Inducibility of Male-Specific Isoforms of Cytochrome P450 by Sex-Dependent Growth Hormone Profiles in Hepatocyte Cultures From Male but Not Female Rats

Abstract

ABSTRACT:Although in vivo expression levels of the male-specific hepatic isoforms of cytochrome P450 (P450) (CYP2C11, CYP2C13, CYP2A2, and CYP3A2) are determined by the episodic growth hormone profile secreted by male rats, these isoforms have been completely refractory to growth hormone regulation in hepatocyte culture. By using species-specific rat growth hormone, at subphysiologic in vivo concentrations administered in two daily episodic pulses, we successfully induced CYP2C11 and CYP2A2 to near normal concentrations. Whereas inductive levels of CYP2C13 were subnormal, CYP3A2 was unresponsive to all hormonal treatments, quickly declining to undetectable concentrations. In agreement with in vivo findings, we observed that induction levels of the isoforms were always greatest when the male hepatocytes were exposed to the masculine-like episodic growth hormone profile and least stimulated by the continuous feminine-like hormone profile. When administered alone, dexamethasone consistently increased isoform levels. However, when administered with growth hormone, the glucocorticoid was always antagonistic, suppressing growth hormone induction of CYP2C11, CYP2C13, and CYP2A2. Finally, the P450 isoforms were completely unresponsive to all treatments when the hepatocytes were derived from female rats, supporting earlier findings that expression levels of sexually dimorphic P450 isoforms are inherently irreversible between sexes.

Sex-dependent expression of CYP2C11 in spleen, thymus and bone marrow regulated by growth hormone

“…Similar to hepatocytes in culture [41], CYP2C11 levels were rapidly depleted in splenocytes cultured in basic media without inducers. Hepatocyte proliferation resulting from regeneration [42] or exposure to mitogens [43] suppresses transcription of adult isoforms of P450, including CYP2C11.…”

Hypothesis: Neuroendocrine Mechanisms (Hypothalamus-Growth Hormone-STAT5 Axis) Contribute to Sex Bias in Pulmonary Hypertension

“…The net result is a cellular phenotype driven by the GH-STAT5 axis consisting of a large array (500-1,000) of genes expressed in a sex-biased manner differently in different species (Figure 1). This patterned activation of cells includes longer-lived chromatin remodeling at the respective male-and femalespecific genes in that respective male-derived hepatocytes were more responsive to the male pulsatile pattern of GH in culture, and female-derived were less so (27,67). From this, we anticipate that this remodeled chromatin will retain sex-biased phenotype when primary cells are continued to be maintained in culture.…”

“…Reconstruction experiments in rats show that exogenous administration of GH in 3-min pulses for up to six pulses per day generated expression of male-specific CYP2A2 and 3A2 subfamily genes in the liver (65). Different aspects of the specific GH patterns (pulse frequency, pulse height, interpulse interval and interpulse levels) affected sex-specific expression of different CYP enzymes differently, even in the same species (65)(66)(67)(68)(69). In an example specifically relevant to the PH focus of this essay, these differences included that the CYP3A subfamily is malespecific in rats, but female-specific in mice and humans (27,62,(65)(66)(67)(68)(69).…”

“…Fourth, the sex-biased expression of genes is duplicated in isolated human or rat hepatocytes exposed to the respective high pulsatile (male) or low, continuous (female) levels of GH in cell culture (27,67). Thus, cells isolated from the body replicate sex-biased gene expression in culture in response to patterns of GH in the absence of any exposure to sex hormones.…”

“…Different aspects of the specific GH patterns (pulse frequency, pulse height, interpulse interval and interpulse levels) affected sex-specific expression of different CYP enzymes differently, even in the same species (65)(66)(67)(68)(69). In an example specifically relevant to the PH focus of this essay, these differences included that the CYP3A subfamily is malespecific in rats, but female-specific in mice and humans (27,62,(65)(66)(67)(68)(69). We note that it is the CYP3A subfamily of enzymes that convert the injected inactive MCT to the bioactive monocrotaline pyrrole (MCTP) in male rats that then induces PH (70,71).…”