miRNA-145 is downregulated in atypical and anaplastic meningiomas and negatively regulates motility and proliferation of meningioma cells.

Meningiomas are frequent, mostly benign intracranial or spinal tumors. A small subset of meningiomas is characterized by histological features of atypia or anaplasia that are associated with more aggressive biological behavior resulting in increased morbidity and mortality. Infiltration into the adjacent brain tissue is a major factor linked to higher recurrence rates. The molecular mechanisms of progression, including brain invasion are still poorly understood. We have studied the role of micro-RNA 145 (miR-145) in meningiomas and detected significantly reduced miR-145 expression in atypical and anaplastic tumors as compared with benign meningiomas. Overexpression of miR-145 in IOMM-Lee meningioma cells resulted in reduced proliferation, increased sensitivity to apoptosis, reduced anchorage-independent growth and reduction of orthotopic tumor growth in nude mice as compared with control cells. Moreover, meningioma cells with high miR-145 levels had impaired migratory and invasive potential in vitro and in vivo. PCR-array studies of miR145-overexpressing cells suggested that collagen type V alpha (COL5A1) expression is downregulated by miR-145 overexpression. Accordingly, COL5A1 expression was significantly upregulated in atypical and anaplastic meningiomas. Collectively, our data indicate an important anti-migratory and anti-proliferative function of miR-145 in meningiomas.

Cellular expression pattern of the protease-activated receptor 4 in the hippocampus in naïve rats and after global ischaemia.

A pronounced hippocampal expression of the Protease-activated Receptor 4 (PAR4) has recently been shown. In the current study the authors define the PAR4-associated sub-cellular structures and the influence of global ischaemia on the expression of PAR4. For that purpose the authors performed double labelling with fluorescence immunohistochemistry on tissue from naïve and post-ischaemic rats. In naïve animals - apart from the expression in granular and pyramidal neurons - there was an intensive lamellar expression of PAR4 in the CA4 region. Further analysis revealed that PAR4 was localised exclusively on mossy fibre axons in CA4 as detected by double-labelling with calbindin D-28k, but there was no overlap with markers of the neuronal cell body, interneurons, and post-synaptic, pre-synaptic and dendritic structures. Three and 14 days post ischaemia, CA1 neurons were degenerated and, consequently, there was no PAR4 signal in the CA1 band. In most other hippocampal structures no change in the PAR4 expression was detectable, with the exception of the CA3 region. Here, the fibre-associated PAR4 signal was diminished and disintegrated post ischaemia. Additionally, a redistribution from the membrane-bound neuronal localisation of PAR4 in control animals to a diffuse localisation all over the cell soma was revealed in the CA3 area 14 days post ischaemia. In conclusion, the current study proves for the first time that PAR4 is localised in mossy fibre axons. The altered expression in CA3 neurons after ischaemia indicates that PAR4 may be involved in post-ischaemic adaptive mechanisms.

No improvement of functional and histological outcome after application of the metabotropic glutamate receptor 5 agonist CHPG in a model of endothelin-1-induced focal ischemia in rats.

The role of group I metabotropic glutamate receptors (mGluRs) in neurodegeneration is as yet unclear as mGluR1/5 antagonists and agonists yielded contradictory effects in different disease models. In the present study, we examined the neuroprotective potency of the selective mGluR5 agonist, (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG), in endothelin-1(ET-1)-induced focal ischemia in rats. In addition to the effect of CHPG on the histologically defined infarct size, we studied its influence on sensorimotor impairments in the ladder rung walking test at late time points up to 4 weeks after the ischemic insult. Rats were treated i.c.v. with an injection of 1mM CHPG beginning 10min after the application of ET-1. Histological analyses 4 weeks after ET-1-induced ischemia demonstrated only a small, insignificant reduction in infarct size after CHPG application. In accordance with this result, there were no significant effects of the used CHPG concentration on sensorimotor impairments in the ladder rung walking test. In conclusion, our data point to the restricted value of CHPG as a neuroprotectant after transient focal ischemia and to the importance of evaluating neuroprotective effects at late post-ischemic time points.

Increase of prothrombin-mRNA after global cerebral ischemia in rats, with constant expression of protease nexin-1 and protease-activated receptors.

Prothrombin, protease-activated receptors (PARs) and the specific thrombin inhibitor protease nexin-1 (PN-1) are expressed in the brain. Recent studies have shown that the serine protease thrombin, depending on its concentration, plays an important role in neuronal degeneration or protection after cerebral ischemia. However, it is still uncertain whether a change in prothrombin or alterations in the expression of specific PAR-subtypes or PN-1 are associated with postischemic thrombin effects. Using semi-quantitative reverse transcription-polymerase chain reaction analysis, we show that prothrombin was up-regulated in the hippocampal formation 24 h after transient global ischemia in rats (two-vessel occlusion with hypotension), whereas the expression of PN-1 and the expression of PAR-subtypes 1-3 did not change significantly. Thus, control of the balance between the expression of prothrombin and PN-1 may reflect an important mechanism that underlies postischemic thrombin effects.

Four different types of protease-activated receptors are widely expressed in the brain and are up-regulated in hippocampus by severe ischemia.

A variety of extracellular serine proteases are expressed in the central nervous system or might permeate the blood-brain barrier under pathological conditions. However, their intracerebral targets and physiological functions are largely unknown. Here, we show that four distinct subtypes of protease-activated receptors (PARs) are abundantly expressed in the adult rat brain and in organotypic hippocampal slice cultures. PAR-1 expression was significant in the hippocampus, cortex and amygdala. Highest densities of PAR-2 and PAR-3 were observed in hippocampus, cortex, amygdala, thalamus, hypothalamus and striatum. Apart from the striatum, a similar localization was found for PAR-4. Within the hippocampal formation, each PAR subtype was predominantly localized in the pyramidal cell layers. Additionally, we identified PAR-2 in mossy fibers between dentate gyrus and CA3, PAR-3 in the subiculum and PAR-4 in CA3 and in mossy fibres as well as in the stratum lacunosum moleculare. After exposing hippocampal slice cultures to a severe experimental ischemia (oxygen-glucose deprivation), the expression of PARs 1-3 was up-regulated with subtype-specific kinetics. The localization of PARs in brain regions particularly vulnerable to ischemic insults as well as distinct alterations in the expression pattern after experimental ischemia support the notion of an important role of extracellular serine proteases and PARs in cerebral ischemia.