Pharmacological characterization of mammalian D1 and D2 dopamine receptors expressed in Drosophila Schneider-2 cells

TP10-Dopamine Conjugate as a Potential Therapeutic Agent in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is a common progressive neurodegenerative disorder for which the current treatment is not fully satisfactory. One of the major drawbacks of current PD therapy is poor penetration of drugs across the blood-brain barrier (BBB). In recent years, cell-penetrating peptides (CPPs) such as Tat, SynB, or TP10 have gained great interest due to their ability to penetrate cell membranes and to deliver different cargos to their targets including the central nervous system (CNS). However, there is no data with respect to the use of CPPs as drug carriers to the brain for the treatment of PD. In the presented research, the covalent TP10-dopamine conjugate was synthesized and its pharmacological properties were characterized in terms of its ability to penetrate the BBB and anti-parkinsonian activity. The results showed that dopamine (DA) in the form of a conjugate with TP10 evidently gained access to the brain tissue, exhibited low susceptibility to O-methylation reaction by catechol- O-methyltransferase (lower than that of DA), possessed a relatively high affinity to both dopamine D₁ and D₂ receptors (in the case of D₁, a much higher than that of DA), and showed anti-parkinsonian activity (higher than that of l-DOPA) in the MPTP-induced preclinical animal model of PD. The presented results prove that the conjugation of TP10 with DA may be a good starting point for the development of a new strategy for the treatment of PD.

The Sensitivity of the Crayfish Reward System to Mammalian Drugs of Abuse

The idea that addiction occurs when the brain is not able to differentiate whether specific reward circuits were triggered by adaptive natural rewards or falsely activated by addictive drugs exist in several models of drug addiction. The suitability of crayfish (Orconectes rusticus) for drug addiction research arises from developmental variation of growth, life span, reproduction, behavior and some quantitative traits, especially among isogenic mates reared in the same environment. This broad spectrum of traits makes it easier to analyze the effect of mammalian drugs of abuse in shaping behavioral phenotype. Moreover, the broad behavioral repertoire allows the investigation of self-reinforcing circuitries involving appetitive and exploratory motor behavior, while the step-wise alteration of the phenotype by metamorphosis allows accurate longitudinal analysis of different behavioral states. This paper reviews a series of recent experimental findings that evidence the suitability of crayfish as an invertebrate model system for the study of drug addiction. Results from these studies reveal that unconditioned exposure to mammalian drugs of abuse produces a variety of stereotyped behaviors. Moreover, if presented in the context of novelty, drugs directly stimulate exploration and appetitive motor patterns along with molecular processes for drug conditioned reward. Findings from these studies indicate the existence of drug sensitive circuitry in crayfish that facilitates exploratory behavior and appetitive motor patterns via increased incentive salience of environmental stimuli or by increasing exploratory motor patterns. This work demonstrates the potential of crayfish as a model system for research into the neural mechanisms of addiction, by contributing an evolutionary, comparative context to our understanding of natural reward as an important life-sustaining process.

Dopamine Receptor D1 Agonism and Antagonism Using a Field-Effect Transistor Assay

The field-effect transistor (FET) has been used in the development of diagnostic tools for several decades, leading to high-performance biosensors. Therefore, the FET platform can provide the foundation for the next generation of analytical methods. A major role of G-protein-coupled receptors (GPCRs) is in the transfer of external signals into the cell and promoting human body functions; thus, their principle application is in the screening of new drugs. The research community uses efficient systems to screen potential GPCR drugs; nevertheless, the need to develop GPCR-conjugated analytical devices remains for next-generation new drug screening. In this study, we proposed an approach for studying receptor agonism and antagonism by combining the roles of FETs and GPCRs in a dopamine receptor D1 (DRD1)-conjugated FET system, which is a suitable substitute for conventional cell-based receptor assays. DRD1 was reconstituted and purified to mimic native binding pockets that have highly discriminative interactions with DRD1 agonists/antagonists. The real-time responses from the DRD1-nanohybrid FET were highly sensitive and selective for dopamine agonists/antagonists, and their maximal response levels were clearly different depending on their DRD1 affinities. Moreover, the equilibrium constants (K) were estimated by fitting the response levels. Each K value indicates the variation in the affinity between DRD1 and the agonists/antagonists; a greater K value corresponds to a stronger DRD1 affinity in agonism, whereas a lower K value in antagonism indicates a stronger dopamine-blocking effect.

Optimized expression of the antimicrobial protein Gloverin from Galleria mellonella using stably transformed Drosophila melanogaster S2 cells

Antimicrobial proteins and peptides (AMPs) are valuable as leads in the pharmaceutical industry for the development of novel anti-infective drugs. Here we describe the efficient heterologous expression and basic characterization of a Gloverin-family AMP derived from the greater wax moth Galleria mellonella. Highly productive single-cell clones prepared by limiting dilution achieved a 100% increase in productivity compared to the original polyclonal Drosophila melanogaster S2 cell line. Comprehensive screening for suitable expression conditions using statistical experimental designs revealed that optimal induction was achieved using 600 µM CuSO4 at the mid-exponential growth phase. Under these conditions, 25 mg/L of the AMP was expressed at the 1-L bioreactor scale, with optimal induction and harvest times ensured by dielectric spectroscopy and the online measurement of optical density. Gloverin was purified from the supernatant by immobilized metal ion affinity chromatography followed by dialysis. In growth assays, the purified protein showed specific antimicrobial activity against two different strains of Escherichia coli.

Drosophila S2 Schneider cells: a useful tool for rebuilding and redesigning approaches in synthetic biology

Synthetic biology is an engineering approach to biology. A synthetic biologist wants to describe biological molecules and their subdomains as well-defined parts of a molecular machine. To achieve this goal, synthetic biologists rebuild minimal functional biological systems from well-defined parts or they design new molecules that do not exist in nature but have new and useful functions. In short, these engineering approaches can be summarized as "rebuild, alter, and understand." The Drosophila S2 Schneider cell is a useful tool for both rebuilding and redesigning approaches. S2 cells are phagocytic cells that easily take up large amounts of DNA from the cell culture. They, thus, have a high cotransfection rate, allowing the coexpression of up to 12 different proteins. We have developed a transient transfection protocol allowing the rapid and parallel analysis of wild-type and altered forms of a biological system. This chapter describes our methods to rebuild and better understand mammalian signaling systems in the evolutionary distant environment of Drosophila S2 cells.

Pharmacology of signaling induced by dopamine D(1)-like receptor activation

Dopamine D(1)-like receptors consisting of D(1) and D(5) subtypes are intimately implicated in dopaminergic regulation of fundamental neurophysiologic processes such as mood, motivation, cognitive function, and motor activity. Upon stimulation, D(1)-like receptors initiate signal transduction cascades that are mediated through adenylyl cyclase or phosphoinositide metabolism, with subsequent enhancement of multiple downstream kinase cascades. The latter actions propagate and further amplify the receptor signals, thus predisposing D(1)-like receptors to multifaceted interactions with various other mediators and receptor systems. The adenylyl cyclase response to dopamine or selective D(1)-like receptor agonists is reliably associated with the D(1) subtype, while emerging evidence indicates that the phosphoinositide responses in native brain tissues may be preferentially mediated through stimulation of the D(5) receptor. Besides classic coupling of each receptor subtype to specific G proteins, additional biophysical models are advanced in attempts to account for differential subcellular distribution, heteromolecular oligomerization, and activity-dependent selectivity of the receptors. It is expected that significant advances in understanding of dopamine neurobiology will emerge from current and anticipated studies directed at uncovering the molecular mechanisms of D(5) coupling to phosphoinositide signaling, the structural features that might enhance pharmacological selectivity for D(5) versus D(1) subtypes, the mechanism by which dopamine may modulate phosphoinositide synthesis, the contributions of the various responsive signal mediators to D(1) or D(5) interactions with D(2)-like receptors, and the spectrum of dopaminergic functions that may be attributed to each receptor subtype and signaling pathway.

Heterologous expression of membrane proteins for structural analysis

Membrane proteins (MPs) are responsible for the interface between the exterior and the interior of the cell. These proteins are involved in numerous diseases, like cancer, cystic fibrosis, epilepsy, hyperinsulinism, heart failure, hypertension and Alzheimer disease. However, studies of these disorders are hampered by a lack of structural information about the proteins involved. Structural analysis requires large quantities of pure and active proteins. The majority of medically and pharmaceutically relevant MPs are present in tissues at low concentration, which makes heterologous expression in large-scale production-adapted cells a prerequisite for structural studies. Obtaining mammalian MP structural data depends on the development of methods that allow the production of large quantities of MPs. This review focuses on the heterologous expression systems now available to produce large amounts of MPs for structural proteomics, and describes the strategies that allowed the determination of the structure of the first heterologously expressed mammalian MPs.

Expression of membrane proteins in Drosophila Melanogaster S2 cells: Production and analysis of a EGFP-fused G protein-coupled receptor as a model

In the process of selecting an appropriate host for the heterologous expression of functional eukaryotic membrane proteins, Drosophila S2 cells, although not yet fully explored, appear as a valuable alternative to mammalian cell lines or other virus-infected insect cell systems. This nonlytic, plasmid-based system actually combines several major physiological and bioprocess advantages that make it a highly potential and scalable cellular tool for the production of membrane proteins in a variety of applications, including functional characterization, pharmacological profiling, molecular simulations, structural analyses, or generation of vaccines. We present here a series of protocols and hints that would serve the successful expression of membrane proteins in S2 cells, using an enhanced green fluorescent protein (EGFP)/G protein-coupled receptor (EGFP-GPCR) as a model.

Protein expression in the Drosophila Schneider 2 cell system

The Schneider-2 (S2) Drosophila cell line is well suited for the stable overexpression of recombinant proteins using plasmid-based protein expression vectors. Following drug selection, a polyclonal S2 cell line can be induced to express on the order of 2 to 100 pmol/mg membrane protein for G-coupled protein receptors, 4000 to 100,000 sites/cell for other membrane receptors and 3 to 35 mg/liter for soluble and secreted proteins.