Defining the mechanisms of neuroinflammation and antepartum neuroprotection in human neural progenitor cells and microglia.

BACKGROUND: Corticosteroids and magnesium sulfate are neuroprotective agents that decrease disabilities in children born prematurely. The neuroprotective mechanisms of these drugs remain unclear, and despite widespread use, gestational age remains a major risk factor for fetal neurological injury. Towards full term, the abundance of neural progenitor cells declines, and microglia increase in number. The efficacy of neuroprotective agents may be cell-type specific at the time of prematurity. We hypothesize that the relationship between gestational age and neuroprotection is because of cell-specific responses to antepartum treatments.

OBJECTIVE: This study evaluates in vitro inflammatory cytokine production by human fetal microglia and neural progenitor cells exposed to magnesium sulfate and betamethasone to determine the neuroprotective mechanisms of these drugs.

STUDY DESIGN: Commercially available human fetal microglia (HMC3) and neural progenitor cells (ReNcells) were exposed to interleukin-1 beta, a known instigator of perinatal neuroinflammatory injury. Cells were also given magnesium sulfate, betamethasone, magnesium sulfate and betamethasone, or the vehicle (control) for 24 hours. Inflammatory responses were evaluated by gene expression and Milliplex immunology assay of the cell media to measure cytokine production and secretion.

RESULTS: With interleukin-1 beta exposure, inflammatory cytokines were upregulated in both cell types according to gene expression and were found at elevated concentrations within cell media. Substantial production of the pro-inflammatory cytokines interleukin-6 and interleukin-8 was observed by both cell types, but only microglia produced the anti-inflammatory cytokine interleukin-10. In interleukin-1 beta exposed neural progenitor cells, treatment with magnesium sulfate slightly lowered interleukin-6 and interleukin-8, but this did not occur with betamethasone or magnesium sulfate/betamethasone. In microglia, betamethasone alone and magnesium sulfate/betamethasone substantially reduced most cytokines upregulated by interleukin-1 beta. A discordance was observed between interleukin-8 expression within microglia and its concentration measured in cell media. Additional analysis revealed that betamethasone reduced the translation of interleukin-8 rather than its extracellular secretion.

CONCLUSION: Pro-inflammatory cytokine expression and production by microglia and neural progenitor cells were impacted differently by each drug. Microglial responses to interleukin-1 beta were substantially attenuated by betamethasone, whereas magnesium sulfate had a mild influence on neural progenitor cells. Furthermore, our results suggest that the neuroprotective mechanisms of betamethasone may be attributed to the reduction of cytokine translation within microglia. Additional investigation is warranted to elucidate whether neuroprotection is attributed to cell-specific drug interactions at the time of the inciting event.