In the current study, the expression profile of miRNAs in cardiac IP was identified. The results revealed that multiple miRNAs were regulated by IP (Table
). The multiple IP-regulated miRNAs found in this study match the complexity of IP, in which many genes are modulated.2
It is well established that an individual miRNA is functionally important as a transcription factor because of the ability to regulate the expression of its multiple target genes. Thus, miRNAs may play important roles in IP-mediated cardiac protection against ischaemic injury via regulating protection- or injury-related genes.
Recent studies revealed that miRNAs participated in ischaemic injury of the hearts, which provided indirect evidence that miRNAs may have potential roles in IP-mediated cardiac protection. First, multiple miRNAs are deregulated in human hearts with coronary artery disease.16
The potential involvement of miRNAs in acute myocardial infarction (AMI) is suggested in a study using miR-126 null mice, in which Wang et al
have found that the survival rate in miR-126 deficient mice following AMI is significantly reduced compared with that in wild-type mice. The expression signature in the late phase of AMI has just been identified by an excellent study reported by van Rooij et al
These investigators found that miR-29 plays an important role in cardiac fibrosis during the repair process after AMI. In an in vitro
I/R injury model, Yin et al
demonstrated that, in mouse hearts pre-injected with heat-shock (HS)-induced miRNAs including miR-21, myocardial infarct size after I/R injury in vitro
is reduced. More recently, using miR-320 transgenic mice, Fan and colleagues found that miR-320 was involved in the regulation of cardiac I/R by targeting Hsp20.20
In our recent study, miRNA expression signature in the early phase of AMI was identified. Moreover, we found that overexpression of miR-21 inhibited infarct size in rat hearts with AMI.10
The direct evidence showing that miRNAs are involved in cardiac IP was from recent two reports,8,9
in which the expression of miR-1, miR-21, miR-24, and miR-199a was regulated by IP. Moreover, injection of IP-miRNAs protected the hearts against I/R in a Langendorff mouse model.8
In the current study, we demonstrated in an in vivo
cardiac IP model that miR-21 was quickly upregulated by IP. Although miR-1, miR-24, and miR-199a were also mildly regulated by IP, the difference did not reach the 30% limitation compared with the controls. Notably, IP-mediated cardiac protection in rat heart in vivo
was inhibited by knockdown of cardiac miR-21 expression. The protective effect of miR-21 on ischaemic injury was further verified in an in vitro
cardiac cell H/R model. It should be noted that IP-mediated cardiac protection in rat hearts was only partially blocked by miR-21, suggesting that other mechanisms should be identified in future studies.
miR-21 is found to be an anti-apoptotic miRNA. However, its anti-apoptotic is cell specific. For example, miR-21 has a strong anti-apoptotic effect on many cancer cells; however, it has no effect on HeLa cell apoptosis.21
In our recent studies, we have found that vascular smooth muscle cell apoptosis is controlled by miR-21.11
In addition, miR-21 also has an apoptotic effect on cardiac cells induced by hydrogen peroxide (H2
In the current study, we identified that miR-21 was involved in IP-induced cardiac protection both in cultured cells in vitro
and in rat heart with I/R in vivo
PDCD4 is a critical mediator for cancer cell apoptosis. Our recent studies have revealed that PDCD4 is an important target gene of miR-21 that is related to miR-21-mediated anti-apoptotic effect on vascular smooth muscle cells.15
In the current study, the roles of PDCD4 as a target gene of miR-21 and a mediator in miR-21-mediated cardiac cell protection were further verified in cultured cardiac cells and in cardiac cell I/R model. It is still unclear that how quickly the PDCD4 could be regulated by miR-21 at the protein level. However, in a PDGF-stimulated rat cell model and in balloon-injured rat carotid arteries, we have found that both miR-21 and PDCD4 are able to be modulated quickly (data not shown). Thus, PDCD4 could be an active molecule under disease conditions.
In summary, miRNA signature in rat hearts with IP has revealed that multiple miRNAs are regulated by IP. Among them, miR-21 has a protective effect on I/R by reducing cardiac cell apoptosis via its target gene PDCD4. Identifying the roles of IP-regulated miRNAs in cardiac protection may provide novel therapeutic and preventive targets for ischaemic heart diseases.
Conflict of interest: none declared.