DYRK1A-Related Trabecular Defects in Male Ts65Dn Mice Emerge During a Critical Developmental Window

Abstract

Down syndrome (DS) is a complex genetic disorder caused by\nthe triplication of human chromosome 21 (Hsa21). The presence of an extra copy\nof an entire chromosome greatly disrupts the copy number and expression of over\n350 protein coding genes. This gene dosage imbalance has far-reaching effects on\nnormal development and aging, leading to cognitive and skeletal defects that\nemerge earlier in life than the general population.\n\n The present\nstudy begins by characterizing skeletal development in young male Ts65Dn mice to\ntest the hypothesis that skeletal defects in male Ts65Dn mice are developmental\nin nature.Femurs from young mice ranging from postnatal day 12- to 42-days of\nage (P12-42) were measured and analyzed by microcomputed tomography (μCT). Cortical\ndefects were present generally throughout development, but trabecular defects emerged\nat P30 and persisted until P42. The gene Dual-specificity\ntyrosine-regulated kinase 1a (Dyrk1a) is triplicated in both\nDS and in Ts65Dn mice and has been implicated as a putative cause of both\ncognitive and skeletal defects. To test the hypothesis that trisomic Dyrk1a\nis related to the emergence of trabecular defects at P30, expression of Dyrk1a\nin the femurs of male Ts65Dn mice was quantified by qPCR. Expression was shown\nto fluctuate throughout development and overexpression generally aligned with\nthe emergence of trabecular defects at P30.\n\n The growth\nrate in trabecular measures between male Ts65Dn and euploid littermates was\nsimilar between P30 and P42, suggesting a closer look into cellular mechanisms\nat P42. Assessment of proliferation of BMSCs, differentiation and activity of\nosteoblasts showed no significant differences between Ts65Dn and euploid\ncellular activity, suggesting that the cellular microenvironment has a greater\ninfluence on cellular activity than genetic background.\n\n These\ndata led to the hypothesis that reduction of Dyrk1a gene expression and\npharmacological inhibition of DYRK1A could be executed during a critical period\nto prevent the emergence of trabecular defects at P30. To tests this hypothesis,\ndoxycycline-induced cre-lox recombination to reduce Dyrk1a gene copy\nnumber or the DYRK1A inhibitor CX-4945 began at P21. The results of both\ngenetic and pharmacological interventions suggest that trisomic Dyrk1a\ndoes not influence the emergence of trabecular defects up to P30. Instead, data\nsuggest that the critical window for the rescue of trabecular defects lies\nbetween P30 and P42.