Sex differences in microRNA regulation of gene expression: no smoke, just miRs

Sexual differentiation of the nervous system occurs via the interplay of genetics, endocrinology and social experience through development. Much of the research into mechanisms of sexual differentiation has been driven by an implicit theoretical framework in which these causal factors act primarily and directly on sexually dimorphic neural populations within the central nervous system. This review will examine an alternative explanation by describing what is known about the role of peripheral structures and mechanisms (both neural and non-neural) in producing sex differences in the central nervous system. The focus of the review will be on experimental evidence obtained from studies of androgenic masculinization of the spinal nucleus of the bulbocavernosus, but other systems will also be considered.     

Influence of aging on sex differences in muscle fatigability.

The purpose of this study was to compare time to task failure for a sustained isometric contraction performed at a submaximal intensity with elbow flexor muscles by young and old men and women. Twenty-seven young (14 men and 13 women, 18-35 yr) and 18 old (10 men and 8 women, 65-80 yr) adults sustained an isometric contraction at 20% of maximal voluntary contraction torque until target torque could no longer be achieved for > or = 5 s. Young adults were stronger than old adults (66.8 +/- 17.9 vs. 47.7 +/- 18.1 N x m, P < 0.05), and men were stronger than women (69.8 +/- 17.9 vs. 47.1 +/- 15.3 N x m, P < 0.05), with no interaction between age and sex (P > 0.05). Time to task failure was longer for old than for young adults (22.8 +/- 9.1 vs. 14.4 +/- 7.6 min, P < 0.05) and for young women than for young men (18.3 +/- 8.0 vs. 10.8 +/- 5.2, P < 0.05), but there was no difference between old women and men (21.3 +/- 10.7 and 24.1 +/- 8.0 min, respectively, P > 0.05) or between young women and old adults (P > 0.05). Mean arterial pressure, heart rate, average electromyographic (EMG) activity, and torque fluctuations of elbow flexor muscles increased during the fatiguing contraction (P < 0.05) for all subjects. Rates of increase in mean arterial pressure, heart rate, and torque fluctuations were greater for young men and old adults, with no differences between old men and women (P > 0.05). Similarly, the rate of increase in EMG activity was greater for young men than for the other three groups. EMG bursts were less frequent for old adults (P < 0.05) at the end of the fatiguing contraction, and this was accompanied by reduced fluctuations in torque. Consequently, time to task failure was related to target torque for young, but not old, adults, and differences in task duration were accompanied by parallel changes in the pressor response.     

Endocrine regulation of sex differences in hepatic histidase activity.

Hepatic histidase activity in adult female rats is twice that in adult male rats. Hypophysectomy and thyroidectomy result in a significant increase in hepatic histidase activities in males, but not in females. This effect on histidase is reversed by the exogenous administration of tri-iodothyronine, but not by ectopic pituitary glands or purified pituitary hormones.     

Testosterone regulation of sex differences in fetal lung development.

Fetal lung development, in particular surfactant synthesis, exhibits a sexual dimorphism. Dihydrotestosterone (DHT) has been shown to delay fetal pulmonary surfactant production, but the potential role for testosterone is unknown. Both testosterone and DHT are potent masculinizing hormones, yet in some instances, an end organ specificity for DHT is present. We hypothesized that the delay in fetal lung surfactant production is dependent upon DHT such that inhibition of the synthesis of DHT from the precursor hormone testosterone would eliminate the sex difference by allowing the male fetus to produce surfactant at the female level. We tested this hypothesis using 17 beta-N,N-diethylcarbamoyl-4-aza-4-methyl-5-alpha-androstane-3-one (4-MA), a potent inhibitor of the enzyme 5 alpha-reductase, which converts testosterone into DHT. First, studies were performed in vivo. 4-MA (20 mg/kg/day) or an equivalent volume of vehicle was injected into pregnant rabbits from Day 12 through Day 26 of gestation. On Day 26, the fetuses were delivered, the lungs were lavaged, and fetal sex was noted. Treatment with 4-MA resulted in a lack of any male-female difference in the anogenital distance and no DHT was detected in the serum of any treated fetus. Phosphatidylcholine (PC), saturated phosphatidylcholine (SPC), and sphingomyelin (S) were measured in the lung lavage, and were expressed as the ratios of PC to sphingomyelin (PC:S) and SPC to sphingomyelin (SPC:S). Sex differences in the PC to sphingomyelin ratio of 4-MA-treated fetuses (female PC:S ratio, 1.43 +/- 0.14; male PC:S ratio, 1.00 +/- 0.13 [mean +/- SE]; P = 0.04) and in the SPC:S ratio of the 4-MA-treated group (female SPC:S ratio, 0.68 +/- 0.10; male SPC:S ratio, 0.35 +/- 0.10; P = 0.03) were present after treatment with 4-MA. The effect of testosterone and of 4-MA on fibroblast pneumonocyte factor (FPF) production was studied in vitro. Fetal rat lung fibroblasts were cultured to confluence with either no added androgen, DHT, testosterone, or testosterone plus 4-MA, and conditioned media for FPF were prepared. Conditioned media were added to fetal Type II cell cultures and FPF activity was measured as the degree of stimulation of the incorporation of [3H] choline into SPC. The conversion of radiolabeled testosterone to DHT by the fibroblasts was inhibited by 4-MA (10(-5) M). Conditioned media from untreated female fibroblasts stimulated with cortisol exhibited significant FPF activity ([3H]choline incorporation into SPC, 140 +/- 17% of control).(ABSTRACT TRUNCATED AT 400 WORDS)     

Meta-analysis of sex differences in gene expression in schizophrenia

Schizophrenia is a severe psychiatric disorder which influences around 1 % of the worldwide population. Differences between male and female patients with schizophrenia have been noted. There is an earlier age of onset in males compared with females with this diagnosis, and in addition, there are differences in symptom profiles between the sexes. The underlying molecular mechanism of sex difference remains unclear. Here we present a comprehensive analysis to reveal the sex differences in gene expression in schizophrenia with stringent statistics criteria. We compiled a data set consisting of 89 male controls, 90 male schizophrenia patients, 35 female controls and 32 female schizophrenia patients from six independent studies of the prefrontal cortex (PFC) in postmortem brain. When we tested for a sex by diagnosis interaction on gene expression, 23 genes were up-regulated and 23 genes were down-regulated in the male group (q-value?<?0.05), several genes are related to energy metabolism, while 4 genes are located on sex chromosome. No genes were statistically significant in the female group when multiple testing correction were conducted (q-value <0.05), most likely due to the small sample size. Our protocol and results from the male group provide a starting point for identifying the underlying different mechanism between male and female schizophrenia patients.     

Mechanisms underlying sex differences in progressive renal disease

Men with nondiabetic renal disease exhibit a faster rate of decline in renal function compared with women. To investigate this sex difference in renal disease progression, our research group has been studying the renal wrap (RW) model of hypertension in rats. Compared with RW female rats, the glomerulosclerosis index, mean glomerular volume, and proteinuria were greater (3.1-, 1.7-, and 1.8-fold, respectively) in RW males under conditions in which no differences in the degree of hypertension were detected, suggesting that sex differences may exist in the mechanisms underlying renal injury, independent of blood pressure. Gonadal steroids contribute to these sex differences, because orchidectomy attenuated and ovariectomy exacerbated the severity of renal injury, whereas dihydrotestosterone and 17β-estradiol (E₂) replacement prevented these respective effects. Chronic renal disease is associated with impairment in nitric oxide (NO) signaling and elevated levels of superoxide. Sex differences were observed in RW-induced changes in renal nitric oxide synthesis (NOS) protein abundance. Whereas RW had no effect on NOS in the female kidney, endothelial NOS was elevated and neuronal NOS was decreased in the male kidney, suggesting that renal injury may cause dysfunction in NO metabolism in the male. Sex differences in superoxide signaling were also observed. Renal cortical nicotinamide adenine dinucleotide phosphate oxidase activity was 1.3-fold higher in RW males than in RW females, and ovariectomy increased enzyme activity 1.4-fold, whereas E₂ replacement prevented this effect. These changes in enzyme activity were mirrored by changes in protein abundance of the p22^phox regulatory subunit. Our findings suggest that E₂ may protect the female kidney from hypertension-associated renal disease by attenuating injury-induced superoxide production.     

基因表达调控多面手——microRNA和siRNA的作用机制

miRNA(microRNA)是一类广泛存在于高等真核细胞中的长度约为21个碱基的小分子非编码RNA,参与调控三分之一以上基因的表达,并与多种人类疾病存在重要关联。而siRNA(small interfering RNA)是RNA干扰(RNA interference,RNAi)中的效应分子,其结构和作用机制与miRNA存在许多类似之处。由于miRNA和siRNA具有重要的生物学功能。因此,对它们作用机制的理解具有非常重要的理论意义和应用指导价值。该综述将对它们作用机制的研究进展做一总结和回顾。     

miRNA的生物形成及调控基因表达机制

微RNA(microRNA,miRNA)通过调节靶基因的表达水平影响细胞分化、增殖、凋亡等特性,在生物的生长发育和疾病发生发展中发挥重要的作用。将miRNA用于基因功能研究,药物靶点验证,基因治疗等领域有非常好的前景。揭示miRNA的生成和加工过程以及miRNA调节靶基因基因表达水平的作用机制对于阐述miRNA在生理病理过程中的作用有重要意义。因此,本文对miRNA的发生,成熟以及作用机制的研究进展作综述。     

Age and sex differences in kidney microRNA expression during the life span of F344 rats

Background

Growing evidence suggests that epigenetic mechanisms of gene regulation may play a role in susceptibilities to specific toxicities and adverse drug reactions. MiRNAs in particular have been shown to be important regulators in cancer and other diseases and show promise as predictive biomarkers for diagnosis and prognosis. In this study, we characterized the global kidney miRNA expression profile in untreated male and female F344 rats throughout the life span. These findings were correlated with sex-specific susceptibilities to adverse renal events, such as male-biased renal fibrosis and inflammation in old age.

Methods

Kidney miRNA expression was examined in F344 rats at 2, 5, 6, 8, 15, 21, 78, and 104 weeks of age in both sexes using Agilent miRNA microarrays. Differential expression was determined using filtering criteria of ≥1.5 fold change and ANOVA or pairwise t-test (FDR <5%) to determine significant age and sex effects, respectively. Pathway analysis software was used to investigate the possible roles of these target genes in age- and sex-specific differences.

Results

Three hundred eleven miRNAs were found to be expressed in at least one age and sex. Filtering criteria revealed 174 differentially expressed miRNAs in the kidney; 173 and 34 miRNAs exhibiting age and sex effects, respectively. Principal component analysis revealed age effects predominated over sex effects, with 2-week miRNA expression being much different from other ages. No significant sexually dimorphic miRNA expression was observed from 5 to 8 weeks, while the most differential expression (13 miRNAs) was observed at 21 weeks. Potential target genes of these differentially expressed miRNAs were identified.

Conclusions

The expression of 56% of detected renal miRNAs was found to vary significantly with age and/or sex during the life span of F344 rats. Pathway analysis suggested that 2-week-expressed miRNAs may be related to organ and cellular development and proliferation pathways. Male-biased miRNA expression at older ages correlated with male-biased renal fibrosis and mononuclear cell infiltration. These miRNAs showed high representation in renal inflammation and nephritis pathways, and included miR-214, miR-130b, miR-150, miR-223, miR-142-5p, miR-185, and miR-296*. Analysis of kidney miRNA expression throughout the rat life span will improve the use of current and future renal biomarkers and inform our assessments of kidney injury and disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-014-0019-1) contains supplementary material, which is available to authorized users.     

Differential regulation drives plasticity in sex determination gene networks

Background  

Sex determination networks evolve rapidly and have been studied intensely across many species, particularly in insects, thus presenting good models to study the evolutionary plasticity of gene networks.     

Model-projected mechanistic bases for sex differences in growth hormone regulation in humans

Models of physiological systems facilitate rational experimental design, inference, and prediction. A recent construct of regulated growth hormone (GH) secretion interlinks the actions of GH-releasing hormone (GHRH), somatostatin (SRIF), and GH secretagogues (GHS) with GH feedback in the rat (Farhy LS, Veldhuis JD. Am J Physiol Regul Integr Comp Physiol 288: R1649-R1663, 2005). In contrast, no comparable formalism exists to explicate GH dynamics in any other species. The present analyses explore whether a unifying model structure can represent species- and sex-defined distinctions in the human and rodent. The consensus principle that GHRH and GHS synergize in vivo but not in vitro was explicable by assuming that GHS 1) evokes GHRH release from the brain, 2) opposes inhibition by SRIF both in the hypothalamus and on the pituitary gland, and 3) stimulates pituitary GH release directly and additively with GHRH. The gender-selective principle that GH pulses are larger and more irregular in women than men was conferrable by way of 4) higher GHRH potency and 5) greater GHS efficacy. The overall construct predicts GHRH/GHS synergy in the human only in the presence of SRIF when the brain-pituitary nexus is intact, larger and more irregular GH pulses in women, and observed gender differences in feedback by GH and the single and paired actions of GHRH, GHS, and SRIF. The proposed model platform should enhance the framing and interpretation of novel clinical hypotheses and create a basis for interspecies generalization of GH-axis regulation.     

The role of microRNA in the delayed negative feedback regulation of gene expression

Oscillatory gene expression plays an important role in somite segmentation during the early developmental stages of vertebrates. Recent experimental studies have shown that microRNA can regulate gene expression by stimulating degradation of mRNA and/or repression of translation. In this communication, we incorporate miRNA into a previous mathematical model of gene expression with delayed negative feedback and demonstrate how this modified model can elucidate the possible effect of miRNA on the oscillatory gene expression. Our finding suggests that miRNA maybe a destabilizing or stabilizing factor in the dynamics of gene expression depending on the severity of its effect on mRNA degradation. Our finding provides testable hypothesis for experimental biologists to further investigate miRNA's increasing functional roles in regulating cellular processes and development.     

Aromatase activity in the rat brain: Hormonal regulation and sex differences

The intracellular conversion of testosterone to estradiol by the aromatase enzyme complex is an important step in many of the central actions of testosterone. In rats, estrogen given alone, or in combination with dihydrotestosterone, mimics most of the behavioral effects of testosterone, whereas treatment with antiestrogens or aromatase inhibitors block facilitation of copulatory behavior by testosterone. We used a highly sensitive in vitro radiometric assay to analyze the distribution and regulation of brain aromatase activity. Studies using micropunch dissections revealed that the highest levels of aromatase activity are found in an interconnected group of sexually dimorphic nuclei which constitutes a neural circuit important in the control of male sexual behavior. Androgen regulated aromatase activity in many diencephalic nucleic, including the medial preoptic nucleus, but not in the medial and cortical nuclei of the amygdala. Additional genetic evidence for both androgen-dependent and -independent control of brain AA was obtained by studies of androgen-insensitive testicular-feminized rats. These observations suggest that critical differences in enzyme responsiveness are present in different brain areas. Within several nuclei, sex differences in aromatase induction correlated with differences in nuclear androgen receptor concentrations suggesting that neural responsiveness to testosterone is sexually differentiated. Estradiol and dihydrotestosterone acted synergistically to regulate aromatase activity in the preoptic area. In addition, time-course studies showed that estrogen treatment increased the duration of nuclear androgen receptor occupation in the preoptic area of male rats treated with dihydrotestosterone. These results suggest possible ways that estrogens and androgens may interact at the cellular level to regulate neural function and behavior.     

Stress amplifies sex differences in primate prefrontal profiles of gene expression

Background

Stress is a recognized risk factor for mood and anxiety disorders that occur more often in women than men. Prefrontal brain regions mediate stress coping, cognitive control, and emotion. Here, we investigate sex differences and stress effects on prefrontal cortical profiles of gene expression in squirrel monkey adults.

Methods

Dorsolateral, ventrolateral, and ventromedial prefrontal cortical regions from 18 females and 12 males were collected after stress or no-stress treatment conditions. Gene expression profiles were acquired using HumanHT-12v4.0 Expression BeadChip arrays adapted for squirrel monkeys.

Results

Extensive variation between prefrontal cortical regions was discerned in the expression of numerous autosomal and sex chromosome genes. Robust sex differences were also identified across prefrontal cortical regions in the expression of mostly autosomal genes. Genes with increased expression in females compared to males were overrepresented in mitogen-activated protein kinase and neurotrophin signaling pathways. Many fewer genes with increased expression in males compared to females were discerned, and no molecular pathways were identified. Effect sizes for sex differences were greater in stress compared to no-stress conditions for ventromedial and ventrolateral prefrontal cortical regions but not dorsolateral prefrontal cortex.

Conclusions

Stress amplifies sex differences in gene expression profiles for prefrontal cortical regions involved in stress coping and emotion regulation. Results suggest molecular targets for new treatments of stress disorders in human mental health.