The role of myeloid cells and Hif-1 in a multi-hit model of Acute Lung Injury
Lead Research Organisation:
University of Edinburgh
Department Name: MRC Centre for Inflammation Research
Abstract
Critically ill patients who have suffered severe trauma and infection are at risk of severe lung damage that requires mechanical ventilation. The cells and cell signals that control this are not well understood. I plan to develop a mouse model of haemorrhage and body-wide inflammation to mimic the complex situation seen in patients. Using this model I will investigate the role of the monocyte, a circulating white blood cell, in controlling the development of lung damage by comparing the damage seen in normal animals with that seen in genetically modified mice in which I am able to deplete the monocyte level without affecting other cells. I will also study the role of Hypoxia-inducible Factor-1, a cell protein which controls cells‘ ability to generate inflammatory responses. I will do this by studying the effects of injury in mice which under and over-express Hif-1 in their inflammatory cells. To take my findings back to the clinical setting I am able to study the effects of exposing mice to varying levels of oxygen. I expect to show that in these injured animals raised levels of oxygen in the lung are specifically anti-inflammatory and this will help guide clinicians on how much extra oxygen to prescribe to patients.
Technical Summary
Acute Respiratory Distress Syndrome (ARDS) is an important cause of morbidity and mortality in critically ill patients for which there is no specific therapy. Elucidating the cells and mediators central to the development of the ARDS should provide targeted therapeutic options.
I have developed a murine model of non-resuscitated haemorrhagic shock in which we propose to add the administration of systemic endotoxin to generate a 2-hit model of acute lung injury which reflects the clinical scenario of major trauma, a common cause of ARDS. In this model we aim to test the following hypotheses:
1) Circulating monocytes mediate acute lung injury (ALI). We will use an in-house conditional monocyte depletion model in which circulating monocytes but not resident alveolar macrophages are selectively depleted. We predict that monocyte depleted mice will exhibit attenuated lung injury.
2) Hypoxia-inducible Factor-1 (Hif-1) is a critical mediator in ALI. Hif-1 plays a central role in the myeloid cell inflammatory responses to hypoxia and infection.
Using myeloid cell Hif-1 over- and under-expressing transgenic mice the pathogenesis of lung injury in the model will be studied. We predict that myeloid cell Hif-1-deficient mice will exhibit attenuated injury. Adoptive transfer studies of wild-type neutrophils or monocytes to Hif-1-null mice will be performed to define the role of monocyte-Hif-1 expression in lung injury.
3) Lung injury may be modulated through varying oxygenation. Both hypoxia and hyperoxia are of direct clinical relevance to patients with major trauma and sepsis. Although we predict that hypoxia will exacerbate lung injury, Hif-1 is thought be a necessary component of the innate host defence and hypoxia may indeed prove protective. Hif-1 expression will also be manipulated pharmacologically using a specific prolyl-hydroxylase inhibitor (FG4095).
These experiments performed in a complex but highly clinically relevant model will yield insights into the pathogenesis of ARDS that may generate novel therapeutic strategies.
I have developed a murine model of non-resuscitated haemorrhagic shock in which we propose to add the administration of systemic endotoxin to generate a 2-hit model of acute lung injury which reflects the clinical scenario of major trauma, a common cause of ARDS. In this model we aim to test the following hypotheses:
1) Circulating monocytes mediate acute lung injury (ALI). We will use an in-house conditional monocyte depletion model in which circulating monocytes but not resident alveolar macrophages are selectively depleted. We predict that monocyte depleted mice will exhibit attenuated lung injury.
2) Hypoxia-inducible Factor-1 (Hif-1) is a critical mediator in ALI. Hif-1 plays a central role in the myeloid cell inflammatory responses to hypoxia and infection.
Using myeloid cell Hif-1 over- and under-expressing transgenic mice the pathogenesis of lung injury in the model will be studied. We predict that myeloid cell Hif-1-deficient mice will exhibit attenuated injury. Adoptive transfer studies of wild-type neutrophils or monocytes to Hif-1-null mice will be performed to define the role of monocyte-Hif-1 expression in lung injury.
3) Lung injury may be modulated through varying oxygenation. Both hypoxia and hyperoxia are of direct clinical relevance to patients with major trauma and sepsis. Although we predict that hypoxia will exacerbate lung injury, Hif-1 is thought be a necessary component of the innate host defence and hypoxia may indeed prove protective. Hif-1 expression will also be manipulated pharmacologically using a specific prolyl-hydroxylase inhibitor (FG4095).
These experiments performed in a complex but highly clinically relevant model will yield insights into the pathogenesis of ARDS that may generate novel therapeutic strategies.
