mob-1: A novel mediator of ARDS
Adult respiratory distress syndrome (ARDS) is a pulmonary inflammatory process triggered by a variety of stress conditions some remote from the lung, which leads to microvascular injury with subsequent respiratory failure and death. The present work aimed to implicate mob-1, a recently cloned member of the $\alpha$ chemokine family, in the pathogenesis of this grave syndrome using a rat model of ARDS-like lung injury produced by IL-2. To that end, differential display was utilized to identify pulmonary mob-1 and time course as well as cellular localization of mob-1 mRNA were established. Furthermore, to delineate mob-1 function, the protein was recombinantly produced using a bacterial expression system and tested for in vivo, in vitro, and ex vivo effects. Differential display of lungs harvested from IL-2-treated rats identified a highly-inducible band ($\sim$250 bp), termed B1, which presented 99.14% homology to the previously cloned mob-1. Pulmonary mob-1 mRNA was upregulated prior (1 hr) to the onset of lung injury (4 hrs), localized to pulmonary alveolar macrophages by in situ hybridization, and suppressed by TNF$\alpha$ inhibition (neutralizing anti-TNF$\alpha$ mAb or rolipram). Recombinant mob-1 was successfully expressed as a histidine-tagged fusion protein in E. coli and purified using nickel chromatography with subsequent enterokinase digestion. The purified recombinant protein was then subjected to SDS-PAGE and sized to $\sim$8kD by silver stain and Western Blot analysis. In vivo, intratracheal injection of mob-1 (50 $\mu$g/rat) induced leukocyte accumulation in lung tissue (MPO +93 $\pm$ 8% vs. control, p $<$ 0.05) with preferential accumulation of neutrophils in bronchoalveolar lavage fluid (36.0 $\pm$ 1.0% vs. 0.1 $\pm$ 0.1% in controls, p $<$ 0.01). In contrast, mob-1 had no effect on pulmonary edema and bronchoalveolar lavage fluid protein concentration. In vitro, transwell migration studies demonstrated chemotactic activity of mob-1 towards human monocytes (+151 $\pm$ 34% vs. mob-1 vehicle, p $<$ 0.01) and only weak chemotaxis for human neutrophils (+15 $\pm$ 0% vs. mob-1 vehicle, p $<$ 0.01). In concert, these data suggest that mob-1 promotes lung injury by chemoattraction of leukocytes through an indirect effect. Since angiogenesis is a major component of the resolution process of ARDS and because IP-10, the human homologue of mob-1, is known to exert angiostatic properties, the ability of mob-1 to affect angiogenesis was tested in a rat aortic ring model ex vivo. Indeed, mob-1 (100 ng/ml) exerted a very potent inhibitory effect on bFGF-induced angiogenesis (21.3 $\pm$ 6.3%, p $<$ 0.01). Taken together, these data support the involvement of mob-1 in the development of ARDS, conceivably through chemotactic actions on inflammatory cells and modulation of angiogenesis in the recovery phase of the syndrome. The clinical relevance of these findings awaits further investigation.
Abdullah, Fizan, "mob-1: A novel mediator of ARDS" (1996). ETD Collection for Thomas Jefferson University. AAI9625285.