Alveolar heparan sulfate shedding impedes recovery from bleomycin-induced lung injury

The pulmonary epithelial glycocalyx, an anionic cell surface layer enriched in glycosaminoglycans such as heparan sulfate and chondroitin sulfate, contributes to the alveolar barrier. Direct injury to the pulmonary epithelium induces shedding of heparan sulfate into the air space; the impact of this shedding on recovery after lung injury is unknown. Using mass spectrometry, we found that heparan sulfate was shed into the air space for up to 3 wk after intratracheal bleomycin-induced lung injury and coincided with induction of matrix metalloproteinases (MMPs), including MMP2. Delayed inhibition of metalloproteinases, beginning 7 days after bleomycin using the nonspecific MMP inhibitor doxycycline, attenuated heparan sulfate shedding and improved lung function, suggesting that heparan sulfate shedding may impair lung recovery. While we also observed an increase in air space heparanase activity after bleomycin, pharmacological and transgenic inhibition of heparanase in vivo failed to attenuate heparan sulfate shedding or protect against bleomycin-induced lung injury. However, experimental augmentation of airway heparanase activity significantly worsened post-bleomycin outcomes, confirming the importance of epithelial glycocalyx integrity to lung recovery. We hypothesized that MMP-associated heparan sulfate shedding contributed to delayed lung recovery, in part, by the release of large, highly sulfated fragments that sequestered lung-reparative growth factors such as hepatocyte growth factor. In vitro, heparan sulfate bound hepatocyte growth factor and attenuated growth factor signaling, suggesting that heparan sulfate shed into the air space after injury may directly impair lung repair. Accordingly, administration of exogenous heparan sulfate to mice after bleomycin injury increased the likelihood of death due to severe lung dysfunction. Together, our findings demonstrate that alveolar epithelial heparan sulfate shedding impedes lung recovery after bleomycin.

High dose inhaled fluticasone propionate improves FEV1 and results in reduction of oral glucocorticoid dose in glucocorticoid-dependent children with severe asthma

A retrospective chart review was performed on eight pediatric patients with glucocorticoid (GC)-dependent asthma who had been switched to fluticasone propionate (FP). A significant increase was noted in average forced expiratory volume in 1 second (FEV1) and forced expiratory flow 25-75% (FEF25-75) at 6 and 12 months. Significant reductions were noted in the oral GC dose at 6 and 12 months with a reduction at 12 months of almost 16.5 mg/day or 65% of the initial oral GC dose. This study suggests that high-dose FP use in children with oral GC-dependent asthma has oral GC sparing effects while improving FEV1 and FEF25-75.

Transcriptional regulation of CD6 expression on human T lymphocytes by phorbol ester

Activation of protein kinase C (PKC) has emerged as a major common signal-transducing mechanism for T cell activation and regulation of expression of T cell surface glycoproteins. Surface expression of the CD6 Ag is known to increase with T cell activation and CD6 itself may be involved in regulation of T cell activation. Therefore, we performed experiments to determine whether activation of PKC by phorbol ester induced an increase in CD6 expression and to investigate the mechanisms of such an effect. CD6 surface expression was up-regulated substantially in response to PMA on both mature and immature T cells, but only negligibly on B cell lines. This increase was blocked by PKC inhibitors. The PMA-induced increase in CD6 surface expression was accompanied by an increase in total CD6 protein, as detected by using Western blot analysis of whole cell lysates. After PMA stimulation, Northern blot analysis showed that steady state levels of CD6 mRNA increased in response to PMA treatment. This increase was blocked by cycloheximide, demonstrating that it was dependent on new protein synthesis. Nuclear run-on analysis showed that the rate of CD6 mRNA transcription increased by approximately two to threefold after PMA stimulation of Jurkat cells. Experiments in which we used actinomycin D showed that PMA had no significant effect on the t1/2 of CD6 mRNA. The data suggest that the effect of PMA on CD6 expression is mediated primarily by an increase in CD6 mRNA transcription after PKC activation. mAbs were used to determine whether augmented CD6 expression could be induced by perturbation of specific T cell surface molecules. Up-regulation of CD6 expression occurred when thymocytes were cultured with anti-CD2 Abs, but not with Abs to other functional T cell surface structures, and not when mature T cells were cultured with the anti-CD2 mAbs. Up-regulation of CD6 expression by activation of PKC, triggered in thymocytes by ligation of CD2, could allow CD6 to provide additional regulatory signals required for events in later stages of T cell activation and differentiation.

Transcriptional regulation of CD6 expression on human T lymphocytes by phorbol ester

Activation of protein kinase C (PKC) has emerged as a major common signal-transducing mechanism for T cell activation and regulation of expression of T cell surface glycoproteins. Surface expression of the CD6 Ag is known to increase with T cell activation and CD6 itself may be involved in regulation of T cell activation. Therefore, we performed experiments to determine whether activation of PKC by phorbol ester induced an increase in CD6 expression and to investigate the mechanisms of such an effect. CD6 surface expression was up-regulated substantially in response to PMA on both mature and immature T cells, but only negligibly on B cell lines. This increase was blocked by PKC inhibitors. The PMA-induced increase in CD6 surface expression was accompanied by an increase in total CD6 protein, as detected by using Western blot analysis of whole cell lysates. After PMA stimulation, Northern blot analysis showed that steady state levels of CD6 mRNA increased in response to PMA treatment. This increase was blocked by cycloheximide, demonstrating that it was dependent on new protein synthesis. Nuclear run-on analysis showed that the rate of CD6 mRNA transcription increased by approximately two to threefold after PMA stimulation of Jurkat cells. Experiments in which we used actinomycin D showed that PMA had no significant effect on the t1/2 of CD6 mRNA. The data suggest that the effect of PMA on CD6 expression is mediated primarily by an increase in CD6 mRNA transcription after PKC activation. mAbs were used to determine whether augmented CD6 expression could be induced by perturbation of specific T cell surface molecules. Up-regulation of CD6 expression occurred when thymocytes were cultured with anti-CD2 Abs, but not with Abs to other functional T cell surface structures, and not when mature T cells were cultured with the anti-CD2 mAbs. Up-regulation of CD6 expression by activation of PKC, triggered in thymocytes by ligation of CD2, could allow CD6 to provide additional regulatory signals required for events in later stages of T cell activation and differentiation.