Abstract 3312: Syndecan-4 Regulates Leukocyte Extravasation in Acute Lung Injury
Background: The pathophysiology of pulmonary inflammation leading to acute respiratory distress syndrome remains elusive. Its mortality remains high. Syndecan-4 (Sdc4), a transmembrane heparan-sulfate proteoglycan is upregulated in recruited alveolar monocytes after LPS-administration. We here examined the role of Sdc4 in pulmonary inflammation induced by LPS instillation.
Methods: LPS (15 μg; E. coli serotype 0111:B4) was intratracheally instilled in anesthetized Sdc4−/− and C57BL/6 wild-type (WT) mice. After 24h, blood was drawn from the infrarenal aorta for blood gas analysis. Leukocyte subpopulations were differentiated in cytospins of bronchoalveolar lavage fluid (BALF, 5 ml). Expression of cytokines and adhesion molecules was analyzed by real-time PCR in homogenized lung tissue. PMN and MØ distribution was immunochemically evaluated in PFA-fixed lung tissue. Transmigration of Sdc4−/− and WT PMNs through TNFα activated endothelial cells was analyzed in transmigration assays.
Results: Pulmonary LPS instillation in Sdc4−/− mice led to an increased inflammatory reaction in the lung signified by enhanced expression of IL-6 (5.3-fold) and TNFα (4.1-fold) (n=5) in lung tissue compared to WT. Sdc4−/− mice demonstrated an impaired gas exchange with lower arterial pO2 (107.2±27 vs.142±15.8mmHg) and elevated pCO2 (27.8±7.2 vs 43.6±12.1mmHg; n=8, p<0.05). LPS-treated Sdc4−/− lung tissue exhibited 2-fold higher PMN counts (124.7±15.4 vs. 59.6±11; p<0.05), whereas numbers of PMNs in BALF were equal in Sdc4−/− and WT lungs. However, expression of ICAM-1, an endothelial adhesion molecule was reduced in Sdc4−/− mice (4.5±3.7 vs 6.4±1.5 fold, n=7, p<0.05). Transmigration rate through TNFα activated endothelial cells was reduced, when Sdc4−/− PMNs (3.9±0.3 vs 5.2±0.4) or Sdc4-specific-antibodies (3.0±0.2 vs 4.9±0.4) or a combination of both (1.6±0.1 vs 4.8±0.3) was used in comparison to WT PMNs or IgG controls.
Discussion: We demonstrate an anti-inflammatory effect of Sdc4 in lung tissue injury. On endothelial cells Sdc4 seems to regulate PMN transmigration through ICAM-1 expression, whereas on PMNs Sdc4 function need further examination, but provide already new molecular targets for interventions in lung inflammation.