Sex and the Liver – A Journey Through Five Decades

Transcriptomic and lipid profiling analysis reveals a functional interplay between testosterone and growth hormone in hypothyroid liver

Preclinical and clinical studies suggest that hypothyroidism might cause hepatic endocrine and metabolic disturbances with features that mimic deficiencies of testosterone and/or GH. The absence of physiological interactions between testosterone and GH can be linked to male differentiated liver diseases. Testosterone plays relevant physiological effects on somatotropic-liver axis and liver composition and the liver is a primary organ of interactions between testosterone and GH. However, testosterone exerts many effects on liver through complex and poorly understood mechanisms. Testosterone impacts liver functions by binding to the Androgen Receptor, and, indirectly, through its conversion to estradiol, and cooperation with GH. However, the role of testosterone, and its interaction with GH, in the hypothyroid liver, remains unclear. In the present work, the effects of testosterone, and how they impact on GH-regulated whole transcriptome and lipid composition in the liver, were studied in the context of adult hypothyroid-orchiectomized rats. Testosterone replacement positively modulated somatotropic-liver axis and impacted liver transcriptome involved in lipid and glucose metabolism. In addition, testosterone enhanced the effects of GH on the transcriptome linked to lipid biosynthesis, oxidation-reduction, and metabolism of unsaturated and long-chain fatty acids (FA). However, testosterone decreased the hepatic content of cholesterol esters and triacylglycerols and increased fatty acids whereas GH increased neutral lipids and decreased polar lipids. Biological network analysis of the effects of testosterone on GH-regulated transcriptome confirmed a close connection with crucial proteins involved in steroid and fatty acid metabolism. Taken together, this comprehensive analysis of gene expression and lipid profiling in hypothyroid male liver reveals a functional interplay between testosterone and pulsed GH administration.

Transcriptomics-based analysis of sex-differentiated mechanisms of hepatotoxicity in zebrafish after long-term exposure to bisphenol AF

Bisphenol AF (BPAF) is an emerging endocrine-disrupting chemical (EDC) prevalent in the environment as one of the main substitutes for bisphenol A. Sex-specific effects of EDCs have been commonly reported and closely linked to sexually dimorphic patterns of hormone metabolism and related gene expression during different exposure windows, but our understanding of these mechanisms is still limited. Here, following 28-day exposure of adult zebrafish to an environmentally relevant concentration of BPAF at 10 μg/L, the global transcriptional networks applying RNA sequencing (RNA-seq) and Ingenuity Pathway Analysis (IPA) were respectively investigated in the male and female fish liver, connecting the sex-dependent toxicity of the long-term exposure of BPAF to molecular responses. As a result, more differentially expressed genes (DEGs) were detected in males (811) than in females (195), and spermatogenesis was the most enriched Gene Ontology (GO) functional classification in males, while circadian regulation of gene expression was the most enriched GO term in females. The expression levels of selected DEGs were routinely verified using qRT-PCR, which showed consistent alterations with the transcriptional changes in RNA-seq data. The causal network analysis by IPA suggested that the adverse outcomes of BPAF in males including liver damage, apoptosis, inflammation of organ, and liver carcinoma, associated with the regulation of several key DEGs detected in RNA-seq, could be linked to the activation of upstream regulatory molecules ifnα, yap1, and ptger2; while, the inhibition of upstream regulators hif1α, ifng, and igf1, leading to the down-regulated expression of several key DEGs, might be involved in BPAF's effects in females. Furthermore, BPAF exposure altered hepatic histological structure and inhibited antioxidant capability in both male and female livers. Overall, this study revealed different regulation networks involved in the sex-dependent effects of BPAF on the fish liver, and these detected DEGs upon BPAF exposure might be used as potential biomarkers for further assessing sex-specific hepatotoxicity following environmental EDC exposure.

Hallmarks of the human intestinal microbiome on liver maturation and function

As one of the most metabolically complex systems in the body, the liver ensures multi-organ homeostasis and ultimately sustains life. Nevertheless, during early postnatal development, the liver is highly immature and takes about 2 years to acquire and develop almost all of its functions. Different events occurring at the environmental and cellular levels are thought to mediate hepatic maturation and function postnatally. The crosstalk between the liver, the gut and its microbiome has been well appreciated in the context of liver disease, but recent evidence suggests that the latter could also be critical for hepatic function under physiological conditions. The gut-liver crosstalk is thought to be mediated by a rich repertoire of microbial metabolites that can participate in a myriad of biological processes in hepatic sinusoids, from energy metabolism to tissue regeneration. Studies on germ-free animals have revealed the gut microbiome as a critical contributor in early hepatic programming, and this influence extends throughout life, mediating liver function and body homeostasis. In this seminar, we describe the microbial molecules that have a known effect on the liver and discuss how the gut microbiome and the liver evolve throughout life. We also provide insights on current and future strategies to target the gut microbiome in the context of hepatology research.

Characterization of Androgen Receptor Complex Associated Protein (ARCAP) in hepatocellular carcinoma and liver

BACKGROUND

Hepatocellular carcinoma (HCC) ranks many tasks in clinical oncology due to possibly developing a general tumor in men and, usually lead to malignant to death within years. Researches had reported about major factors for being HCC was male sex and HCC associated with cirrhosis in childhood was found more common in males than females. In certain mouse strains as studied, breeding with testosterone significantly increases the development of HCC. Furthermore, castration of male mice diminished the frequency of the development of liver tumors. Meanwhile male hepatitis B virus transgenic mice have a greater occurrence of HCC than females.

METHODS

We apply degenerate priming PCR to observe the expression of various steroid receptors in livers. Yeast-two hybrid screening to search a novel RNA fragment helps to find a new full-length gene by RACE experiment. RT-PCR is applied to detect various expressions in tissues and cell lines. In situ hybridization detects DNA in Chromosome mapping. GFP-constructs transfection proves the gene localization in cells. Immunoprecipitation pulldown assay verifies protein interaction. Gene transfection followed with luciferase assay demonstrates the interaction of genes within cellular signaling. Genomic alignment analysis for observing sequences data perform from NCBI database website (http://www.ncbi.nim.nih.gov/genebank/).

RESULTS

The androgen receptor (AR) expression level is found at the highest level among the steroid receptors families detected in liver tumors. By yeast-two hybrid screening, we cloned an Androgen Receptor Complex Associated Protein (ARCAP), of 95 Kd in molecular weight and its cDNA. ARCAP locates at Chromosome 1. Our findings indicate ARCAP is highly expressed in hepatoma cell lines and liver tumors and their adjacent tumors as observed. Yeast two-hybrid assay and in vitro immunoprecipitation assays demonstrated an interaction between AR and ARCAP.

CONCLUSION

We aim to search for different types and levels of steroid receptors expressed within human HCCs and in the adjacent liver tissues. To verify possible molecular mechanisms by which AR might affect hepatoma cells, we had characterized a novel protein ARCAP which functions as a coregulator to interact with AR within liver. The ligand-dependent AR with its cofactor, ARCAP, can induce a signal cascade by transactivation.

Sex Dimorphism of Nonalcoholic Fatty Liver Disease (NAFLD) in Pparg-Null Mice

Men with nonalcoholic fatty liver disease (NAFLD) are more exposed to nonalcoholic steatohepatitis (NASH) and liver fibrosis than women. However, the underlying molecular mechanisms of NALFD sex dimorphism are unclear. We combined gene expression, histological and lipidomic analyses to systematically compare male and female liver steatosis. We characterized hepatosteatosis in three independent mouse models of NAFLD, ob/ob and lipodystrophic fat-specific (PpargFΔ/Δ) and whole-body PPARγ-null (PpargΔ/Δ) mice. We identified a clear sex dimorphism occurring only in PpargΔ/Δ mice, with females showing macro- and microvesicular hepatosteatosis throughout their entire life, while males had fewer lipid droplets starting from 20 weeks. This sex dimorphism in hepatosteatosis was lost in gonadectomized PpargΔ/Δ mice. Lipidomics revealed hepatic accumulation of short and highly saturated TGs in females, while TGs were enriched in long and unsaturated hydrocarbon chains in males. Strikingly, sex-biased genes were particularly perturbed in both sexes, affecting lipid metabolism, drug metabolism, inflammatory and cellular stress response pathways. Most importantly, we found that the expression of key sex-biased genes was severely affected in all the NAFLD models we tested. Thus, hepatosteatosis strongly affects hepatic sex-biased gene expression. With NAFLD increasing in prevalence, this emphasizes the urgent need to specifically address the consequences of this deregulation in humans.

Estrogen Receptor-α Suppresses Liver Carcinogenesis and Establishes Sex-Specific Gene Expression

Estrogen protects females from hepatocellular carcinoma (HCC). To determine whether this protection is mediated by classic estrogen receptors, we tested HCC susceptibility in estrogen receptor-deficient mice. In contrast to a previous study, we found that diethylnitrosamine induces hepatocarcinogenesis to a significantly greater extent when females lack Esr1, which encodes Estrogen Receptor-α. Relative to wild-type littermates, Esr1 knockout females developed 9-fold more tumors. Deficiency of Esr2, which encodes Estrogen Receptor-β, did not affect liver carcinogenesis in females. Using microarrays and QPCR to examine estrogen receptor effects on hepatic gene expression patterns, we found that germline Esr1 deficiency resulted in the masculinization of gene expression in the female liver. Six of the most dysregulated genes have previously been implicated in HCC. In contrast, Esr1 deletion specifically in hepatocytes of Esr1 conditional null female mice (in which Cre was expressed from the albumin promoter) resulted in the maintenance of female-specific liver gene expression. Wild-type adult females lacking ovarian estrogen due to ovariectomy, which is known to make females susceptible to HCC, also maintained female-specific expression in the liver of females. These studies indicate that Esr1 mediates liver cancer risk, and its control of sex-specific liver gene expression involves cells other than hepatocytes.

Effect of endurance exercise training on liver gene expression in male and female mice

Chronic endurance exercise is a therapeutic strategy in the treatment of many chronic diseases in humans, including the prevention and treatment of metabolic diseases such as diabetes mellitus. Metabolic, cardiorespiratory, and endocrine pathways targeted by chronic endurance exercise have been identified. In the liver, however, the cellular and molecular pathways that are modified by exercise and have preventive or therapeutic relevance to metabolic disease need to be elucidated. The mouse model used in the current study allows for the quantification of a human-relevant exercise "dosage". In this study we show hepatic gene expression differences between sedentary female and sedentary male mice and that chronic exercise modifies the transcription of hepatic genes related to metabolic disease and steatosis in both male and female mice. Chronic exercise induces molecular pathways involved in glucose tolerance, glycolysis, and gluconeogenesis while producing a decrease in pathways related to insulin resistance, steatosis, fibrosis, and inflammation. Given these findings, this mouse exercise model has potential to dissect the cellular and molecular hepatic changes following chronic exercise with application to understanding the role that chronic exercise plays in preventing human diseases. Novelty: Exercise modifies the hepatic gene expression and hepatic pathways related to metabolic disease in male and female mice. Sex differences were seen in hepatic gene expression between sedentary and exercised mice. The mouse exercise model used in this study allows for application and evaluation of exercise effects in human disease.

Non-alcoholic Fatty Liver Disease as a Canonical Example of Metabolic Inflammatory-Based Liver Disease Showing a Sex-Specific Prevalence: Relevance of Estrogen Signaling

There is extensive evidence supporting the interplay between metabolism and immune response, that have evolved in close relationship, sharing regulatory molecules and signaling systems, to support biological functions. Nowadays, the disruption of this interaction in the context of obesity and overnutrition underlies the increasing incidence of many inflammatory-based metabolic diseases, even in a sex-specific fashion. During evolution, the interplay between metabolism and reproduction has reached a degree of complexity particularly high in female mammals, likely to ensure reproduction only under favorable conditions. Several factors may account for differences in the incidence and progression of inflammatory-based metabolic diseases between females and males, thus contributing to age-related disease development and difference in life expectancy between the two sexes. Among these factors, estrogens, acting mainly through Estrogen Receptors (ERs), have been reported to regulate several metabolic pathways and inflammatory processes particularly in the liver, the metabolic organ showing the highest degree of sexual dimorphism. This review aims to investigate on the interaction between metabolism and inflammation in the liver, focusing on the relevance of estrogen signaling in counteracting the development and progression of non-alcoholic fatty liver disease (NAFLD), a canonical example of metabolic inflammatory-based liver disease showing a sex-specific prevalence. Understanding the role of estrogens/ERs in the regulation of hepatic metabolism and inflammation may provide the basis for the development of sex-specific therapeutic strategies for the management of such an inflammatory-based metabolic disease and its cardio-metabolic consequences.

Sex steroid hormones differentially regulate CYP2D in female wild-type and CYP2D6-humanized mice

The CYP2D subfamily catalyses the metabolism of about 25% of prescribed drugs, including the majority of antidepressants and antipsychotics. At present, the mechanism of hepatic CYP2D regulation remains largely unknown. This study investigated the role of sex steroid hormones in CYP2D regulation. For this purpose, Cyp2d22 expression was assessed in the distinct phases of the estrous cycle of normocyclic C57BL/6J (WT) female mice. Cyp2d22 was also evaluated in ovariectomised WT and CYP2D6-humanized (hCYP2D6) mice that received hormonal supplementation with either 17β-estradiol (E2) and/or progesterone. Comparisons were also made to male mice. The data revealed that hepatic Cyp2d22 mRNA, protein and activity levels were higher at estrous compared to the other phases of the estrous cycle and that ovariectomy repressed Cyp2d22 expression in WT mice. Tamoxifen, an anti-estrogenic compound, also repressed hepatic Cyp2d22 via activation of GH/STAT5b and PI3k/AKT signaling pathways. Both hormones prevented the ovariectomy-mediated Cyp2d22 repression. In case of progesterone, this may be mediated by inhibition of the PI3k/AKT/FOX01 pathway. Notably, Cyp2d22 mRNA levels in WT males were similar to those in ovariectomised mice and were markedly lower compared to females at estrous, a differentiation potentially regulated by the GH/STAT5b pathway. Sex steroid hormone-related alterations in Cyp2d22 mRNA expression were highly correlated with Hnf1a mRNA. Interestingly, fluctuations in Cyp2d22 in hippocampus and cerebellum followed those in liver. In contrast to WT mice, ovariectomy induced hepatic CYP2D6 expression in hCYP2D6 mice, whereas E2 and/or progesterone prevented this induction. Apparently, sex steroid hormones display a significant gender- and species-specific role in the regulation of CYP2D.

Growth signaling and longevity in mouse models

Reduction of insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) extends the lifespan of various species. So far, several longevity mouse models have been developed containing mutations related to growth signaling deficiency by targeting growth hormone (GH), IGF1, IGF1 receptor, insulin receptor, and insulin receptor substrate. In addition, p70 ribosomal protein S6 kinase 1 (S6K1) knockout leads to lifespan extension. S6K1 encodes an important kinase in the regulation of cell growth. S6K1 is regulated by mechanistic target of rapamycin (mTOR) complex 1. The v-myc myelocytomatosis viral oncogene homolog (MYC)-deficient mice also exhibits a longevity phenotype. The gene expression profiles of these mice models have been measured to identify their longevity mechanisms. Here, we summarize our knowledge of long-lived mouse models related to growth and discuss phenotypic characteristics, including organ-specific gene expression patterns.

Reproductive Endocrinology of Nonalcoholic Fatty Liver Disease

The liver and the reproductive system interact in a multifaceted bidirectional fashion. Sex steroid signaling influences hepatic endobiotic and xenobiotic metabolism and contributes to the pathogenesis of functional and structural disorders of the liver. In turn, liver function affects the reproductive axis via modulating sex steroid metabolism and transport to tissues via sex hormone-binding globulin (SHBG). The liver senses the body's metabolic status and adapts its energy homeostasis in a sex-dependent fashion, a dimorphism signaled by the sex steroid milieu and possibly related to the metabolic costs of reproduction. Sex steroids impact the pathogenesis of nonalcoholic fatty liver disease, including development of hepatic steatosis, fibrosis, and carcinogenesis. Preclinical studies in male rodents demonstrate that androgens protect against hepatic steatosis and insulin resistance both via androgen receptor signaling and, following aromatization to estradiol, estrogen receptor signaling, through regulating genes involved in hepatic lipogenesis and glucose metabolism. In female rodents in contrast to males, androgens promote hepatic steatosis and dysglycemia, whereas estradiol is similarly protective against liver disease. In men, hepatic steatosis is associated with modest reductions in circulating testosterone, in part consequent to a reduction in circulating SHBG. Testosterone treatment has not been demonstrated to improve hepatic steatosis in randomized controlled clinical trials. Consistent with sex-dimorphic preclinical findings, androgens promote hepatic steatosis and dysglycemia in women, whereas endogenous estradiol appears protective in both men and women. In both sexes, androgens promote hepatic fibrosis and the development of hepatocellular carcinoma, whereas estradiol is protective.

Sexual dimorphism in hepatitis B and C and hepatocellular carcinoma

The incidence of viral hepatitis B or C (HBV/HCV) infection and hepatocellular carcinoma is higher in male compared to female populations, showing a faster disease progression and results in a worse overall survival. Indeed, women are in general better protected from viral infections and show a lower risk of death from malignant cancer in comparison to men. Females mount stronger innate and adaptive immune responses than males, and therefore, most of the autoimmune diseases occur predominantly in females. Next to occupational and/or behavioral factors, cellular and molecular differences between the two sexes contribute to this observation. In this review, we will discuss underlying mechanisms that are important for the observed sex-related differences in liver diseases. A better appreciation of these differences between the two sexes might be of value for better and gender-specific treatment options.

Short-Term Fasting Reveals Amino Acid Metabolism as a Major Sex-Discriminating Factor in the Liver

Sex impacts on liver physiology with severe consequences for energy metabolism and response to xenobiotic, hepatic, and extra-hepatic diseases. The comprehension of the biology subtending sex-related hepatic differences is therefore very relevant in the medical, pharmacological, and dietary perspective. The extensive application of metabolomics paired to transcriptomics here shows that, in the case of short-term fasting, the decision to maintain lipid synthesis using amino acids (aa) as a source of fuel is the key discriminant for the hepatic metabolism of male and female mice. Pharmacological and genetic interventions indicate that the hepatic estrogen receptor (ERα) has a key role in this sex-related strategy that is primed around birth by the aromatase-dependent conversion of testosterone into estradiol. This energy partition strategy, possibly the result of an evolutionary pressure enabling mammals to tailor their reproductive capacities to nutritional status, is most important to direct future sex-specific dietary and medical interventions.

Analysis of gene expression for microminipig liver transcriptomes using parallel long-read technology and short-read sequencing

The microminipig is one of the smallest minipigs that has emerged as a possible experimental animal model, because it shares many anatomical and/or physiological similarities with humans, including the coronary artery distribution in the heart, the digestive physiology, the kidney size and its structure, and so on. However, information on gene expression profiles, including those on drug-metabolizing phase I and II enzymes, in the microminipig is limited. Therefore, the aim of the present study was to identify transcripts in microminipig livers and to determine gene expression profiles. De novo assembly and expression analyses of microminipig transcripts were conducted with liver samples from three male and three female microminipigs using parallel long-read and short-read sequencing technologies. After unique sequences had been automatically aligned by assembling software, the mean contig length of 50843 transcripts was 707 bp. The expression profiles of cytochrome P450 (P450) 1A2, 2C, 2E1 and 3A genes in livers in microminipigs were similar to those in humans. Liver carboxylesterase (CES) precursor, liver CES-like, UDP-glucuronosyltransferase (UGT) 2C1-like, amine sulfotransferase (SULT)-like, N-acetyltransferases (NAT8) and glutathione S-transferase (GST) A2 genes, which are relatively unknown genes in pigs and/or humans, were expressed strongly. Furthermore, no significant gender differences were observed in the gene expression profiles of phase I enzymes, whereas UGT2B17, SULT1E1, SULT2A1, amine SULT-like, NAT8 and GSTT4 genes were different between males and females among phase II enzyme genes under the present sample conditions. These results provide a foundation for mechanistic studies and the use of microminipigs as model animals for drug development in the future. Copyright © 2016 John Wiley & Sons, Ltd.

Role of rs3846662 and HMGCR alternative splicing in statin efficacy and baseline lipid levels in familial hypercholesterolemia

OBJECTIVES

To assess the contribution of the rs3846662 polymorphism of HMGCR on serum lipid levels and statin efficacy, we measured in vivo HMGCR mRNA and lipid levels in French Canadian individuals affected by heterozygous familial hypercholesterolemia due to the deletion of more than 15 kb of the LDLR gene.

RESULTS

Men and women carrying the AA genotype at rs3846662, and no APOE4 allele, had higher levels of total cholesterol (5.43 vs. 4.58 mmol/l, P<0.05) and LDL-cholesterol (5.20 vs. 4.39 mmol/l, P<0.05) at baseline. However, with regard to statin efficacy, the penetrance of the AA genotype was sex dependent. Indeed, the percentage reduction in LDL-cholesterol upon statin treatment was significantly decreased in women with the AA genotype compared with women without it (38.4 vs. 46.2%, P<0.05), whereas this was not observed in men. Although both men and women bearing the AA genotype showed a higher ratio of full-length HMGCR mRNA/total HMGCR mRNA compared with individuals without it (n=37, P<0.05), overall transcription of HMGCR was decreased and increased in men and women carrying this genotype, respectively (n=37, P<0.01 and P<0.05). Finally, in our familial hypercholesterolemia cohort, HMGCR alternative splicing explained between 22 and 55% of the variance in statin response.

CONCLUSION

rs3846662 polymorphism and the alternative splicing of HMGCR mRNA significantly impact women's response to statin therapy.

Deep sexual dimorphism in adult medaka fish liver highlighted by multi-omic approach

Sexual dimorphism describes the features that discriminate between the two sexes at various biological levels. Especially, during the reproductive phase, the liver is one of the most sexually dimorphic organs, because of different metabolic demands between the two sexes. The liver is a key organ that plays fundamental roles in various physiological processes, including digestion, energetic metabolism, xenobiotic detoxification, biosynthesis of serum proteins, and also in endocrine or immune response. The sex-dimorphism of the liver is particularly obvious in oviparous animals, as the female liver is the main organ for the synthesis of oocyte constituents. In this work, we are interested in identifying molecular sexual dimorphism in the liver of adult medaka fish and their sex-variation in response to hepatotoxic exposures. By developing an integrative approach combining histology and different high-throughput omic investigations (metabolomics, proteomics and transcriptomics), we were able to globally depict the strong sexual dimorphism that concerns various cellular and molecular processes of hepatocytes comprising protein synthesis, amino acid, lipid and polysaccharide metabolism, along with steroidogenesis and detoxification. The results of this work imply noticeable repercussions on the biology of oviparous organisms environmentally exposed to chemical or toxin issues.

Sexual dimorphism in cancer

The incidence of many types of cancer arising in organs with non-reproductive functions is significantly higher in male populations than in female populations, with associated differences in survival. Occupational and/or behavioural factors are well-known underlying determinants. However, cellular and molecular differences between the two sexes are also likely to be important. In this Opinion article, we focus on the complex interplay that sex hormones and sex chromosomes can have in intrinsic control of cancer-initiating cell populations, the tumour microenvironment and systemic determinants of cancer development, such as the immune system and metabolism. A better appreciation of these differences between the two sexes could be of substantial value for cancer prevention as well as treatment.

The somatotropic axis and aging: Benefits of endocrine defects

Reduced somatotropic [growth hormone (GH) and insulin-like growth factor-1 (IGF-1)] action has been associated with delayed and slower aging, reduced risk of frailty, reduced age-related disease and functional decline, and with remarkably extended longevity. Recent studies have added to the evidence that these relationships discovered in laboratory populations of mice apply to other mammalian species. However, the relationship of the somatotropic signaling to human aging is less striking, complex and controversial. In mice, targeted deletion of GH receptors (GHR) in the liver, muscle or adipose tissue affected multiple metabolic parameters but failed to reproduce the effects of global GHR deletion on longevity. Continued search for mechanisms of extended longevity in animals with GH deficiency or resistance focused attention on different pathways of mechanistic target of rapamycin (mTOR), energy metabolism, regulation of local IGF-1 levels and resistance to high-fat diet (HFD).

Sex steroids and growth hormone interactions

GH and sex hormones are critical regulators of body growth and composition, somatic development, intermediate metabolism, and sexual dimorphism. Deficiencies in GH- or sex hormone-dependent signaling and the influence of sex hormones on GH biology may have a dramatic impact on liver physiology during somatic development and in adulthood. Effects of sex hormones on the liver may be direct, through hepatic receptors, or indirect by modulating endocrine, metabolic, and gender-differentiated functions of GH. Sex hormones can modulate GH actions by acting centrally, regulating pituitary GH secretion, and peripherally, by modulating GH signaling pathways. The endocrine and/or metabolic consequences of long-term exposure to sex hormone-related compounds and their influence on the GH-liver axis are largely unknown. A better understanding of these interactions in physiological and pathological states will contribute to preserve health and to improve clinical management of patients with growth, developmental, and metabolic disorders.

Application of capillary immunoelectrophoresis revealed an age- and gender-dependent regulated expression of PrPC in liver

The cellular prion protein (PrPC) is a glycoprotein, anchored to the plasma membrane and abundantly expressed in the central nervous system. The expression of PrPC in the peripheral tissues is low and only little information is available on its functions in the nonneuronal tissues. The antioxidant function of PrPC during the activation of hepatic stellate cells has already been reported. Therefore, the aim of the study was to expand our knowledge on the functions of PrPC by detailed characterization of its expressional profile in the liver. In a combined strategy by using capillary immunoelectrophoresis and standard techniques, we have shown a sexually dimorphic expression of PrPC in mice and human liver tissues. Further, we showed a significant age-dependent upregulation of PrPC expression in the liver of 14- and 9-month-old mice as compared to 3 months of age. Therefore, this study may provide new insights into the gender-specific role of PrPC in the liver, which may further be linked to its protective role against oxidative stress during aging. In addition, the current study also shows an application of immunoelectrophoresis with a low coefficient of variation to analyze the miniscule amount of PrPC in the mouse liver tissue.

Sex differences in the brain: a whole body perspective

Most writing on sexual differentiation of the mammalian brain (including our own) considers just two organs: the gonads and the brain. This perspective, which leaves out all other body parts, misleads us in several ways. First, there is accumulating evidence that all organs are sexually differentiated, and that sex differences in peripheral organs affect the brain. We demonstrate this by reviewing examples involving sex differences in muscles, adipose tissue, the liver, immune system, gut, kidneys, bladder, and placenta that affect the nervous system and behavior. The second consequence of ignoring other organs when considering neural sex differences is that we are likely to miss the fact that some brain sex differences develop to compensate for differences in the internal environment (i.e., because male and female brains operate in different bodies, sex differences are required to make output/function more similar in the two sexes). We also consider evidence that sex differences in sensory systems cause male and female brains to perceive different information about the world; the two sexes are also perceived by the world differently and therefore exposed to differences in experience via treatment by others. Although the topic of sex differences in the brain is often seen as much more emotionally charged than studies of sex differences in other organs, the dichotomy is largely false. By putting the brain firmly back in the body, sex differences in the brain are predictable and can be more completely understood.

Growth hormone dose-dependent pubertal growth: a randomized trial in short children with low growth hormone secretion

BACKGROUND/AIMS

Growth hormone (GH) treatment regimens do not account for the pubertal increase in endogenous GH secretion. This study assessed whether increasing the GH dose and/or frequency of administration improves pubertal height gain and adult height (AH) in children with low GH secretion during stimulation tests, i.e. idiopathic isolated GH deficiency.

METHODS

A multicenter, randomized, clinical trial (No. 88-177) followed 111 children (96 boys) at study start from onset of puberty to AH who had received GH 33 µg/kg/day for ≥1 year. They were randomized to receive 67 µg/kg/day (GH(67)) given as one (GH(67×1); n = 35) or two daily injections (GH(33×2); n = 36), or to remain on a single 33 µg/kg/day dose (GH(33×1); n = 40). Growth was assessed as heightSDSgain for prepubertal, pubertal and total periods, as well as AHSDS versus the population and the midparental height.

RESULTS

Pubertal heightSDSgain was greater for patients receiving a high dose (GH(67), 0.73) than a low dose (GH(33×1), 0.41, p < 0.05). AHSDS was greater on GH(67) (GH(67×1), -0.84; GH(33×2), -0.83) than GH(33) (-1.25, p < 0.05), and heightSDSgain was greater on GH(67) than GH(33) (2.04 and 1.56, respectively; p < 0.01). All groups reached their target heightSDS.

CONCLUSION

Pubertal heightSDSgain and AHSDS were dose dependent, with greater growth being observed for the GH(67) than the GH(33) randomization group; however, there were no differences between the once- and twice-daily GH(67) regimens. © 2014 S. Karger AG, Basel.

The elusive rat model of conditioned placebo analgesia

Recent research on human placebo analgesia has suggested the need for rodent models to further elucidate the neural substrates of the placebo effect. This series of 3 experiments therefore was performed in an attempt to develop a model of placebo analgesia in rats. In each study, female Sprague-Dawley rats received an L5 spinal nerve ligation to induce a neuropathic pain condition. Each rat then underwent a 4-day conditioning procedure in which an active analgesic drug or its vehicle (unconditioned stimulus) was associated with the following cues (conditioned stimuli): novel testing room (environmental), vanilla scent cue (olfactory), dim incandescent lighting (visual), restraint procedure/injection (tactile), and time of day and injection-test latency (temporal). The analgesics for each experiment were as follows: Experiment 1 used 90 mg/kg gabapentin, experiment 2 used 3mg/kg loperamide hydrochloride, and experiment 3 used 6 mg/kg morphine sulfate. On the following test day, half of the animals received the opposite treatment, resulting in 4 conditioning manipulations: drug/drug, drug/vehicle, vehicle/drug, and vehicle/vehicle. Nociceptive thresholds were assessed with the mechanical paw withdrawal threshold test each day after the conditioning procedure. In all 3 experiments, no significant differences were detected on test day between control and placebo groups, indicating a lack of a conditioned placebo analgesic response. Our results contrast with prior research that implies the existence of a reliable and robust response to placebo treatment. We conclude that placebo analgesia in rats is not particularly robust and that it is difficult to achieve using conventional procedures and proper experimental design.

Lipid profiling and transcriptomic analysis reveals a functional interplay between estradiol and growth hormone in liver

17β-estradiol (E2) may interfere with endocrine, metabolic, and gender-differentiated functions in liver in both females and males. Indirect mechanisms play a crucial role because of the E2 influence on the pituitary GH secretion and the GHR-JAK2-STAT5 signaling pathway in the target tissues. E2, through its interaction with the estrogen receptor, exerts direct effects on liver. Hypothyroidism also affects endocrine and metabolic functions of the liver, rendering a metabolic phenotype with features that mimic deficiencies in E2 or GH. In this work, we combined the lipid and transcriptomic analysis to obtain comprehensive information on the molecular mechanisms of E2 effects, alone and in combination with GH, to regulate liver functions in males. We used the adult hypothyroid-orchidectomized rat model to minimize the influence of internal hormones on E2 treatment and to explore its role in male-differentiated functions. E2 influenced genes involved in metabolism of lipids and endo-xenobiotics, and the GH-regulated endocrine, metabolic, immune, and male-specific responses. E2 induced a female-pattern of gene expression and inhibited GH-regulated STAT5b targeted genes. E2 did not prevent the inhibitory effects of GH on urea and amino acid metabolism-related genes. The combination of E2 and GH decreased transcriptional immune responses. E2 decreased the hepatic content of saturated fatty acids and induced a transcriptional program that seems to be mediated by the activation of PPARα. In contrast, GH inhibited fatty acid oxidation. Both E2 and GH replacements reduced hepatic CHO levels and increased the formation of cholesterol esters and triacylglycerols. Notably, the hepatic lipid profiles were endowed with singular fingerprints that may be used to segregate the effects of different hormonal replacements. In summary, we provide in vivo evidence that E2 has a significant impact on lipid content and transcriptome in male liver and that E2 exerts a marked influence on GH physiology, with implications in human therapy.

Direct and indirect effects of growth hormone receptor ablation on liver expression of xenobiotic metabolizing genes

Detoxification of ingested xenobiotic chemicals, and of potentially toxic endogenous metabolites, is carried out largely through a series of enzymes synthesized in the liver, sometimes called "xenobiotic metabolizing enzymes" (XME). Expression of these XME is sexually dimorphic in rodents and humans, with many of the XME expressed at higher levels in females. This expression pattern is thought to be regulated, in part, by the sex differences in circadian growth hormone (GH) pulsatility. We have evaluated mRNA, in the liver, for 52 XME genes in male and female mice of four mutant stocks, with diminished levels of GH receptor (GHR) either globally (GKO), or in liver (LKO), fat (FKO), or muscle (MKO) tissue specifically. The data show complex, sex-specific changes. For some XME, the expression pattern is consistent with direct control of hepatic mRNA by GHR in the liver. In contrast, other XME show evidence for indirect pathways in which hepatic XME expression is altered by GH signals in fat or skeletal muscle. The effects of GHR-null mutations on glucose control, responses to dietary interventions, steroid metabolism, detoxification pathways, and lifespan may depend on a mixture of direct hepatic effects and cross talk between different GH-responsive tissues.

Regulation of 3β-hydroxysteroid dehydrogenase/Δ⁵-Δ⁴ isomerase: a review

This review focuses on the expression and regulation of 3β-hydroxysteroid dehydrogenase/Δ⁵-Δ⁴ isomerase (3β-HSD), with emphasis on the porcine version. 3β-HSD is often associated with steroidogenesis, but its function in the metabolism of both steroids and xenobiotics is more obscure. Based on currently available literature covering humans, rodents and pigs, this review provides an overview of the present knowledge concerning the regulatory mechanisms for 3β-HSD at all omic levels. The HSD isoenzymes are essential in steroid hormone metabolism, both in the synthesis and degradation of steroids. They display tissue-specific expression and factors influencing their activity, which therefore indicates their tissue-specific responses. 3β-HSD is involved in the synthesis of a number of natural steroid hormones, including progesterone and testosterone, and the hepatic degradation of the pheromone androstenone. In general, a number of signaling and regulatory pathways have been demonstrated to influence 3β-HSD transcription and activity, e.g., JAK-STAT, LH/hCG, ERα, AR, SF-1 and PPARα. The expression and enzymic activity of 3β-HSD are also influenced by external factors, such as dietary composition. Much of the research conducted on porcine 3β-HSD is motivated by its importance for the occurrence of the boar taint phenomenon that results from high concentrations of steroids such as androstenone. This topic is also examined in this review.

Sex steroid hormones regulate constitutive expression of Cyp2e1 in female mouse liver

CYP2E1 is of paramount toxicological significance because it metabolically activates a large number of low-molecular-weight toxicants and carcinogens. In this context, factors that interfere with Cyp2e1 regulation may critically affect xenobiotic toxicity and carcinogenicity. The aim of this study was to investigate the role of female steroid hormones in the regulation of CYP2E1, as estrogens and progesterone are the bases of contraceptives and hormonal replacement therapy in menopausal women. Interestingly, a fluctuation in the hepatic expression pattern of Cyp2e1 was revealed in the different phases of the estrous cycle of female mice, with higher Cyp2e1 expression at estrus (E) and lower at methestrus (ME), highly correlated with that in plasma gonadal hormone levels. Depletion of sex steroids by ovariectomy repressed Cyp2e1 expression to levels similar to those detected in males and cyclic females at ME. Hormonal supplementation brought Cyp2e1 expression back to levels detected at E. The role of progesterone appeared to be more prominent than that of 17β-estradiol. Progesterone-induced Cyp2e1 upregulation could be attributed to inactivation of the insulin/PI3K/Akt/FOXO1 signaling pathway. Tamoxifen, an anti-estrogen, repressed Cyp2e1 expression potentially via activation of the PI3K/Akt/FOXO1 and GH/STAT5b-linked pathways. The sex steroid hormone-related changes in hepatic Cyp2e1 expression were highly correlated with those observed in Hnf-1α, β-catenin, and Srebp-1c. In conclusion, female steroid hormones are clearly involved in the regulation of CYP2E1, thus affecting the metabolism of a plethora of toxicants and carcinogenic agents, conditions that may trigger several pathologies or exacerbate the outcomes of various pathophysiological states.

A perspective on free radical autoxidation: the physical organic chemistry of polyunsaturated fatty acid and sterol peroxidation

This Perspective describes advances from the author's laboratory on the free radical reactions of organic compounds with molecular oxygen. Polyunsaturated fatty acids (PUFAs) and sterols are particularly prone to undergo radical chain oxidation, and evidence suggests that this process, known as lipid peroxidation, occurs in vivo under a variety of conditions that are the result of an oxidative stress. Cyclic peroxides, hydroperoxides, and epoxy alcohols are major products formed from peroxidation, and the basic mechanisms of product formation are now reasonably well understood. These mechanisms include reversible addition of oxygen to carbon radicals, rearrangement and cyclization of allyl and pentadienyl peroxyl radicals, and homolytic substitution of carbon radicals on the peroxide bond. A physical organic approach to the problem of free radicals in biology and medicine is highlighted in this Perspective with stereochemical, kinetic, and extrathermodynamic probes applied to the study of mechanism. A radical clock permits the determination of free radical propagation rate constants, and 7-dehydrocholesterol, the immediate biosynthetic precursor of cholesterol, is found by this clock to be one of the most oxidizable lipids known. The consequences of the extreme reactivity of 7-dehydrocholesterol on human health is the focus of a current research theme in the author's laboratory.

Transcriptomic analyses of sexual dimorphism of the zebrafish liver and the effect of sex hormones

The liver is one of the most sex-dimorphic organs in both oviparous and viviparous animals. In order to understand the molecular basis of the difference between male and female livers, high-throughput RNA-SAGE (serial analysis of gene expression) sequencing was performed for zebrafish livers of both sexes and their transcriptomes were compared. Both sexes had abundantly expressed genes involved in translation, coagulation and lipid metabolism, consistent with the general function of the liver. For sex-biased transcripts, from in addition to the high enrichment of vitellogenin transcripts in spawning female livers, which constituted nearly 80% of total mRNA, it is apparent that the female-biased genes were mostly involved in ribosome/translation, estrogen pathway, lipid transport, etc, while the male-biased genes were enriched for oxidation reduction, carbohydrate metabolism, coagulation, protein transport and localization, etc. Sexual dimorphism on xenobiotic metabolism and anti-oxidation was also noted and it is likely that retinol x receptor (RXR) and liver x receptor (LXR) play central roles in regulating the sexual differences of lipid and cholesterol metabolisms. Consistent with high ribosomal/translational activities in the female liver, female-biased genes were significantly regulated by two important transcription factors, Myc and Mycn. In contrast, Male livers showed activation of transcription factors Ppargc1b, Hnf4a, and Stat4, which regulate lipid and glucose metabolisms and various cellular activities. The transcriptomic responses to sex hormones, 17β-estradiol (E2) or 11-keto testosterone (KT11), were also investigated in both male and female livers and we found that female livers were relatively insensitive to sex hormone disturbance, while the male livers were readily affected. E2 feminized male liver by up-regulating female-biased transcripts and down-regulating male-biased transcripts. The information obtained in this study provides comprehensive insights into the sexual dimorphism of zebrafish liver transcriptome and will facilitate further development of the zebrafish as a human liver disease model.

Estrogens regulate the hepatic effects of growth hormone, a hormonal interplay with multiple fates

The liver responds to estrogens and growth hormone (GH) which are critical regulators of body growth, gender-related hepatic functions, and intermediate metabolism. The effects of estrogens on liver can be direct, through the direct actions of hepatic ER, or indirect, which include the crosstalk with endocrine, metabolic, and sex-differentiated functions of GH. Most previous studies have been focused on the influence of estrogens on pituitary GH secretion, which has a great impact on hepatic transcriptional regulation. However, there is strong evidence that estrogens can influence the GH-regulated endocrine and metabolic functions in the human liver by acting at the level of GHR-STAT5 signaling pathway. This crosstalk is relevant because the widespread exposition of estrogen or estrogen-related compounds in human. Therefore, GH or estrogen signaling deficiency as well as the influence of estrogens on GH biology can cause a dramatic impact in liver physiology during mammalian development and in adulthood. In this review, we will summarize the current status of the influence of estrogen on GH actions in liver. A better understanding of estrogen-GH interplay in liver will lead to improved therapy of children with growth disorders and of adults with GH deficiency.

Impact of CUX2 on the female mouse liver transcriptome: activation of female-biased genes and repression of male-biased genes

The growth hormone-regulated transcription factors STAT5 and BCL6 coordinately regulate sex differences in mouse liver, primarily through effects in male liver, where male-biased genes are upregulated and many female-biased genes are actively repressed. Here we investigated whether CUX2, a highly female-specific liver transcription factor, contributes to an analogous regulatory network in female liver. Adenoviral overexpression of CUX2 in male liver induced 36% of female-biased genes and repressed 35% of male-biased genes. In female liver, CUX2 small interfering RNA (siRNA) preferentially induced genes repressed by adenovirus expressing CUX2 (adeno-CUX2) in male liver, and it preferentially repressed genes induced by adeno-CUX2 in male liver. CUX2 binding in female liver chromatin was enriched at sites of male-biased DNase hypersensitivity and at genomic regions showing male-enriched STAT5 binding. CUX2 binding was also enriched near genes repressed by adeno-CUX2 in male liver or induced by CUX2 siRNA in female liver but not at genes induced by adeno-CUX2, indicating that CUX2 binding is preferentially associated with gene repression. Nevertheless, direct CUX2 binding was seen at several highly female-specific genes that were positively regulated by CUX2, including A1bg, Cyp2b9, Cyp3a44, Tox, and Trim24. CUX2 expression and chromatin binding were high in immature male liver, where repression of adult male-biased genes and expression of adult female-biased genes are common, suggesting that the downregulation of CUX2 in male liver at puberty contributes to the developmental changes establishing adult patterns of sex-specific gene expression.

The influence of estrogens on the biological and therapeutic actions of growth hormone in the liver

GH is main regulator of body growth and composition, somatic development, intermediate metabolism and gender-dependent dimorphism in mammals. The liver is a direct target of estrogens because it expresses estrogen receptors which are connected with development, lipid metabolism and insulin sensitivity, hepatic carcinogenesis, protection from drug-induced toxicity and fertility. In addition, estrogens can modulate GH actions in liver by acting centrally, regulating pituitary GH secretion, and, peripherally, by modulating GHR-JAK2-STAT5 signalling pathway. Therefore, the interactions of estrogens with GH actions in liver are biologically and clinically relevant because disruption of GH signaling may cause alterations of its endocrine, metabolic, and gender differentiated functions and it could be linked to dramatic impact in liver physiology during development as well as in adulthood. Finally, the interplay of estrogens with GH is relevant because physiological roles these hormones have in human, and the widespread exposition of estrogen or estrogen-related compounds in human. This review highlights the importance of these hormones in liver physiology as well as how estrogens modulate GH actions in liver which will help to improve the clinical use of these hormones.

Sex-specific mouse liver gene expression: genome-wide analysis of developmental changes from pre-pubertal period to young adulthood

BACKGROUND

Early liver development and the transcriptional transitions during hepatogenesis are well characterized. However, gene expression changes during the late postnatal/pre-pubertal to young adulthood period are less well understood, especially with regards to sex-specific gene expression.

METHODS

Microarray analysis of male and female mouse liver was carried out at 3, 4, and 8 wk of age to elucidate developmental changes in gene expression from the late postnatal/pre-pubertal period to young adulthood.

RESULTS

A large number of sex-biased and sex-independent genes showed significant changes during this developmental period. Notably, sex-independent genes involved in cell cycle, chromosome condensation, and DNA replication were down regulated from 3 wk to 8 wk, while genes associated with metal ion binding, ion transport and kinase activity were up regulated. A majority of genes showing sex differential expression in adult liver did not display sex differences prior to puberty, at which time extensive changes in sex-specific gene expression were seen, primarily in males. Thus, in male liver, 76% of male-specific genes were up regulated and 47% of female-specific genes were down regulated from 3 to 8 wk of age, whereas in female liver 67% of sex-specific genes showed no significant change in expression. In both sexes, genes up regulated from 3 to 8 wk were significantly enriched (p < E-76) in the set of genes positively regulated by the liver transcription factor HNF4α, as determined in a liver-specific HNF4α knockout mouse model, while genes down regulated during this developmental period showed significant enrichment (p < E-65) for negative regulation by HNF4α. Significant enrichment of the developmentally regulated genes in the set of genes subject to positive and negative regulation by pituitary hormone was also observed. Five sex-specific transcriptional regulators showed sex-specific expression at 4 wk (male-specific Ihh; female-specific Cdx4, Cux2, Tox, and Trim24) and may contribute to the developmental changes that lead to global acquisition of liver sex-specificity by 8 wk of age.

CONCLUSIONS

Overall, the observed changes in gene expression during postnatal liver development reflect the deceleration of liver growth and the induction of specialized liver functions, with widespread changes in sex-specific gene expression primarily occurring in male liver.

Dynamic, sex-differential STAT5 and BCL6 binding to sex-biased, growth hormone-regulated genes in adult mouse liver

Sex-dependent pituitary growth hormone (GH) secretory patterns determine the sex-biased expression of >1,000 genes in mouse and rat liver, affecting lipid and drug metabolism, inflammation, and disease. A fundamental biological question is how robust differential expression can be achieved for hundreds of sex-biased genes simply based on the GH input signal pattern: pulsatile GH stimulation in males versus near-continuous GH exposure in females. STAT5 is an essential transcriptional mediator of the sex-dependent effects of GH in the liver, but the mechanisms that underlie its sex-dependent actions are obscure. Here we elucidate the dynamic, sex-dependent binding of STAT5 and the GH/STAT5-regulated repressor BCL6 to mouse liver chromatin genome wide, revealing a counteractive interplay between these two regulators of sex differences in liver gene expression. Our findings establish a close correlation between sex-dependent STAT5 binding and sex-biased target gene expression. Moreover, sex-dependent STAT5 binding correlated positively with sex-biased DNase hypersensitivity and H3-K4me1 and H3-K4me3 (activating) marks, correlated negatively with sex-biased H3-K27me3 (repressive) marks, and was associated with sex-differentially enriched motifs for HNF6/CDP factors. Importantly, BCL6 binding was preferentially associated with repression of female-biased STAT5 targets in male liver. Furthermore, BCL6 and STAT5 common targets but not BCL6 unique targets showed strong enrichment for lipid and drug metabolism. These findings provide a comprehensive, genome-wide view of the mechanisms whereby these two GH-regulated transcription factors establish and maintain sex differences affecting liver physiology and disease. The approaches used here to characterize sex-dependent STAT5 and BCL6 binding can be applied to other condition-specific regulatory factors and binding sites and their interplay with cooperative chromatin binding factors.

Child health, developmental plasticity, and epigenetic programming

Plasticity in developmental programming has evolved in order to provide the best chances of survival and reproductive success to the organism under changing environments. Environmental conditions that are experienced in early life can profoundly influence human biology and long-term health. Developmental origins of health and disease and life-history transitions are purported to use placental, nutritional, and endocrine cues for setting long-term biological, mental, and behavioral strategies in response to local ecological and/or social conditions. The window of developmental plasticity extends from preconception to early childhood and involves epigenetic responses to environmental changes, which exert their effects during life-history phase transitions. These epigenetic responses influence development, cell- and tissue-specific gene expression, and sexual dimorphism, and, in exceptional cases, could be transmitted transgenerationally. Translational epigenetic research in child health is a reiterative process that ranges from research in the basic sciences, preclinical research, and pediatric clinical research. Identifying the epigenetic consequences of fetal programming creates potential applications in clinical practice: the development of epigenetic biomarkers for early diagnosis of disease, the ability to identify susceptible individuals at risk for adult diseases, and the development of novel preventive and curative measures that are based on diet and/or novel epigenetic drugs.

Sex differences in nuclear receptor-regulated liver metabolic pathways

Liver metabolism is markedly sex-dimorphic; accordingly, the prevalence of liver diseases is different between sexes. The superfamily of nuclear receptors (NRs) governs the proper expression of key liver metabolism genes by sensing lipid-soluble hormones and dietary lipids. When the expression of those genes is deregulated, disease development is favored. However, we lack a comprehensive picture of the differences between NR actions in males and females. Here, we reviewed explorative studies that assessed NR functions in both sexes, and we propose a first map of sex-dimorphic NR expression in the liver. Our analysis suggested that NRs in the female liver exhibited cross-talk with more liver-protective potential than NRs in male liver. This study provides empirical support to the hypothesis that women are more resilient to some liver diseases than men, based on a more compensative NR network. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Pituitary growth hormone network responses are sexually dimorphic and regulated by gonadal steroids in adulthood

There are well-recognized sex differences in many pituitary endocrine axes, usually thought to be generated by gonadal steroid imprinting of the neuroendocrine hypothalamus. However, the recognition that growth hormone (GH) cells are arranged in functionally organized networks raises the possibility that the responses of the network are different in males and females. We studied this by directly monitoring the calcium responses to an identical GH-releasing hormone (GHRH) stimulus in populations of individual GH cells in slices taken from male and female murine GH-eGFP pituitary glands. We found that the GH cell network responses are sexually dimorphic, with a higher proportion of responding cells in males than in females, correlated with greater GH release from male slices. Repetitive waves of calcium spiking activity were triggered by GHRH in some males, but were never observed in females. This was not due to a permanent difference in the network architecture between male and female mice; rather, the sex difference in the proportions of GH cells responding to GHRH were switched by postpubertal gonadectomy and reversed with hormone replacements, suggesting that the network responses are dynamically regulated in adulthood by gonadal steroids. Thus, the pituitary gland contributes to the sexually dimorphic patterns of GH secretion that play an important role in differences in growth and metabolism between the sexes.

Same sex, no sex, and unaware sex in neurotoxicology

Males and females of virtually all species differ in how they respond to their environment. Because such differences exist in almost all biological realms, including disease patterns and therapeutic outcomes, they have evoked calls by various bodies to incorporate their assessment in research. Neurobehavioral indices pose special questions because, unlike outwardly visible markers, they are described by complex functional outcomes or subtle alterations in brain structure. These divergent responses arise because they are inscribed in the genome itself and then by endocrine mechanisms that govern sexual differentiation of the brain during development and operate throughout life. Other organ systems that exhibit sex differences include the liver, an important consideration for neurotoxicology because it may process many toxic chemicals differentially in males and females. Despite the scope and pervasiveness of sex differences, however, they are disregarded by much of neurotoxicology research. Males predominate in behavioral experiments, few such experiments study both sexes, some investigators fail to even describe the sex of their subjects, and in vitro studies tend to wholly ignore sex, even for model systems aimed at neurological disorders that display marked sex differences. The public is acutely aware of sex differences in behavior, as attested by its appetite for books on the topic. It closely follows debates about the proportion of women in professions that feature science and mathematics. Neurotoxicology, especially in the domain of laboratory research, will be hindered in its ability to translate its findings into human health measures if it assigns sex differences to a minor role. It must also be sensitive to how such debates are framed. Often, the differences evoking the most discussion are subtle in scope. They do not lend themselves to the typical analyses conducted by experimenters; that is, reliance on mean differences and null hypothesis testing.

Sex-specific gene expression in the BXD mouse liver

Differences in clinical phenotypes between the sexes are well documented and have their roots in differential gene expression. While sex has a major effect on gene expression, transcription is also influenced by complex interactions between individual genetic variation and environmental stimuli. In this study, we sought to understand how genetic variation affects sex-related differences in liver gene expression by performing genetic mapping of genomewide liver mRNA expression data in a genetically defined population of naive male and female mice from C57BL/6J, DBA/2J, B6D2F1, and 37 C57BL/6J x DBA/2J (BXD) recombinant inbred strains. As expected, we found that many genes important to xenobiotic metabolism and other important pathways exhibit sexually dimorphic expression. We also performed gene expression quantitative trait locus mapping in this panel and report that the most significant loci that appear to regulate a larger number of genes than expected by chance are largely sex independent. Importantly, we found that the degree of correlation within gene expression networks differs substantially between the sexes. Finally, we compare our results to a recently released human liver gene expression data set and report on important similarities in sexually dimorphic liver gene expression between mouse and human. This study enhances our understanding of sex differences at the genome level and between species, as well as increasing our knowledge of the molecular underpinnings of sex differences in responses to xenobiotics.

Pharmacogenetic biomarkers as tools for improved drug therapy; emphasis on the cytochrome P450 system

Important interindividual differences in drug pharmacokinetics cause absence of drug response or adverse drug reactions in significant fractions of the populations. The identification of the major enzymes participating, and the elucidation of the genetic basis for this variation in particular among cytochromes P450, provide tools for a personalized medicine treatment, which can make drug therapy much more effective at a lower cost. Much of the pioneering work linking drug metabolizing phenotype to genetic polymorphism among the P450 enzymes has been carried out at Karolinska Institutet. In this review we give a background and description of this work as well as the important implications for future medicine.

Intrinsic sex differences in the early growth hormone responsiveness of sex-specific genes in mouse liver

Sex differences in liver gene expression are dictated by sex differences in circulating GH profiles. Presently, the pituitary hormone dependence of mouse liver gene expression was investigated on a global scale to discover sex-specific early GH response genes that could contribute to sex-specific regulation of downstream GH targets and to ascertain whether intrinsic sex differences characterize hepatic responses to plasma GH stimulation. Global RNA expression analysis identified two distinct classes of sex-specific mouse liver genes: genes subject to positive regulation (class I) and genes subject to negative regulation by pituitary hormones (class II). Genes activated or repressed in hypophysectomized (Hypox) mouse liver within 30-90 min of GH pulse treatment at a physiological dose were identified as putative direct targets of GH action (early response genes). Intrinsic sex differences in the GH responsiveness of a subset of these early response genes were observed. Notably, 45 male-specific genes, including five encoding transcriptional regulators that may mediate downstream sex-specific transcriptional responses, were induced by GH within 30 min in Hypox male but not Hypox female mouse liver. The early GH response genes were enriched in 29 male-specific targets of the transcription factor myocyte enhancer factor 2, whose activation in hepatic stellate cells is associated with liver fibrosis leading to hepatocellular carcinoma, a male-predominant disease. Thus, the rapid activation by GH pulses of certain sex-specific genes is modulated by intrinsic sex-specific factors, which may be associated with prior hormone exposure (epigenetic mechanisms) or genetic factors that are pituitary-independent, and could contribute to sex differences in predisposition to liver cancer or other hepatic patho-physiologies.

Gender differences in drug toxicity

Clinical data suggest that gender dimorphic profiles are emerging in terms of both drug efficacy and adverse drug reactions (ADRs). With an increasing emphasis on individualised therapies and the need to prevent drug attrition there is a compelling need to understand the molecular basis for gender dimorphic profiles in ADRs and the consequences. Classes of agents exhibiting gender-based variation in pharmaceutical efficacy and toxicity include anaesthetics, HIV-1 therapies and antiarrhythmic drugs. Body weight differences are often cited as a reason for differences in drug pharmacokinetics and subsequent toxicity. However, some studies accounted for these factors and still found significance suggesting that dosage versus body weight does not explain the outcome. Here, we present an overview of current understanding of gender-specific drug toxicity and present rational molecular explanations for these adverse events. There is mounting evidence in support of hormonal effects underpinning the majority of the ADR differences observed between the sexes.