Copper regulates cyclic-AMP-dependent lipolysis

Abstract

Cell signaling relies extensively on dynamic pools of redox-inactive metal ions such as sodium, potassium, calcium, and zinc, but their redox-active transition metal counterparts such as copper and iron have been studied primarily as static enzyme cofactors. Here we report that copper is an endogenous regulator of lipolysis, the breakdown of fat, which is an essential process in maintaining the body's weight and energy stores. Utilizing a murine model of genetic copper misregulation, in combination with pharmacological alterations in copper status and imaging studies in a 3T3-L1 white adipocyte model, we demonstrate that copper regulates lipolysis at the level of the second messenger, cyclic AMP (cAMP), by altering the activity of the cAMP-degrading phosphodiesterase PDE3B. Biochemical studies of the copper-PDE3B interaction establish copper-dependent inhibition of enzyme activity and identify a key conserved cysteine residue within a PDE3-specific loop that is essential for the observed copper-dependent lipolytic phenotype.

Copper signaling in the brain and beyond

“…A liver-specific ATP7B knockout mouse develops lipid dysregulation without inflammation, suggesting that metabolic symptoms may be directly linked to copper levels and not a secondary symptom of liver inflammation observed in Wilson disease (89). Consistent with dietary and genetic studies linking long-term changes in copper to changes in fat metabolism (90,91), work from our laboratory identified copper as a newly recognized allosteric regulator of phosphodiesterase 3B (PDE3B), a phosphodiesterase that controls lipolysis in adipocytes (92). Lipolysis, the breakdown of triglycerides into glycerol and fatty acids, may be induced in tissues and cells by treatment with isoproterenol, which stimulates the betaadrenergic receptor and induces a signaling cascade mediated by the second messenger cyclicadenosine monophosphate (cAMP).…”

“…In differentiated 3T3-L1 cells, a cell culture model of white fat, copper supplementation potentiated and copper chelation inhibited isoproterenol-induced glycerol release, demonstrating that fat metabolism is influenced by manipulation of the labile copper pool. Additionally, the fluorescent copper sensor Copper Silicon Rhodol 1 (CSR1), but not the Control CSR1 analog lacking copper-responsive binding groups, revealed an acute decrease in labile copper after isoproterenol treatment within 5-10 min, before the onset of fatty acid release, suggesting that changes in labile copper are upstream of lipid breakdown (92).…”

“…Elevated cAMP levels stimulate protein kinase A (PKA), leading to downstream events that culminate in lipid breakdown (93). Copper-deficient adipose tissue isolated from ATP7B knockout mice and stimulated with isoproterenol releases less glycerol and has lower cAMP levels than isoproterenolstimulated adipose tissue isolated from healthy heterozygous siblings (92). In differentiated 3T3-L1 cells, a cell culture model of white fat, copper supplementation potentiated and copper chelation inhibited isoproterenol-induced glycerol release, demonstrating that fat metabolism is influenced by manipulation of the labile copper pool.…”

In vivo bioluminescence imaging reveals copper deficiency in a murine model of nonalcoholic fatty liver disease

“…metal homeostasis | molecular imaging | luciferin | metabolic liver disease | copper C opper is an essential mineral for all higher organisms, serving as a redox-active cofactor for physiological processes, including respiration (1,2), antioxidant defense (3,4), neurotransmitter synthesis and metabolism (5), epigenetic modifications (6), and emerging roles in dynamic signaling networks (7)(8)(9)(10)(11). This same redox activity also poses a potential danger, requiring highly orchestrated regulation of copper pools to prevent oxidative stress and free radical damage events that are detrimental to health (12)(13)(14)(15)(16)(17)(18).…”

A highly sensitive protocol for microscopy of alkyne lipids and fluorescently tagged or immunostained proteins

“…However, live cell imaging with CuAAC is further complicated by the cytotoxicity of the copper catalyst. While labeling of lipids in the plasma membrane and in internal membranes (47) of living cells with classical CuAAC has been reported, copper shows significant toxicity at micromolar concentrations and has a profound impact on lipid metabolism, especially if present in loosely bound form (48,49). More biocompatible copper catalysts (50) or additional ligands (48) for CuAAC, and copper-free coupling of azides to strain-promoted alkynes [strainpromoted azide-alkyne cycloaddition (SPAAC)] (29), have been developed to overcome these difficulties.…”