Metabolic syndrome without obesity: Hepatic overexpression of 11beta-hydroxysteroid dehydrogenase type 1 in transgenic mice

Abstract

In obese humans and rodents there is increased expression of the key glucocorticoid (GC) regenerating enzyme, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), in adipose tissue. This increased expression appears to be of pathogenic importance because transgenic mice overexpressing 11beta-HSD1 selectively in adipose tissue exhibit a full metabolic syndrome with visceral obesity, dyslipidemia, insulin-resistant diabetes, and hypertension. In this model, while systemic plasma GC levels are unaltered, GC delivery to the liver via the portal vein is increased. 11beta-HSD1 is most highly expressed in liver where inhibition or deficiency of its activity improves glucose and lipid homeostasis. To determine the potential contribution of elevated intrahepatic GCs alone toward development of insulin-resistant syndromes we generated transgenic mice expressing increased 11beta-HSD1 activity selectively in the liver under transcriptional control of hepatic regulatory sequences derived from the human apoE gene (apoE-HSD1). Transgenic lines with 2- and 5-fold-elevated 11beta-HSD1 activity exhibited mild insulin resistance without altered fat depot mass. ApoE-HSD1 transgenic mice exhibited fatty liver and dyslipidemia with increased hepatic lipid synthesis/flux associated with elevated hepatic LXRalpha and PPARalpha mRNA levels as well as impaired hepatic lipid clearance. Further, apoE-HSD1 transgenic mice have a marked, transgene-dose-associated hypertension paralleled by incrementally increased liver angiotensinogen expression. These data suggest that elevated hepatic expression of 11beta-HSD1 may relate to the pathogenesis of specific fatty liver, insulin-resistant, and hypertensive syndromes without obesity in humans as may occur in, for example, myotonic dystrophy, and possibly, the metabolically obese, normal-weight individual.

Fig. 1.

ApoE-HSD1 TG mice. (a) ApoE-HSD1 mice propagated from TG founder males 1066 and 1065 bearing a single insertion of transgene genotyped by Southern blot. Lane 1, non-TG; lane 2, 1066 TG; lane 3, 1065 TG. (b) Expression of epitope-tagged 11β-HSD1 (arrowhead) in tissue extracts (L, liver; H, heart; K, kidney; A, adipose; P, pancreas; T, testes; E, epididymis; B, brain) determined by anti-HA immunoblot. (c) In liver, V_max for 11β-HSD1 activity in 1066 TG (stippled bar) and 1065 TG (black bar) increased 2- and 5-fold above non-TG controls (gray bar), respectively.

Fig. 2.

Glucose homeostasis. IPGTT of chow-fed mice aged 18 weeks. Plasma glucose (a) and insulin (b) in apoE-HSD1 TG mice (black) and controls (gray) are shown. (c) Twenty-four-hour fasting plasma insulin levels in male mice aged 24 weeks [non-TG (n = 12), gray bar; 1066 TG (n = 6), stippled bar; 1065 TG (n = 6), black bar; ANOVA; mean ± SEM; *, P < 0.05 with respect to genotype].

Fig. 3.

Cholesterol lipoprotein distribution profiles. FPLC fractionation of pooled serum from apoE-HSD1 TG mice (black squares) and non-TG littermates [gray triangles; n = 5–7 per group, except 1066 non-TG (n = 2) because of unexpected deaths] with cholesterol content (mg/dl; y axis) plotted for each fraction (x axis). VLDL-, IDL+LDL-, and HDL-associated cholesterol fractions usually elute in fractions 30–35, 45–55, and 55–60, respectively. Cholesterol profiles from animals fed control LF diet (a and b) or HF diet (c and d) from line 1066 (a and c) and 1065 (b and d) are shown.

Fig. 4.

Blood pressure and hepatic AGT mRNA expression. Mean arterial pressure (MAP) (mmHg) measured by radio telemetry in chow-fed apoE-HSD1 TG (black bar) and non-TG control mice (gray bar) in line 1065 (a) (n = 3 TG and 3 non-TG) and line 1066 (b)(n = 3 TG and 6 non-TG). Significant differences in MAP were detected between TGs and control littermates in both lines (1066 TG P < 0.05; 1065 TG P < 0.001). Expression of hepatic AGT mRNA in representative non-TG (-) and TG (+) individuals (c) and values summarized from groups of non-TG (gray bar), 1066 TG (stippled bar), and 1065 TG (black bar) mice (d) are shown. [ANOVA; mean ± SEM; **, P < 0.01 with respect to genotype (n = 6–10 per group)].