G. D. Doobay1, E. S. Miller1, T. J. Loftus1, K. B. Kannan1, P. A. Efron1, A. M. Mohr1 1University Of Flordia College Of Medicine,Department Of Surgery,Gainesville, FL, USA
Introduction: Using a clinically relevant rodent model for persistent-injury associated anemia with lung contusion, hemorrhagic shock and chronic stress (LCHS/CS), persistent elevation of norepinephrine was shown to be associated with prolonged mobilization of hematopoietic progenitor cells (HPC) to the peripheral blood and sites of injury. The use of propranolol has been shown to decrease prolonged HPC mobilization following trauma. Norepinephrine induces secretion of high mobility growth box 1 (HMGB1) as well as granulocyte colony stimulating factor (G-CSF). Along with neutrophil elastase, all are key factors in the mobilization of HPC via cleavage of homing protein, stromal cell-derived factor 1 (SDF-1), and adhesion protein, vascular cell adhesion molecule 1 (VCAM1). We hypothesize that prolonged HPC mobilization is due to the destruction of anchors in the bone marrow mediated by persistent hypercatecholaminemia following LCHS/CS.
Methods: Male Sprague-Dawley rats (n=6/group) were subjected to LCHS/CS ± daily propranolol (10mg/kg) (LCHS/CS+BB) and compared to naïve controls. Animals underwent two hours of daily restraint stress until the day of sacrifice (day 7). Bone marrow mRNA was analyzed with RT-PCR for HMGB1, G-CSF, neutrophil elastase, SDF-1 and VCAM1 expression. Neutrophil elastase enzymatic activity in bone marrow was also assayed. All data were presented as mean±SD indexed to naïve control mRNA expression. Data significance was defined as bp<0.05 relative to untreated groups.
Results: Bone marrow expression of HMGB1, G-CSF, and neutrophil elastase was significantly elevated in LCHS/CS relative to naïve control (Table). The use of propranolol following LCHS/CS significantly reduced expression of HMGB1, G-CSF and neutrophil elastase when compare to LCHS/CS alone (Table). Bone marrow expression of SDF-1 and VCAM1 were significantly decreased on day seven following LCHS/CS and LCHS/CS+BB. Neutrophil elastase enzyme activity (units/L) in bone marrow was significantly elevated following LCHS/CS when compared to naïve control (2.5±0.6 vs. 0.9±0.7 units/L). The use of propranolol following LCHS/CS significantly reduced neutrophil elastase expression (1.2±0.8b units/L).
Conclusion: Increased bone marrow expression of HMGB1 and G-CSF following LCHS/CS is associated with elevated neutrophil elastase. Decreased expression of bone marrow anchoring molecules, SDF-1 and VCAM1, following LCHS/CS, likely mediates prolonged HPC mobilization. Propranolol’s ability to reduce HMGB1, G-CSF, and neutrophil elastase expression to that of control levels suggests that this is a pro-inflammatory proteolysis-mediated mobilization of HPC driven by persistent hypercatecholaminemia.
