Reduced Serum and Cerebrospinal Fluid Levels of Autotaxin in Major Depressive Disorder

Effects of autotaxin and lysophosphatidic acid deficiencies on depression-like behaviors in mice exposed to chronic unpredictable mild stress

The involvement of lipids in the mechanism of depression has triggered extensive discussions. Earlier studies have identified diminished levels of lysophosphatidic acid (LPA) and autotaxin (ATX) in individuals experiencing depression. However, the exact significance of this phenomenon in relation to depression remains inconclusive. This study seeks to explore the deeper implications of these observations. We assessed alterations in ATX and LPA in both the control group and the chronic unpredictable mild stress (CUMS) model group. Additionally, the impact of ATX adeno-associated virus (AAV-ATX) injection into the hippocampus was validated through behavioral tests in CUMS-exposed mice. Furthermore, we probed the effects of LPA on synapse-associated proteins both in HT22 cells and within the mouse hippocampus. The mechanisms underpinning the LPA-triggered shifts in protein expression were further scrutinized. Hippocampal tissues were augmented with ATX to assess its potential to alleviate depression-like behavior by modulating synaptic-related proteins. Our findings suggest that the decrement in ATX and LPA levels alters the expression of proteins associated with synaptic plasticity in vitro and in vivo, such as synapsin-I (SYN), synaptophysin (SYP), and brain-derived neurotrophic factor (BDNF). Moreover, we discerned a role for the ERK/CREB signaling pathway in mediating the effects of ATX and LPA. Importantly, strategic supplementation of ATX effectively mitigated depression-like behaviors. This study indicates that the ATX-LPA pathway may influence depression-like behaviors by modulating synaptic plasticity in the brains of CUMS-exposed mice. These insights augment our understanding of depression's potential pathogenic mechanism in the context of lipid metabolism and propose promising therapeutic strategies for ameliorating the disease.

Autotaxin Activity in Chronic Subdural Hematoma: A Prospective Clinical Study

Autotaxin (ATX) is the ectoenzyme producing the bulk of lysophosphatidic acid (LPA) in circulation. ATX and LPA-mediated signaling (the ATX-LPA axis) play critical roles in the vascular and nervous system development. In adults, this axis contributes to diverse processes, including coagulation, inflammation, fibroproliferation and angiogenesis under physiological and/or pathophysiological conditions. Given evidence implicating several of these processes in chronic subdural hematoma (CSDH) pathogenesis and development, we assessed ATX activity in CSDH patients. Twenty-eight patients were recruited. Blood and hematoma fluid were collected. Enzymatic assays were used to establish serum and hematoma ATX activity. Enzyme-linked immunosorbent assays were used to establish hematoma beta trace (BT) levels, a cerebrospinal fluid (CSF) marker, in a hematoma. ATX activity was nearly three folds higher in hematoma compared to serum (P < 0.001). There was no significant correlation between BT levels and ATX activity in a hematoma. The present results show, for the first time, that ATX is catalytically active in the hematoma fluid of CSDH patients. Moreover, our findings of significantly elevated ATX activity in hematoma compared to serum, implicate the ATX-LPA axis in CSDH pathophysiology. The CSF origin of ATX could not be inferred with the present results. Additional research is warranted to establish the significance of the ATX-LPA axis in CSDH and its potential as a biomarker and/or therapeutic target.

Downregulation of connexin 43 potentiates amitriptyline-induced brain-derived neurotrophic factor expression in primary astrocytes through lysophosphatidic acid receptor1/3, Src, and extracellular signal-regulated kinase

Connexin 43 (Cx43) expression is decreased in the prefrontal cortex of patients with depression, but its significance is still unknown. Neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), are involved in the effects of antidepressant. However, the relationship between Cx43 expression and induction of brain-derived neurotrophic factor production by antidepressants is unknown. On the basis of our previous study, which showed that adrenergic receptors stimulation results in potentiation of BDNF expression in astrocytes with downregulated Cx43 expression, we investigated the induction of BDNF expression by amitriptyline, a tricyclic antidepressant, in Cx43-knockdown astrocytes. Amitriptyline treatment potentiated BDNF expression in Cx43-knockdown astrocytes compared with those treated with non-targeting small interfering RNA (siRNA). Using a pharmacological approach, we revealed that the potentiating effect of amitriptyline on BDNF expression was mediated by lysophosphatidic acid (LPA) receptor_1/3 (LPA_1/3) stimulation and subsequent activation of Src-extracellular signal-regulated kinase (ERK) signaling. These findings suggest that downregulation of Cx43 in patients with depression might contribute to the therapeutic efficacy of antidepressants rather than the pathogenesis of depression.

Reduced Cerebrospinal Fluid Levels of Lysophosphatidic Acid Docosahexaenoic Acid in Patients With Major Depressive Disorder and Schizophrenia

BACKGROUND

Lysophosphatidic acid (LPA) is involved in numerous biological processes, including neurodevelopment, chronic inflammation, and immunologic response in the central nervous system. Autotaxin (ATX) is a secreted enzyme that produces LPA from lysophosphatidylcholine (LPC). Previous studies have demonstrated decreased protein levels of ATX in cerebrospinal fluid (CSF) of patients with major depressive disorder (MDD). Based on those studies, the current study investigated the levels of lysophospholipids species including LPA and related metabolic enzymes, in CSF of patients with MDD and schizophrenia (SCZ).

METHODS

The levels of lysophospholipids species and related metabolic enzymes were measured with either liquid chromatography-tandem mass spectrometry or enzyme-linked immunosorbent assay. Japanese patients were diagnosed with DSM-IV-TR. CSF was obtained from age- and sex-matched healthy controls (n = 27) and patients with MDD (n = 26) and SCZ (n = 27).

RESULTS

Of all lysophospholipids species, the levels of LPA 22:6 (LPA - docosahexaenoic acid) were significantly lower in patients with MDD and SCZ than in healthy controls. These levels were negatively correlated with several clinical symptomatic scores of MDD, but not those of SCZ. In addition, the levels of LPA 22:6 were significantly correlated with the levels of LPC 22:6 among all 3 groups. On the other hand, the levels of LPA 22:6 were not correlated with ATX activity in patients with MDD and SCZ.

CONCLUSION

The lower levels of LPA 22:6 in patients with MDD and SCZ suggest an abnormality of LPA 22:6 metabolism. In addition, several depressive symptoms in patients with MDD were significantly associated with the lower levels of LPA 22:6, suggesting an involvement of LPA 22:6 in the pathophysiology of MDD.

Lysophosphatidic Acid Signalling in Nervous System Development and Function

One class of molecules that are now coming to be recognized as essential for our understanding of the nervous system are the lysophospholipids. One of the major signaling lysophospholipids is lysophosphatidic acid, also known as LPA. LPA activates a variety of G protein-coupled receptors (GPCRs) leading to a multitude of physiological responses. In this review, I describe our current understanding of the role of LPA and LPA receptor signaling in the development and function of the nervous system, especially the central nervous system (CNS). In addition, I highlight how aberrant LPA receptor signaling may underlie neuropathological conditions, with important clinical application.

Lysophosphatidic acid induces thrombospondin-1 production in primary cultured rat cortical astrocytes

Lysophosphatidic acid (LPA), a brain membrane-derived lipid mediator, plays important roles including neural development, function, and behavior. In the present study, the effects of LPA on astrocyte-derived synaptogenesis factor thrombospondins (TSPs) production were examined by real-time PCR and western blotting, and the mechanism underlying this event was examined by pharmacological approaches in primary cultured rat cortical astrocytes. Treatment of astrocytes with LPA increased TSP-1 mRNA, and TSP-2 mRNA, but not TSP-4 mRNA expression. TSP-1 protein expression and release were also increased by LPA. LPA-induced TSP-1 production were inhibited by AM966 a LPA₁ receptor antagonist, and Ki16425, LPA_1/3 receptors antagonist, but not by H2L5146303, LPA₂ receptor antagonist. Pertussis toxin, Gi/o inhibitor, but not YM-254890, Gq inhibitor, and NF499, Gs inhibitor, inhibited LPA-induced TSP-1 production, indicating that LPA increases TSP-1 production through Gi/o-coupled LPA₁ and LPA₃ receptors. LPA treatment increased phosphorylation of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK). LPA-induced TSP-1 mRNA expression was inhibited by U0126, MAPK/ERK kinase (MEK) inhibitor, but not SB202190, p38 MAPK inhibitor, or SP600125, JNK inhibitor. However, LPA-induced TSP-1 protein expression was diminished with inhibition of all three MAPKs, indicating that these signaling molecules are involved in TSP-1 protein production. Treatment with antidepressants, which bind to astrocytic LPA₁ receptors, increased TSP-1 mRNA and protein production. The current findings show that LPA/LPA_1/3 receptors signaling increases TSP-1 production in astrocytes, which could be important in the pathogenesis of affective disorders and could potentially be a target for the treatment of affective disorders.

Potential association of plasma lysophosphatidic acid (LPA) species with cognitive impairment in abstinent alcohol use disorders outpatients

Lysophosphatidic acid (LPA) species are bioactive lipids participating in neurodevelopmental processes. The aim was to investigate whether the relevant species of LPA were associated with clinical features of alcohol addiction. A total of 55 abstinent alcohol use disorder (AUD) patients were compared with 34 age/sex/body mass index-matched controls. Concentrations of total LPA and 16:0-LPA, 18:0-LPA, 18:1-LPA, 18:2-LPA and 20:4-LPA species were quantified and correlated with neuroplasticity-associated growth factors including brain derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1) and IGF-2, and neurotrophin-3 (NT-3). AUD patients showed dysexecutive syndrome (22.4%) and memory impairment (32.6%). Total LPA, 16:0-LPA, 18:0-LPA and 18:1-LPA concentrations, were decreased in the AUD group compared to control group. Total LPA, 16:0-LPA, 18:2-LPA and 20:4-LPA concentrations were decreased in men compared to women. Frontal lobe functions correlated with plasma LPA species. Alcohol-cognitive impairments could be related with the deregulation of the LPA species, especially in 16:0-LPA, 18:1-LPA and 20:4-LPA. Concentrations of BDNF correlated with total LPA, 18:2-LPA and 20:4-LPA species. The relation between LPA species and BDNF is interesting in plasticity and neurogenesis functions, their involvement in AUD might serve as a biomarker of cognitive impairment.

Differential anatomical and cellular expression of lysophosphatidic acid receptor 1 in adult mouse brain

Lysophosphatidic acid (LPA) is a bioactive phospholipid that acts as an extracellular signaling molecule through six G-protein-coupled receptors: LPA₁-LPA₆. Recent studies have demonstrated that LPA signaling via LPA₁ receptor plays a crucial role in cognition and emotion. However, because of limited availability of reliable antibodies, it is currently difficult to identify the cell types expressing LPA₁ receptor in the brain. The current study explored the cellular distribution pattern of LPA₁ receptor in the brain using the LPA₁ lacZ-knock-in reporter mice. In situ hybridization and immunohistochemistry revealed that LacZ gene expression in these mice reflected the expression of endogenous LPA₁ receptor in the brain. Overall, some brain nuclei contained higher levels of LPA₁ receptor than others. The majority of LPA₁ receptor-expressing cells were Olig2⁺ oligodendrocytes. In addition, ALDH1l1⁺ astrocytes and CD31⁺ vascular endothelial cells also expressed LPA₁ receptor. By contrast, NeuN⁺ neuron and Iba1⁺ microglia expressed little or no LPA₁ receptor. The current neuroanatomical findings will aid in elucidating a role of brain LPA₁ receptor, especially those involved in cognition and emotion.

Aerobic Exercise Inhibits CUMS-Depressed Mice Hippocampal Inflammatory Response via Activating Hippocampal miR-223/TLR4/MyD88-NF-κB Pathway

Objective: To investigate the role of aerobic exercise in inhibiting chronic unpredictable mild stress (CUMS) depressed mice hippocampal inflammatory response and its potential mechanisms. Methods: Fifty-four male eight-week-old C57BL/6 mice were divided as control group (CG) (18 mice) and model group (36 mice). Model group mice were treated with 13 chronic stimulating factors for 28 days to set up the CUMS depression model. Neurobehavioral assessment was performed after modeling. The mice in the model group were randomly divided into the control model group (MG) and the aerobic exercise group (EG), with 18mice in each group. The EG group carried out the adaptive training of the running platform: 10 m/min, 0° slope, and increased by 10 minutes per day for 6 days. The formal training was carried for 8 weeks with 10 m/min speed, 0° slope, 60 min/d, 6 d/Week. After the training, a neurobehavioral assessment was performed, and hippocampus IL-1β and IL-10 protein levels were detected by ELISA. RT–PCR was used to detect the expression of miR-223 and TLR4, MyD88, and NF-κB in the hippocampus. Western blot was used to detect the expression of TLR4 and phosphorylated NF-κBp65 protein in the hippocampus. Results: The hippocampus function of CUMS depression model mice was impaired. The forced swimming and forced tail suspension time were significantly prolonged, and inflammatory factors IL-1β were significantly increased in the hippocampus. Aerobic exercise significantly improves CUMS-depressed mice hippocampal function, effectively reducing depressive behavior and IL-1β levels, and increasing IL-10 levels. Besides, aerobic exercise significantly upregulates the expression level of miR-223 and inhibits the high expression of TLR4, MyD88, and NF-κB. Conclusion: Aerobic exercise significantly increases the CUMS-depressed mice hippocampus expression of miR-223, and inhibits the downstream TLR4/MyD88-NF-κB signaling pathway and the hippocampal inflammatory response, which contributes to the improvement of the hippocampal function.

Pleotropic Roles of Autotaxin in the Nervous System Present Opportunities for the Development of Novel Therapeutics for Neurological Diseases

Autotaxin (ATX) is a soluble extracellular enzyme that is abundant in mammalian plasma and cerebrospinal fluid (CSF). It has two known enzymatic activities, acting as both a phosphodiesterase and a phospholipase. The majority of its biological effects have been associated with its ability to liberate lysophosphatidic acid (LPA) from its substrate, lysophosphatidylcholine (LPC). LPA has diverse pleiotropic effects in the central nervous system (CNS) and other tissues via the activation of a family of six cognate G protein-coupled receptors. These LPA receptors (LPARs) are expressed in some combination in all known cell types in the CNS where they mediate such fundamental cellular processes as proliferation, differentiation, migration, chronic inflammation, and cytoskeletal organization. As a result, dysregulation of LPA content may contribute to many CNS and PNS disorders such as chronic inflammatory or neuropathic pain, glioblastoma multiforme (GBM), hemorrhagic hydrocephalus, schizophrenia, multiple sclerosis, Alzheimer's disease, metabolic syndrome-induced brain damage, traumatic brain injury, hepatic encephalopathy-induced cerebral edema, macular edema, major depressive disorder, stress-induced psychiatric disorder, alcohol-induced brain damage, HIV-induced brain injury, pruritus, and peripheral nerve injury. ATX activity is now known to be the primary biological source of this bioactive signaling lipid, and as such, represents a potentially high-value drug target. There is currently one ATX inhibitor entering phase III clinical trials, with several additional preclinical compounds under investigation. This review discusses the physiological and pathological significance of the ATX-LPA-LPA receptor signaling axis and summarizes the evidence for targeting this pathway for the treatment of CNS diseases.