Methylation at the CpG island shore region upregulates Nr3c1 promoter activity after early-life stress

Early-life stress (ELS) induces long-lasting changes in gene expression conferring an increased risk for the development of stress-related mental disorders. Glucocorticoid receptors (GR) mediate the negative feedback actions of glucocorticoids (GC) in the paraventricular nucleus (PVN) of the hypothalamus and anterior pituitary and therefore play a key role in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis and the endocrine response to stress. We here show that ELS programs the expression of the GR gene (Nr3c1) by site-specific hypermethylation at the CpG island (CGI) shore in hypothalamic neurons that produce corticotropin-releasing hormone (Crh), thus preventing Crh upregulation under conditions of chronic stress. CpGs mapping to the Nr3c1 CGI shore region are dynamically regulated by ELS and underpin methylation-sensitive control of this region's insulation-like function via Ying Yang 1 (YY1) binding. Our results provide new insight into how a genomic element integrates experience-dependent epigenetic programming of the composite proximal Nr3c1 promoter, and assigns an insulating role to the CGI shore.

The role of the mammalian DNA end-processing enzyme polynucleotide kinase 3'-phosphatase in spinocerebellar ataxia Type 3 pathogenesis

DNA strand-breaks (SBs) with non-ligatable ends are generated by ionizing radiation, oxidative stress, various chemotherapeutic agents, and also as base excision repair (BER) intermediates. Several neurological diseases have already been identified as being due to a deficiency in DNA end-processing activities. Two common dirty ends, 3'-P and 5'-OH, are processed by mammalian polynucleotide kinase 3'-phosphatase (PNKP), a bifunctional enzyme with 3'-phosphatase and 5'-kinase activities. We have made the unexpected observation that PNKP stably associates with Ataxin-3 (ATXN3), a polyglutamine repeat-containing protein mutated in spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph Disease (MJD). This disease is one of the most common dominantly inherited ataxias worldwide; the defect in SCA3 is due to CAG repeat expansion (from the normal 14-41 to 55-82 repeats) in the ATXN3 coding region. However, how the expanded form gains its toxic function is still not clearly understood. Here we report that purified wild-type (WT) ATXN3 stimulates, and by contrast the mutant form specifically inhibits, PNKP's 3' phosphatase activity in vitro. ATXN3-deficient cells also show decreased PNKP activity. Furthermore, transgenic mice conditionally expressing the pathological form of human ATXN3 also showed decreased 3'-phosphatase activity of PNKP, mostly in the deep cerebellar nuclei, one of the most affected regions in MJD patients' brain. Finally, long amplicon quantitative PCR analysis of human MJD patients' brain samples showed a significant accumulation of DNA strand breaks. Our results thus indicate that the accumulation of DNA strand breaks due to functional deficiency of PNKP is etiologically linked to the pathogenesis of SCA3/MJD.

A qualidade de vida da pessoa com doença renal crónica em programa regular de hemodiálise

Dissertação de mestrado em Enfermagem

Female hippocampus vulnerability to environmental stress, a precipitating factor in tau aggregation pathology

Tau-mediated neurodegeneration is a central event in Alzheimer's disease (AD) and other tauopathies. Consistent with suggestions that lifetime stress may be a clinically-relevant precipitant of AD pathology, we previously showed that stress triggers tau hyperphosphorylation and accumulation; however, little is known about the etiopathogenic interaction of chronic stress with other AD risk factors, such as sex and aging. This study focused on how these various factors converge on the cellular mechanisms underlying tau aggregation in the hippocampus of chronically stressed male and female (middle-aged and old) mice expressing the most commonly found disease-associated Tau mutation in humans, P301L-Tau. We report that environmental stress triggers memory impairments in female, but not male, P301L-Tau transgenic mice. Furthermore, stress elevates levels of caspase-3-truncated tau and insoluble tau aggregates exclusively in the female hippocampus while it also alters the expression of the molecular chaperones Hsp90, Hsp70, and Hsp105, thus favoring accumulation of tau aggregates. Our findings provide new insights into the molecular mechanisms through which clinically-relevant precipitating factors contribute to the pathophysiology of AD. Our data point to the exquisite sensitivity of the female hippocampus to stress-triggered tau pathology.