M L Steer

Tufts Medical Center, Boston, Massachusetts, United States

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Publications (133)971.22 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Pancreatic acinar cells express proteinase-activated receptor-2 (PAR2) that is activated by trypsin-like serine proteases and has been shown to exert model-specific effects on the severity of experimental pancreatitis - i.e. PAR2(-/-) mice are protected from experimental acute biliary pancreatitis but develop more severe secretagogue-induced pancreatitis. P2pal-18S is a novel pepducin lipopeptide that targets and inhibits PAR2. In studies monitoring PAR2-stimulated [Ca(2+)](i) changes, we show that P2pal-18S is a full PAR2 inhibitor in acinar cells. Our in vivo studies show that P2pal-18S significantly reduces the severity of experimental biliary pancreatitis induced by retrograde intraductal bile acid infusion which mimics injury induced by endoscopic retrograde cholangio-pancreatography (ERCP). This reduction in pancreatitis severity is observed when the pepducin is given before or 2 hours after bile acid infusion but not when it is given 5 hours after bile acid infusion. Conversely, P2pal-18S increases the severity of secretagogue-induced pancreatitis. In-vitro studies indicate that P2pal-18S protects acinar cells against bile acid-induced injury/death but it does not alter bile acid-induced intracellular zymogen activation. These studies are the first to report the effects of an effective PAR2 pharmacological inhibitor on pancreatic acinar cells and on the severity of experimental pancreatitis. They raise the possibility that a pepducin such as P2pal-18S might prove useful in the clinical management of patients at risk for developing severe biliary pancreatitis such as occurs following ERCP.
    AJP Gastrointestinal and Liver Physiology 12/2012; · 3.65 Impact Factor
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    ABSTRACT: The roles of monocytes/macrophages and their mechanisms of action in the regulation of pancreatitis are poorly understood. To address these issues, we have employed genetically altered mouse strains that either express the human diphtheria toxin receptor (DTR) coupled to the CD11b promoter or have global deletion of TNF-α. Targeted, conditional depletion of monocytes/macrophages was achieved by administration of diphtheria toxin (DT) to CD11b-DTR mice. We show that in the absence of DT administration, pancreatitis is associated with an increase in pancreatic content of Ly-6C(hi) monocytes/macrophages but that this response is prevented by prior administration of DT to CD11b-DTR mice. DT administration also reduces pancreatic edema and acinar cell injury/necrosis in two dissimilar experimental models of acute pancreatitis (a secretagogue-induced model and a model elicited by retrograde pancreatic duct infusion of sodium taurocholate). In the secretagogue-elicited model, the DT-induced decrease in pancreatitis severity is reversed by adoptive transfer of purified Ly-6C(hi) monocytes harvested from non-DT-treated CD11b-DTR mice or by the transfer of purified Ly-6C(hi) monocytes harvested from TNF-α(+/+) donor mice, but it is not reversed by the transfer of Ly-6C(hi) monocytes harvested from TNF-α(-/-) donors. Our studies indicate that the Ly-6C(hi) monocyte subset regulates the severity of pancreatitis by promoting pancreatic edema and acinar cell injury/necrosis and that this phenomenon is dependent upon the expression of TNF-α by those cells. They suggest that therapies targeting Ly-6C(hi) monocytes and/or TNF-α expression by Ly-6C(hi) monocytes might prove beneficial in the prevention or treatment of acute pancreatitis.
    Journal of Biological Chemistry 02/2011; 286(15):13327-35. · 4.65 Impact Factor
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    ABSTRACT: Mechanistic studies of acute pancreatitis require animal models because clinical material is generally not available during the early phases of the disease. Here we describe a protocol to induce biliary pancreatitis by retrogradely infusing bile acids into the pancreatic duct of anesthetized mice. The resulting model replicates events believed to be responsible for the onset of clinical biliary (i.e., gallstone) pancreatitis and creates highly reproducible pancreatitis with a severity that depends on the concentration of infused bile acid. Pancreatitis reaches its maximal level of severity within 24 h of induction, and it resolves over the subsequent week. This protocol enables the investigator to use genetically modified strains of mice, and it requires only relatively simple and easily learned techniques of small animal surgery. With practice and gentle technique, the surgery (from induction of anesthesia to completion of the infusion) can be completed within 25 min per animal.
    Nature Protocol 01/2010; 5(2):335-41. · 8.36 Impact Factor
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    ABSTRACT: The mechanisms by which reflux of bile acids into the pancreas induces pancreatitis are unknown. We reasoned that key events responsible for this phenomenon might be mediated by Gpbar1, a recently identified and widely expressed G-protein-coupled, cell surface bile acid receptor. Acute pancreatitis was induced in wild-type and Gpbar1(-/-) mice by either retrograde ductal infusion of taurolithocholic acid-3-sulfate (TLCS) or supramaximal secretagogue stimulation with caerulein. In vitro experiments were performed in which acini obtained from wild-type and Gpbar1(-/-) mice were exposed to either submicellar concentrations of TLCS (200-500 microM) or a supramaximally stimulating concentration of caerulein (10 nM). Gpbar1 is expressed at the apical pole of acinar cells and its genetic deletion is associated with reduced hyperamylasemia, edema, inflammation, and acinar cell injury in TLCS-induced, but not caerulein-induced, pancreatitis. In vitro, genetic deletion of Gpbar1 is associated with markedly reduced generation of pathological calcium transients, intracellular activation of digestive zymogens, and cell injury when these responses are induced by exposure to TLCS, but not when they are induced by exposure to caerulein. Gpbar1 may play a critical role in the evolution of bile-acid-induced pancreatitis by coupling exposure to bile acids with generation of pathological intracellular calcium transients, intra-acinar cell zymogen activation, and acinar cell injury. Acute biliary pancreatitis may be a "receptor-mediated" disease and interventions that interfere with Gpbar1 function might prove beneficial in the treatment and/or prevention of biliary acute pancreatitis.
    Gastroenterology 11/2009; 138(2):715-25. · 12.82 Impact Factor
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    ABSTRACT: Protease-activated receptor-2 (PAR2) is a 7-transmembrane G-protein-coupled tethered ligand receptor that is expressed by pancreatic acinar and ductal cells. It can be physiologically activated by trypsin. Previously reported studies (Namkung, W., Han, W., Luo, X., Muallem, S., Cho, K. H., Kim, K. H., and Lee, M. G. (2004) Gastroenterology 126, 1844-1859; Sharma, A., Tao, X., Gopal, A., Ligon, B., Andrade-Gordon, P., Steer, M. L., and Perides, G. (2005) Am. J. Physiol. 288, G388-G395) have shown that PAR2 activation exerts a protective effect on the experimental model of pancreatitis induced by supramaximal secretagogue (caerulein) stimulation. We now show that PAR2 exerts a worsening effect on a different model of experimental pancreatitis, i.e. one induced by retrograde pancreatic ductal infusion of bile salts. In vitro studies using freshly prepared pancreatic acini show that genetic deletion of PAR2 reduces bile salt-induced pathological calcium transients, acinar cell injury, and activation of c-Jun N-terminal kinase, whereas genetic deletion of PAR2 has the opposite or no effect on these pancreatitis-related events when they are elicited, in vitro, by caerulein stimulation. Studies employing a combination of trypsin inhibition and activation of PAR2 with the activating peptide SLIGRL show that all these differences indeed depend on the activation of PAR2. These studies are the first to report that a single perturbation can have model-specific and opposite effects on pancreatitis, and they underscore the importance of performing mechanistic pancreatitis studies using two dissimilar models of the disease to detect idiosyncratic, model-specific events. We suggest PAR2 activation exerts a worsening effect on the severity of clinical pancreatitis and that interventions interfering with PAR2 activation may be of benefit in the treatment of patients with severe pancreatitis.
    Journal of Biological Chemistry 08/2008; 283(30):20703-12. · 4.65 Impact Factor
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    ABSTRACT: Acute pancreatitis is an inflammatory disease of the pancreas. Acute abdominal pain is the most common symptom, and increased concentrations of serum amylase and lipase confirm the diagnosis. Pancreatic injury is mild in 80% of patients, who recover without complications. The remaining patients have a severe disease with local and systemic complications. Gallstone migration into the common bile duct and alcohol abuse are the most frequent causes of pancreatitis in adults. About 15-25% of pancreatitis episodes are of unknown origin. Treatment of mild disease is supportive, but severe episodes need management by a multidisciplinary team including gastroenterologists, interventional radiologists, intensivists, and surgeons. Improved understanding of pathophysiology and better assessments of disease severity should ameliorate the management and outcome of this complex disease.
    The Lancet 02/2008; 371(9607):143-52. · 39.06 Impact Factor
  • Pancreas 01/2008; 37(4). · 2.95 Impact Factor
  • Pancreas 01/2008; 37(4). · 2.95 Impact Factor
  • Pancreas 01/2008; 37(4). · 2.95 Impact Factor
  • Lancet. 01/2008; 371(9618):1072-1072.
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    ABSTRACT: Most mechanistic studies of pancreatitis in mice employ the secretagogue-induced model. The currently reported studies were designed to develop an alternative, and possibly more clinically relevant, mouse model of pancreatitis. Na-taurocholate (10-50 microl, 1-5%) in saline, or saline alone, was retrogradely infused into the mouse pancreatic duct. The animals were killed 6-24 hours later and the severity of pancreatitis in the pancreatic head and tail was examined by quantitating hyperamylasemia, pancreatic edema, acinar cell necrosis, and pancreatic inflammation. In addition, intrapancreatic activation of trypsinogen, generation of IL-6, intrapulmonary sequestration of neutrophils, and alterations in lung compliance were evaluated. The effects of Na-taurocholate on in-vitro acinar cell calcium transients, viability, and trypsinogen activation were examined. Little or no evidence of pancreatitis was observed in mice infused with saline alone or in the tail of pancreata removed from animals infused with Na-taurocholate. In the head of the pancreas, evidence of pancreatitis was observed 12-24 hours after infusion of 20-50 microl 2-5% Na-taurocholate and the earliest morphological changes involved terminal duct and acinar cells. Intrapancreatic trypsin activity was transiently elevated within 5 minutes of Na-taurocholate infusion and pancreatic IL-6 levels were elevated 24 hours later. Under in-vitro conditions, Na-taurocholate triggered pathological acinar cell calcium transients, cell death, and calcium-dependent trypsinogen activation. This clinically relevant model of acute biliary pancreatitis yields reproducible results and its severity can be easily manipulated. It is ideally suited for use in mechanistic studies employing genetically modified mouse strains.
    Gut 12/2007; 56(11):1590-8. · 10.73 Impact Factor
  • Michael L. Steer, George Perides
    10/2007: pages 10 - 26; , ISBN: 9780470987506
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    ABSTRACT: Pancreatic and lung inflammation during acute pancreatitis is a poorly understood, but clinically important, phenomenon. The proto-oncogene Tpl2 (tumor progression locus-2) has recently been shown to have important immunomodulatory effects on some inflammatory processes, but its importance to pancreatitis has not been previously examined. Our studies were designed to (a) define the effects of Tpl2 on pancreatic and lung inflammation during pancreatitis and (b) identify mechanisms and cell types responsible for those effects. We examined pancreatitis-associated Tpl2 effects in wild type and Tpl2(-/-) mice subjected to either secretagogue-induced or bile salt-induced pancreatitis. To determine the myeloid or non-myeloid lineage of cells responsible for the Tpl2 effects, we used Tpl2(-/-) chimeric mice generated by lethal irradiation followed by bone marrow transplantation. Mechanisms responsible for the effects of Tpl2 ablation on caerulein-induced proinflammatory events were evaluated under in vivo and in vitro conditions using the techniques of electrophoretic mobility shift assay, immunoblot analysis, and quantitative reverse transcription-PCR. We found that Tpl2 ablation markedly reduced pancreatic and lung inflammation in these two dissimilar models of pancreatitis, but it did not alter pancreatic injury/necrosis in either model. The reduction in caerulein-induced pancreatic inflammation is dependent upon Tpl2 ablation in non-myeloid cells and is associated with both in vivo and in vitro inhibition of MEK, JNK, and AP-1 activation and the expression of MCP-1, MIP-2, and interleukin-6. Non-myeloid cell expression of Tpl2 regulates pancreatic inflammation during pancreatitis by mediating proinflammatory signals and the generation of neutrophil chemoattracting factors.
    Journal of Biological Chemistry 08/2007; 282(30):22140-9. · 4.65 Impact Factor
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    ABSTRACT: We have hypothesized that the colocalization of digestive zymogens with lysosomal hydrolases, which occurs during the early stages of every experimental pancreatitis model, facilitates activation of those zymogens by lysosomal hydrolases such as cathepsin B and that this activation triggers acute pancreatitis by leading to acinar cell injury. Some, however, have argued that the colocalization phenomenon may be the result, rather than the cause, of zymogen activation during pancreatitis. To resolve this controversy and explore the causal relationships between zymogen activation and other early pancreatitis events, we induced pancreatitis in mice by repeated supramaximal secretagogue stimulation with caerulein. Some animals were pretreated with the cathepsin B inhibitor CA-074 me to inhibit cathepsin B, prevent intrapancreatic activation of digestive zymogens, and reduce the severity of pancreatitis. We show that inhibition of cathepsin B by pretreatment with CA-074 me prevents intrapancreatic zymogen activation and reduces organellar fragility, but it does not alter the caerulein-induced colocalization phenomenon or subcellular F-actin redistribution or prevent caerulein-induced activation of NF-kappaB, ERK1/2, and JNK or upregulated expression of cytochemokines. We conclude 1) that the colocalization phenomenon, F-actin redistribution, activation of proinflammatory transcription factors, and upregulated expression of cytochemokines are not the results of zymogen activation, and 2) that these early events in pancreatitis are not dependent on cathepsin B activity. In contrast, zymogen activation and increased subcellular organellar fragility during caerulein-induced pancreatitis are dependent on cathepsin B activity.
    AJP Gastrointestinal and Liver Physiology 07/2007; 292(6):G1738-46. · 3.65 Impact Factor
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    ABSTRACT: Pancreatic islets have evolved remarkable, though poorly understood mechanisms to modify beta cell mass when nutrient intake fluctuates or cells are damaged. We hypothesised that appropriate and timely adjustments in cell number occur because beta cells release proliferative signals to surrounding cells when stimulated by nutrients and 'bleed' these growth factors upon injury. In rat pancreatic islets, we measured DNA content, insulin content, insulin secretion after treatment, immunoblots of apoptotic proteins and the uptake of nucleoside analogues to assess the ability of gamma-aminobutyric acid (GABA), which is highly concentrated in beta cells, to act as a growth and survival factor. This focus is supported by work from others demonstrating that GABA increases cell proliferation in the developing nervous system, acts as a survival factor for differentiated neurons and, interestingly, protects plants under stress. Our results show that DNA, insulin content and insulin secretion are higher in freshly isolated islets treated with GABA or GABA B receptor agonists. Exposure to GABA upregulated the anti-apoptotic protein B-cell chronic lymphocytic leukaemia XL and limited activation of caspase 3 in islets. The cellular proliferation rate in GABA-treated islets was twice that of untreated controls. We conclude that GABA serves diverse purposes in the islet, meeting a number of functional criteria to act as an endogenous co-regulator of beta cell mass.
    Diabetologia 05/2007; 50(4):764-73. · 6.49 Impact Factor
  • Pancreas 01/2007; 35(4). · 2.95 Impact Factor
  • Pancreas 01/2007; 35(4). · 2.95 Impact Factor
  • Pancreas 01/2007; 35(4). · 2.95 Impact Factor
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    ABSTRACT: Acute pancreatitis is generally believed to be a disease in which the pancreas is injured by digestive enzymes that it normally produces. Most of the potentially harmful digestive enzymes produced by pancreatic acinar cells are synthesized and secreted as inactive zymogens which are normally activated only upon entry into the duodenum but, during the early stages of acute pancreatitis, those zymogens become prematurely activated within the pancreas and, presumably, that activation occurs within pancreatic acinar cells. The mechanisms responsible for intracellular activation of digestive enzyme zymogens have not been elucidated with certainty but, according to one widely recognized theory (the "co-localization hypothesis"), digestive enzyme zymogens are activated by lysosomal hydrolases when the two types of enzymes become co-localized within the same intracellular compartment. This review focuses on the evidence supporting the validity of the co-localization hypothesis as an explanation for digestive enzyme activation during the early stages of pancreatitis. The findings, summarized in this review, support the conclusion that co-localization of lysosomal hydrolases with digestive enzyme zymogens plays a critical role in permitting the intracellular activation of digestive enzymes that leads to acinar cell injury and pancreatitis.
    World Journal of Gastroenterology 05/2006; 12(13):1985-90. · 2.55 Impact Factor
  • Pancreas 01/2006; 33(4). · 2.95 Impact Factor

Publication Stats

4k Citations
971.22 Total Impact Points

Institutions

  • 2005–2011
    • Tufts Medical Center
      • Department of Surgery
      Boston, Massachusetts, United States
    • Boston Medical Center
      Boston, Massachusetts, United States
  • 2005–2009
    • Tufts University
      • Department of Surgery
      Medford, MA, United States
  • 2007
    • University of Tampere
      • Department of Gastroenterology and Alimentary Tract Surgery
      Tampere, Western Finland, Finland
    • Otto-von-Guericke-Universität Magdeburg
      Magdeburg, Saxony-Anhalt, Germany
  • 2002
    • University of Geneva
      • Division of Gastroenterology and Hepatology
      Genève, GE, Switzerland
  • 1984–2002
    • Beth Israel Deaconess Medical Center
      • Department of Surgery
      Boston, MA, United States
  • 2000
    • Yonsei University Hospital
      • Department of Internal Medicine
      Seoul, Seoul, South Korea
  • 1999
    • University of Zurich
      Zürich, Zurich, Switzerland
  • 1995
    • Yale University
      • Department of Internal Medicine
      New Haven, CT, United States
  • 1989–1995
    • Harvard Medical School
      • Department of Surgery
      Boston, Massachusetts, United States
  • 1992
    • Kyoto University
      • Graduate School of Medicine / Faculty of Medicine
      Kioto, Kyōto, Japan
    • University of Massachusetts Boston
      Boston, Massachusetts, United States
  • 1987
    • University of Milan
      Milano, Lombardy, Italy