Funding: NIH K08HL0086671 (Project period: 9/17/2009 - 7/31/2014)
Sepsis is the most common cause of death in non-coronary critical care units in the United States with more than 750,000 cases/year. A better understanding of the mechanisms of sepsis could lead to more effective therapies for patients. The focus of the mentor’s laboratory has been the (patho)biological roles of proteinases in inflammatory diseases. The PI, an anesthesiologist and intensivist, has concentrated on the role of proteinases in lung injury and sepsis. Survival from sepsis requires rapid recruitment of neutrophils to kill bacteria. Neutrophils kill bacteria predominantly via intracellular oxidant and proteolytic mechanisms. Neutrophils also secrete antimicrobial factors, and recently neutrophil extracellular traps (NETs) have been described composed of DNA and antimicrobial agents that trap and kill bacteria.
Application of neutrophil collagenase (MMP-8) deficient mice that our laboratory generated has led to consistent findings regarding the importance of MMP-8 in controlling neutrophil (PMN) recruitment in various disease models. Hence, we sought to determine a potential role of MMP-8 in sepsis.In this proposal, we present preliminary data showing that: (a) In a cecal-ligation and puncture (CLP) model of sepsis, MMP-8 deficient (MMP-8-/-) mice have greater number of PMNs in the peritoneum, enhanced bacterial clearance, and improved survival compared to wild type (WT) mice. (b) A CXC-chemokine, macrophage inflammatory protein (MIP)-2, is elevated during CLP and LPS-induced acute peritoneal inflammation and MMP-8 can cleave this chemokines (16-21). (c) The MMP-8-/- mice form NETs more avidly that the WT controls leading to more efficient extracellular anti-bacterial function.
Hence, we hypothesize that neutrophil collagenase (MMP-8) serves to resolve inflammation and to “clean up the mess.” Specifically, following massive neutrophil recruitment, MMP-8 degrades the neutrophil chemotactic gradient limiting further neutrophil influx. Moreover, MMP-8 aids in resolution of NETs, removing a nidus of potential scarring. Perhaps ironcially, the absence of MMP-8 has beneficial effects on sepsis, by increasing the number of neutrophils and promoting NET formation. These properties enhance both intracellular and extracellular bacterial killing respectively, attenuating the severity of sepsis syndrome. To test this hypothesis we propose the following specific aims that will define the mechanism of MMP-8 in PMN recruitment, and determine the mechanisms whereby MMP-8 aids in the resolution of NET formation.
"Combined Viral and Bacterial Infection and Zinc Homeostasis in Distal Lung" R01HL126711 NIH/NHLBI (PI: Kaynar) (Project period: 4/1/2015 – 3/31/2020)