Collapse of complexity of brain and body activity due to excessive inhibition and MeCP2 disruption

Complex body movements require complex dynamics and coordination among neurons in motor cortex. Conversely, a long-standing theoretical notion supposes that if many neurons in motor cortex become excessively synchronized, they may lack the necessary complexity for healthy motor coding. However, direct experimental support for this idea is rare and underlying mechanisms are unclear. Here we recorded three-dimensional body movements and spiking activity of many single neurons in motor cortex of rats with enhanced synaptic inhibition and a transgenic rat model of Rett syndrome (RTT). For both cases, we found a collapse of complexity in the motor system. Reduced complexity was apparent in lower-dimensional, stereotyped brain–body interactions, neural synchrony, and simpler behavior. Our results demonstrate how imbalanced inhibition can cause excessive synchrony among movement-related neurons and, consequently, a stereotyped motor code. Excessive inhibition and synchrony may underlie abnormal motor function in RTT.

A diverse and complex repertoire of body movements requires diverse and complex neural activity among cortical neurons. Moreover, interactions between movement-related neurons and the body must be sufficiently high dimensional to carry these movement signals with high fidelity. The complexity of movement-related neural activity and neuron–body interactions can be compromised if synchrony among neurons is excessive. Indeed, it is well understood theoretically that excessive correlations can limit the information capacity of any neural code (1–3)—if all neurons are perfectly synchronized, then different neurons cannot encode different motor signals. Synchrony is also known to play a role in pathophysiology of movement-related disorders, like Parkinson’s disease (4–6). However, synchrony and correlations also contribute to healthy function in the motor system (7–14). For instance, particular groups of synchronized neurons seem to send control signals to particular muscle groups (7, 8) and propagation of correlated firing contributes to motor planning (10). Synchrony can also play a role in motor learning (12–14). These findings suggest that correlated activity among specific subsets of neurons encodes specific motor functions. Thus, it stands to reason that if this synchrony became less selective and more stereotyped across neurons, then the motor code would become less complex and lose specificity, resulting in compromised motor function.Here we explored this possibility in rats, in the caudal part of motor cortex where neurons associated with hindlimb, forelimb, and trunk body movement are located (15–17). We focused on two conditions. First, we studied a transgenic rat model of Rett syndrome (RTT), which has disrupted expression of the MeCP2 gene. Second, we studied normal rats with acutely altered inhibitory neural interactions. Both of these cases are associated with abnormal motor behavior and, possibly, abnormal synchrony. Abnormal synchrony is a possibility, because both of these cases are linked to an imbalance between excitatory (E) and inhibitory (I) neural interactions, which in turn is likely to result in abnormal synchrony. For instance, many computational models suggest that synchrony is strongly dependent on E/I interactions (18–21). Likewise, in experiments, pharmacological manipulation of E/I causes changes in synchrony (19, 22, 23) and the excessive synchrony that occurs during epileptic seizures is often attributed to an E/I imbalance (24, 25). Similarly, the majority of people with RTT suffer from seizures (26) and many previous studies establish E/I imbalance as a common problem in RTT (27). MeCP2 dysfunction, which is known to cause RTT, seems to be particularly important in inhibitory neurons (28). For instance, two studies have shown that disrupting MeCP2 only in specific inhibitory neuron types can recapitulate the effects of brain-wide disruption of MeCP2 (29, 30). However, whether the E/I imbalance favors E or I at the population level seems to vary across different brain regions in RTT. Studies of visual cortex (29) and hippocampus (31) suggest that the balance tips toward too much excitation (perhaps explaining the prevalence of seizures), while studies of somatosensory cortex (32, 33) and a brain-wide study of Fos expression (34) suggest that frontal areas, including motor cortex, are tipped toward excessive inhibition. These facts motivated our choice to study pharmacological disruption of inhibition here. While it is clear that E/I imbalance is important in RTT, it is much less clear how it manifests at the level of dynamics and complexity of neural activity that is responsible for coordinating body movements. Thus, in addition to pursuing the general questions about synchrony and complexity in the motor system discussed above, a second goal of our work was to improve understanding of motor dysfunction due to MeCP2 disruption.Taken together, these facts led us to the following questions: How does MeCP2 disruption impact the complexity of body movements, movement-related neural activity, and motor coding? Are abnormalities in the MeCP2-disrupted motor system consistent with excessive inhibition in motor cortex? We hypothesized that both MeCP2 disruption and excessive inhibition lead to reduced complexity of interactions between cortical neurons and body movements, excessive cortical synchrony, and reduced complexity of body movements. Our findings confirmed this hypothesis and suggest that RTT-related motor dysfunction may be due, in part, to excessive synchrony and inhibition in motor cortex.     

老年甲状腺结节合并糖尿病患者外周血DNA甲基化/羟甲基化的检测及其临床意义

目的 探讨老年甲状腺结节合并糖尿病患者外周血DNA甲基化/羟甲基化的检测及其临床意义。方法 选择2021年1月至2022年12月兰州市第一人民医院收治的136例老年甲状腺结节合并糖尿病患者为研究组,另选同期体检正常的135例老年人为对照组。采集所有入组对象一般资料,测定空腹血糖(FPG)、餐后2h血糖(2hPBG)、糖化血红蛋白(HbA1c)、甘油三酯(TG)、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)、游离三碘甲状腺原氨酸(FT3)、游离四碘甲状腺原氨酸(FT4)、促甲状腺激素(TSH)、甲状腺球蛋白抗体(TGAb)和甲状腺过氧化物酶抗体(TPOAb)水平。采用酶联免疫吸附法检测外周血全基因组5-甲基胞嘧啶(5-mC)、5羟甲基胞嘧啶(5-hmC)、细胞间黏附分子-1(ICAM-1)和甲基双加氧酶(TET2)水平。采用SPSS 21.0统计软件进行数据分析。根据数据类型,分别采用t检验、Mann-Whitney U检验或χ²检验进行组间比较。采用Spearman相关性分析探讨外周血5-mC、5-hmC与甲状腺结节合并糖尿病的相关性。结果 研究组患者FPG、2hPBG、HbA1c、TSH、TgAb和TPOAb水平均高于对照组,FT3低于对照组,差异均有统计学意义(P<0.05)。研究组外周血5-mC、5-hmC水平均高于对照组[6.64%(3.53%,8.53%)和4.28%(1.70%,7.20%);50.41%(35.00%,63.27%)和36.51%(17.81%,50.06%)];外周血TET2、ICAM-1水平均高于对照组[9.37(5.70,13.56)和4.56(1.52,6.99)pg/ml;4.98(2.35,7.01)和0.97(0.15,1.60)ng/ml],差异均有统计学意义(P<0.001)。Spearman相关性分析结果显示,5-mC与TgAb、TPOAb和HbA1c呈正相关(r=0.413,0.348,0.405;P<0.05);5-hmC与TgAb、TPOAb、FBG和2hPG呈正相关(r=0.375,0.406,0.376,0.311;P<0.05);5-mC与5-hmC呈正相关(r=0.256;P<0.05)。结论 老年甲状腺结节合并糖尿病患者外周血全基因组DNA甲基化与羟甲基化水平显著正常人群,外周血5-mC、5-hmC水平与老年甲状腺结节、糖尿病发病显著相关。     

Loss of MeCP2 in aminergic neurons causes cell-autonomous defects in neurotransmitter synthesis and specific behavioral abnormalities

Rett syndrome (RTT) is characterized by specific motor, cognitive, and behavioral deficits. Because several of these abnormalities occur in other disease states associated with alterations in aminergic neurotransmitters, we investigated the contribution of such alterations to RTT pathogenesis. We found that both individuals with RTT and Mecp2-null mice have lower-than-normal levels of aminergic metabolites and content. Deleting Mecp2 from either TH-positive dopaminergic and noradrenergic neurons or PET1-positive serotonergic neurons in mice decreased corresponding neurotransmitter concentration and specific phenotypes, likely through MeCP2 regulation of rate-limiting enzymes involved in aminergic neurotransmitter production. These data support a cell-autonomous, MeCP2-dependent mechanism for the regulation of aminergic neurotransmitter synthesis contributing to unique behavioral phenotypes.     

Epigenetic MRI: Noninvasive imaging of DNA methylation in the brain

Both neuronal and genetic mechanisms regulate brain function. While there are excellent methods to study neuronal activity in vivo, there are no nondestructive methods to measure global gene expression in living brains. Here, we present a method, epigenetic MRI (eMRI), that overcomes this limitation via direct imaging of DNA methylation, a major gene-expression regulator. eMRI exploits the methionine metabolic pathways for DNA methylation to label genomic DNA through ¹³C-enriched diets. A ¹³C magnetic resonance spectroscopic imaging method then maps the spatial distribution of labeled DNA. We validated eMRI using pigs, whose brains have stronger similarity to humans in volume and anatomy than rodents, and confirmed efficient ¹³C-labeling of brain DNA. We also discovered strong regional differences in global DNA methylation. Just as functional MRI measurements of regional neuronal activity have had a transformational effect on neuroscience, we expect that the eMRI signal, both as a measure of regional epigenetic activity and as a possible surrogate for regional gene expression, will enable many new investigations of human brain function, behavior, and disease.

The brain is ever-changing in structure and function as a result of development, aging, environmental influence, and disease. Two fundamental mechanisms underpin these changes: neuronal activation, which occurs over relatively short time scales (milliseconds, seconds, and minutes), and gene expression, which occurs over longer time scales (hours, days, or even longer) (1–3). Advances in imaging technology have transformed how we investigate these mechanisms.Functional MRI (fMRI) has revolutionized our understanding of the human brain by providing a powerful nondestructive method to image neural activity (4–7). In contrast, the technologies to image gene expression have been limited to methods that require invasive sampling and tissue processing (8–11). Although these techniques have provided tremendous knowledge about gene expression and gene regulation in the brain, especially in animal models, their destructive nature makes longitudinal studies of the same samples impossible, thus limiting our ability to translate and expand scientific discoveries to human brains. This is especially unfortunate because longer-term changes in brain function play critical roles in both brain diseases and responses of the brain to environmental change (1–3). The ability to measure and visualize gene expression and regulation in the brain noninvasively would revolutionize the study of brain function, behavior, and disease (12).Efforts to map brain gene expression and regulation in living organisms to date have involved imaging reporter genes or associated enzymes using optical techniques, positron emission tomography (PET), or MRI (13–17). These methods are either limited to model organisms or require transgenic animals engineered to express a particular reporter gene and an exogenous contrast probe interacting with the reporter gene to produce the desired images (15, 16). Therefore, such methods have no clear path for translation to humans. Furthermore, these methods are limited to just a few genes and, therefore, cannot provide a comprehensive portrait of gene expression.PET imaging of histone deacetylases (HDACs) in the human brain was recently demonstrated, using a radioactive tracer that can pass the blood–brain barrier (BBB) and target HDAC isoforms (18, 19). This probes a major form of epigenetic gene regulation, histone acetylation, but PET requires introducing radioactive materials into the body, and it only targets one of the enzymes that regulates histone acetylation, rather than histone acetylation itself. Moreover, PET lacks the specificity to distinguish between the target molecule and downstream metabolic products (20–22). Other imaging epigenetics approaches have studied correlations between brain MRI and gene expression or methylation in postmortem tissues, saliva, or blood (23–28); although useful, they can only provide indirect insights into the brain gene expression and regulation.We present successful direct imaging of brain DNA methylation using an approach we call epigenetic MRI (eMRI), which integrates stable isotope 5-methyl-2′-deoxycytidine (5mdC) labeling through diet and magnetic resonance spectroscopic imaging (MRSI). Using pigs fed by a customized diet enriched in ¹³C-methionine (¹³C-Met) and innovations to ¹³C-MRSI, we report robust mapping in intact brain hemispheres that revealed strong regional differences in DNA methylation. We chose pigs as a surrogate to assess feasibility of translation to humans because of stronger similarities in brain size and anatomy than rodent models (29). Significant eMRI signal differences were observed in animals fed with enriched diet for different numbers of days, demonstrating the dynamic nature of this signal. Given the noninvasiveness of our method, these results provide a path toward a global DNA-methylation brain-imaging paradigm for humans. Because DNA methylation is one of the major regulators of gene expression, eMRI promises to become a powerful tool to understand the molecular basis of brain function and disease.     

肝癌组织中p57kip2基因表达缺失与甲基化的关系

p57kip2属于CIP/KIP家族成员,抑制细胞周期从G1期到S期转化,使细胞周期停滞在G1期,进而阻止细胞增殖.肝癌组织中普遍存在p57kip2 mRNA表达水平的下降,提示p57kip2与肝癌发生关系密切[1].本研究采用原位分子杂交和甲基化特异性PCR方法检测p57kip2 mRNA的表达及启动子区甲基化情况,探讨p57kip2 基因失表达机制.     

Features of the Arabidopsis recombination landscape resulting from the combined loss of sequence variation and DNA methylation

The rate of meiotic crossing over (CO) varies considerably along chromosomes, leading to marked distortions between physical and genetic distances. The causes underlying this variation are being unraveled, and DNA sequence and chromatin states have emerged as key factors. However, the extent to which the suppression of COs within the repeat-rich pericentromeric regions of plant and mammalian chromosomes results from their high level of DNA polymorphisms and from their heterochromatic state, notably their dense DNA methylation, remains unknown. Here, we test the combined effect of removing sequence polymorphisms and repeat-associated DNA methylation on the meiotic recombination landscape of an Arabidopsis mapping population. To do so, we use genome-wide DNA methylation data from a large panel of isogenic epigenetic recombinant inbred lines (epiRILs) to derive a recombination map based on 126 meiotically stable, differentially methylated regions covering 81.9% of the genome. We demonstrate that the suppression of COs within pericentromeric regions of chromosomes persists in this experimental setting. Moreover, suppression is reinforced within 3-Mb regions flanking pericentromeric boundaries, and this effect appears to be compensated by increased recombination activity in chromosome arms. A direct comparison with 17 classical Arabidopsis crosses shows that these recombination changes place the epiRILs at the boundary of the range of natural variation but are not severe enough to transgress that boundary significantly. This level of robustness is remarkable, considering that this population represents an extreme with key recombination barriers having been forced to a minimum.     

Alterations of DNA methylation and histone modifications contribute to gene silencing in hepatocellular carcinomas

Aim: The aim of the present study was to examine DNA methylation and histone modification changes in hepatocellular carcinomas (HCC). Methods: DNA methylation in the P16, RASSF1a, progesterone receptor (PGR) and estrogen receptor alpha (ERalpha) promoters was determined by quantitative bisulfite-pyrosequencing technique in HCC patients. Histone H3-lysine (K) 4, H3-K9 and H3-K27 modifications in all these four genes were examined by chromatin immunoprecipitation (ChIP) assay in HCC cell lines. Expression of two DNA methyltransferases (DNMT1 and DNMT3b) and three histone methyltransferases (SUV39H1, G9a and EZH2) in HCC patients was measured by real-time polymerase chain reaction. Results: Aberrant DNA methylation was detected in all the HCC. Patients with DNA methylation in the RASSF1a, PGR andERalpha promoters in cancers also had substantial DNA methylation in their non-cancerous liver tissues, whereas DNA methylation in the P16 promoter was cancer specific. Epigenetic states in HCC cell lines showed that silencing of P16 and RASSF1a depended on DNA methylation and histone H3-K9 methylation. However, silencing of the PGR and ERalpha genes was more closely related to H3-K27 methylation rather than DNA methylation. Consistent with the alteration of histone status, higher expression of G9a and EZH2 was found in HCC than in non-cancerous liver tissues (P < 0.01). Conclusion: These data suggest that multiple epigenetic silencing mechanisms are inappropriately active in HCC cells.