About

Robert Lee is an Assistant Professor in the Department of Biochemistry and Biophysics at the University of North Carolina at Chapel Hill. His research interests are centered around platelet signaling and function, with a focus on two main areas of platelet research: the utility of platelet transfusion in various bleeding disorders and the mechanisms regulating platelet lifespan in blood and platelet clearance in organs such as the spleen and liver. He utilizes mouse models of platelet dysfunction and has established state-of-the-art imaging techniques to visualize platelet adhesion and aggregation at sites of vascular injury in vivo, as well as real-time clearance of platelets in various organs. As part of the Bergmeier research group, Dr. Lee collaborates within the UNC Blood Research Center, which provides a collective of researchers and clinicians specializing in coagulation and disorders of bleeding and thrombosis. His work aims to advance understanding of platelet behavior and improve therapeutic strategies for bleeding disorders.

Research topics

• Medicine
• Internal medicine
• Pathology
• Immunology
• Chemistry
• Pharmacology
• Demography
• Surgery
• Gastroenterology

Selected publications

• A Novel G13-RAPGEF2-RAP1 Signaling Pathway Critical for Platelet Adhesion

  Blood · 2026-04-08

  articleOpen access

  Hemostasis and thrombosis are strongly dependent on the unique ability of platelets to rapidly activate integrin receptors and to firmly adhere to sites of injury under shear stress conditions. Central to integrin activation is the small GTPase RAP1, which itself is activated by guanine nucleotide exchange factors (GEFs). CalDAG-GEFI (RASGRP2) is the highest expressed and functionally dominant platelet RAP-GEF. However, a genome-wide association study also suggested a significant role for RAPGEF2 (PDZ-GEFI), a low expressed RAP-GEF, in human platelet aggregation. Here, we used mice deficient in RAPGEF2 (megakaryocyte-specific, Rapgef2mKO), CalDAG-GEFI (Caldaggef1-/-), or both RAPGEF2 and CalDAG-GEFI (DKO) to characterize the contribution of RAPGEF2 signaling to platelet function, hemostasis and thrombosis. RAPGEF2 protein was detected in murine and human platelets. Compared to control or Caldaggef1-/- platelets, both RAP1 activation and integrin aIIbb3-mediated aggregation were significantly diminished in DKO platelets. When compared to controls, Rapgef2mKO platelets exhibited reduced integrin activation, a more reversible aggregation response, and impaired adhesion under conditions of shear stress ex vivo and in vivo. Mechanistic studies strongly suggest that RAPGEF2 operates downstream of receptors coupled to the heterotrimeric G protein, G13 (GNA13), such as aIIbb3 and the thromboxane receptor. Together, our studies provide genetic evidence that RAPGEF2 in platelets operates downstream of G13 as an important regulator of RAP1 signaling and integrin activation, especially under conditions of elevated shear stress. These findings markedly improve our understanding of G protein signaling and integrin function in platelets, with potential implications for the development of improved platelet-targeted therapies for cardiovascular disease.

  PublisherDOI

• Genetic deletion of platelet PAR4 results in reduced thrombosis and impaired hemostatic plug stability

  UNC Libraries · 2026-03-12

  articleOpen access
  PublisherDOI

• RAP1-RHO small GTPase cross-talk mediates integrin-dependent and - independent platelet procoagulant response

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-05-23

  preprintOpen access

  Abstract Platelet adhesion and procoagulant activity are critical for primary and secondary hemostasis, respectively. The small GTPase RAP1 is a central regulator of platelet aggregation as it controls αIIbβ3 integrin activation through direct interaction with the integrin adapter protein, TALIN-1 (Tln-1). In addition to their aggregation defect, activated platelets lacking RAP1 ( Rap1 mKO ) exhibited a marked impairment in surface exposure of phosphatidylserine (PtdSer), a negatively charged phospholipid with procoagulant activity. However, the mechanisms by which RAP1 regulates PtdSer exposure are unclear. Here we investigated the hypothesis that RAP1 regulates platelet PtdSer exposure through cross-talk with small GTPases of the Rho family. Consistent with their defect in PtdSer exposure, Rap1 mKO platelets showed reduced procoagulant activity in vitro and in vivo when compared to controls. Stimulated Rap1 mKO platelets exhibited elevated RHOA-GTP levels, and inhibition of the RHOA effector, Rho associated coiled-coil kinase (ROCK), partially restored PtdSer exposure in these cells. A milder defect in PtdSer exposure was observed for platelets from Tln-1 mR35/118E mice, i.e. mice with impaired RAP1-Tln-1 interaction but otherwise intact RAP1 signaling. ROCK inhibition fully restored PtdSer exposure in Tln-1 mR35/118E platelets. Opening of the mitochondrial permeability transition pore, a cellular response critical to PtdSer exposure, was impaired in Rap1 mKO platelets and restored by pretreatment of cells with the ROCK inhibitor. Our study provides first evidence that platelet RAP1 signaling affects hemostatic plug formation independent of its key role in platelet adhesion. Additionally, our studies strongly suggest that RAP1 regulates PtdSer exposure and procoagulant activity in a RHOA/integrin-dependent and -independent manner.

  PublisherOA PDFDOI

• Nature of Antireflux Barrier Formed by Nissen Fundoplication Surgery

  Research Square · 2025-06-29

  preprintOpen access
  PublisherOA PDFDOI

• Platelet-mediated activation of perivascular mast cells triggers progression of sepsis to septic shock in mice

  Nature Communications · 2025-12-03 · 2 citations

  articleOpen access

  The critical events that trigger sepsis progression into life-threatening septic shock remain unclear. In agreement with reports that link a drop in platelet count to a complicated clinical course in sepsis patients, here we report that, during sepsis, mouse platelets become activated, deposit systemically on vascular walls, and stimulate perivascular mast cells (MC) by releasing platelet activating factor (PAF). In mouse models and patient samples, MC activation correlates with the development of shock in sepsis and is mechanistically linked to shock by inducing systemic hypotension, vascular leakage and microvascular perfusion abnormalities. Preventing platelet or MC activation, or inhibiting the activity of the major MC granule constituent chymase, averts progression from sepsis to shock and reduces mortality of septic mice. Thus, our work establishes that, during sepsis progression, platelet microvascular adhesion leads to MC-mediated vascular changes to culminate in septic shock and septic shock-associated mortality. Sepsis may progress into lethal septic shock, but the cellular mechanisms are still unclear. Here the authors show that, in septic mice, platelets activate perivascular mast cells to cause systemic hypotension and vascular pathology, while inhibiting platelets or mast cell activation suppresses septic shock induction, thereby implicating potential therapy targets.

  PublisherOA PDFDOI

• HTRS2025.P1.46 Evaluation of bleeding and platelet dysfunction in a mouse model of vascular Ehlers Danlos syndrome

  Research and Practice in Thrombosis and Haemostasis · 2025-11-01

  articleOpen access1st authorCorresponding
  PublisherOA PDFDOI

• Abstract Wed169: Platelet Transfusion Simulation Effectively Reverses Aspirin-Induced Platelet Inhibition In Vitro: A Role for Stored Platelets?

  Circulation Research · 2025-08-01

  article

  Aspirin (ASA) irreversibly inhibits platelet cyclooxygenase-1, impairing thromboxane A2 synthesis and reducing platelet aggregation. Platelet (PLT) transfusion can be used to restore function, yet the impact of cold storage (CS) on transfusion efficacy in this context in bleeding patients and other disease etiologies remains unclear. There is a lack of preclinical human models for high-throughput developmental research. We hypothesized that PLT transfusion would restore function in ASA-treated blood and CS-PLTs would have equivalent efficacy to Day 0 PLTs in a high throughput in vitro model. This exploratory in vitro study assessed PLT function before and after simulated PLT transfusion in ASA (125 μM)-treated whole blood using two assays: TEG 6s platelet mapping (PM) and Impedance Aggregometry (IA). For TEG (n=5), fresh (Day 0, n=2) or CS PLTs (≤Day 14, n=3) were mixed at 20% of whole blood volume. For IA (n=4), CS PLTs (≤21 days, n=4) were tested at 30% and 40%, maintaining constant hematocrit with autologous RBCs. A paired t-test and repeated-measures ANOVA were used for statistical analysis. ASA induced 94 ± 4.2% inhibition of arachidonic acid (AA) response on TEG in vitro. PLT mixing significantly restored Maximum Amplitude (MA) from 14.5 ± 4.4 to 48.2± 20.7 (p = 0.01) (Figure 1). CS PLTs on Day 6 (n = 2) had the highest recovery (MA = 65.5 ± 0.5) compared to fresh PLTs at Day 0 (n = 2, MA = 26.9 ± 11.7). Day 14 (n=1) also reversed dysfunction (MA = 56.2). CS PLT mixing however did not change PLT count (227.0 ± 90.0 vs. 221.0 ± 81.0 pre-mixing), confirming platelet activity recovery rather than a numerical increase. IA (Figure 2) showed that 40% CS PLT (≤21 days, n=4) mixing increased function with no significant difference from baseline. (AA Max 4.5 ± 2.4 vs. 7.8 ± 1.7). Similarly, 30% PLT transfusion showed partial recovery, while 20% resulted in limited recovery. PLT counts trended upward but without statistically significant differences across conditions. PLT transfusion in vitro effectively restores PLT function following ASA-induced inhibition, supporting its role as rapid strategy for urgent reversal. CS PLTs show strong efficacy, reinforcing their clinical viability in transfusion protocols. Further research with a larger sample size and additional assays is needed to comprehensively assess their efficacy, though our preliminary data support feasibility of this model to be used in future research to refine approaches and develop novel strategies.

  PublisherDOI

• Su1351: ASSESSING THE INTER-OBSERVER VARIABILITY OF HIGH-RESOLUTION MANOMETRY GERD-REALATED FEATURES AND MILAN SCORE

  Gastroenterology · 2025-05-01

  article
  PublisherDOI

• Platelet-mediated activation of perivascular mast cells triggers progression of sepsis to septic shock in mice

  UNC Libraries · 2025-12-11

  articleOpen access
  PublisherDOI

• Lack of overt bleeding or platelet dysfunction in a mouse model of vascular Ehlers–Danlos syndrome

  Journal of Thrombosis and Haemostasis · 2025-05-17

  letter1st authorCorresponding
  PublisherDOI

Recent grants

• NIH Grant R01NS046851

  NIH · $1.3M · 2008

• NIH Grant R01NS045199

  NIH · $793k · 2009

Frequent coauthors

• Wolfgang Bergmeier

  University of North Carolina at Chapel Hill

  50 shared

• David S. Paul

  University of North Carolina at Chapel Hill

  22 shared

• Raymond Piatt

  Dignify Therapeutics (United States)

  16 shared

• Nigel Mackman

  14 shared

• Tomas Ø. Jensen

  Centre of Excellence for Health, Immunity and Infections

  13 shared

• Yacine Boulaftali

  Université Paris Cité

  13 shared

• Anna L. Goodman

  13 shared

• Lida Jafari Saraf

  VA Long Beach Healthcare System

  11 shared

Labs

• UNC Biochemistry and BiophysicsPI