Rett syndrome: from the gene to the disease

Rett syndrome (RTT, MIM No. 312750) is a progressive neurodevelopmental disorder and one of the most common causes of mental retardation. It is transmitted as an X-linked dominant trait, therefore almost exclusively affecting females. About 80% of RTT cases are sporadic caused by mutations in the MECP2 gene located on Xq28. The gene codes for two isoforms of the methyl-CpG-binding protein (MeCP2, MeCP2B) which are involved in transcriptional silencing through DNA methylation. The gene has 4 exons. The fourth one is the largest. Almost all mutations in MECP2 occur de novo. Although mutations are dispersed throughout the gene, about 67% of all MECP2 mutations, caused by C>T transitions at 8 CpG dinucleotides, are located in the third and fourth exon. The most common mutation is R168X. So far, there is no clear evidence on genotype-phenotype correlations. There are also reports claiming that the same mutation can provoke different phenotypes. It was shown that MeCP2 can silence certain genes. One of them, brain-derived neurotrophic factor, is essential for neural plasticity, learning and memory. This discovery revealed the role of MeCP2 in the control of neuronal activity-dependent gene regulation and suggested that the pathology of RTT may result from deregulation of this process.

Monoamine oxidase (MAO) intron 13 polymorphism and platelet MAO-B activity in combat-related posttraumatic stress disorder

BACKGROUND

The neurobiology of posttraumatic stress disorder (PTSD) involves alterations in multiple neuroendocrine and neurotransmitter systems. Platelet monoamine oxidase (MAO-B) has been associated with susceptibility to various psychiatric disorders, personality traits and behaviors.

METHODS

Platelet MAO-B activity and MAO-B intron 13 polymorphism (a G/A substitution) were determined in male war veterans (n=106) with DSM-IV diagnosed current and chronic PTSD, divided into subgroups of PTSD patients with (n=28) or without (n=78) psychotic features, combat exposed veterans (n=41) who did not develop PTSD, and healthy control men (n=242).

RESULTS

Two-way ANOVAs revealed a significant effect of diagnosis and smoking, a significant effect of smoking, no significant effect of genotype, and no significant interaction between genotype, smoking or diagnosis, on platelet MAO-B activity. One-way ANOVAs showed significantly lower platelet MAO-B activity in smokers than in nonsmokers. After controlling for smoking, veterans with psychotic PTSD had significantly higher platelet MAO-B activity than veterans with or without PTSD, or healthy subjects.

LIMITATIONS

The results were obtained on peripheral biochemical marker, i.e. platelet MAO activity.

CONCLUSIONS

The MAO-B intron 13 polymorphism was not functional, and did not affect platelet MAO-B activity. The allele frequencies of the MAO-B genotype were similarly distributed among healthy controls and veterans with or without PTSD and/or psychotic symptoms. The results suggest that platelet MAO-B activity, controlled for smoking status, might be used as a peripheral marker of the psychotic symptoms in PTSD.

Saccharomyces cerevisiae strain expressing a plant fatty acid desaturase produces polyunsaturated fatty acids and is susceptible to oxidative stress induced by lipid peroxidation

Although oxygen is essential for aerobic organisms, it also forms potentially harmful reactive oxygen species. For its simplicity, easy manipulation, and cultivation conditions, yeast is used as an attractive model in oxidative stress research. However, lack of polyunsaturated fatty acids in yeast membranes makes yeast unsuitable for research in the field of lipid peroxidation. Therefore, we have constructed a yeast strain expressing a Delta12 desaturase gene from the tropical rubber tree, Hevea brasiliensis. This yeast strain expresses the heterologous desaturase in an active form and, consequently, produces Delta9/Delta12 polyunsaturated fatty acids under inducing conditions. The functional expression of the heterologous desaturase did not affect cellular morphology or growth, indicating no general adverse effect on cellular physiology. However, the presence of polyunsaturated fatty acids changed the yeast's sensitivity to oxidative stress induced by addition of paraquat, tert-butylhydroperoxide, and hydrogen peroxide. This difference in sensitivity to the latter was followed by the formation of 4-hydroxy-2-nonenal, one of the end products of linoleic fatty acid peroxidation, which is known to play a role in cell growth control and signaling. Here we show that this yeast strain conditionally expressing the Delta12 desaturase gene provides a novel and well-defined eukaryotic model in lipid peroxidation research. Its potential to investigate the molecular basis of responses to oxidative stress, in particular the involvement of reactive aldehydes derived from fatty acid peroxidation, especially 4-hydroxy-2-nonenal, will be addressed.

Functionally active toll-like receptor 3 on human primary and metastatic cancer cells

Toll-like receptor 3 (TLR3) is a member of Toll-like receptors who recognize structurally conserved molecules derived from pathogens and trigger the immune response. To clarify if TLR3, is expressed in certain tumour cell lines and whether it is functional and what is the response of these cell lines to different concentrations of poly I:C treatment, we have screened SW480, SW620, FaDu and Detroit 562 cell lines using real-time PCR, flow cytometry and ELISA. We have shown that all these cell lines express TLR3 on mRNA and protein level but it is only functional in Detroit 562 cell line since only in these cells poly I:C treatment triggered the IL-6 secretion. In addition, poly I:C treatment inhibited cell growth and triggered up-regulation of IL-12p40, IL-8 and Il-1alpha in Detroit 562 cell line. By using annexin-V apoptosis detection kit, we have found that poly I:C triggers apoptosis in Detroit 562 cell line. We have found here that based on the results of TLR3 functionality there is a huge difference between FaDu and Detroit 562 cell lines which are of the same origin (pharynx) but FaDu is primary and Detroit 562 metastatic carcinoma. Our study also shows that Detroit 562 cell line could be a good model for cancer therapy research and development as it is responsive to TLR3 agonists which consequently drives it to apoptosis.

The dual role of TLR3 in metastatic cell line

Toll-like receptors (TLRs) are members of transmembrane proteins that recognize conserved molecular motifs of viral and bacterial origin and initiate innate immune response. As the role of TLRs in tumors cells is still not clear, our aim was to investigate the role of TLR3 in primary tumor and metastatic cells (SW480, SW620, FaDu and Detroit 562). We have reported here on the dual role of TLR3 in pharynx metastatic cell line (Detroit 562); on one hand TLR3 activation drove cells to apoptosis while on the other its stimulation contributed to tumor progression by altering the expression of tumor promoting genes (PLAUR, RORB) and enhancing the cell migration potential. In addition, we have shown TLR3 signaling pathway is functional in another metastatic cancer cell line (SW620) suggesting TLR3 might be important in the process of tumor metastasis. Since TLR3 agonists have been used in tumor therapy with the aim to activate immune system, scientific contribution of this work is drawing attention to the importance of further work on this topic, especially pro-tumor effect of TLR3, in order to avoid possible side-effects.

Induction of CMV-1 promoter by 4-hydroxy-2-nonenal in human embryonic kidney cells

Oxidative stress, i.e., excessive production of oxygen free radicals and reactive oxygen species, leads to lipid peroxidation and to formation of reactive aldehydes which act as second messengers of free radicals. It has previously been shown that oxidative stress may be involved in the transcriptional regulation of cytomegalovirus (CMV) immediate early promoter, involved in viral reactivation from latency. In the current study we used a plasmid containing the yellow fluorescent protein (YFP) gene under the control of CMV-1 promoter to monitor the influence of hydrogen peroxide and reactive aldehydes, 4-hydroxy-2-nonenal (HNE) and acrolein, on CMV-1 promoter activation in human embryonic kidney cells (HEK293). While acrolein was ineffective, hydrogen peroxide slightly (50 %) stimulated the CMV promoter. In contrast, HNE had a strong, up to 3-fold, enhancing effect on the CMV-1 promoter within four as well as after 24h of treatment. The most effective was the treatment with 24 microM HNE. This effect of HNE suggests that stressful conditions associated with lipid peroxidation could lead to CMV activation.

The lack of association between monoamine oxidase (MAO) intron 13 polymorphism and platelet MAO-B activity among men

Monoamine oxidase (MAO), a mitochondrial flavine containing enzyme, exists in two isoenzymes, MAO-A and MAO-B. Platelets contain MAO-B subtype, proposed to be a biomarker for different personality characteristics and vulnerability for substance abuse. The most common polymorphism of MAO-B gene, a single base change (A or G) occurs in intron 13. It has been proposed to be a functional polymorphism, controlling the activity of MAO-B in platelets. The aim of the study was to determine the association between platelet MAO-B activity and MAO-B intron 13 polymorphism in 225 racially and ethnically uniform healthy Caucasian men of the Croatian origin. Our results showed that platelet MAO-B activity did not differ between subjects subdivided into those with <<A-allele>> or <<G-allele>>. This polymorphism of the MAO-B gene did not control the activity of the MAO-B in platelets. Platelet MAO-B activity was associated only with the smoking status, and it was significantly decreased in smokers when compared to nonsmokers. No significant association was found between MAO-B polymorphism and smoking status. In healthy individuals of the Croatian origin, the studied MAO-B polymorphism showed a lack of functional importance in regulating MAO-B activity in platelets. Since different populations may vary in the association between functional polymorphism and the MAO-B activity, and the genotype of transcription factor AP-2 beta was reported to be associated with altered platelet MAO-B activity, and with specific personality traits, further studies on different populations should be conducted to elucidate the molecular mechanism/s regulating platelet MAO-B activity.

Induction of CMV-1 promoter by 4-hydroxy-2-nonenal in human embryonic kidney cells

Oxidative stress, i.e., excessive production of oxygen free radicals and reactive oxygen species, leads to lipid peroxidation and to formation of reactive aldehydes which act as second messengers of free radicals. It has previously been shown that oxidative stress may be involved in the transcriptional regulation of cytomegalovirus (CMV) immediate early promoter, involved in viral reactivation from latency. In the current study we used a plasmid containing the yellow fluorescent protein (YFP) gene under the control of CMV-1 promoter to monitor the influence of hydrogen peroxide and reactive aldehydes, 4-hydroxy-2-nonenal (HNE) and acrolein, on CMV-1 promoter activation in human embryonic kidney cells (HEK293). While acrolein was ineffective, hydrogen peroxide slightly (50 %) stimulated the CMV promoter. In contrast, HNE had a strong, up to 3-fold, enhancing effect on the CMV-1 promoter within four as well as after 24h of treatment. The most effective was the treatment with 24 microM HNE. This effect of HNE suggests that stressful conditions associated with lipid peroxidation could lead to CMV activation.