An intrinsic GABAergic system in human lymphocytes
Research highlights
►Human Lymphocytes have a functional GABAergic system, similar to the neuronal one. ► Lymphocytes express the necessary components to synthesize, store and degradate GABA. ► Lymphocytes also express functional GABA transporters and ionotropic receptor subunits. ► GABA and Muscimol inhibit lymphocyte proliferation.
Introduction
Several reports concerning the presence of typical neurotransmitter systems in non-neuronal cells have displaced the concept that these molecules are exclusively expressed in nervous system. For example, it has been described that lymphocytes possess a complete cholinergic system as well as receptors for serotonin, histamine and dopamine (Akdis and Simons, 2006, De Rosa et al., 2005, Kawashima and Fujii, 2003, Kirillova et al., 2008, Yin et al., 2006). However, the physiological relevance of these extraneuronal systems is not completely understood. It has been proposed that they control cell proliferation, differentiation and cell–cell contact (De Rosa et al., 2009, Gladkevich et al., 2006, Wessler and Kirkpatrick, 2008). GABA, the principal inhibitory neurotransmitter in central nervous system, has been also detected in immune cells like monocytes and macrophages (Stuckey et al., 2005). It has been also postulated that GABA is involved in the progression of autoimmune diseases, such as Type-1 diabetes and multiple sclerosis (Bhat et al., 2010, Bjurstom et al., 2008, Tian et al., 2004).
The concentration of GABA in the brain is controlled by three main events: the synthesis by the enzyme glutamate decarboxilase (GAD), the catabolism by the enzyme GABA transaminase (GABA-T) and the uptake of released GABA by GABA transporters (GATs). At least two isoforms of GAD, GAD65 and GAD67, exist in mammals (Metzeler et al., 2004). Once synthesized, the vesicular inhibitory amino acid transporter (VIAAT) mediates the uptake of GABA into secretory vesicles. After being released, the synaptic action of GABA ends by the recapture of the neurotransmitter by specific high-affinity transporters (GATs). Four different GAT subtypes (GAT-1–3 and BGT-1) have been identified in humans. GAT-1 and GAT-3 are abundantly expressed in CNS and absent from the periphery, whereas BGT-1 and GAT-2 are expressed in human kidney, brain, lung and testis (Christiansen et al., 2007).
Once released, GABA exerts its effects through GABAA, GABAB and GABAC receptors. Whereas GABAA and GABAC receptors are ligand-gated ion channels permeable to chloride ions, GABAB receptors are associated to G-proteins. We here focused on ionotropic GABA receptors. Sixteen subunits (α1-6, β1-3, γ1-3, δ, ɛ, π and θ) can differently combine to form heteropentameric GABAA receptors. Most of the GABAA receptors contain at least α and β subunits. The rho subunits (ρ1–3) combine as homo or heteropentamers to conform GABAC receptors (Birnir and Korpi, 2007, Ong and Kerr, 2000).
Our study shows that lymphocytes contain the necessary components to constitute an independent GABAergic system. Furthermore, we describe the effects of GABA and muscimol on proliferation of mitogen-stimulated lymphocytes.
Section snippets
Isolation and culture of human peripheral lymphocytes
The experiments on human subjects were conducted in accordance with the Declaration of Helsinski. All procedures were carried out with the adequate understanding and written consent of the subjects. Lymphocytes were obtained from healthy volunteers (22–40 years old) essentially as described before (De Rosa et al., 2005). Blood was withdrawn from the antecubital vein using EDTA as anticoagulant. The diluted blood was loaded on 3 ml Ficoll separating solution (Amersham Biosciences, AB, Sweden)
Expression of GAD, VIAAT and GABA-T in human lymphocytes
Using RT-PCR we first explored if GAD isoforms (GAD67 and GAD65), VIAAT and GABA-T are expressed in resting and mitogen-activated lymphocytes. Human peripheral lymphocytes were incubated for 72 h in the absence and presence of PHA (10 μg/ml). No GAD65 mRNA expression was detected in samples of either resting or activated lymphocytes (n = 3). By contrast, mRNAs corresponding to GAD67 and VIAAT were detected in 70–80% of samples corresponding to resting cells and 100% of those of activated
Discussion
Our results reveal the presence of a GABAergic system in human peripheral lymphocytes. We determine GAD and VIAAT mRNA expression, which are indicators of GABA-producing cells. Blood GABA concentration in healthy individuals is around 0.1 μM, however the precise origin of this molecule is not known (Bjork et al., 2001). Our results suggest that peripheral lymphocytes are a source of plasmatic GABA. RT-PCR experiments show that mRNA corresponding to GAD67 is present in lymphocytes, whereas GAD65
Acknowledgements
We thank Dr. B. Gasnier (Institut de Biologie Physico-Chimique, Paris, France) for generously supplying the anti-VIAAT antibody. Leonardo Dionisio is a fellow of the Comisión de Investigaciones Científicas (CIC) from Argentina. The present work was supported by grants from Universidad Nacional del Sur (MCE, CB), Agencia Nacional de Promoción Científica y Tecnológica (CB) and CONICET (CB).
References (45)
- et al.
Histamine receptors are hot in immunopharmacology
Eur. J. Pharmacol.
(2006) - et al.
Human peripheral blood mononuclear cells express GABAA receptor subunits
Mol. Immunol.
(2006) - et al.
Identification of dopamine plasma membrane and vesicular transporters in human peripheral blood lymphocytes
J. Neuroimmunol.
(2001) - et al.
Plasma GABA levels correlate with aggressiveness in relatives of patients with unipolar depressive disorder
Psychiatry Res.
(2001) - et al.
GABA, a natural immunomodulator of T lymphocytes
J. Neuroimmunol.
(2008) - et al.
A novel mechanism for GABA synthesis and packaging into synaptic vesicles
Neurochem. Int.
(2009) - et al.
Gamma-aminobutyric acid-transaminase activity in the human thymus after administration of interferons
Hum. Immunol.
(2000) - et al.
Cloning and characterization of a functional human gamma-aminobutyric acid (GABA) transporter, human GAT-2
J. Biol. Chem.
(2007) - et al.
Single-channel kinetic analysis for activation and desensitization of homomeric 5-HT(3)A receptors
Biophys. J.
(2009) - et al.
Relationship between alpha 7 nAChR and apoptosis in human lymphocytes
J. Neuroimmunol.
(2005)
Alpha 7 nicotinic acetylcholine receptor modulates lymphocyte activation
Life Sci.
Diabetes-related antibodies in adult diabetic patients
Best Pract. Res. Clin. Endocrinol. Metab.
Induction of choline acetyltransferase mRNA in human mononuclear leukocytes stimulated by phytohemagglutinin, a T-cell activator
J. Neuroimmunol.
The peripheral GABAergic system as a target in endocrine disorders
Auton. Neurosci.
The lymphocytic cholinergic system and its contribution to the regulation of immune activity
Life Sci.
Dopamine receptors in human lymphocytes: radioligand binding and quantitative RT-PCR assays
J. Neurosci. Methods
Secretory lysosomes and their cargo in T and NK cells
Immunol. Lett.
Role of Cl− in electrogenic Na+-coupled cotransporters GAT1 and SGLT1
J. Biol. Chem.
Anti-inflammatory properties of cholinergic up-regulation: a new role for acetylcholinesterase inhibitors
Neuropharmacology
A novel form of immune signaling revealed by transmission of the inflammatory mediator serotonin between dendritic cells and T cells
Blood
Immunochemical and immunocytochemical characterization of cholinergic markers in human peripheral blood lymphocytes
J. Neuroimmunol
GABA(A) receptors mediate inhibition of T cell responses
J. Neuroimmunol
Cited by (85)
Neuroimmune interactions: From bench to bedside
2023, Translational Neuroimmunology: Neuroinflammation: Volume 7Secreted immune metabolites that mediate immune cell communication and function
2022, Trends in ImmunologyCitation Excerpt :For instance, GABAA receptor signaling suppresses T cell proliferation and effector functions [32], induces migration of DCs upon Toxoplasma gondii infection [33,34], promotes activation of autophagy in macrophages with mycobacterial infection [35], and facilitates anti-inflammatory macrophage differentiation such as IL-10-producing macrophages [24]. Of note, as in neurons, the GABAA receptor in immune cells can comprise different combinations of multiple subunits, and the presence of distinct receptor subunits may determine the affinity of GABA to bind to its receptors in the brain or in various cell subsets of the immune system [36–38]. Other GABA receptors that are broadly expressed in neurons and among some cells of the immune system are the metabotropic GABAB receptors.
Characterization of the GABAergic system in Asian clam Corbicula fluminea: Phylogenetic analysis, tissue distribution, and response to the aquatic contaminant carbamazepine
2021, Comparative Biochemistry and Physiology Part - C: Toxicology and PharmacologySub-basal increases of GABA enhance the synthesis of TNF-α, TGF-β, and IL-1β in the immune system organs of the Nile tilapia
2020, Journal of Neuroimmunology
- 1
These authors contributed equally to the work.