NF-κB driven cardioprotective gene programs; Hsp70.3 and cardioprotection after late ischemic preconditioning

It has been shown that the transcription factor NF-κB is necessary for late phase cardioprotection after ischemic preconditioning (IPC) in the heart, and yet is injurious after ischemia/reperfusion (I/R). However the downstream gene expression programs that underlie the contribution of NF-κB to cardioprotection after late IPC are incompletely understood. The objective of this study was to delineate the specific genes that are regulated by NF-κB immediately after a late IPC stimulus and validate the methodology for the identification of NF-κB-dependent genes that contribute to cardioprotection. A directed microarray analysis identified 238 genes as up or downregulated in an NF-κB-dependent manner 3.5 h after late IPC. Among these are several genes previously implicated in late IPC. Gene ontological analysis showed that the most significant group of NF-κB-dependent genes are heat shock response genes, including the genes encoding Hsp70.1 and Hsp70.3. Though an Hsp70.1/70.3 double knockout failed to exhibit cardioprotection, late IPC was intact in the Hsp70.1 single knockout. After I/R, the Hsp70.1/70.3 double knockout and the Hsp70.1 single knockout had significantly increased and reduced infarct size, respectively. These results delineate the immediate NF-κB-dependent transcriptome after late IPC. One of the major categories of NF-κB-dependent genes induced by late IPC is the heat shock response. The results of infarct studies confirm that Hsp70.3 is protective after IPC. However, though Hsp70.1 and Hsp70.3 are coordinately regulated, their functions are opposing after I/R injury.

Research highlights
► Our results show that NF-κB regulates a unique set of 238 genes after late IPC; several of these have been previously implicated in late IPC.
► NF-κB regulates genes that fall primarily into three functional categories; angiogenesis, programmed cell death and heat shock response.
► One of these genes, Hsp70.3, is shown to be functionally cardioprotective, while the related Hsp70.1 is not.
► Hsp 70.1 is injurious after I/R injury, and thus functionally opposed to Hsp70.3.
► NF-κB thus regulates multiple genes which contribute to late IPC.