Rescue of the abnormal skeletal phenotype in Ts65Dn Down syndrome mice using genetic and therapeutic modulation of trisomicDyrk1a

Abstract

Trisomy 21 causes skeletal alterations in individuals with Down syndrome (DS), but the causative trisomic gene and a therapeutic approach to rescue these abnormalities are unknown. Individuals with DS display skeletal alterations including reduced bone mineral density, modified bone structure and distinctive facial features. Due to peripheral skeletal anomalies and extended longevity, individuals with DS are increasingly more susceptible to bone fractures. Understanding the genetic and developmental origin of DS skeletal abnormalities would facilitate the development of therapies to rescue these and other deficiencies associated with DS. DYRK1A is found in three copies in individuals with DS and Ts65Dn DS mice and has been hypothesized to be involved in many Trisomy 21 phenotypes including skeletal abnormalities. Return of Dyrk1a copy number to normal levels in Ts65Dn mice rescued the appendicular bone abnormalities, suggesting that appropriate levels of DYRK1A expression are critical for the development and maintenance of the DS appendicular skeleton. Therapy using the DYRK1A inhibitor epigallocatechin-3-gallate improved Ts65Dn skeletal phenotypes. These outcomes suggest that the osteopenic phenotype associated with DS may be rescued postnatally by targeting trisomic Dyrk1a.

Low dose EGCG treatment beginning in adolescence does not improve cognitive impairment in a Down syndrome mouse model

“…Three important candidate factors that may account for differences are dosage, the developmental timing of the treatment, or interactions with other substances included in some EGCG supplements. We have shown that a three week treatment of ~10 mg/kg/day EGCG improved skeletal deficits in Ts65Dn mice (Blazek et al, 2015). A higher concentration of EGCG may be necessary to significantly improve cognitive deficits in the Ts65Dn mouse.…”

“…Previous work in our lab using a three-week low-dose EGCG treatment (~10 mg/kg/day) during adolescence resulted in improvements in skeletal deficits in trisomic mice (Blazek, Abeysekera, Li, & Roper, 2015). A similar dose (~9 mg/kg/day in capsule form) was used in the human study that showed improvements in cognition and more positive caregiver reports (De la Torre et al, 2014).…”

Epigallocatechin-3-gallate (EGCG) consumption in the Ts65Dn model of Down syndrome fails to improve behavioral deficits and is detrimental to skeletal phenotypes

“…For skeletal parameters in DS mouse models, we and others have identified significant deficits in BMD, trabecular bone parameters (thickness, separation and number) and cortical bone measures in Ts65Dn mice compared to euploid control mice [17]. Significant deficits in mineral apposition rate (MAR), bone formation rate (BFR), and strength properties in trisomic mice compared to controls were also observed [17, 26, 27]. …”

“…EGCG is a small molecular inhibitor of DYRK1A activity and is thought to function by binding to the ATP binding domain of the protein thereby inhibiting its kinase activity [42, 43]. EGCG, either alone or in supplements containing EGCG, has been tested as a potential therapy in mouse models of DS [23, 26, 44–48] and in humans with DS [45, 49, 50]. In one recent study [45] trisomic mice were given an EGCG-containing supplement (Life Extension ® Mega Green Tea Extract, Lightly Caffeinated) in drinking water that was reported to deliver 2–3 mg of EGCG per day per mouse (i.e., a daily dosage of ~80–120 mg/kg [for a 25 g mouse] that would yield a final effective dosage of ~40–60 mg/kg per day after accounting for the known degradation of EGCG [23, 44]).…”

“…Those findings stand in contrast with studies in our laboratory that used either a three-week or a seven-week treatment of pure EGCG (concentration of 0.124 mg/mL) beginning in early adolescence that delivered a dosage of either ~10 mg/kg/day (EGCG in water) or ~20 mg/kg/day (stabilized EGCG in acidified water and corrected for degradation). The 10 mg/kg/day dosage improved skeletal deficits including femoral BMD, percent trabecular bone volume, trabecular number and trabecular thickness in Ts65Dn mice [26], but neither the 10 nor the 20 mg/kg/day dosage improved performance in the MWM, NOR, or balance beam motor coordination task [23]. …”