Microglia up‑regulate thromboxane A2 synthesis genes in response to C6 glioma‑conditioned medium

Microglia accumulate in malignant gliomas and play a pivotal role in tumor progression. Using single‑cell RNA sequencing studies researchers have probed gene expression in the myeloid cells in experimental gliomas at relatively late stages of the tumor development. Therefore, the early changes in gene expression in microglia in response to glioma are not fully characterized. We have previously reported distinct profiles of gene expression in the rat primary microglia cultures treated for 6 hours with either rat C6 glioma‑conditioned medium (GCM) or lipopolysaccharide. In the current study, using RNA‑seq, we characterized the transcriptional response of rat primary microglia to GCM in vitro at different time‑points: 6 h, 24 h, and 48 h, as compared to the control treated for 6 h with its own medium. We observed that during the GCM treatment gene expression changes in a biphasic, swing‑like pattern. This includes the genes involved in innate immune response, which are mostly down‑regulated at 6 h by the GCM treatment, as compared to the time‑matched control, and subsequently up‑regulated at 48 h, as compared to the earlier time‑points of the GCM treatment. Conversely, the genes involved in the cell cycle are up‑regulated at 6 h and down‑regulated at 48 h, which coincides with the induction of Tgfb1. Notable exceptions to this biphasic pattern include key genes activating immune response, such as Tlr9 and Myd88, which are down‑regulated early and persistently, while genes inhibiting immune activation, such as Trem1, and genes involved in a metabolic switch, such as Pfkl, are persistently up‑regulated. Most notably, the up‑regulated genes include Ptgs1 (alias Cox1) and Tbxas1, which encode the enzymes catalyzing the synthesis of thromboxane A2, a known inducer of T cell suppression. Further studies are needed to test the functional consequences of their up‑regulation.