Alteration of miRNA Biogenesis Regulating Proteins in the Human Microglial Cell Line HMC-3 After Ischemic Stress.

MicroRNAs (miRNA) are small noncoding sequences that control apoptosis, proliferation, and neuroinflammatory pathways in microglia cells. The expression of distinct miRNAs is altered after ischemia in the brain. Only minor information is available about the biogenesis and maturation of miRNAs after ischemia. We aimed at examining the impact of oxygen-glucose deprivation (OGD) and hydrogen peroxide (H2O2)-induced stress on the expression of miRNA regulating proteins such as DROSHA, DGCR8, XPO5, DICER, TARBP2, and AGO2 in the cultured human microglial cell line HMC-3 (human microglial cell line clone 3). OGD duration of 2.5 h or H2O2 stimulation at a concentration of 100 µM for 24 h resulted in a marked increase of the hypoxia sensor hypoxia-inducible factor1-α in HMC-3 cells. These treatments also led to an upregulation of DROSHA, DICER1, and AGO2 detected by semiquantitative real-time PCR (qrtPCR). XPO5 and TARBP2 were only upregulated after stimulation with H2O2, while DGCR8 responded only to OGD. We found elevated DICER1, DROSHA, and AGO2 protein levels by western blot and immunohistochemistry staining. Interestingly, the latter also exposed a colocalization of AGO2 with stress granules (G3BP1) after OGD. Our data indicate that DICER, DROSHA, and AGO2 are induced in microglial cells under hypoxia-like conditions. It might be speculated that their inductions might increase the miRNA synthesis rate. Future studies should investigate this correlation to determine which miRNAs are preferably expressed by microglia cells after ischemia and which functions they could exert.