Dissecting copper homeostasis in diabetes mellitus.

Diabetes Mellitus (DM) is characterized by elevated blood glucose levels (hyperglycemia). It can occur due to impaired secretion or action of the hormone insulin, which is produced by pancreatic beta-cells to promote the entry of glucose into the cells. It is known that hyperglycemia has an important role in the production of reactive oxygen species in all types of DM and that an imbalance of transition metal as Cu and Fe plays a pivotal role in stimulating the oxidative stress. Different levels of some transition metals, as Cu, Fe, Mn, and Zn has been reported comparing diabetic animal models with the control group. An increased Cu status is also described in diabetic patients. Homeostasis of Cu depends on distinct proteins, where Cu(I)-ATPases are important transmembrane proteins for acquisition, active transport, distribution and elimination of Cu ions. In this review we first provide an overview of the literature about the relationship between diabetes and copper, the modulation of Cu(I)-ATPases activity and protein expression in DM, to next discuss the alternative treatments for diabetes using Cu chelation. © 2016 IUBMB Life, 69(4):255-262, 2017.

Modulation of hepatic copper-ATPase activity by insulin and glucagon involves protein kinase A (PKA) signaling pathway.

Different studies have revealed copper imbalance in individuals suffering from diabetes and obesity, suggesting that regulation of glucose and/or fat metabolism could modulate cellular copper homeostasis. To test this hypothesis we investigated whether the key hormones of energy metabolism, insulin and glucagon, regulate the functional properties of the major hepatic copper-transporter, ATP7B (i.e., copper-dependent ATPase activity). We demonstrated that insulin reverses the effect of copper and stimulates retrograde trafficking of ATP7B from the canalicular membranes, consistent with the enhanced ability of ATP7B to sequester copper away from the cytosol. Physiological concentrations of insulin increase endogenous ATP7B activity in cultured hepatic cells and in tissues by 40%, whereas glucagon inhibits this activity by 70%. These effects were cancelled out when insulin and glucagon were combined. We also demonstrated that the opposite effects of the hormones on ATP7B activity involve receptor-mediated signaling pathways and membrane-bound kinases (PKA and PKB/Akt), which are reciprocally regulated by insulin and glucagon. Inhibiting insulin signaling at the level of its Tyr-kinase receptor, PI3K or PKB/Akt restored the basal activity of ATP7B. Insulin reduced endogenous PKA activity, whereas glucagon promoted PKA stimulation by approximately 100%. These findings demonstrate that the physiological modulation of ATP7B activity is linked to energy metabolism via insulin and glucagon, and could help to understand the mechanisms involved in the disruption of copper homeostasis in diabetic and obese patients.

Golgi membranes from liver express an ATPase with femtomolar copper affinity, inhibited by cAMP-dependent protein kinase.

Copper-stimulated P-type ATPases are essential in the fine-tuning of intracellular copper. In the present work we characterized a copper-dependent ATPase hydrolysis in a native Golgi-enriched preparation from liver and investigated its modulation by cyclic AMP-dependent protein kinase (PKA). The very high-affinity Atp7b copper pump presented here shows a K(0.5) for free copper of 2.5×10(-17) M in bathocuproine disulfonate/copper buffer and ATP hydrolysis was inhibited 50% upon stimulation of PKA pathway, using forskolin, cAMP or cholera toxin. Incubation with PKA inhibitor (PKAi(5-24) peptide) raises Cu(I)-ATPase activity by 50%. Addition of purified PKA α-catalytic subunit increases K(0.5) for free copper (6.2×10(-17) M) without modification in the affinity for ATP in the low-affinity range of the substrate curve (∼1 mM). The Hill coefficient for free copper activation also remains unchanged if exogenous PKA is added (2.7 and 2.3 in the absence and presence of PKA, respectively). The results demonstrate that this high-affinity copper pump in its natural environment is a target of the liver PKA pathway, being regulatory phosphorylation able to influence both turnover rate and ion affinity.