Illuminating compartmentalized AMPK signaling in single cells.

AMP-activated protein kinase (AMPK) is a crucial regulator of cellular energy balance, affecting numerous downstream targets across various subcellular locations. Under cellular energy stress, AMPK becomes fully activated when it binds AMP and is phosphorylated by upstream kinases, including liver kinase B1 and calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2), and works to restore metabolic equilibrium. Additionally, CaMKK2 can activate AMPK independent of AMP in response to calcium signaling. In the present review, we summarize how genetically encoded kinase activity reporters for measuring AMPK activity have evolved for a comprehensive measurement of spatial and temporal AMPK activity in single cells. These reporters have provided important insights into AMPK activity dependent upon upstream kinases, location, and signaling cues. We also discuss the use of genetic actuators such as the AMPK inhibitory peptide that can be targeted to suppress AMPK activity at specific compartments. Together, these advances have established AMPK as a key regulator of metabolism with distinct spatial and temporal signaling patterns, suggesting compartmentalization of AMPK activity in the cell.