The juxtaparanodal proteins CNTNAP2 and TAG1 regulate diet-induced obesity

Abstract

Despite considerable effort, the identification of genes that regulate complex multigenic traits such as obesity has proven difficult with conventional methodologies. The use of a chromosome substitution strain-based mapping strategy based on deep congenic analysis overcame many of the difficulties associated with gene discovery and led to the finding that the juxtaparanodal proteins CNTNAP2 and TAG1 regulate diet-induced obesity. The effects of a mild Cntnap2 mutation on body weight were highly dependent on genetic background, as both obesity-promoting and obesity-resistant effects of Cntnap2 were observed on different genetic backgrounds. The more severe effect of complete TAG1 deficiency, by decreasing food intake, completely prevented the weight gain normally associated with high-fat-diet feeding. Together, these studies implicate two novel proteins in the regulation of diet-induced obesity. Moreover, as juxtaparanodal proteins have previously been implicated in various neurological disorders, our results suggest a potential genetic and molecular link between obesity and diseases such as autism and epilepsy.

Fig. 1

Schematic of subcongenic strains derived from strains 6C2 and 6C3. a Locations of Obrq2 and Obrq3 are indicated relative to chromosome 6. b Subcongenic panels that define the body weight QTLs Obrq3a and Obrq3b. Strain names are indicated on the left. Body weight data are presented as mean ± SEM. c Strains 6C3bR1 and 6C3b-R2 carry the A/J-derived allele of Obrq3b on an otherwise B6 background and were used to test for epistasis between Obrq2 and Obrq3b

Fig. 2

Location of amino acid variants in CNTNAP2 between B6 and A/J. Amino acid sequence of the CNTNAP2 protein flanking the a V161I or b H538Q variant is indicated. All sequences were obtained from the Ensembl genome browser

Fig. 3

Decreased absolute and adjusted energy expenditure in Tag1-deficient mice. Respiratory quotient (a), unadjusted energy expenditure (b), and energy expenditure adjusted for body mass (c) were measured in control and Tag1 knockout mice fed the HFSC diet as indicated. Measurements were taken during the light phase (light 1), the dark phase (dark), and then again in the light phase (light 2) over a 24-h period; n = 8 per group. d Total activity was measured with an implanted E-Mitter over 5 days in mice (n = 4 per group) fed the HFSC diet. e Core body temperature was recorded (n = 4 per group) every 30 s with an implanted E-Mitter during a 4-h cold challenge at 4 °C. *p < 0.05; **p < 0.001; ***p < 0.0001

Fig. 4

Localization of ezrin and Kv1.2 in sciatic nerve. Sciatic nerve from adult mice fed the HFSC diet was labeled with antibodies to ezrin (green) and Kv1.2 (red). Nodes were identified by ezrin staining and scored as demonstrating normal, heminodal, or an absence of Kv1.2 staining (n = 100 per strain). The distribution of Kv1.2 staining patterns was compared using a v² test and shown to be significantly different between strains 6C2 and 6C3b (p < 0.0001) (Color figure online)