AMP Deaminase 3 Deficiency Enhanced 5′-AMP Induction of Hypometabolism

Abstract

A hypometabolic state can be induced in mice by 5′-AMP administration. Previously we proposed that an underlying mechanism for this hypometabolism is linked to reduced erythrocyte oxygen transport function due to 5′-AMP uptake altering the cellular adenylate equilibrium. To test this hypothesis, we generated mice deficient in adenosine monophosphate deaminase 3 (AMPD3), the key catabolic enzyme for 5′-AMP in erythrocytes. Mice deficient in AMPD3 maintained AMPD activities in all tissues except erythrocytes. Developmentally and morphologically, the Ampd3−/− mice were indistinguishable from their wild type siblings. The levels of ATP, ADP but not 5′-AMP in erythrocytes of Ampd3−/− mice were significantly elevated. Fasting blood glucose levels of the Ampd3−/− mice were comparable to wild type siblings. In comparison to wild type mice, the Ampd3−/− mice displayed a deeper hypometabolism with a significantly delayed average arousal time in response to 5′-AMP administration. Together, these findings demonstrate a central role of AMPD3 in the regulation of 5′-AMP mediated hypometabolism and further implicate erythrocytes in this behavioral response.

Interplay between adenylate metabolizing enzymes and AMP‐activated protein kinase

“…This effect of AMP was increased in AMPD3 knock‐out mice . While extracellular adenosine production and interaction with specific receptors appeared to play only a marginal role in this phenomenon, a relevant metabolic effect, caused by the absence of AMPD3, was a considerable increase in ATP and ADP concentrations in erythrocytes due to the decrease in adenylate catabolism . The potentiation of the hypometabolic effect exerted by AMP in AMPD2 −/− mice indicates that the intracellular adenylate compound might be directly involved in the hypometabolic effect; however, the implication of AMPK is still to be unravelled.…”

“…The role of AMPD3, expressed particularly in erythrocytes, has been studied mainly in mice, in which the injection of a high AMP concentration causes torpor and hypometabolism. This effect of AMP was increased in AMPD3 knock-out mice [77]. While extracellular adenosine production and interaction with specific receptors appeared to play only a marginal role in this phenomenon, a relevant metabolic effect, caused by the absence of AMPD3, was a considerable increase in ATP and ADP concentrations in erythrocytes due to the decrease in adenylate catabolism [77].…”

CD73 and AMPD3 deficiency enhance metabolic performance via erythrocyte ATP that decreases hemoglobin oxygen affinity

“…All animal studies were carried out in an approved animal facility by trained personnel under protocols HSC-AWC-13-012 and HSC-AWC-12-079 approved by Animal Welfare Committee (AWC), the institutional animal care and use committee (IACUC) at UTHSC-Houston. The Ampd3 −/− / Cd73 −/− mouse line was generated by crossing Ampd3 −/− and Cd73 −/− mice previously described, back crossing the F1 mice, and selecting for Ampd3 −/− / Cd73 −/− mice based on genotyping 3 12 .…”

“…We have previously reported that 5′-adenosine monophosphate (AMP) can safely induce mammals to enter a transient hypometabolism state that resembles the behavior of torpor observed naturally in many species of animals during prolonged periods of metabolic stress 1 . Our previous findings suggested that the uptake of AMP by erythrocytes alters intracellular adenine nucleotide ratios, leading to reduced oxygen transport capacity and induction of hypometabolism 2 3 . These findings prompted our further investigation into how erythrocyte AMP regulates oxygen transport by hemoglobin (Hb) in erythrocytes thus modulating systemic metabolism.…”

“…Although there are three known AMPD isoforms, erythrocytes have only AMPD3 10 . To further validate the erythrocyte’s role in mediating 5′-AMP induced hypometabolism (AIHM), we generated mice deficient in AMPD3 3 . We reported that AMPD enzymatic activities were present in all tissues of Ampd3 −/− mice except the erythrocytes and that Ampd3 −/− mice were much more sensitive to AIHM, supporting our previous findings that erythrocytes are the cellular initiators of AIHM.…”