Spatiotemporal expression of heme oxygenase-1 detected by in vivo bioluminescence after hepatic ischemia in HO-1/luc mice

Upregulation of heme oxygenase-1 (HO-1) has been proposed as a critical mechanism protecting against cellular stress during liver transplantation, providing a potential target for new therapeutic interventions. We investigated the feasibility of in vivo bioluminescence imaging (BLI) to noninvasively quantify the spatiotemporal expression of HO-1 after warm hepatic ischemia in living animals. Luciferase activity was measured by BLI as an index of HO-1 transcription in transgenic reporter mice (Ho1-luc) at standardized time points after 60 minutes of warm hepatic ischemia. HO-1 mRNA levels were measured in postischemic livers of mice sacrificed at the same time points in separate experiments. Bioluminescent signals from postischemic liver lobes were first detected at 3 hours after reperfusion. Peak levels were reached at 9 hours, after which bioluminescent activity declined and returned to baseline values at 48 hours after reperfusion. Upregulation of HO-1 as detected by in vivo BLI was preceded by increased HO-1 mRNA expression and confirmed by enhanced immunohistochemical staining of hepatocytes. In conclusion, this study shows that in vivo BLI allows a sensitive assessment of HO-1 expression after hepatic ischemia in living animals. The capability of whole-body temporal imaging of HO-1 expression provides a valuable tool in the evelopment of novel strategies to modulate HO-1 expression in liver transplantation.