin under flow was observed in whole blood from MPN patients (4-fold increase) and in romiplostim-treated whole blood from healthy volunteers (3.6 fold increase). Romiplostim treatment of WT blood also led to increased platelet adhesion to immobilized-VWF under flow. Romiplostim-induced E+H-αIIbβ3 and platelet adhesiveness under shear conditions were sensitive to the PI3 kinase inhibitor, wortmannin (>75% decrease of adhesiveness). In line with this observation, the induction of E+H-αIIbβ3 is controlled by the RAP1 GTPase-activating protein, RASA3, a PI3K-regulated inhibitor of platelet integrin activation. Conclusion: Together, these findings for the first time demonstrate that platelet priming in MPN causes increased adhesiveness due to surface expression of αIIbβ3 in an intermediate affinity state, mediated by PI3K/RASA3 signaling. Our studies further suggest that platelet priming may contribute to increased venous thrombosis risk observed in MPN, while impaired platelet response to agonist stimulation and alterations in coagulation proteins may explain the increased bleeding risk.

  PublisherDOI

• 4D intravital imaging studies identify platelets as the predominant cellular procoagulant surface in a mouse hemostasis model

  UNC Libraries · 2024-09-06

  articleOpen access

  Interplay between platelets, coagulation factors, endothelial cells (ECs) and fibrinolytic factors is necessary for effective hemostatic plug formation. This study describes a four-dimensional (4D) imaging platform to visualize and quantify hemostatic plug components in mice with high spatiotemporal resolution. Fibrin accumulation following laser-induced vascular injury was observed at the platelet plug-EC interface, controlled by the antagonistic balance between fibrin generation and breakdown. We observed less fibrin accumulation in mice expressing low levels of tissue factor (TFlow) or F12-/- mice compared to controls, whereas increased fibrin accumulation, including on the vasculature adjacent to the platelet plug, was observed in plasminogen-deficient mice or wild-type mice treated with tranexamic acid (TXA). Phosphatidylserine (PS), a membrane lipid critical for the assembly of coagulation factors, was first detected at the platelet plug-EC interface, followed by exposure across the endothelium. Impaired PS exposure resulted in a significant reduction in fibrin accumulation in cyclophilin D-/- mice. Adoptive transfer studies demonstrated a key role for PS exposure on platelets, and to a lesser degree on ECs, in fibrin accumulation during hemostatic plug formation. Together, these studies suggest that (1) platelets are the functionally dominant procoagulant cellular surface, and (2) plasmin is critical for limiting fibrin accumulation at the site of a forming hemostatic plug.

  PublisherDOI

• 4D intravital imaging studies identify platelets as the predominant cellular procoagulant surface in a mouse hemostasis model

  Blood · 2024-05-31 · 19 citations

  articleOpen access

  ABSTRACT: Interplay between platelets, coagulation factors, endothelial cells (ECs), and fibrinolytic factors is necessary for effective hemostatic plug formation. This study describes a 4-dimensional (4D) imaging platform to visualize and quantify hemostatic plug components in mice with high spatiotemporal resolution. Fibrin accumulation after laser-induced vascular injury was observed at the platelet plug-EC interface, controlled by the antagonistic balance between fibrin generation and breakdown. We observed less fibrin accumulation in mice expressing low levels of tissue factor or F12-/-mice compared with controls, whereas increased fibrin accumulation, including on the vasculature adjacent to the platelet plug, was observed in plasminogen-deficient mice or wild-type mice treated with tranexamic acid. Phosphatidylserine (PS), a membrane lipid critical for the assembly of coagulation factors, was first detected at the platelet plug-EC interface, followed by exposure across the endothelium. Impaired PS exposure resulted in a significant reduction in fibrin accumulation in cyclophilin D-/-mice. Adoptive transfer studies demonstrated a key role for PS exposure on platelets, and to a lesser degree on ECs, in fibrin accumulation during hemostatic plug formation. Together, these studies suggest that (1) platelets are the functionally dominant procoagulant cellular surface, and (2) plasmin is critical for limiting fibrin accumulation at the site of a forming hemostatic plug.

  PublisherOA PDFDOI

• Coagulation Factor XII (<i>F12</i>) Haploinsufficiency Is Protective Against Venous Thromboembolism

  Blood · 2024-11-05

  articleOpen access

  Background: Inhibition of factor XII (FXII, gene: F12) represents a potentially transformative approach to antithrombotic therapy, as severe congenital deficiency in humans is not associated with bleeding while deletion or inhibition of FXII in preclinical models consistently protects against thrombosis. However, the impact of FXII deficiency on venous thromboembolism (VTE) risk in humans is controversial. Prior studies suffered from significant limitations such as small sample size, ascertainment bias, and heterogenous case/control groups. An accurate, population-level assessment of the clinical impacts associated with FXII deficiency could significantly impact ongoing efforts to develop novel anti-FXII therapies. Here, we combine analysis of large-scale genomic datasets with in vitro and in vivo translational studies to probe the role of FXII in VTE. Methods: We employed data from the UK Biobank (UKB, N=415,921) and NIH All of Us program (AoU, N=191,686), which contain paired genetic and clinical data. We identified participants with rare (MAF ≤ 1%) loss-of-function (LOF) variants in F12 (frameshift, essential splice site, and nonsense mutations). We used Firth's penalized likelihood Cox regression modeling to evaluate the association between VTE and loss-of-function variants in F12 through single-gene burden analysis. Results from UKB and AoU were meta-analyzed using a random-effects model. Circulating FXII levels were measured in a subset of UKB participants using the Olink® Explore 3072 plasma proteomics panel (N=44,864). We directly measured plasma FXII levels on samples from mice and the Mass General Brigham (MGB) Biobank by ELISA. Kaolin-initiated thrombin generation assays were used to evaluate FXII-reconstituted plasma sampls. The femoral vein electrolytic injury model was used to compare thrombus formation in wild-type (N=10), F12 heterozygous (N=9), and F12 homozygous knockout (N=8) mice. Results: Across the UKB and AoU datasets, 1920 participants had qualifying variants in F12 (99.9% heterozygous). Variant carrier status was significantly associated with protection against VTE (HR=0.65, 95% CI: 0.49-0.86, P=0.002). Modeling replicated known risk factors for VTE such as age, BMI, and blood group, thereby confirming that clinical annotation of the datasets was accurate. A leave-one-variant-out analysis showed that no single variant was responsible for the protective signal, and sensitivity analyses incorporating a polygenic risk score for VTE did not change the effect-size estimate for F12 LOF, indicating that F12 likely functions independently of known common genetic risk factors for VTE. F12 variant carriers had significantly lower circulating FXII levels (mean: 46.1%, P &amp;lt;0.0001) compared to non-carriers (mean 100% L-NPX, P=8.8 x 10-8). These findings were corroborated by ELISA performed on plasma samples from 29 F12 variant carriers and matched 29 controls (12.68 mcg/ml in carriers vs. 25.17 mcg/ml in controls, P=4.8 x 10-6). Thrombin generation assays performed on reconstituted FXII-deficient plasma showed significantly reduced peak thrombin generation at 50% FXII plasma levels (P=0.0002). Using a mouse femoral vein electrolytic injury model, we observed significant reductions in both platelet accumulation (P=0.032) and fibrin formation (P=0.025) in F12 heterozygous knockout mice compared to wild-type. Conclusions: In this multi-modal study, we show that inherited FXII deficiency is protective against VTE. Our data are consistent with the growing recognition that haploinsufficient states in coagulation can have biological effects without requiring total loss of function. Taken together, these findings suggest that targeting FXII is likely to be a safe and effective antithrombotic strategy.

  PublisherOA PDFDOI

• Mucin 1 and venous thrombosis in tumor-bearing mice and patients with cancer

  Thrombosis Research · 2024-03-21 · 11 citations

  articleOpen access
  PublisherOA PDFDOI

• Synthesis and dephosphorylation of MARCKS in the late stages of megakaryocyte maturation drive proplatelet formation

  UNC Libraries · 2024-08-27 · 1 citations

  articleOpen access

  Platelets are essential for hemostasis, and thrombocytopenia is a major clinical problem. Megakaryocytes (MKs) generate platelets by extending long processes, proplatelets, into sinusoidal blood vessels. However, very little is known about what regulates proplatelet formation. To uncover which proteins were dynamically changing during this process, we compared the proteome and transcriptome of round vs proplatelet-producing MKs by 2D difference gel electrophoresis (DIGE) and polysome profiling, respectively. Our data revealed a significant increase in a poorly-characterized MK protein, myristoylated alanine-rich C-kinase substrate (MARCKS), which was upregulated 3.4- and 5.7-fold in proplatelet-producing MKs in 2D DIGE and polysome profiling analyses, respectively. MARCKS is a protein kinase C (PKC) substrate that binds PIP2. In MKs, it localized to both the plasma and demarcation membranes. MARCKS inhibition by peptide significantly decreased proplatelet formation 53%. To examine the role of MARCKS in the PKC pathway, we treated MKs with polymethacrylate (PMA), which markedly increased MARCKS phosphorylation while significantly inhibiting proplatelet formation 84%, suggesting that MARCKS phosphorylation reduces proplatelet formation. We hypothesized that MARCKS phosphorylation promotes Arp2/3 phosphorylation, which subsequently downregulates proplatelet formation; both MARCKS and Arp2 were dephosphorylated in MKs making proplatelets, and Arp2 inhibition enhanced proplatelet formation. Finally, we used MARCKS knockout (KO) mice to probe the direct role of MARCKS in proplatelet formation; MARCKS KO MKs displayed significantly decreased proplatelet levels. MARCKS expression and signaling in primary MKs is a novel finding. We propose that MARCKS acts as a "molecular switch," binding to and regulating PIP2 signaling to regulate processes like proplatelet extension (microtubule-driven) vs proplatelet branching (Arp2/3 and actin polymerization-driven).

  PublisherDOI

Frequent coauthors

• Bernard McGinn

  170 shared

• Leigh Eric Schmidt

  170 shared

• Wilbert Law

  Education University of Hong Kong

  121 shared

• Eriugena Otten

  Swift Engineering (United States)

  121 shared

• Jane Douglass

  121 shared

• Renna Thomas

  Bridge University

  121 shared

• Jerald Bkauer T H E D I V J N I

  University of Divinity

  121 shared

• William T. Trent

  University of Illinois Urbana-Champaign

  121 shared

Labs

• UNC Department of Biochemistry and BiophysicsPI

Education

• Ph.D., Biochemistry and Biophysics

  University of North Carolina at Chapel Hill

  2019