The Impact of Alpha-Syntrophin Deletion on the Changes in Tissue Structure and Extracellular Diffusion Associated with Cell Swelling under Physiological and Pathological Conditions

Aquaporin-4 (AQP4) is the primary cellular water channel in the brain and is abundantly expressed by astrocytes along the blood-brain barrier and brain-cerebrospinal fluid interfaces. Water transport via AQP4 contributes to the activity-dependent volume changes of the extracellular space (ECS), which affect extracellular solute concentrations and neuronal excitability. AQP4 is anchored by α-syntrophin (α-syn), the deletion of which leads to reduced AQP4 levels in perivascular and subpial membranes. We used the real-time iontophoretic method and/or diffusion-weighted magnetic resonance imaging to clarify the impact of α-syn deletion on astrocyte morphology and changes in extracellular diffusion associated with cell swelling in vitro and in vivo. In mice lacking α-syn, we found higher resting values of the apparent diffusion coefficient of water (ADC_W) and the extracellular volume fraction (α). No significant differences in tortuosity (λ) or non-specific uptake (k′), were found between α-syn-negative (α-syn −/−) and α-syn-positive (α-syn +/+) mice. The deletion of α-syn resulted in a significantly smaller relative decrease in α observed during elevated K⁺ (10 mM) and severe hypotonic stress (−100 mOsmol/l), but not during mild hypotonic stress (−50 mOsmol/l). After the induction of terminal ischemia/anoxia, the final values of ADC_W as well as of the ECS volume fraction α indicate milder cell swelling in α-syn −/− in comparison with α-syn +/+ mice. Shortly after terminal ischemia/anoxia induction, the onset of a steep rise in the extracellular potassium concentration and an increase in λ was faster in α-syn −/− mice, but the final values did not differ between α-syn −/− and α-syn +/+ mice. This study reveals that water transport through AQP4 channels enhances and accelerates astrocyte swelling. The substantially altered ECS diffusion parameters will likely affect the movement of neuroactive substances and/or trophic factors, which in turn may modulate the extent of tissue damage and/or drug distribution.     

Bral1: "Superglue" for the extracellular matrix in the brain white matter

Bral1 is a link protein that stabilizes the binding between lecticans and hyaluronic acid and thus maintains the extracellular matrix assembly in the CNS. Bral1 is specifically located in the white matter around the nodes of Ranvier. Recent studies suggest its function in promoting saltatory neural conduction. This article reviews the current knowledge about the structure, expression and function of this link protein.     

Altered Astrocytic Swelling in the Cortex of α-Syntrophin-Negative GFAP/EGFP Mice

Brain edema accompanying ischemic or traumatic brain injuries, originates from a disruption of ionic/neurotransmitter homeostasis that leads to accumulation of K⁺ and glutamate in the extracellular space. Their increased uptake, predominantly provided by astrocytes, is associated with water influx via aquaporin-4 (AQP4). As the removal of perivascular AQP4 via the deletion of α-syntrophin was shown to delay edema formation and K⁺ clearance, we aimed to elucidate the impact of α-syntrophin knockout on volume changes in individual astrocytes in situ evoked by pathological stimuli using three dimensional confocal morphometry and changes in the extracellular space volume fraction (α) in situ and in vivo in the mouse cortex employing the real-time iontophoretic method. RT-qPCR profiling was used to reveal possible differences in the expression of ion channels/transporters that participate in maintaining ionic/neurotransmitter homeostasis. To visualize individual astrocytes in mice lacking α-syntrophin we crossbred GFAP/EGFP mice, in which the astrocytes are labeled by the enhanced green fluorescent protein under the human glial fibrillary acidic protein promoter, with α-syntrophin knockout mice. Three-dimensional confocal morphometry revealed that α-syntrophin deletion results in significantly smaller astrocyte swelling when induced by severe hypoosmotic stress, oxygen glucose deprivation (OGD) or 50 mM K⁺. As for the mild stimuli, such as mild hypoosmotic or hyperosmotic stress or 10 mM K⁺, α-syntrophin deletion had no effect on astrocyte swelling. Similarly, evaluation of relative α changes showed a significantly smaller decrease in α-syntrophin knockout mice only during severe pathological conditions, but not during mild stimuli. In summary, the deletion of α-syntrophin markedly alters astrocyte swelling during severe hypoosmotic stress, OGD or high K⁺.     

Evolution of temperature and chemical parameters during composting of the pig slurry solid fraction amended with natural zeolite

A 3-month experiment was conducted at a 300 kg scale to observe decomposition processes in pig slurry solids amended with two different doses of natural Slovak zeolite-clinoptilolite (substrates S1 and S2, 1% and 2% of zeolite by weight, respectively) in comparison with the control (unamended solids). The experimental and control substrates were stored outdoors in sheltered static piles at ambient temperatures ranging from 8.0 to 34.7 degrees C. The solid fraction (SF) of pig slurry was obtained by separation on vibration sieves prior to slurry treatment with activated sludge. The initial water content of the SF was 77.1% and no water was added to the piles during the storage. The temperature in the core of the piles was recorded throughout the experiment. By day 3 and 5 of storage (1% and 2% zeolite, resp.), the temperature in the substrates S1 and S2 exceeded 55 degrees C and remained above this level for 15 days while the highest temperature recorded in the control during the experiment was 29.8 degrees C. Samples from the core of the piles were taken periodically to determine pH, dry matter at 105 degrees C (DM), ash (550 degrees C/4 h), ammonia nitrogen (N-NH(4)(+)), nitrate nitrogen (N-NO(3)(-)), total nitrogen (N(t)), total phosphorus (P(t)); total organic carbon (TOC) was computed. The results showed that pH levels in S1 and S2 remained below that in the control for most of the thermophilic stage. This may be related to water-soluble ammonia and the affinity of zeolites to ammonium ions. A significant decrease in the level of ammonia nitrogen in water extracts from S1 and S2 was observed between days 5 and 35 in comparison with the control. The values of ash also differed and corresponded to the intensity of the decomposition processes in the respective substrates.     

Activation of poly(ADP-ribose) polymerase by myocardial ischemia and coronary reperfusion in human circulating leukocytes

Reactive free radical and oxidant production leads to DNA damage during myocardial ischemia/reperfusion. Consequent overactivation of poly(ADP-ribose) polymerase (PARP) promotes cellular energy deficit and necrosis. We hypothesized that PARP is activated in circulating leukocytes in patients with myocardial infarction and reperfusion during primary percutaneous coronary intervention (PCI). In 15 patients with ST segment elevation acute myocardial infarction, before and after primary PCI and 24 and 96 h later, we determined serum hydrogen peroxide concentrations, plasma levels of the oxidative DNA adduct 8-hydroxy-2'-deoxyguanosine (8OHdG), tyrosine nitration, PARP activation, and translocation of apoptosis-inducing factor (AIF) in circulating leukocytes. Plasma 8OHdG levels and leukocyte tyrosine nitration were rapidly increased by PCI. Similarly, poly(ADP-ribose) content of the leukocytes increased in cells isolated just after PCI, indicating immediate PARP activation triggered by reperfusion of the myocardium. In contrast, serum hydrogen peroxide concentrations and the translocation of AIF gradually increased over time and were most pronounced at 96 h. Reperfusion-related oxidative/nitrosative stress triggers DNA damage, which leads to PARP activation in circulating leukocytes. Translocation of AIF and lipid peroxidation occurs at a later stage. These results represent the first direct demonstration of PARP activation in human myocardial infarction. Future work is required to test whether pharmacological inhibition of PARP may offer myocardial protection during primary PCI.     

The Effect of Hapln4 Link Protein Deficiency on Extracellular Space Diffusion Parameters and Perineuronal Nets in the Auditory System During Aging

Neurochemical Research - Hapln4 is a link protein which stabilizes the binding between lecticans and hyaluronan in perineuronal nets (PNNs) in specific brain regions, including the medial nucleus...