Association study of CYP17 and HSD11B1 in polycystic ovary syndrome utilizing comprehensive gene coverage

Cytochrome P450-C17 enzyme (CYP17) is an important component of the androgen synthesis pathway, a pathway that is dysfunctional in polycystic ovary syndrome (PCOS). Variation in 11-beta hydroxysteroid dehydrogenase (HSD11B1) is associated with cortisone reductase deficiency, a condition with a phenotype similar to PCOS. Both CYP17 and HSD11B1 genes have been previously studied for their possible relationship with PCOS, yielding inconsistent results. In this study, we evaluated the association between variation in these genes and PCOS. Two-hundred and eighty-seven Caucasian PCOS women and 187 Caucasian controls were genotyped for single nucleotide polymorphisms (SNPs) that were specifically chosen to allow full coverage of CYP17 and HSD11B1, including four SNPs in CYP17 and eight SNPs in HSD11B1. SNP and haplotype association analyses were conducted. Our results indicate that variants in the two genes are not associated with PCOS, or with the quantitative traits characteristic of PCOS, suggesting that these genes are not major risk factors for the syndrome.     

Three SNPs in the GSTO1, GSTO2 and PRSS11 genes on chromosome 10 are not associated with age-at-onset of Alzheimer's disease

Linkage studies suggest the presence of putative risk and/or age-at-onset genes for Alzheimer's disease on Chromosome 10. Recently, a genomic converging approach using a combination of linkage, expression and association studies has reported significant associations of the glutathione S-transferase omega 1 and 2 (GSTO1 and GSTO2) genes and possibly the protease serine 11 (PRSS11) gene on chromosome 10 with age-at-onset, but not risk, for Alzheimer's disease (AD) and Parkinson disease. We investigated the association of the reported three polymorphisms in 990 sporadic late-onset AD cases (26% autopsy confirmed) and 735 controls. In our sample, we found no association either with age-at-onset in AD cases or with disease risk in the case-control cohort. However, haplotype analysis revealed a modest association of one haplotype with AD risk (p = 0.04). Additional markers in these genes need to be screened to explore their role in the etiology of AD.     

Polymorphisms in the gene encoding 11B-hydroxysteroid dehydrogenase type 1 (HSD11B1) and lifetime cognitive change

A rare polymorphism in the gene encoding 11B-hydroxysteroid dehydrogenase type 1 (HSD11B1: rs846911-C/A) has been associated with an increased risk of Alzheimer's disease. We tested the hypothesis that this and 2 other HSD11B1 polymorphisms (rs12086634-G/T and rs846910-A/G) were associated with lifetime cognitive change in humans. Subjects were 194 participants of the Scottish Mental Survey of 1932 who took the same well-validated mental test at age 11 and age 79. The subjects represented the highest and lowest quintiles with respect to cognitive decline between ages 11 and 79. Despite having non-significantly different IQs at age 11, by age 79 the groups had mean (S.D.) IQs of 80.3 (14.1) and 109.6 (9.1), respectively (p<.001). The polymorphism rs846911-C/A was absent from both groups. There were no significant differences in the frequency of polymorphisms of rs12086634-G/T (p=.91) and rs846910-A/G (p=.90) between the groups. We conclude that these variants in HSD11B1 are not significant contributors to the range of cognitive ageing examined here.     

Site-specific methylation of placental HSD11B2 gene promoter is related to intrauterine growth restriction

Intrauterine growth restriction (IUGR) is associated with detrimental effects on neurodevelopmental progress in childhood and higher risk of degenerative diseases in adulthood. Placental 11β-hydroxysteroid dehydrogenase (HSD11B2) is a key gene involved in glucocorticoid metabolism, which in turn seems to be related to fetal growth impairment. As reduction of placental HSD11B2 gene expression has been associated with reduced human fetal growth, and methylation of HSD11B2 gene promoter has been shown to have an important role in HSD11B2 gene repression, we seek to investigate the relationship between IUGR and HSD11B2 gene promoter methylation in human placentas. We found that methylation levels of all studied CpG sites were significantly higher in IUGR newborns than those in controls. Further, methylation levels of the first and the third CpG sites were inversely associated with measures of fetal growth (birth weight and ponderal index). In addition, consistent with the above negative correlation, methylation levels of the first and the third CpG sites were inversely associated with HSD11B2 gene expression. These results together show a link between the site-specific methylation of placental HSD11B2 promoter and the development of IUGR.     

DNA sequence variations in the prolyl isomerase Pin1 gene and Alzheimer's disease

Senile plaques and neurofibrillary tangles (NFT) are the prominent lesions in the brain of Alzheimer's disease (AD) patients. NFT are mainly composed of an abnormally phosphorylated form of tau protein, which has lost its function to bind microtubules and promote their assembly. Tau hyperphosphorylation critically decreases tau function and precedes neurodegeneration. The majority of tau phosphorylation sites are Ser/Thr-Pro motifs, which are known to exist in two distinct cis and trans conformations. The prolyl isomerase Pin1 catalyses the conversion of those conformations. Pin1 binds to tau specifically at the Thr231-Pro site and restores tau function, either by inducing conformational changes or facilitating dephosphorylation. It has been shown that Pin1 expression levels inversely correlate with the predicted vulnerability of different brain areas to neurodegeneration and soluble Pin1 is depleted in neurons from AD brains; furthermore, Pin1 knock-out mice develop signs and symptoms of tau-related pathologies late in life. It seems that Pin1 plays an important role in maintaining tau function, thereby preserving neuronal homeostasis and preventing age-dependent neurodegeneration. DNA sequence variations in Pin1 gene may affect its expression level or function and influence the individual risk for developing AD. We screened by denaturing high performance liquid chromatography the genomic DNA of 120 AD subjects and 134 age-matched controls and we found very few and rare sequence variations in the promoter region and in exons 2 and 3. We conclude that Pin1 is a very well conserved gene, whose rare nucleotide variations have no effect on the individual genetic risk for AD.     

Stress, exercise, and Alzheimer's disease: a neurovascular pathway

Genetic factors are known to play a role in Alzheimer's disease (AD) vulnerability, yet less than 1% of incident AD cases are directly linked to genetic causes, suggesting that environmental variables likely play a role in the majority of cases. Several recent human and animal studies have examined the effects of behavioral factors, specifically psychological stress and exercise, on AD vulnerability. Numerous animal studies have found that, while stress exacerbates neuropathological changes associated with AD, exercise reduces these changes. Some human studies suggest that psychological stress can increase the risk of developing AD, while other studies suggest that exercise can significantly reduce AD risk. Most animal studies investigating the mechanisms responsible for the effects of these behavioral factors have focused on neuronal processes, including the effects of stress hormones and neurotrophic factors on the neuropathological hallmarks of AD, namely amyloid-beta (Aβ) deposition and tau-phosphorylation. However, cumulative evidence indicates that, in humans, AD is associated with the presence of cerebrovascular disease, and cardiovascular risk factors are associated with increased risk of developing AD. There is an extensive literature demonstrating that behavioral factors, particularly stress and exercise, can powerfully modulate the pathophysiology of vascular disease. Thus, the following model proposes that the influence of stress and exercise on AD risk may be partially due to the effects of these behavioral factors on vascular homeostasis and pathology. These effects are likely due to both indirect modification of AD risk through alterations in vascular risk factors, such as hypertension, diabetes, and aortic stiffening, as well as direct influence on the cerebrovasculature, including changes in cerebral blood flow, angiogenesis, and vascular disease. Future studies examining the effects of behavioral factors on AD risk should incorporate measures of both peripheral and cerebral vascular function to further our understanding of the mechanisms by which behavior can modify AD susceptibility. Greater knowledge of the molecular mechanisms behind these behavioral effects would further our understanding of the disease and lead to innovative treatment and preventive approaches.     

Plasticity, pathology, and Alzheimer's disease

Much basic data support the notion that growth factors are important in the maintenance and repair of the CNS. Although local increases in growth factors might contribute to aberrant growth and senile plaque formation in Alzheimer's disease (AD), the administration of growth factor inhibitors as a therapeutic intervention would be predicted to decrease the vulnerability of remaining healthy neurons. The administration of neurotrophic agents in AD may help to protect and maintain neurons, and thereby minimize neuronal death and the resultant sprouting response.     

Tumour necrosis factor-alpha gene polymorphisms and Alzheimer's disease

Recent findings suggest that production of pro-inflammatory cytokines, such as tumour necrosis factor-alpha (TNF-alpha), is increased in the brains of people with Alzheimer's disease (AD). We used direct sequencing methods on a section of the enhancer/promoter region and on a smaller fragment located 10.5 kb upstream of the TNF-alpha gene to respectively examine TNF-alpha polymorphisms and TNF-a and -b microsatellite alleles in a cohort of 235 post-mortem confirmed AD and 130 control cases. None of the TNF-alpha point mutations or microsatellite alleles investigated proved to be independent risk factors for AD. However, when -308/A, -238/G and TNF-a2 were examined as a 2-1-2 haplotype, we observed that the absence of that haplotype was significantly associated with AD (P = 0.014, Fisher's exact test) suggesting that the 2-1-2 haplotype may be protective against AD.     

Risk and protective factors for sporadic Alzheimer's disease

Alzheimer's disease (AD) is the most common form of senile dementia. There are 24.3 million people suffering from this progressive neurodegenerative disorder worldwide. A century ago, AD was characterized with regard to the clinical manifestations and pathology for the first time. Up till now, there is a lack of full understanding of the underlying causes and molecular mechanisms leading to this progressive form of dementia. The majority of AD cases occur sporadically, what suggested that they could arise through interactions among various genetic and environmental factors. Current epidemiological investigations show that midlife hypertension, cardiovascular diseases, hypercholesterolemia, diabetes, obesity, inflammation, and viral infections can significantly contribute to the development and progression of AD, whereas active engagement in social, mental and physical activities may delay the onset of the disease. Apolipoprotein E (ApoE) is considered as the main genetic risk factor in the sporadic AD that is closely connected to lipid metabolism. Other genes involved in the disease pathways related to AD pathology in addition to cholesterol metabolism, neuroinflammation, amyloid and tau cascade, neuronal signalling, and plasticity are under investigation. In spite of the significant progress achieved, it is still not clear how genetic vulnerability and environmental exposures may contribute to the susceptibility of the disease. Therefore, understanding the role of disease-related risk factors for AD pathogenesis may help to identify specific modifiable risk factors that could provide possibility for the prevention of Alzheimer's dementia.     

Immunohistochemical Analysis of 11-β-Hydroxysteroid Dehydrogenase Type 2 and Glucocorticoid Receptor in Subclinical Cushing’s Disease due to Pituitary Macroadenoma

Subclinical Cushing’s disease (SCD) is characterized by lack of clinically evident Cushingoid features, despite abnormal hypersecretion of ACTH. Nearly half the cases of SCD are due to macroadenomas, and in the majority of them, ACTH secretion is not inhibited even by high-dose dexamethasone. Impaired glucocorticoid (GC) action may be correlated with the proliferation and development of pituitary macroadenomas causing SCD. In this study, immunohistochemical analysis of the resected tumors were performed to evaluate the expression of 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) and glucocorticoid receptor (GR) in pituitary tissues obtained from two SCD (macroadenomas), eight Cushing’s disease (CD) (microadenomas), nine acromegaly, and nine normal pituitary (NP). Scattered 11βHSD2-immunopositive cells were detected in all NP tissues, but its immunoreactivity was totally absent in any tumorous tissues except two CD. Scattered GR-immunopositive cells were also detected and GR immunostaining was restricted to the cytosol in NP tissue. In contrast, GR-immunopositive cells were abundantly present and GR immunostaining was restricted to the nucleus in all the tumorous tissues. There were marked differences in both expression levels and localization between NP tissues and all the tumors. There may be a mechanism other than that via 11βHSD2 for causes of impaired negative feedback action by GC in SCD and CD, but results of our present study suggest that impaired GC action may be involved, at least in part, in tumorigenesis of SCD and CD.     

The CDC2 I-G-T haplotype associated with the APOE epsilon4 allele increases the risk of sporadic Alzheimer's disease in Sicily

The cell division cycle 2 (CDC2) gene is a candidate susceptibility gene for Alzheimer's disease (AD). We investigated the CDC2 genotype, and allele and haplotype frequencies in AD patients and matched controls, distinguishing between apolipoprotein E (APOE) epsilon4 allele carriers and non-carriers. APOE epsilon4 is an established predictor of AD risk. APOE and CDC2 genotypes were examined in 109 sporadic AD patients and in 110 healthy age- and sex-matched controls from Sicily. The epsilon4 allele of APOE was predictive of AD risk in our study group (odds ratio: 5.37, 95% CI 2.77-10.41; P<0.0001). Genotype and allele frequencies of the three tested CDC2 polymorphisms (Ex6+7I/D, Ex7-15 G>A, Ex7-14 T>A) were not significantly different between AD patients and controls. However, a significant different distribution of a specific CDC2 haplotype (I-G-T) was found between AD patients and controls when analyzing APOE epsilon4-positive subjects (P=0.0288). Moreover, the combined presence of the I-G-T haplotype and the epsilon4 allele almost doubled the risk of AD (odds ratio: 10.09, 95% CI 3.88-26.25; P<0.0001) compared to carriers of epsilon4 alone. This study suggests that the I-G-T haplotype of the CDC2 gene increases the risk of AD in APOE epsilon4 carriers.     

Foetal and placental 11β‐HSD2: a hub for developmental programming

Foetal growth restriction (FGR), reflective of an adverse intrauterine environment, confers a significantly increased risk of perinatal mortality and morbidity. In addition, low birthweight associates with adult diseases including hypertension, metabolic dysfunction and behavioural disorders. A key mechanism underlying FGR is exposure of the foetus to glucocorticoids which, while critical for foetal development, in excess can reduce foetal growth and permanently alter organ structure and function, predisposing to disease in later life. Foetal glucocorticoid exposure is regulated, at least in part, by the enzyme 11β‐hydroxysteroid dehydrogenase type 2 (11β‐HSD2), which catalyses the intracellular inactivation of glucocorticoids. This enzyme is highly expressed within the placenta at the maternal–foetal interface, limiting the passage of glucocorticoids to the foetus. Expression of 11β‐HSD2 is also high in foetal tissues, particularly within the developing central nervous system. Down‐regulation or genetic deficiency of placental 11β‐HSD2 is associated with significant reductions in foetal growth and birth weight, and programmed outcomes in adulthood. To unravel the direct significance of 11β‐HSD2 for developmental programming, placental function, neurodevelopment and adult behaviour have been extensively investigated in a mouse knockout of 11β‐HSD2. This review highlights the evidence obtained from this mouse model for a critical role of feto‐placental 11β‐HSD2 in determining the adverse programming outcomes.     

Evidence for a role of the rare p.A152T variant in MAPT in increasing the risk for FTD-spectrum and Alzheimer's diseases

Rare mutations in the gene encoding for tau (MAPT, microtubule-associated protein tau) cause frontotemporal dementia-spectrum (FTD-s) disorders, including FTD, progressive supranuclear palsy (PSP) and corticobasal syndrome, and a common extended haplotype spanning across the MAPT locus is associated with increased risk of PSP and Parkinson's disease. We identified a rare tau variant (p.A152T) in a patient with a clinical diagnosis of PSP and assessed its frequency in multiple independent series of patients with neurodegenerative conditions and controls, in a total of 15 369 subjects. Tau p.A152T significantly increases the risk for both FTD-s (n = 2139, OR = 3.0, CI: 1.6-5.6, P = 0.0005) and Alzheimer's disease (AD) (n = 3345, OR = 2.3, CI: 1.3-4.2, P = 0.004) compared with 9047 controls. Functionally, p.A152T (i) decreases the binding of tau to microtubules and therefore promotes microtubule assembly less efficiently; and (ii) reduces the tendency to form abnormal fibers. However, there is a pronounced increase in the formation of tau oligomers. Importantly, these findings suggest that other regions of the tau protein may be crucial in regulating normal function, as the p.A152 residue is distal to the domains considered responsible for microtubule interactions or aggregation. These data provide both the first genetic evidence and functional studies supporting the role of MAPT p.A152T as a rare risk factor for both FTD-s and AD and the concept that rare variants can increase the risk for relatively common, complex neurodegenerative diseases, but since no clear significance threshold for rare genetic variation has been established, some caution is warranted until the findings are further replicated.     

HSD17B10: a gene involved in cognitive function through metabolism of isoleucine and neuroactive steroids

The HSD17B10 gene maps on chromosome Xp11.2, a region highly associated with X-linked mental retardation. This gene encodes HSD10, a mitochondrial multifunctional enzyme that plays a significant part in the metabolism of neuroactive steroids and the degradation of isoleucine. The HSD17B10 gene is composed of six exons and five introns. Its exon 5 is an alternative exon such that there are several HSD17B10 mRNA isoforms in brain. A silent mutation (c.605C-->A) and three missense mutations (c.395C-->G; c.419C-->T; c.771A-->G), respectively, cause the X-linked mental retardation, choreoathetosis, and abnormal behavior (MRXS10) and the hydroxyacyl-CoA dehydrogenase II deficiency. The latter condition seems to be a multifactorial disease due to the disturbance of more than one metabolic pathway by the HSD10 deficiency. HSD10 inactivates the positive modulators of GABAA receptors, and plays a role in the maintenance of GABAergic neuronal function. This working model may account for the mental retardation of these patients. The dehydrogenase activity is slightly inhibited by the binding of amyloid-beta peptide to the loop D of HSD10. Elevated levels of HSD10 were observed in hippocampi of Alzheimer disease patients so this multifunctional enzyme may be related to Alzheimer disease pathogenesis; however, the molecular mechanism of its involvement remains to be ascertained.     

Methylation and acetylation in nervous system development and neurodegenerative disorders

The cytoarchitecture and cellular signaling mechanisms of the nervous system are complex, and this complexity is reflected at the molecular level with more genes being expressed in the nervous system than in any other tissue. Gene expression and protein function in neural cells can be regulated by methylation and acetylation. Studies of mice deficient in enzymes that control DNA methylation and of animals with a dietary deficiency of folate have established critical roles for methylation in development of the nervous system. Various neuronal proteins including histones and tubulin are regulated by acetylation which appears to serve important functions in the development, stability and plasticity of neuronal networks. Some inherited neurological disorders have recently been linked to mutations in genes that regulate DNA methylation, and alterations in DNA and protein methylation and/or acetylation have been documented in studies of age-related neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). Manipulations of methylation and acetylation can affect the vulnerability of neurons to degeneration and apoptosis in experimental models of neurodegenerative disorders, suggesting a contribution to altered methylation and acetylation to the disease processes. Interestingly, dietary factors that influence DNA methylation may affect the risk of neurodegenerative disorders, for example, individuals with low dietary folate intake are at increased risk of Alzheimer's and Parkinson's diseases.     

Pharmacogenetics of glucocorticoid replacement could optimize the treatment of congenital adrenal hyperplasia due to 21-hydroxylase deficiency

INTRODUCTION:

21-hydroxylase deficiency is an autosomal recessive disorder that causes glucocorticoid deficiency and increased androgen production. Treatment is based on glucocorticoid replacement; however, interindividual variability in the glucocorticoid dose required to achieve adequate hormonal control has been observed.

OBJECTIVE:

The present study aimed to evaluate the association between polymorphic variants involved in glucocorticoid action and/or metabolism and the mean daily glucocorticoid dose in 21-hydroxylase deficiency patients.

METHODS:

We evaluated 53 patients with classical forms of 21-hydroxylase deficiency who were receiving cortisone acetate. All patients were between four and six years of age and had normal androgen levels.

RESULTS:

The P450 oxidoreductase A503V, HSD11B1 rs12086634, and CYP3A7*1C variants were found in 19%, 11.3% and 3.8% of the patients, respectively. The mean±SD glucocorticoid dose in patients with the CYP3A7*1C and wild-type alleles was 13.9±0.8 and 19.5±3.2 mg/m²/d, respectively. We did not identify an association between the P450 oxidoreductase or HSD11B1 allelic variants and the mean glucocorticoid dose.

CONCLUSION:

Patients carrying the CYP3A7*1C variant required a significantly lower mean glucocorticoid dose. Indeed, the CYP3A7*1C allele accounted for 20% of the variability in the cortisone acetate dose. The analysis of genes involved in glucocorticoid metabolism may be useful in the optimization of treatment of 21-hydroxylase deficiency.     

Interleukin-1 in the genesis and progression of and risk for development of neuronal degeneration in Alzheimer's disease

Interleukin-1 (IL-1), a key molecule in systemic immune responses in health and disease, has analogous roles in the brain where it may contribute to neuronal degeneration. Numerous findings suggest that this is the case. For example, IL-1 overexpression in the brain of Alzheimer patients relates directly to the development and progression of the cardinal neuropathological changes of Alzheimer's disease, i.e., the genesis and accumulation of beta-amyloid (Abeta) plaques and the formation and accumulation of neurofibrillary tangles in neurons, both of which contribute to neuronal dysfunction and demise. Several genetic studies show that inheritance of a specific IL-1A gene polymorphism increases risk for development of Alzheimer's disease by as much as sixfold. Moreover, this increased risk is associated with earlier age of onset of the disease. Homozygosity for this polymorphism in combination with another in the IL-1B gene further increases risk.     

Selective neuronal vulnerability in Alzheimer’s disease

Alzheimer's disease (AD) is defined by a deficiency in specific behavioural and/or cognitive domains, pointing to selective vulnerabilities of specific neurons from different brain regions. These vulnerabilities can be compared across neuron subgroups to identify the most vulnerable neuronal types, regions, and time points for further investigation. Thus, the relevant organizational frameworks for brain subgroups will hold great values for a clear understanding of the progression in AD. Presently, the neuronal vulnerability has yet urgently required to be elucidated as not yet been clearly defined. It is suggested that cell-autonomous and non-cell-autonomous mechanisms can affect the neuronal vulnerability to stressors, and in turn modulates AD progression. This review examines cell-autonomous and non-cell-autonomous mechanisms that contribute to the neuronal vulnerability. Collectively, the cell-autonomous mechanisms seem to be the primary drivers responsible for initiating specific stressor-related neuronal vulnerability with pathological changes in certain brain areas, which then utilize non-cell-autonomous mechanisms and result in subsequent progression of AD. In summary, this article has provided a new perspective on the preventative and therapeutic options for AD.     

The role of metabotropic glutamate receptors in Alzheimer's disease

While glutamatergic transmission is severely altered by early degeneration of cortico-cortical connections and hippocampal projections in Alzheimer's disease (AD), the role of glutamate receptors in the pathogenesis of AD is not yet defined clearly. Nonetheless, as reviewed here, the topographical distribution of different types of receptors likely contributes to the regional selective nature of neuronal degeneration. In particular, metabotropic glutamate receptors (mGluR) may contribute the pathogenesis of many neurological conditions and also regulate neuronal vulnerability against cytotoxic stress. Thus, we here discuss the possible role of mGluR in the pathogenesis of AD based on the results from other neurodegenerative diseases that may give us clues to solve the mysterious selective neurodegeneration evident in AD.