Pituitary Adenylate Cyclase–Activating Peptide (PACAP) Stimulates Proliferation and Production of Interleukin–6 in Cultured Rat Muller Cells

Abstract

Abstract: : Purpose: Pituitary adenylate cyclase–activating peptide (PACAP) is known to prevent delayed neuronal cell death after an ischemic event in the hippocampus, partly thorough Interleukin 6 (IL–6) released from astrocytes. In order to elucidate neuroprotective effect of PACAP in the retina, we investigated (1) the mitogenic effects and (2) the changes of IL–6 production by PACAP in cultured rat Muller cells, which are dominant glial cells in the retina. Methods: Muller cells were isolated from 14– or 15–day–old Wistar rat, and cultured with DMEM with 10% fetal bovine serum at 37 degrees C in 5% CO₂. After two passages, the cells were treated with different concentrations of PACAP 38 in serum–free medium for 48 hours. Cell proliferation was assayed by the incorporation of thymidine analog BrdU. IL–6 levels in the supernatants obtained from 24–hour cultures were determined by a bioassay using B9 cells, which is the IL–6 dependent murine hybridoma subclone cell. Results: Incorporation of BrdU was significantly stimulated by PACAP 38 at 10^–9, 10^–8 and 10^–7 M. The maximum stimulation seen at 10^–9M was 2.23–fold above the control. IL–6 production was enhanced by PACAP 38 from 10^–12M to 10^–6M. Compared with the IL–6 level of 0.40 +/– 0.33 pg/mL (mean +/– SD; n = 4) in the control medium, IL–6 levels in PACAP exposed media were 40–fold higher with the PACAP concentration as low as 10^–12 M. Conclusions: These results demonstrate that Muller cells are target cells of PACAP in the retina, and may play a neuroprotective role thorough the release of IL–6 triggered by PACAP.

Keywords: Muller cells • neuropeptides • retinal culture