LPA1 is a key mediator of intracellular signalling and neuroprotection triggered by tetracyclic antidepressants in hippocampal neurons

Differential targeting of lysophosphatidic acid LPA1, LPA2, and LPA3 receptor signalling by tricyclic and tetracyclic antidepressants

We previously reported that in different cell types antidepressant drugs activate lysophosphatidic acid (LPA) LPA1 receptor to induce proliferative and prosurvival responses. Here, we further characterize this unique action of antidepressants by examining their effects on two additional LPA receptor family members, LPA2 and LPA3. Human LPA1-3 receptors were stably expressed in HEK-293 cells (HEK-LPA1, -LPA2 and -LPA3 cells) and their functional activity was determined by Western blot and immunofluorescence. LPA effectively stimulated the phosphorylation of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) in HEK-LPA1, -LPA2, and -LPA3 cells. The tricyclic antidepressants amitriptyline, clomipramine, imipramine and desipramine increased phospho-ERK1/2 levels in HEK-LPA1 and -LPA3 cells but were relatively poor agonists in LPA2-expressing cells. The tetracyclic antidepressants mianserin and mirtazapine were active at all three LPA receptors. When combined with LPA, both amitriptyline and mianserin potentiated Gi/o-mediated phosphorylation of ERK1/2 induced by LPA in HEK-LPA1, -LPA2 and -LPA3 cells, CHO-K1 fibroblasts and HT22 hippocampal neuroblasts. This potentiation was associated with enhanced phosphorylation of CREB and S6 ribosomal protein, two molecular targets of activated ERK1/2. The antidepressants also potentiated LPA-induced Gq/11-mediated phosphorylation of AMP-activated protein kinase in HEK-LPA1 and -LPA3 cells. Conversely, amitriptyline and mianserin were found to inhibit LPA-induced Rho activation in HEK-LPA1 and LPA2 cells. These results indicate that tricyclic and tetracyclic antidepressants can act on LPA1, LPA2 and LPA3 receptor subtypes and exert differential effects on LPA signalling through these receptors.

A systematic study on the use of multifunctional nanodiamonds for neuritogenesis and super-resolution imaging

BACKGROUND

Regeneration of defective neurons in central nervous system is a highlighted issue for neurodegenerative disease treatment. Various tissue engineering approaches have focused on neuritogenesis to achieve the regeneration of damaged neuronal cells because damaged neurons often fail to achieve spontaneous restoration of neonatal neurites. Meanwhile, owing to the demand for a better diagnosis, studies of super-resolution imaging techniques in fluorescence microscopy have triggered the technological development to surpass the classical resolution dictated by the optical diffraction limit for precise observations of neuronal behaviors. Herein, the multifunctional nanodiamonds (NDs) as neuritogenesis promoters and super-resolution imaging probes were studied.

METHODS

To investigate the neuritogenesis-inducing capability of NDs, ND-containing growing medium and differentiation medium were added to the HT-22 hippocampal neuronal cells and incubated for 10 d. In vitro and ex vivo images were visualized through custom-built two-photon microscopy using NDs as imaging probes and the direct stochastic optical reconstruction microscopy (dSTORM) process was performed for the super-resolution reconstruction owing to the photoblinking properties of NDs. Moreover, ex vivo imaging of the mouse brain was performed 24 h after the intravenous injection of NDs.

RESULTS

NDs were endocytosed by the cells and promoted spontaneous neuritogenesis without any differentiation factors, where NDs exhibited no significant toxicity with their outstanding biocompatibility. The images of ND-endocytosed cells were reconstructed into super-resolution images through dSTORM, thereby addressing the problem of image distortion due to nano-sized particles, including size expansion and the challenge in distinguishing the nearby located particles. Furthermore, the ex vivo images of NDs in mouse brain confirmed that NDs could penetrate the blood-brain barrier (BBB) and retain their photoblinking property for dSTORM application.

CONCLUSIONS

It was demonstrated that the NDs are capable of dSTORM super-resolution imaging, neuritogenic facilitation, and BBB penetration, suggesting their remarkable potential in biological applications.

Gintonin stimulates dendritic growth in striatal neurons by activating Akt and CREB

Gintonin, a glycolipid protein conjugated with lysophosphatidic acid (LPA), is a newly identified compound extracted from Korean ginseng. LPA receptor isotypes exhibit high affinity for gintonin and mediate intracellular calcium signaling in various animal cell models. In this study, we found that gintonin induced the activation of Akt and cAMP-response element binding protein (CREB) in mouse striatal neurons, and chronic treatment with gintonin potently induced dendritic growth and filopodia formation. Gintonin-induced Akt/CREB activation and dendritic development were significantly impaired by LPA receptor (LPAR1/3) inhibition with Ki16425. Intriguingly, prolonged treatment with gintonin ameliorated the reduction in dendritic formation caused by Shank3 and Slitrk5 deficiency in the striatal neurons. In addition, gintonin and brain-derived neurotrophic factor (BDNF) had a synergistic effect on AKT/CREB activation and dendritic growth at suboptimal concentrations. These findings imply that gintonin-stimulated LPA receptors play a role in dendritic growth in striatal neurons and that they may act synergistically with BDNF, which is known to play a role in dendritogenesis.

Protective Effects of Gintonin on Reactive Oxygen Species-Induced HT22 Cell Damages: Involvement of LPA1 Receptor-BDNF-AKT Signaling Pathway

Gintonin is a kind of ginseng-derived glycolipoprotein that acts as an exogenous LPA receptor ligand. Gintonin has in vitro and in vivo neuroprotective effects; however, little is known about the cellular mechanisms underlying the neuroprotection. In the present study, we aimed to clarify how gintonin attenuates iodoacetic acid (IAA)-induced oxidative stress. The mouse hippocampal cell line HT22 was used. Gintonin treatment significantly attenuated IAA-induced reactive oxygen species (ROS) overproduction, ATP depletion, and cell death. However, treatment with Ki16425, an LPA1/3 receptor antagonist, suppressed the neuroprotective effects of gintonin. Gintonin elicited [Ca²⁺]_i transients in HT22 cells. Gintonin-mediated [Ca²⁺]_i transients through the LPA1 receptor-PLC-IP₃ signaling pathway were coupled to increase both the expression and release of BDNF. The released BDNF activated the TrkB receptor. Induction of TrkB phosphorylation was further linked to Akt activation. Phosphorylated Akt reduced IAA-induced oxidative stress and increased cell survival. Our results indicate that gintonin attenuated IAA-induced oxidative stress in neuronal cells by activating the LPA1 receptor-BDNF-TrkB-Akt signaling pathway. One of the gintonin-mediated neuroprotective effects may be achieved via anti-oxidative stress in nervous systems.

Cannabinoid CB1 and CB2 receptors differentially regulate TNF-α-induced apoptosis and LPA1-mediated pro-survival signaling in HT22 hippocampal cells

AIMS

The aim of the study was to investigate the interaction between cannabinoid CB₁/CB₂ and lysophosphatidic acid (LPA) receptors in controlling neuronal signaling and fate.

METHODS

HT22 hippocampal cells were treated with different cannabinoid and LPA receptor agonists and antagonists. Western blot and immunofluorescence microscopy were used to study intracellular signaling and the expression of apoptotic markers. Cell viability was determined by a luminescence assay.

KEY FINDINGS

Cannabinoid agonists induced activation of both ERK1/2 and p38 MAP kinases. The effects of the CB₁/CB₂ receptor agonist HU210 were antagonized by the CB₁ antagonist rimonabant, whereas the responses to the CB₂ agonist JWH133 were blocked by the CB₂ antagonist SR144528. HU210 reduced the apoptotic cell death induced by the pro-inflammatory cytokine TNF-α, whereas JWH133 enhanced the cytokine cytotoxicity. Blockade of ERK1/2 and p38 MAPK activation abrogated the HU210 pro-survival and the JWH133 pro-apoptotic effects, respectively. HU210 and the endocannabinoid anandamide, but not JWH133, potentiated ERK1/2 stimulation by LPA and the tricyclic antidepressant amitriptyline acting through the LPA₁ receptor. HU210 enhanced amitriptyline-stimulated CREB phosphorylation and protection against TNF-α-induced apoptosis, whereas JWH133 had no effect. ERK1/2 stimulation by either HU210 or amitriptyline was dependent on fibroblast growth factor receptor (FGF-R) kinase activity and the combination of the two stimulants induced FGF-R phosphorylation. Moreover, the CB₁ receptor was found to co-immunoprecipitate with the LPA₁ receptor.

CONCLUSIONS

In HT22 hippocampal cells CB₁ and CB₂ receptors differentially regulate TNF-α-induced apoptosis and CB₁ receptors positively interact with amitriptyline-stimulated LPA₁ in promoting FGF-R-mediated ERK1/2 signaling and neuroprotection.

Antidepressants induce profibrotic responses via the lysophosphatidic acid receptor LPA1

Preclinical and clinical studies have indicated that antidepressants can promote inflammation and fibrogenesis, particularly in the lung, by mechanisms not fully elucidated. We have previously shown that different classes of antidepressants can activate the lysophosphatidic acid (LPA) receptor LPA₁, a major pathogenetic mediator of tissue fibrosis. The aim of the present study was to investigate whether in cultured human dermal and lung fibroblasts antidepressants could trigger LPA₁-mediated profibrotic responses. In both cell types amitriptyline, clomipramine and mianserin mimicked the ability of LPA to induce the phosphorylation/activation of extracellular signal -regulated kinases 1 and 2 (ERK1/2), which was blocked by the selective LPA₁ receptor antagonist AM966 and the LPA_1/3 antagonist Ki16425. Antidepressant-induced ERK1/2 stimulation was absent in fibroblasts stably depleted of LPA₁ by short hairpin RNA transfection and was prevented by pertussis toxin, an uncoupler of receptors from Gi/o proteins. Like LPA, antidepressants stimulated fibroblasts proliferation and this effect was blocked by either AM966 or the MEK1/2 inhibitor PD98059. Moreover, by acting through LPA₁ antidepressants induced the expression of α-smooth muscle actin (α-SMA), a marker of myofibroblast differentiation, and caused an ERK1/2-dependent increase in the cellular levels of transforming growth factor-β (TGF-β)1, a potent fibrogenic cytokine. Pharmacological blockade of TGF-β receptor type 1 prevented antidepressant- and LPA-induced α-SMA expression. These data indicate that in human dermal and lung fibroblasts different antidepressants can induce proliferative and differentiating responses by activating the LPA₁ receptor coupled to ERK1/2 signalling and suggest that this property may contribute to the promotion of tissue fibrosis by these drugs.

Mirtazapine increases glial cell line-derived neurotrophic factor production through lysophosphatidic acid 1 receptor-mediated extracellular signal-regulated kinase signaling in astrocytes

Different classes of antidepressants, such as tricyclic antidepressants, selective serotonin reuptake inhibitor (SSRI), and serotonin and norepinephrine reuptake inhibitor (SNRI), have been shown to increase GDNF production in astrocytes, which could be a key mechanism of the psychotropic effect of antidepressants. The antidepressant mirtazapine is a noradrenaline and specific serotonergic antidepressant (NaSSA) and does not block reuptake of catecholamines and serotonin. The present study examined the effect of mirtazapine on GDNF expression in rat C6 astroglial cells (C6 cells) and rat primary cultured cortical astrocytes (primary astrocytes). Mirtazapine treatment significantly increased GDNF mRNA expression and GDNF release in both C6 cells and primary astrocytes. In primary astrocytes, mirtazapine also increased the expressions of brain-derived neurotrophic factor mRNA. To mimic mirtazapine's putative mechanism of action, cells were treated with either a α₂-adrenoceptor antagonist (yohimbine), 5-HT₂ receptor antagonist (ketanserin), 5-HT₃ receptor antagonist (ondansetron), or a mixture of these--no effect on GDNF mRNA expression was observed. Mirtazapine treatment increased phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, and the mirtazapine-induced GDNF and BDNF expression were blocked by MAPK/ERK kinase (MEK) inhibitor (U0126). Furthermore, the effect of mirtazapine on ERK phosphorylation and expressions of GDNF and BDNF was antagonized by Gi/o inhibitor (pertussis toxin), lysophosphatidic acid-1 (LPA₁) receptor antagonist (AM966), and LPA₁/LPA₃ receptors antagonist (Ki16425). The current findings demonstrate that the NaSSA mirtazapine, similar to other classes of antidepressants, increases GDNF expression through a Gi/o coupled LPA₁ receptor-mediated ERK pathway. The current findings suggest a general mechanism underlying the psychotropic effect antidepressants.

The Chinese Herbal Formula PAPZ Ameliorates Behavioral Abnormalities in Depressive Mice

Major depressive disorder (MDD) is a chronic mental disorder characterized by mixed symptoms and complex pathogenesis. With long history of practical application, traditional Chinese medicine (TCM) offers many herbs for the treatment and rehabilitation of chronic disease. In this study, we developed a modified Chinese herbal formula using Panax ginseng, Angelica Sinensis, Polygala tenuifolia Willd, and Ziziphi spinosae Semen (PAPZ), based on an ancient TCM prescription. The antidepressant effects of PAPZ were investigated with a corticosterone (CORT) model of depression in mice. Our results showed that administration of PAPZ ameliorated depression-like phenotypes in the CORT model. An anatomic study showed that chronic PAPZ administration upregulated the protein expression of brain-derived neurotrophic factor (BDNF) in hippocampal tissue. The enzyme activity of superoxide dismutase was enhanced in hippocampal tissue, in line with a decreased malondialdehyde level. Taken together, these findings suggested that PAPZ has therapeutic effects in a mice depression model through increasing protein expression of BDNF and improving the anti-oxidation ability of the brain.

LPA1 , LPA2 , LPA4 , and LPA6 receptor expression during mouse brain development

Background

LPA is a small bioactive phospholipid that acts as an extracellular signaling molecule and is involved in cellular processes, including cell proliferation, migration, and differentiation. LPA acts by binding and activating at least six known G protein–coupled receptors: LPA_1–6. In recent years, LPA has been suggested to play an important role both in normal neuronal development and under pathological conditions in the nervous system.

Results

We show the expression pattern of LPA receptors during mouse brain development by using qRT‐PCR, in situ hybridization, and immunocytochemistry. Only LPA₁, LPA_2,LPA_4, and LPA₆ mRNA transcripts were detected throughout development stages from embryonic day 16 until postnatal day 30 of hippocampus, neocortex, cerebellum, and bulbus olfactorius in our experiments, while expression of LPA₃ and LPA₅ genes was below detection level. In addition to our qRT‐PCR results, we also analyzed the cellular protein expression of endogenous LPA receptors, with focus on LPA₁ and LPA₂ within postnatal brain slices and primary neuron differentiation with and without cytoskeleton stabilization and destabilization.

Conclusions

The expression of LPA receptors changes depends on the developmental stage in mouse brain and in cultured hippocampal primary neurons. Interestingly, we found that commercially available antibodies for LPA receptors are largely unspecific.

LPA1, ‐2, ‐4, and ‐6 genes are dynamically expressed during postnatal brain development.

LPA1, ‐2, ‐4, and ‐6 genes are differently expressed in the hippocampus, neocortex, cerebellum, and bulbus olfactorius.

LPA1 and ‐2 gene expression alters during neuronal differentiation.

LPA1, ‐2, ‐3, ‐4, and ‐6 genes are expressed in glia cells, but differed in gene expression levels.