Dopamine (DA) in the striatum is vital for motor and cognitive behaviors. Midbrain dopaminergic neurons generate both tonic and phasic action potential (AP) firing patterns in behavior mice. Besides AP numbers, whether and how different AP firing patterns per se modulate DA release remain largely unknown. Here by using in vivo and ex vivo models, it is shown that the AP frequency per se modulates DA release through the D2 receptor (D2R), which contributes up to 50% of total DA release. D2R has a voltage-sensing site at D131 and can be deactivated in a frequency-dependent manner by membrane depolarization. This voltage-dependent D2R inhibition of DA release is mediated via the facilitation of voltage-gated Ca2+ channels (VGCCs). Collectively, this work establishes a novel mechanism that APs per se modulate DA overflow by disinhibiting the voltage-sensitive autoreceptor D2R and thus the facilitation of VGCCs, providing a pivotal pathway and insight into mammalian DA-dependent functions in vivo.
Abstract The ability to identify a specific type of leukemia using minimally invasive biopsies holds great promise to improve the diagnosis, treatment selection, and prognosis prediction of patients. Using genome-wide methylation profiling and machine learning methods, we investigated the utility of CpG methylation status to differentiate blood from patients with acute lymphocytic leukemia (ALL) or acute myelogenous leukemia (AML) from normal blood. We established a CpG methylation panel that can distinguish ALL and AML blood from normal blood as well as ALL blood from AML blood with high sensitivity and specificity. We then developed a methylation-based survival classifier with 23 CpGs for ALL and 20 CpGs for AML that could successfully divide patients into high-risk and low-risk groups, with significant differences in clinical outcome in each leukemia type. Together, these findings demonstrate that methylation profiles can be highly sensitive and specific in the accurate diagnosis of ALL and AML, with implications for the prediction of prognosis and treatment selection.
Objective To evaluate the performance of a DNA methylation-based digital droplet polymerase chain reaction (ddPCR) assay to detect aberrant DNA methylation in cell-free DNA (cfDNA) and to determine its application in the detection of hepatocellular carcinoma (HCC). Methods The present study recruited patients with liver-related diseases and healthy control subjects. Blood samples were used for the extraction of cfDNA, which was then bisulfite converted and the extent of DNA methylation quantified using a ddPCR platform. Results A total of 97 patients with HCC, 80 healthy control subjects and 46 patients with chronic hepatitis B/C virus infection were enrolled in the study. The level of cfDNA in the HCC group was significantly higher than that in the healthy control group. For the detection of HCC, based on a cut-off value of 15.7% for the cfDNA methylation ratio, the sensitivity and specificity were 78.57% and 89.38%, respectively. The diagnostic accuracy was 85.27%, the positive predictive value was 81.91% and the negative predictive value was 87.20%. The positive likelihood ratio of 15.7% in HCC diagnosis was 7.40, while the negative likelihood ratio was 0.24. Conclusions A sensitive methylation-based assay might serve as a liquid biopsy test for diagnosing HCC.
Glaucoma, a blinding neurodegenerative disease, whose risk factors include elevated intraocular pressure (IOP), age, and genetics, is characterized by accelerated and progressive retinal ganglion cell (RGC) death. Despite decades of research, the mechanism of RGC death in glaucoma is still unknown. Here, we demonstrate that the genetic effect of the SIX6 risk variant (rs33912345, His141Asn) is enhanced by another major POAG risk gene, p16INK4a (cyclin-dependent kinase inhibitor 2A, isoform INK4a). We further show that the upregulation of homozygous SIX6 risk alleles (CC) leads to an increase in p16INK4a expression, with subsequent cellular senescence, as evidenced in a mouse model of elevated IOP and in human POAG eyes. Our data indicate that SIX6 and/or IOP promotes POAG by directly increasing p16INK4a expression, leading to RGC senescence in adult human retinas. Our study provides important insights linking genetic susceptibility to the underlying mechanism of RGC death and provides a unified theory of glaucoma pathogenesis.
Under physiological conditions, astrocytes not only passively support and nourish adjacent neurons, but also actively modulate neuronal transmission by releasing “glial transmitters,” such as glutamate, ATP, and d -serine. Unlike the case for neurons, the mechanisms by which glia release transmitters are essentially unknown. Here, by using electrochemical amperometry and frequency-modulated single-vesicle imaging, we discovered that hippocampal astrocytes exhibit two modes of exocytosis of glutamate in response to various stimuli. After physiological stimulation, a glial vesicle releases a quantal content that is only 10% of that induced by nonphysiological, mechanical stimulation. The small release event arises from a brief (∼2 ms) opening of the fusion pore. We conclude that, after physiological stimulation, astrocytes release glutamate via a vesicular “kiss-and-run” mechanism.
Anxiety is a major early-onset non-motor symptom in Parkinson’s disease, but the underlying mechanisms remain largely unknown. By imaging brain circuits in an awake parkinsonian mouse model, Li, Xu et al. provide evidence that Parkinson’s disease-associated anxiety is caused by impaired postsynaptic D2 receptor-dependent dopaminergic transmission in prefrontal cortex.
An effective and accurate diagnostic method for leukemia has not yet been developed. Using genome‐wide methylation profiling and machine learning methods, we evaluated the utility of CpG methylation status to differentiate blood from patients with acute lymphocytic leukemia (ALL) or acute myelogenous leukemia (AML) from normal blood. We constructed a diagnostic prediction model that can differentiate ALL and AML blood from normal blood as well as ALL blood from AML blood with high diagnostic specificity and sensitivity by utilizing a CpG methylation panel. We then developed a methylation‐based survival classifier with 23 CpGs for ALL and 20 CpGs for AML that could successfully divide patients into high‐risk and low‐risk groups, with significant differences in clinical outcome in each leukemia type. These methylation markers have outperformed existing methods in their high sensitivity and specificity for diagnosis of ALL and AML, and have implications for the prediction of prognosis and treatment selection. Support or Funding Information Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou 510623, China Using 11 markers, the methylation profile can differentiate subtype of leukemia and normal blood. Unsupervised hierarchical clustering and heatmap associated with ALL, AML and normal blood. Figure 1 Methylation markers can predict five‐year overall survival of patients. A. AML training set (n=125); B. AML validation set (n=55); C. ALL training set (n=55); and D. ALL validation set (n=34). Figure 2
Significance Noninvasive prenatal testing (NIPT) using sequencing of fetal cell-free DNA from maternal plasma has allowed accurate prenatal diagnosis of aneuploidy without requirement of an invasive procedure; this approach has gained increasing clinical acceptance. In this manuscript, we evaluate whether NIPT using semiconductor sequencing platform (SSP) could reliably detect subchromosomal deletions/duplications in women carrying a high-risk fetus. We show that detection of fetal subchromosomal abnormalities is a viable extension of NIPT using SSP. Given the recent strong interest in NIPT using cell-free DNA, these results should be of broad interest and immediate clinical importance, even beyond the NIPT field, such as for detection of cell-free tumor DNA.
While glucose-stimulated insulin secretion depends on Ca(2+) influx through voltage-gated Ca(2+) channels in the cell membrane of the pancreatic β-cell, there is also ample evidence for an important role of intracellular Ca(2+) stores in insulin secretion, particularly in relation to drug stimuli. We report here that thiopental, a common anesthetic agent, triggers insulin secretion from the intact pancreas and primary cultured rat pancreatic β-cells. We investigated the underlying mechanisms by measurements of whole cell K(+) and Ca(2+) currents, membrane potential, cytoplasmic Ca(2+) concentration ([Ca(2+)](i)), and membrane capacitance. Thiopental-induced insulin secretion was first detected by enzyme-linked immunoassay, then further assessed by membrane capacitance measurement, which revealed kinetics distinct from glucose-induced insulin secretion. The thiopental-induced secretion was independent of cell membrane depolarization and closure of ATP-sensitive potassium (K(ATP)) channels. However, accompanied by the insulin secretion stimulated by thiopental, we recorded a significant intracellular [Ca(2+)] increase that was not from Ca(2+) influx across the cell membrane, but from intracellular Ca(2+) stores. The thiopental-induced [Ca(2+)](i) rise in β-cells was sensitive to thapsigargin, a blocker of the endoplasmic reticulum Ca(2+) pump, as well as to heparin (0.1 mg/ml) and 2-aminoethoxydiphenyl borate (2-APB; 100 μM), drugs that inhibit inositol 1,4,5-trisphosphate (IP(3)) binding to the IP(3) receptor, and to U-73122, a phospholipase C inhibitor, but insensitive to ryanodine. Thapsigargin also diminished thiopental-induced insulin secretion. Thus, we conclude that thiopental-induced insulin secretion is mediated by activation of the intracellular IP(3)-sensitive Ca(2+) store.
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