Abstract
Purpose: :
Microglia in the retina have been implicated in the pathogenesis of retinal diseases such as diabetic retinopathy and AMD. In vitro microglia systems offer an important tool for investigating microglial physiology. Immortalized cell lines and cultured microglia isolated from the retina represent two main systems for in vitro study. We aim to compare the BV-2 immortalized cell line with cultured microglia isolated from mouse retina.
Methods: :
Cultured retinal microglia (RMG) and BV-2 cells, cultured under similar conditions, were assessed for expression of inflammatory factors, growth factors, chemokines, and chemokine receptors using rt-PCR and ELISA. Microglial migration was assayed with a Boyden chamber assay, and phagocytosis was evaluated using a fluorescent-bead assay.
Results: :
RMG and BV-2 cells display distinct morphologies with RMG having a spindle/bipolar shape and long processes, and BV-2 cells having a more rounded shape and shorter process. BV-2 cells, compared to RMG, express lower basal levels of inflammatory cytokines (IL-1β, IL-6, TNF-α, NF-ΚB, IFN-γ, TGF-β), chemotactic chemokines and their receptors (CCL2, CCL5, CCR5, CX3CR4, CX3CR1), growth factors (bFGF, GDNF, VEGF, PEDF), and microglia activation markers (F4/80, CD11b, MAC-2, NOX2, iNOS). In general, BV-2 cells also had lower levels of these factors compared to RMG even after LPS stimulation. Interestingly, BV-2 cells express sox2, a transcription factor associated with undifferentiated stem cells, while RMG do not. BV-2 cells also demonstrate a markedly lower level of migration in response to chemokines CCL2 and CCL3, and a decreased phagocytic capability compared to RMG.
Conclusions: :
While BV-2 cells express many similar genes as cultured RMG, they express significantly lower levels of microglia-relevant proteins, respond less robustly to LPS stimulation, and display lower migratory and phagocytic capabilities. BV-2 cells may have properties of less differentiated immune progenitor cells and may be a less appropriate in vitro model of microglia function in the mature retina than cultured retinal microglia.
Keywords: microglia • inflammation • gene/expression