Peroxisome Proliferator-Activated Receptor gamma (PPARγ) is a ligand-activated transcription factor which belongs to the nuclear hormone superfamily and has multiple pharmacological ligands called Thiazolidinediones (TZDs). TZDs are a class of drugs used in the treatment of type 2 diabetic patients. Rosiglitazone is one such TZD, and is used clinically to treat type 2 diabetes. In this study, the effect of Rosiglitazone on cell growth and apoptosis in cultured monocytic monomac 6 (MM6) cells was investigated. Over a 14 day period, MM6 cells were cultured in vitro and treated with 1μM and 10μM Rosiglitazone. Cell viability and proliferation were evaluated by Haemocytometer cell count and MTS assay respectively. Turbidity due to cell density was assessed spectrophotometrically. Apoptosis was determined by Caspase-Glo 3/7 assay. Expression of the endoplasmic reticulum (ER) stress-inducible protein sarco-endoplasmic reticulum Ca2+ATPase-2b (SERCA2b) was determined by Western blot. Neither 1μM nor 10μM Rosiglitazone exerted statistically significant inhibitory effects on cell proliferation, turbidity due to cell density, or cell viability (p > 0.05 in all cases). In contrast, Rosiglitazone induced increased apoptosis, but a significant difference was only observed in 10μM-treated cells compared with control cells (3.04 ± 0.52 control; p < 0.05) while 1μM-treated cells showed a non-significant increase (1.50 ± .06
control; p > 0.05). Meanwhile the expression of SERCA2b was up-regulated significantly in cells treated for >4hrs (e.g 2.45 ± 0.06 control at 24 hrs; p < 0.05) with 10μM Rosiglitazone. It was
concluded that high doses (10μM) of Rosiglitazone up-regulate SERCA2b expression and induce apoptosis of MM6 cells by activating an ER stress response via a PPARγ-independent mechanism. The therapeutic relevance of these observations is a matter for further investigations.
Key words: Rosiglitazone, PPARγ, Monocytes, ER Stress, SERCA2b, Apoptosis