muramidase and Acute-Lung-Injury

Lysozyme is an important component of the innate immune system and has roles in peptidoglycan cleavage of gram-positive organisms. Myeloid cells highly express the isoform, lysozyme M, and its promoter has been used to direct Cre recombinase expression to target deletion of floxed genes in myeloid cells. However, generation of the LysMCre mouse effectively disrupts the LysM gene, and mice homozygous for the Cre allele lack the LysM gene product. To test the contribution of LysM in sterile acute lung injury, we generated LysMCre mice homozygous for the Cre allele (+/+) or wild-type allele (-/-). These mice were challenged with LPS delivered via oropharygneal aspiration. Mice were monitored and weighed daily, and BAL cell counts, differential, protein, and cytokine levels were assessed at days 2 and 4. LysMCre+/+ and LysMCre-/- had similar weight loss and recovery, and similar inflammatory responses to LPS at days 2 and 4. These findings indicate that loss of LysM and expression of Cre recombinase are non-contributory in sterile acute lung injury.

Topics: Acute Lung Injury; Animals; Bronchoalveolar Lavage Fluid; Chemokine CCL2; Chemokine CXCL1; Cytokines; Gene Targeting; Homozygote; Inflammation; Integrases; Lipopolysaccharides; Mice; Muramidase; Myeloid Cells; Real-Time Polymerase Chain Reaction; Recovery of Function; Weight Loss

Type II alveolar epithelial cells (AEC2s) play a crucial role in the regeneration of type I AECs after acute lung injury. The mechanisms underlying the regeneration of AEC2s are not fully understood. To address this issue, here, we investigated a murine model of acute lung injury using mice expressing human Diphtheria Toxin Receptor (DTR) under the control of Lysozyme M promoter (LysM-DTR). DT injection induced the depletion of AEC2s, alveolar macrophages, and bone marrow (BM)-derived myeloid cells in LysM-DTR mice, and the mice died within 6 days after DT injection. Apoptotic AEC2s and bronchiolar epithelial cells appeared at 24 hr, whereas Ki67-positive proliferating cells appeared in the alveoli and bronchioles in the lung of LysM-DTR mice at 72-96 hr after DT injection. Transfer of wild-type BM cells into LysM-DTR mice accelerated the regeneration of AEC2s along with the up-regulation of several growth factors. Moreover, several metabolites were significantly decreased in the sera of LysM-DTR mice compared with WT mice after DT injection, suggesting that these metabolites might be biomarkers to predict AEC2s injury. Together, LysM-DTR mice might be useful to identify growth factors to promote lung repair and the metabolites to predict the severity of lung injury.

Topics: Acute Lung Injury; Alveolar Epithelial Cells; Animals; Biomarkers; Bone Marrow Transplantation; Diphtheria Toxin; Disease Models, Animal; Female; Gene Expression Profiling; Heparin-binding EGF-like Growth Factor; Humans; Intercellular Signaling Peptides and Proteins; Male; Metabolome; Mice; Mice, Inbred C57BL; Mice, Transgenic; Muramidase; Promoter Regions, Genetic; Wound Healing