Interdependent Nuclear Co-Trafficking of ASPP1 and p53 Aggravates Cardiac Ischemia/Reperfusion Injury

Abstract

OBJECTIVE: ASPP1 (apoptosis stimulating of p53 protein 1) is critical in regulating cell apoptosis as a cofactor of p53 to promote its transcriptional activity in the nucleus. However, whether cytoplasmic ASPP1 affects p53 nuclear trafficking and its role in cardiac diseases remains unknown. This study aims to explore the mechanism by which ASPP1 modulates p53 nuclear trafficking and the subsequent contribution to cardiac ischemia/reperfusion (I/R) injury. METHODS AND RESULTS: The immunofluorescent staining showed that under normal condition ASPP1 and p53 colocalized in the cytoplasm of neonatal mouse ventricular cardiomyocytes, while they were both upregulated and translocated to the nuclei upon hypoxia/reoxygenation treatment. The nuclear translocation of ASPP1 and p53 was interdependent, as knockdown of either ASPP1 or p53 attenuated nuclear translocation of the other one. Inhibition of importin-β1 resulted in the cytoplasmic sequestration of both p53 and ASPP1 in neonatal mouse ventricular cardiomyocytes with hypoxia/reoxygenation stimulation. Overexpression of ASPP1 potentiated, whereas knockdown of ASPP1 inhibited the expression of Bax (Bcl2-associated X), PUMA (p53 upregulated modulator of apoptosis), and Noxa, direct apoptosis-associated targets of p53. ASPP1 was also increased in the I/R myocardium. Cardiomyocyte-specific transgenic overexpression of ASPP1 aggravated I/R injury as indicated by increased infarct size and impaired cardiac function. Conversely, knockout of ASPP1 mitigated cardiac I/R injury. The same qualitative data were observed in neonatal mouse ventricular cardiomyocytes exposed to hypoxia/reoxygenation injury. Furthermore, inhibition of p53 significantly blunted the proapoptotic activity and detrimental effects of ASPP1 both in vitro and in vivo. CONCLUSIONS: Binding of ASPP1 to p53 triggers their nuclear cotranslocation via importin-β1 that eventually exacerbates cardiac I/R injury. The findings imply that interfering the expression of ASPP1 or the interaction between ASPP1 and p53 to block their nuclear trafficking represents an important therapeutic strategy for cardiac I/R injury.

Myofibroblast-specific inhibition of ASPP1 alleviates myocardial fibrosis by enhancing p53 degradation

“…In cardiac ischemia-reperfusion injury, ASPP1 promotes cardiomyocyte apoptosis and severely impairs cardiac function. Different from the pro-apoptotic effects of ASPP1 in cancer cells and cardiomyocytes 9,22 , we discovered an interesting ability of ASPP1 to promote cardiac broblast proliferation and facilitate the development of cardiac brosis in the present study. ASPP1 exerts pro-apoptotic effects by tra cking to the nucleus to activate p53 or p53 family members and selectively enhance the transcription of pro-apoptotic genes downstream of p53 22,23 .…”

“…Among them, ASPP1 and ASPP2 augment the proapoptotic function of p53 by activating p53mediated transcription of proapoptotic genes, whereas iASPP has the opposite effect 8 . In a recent work, we found that ASPP1 exacerbates myocardial dysfunction following ischemia-reperfusion injury by binding to p53 and promoting myocardial apoptosis 9 . Mechanistically, ASPP1 facilitates the nuclear translocation of p53 and enhances the transcription of pro-apoptotic genes.…”

“…As deletion of ASPP1 is protective on cardiomyocytes during ischemia injury 9 , the above observed bene cial effects of ASPP1 deletion on chronic MI may be caused by the effects of ASPP1 de ciency in cardiomyocytes. We then generated conditional myo broblast ASPP1 deletion mice using tamoxifeninducible Postn promoter-driven MerCreMer transgene (Postn MCM ) technology to explore the contribution of myo broblast ASPP1 on post-infarct cardiac remodeling.…”

“…accumulates and drives p53 and p53 family members in the nucleus, enhancing p53 transcription and apoptosis function 22,23,29 . In cardiac ischemia/reperfusion (I/R) injury, the interaction between ASPP1 and p53 leads to their simultaneous translocation into the nucleus through importin-β1, ultimately facilitating cardiomyocytes apoptosis 9 . In this study, we found that in cardiac broblasts ASPP1 inhibits p53 and enhances broblast proliferation.…”

Early growth response-1: Key mediators of cell death and novel targets for cardiovascular disease therapy

“…Activated EGR1 can also promote apoptosis by transactivating the proapoptotic targets, such as Egr-1 itself. In an earlier study, the researchers identified a novel EGR1/ASPP inter-regulatory loop and determined the proapoptotic function of cytoplasmic ASPP by stabilizing EGR1 and inhibiting the autophagy promoter ATG5 (Autophagy protein 5) -ATG12/ATG16 ( 57 , 58 ). The Tp53 controls TP53 by increasing its DNA binding and transactivation capabilities on proapoptotic gene promoters.…”