SUMMARY:
Despite decades of targeted research, no effective pharmacologic interventions have been identified for the
Acute Respiratory Distress Syndrome (ARDS), which is a life-threatening disease process characterized by
dysregulated immune responses. Sepsis is a major cause of ARDS, and the pathophysiology of both
processes is characterized by alterations in microcirculatory blood flow, with vascular endothelial cell (EC)
dysfunction playing a major role in organ injury. Novel mechanistic insights are needed to assist the
development of therapies to address the EC barrier dysfunction that underlies ARDS and sepsis.
Staphylococcus (S.) aureus is a frequently identified organism in gram-positive sepsis, and the highly virulent,
antibiotic-resistant methicillin-resistant S. aureus (MRSA) strain is particularly challenging to treat and a major
cause of ARDS. Important knowledge gaps exist both in MRSA-induced pathophysiology relevant to ARDS
and in the mechanistic understanding of EC-specific processes that can be targeted therapeutically.
Endogenous sphingosine-1-phosphate (S1P) and the structurally similar pharmaceutical compound, FTY720
(FTY), have EC barrier-enhancing effects in preclinical models of ARDS. However, both S1P and FTY also
induce a myriad of other effects that are potentially harmful in critically ill patients and make them poor
therapeutic candidates. We therefore have explored the barrier-regulatory properties of novel FTY720 analogs
to better understand how these compounds regulate permeability. Our work has revealed that FTY720 (S)-
phosphonate (Tys) has superior efficacy in several preclinical models and maintains expression levels of the
essential S1PR1 receptor, unlike other agonists which induce its degradation. In addition, epigenetic processes
are increasingly being recognized as important pathogenic steps during inflammatory acute lung injury
(ALI)/ARDS and sepsis, and epigenetic responses (such as histone acetylation) can be altered by S1P-related
signaling. Our central hypothesis is that MRSA causes EC dysfunction relevant to ARDS by epigenetic and
other pathophysiologic mechanisms that can be targeted by Tys/S1PR1-related signaling. Using ChIP-seq
analysis and other epigenetic tools, we have generated new insights that MRSA triggers histone acetylation in
lung EC to regulate genes involved in lung EC dysfunction. Exciting new data suggest Tys-S1PR1 signaling
may ameliorate key aspects of these epigenetic effects. Aim #1 will determine the mechanisms by which
Tys/S1PR1 signaling protects against MRSA-induced lung EC barrier disruption in vitro. Aim #2 will use state-
of-the-art ChIP-seq and other approaches to characterize novel MRSA- and Tys/S1PR1-induced epigenetic
changes that have functional consequences in lung EC, including the novel MRSA target identified by our
epigenetic screening, CYP1A1. Aim #3 will extend these studies in vivo by characterizing epigenetic and other
mechanisms of MRSA-induced lung injury in mice and determine the efficacy of Tys. Overall, these studies will
advance our mechanistic understanding of MRSA-induced ARDS to identify novel therapeutic targets.