MiR-21 Lowers Blood Pressure in Spontaneous Hypertensive Rats By Up-Regulating Mitochondrial Translation
Background—Excessive reactive oxygen species (ROS) generated in mitochondria has been implicated as a causal event in hypertensive cardiomyopathy. Multiple recent studies suggest that miRNAs are able to translocate to mitochondria to modulate mitochondrial activities, but the medical significance of such new miRNA function has remained unclear. Here we characterized spontaneous hypertensive rats (SHRs) in comparison with Wistar rats, finding that miR-21 was dramatically induced in SHRs relative to Wistar rats. We designed a series of experiments to determine whether miR-21 is involved in regulating ROS generation in mitochondria, and if so, how induced miR-21 may either contribute to hypertensive cardiomyopathy or represent a compensatory response.
Methods—Western blotting was used to compare the expression of key nuclear genome (nDNA)-encoded and mitochondrial genome (mtDNA)-encoded genes involved in ROS production in SHRs and Wistar rats. Bioinformatics was used to predict miRNA targets followed by biochemcial validation using real-time PCR (qRT-PCR) and Ago2 immunoprecipitation. Direct role of miRNA in mitochondria was determined by GW182 dependency, which is required for miRNA to function in the cytoplasm, but not in mitochondria. rAAV9 was used to deliver miRNA mimic to rats via tail vein and blood pressure was monitored with a photoelectric tail-cuff system. Cardiac structure and functions were assessed by echocardiography and catheter manometer system.
Results—We observed a marked reduction of mt-Cytb in the heart of SHRs. Down-regulation of mt-Cytb by siRNA in mitochondria recapitulates some key disease features, including elevated ROS production. Computational prediction coupled with biochemical analysis revealed that miR-21 directly targeted mt-Cytb to positively modulate mt-Cytb translation in mitochondria. Circulating miR-21 levels in hypertensive patients were significantly higher than those in controls, showing a positive correlation between miR-21 expression and blood pressure. Remarkably, rAAV-mediated delivery of miR-21 was sufficient to reduce blood pressure and attenuate cardiac hypertrophy in SHRs.
Conclusions—Our findings reveal a positive function of miR-21 in mitochondrial translation, which is sufficient to reduce blood pressure and alleviate cardiac hypertrophy in SHRs. This observation indicates that induced miR-21 is part of the compensatory program and suggests a novel theoretical ground for developing miRNA-based therapeutics against hypertension.
- Received November 26, 2015.
- Revision received July 4, 2016.
- Accepted July 20, 2016.