Serum total cholesterol amounts in the stroke-prone hypertensive rat (SHRSP) strain are lower than in the normotensive control strain, Wistar-Kyoto (WKY) rat. To understand the strain difference, constitutive gene expression levels of hepatic cholesterol biosynthetic enzymes in male 8-week-old SHRSP and WKY rats were comparatively examined by DNA microarray and real-time reverse transcription-polymerase chain reaction (RT-PCR) analyses. Of 22 cholesterol biosynthetic enzyme genes, expression levels of 8 genes, Pmvk, Idi1, Fdps, Fdft1, Sqle, Lss, Sc4mol, and Hsd17b7, in SHRSP were less than 50% those of the WKY rats; especially, the expression level of Sqle gene, encoding squalene epoxidase, a rate-limiting enzyme in cholesterol biosynthesis pathway, was about 20%. The gene expression level of sterol regulatory element-binding protein-2 (SREBP-2), which functions as a transcription factor upregulating gene expression of cholesterol biosynthetic enzymes, in SHRSP was about 70% of that in WKY rats. These results demonstrate the possibility that the lower serum total cholesterol level in SHRSP is defined by lower gene expression of most hepatic cholesterol biosynthetic enzymes. In particular, decreased gene expression level of Sqle gene might be the most essential factor. Moreover, the broad range of lowered rates of these genes in SHRSP suggests that the abnormal function and/or expression not only of SREBP-2 but also of one or more other transcription factors for those gene expressions exist in SHRSP.Key words cholesterol biosynthesis; stroke-prone hypertensive rat; Wistar-Kyoto rat; strain difference; sterol regulatory element-binding protein-2; gene expression Stroke-prone spontaneously hypertensive rats (SHRSP) are widely used as a genetic model animal for hypertension and stroke.1,2) This strain also shows significantly lower serum total cholesterol (T-CHO) than the normotensive control strain, Wistar-Kyoto (WKY) rats, when both strains are maintained on a standard diet.3-5) However, the high-fat and highcholesterol diet-mediated development of hypercholesterolemia occurs more efficiently in SHRSP than in WKY rats.6-8) These findings suggest that there are differences in genetic factors responsible for cholesterol homeostasis.Serum T-CHO amount is primarily regulated by cholesterol biosynthesis, metabolism of cholesterol to bile acids, and uptake of cholesterol into cells via low-density lipoprotein (LDL) receptor in the liver. It is therefore one of important subjects for understanding the mechanism of strain difference between SHRSP and WKY strains, maintained on a standard diet, in serum T-CHO amount to look into strain differences in the expression and/or function of hepatic enzymes involved in cholesterol biosynthesis (Fig. 1). As for such differences, only two enzymes, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) and mevalonate pyrophosphate decarboxylase (MVD), have been reported. [9][10][11][12] Since HMGCR activity was higher in SHRSP than in WKY rats, 9) HMGCR is hardly thought to be a cause of t...

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The administration of inorganic lead (Pb) ion to rats is well known to induce liver hyperplasia with liver enlargement and hypercholesterolemia. In the present study, the sensitivities of stroke-prone spontaneously hypertensive rat (SHRSP) and its normotensive control strain, Wistar-Kyoto rat (WKY), to these effects of Pb ion were estimated. Lead nitrate (LN) dissolved in a distillated water for injection was administered to male SHRSP and WKY by a single intravenous injection at a dose of 100 µmol/kg body weight. In WKY, significant increases in the liver weight were observed at 24 and 48 hr after LNadministration, while in SHRSP, no such significant increases were observed up to 48 hr later. On the other hand, increased levels of serum total cholesterol after LN-administration were significantly higher in SHRSP than in WKY at each time, although the constitutive (control) level was the opposite. The present findings suggest that there is different susceptibility between SHRSP and WKY to LN-induced liver hyperplasia and hypercholesterolemia and further indicate that development of hypercholesterolemia is not necessarily correlated with that of liver hyperplasia.

-Administration of lead ion (Pb) to rats and mice affects hepatic functions such as the induction of hepatic cell proliferation and upregulation of cholesterol biosynthesis. To identify the genes for which expression changes in response to Pb-administration, we analyzed hepatic gene expression patterns in stroke-prone spontaneously hypertensive rat (SHRSP), its normotensive control, Wistar-Kyoto rat (WKY), and Spraque-Dawley (SD) rat strains, 3, 6, and 12 hr later after single i.v. injection of lead nitrate (LN) at a dose of 100 μmol using a DNA microarray technique. The data analysis demonstrated that the expression of a great number of genes was transiently and remarkably downregulated 3 hr after LN-injection, and then recovered to control levels only in LN-injected WKY. These normal hepatic expression levels in WKY and SHRSP were much higher than those in SD rats. Furthermore, most of these genes were ones thought to be expressed specifically in the spermatids and/or testes; i.e. genes encoding protamin 1, transition protein 1, and transition protein 2. These findings suggest that the regulation system common to expression of all of these genes could be a target site of Pb-toxic action, at least, in the liver of WKY, and that this system might be similar to the system essential for spermatogenesis, especially spermiogenesis, in the testis. In addition, it appears that clarifying the cause of the difference between the systems of WKY and SHRSP might aid in identifying the pathologic genes in SHRSP. Finally, it will be an important to clarify how the products of the genes related to spermatogenesis, including spermiogenesis, are functional in the livers of WKY and SHRSP.