Micro-RNA expression profiling in Paget's disease of bone

Since their initial discovery, microRNAs (miRNAs) have emerged as critical post-transcriptional regulators of gene expression that are able to modulate bone remodeling. Nonetheless, despite the peculiar and aggressive phenotype of pagetic osteoclasts and the associated increase in osteoblast activity, whether deregulation of miRNAs is involved in Paget’s disease of bone (PDB) remains unknown. Here, we performed a serum miRNA expression profile (Taqman Human MicroRNA Array Card Set v3.0) in peripheral blood mononuclear cells (PBMCs) from 20 PDB patients (ten with and ten without Q16STM1 mutation) and 20 age-matched subjects with or without osteoporosis. Data from Array Cards were exported using ViiA7 RUO software and then analyzed using Expression Suite Software v1.0.1 (Applied Biosystem). All values were normalized using different housekeeping miRNAs. Overall, 22 miRNAs were significantly upregulated in PBMCs from PDB cases, with a fold change above three (miRNAs-31, -32, -124a, -132, -182, -221, -339, -345, -410, -451, -485.3p) or between 2 and 3 (miRNAs-19a, -30b, -30c, -27a, -125a, -146a, -148a, -200c, -223, -301, -365) than in non-pagetic controls. For most of these miRNAs (miRNAs-19a, -27a, -30c, -32, -125a, -132, -200c, -221, -223, -301, -345, -365, -410, -485.3p) the association was significantly higher in carriers of Q16STM1 mutation. Moreover, seven miRNAs (miRNAs-124a, -132, -148a, -182, -200c, -221, -451) were also significantly upregulated in osteoporotic than non-osteoporotic subjects. Taken together, eight of these miRNAs (miRNAs-26a, -30c, -31, -124a, -146a, -148a, -182, -223) were previously related with bone homeostasis. In particular, while the increase in miRNAs146a, -148a and -223 is consistent with their pro-osteoclastogenic effects observed in vitro by previous studies, and might account for the increase in osteoclast activity of PDB, the upregulation of miR-26a and -124a was unexpected, given their role as suppressors of osteoclastogenesis, possibly reflecting counteracting mechanisms on osteoclasts precursors. Conversely, miRNAs-30c and -182 have been mainly related to osteoblastogenesis and the regulation of bone formation. Further studies are required to better address the mechanisms leading to miRNAs deregulation and assess the role of the identified miRNAs as potential biomarkers or therapeutic targets in PDB as well as in other disorders of bone metabolism.