LPS-induced complex polarization of astrocytes and microglia in rats

Abstract A1 astrocytes are activated through M1 microglial secretion, which often be induced via 0.1 mg/kg systemic lipopolysaccharides (LPS). While a larger dose of 5 mg/kg LPS, similar to the dose used for liver injury or sepsis model, was adopted to induce A1. This study was designed to investigate a safer and effective LPS dose to induce A1, and the synchronized changes of other glial phenotypes since both astrocytes and microglia can be activated by LPS. Gene expression changes in 72 specific phenotypic markers of astrocytes and microglia were tested following the administration of systemic LPS ranging from 0.1 to 5 mg/kg, after exposure for 24 h in the cortex, hippocampus and spinal cord, using methods including RT-PCR, co-immunofluorescence, and single-cell RNA sequence. The results showed that anti-inflammatory A2 and M2 phenotypes were also activated by LPS, not the pro-inflammatory A1, M1, and A-pan phenotypes alone. But more A1 than A2 were activated even with low-dose LPS exposure. With respect to microglia, LPS induced a mild and equal level of M1 and M2 activation, indicating 24 h exposure is not proper to stimulate M1. Only several activated markers like C3, Marco and Ym1 showed good consistency among tissues with various dose of LPS. Collectively, systemic LPS induced a rather complex polarization of A1, A2, A-pan, M1, and M2. A smaller LPS dose like 1 or 3 mg/kg could be available to induce A1, and selection of phenotypic markers should be optimized by considering the LPS dose and target tissue.