hsa-miR-346 is a potential serum biomarker of Mycobacterium avium complex pulmonary disease activity

MicroRNA (miRNA) has been recently recognized as a biomarker of various diseases; however, there are no known miRNAs associated with Mycobacterium avium complex (MAC) pulmonary disease. In addition, there are no known biomarkers to precisely reflect disease activity after the diagnosis of MAC pulmonary disease. Thus, we sought to identify a miRNA which is a candidate biomarker of MAC pulmonary disease activity. Serum hsa-miR-346 concentrations of 16 patients with M. avium pulmonary disease were significantly higher than those of 16 healthy controls (p = 0.047). The secretion of hsa-miR-346 increased in a multiplicity of infection-dependent manner in M. avium-infected macrophages. Serum hsa-miR-346 levels of 5 patients with bacterial conversion at the end of follow-up were significantly lower than those at the beginning of the follow-up (p = 0.043). In addition, the longitudinal change in serum hsa-miR-346 concentration correlated with bacterial load in 2 patients with M. avium pulmonary disease. Based on our results, it is supposed that MAC-infected macrophages in pulmonary lesions produce hsa-miR-346, which is then secreted into the bloodstream. The magnitude of this process could be quantitatively controlled by the bacterial load, suggesting that serum hsa-miR-346 is a potentially useful biomarker of MAC pulmonary disease activity.