Studies on the regulation of adipose tissue secreted proteins
White adipose tissue (WAT) is now recognised as an endocrine organ through its secretion of hormones and protein factors - ‘adipokines’. This thesis examined the regulation of two adipose expressed genes, retinol binding agent (RBP) involved in retinol transport, and tissue factor (TF) which initiates the extrinsic coagulation cascade. RNA was isolated and RBP and mRNA levels determined by chemiluminescence-based Northern blotting. TF and mRNA levels were determined by real-time PCR. WAT RBP mRNA levels were second only to liver, and TF mRNA levels were highest in WAT depots. RBP and TF mRNA were detected predominantly from mature adipocytes. Obesity was not associated with altered RBP and TF gene expression except of for a significant (p<0.05) decrease in RBP mRNA from subcutaneous WAT of obese rodent models. Primary adipocytes were treated with b-agonists, dexamethasone or leptin. Only dexamethasone significantly (p<0.05) reduced RBP mRNA levels. TF mRNA levels were unaltered following b-agonists, forskolin, or dexamethasone treatment except for a significant (p<0.05) increase with a high dose of BRL 37344 (a b3 agonist). Administration of two isoforms of retinoic acid significantly decreased RBP gene expression, with 9-cis showing more potency (p£ 0.001) that all-trans (p<0.05. The thiazolidinediones ciglitazone and rosiglitazone were administered, high doses significantly reducing RBP gene expression (p £ 0.001 and p £ 0.05 respectively). Fasting and cold exposure are two physiological stimuli which stimulate substrate flux and the release of fatty acids from WAT. RBP gene expression in WAT was unaltered with fasting, cold exposure and b-agonist injection. These studies suggest WAT may be an important source of RBP and TF. In contrast to lipolysis and leptin production, the SNS does not significantly regulate RBP and TF gene expression. The high TF gene expression in rodent WAT suggests an association between TF and the cardiovascular disease seen with obesity.