Rationale: MicroRNAs (miRs) are small, non-coding RNAs that function to post-transcriptionally regulate gene expression. First transcribed as long primary miR transcripts (pri-miRs), they are enzymatically processed in the nucleus by Drosha into hairpin intermediate miRs (pre-miRs) and further processed in the cytoplasm by Dicer into mature miRs where they regulate cellular processes following activation by a variety of signals such as those stimulated by β-adrenergic receptors (βARs). Initially discovered to desensitize βAR signaling, β-arrestins are now appreciated to transduce multiple effector pathways independent of G protein-mediated second messenger accumulation, a concept known as biased signaling. We previously showed that the β-arrestin-biased βAR agonist carvedilol activates cellular pathways in the heart. Objective: Here, we tested whether carvedilol could activate β-arrestin-mediated miR maturation, thereby providing a novel potential mechanism for its cardioprotective effects. Methods and Results: In human cells and mouse hearts, carvedilol upregulates a subset of mature and pre-miRs but not their pri-miRs in β1AR-, G protein-coupled receptor kinase 5/6- and β-arrestin1-dependent manner. Mechanistically, β-arrestin1 regulates miR processing by forming a nuclear complex with hnRNPA1 and Drosha on pri-miRs. Conclusions: Our findings indicate a novel function for β1AR-mediated β-arrestin1 signaling activated by carvedilol in miR biogenesis, which may be linked, in part, to its mechanism for cell survival.

These estimates may help guide medical school administrators and policymakers to expand underserved clinical training programs to help relieve some of the problems associated with access to medical care among underserved populations.

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