The influence of peroxisome proliferator-activated receptor γ1 during differentiation of mouse embryonic stem cells to neural cells

Induction of MYCN-amplified neuroblastoma differentiation through NMYC suppression using PPAR-γ antagonist

Neuroblastomas are the most common extracranial solid tumors in children and have a unique feature of neuronal differentiation. Peroxisome proliferator-activated receptor (PPAR)-γ is reported to have neuroprotective effects in addition to having antitumor effects in various cancers. Thus, we aimed to clarify the role of PPAR-γ agonist and antagonist in malignant neuroblastomas, which also possess neuronal features. In MYCN-amplified neuroblastoma CHP212 cells, treatment with the PPAR-γ antagonist GW9662 induced growth inhibition in a dose-dependent manner. In addition, the PPAR-γ antagonist treatment changed cell morphology with increasing expression of the neuronal differentiation marker tubulin beta 3 (TUBB3) and induced G1 phase arrest and apoptosis in MYCN-amplified neuroblastoma. Notably, the PPAR-γ antagonist treatment significantly decreased expression of NMYC, B-cell lymphoma 2 (BCL2) and bromodomain-containing protein 4 (BRD4). It is implied that BRD4, NMYC, BCL2 suppression by the PPAR-γ antagonist resulted in cell growth inhibition, differentiation, and apoptosis induction. In our in vivo study, the PPAR-γ antagonist treatment induced CHP212 cells differentiation and resultant tumor growth inhibition. Our results provide a deeper understanding of the mechanisms of tumor cell differentiation and suggest that PPAR-γ antagonist is a new therapeutic and prevention option for neuroblastomas.

Simvastatin Improves Benign Prostatic Hyperplasia: Role of Peroxisome-Proliferator-Activated Receptor-γ and Classic WNT/β-Catenin Pathway

Benign prostatic hyperplasia (BPH) is a common disease in elderly men with an uncertain etiology and mechanistic basis. Metabolic syndrome (MetS) is also a very common illness and is closely related to BPH. Simvastatin (SV) is one of the widely used statins for MetS. Peroxisome-proliferator-activated receptor gamma (PPARγ), crosstalking with the WNT/β-catenin pathway, plays important roles in MetS. Our current study aimed to examine SV-PPARγ-WNT/β-catenin signaling in the development of BPH. Human prostate tissues and cell lines plus a BPH rat model were utilized. Immunohistochemical, immunofluorescence, hematoxylin and eosin (H&E) and Masson's trichrome staining, construction of a tissue microarray (TMA), ELISA, CCK-8 assay, qRT-PCR, flow cytometry, and Western blotting were also performed. PPARγ was expressed in both prostate stroma and epithelial compartments and downregulated in BPH tissues. Furthermore, SV dose-dependently triggered cell apoptosis and cell cycle arrest at the G0/G1 phase and attenuated tissue fibrosis and the epithelial-mesenchymal transition (EMT) process both in vitro and in vivo. SV also upregulated the PPARγ pathway, whose antagonist could reverse SV produced in the aforementioned biological process. Additionally, crosstalk between PPARγ and WNT/β-catenin signaling was demonstrated. Finally, correlation analysis with our TMA containing 104 BPH specimens showed that PPARγ was negatively related with prostate volume (PV) and free prostate-specific antigen (fPSA) and positively correlated with maximum urinary flow rate (Qmax). WNT-1 and β-catenin were positively related with International Prostate Symptom Score (IPSS) and nocturia, respectively. Our novel data demonstrate that SV could modulate cell proliferation, apoptosis, tissue fibrosis, and the EMT process in the prostate through crosstalk between PPARγ and WNT/β-catenin pathways.

The Role of PPARs in Breast Cancer

Breast cancer is a malignant tumor with high morbidity and lethality. Its pathogenesis is related to the abnormal expression of many genes. The peroxisome proliferator-activated receptors (PPARs) are a class of ligand-dependent transcription factors in the nuclear receptor superfamily. They can regulate the transcription of a large number of target genes, which are involved in life activities such as cell proliferation, differentiation, metabolism, and apoptosis, and regulate physiological processes such as glucose metabolism, lipid metabolism, inflammation, and wound healing. Further, the changes in its expression are associated with various diseases, including breast cancer. The experimental reports related to "PPAR" and "breast cancer" were retrieved from PubMed since the discovery of PPARs and summarized in this paper. This review (1) analyzed the roles and potential molecular mechanisms of non-coordinated and ligand-activated subtypes of PPARs in breast cancer progression; (2) discussed the correlations between PPARs and estrogen receptors (ERs) as the nuclear receptor superfamily; and (3) investigated the interaction between PPARs and key regulators in several signaling pathways. As a result, this paper identifies PPARs as targets for breast cancer prevention and treatment in order to provide more evidence for the synthesis of new drugs targeting PPARs or the search for new drug combination treatments.

Genome-wide identification and expression of the peroxisome proliferator-activated receptor gene family in the Tibetan highland fish Gymnocypris przewalskii

Peroxisome proliferator-activated receptor (PPAR) plays an important role in the regulation of lipid metabolism and has been widely identified in diverse species. Gymnocypris przewalskii is a native fish of the Qinghai Tibetan Plateau that survives in a chronically cold environment. In the current study, we conducted genome-wide identification of PPAR genes, revealing the existence of seven PPARs in the G. przewalskii genome. Collinearity was observed between two copies of PPARαb and PPARγ in G. przewalskii, suggesting that the additional copy might be gained through whole genome duplication. Both phylogenetic and multiple sequence alignment analyses indicated that PPARs in G. przewalskii were conserved with teleosts. The cold treatment (10 °C and 4 °C) led to the developmental delay of G. przewalskii embryos. Continuous expression of PPARs was observed during the embryonic development of G. przewalskii under normal and cold conditions, with significantly different transcriptional patterns. These results indicated that PPARs participated in the embryonic development of G. przewalskii, and were involved in the cold response during development. The current study proposed a potential role of PPARs in the cold response in the embryonic development of G. przewalskii, which shed light on understanding cold adaptation in Tibetan highland fish.

Murine cerebral organoids develop network of functional neurons and hippocampal brain region identity

Brain organoids are in vitro three-dimensional (3D) self-organized neural structures, which can enable disease modeling and drug screening. However, their use for standardized large-scale drug screening studies is limited by their high batch-to-batch variability, long differentiation time (10-20 weeks), and high production costs. This is particularly relevant when brain organoids are obtained from human induced pluripotent stem cells (iPSCs). Here, we developed, for the first time, a highly standardized, reproducible, and fast (5 weeks) murine brain organoid model starting from embryonic neural stem cells. We obtained brain organoids, which progressively differentiated and self-organized into 3D networks of functional neurons with dorsal forebrain phenotype. Furthermore, by adding the morphogen WNT3a, we generated brain organoids with specific hippocampal region identity. Overall, our results showed the establishment of a fast, robust and reproducible murine 3D in vitro brain model that may represent a useful tool for high-throughput drug screening and disease modeling.

Peroxisome proliferator-activated receptor gamma: a novel therapeutic target for cognitive impairment and mood disorders that functions via the regulation of adult neurogenesis

The proliferation, differentiation, and migration of neural precursor cells occur not only during embryonic development but also within distinct regions of the adult brain through the process of adult neurogenesis. As neurogenesis can potentially regulate brain cognition and neuronal plasticity, the factors that enhance neurogenesis can be attractive therapeutic targets for improving cognitive function and regulating neurodegenerative and neuropsychiatric disorders, including affective and mood disorders. Peroxisome proliferator-activated receptors (PPARs) are a class of ligand-activated transcription factors belonging to the nuclear receptor superfamily. PPARγ is a target for insulin sensitizers and plays an essential role in regulating various metabolic processes, including adipogenesis and glucose homeostasis. Interestingly, evidence demonstrates the role of PPARγ activation in regulating neurogenesis. The pharmacological activation of PPARγ using specific ligands increases the proliferation and differentiation of neural stem cells in specific brain regions, including the hippocampus, and prevents neurodegeneration and improves cognition and anxiety/depression-like behaviors in animal models. We summarize here recent reports on the role of PPARγ in adult neurogenesis, as well as the mechanisms involved, and suggest that PPARγ can serve as a potential therapeutic target for neurological and/or neurodegenerative diseases.

Rosiglitazone up-regulates glial fibrillary acidic protein via HB-EGF secreted from astrocytes and neurons through PPARγ pathway and reduces apoptosis in high-fat diet-fed mice

The anti-diabetic drug and peroxisome proliferator-activated receptor-gamma (PPARγ) agonist, rosiglitazone, alters astrocyte activation; however, its mechanism remains less-known. We hypothesized participation of epidermal growth factor receptor (EGFR), known to control astrocyte reactivity. We first detected that rosiglitazone promoted glial fibrillary acidic protein (GFAP) expression in primary astrocytes as well as the mouse cerebral cortex, associated with increased EGFR activation. Screening for EGFR ligands revealed a rosiglitazone-mediated increase of heparin-binding epidermal growth factor (HB-EGF) in astrocytes, resulting in HB-EGF release into culture medium and mouse cerebrospinal fluid too. Treatment with HB-EGF-siRNA and EGFR inhibitors showed that the rosiglitazone-induced HB-EGF and p-EFGR were interdependent, which participated in GFAP increase. Interestingly, we observed that rosiglitazone could induce cellular and secreted-HB-EGF in neurons also, contributing toward the activated EGFR-induced GFAP in astrocytes. Probing whether these effects of rosiglitazone were PPARγ-linked, revealed potential PPARγ-responsive elements within HB-EGF gene. Moreover, gel-shift, site-directed mutagenesis, chromatin-immunoprecipitation and luciferase-reporter assays demonstrated a PPARγ-dependent HB-EGF transactivation. Subsequently, we examined effects of rosiglitazone in a high-fat diet-fed diabetes mouse model, and supporting observations in the normal cortical cells, identified a rosiglitazone-induced GFAP, astrocyte and neuronal HB-EGF and secreted-HB-EGF in the cerebral cortex of diabetic mice. Moreover, assessing relevance of increased HB-EGF and GFAP revealed an anti-apoptotic role of rosiglitazone in the cerebral cortex, supported by a GFAP-siRNA as well as HB-EGF-siRNA-mediated increase in cleaved-caspase 3 and 9 levels in the rosiglitazone-treated astrocyte-neuron coculture. Overall, our study indicates that rosiglitazone may protect the brain, via a PPARγ-dependent HB-EGF/EGFR signaling and increased GFAP.

Comparison of two different media for maturation rate of neural progenitor cells to neuronal and glial cells emphasizing on expression of neurotrophins and their respective receptors

Neural cells derived from embryonic stem cells (ESCs) have potential usefulness for the treatment of neurodegenerative disorders. Modulation of intrinsic growth factors expression such as neurotrophins and their respective receptors by these cells is necessary to obtain functional neural cells for transplantation. In present study, we compared neural differentiation potential of two different media, NB + 5%ES-FBS + N2B27 and Ko-DMEM + 5%ES-FBS for conversion of mESC derived neural progenitors (NPs) into mature neural cells with emphasis on effect of the these two media on neurotrophins and their respective receptors expression. Immunofluorescence staining, RT-qPCR and western blot analysis showed that the expression of neuronal specific markers, MAP2 and Tuj-1, in NB + 5%ES-FBS + N2B27 medium was significantly higher than the other medium. Western blot assay revealed that the expression of BDNF and NGF increased significantly in mature neural cells obtained from NB + 5%ES-FBS + N2B27 medium but decreased in neural cells from Ko-DMEM + 5%ES-FBS medium compared to mESCs. TrkB protein was not detectable in mESCs but its expression increased in neural cells obtained from both media although its expression in NB + 5%ES-FBS + N2B27 medium was significantly higher than the other medium. In contrast to TrkB, p75NTR protein was detectable in mESCs and is remained constant in neural cells cultured in NB + 5%ES-FBS + N2B27 medium but decreased significantly in the other medium. In conclusion, our results indicated that NB + 5%ES-FBS + N2B27 medium promoted neural differentiation process of mESCs and caused enhancement of neurotrophins protein expression in addition to their cognate receptors.

RXRG associated in PPAR signal regulated the differentiation of primordial germ cell

Primitive germ cells (PGCs) are the "ancestor" of sex germ cells. However, their regulation mechanism is not clear at present. The aim of this study is to investigate the effect of PPAR signaling pathway on the differentiation of chicken embryonic stem cells (ESCs) into PGCs, providing theoretical support for the further study of the mechanism of regulation of chicken PGCs. Based on the results of RNA-Seq analysis, the key signal pathway PPAR and the key signal molecule RXRG in the pathway were successfully screened. Also, we made the PPAR signal transduction pathway be activated in vivo and in vitro. The results showed that the expression of FABP3 and SCD-1 was up-regulated by high expression of RXRG, which significantly up-regulated the expression of Cvh, C-kit, and the ratio of Cvh + C-kit+ cells was higher than that of control group. The formation of PGCs was blocked by interfering with PPAR signaling pathway. We conclude that RXRG positively regulates the PPAR signaling pathway and promotes differentiation of chicken ESCs into PGCs. Thus, gene RXRG can be used to study the regulation of PGCs differentiation in chickens.

Nuclear deterrents: Intrinsic regulators of IL-1β-induced effects on hippocampal neurogenesis

Hippocampal neurogenesis, the process by which new neurons are born and develop into the host circuitry, begins during embryonic development and persists throughout adulthood. Over the last decade considerable insights have been made into the role of hippocampal neurogenesis in cognitive function and the cellular mechanisms behind this process. Additionally, an increasing amount of evidence exists on the impact of environmental factors, such as stress and neuroinflammation on hippocampal neurogenesis and subsequent impairments in cognition. Elevated expression of the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus is established as a significant contributor to the neuronal demise evident in many neurological and psychiatric disorders and is now known to negatively regulate hippocampal neurogenesis. In order to prevent the deleterious effects of IL-1β on neurogenesis it is necessary to identify signalling pathways and regulators of neurogenesis within neural progenitor cells that can interact with IL-1β. Nuclear receptors are ligand regulated transcription factors that are involved in modulating a large number of cellular processes including neurogenesis. In this review we focus on the signalling mechanisms of specific nuclear receptors involved in regulating neurogenesis (glucocorticoid receptors, peroxisome proliferator activated receptors, estrogen receptors, and nuclear receptor subfamily 2 group E member 1 (NR2E1 or TLX)). We propose that these nuclear receptors could be targeted to inhibit neuroinflammatory signalling pathways associated with IL-1β. We discuss their potential to be therapeutic targets for neuroinflammatory disorders affecting hippocampal neurogenesis and associated cognitive function.

Peroxisome Proliferator-Activated Receptor γ Activity is Required for Appropriate Cardiomyocyte Differentiation

Objective

Peroxisome proliferator-activated receptor γ (PPARγ) is a member of the PPAR nuclear receptor superfamily. Although PPARγ acts as a master transcription factor in adipocyte differentiation, it is also associated with a variety of cell functions including carbohydrate and lipid metabolism, glucose homeostasis, cell proliferation and cell differentiation. This study aimed to assess the expression level of PPARγ in order to address its role in cardiac cell differentiation of mouse embryonic stem cells (mESCs).

Materials and Methods

In this an intervening study, mESCs were subjected to cardiac differentiation. Total RNA was extracted from the cells and quantitative real time polymerase chain reaction (qPCR) was carried out to estimate level of gene expression. Furthermore, the requirement of PPARγ in cardiac differentiation of mESCs, during cardiac progenitor cells (CPCs) formation, was examined by applying the respective agonist and antagonist.

Results

The obtained data revealed an elevation in the expression level of PPARγ during spontaneous formation of CPCs and cardiomyocytes. Our results indicated that during CPC formation, PPARγ inactivation via treatment with GW9662 (GW) reduced expression of CPC and cardiac markers.

Conclusion

We conclude that PPARγ modulation has an effective role on cardiac differentiation of mESCs at the early stage of cardiomyogenesis.

Systematic selection of small molecules to promote differentiation of embryonic stem cells and experimental validation for generating cardiomyocytes

Small molecules are being increasingly used for inducing the targeted differentiation of stem cells to different cell types. However, until now no systematic method for selecting suitable small molecules for this purpose has been presented. In this work, we propose an integrated and general bioinformatics- and cheminformatics-based approach for selecting small molecules which direct cellular differentiation in the desired way. The approach was successfully experimentally validated for differentiating stem cells into cardiomyocytes. All predicted compounds enhanced expression of cardiac progenitor (Gata4, Nkx2-5 and Mef2c) and mature cardiac markers (Actc1, myh6) significantly during and post-cardiac progenitor formation. The best-performing compound, Famotidine, increased the percentage of Myh6-positive cells from 33 to 56%, and enhanced the expression of Nkx2.5 and Tnnt2 cardiac progenitor and cardiac markers in protein level. The approach employed in the study is applicable to all other stem cell differentiation settings where gene expression data are available.

Different methods for inducing adipose-derived stem cells to differentiate into Schwann-like cells

INTRODUCTION

The aim of the study was to explore an effective method to induce adipose-derived stem cells (ADSCs) to differentiate into Schwann-like cells in vitro.

MATERIAL AND METHODS

Reagents were applied in two different ways (Dezawa inducing method and modified inducing method) in which inducers including β-mercaptoethanol (β-ME), all-trans-retinoic acid (ATRA), type I collagenase, forskolin, heregulin, basic fibroblast growth factor (BFGF) and brain-derived neurotrophic factor (BDNF) were used in different ways to induce ADSCs of rats to differentiate into Schwann-like cells. After induction, the cell morphologic characteristics and the cellular immunohistochemical staining positive rate of anti-S100 and anti-GFAP (glial fibrillary acidic protein) antibodies and the gray value of immunocytochemical dye with anti-S100 and anti-GFAP antibodies and cell activity measured by the MTT method were compared with each other to evaluate the induction effects.

RESULTS

Both methods can induce differentiation of ADSCs of rats into Schwann-like cells, but the cellular morphology of the modified method was more similar to Schwann cells than that of the Dezawa inducing method, there was a higher cellular immunohistochemical staining positive rate and staining grey value in immunocytochemical dye with anti-S100 and anti-GFAP antibodies, and less damage in the cell activity of the modified inducing method than that of the Dezawa inducing method.

CONCLUSIONS

The effect of the modified method to induce ADSCs to differentiate into Schwann-like cells in vitro is superior to that of the Dezawa inducing method.

A ground state of PPARγ activity and expression is required for appropriate neural differentiation of hESCs

BACKGROUND

Several evidences indicate stimulation of peroxisome proliferator activated receptor γ (PPARg), promotes neuronal differentiation. This study was conducted to testify the prominence of PPARγ during neural differentiation of human embryonic stem cells (hESCs).

METHODS

PPARγ expression level was assessed during neural differentiation of hESCs. Meanwhile, the level of endogenous miRNAs, which could be engaged in regulation of PPARγ expression, was measured. Next, natural and synthetic components of PPARγ agonists and antagonist were implemented on neural progenitor formation during neural differentiation of hESCs.

RESULTS

Data showed an increasing wave of PPARγ expression level when human neural progenitors (NPs) were formed upon retinoic acid treatment. Interestingly, there was no significant difference in the amount of PPARγ proteins during the differentiation of hESCs that is inconsistent with what we observed for RNA level. Our results indicated that miRNAs are not involved in the regulation of PPARγ expression, while proteasome-mediated degradation may to some degree be involved in this process. Among numerous treatments, PPARγ inactivation during NPs formation significantly decreased expression of NP markers.

CONCLUSIONS

We conclude that a ground state of PPARγ activity is required for NP formation of hESCs during early neural differentiation. However, high expression and activity of PPARγ could not enhance the required neural differentiation, whereas the PPARγ inactivation could negatively influence NP formation from hESCs by antagonist.

Cardiac differentiation of mouse embryonic stem cells is influenced by a PPAR γ/PGC-1α-FNDC5 pathway during the stage of cardiac precursor cell formation

Peroxisome proliferator-activated receptor (PPAR) γ co-activator 1α (PGC-1α) up-regulation induces FNDC5 expression in muscle and consequently causes browning of white adipose tissue (WAT). In addition to skeletal muscle, FNDC5 is mainly expressed in heart and brain tissues. Here, we demonstrate that FNDC5 expression increased during the process of cardiac differentiation of mouse embryonic stem cells (mESCs) similar to PGC-1α and PPARα. To testify the correlation between PGC-1α and FNDC5 in cardiac cell differentiation of mESCs, we utilized specific PPARγ agonist and antagonist in two stages of cardiac differentiation, during and post-cardiac precursor cells (CPCs) formation. Our results indicated that a reduction in PGC-1α expression, via treatment with GW9662 during CPCs formation stage, down-regulated FNDC5 transcript levels as well as mitochondrial markers which negatively influenced on the whole process of cardiac differentiation efficiency. On the other hand, increase PGC-1α expression during CPCs formation stage via rosiglitazone treatment increase FNDC5 and mitochondrial markers transcript levels which enhanced cardiac differentiation efficiency. Importantly, such alteration in PGC-1α expression at post-CPCs formation stage did not affect overall cardiac differentiation rate as expression of FNDC5 and mitochondrial markers were not significantly changed. We concluded that PPARγ agonist and antagonist induced up and down-regulation of PGC-1α and subsequently modulated the process of CPCs formation through an alteration in FNDC5 and mitochondrial markers expression.

PPARβ/δ and PPARγ maintain undifferentiated phenotypes of mouse adult neural precursor cells from the subventricular zone

The subventricular zone (SVZ) is one of the main niches of neural stem cells in the adult mammalian brain. Stem and precursor cells in this region are the source for neurogenesis and oligodendrogesis, mainly in the olfactory bulb and corpus callosum, respectively. The identification of the molecular components regulating the decision of these cells to differentiate or maintain an undifferentiated state is important in order to understand the modulation of neurogenic processes in physiological and pathological conditions. PPARs are a group of transcription factors, activated by lipid ligands, with important functions in cellular differentiation and proliferation in several tissues. In this work, we demonstrate that mouse adult neural precursor cells (NPCs), in situ and in vitro, express PPARβ/δ and PPARγ. Pharmacological activation of both PPARs isoforms induces proliferation and maintenance of the undifferentiated phenotype. Congruently, inhibition of PPARβ/δ and PPARγ results in a decrease of proliferation and loss of the undifferentiated phenotype. Interestingly, PPARγ regulates the level of EGFR in adult NPCs, concurrent with it is function described in embryonic NPCs. Furthermore, we describe for the first time that PPARβ/δ regulates SOX2 level in adult NPCs, probably through a direct transcriptional regulation, as we identified two putative PPAR response elements in the promoter region of Sox2. EGFR and SOX2 are key players in neural stem/precursor cells self-renewal. Finally, rosiglitazone, a PPARγ ligand, increases PPARβ/δ level, suggesting a possible cooperation between these two PPARs in the control of cell fate behavior. Our work contributes to the understanding of the molecular mechanisms associated to neural cell fate decision and places PPARβ/δ and PPARγ as interesting new targets of modulation of mammalian brain homeostasis.

Acute course of deferoxamine promoted neuronal differentiation of neural progenitor cells through suppression of Wnt/β-catenin pathway: a novel efficient protocol for neuronal differentiation

Neural progenitor cells (NPCs) are feasible therapeutically model cells in regenerative medicine. However, a number of obstacles oppose their applications including insufficiency in differentiation protocols. These complications should be overwhelmed to obtain a significant clinical application. Deferoxamine (DFO), as a small molecule with a clinically high-affinity to chelate intracellular Iron, has been granted orphan drug status for treatment of traumatic spinal cord injury, while its neuroprotective function is not well understood. The aim of the present study is evaluating whether DFO could modulate neuronal differentiation process of NPCs. A varies concentrations of DFO were used to promote neuronal differentiation of mouse and human NPCs with different serum condition as an extracellular source of Iron. Several neural markers were assessed by RT-qPCR and Western analysis. Meanwhile β-catenin content was evaluated as key member of Wnt pathway. The maximal neuronal differentiation rate was observed when treating cells were treated with acute dosage of DFO (100 μM) for 6h in serum free condition. This treatment produced a significant increase in expression of neuronal markers and resulted in dramatically decrease in expression of glial markers. The protein content of β-catenin was also decreased by this treatment. Despite of chronic concentration of DFO, which reduced the size of EBs apparently due to G1/S arrest of cell cycle as known features of DFO. Application of acute courses of DFO increased neuronal differentiation rate of NPCs in serum free conditions. We concluded that suppression of Wnt/β-catenin pathway was induced through chelating of intracellular Iron due to DFO treatment. These findings help to understand therapeutic benefit of DFO as a neuroprotective agent.

Expression of peroxisome proliferator-activated receptor γ in rat retina during development

AIM

To evaluate the spatiotemporal expression pattern of PPARγ in embryonic and early postnatal stages of rat retina.

METHODS

Fetal rats were collected at 13-18d of gestation (GD) from pregnant females and postnatal rats at 1d (P1) and 5d (P5) after birth were also used. We used RT-PCR to detect PPARγ mRNA and immunohistochemical to observe PPARγ protein. And at last, we chose HE staining showed the structural changes of rat retina during development.

RESULTS

RT-PCR analysis showed that PPARγ mRNA was expressed as early as GD13 and gradually decreased as maturation continued. However, the PPARγ gene expression significantly increased after birth, especially in P5. Immunohistochemical analysis showed PPARγ protein was expressed throughout the retinal neuroepithelium at GD13 and GD14, and then decreased during late embryogenesis but remained relatively high in the predicted ganglion cell zone. During postnatal development, PPARγ protein was remarkably increased and the positive signals were mainly located in nerve fiber layer (NFL), ganglion cell layer (GCL) and outer layers of the retina.

CONCLUSION

The spatiotemporal changes of PPARγ expression demonstrated that PPARγ might play a role in regulating the differentiation and maturation of retinal cells.

Role of PPAR γ in the Differentiation and Function of Neurons

Neuronal processes (neurites and axons) have an important role in brain cells communication and, generally, they are damaged in neurodegenerative diseases. Recent evidence has showed that the activation of PPARγ pathway promoted neuronal differentiation and axon polarity. In addition, activation of PPARγ using thiazolidinediones (TZDs) prevented neurodegeneration by reducing neuronal death, improving mitochondrial function, and decreasing neuroinflammation in neuropathic pain. In this review, we will discuss important evidence that supports a possible role of PPARγ in neuronal development, improvement of neuronal health, and pain signaling. Therefore, activation of PPARγ is a potential target with therapeutic applications against neurodegenerative disorders, brain injury, and pain regulation.

CDK5-induced p-PPARγ(Ser 112) downregulates GFAP via PPREs in developing rat brain: effect of metal mixture and troglitazone in astrocytes

The peroxisome proliferator-activated receptor gamma (PPARγ), a group of ligand-activated transcriptional factors, is expressed in glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes. Here, we investigated the role of PPARγ in regulating GFAP using a mixture of As, Cd and Pb (metal mixture, MM) that induces apoptosis and aberrant morphology in rat brain astrocytes. We observed a phospho PPARγ (serine 112 (S112)) (p-PPARγ (S112))-mediated downregulation of GFAP in the MM-exposed astrocytes. We validated this using pure PPARγ agonist, troglitazone (TZ). As reported with MM, TZ induced astrocyte damage owing to reduced GFAP. In silico analysis in the non-coding region of GFAP gene revealed two PPARγ response elements (PPREs); inverted repeat 10 and direct repeat 1 sequences. Gel shift and chromatin immunoprecipitation assays demonstrated enhancement in binding of p-PPARγ (S112) to the sequences, and luciferase reporter assay revealed strong repression of GFAP via PPREs, in response to both MM and TZ. This indicated that suppression in GFAP indeed occurs through direct regulation of these elements by p-PPARγ (S112). Signaling studies proved that MM, as well as TZ, activated the cyclin-dependent kinase 5 (CDK5) and enhanced its interaction with PPARγ resulting into increased p-PPARγ (S112). The p-CDK5 levels were dependent on proximal activation of extracellular signal-regulated protein kinase 1/2 and downstream Jun N-terminal kinase. Taken together, these results are the first to delineate downregulation of GFAP through genomic and non-genomic signaling of PPARγ. It also brings forth a resemblance of TZ with MM in terms of astrocyte disarray in developing brain.

Peroxisome proliferator activated receptor gamma (PPARγ) as a therapeutic target for improvement of cognitive performance in Fragile-X

Rare disorders leading to intellectual disability, such as Fragile X syndrome (FXS) alter synaptic plasticity. Ligand identification of orphan nuclear receptors has led to the discovery of many signaling pathways and has revealed a direct link of nuclear receptors with human conditions such as mental retardation and neurodegenerative diseases. PPARγ agonists can act as neuroprotective agents, promoting synaptic plasticity and neurite outgrowth. Therefore, selective PPARγ agonists are good candidates for therapeutic evaluation in intellectual disabilities. Preliminary results suggest that PPARγ agonists such as Pioglitazone, Rosiglitazone and synthetic agonist, GW1929, are used as the therapeutic agent in neurological disorders. These components interact with intracellular transduction signals (e.g. GSK3β, PI3K/Akt, Wnt/β-Catenin, Rac1 and MMP-9). It seems that interaction with these pathways can improve memory recognition in FXS animal models. The present hypothesis consists of enhancing synaptic plasticity that may then rescue the learning and memory in FXS. This will open many new therapeutic avenues for a variety of human diseases.

Thiazolidinediones promote axonal growth through the activation of the JNK pathway

The axon is a neuronal process involved in protein transport, synaptic plasticity, and neural regeneration. It has been suggested that their structure and function are profoundly impaired in neurodegenerative diseases. Previous evidence suggest that Peroxisome Proliferator-Activated Receptors-γ (PPARγ promote neuronal differentiation on various neuronal cell types. In addition, we demonstrated that activation of PPARγby thiazolidinediones (TZDs) drugs that selectively activate PPARγ prevent neurite loss and axonal damage induced by amyloid-β (Aβ). However, the potential role of TZDs in axonal elongation and neuronal polarity has not been explored. We report here that the activation of PPARγ by TZDs promoted axon elongation in primary hippocampal neurons. Treatments with different TZDs significantly increased axonal growth and branching area, but no significant effects were observed in neurite elongation compared to untreated neurons. Treatment with PPARγ antagonist (GW 9662) prevented TZDs-induced axonal growth. Recently, it has been suggested that the c-Jun N-terminal kinase (JNK) plays an important role regulating axonal growth and neuronal polarity. Interestingly, in our studies, treatment with TZDs induced activation of the JNK pathway, and the pharmacological blockage of this pathway prevented axon elongation induced by TZDs. Altogether, these results indicate that activation of JNK induced by PPARγactivators stimulates axonal growth and accelerates neuronal polarity. These novel findings may contribute to the understanding of the effects of PPARγ on neuronal differentiation and validate the use of PPARγ activators as therapeutic agents in neurodegenerative diseases.

Perfluorooctane sulfonate induces neuronal and oligodendrocytic differentiation in neural stem cells and alters the expression of PPARγ in vitro and in vivo

Perfluorinated compounds are ubiquitous chemicals of major concern for their potential adverse effects on the human population. We have used primary rat embryonic neural stem cells (NSCs) to study the effects of perfluorooctane sulfonate (PFOS) on the process of NSC spontaneous differentiation. Upon removal of basic fibroblast growth factor, NSCs were exposed to nanomolar concentrations of PFOS for 48 h, and then allowed to differentiate for additional 5 days. Exposure to 25 or 50 nM concentration resulted in a lower number of proliferating cells and a higher number of neurite-bearing TuJ1-positive cells, indicating an increase in neuronal differentiation. Exposure to 50 nM also significantly increased the number of CNPase-positive cells, pointing to facilitation of oligodendrocytic differentiation. PPAR genes have been shown to be involved in PFOS toxicity. By q-PCR we detected an upregulation of PPARγ with no changes in PPARα or PPARδ genes. One of the downstream targets of PPARs, the mitochondrial uncoupling protein 2 (UCP2) was also upregulated. The number of TuJ1- and CNPase-positive cells increased after exposure to PPARγ agonist rosiglitazone (RGZ, 3 μM) and decreased after pre-incubation with the PPARγ antagonist GW9662 (5 μM). RGZ also upregulated the expression of PPARγ and UCP2 genes. Meanwhile GW9662 abolished the UCP2 upregulation and decreased Ca²⁺ activity induced by PFOS. Interestingly, a significantly higher expression of PPARγ and UCP3 genes was also detected in mouse neonatal brain after prenatal exposure to PFOS. These data suggest that PPARγ plays a role in the alteration of spontaneous differentiation of NSCs induced by nanomolar concentrations of PFOS.