HNF1alpha controls renal glucose reabsorption in mouse and man

Abstract

Recently it has been shown that dominant mutations in the human hepatocyte nuclear factor 1alpha (HNF1alpha) gene, encoding for a homeoprotein that is expressed in liver, kidney, pancreas and intestine, result in maturity onset diabetes of the young type 3 (MODY3). HNF1alpha-null mice are diabetic, but at the same time suffer from a renal Fanconi syndrome characterized by urinary glucose loss. Here we show that MODY3 patients are also characterized by a reduced tubular reabsorption of glucose. The renal murine defect is due to reduced expression of the low affinity/high capacity glucose cotransporter (SGLT2). Our results show that HNF1alpha directly controls SGLT2 gene expression. Together these data indicate that HNF1alpha plays a key role in glucose homeostasis in mammals.

Fig. 1. Renal tubule uptakes. Uptake of glucose or analogues and alanine in renal tubules (A and C) or in brush-border membranes (B) from wild-type (grey bars) and homozygous HNF1α^–/– mice (solid bars). α-methyl-d-glucopyranoside, MGP; 2-deoxy-glucose, 2-DG. The results are the mean from three independent experiments. Error bars represent SE. (*) p <0.005.

Fig. 2. Northern blot on total kidney RNA. Northern blot analysis on total RNA from kidneys of animals of 12–15 days of age. Four samples for each genotype are shown, from left to right: wild-type, heterozygous and mutant homozygous animals. SGLT1, sodium glucose transporter type 1; SGLT2, sodium glucose transporter type 2; SAAT1, sodium-dependent glucose cotransporter type 2 also known as SGLT3; Glut2, glucose transporter type 2; Na⁺/K⁺ ATPase α subunit of the Na⁺/K⁺ ATPase pump.

Fig. 3. SGLT2 promoter analysis. (A) Schematic representation of the genomic structure of the mouse SGLT2 promoter. (B) Bandshift experiments on the SGLT2 promoter HNF1 binding sites. A β-fibrinogen HNF1 binding site is shown as control. (C) HNF1α-dependent transactivation of SGLT2 promoter constructs in C33-transfected cells. Either long (2 kb) or short (400 bp) promoter fragments driving a luciferase reporter cassette were cotransfected together with 1 µg of HNF1α expression vector (RSV–HNF1) (Chouard et al., 1990).

Fig. 4. Maximal glucose transport in MODY3 patients. MODY3 maximal glucose transport values (Tm/GFR/1.73 m² expressed in mM/1.73 m²), calculated as described in Methods, are plotted in comparison with the values obtained with type-2-diabetic non-MODY3 subjects.