Intra-Bone Marrow Administration of miR-140-3p Improves Bone Metabolism in a Growing Senescence-Accelerated Mouse Prone 6 Strain

<b>Background</b>: Our previous study demonstrated that miR-140-3p induced osteocalcin expression in osteoblastic MC3T3-E1 cells. In this study, we investigated the direct effects of miR-140-3p on bone turnover in senescence-accelerated mice. <b>Methods</b>: In order to evaluate the effects of miR-140-3p, we formulated lipid nanoparticles (LNPs) containing miR-140-3p (100 μg/mL), with or without flotillin-2 (Flo2), a microvesicle marker excreted by osteoblasts. LNP was administered into the right tibia of the P6 strain of senescence-accelerated mice (SAMP6). Four-week-old SAMP6 males were divided into three groups: control, LNP, and LNP + Flo2. LNPs were administered five times, once every three days. No gait abnormalities were observed in any group. Two days after the last administration of LNPs, blood and urine samples were collected to measure bone turnover markers and blood chemistry and to perform urinalysis. Bone histomorphometry was performed on the left femur, contralateral to the administration site. The pancreas was removed for insulin staining of the Langerhans islets. <b>Results</b>: The LNP + Flo2 group showed greater bone volume, trabecular thickness, and osteoid thickness in bone histomorphometry. Carboxylated osteocalcin, a bone formation marker, was also higher in the LNP + Flo2 group, indicating that LNP + Flo2 activated osteoblastic function. Insulin levels in the islets of Langerhans did not differ across the groups, consistent with under-carboxylated osteocalcin levels. <b>Conclusions</b>: LNP + Flo2 effectively improved bone metabolism.