BACKGROUND Airway remodeling is a significant contributor to impaired lung function in chronic allergic airway disease. Currently, no therapy exists that is capable of targeting these structural changes and the consequent loss of function. In the context of chronic allergic inflammation, pericytes have been shown to uncouple from the pulmonary microvasculature, migrate to areas of inflammation, and significantly contribute to airway wall remodeling and lung dysfunction. This study aimed to elucidate the mechanism by which pulmonary pericytes accumulate in the airway wall in a model of chronic allergic airway inflammation. METHODS Mice were subjected to a protocol of chronic airway inflammation driven by the common environmental aeroallergen house dust mite. Phenotypic changes to lung pericytes were assessed by flow cytometry and immunostaining, and the functional capacity of these cells was evaluated using in vitro migration assays. The molecular mechanisms driving these processes were targeted pharmacologically in vivo and in vitro. RESULTS Pericytes demonstrated increased CXCR4 expression in response to chronic allergic inflammation and migrated more readily to its cognate chemokine, CXCL12. This increase in migratory capacity was accompanied by pericyte accumulation in the airway wall, increased smooth muscle thickness, and symptoms of respiratory distress. Pericyte uncoupling from pulmonary vessels and subsequent migration to the airway wall were abrogated following topical treatment with the CXCL12 neutraligand LIT-927. CONCLUSION These results provide new insight into the role of the CXCL12/CXCR4 signaling axis in promoting pulmonary pericyte accumulation and airway remodeling and validate a novel target to address tissue remodeling associated with chronic inflammation.

Sepsis remains an important health problem worldwide due to inefficient treatments often resulting in multi-organ failure. Neutrophil recruitment is critical during sepsis. While neutrophils are required to combat invading bacteria, excessive neutrophil recruitment contributes to tissue damage due to their arsenal of molecular weapons that do not distinguish between host and pathogen. Thus, neutrophil recruitment needs to be fine-tuned to ensure bacterial killing, while avoiding neutrophil-inflicted tissue damage. We recently showed that the actin-binding protein HS1 promotes neutrophil extravasation; and hypothesized that HS1 is also a critical regulator of sepsis progression. We evaluated the role of HS1 in a model of lethal sepsis induced by cecal-ligation and puncture. We found that septic HS1-deficient mice had a better survival rate compared to WT mice due to absence of lung damage. Lungs of septic HS1-deficient mice showed less inflammation, fibrosis, and vascular congestion. Importantly, systemic CLP-induced neutrophil recruitment was attenuated in the lungs, the peritoneum and the cremaster in the absence of HS1. Lungs of HS1-deficient mice produced significantly more interleukin-10. Compared to WT neutrophils, those HS1-deficient neutrophils that reached the lungs had increased surface levels of Gr-1, ICAM-1, and L-selectin. Interestingly, HS1-deficient neutrophils had similar F-actin content and phagocytic activity, but they failed to polymerize actin and deform in response to CXCL-1 likely explaining the reduced systemic neutrophil recruitment in HS1-deficient mice. Our data show that HS1 deficiency protects against sepsis by attenuating neutrophil recruitment to amounts sufficient to combat bacterial infection, but insufficient to induce tissue damage.

Structural bone allografts are widely used in the clinic to treat critical sized bone defects, despite lacking the osteoinductive characteristics of live autografts. To address this, we generated revitalized structural allografts wrapped with mesenchymal stem/progenitor cell (MSC) sheets, which were produced by expanding primary syngenic bone marrow derived cells on temperature-responsive plates, as a tissue-engineered periosteum. In vitro assays demonstrated maintenance of the MSC phenotype in the sheets, suggesting that short-term culturing of MSC sheets is not detrimental. To test their efficacy in vivo, allografts wrapped with MSC sheets were transplanted into 4-mm murine femoral defects and compared to allografts with direct seeding of MSCs and allografts without cells. Evaluations consisted of X-ray plain radiography, 3D microCT, histology, and biomechanical testing at 4- and 6-weeks post-surgery. Our findings demonstrate that MSC sheets induce prolonged cartilage formation at the graft-host junction and enhanced bone callus formation, as well as graft-host osteointegration. Moreover, a large periosteal callus was observed spanning the allografts with MSC sheets, which partially mimics live autograft healing. Finally, biomechanical testing showed a significant increase in the structural and functional properties of MSC sheet grafted femurs. Taken together, MSC sheets exhibit enhanced osteogenicity during critical sized bone defect repair, demonstrating the feasibility of this tissue engineering solution for massive allograft healing.