Nucleolin protects the heart from ischaemiareperfusion injury by up-regulating heat shock protein 32

Nucleolin plays important roles in a variety of cellular processes. In this study, we aimed to investigate the role of nucleolin in cardiac ischaemiareperfusion (IR) injury. We investigated the expression pattern of nucleolin in hearts subjected to IR, or neonatal rat cardiomyocytes subjected to hypoxiare-oxygenation. We found that nucleolin expression was significantly down-regulated and the cleaved protein was present, both in vivo and in vitro. Gene transfection and RNA interference approaches were employed in cardiomyocytes to investigate the function of nucleolin. Over-expression of nucleolin was cytoprotective, whereas nucleolin ablation enhanced both hypoxia- and H2O2-induced cardiomyocyte death. Furthermore, transgenic mice with cardiac-specific over-expression of nucleolin were resistant to IR injury as indicated by decreased cellular necrosis and decreased infarct size. The cardio-protective roles of nucleolin in cardiomyocytes, are attributable to the interaction of nucleolin with the mRNA of heat shock protein 32 (Hsp32), resulting in an increase of Hsp32 mRNA stability, and subsequent up-regulation of Hsp32 expression. The selective Hsp32 inhibitor, zinc protoporphyrin-IX, abrograted the cardiac protection mediated by nucleolin. This study has demonstrated that nucleolin is involved in the regulation of IR-induced cardiac injury and dysfunction via the regulation of Hsp32, and may be a novel therapeutic target for ischaemic heart diseases.