Endocrine Abstracts

Polycystic ovary syndrome (PCOS) is associated with insulin resistance. Abnormally low glucose transporter 4 (GLUT4) expression has been shown in adipocytes from subjects with PCOS¹ and skeletal muscle from type 2 diabetics². Although GLUT4 expression is mostly restricted to classic insulin target tissues such as skeletal muscle, cardiac muscle and adipose, we have found it in granulosa cells (GCs) of mice³. Glucose uptake and metabolism by GCs is impaired in PCOS⁴. Intracellular trafficking of GLUT4 has been studied in muscle and adipose tissue, but little work has been done on investigating GLUT4 expression and translocation in granulosa cells.

We studied GLUT4 expression in an immortalised luteinizing mouse granulosa tumour cell line (KK1 cells)⁵. Immunocytochemistry was used to analyse the response of the KK1 cells to insulin 100 ng/ml and forskolin 10 μmol. GLUT4 protein expression increased in response to insulin. The KK1 cells were then transfected with an HA-GLUT4-GFP plasmid (a gift from J Tavare, Bristol) and, using live confocal imaging⁶, we analysed intracellular trafficking of GLUT4-GFP in response to either insulin or FSH (FSH upregulates GLUT4 in mouse GCs³). GLUT4 was seen to move toward the cell membrane after 5 min of adding insulin 100 ng/ml and after 6 min of the addition of FSH 20 ng/ml. These results support the hypothesis that, in common with classic insulin target tissues, GLUT4 has a key role in glucose uptake by GCs and is regulated by both insulin and gonadotrophins.

Acknowledgments: Wellbeing of Women.

References:

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2. Gaster et al. Diabetes 2001 50 (6) 1324–9.

3. Roberts et al. Biol Reprod 2004 71 (1) 199–209.

4. Rice et al. Hum Reprod 2005.

5. Kananen et al. Mol Endocrinol 1995 9 (5) 616–27.

6. Dawson et al. Biochem Biophys Res Commun 2001 287 (2) 445–54.