Nucleostemin dysregulation contributes to ischemic vulnerability of diabetic hearts: Role of ribosomal biogenesis

Diabetes is a major health problem worldwide. As well-known, diabetes greatly increases cardiac vulnerability to ischemia/reperfusion (I/R) injury, but the underlying mechanisms remain elusive. Nucleostemin (NS) is a nucleolar protein that controls ribosomal biogenesis and exerts cardioprotective effects against I/R injury. However, whether NS-mediated ribosomal biogenesis regulates ischemic vulnerability of diabetic hearts remains unanswered. Utilizing myocardial I/R mouse models, we found that cardiac NS expression significantly increased in response to I/R in normal diet (ND)-fed mice. Surprisingly, cardiac NS failed to be upregulated in high fat diet (HFD)-induced diabetic mice, accompanied by obvious ribosomal dysfunction. Compared with ND group, cardiac specific overexpression of NS by adenovirus (AV) injection significantly restored I/R-induced ribosomal function enhancement, reduced cardiomyocyte apoptosis, improved cardiac function, and decreased infarct sizes in diabetic mice. Notably, co-treatment of homoharringtonine (HHT), a selective inhibitor of ribosomal function, totally blocked NS-mediated cardioprotective effects against I/R injury. Furthermore, in cultured cardiomyocytes, saturated fatty acids treatment, but not high glucose exposure, significantly inhibited simulated I/R-induced NS upregulation and ribosomal function improvement. In conclusion, these data for the first time demonstrate that NS dysregulation induced by saturated fatty acids exposure might be an important cause of increased ischemic vulnerability to I/R injury in diabetic hearts. Targeting NS dysregulation and subsequent ribosomal dysfunction could be a promising therapeutic strategy for diabetic I/R injury management.