Adipose tissue protein kinase D: regulation of signaling networks and its sex-dependent effects on metabolism

The protein kinase D (PKD) family of three highly homologous isoforms (PKD1, PKD2, and PKD3) is implicated as nutrient sensing signaling 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 signaling targets are not well characterized. Here, we used phosphoproteomics that was performed to elucidate signaling events downstream of PKD activation in differentiated 3T3-L1 adipocytes using a triple isoform siRNA knockdown model. This revealed PKD-regulated pathways including insulin and cAMP signaling, 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 in female, atDNPKD mice compared with control mice. Female, but not male, atDNPKD mice had higher fasting insulin but normal insulin action. Male atDNPKD mice showed greater sensitivity to the β₃-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 that was lost during fasting. These effects were not observed in female mice. These findings indicate that PKD provides sex-dependent fine-tuning control of cAMP signaling in adipose tissue which is important for the coordination of energy balance during fasting and refeeding. <b>NEW & NOTEWORTHY</b> The protein kinase D (PKD) family is a target for the treatment of obesity-related disorders. However, the physiological role of PKD in adipose tissue remains to be resolved. Using phosphoproteomics and an adipose tissue PKD loss-of-function mouse model, results demonstrate that PKD provides fine-tuning of metabolic signaling in adipose tissue and metabolic responses to fasting and refeeding challenges, via coordination of feeding behavior and regulation of body weight.