Investigating miRNA-Mediated Bone Loss from Morphine Treatment

SUMMARY/ABSTRACT Opioids significantly decrease bone density and subsequently increase fracture risk, but preclinical studies addressing potential mechanisms are lacking. The nervous system is a primary target of opioids through activation of opioid receptors, and the innervation of bone, specifically by sensory neurons, is integral for bone homeostasis. MicroRNAs (miRNA) are small non-coding RNAs that regulate gene expression and can be secreted to affect various cell types, including bone cells. We have developed a model of opioid-induced bone loss through systemic morphine treatment, which significantly reduced trabecular bone microarchitecture, bone formation, and circulating miRNAs in male mice. Furthermore, several of the circulating miRNAs we identified were also significantly decreased in the bone of morphine-treated mice and have known associations with bone outcomes and/or opioid use. miRNA, miR-484 may be integral to reduced osteoblast mineralization based on high expression in healthy mouse and human bone, and it targets genes relevant to osteoblasts. This proposal will test the hypothesis that morphine suppresses neuronal miRNA expression, which impairs sensory-osteoblast communication through changes in gene expression and contributes to overall bone loss. In Aim 1, we will explore the mechanism of miRNA suppression by morphine through decreased biogenesis and/or secretion within the dorsal root ganglion (DRG), which house the cell bodies of sensory neurons. Specifically, we will treat mice with morphine for 2 or 4 weeks and determine how miRNA expression, biogenesis, and secretion are associated with progressive bone loss. Conditioned media treatment of primary osteoblasts from morphine-treated DRG will determine whether morphine indirectly impairs osteoblast mineralization. In Aim 2, we will identify the specific role of miR-484 in osteoblast function through in situ analysis of miR-484 in femora of morphine-treated mice as well as overexpression or knockdown of miR-484 in primary osteoblasts. miR-484 gene targets will be assessed at the gene and protein level in addition to identification of novel genes and pathways impacted by miR-484 through RNA sequencing. I will be trained and mentored by experts in the field at MHIR and external consultants, which will support my transition to a postdoctoral fellow focused on skeletal health. Findings will expand our understanding of opioid-induced bone loss through neural-skeletal miRNA communication. Further preclinical studies may then develop strategies to mitigate opioid-induced bone loss and inform clinical decisions in the face of the ongoing opioid epidemic.