Adipose tissue protein kinase D (PKD): regulation of signalling networks and its sex-dependent effects on metabolism

The protein kinase D (PKD) family of three highly homologous isoforms (PKD1, PKD2, and PKD3) are implicated as nutrient sensing signalling kinases that regulate the response of adipose and other tissues to the nutrient environment. However, the physiological role of adipose tissue PKD and its downstream cellular signalling targets are not well characterised. Phosphoproteomics was performed to elucidate signalling events downstream of PKD activation in differentiated 3T3L1 adipocytes using a triple isoform siRNA knockdown model. This revealed PKD-regulated pathways including insulin and cAMP signalling, which control metabolic responses in adipose tissue. An adipose tissue-specific and inducible dominant negative PKD (atDNPKD) mouse model that achieves functional inhibition of all three PKD isoforms was generated to assess the function of adipose PKD on whole-body metabolism in vivo in both male and female mice. Insulin-stimulated suppression of lipolysis was blunted in male, but not female, atDNPKD mice compared to control mice. Female, but not male, atDNPKD mice had higher fasting insulin but normal insulin action. Male atDNPKD mice showed greater sensitivity to the β ₃ -adrenergic receptor agonist CL316,243 on measures of lipolysis and energy expenditure, and displayed greater fat oxidation during fasting. During refeeding, male atDNPKD mice consumed less food and took longer to regain body weight lost during fasting. These effects were not observed in female mice. These findings indicate that PKD provides sex-dependent fine-tuning control of cAMP signalling in adipose tissue that is important for the coordination of energy balance during fasting and refeeding.