Nuclear receptors and microRNAs: Who regulates the regulators in neural stem cells?

In this mini-review, we focus on regulatory loops between nuclear receptors and microRNAs, an emerging class of small RNA regulators of gene expression. Evidence supporting interactions between microRNAs and nuclear receptors in the regulation of gene expression networks is discussed in relation to its possible role in neural stem cell self renewal and differentiation. Furthermore, we discuss possible disturbances of the regulatory loops between microRNAs and nuclear receptors in human neurodegenerative disease. Finally, we discuss the possible use of nuclear receptors as pharmacological entry points to regulate neural stem cell self-renewal and differentiation

The androgen receptor gene CAG repeat in relation to 4-year changes in androgen-sensitive endpoints in community-dwelling older European men

Context: The Androgen Receptor (AR) gene exon 1 CAG repeat length has been proposed to be a determinant of between-individual variations in androgen action in target tissues, which might regulate phenotypic differences of human ageing. However, findings on its phenotypic effects are inconclusive.Objective: To assess whether the AR CAG repeat length is associated with longitudinal changes in endpoints which are influenced by testosterone (T) levels in middle-aged and elderly European men.Design: Multinational European observational prospective cohort studyParticipants: 1887 men (mean±sd age: 63±11 years; median follow-up: 4.3 years) from centres of 8 European countries comprised the analysis sample after exclusion of those with diagnosed diseases of the hypothalamic-pituitary-testicular (HPT) axis.Main outcome measures: Longitudinal associations between the AR CAG repeat and changes in androgen-sensitive endpoints (ASEs) and medical conditions were assessed using regression analysis adjusting for age and centre. The AR CAG repeat length was treated both as a continuous and categorical (6-20; 21-23; 24-39 repeats) predictor. Additional analysis investigated whether results were independent of baseline T or oestradiol (E2) levels.Results: The AR CAG repeat, when used as a continuous or categorical predictor, was not associated with longitudinal changes in ASEs or medical conditions after adjustments. These results were independent of T and E2 levels.Conclusion: Within a 4-year timeframe, variations in the AR CAG repeat do not contribute to the rate of phenotypic ageing, over and above, that, which might be associated with the age-related decline in T levels

Reproductive hormone levels predict changes in frailty status in community-dwelling older men:European Male Ageing Study prospective data

Context: Clinical sequelae of androgen deficiency share common features with frailty. Evidence supporting the role of androgens in the development of frailty is limited and conflicting. Objective: To determine associations between male reproductive hormones and prospective changes in frailty status. Design/ Setting: 4.3-year prospective cohort study of community-dwelling men participating in the European Male Ageing Study. Participants: 3369 men aged 40-79 from 8 European centres. Intervention: nil. Main Outcome Measure: Frailty status was determined using frailty index (FI n=2278) and frailty phenotype (FP, n=1980). Results: After adjusting for baseline frailty, age, centre and smoking, the risk of worsening FI decreased with higher testosterone (T), free T and dihydrotestosterone (DHT) [% change (95%CI) in FI associated with 1SD higher hormone level: -3.0 (-5.9, -1.0) for total T; -3.9 (-6.8, -2.0) for free T; and -3.9 (-6.8, -2.0) for DHT]. After further adjustment for BMI, only free T remained a significant predictor of FI change. In fully adjusted models, higher LH and FSH were positively related to worsening FI only in men <60 years and higher estradiol predicted lower likelihood of improving FP [OR 0.68 (0.52, 0.88)]. Conclusions: These prospective data support the hypothesis that higher androgen levels may protect elderly men from worsening frailty. However, the causal nature of these relationships requires further investigation. Whereas raised gonadotropins in men <60 yr might be an early marker of frailty, the role of estradiol in frailty needs further clarification