The Role of microRNAs in Osteoporosis Diagnostics

MicroRNAs (miRNAs) are short (18-24 nucleotides) non-coding RNA sequences that regulate gene expression via binding of messenger RNA. It is estimated that miRNAs co-regulate the expression of more than 70 % of all human genes, many of which fulfil important roles in bone metabolism and muscle function. In-vitro and in-vivo experiments have shown that the targeted loss of miRNAs in distinct bone cell types (osteoblasts and osteoclasts) results in altered bone mass and bone architecture. These results emphasize the biological relevance of miRNAs for bone health. MiRNAs are not only considered as novel bone biomarkers because of their biological importance to bone metabolism, but also on the basis of other favorable properties: 1) Secretion of miRNAs from cells enables " minimally invasive" detection in biological fluids such as serum. 2) High stability of miRNAs in serum enables the retrospective analysis of frozen blood specimens. 3) Quantification of miRNAs in the serum is based on the RT-PCR - a robust method that is considered as the gold standard for the analysis of nucleic acids in clinical diagnostics. With regard to osteoporosis, it has been shown that many of the known risk factors are characterized by distinct miRNA profiles in the affected tissues: i) age-related loss of bone mass, ii) sarcopenia, iii) changes in estrogen metabolism and related changes Loss of bone mass, and iv) diabetes. Therefore, numerous studies in recent years have dealt with the characterization of miRNAs in the serum of osteoporosis patients and healthy controls, and were able to identify recurring miRNA patterns that are characteristic of osteoporosis. These novel biomarkers have great potential for the diagnosis and prognosis of osteoporosis and its clinical outcomes. The aim of this article is to give a summary of the current state of knowledge on the research and application of miRNA biomarkers in osteoporosis.