Granulocyte-Colony Stimulating Factor Enhances Uncoupling Protein-1 Expression via Mitogen-Activated Protein Kinase Pathway in Rat Brown Adipocytes

Abstract

Background: The structures and the receptor’s intracellular signal pathways of Granulocyte-colony stimulating factor (G-CSF) are similar to those of leptin and ciliary neurotropic factor, which are known to increase uncoupling protein-1 (UCP-1) expression in brown adipose tissue (BAT) and have anti-obesity effects. We also observed in our previous experiments that G-CSF treatment reduced body weight and increased energy expenditure and UCP-1 expression in BAT of Otsuka Long-Evans Takushima fatty (OLETF) rats. The best-known mechanism to increase UCP-1 expression in BAT involves p38 mitogen-activated protein kinase (p38 MAPK) activation, which is also a well-known intracellular signaling pathway of G-CSF. Therefore, we investigated whether G-CSF enhanced UCP-1 expression in BAT via p38 MAPK. Methods: Interscapular BATs were obtained from a 20 week-old male OLETF rat to examine for the presence of G-CSF receptors (G-CSFRs). Brown pre-adipocytes were isolated from the interscapular area of post-natal Sprague-Dawley rats, and cultured and differentiated into mature brown adipocytes. RT-PCR (reverse-transcription-PCR) and immunofluorescence staining were used to identify G-CSFRs. RT-PCR was used to identify UCP-1 mRNA expression in brown adipocytes. Western blotting was used to measure p38 mitogen-activated protein kinase (MAPK) activity. Results: G-CSFR mRNA expression was identified in the BAT of an OLETF rat. Immunofluorescence staining also revealed that G-CSFRs were located in the islands of brown adipocytes in BAT. Brown adipocytes were fully differentiated 2 days after expose to differentiation cocktails. G-CSFR expression was also identified before and 4 days after differentiation (D4). p38 MAPK phosphorylation was enhanced at 30 minutes and UCP-1 mRNA expression was increased at 1 hour after G-CSF treatment in brown adipocytes at D4. The increase in p38 MAPK phosphorylation and UCP-1 mRNA expression following G-CSF treatment disappeared completely when brown adipocytes were pre-treated with the p38 MAPK inhibitor, SB203580. Conclusion: G-CSFRs were present in the BAT of OLETF rats, and G-CSF enhances UCP-1 expression in brown adipocytes via p38 MAPK pathway. These data suggest that the reduction in body weight following G-CSF treatment in OLETF rats, as we previously observed, may result from G-CSF-mediated enhanced UCP-1 expression in brown adipocytes.