Let-7 in Sperm Impacts Offspring Opioid System

The United States is in the midst of an opioid addiction crisis, with exposure rates to opioids estimated to be over 3.3% of the population in 2021 alone. In addition to the devastating consequences to the current population, which include addiction, overdose, lost productivity, socioeconomic burdens, and social and familial

deterioration, a growing body of evidence indicates that opioid exposure will also affect subsequent generations and contributes to the inheritance of increased susceptibility to develop opioid use disorder. Using a rat model, we recently demonstrated that adolescent exposure to opioids increases addiction-like behaviors

in offspring (F1). In addition, we observe changes in the endogenous opioid system at early developmental timepoints in these rats. The endogenous opioid system plays a critical role in many functions including regulation of pain, immune response, gastrointestinal motility, and response to drugs of abuse. The

experiments proposed here will examine potential mechanisms underlying transmission of environmental exposure to opioids in sires to offspring. Paternal transmission is ideal because the confound of gestational and rearing environment is mitigated, as the only contribution from the sire is semen. Semen, and specifically

spermatozoa represent a cell type that undergoes vast epigenetic modifications and is well poised to carry environmental changes to the oocyte where it can regulate fetal development. Indeed, a growing body of evidence suggests that micro RNAs (miRNA) within sperm are one potential carrier by which changes in one

generation may affect the next. Recently, it was shown that exposure to morphine increases the expression of a let-7, which is a family of highly conserved miRNAs. Let-7 in turn, was shown to regulate the expression of opioid receptors. The goal of this grant is to utilize our rat model of familial inheritance of opioid use disorder to

test the role of let-7 in the transmission of increased susceptibility to self-administer oxycodone. In Aim 1 we will use miRNA inhibitors in sperm combined with artificial insemination to test if let-7 plays a role in the transmission of the behavioral phenotype observed in our model. We have preliminary data that demonstrates

increased levels of let-7 in sperm as well as dysregulation of opioid receptors at early developmental timepoints. We predict that decreasing let-7 in sperm will rescue the molecular and behavioral phenotypes in F1 offspring. In Aim 2 we will test if the consequences of male adolescent opioid exposure extend to the next

generation by measuring the self-administration behavior of the grand offspring (F2). These animals had no direct exposure to opioids. We predict that they will demonstrate increased oxycodone self-administration. The data that will be produced from the proposed experiments will directly test the role of let-7 as a mechanism of

transmission of behavioral phenotypes associated with paternal opioid exposure. In addition, these mechanisms can be expanded more broadly and represent means by which environmental stimuli can impact phenotypic variation of future progeny.