Sexual Dimorphism of Rat Liver Nuclear Proteins

Abstract

Many genes are expressed in mammalian liver in a sexually dimorphic manner. DNA microarray analysis has shown that growth hormone (GH) and its sex-dependent pattern of pituitary secretion play a major role in establishing the sexually dimorphic patterns of liver gene expression. However, GH may exert effects on protein post-translational modification and nuclear localization that are not reflected at the mRNA level. To investigate these potential effects of GH, we used two-dimensional gel electrophoresis followed by LC-MS/MS to: 1) identify rat liver nuclear proteins whose abundance or state of post-translational modification displays sex-dependent differences; and 2) determine the role of the plasma GH profile in establishing these differences. Nuclear extracts prepared from livers of individual male (n ‫؍‬ 9) and female (n ‫؍‬ 5) adult rats, and from males given GH by continuous infusion for 7 days to feminize liver gene expression (n ‫؍‬ 5 rats), were resolved by two-dimensional electrophoresis. Image analysis of SYPRO Ruby-stained gels revealed 165 sexually dimorphic protein spots that differ in normalized volume between male and female groups by >1.5-fold at p < 0.05. Sixty of these proteins exhibited female-like changes in spot abundance following continuous GH treatment. Comparison of male and GH-treated male groups revealed 130 proteins that displayed >1.5-fold differences in abundance, with 60 of these GH-responsive spots being sexually dimorphic. Thus, GH plays an important role in establishing the sex-dependent differences in liver nuclear protein content. Twenty-eight of the sexually dimorphic and/or GH-regulated protein spots were identified by LC-MS/MS. Proteins identified include regucalcin, nuclear factor 45, and heterogeneous nuclear ribonucleoproteins A3, D-like, and K, in addition to proteins such as GST, normally associated with cytosolic extracts but also reported to be localized in the nucleus.

Sex Differences: A Resultant of an Evolutionary Pressure?

“…Indeed, for quite longtime it has been known that liver metabolism in male and female mammals is very dissimilar (Gustafsson et al, 1983). However, only more recently the availability of unbiased general surveys of transcriptomes (Waxman and Holloway, 2009;Waxman and O'Connor, 2006;Yang et al, 2006) and protein profile analyses (Laz et al, 2004) revealed that in liver 72% of the genes are expressed in a sex-specific way. Interestingly, several somatic organs show a certain degree of sex variability in gene expression that ranges from 14% in brain up to 68% in adipose tissue (Yang et al, 2006).…”

Sex Difference in Ischemic Acute Renal Failure in Rats: Approach by Proteomic Analysis

“…Among the identified proteins (Table 1), sex-dependent expression of ornithine aminotransferase, carbonic anhydrase 2 or regucalcin was in accordance with that obtained by other immunochemical or proteomic analysis: expression of ornithine aminotransferase is higher in females than males when analyzed by Western blotting of kidney homogenates from mice 20) ; contents of carbonic anhydrase 2 are higher in females than males when measured by radioimmunoassay of rat liver extracts 21) ; and regucalcin has been shown to be lower in females than males by proteomic analysis of nuclear proteins from the rat liver. 22) Thus, our proteomic analysis used in the present study is considered to be sufficiently applicable for clarifying difference in the expression of renal proteins between I/R-treated male and female rats.…”

Circadian modulation of hepatic transcriptome in transgenic rats expressing human growth hormone

“…The enzyme activity of mu class GST in TG rats were significantly lower than those in WT rats at both ZT6 and ZT18. The expression levels of Gstm1 and Gstm2 in females are known to be lower than those in males (Laz et al, 2004;Mugford and Kedderis, 1998;Srivastava and Waxman, 1993), implying that the phenotype of GST in TG rats is also feminized. Taken together with the above information, the present results verify that the sexually dimorphic profile of GH rather than genetic sexuality is a stronger sex-determining factor on the hepatic transcriptome in rats.…”