Treadmill exercise influences the microRNA profiles in the bone tissues of mice

Abstract

As an important regulator involved in cell activity, microRNAs (miRNAs) are important in the process of exercise influencing bone metabolism. The present study aimed to detect and select differentially expressed miRNAs in the bone tissues of mice trained on a treadmill, predict the target genes of these differentially expressed miRNAs and lay a foundation for exploring the effect of treadmill training on bone metabolism through miRNAs. In this experiment, after the mice were trained on a treadmill for 8 weeks, the mechanical properties of mouse femur bone were assessed, and the alkaline phosphatase (ALP) activity and osteocalcin (OCN) protein levels of the bone were assayed. miRNA microarray and reverse transcription-quantitative (RT-q)PCR were performed to select and validate differentially expressed miRNAs in the bone, and the target genes of these miRNAs were predicted with bioinformatics methods. In addition, the differentially expressed miRNAs in the bone tissues were compared with those in mechanically strained osteocytes in vitro. Treadmill training improved the mechanical properties of the femur bones of mice, and elevated the ALP activity and OCN protein level in the bone. In addition, 122 differentially expressed miRNAs were detected in the bone, of which nine were validated via RT-qPCR. Among the target genes of these differentially expressed miRNAs, certain candidates were involved in bone metabolism. A total of eight miRNAs were differentially expressed in both bone tissue and osteocytes, exhibiting the same expression trends, and various target genes of these eight miRNAs were also involved in bone metabolism. Treadmill training resulted in altered miRNA expression profiles in the bones of mice (mainly in osteocytes) and the differentially expressed miRNAs may serve important roles in regulating bone metabolism and osteogenic differentiation.

Keywords: bioinformatics; bone; microRNA; osteocyte; treadmill exercise.

Figure 1

Mechanical properties of the femur bones in mice that were trained on a treadmill for 8 weeks. Training parameters: Speed, 13 m/min; slope, 9˚; training for 40 min/day, 6 days/week. Treadmill training improved the mechanical properties of the femur bone. n=6. ^*P<0.05, ^**P<0.01 vs. Control.

Figure 2

ALP activity and OCN content in the mouse femurs after treadmill training for 8 weeks. Treadmill training increased the ALP activity and OCN content in the femur tissues. n=5. ^*P<0.05, ^**P<0.01 vs. Control. ALP, alkaline phosphatase; OCN, osteocalcin.

Figure 3

Microarray screening and qPCR verification of differentially expressed miRNAs in bone tissues of mice after treadmill training. The results of the chip screening are provided in the top panel and the results of qPCR are displayed below. n=5. ^**P<0.01 vs. Control. miR, microRNA; qPCR, quantitative PCR.