Blockade or deletion of transient receptor potential vanilloid 4 (TRPV4) is not protective in a murine model of sepsis.

Claire A Sand,Manasi Nandi,Anna Starr,Andrew D Grant

doi:10.12688/f1000research.6298.1

Abstract

Sepsis is a systemic inflammatory response triggered by microbial infection that can cause cardiovascular collapse, insufficient tissue perfusion and multi-organ failure. The cation channel transient receptor potential vanilloid 4 (TRPV4) is expressed in vascular endothelium and causes vasodilatation, but excessive TRPV4 activation leads to profound hypotension and circulatory collapse - key features of sepsis pathogenesis. We hypothesised that loss of TRPV4 signaling would protect against cardiovascular dysfunction in a mouse model of sepsis (endotoxaemia). Multi-parameter monitoring of conscious systemic haemodynamics (by radiotelemetry probe), mesenteric microvascular blood flow (laser speckle contrast imaging) and blood biochemistry (iSTAT blood gas analysis) was carried out in wild type (WT) and TRPV4 knockout (KO) mice. Endotoxaemia was induced by a single intravenous injection of lipopolysaccharide (LPS; 12.5 mg/kg) and systemic haemodynamics monitored for 24 h. Blood flow recording was then conducted under terminal anaesthesia after which blood was obtained for haematological/biochemical analysis. No significant differences were observed in baseline haemodynamics or mesenteric blood flow. Naïve TRPV4 KO mice were significantly acidotic relative to WT counterparts. Following induction of sepsis, all mice became significantly hypotensive, though there was no significant difference in the degree of hypotension between TRPV4 WT and KO mice. TRPV4 KO mice exhibited a higher sepsis severity score. While septic WT mice became significantly hypernatraemic relative to the naïve state, this was not observed in septic KO mice. Mesenteric blood flow was inhibited by topical application of the TRPV4 agonist GSK1016790A in naïve WT mice, but enhanced 24 h following LPS injection. Contrary to the initial hypothesis, loss of TRPV4 signaling (either through gene deletion or pharmacological antagonism) did not attenuate sepsis-induced cardiovascular dysfunction: in fact, pathology appeared to be modestly exaggerated in mice lacking TRPV4. Local targeting of TRPV4 signalling may be more beneficial than global inhibition in sepsis treatment.

Highlights

Sepsis, the systemic inflammatory syndrome that can occur in response to infection, represents an enormous global healthcare burden; it can progress to septic shock, characterised by refractory hypotension and insufficient organ perfusion, with associated mortality rates of up to 80% (Martin, 2012)
Given that numerous endogenous agonists and sensitisers of transient receptor potential vanilloid 4 (TRPV4) are upregulated in sepsis, we hypothesised that blockade of TRPV4 activity using a pharmacological antagonist HC-067047, or genetic deletion of the channel would be protective in a murine model of sepsis, attenuating the cardiovascular collapse associated with the development of septic shock
That inflammation-induced upregulation of endogenous factors could contribute to sepsis-associated circulatory failure via excessive TRPV4 activation

Summary

Introduction

The systemic inflammatory syndrome that can occur in response to infection, represents an enormous global healthcare burden; it can progress to septic shock, characterised by refractory hypotension and insufficient organ perfusion, with associated mortality rates of up to 80% (Martin, 2012). TRPV4, originally identified as an osmosensor in the kidney (Liedtke et al, 2000; Strotmann et al, 2000; Wissenbach et al, 2000), is expressed in numerous tissues, including the heart and vasculature (Wissenbach et al, 2000) Its expression in both endothelial and smooth muscle cells is well-established, and its activation in vascular tissue is associated with endothelium-dependent vasodilatation, and both direct and indirect smooth muscle hyperpolarisation (Baylie & Brayden, 2011). In addition to extracellular hypotonicity, it is gated by various physical and chemical stimuli, including shear stress, arachidonic acid metabolites ( epoxyeicosatrienoic acids) and endocannabinoids (Nilius et al, 2004) These chemical factors may be increased under inflammatory conditions (Kiss et al, 2010; Theken et al, 2011; Varga et al, 1998). Given that numerous endogenous agonists and sensitisers of TRPV4 are upregulated in sepsis, we hypothesised that blockade of TRPV4 activity using a pharmacological antagonist HC-067047, or genetic deletion of the channel (in global knockout mice) would be protective in a murine model of sepsis, attenuating the cardiovascular collapse associated with the development of septic shock

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