Post-synaptic scaffold protein TANC2 in psychiatric and somatic disease risk

Abstract

Understanding the shared genetic aetiology of psychiatric and medical comorbidity in neurodevelopmental disorders (NDDs) could improve patient diagnosis, stratification and treatment options. Rare tetratricopeptide repeat, ankyrin repeat and coiled-coil containing 2 (TANC2)-disrupting variants were disease causing in NDD patients. The post-synaptic scaffold protein TANC2 is essential for dendrite formation in synaptic plasticity and plays an unclarified but critical role in development. We here report a novel homozygous-viable Tanc2-disrupted function model in which mutant mice were hyperactive and had impaired sensorimotor gating consistent with NDD patient psychiatric endophenotypes. Yet, a multi-systemic analysis revealed the pleiotropic effects of Tanc2 outside the brain, such as growth failure and hepatocellular damage. This was associated with aberrant liver function including altered hepatocellular metabolism. Integrative analysis indicates that these disrupted Tanc2 systemic effects relate to interaction with Hippo developmental signalling pathway proteins and will increase the risk for comorbid somatic disease. This highlights how NDD gene pleiotropy can augment medical comorbidity susceptibility, underscoring the benefit of holistic NDD patient diagnosis and treatment for which large-scale preclinical functional genomics can provide complementary pleiotropic gene function information.

Keywords: Mouse models; Neurodevelopmental disorder; Somatic comorbidity; TANC2.

Fig. 1.

Disruption of Tanc2 causes hyperactivity in both novel and homecage environments and impairs sensorimotor gating. (A-E) Tanc2^−/− mutant mice were clearly hyperactive in response to a novel open field [increased distance travelled (A) and speed (B)] and SHIRPA [increased lines crossed (C)] environment and showed both increased distance travelled (D) and rearing activity (E) during the dark phase while housed in the metabolic cages for 21 h. Shaded areas indicate dark phase, 18:00-06:00. (F-H) Tanc2^−/− mutant mice showed a pattern of increased % centre time (F), % centre distance (G) and centre entries (H) in open field, suggesting a slight anxiolytic effect. (I) % Prepulse inhibition (PPI) was also decreased in the mutant mice and significant at 67 dB and 73 dB prepulse (PP) intensities and global, the mean of all four prepulses. The PPI deficit was not evident at the 81 dB PP intensity [16 dB above background noise (65 dB)]. *P<0.05, **P<0.01, ***P<0.001 +/+ versus −/−, males and females pooled (unpaired Student's t-test) (see Table S1 for sex and genotype group numbers for each test). Data are mean±s.d.

Fig. 2.

Tanc2 disruption alters body size and adipose tissue distribution. (A) Tanc2^−/− mice showed decreased body weight at all time points over the course of the analysis period, yet no difference in body weight gain was detected. (B-E) Body length (B), bone mineral content (BMC) (C) and bone mineral density (BMD) (D) were decreased, and BMC correlated positively with body weight (BW) (E). (F) BMD was not strongly predicted by BW. (G-I) Lean mass (G) and fat mass (H) were reduced, and there was a shift in body composition towards less fat in favour of lean mass, as indexed by decreased fat mass/lean mass ratio (I). Data are mean±s.d., males and females pooled. **P<0.01, ***P<0.001, +/+ versus −/− [linear mixed effect model (body weight), unpaired Student's t-test].

Fig. 3.

Tanc2 disruption alters metabolic rate, food intake and substrate utilisation profiles. (A,B) Tanc2 disruption in mice leads to decreased oxygen consumption (VO₂) during indirect calorimetry analysis in metabolic homecages (A), while respiratory exchange ratio (RER; VCO₂/VO₂) was not markedly altered but tended to decrease (B). (C) Furthermore, the metabolic rate, as indexed by energy expenditure in kJ/h, was significantly decreased. (D-F) Tanc2 disruption led also to decreased food intake (D); however, both energy expenditure (EE; E) and food intake (F) were correlated with the lower body weight of the mice. (G,H) Tanc2 disruption also caused an altered substrate utilisation profile in which carbohydrate oxidation (G) was decreased and more lipids were oxidised relative to carbohydrates, as shown in the increased lipid/carbohydrate oxidation ratio (H). *P<0.05, **P<0.01, ***P<0.001 +/+ versus −/− [unpaired Student's t-test or repeated measures (RM) ANOVA with post-hoc Sidak's test]. Grey shaded area demarcates the dark phase. Data are mean±s.d., males and females pooled.

Fig. 4.

Histopathological findings in the mouse liver at 16 weeks of age. (A,B) Representative liver sections stained with H&E, 800×magnification, from a control mouse (A) and from a Tanc2^−/− mouse (B). A shows the normal appearance of hepatocytes, with the round nucleus centrally located and cytoplasm containing glycogen. B shows, by comparison, in the liver of a Tanc2^−/− mouse, abnormal hepatocytes (arrows) with nuclear alterations consisting of linear chromatin with small lateral projections.

Fig. 5.

Tanc2 disruption alters markers of liver damage. (A,B) Tanc2 disruption in −/− mice led to decreased circulating cholesterol (A) and high-density lipoprotein (HDL) levels (B), suggesting altered lipoprotein metabolism. (C,D) Bilirubin (C) and total iron binding capacity (TIBC; D) were decreased in −/− mice, indicating altered hepatocellular metabolism. (E,F) Alanine aminotransferase (E) and aspartate aminotransferase (F) levels were increased in −/− mice, signifying liver cell damage. (G,H) Alkaline phosphatase (G) tended to increase while alpha-amylase (H) decreased in −/− mice, implying altered hepatocellular function. (I) In the glucose tolerance test, the peak glucose level was increased in the mutant mice at 30 min post-glucose injection. *P<0.05, **P<0.01, ***P<0.001 +/+ versus −/− (unpaired Students's t-test or RM ANOVA with post-hoc Sidak's test). Data are mean±s.d., males and females pooled.

Fig. 6.

Dimensionality reduction of psychiatric and systemic variable effects of Tanc2 disruption. We performed a principal component analysis (PCA) to reduce the dimensionality of the variables related to Tanc2 disruption. (A,B) The contribution of variables to principal component (PC) 1 (A) and 2 (B). (C) Correlation circle showing clustering of variables in PC1 and 2. (D) Biplot depicting the variables and individual PC scores for the two genotypes, control (+/+) and Tanc2-disrupted mutants (−/−). Males and females were separated for PCA. (E) Individual plot of Ywhab^−/− mice and control PC scores with Tanc2^−/− mice PC scores and their respective controls. The coloured clouds denote animals from the same experimental group. AP, alkaline phosphatase; AT, aminotransferase; BMD, bone mineral density; carb, carbohydrate; HDL, high-density lipoprotein; MHC, metabolic home cage; OF, open field; PPI, prepulse inhibition; Min RER, minimum respiratory exchange ratio; TIBC, total iron-binding capacity.