ARDS Redux

Post-transcriptional regulation of urokinase-type plasminogen activator receptor expression in lipopolysaccharide-induced acute lung injury

RATIONALE

Urokinase-type plasminogen activator (uPA) receptor (uPAR) is required for the recruitment of neutrophils in response to infection. uPA induces its own expression in lung epithelial cells, which involves its interaction with cell surface uPAR. Regulation of uPAR expression is therefore crucial for uPA-mediated signaling in infectious acute lung injury (ALI).

OBJECTIVES

To determine the role of uPA in uPAR expression during ALI caused by sepsis.

METHODS

We used Western blot, Northern blot, Northwestern assay, and immunohistochemistry. Phosphate-buffered saline- and lipopolysaccharide (LPS)-treated wild-type and uPA(-/-) mice were used.

MEASUREMENTS AND MAIN RESULTS

Biological activities of uPA, including proteolysis, cell adhesion, migration, proliferation, and differentiation, are dependent on its association with uPAR. Bacterial endotoxin (LPS) is a major cause of pulmonary dysfunction and infection-associated mortality. The present study shows that LPS induces uPAR expression both in vitro and in vivo, and that the mechanism involves post-transcriptional stabilization of uPAR mRNA by reciprocal interaction of phosphoglycerate kinase (PGK) and heterogeneous nuclear ribonucleoprotein C (hnRNPC) with uPAR mRNA coding region and 3' untranslated region determinants, respectively. The process involves tyrosine phosphorylation of PGK and hnRNPC. uPA(-/-) mice failed to induce uPAR expression after LPS treatment. In these mice, LPS treatment failed to alter the binding of PGK and hnRNPC protein with uPAR mRNA due to lack of tyrosine phosphorylation.

CONCLUSIONS

Our study shows that induction of LPS-mediated uPAR expression is mediated through tyrosine phosphorylation of PGK and hnRNPC. This involves expression of uPA as an obligate intermediary.

Sepsis in critical care

Sepsis is a syndrome produced by the accelerated activity of the inflammatory immune response, the clotting cascade, and endothelial damage. It is a systematic process that can progress easily into septic shock and MODS. The chemical mediators or cytokines produce a complex self-perpetuating process that impacts all body systems. It is critical for the nurse first to identify patients at risk for developing sepsis and to assess patients who have SIRS and sepsis continually for signs and symptoms of organ involvement and organ dysfunction. Once sepsis has been diagnosed, evidence-based practice indicates initiation of fluid resuscitation. Vasopressor therapy, positive inotropic support, and appropriate antibiotic therapy should be started within the first hour. Within a 6-hour timeframe the goal is stabilization of the CVP, MAP, and UOP to prevent further organ damage. The challenge for nurses caring for septic patients is to support the treatment goals, to prevent added complications including stress ulcers, DVTs, aspiration pneumonia, and the progression to MODS, and to address the patient's and the family's psychosocial needs. As complex as the pathophysiology of sepsis is, the nursing care is equally complex but also rewarding. Patients who previously might have died now recover as vigilant nursing care combines forces with new drug therapies and evidence-based practice guidelines.