An improved method for expression and purification of functional human Ca(2+) transporter PMCA4b in Saccharomyces cerevisiae.

Human plasma membrane calcium ATPases (PMCAs) are highly regulated transporters responsible for the extrusion of calcium out of the cell. Since calcium homeostasis is implicated in several diseases and neurodegenerative disorders, understanding PMCAs activity is crucial. One of the major hindrances is the availability of these proteins for functional and structural analysis. Here, using the yeast Saccharomyces cerevisiae system, we show a new and enhanced method for the expression of the full-length human PMCA isoform 4b (hPMCA4b) and a truncated form lacking its auto-inhibitory domain. We have also improved a method for the purification of the native isoform by calmodulin-agarose affinity chromatography, and developed a new method to purify the truncated isoform by glutathione-Sepharose affinity chromatography. One of the most relevant features of this work is that, when compared to PMCAs purification from pig brain, our method provides a pure single isoform instead of a mixture of isoforms, essential for fine-tuning the activity of PMCA4b. Another relevant feature is that the method described in this work has a superior yield of protein than previously established methods to purify PMCA proteins expressed in yeasts.

Dual effects of noradrenaline on astroglial production of chemokines and pro-inflammatory mediators.

BACKGROUND: Noradrenaline (NA) is known to limit neuroinflammation. However, the previously described induction by NA of a chemokine involved in the progression of immune/inflammatory processes, such as chemokine (C-C motif) ligand 2 (CCL2)/monocyte chemotactic protein-1 (MCP-1), apparently contradicts NA anti-inflammatory actions. In the current study we analyzed NA regulation of astroglial chemokine (C-X3-C motif) ligand 1 (CX3CL1), also known as fractalkine, another chemokine to which both neuroprotective and neurodegenerative actions have been attributed. In addition, NA effects on other chemokines and pro-inflammatory mediators were also analyzed. METHODS: Primary astrocyte-enriched cultures were obtained from neonatal Wistar rats. These cells were incubated for different time durations with combinations of NA and lipopolysaccharide (LPS). The expression and synthesis of different proteins was measured by RT-PCR and enzyme-linked immunosorbent assay (ELISA) or enzyme immunoassays. Data were analyzed by one-way analysis of variance (ANOVA), followed by Newman-Keuls multiple comparison tests. RESULTS: The data presented here show that in control conditions, NA induces the production of CX3CL1 in rat cultured astrocytes, but in the presence of an inflammatory stimulus, such as LPS, NA has the opposite effect inhibiting CX3CL1 production. This inversion of NA effect was also observed for MCP-1. Based on the observation of this dual action, NA regulation of different chemokines and pro-inflammatory cytokines was also analyzed, observing that in most cases NA exerts an inhibitory effect in the presence of LPS. One characteristic exception was the induction of cyclooxygenase-2 (COX-2), where a summative effect was detected for both LPS and NA. CONCLUSION: These data suggest that NA effects on astrocytes can adapt to the presence of an inflammatory agent reducing the production of certain cytokines, while in basal conditions NA may have the opposite effect and help to maintain moderate levels of these cytokines.

Regulation of CCL2/MCP-1 production in astrocytes by desipramine and atomoxetine: involvement of α2 adrenergic receptors.

Having previously observed that noradrenaline activation of ß adrenergic receptors induces the synthesis of the chemokine monocyte chemoattractant protein (CCL2/MCP-1) in astrocytes, it is our interest to analyze the mechanisms involved in this process, particularly the possible effect of noradrenaline-modulating drugs. The treatment of primary rat astrocyte cultures with the noradrenaline transporter inhibitors desipramine or atomoxetine induced the expression and synthesis of CCL2/MCP-1 in these cells. This effect of both drugs in vitro suggests that CCL2/MCP-1 expression could also be modulated by some mechanism independent of the elevation of brain noradrenaline levels. This was confirmed by measuring a reduction in CCL2/MCP-1 production by the treatment with the α2 adrenergic receptor agonist clonidine. Accordingly, the blockade of α2 adrenergic receptors with yohimbine potentiated the production of MCP-1 stimulated by the activation of ß receptors. While the activation of ß adrenergic receptors and the subsequent elevation of cAMP levels seem to be the main pathway for noradrenaline to induce CCL2/MCP-1 in astrocytes, our data indicate that the α2 adrenergic receptors also regulate CCL2/MCP-1 expression working as inhibitory mediators.

CCL2/MCP-1 modulation of microglial activation and proliferation.

BACKGROUND: Monocyte chemoattractant protein (CCL2/MCP-1) is a chemokine that attracts cells involved in the immune/inflammatory response. As microglia are one of the main cell types sustaining inflammation in brain, we proposed here to analyze the direct effects of MCP-1 on cultured primary microglia. METHODS: Primary microglia and neuronal cultures were obtained from neonatal and embryonic Wistar rats, respectively. Microglia were incubated with different concentrations of recombinant MCP-1 and LPS. Cell proliferation was quantified by measuring incorporation of bromodeoxyuridine (BrdU). Nitrite accumulation was measured using the Griess assay. The expression and synthesis of different proteins was measured by RT-PCR and ELISA. Cell death was quantified by measuring release of LDH into the culture medium. RESULTS: MCP-1 treatment (50 ng/ml, 24 h) did not induce morphological changes in microglial cultures. Protein and mRNA levels of different cytokines were measured, showing that MCP-1 was not able to induce proinflammatory cytokines (IL-1ß, IL6, MIP-1α), either by itself or in combination with LPS. A similar lack of effect was observed when measuring inducible nitric oxide synthase (NOS2) expression or accumulation of nitrites in the culture media as a different indicator of microglial activation. MCP-1 was also unable to alter the expression of different trophic factors that were reduced by LPS treatment. In order to explore the possible release of other products by microglia and their potential neurotoxicity, neurons were co-cultured with microglia: no death of neurons could be detected when treated with MCP-1. However, the presence of MCP-1 induced proliferation of microglia, an effect opposite to that observed with LPS. CONCLUSION: These data indicate that, while causing migration and proliferation of microglia, MCP-1 does not appear to directly activate an inflammatory response in this cell type, and therefore, other factors may be necessary to cause the changes that result in the neuronal damage commonly observed in situations where MCP-1 levels are elevated.

Regulation of MCP-1 production in brain by stress and noradrenaline-modulating drugs.

While it is accepted that noradrenaline (NA) reduction in brain contributes to the progression of certain neurodegenerative diseases, the mechanisms through which NA exerts its protective actions are not well known. We previously reported that NA induced production of monocyte chemoattractant protein (MCP-1/CCL2) in cultured astrocytes mediated some of the neuroprotective actions of NA. We have now examined the regulation of MCP-1 production in vivo. Treatment of mice with the NA precursor l-threo-3,4-dihydroxyphenylserine induced the production of MCP-1 in astrocytes. In contrast, exposure to stress (a process known to elevate brain NA levels) produced only a moderate increase of MCP-1 because of the inhibitory activity of glucocorticoids released during the stress response. Similarly, corticosterone treatment of astrocytes caused a reduction of constitutive as well as the NA-induced MCP-1 production. When stressed rats had the production of glucocorticoids blocked by the selective inhibitor metyrapone, a large increase of MCP-1 concentration was observed in cortex, whereas propranolol (a beta adrenergic receptor blocker) avoided modifications of MCP-1 after stress. Desipramine (an inhibitor of NA reuptake) also caused an increase of MCP-1 in cortex. These data suggest that some phenomena caused by the alteration of NA or glucocorticoids could be mediated by MCP-1.