Neurokinin B and serum albumin limit copper binding to mammalian gonadotropin releasing hormone

Investigation of the Association of Serum Trace Elements Concentrations and Serum Biochemical Parameters with the Risk of Polycystic Ovary Syndrome: a Case-Control Study

Polycystic ovary syndrome (PCOS) is a heterogeneous endocrinological syndrome characterized by hyperandrogenism of ovarian origin and is often considered a predisposing factor for metabolic disorders. The objective of the study was to investigate serum levels of (a) trace elements (copper (Cu), zinc (Zn), magnesium (Mg), selenium (Se), iron (Fe), chromium (Cr), and manganese (Mn)); and (b) biochemical parameters (glucose, cholesterol, triglycerides, high-density lipoprotein (HDL-C), low-density lipoprotein (LDL-C), albumin, total protein, creatinine, and C-reactive protein (CRP) with risk of PCOS. Another objective was to explore the relationship between serum trace elements and biochemical variables. Serum trace elements were estimated by inductively coupled plasma mass spectrometry (ICP-MS) and biochemical parameters were estimated by colorimetric methods in 99 PCOS cases and 82 controls. Linear and non-linear associations of serum variables with PCOS risk were studied under logistic, probit, GAM, and BKMR model. Statistical analyses were performed using IBM SPSS 22.0 and R package version 4.2.1. All studied serum trace elements (except Zn) are significantly associated with PCOS. Combined effect analysis revealed Mg-Se and Fe-Cu association with PCOS risk. A significant association of cholesterol, HDL-C, LDL-C, CRP, and albumin was observed. Furthermore, linear regression analysis suggests an association between Mg-Cu and Mg-Fe-Mn with HDL-C; Fe and Cr-Cu with albumin; and Cu-Se with cholesterol and LDL-C both.

Non-Ceruloplasmin Copper Identifies a Subtype of Alzheimer’s Disease (CuAD): Characterization of the Cognitive Profile and Case of a CuAD Patient Carrying an RGS7 Stop-Loss Variant

Alzheimer’s disease (AD) is a type of dementia whose cause is incompletely defined. Copper (Cu) involvement in AD etiology was confirmed by a meta-analysis on about 6000 participants, showing that Cu levels were decreased in AD brain specimens, while Cu and non-bound ceruloplasmin Cu (non-Cp Cu) levels were increased in serum/plasma samples. Non-Cp Cu was advocated as a stratification add-on biomarker of a Cu subtype of AD (CuAD subtype). To further circumstantiate this concept, we evaluated non-Cp Cu reliability in classifying subtypes of AD based on the characterization of the cognitive profile. The stratification of the AD patients into normal AD (non-Cp Cu ≤ 1.6 µmol/L) and CuAD (non-Cp Cu > 1.6 µmol/L) showed a significant difference in executive function outcomes, even though patients did not differ in disease duration and severity. Among the Cu-AD patients, a 76-year-old woman showed significantly abnormal levels in the Cu panel and underwent whole exome sequencing. The CuAD patient was detected with possessing the homozygous (c.1486T > C; p.(Ter496Argext*19) stop-loss variant in the RGS7 gene (MIM*602517), which encodes for Regulator of G Protein Signaling 7. Non-Cp Cu as an add-on test in the AD diagnostic pathway can provide relevant information about the underlying pathological processes in subtypes of AD and suggest specific therapeutic options.

Interactions of neurokinin B with copper(II) ions and their potential biological consequences

Preeclampsia is a blood pressure disorder associated with significant proteinuria. Hypertensive women have increased levels of neurokinin B (NKB) and Cu(II) ions in blood plasma during pregnancy. NKB bears the...

A copper complex formed with neurokinin B: binding stoichiometry, redox properties, self-assembly and cytotoxicity

The tachykinin neuropeptide of neurokinin B (NKB) is a copper-binding amyloid peptide with important roles in the regulation of physiological functions and pathophysiological processes in the central and peripheral nervous systems. In this work, the formation of a NKB-Cu²⁺ complex in a 1 : 1 stoichiometry was confirmed by mass spectrometry. The self-assembly of NKB and its mutant species was investigated by Thioflavin T (ThT) fluorescence assay and atomic force microscopy (AFM), and at the same time, the effect of Cu²⁺ on the aggregation of NKB was studied. As evidenced by cyclic voltammetry, the redox potential of NKB-Cu²⁺ was determined to be 0.77 V (vs. Ag/AgCl). It has been demonstrated that NKB at low concentrations exerts its neuroprotective function by inhibiting Cu²⁺-mediated reactive oxygen species (ROS) production in the presence of ascorbic acid (AA). In comparison with equivalent Cu²⁺, the peptide-Cu²⁺ aggregates aggravated the viability of PC-12 cells more seriously in the absence of AA. These results should be extremely valuable for understanding the NKB/Cu²⁺ interactions and the toxicity mechanism of Cu²⁺ associated with neurodegenerative diseases.

Copper(II) Binding by the Earliest Vertebrate Gonadotropin-Releasing Hormone, the Type II Isoform, Suggests an Ancient Role for the Metal

In vertebrate reproductive biology copper can influence peptide and protein function both in the pituitary and in the gonads. In the pituitary, copper binds to the key reproductive peptides gonadotropin-releasing hormone I (GnRH-I) and neurokinin B, to modify their structure and function, and in the male gonads, copper plays a role in testosterone production, sperm morphology and, thus, fertility. In addition to GnRH-I, most vertebrates express a second isoform, GnRH-II. GnRH-II can promote testosterone release in some species and has other non-reproductive roles. The primary sequence of GnRH-II has remained largely invariant over millennia, and it is considered the ancestral GnRH peptide in vertebrates. In this work, we use a range of spectroscopic techniques to show that, like GnRH-I, GnRH-II can bind copper. Phylogenetic analysis shows that the proposed copper-binding ligands are retained in GnRH-II peptides from all vertebrates, suggesting that copper-binding is an ancient feature of GnRH peptides.

A gonadotropin-releasing hormone type neuropeptide with a high affinity binding site for copper(ii) and nickel(ii)

In vertebrates gonadotropin-releasing hormone I (GnRH-I) is a key regulator of reproductive development and function. The receptor-binding activity of human GnRH-I can be modified by the presence of divalent copper. Thus, copper binding to N-terminal amino acids in GnRH-I induces structural changes that influence receptor interactions and downstream intracellular signalling cascades. It is not known if copper-binding is restricted to human GnRH-I or if it is also a feature of GnRH-type peptides that have been identified in other taxa. To investigate this, we have characterised copper binding to a recently discovered GnRH-type peptide from the starfish Asterias rubens (ArGnRH). Using a range of spectroscopic and biophysical techniques we show that this peptide can bind copper(ii) and nickel(ii). Copper(ii) is bound in a square-planar, high-affinity (Kd ∼ 10-12 M) site incorporating four nitrogen donor atoms from a histidine imidazole group, two amides and the N-terminal amine group. The ArGnRH copper affinity and geometry are quite different to GnRH-I suggesting the copper sites have evolved to suit the environment the peptides are exposed to. By comparing the copper binding sites in ArGnRH and human GnRH-I and conducting a phylogenetic analysis of GnRH-type peptide sequences from a range of species, we predict that copper-binding is an evolutionarily ancient feature of GnRH-type peptides that has been retained, modified or lost in different lineages.

Endocytic recycling prevents copper accumulation in astrocytoma cells stimulated with copper-bound neurokinin B

Neurokinin B (NKB) is a key neuropeptide in reproductive endocrinology where it contributes to the generation of pulses of gonadotropin-releasing hormone. NKB is a copper-binding peptide; in the absence of metal NKB rapidly adopts an amyloid structure, but copper binding inhibits amyloid formation and generates a structure that can activate the neurokinin 3 receptor. The fate of copper once it binds NKB and activates the neurokinin 3 receptor is not understood, but endocytosis of NKB occurs even when the peptide is coordinated to copper. Using astrocytoma cells that express endogenous neurokinin 3 receptor, this work shows that endocytosis of apo- and copper-bound NKB occurs in concert with the receptor via a trafficking pathway that includes the early endosome. When cells are stimulated with copper-bound NKB the cellular copper concentration does not significantly increase, however when the cells are pre-treated with the recycling inhibitor, brefeldin A, they are capable of accumulating copper. This data shows that copper-bound NKB can activate the neurokinin 3 receptor then endocytosis abstracts metal, peptide and receptor from the cell surface. The cell does not accumulate the copper but instead it enters recycling pathways that ultimately leads to metal release from the cell. The work reveals a novel receptor-mediated copper trafficking pathway that retains metal in membrane bound organelles until it is exported from the cell.

Roles of copper in neurokinin B and gonadotropin-releasing hormone structure and function and the endocrinology of reproduction

Copper is a metal ion present in all organisms, where it has well-known roles in association with proteins and enzymes essential for cellular processes. In the early decades of the twentieth century copper was shown to influence mammalian reproductive biology, and it was subsequently shown to exert effects primarily at the level of the pituitary gland and/or hypothalamic regions of the brain. Furthermore, it has been reported that copper can interact with key neuropeptides in the hypothalamic-pituitary-gonadal axis, notably gonadotropin-releasing hormone (GnRH) and neurokinin B. Interestingly, recent phylogenetic analysis of the sequences of GnRH-related peptides indicates that copper binding is an evolutionarily ancient property of this neuropeptide family, which has been variously retained, modified or lost in the different taxa. In this mini-review the metal-binding properties of neuropeptides in the vertebrate reproductive pathway are reviewed and the evolutionary and functional significance of copper binding by GnRH-related neuropeptides in vertebrates and invertebrates are discussed.

Endocytosis of G Protein-Coupled Receptors and Their Ligands: Is There a Role in Metal Trafficking?

The prevalence of metal dysregulation in many neurodegenerative and neurocognitive disorders has compelled many studying such diseases to investigate the mechanisms underlying metal regulation in the central nervous system. Metal homoeostasis is often complex, with sophisticated, multilayered pathways in operation. G protein-coupled receptors are omnipresent on cell membranes and have intriguing mechanisms of endocytosis and trafficking that may be useful in metal homoeostasis. Indeed, many receptors and/or their cognate ligands are able to bind metals, and in many cases metals are considered to have neuromodulatory roles as a result of receptor binding. In this mini-review, we outline the structural and functional aspects of G protein-coupled receptors with a focus on the mechanisms leading to endocytosis and cellular trafficking. We further highlight how this may help in the trafficking of metal ions, notably copper.