Growth Differentiation Factor 15 Expression in Astrocytes After Excitotoxic Lesion in the Mouse Hippocampus

NAG-1/GDF-15 Transgenic Female Mouse Shows Delayed Peak Period of the Second Phase Nociception in Formalin-induced Inflammatory Pain

Non-steroidal anti-inflammatory drug-activated gene-1 (NAG-1), also known as growth differentiation factor-15 (GDF-15), is associated with cancer, diabetes, and inflammation, while there is limited understanding of the role of NAG-1 in nociception. Here, we examined the nociceptive behaviors of NAG-1 transgenic (TG) mice and wild-type (WT) littermates. Mechanical sensitivity was evaluated by using the von Frey filament test, and thermal sensitivity was assessed by the hot-plate, Hargreaves, and acetone tests. c-Fos, glial fibrillary acidic protein (GFAP), and ionized calcium binding adaptor molecule-1 (Iba-1) immunoreactivity was examined in the spinal cord following observation of the formalin-induced nociceptive behaviors. There was no difference in mechanical or thermal sensitivity for NAG-1 TG and WT mice. Intraplantar formalin injection induced nociceptive behaviors in both male and female NAG-1 TG and WT mice. The peak period in the second phase was delayed in NAG-1 TG female mice compared with that of WT female mice, while there was no difference in the cumulative time of nociceptive behaviors between the two groups of mice. Formalin increased spinal c-Fos immunoreactivity in both TG and WT female mice. Neither GFAP nor Iba-1 immunoreactivity was increased in the spinal cord of TG and WT female mice. These findings indicate that NAG-1 TG mice have comparable baseline sensitivity to mechanical and thermal stimulation as WT mice and that NAG-1 in female mice may have an inhibitory effect on the second phase of inflammatory pain. Therefore, it could be a novel target to inhibit central nervous system response in pain.

GDF15, an emerging key player in human aging

Growth differentiation factor 15 (GDF15) is recently emerging not only as a stress-related mitokine, but also as a key player in the aging process, being one of the most up-regulated protein with age and associated with a variety of age-related diseases (ARDs). Many data indicate that GDF15 has protective roles in several tissues during different stress and aging, thus playing a beneficial role in apparent contrast with the observed association with many ARDs. A possible detrimental role for this protein is then hypothesized to emerge with age. Therefore, GDF15 can be considered as a pleiotropic factor with beneficial activities that can turn detrimental in old age possibly when it is chronically elevated. In this review, we summarize the current knowledge on the biology of GDF15 during aging. We also propose GDF15 as a part of a dormancy program, where it may play a role as a mediator of defense processes aimed to protect from inflammatory damage and other stresses, according to the life history theory.

Rediscovering potential molecular targets for glioma therapy through the analysis of the cell of origin, microenvironment, and metabolism

Gliomas are the most common type of malignant brain tumors. Despite significant medical advances, gliomas remain incurable and are associated with high mortality. Although numerous biomarkers of diagnostic value have been identified and significant progress in the prognosis of the outcome has been made, the treatment has not been parallelly improved during the last three decades. This review summarizes and discusses three aspects of recent discoveries related to glioma, with the objective to highlight the advantages of glioma-specific drugs targeting the cell of origin, microenvironment, and metabolism. Given the heterogeneous nature of gliomas, various cell populations have been implicated as likely sources of the tumor. Depending on the mutation(s) acquired by the cells, it is believed that neuronal stem/progenitor cells, oligodendrocyte progenitor cells, mature neurons, and glial cells can initiate cell transformation into a malignant phenotype. The level of tumorigenicity appears to be inversely correlated with the maturation of a given cell population. The microenvironment of gliomas includes non-cancer cells such as immune cells, fibroblasts, and cells of blood vessels, as well as secreted molecules and the extracellular matrix, and all these components play a vital role during tumor initiation and progression. We will discuss in detail how the tumor microenvironment can stimulate and drive the transformation of non-tumor cell populations into tumor-supporting cells or glioma cells. Metabolic reprogramming is a key feature of gliomas and is thought to reflect the adaptation to the increased nutritional requirements of tumor cell proliferation, growth, and survival. Mutations in the IDH gene can shape metabolic reprogramming and may generate some vulnerabilities in glioma cells, such as abnormal lipid metabolism and sensitivity to endoplasmic reticulum stress (ERS). We will analyze the prominent metabolic features of malignant gliomas and the key pathways regulating glioma metabolism. This review is intended to provide a conceptual background for the development of glioma therapies based on the properties of tumor cell populations, microenvironment, and metabolism.

Treatment with GDF15, a TGFβ superfamily protein, induces protective effect on retinal ganglion cells

Growth differentiation factor 15 (GDF15) is a protein belonging to the transforming growth factor beta (TGF-β) superfamily. The precursor GDF15 is cleaved and activated as a mature GDF15 by protease. GDF15 has been detected in the aqueous humor of the primary open angle glaucoma patients, however the localization and the effect on the retinal ganglion cells (RGCs) are still unknown. Thus, the purpose of this study was to elucidate the effect of GDF15 on mouse optic nerve crush (ONC) model and primary culture of rat RGCs. Immunostaining showed that the GDF15 was in the ganglion cell layer (GCL), and colocalized with GFAP-positive cells in the GCL and the optic nerve. Western blotting analysis showed that the mature GDF15 was upregulated in the retina and the optic nerve after the ONC. Intravitreal injection of GDF15 suppressed RGCs loss of the ONC model mice in vivo. The neurites length of the primary culture of rat RGCs were increased by mature GDF15 treatment. In addition, the neurotrophic effect of GDF15 was canceled by RET inhibitor treatment. These findings indicate that GDF15 has neuroprotective effect on RGCs via GFRAL-RET pathway. Therefore, GDF15 may be one of novel therapeutic targets in RGC degenerative diseases.

GDF15, an update of the physiological and pathological roles it plays: a review

Growth differentiation factor 15 (GDF15) is a peptide hormone, and a divergent member of the transforming growth factor beta (TGFβ) superfamily. In normal physiology, GDF15 is expressed in multiple tissues at a low concentration. GDF15 is overexpressed during and following many pathological conditions such as tissue injury and inflammation in order to play a protective role. However, GDF15 appears to promote tumour growth in the later stages of malignant cancer. The recently identified endogenous receptor for GDF15, GDNF family receptor a-like (GFRAL), has allowed elucidation of a physiological pathway in which GDF15 regulates energy homeostasis and body weight, primarily via appetite suppression. The anorectic effect of GDF15 provides some therapeutic potential in management of cancer-related anorexia/cachexia and obesity. Despite the identification of GFRAL as a GDF15 receptor, there appears to be other signalling mechanisms utilized by GDF15 that further increase the possibility of development of therapeutic treatments, should these pathways be fully characterized. In this review, GDF15 function in both physiological and pathological conditions in various tissues will be discussed.

Primary cilia modulate TLR4-mediated inflammatory responses in hippocampal neurons

Background

The primary cilium is an organelle that can act as a master regulator of cellular signaling. Despite the presence of primary cilia in hippocampal neurons, their function is not fully understood. Recent studies have demonstrated that the primary cilium influences interleukin (IL)-1β-induced NF-κB signaling, ultimately mediating the inflammatory response. We, therefore, investigated ciliary function and NF-κB signaling in lipopolysaccharide (LPS)-induced neuroinflammation in conjunction with ciliary length analysis.

Methods

Since TLR4/NF-κB signaling is a well-known inflammatory pathway, we measured ciliary length and inflammatory mediators in wild type (WT) and TLR4^−/− mice injected with LPS. Next, to exclude the effects of microglial TLR4, we examined the ciliary length, ciliary components, inflammatory cytokine, and mediators in HT22 hippocampal neuronal cells.

Results

Primary ciliary length decreased in hippocampal pyramidal neurons after intracerebroventricular injection of LPS in WT mice, whereas it increased in TLR4^−/− mice. LPS treatment decreased primary ciliary length, activated NF-κB signaling, and increased Cox2 and iNOS levels in HT22 hippocampal neurons. In contrast, silencing Kif3a, a key protein component of cilia, increased ARL13B ciliary protein levels and suppressed NF-κB signaling and expression of inflammatory mediators.

Conclusions

These data suggest that LPS-induced NF-κB signaling and inflammatory mediator expression are modulated by cilia and that the blockade of primary cilium formation by Kif3a siRNA regulates TLR4-induced NF-κB signaling. We propose that primary cilia are critical for regulating NF-κB signaling events in neuroinflammation and in the innate immune response.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0958-7) contains supplementary material, which is available to authorized users.

Plasma GDF15 level is elevated in psychosis and inversely correlated with severity

Accumulating evidence suggests that GDF15 is a biomarker for ageing and morbidity of many somatic disorders such as cancer and inflammatory disorders. Recently, elevated serum GDF15 level was proposed as a marker for mood disorder. However, psychosis severity was not investigated in relation to plasma GDF15 levels. In the present study we measured GDF15 levels in plasma of 120 psychosis patients compared to 120 age and gender matched healthy controls. Within the patient cohort GDF15 levels were evaluated for association with age, gender, lifestyle factors, C-reactive protein levels, psychosis severity and metabolic disorder. Psychosis patients had elevated GDF15 levels compared to controls (median_Psychosis = 744 ng/mL, median_controls = 516 ng/mL, p < 0.001). Within the psychosis cohort, GDF15 levels, when corrected for age, metabolic health and lifestyle factors, were negatively correlated with psychosis severity (β = −0.218, p = 0.012). While GDF15 levels were elevated in patients versus healthy controls, the negative correlation between psychosis severity and GDF15 suggests a loss of anti-inflammatory GDF15 mediated functionality in severe psychosis. Study replication in larger cohorts will be necessary to assess the potential of GDF15 as a prognostic biomarker in psychosis.

The anti-inflammatory role of extranuclear apurinic/apyrimidinic endonuclease 1/redox effector factor-1 in reactive astrocytes

Apurinic/apyrimidinic endonuclease 1 (APE1), a ubiquitous multipurpose protein, is also known as redox effector factor-1 (Ref-1). It is involved in DNA repair and redox signaling and, in turn, oxidative stress-induced neurodegeneration. Although previous studies have demonstrated that APE1/Ref-1 functions as a negative regulator of inflammatory response via several mechanisms in neuronal cells, little is known about the roles of APE1/Ref-1 in glial cells. In this study, we found that cytoplasmic APE1/Ref-1 expression was upregulated in reactive astrocytes of the kainic acid- or lipopolysaccharide (LPS)-injected hippocampus. Analysis of the inflammatory response induced by extranuclear APE1/Ref-1 (ΔNLS-Ref-1) in cultured primary astrocytes revealed that it markedly suppressed inducible nitric oxide synthase (iNOS) expression and tumor necrosis factor-α (TNF-α) secretion induced by LPS to a similar extent as did wild type APE1/Ref-1 (WT-Ref-1), supporting the concept an anti-inflammatory role of extranuclear APE1/Ref-1 in astrocytes. Additionally, overexpression of WT- and ΔNLS-Ref-1 suppressed the transcriptional activity of nuclear factor-κB (NF-κB), although it effectively enhanced activator protein 1 (AP-1) activity. The blunting effect of APE1/Ref-1 on LPS-induced NF-κB activation was not mediated by IκB kinase (IKK) activity. Instead, APE1/Ref-1 inhibited p300-mediated acetylation of p65 by suppressing intracellular reactive oxygen species (ROS) levels following LPS treatment. Taken together, our results showed that altered expression and/or subcellular distribution of APE1/Ref-1 in activated astrocytes regulated the neuroinflammatory response to excitotoxin and endotoxin insults used in model of neurodegenerative brain diseases.

Astrocytic Expression of CTMP Following an Excitotoxic Lesion in the Mouse Hippocampus

Akt (also known as protein kinase B, PKB) has been seen to play a role in astrocyte activation of neuroprotection; however, the underlying mechanism on deregulation of Akt signaling in brain injuries is not fully understood. We investigated the role of carboxy-terminal modulator protein (CTMP), an endogenous Akt inhibitor, in brain injury following kainic acid (KA)-induced neurodegeneration of mouse hippocampus. In control mice, there was a weak signal for CTMP in the hippocampus, but CTMP was markedly increased in the astrocytes 3 days after KA treatment. To further investigate the effectiveness of Akt signaling, the phosphorylation of CTMP was examined. KA treatment induced an increased p-CTMP expression in the astrocytes of hippocampus at 1 day. LPS/IFN-γ-treatment on primary astrocytes promoted the p-CTMP was followed by phosphorylation of Akt and finally upregulation of CTMP and p-CREB. Time-dependent expression of p-CTMP, p-Akt, p-CREB, and CTMP indicate that LPS/IFN-γ-induced phosphorylation of CTMP can activate Akt/CREB signaling, whereas lately emerging enhancement of CTMP can inhibit it. These results suggest that elevation of CTMP in the astrocytes may suppress Akt activity and ultimately negatively affect the outcome of astrocyte activation (astroglisiois). Early time point enhancers of phosphorylation of CTMP and/or late time inhibitors specifically targeting CTMP may be beneficial in astrocyte activation for neuroprotection within treatment in neuroinflammatory conditions.

CD200R/Foxp3-mediated signalling regulates microglial activation

The heterogeneity of microglial functions have either beneficial or detrimental roles in specific physiological or pathological environments. However, the details of what transcriptional mechanisms induce microglia to take beneficial phenotypes remain unknown. Here, we report that Foxp3 is essential for beneficial outcome of the microglial response and depends upon signalling by the immunoglobulin CD200 through its receptor (CD200R). Foxp3 expression was up-regulated in microglia activated by excitotoxicity-induced hippocampal neuroinflammation. Suppression of CD200R prevented anti-inflammatory phenotype of microglia, but over-expression of Foxp3 enhanced it. Phosphorylation of STAT6, a downstream effector of CD200R, modulated transcription of Foxp3. Finally, CD200R/Foxp3-mediated signalling enhanced hippocampal neuronal viability and conferred a degree of neuroprotection, presumably by counteracting inducible nitric oxide synthase. We conclude that enhancement of Foxp3 through CD200R could be neuroprotective by targeting the microglia.

GDF15/MIC1 and MMP9 Cerebrospinal Fluid Levels in Parkinson's Disease and Lewy Body Dementia

Based on animal and ex-vivo experiments, Growth/Differentiation Factor-15 (GDF15, also called Macrophage Inhibitory Cytokine-1, MIC1), a member of the transforming growth factor-beta family, and Matrix Metalloproteinase-9 (MMP9), a member of the matrix metalloprotease family may be potential markers for Lewy body disorders, i.e. Parkinson’s disease with (PDD) and without dementia (PDND) and Lewy body dementia (DLB). GDF15 has a prominent role in development, cell proliferation, differentiation, and repair, whereas MMP9 degrades, as a proteolytic enzyme, components of the extracellular matrix. In this study, cerebrospinal fluid GDF15 and MMP9 levels of 59 PDND, 17 PDD and 23 DLB patients, as well as of 95 controls were determined, and associated with demographic, clinical and biochemical parameters. Our analysis confirmed the already described association of GDF15 levels with age and gender. Corrected GDF15 levels were significantly higher in PDD than in PDND patients, and intermediate in DLB patients. Within Lewy body disorders, GDF15 levels correlated positively with age at onset of Parkinsonism and dementia, Hoehn & Yahr stage and cerebrospinal fluid t-Tau and p-Tau levels, and negatively with the Mini Mental State Examination. Remarkably, it does not relevantly correlate with disease duration. MMP9 was not relevantly associated with any of these parameters. Cerebrospinal GDF15, but not MMP9, may be a potential marker of and in Lewy body disorders.

Macrophage inhibitory cytokine-1/growth differentiation factor 15 as a marker of cognitive ageing and dementia

PURPOSE OF REVIEW

As a divergent member of the transforming growth factor-β superfamily, macrophage inhibitory cytokine-1 (MIC-1/GDF15) is an autocrine regulatory molecule that plays important roles in diseases, such as cancer and cardiovascular disorders. More recently, this cytokine has been investigated for its contribution to ageing and age-related cognitive decline. This review aims at summarizing existing findings on the relationships of MIC-1/GDF15 with cognition, brain, and dementia in ageing populations and animal models.

RECENT FINDINGS

In community-dwelling samples, higher circulating MIC-1/GDF15 levels were associated with worsening cognitive function and decline from cognitively normal status to mild cognitive impairment or dementia. Higher MIC-1/GDF15 serum levels were also linked to decreased grey matter volumes and white matter integrity. Brain structural changes were shown to mediate the inverse relationships of MIC-1/GDF15 serum levels with cognition. Animal studies indicated that the expression of MIC-1/GDF15 in response to stress was neuroprotective and even promoted neurogenesis.

SUMMARY

From the available findings, MIC-1/GDF15 can be considered as a marker of age-related cognitive decline and brain structural changes. Combining MIC-1/GDF15 with other biomarkers may provide clinical diagnostic and prognostic utility. Threshold effects should be considered in future studies.