REDUCED EXPRESSION OF TUMOR NECROSIS FACTOR AND INTERLEUKIN-1B IN BIPOLAR/ROD-SHAPED MICROGLIA – AN IN VITRO STUDY

Microglia are the primary resident immune cells in the central nervous system (CNS) that regulate the primary events of neuroinflammatory response. They also play key roles in the repair and regeneration of the CNS after injury. Recent studies showed that cluster of bipolar/rod-shaped microglia are aligned end-to-end along the damaged site of CNS injury during initial phase. However, the functional roles of these bipolar/rod-shaped microglia remain unclear, as compared to the well-characterized surveying ramified microglia and phagocytotic amoeboid microglia. In the present study, we established a simple and highly reproducible in vitro culture model system to enrich bipolar/rod-shaped microglia. By making multiple scratches on the poly-d-lysine/laminin coated culture dish, trains of bipolar/rod-shaped microglia formed and aligned end-to-end along the scratches which resembled microglia alignment observed in the injury site of CNS in vivo. We found that bipolar/rod-shaped microglia were highly proliferative (PCNA positive) and expressed reduced level of cytokines Tnf and Il-1b when compared with amoeboid microglia. Upon lipopolysaccharide treatment, bipolar/rod-shaped microglia transformed into amoeboid microglia within 30 minutes and the expressions of Tnf and Il-1b were induced significantly through the up-regulation of Jak1/Stat3 signaling pathway. Our data indicated that bipolar/rod-shaped microglia were in the proliferating stage which in line with the increasing number of bipolar/rod-shaped microglia observed at the early phase of CNS damage in vivo. We propose that our in vitro culture system can be used for gene expression studies and functional characterization of bipolar/rod-shaped microglia. Grant/Other Support: This work is supported in part by The Health and Medical Research Fund (HMRF), Food and Health Bureau, Hong Kong Special Administrative Region Government (Ref. No: 01122026) and ECS/GRF grants from the Research Grant Council of the Hong Kong Special Administrative Region Government (CityU 161212 and CityU 160813).