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Featured researches published by David T. Berg.


Nature Medicine | 2007

Activated protein C protects against diabetic nephropathy by inhibiting endothelial and podocyte apoptosis.

Berend Isermann; Ilya A. Vinnikov; Thati Madhusudhan; S. Herzog; Muhammed Kashif; Janusch Blautzik; Marcus Alexandre Finzi Corat; Martin Zeier; Erwin Blessing; Jun Oh; Bruce Gerlitz; David T. Berg; Brian W. Grinnell; Triantafyllos Chavakis; Charles T. Esmon; Hartmut Weiler; Angelika Bierhaus; Peter P. Nawroth

Data providing direct evidence for a causative link between endothelial dysfunction, microvascular disease and diabetic end-organ damage are scarce. Here we show that activated protein C (APC) formation, which is regulated by endothelial thrombomodulin, is reduced in diabetic mice and causally linked to nephropathy. Thrombomodulin-dependent APC formation mediates cytoprotection in diabetic nephropathy by inhibiting glomerular apoptosis. APC prevents glucose-induced apoptosis in endothelial cells and podocytes, the cellular components of the glomerular filtration barrier. APC modulates the mitochondrial apoptosis pathway via the protease-activated receptor PAR-1 and the endothelial protein C receptor EPCR in glucose-stressed cells. These experiments establish a new pathway, in which hyperglycemia impairs endothelial thrombomodulin-dependent APC formation. Loss of thrombomodulin-dependent APC formation interrupts cross-talk between the vascular compartment and podocytes, causing glomerular apoptosis and diabetic nephropathy. Conversely, maintaining high APC levels during long-term diabetes protects against diabetic nephropathy.


Journal of The American Society of Nephrology | 2009

Soluble Thrombomodulin Protects Ischemic Kidneys

Asif Sharfuddin; Ruben M. Sandoval; David T. Berg; Grant McDougal; Silvia B. Campos; Carrie L. Phillips; Bryan Edward Jones; Akanksha Gupta; Brian W. Grinnell; Bruce A. Molitoris

Altered coagulation and inflammation contribute to the pathogenesis of ischemic renal injury. Thrombomodulin is a necessary factor in the anticoagulant protein C pathway and has inherent anti-inflammatory properties. We studied the effect of soluble thrombomodulin (sTM) in a hypoperfusion model of ischemic kidney injury. To markedly reduce infrarenal aortic blood flow and femoral arterial pressures, we clamped the suprarenal aorta of rats, occluding them 90%, for 60 min. Reversible acute kidney injury (AKI) occurred at 24 h in rats subjected to hypoperfusion. Histologic analysis at 24 h revealed acute tubular necrosis (ATN), and intravital two-photon microscopy showed flow abnormalities in the microvasculature and defects of endothelial permeability. Pretreatment with rat sTM markedly reduced both I-R-induced renal dysfunction and tubular histologic injury scores. sTM also significantly improved microvascular erythrocyte flow rates, reduced microvascular endothelial leukocyte rolling and attachment, and minimized endothelial permeability to infused fluorescence dextrans, assessed by intravital quantitative multiphoton microscopy. Furthermore, sTM administered 2 h after reperfusion protected against ischemia-induced renal dysfunction at 24 h and improved survival. By using an sTM variant, we also determined that the protective effects of sTM were independent of its ability to generate activated protein C. These data suggest that sTM may have therapeutic potential for ischemic AKI.


Proceedings of the National Academy of Sciences of the United States of America | 2003

Engineering the proteolytic specificity of activated protein C improves its pharmacological properties

David T. Berg; Bruce Gerlitz; Jing Shang; Tommy Smith; Paula Santa; Mark A. Richardson; Ken D. Kurz; Brian W. Grinnell; Ken Mace; Bryan Edward Jones

Human activated protein C (APC) is an antithrombotic, antiinflammatory serine protease that plays a central role in vascular homeostasis, and activated recombinant protein C, drotrecogin alfa (activated), has been shown to reduce mortality in patients with severe sepsis. Similar to other serine proteases, functional APC levels are regulated by the serine protease inhibitor family of proteins including α1-antitrypsin and protein C inhibitor. Using APC–substrate modeling, we designed and produced a number of derivatives with the goal of altering the proteolytic specificity of APC such that the variants exhibited resistance to inactivation by protein C inhibitor and α1-antitrypsin yet maintained their primary anticoagulant activity. Substitutions at Leu-194 were of particular interest, because they exhibited 4- to 6-fold reductions in the rate of inactivation in human plasma and substantially increased pharmacokinetic profiles compared with wild-type APC. This was achieved with minimal impairment of the anticoagulant/antithrombotic activity of APC. These data demonstrate the ability to selectively modulate substrate specificity and subsequently affect in vivo performance and suggest therapeutic opportunities for the use of protein C derivatives in disease states with elevated serine protease inhibitor levels.


Critical Care Medicine | 2004

Evaluation of protein C and other biomarkers as predictors of mortality in a rat cecal ligation and puncture model of sepsis.

Josef G. Heuer; Ganesh R. Sharma; Bruce Gerlitz; Tonghai Zhang; Dianna L. Bailey; Chunjin Ding; David T. Berg; Douglas Perkins; Eddie J. Stephens; Kimberly C. Holmes; Renee L. Grubbs; Kelly A. Fynboe; Yun-Fei Chen; Brian W. Grinnell; Joseph A. Jakubowski

Objective:To evaluate protein C and other factors associated with the septic response as predictors of mortality in a clinically relevant animal model of sepsis. Design:Laboratory investigation. Setting:Eli Lilly and Company discovery research laboratory. Subjects:Forty female Sprague Dawley Rats weighing 245–265 g. Interventions:Polyethylene catheters were surgically implanted into the femoral vein and sepsis was induced by cecal ligation and puncture (CLP). A solution of 5% dextrose in 0.9% saline was continuously infused via femoral catheters immediately following surgery. Blood sampling was done before surgery and at 6 and 20 hrs after surgery. Rats were then monitored for survival out to 4 days. Measurements and Main Results:Blood collections were used to measure blood glucose, bacteremia, plasma protein C, D-dimer, hormones, chemokines, cytokines, and myoglobin (as a marker of organ damage). Mortality was categorized into three groups: early death (before 30 hrs post-CLP), late death (after 30 hrs post-CLP), and survivors (96 hrs post-CLP). Compared with survivors, early death rats had statistically significant differences in 30 variables indicative of severe inflammation, coagulopathy, and muscle damage including less bacterial clearance, hypoglycemia, lower plasma protein C, higher plasma D dimer, higher plasma cytokine/ chemokines, and higher plasma myoglobin concentrations. Twenty variables had a moderate to strong correlation with time of death. Receiver operator characteristic curves generated from a simple logistic regression model indicated that KC and macrophage inflammatory protein-2, rodent homologues of the human growth related oncogene CXC chemokine family, and protein C were the best predictors of mortality in this model. Conclusions:The data from this study indicate that an early decrease in protein C concentration predicts poor outcome in a rat sepsis model. The data further indicate that increases in the CXC chemokines macrophage inflammatory protein-2 and KC precede poor outcome.


Journal of The American Society of Nephrology | 2007

Role of Protein C in Renal Dysfunction after Polymicrobial Sepsis

Akanksha Gupta; David T. Berg; Bruce Gerlitz; Ganesh R. Sharma; Samreen K. Syed; Mark A. Richardson; George E. Sandusky; Josef G. Heuer; Elizabeth Galbreath; Brian W. Grinnell

Protein C (PC) plays an important role in vascular function, and acquired deficiency during sepsis is associated with increased mortality in both animal models and in clinical studies. This study explored the consequences of PC suppression on the kidney in a cecal ligation and puncture model of polymicrobial sepsis. This study shows that a rapid drop in PC after sepsis is strongly associated with an increase in blood urea nitrogen, renal pathology, and expression of known markers of renal injury, including neutrophil gelatinase-associated lipocalin, CXCL1, and CXCL2. The endothelial PC receptor, which is required for the anti-inflammatory and antiapoptotic activity of activated PC (APC), was significantly increased after cecal ligation and puncture as well as in the microvasculature of human kidneys after injury. Treatment of septic animals with APC reduced blood urea nitrogen, renal pathology, and chemokine expression and dramatically reduced the induction of inducible nitric oxide synthase and caspase-3 activation in the kidney. The data demonstrate a clear link between acquired PC deficiency and renal dysfunction in sepsis and suggest a compensatory upregulation of the signaling receptor. Moreover, these data suggest that APC treatment may be effective in reducing inflammatory and apoptotic insult during sepsis-induced acute renal failure.


Arteriosclerosis, Thrombosis, and Vascular Biology | 2007

Activated Protein C Decreases Tumor Necrosis Factor–Related Apoptosis-Inducing Ligand by an EPCR- Independent Mechanism Involving Egr-1/Erk-1/2 Activation

Lee A. O’Brien; Mark A. Richardson; Sean F. Mehrbod; David T. Berg; Bruce Gerlitz; Akanksha Gupta; Brian W. Grinnell

Background—APC is an antithrombotic and antiinflammatory serine protease that plays an important role in vascular function. We report that APC can suppress the proapoptotic mediator TRAIL in human umbilical vein endothelial cells, and we have investigated the signaling mechanism. Methods and Results—APC inhibited endothelial TRAIL expression and secretion and its induction by cell activation. To explore the mechanism, we examined factors associated with TRAIL regulation and demonstrated that APC increased the level of EGR-1, a transcriptional factor known to suppress the TRAIL promoter. APC also induced a significant increase in phosphorylation of ERK-1/2, required to activate EGR-1 expression. Activation of ERK-1/2 was dependent on the protease activated receptor-1 (PAR-1), but independent of the endothelial protein C receptor (EPCR). Using siRNA, we found that the effect of APC on the EGR-1/ERK signaling required for TRAIL inhibition was dependent on the S1P1 receptor and S1P1 kinase. Conclusions—Our data suggest that APC may provide cytoprotective activity by activating the ERK pathway, which upregulates EGR-1 thereby suppressing the expression of TRAIL. Moreover, we provide evidence that APC can induce a cell signaling response through a PAR-1/S1P1-dependent but EPCR-independent mechanism.


Journal of The American Society of Nephrology | 2009

Distinct Functions of Activated Protein C Differentially Attenuate Acute Kidney Injury

Akanksha Gupta; Bruce Gerlitz; Mark A. Richardson; Christopher Bull; David T. Berg; Samreen K. Syed; Elizabeth Galbreath; Barbara A. Swanson; Bryan Edward Jones; Brian W. Grinnell

Administration of activated protein C (APC) protects from renal dysfunction, but the underlying mechanism is unknown. APC exerts both antithrombotic and cytoprotective properties, the latter via modulation of protease-activated receptor-1 (PAR-1) signaling. We generated APC variants to study the relative importance of the two functions of APC in a model of LPS-induced renal microvascular dysfunction. Compared with wild-type APC, the K193E variant exhibited impaired anticoagulant activity but retained the ability to mediate PAR-1-dependent signaling. In contrast, the L8W variant retained anticoagulant activity but lost its ability to modulate PAR-1. By administering wild-type APC or these mutants in a rat model of LPS-induced injury, we found that the PAR-1 agonism, but not the anticoagulant function of APC, reversed LPS-induced systemic hypotension. In contrast, both functions of APC played a role in reversing LPS-induced decreases in renal blood flow and volume, although the effects on PAR-1-dependent signaling were more potent. Regarding potential mechanisms for these findings, APC-mediated PAR-1 agonism suppressed LPS-induced increases in the vasoactive peptide adrenomedullin and infiltration of iNOS-positive leukocytes into renal tissue. However, the anticoagulant function of APC was responsible for suppressing LPS-induced stimulation of the proinflammatory mediators ACE-1, IL-6, and IL-18, perhaps accounting for its ability to modulate renal hemodynamics. Both variants reduced active caspase-3 and abrogated LPS-induced renal dysfunction and pathology. We conclude that although PAR-1 agonism is solely responsible for APC-mediated improvement in systemic hemodynamics, both functions of APC play distinct roles in attenuating the response to injury in the kidney.


Science | 1996

Enhanced Protein C Activation and Inhibition of Fibrinogen Cleavage by a Thrombin Modulator

David T. Berg; Michael R. Wiley; Brian W. Grinnell

A modulator of the enzymatic activity of human thrombin, designated LY254603, was identified that enhances the thrombin-catalyzed generation of the anticoagulant factor activated protein C, yet inhibits thrombin-dependent fibrinogen clotting. By means of mutant substrates, it was shown that LY254603 mediates the change in enzymatic substrate specificity through an alteration in thrombins S3 substrate recognition site, a mechanism that appeared to be independent of allosteric changes induced by either sodium ions or by thrombomodulin. This compound may represent the prototype of a class of agents that specifically modulates the balance between thrombins procoagulant and anticoagulant functions.


Journal of Biological Chemistry | 2007

Negative Regulation of Inducible Nitric-oxide Synthase Expression Mediated through Transforming Growth Factor-β-dependent Modulation of Transcription Factor TCF11

David T. Berg; Akanksha Gupta; Mark A. Richardson; Lee A. O'Brien; David Scott Calnek; Brian W. Grinnell

Inducible nitric-oxide synthase (iNOS) plays a central role in the regulation of vascular function and response to injury. A central mediator controlling iNOS expression is transforming growth factor-β (TGF-β), which represses its expression through a mechanism that is poorly understood. We have identified a binding site in the iNOS promoter that interacts with the nuclear heterodimer TCF11/MafG using chromatin immunoprecipitation and mutation analyses. We demonstrate that binding at this site acts to repress the induction of iNOS gene expression by cytokines. We show that this repressor is induced by TGF-β1 and by Smad6-short, which enhances TGF-β signaling. In contrast, the up-regulation of TCF11/MafG binding could be suppressed by overexpression of the TGF-β inhibitor Smad7, and a small interfering RNA to TCF11 blocked the suppression of iNOS by TGF-β. The binding of TCF11/MafG to the iNOS promoter could be enhanced by phorbol 12-myristate 13-acetate and suppressed by the protein kinase C inhibitor staurosporine. Moreover, the induction of TCF11/MafG binding by TGF-β and Smad6-short could be blocked by staurosporine, and the effect of TGF-β was blocked by the selective protein kinase C inhibitor calphostin C. Consistent with the in vitro data, we found suppression of TCF11 coincident with iNOS up-regulation in a rat model of endotoxemia, and we observed a highly significant negative correlation between TCF11 and nitric oxide production. Furthermore, treatment with activated protein C, a serine protease effective in septic shock, blocked the down-regulation of TCF11 and suppressed endotoxin-induced iNOS. Overall, our results demonstrate a novel mechanism by which iNOS expression is regulated in the context of inflammatory activation.


Journal of Biological Chemistry | 2002

Modulation of thrombomodulin-dependent activation of human protein C through differential expression of endothelial Smads.

George E. Sandusky; David T. Berg; Mark A. Richardson; Laura Myers; Brian W. Grinnell

Protein C is a plasma protease that in its active form plays a central role in the regulation of vascular function by modulating thrombosis, inflammation, and apoptosis. A central player in this pathway is the cytokine-regulated receptor thrombomodulin (TM), which functions as a co-factor for the thrombin-dependent generation of activated protein C. We have found that tumor necrosis factor-β (TGF-β)-dependent suppression of TM on endothelial cells is differentially regulated by endothelial Smad6s and Smad7. Overexpression of Smad6s resulted in activation of a TGF-β reporter alone and enhanced TGF-β response. Moreover, Smad6s overexpression suppressed TM and subsequently reduced activated protein C generation. Antisense inhibition of Smad6s expression enhanced the TM-dependent activation of protein C, whereas blocking the inhibitory Smad7 by antisense resulted in reduced TM-dependent activation of protein C. The effect of Smad6s appeared to be due, at least in part, to up-regulation of TGF-β itself. Immunohistochemisty studies in normal versusatherosclerotic vessels showed that TM levels were suppressed in the endothelium over plaque. Consistent with the in vitro data, we found differential expression of Smad6s and Smad7 in normalversus atherosclerotic vessels, with Smad6s expression low in normal vessels but elevated in atherosclerotic vessels. In contrast, the opposite expression pattern was observed for Smad7. Overall, our results suggest that the relative balance of these intracellular Smads modulate the balance of endothelial function with regard to protein C activation.

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Brian W. Grinnell

University of Wisconsin-Madison

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