Mest/Peg1 Is Essential for the Development and Maintenance of a SNc Neuronal Subset

Development, wiring and function of dopamine neuron subtypes

The midbrain dopamine (mDA) system is composed of molecularly and functionally distinct neuron subtypes that mediate specific behaviours and are linked to various brain diseases. Considerable progress has been made in identifying mDA neuron subtypes, and recent work has begun to unveil how these neuronal subtypes develop and organize into functional brain structures. This progress is important for further understanding the disparate physiological functions of mDA neurons and their selective vulnerability in disease, and will ultimately accelerate therapy development. This Review discusses recent advances in our understanding of molecularly defined mDA neuron subtypes and their circuits, ranging from early developmental events, such as neuron migration and axon guidance, to their wiring and function, and future implications for therapeutic strategies.

Developmental pathways linked to the vulnerability of adult midbrain dopaminergic neurons to neurodegeneration

The degeneration of dopaminergic and other neurons in the aging brain is considered a process starting well beyond the infantile and juvenile period. In contrast to other dopamine-associated neuropsychiatric disorders, such as schizophrenia and drug addiction, typically diagnosed during adolescence or young adulthood and, thus, thought to be rooted in the developing brain, Parkinson's Disease (PD) is rarely viewed as such. However, evidences have accumulated suggesting that several factors might contribute to an increased vulnerability to death of the dopaminergic neurons at an already very early (developmental) phase in life. Despite the remarkable ability of the brain to compensate such dopamine deficits, the early loss or dysfunction of these neurons might predispose an individual to suffer from PD because the critical threshold of dopamine function will be reached much earlier in life, even if the time-course and strength of naturally occurring and age-dependent dopaminergic cell death is not markedly altered in this individual. Several signaling and transcriptional pathways required for the proper embryonic development of the midbrain dopaminergic neurons, which are the most affected in PD, either continue to be active in the adult mammalian midbrain or are reactivated at the transition to adulthood and under neurotoxic conditions. The persistent activity of these pathways often has neuroprotective functions in adult midbrain dopaminergic neurons, whereas the reactivation of silenced pathways under pathological conditions can promote the survival and even regeneration of these neurons in the lesioned or aging brain. This article summarizes our current knowledge about signaling and transcription factors involved in midbrain dopaminergic neuron development, whose reduced gene dosage or signaling activity are implicated in a lower survival rate of these neurons in the postnatal or aging brain. It also discusses the evidences supporting the neuroprotection of the midbrain dopaminergic system after the external supply or ectopic expression of some of these secreted and nuclear factors in the adult and aging brain. Altogether, the timely monitoring and/or correction of these signaling and transcriptional pathways might be a promising approach to a much earlier diagnosis and/or prevention of PD.

Hypermethylation of Mest promoter causes aberrant Wnt signaling in patients with Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and behavioral changes. Extracellular deposition of amyloid plaques (Aβ) and intracellular deposition of neurofibrillary tangles in neurons are the major pathogenicities of AD. However, drugs targeting these therapeutic targets are not effective. Therefore, novel targets for the treatment of AD urgently need to be identified. Expression of the mesoderm-specific transcript (Mest) is regulated by genomic imprinting, where only the paternal allele is active for transcription. We identified hypermethylation on the Mest promoter, which led to a reduction in Mest mRNA levels and activation of Wnt signaling in brain tissues of AD patients. Mest knockout (KO) using the CRIPSR/Cas9 system in mouse embryonic stem cells and P19 embryonic carcinoma cells leads to neuronal differentiation arrest. Depletion of Mest in primary hippocampal neurons via lentivirus expressing shMest or inducible KO system causes neurodegeneration. Notably, depletion of Mest in primary cortical neurons of rats leads to tau phosphorylation at the S199 and T231 sites. Overall, our data suggest that hypermethylation of the Mest promoter may cause or facilitate the progression of AD.

The low doses of SWCNTs affect the expression of proliferation and apoptosis related genes in normal human astrocytes

The unique properties of single-walled carbon nanotubes (SWCNTs) make them viable candidates for versatile implementation in the biomedical devices. They are able to cross the blood-brain barrier, enter cells and accumulate in cell nuclei. We studied the effect of these carbon nanoparticles on the expression of genes associated with endoplasmic reticulum stress and proliferation, cell viability and cancerogenesis as well as microRNAs in normal human astrocytes. We have shown that treatment of normal human astrocytes by small doses of SWCNTs (2 and 8 ng/ml of medium for 24 hrs) affect the expression of DNAJB9, IGFBP3, IGFBP6, CLU, ZNF395, KRT18, GJA1, HILPDA, and MEST mRNAs as well as several miRNAs, which have binding sites at 3'-UTR of these mRNAs. These changes in the expression profile of individual mRNAs introduced by SWCNTs are dissimilar in magnitude and direction and are the result of both transcriptional and posttranscriptional mechanisms of regulation. It is possible that these changes in gene expressions are mediated by the endoplasmic reticulum stress introduced by carbon nanotubes and reflect the disturbance of the genome stability. In conclusion, the low doses of SWCNTs disrupt the functional integrity of the genome and possibly exhibit a genotoxic effect.

Tumor Necrosis Factor α Influences Phenotypic Plasticity and Promotes Epigenetic Changes in Human Basal Forebrain Cholinergic Neuroblasts

TNFα is the main proinflammatory cytokine implicated in the pathogenesis of neurodegenerative disorders, but it also modulates physiological functions in both the developing and adult brain. In this study, we investigated a potential direct role of TNFα in determining phenotypic changes of a recently established cellular model of human basal forebrain cholinergic neuroblasts isolated from the nucleus basalis of Meynert (hfNBMs). Exposing hfNBMs to TNFα reduced the expression of immature markers, such as nestin and β-tubulin III, and inhibited primary cilium formation. On the contrary, TNFα increased the expression of TNFα receptor TNFR2 and the mature neuron marker MAP2, also promoting neurite elongation. Moreover, TNFα affected nerve growth factor receptor expression. We also found that TNFα induced the expression of DNA-methylation enzymes and, accordingly, downregulated genes involved in neuronal development through epigenetic mechanisms, as demonstrated by methylome analysis. In summary, TNFα showed a dual role on hfNBMs phenotypic plasticity, exerting a negative influence on neurogenesis despite a positive effect on differentiation, through mechanisms that remain to be elucidated. Our results help to clarify the complexity of TNFα effects in human neurons and suggest that manipulation of TNFα signaling could provide a potential therapeutic approach against neurodegenerative disorders.

KDM3A/Ets1 epigenetic axis contributes to PAX3/FOXO1-driven and independent disease-promoting gene expression in fusion-positive Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and young adults. RMS exists as two major disease subtypes, oncofusion-negative RMS (FN-RMS) and oncofusion-positive RMS (FP-RMS). FP-RMS is characterized by recurrent PAX3/7-FOXO1 driver oncofusions and is a biologically and clinically aggressive disease. Recent studies have revealed FP-RMS to have a strong epigenetic basis. Epigenetic mechanisms represent potential new therapeutic vulnerabilities in FP-RMS, but their complex details remain to be defined. We previously identified a new disease-promoting epigenetic axis in RMS, involving the chromatin factor KDM3A and the Ets1 transcription factor. In the present study, we define the KDM3A and Ets1 FP-RMS transcriptomes and show that these interface with the recently characterized PAX3/FOXO1-driven gene expression program. KDM3A and Ets1 positively control numerous known and candidate novel PAX3/FOXO1-induced RMS-promoting genes, including subsets under control of PAX3/FOXO1-associated superenhancers (SE), such as MEST. Interestingly, KDM3A and Ets1 also positively control a number of known and candidate novel FP-RMS-promoting, but not PAX3/FOXO1-dependent, genes. Epistatically, Ets1 is downstream of, and exerts disease-promoting effects similar to, both KDM3A and PAX3/FOXO1. MEST also manifests disease-promoting properties in FP-RMS, and KDM3A and Ets1 each impacts activation of the PAX3/FOXO1-associated MEST SE. Taken together, our studies show that the KDM3A/Ets1 epigenetic axis plays an important role in disease promotion in FP-RMS, and provide insight into potential new ways to target aggressive phenotypes in this disease.

Acquisition of the Midbrain Dopaminergic Neuronal Identity

The mesodiencephalic dopaminergic (mdDA) group of neurons comprises molecularly distinct subgroups, of which the substantia nigra (SN) and ventral tegmental area (VTA) are the best known, due to the selective degeneration of the SN during Parkinson’s disease. However, although significant research has been conducted on the molecular build-up of these subsets, much is still unknown about how these subsets develop and which factors are involved in this process. In this review, we aim to describe the life of an mdDA neuron, from specification in the floor plate to differentiation into the different subsets. All mdDA neurons are born in the mesodiencephalic floor plate under the influence of both SHH-signaling, important for floor plate patterning, and WNT-signaling, involved in establishing the progenitor pool and the start of the specification of mdDA neurons. Furthermore, transcription factors, like Ngn2, Ascl1, Lmx1a, and En1, and epigenetic factors, like Ezh2, are important in the correct specification of dopamine (DA) progenitors. Later during development, mdDA neurons are further subdivided into different molecular subsets by, amongst others, Otx2, involved in the specification of subsets in the VTA, and En1, Pitx3, Lmx1a, and WNT-signaling, involved in the specification of subsets in the SN. Interestingly, factors involved in early specification in the floor plate can serve a dual function and can also be involved in subset specification. Besides the mdDA group of neurons, other systems in the embryo contain different subsets, like the immune system. Interestingly, many factors involved in the development of mdDA neurons are similarly involved in immune system development and vice versa. This indicates that similar mechanisms are used in the development of these systems, and that knowledge about the development of the immune system may hold clues for the factors involved in the development of mdDA neurons, which may be used in culture protocols for cell replacement therapies.

The effect of folic acid deficiency on Mest/Peg1 in neural tube defects

OBJECTIVE

Neural tube defects (NTDs) are one of the most common and serious birth defects in human beings caused by genetic and environmental factors. Folate insufficiency is involved in the occurrence of NTDs and folic acid supplementation can prevent NTDs occurrence, however, the underlying mechanism remains poorly understood.

METHODS

We established cell and animal models of folic acid deficiency to detect the methylation modification and expression levels of genes by MassARRAY and real-time PCR, respectively. Results and conclusion: In the present study, we found firstly that in human folic acid-insufficient NTDs, the methylation level of imprinted gene Mest/Peg1 was decreased. By using a folic acid-deficient cell model, we demonstrated that Mest/Peg1 methylation was descended. Meanwhile, the mRNA level of Mest/Peg1 was up-regulated via hypomethylation modification under low folic acid conditions. Consistent with the results in cell models, Mest/Peg1 expression was elevated through hypomethylation regulation in folate-deficient animal models. Furthermore, the up-regulation of Mest/Peg1 inhibited the expression of Lrp6 gene, a crucial component of Wnt pathway. Similar results with Lrp6 down-regulation of fetal brain were verified in animal models under folic acid-deficient condition. Taken together, our findings indicated folic acid increased the expression of Mest/Peg1 via hypomethylation modification, and then inhibited Lrp6 expression, which may ultimately impact on the development of nervous system through the inactivation of Wnt pathway.

Molecular Programming of Mesodiencephalic Dopaminergic Neuronal Subsets

Dopamine neurons of the substantia nigra compacta (SNc) and ventral tegmental area (VTA) are critical components of the neuronal machinery to control emotion and movement in mammals. The slow and gradual death of these neurons as seen in Parkinson's disease has triggered a large investment in research toward unraveling the molecular determinants that are used to generate these neurons and to get an insight in their apparent selective vulnerability. Here, I set out to summarize the current view on the molecular distinctions that exist within this mesodiencephalic dopamine (mdDA) system and elaborate on the molecular programming that is responsible for creating such diversity.