Clusterin Protects the Lung from Leukocyte-Induced Injury

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Abstract
Clusterin (CLU) is a multifunctional 75- to 80-kDa glycoprotein that is upregulated during cellular stress and might represent a defense mechanism during local cellular damage. Mechanisms discussed are antiapoptotic, antioxidative, and anticomplement properties as well as chaperone-like features protecting stressed proteins. The aim of this study was to investigate potential protective effects of CLU on pulmonary vasculature after in situ PMN activation in isolated rabbit lungs. The experiments were performed on 24 isolated and ventilated rabbit lungs that were perfused with 200 mL of Krebs-Henseleit-10% blood buffer with a constant flow of 150 mL/min in a recirculating system. It was tested whether pretreatment with CLU (2.5 μg/mL; n = 8) or catalase (CAT, 5000 U/mL; n = 8) before N-formyl-Met-Leu-Phe (fMLP; 10−8 M) injection influenced pulmonary artery pressure (PAP) peak airway pressures (PAW) and edema formation as compared with controls (n = 8). Baseline values of PAP were 9–11 mmHg and PAW 11–13 cmH2O. Application of fMLP resulted in an acute significant (P < 0.01) increase of PAP (48 ± 29 mmHg) within 2 min in the control group and PAW increased to 35 ± 7 cmH2O within 30min. Pretreatment with CLU completely suppressed the PAP and PAW response as a result of the fMLP challenge (P < 0.001), whereas a transient PAW increase up to 27 ± 15 mmHg was observed after CAT. Complement factor C3a release was suppressed by CAT, whereas CLU blocked the complement cascade at the level of C5b-9 formation. Moreover, generation of thromboxane A2 was reduced after CLU and CAT. Lung edema occurred in the fMLP group but was absent (P < 0.001) after CLU and CAT treatment. Both CLU and CAT prevented fMLP-induced lung injury. Stabilizing effects of CLU, point towards complement regulating features at the level of the terminal complement sequence. Elevated levels of CLU during inflammation could reflect a compensatory organ protective mechanism. Further studies are required to elucidate the clinical impact of the observed organ-protective properties of CLU.