Depression of cell metabolism and proliferation by membrane-permeable and -impermeable modulators: role for AMP-to-ATP ratio.
The metabolic and developmental depression commonly observed during natural states of dormancy, such as diapause and quiescence, is typically accompanied by an increase in the intracellular ratio of AMP to ATP. We investigated the impact of artificially increasing the AMP-to-ATP ratio in mouse macrophages. Evidence is presented here that the P2X7 receptor channel can be used as an effective means to load cells with membrane-impermeable compounds. Intracellular loading of adenosine-5'-O-thiomonophosphate (AMPS), a nonhydrolyzable analog of 5'-AMP and potent activator of AMP-activated protein kinase, significantly depresses metabolism and proliferation of macrophages. The intracellular effective AMP-to-ATP ratio obtained (the sum of AMPS plus endogenous 5'-AMP) was 0.073, well above that reported to activate AMP-activated protein kinase in vitro. Optimizing both the conditions under which the P2X7 receptor channel is opened and the duration of opening facilitates high analog uptake and approximately 98% survivorship. An advantage to AMPS is its minimal impact on other components of the nucleotide pool, most notably the unchanged concentration of ADP. An alternative way to shift the effective AMP-to-ATP ratio is by incubation with the membrane-permeable compound 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), which is phosphorylated intracellularly to form the 5'-AMP analog ZMP. Despite a rapid intracellular accumulation of AICAR, conversion to ZMP was slow and inefficient. Furthermore, AICAR incubation increased cellular ADP, and, although cell proliferation was depressed, the overall cellular energy flow was unchanged. The rapid action of AMPS avoids upregulation of compensatory metabolic pathways and may provide a viable approach for promoting cell stasis.
Division of Cellular, Developmental and Integrative Biology, Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA. menze@lsu.edu
Michael A
MA
Menze
Matthew J
MJ
Clavenna
Steven C
SC
Hand
D000249:Adenosine Monophosphate / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000502:physiology*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability; D049109:Cell Proliferation / Q000187:drug effects; D008264:Macrophages / Q000502:physiology; D008660:Metabolism / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D058486:Receptors, Purinergic P2X7; D012265:Ribonucleotides / Q000378:metabolism / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D013997:Time Factors
C546469:P2rx7 protein, mouse; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D012265:Ribonucleotides; D013873:Thionucleotides; C014308:adenosine 5'-phosphorothioate; D000620:Aminoimidazole Carboxamide; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; C031143:AICA ribonucleotide