Acute lung injury (ALI) is a severe inflammatory lung disease with high mortality.
Previous studies revealed several important concepts in ALI, including cellular
interaction between lung-marginated leukocytes and pulmonary endothelium, and
decompartmentalisation of soluble mediators. However, there are inherent
limitations within both in vivo and in vitro models to identify the detailed mechanism
underlying these concepts. In this PhD project, we attempted to address these
unanswered questions, using an in situ isolated perfused mouse lung (IPL).
Specifically, we aimed to 1) develop, characterise, and optimise the mouse IPL
model; 2) investigate soluble and cellular aspects of two models of ALI that are
particularly amenable to study using the IPL, namely ventilator-induced lung injury
(VILI) and ischaemia-reperfusion injury.
From a physiological viewpoint, VILI consists of 2 primary components, high-stretch
and atelectasis. Modelling atelectasis-related injury in vivo is difficult due to negative
pleural pressure. We took advantage of the zero pleural pressure of open-chest IPL
system to develop an atelectasis-related VILI model. Comparison of this
‘atelectrauma’ and a high-stretch ‘volutrauma’ model demonstrated that both cause
lung oedema and pulmonary inflammation, but the inflammatory impact was different
between them. Volutrauma, but not atelectrauma, facilitated systemic cytokine
release, in which lung-marginated monocytes seem to play an important role. This
finding in the VILI model drove us to further investigate the role of these monocytes
in an ischaemia-reperfusion model, which is clinically highly relevant and simulates a
lung transplantation setting. Our results suggested that lung-marginated monocytes may also contribute to develop ischaemia-reperfusion injury, potentially involving
TNF upregulation.
Through this PhD project, we have successfully developed a technically very
challenging mouse IPL model. We utilised the unique features of the IPL to develop
experimental models that we believe will be strong tools to fill the gap between in
vivo physiological significance and in vitro mechanistic understanding.