Effect of modulating adenine nucleotide levels on AMPK activation by targeting AMP-metabolizing enzymes
(2013)
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- Abstract
- The AMP-activated protein kinase (AMPK) acts as a sensor of cellular and whole body energy homeostasis. Once activated, it inhibits energy consuming anabolic pathways while at the same time stimulating energy producing catabolic pathways. AMPK activation in skeletal muscle stimulates glucose uptake, which contributes towards the beneficial effects of exercise in counteracting the symptoms of type 2 diabetes. AMP is mainly degraded by AMP-deaminase (AMPD) or soluble 5’-nucleotidases. Three separate genes code for AMPD isozymes: AMPD1 (expressed in skeletal muscle), AMPD2 (expressed in liver) and AMPD3 (expressed in erythrocytes). The soluble 5’-nucleotidase IA (cN-IA) is mainly expressed in skeletal muscle and heart, whereas the other soluble 5’-nucleotidase (cN-II) is ubiquitous. In this study, it was first investigated whether overexpression of AMPD1, AMPD2 and cN-IA would antagonize oligomycin-induced AMPK activation in HEK293T cells. In this model, cN-IA rather than AMPDs, exerted most control over AMP and ADP concentrations. Overexpression of cN-IA markedly reduced oligomycin-induced AMPK activation, whereas overexpression of AMPD1 and AMPD2 effects on AMPK activation were much less. The design of cN-IA inhibitors could be an alternative strategy to direct kinase activators for achieving AMPK activation. The data also support the idea that ADP as well as AMP are important for AMPK activation and that AMPK is regulated by the AEC. As most of the circulating glucose is taken up by muscle, the second part of the thesis focuses on the consequences of AMPD inhibition for AMPK activation in this tissue. Pharmacological AMPD inhibition as well as AMPD1 deletion in mice led to a substantial enhancement of contraction-induced AMP and ADP accumulation in incubated skeletal muscles. However, this did not systematically lead to potentiation of AMPK phosphorylation and activation in response to electrical stimulation. Also, pharmacological AMPD inhibition did not enhance contraction-stimulated glucose-uptake, supporting the notion that pathways other than AMPK are involved. Clearly, AMPD inhibitors are not exercise mimetics but can be used to modulate adenine nucleotide levels to achieve AMPK activation under energy stress. They will thus be useful tools for exploring AMPK activation in cells and tissues other than muscle. The data also support a role for AMPD isoenzymes in protecting cells against loss of adenine nucleotides.
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Plaideau, C. (2013). Effect of modulating adenine nucleotide levels on AMPK activation by targeting AMP-metabolizing enzymes. https://hdl.handle.net/2078.5/25851