Activation of tachykinin, neurokinin 3 receptors affects chromatin structure and gene expression by means of histone acetylation

A Second Wave for the Neurokinin Tac2 Pathway in Brain Research

Despite promising advances in basic research of the neurokinin B/Tac2 pathway in both animals and humans, clinical applications are yet to be implemented. This is likely because of our limited understanding of the action of the pathway in the brain. While this system controls neuronal activity in multiple regions, the precise impact of Tac2-induced cellular responses on behavior remains unclear. Recently, elegant studies revealed a key contribution to stress-related behaviors and memory. Here, we discuss the crucial importance of bridging the gap between the Tac2 pathway's involvement in cell physiology and cognition to comprehend its role in health and disease. We propose that a better understanding of the Tac2 pathway in the brain could provide an essential perspective for basic investigations, which in turn will feed clinical research.

Endocytosis of the tachykinin neuropeptide, neurokinin B, in astrocytes and its role in cellular copper uptake

The tachykinin neuropeptide, neurokinin B (NKB), belongs to a family of peptides having diverse roles in the brain. NKB, along with several other tachykinins, has been identified as a copper-binding peptide, however the physiological relevance of the binding is unclear. Previously, NKB was shown to limit the ability of copper to enter astrocytes and disrupt calcium homeostasis and it was thought that the peptide was sequestering the metal extracellularly. Here we use a fluorescein-labelled NKB peptide (F-NKB) to show that NKB is not retained extracellularly, but is endocytosed within 10-20min after addition to the cell media. The endocytosis is not inhibited when NKB is delivered as a copper-complex, [Cu^II(F-NKB)₂]. Endocytosis of NKB can increase intracellular copper. Comparison to cells cultured in copper-free buffer indicated that apo-NKB can facilitate uptake of copper found in normal culture media. To achieve this NKB must compete with a variety of copper proteins, and we show that NKB can successfully compete with copper-binding peptides derived from the prion protein, itself associated with Cu(II) and Zn(II) metabolism. We suggest a mechanism of receptor mediated endocytosis to account for the observations.

Activation of the neurokinin 3 receptor promotes filopodia growth and sprouting in rat embryonic hypothalamic cells

Members of the tachykinin family have trophic effects on developing neurons. The tachykinin neurokinin 3 receptor (NK3R) appears early in embryonic development; during the peak birthdates of hypothalamic neurons, but its involvement in neural development has not been examined. To address its possible role, immortalized embryonic hypothalamic neurons (CLU209) were treated with CellMask, a plasma membrane stain, or the membranes were imaged in CLU209 cells that were transfected with a pEGFP-NK3R expression vector. Nontransfected cells and transfected cells were then treated with senktide, a NK3R agonist, or Dulbecco's Modified Eagle's Medium (DMEM) and time-lapse confocal images were captured for the following 30 min. Compared to DMEM, senktide treatment led to filopodia initiation from the soma of both nontransfected and transfected CLU209 cells. These filopodia had diameters and lengths of approximately 200 nm and 3 µm, respectively. Pretreatment with an IP3 receptor blocker, 2-aminoethoxydiphenyl borate (2-APB), prevented the senktide-induced growth in filopodia; demonstrating that NK3R-induced outgrowth of filopodia likely involves the release of intracellular calcium. Exposure of transfected CLU209 cells to senktide for 24 h led to further growth of filopodia and processes that extended 10-20 µm. A mathematical model, composed of a linear and population model was developed to account for the dynamics of filopodia growth during a timescale of minutes. The results suggest that the ligand-induced activation of NK3R affects early developmental processes by initiating filopodia formation that are a prerequisite for neuritogenesis.