Differences in expression of junctional adhesion molecule-A and beta-catenin in multiple sclerosis brain tissue: increasing evidence for the role of tight junction pathology

Changes of AXIN-1 and beta-catenin in neuroepithelial brain tumors

In the present study changes of components of Wnt signaling pathway--axin (AXIN1) and beta-catenin (CTNNB1) in a sample of 72 neuroepithelial brain tumors were investigated. AXIN-1 gene was tested by PCR/loss of heterozygosity (LOH). Immunostaining and image analysis revealed the quantity and localization of relevant proteins. Polymorphic marker for AXIN-1, showed LOH in 11.1% of tumors. LOH was distributed to 6.3% of glioblastomas, one was found in neuroepithelial dysembrioplastic tumor and one in medulloblastoma. Down regulation of axin expression and up regulation of beta-catenin were detected in the analyzed tumors. Axin was observed in the cytoplasm in 68.8% of samples, in 28.1% in both the cytoplasm and nucleus and 3.1% had no expression. Beta-catenin was observed mainly in the nucleus and cytoplasm (59.4%). Expression in 34.4% of samples was in the cytoplasm and 6.3% showed no expression. Comparison of mean values of relative increase of axin and beta-catenin showed that they are significantly reversely proportional (P = 0.014). Relative quantity of beta-catenin in patients with gross deletion of AXIN1 was significantly higher in comparison to patients without LOH (P = 0.040). Our results demonstrate that changes of key components of the Wnt signaling play a role in neuroepithelial brain tumors.

Keratinocytes as depository of ammonium-inducible glutamine synthetase: age- and anatomy-dependent distribution in human and rat skin

In inner organs, glutamine contributes to proliferation, detoxification and establishment of a mechanical barrier, i.e., functions essential for skin, as well. However, the age-dependent and regional peculiarities of distribution of glutamine synthetase (GS), an enzyme responsible for generation of glutamine, and factors regulating its enzymatic activity in mammalian skin remain undisclosed. To explore this, GS localization was investigated using immunohistochemistry and double-labeling of young and adult human and rat skin sections as well as skin cells in culture. In human and rat skin GS was almost completely co-localized with astrocyte-specific proteins (e.g. GFAP). While GS staining was pronounced in all layers of the epidermis of young human skin, staining was reduced and more differentiated among different layers with age. In stratum basale and in stratum spinosum GS was co-localized with the adherens junction component beta-catenin. Inhibition of, glycogen synthase kinase 3beta in cultured keratinocytes and HaCaT cells, however, did not support a direct role of beta-catenin in regulation of GS. Enzymatic and reverse transcriptase polymerase chain reaction studies revealed an unusual mode of regulation of this enzyme in keratinocytes, i.e., GS activity, but not expression, was enhanced about 8-10 fold when the cells were exposed to ammonium ions. Prominent posttranscriptional up-regulation of GS activity in keratinocytes by ammonium ions in conjunction with widespread distribution of GS immunoreactivity throughout the epidermis allows considering the skin as a large reservoir of latent GS. Such a depository of glutamine-generating enzyme seems essential for continuous renewal of epidermal permeability barrier and during pathological processes accompanied by hyperammonemia.

The effects of blood–brain barrier disruption on glial cell function in multiple sclerosis

Dysfunction of the BBB (blood–brain barrier) is a major hallmark of MS (multiple sclerosis). Studies in our laboratories over the last decade have shown that increased BBB permeability is associated with decreased expression of TJ (tight junction) proteins in brain capillary endothelial cells. Results have revealed that TJ abnormalities were most common in active lesions (42% of vessels affected), but were also present in inactive lesions (23%) and in MS normal-appearing white matter (13%). Importantly, TJ abnormality was also positively associated with leakage of the serum protein fibrinogen which has recently been shown to be an activator of microglia. TJ abnormality and the resultant vascular permeability in both lesional and non-lesional white matter may impair tissue homoeostasis, which may have effects on disease progression, repair mechanisms and drug delivery.

Decreased junctional adhesion molecule-A expression during blood-brain barrier breakdown

Tight junctions between brain endothelial cells are one of the specialized structural components of the blood-brain barrier (BBB) to proteins. Research in the last decade has demonstrated that the integral membrane proteins of cerebral endothelial tight junctions are claudin, occludin, and junctional adhesion molecule (JAM). Altered expression of these tight junction proteins could cause BBB breakdown following brain injury leading to edema. In this study, expression of JAM-A, was analyzed by immunostaining and immunoblotting in the rat cortical cold injury model, a well-characterized in vivo model of BBB breakdown. Temporal and spatial expression of JAM-A was examined at 12 hours, days 2, 4, and 6 post-lesion in cold-injured and control rats. Control rats showed punctate JAM-A immunoreactivity at intervals along the circumference of the endothelial layer at tight junctions where JAM-A colocalized with occludin. A significant decrease in JAM-A expression was noted at the lesion site by immunoblotting at 12 h only. At this time period, lesion vessels showed loss of endothelial JAM-A immunostaining while day 2 onwards, there was recovery of endothelial JAM-A immunoreactivity. Dual labelling for JAM-A and fibronectin showed that only lesion vessels with BBB breakdown to fibronectin at 12 h also showed lack of endothelial JAM-A immunoreactivity supporting the evidence that JAM-A contributes to tight junction integrity.

The blood-brain barrier in health and chronic neurodegenerative disorders

The blood-brain barrier (BBB) is a highly specialized brain endothelial structure of the fully differentiated neurovascular system. In concert with pericytes, astrocytes, and microglia, the BBB separates components of the circulating blood from neurons. Moreover, the BBB maintains the chemical composition of the neuronal "milieu," which is required for proper functioning of neuronal circuits, synaptic transmission, synaptic remodeling, angiogenesis, and neurogenesis in the adult brain. BBB breakdown, due to disruption of the tight junctions, altered transport of molecules between blood and brain and brain and blood, aberrant angiogenesis, vessel regression, brain hypoperfusion, and inflammatory responses, may initiate and/or contribute to a "vicious circle" of the disease process, resulting in progressive synaptic and neuronal dysfunction and loss in disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and others. These findings support developments of new therapeutic approaches for chronic neurodegenerative disorders directed at the BBB and other nonneuronal cells of the neurovascular unit.