Pumping up the synapse

Therapeutic potential for KCC2-targeted neurological diseases

Patients with neurological diseases, such as schizophrenia, tend to show low K+-Cl- co-transporter 2 (KCC2) levels in the brain. The cause of these diseases has been associated with stress and neuroinflammation. However, since the pathogenesis of these diseases is not yet fully investigated, drug therapy is still limited to symptomatic therapy. Targeting KCC2, which is mainly expressed in the brain, seems to be an appropriate approach in the treatment of these diseases. In this review, we aimed to discuss about stress and inflammation, KCC2 and Gamma-aminobutyric acid (GABA) function, diseases which decrease the KCC2 levels in the brain, factors that regulate KCC2 activity, and the possibility to overcome neuronal dysfunction targeting KCC2. We also aimed to discuss the relationships between neurological diseases and LPS caused by Porphyromonas gingivalis (P. g), which is a type of oral bacterium. Clinical trials on oxytocin, sirtuin 1 (SIRT1) activator, and transient receptor potential cation channel subfamily V Member 1 activator have been conducted to develop effective treatment methods. We believe that KCC2 modulators that regulate mitochondria, such as oxytocin, glycogen synthase kinase 3β (GSK3β), and SIRT1, can be potential targets for neurological diseases.

The Protein 4.1 family: hub proteins in animals for organizing membrane proteins

Proteins of the 4.1 family are characteristic of eumetazoan organisms. Invertebrates contain single 4.1 genes and the Drosophila model suggests that 4.1 is essential for animal life. Vertebrates have four paralogues, known as 4.1R, 4.1N, 4.1G and 4.1B, which are additionally duplicated in the ray-finned fish. Protein 4.1R was the first to be discovered: it is a major mammalian erythrocyte cytoskeletal protein, essential to the mechanochemical properties of red cell membranes because it promotes the interaction between spectrin and actin in the membrane cytoskeleton. 4.1R also binds certain phospholipids and is required for the stable cell surface accumulation of a number of erythrocyte transmembrane proteins that span multiple functional classes; these include cell adhesion molecules, transporters and a chemokine receptor. The vertebrate 4.1 proteins are expressed in most tissues, and they are required for the correct cell surface accumulation of a very wide variety of membrane proteins including G-Protein coupled receptors, voltage-gated and ligand-gated channels, as well as the classes identified in erythrocytes. Indeed, such large numbers of protein interactions have been mapped for mammalian 4.1 proteins, most especially 4.1R, that it appears that they can act as hubs for membrane protein organization. The range of critical interactions of 4.1 proteins is reflected in disease relationships that include hereditary anaemias, tumour suppression, control of heartbeat and nervous system function. The 4.1 proteins are defined by their domain structure: apart from the spectrin/actin-binding domain they have FERM and FERM-adjacent domains and a unique C-terminal domain. Both the FERM and C-terminal domains can bind transmembrane proteins, thus they have the potential to be cross-linkers for membrane proteins. The activity of the FERM domain is subject to multiple modes of regulation via binding of regulatory ligands, phosphorylation of the FERM associated domain and differential mRNA splicing. Finally, the spectrum of interactions of the 4.1 proteins overlaps with that of another membrane-cytoskeleton linker, ankyrin. Both ankyrin and 4.1 link to the actin cytoskeleton via spectrin, and we hypothesize that differential regulation of 4.1 proteins and ankyrins allows highly selective control of cell surface protein accumulation and, hence, function. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé

GRK5 promotes F-actin bundling and targets bundles to membrane structures to control neuronal morphogenesis

Neuronal morphogenesis requires extensive membrane remodeling and cytoskeleton dynamics. In this paper, we show that GRK5, a G protein-coupled receptor kinase, is critically involved in neurite outgrowth, dendrite branching, and spine morphogenesis through promotion of filopodial protrusion. Interestingly, GRK5 is not acting as a kinase but rather provides a key link between the plasma membrane and the actin cytoskeleton. GRK5 promoted filamentous actin (F-actin) bundling at the membranes of dynamic neuronal structures by interacting with both F-actin and phosphatidylinositol-4,5-bisphosphate. Moreover, separate domains of GRK5 mediated the coupling of actin cytoskeleton dynamics and membrane remodeling and were required for its effects on neuronal morphogenesis. Accordingly, GRK5 knockout mice exhibited immature spine morphology and deficient learning and memory. Our findings identify GRK5 as a critical mediator of dendritic development and suggest that coordinated actin cytoskeleton and membrane remodeling mediated by bifunctional actin-bundling and membrane-targeting molecules, such as GRK5, is crucial for proper neuronal morphogenesis and the establishment of functional neuronal circuitry.

Dendritic spine dynamics--a key role for kalirin-7

Changes in the structure and function of dendritic spines contribute to numerous physiological processes such as synaptic transmission and plasticity, as well as behavior, including learning and memory. Moreover, altered dendritic spine morphogenesis and plasticity is an endophenotype of many neurodevelopmental and neuropsychiatric disorders. Hence, the molecular mechanisms that control spine plasticity and pathology have been under intense investigation over the past few years. A series of recent studies has improved our understanding of spine dynamics by establishing kalirin-7 as an important regulator of dendritic spine development as well as structural and functional plasticity, providing a model for the molecular control of structural plasticity and implicating kalirin-7 in synaptic pathology in several disorders including schizophrenia and Alzheimer's disease.