Organizing principles of astrocytic nanoarchitecture in the mouse cerebral cortex.

Astrocytes are increasingly understood to be important regulators of central nervous system (CNS) function in health and disease; yet, we have little quantitative understanding of their complex architecture. While broad categories of astrocytic structures are known, the discrete building blocks that compose them, along with their geometry and organizing principles, are poorly understood. Quantitative investigation of astrocytic complexity is impeded by the absence of high-resolution datasets and robust computational approaches to analyze these intricate cells. To address this, we produced four ultra-high-resolution datasets of mouse cerebral cortex using serial electron microscopy and developed astrocyte-tailored computer vision methods for accurate structural analysis. We unearthed specific anatomical building blocks, structural motifs, connectivity hubs, and hierarchical organizations of astrocytes. Furthermore, we found that astrocytes interact with discrete clusters of synapses and that astrocytic mitochondria are distributed to lie closer to larger clusters of synapses. Our findings provide a geometrically principled, quantitative understanding of astrocytic nanoarchitecture and point to an unexpected level of complexity in how astrocytes interact with CNS microanatomy.

Astrocytes Transplanted during Early Postnatal Development Integrate, Mature, and Survive Long Term in Mouse Cortex.

Astrocytes have complex structural, molecular, and physiological properties and form specialized microenvironments that support circuit-specific functions in the CNS. To better understand how astrocytes acquire their unique features, we transplanted immature mouse cortical astrocytes into the developing cortex of male and female mice and assessed their integration, maturation, and survival. Within days, transplanted astrocytes developed morphologies and acquired territories and tiling behavior typical of cortical astrocytes. At 35-47 d post-transplantation, astrocytes appeared morphologically mature and expressed levels of EAAT2/GLT1 similar to nontransplanted astrocytes. Transplanted astrocytes also supported excitatory/inhibitory (E/I) presynaptic terminals within their territories, and displayed normal Ca2+ events. Transplanted astrocytes showed initially reduced expression of aquaporin 4 (AQP4) at endfeet and elevated expression of EAAT1/GLAST, with both proteins showing normalized expression by 110 d and one year post-transplantation, respectively. To understand how specific brain regions support astrocytic integration and maturation, we transplanted cortical astrocytes into the developing cerebellum. Cortical astrocytes interlaced with Bergmann glia (BG) in the cerebellar molecular layer to establish discrete territories. However, transplanted astrocytes retained many cortical astrocytic features including higher levels of EAAT2/GLT1, lower levels of EAAT1/GLAST, and the absence of expression of the AMPAR subunit GluA1. Collectively, our findings demonstrate that immature cortical astrocytes integrate, mature, and survive (more than one year) following transplantation and retain cortical astrocytic properties. Astrocytic transplantation can be useful for investigating cell-autonomous (intrinsic) and non-cell-autonomous (environmental) mechanisms contributing to astrocytic development/diversity, and for determining the optimal timing for transplanting astrocytes for cellular delivery or replacement in regenerative medicine.SIGNIFICANCE STATEMENT The mechanisms that enable astrocytes to acquire diverse molecular and structural properties remain to be better understood. In this study, we systematically analyzed the properties of cortical astrocytes following their transplantation to the early postnatal brain. We found that immature cortical astrocytes transplanted into cerebral cortex during early postnatal mouse development integrate and establish normal astrocytic properties, and show long-term survival in vivo (more than one year). In contrast, transplanted cortical astrocytes display reduced or altered ability to integrate into the more mature cerebral cortex or developing cerebellum, respectively. This study demonstrates the developmental potential of transplanted cortical astrocytes and provides an approach to tease apart cell-autonomous (intrinsic) and non-cell-autonomous (environmental) mechanisms that determine the structural, molecular, and physiological phenotype of astrocytes.

Interpericyte tunnelling nanotubes regulate neurovascular coupling.

Signalling between cells of the neurovascular unit, or neurovascular coupling, is essential to match local blood flow with neuronal activity. Pericytes interact with endothelial cells and extend processes that wrap capillaries, covering up to 90% of their surface area1,2. Pericytes are candidates to regulate microcirculatory blood flow because they are strategically positioned along capillaries, contain contractile proteins and respond rapidly to neuronal stimulation3,4, but whether they synchronize microvascular dynamics and neurovascular coupling within a capillary network was unknown. Here we identify nanotube-like processes that connect two bona fide pericytes on separate capillary systems, forming a functional network in the mouse retina, which we named interpericyte tunnelling nanotubes (IP-TNTs). We provide evidence that these (i) have an open-ended proximal side and a closed-ended terminal (end-foot) that connects with distal pericyte processes via gap junctions, (ii) carry organelles including mitochondria, which can travel along these processes, and (iii) serve as a conduit for intercellular Ca2+ waves, thus mediating communication between pericytes. Using two-photon microscope live imaging, we demonstrate that retinal pericytes rely on IP-TNTs to control local neurovascular coupling and coordinate light-evoked responses between adjacent capillaries. IP-TNT damage following ablation or ischaemia disrupts intercellular Ca2+ waves, impairing blood flow regulation and neurovascular coupling. Notably, pharmacological blockade of Ca2+ influx preserves IP-TNTs, rescues light-evoked capillary responses and restores blood flow after reperfusion. Our study thus defines IP-TNTs and characterizes their critical role in regulating neurovascular coupling in the living retina under both physiological and pathological conditions.

Human iPSC-derived Down syndrome astrocytes display genome-wide perturbations in gene expression, an altered adhesion profile, and increased cellular dynamics.

Down syndrome (DS), caused by the triplication of human chromosome 21, leads to significant alterations in brain development and is a major genetic cause of intellectual disability. While much is known about changes to neurons in DS, the effects of trisomy 21 on non-neuronal cells such as astrocytes are poorly understood. Astrocytes are critical for brain development and function, and their alteration may contribute to DS pathophysiology. To better understand the impact of trisomy 21 on astrocytes, we performed RNA-sequencing on astrocytes from newly produced DS human induced pluripotent stem cells (hiPSCs). While chromosome 21 genes were upregulated in DS astrocytes, we found consistent up- and down-regulation of genes across the genome with a strong dysregulation of neurodevelopmental, cell adhesion and extracellular matrix molecules. ATAC (assay for transposase-accessible chromatin)-seq also revealed a global alteration in chromatin state in DS astrocytes, showing modified chromatin accessibility at promoters of cell adhesion and extracellular matrix genes. Along with these transcriptomic and epigenomic changes, DS astrocytes displayed perturbations in cell size and cell spreading as well as modifications to cell-cell and cell-substrate recognition/adhesion, and increases in cellular motility and dynamics. Thus, triplication of chromosome 21 is associated with genome-wide transcriptional, epigenomic and functional alterations in astrocytes that may contribute to altered brain development and function in DS.

Stargazing: Monitoring subcellular dynamics of brain astrocytes.

Astrocytes are major non-neuronal cell types in the central nervous system that regulate a variety of processes in the brain including synaptic transmission, neurometabolism, and cerebrovasculature tone. Recent discoveries have revealed that astrocytes perform very specialized and heterogeneous roles in brain homeostasis and function. Exactly how astrocytes fulfill such diverse roles in the brain remains to be fully understood and is an active area of research. In this review, we focus on the complex subcellular anatomical features of protoplasmic gray matter astrocytes in the mature, healthy brain that likely empower these cells with the ability to detect and respond to changes in neuronal and synaptic activity. In particular, we discuss how intricate processes on astrocytes allow these cells to communicate with neurons and their synapses and strategically deliver specific cellular organelles such as mitochondria and ribosomes to active compartments within the neuropil. Understanding the properties of these structural elements will lead to a better understanding of how astrocytes function in the healthy and diseased brain.

[Monitoring the important mycotoxin biomarkers (ochratoxin A, aflatoxin M1) in the Czech population]. / Stav sledováni významných biomarkeru mykotoxinu (ochratoxinu A, aflatoxinu M1) u populace v Ceské republice.

BACKGROUND: In among mycotoxins, secondary metabolites of toxinogenic moulds, ochratoxin A and aflatoxins occupy a prominent place. These mycotoxins have been--as etiologic agents-- associated with a wide numbers of acute and chronic human diseases including mycotoxicoses like Balkan endemic nephropathy or liver cancer. While the risk of acute toxic effects of ochratoxin A and aflatoxin B1 is usually considered to be minimal in the Czech Republic, the situation is different as far as the risk of the late toxic effects (particularly carcinogenic), which result from a single or repeated intake of low doses of these mycotoxins from foodstuffs is concerned. METHODS AND RESULTS: The presence of ochratoxin A and aflatoxins in human environment has been monitored within the program "Monitoring the health state of the population". As for ochratoxin A, 2206 samples of blood serum were investigated, 2077 (94 %) of them turned out to be positive (with levels > or = 0.1 microg x l(-1)), the average was 0.28 microg x l(-1), the median was 0.2 microg x (l(-1), and the percentile (90%) was 0.5 microg x l(-1). The ochratoxin A levels ranged from 0.1 to 13.7 microg x l(-1) of sera. The presence of ochratoxin A was also analyzed in 30 samples of human kidneys; 12 samples were positive (with levels > or = 0.1 microg l(-2), the average was 0.07 microg x kg(-1), the median was 0,05 microg x kg(-1). As for aflatoxins, in 1997-1998 the presence of aflatoxin M1 was investigated in 205 samples of human urine; 118 samples (58%) were positive (with levels >125 pg x l(-1) of urine). CONCLUSIONS: When calculated to a concentration of creatinine in urine, the average was 391 pg x g(-1), the median was 127 pg x g(-1), and the percentile (90%) was 585 pg x g(-1). The aflatoxin M1 levels ranged from 19 to 19 219 pg x g(-1) of creatinine.

The dialysis of Ochratoxin A (OTA).

Standard dialysis did not result in a decrease of the OTA level in the blood serum of patients regularly treated by dialysis. Therefore, we examined the effect of dialysis on both OTA bound to the blood plasma proteins and free OTA. We carried out an in vivo experiment to determine OTA levels in the serum of patients in the terminal stage of chronic renal insufficiency (CHRI) before and after dialysis and also in the dialysate in which we did not find OTA. OTA bound to blood plasma proteins did not penetrate the dialysis membrane. In contrast, free OTA during an in vitro experiment with the identical dialyzer (as during the in vivo experiment), easily penetrated the same dialysis membrane.

The effect of bopindolol on lipids and platelet aggregation.

An open ambulatory study was performed to assess the effect of bopindolol in 19 hypertensive patients (W.H.O. stage I-II). A statistically significant decrease in systolic and diastolic pressure as well as heart rate (never below 60 beats per minute) was demonstrated. No undesirable subjective side-effects of the drug were reported. Compared with the serum concentrations after placebo, a decrease in all low-density fractions was observed after 12 months. The total cholesterol/HDL cholesterol ratio did not deteriorate and the apolipoprotein A/apolipoprotein B ratio increased. The values of triacylglycerols during 8 months of therapy did not exceed initial serum concentrations following placebo administration. Patients treated with bopindolol exhibited decreased platelet aggregation due to collagen.

Systemic mastocytosis. Report of a case.

The case of a 20-year-old woman with systemic mastocytosis is reported. The disorder was not preceded by a clinically diagnosed local form of the disease; fibrous changes in organs, bone changes, eosinophilia and increased serotonin, heparin or histamine levels had not been observed. Clinical symptomatology was typical and the patient died one year after the first signs of the disease.