Gary A. Visner

Oxidants and Antioxidants

Oxidants are an important source of injury to cells and tissues. The lung is exposed to significantly more oxidants than are most other organs. The lung is unique because of its large epithelial surface area that is directly exposed to high levels of oxygen tension, that is, oxygen pressure in inhaled air is 20 kPa (150 mm Hg). Ambient air contains additional oxidants, including cigarette smoke, asbestos fibers, mineral dust, and environmental carcinogens. A common component in most lung disease is activation of the inflammatory response, which leads to the generation of a relatively large quantity of oxidants. Even some therapeutic interventions, such as ventilation and oxygen therapy in the treatment of prematurely born neonates and acute respiratory distress syndrome, or chemotherapeutic agents, including bleomycin, carmustine, and anthracyclines, enhance oxidant burden to lung tissue.1 Thus, the lung represents a unique tissue exposed not only directly to external environmental oxidants under nor mal conditions but also to inflammation- and therapy-associated oxidants in disease state.

The Ashwell-Morell receptor regulates hepatic thrombopoietin production via JAK2-STAT3 signaling

The hepatic Ashwell-Morell receptor (AMR) can bind and remove desialylated platelets. Here we demonstrate that platelets become desialylated as they circulate and age in blood. Binding of desialylated platelets to the AMR induces hepatic expression of thrombopoietin (TPO) mRNA and protein, thereby regulating platelet production. Endocytic AMR controls TPO expression through Janus kinase 2 (JAK2) and the acute phase response signal transducer and activator of transcription 3 (STAT3) in vivo and in vitro. Recognition of this newly identified physiological feedback mechanism illuminates the pathophysiology of platelet diseases, such as essential thrombocythemia and immune thrombocytopenia, and contributes to an understanding of the mechanisms of thrombocytopenia observed with JAK1/2 inhibition.

Rapamycin Induces Heme Oxygenase-1 in Human Pulmonary Vascular Cells Implications in the Antiproliferative Response to Rapamycin

Background—Rapamycin is an immunosuppressive agent with antiproliferative properties against not only lymphocytes but also vascular endothelial and smooth muscle cells, and it reduces the fibroproliferative response to vascular injury. Heme oxygenase-1 (HO-1) has also been shown to have graft protective effects and to inhibit vascular remodeling. In this study, we evaluated whether there is an interaction between rapamycin and HO-1. Methods and Results—In human pulmonary artery endothelial or smooth muscle cells, HO-1 expression was evaluated in response to rapamycin or wortmannin, an inhibitor of the upstream modulator of mammalian target of rapamycin (mTOR) PI-3K. We also evaluated whether the inhibitory actions of rapamycin on platelet-derived growth factor–dependent proliferation was mediated by HO using the chemical inhibitor tin protoporphyrin. Rapamycin induced HO-1 expression in both pulmonary endothelial and smooth muscle cells, whereas no to little increase was seen in response to another immunosuppressive agent, cyclosporin A. HO-1 expression was also increased in response to wortmannin, suggesting that the PI-3K–mTOR pathway is required for this induction. Inhibition of HO activity resulted in a loss of the antiproliferative activity of rapamycin in growth factor–stimulated smooth muscle cells. Conclusions—The induction of HO-1 expression by rapamycin and, more importantly, the effects of tin protoporphyrin, an inhibitor of HO activity, on the antiproliferative actions of rapamycin suggest that the effects of rapamycin may be, at least in part, modulated by its actions on HO-1.

Smad7-dependent Regulation of Heme Oxygenase-1 by Transforming Growth Factor-β in Human Renal Epithelial Cells

Heme oxygenase-1 (HO-1), a 32-kDa microsomal enzyme, is induced as a beneficial and adaptive response in cells/tissues exposed to oxidative stress. Transforming growth factor-β1 (TGF-β1) is a regulatory cytokine that has been implicated in a variety of renal diseases where it promotes extracellular matrix deposition and proinflammatory events. We hypothesize that the release of TGF-β1 via autocrine and/or paracrine pathways may induce HO-1 and serve as a protective response in renal injury. To understand the molecular mechanism of HO-1 induction by TGF-β1, we exposed confluent human renal proximal tubule cells to TGF-β1 and observed a significant induction of HO-1 mRNA at 4 h with a maximal induction at 8 h. This induction was accompanied by increased expression of HO-1 protein. TGF-β1 treatment in conjunction with actinomycin D or cycloheximide demonstrated that induction of HO-1 mRNA requires de novo transcription and, in part, protein synthesis. Exposure to TGF-β1 resulted in marked induction of Smad7 mRNA with no effect on Smad6 expression. Overexpression of Smad7, but not Smad6, inhibited TGF-β1-mediated induction of endogenous HO-1 gene expression. We speculate that the induction of HO-1 in the kidney is an adaptive response to the inflammatory effects of TGF-β1 and manipulations of the Smad pathway to alter HO-1 expression may serve as a potential therapeutic target.

Sleeping Beauty-based gene therapy with indoleamine 2,3-dioxygenase inhibits lung allograft fibrosis

Sleeping Beauty (SB) transposon is a natural nonviral gene transfer system that can mediate long‐term transgene expression. Its potential utility in treating organ transplantation‐associated long‐term complications has not yet been explored. In the present study we generated an improved SB transposon encoding the human gene indoleamine‐2,3‐dioxygenase (hIDO), an enzyme that possesses both T cell‐suppressive and antioxidant properties and selectively delivered the SB transposon in combination with a hyperactive transposase plasmid to donor lung using the cationic polymer polyethylenimine (PEI) as transfection reagent. This nonviral gene therapeutic approach led to persistent and uniform transgene expression in the rat lung tissue without noticeable toxicity and inflammation. Importantly, IDO activity produced by hIDO transgene showed a remarkable therapeutic response, as evident by near normal pulmonary function (peak airway pressure and oxygenation), histological appearance, and reduced collagen content in lung allografts. In addition, we established a hIDO‐overexpressing type II cell line using the SB‐based gene transfer system and found that hIDO‐overexpressing lung cells effectively inhibited transforming growth factor–stimulated fibroblast proliferation in vitro. In summary, the SB‐based gene therapy with hIDO represents a new strategy for treating lung transplantation‐associated chronic complications, e.g., obliterative bronchiolitis.—Liu, H., Liu, L., Fletcher, B. S., Visner, G. A. Sleeping Beauty‐based gene therapy with indoleamine 2,3‐dioxygenase inhibits lung allograft fibrosis. FASEB J. 20, E1694 –E1703 (2006)

Regulation of manganese superoxide dismutase: IL-1 and TNF induction in pulmonary artery and microvascular endothelial cells

IL-1 and TNF are important mediators in the inflammatory response, and have been associated with endothelial cell damage in the lung. TNF and IL-1 cell-mediated injury has been proposed to occur through an increase in intracellular oxygen free radical production. However, these cytokines have also been shown to protect the lung from hyperoxia-mediated oxidant injury. In this paper we evaluated the response of the antioxidant enzymes, MnSOD and Cu/ZnSOD to IL-1, TNF, and LPS in both rat pulmonary artery and microvascular endothelial cells. These mediators produced an increase in MnSOD but not Cu/ZnSOD expression in both rat pulmonary endothelial cells. An additive effect was observed with co-treatment by the cytokines with LPS. The MnSOD mRNA induction is dependent upon a transcriptional event, but did not require de novo protein synthesis.

Resistance to hyperoxia with heme oxygenase-1 disruption: role of iron

In many models, a protective role for heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, has been demonstrated. Also, HO-1 null mice (KO) are more susceptible to inflammation and hypoxia and transplant rejection. Nonetheless, their response to hyperoxia (> 95% O(2)) has not yet been evaluated. Surprisingly, after acute hyperoxic exposure, KO had significantly decreased markers of lung oxidative injury and survived chronic hyperoxia as well as wild-type (WT) controls. Disrupted HO-1 expression was associated with decreased lung reactive iron and iron-associated proteins, decreased NADPH cytochrome cp450 reductase activity, and decreased lung peroxidase activity compared to WT. Injection of tin protoporphyrin, an inhibitor of HO, in the WT decreased acute hyperoxic lung injury, whereas transduction of human HO-1 in the KO reversed the relative protection of the KO to acute injury and worsened hyperoxic survival. This suggests that disruption of HO-1 protects against hyperoxia by diminishing the generation of toxic reactive intermediates in the lung via iron and H(2)O(2).

Heme oxygenase-1 mediates the protective effects of rapamycin in monocrotaline-induced pulmonary hypertension

Rapamycin inhibits the development and progression of vascular disease. We previously showed that rapamycin induces the cytoprotective protein, heme oxygenase-1 (HO-1), and more importantly, chemically inhibiting HO-1 blocked the antiproliferative actions of rapamycin. In this study, we evaluated whether HO-1 is required for the vascular protective effects of rapamycin in vivo using a rat monocrotaline-induced pulmonary hypertension model. Rats were exposed to monocrotaline with or without rapamycin and HO activity was altered using the chemical inhibitor, tin protoporphyrin or the inducer, cobalt protoporphyrin. We also evaluated possible mechanisms of rapamycin-dependent induction of HO-1, and how HO-1 mediates growth factor-dependent antiproliferative actions of rapamycin. Proliferation and cell cycle progression were examined in smooth muscle cells derived from both wild-type and HO-1 knockout (HO-1−/−) mice in response to growth factors and rapamycin. Similar to our previous findings in vitro, rapamycin induced HO-1 in rat lung. Rapamycin also inhibited the development of monocrotaline-induced pulmonary hypertension, and this protective effect was blocked with the addition of tin protoporphyrin. In addition, treatment with cobalt protoporphyrin resulted in a substantial protection in this model of pulmonary hypertension. Rapamycin induction of HO-1 was dependent upon a transcriptional event; however, it was not mediated through an altered redox state or mammalian targets of rapamycin inhibition. Unlike wild-type cells, the growth of HO-1−/− mouse aortic smooth muscle cells was not inhibited or cell cycle arrested in G1 in response to rapamycin. This study demonstrates that HO-1 is critical for the antiproliferative and vascular protective effects of rapamycin in vitro and in vivo in monocrotaline-induced pulmonary hypertension.

Long-Term Heart Transplant Survival by Targeting the Ionotropic Purinergic Receptor P2X7

Background— Heart transplantation is a lifesaving procedure for patients with end-stage heart failure. Despite much effort and advances in the field, current immunosuppressive regimens are still associated with poor long-term cardiac allograft outcomes, and with the development of complications, including infections and malignancies, as well. The development of a novel, short-term, and effective immunomodulatory protocol will thus be an important achievement. The purine ATP, released during cell damage/activation, is sensed by the ionotropic purinergic receptor P2X7 (P2X7R) on lymphocytes and regulates T-cell activation. Novel clinical-grade P2X7R inhibitors are available, rendering the targeting of P2X7R a potential therapy in cardiac transplantation. Methods and Results— We analyzed P2X7R expression in patients and mice and P2X7R targeting in murine recipients in the context of cardiac transplantation. Our data demonstrate that P2X7R is specifically upregulated in graft-infiltrating lymphocytes in cardiac-transplanted humans and mice. Short-term P2X7R targeting with periodate-oxidized ATP promotes long-term cardiac transplant survival in 80% of murine recipients of a fully mismatched allograft. Long-term survival of cardiac transplants was associated with reduced T-cell activation, T-helper cell 1/T-helper cell 17 differentiation, and inhibition of STAT3 phosphorylation in T cells, thus leading to a reduced transplant infiltrate and coronaropathy. In vitro genetic upregulation of the P2X7R pathway was also shown to stimulate T-helper cell 1/T-helper cell 17 cell generation. Finally, P2X7R targeting halted the progression of coronaropathy in a murine model of chronic rejection as well. Conclusions— P2X7R targeting is a novel clinically relevant strategy to prolong cardiac transplant survival.

Pirfenidone Inhibits Lung Allograft Fibrosis through L-Arginine-Arginase Pathway

Transplant‐related lung fibrosis is characterized by excessive fibro‐collagenous deposition. Induction of arginase, an enzyme that metabolizes L‐arginine to urea and L‐ornithine, is vital for collagen synthesis. Pirfenidone is an investigational anti‐fibrotic agent shown to be effective in blocking pulmonary fibrosis. The purpose of this study was to determine if pirfenidone was protective against the development of fibro‐collagenous injury in rat lung orthotopic transplants through altering L‐arginine–arginase metabolic pathways. Lung transplants were performed using Lewis donors and Sprague‐Dawley recipients (allografts) or the same strain (isografts). Recipients were given pirfenidone (0.5% chow) 1–21‐day post‐transplantation. A significantly increased peak airway pressure (PawP) with excessive collagen deposition was found in untreated lung allografts. Pirfenidone treatment decreased PawP and collagen content in lung allografts. The beneficial effects were associated with downregulation of arginase protein expression and activity. In addition, pirfenidone decreased endogenous transforming growth factor (TGF)‐β level in lung allografts, and TGF‐β stimulated arginase activity in a dose‐dependent manner in both lung tissue and fibroblasts. These results suggest that pirfenidone inhibits local arginase activity possibly through suppression of endogenous TGF‐β, hence, limiting the development of fibrosis in lung allografts.