Regulation of Opioid Tolerance by let-7 Family MicroRNA Targeting the μ Opioid Receptor

TLDR

MicroRNAs are critical regulators of neuronal functions. The study tests whether let‑7 microRNAs regulate the μ‑opioid receptor and opioid tolerance. Bioinformatics identified a let‑7 binding site in the 3′‑UTR of MOR mRNA, experimentally confirmed as a direct target, and LNA‑let‑7 inhibition in SH‑SY5Y cells showed that let‑7 represses MOR by translocating its mRNA to P‑bodies and blocking translation. Morphine upregulates let‑7, and LNA‑let‑7 inhibition reduces brain let‑7 and partially reverses opioid tolerance, with let‑7 mediating translational repression of MOR without altering total transcript, indicating let‑7’s key role in opioid tolerance.

Abstract

MicroRNA has emerged as a critical regulator of neuronal functions. This study aimed to test whether let-7 microRNAs can regulate the μ opioid receptor (MOR) and opioid tolerance. Employing bioinformatics, we identified a let-7 binding site in the 3′-untranslated region (UTR) of MOR mRNA, which was experimentally confirmed as a direct target of let-7. The repressive regulation of MOR by let-7 was revealed using a LNA-let-7 inhibitor to knockdown let-7 in SH-SY5Y cells. Conversely, morphine significantly upregulated let-7 expression in SH-SY5Y cells and in a mouse model of opioid tolerance. The LNA-let-7 inhibitor decreased brain let-7 levels and partially attenuated opioid antinociceptive tolerance in mice. Although chronic morphine treatment did not change overall MOR transcript, polysome-associated mRNA declined in a let-7-dependent manner. let-7 was identified as a mediator translocating and sequestering MOR mRNA to P-bodies, leading to translation repression. These results suggest that let-7 plays an integral role in opioid tolerance.