It has become widely accepted that cAMP acts locally, in independently regulated signaling microdomains. Soluble adenylyl cyclase (sAC) is molecularly, biochemically and functionally distinct from the other known mammalian sources of cAMP, the transmembrane adenylyl cyclases (tmACs). While tmACs are positioned at the plasma membrane where they are regulated by heterotrimeric G proteins in response to extracellular cues such as hormones and neurotransmitters, sAC is distributed throughout the cytoplasm and in intracellular compartments, including mitochondria, where it is poised to provide the second messenger regulating the intracellular and intra-organellar targets of cAMP. Inside mitochondria, sAC-generated cAMP regulates components of the electron transport chain (ETC), increasing electron flux and the overall rate of ATP synthesis. This intramitochondrial sAC-cAMP signaling pathway linking cellular nutrient utilization with energy production defines a mechanism of short-term modulation of oxidative phosphorylation which allows the cell's respiratory machinery to respond to transient changes in nutritional availability, environmental conditions, and energy requirements. In this application, we propose to elucidate the physiological significance of this pathway. We propose to (1) determine the consequences of both chronic and acute abrogation of the intramitochondrial sAC-cAMP pathway in cultured cells using pharmacological inhibitors and cells derived from sAC-C1 KO mice;and (2) discern which of the known metabolic phenotypes seen in sAC-C1 KO mice are caused by abrogation of the intramitochondrial sAC-cAMP pathway. Understanding the role of this pathway is likely to have important implications for cell intrinsic nutrient sensing, diabetes, and metabolism in general, and it will reveal the functional significance of this intracellular cAMP microdomain.
The mitochondrion is the cell's powerhouse. We discovered a new mechanism of regulation, wholly contained inside the mitochondria, that modulates the activity of energy producing pathways depending on the rate at which nutrients are utilized. We now propose to study how this regulatory mechanism affects metabolism in cells and animals.