Exp Clin Endocrinol Diabetes 2014; 122 - OP3_08
DOI: 10.1055/s-0034-1371983

Calcium-dependent release of adipocyte fatty acid binding protein from human adipocytes

I Schlottmann 1, M Ehrhart-Bornstein 1, M Wabitsch 2, SR Bornstein 1, V Lamounier-Zepter 1
  • 1Universitätsklinikum Carl-Gistav Carus an der TU Dresden, Molecular Endocrinology (MK III), Dresden, Germany
  • 2Division of Paediatric Endocrinology and Diabetes, Department of Paediatrics and Adolescent Medicine, Ulm, Germany

Background: Fatty acid binding protein 4 (FABP4) is a predominantly cytosolic protein of adipocytes, but also abundantly present in human plasma; its plasma concentrations were linked to obesity and metabolic syndrome. Recent studies have suggested a direct extracellular effect of FABP4 in the regulation of glucose metabolism and heart function independently of its effect as a carrier protein. Interestingly, FABP4 has no secretory signal sequence, so that the mechanisms how FABP4 is released from adipocytes are unclear.

Methods and Results: In this study we investigated the mechanisms for FABP4 secretion from human adipocytes by using isolated primary preadipocytes and the human adipocyte cell strain SGBS. In undifferentiated preadipocytes FABP4 expression was barely detectable and increased continuously during differentiation. The increase in FABP4 mRNA expression was accompanied by high levels of FABP4 secretion. In differentiated human adipocytes FABP4 secretion was not abolished by blocking the Golgi-dependent secretory pathway in vitro, supporting a non-classical secretion mechanism for FABP4. However, raising intracellular Ca2+ levels enhanced FABP4 secretion in a concentration dependent-manner.

Conclusion: This study shows that FABP4 is actively released from human adipocytes in vitro via a non-classical, calcium-dependent mechanism.