Understanding the roles of salt-inducible kinases in cardiometabolic disease

Salt-inducible Kinase Regulation of Adipose Tissue Metabolism

Salt-inducible kinases (SIKs) are a subfamily of the adenosine monophosphate-activated protein kinase-related kinase family. To be activated, SIKs require phosphorylation in the catalytic kinase domain by liver kinase B1. In response to extracellular stimulations, their activity can be further regulated through phosphorylation by protein kinase A (PKA), and Ca2+/calmodulin-dependent protein kinases. PKA-mediated SIK inhibition is a major link between G-protein coupled receptor activation and the target gene transcription program. All 3 SIK isoforms-SIK1, SIK2, and SIK3-are expressed in adipocytes, with SIK2 being the most abundant in both rodents and humans. SIKs play essential roles in maintaining adipose tissue homeostasis by regulating physiological processes involving insulin signaling, glucose uptake, lipogenesis, and thermogenesis. Each SIK isoform could play both redundant and unique roles in these physiological processes. Many of the substrates that mediate their physiological functions in adipocytes have been characterized, and downstream mechanisms of action have also been proposed. However, due to the functional redundancy of SIKs, a major challenge is to delineate their isoform-specific roles in adipose tissue in vivo using genetic mouse models. In addition, common genetic variants and rare mutations in the SIK genes have been identified to be associated with metabolic, cardiovascular, and developmental conditions, suggesting a translational implication for human disease that deserves investigation. Furthermore, small molecular SIK inhibitors have been developed and have shown therapeutic potential in multiple disease areas. Evaluation of their metabolic and cardiovascular effects will be required for future clinical development of SIK inhibitors.

Central and Peripheral Roles of Salt-inducible Kinases in Metabolic Regulation

Salt-inducible kinases (SIKs), a member of the serine/threonine protein kinase family, have recently garnered considerable research interest as one of the emerging key regulators of metabolism. The 3 SIK isoforms-SIK1, SIK2, and SIK3-exhibit diverse roles both in central and peripheral physiological processes. While early studies focused on their role in inflammation, spurring the development of SIK inhibitors for chronic inflammatory diseases currently in clinical trials, emerging evidence highlights their broader functions in metabolism. In this review, we will summarize the current state of research on the central roles of SIKs in the brain, particularly in regulating energy balance and glucose homeostasis, alongside their peripheral functions in critical metabolic tissues such as the liver, adipose tissue, and pancreas. By integrating insights into their central and peripheral roles, this review underscores the importance of SIKs in maintaining metabolic homeostasis and highlights their therapeutic potential as novel targets for metabolic disease.