miR-125b controls mitochondrial metabolism and dynamics by targeting BIK and MTP18

Abnormal mitochondria metabolism and innate immune responses participate in the pathogenesis of many inflammatory disorders. The molecular events regulating mitochondrial activity to control survival and cell death in monocytes/macrophages are poorly understood. Here we show that miR-125b attenuates the activity of the mitochondrial respiratory chain through BIK silencing, and promotes the elongation of mitochondrial network through MTP18 targeting, without impacting autophagy, in the human monocytes. Proinflammatory activation is associated with a concomitant increase in miR-125b expression, decrease in BIK and MTP-18 expression, reduced oxidative phosphorylation, and enhanced mitochondrial fusion. Furthermore, expression of M1-associated transcripts as well as mitochondrial dynamics and energy metabolism are induced upon ectopic expression of miR-125b. In turn, by repressing miR-125b, mitochondrial dynamics was preserved, LPS-induced repression of BIK expression and of mitochondrial respiration were prevented, and M1 polarization of macrophages was inhibited. Altogether, our data reveal a novel role for miR-125b in controlling mitochondrial metabolism and dynamics by targeting BIK and MTP18, respectively, two novel cellular target proteins involved in maintaining the mitochondrial integrity in human monocytes. These findings not only suggest a novel function for miR-125b in regulating metabolic adaptation of monocytes to inflammation but also unravel new molecular mechanisms for its pro-apoptotic role and identify potential targets for interfering with inflammatory activation of monocytes. To identify specific targets of miR-125b, we over- and down-expressed miR-125b as well as a control miRNA in THP-1 cells. Chemically synthesized miRNA duplexes, called pre-miR-125b and pre-miRCTRL, as well as anti-miR-125b were purchased from lifetechnology. Cells were transfected with pre-miRNA, anti-miR and pre-miR control at a final concentration of 50 nM using Lipofectamin 2000 (Invitrogen) according to the manufacturer’s instructions. RNA samples were harvested at 48 hours post-transfection. 2 independent experiments (biological duplicates) were carried out for a total of 6 samples. Total RNA was isolated using an RNeasy mini kit (Qiagen). Quality control was ensured with Bioanalyzer (Agilent Technologies) and RNA quantification with NanoDrop ND-1000 spectrophotometer (NanoDrop Technologies). The generation of cRNA, sample hybridization (using Affymetrix HG U133 plus 2.0 arrays) and scanning with a GeneChip Scanner 3000 (Affymetrix) were performed according to the manufacturer’s instructions. Data were analyzed with High Performance Chip Data Analysis (HPCDA) with BioRetis database.