Dysregulated systemic metabolism in a Down syndrome mouse model

Role of cystathionine-β-synthase and hydrogen sulfide in down syndrome

Down syndrome (DS) is a genetic condition where the person affected by it is born with an additional - full or partial - copy of chromosome 21. DS presents with characteristic morphological features and is associated with a wide range of biochemical alterations and maladaptations. Cystathionine-β-synthase (CBS) - one of the key mammalian enzymes responsible for the biogenesis of the gaseous transmitter hydrogen sulfide (H2S) - is located on chromosome 21, and people with DS exhibit a significant upregulation of this enzyme in their brain and other organs. Even though 3-mercaptopyruvate sulfurtransferase - another key mammalian enzyme responsible for the biogenesis of H2S and of reactive polysulfides - is not located on chromosome 21, there is also evidence for the upregulation of this enzyme in DS cells. The hypothesis that excess H2S in DS impairs mitochondrial function and cellular bioenergetics was first proposed in the 1990s and has been substantiated and expanded upon over the past 25 years. DS cells are in a state of metabolic suppression due to H2S-induced, reversible inhibition of mitochondrial Complex IV activity. The impairment of aerobic ATP generation in DS cells is partially compensated by an upregulation of glycolysis. The DS-associated metabolic impairment can be reversed by pharmacological CBS inhibition or CBS silencing. In rodent models of DS, CBS upregulation and H2S overproduction contribute to the development of cognitive dysfunction, alter brain electrical activity, and promote reactive gliosis: pharmacological inhibition or genetic correction of CBS overactivation reverses these alterations. CBS can be considered a preclinically validated drug target for the experimental therapy of DS.

Loss of CTRP10 results in female obesity with preserved metabolic health

Obesity is a major risk factor for type 2 diabetes, dyslipidemia, cardiovascular disease, and hypertension. Intriguingly, there is a subset of metabolically healthy obese (MHO) individuals who are seemingly able to maintain a healthy metabolic profile free of metabolic syndrome. The molecular underpinnings of MHO, however, are not well understood. Here, we report that CTRP10/C1QL2-deficient mice represent a unique female model of MHO. CTRP10 modulates weight gain in a striking and sexually dimorphic manner. Female, but not male, mice lacking CTRP10 develop obesity with age on a low-fat diet while maintaining an otherwise healthy metabolic profile. When fed an obesogenic diet, female Ctrp10 knockout (KO) mice show rapid weight gain. Despite pronounced obesity, Ctrp10 KO female mice do not develop steatosis, dyslipidemia, glucose intolerance, insulin resistance, oxidative stress, or low-grade inflammation. Obesity is largely uncoupled from metabolic dysregulation in female KO mice. Multi-tissue transcriptomic analyses highlighted gene expression changes and pathways associated with insulin-sensitive obesity. Transcriptional correlation of the differentially expressed gene (DEG) orthologs in humans also shows sex differences in gene connectivity within and across metabolic tissues, underscoring the conserved sex-dependent function of CTRP10. Collectively, our findings suggest that CTRP10 negatively regulates body weight in females, and that loss of CTRP10 results in benign obesity with largely preserved insulin sensitivity and metabolic health. This female MHO mouse model is valuable for understanding sex-biased mechanisms that uncouple obesity from metabolic dysfunction.

Male Down syndrome Ts65Dn mice have impaired bone regeneration

Trisomy of human chromosome 21 (Ts21) individuals present with a spectrum of low bone mineral density (BMD) that predisposes this vulnerable group to skeletal injuries. To determine the bone regenerative capacity of Down syndrome (DS) mice, male and female Dp16 and Ts65Dn DS mice underwent amputation of the digit tip (the terminal phalanx (P3)). This is a well-established mammalian model of bone regeneration that restores the amputated skeletal segment and all associated soft tissues. P3 amputation was performed in 8-week-old male and female DS mice and WT controls and followed by in vivo μCT, histology and immunofluorescence. Following P3 amputation, the bone degradation phase was attenuated in both Dp16 and Ts65Dn males. In Dp16 males, P3 regeneration was delayed but complete by 63 days post amputation (DPA); however, male Ts65Dn exhibited attenuated regeneration by 63 DPA. In both Dp16 and Ts65Dn female DS mice, P3 regenerates were indistinguishable from WT by 42 DPA. In Ts65Dn males, osteoclasts and eroded bone surface were significantly reduced, and osteoblast number significantly decreased in the regenerating digit. In Ts65Dn females, no significant differences were observed in any osteoclast or osteoblast parameter. Like Ts21 individuals and DS mice with sex differences in bone mass, these data expand the characteristic sexually dimorphism to include bone resorption and regeneration in response to skeletal injury in Ts65Dn mice. These observations suggest that sex differences contribute to the poor bone healing of DS and compound the increased risk of bone injury in the Ts21 population.

Beta cell function and global glucose metabolism are impaired in Dp(16)1Yey mouse model of Down syndrome

AIMS

Down syndrome (DS) or trisomy 21 is the most prevalent genetic disorder in the world. In addition to common symptoms such as intellectual disabilities and morphological abnormalities, several comorbidities are associated with DS, including metabolic dysfunction. Obesity and diabetes are more prevalent in people with DS compared with the general population. However, the mechanisms linking obesity/diabetes to DS remain poorly understood. Systematic investigation of metabolic disorders in animal models of DS is scarce.

MATERIALS AND METHODS

We used the Dp(16)1Yey mouse model of DS to evaluate the energy and glucose metabolism in both male and female Dp(16)1Yey mice at 3 and 6 months of age. We assessed the whole-body glucose metabolism by glucose and insulin tolerance tests, and investigated the pancreatic functions in terms of insulin synthesis, ß cell mass and the glucose-induced insulin secretion in vivo.

RESULTS

We show that Dp(16)1Yey mice do not present signs of obesity when they are fed with chow diet. However, these mice are glucose intolerant and insulin resistant, and exhibit dysfunctions of their endocrine pancreas, reflected by decreased insulin content and defective glucose-induced insulin secretion (GIIS) in vivo. The impairment of metabolic parameters is similar between males and females trisomic mice, indicating the absence of metabolic sexual dimorphism in this model.

CONCLUSIONS

Our study suggests that Dp(16)1Yey model is suitable for the assessment of metabolic disorders associated with DS.

Carbonyl reductase 1: a novel regulator of blood pressure in Down syndrome

Approximately one in every 800 children is born with the severe aneuploid condition of Down syndrome (DS), a trisomy of chromosome 21. Low blood pressure (hypotension) is a common condition associated with DS and can have a significant impact on exercise tolerance and quality of life. Little is known about the factors driving this hypotensive phenotype, therefore therapeutic interventions are limited. Carbonyl reductase 1 (CBR1) is an enzyme contributing to the metabolism of prostaglandins, glucocorticoids, reactive oxygen species and neurotransmitters, encoded by a gene (CBR1) positioned on chromosome 21 with the potential to affect blood pressure. Utilising telemetric blood pressure measurement of genetically modified mice, we tested the hypothesis that CBR1 influences blood pressure and that its overexpression contributes to hypotension in DS by evaluating possible contributing mechanisms in vitro. In a mouse model of DS (Ts65Dn), which exhibits hypotension, CBR1 activity was increased and pharmacological inhibition of CBR1 ed to increased blood pressure. Mice heterozygous null for Cbr1 had reduced CBR1 enzyme activity and elevated blood pressure. Further experiments indicate that the underlying mechanisms include alterations in both sympathetic tone and prostaglandin metabolism. We conclude that CBR1 activity contributes to blood pressure homeostasis and inhibition of CBR1 may present a novel therapeutic opportunity to correct symptomatic hypotension in DS.

Loss of CTRP10 results in female obesity with preserved metabolic health

Obesity is a major risk factor for type 2 diabetes, dyslipidemia, cardiovascular disease, and hypertension. Intriguingly, there is a subset of metabolically healthy obese (MHO) individuals who are seemingly able to maintain a healthy metabolic profile free of metabolic syndrome. The molecular underpinnings of MHO, however, are not well understood. Here, we report that CTRP10/C1QL2-deficient mice represent a unique female model of MHO. CTRP10 modulates weight gain in a striking and sexually dimorphic manner. Female, but not male, mice lacking CTRP10 develop obesity with age on a low-fat diet while maintaining an otherwise healthy metabolic profile. When fed an obesogenic diet, female Ctrp10 knockout (KO) mice show rapid weight gain. Despite pronounced obesity, Ctrp10 KO female mice do not develop steatosis, dyslipidemia, glucose intolerance, insulin resistance, oxidative stress, or low-grade inflammation. Obesity is largely uncoupled from metabolic dysregulation in female KO mice. Multi-tissue transcriptomic analyses highlighted gene expression changes and pathways associated with insulin-sensitive obesity. Transcriptional correlation of the differentially expressed gene (DEG) orthologous in humans also shows sex differences in gene connectivity within and across metabolic tissues, underscoring the conserved sex-dependent function of CTRP10. Collectively, our findings suggest that CTRP10 negatively regulates body weight in females, and that loss of CTRP10 results in benign obesity with largely preserved insulin sensitivity and metabolic health. This female MHO mouse model is valuable for understanding sex-biased mechanisms that uncouple obesity from metabolic dysfunction.

A Pathway-Level Information ExtractoR (PLIER) framework to gain mechanistic insights into obesity in Down syndrome

Down syndrome (DS), caused by the triplication of chromosome 21 (T21), is a prevalent genetic disorder with a higher incidence of obesity. Traditional approaches have struggled to differentiate T21-specific molecular dysregulation from general obesity-related processes. This study introduces the omni-PLIER framework, combining the Pathway-Level Information ExtractoR (PLIER) with the omnigenic model, to uncover molecular mechanisms underlying obesity in DS. The PLIER framework aligns gene expression data with biological pathways, facilitating the identification of relevant molecular patterns. Using RNA sequencing data from the Human Trisome Project, omni-PLIER identified latent variables (LVs) significantly associated with both T21 and body mass index (BMI). Elastic net regression and causal mediation analysis revealed LVs mediating the effect of karyotype on BMI. Notably, LVs involving glutathione peroxidase-1 (GPX1) and MCL1 apoptosis regulator, BCL2 family members emerged as crucial mediators. These findings provide insights into the molecular interplay between DS and obesity. The omni-PLIER model offers a robust methodological advancement for dissecting complex genetic disorders, with implications for understanding obesity-related processes in both DS and the general population.

Developmental deglutition and intrinsic tongue muscle maturation phenotypes in the Ts65Dn mouse model of Down syndrome

Introduction

Down syndrome (DS) is associated with difficulties with feeding during infancy and childhood. Weaning, or transitioning from nursing to independent deglutition, requires developmental progression in tongue function. However, little is known about whether postnatal tongue muscle maturation is impacted in DS. This study tested the hypothesis that the Ts65Dn mouse model of DS has developmental delays in deglutition, comprised of differences in eating and drinking behaviors relative to euploid controls, coinciding with atypical measures of intrinsic tongue muscle microanatomy.

Methods

The Ts65Dn mouse model of DS and euploid controls were evaluated at 7 days of age (p7; nursing), p21 (weaning), and p35 (mature deglutition) (n = 13-18 mice per group). Eating behavior, drinking behavior, and body weight changes were quantified in p21 and p35 mice through the use of automated monitoring over 24 h. Intrinsic tongues of mice at all three ages were sectioned and stained to permit quantification of the sizes of the four major intrinsic tongue muscles. Transverse intrinsic tongue muscles were evaluated for myofiber size (average myofiber cross sectional area (CSA) of all fibers, MyHC2a fibers, MyHC 2b fibers, and minimum Feret fiber diameter), and percentage of MyHC isoforms (%MyHC2a + fibers, and %MyHC 2b + fibers) in anterior, middle, and posterior regions.

Results

Ts65Dn showed significant differences from euploid in deglutition measures. Compared to euploid, Ts65Dn also showed differences in intrinsic tongue muscle microanatomy and biology. Specifically, Ts65Dn intrinsic tongues had smaller transverse muscle myofiber size measures than control in the anterior and middle tongue, but not in the posterior tongue.

Conclusion

Differences in intrinsic tongue muscles coincide with feeding phenotypes in the Ts65Dn mouse model of DS.

Assessing the Benefit of Dietary Choline Supplementation Throughout Adulthood in the Ts65Dn Mouse Model of Down Syndrome

BACKGROUND/OBJECTIVES

Down syndrome (DS) is the most common cause of early-onset Alzheimer's disease (AD). Dietary choline has been proposed as a modifiable factor to improve the cognitive and pathological outcomes of AD and DS, especially as many do not reach adequate daily intake levels of choline. While lower circulating choline levels correlate with worse pathological measures in AD patients, choline status and intake in DS is widely understudied. Perinatal choline supplementation (Ch+) in the Ts65Dn mouse model of DS protects offspring against AD-relevant pathology and improves cognition. Further, dietary Ch+ in adult AD models also ameliorates pathology and improves cognition. However, dietary Ch+ in adult Ts65Dn mice has not yet been explored; thus, this study aimed to supply Ch+ throughout adulthood to determine the effects on cognition and DS co-morbidities.

METHODS

We fed trisomic Ts65Dn mice and disomic littermate controls either a choline normal (ChN; 1.1 g/kg) or a Ch+ (5 g/kg) diet from 4.5 to 14 months of age.

RESULTS

We found that Ch+ in adulthood failed to improve genotype-specific deficits in spatial learning. However, in both genotypes of female mice, Ch+ significantly improved cognitive flexibility in a reverse place preference task in the IntelliCage behavioral phenotyping system. Further, Ch+ significantly reduced weight gain and peripheral inflammation in female mice of both genotypes, and significantly improved glucose metabolism in male mice of both genotypes.

CONCLUSIONS

Our findings suggest that adulthood choline supplementation benefits behavioral and biological factors important for general well-being in DS and related to AD risk.

Body composition parameters and sarcopenia in adults with Down syndrome: a case-control study

BACKGROUND

Individuals with Down syndrome (DS) experience premature aging. Whether accelerated aging involves changes in body composition parameters and is associated with early development of sarcopenia is unclear.

AIMS

To compare parameters of body composition and the prevalence of sarcopenia between adults with DS and the general population.

METHODS

Body composition was assessed by whole-body dual-energy X-ray absorptiometry (DXA). Fat mass (FMI) and skeletal mass indices (SMI) were calculated as the ratio between total body fat mass and appendicular lean mass and the square of height, respectively. Fat mass distribution was assessed by the android/gynoid fat ratio (A/G). Sarcopenia was defined according to the criteria and cut-points recommended by the European Working Group on Sarcopenia in Older People 2 (EWGSOP2). Data on age- and sex-matched non-DS controls were retrieved from the 2001-2002 National Health and Nutrition Examination Survey (NHANES) population.

RESULTS

Sixty-four DS adults (mean age 37.2 ± 12.0 years, 20.3% women) were enrolled and compared with age- and sex-matched NHANES participants (n = 256), in a 1:4 ratio. FMI (7.96 ± 3.18 kg/m2 vs. 8.92 ± 4.83 kg/m2, p = 0.135), SMI (7.38 ± 1.01 kg/m2 vs. 7.46 ± 2.77 kg/m2, p = 0.825) and A/G (0.98 ± 0.17 vs. 1.01 ± 0.22, p = 0.115) were not significantly different between DS and control participants. When the sample was stratified by sex, women with DS had a higher FMI compared with their NHANES controls (10.16 ± 4.35 kg/m2 vs. 8.11 ± 4.29 kg/m2, p < 0.001), while men with DS had lower A/G ratio (1.04 ± 0.16 vs. 1.11 ± 0.22, p = 0.002). Sarcopenia was more frequent in individuals with DS than in controls (35.6% vs. 19.9%, p = 0.007). This association was stronger in men 40 years and older.

CONCLUSIONS

Adults with DS have a higher prevalence of sarcopenia compared with the general population. This finding suggests that DS is associated with early muscle aging and calls for the design of interventions targeting the skeletal muscle to prevent or treat sarcopenia.

Senescent hearts from male Ts65Dn mice exhibit preserved function but altered size and nicotinamide adenine dinucleotide pathway signaling

Down syndrome (DS) is associated with congenital heart defects at birth, but cardiac function has not been assessed at older ages. We used the Ts65Dn mouse, a model of DS, to quantify heart structure and function with echocardiography in 18-mo male Ts65Dn and wild-type (WT) mice. Heart weight, nicotinamide adenine dinucleotide (NAD) signaling, and mitochondrial (citrate synthase) activity were investigated, as these pathways may be implicated in the cardiac pathology of DS. The left ventricle was smaller in Ts65Dn versus WT, as well as the anterior wall thickness of the left ventricle during both diastole (LVAW_d; mm) and systole (LVAW_s; mm) as assessed by echocardiography. Other functional metrics were similar between groups including left ventricular area end systole (mm2), left ventricular area end diastole (mm2), left ventricular diameter end systole (mm), left ventricular diameter end diastole (mm), isovolumetric relaxation time (ms), mitral valve atrial peak velocity (mm/s), mitral valve early peak velocity (mm/s), ratio of atrial and early peak velocities (E/A), heart rate (beats/min), ejection fraction (%), and fractional shortening (%). Nicotinamide phosphoribosyltransferase (NAMPT) protein expression, NAD concentration, and tissue weight were lower in the left ventricle of Ts65Dn versus WT mice. Sirtuin 3 (SIRT3) protein expression and citrate synthase activity were not different between groups. Although cardiac function was generally preserved in male Ts65Dn, the altered heart size and bioenergetic disturbances may contribute to differences in aging for DS.

Brain Mitochondrial Bioenergetics in Genetic Neurodevelopmental Disorders: Focus on Down, Rett and Fragile X Syndromes

Mitochondria, far beyond their prominent role as cellular powerhouses, are complex cellular organelles active as central metabolic hubs that are capable of integrating and controlling several signaling pathways essential for neurological processes, including neurogenesis and neuroplasticity. On the other hand, mitochondria are themselves regulated from a series of signaling proteins to achieve the best efficiency in producing energy, in establishing a network and in performing their own de novo synthesis or clearance. Dysfunctions in signaling processes that control mitochondrial biogenesis, dynamics and bioenergetics are increasingly associated with impairment in brain development and involved in a wide variety of neurodevelopmental disorders. Here, we review recent evidence proving the emerging role of mitochondria as master regulators of brain bioenergetics, highlighting their control skills in brain neurodevelopment and cognition. We analyze, from a mechanistic point of view, mitochondrial bioenergetic dysfunction as causally interrelated to the origins of typical genetic intellectual disability-related neurodevelopmental disorders, such as Down, Rett and Fragile X syndromes. Finally, we discuss whether mitochondria can become therapeutic targets to improve brain development and function from a holistic perspective.

Single-Nucleus Profiling Identifies Accelerated Oligodendrocyte Precursor Cell Senescence in a Mouse Model of Down Syndrome

Down syndrome (DS), the most common genetic cause of intellectual disability, is associated with lifelong cognitive deficits. However, the mechanisms by which triplication of chromosome 21 genes drive neuroinflammation and cognitive dysfunction are poorly understood. Here, using the Ts65Dn mouse model of DS, we performed an integrated single-nucleus ATAC and RNA-sequencing (snATAC-seq and snRNA-seq) analysis of the adult cortex. We identified cell type-specific transcriptional and chromatin-associated changes in the Ts65Dn cortex, including regulators of neuroinflammation, transcription and translation, myelination, and mitochondrial function. We discovered enrichment of a senescence-associated transcriptional signature in Ts65Dn oligodendrocyte (OL) precursor cells (OPCs) and epigenetic changes consistent with a loss of heterochromatin. We found that senescence is restricted to a subset of OPCs concentrated in deep cortical layers. Treatment of Ts65Dn mice with a senescence-reducing flavonoid rescued cortical OPC proliferation, restored microglial homeostasis, and improved contextual fear memory. Together, these findings suggest that cortical OPC senescence may be an important driver of neuropathology in DS.

Hypermetabolism in mice carrying a near-complete human chromosome 21

The consequences of aneuploidy have traditionally been studied in cell and animal models in which the extrachromosomal DNA is from the same species. Here, we explore a fundamental question concerning the impact of aneuploidy on systemic metabolism using a non-mosaic transchromosomic mouse model (TcMAC21) carrying a near-complete human chromosome 21. Independent of diets and housing temperatures, TcMAC21 mice consume more calories, are hyperactive and hypermetabolic, remain consistently lean and profoundly insulin sensitive, and have a higher body temperature. The hypermetabolism and elevated thermogenesis are likely due to a combination of increased activity level and sarcolipin overexpression in the skeletal muscle, resulting in futile sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) activity and energy dissipation. Mitochondrial respiration is also markedly increased in skeletal muscle to meet the high ATP demand created by the futile cycle and hyperactivity. This serendipitous discovery provides proof-of-concept that sarcolipin-mediated thermogenesis via uncoupling of the SERCA pump can be harnessed to promote energy expenditure and metabolic health.

Hypermetabolism in mice carrying a near complete human chromosome 21

The consequences of aneuploidy have traditionally been studied in cell and animal models in which the extrachromosomal DNA is from the same species. Here, we explore a fundamental question concerning the impact of aneuploidy on systemic metabolism using a non-mosaic transchromosomic mouse model (TcMAC21) carrying a near complete human chromosome 21. Independent of diets and housing temperatures, TcMAC21 mice consume more calories, are hyperactive and hypermetabolic, remain consistently lean and profoundly insulin sensitive, and have a higher body temperature. The hypermetabolism and elevated thermogenesis are due to sarcolipin overexpression in the skeletal muscle, resulting in futile sarco(endo)plasmic reticulum Ca ²⁺ ATPase (SERCA) activity and energy dissipation. Mitochondrial respiration is also markedly increased in skeletal muscle to meet the high ATP demand created by the futile cycle. This serendipitous discovery provides proof-of-concept that sarcolipin-mediated thermogenesis via uncoupling of the SERCA pump can be harnessed to promote energy expenditure and metabolic health.