Investigating the Role of JNK Activation and Circulating BNP in Septic Hypotension

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PROJECT SUMMARY/ABSTRACT Sepsis results from the overwhelming immune response to infection leading to tissue hypoperfusion, organ failure, and eventually death. Myocardial depression resulting from severe sepsis is associated with high in-hospital mortality. Elevated circulating B-type natriuretic peptide (BNP) has previously been identified as a marker of cardiac dysfunction in sepsis which correlates with poor prognosis in septic patients. BNP is encoded by the Nppb gene and is produced by the ventricular myocytes in response to myocardial stress. BNP reduces blood pressure peripherally by promoting vasodilation to reduce afterload, and by increasing venous capacitance and promoting natriuresis to reduce blood volume and preload. Whether or not these effects of BNP on the cardiovascular system are active during sepsis has not been evaluated and will be addressed in this application. Previous studies have shown that pharmacological JNK inhibition protects against LPS associated cardiac dysfunction by restoring expression of genes involved in fatty acid oxidation. Treatment with JNK inhibitor completely ablates the LPS-induced BNP mRNA upregulation. To identify the mechanisms by which JNK inhibition prevents BNP production, our application focuses on cJun, a well described substrate of JNK and member of the activating protein (AP)-1 complex. Promoter analysis followed by Clustal alignment of the human and mouse Nppb promoters reveals a phylogenetically conserved AP-1 motif within both promoters. Preliminary data shows that adenoviral delivery of active cJun in the human cardiomyocyte AC16 cell line promotes BNP transcription via direct binding to the Nppb promoter. Our proposal will investigate the causative association between BNP upregulation and cardiac cJun activation, which will be evaluated in vivo using LPS and CLP induced murine sepsis to evaluate the potential of JNK inhibition to prevent BNP upregulation. Our preliminary data suggests that circulating BNP levels correlate with disease severity and myocardial dysfunction in sepsis animal models, and that JNK inhibition reduces BNP production and protects against sepsis-induced hypotension. For specific aim 2, our proposal will identify mechanistically if BNP suppression is involved in the JNK inhibitor’s mechanism of action and if BNP inhibition will protect against hypotension, reduced preload, and reduced cardiac output in sepsis animal models where these parameters are impaired. We will translate these findings in human patients by comparing circulating BNP levels in patients with sepsis and septic shock with control subjects and by identifying the correlation between elevated BNP and reduced cardiac output and myocardial systolic function. The proposed studies will test the central hypothesis that cJun is responsible for BNP upregulation in sepsis, and that preventing BNP or JNK signaling will improve survival by increasing blood pressure and tissue perfusion. Results from these studies may serve as the basis for future therapies aimed at inhibiting circulating BNP to increase blood pressure in patients with refractory hypotension.