Serum androgen level is determined by autosomal dominant inheritance and regulates sex-related CYP genes in pigs

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Abstract

We have previously demonstrated differences between Meishan and Landrace pigs in their serum androgen levels (Meishan > Landrace) and the expression of genes encoding hepatic cytochrome P450 (CYP) 1A subfamily enzymes (Meishan < Landrace). In the present study, to clarify whether such differences are genetically controlled, we crossbred these pigs (female Meishan × male Landrace, ML; female Landrace × male Meishan, LM) and examined the expression levels of serum androgen and hepatic CYP family genes (CYP1A1, CYP1A2, CYP2A19, and CYP2E1) among ML, LM, and their parents. In sexually mature (5-month-old) male ML or LM pigs, not only the serum androgen level, but also the hepatic expression levels of all the CYPs examined were similar to those in male Meishan pigs. In addition, there were few breed differences among the females of Meishan, Landrace, ML and LM pigs in the expression of all the CYP genes examined. Furthermore, the expression levels of these CYPs in the females of Meishan and Landrace pigs could be decreased to the corresponding levels in male Meishan pigs by administration of testosterone propionate. The present findings demonstrate that serum androgen level is determined by autosomal dominant inheritance and that the level of serum androgen is one of the host factors regulating the constitutive expression of CYP1A1, CYP1A2, CYP2A19, and CYP2E1 in the pig liver.

Highlights

► The serum androgen level in males is higher in Meishan pigs than Landrace pigs. ► Crossbreeding was performed between Meishan and Landrace pigs. ► Serum androgen level is determined by autosomal dominant inheritance. ► Serum androgen level is not regulated by only one gene. ► Androgen is a host factor for the constitutive expression of hepatic CYPs in pigs.

Introduction

Most xenobiotics, including drugs, are metabolized by hepatic cytochrome P450 (CYP), which consists of several subfamilies [1]. These CYP enzymes have different substrate-specificities [2], [3], and their expression levels are influenced not only by physiological factors, but also by exposure to xenobiotics [4], [5], [6], [7]. Therefore, studies on the expression of CYPs responsible for the metabolism of xenobiotics are important for understanding of the sex and species differences in the response to xenobiotics.

Androgen is one of the physiological factors that determine sexual dimorphism in the constitutive and/or xenobiotic-induced expression of CYPs, including Cyp1a2 [8], [9], [10] and Cyp2a/2b [11], [12] in mice. In conventional pigs and minipigs, there are sex differences in the expression of several CYPs including CYP1A2, CYP2A, and CYP2E [13], [14], [15], [16]. Recently, we have demonstrated that sex and breed differences in the constitutive expression levels of hepatic CYP1A subfamily enzymes, CYP1A1 and CYP1A2, in Meishan and Landrace pigs are closely correlated with differences in the level of serum androgen [17], [18]. Incidentally, in sexually mature male Meishan pigs with high levels of serum androgen (around 50 ng/ml), the constitutive expression levels of hepatic CYP1A subfamily enzymes are much lower than those in female Meishan pigs and both sexes of Landrace pigs, whose serum androgen levels are less than 20 ng/ml [18]. However, the causes of the breed differences in the level of serum androgen and the expression levels of hepatic CYP1A subfamily enzymes between male Meishan and Landrace pigs remain unclear.

The pig is a mammalian species of particular interest in pharmacological and toxicological studies because it can be used as a laboratory model for human metabolism, without the requirement to induce the enzymes that carry out biotransformations [19], [20]. Further analyses of the breed difference and the mechanism of androgen-associated gene expression of hepatic CYPs in Meishan and Landrace pigs will contribute to our understanding of sex and inter-individual differences in responses to xenobiotics, such as drugs and environmental chemicals, in humans.

In the present study, we crossbred Meishan and Landrace pigs and used their F1 pigs together with the parent pigs, to examine whether the differences between male Meishan and Landrace pigs in the expression levels of serum androgen and hepatic CYP genes, including CYP1A1 and CYP1A2, are genetically determined.

Section snippets

Animals

Meishan, Landrace, and their crossbred F1 (ML, Meishan × Landrace; LM, Landrace × Meishan) pigs were kept at the National Institute of Livestock and Grassland Science, Tsukuba, Japan. These F1 pigs were produced by mating between one sire of each breed and two dams of the other breed. All the pigs used were fed a commercial grain diet and provided with water ad libitum. Pigs were killed between 10:00 and 11:00 am at the age of 1, 2, 3, or 5 months. Some of male Meishan and Landrace pigs were

Serum testosterone levels in male Meishan, Landrace, and their F1 pigs

The levels of serum testosterone in sexually mature (5-month-old) male Meishan pigs were approximately 3-fold higher than those in the corresponding Landrace pigs (Fig. 1). The levels of serum testosterone (45–85 ng/ml) in 5-month-old F1 (ML and LM) pigs were similar to those (40–60 ng/ml) in Meishan pigs. However, age-dependent increases in the testosterone levels during the 2–4 months after the birth in LM pigs were slightly low compared with those in the age-matched ML and Meishan pigs. In

Discussion

We have previously demonstrated that there are sex and/or breed differences in the levels of serum testosterone and the constitutive expression levels of hepatic CYP1A1 and CYP1A2 in Meishan and Landrace pigs [17], [18]. Incidentally, constitutive expression levels of hepatic CYP1A and CYP1A2 mRNAs were considerably lower in the pigs with high levels (more than 33 ng/ml) of serum testosterone compared with those in the pigs with lower levels (e.g. the mean concentrations of serum testosterone

Acknowledgments

We thank the Swine Management Section of the National Institute of Livestock and Grassland Science (Tsukuba, Japan) for the care of the animals and for collecting tissue samples. This work was supported in part by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (No. 22590166, M.K.).

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