Metabolic dysfunction in Down syndrome long remained in the shadow of cognitive and cardiac problems, even though diabetes in such people is diagnosed on average 15 years earlier, and obesity occurs several times more often. Studies on cell cultures pointed to mitochondrial defects, but the limitations of mouse models got in the way of translating those findings to a whole organism: in one model (TcMAC21) metabolism turned out to be accelerated, contrary to the clinical picture, while another (Ts65Dn) carried extra triplicated genes unrelated to chromosome 21. The new Ts66Yah model, created by genome editing, removes this source of confusion and makes it possible for the first time to cleanly assess the contribution of the triplicated genes of chromosome 21 themselves to systemic metabolism. The work continues years of efforts to build adequate animal models of trisomy 21, alongside studies on Dp16 and Ts65Dn, but differs from them in being the first to combine a freely segregating extra chromosome with precise control over gene content.
Ts66Yah mice and their euploid siblings were fed a standard chow or a high-fat diet (60% of calories from fat) for 17-18 weeks. The metabolic phenotype was assessed by indirect calorimetry, glucose, insulin, pyruvate and lipid tolerance tests, and lipoprotein analysis by FPLC. Mitochondrial respiration was measured in five tissues on a Seahorse analyzer, using specific substrates for complexes I, II and IV and ATP synthase. For molecular profiling, bulk RNA sequencing of six metabolic tissues and untargeted metabolomics of liver and serum were performed on a TripleTOF 6600 platform. Fibrosis, oxidative stress and inflammation were assessed by hydroxyproline, malondialdehyde and multiplex cytokine analysis. All experiments included both sexes, and energy expenditure was analyzed with ANCOVA adjustment for lean mass.
On a standard diet, Ts66Yah mice developed pronounced glucose intolerance, insulin resistance and dyslipidemia, with females affected more severely than males. In visceral fat, maximal mitochondrial respiratory capacity fell in both sexes, and in females markers of fibrosis and liver damage (ALT) additionally rose. Serum levels of the pro-inflammatory cytokines IL-2, IL-5 and IL-10 increased. Metabolomic analysis revealed extensive remodeling of lipid and bile acid metabolism: bile acid levels dropped in the liver and rose in the blood, pointing to impaired enterohepatic circulation. On the high-fat diet, sex differences grew more pronounced: in females glucose intolerance worsened and mitochondrial function fell in brown fat, liver and muscle, whereas in males insulin sensitivity paradoxically improved. Comparison with the Ts65Dn model showed that removing extraneous triplicated genes makes the metabolic phenotype more severe, while comparison with Dp16 revealed substantial differences in transcriptomes despite an almost identical set of triplicated genes.
The work is the first to demonstrate that a mouse model of trisomy 21 purged of extraneous triplicated genes reproduces the key metabolic disturbances of Down syndrome, including insulin resistance and dyslipidemia. Unlike neighboring studies on Ts65Dn, where extra genes masked some of the effects, and on Dp16, which lacks a free extra chromosome, Ts66Yah makes it possible to separate the contribution of gene dosage from that of aneuploidy itself. The sex differences found in the response to diet underscore the need to include both sexes in preclinical trials. The model is becoming a benchmark for studying the metabolic aspects of Down syndrome and for finding therapeutic targets.
Further studies could aim to identify the specific triplicated genes responsible for metabolic disturbances through genetic dissection (for example, by normalizing the dosage of individual genes). Studying the role of bile acids and the gut microbiome in metabolic dysfunction looks promising, as does testing how aneuploidy affects the three-dimensional organization of the genome in metabolic tissues. Comparing Ts66Yah with models carrying the full set of triplicated genes of chromosome 21 will help assess how completely this model reflects Down syndrome.
The results will influence preclinical studies of the metabolic complications of Down syndrome and the choice of adequate animal models for drug testing. They are also important for understanding the general mechanisms of aneuploidy in the development of metabolic diseases.
The immediate steps include normalizing the expression of individual triplicated candidate genes (for example, Dyrk1a, Bach1, Runx1) to identify causal factors, and assessing pancreatic beta-cell function in Ts66Yah.
The work speaks directly to an unsolved problem in the biology of Down syndrome: which genes of chromosome 21, and in what combination, cause metabolic disturbances, and what contribution the extra chromosome itself makes independently of gene dosage. It also touches on the question of sex differences in sensitivity to metabolic stress in trisomy.
On ordinary chow, female Ts66Yah mice weigh more than their euploid counterparts even though they eat and move just as much, while males have a lower body temperature during the resting phase. And on a high-fat diet, males actually improve their insulin sensitivity, which looks paradoxical against the backdrop of obesity.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.