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. 2018 Feb;8:180-188.
doi: 10.1016/j.molmet.2017.11.010. Epub 2017 Nov 22.

Cadm2 Regulates Body Weight and Energy Homeostasis in Mice

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Free PMC article

Cadm2 Regulates Body Weight and Energy Homeostasis in Mice

Xin Yan et al. Mol Metab. .
Free PMC article

Abstract

Objective: Obesity is strongly linked to genes regulating neuronal signaling and function, implicating the central nervous system in the maintenance of body weight and energy metabolism. Genome-wide association studies identified significant associations between body mass index (BMI) and multiple loci near Cell adhesion molecule2 (CADM2), which encodes a mediator of synaptic signaling enriched in the brain. Here we sought to further understand the role of Cadm2 in the pathogenesis of hyperglycemia and weight gain.

Methods: We first analyzed Cadm2 expression in the brain of both human subjects and mouse models and subsequently characterized a loss-of-function mouse model of Cadm2 for alterations in glucose and energy homeostasis.

Results: We show that the risk variant rs13078960 associates with increased CADM2 expression in the hypothalamus of human subjects. Increased Cadm2 expression in several brain regions of Lepob/ob mice was ameliorated after leptin treatment. Deletion of Cadm2 in obese mice (Cadm2/ob) resulted in reduced adiposity, systemic glucose levels, and improved insulin sensitivity. Cadm2-deficient mice exhibited increased locomotor activity, energy expenditure rate, and core body temperature identifying Cadm2 as a potent regulator of systemic energy homeostasis.

Conclusions: Together these data illustrate that reducing Cadm2 expression can reverse several traits associated with the metabolic syndrome including obesity, insulin resistance, and impaired glucose homeostasis.

Keywords: Cadm2/SynCAM2; Energy homeostasis; Genome-wide association studies; Insulin sensitivity; Leptin signaling.

Figures

Figure 1
Figure 1
BMI risk SNPs associate with increased CADM2 expression in several brain regions of human subjects. Boxplots show the 25% and 75% quantiles of normalized gene expression levels (y-axis), solid horizontal lines indicate the median, and whiskers indicate the 10% and 90% quantiles. A-D, Elevated expression of CADM2 associates with risk allele (G) of rs13078960 in caudate basal ganglia, putamen basal ganglia, cerebellum, and hypothalamus, respectively. The risk allele (G) is associated with higher expression levels in human brain. E, Plot showing the linkage disequilibrium (R2) in the 1000 genomes population between the lead SNP rs13078960 (blue box) on the (left) y-axis for all SNPs in a region around the lead SNP plotted against the position of the SNP (x-axis). Genes locations are shown as green horizontal lines. The strand of each gene is indicated by the arrows ‘>’ and ‘<’ next to the gene symbols. Regulatory elements annotated by the SNIPa webserver are indicated as blue lines. The right y-axis indicates the recombination rate, which is shown as light blue line. Color-coding of each SNP reflects the strength of linkage disequilibrium. The SNP highlighted in blue is the lead SNP identified in .
Figure 2
Figure 2
Loss of Cadm2 expression results in decreased body weight and improved leptin sensitivity. A, Western blot analysis of Cadm2 and Cadm1 in total lysates from hypothalamus of wild-type mice on normal chow diet and littermate controls on high fat diet (HFD) feeding. B, Western blot analysis of Cadm2 in brain, pancreas, intestine, liver, BAT, WAT, muscle, heart in the wild-type mice. C, Western blot analysis of Cadm2 expression in wild-type brain from 1 week to 15 weeks. D, Representative confocal images of Cadm1 and Cadm2 expression in VGLUT2-positive primary hippocampal neurons. Immunostaining for Cadm1 (red), Cadm2 (green), and VGLUT2 (cyan) identify points of co-localization in dendritic branch (white arrows). E, Representative confocal images of Cadm1 and Cadm2 expression in VGAT-positive primary hippocampal neurons. Immunostaining for Cadm1 (red), Cadm2 (green), and VGAT (cyan) identify points of co-localization in dendritic branch (white arrows). F, Western blot analysis of Cadm1 and Cadm2 in total and synaptosome-enriched lysates from hypothalamus of 12-week-old Cadm2KO mice and littermate controls. G, Body weight curves of Cadm2KO mice (n = 9) and littermate controls (n = 19). H, Quantification of food intake and body weight change in 11-week old Cadm2KO (n = 4) and littermate controls (n = 4) during leptin challenge. Daily food intake and body weight was measured for 5 days prior to leptin administration for base line. I, Western blot analysis of STAT3 phosphorylation in the hypothalamus of Cadm2KO and wild-type (WT) littermates after leptin injection (0.75 μg/g body weight). p-STAT3, phosphorylated STAT3. J, Western blot analysis of Cadm1, Cadm2, and p-STAT3 in the hypothalamus of 12-week-old wild-type mice, Lepob/ob mice after 5 days PBS or leptin injection. Results are presented as mean ± SEM. *P < 0.05.
Figure 3
Figure 3
Cadm2-deficient mice are protected from genetic obesity. A, Western blot analysis of Cadm1 and Cadm2 in total and synaptosome-enriched lysates from hypothalamus of 12-week-old Lepob/ob mice and Cadm2/ob. B, Body weight in male Cadm2/ob mice (n = 8), Lepob/ob mice (n = 13) and littermate controls (WT, n = 19) from 4 to 16 weeks of age. C, Random and fasting glucose measurements in 16-week-old Cadm2/ob mice, Lepob/ob mice and littermate controls (n = 3–7). D, Plasma insulin measurements in 16-week-old Cadm2/ob mice, Lepob/ob mice and littermate controls (n = 3–6). E, Glucose measurements during an insulin tolerance test on 12-week old Cadm2/ob mice, Lepob/ob mice and littermate controls (n = 4–6). F, Glucose measurements during a glucose tolerance test on 11-week old Cadm2/ob mice, Lepob/ob mice and littermate controls (n = 4–6). G, Glucose measurements during pyruvate tolerance test on 12-week old Cadm2/ob mice, Lepob/ob mice and littermate controls (n = 4–6). H-K, Quantification of O2 consumption, CO2 production, RER, and locomotor activity in 12-week old Cadm2/ob mice and Lepob/ob mice (n = 6–8). L, Body composition analysis of male Cadm2/ob mice and Lepob/ob mice (n = 6–9). M, Energy expenditure of individual animals plotted against lean body mass from 12-week old Cadm2/ob mice (n = 6) and Lepob/ob mice (n = 8). N, Energy expenditure of individual animals plotted against locomotor activity from 12-week old Cadm2/ob mice (n = 6) and Lepob/ob mice (n = 8). O, Quantification of daily food intake of Cadm2/ob mice (n = 6) and Lepob/ob mice (n = 8). P, Western blot analysis of STAT3 phosphorylation in the hypothalamus of Cadm2/ob mice and Lepob/ob mice after leptin injection (0.75 μg/g body weight). p-STAT3, phosphorylated STAT3. Q, Body weight in male Cadm2 mice and littermate controls (WT) from 5 to 20 weeks of age (n = 6–9). High fat diet feeding was initiated on 4 weeks old. R, Glucose measurements during an insulin tolerance test on 21-week old Cadm2 mice and littermate controls (n = 6–9). High fat diet feeding was initiated on 4 weeks-old. S, Glucose measurements during a glucose tolerance test on 22-week old Cadm2 mice and littermate controls (n = 6–9). High fat diet feeding was initiated on 4 weeks-old. Results are presented as mean ± SEM. *P < 0.05, **P < 0.01 and ***P < 0.001.
Figure 4
Figure 4
Increased thermogenesis in Cadm2-deficient Lepob/obmice. A, Core body temperature in 12-week-old mice (n = 4–16). B, Inguinal WAT (ingWAT) and liver mass in 12-week-old mice (n = 3–5). C, Western blot analysis of interscapular BAT extracts from 12-week-old wild-type (WT), Lepob/ob mice and Cadm2/ob mice using antibodies against Cadm2, Ucp1, tyrosine hydroxylase (TH) and α-tubulin. D–F, Haematoxilin and eosin staining of interscapular BAT, ingWAT, and liver and qRT-PCR gene expression analysis from 12-week-old wild-type (WT), Lepob/ob mice and Cadm2/ob mice (n = 3–6). Results are presented as mean ± SEM. *P < 0.05, **P < 0.01 and ***P < 0.001.

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